diff --git a/clang/include/clang/ASTMatchers/ASTMatchers.h b/clang/include/clang/ASTMatchers/ASTMatchers.h
index ce5d529e813fd..2fed66622850d 100644
--- a/clang/include/clang/ASTMatchers/ASTMatchers.h
+++ b/clang/include/clang/ASTMatchers/ASTMatchers.h
@@ -222,6 +222,19 @@ extern const internal::VariadicDynCastAllOfMatcher<Decl, TypedefNameDecl>
 extern const internal::VariadicDynCastAllOfMatcher<Decl, TypeAliasDecl>
     typeAliasDecl;
 
+/// \brief Matches shadow declarations introduced into a scope by a
+///        (resolved) using declaration.
+///
+/// Given
+/// \code
+///   namespace n { int f; }
+///   namespace declToImport { using n::f; }
+/// \endcode
+/// usingShadowDecl()
+///   matches \code f \endcode
+extern const internal::VariadicDynCastAllOfMatcher<Decl, UsingShadowDecl>
+    usingShadowDecl;
+
 /// Matches type alias template declarations.
 ///
 /// typeAliasTemplateDecl() matches
@@ -3739,7 +3752,7 @@ extern const internal::VariadicOperatorMatcherFunc<1, 1> unless;
 ///   Matcher<MemberExpr>, Matcher<QualType>, Matcher<RecordType>,
 ///   Matcher<TagType>, Matcher<TemplateSpecializationType>,
 ///   Matcher<TemplateTypeParmType>, Matcher<TypedefType>,
-///   Matcher<UnresolvedUsingType>
+///   Matcher<UnresolvedUsingType>, Matcher<UsingType>
 inline internal::PolymorphicMatcher<
     internal::HasDeclarationMatcher,
     void(internal::HasDeclarationSupportedTypes), internal::Matcher<Decl>>
@@ -4374,7 +4387,13 @@ AST_POLYMORPHIC_MATCHER_P(throughUsingDecl,
                           AST_POLYMORPHIC_SUPPORTED_TYPES(DeclRefExpr,
                                                           UsingType),
                           internal::Matcher<UsingShadowDecl>, Inner) {
-  const NamedDecl *FoundDecl = Node.getFoundDecl();
+  const NamedDecl *FoundDecl;
+  if constexpr (std::is_same_v<NodeType, UsingType>) {
+    FoundDecl = Node.getDecl();
+  } else {
+    static_assert(std::is_same_v<NodeType, DeclRefExpr>);
+    FoundDecl = Node.getFoundDecl();
+  }
   if (const UsingShadowDecl *UsingDecl = dyn_cast<UsingShadowDecl>(FoundDecl))
     return Inner.matches(*UsingDecl, Finder, Builder);
   return false;
@@ -7003,37 +7022,6 @@ AST_POLYMORPHIC_MATCHER_P2(
          InnerMatcher.matches(Args[Index], Finder, Builder);
 }
 
-/// Matches C or C++ elaborated `TypeLoc`s.
-///
-/// Given
-/// \code
-///   struct s {};
-///   struct s ss;
-/// \endcode
-/// elaboratedTypeLoc()
-///   matches the `TypeLoc` of the variable declaration of `ss`.
-extern const internal::VariadicDynCastAllOfMatcher<TypeLoc, ElaboratedTypeLoc>
-    elaboratedTypeLoc;
-
-/// Matches elaborated `TypeLoc`s that have a named `TypeLoc` matching
-/// `InnerMatcher`.
-///
-/// Given
-/// \code
-///   template <typename T>
-///   class C {};
-///   class C<int> c;
-///
-///   class D {};
-///   class D d;
-/// \endcode
-/// elaboratedTypeLoc(hasNamedTypeLoc(templateSpecializationTypeLoc()));
-///   matches the `TypeLoc` of the variable declaration of `c`, but not `d`.
-AST_MATCHER_P(ElaboratedTypeLoc, hasNamedTypeLoc, internal::Matcher<TypeLoc>,
-              InnerMatcher) {
-  return InnerMatcher.matches(Node.getNamedTypeLoc(), Finder, Builder);
-}
-
 /// Matches type \c bool.
 ///
 /// Given
@@ -7300,7 +7288,7 @@ extern const AstTypeMatcher<DecltypeType> decltypeType;
 AST_TYPE_TRAVERSE_MATCHER(hasDeducedType, getDeducedType,
                           AST_POLYMORPHIC_SUPPORTED_TYPES(AutoType));
 
-/// Matches \c DecltypeType or \c UsingType nodes to find the underlying type.
+/// Matches \c QualType nodes to find the underlying type.
 ///
 /// Given
 /// \code
@@ -7310,10 +7298,13 @@ AST_TYPE_TRAVERSE_MATCHER(hasDeducedType, getDeducedType,
 /// decltypeType(hasUnderlyingType(isInteger()))
 ///   matches the type of "a"
 ///
-/// Usable as: Matcher<DecltypeType>, Matcher<UsingType>
-AST_TYPE_TRAVERSE_MATCHER(hasUnderlyingType, getUnderlyingType,
-                          AST_POLYMORPHIC_SUPPORTED_TYPES(DecltypeType,
-                                                          UsingType));
+/// Usable as: Matcher<QualType>
+AST_MATCHER_P(Type, hasUnderlyingType, internal::Matcher<QualType>, Inner) {
+  QualType QT = Node.getLocallyUnqualifiedSingleStepDesugaredType();
+  if (QT == QualType(&Node, 0))
+    return false;
+  return Inner.matches(QT, Finder, Builder);
+}
 
 /// Matches \c FunctionType nodes.
 ///
@@ -7592,27 +7583,7 @@ extern const AstTypeMatcher<RecordType> recordType;
 /// and \c c.
 extern const AstTypeMatcher<TagType> tagType;
 
-/// Matches types specified with an elaborated type keyword or with a
-/// qualified name.
-///
-/// Given
-/// \code
-///   namespace N {
-///     namespace M {
-///       class D {};
-///     }
-///   }
-///   class C {};
-///
-///   class C c;
-///   N::M::D d;
-/// \endcode
-///
-/// \c elaboratedType() matches the type of the variable declarations of both
-/// \c c and \c d.
-extern const AstTypeMatcher<ElaboratedType> elaboratedType;
-
-/// Matches ElaboratedTypes whose qualifier, a NestedNameSpecifier,
+/// Matches Types whose qualifier, a NestedNameSpecifier,
 /// matches \c InnerMatcher if the qualifier exists.
 ///
 /// Given
@@ -7627,34 +7598,14 @@ extern const AstTypeMatcher<ElaboratedType> elaboratedType;
 ///
 /// \c elaboratedType(hasQualifier(hasPrefix(specifiesNamespace(hasName("N"))))
 /// matches the type of the variable declaration of \c d.
-AST_MATCHER_P(ElaboratedType, hasQualifier,
-              internal::Matcher<NestedNameSpecifier>, InnerMatcher) {
-  if (const NestedNameSpecifier *Qualifier = Node.getQualifier())
-    return InnerMatcher.matches(*Qualifier, Finder, Builder);
+AST_MATCHER_P(Type, hasQualifier, internal::Matcher<NestedNameSpecifier>,
+              InnerMatcher) {
+  if (NestedNameSpecifier Qualifier = Node.getPrefix())
+    return InnerMatcher.matches(Qualifier, Finder, Builder);
 
   return false;
 }
 
-/// Matches ElaboratedTypes whose named type matches \c InnerMatcher.
-///
-/// Given
-/// \code
-///   namespace N {
-///     namespace M {
-///       class D {};
-///     }
-///   }
-///   N::M::D d;
-/// \endcode
-///
-/// \c elaboratedType(namesType(recordType(
-/// hasDeclaration(namedDecl(hasName("D")))))) matches the type of the variable
-/// declaration of \c d.
-AST_MATCHER_P(ElaboratedType, namesType, internal::Matcher<QualType>,
-              InnerMatcher) {
-  return InnerMatcher.matches(Node.getNamedType(), Finder, Builder);
-}
-
 /// Matches types specified through a using declaration.
 ///
 /// Given
@@ -7823,7 +7774,7 @@ AST_MATCHER_FUNCTION_P_OVERLOAD(
 ///   matches "A::"
 AST_MATCHER_P(NestedNameSpecifier, specifiesType,
               internal::Matcher<QualType>, InnerMatcher) {
-  if (!Node.getAsType())
+  if (Node.getKind() != NestedNameSpecifier::Kind::Type)
     return false;
   return InnerMatcher.matches(QualType(Node.getAsType(), 0), Finder, Builder);
 }
@@ -7841,8 +7792,12 @@ AST_MATCHER_P(NestedNameSpecifier, specifiesType,
 ///   matches "A::"
 AST_MATCHER_P(NestedNameSpecifierLoc, specifiesTypeLoc,
               internal::Matcher<TypeLoc>, InnerMatcher) {
-  return Node && Node.getNestedNameSpecifier()->getAsType() &&
-         InnerMatcher.matches(Node.getTypeLoc(), Finder, Builder);
+  if (!Node)
+    return false;
+  TypeLoc TL = Node.getAsTypeLoc();
+  if (!TL)
+    return false;
+  return InnerMatcher.matches(TL, Finder, Builder);
 }
 
 /// Matches on the prefix of a \c NestedNameSpecifier.
@@ -7857,10 +7812,21 @@ AST_MATCHER_P(NestedNameSpecifierLoc, specifiesTypeLoc,
 AST_MATCHER_P_OVERLOAD(NestedNameSpecifier, hasPrefix,
                        internal::Matcher<NestedNameSpecifier>, InnerMatcher,
                        0) {
-  const NestedNameSpecifier *NextNode = Node.getPrefix();
+  NestedNameSpecifier NextNode = std::nullopt;
+  switch (Node.getKind()) {
+  case NestedNameSpecifier::Kind::Namespace:
+    NextNode = Node.getAsNamespaceAndPrefix().Prefix;
+    break;
+  case NestedNameSpecifier::Kind::Type:
+    NextNode = Node.getAsType()->getPrefix();
+    break;
+  default:
+    break;
+  }
+
   if (!NextNode)
     return false;
-  return InnerMatcher.matches(*NextNode, Finder, Builder);
+  return InnerMatcher.matches(NextNode, Finder, Builder);
 }
 
 /// Matches on the prefix of a \c NestedNameSpecifierLoc.
@@ -7875,7 +7841,12 @@ AST_MATCHER_P_OVERLOAD(NestedNameSpecifier, hasPrefix,
 AST_MATCHER_P_OVERLOAD(NestedNameSpecifierLoc, hasPrefix,
                        internal::Matcher<NestedNameSpecifierLoc>, InnerMatcher,
                        1) {
-  NestedNameSpecifierLoc NextNode = Node.getPrefix();
+  NestedNameSpecifierLoc NextNode;
+  if (TypeLoc TL = Node.getAsTypeLoc())
+    NextNode = TL.getPrefix();
+  else
+    NextNode = Node.getAsNamespaceAndPrefix().Prefix;
+
   if (!NextNode)
     return false;
   return InnerMatcher.matches(NextNode, Finder, Builder);
@@ -7893,9 +7864,13 @@ AST_MATCHER_P_OVERLOAD(NestedNameSpecifierLoc, hasPrefix,
 ///   matches "ns::"
 AST_MATCHER_P(NestedNameSpecifier, specifiesNamespace,
               internal::Matcher<NamespaceDecl>, InnerMatcher) {
-  if (!Node.getAsNamespace())
+  if (Node.getKind() != NestedNameSpecifier::Kind::Namespace)
+    return false;
+  const auto *Namespace =
+      dyn_cast<NamespaceDecl>(Node.getAsNamespaceAndPrefix().Namespace);
+  if (!Namespace)
     return false;
-  return InnerMatcher.matches(*Node.getAsNamespace(), Finder, Builder);
+  return InnerMatcher.matches(*Namespace, Finder, Builder);
 }
 
 /// Matches attributes.
diff --git a/clang/include/clang/ASTMatchers/ASTMatchersInternal.h b/clang/include/clang/ASTMatchers/ASTMatchersInternal.h
index 5df2294792552..1ab6f11a23e12 100644
--- a/clang/include/clang/ASTMatchers/ASTMatchersInternal.h
+++ b/clang/include/clang/ASTMatchers/ASTMatchersInternal.h
@@ -1017,10 +1017,7 @@ class HasDeclarationMatcher : public MatcherInterface<T> {
     // First, for any types that have a declaration, extract the declaration and
     // match on it.
     if (const auto *S = dyn_cast<TagType>(&Node)) {
-      return matchesDecl(S->getDecl(), Finder, Builder);
-    }
-    if (const auto *S = dyn_cast<InjectedClassNameType>(&Node)) {
-      return matchesDecl(S->getDecl(), Finder, Builder);
+      return matchesDecl(S->getOriginalDecl(), Finder, Builder);
     }
     if (const auto *S = dyn_cast<TemplateTypeParmType>(&Node)) {
       return matchesDecl(S->getDecl(), Finder, Builder);
@@ -1031,6 +1028,9 @@ class HasDeclarationMatcher : public MatcherInterface<T> {
     if (const auto *S = dyn_cast<UnresolvedUsingType>(&Node)) {
       return matchesDecl(S->getDecl(), Finder, Builder);
     }
+    if (const auto *S = dyn_cast<UsingType>(&Node)) {
+      return matchesDecl(S->getDecl(), Finder, Builder);
+    }
     if (const auto *S = dyn_cast<ObjCObjectType>(&Node)) {
       return matchesDecl(S->getInterface(), Finder, Builder);
     }
@@ -1066,12 +1066,6 @@ class HasDeclarationMatcher : public MatcherInterface<T> {
                          Builder);
     }
 
-    // FIXME: We desugar elaborated types. This makes the assumption that users
-    // do never want to match on whether a type is elaborated - there are
-    // arguments for both sides; for now, continue desugaring.
-    if (const auto *S = dyn_cast<ElaboratedType>(&Node)) {
-      return matchesSpecialized(S->desugar(), Finder, Builder);
-    }
     // Similarly types found via using declarations.
     // These are *usually* meaningless sugar, and this matches the historical
     // behavior prior to the introduction of UsingType.
@@ -1211,8 +1205,8 @@ using AdaptativeDefaultToTypes =
 /// All types that are supported by HasDeclarationMatcher above.
 using HasDeclarationSupportedTypes =
     TypeList<CallExpr, CXXConstructExpr, CXXNewExpr, DeclRefExpr, EnumType,
-             ElaboratedType, InjectedClassNameType, LabelStmt, AddrLabelExpr,
-             MemberExpr, QualType, RecordType, TagType,
+             InjectedClassNameType, LabelStmt, AddrLabelExpr, MemberExpr,
+             QualType, RecordType, TagType, UsingType,
              TemplateSpecializationType, TemplateTypeParmType, TypedefType,
              UnresolvedUsingType, ObjCIvarRefExpr, ObjCInterfaceDecl>;
 
@@ -1789,7 +1783,7 @@ class LocMatcher : public MatcherInterface<TLoc> {
 
 private:
   static DynTypedNode extract(const NestedNameSpecifierLoc &Loc) {
-    return DynTypedNode::create(*Loc.getNestedNameSpecifier());
+    return DynTypedNode::create(Loc.getNestedNameSpecifier());
   }
 };
 
diff --git a/clang/include/clang/Analysis/FlowSensitive/ASTOps.h b/clang/include/clang/Analysis/FlowSensitive/ASTOps.h
index 8c7ee86d15c06..a404b06cd62ca 100644
--- a/clang/include/clang/Analysis/FlowSensitive/ASTOps.h
+++ b/clang/include/clang/Analysis/FlowSensitive/ASTOps.h
@@ -112,8 +112,14 @@ class AnalysisASTVisitor : public DynamicRecursiveASTVisitor {
   // fields that are only used in these.
   // Note: The operand of the `noexcept` operator is an unevaluated operand, but
   // nevertheless it appears in the Clang CFG, so we don't exclude it here.
-  bool TraverseDecltypeTypeLoc(DecltypeTypeLoc) override { return true; }
-  bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc) override { return true; }
+  bool TraverseDecltypeTypeLoc(DecltypeTypeLoc,
+                               bool TraverseQualifier) override {
+    return true;
+  }
+  bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc,
+                                 bool TraverseQualifier) override {
+    return true;
+  }
   bool TraverseCXXTypeidExpr(CXXTypeidExpr *TIE) override {
     if (TIE->isPotentiallyEvaluated())
       return DynamicRecursiveASTVisitor::TraverseCXXTypeidExpr(TIE);
diff --git a/clang/include/clang/Basic/DeclNodes.td b/clang/include/clang/Basic/DeclNodes.td
index f1ebaf1db3fc0..b4c02949426a1 100644
--- a/clang/include/clang/Basic/DeclNodes.td
+++ b/clang/include/clang/Basic/DeclNodes.td
@@ -15,81 +15,80 @@ def PragmaComment : DeclNode<Decl>;
 def PragmaDetectMismatch : DeclNode<Decl>;
 def ExternCContext : DeclNode<Decl>, DeclContext;
 def Named : DeclNode<Decl, "named declarations", 1>;
-  def Namespace : DeclNode<Named, "namespaces">, DeclContext;
-  def UsingDirective : DeclNode<Named>;
-  def NamespaceAlias : DeclNode<Named>;
-  def Label : DeclNode<Named, "labels">;
-  def Type : DeclNode<Named, "types", 1>;
-    def TypedefName : DeclNode<Type, "typedefs", 1>;
-      def Typedef : DeclNode<TypedefName>;
-      def TypeAlias : DeclNode<TypedefName>;
-      def ObjCTypeParam : DeclNode<TypedefName>;
-    def UnresolvedUsingTypename : DeclNode<Type>;
-    def Tag : DeclNode<Type, "tag types", 1>, DeclContext;
-      def Enum : DeclNode<Tag, "enums">;
-      def Record : DeclNode<Tag, "structs, unions, classes">;
-        def CXXRecord : DeclNode<Record, "classes">;
-          def ClassTemplateSpecialization : DeclNode<CXXRecord>;
-            def ClassTemplatePartialSpecialization
-              : DeclNode<ClassTemplateSpecialization>;
-    def TemplateTypeParm : DeclNode<Type>;
-  def Value : DeclNode<Named, "value declarations", 1>;
-    def EnumConstant : DeclNode<Value, "enumerators">;
-    def UnresolvedUsingValue : DeclNode<Value>;
-    def IndirectField : DeclNode<Value>;
-    def Binding : DeclNode<Value>;
-    def OMPDeclareReduction : DeclNode<Value>, DeclContext;
-    def OMPDeclareMapper : DeclNode<Value>, DeclContext;
-    def MSGuid : DeclNode<Value>;
-    def UnnamedGlobalConstant : DeclNode<Value>;
-    def TemplateParamObject : DeclNode<Value>;
-    def Declarator : DeclNode<Value, "declarators", 1>;
-      def Field : DeclNode<Declarator, "non-static data members">;
-        def ObjCIvar : DeclNode<Field>;
-        def ObjCAtDefsField : DeclNode<Field>;
-      def MSProperty : DeclNode<Declarator>;
-      def Function : DeclNode<Declarator, "functions">, DeclContext;
-        def CXXDeductionGuide : DeclNode<Function>;
-        def CXXMethod : DeclNode<Function>;
-          def CXXConstructor : DeclNode<CXXMethod>;
-          def CXXDestructor : DeclNode<CXXMethod>;
-          def CXXConversion : DeclNode<CXXMethod>;
-      def Var : DeclNode<Declarator, "variables">;
-        def VarTemplateSpecialization : DeclNode<Var>;
-          def VarTemplatePartialSpecialization
-            : DeclNode<VarTemplateSpecialization>;
-        def ImplicitParam : DeclNode<Var>;
-        def ParmVar : DeclNode<Var, "parameters">;
-        def Decomposition : DeclNode<Var>;
-        def OMPCapturedExpr : DeclNode<Var>;
-      def NonTypeTemplateParm : DeclNode<Declarator>;
-  def Template : DeclNode<Named, "templates", 1>;
-    def RedeclarableTemplate : DeclNode<Template, "redeclarable templates", 1>;
-      def FunctionTemplate : DeclNode<RedeclarableTemplate>;
-      def ClassTemplate : DeclNode<RedeclarableTemplate>;
-      def VarTemplate : DeclNode<RedeclarableTemplate>;
-      def TypeAliasTemplate : DeclNode<RedeclarableTemplate>;
-    def TemplateTemplateParm : DeclNode<Template>;
-    def BuiltinTemplate : DeclNode<Template>;
-    def Concept : DeclNode<Template>;
-  def BaseUsing : DeclNode<Named, "", 1>;
-    def Using : DeclNode<BaseUsing>;
-    def UsingEnum : DeclNode<BaseUsing>;
-  def UsingPack : DeclNode<Named>;
-  def UsingShadow : DeclNode<Named>;
-    def ConstructorUsingShadow : DeclNode<UsingShadow>;
-  def UnresolvedUsingIfExists : DeclNode<Named>;
-  def ObjCMethod : DeclNode<Named, "Objective-C methods">, DeclContext;
-  def ObjCContainer : DeclNode<Named, "Objective-C containers", 1>, DeclContext;
-    def ObjCCategory : DeclNode<ObjCContainer>;
-    def ObjCProtocol : DeclNode<ObjCContainer, "Objective-C protocols">;
-    def ObjCInterface : DeclNode<ObjCContainer, "Objective-C interfaces">;
-    def ObjCImpl
-        : DeclNode<ObjCContainer, "Objective-C implementation declarations", 1>;
-      def ObjCCategoryImpl : DeclNode<ObjCImpl>;
-      def ObjCImplementation : DeclNode<ObjCImpl>;
-  def ObjCProperty : DeclNode<Named, "Objective-C properties">;
-  def ObjCCompatibleAlias : DeclNode<Named>;
+def NamespaceBase : DeclNode<Named, "namespace declarations", 1>;
+def Namespace : DeclNode<NamespaceBase, "namespaces">, DeclContext;
+def NamespaceAlias : DeclNode<NamespaceBase>;
+def UsingDirective : DeclNode<Named>;
+def Label : DeclNode<Named, "labels">;
+def Type : DeclNode<Named, "types", 1>;
+def TypedefName : DeclNode<Type, "typedefs", 1>;
+def Typedef : DeclNode<TypedefName>;
+def TypeAlias : DeclNode<TypedefName>;
+def ObjCTypeParam : DeclNode<TypedefName>;
+def UnresolvedUsingTypename : DeclNode<Type>;
+def Tag : DeclNode<Type, "tag types", 1>, DeclContext;
+def Enum : DeclNode<Tag, "enums">;
+def Record : DeclNode<Tag, "structs, unions, classes">;
+def CXXRecord : DeclNode<Record, "classes">;
+def ClassTemplateSpecialization : DeclNode<CXXRecord>;
+def ClassTemplatePartialSpecialization : DeclNode<ClassTemplateSpecialization>;
+def TemplateTypeParm : DeclNode<Type>;
+def Value : DeclNode<Named, "value declarations", 1>;
+def EnumConstant : DeclNode<Value, "enumerators">;
+def UnresolvedUsingValue : DeclNode<Value>;
+def IndirectField : DeclNode<Value>;
+def Binding : DeclNode<Value>;
+def OMPDeclareReduction : DeclNode<Value>, DeclContext;
+def OMPDeclareMapper : DeclNode<Value>, DeclContext;
+def MSGuid : DeclNode<Value>;
+def UnnamedGlobalConstant : DeclNode<Value>;
+def TemplateParamObject : DeclNode<Value>;
+def Declarator : DeclNode<Value, "declarators", 1>;
+def Field : DeclNode<Declarator, "non-static data members">;
+def ObjCIvar : DeclNode<Field>;
+def ObjCAtDefsField : DeclNode<Field>;
+def MSProperty : DeclNode<Declarator>;
+def Function : DeclNode<Declarator, "functions">, DeclContext;
+def CXXDeductionGuide : DeclNode<Function>;
+def CXXMethod : DeclNode<Function>;
+def CXXConstructor : DeclNode<CXXMethod>;
+def CXXDestructor : DeclNode<CXXMethod>;
+def CXXConversion : DeclNode<CXXMethod>;
+def Var : DeclNode<Declarator, "variables">;
+def VarTemplateSpecialization : DeclNode<Var>;
+def VarTemplatePartialSpecialization : DeclNode<VarTemplateSpecialization>;
+def ImplicitParam : DeclNode<Var>;
+def ParmVar : DeclNode<Var, "parameters">;
+def Decomposition : DeclNode<Var>;
+def OMPCapturedExpr : DeclNode<Var>;
+def NonTypeTemplateParm : DeclNode<Declarator>;
+def Template : DeclNode<Named, "templates", 1>;
+def RedeclarableTemplate : DeclNode<Template, "redeclarable templates", 1>;
+def FunctionTemplate : DeclNode<RedeclarableTemplate>;
+def ClassTemplate : DeclNode<RedeclarableTemplate>;
+def VarTemplate : DeclNode<RedeclarableTemplate>;
+def TypeAliasTemplate : DeclNode<RedeclarableTemplate>;
+def TemplateTemplateParm : DeclNode<Template>;
+def BuiltinTemplate : DeclNode<Template>;
+def Concept : DeclNode<Template>;
+def BaseUsing : DeclNode<Named, "", 1>;
+def Using : DeclNode<BaseUsing>;
+def UsingEnum : DeclNode<BaseUsing>;
+def UsingPack : DeclNode<Named>;
+def UsingShadow : DeclNode<Named>;
+def ConstructorUsingShadow : DeclNode<UsingShadow>;
+def UnresolvedUsingIfExists : DeclNode<Named>;
+def ObjCMethod : DeclNode<Named, "Objective-C methods">, DeclContext;
+def ObjCContainer : DeclNode<Named, "Objective-C containers", 1>, DeclContext;
+def ObjCCategory : DeclNode<ObjCContainer>;
+def ObjCProtocol : DeclNode<ObjCContainer, "Objective-C protocols">;
+def ObjCInterface : DeclNode<ObjCContainer, "Objective-C interfaces">;
+def ObjCImpl
+    : DeclNode<ObjCContainer, "Objective-C implementation declarations", 1>;
+def ObjCCategoryImpl : DeclNode<ObjCImpl>;
+def ObjCImplementation : DeclNode<ObjCImpl>;
+def ObjCProperty : DeclNode<Named, "Objective-C properties">;
+def ObjCCompatibleAlias : DeclNode<Named>;
 def ImplicitConceptSpecialization : DeclNode<Decl>;
 def LinkageSpec : DeclNode<Decl>, DeclContext;
 def Export : DeclNode<Decl>, DeclContext;
diff --git a/clang/include/clang/Basic/TypeNodes.td b/clang/include/clang/Basic/TypeNodes.td
index 567b8a5ca5a4d..5f3b20e4f3245 100644
--- a/clang/include/clang/Basic/TypeNodes.td
+++ b/clang/include/clang/Basic/TypeNodes.td
@@ -90,7 +90,7 @@ def UnaryTransformType : TypeNode<Type>, NeverCanonicalUnlessDependent;
 def TagType : TypeNode<Type, 1>;
 def RecordType : TypeNode<TagType>, LeafType;
 def EnumType : TypeNode<TagType>, LeafType;
-def ElaboratedType : TypeNode<Type>, NeverCanonical;
+def InjectedClassNameType : TypeNode<TagType>, AlwaysDependent, LeafType;
 def AttributedType : TypeNode<Type>, NeverCanonical;
 def BTFTagAttributedType : TypeNode<Type>, NeverCanonical;
 def HLSLAttributedResourceType : TypeNode<Type>;
@@ -102,7 +102,6 @@ def TemplateSpecializationType : TypeNode<Type>, NeverCanonicalUnlessDependent;
 def DeducedType : TypeNode<Type, 1>;
 def AutoType : TypeNode<DeducedType>;
 def DeducedTemplateSpecializationType : TypeNode<DeducedType>;
-def InjectedClassNameType : TypeNode<Type>, AlwaysDependent, LeafType;
 def DependentNameType : TypeNode<Type>, AlwaysDependent;
 def DependentTemplateSpecializationType : TypeNode<Type>, AlwaysDependent;
 def PackExpansionType : TypeNode<Type>, AlwaysDependent;
diff --git a/clang/include/clang/ExtractAPI/DeclarationFragments.h b/clang/include/clang/ExtractAPI/DeclarationFragments.h
index 4ac744459031e..4859225ef4ced 100644
--- a/clang/include/clang/ExtractAPI/DeclarationFragments.h
+++ b/clang/include/clang/ExtractAPI/DeclarationFragments.h
@@ -440,9 +440,8 @@ class DeclarationFragmentsBuilder {
                                                   DeclarationFragments &);
 
   /// Build DeclarationFragments for a NestedNameSpecifier.
-  static DeclarationFragments getFragmentsForNNS(const NestedNameSpecifier *,
-                                                 ASTContext &,
-                                                 DeclarationFragments &);
+  static DeclarationFragments
+  getFragmentsForNNS(NestedNameSpecifier, ASTContext &, DeclarationFragments &);
 
   /// Build DeclarationFragments for Qualifiers.
   static DeclarationFragments getFragmentsForQualifiers(const Qualifiers quals);
diff --git a/clang/include/clang/Sema/CodeCompleteConsumer.h b/clang/include/clang/Sema/CodeCompleteConsumer.h
index 2dd27593778c7..c26f4e33d289c 100644
--- a/clang/include/clang/Sema/CodeCompleteConsumer.h
+++ b/clang/include/clang/Sema/CodeCompleteConsumer.h
@@ -162,7 +162,8 @@ SimplifiedTypeClass getSimplifiedTypeClass(CanQualType T);
 
 /// Determine the type that this declaration will have if it is used
 /// as a type or in an expression.
-QualType getDeclUsageType(ASTContext &C, const NamedDecl *ND);
+QualType getDeclUsageType(ASTContext &C, NestedNameSpecifier Qualifier,
+                          const NamedDecl *ND);
 
 /// Determine the priority to be given to a macro code completion result
 /// with the given name.
@@ -867,7 +868,7 @@ class CodeCompletionResult {
   /// If the result should have a nested-name-specifier, this is it.
   /// When \c QualifierIsInformative, the nested-name-specifier is
   /// informative rather than required.
-  NestedNameSpecifier *Qualifier = nullptr;
+  NestedNameSpecifier Qualifier = std::nullopt;
 
   /// If this Decl was unshadowed by using declaration, this can store a
   /// pointer to the UsingShadowDecl which was used in the unshadowing process.
@@ -882,7 +883,7 @@ class CodeCompletionResult {
 
   /// Build a result that refers to a declaration.
   CodeCompletionResult(const NamedDecl *Declaration, unsigned Priority,
-                       NestedNameSpecifier *Qualifier = nullptr,
+                       NestedNameSpecifier Qualifier = std::nullopt,
                        bool QualifierIsInformative = false,
                        bool Accessible = true,
                        std::vector<FixItHint> FixIts = std::vector<FixItHint>())
diff --git a/clang/include/clang/Sema/DeclSpec.h b/clang/include/clang/Sema/DeclSpec.h
index 567ad2d5934d4..f16d9b5680ee2 100644
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -92,12 +92,11 @@ class CXXScopeSpec {
   }
 
   /// Retrieve the representation of the nested-name-specifier.
-  NestedNameSpecifier *getScopeRep() const {
+  NestedNameSpecifier getScopeRep() const {
     return Builder.getRepresentation();
   }
 
-  /// Extend the current nested-name-specifier by another
-  /// nested-name-specifier component of the form 'type::'.
+  /// Make a nested-name-specifier of the form 'type::'.
   ///
   /// \param Context The AST context in which this nested-name-specifier
   /// resides.
@@ -107,21 +106,7 @@ class CXXScopeSpec {
   /// \param TL The TypeLoc that describes the type preceding the '::'.
   ///
   /// \param ColonColonLoc The location of the trailing '::'.
-  void Extend(ASTContext &Context, TypeLoc TL, SourceLocation ColonColonLoc);
-
-  /// Extend the current nested-name-specifier by another
-  /// nested-name-specifier component of the form 'identifier::'.
-  ///
-  /// \param Context The AST context in which this nested-name-specifier
-  /// resides.
-  ///
-  /// \param Identifier The identifier.
-  ///
-  /// \param IdentifierLoc The location of the identifier.
-  ///
-  /// \param ColonColonLoc The location of the trailing '::'.
-  void Extend(ASTContext &Context, IdentifierInfo *Identifier,
-              SourceLocation IdentifierLoc, SourceLocation ColonColonLoc);
+  void Make(ASTContext &Context, TypeLoc TL, SourceLocation ColonColonLoc);
 
   /// Extend the current nested-name-specifier by another
   /// nested-name-specifier component of the form 'namespace::'.
@@ -134,24 +119,9 @@ class CXXScopeSpec {
   /// \param NamespaceLoc The location of the namespace name.
   ///
   /// \param ColonColonLoc The location of the trailing '::'.
-  void Extend(ASTContext &Context, NamespaceDecl *Namespace,
+  void Extend(ASTContext &Context, NamespaceBaseDecl *Namespace,
               SourceLocation NamespaceLoc, SourceLocation ColonColonLoc);
 
-  /// Extend the current nested-name-specifier by another
-  /// nested-name-specifier component of the form 'namespace-alias::'.
-  ///
-  /// \param Context The AST context in which this nested-name-specifier
-  /// resides.
-  ///
-  /// \param Alias The namespace alias.
-  ///
-  /// \param AliasLoc The location of the namespace alias
-  /// name.
-  ///
-  /// \param ColonColonLoc The location of the trailing '::'.
-  void Extend(ASTContext &Context, NamespaceAliasDecl *Alias,
-              SourceLocation AliasLoc, SourceLocation ColonColonLoc);
-
   /// Turn this (empty) nested-name-specifier into the global
   /// nested-name-specifier '::'.
   void MakeGlobal(ASTContext &Context, SourceLocation ColonColonLoc);
@@ -178,7 +148,7 @@ class CXXScopeSpec {
   /// FIXME: This routine should be used very, very rarely, in cases where we
   /// need to synthesize a nested-name-specifier. Most code should instead use
   /// \c Adopt() with a proper \c NestedNameSpecifierLoc.
-  void MakeTrivial(ASTContext &Context, NestedNameSpecifier *Qualifier,
+  void MakeTrivial(ASTContext &Context, NestedNameSpecifier Qualifier,
                    SourceRange R);
 
   /// Adopt an existing nested-name-specifier (with source-range
@@ -204,14 +174,14 @@ class CXXScopeSpec {
   SourceLocation getLastQualifierNameLoc() const;
 
   /// No scope specifier.
-  bool isEmpty() const { return Range.isInvalid() && getScopeRep() == nullptr; }
+  bool isEmpty() const { return Range.isInvalid() && !getScopeRep(); }
   /// A scope specifier is present, but may be valid or invalid.
   bool isNotEmpty() const { return !isEmpty(); }
 
   /// An error occurred during parsing of the scope specifier.
-  bool isInvalid() const { return Range.isValid() && getScopeRep() == nullptr; }
+  bool isInvalid() const { return Range.isValid() && !getScopeRep(); }
   /// A scope specifier is present, and it refers to a real scope.
-  bool isValid() const { return getScopeRep() != nullptr; }
+  bool isValid() const { return bool(getScopeRep()); }
 
   /// Indicate that this nested-name-specifier is invalid.
   void SetInvalid(SourceRange R) {
@@ -224,7 +194,7 @@ class CXXScopeSpec {
 
   /// Deprecated.  Some call sites intend isNotEmpty() while others intend
   /// isValid().
-  bool isSet() const { return getScopeRep() != nullptr; }
+  bool isSet() const { return bool(getScopeRep()); }
 
   void clear() {
     Range = SourceRange();
diff --git a/clang/include/clang/Sema/HeuristicResolver.h b/clang/include/clang/Sema/HeuristicResolver.h
index e193c0bc14cd9..71588bee92d16 100644
--- a/clang/include/clang/Sema/HeuristicResolver.h
+++ b/clang/include/clang/Sema/HeuristicResolver.h
@@ -67,8 +67,7 @@ class HeuristicResolver {
   // Try to heuristically resolve a dependent nested name specifier
   // to the type it likely denotes. Note that *dependent* name specifiers always
   // denote types, not namespaces.
-  QualType
-  resolveNestedNameSpecifierToType(const NestedNameSpecifier *NNS) const;
+  QualType resolveNestedNameSpecifierToType(NestedNameSpecifier NNS) const;
 
   // Perform an imprecise lookup of a dependent name in `RD`.
   // This function does not follow strict semantic rules and should be used
diff --git a/clang/include/clang/Sema/ParsedTemplate.h b/clang/include/clang/Sema/ParsedTemplate.h
index 3a8050f9a0a3d..4a3df781b5a58 100644
--- a/clang/include/clang/Sema/ParsedTemplate.h
+++ b/clang/include/clang/Sema/ParsedTemplate.h
@@ -48,8 +48,8 @@ namespace clang {
     ///
     /// \param Arg the template type argument or non-type template argument.
     /// \param Loc the location of the type.
-    ParsedTemplateArgument(KindType Kind, void *Arg, SourceLocation Loc)
-      : Kind(Kind), Arg(Arg), Loc(Loc) { }
+    ParsedTemplateArgument(KindType Kind, void *Arg, SourceLocation NameLoc)
+        : Kind(Kind), Arg(Arg), NameLoc(NameLoc) {}
 
     /// Create a template template argument.
     ///
@@ -60,11 +60,11 @@ namespace clang {
     /// argument refers.
     ///
     /// \param TemplateLoc the location of the template name.
-    ParsedTemplateArgument(const CXXScopeSpec &SS,
-                           ParsedTemplateTy Template,
-                           SourceLocation TemplateLoc)
-      : Kind(ParsedTemplateArgument::Template),
-        Arg(Template.getAsOpaquePtr()), SS(SS), Loc(TemplateLoc) {}
+    ParsedTemplateArgument(SourceLocation TemplateKwLoc, const CXXScopeSpec &SS,
+                           ParsedTemplateTy Template, SourceLocation NameLoc)
+        : Kind(ParsedTemplateArgument::Template),
+          Arg(Template.getAsOpaquePtr()), SS(SS), TemplateKwLoc(TemplateKwLoc),
+          NameLoc(NameLoc) {}
 
     /// Determine whether the given template argument is invalid.
     bool isInvalid() const { return Arg == nullptr; }
@@ -91,7 +91,10 @@ namespace clang {
     }
 
     /// Retrieve the location of the template argument.
-    SourceLocation getLocation() const { return Loc; }
+    SourceLocation getTemplateKwLoc() const { return TemplateKwLoc; }
+
+    /// Retrieve the location of the template argument.
+    SourceLocation getNameLoc() const { return NameLoc; }
 
     /// Retrieve the nested-name-specifier that precedes the template
     /// name in a template template argument.
@@ -128,8 +131,11 @@ namespace clang {
     /// argument.
     CXXScopeSpec SS;
 
-    /// the location of the template argument.
-    SourceLocation Loc;
+    /// the location of the template keyword.
+    SourceLocation TemplateKwLoc;
+
+    /// the location of the template name.
+    SourceLocation NameLoc;
 
     /// The ellipsis location that can accompany a template template
     /// argument (turning it into a template template argument expansion).
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index b331acbe606b7..1655c855d119e 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -3218,7 +3218,7 @@ class Sema final : public SemaBase {
   /// current instantiation (C++0x [temp.dep.type]p1).
   ///
   /// \param NNS a dependent nested name specifier.
-  CXXRecordDecl *getCurrentInstantiationOf(NestedNameSpecifier *NNS);
+  CXXRecordDecl *getCurrentInstantiationOf(NestedNameSpecifier NNS);
 
   /// The parser has parsed a global nested-name-specifier '::'.
   ///
@@ -3255,7 +3255,7 @@ class Sema final : public SemaBase {
   /// (e.g., Base::), perform name lookup for that identifier as a
   /// nested-name-specifier within the given scope, and return the result of
   /// that name lookup.
-  NamedDecl *FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS);
+  NamedDecl *FindFirstQualifierInScope(Scope *S, NestedNameSpecifier NNS);
 
   /// Keeps information about an identifier in a nested-name-spec.
   ///
@@ -3574,8 +3574,8 @@ class Sema final : public SemaBase {
   /// Returns the TypeDeclType for the given type declaration,
   /// as ASTContext::getTypeDeclType would, but
   /// performs the required semantic checks for name lookup of said entity.
-  QualType getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
-                           TypeDecl *TD, SourceLocation NameLoc);
+  void checkTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK, TypeDecl *TD,
+                         SourceLocation NameLoc);
 
   /// If the identifier refers to a type name within this scope,
   /// return the declaration of that type.
@@ -7618,7 +7618,7 @@ class Sema final : public SemaBase {
   /// "real" base class is checked as appropriate when checking the access of
   /// the member name.
   ExprResult PerformObjectMemberConversion(Expr *From,
-                                           NestedNameSpecifier *Qualifier,
+                                           NestedNameSpecifier Qualifier,
                                            NamedDecl *FoundDecl,
                                            NamedDecl *Member);
 
@@ -10196,7 +10196,7 @@ class Sema final : public SemaBase {
   ExprResult InitializeExplicitObjectArgument(Sema &S, Expr *Obj,
                                               FunctionDecl *Fun);
   ExprResult PerformImplicitObjectArgumentInitialization(
-      Expr *From, NestedNameSpecifier *Qualifier, NamedDecl *FoundDecl,
+      Expr *From, NestedNameSpecifier Qualifier, NamedDecl *FoundDecl,
       CXXMethodDecl *Method);
 
   /// PerformContextuallyConvertToBool - Perform a contextual conversion
@@ -11603,13 +11603,16 @@ class Sema final : public SemaBase {
 
   void NoteAllFoundTemplates(TemplateName Name);
 
-  QualType CheckTemplateIdType(TemplateName Template,
+  QualType CheckTemplateIdType(ElaboratedTypeKeyword Keyword,
+                               TemplateName Template,
                                SourceLocation TemplateLoc,
                                TemplateArgumentListInfo &TemplateArgs);
 
   TypeResult
-  ActOnTemplateIdType(Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
-                      TemplateTy Template, const IdentifierInfo *TemplateII,
+  ActOnTemplateIdType(Scope *S, ElaboratedTypeKeyword ElaboratedKeyword,
+                      SourceLocation ElaboratedKeywordLoc, CXXScopeSpec &SS,
+                      SourceLocation TemplateKWLoc, TemplateTy Template,
+                      const IdentifierInfo *TemplateII,
                       SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
                       ASTTemplateArgsPtr TemplateArgs, SourceLocation RAngleLoc,
                       bool IsCtorOrDtorName = false, bool IsClassName = false,
@@ -11838,8 +11841,8 @@ class Sema final : public SemaBase {
   /// argument, substitute into that default template argument and
   /// return the corresponding template argument.
   TemplateArgumentLoc SubstDefaultTemplateArgumentIfAvailable(
-      TemplateDecl *Template, SourceLocation TemplateLoc,
-      SourceLocation RAngleLoc, Decl *Param,
+      TemplateDecl *Template, SourceLocation TemplateKWLoc,
+      SourceLocation TemplateNameLoc, SourceLocation RAngleLoc, Decl *Param,
       ArrayRef<TemplateArgument> SugaredConverted,
       ArrayRef<TemplateArgument> CanonicalConverted, bool &HasDefaultArg);
 
@@ -13738,8 +13741,9 @@ class Sema final : public SemaBase {
   SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
                            const MultiLevelTemplateArgumentList &TemplateArgs);
   TemplateName
-  SubstTemplateName(NestedNameSpecifierLoc QualifierLoc, TemplateName Name,
-                    SourceLocation Loc,
+  SubstTemplateName(SourceLocation TemplateKWLoc,
+                    NestedNameSpecifierLoc &QualifierLoc, TemplateName Name,
+                    SourceLocation NameLoc,
                     const MultiLevelTemplateArgumentList &TemplateArgs);
 
   bool SubstTypeConstraint(TemplateTypeParmDecl *Inst, const TypeConstraint *TC,
@@ -15155,14 +15159,6 @@ class Sema final : public SemaBase {
     return RequireCompleteExprType(E, CompleteTypeKind::Default, Diagnoser);
   }
 
-  /// Retrieve a version of the type 'T' that is elaborated by Keyword,
-  /// qualified by the nested-name-specifier contained in SS, and that is
-  /// (re)declared by OwnedTagDecl, which is nullptr if this is not a
-  /// (re)declaration.
-  QualType getElaboratedType(ElaboratedTypeKeyword Keyword,
-                             const CXXScopeSpec &SS, QualType T,
-                             TagDecl *OwnedTagDecl = nullptr);
-
   // Returns the underlying type of a decltype with the given expression.
   QualType getDecltypeForExpr(Expr *E);
 
diff --git a/clang/include/clang/Sema/SemaInternal.h b/clang/include/clang/Sema/SemaInternal.h
index 4d0da1102bb59..c6287f4c76a11 100644
--- a/clang/include/clang/Sema/SemaInternal.h
+++ b/clang/include/clang/Sema/SemaInternal.h
@@ -208,7 +208,7 @@ class TypoCorrectionConsumer : public VisibleDeclConsumer {
   class NamespaceSpecifierSet {
     struct SpecifierInfo {
       DeclContext* DeclCtx;
-      NestedNameSpecifier* NameSpecifier;
+      NestedNameSpecifier NameSpecifier;
       unsigned EditDistance;
     };
 
@@ -228,9 +228,9 @@ class TypoCorrectionConsumer : public VisibleDeclConsumer {
     static DeclContextList buildContextChain(DeclContext *Start);
 
     unsigned buildNestedNameSpecifier(DeclContextList &DeclChain,
-                                      NestedNameSpecifier *&NNS);
+                                      NestedNameSpecifier &NNS);
 
-   public:
+  public:
     NamespaceSpecifierSet(ASTContext &Context, DeclContext *CurContext,
                           CXXScopeSpec *CurScopeSpec);
 
@@ -275,7 +275,7 @@ class TypoCorrectionConsumer : public VisibleDeclConsumer {
   };
 
   void addName(StringRef Name, NamedDecl *ND,
-               NestedNameSpecifier *NNS = nullptr, bool isKeyword = false);
+               NestedNameSpecifier NNS = std::nullopt, bool isKeyword = false);
 
   /// Find any visible decls for the given typo correction candidate.
   /// If none are found, it to the set of candidates for which qualified lookups
diff --git a/clang/include/clang/Sema/TypoCorrection.h b/clang/include/clang/Sema/TypoCorrection.h
index 09de164297e7b..1d780c45efd55 100644
--- a/clang/include/clang/Sema/TypoCorrection.h
+++ b/clang/include/clang/Sema/TypoCorrection.h
@@ -57,15 +57,15 @@ class TypoCorrection {
   static const unsigned CallbackDistanceWeight = 150U;
 
   TypoCorrection(const DeclarationName &Name, NamedDecl *NameDecl,
-                 NestedNameSpecifier *NNS = nullptr, unsigned CharDistance = 0,
-                 unsigned QualifierDistance = 0)
+                 NestedNameSpecifier NNS = std::nullopt,
+                 unsigned CharDistance = 0, unsigned QualifierDistance = 0)
       : CorrectionName(Name), CorrectionNameSpec(NNS),
         CharDistance(CharDistance), QualifierDistance(QualifierDistance) {
     if (NameDecl)
       CorrectionDecls.push_back(NameDecl);
   }
 
-  TypoCorrection(NamedDecl *Name, NestedNameSpecifier *NNS = nullptr,
+  TypoCorrection(NamedDecl *Name, NestedNameSpecifier NNS = std::nullopt,
                  unsigned CharDistance = 0)
       : CorrectionName(Name->getDeclName()), CorrectionNameSpec(NNS),
         CharDistance(CharDistance) {
@@ -73,7 +73,7 @@ class TypoCorrection {
       CorrectionDecls.push_back(Name);
   }
 
-  TypoCorrection(DeclarationName Name, NestedNameSpecifier *NNS = nullptr,
+  TypoCorrection(DeclarationName Name, NestedNameSpecifier NNS = std::nullopt,
                  unsigned CharDistance = 0)
       : CorrectionName(Name), CorrectionNameSpec(NNS),
         CharDistance(CharDistance) {}
@@ -88,13 +88,13 @@ class TypoCorrection {
   }
 
   /// Gets the NestedNameSpecifier needed to use the typo correction
-  NestedNameSpecifier *getCorrectionSpecifier() const {
+  NestedNameSpecifier getCorrectionSpecifier() const {
     return CorrectionNameSpec;
   }
 
-  void setCorrectionSpecifier(NestedNameSpecifier *NNS) {
+  void setCorrectionSpecifier(NestedNameSpecifier NNS) {
     CorrectionNameSpec = NNS;
-    ForceSpecifierReplacement = (NNS != nullptr);
+    ForceSpecifierReplacement = !!NNS;
   }
 
   void WillReplaceSpecifier(bool ForceReplacement) {
@@ -264,7 +264,7 @@ class TypoCorrection {
 
   // Results.
   DeclarationName CorrectionName;
-  NestedNameSpecifier *CorrectionNameSpec = nullptr;
+  NestedNameSpecifier CorrectionNameSpec = std::nullopt;
   SmallVector<NamedDecl *, 1> CorrectionDecls;
   unsigned CharDistance = 0;
   unsigned QualifierDistance = 0;
@@ -282,8 +282,9 @@ class CorrectionCandidateCallback {
 public:
   static const unsigned InvalidDistance = TypoCorrection::InvalidDistance;
 
-  explicit CorrectionCandidateCallback(const IdentifierInfo *Typo = nullptr,
-                                       NestedNameSpecifier *TypoNNS = nullptr)
+  explicit CorrectionCandidateCallback(
+      const IdentifierInfo *Typo = nullptr,
+      NestedNameSpecifier TypoNNS = std::nullopt)
       : Typo(Typo), TypoNNS(TypoNNS) {}
 
   virtual ~CorrectionCandidateCallback() = default;
@@ -320,7 +321,7 @@ class CorrectionCandidateCallback {
   virtual std::unique_ptr<CorrectionCandidateCallback> clone() = 0;
 
   void setTypoName(const IdentifierInfo *II) { Typo = II; }
-  void setTypoNNS(NestedNameSpecifier *NNS) { TypoNNS = NNS; }
+  void setTypoNNS(NestedNameSpecifier NNS) { TypoNNS = NNS; }
 
   // Flags for context-dependent keywords. WantFunctionLikeCasts is only
   // used/meaningful when WantCXXNamedCasts is false.
@@ -346,13 +347,13 @@ class CorrectionCandidateCallback {
   }
 
   const IdentifierInfo *Typo;
-  NestedNameSpecifier *TypoNNS;
+  NestedNameSpecifier TypoNNS;
 };
 
 class DefaultFilterCCC final : public CorrectionCandidateCallback {
 public:
   explicit DefaultFilterCCC(const IdentifierInfo *Typo = nullptr,
-                            NestedNameSpecifier *TypoNNS = nullptr)
+                            NestedNameSpecifier TypoNNS = std::nullopt)
       : CorrectionCandidateCallback(Typo, TypoNNS) {}
 
   std::unique_ptr<CorrectionCandidateCallback> clone() override {
@@ -366,7 +367,7 @@ template <class C>
 class DeclFilterCCC final : public CorrectionCandidateCallback {
 public:
   explicit DeclFilterCCC(const IdentifierInfo *Typo = nullptr,
-                         NestedNameSpecifier *TypoNNS = nullptr)
+                         NestedNameSpecifier TypoNNS = std::nullopt)
       : CorrectionCandidateCallback(Typo, TypoNNS) {}
 
   bool ValidateCandidate(const TypoCorrection &candidate) override {
diff --git a/clang/include/clang/Serialization/ASTRecordReader.h b/clang/include/clang/Serialization/ASTRecordReader.h
index 1472497ff5e7e..aed1b7d309001 100644
--- a/clang/include/clang/Serialization/ASTRecordReader.h
+++ b/clang/include/clang/Serialization/ASTRecordReader.h
@@ -223,7 +223,7 @@ class ASTRecordReader
   void readQualifierInfo(QualifierInfo &Info);
 
   /// Return a nested name specifier, advancing Idx.
-  // NestedNameSpecifier *readNestedNameSpecifier(); (inherited)
+  // NestedNameSpecifier readNestedNameSpecifier(); (inherited)
 
   NestedNameSpecifierLoc readNestedNameSpecifierLoc();
 
diff --git a/clang/include/clang/Serialization/ASTRecordWriter.h b/clang/include/clang/Serialization/ASTRecordWriter.h
index ee005ec287708..9849ea6b395ab 100644
--- a/clang/include/clang/Serialization/ASTRecordWriter.h
+++ b/clang/include/clang/Serialization/ASTRecordWriter.h
@@ -247,8 +247,7 @@ class ASTRecordWriter
   void AddTypeLoc(TypeLoc TL);
 
   /// Emits a template argument location info.
-  void AddTemplateArgumentLocInfo(TemplateArgument::ArgKind Kind,
-                                  const TemplateArgumentLocInfo &Arg);
+  void AddTemplateArgumentLocInfo(const TemplateArgumentLoc &Arg);
 
   /// Emits a template argument location.
   void AddTemplateArgumentLoc(const TemplateArgumentLoc &Arg);
@@ -280,7 +279,7 @@ class ASTRecordWriter
   void AddQualifierInfo(const QualifierInfo &Info);
 
   /// Emit a nested name specifier.
-  void AddNestedNameSpecifier(NestedNameSpecifier *NNS) {
+  void AddNestedNameSpecifier(NestedNameSpecifier NNS) {
     writeNestedNameSpecifier(NNS);
   }
 
diff --git a/clang/include/clang/Serialization/TypeBitCodes.def b/clang/include/clang/Serialization/TypeBitCodes.def
index b8cde2e370960..8abdf5e842541 100644
--- a/clang/include/clang/Serialization/TypeBitCodes.def
+++ b/clang/include/clang/Serialization/TypeBitCodes.def
@@ -32,7 +32,6 @@ TYPE_BIT_CODE(Enum, ENUM, 20)
 TYPE_BIT_CODE(ObjCInterface, OBJC_INTERFACE, 21)
 TYPE_BIT_CODE(ObjCObjectPointer, OBJC_OBJECT_POINTER, 22)
 TYPE_BIT_CODE(Decltype, DECLTYPE, 23)
-TYPE_BIT_CODE(Elaborated, ELABORATED, 24)
 TYPE_BIT_CODE(SubstTemplateTypeParm, SUBST_TEMPLATE_TYPE_PARM, 25)
 TYPE_BIT_CODE(UnresolvedUsing, UNRESOLVED_USING, 26)
 TYPE_BIT_CODE(InjectedClassName, INJECTED_CLASS_NAME, 27)
diff --git a/clang/include/clang/Tooling/Refactoring/Lookup.h b/clang/include/clang/Tooling/Refactoring/Lookup.h
index dcb40b7eee66c..fe0df8656bce1 100644
--- a/clang/include/clang/Tooling/Refactoring/Lookup.h
+++ b/clang/include/clang/Tooling/Refactoring/Lookup.h
@@ -38,8 +38,7 @@ namespace tooling {
 /// \param ReplacementString The replacement nested name. Must be fully
 ///                          qualified including a leading "::".
 /// \returns The new name to be inserted in place of the current nested name.
-std::string replaceNestedName(const NestedNameSpecifier *Use,
-                              SourceLocation UseLoc,
+std::string replaceNestedName(NestedNameSpecifier Use, SourceLocation UseLoc,
                               const DeclContext *UseContext,
                               const NamedDecl *FromDecl,
                               StringRef ReplacementString);
diff --git a/clang/include/clang/Tooling/Refactoring/RecursiveSymbolVisitor.h b/clang/include/clang/Tooling/Refactoring/RecursiveSymbolVisitor.h
index 015dbba26f688..319569fd5ab33 100644
--- a/clang/include/clang/Tooling/Refactoring/RecursiveSymbolVisitor.h
+++ b/clang/include/clang/Tooling/Refactoring/RecursiveSymbolVisitor.h
@@ -108,18 +108,21 @@ class RecursiveSymbolVisitor
   bool VisitTypedefTypeLoc(TypedefTypeLoc TL) {
     const SourceLocation TypeEndLoc =
         Lexer::getLocForEndOfToken(TL.getBeginLoc(), 0, SM, LangOpts);
-    return visit(TL.getTypedefNameDecl(), TL.getBeginLoc(), TypeEndLoc);
+    return visit(TL.getDecl(), TL.getBeginLoc(), TypeEndLoc);
   }
 
-  bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS) {
+  bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc QualifierLoc) {
     // The base visitor will visit NNSL prefixes, so we should only look at
     // the current NNS.
-    if (NNS) {
-      const NamespaceDecl *ND = NNS.getNestedNameSpecifier()->getAsNamespace();
-      if (!visit(ND, NNS.getLocalBeginLoc(), NNS.getLocalEndLoc()))
+    if (NestedNameSpecifier Qualifier = QualifierLoc.getNestedNameSpecifier();
+        Qualifier.getKind() == NestedNameSpecifier::Kind::Namespace) {
+      const auto *ND = dyn_cast<NamespaceDecl>(
+          Qualifier.getAsNamespaceAndPrefix().Namespace);
+      if (!visit(ND, QualifierLoc.getLocalBeginLoc(),
+                 QualifierLoc.getLocalEndLoc()))
         return false;
     }
-    return BaseType::TraverseNestedNameSpecifierLoc(NNS);
+    return BaseType::TraverseNestedNameSpecifierLoc(QualifierLoc);
   }
 
   bool VisitDesignatedInitExpr(const DesignatedInitExpr *E) {
diff --git a/clang/lib/ASTMatchers/ASTMatchFinder.cpp b/clang/lib/ASTMatchers/ASTMatchFinder.cpp
index 6d0ba0b7907a1..d43d1aec71b29 100644
--- a/clang/lib/ASTMatchers/ASTMatchFinder.cpp
+++ b/clang/lib/ASTMatchers/ASTMatchFinder.cpp
@@ -122,15 +122,15 @@ class MatchChildASTVisitor
     else if (const Stmt *S = DynNode.get<Stmt>())
       traverse(*S);
     else if (const NestedNameSpecifier *NNS =
-             DynNode.get<NestedNameSpecifier>())
+                 DynNode.get<NestedNameSpecifier>())
       traverse(*NNS);
     else if (const NestedNameSpecifierLoc *NNSLoc =
              DynNode.get<NestedNameSpecifierLoc>())
       traverse(*NNSLoc);
     else if (const QualType *Q = DynNode.get<QualType>())
-      traverse(*Q);
+      traverse(*Q, /*TraverseQualifier=*/true);
     else if (const TypeLoc *T = DynNode.get<TypeLoc>())
-      traverse(*T);
+      traverse(*T, /*TraverseQualifier=*/true);
     else if (const auto *C = DynNode.get<CXXCtorInitializer>())
       traverse(*C);
     else if (const TemplateArgumentLoc *TALoc =
@@ -194,7 +194,7 @@ class MatchChildASTVisitor
   }
   // We assume that the QualType and the contained type are on the same
   // hierarchy level. Thus, we try to match either of them.
-  bool TraverseType(QualType TypeNode) {
+  bool TraverseType(QualType TypeNode, bool TraverseQualifier = true) {
     if (TypeNode.isNull())
       return true;
     ScopedIncrement ScopedDepth(&CurrentDepth);
@@ -202,11 +202,11 @@ class MatchChildASTVisitor
     if (!match(*TypeNode))
       return false;
     // The QualType is matched inside traverse.
-    return traverse(TypeNode);
+    return traverse(TypeNode, TraverseQualifier);
   }
   // We assume that the TypeLoc, contained QualType and contained Type all are
   // on the same hierarchy level. Thus, we try to match all of them.
-  bool TraverseTypeLoc(TypeLoc TypeLocNode) {
+  bool TraverseTypeLoc(TypeLoc TypeLocNode, bool TraverseQualifier = true) {
     if (TypeLocNode.isNull())
       return true;
     ScopedIncrement ScopedDepth(&CurrentDepth);
@@ -217,17 +217,17 @@ class MatchChildASTVisitor
     if (!match(TypeLocNode.getType()))
       return false;
     // The TypeLoc is matched inside traverse.
-    return traverse(TypeLocNode);
+    return traverse(TypeLocNode, TraverseQualifier);
   }
-  bool TraverseNestedNameSpecifier(NestedNameSpecifier *NNS) {
+  bool TraverseNestedNameSpecifier(NestedNameSpecifier NNS) {
     ScopedIncrement ScopedDepth(&CurrentDepth);
-    return (NNS == nullptr) || traverse(*NNS);
+    return !NNS || traverse(NNS);
   }
   bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS) {
     if (!NNS)
       return true;
     ScopedIncrement ScopedDepth(&CurrentDepth);
-    if (!match(*NNS.getNestedNameSpecifier()))
+    if (!match(NNS.getNestedNameSpecifier()))
       return false;
     return traverse(NNS);
   }
@@ -340,15 +340,14 @@ class MatchChildASTVisitor
   bool baseTraverse(const Stmt &StmtNode) {
     return VisitorBase::TraverseStmt(const_cast<Stmt*>(&StmtNode));
   }
-  bool baseTraverse(QualType TypeNode) {
-    return VisitorBase::TraverseType(TypeNode);
+  bool baseTraverse(QualType TypeNode, bool TraverseQualifier) {
+    return VisitorBase::TraverseType(TypeNode, TraverseQualifier);
   }
-  bool baseTraverse(TypeLoc TypeLocNode) {
-    return VisitorBase::TraverseTypeLoc(TypeLocNode);
+  bool baseTraverse(TypeLoc TypeLocNode, bool TraverseQualifier) {
+    return VisitorBase::TraverseTypeLoc(TypeLocNode, TraverseQualifier);
   }
-  bool baseTraverse(const NestedNameSpecifier &NNS) {
-    return VisitorBase::TraverseNestedNameSpecifier(
-        const_cast<NestedNameSpecifier*>(&NNS));
+  bool baseTraverse(NestedNameSpecifier NNS) {
+    return VisitorBase::TraverseNestedNameSpecifier(NNS);
   }
   bool baseTraverse(NestedNameSpecifierLoc NNS) {
     return VisitorBase::TraverseNestedNameSpecifierLoc(NNS);
@@ -396,13 +395,13 @@ class MatchChildASTVisitor
 
   // Traverses the subtree rooted at 'Node'; returns true if the
   // traversal should continue after this function returns.
-  template <typename T>
-  bool traverse(const T &Node) {
+  template <typename T, class... Args>
+  bool traverse(const T &Node, Args &&...args) {
     static_assert(IsBaseType<T>::value,
                   "traverse can only be instantiated with base type");
     if (!match(Node))
       return false;
-    return baseTraverse(Node);
+    return baseTraverse(Node, std::forward<Args>(args)...);
   }
 
   const DynTypedMatcher *const Matcher;
@@ -501,9 +500,9 @@ class MatchASTVisitor : public RecursiveASTVisitor<MatchASTVisitor>,
 
   bool TraverseDecl(Decl *DeclNode);
   bool TraverseStmt(Stmt *StmtNode, DataRecursionQueue *Queue = nullptr);
-  bool TraverseType(QualType TypeNode);
-  bool TraverseTypeLoc(TypeLoc TypeNode);
-  bool TraverseNestedNameSpecifier(NestedNameSpecifier *NNS);
+  bool TraverseType(QualType TypeNode, bool TraverseQualifier = true);
+  bool TraverseTypeLoc(TypeLoc TypeNode, bool TraverseQualifier = true);
+  bool TraverseNestedNameSpecifier(NestedNameSpecifier NNS);
   bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS);
   bool TraverseConstructorInitializer(CXXCtorInitializer *CtorInit);
   bool TraverseTemplateArgumentLoc(TemplateArgumentLoc TAL);
@@ -577,13 +576,13 @@ class MatchASTVisitor : public RecursiveASTVisitor<MatchASTVisitor>,
 
         const auto *T = Proto.getTypePtr();
         for (const auto &E : T->exceptions())
-          TraverseType(E);
+          TraverseType(E, /*TraverseQualifier=*/true);
 
         if (Expr *NE = T->getNoexceptExpr())
           TraverseStmt(NE, Queue);
 
         if (LE->hasExplicitResultType())
-          TraverseTypeLoc(Proto.getReturnLoc());
+          TraverseTypeLoc(Proto.getReturnLoc(), /*TraverseQualifier=*/true);
         TraverseStmt(
             const_cast<Expr *>(LE->getTrailingRequiresClause().ConstraintExpr));
       }
@@ -1289,33 +1288,42 @@ class MatchASTVisitor : public RecursiveASTVisitor<MatchASTVisitor>,
     if (Aliases == TypeAliases.end())
       return false;
 
-    if (const auto *ElaboratedTypeNode =
-            llvm::dyn_cast<ElaboratedType>(TypeNode)) {
-      if (ElaboratedTypeNode->isSugared() && Aliases->second.size() > 1) {
-        const auto &DesugaredTypeName =
-            ElaboratedTypeNode->desugar().getAsString();
+    auto matches = [&](const TypedefNameDecl *Alias) {
+      BoundNodesTreeBuilder Result(*Builder);
+      if (Matcher.matches(*Alias, this, &Result)) {
+        *Builder = std::move(Result);
+        return true;
+      }
+      return false;
+    };
 
-        for (const TypedefNameDecl *Alias : Aliases->second) {
-          if (Alias->getName() != DesugaredTypeName) {
-            continue;
-          }
+    if (const auto *T = TypeNode->getAs<TypedefType>()) {
+      const auto *TD = T->getDecl()->getCanonicalDecl();
 
-          BoundNodesTreeBuilder Result(*Builder);
-          if (Matcher.matches(*Alias, this, &Result)) {
-            *Builder = std::move(Result);
-            return true;
-          }
+      // Prioritize exact matches.
+      SmallVector<const TypedefNameDecl *, 8> NonExactMatches;
+      for (const TypedefNameDecl *Alias : Aliases->second) {
+        if (!declaresSameEntity(TD, Alias)) {
+          NonExactMatches.push_back(Alias);
+          continue;
         }
+        if (matches(Alias))
+          return true;
       }
-    }
 
-    for (const TypedefNameDecl *Alias : Aliases->second) {
-      BoundNodesTreeBuilder Result(*Builder);
-      if (Matcher.matches(*Alias, this, &Result)) {
-        *Builder = std::move(Result);
-        return true;
+      for (const TypedefNameDecl *Alias : NonExactMatches) {
+        BoundNodesTreeBuilder Result(*Builder);
+        if (Matcher.matches(*Alias, this, &Result)) {
+          *Builder = std::move(Result);
+          return true;
+        }
       }
+      return false;
     }
+
+    for (const TypedefNameDecl *Alias : Aliases->second)
+      if (matches(Alias))
+        return true;
     return false;
   }
 
@@ -1506,12 +1514,14 @@ bool MatchASTVisitor::TraverseStmt(Stmt *StmtNode, DataRecursionQueue *Queue) {
   return RecursiveASTVisitor<MatchASTVisitor>::TraverseStmt(StmtNode, Queue);
 }
 
-bool MatchASTVisitor::TraverseType(QualType TypeNode) {
+bool MatchASTVisitor::TraverseType(QualType TypeNode, bool TraverseQualifier) {
   match(TypeNode);
-  return RecursiveASTVisitor<MatchASTVisitor>::TraverseType(TypeNode);
+  return RecursiveASTVisitor<MatchASTVisitor>::TraverseType(TypeNode,
+                                                            TraverseQualifier);
 }
 
-bool MatchASTVisitor::TraverseTypeLoc(TypeLoc TypeLocNode) {
+bool MatchASTVisitor::TraverseTypeLoc(TypeLoc TypeLocNode,
+                                      bool TraverseQualifier) {
   // The RecursiveASTVisitor only visits types if they're not within TypeLocs.
   // We still want to find those types via matchers, so we match them here. Note
   // that the TypeLocs are structurally a shadow-hierarchy to the expressed
@@ -1519,11 +1529,12 @@ bool MatchASTVisitor::TraverseTypeLoc(TypeLoc TypeLocNode) {
   // each TypeLoc.
   match(TypeLocNode);
   match(TypeLocNode.getType());
-  return RecursiveASTVisitor<MatchASTVisitor>::TraverseTypeLoc(TypeLocNode);
+  return RecursiveASTVisitor<MatchASTVisitor>::TraverseTypeLoc(
+      TypeLocNode, TraverseQualifier);
 }
 
-bool MatchASTVisitor::TraverseNestedNameSpecifier(NestedNameSpecifier *NNS) {
-  match(*NNS);
+bool MatchASTVisitor::TraverseNestedNameSpecifier(NestedNameSpecifier NNS) {
+  match(NNS);
   return RecursiveASTVisitor<MatchASTVisitor>::TraverseNestedNameSpecifier(NNS);
 }
 
@@ -1537,7 +1548,7 @@ bool MatchASTVisitor::TraverseNestedNameSpecifierLoc(
   // We only match the nested name specifier here (as opposed to traversing it)
   // because the traversal is already done in the parallel "Loc"-hierarchy.
   if (NNS.hasQualifier())
-    match(*NNS.getNestedNameSpecifier());
+    match(NNS.getNestedNameSpecifier());
   return
       RecursiveASTVisitor<MatchASTVisitor>::TraverseNestedNameSpecifierLoc(NNS);
 }
diff --git a/clang/lib/ASTMatchers/ASTMatchersInternal.cpp b/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
index 80dc888811657..653b3810cb68b 100644
--- a/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
+++ b/clang/lib/ASTMatchers/ASTMatchersInternal.cpp
@@ -755,6 +755,8 @@ const internal::VariadicDynCastAllOfMatcher<Decl, TypedefDecl> typedefDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, TypedefNameDecl>
     typedefNameDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, TypeAliasDecl> typeAliasDecl;
+const internal::VariadicDynCastAllOfMatcher<Decl, UsingShadowDecl>
+    usingShadowDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, TypeAliasTemplateDecl>
     typeAliasTemplateDecl;
 const internal::VariadicAllOfMatcher<Decl> decl;
@@ -808,8 +810,6 @@ const internal::VariadicDynCastAllOfMatcher<TypeLoc, ReferenceTypeLoc>
 const internal::VariadicDynCastAllOfMatcher<TypeLoc,
                                             TemplateSpecializationTypeLoc>
     templateSpecializationTypeLoc;
-const internal::VariadicDynCastAllOfMatcher<TypeLoc, ElaboratedTypeLoc>
-    elaboratedTypeLoc;
 
 const internal::VariadicDynCastAllOfMatcher<Stmt, UnaryExprOrTypeTraitExpr>
     unaryExprOrTypeTraitExpr;
@@ -1103,7 +1103,6 @@ const AstTypeMatcher<TemplateSpecializationType> templateSpecializationType;
 const AstTypeMatcher<UnaryTransformType> unaryTransformType;
 const AstTypeMatcher<RecordType> recordType;
 const AstTypeMatcher<TagType> tagType;
-const AstTypeMatcher<ElaboratedType> elaboratedType;
 const AstTypeMatcher<UsingType> usingType;
 const AstTypeMatcher<SubstTemplateTypeParmType> substTemplateTypeParmType;
 const AstTypeMatcher<TemplateTypeParmType> templateTypeParmType;
diff --git a/clang/lib/ASTMatchers/Dynamic/Registry.cpp b/clang/lib/ASTMatchers/Dynamic/Registry.cpp
index 562df715e08ae..7f6a6aaed1734 100644
--- a/clang/lib/ASTMatchers/Dynamic/Registry.cpp
+++ b/clang/lib/ASTMatchers/Dynamic/Registry.cpp
@@ -235,8 +235,6 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(designatorCountIs);
   REGISTER_MATCHER(doStmt);
   REGISTER_MATCHER(eachOf);
-  REGISTER_MATCHER(elaboratedType);
-  REGISTER_MATCHER(elaboratedTypeLoc);
   REGISTER_MATCHER(usingType);
   REGISTER_MATCHER(enumConstantDecl);
   REGISTER_MATCHER(enumDecl);
@@ -341,7 +339,6 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(hasMemberName);
   REGISTER_MATCHER(hasMethod);
   REGISTER_MATCHER(hasName);
-  REGISTER_MATCHER(hasNamedTypeLoc);
   REGISTER_MATCHER(hasNullSelector);
   REGISTER_MATCHER(hasObjectExpression);
   REGISTER_MATCHER(hasOperands);
@@ -503,7 +500,6 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(memberHasSameNameAsBoundNode);
   REGISTER_MATCHER(memberPointerType);
   REGISTER_MATCHER(namedDecl);
-  REGISTER_MATCHER(namesType);
   REGISTER_MATCHER(namespaceAliasDecl);
   REGISTER_MATCHER(namespaceDecl);
   REGISTER_MATCHER(nestedNameSpecifier);
@@ -593,6 +589,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(typeLoc);
   REGISTER_MATCHER(typedefDecl);
   REGISTER_MATCHER(typedefNameDecl);
+  REGISTER_MATCHER(usingShadowDecl);
   REGISTER_MATCHER(typedefType);
   REGISTER_MATCHER(unaryExprOrTypeTraitExpr);
   REGISTER_MATCHER(unaryOperator);
diff --git a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
index 256ea18284189..f14cb43e47dd4 100644
--- a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
+++ b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
@@ -532,9 +532,11 @@ void Environment::initialize() {
           } else if (auto *FieldBeingInitialized =
                          dyn_cast<FieldDecl>(Parent->getLambdaContextDecl())) {
             // This is in a field initializer, rather than a method.
+            const RecordDecl *RD = FieldBeingInitialized->getParent();
+            const ASTContext &Ctx = RD->getASTContext();
+            CanQualType T = Ctx.getCanonicalTagType(RD);
             setThisPointeeStorageLocation(
-                cast<RecordStorageLocation>(createObject(QualType(
-                    FieldBeingInitialized->getParent()->getTypeForDecl(), 0))));
+                cast<RecordStorageLocation>(createObject(T)));
           } else {
             assert(false && "Unexpected this-capturing lambda context.");
           }
diff --git a/clang/lib/Analysis/ThreadSafety.cpp b/clang/lib/Analysis/ThreadSafety.cpp
index 80e7c8eff671a..5037b75542925 100644
--- a/clang/lib/Analysis/ThreadSafety.cpp
+++ b/clang/lib/Analysis/ThreadSafety.cpp
@@ -1875,7 +1875,9 @@ void BuildLockset::handleCall(const Expr *Exp, const NamedDecl *D,
       assert(inserted.second && "Are we visiting the same expression again?");
       if (isa<CXXConstructExpr>(Exp))
         Self = Placeholder;
-      if (TagT->getDecl()->hasAttr<ScopedLockableAttr>())
+      if (TagT->getOriginalDecl()
+              ->getMostRecentDecl()
+              ->hasAttr<ScopedLockableAttr>())
         Scp = CapabilityExpr(Placeholder, Exp->getType(), /*Neg=*/false);
     }
 
diff --git a/clang/lib/Analysis/ThreadSafetyCommon.cpp b/clang/lib/Analysis/ThreadSafetyCommon.cpp
index ddbd0a9ca904b..f560dd8ae1dd1 100644
--- a/clang/lib/Analysis/ThreadSafetyCommon.cpp
+++ b/clang/lib/Analysis/ThreadSafetyCommon.cpp
@@ -84,8 +84,8 @@ static std::pair<StringRef, bool> classifyCapability(QualType QT) {
   // which it is. The type should either be a record or a typedef, or a pointer
   // or reference thereof.
   if (const auto *RT = QT->getAs<RecordType>()) {
-    if (const auto *RD = RT->getDecl())
-      return classifyCapability(*RD);
+    if (const auto *RD = RT->getOriginalDecl())
+      return classifyCapability(*RD->getDefinitionOrSelf());
   } else if (const auto *TT = QT->getAs<TypedefType>()) {
     if (const auto *TD = TT->getDecl())
       return classifyCapability(*TD);
diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index 6048169b56640..dc865cbc335b0 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -181,18 +181,22 @@ class MatchDescendantVisitor : public DynamicRecursiveASTVisitor {
     return DynamicRecursiveASTVisitor::TraverseUnaryExprOrTypeTraitExpr(Node);
   }
 
-  bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc Node) override {
+  bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc Node,
+                                 bool TraverseQualifier) override {
     // Unevaluated context.
     if (ignoreUnevaluatedContext)
       return true;
-    return DynamicRecursiveASTVisitor::TraverseTypeOfExprTypeLoc(Node);
+    return DynamicRecursiveASTVisitor::TraverseTypeOfExprTypeLoc(
+        Node, TraverseQualifier);
   }
 
-  bool TraverseDecltypeTypeLoc(DecltypeTypeLoc Node) override {
+  bool TraverseDecltypeTypeLoc(DecltypeTypeLoc Node,
+                               bool TraverseQualifier) override {
     // Unevaluated context.
     if (ignoreUnevaluatedContext)
       return true;
-    return DynamicRecursiveASTVisitor::TraverseDecltypeTypeLoc(Node);
+    return DynamicRecursiveASTVisitor::TraverseDecltypeTypeLoc(
+        Node, TraverseQualifier);
   }
 
   bool TraverseCXXNoexceptExpr(CXXNoexceptExpr *Node) override {
diff --git a/clang/lib/CodeGen/ABIInfo.cpp b/clang/lib/CodeGen/ABIInfo.cpp
index d981d69913632..b5d5f46dc5b5d 100644
--- a/clang/lib/CodeGen/ABIInfo.cpp
+++ b/clang/lib/CodeGen/ABIInfo.cpp
@@ -68,7 +68,7 @@ bool ABIInfo::isHomogeneousAggregate(QualType Ty, const Type *&Base,
       return false;
     Members *= NElements;
   } else if (const RecordType *RT = Ty->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->hasFlexibleArrayMember())
       return false;
 
diff --git a/clang/lib/CodeGen/ABIInfoImpl.cpp b/clang/lib/CodeGen/ABIInfoImpl.cpp
index 0a612d3461dc2..79dbe70a0c8eb 100644
--- a/clang/lib/CodeGen/ABIInfoImpl.cpp
+++ b/clang/lib/CodeGen/ABIInfoImpl.cpp
@@ -29,7 +29,7 @@ ABIArgInfo DefaultABIInfo::classifyArgumentType(QualType Ty) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   ASTContext &Context = getContext();
   if (const auto *EIT = Ty->getAs<BitIntType>())
@@ -53,7 +53,7 @@ ABIArgInfo DefaultABIInfo::classifyReturnType(QualType RetTy) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-    RetTy = EnumTy->getDecl()->getIntegerType();
+    RetTy = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   if (const auto *EIT = RetTy->getAs<BitIntType>())
     if (EIT->getNumBits() >
@@ -105,13 +105,12 @@ llvm::Type *CodeGen::getVAListElementType(CodeGenFunction &CGF) {
 
 CGCXXABI::RecordArgABI CodeGen::getRecordArgABI(const RecordType *RT,
                                                 CGCXXABI &CXXABI) {
-  const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(RT->getDecl());
-  if (!RD) {
-    if (!RT->getDecl()->canPassInRegisters())
-      return CGCXXABI::RAA_Indirect;
-    return CGCXXABI::RAA_Default;
-  }
-  return CXXABI.getRecordArgABI(RD);
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
+  if (const auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
+    return CXXABI.getRecordArgABI(CXXRD);
+  if (!RD->canPassInRegisters())
+    return CGCXXABI::RAA_Indirect;
+  return CGCXXABI::RAA_Default;
 }
 
 CGCXXABI::RecordArgABI CodeGen::getRecordArgABI(QualType T, CGCXXABI &CXXABI) {
@@ -125,20 +124,21 @@ bool CodeGen::classifyReturnType(const CGCXXABI &CXXABI, CGFunctionInfo &FI,
                                  const ABIInfo &Info) {
   QualType Ty = FI.getReturnType();
 
-  if (const auto *RT = Ty->getAs<RecordType>())
-    if (!isa<CXXRecordDecl>(RT->getDecl()) &&
-        !RT->getDecl()->canPassInRegisters()) {
+  if (const auto *RT = Ty->getAs<RecordType>()) {
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
+    if (!isa<CXXRecordDecl>(RD) && !RD->canPassInRegisters()) {
       FI.getReturnInfo() = Info.getNaturalAlignIndirect(
           Ty, Info.getDataLayout().getAllocaAddrSpace());
       return true;
     }
+  }
 
   return CXXABI.classifyReturnType(FI);
 }
 
 QualType CodeGen::useFirstFieldIfTransparentUnion(QualType Ty) {
   if (const RecordType *UT = Ty->getAsUnionType()) {
-    const RecordDecl *UD = UT->getDecl();
+    const RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
     if (UD->hasAttr<TransparentUnionAttr>()) {
       assert(!UD->field_empty() && "sema created an empty transparent union");
       return UD->field_begin()->getType();
@@ -276,7 +276,7 @@ bool CodeGen::isEmptyField(ASTContext &Context, const FieldDecl *FD,
   // according to the Itanium ABI.  The exception applies only to records,
   // not arrays of records, so we must also check whether we stripped off an
   // array type above.
-  if (isa<CXXRecordDecl>(RT->getDecl()) &&
+  if (isa<CXXRecordDecl>(RT->getOriginalDecl()) &&
       (WasArray || (!AsIfNoUniqueAddr && !FD->hasAttr<NoUniqueAddressAttr>())))
     return false;
 
@@ -288,7 +288,7 @@ bool CodeGen::isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays,
   const RecordType *RT = T->getAs<RecordType>();
   if (!RT)
     return false;
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   if (RD->hasFlexibleArrayMember())
     return false;
 
@@ -320,7 +320,7 @@ bool CodeGen::isEmptyRecordForLayout(const ASTContext &Context, QualType T) {
   if (!RT)
     return false;
 
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
   // If this is a C++ record, check the bases first.
   if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
@@ -344,7 +344,7 @@ const Type *CodeGen::isSingleElementStruct(QualType T, ASTContext &Context) {
   if (!RT)
     return nullptr;
 
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   if (RD->hasFlexibleArrayMember())
     return nullptr;
 
@@ -463,7 +463,7 @@ bool CodeGen::isRecordWithSIMDVectorType(ASTContext &Context, QualType Ty) {
   const RecordType *RT = Ty->getAs<RecordType>();
   if (!RT)
     return false;
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
   // If this is a C++ record, check the bases first.
   if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
diff --git a/clang/lib/CodeGen/CGBlocks.cpp b/clang/lib/CodeGen/CGBlocks.cpp
index f3ddf7bf9a463..7f2f82bc5e62a 100644
--- a/clang/lib/CodeGen/CGBlocks.cpp
+++ b/clang/lib/CodeGen/CGBlocks.cpp
@@ -425,7 +425,8 @@ static bool isSafeForCXXConstantCapture(QualType type) {
   // Only records can be unsafe.
   if (!recordType) return true;
 
-  const auto *record = cast<CXXRecordDecl>(recordType->getDecl());
+  const auto *record =
+      cast<CXXRecordDecl>(recordType->getOriginalDecl())->getDefinitionOrSelf();
 
   // Maintain semantics for classes with non-trivial dtors or copy ctors.
   if (!record->hasTrivialDestructor()) return false;
diff --git a/clang/lib/CodeGen/CGCUDANV.cpp b/clang/lib/CodeGen/CGCUDANV.cpp
index dd26be74e561b..c7f4bf8a21354 100644
--- a/clang/lib/CodeGen/CGCUDANV.cpp
+++ b/clang/lib/CodeGen/CGCUDANV.cpp
@@ -1131,7 +1131,8 @@ void CGNVCUDARuntime::handleVarRegistration(const VarDecl *D,
     // Builtin surfaces and textures and their template arguments are
     // also registered with CUDA runtime.
     const auto *TD = cast<ClassTemplateSpecializationDecl>(
-        D->getType()->castAs<RecordType>()->getDecl());
+                         D->getType()->castAs<RecordType>()->getOriginalDecl())
+                         ->getDefinitionOrSelf();
     const TemplateArgumentList &Args = TD->getTemplateArgs();
     if (TD->hasAttr<CUDADeviceBuiltinSurfaceTypeAttr>()) {
       assert(Args.size() == 2 &&
diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index 78a7b021855b7..f9aff893eb0f0 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -83,8 +83,9 @@ bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
     if (I.isVirtual()) continue;
 
     // Skip base classes with trivial destructors.
-    const auto *Base =
-        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+    const auto *Base = cast<CXXRecordDecl>(
+                           I.getType()->castAs<RecordType>()->getOriginalDecl())
+                           ->getDefinitionOrSelf();
     if (Base->hasTrivialDestructor()) continue;
 
     // If we've already found a base class with a non-trivial
@@ -277,18 +278,18 @@ static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
 /// indirect call to virtual functions. It makes the call through indexing
 /// into the vtable.
-CGCallee
-CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
-                                           NestedNameSpecifier *Qual,
-                                           llvm::Type *Ty) {
-  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
+CGCallee CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
+                                                    NestedNameSpecifier Qual,
+                                                    llvm::Type *Ty) {
+  assert(Qual.getKind() == NestedNameSpecifier::Kind::Type &&
          "BuildAppleKextVirtualCall - bad Qual kind");
 
-  const Type *QTy = Qual->getAsType();
+  const Type *QTy = Qual.getAsType();
   QualType T = QualType(QTy, 0);
   const RecordType *RT = T->getAs<RecordType>();
   assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
-  const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
+  const auto *RD =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
 
   if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
     return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
diff --git a/clang/lib/CodeGen/CGCXXABI.cpp b/clang/lib/CodeGen/CGCXXABI.cpp
index d42e0bb814a88..cca675838644e 100644
--- a/clang/lib/CodeGen/CGCXXABI.cpp
+++ b/clang/lib/CodeGen/CGCXXABI.cpp
@@ -52,7 +52,7 @@ CGCallee CGCXXABI::EmitLoadOfMemberFunctionPointer(
 
   const auto *RD = MPT->getMostRecentCXXRecordDecl();
   ThisPtrForCall =
-      CGF.getAsNaturalPointerTo(This, CGF.getContext().getRecordType(RD));
+      CGF.getAsNaturalPointerTo(This, CGF.getContext().getCanonicalTagType(RD));
   const FunctionProtoType *FPT =
       MPT->getPointeeType()->getAs<FunctionProtoType>();
   llvm::Constant *FnPtr = llvm::Constant::getNullValue(
@@ -106,7 +106,7 @@ CGCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
 
 llvm::Constant *CGCXXABI::EmitMemberFunctionPointer(const CXXMethodDecl *MD) {
   return GetBogusMemberPointer(CGM.getContext().getMemberPointerType(
-      MD->getType(), /*Qualifier=*/nullptr, MD->getParent()));
+      MD->getType(), /*Qualifier=*/std::nullopt, MD->getParent()));
 }
 
 llvm::Constant *CGCXXABI::EmitMemberDataPointer(const MemberPointerType *MPT,
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index c8c3d6b20c496..6cf67be5206a3 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -125,16 +125,16 @@ unsigned CodeGenTypes::ClangCallConvToLLVMCallConv(CallingConv CC) {
 /// calling a method pointer.
 CanQualType CodeGenTypes::DeriveThisType(const CXXRecordDecl *RD,
                                          const CXXMethodDecl *MD) {
-  QualType RecTy;
+  CanQualType RecTy;
   if (RD)
-    RecTy = Context.getTagDeclType(RD)->getCanonicalTypeInternal();
+    RecTy = Context.getCanonicalTagType(RD);
   else
     RecTy = Context.VoidTy;
 
   if (MD)
-    RecTy = Context.getAddrSpaceQualType(
-        RecTy, MD->getMethodQualifiers().getAddressSpace());
-  return Context.getPointerType(CanQualType::CreateUnsafe(RecTy));
+    RecTy = CanQualType::CreateUnsafe(Context.getAddrSpaceQualType(
+        RecTy, MD->getMethodQualifiers().getAddressSpace()));
+  return Context.getPointerType(RecTy);
 }
 
 /// Returns the canonical formal type of the given C++ method.
@@ -1008,7 +1008,7 @@ getTypeExpansion(QualType Ty, const ASTContext &Context) {
   if (const RecordType *RT = Ty->getAs<RecordType>()) {
     SmallVector<const CXXBaseSpecifier *, 1> Bases;
     SmallVector<const FieldDecl *, 1> Fields;
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     assert(!RD->hasFlexibleArrayMember() &&
            "Cannot expand structure with flexible array.");
     if (RD->isUnion()) {
@@ -1895,7 +1895,7 @@ bool CodeGenModule::MayDropFunctionReturn(const ASTContext &Context,
   // complex destructor or a non-trivially copyable type.
   if (const RecordType *RT =
           ReturnType.getCanonicalType()->getAs<RecordType>()) {
-    if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getDecl()))
+    if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl()))
       return ClassDecl->hasTrivialDestructor();
   }
   return ReturnType.isTriviallyCopyableType(Context);
@@ -3807,7 +3807,7 @@ static void setUsedBits(CodeGenModule &CGM, const RecordType *RTy, int Offset,
                         SmallVectorImpl<uint64_t> &Bits) {
   ASTContext &Context = CGM.getContext();
   int CharWidth = Context.getCharWidth();
-  const RecordDecl *RD = RTy->getDecl()->getDefinition();
+  const RecordDecl *RD = RTy->getOriginalDecl()->getDefinition();
   const ASTRecordLayout &ASTLayout = Context.getASTRecordLayout(RD);
   const CGRecordLayout &Layout = CGM.getTypes().getCGRecordLayout(RD);
 
@@ -4268,7 +4268,10 @@ void CodeGenFunction::EmitDelegateCallArg(CallArgList &args,
 
   // Deactivate the cleanup for the callee-destructed param that was pushed.
   if (type->isRecordType() && !CurFuncIsThunk &&
-      type->castAs<RecordType>()->getDecl()->isParamDestroyedInCallee() &&
+      type->castAs<RecordType>()
+          ->getOriginalDecl()
+          ->getDefinitionOrSelf()
+          ->isParamDestroyedInCallee() &&
       param->needsDestruction(getContext())) {
     EHScopeStack::stable_iterator cleanup =
         CalleeDestructedParamCleanups.lookup(cast<ParmVarDecl>(param));
@@ -4864,8 +4867,10 @@ void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E,
   // In the Microsoft C++ ABI, aggregate arguments are destructed by the callee.
   // However, we still have to push an EH-only cleanup in case we unwind before
   // we make it to the call.
-  if (type->isRecordType() &&
-      type->castAs<RecordType>()->getDecl()->isParamDestroyedInCallee()) {
+  if (type->isRecordType() && type->castAs<RecordType>()
+                                  ->getOriginalDecl()
+                                  ->getDefinitionOrSelf()
+                                  ->isParamDestroyedInCallee()) {
     // If we're using inalloca, use the argument memory.  Otherwise, use a
     // temporary.
     AggValueSlot Slot = args.isUsingInAlloca()
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 4a465e6526da0..e9a92ae0f01cb 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -181,7 +181,9 @@ CharUnits CodeGenModule::computeNonVirtualBaseClassOffset(
     const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
 
     const auto *BaseDecl =
-        cast<CXXRecordDecl>(Base->getType()->castAs<RecordType>()->getDecl());
+        cast<CXXRecordDecl>(
+            Base->getType()->castAs<RecordType>()->getOriginalDecl())
+            ->getDefinitionOrSelf();
 
     // Add the offset.
     Offset += Layout.getBaseClassOffset(BaseDecl);
@@ -301,7 +303,8 @@ Address CodeGenFunction::GetAddressOfBaseClass(
   // and hence will not require any further steps.
   if ((*Start)->isVirtual()) {
     VBase = cast<CXXRecordDecl>(
-        (*Start)->getType()->castAs<RecordType>()->getDecl());
+                (*Start)->getType()->castAs<RecordType>()->getOriginalDecl())
+                ->getDefinitionOrSelf();
     ++Start;
   }
 
@@ -326,7 +329,7 @@ Address CodeGenFunction::GetAddressOfBaseClass(
   llvm::Type *PtrTy = llvm::PointerType::get(
       CGM.getLLVMContext(), Value.getType()->getPointerAddressSpace());
 
-  QualType DerivedTy = getContext().getRecordType(Derived);
+  CanQualType DerivedTy = getContext().getCanonicalTagType(Derived);
   CharUnits DerivedAlign = CGM.getClassPointerAlignment(Derived);
 
   // If the static offset is zero and we don't have a virtual step,
@@ -401,8 +404,7 @@ CodeGenFunction::GetAddressOfDerivedClass(Address BaseAddr,
                                           bool NullCheckValue) {
   assert(PathBegin != PathEnd && "Base path should not be empty!");
 
-  QualType DerivedTy =
-      getContext().getCanonicalType(getContext().getTagDeclType(Derived));
+  CanQualType DerivedTy = getContext().getCanonicalTagType(Derived);
   llvm::Type *DerivedValueTy = ConvertType(DerivedTy);
 
   llvm::Value *NonVirtualOffset =
@@ -559,7 +561,8 @@ static void EmitBaseInitializer(CodeGenFunction &CGF,
 
   const Type *BaseType = BaseInit->getBaseClass();
   const auto *BaseClassDecl =
-      cast<CXXRecordDecl>(BaseType->castAs<RecordType>()->getDecl());
+      cast<CXXRecordDecl>(BaseType->castAs<RecordType>()->getOriginalDecl())
+          ->getDefinitionOrSelf();
 
   bool isBaseVirtual = BaseInit->isBaseVirtual();
 
@@ -638,7 +641,7 @@ static void EmitMemberInitializer(CodeGenFunction &CGF,
   QualType FieldType = Field->getType();
 
   llvm::Value *ThisPtr = CGF.LoadCXXThis();
-  QualType RecordTy = CGF.getContext().getTypeDeclType(ClassDecl);
+  CanQualType RecordTy = CGF.getContext().getCanonicalTagType(ClassDecl);
   LValue LHS;
 
   // If a base constructor is being emitted, create an LValue that has the
@@ -974,7 +977,7 @@ namespace {
       }
 
       CharUnits MemcpySize = getMemcpySize(FirstByteOffset);
-      QualType RecordTy = CGF.getContext().getTypeDeclType(ClassDecl);
+      CanQualType RecordTy = CGF.getContext().getCanonicalTagType(ClassDecl);
       Address ThisPtr = CGF.LoadCXXThisAddress();
       LValue DestLV = CGF.MakeAddrLValue(ThisPtr, RecordTy);
       LValue Dest = CGF.EmitLValueForFieldInitialization(DestLV, FirstField);
@@ -1122,7 +1125,7 @@ namespace {
 
     void pushEHDestructors() {
       Address ThisPtr = CGF.LoadCXXThisAddress();
-      QualType RecordTy = CGF.getContext().getTypeDeclType(ClassDecl);
+      CanQualType RecordTy = CGF.getContext().getCanonicalTagType(ClassDecl);
       LValue LHS = CGF.MakeAddrLValue(ThisPtr, RecordTy);
 
       for (unsigned i = 0; i < AggregatedInits.size(); ++i) {
@@ -1265,7 +1268,8 @@ namespace {
 static bool isInitializerOfDynamicClass(const CXXCtorInitializer *BaseInit) {
   const Type *BaseType = BaseInit->getBaseClass();
   const auto *BaseClassDecl =
-      cast<CXXRecordDecl>(BaseType->castAs<RecordType>()->getDecl());
+      cast<CXXRecordDecl>(BaseType->castAs<RecordType>()->getOriginalDecl())
+          ->getDefinitionOrSelf();
   return BaseClassDecl->isDynamicClass();
 }
 
@@ -1374,7 +1378,9 @@ HasTrivialDestructorBody(ASTContext &Context,
       continue;
 
     const CXXRecordDecl *NonVirtualBase =
-      cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+        cast<CXXRecordDecl>(
+            I.getType()->castAs<RecordType>()->getOriginalDecl())
+            ->getDefinitionOrSelf();
     if (!HasTrivialDestructorBody(Context, NonVirtualBase,
                                   MostDerivedClassDecl))
       return false;
@@ -1383,8 +1389,10 @@ HasTrivialDestructorBody(ASTContext &Context,
   if (BaseClassDecl == MostDerivedClassDecl) {
     // Check virtual bases.
     for (const auto &I : BaseClassDecl->vbases()) {
-      const CXXRecordDecl *VirtualBase =
-        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+      const auto *VirtualBase =
+          cast<CXXRecordDecl>(
+              I.getType()->castAs<RecordType>()->getOriginalDecl())
+              ->getDefinitionOrSelf();
       if (!HasTrivialDestructorBody(Context, VirtualBase,
                                     MostDerivedClassDecl))
         return false;
@@ -1404,7 +1412,8 @@ FieldHasTrivialDestructorBody(ASTContext &Context,
   if (!RT)
     return true;
 
-  CXXRecordDecl *FieldClassDecl = cast<CXXRecordDecl>(RT->getDecl());
+  auto *FieldClassDecl =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
 
   // The destructor for an implicit anonymous union member is never invoked.
   if (FieldClassDecl->isUnion() && FieldClassDecl->isAnonymousStructOrUnion())
@@ -1588,7 +1597,7 @@ namespace {
       const CXXRecordDecl *ClassDecl = Dtor->getParent();
       CGF.EmitDeleteCall(Dtor->getOperatorDelete(),
                          LoadThisForDtorDelete(CGF, Dtor),
-                         CGF.getContext().getTagDeclType(ClassDecl));
+                         CGF.getContext().getCanonicalTagType(ClassDecl));
     }
   };
 
@@ -1606,7 +1615,7 @@ namespace {
     const CXXRecordDecl *ClassDecl = Dtor->getParent();
     CGF.EmitDeleteCall(Dtor->getOperatorDelete(),
                        LoadThisForDtorDelete(CGF, Dtor),
-                       CGF.getContext().getTagDeclType(ClassDecl));
+                       CGF.getContext().getCanonicalTagType(ClassDecl));
     assert(Dtor->getOperatorDelete()->isDestroyingOperatorDelete() ==
                ReturnAfterDelete &&
            "unexpected value for ReturnAfterDelete");
@@ -1647,7 +1656,8 @@ namespace {
     void Emit(CodeGenFunction &CGF, Flags flags) override {
       // Find the address of the field.
       Address thisValue = CGF.LoadCXXThisAddress();
-      QualType RecordTy = CGF.getContext().getTagDeclType(field->getParent());
+      CanQualType RecordTy =
+          CGF.getContext().getCanonicalTagType(field->getParent());
       LValue ThisLV = CGF.MakeAddrLValue(thisValue, RecordTy);
       LValue LV = CGF.EmitLValueForField(ThisLV, field);
       assert(LV.isSimple());
@@ -1870,7 +1880,7 @@ void CodeGenFunction::EnterDtorCleanups(const CXXDestructorDecl *DD,
         const CXXRecordDecl *ClassDecl = DD->getParent();
         EmitDeleteCall(DD->getOperatorDelete(),
                        LoadThisForDtorDelete(*this, DD),
-                       getContext().getTagDeclType(ClassDecl));
+                       getContext().getCanonicalTagType(ClassDecl));
         EmitBranchThroughCleanup(ReturnBlock);
       } else {
         EHStack.pushCleanup<CallDtorDelete>(NormalAndEHCleanup);
@@ -1898,7 +1908,9 @@ void CodeGenFunction::EnterDtorCleanups(const CXXDestructorDecl *DD,
     // the reverse order.
     for (const auto &Base : ClassDecl->vbases()) {
       auto *BaseClassDecl =
-          cast<CXXRecordDecl>(Base.getType()->castAs<RecordType>()->getDecl());
+          cast<CXXRecordDecl>(
+              Base.getType()->castAs<RecordType>()->getOriginalDecl())
+              ->getDefinitionOrSelf();
 
       if (BaseClassDecl->hasTrivialDestructor()) {
         // Under SanitizeMemoryUseAfterDtor, poison the trivial base class
@@ -1964,7 +1976,7 @@ void CodeGenFunction::EnterDtorCleanups(const CXXDestructorDecl *DD,
 
     // Anonymous union members do not have their destructors called.
     const RecordType *RT = type->getAsUnionType();
-    if (RT && RT->getDecl()->isAnonymousStructOrUnion())
+    if (RT && RT->getOriginalDecl()->isAnonymousStructOrUnion())
       continue;
 
     CleanupKind cleanupKind = getCleanupKind(dtorKind);
@@ -2057,7 +2069,7 @@ void CodeGenFunction::EmitCXXAggrConstructorCall(const CXXConstructorDecl *ctor,
   //
   // Note that these are complete objects and so we don't need to
   // use the non-virtual size or alignment.
-  QualType type = getContext().getTypeDeclType(ctor->getParent());
+  CanQualType type = getContext().getCanonicalTagType(ctor->getParent());
   CharUnits eltAlignment =
     arrayBase.getAlignment()
              .alignmentOfArrayElement(getContext().getTypeSizeInChars(type));
@@ -2119,7 +2131,8 @@ void CodeGenFunction::destroyCXXObject(CodeGenFunction &CGF,
                                        Address addr,
                                        QualType type) {
   const RecordType *rtype = type->castAs<RecordType>();
-  const CXXRecordDecl *record = cast<CXXRecordDecl>(rtype->getDecl());
+  const auto *record =
+      cast<CXXRecordDecl>(rtype->getOriginalDecl())->getDefinitionOrSelf();
   const CXXDestructorDecl *dtor = record->getDestructor();
   assert(!dtor->isTrivial());
   CGF.EmitCXXDestructorCall(dtor, Dtor_Complete, /*for vbase*/ false,
@@ -2158,7 +2171,7 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
 
     const Expr *Arg = E->getArg(0);
     LValue Src = EmitLValue(Arg);
-    QualType DestTy = getContext().getTypeDeclType(D->getParent());
+    CanQualType DestTy = getContext().getCanonicalTagType(D->getParent());
     LValue Dest = MakeAddrLValue(This, DestTy);
     EmitAggregateCopyCtor(Dest, Src, ThisAVS.mayOverlap());
     return;
@@ -2210,7 +2223,8 @@ void CodeGenFunction::EmitCXXConstructorCall(
 
   if (!NewPointerIsChecked)
     EmitTypeCheck(CodeGenFunction::TCK_ConstructorCall, Loc, This,
-                  getContext().getRecordType(ClassDecl), CharUnits::Zero());
+                  getContext().getCanonicalTagType(ClassDecl),
+                  CharUnits::Zero());
 
   if (D->isTrivial() && D->isDefaultConstructor()) {
     assert(Args.size() == 1 && "trivial default ctor with args");
@@ -2226,7 +2240,7 @@ void CodeGenFunction::EmitCXXConstructorCall(
     Address Src = makeNaturalAddressForPointer(
         Args[1].getRValue(*this).getScalarVal(), SrcTy);
     LValue SrcLVal = MakeAddrLValue(Src, SrcTy);
-    QualType DestTy = getContext().getTypeDeclType(ClassDecl);
+    CanQualType DestTy = getContext().getCanonicalTagType(ClassDecl);
     LValue DestLVal = MakeAddrLValue(This, DestTy);
     EmitAggregateCopyCtor(DestLVal, SrcLVal, Overlap);
     return;
@@ -2638,8 +2652,9 @@ void CodeGenFunction::getVTablePointers(BaseSubobject Base,
 
   // Traverse bases.
   for (const auto &I : RD->bases()) {
-    auto *BaseDecl =
-        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+    auto *BaseDecl = cast<CXXRecordDecl>(
+                         I.getType()->castAs<RecordType>()->getOriginalDecl())
+                         ->getDefinitionOrSelf();
 
     // Ignore classes without a vtable.
     if (!BaseDecl->isDynamicClass())
@@ -2772,7 +2787,7 @@ void CodeGenFunction::EmitTypeMetadataCodeForVCall(const CXXRecordDecl *RD,
            // Don't insert type test assumes if we are forcing public
            // visibility.
            !CGM.AlwaysHasLTOVisibilityPublic(RD)) {
-    QualType Ty = QualType(RD->getTypeForDecl(), 0);
+    CanQualType Ty = CGM.getContext().getCanonicalTagType(RD);
     llvm::Metadata *MD = CGM.CreateMetadataIdentifierForType(Ty);
     llvm::Value *TypeId =
         llvm::MetadataAsValue::get(CGM.getLLVMContext(), MD);
@@ -2839,7 +2854,8 @@ void CodeGenFunction::EmitVTablePtrCheckForCast(QualType T, Address Derived,
   if (!ClassTy)
     return;
 
-  const CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(ClassTy->getDecl());
+  const auto *ClassDecl =
+      cast<CXXRecordDecl>(ClassTy->getOriginalDecl())->getDefinitionOrSelf();
 
   if (!ClassDecl->isCompleteDefinition() || !ClassDecl->isDynamicClass())
     return;
@@ -2896,8 +2912,8 @@ void CodeGenFunction::EmitVTablePtrCheck(const CXXRecordDecl *RD,
 
   EmitSanitizerStatReport(SSK);
 
-  llvm::Metadata *MD =
-      CGM.CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
+  CanQualType T = CGM.getContext().getCanonicalTagType(RD);
+  llvm::Metadata *MD = CGM.CreateMetadataIdentifierForType(T);
   llvm::Value *TypeId = llvm::MetadataAsValue::get(getLLVMContext(), MD);
 
   llvm::Value *TypeTest = Builder.CreateCall(
@@ -2906,7 +2922,7 @@ void CodeGenFunction::EmitVTablePtrCheck(const CXXRecordDecl *RD,
   llvm::Constant *StaticData[] = {
       llvm::ConstantInt::get(Int8Ty, TCK),
       EmitCheckSourceLocation(Loc),
-      EmitCheckTypeDescriptor(QualType(RD->getTypeForDecl(), 0)),
+      EmitCheckTypeDescriptor(T),
   };
 
   auto CrossDsoTypeId = CGM.CreateCrossDsoCfiTypeId(MD);
@@ -2956,8 +2972,8 @@ llvm::Value *CodeGenFunction::EmitVTableTypeCheckedLoad(
 
   EmitSanitizerStatReport(llvm::SanStat_CFI_VCall);
 
-  llvm::Metadata *MD =
-      CGM.CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
+  CanQualType T = CGM.getContext().getCanonicalTagType(RD);
+  llvm::Metadata *MD = CGM.CreateMetadataIdentifierForType(T);
   llvm::Value *TypeId = llvm::MetadataAsValue::get(CGM.getLLVMContext(), MD);
 
   auto CheckedLoadIntrinsic = CGM.getVTables().useRelativeLayout()
@@ -3039,7 +3055,8 @@ void CodeGenFunction::EmitLambdaBlockInvokeBody() {
   // Start building arguments for forwarding call
   CallArgList CallArgs;
 
-  QualType ThisType = getContext().getPointerType(getContext().getRecordType(Lambda));
+  CanQualType ThisType =
+      getContext().getPointerType(getContext().getCanonicalTagType(Lambda));
   Address ThisPtr = GetAddrOfBlockDecl(variable);
   CallArgs.add(RValue::get(getAsNaturalPointerTo(ThisPtr, ThisType)), ThisType);
 
@@ -3066,8 +3083,8 @@ void CodeGenFunction::EmitLambdaStaticInvokeBody(const CXXMethodDecl *MD) {
   // Start building arguments for forwarding call
   CallArgList CallArgs;
 
-  QualType LambdaType = getContext().getRecordType(Lambda);
-  QualType ThisType = getContext().getPointerType(LambdaType);
+  CanQualType LambdaType = getContext().getCanonicalTagType(Lambda);
+  CanQualType ThisType = getContext().getPointerType(LambdaType);
   Address ThisPtr = CreateMemTemp(LambdaType, "unused.capture");
   CallArgs.add(RValue::get(ThisPtr.emitRawPointer(*this)), ThisType);
 
@@ -3118,8 +3135,8 @@ void CodeGenFunction::EmitLambdaInAllocaCallOpBody(const CXXMethodDecl *MD) {
 
   // Forward %this argument.
   CallArgList CallArgs;
-  QualType LambdaType = getContext().getRecordType(MD->getParent());
-  QualType ThisType = getContext().getPointerType(LambdaType);
+  CanQualType LambdaType = getContext().getCanonicalTagType(MD->getParent());
+  CanQualType ThisType = getContext().getPointerType(LambdaType);
   llvm::Value *ThisArg = CurFn->getArg(0);
   CallArgs.add(RValue::get(ThisArg), ThisType);
 
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 8bf7d24d8551d..2df95d59cc8cf 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -369,7 +369,7 @@ llvm::DIScope *CGDebugInfo::getContextDescriptor(const Decl *Context,
 
   if (const auto *RDecl = dyn_cast<RecordDecl>(Context))
     if (!RDecl->isDependentType())
-      return getOrCreateType(CGM.getContext().getTypeDeclType(RDecl),
+      return getOrCreateType(CGM.getContext().getCanonicalTagType(RDecl),
                              TheCU->getFile());
   return Default;
 }
@@ -1294,7 +1294,7 @@ static bool needsTypeIdentifier(const TagDecl *TD, CodeGenModule &CGM,
 static SmallString<256> getTypeIdentifier(const TagType *Ty, CodeGenModule &CGM,
                                           llvm::DICompileUnit *TheCU) {
   SmallString<256> Identifier;
-  const TagDecl *TD = Ty->getDecl();
+  const TagDecl *TD = Ty->getOriginalDecl()->getDefinitionOrSelf();
 
   if (!needsTypeIdentifier(TD, CGM, TheCU))
     return Identifier;
@@ -1330,8 +1330,8 @@ static llvm::dwarf::Tag getTagForRecord(const RecordDecl *RD) {
 llvm::DICompositeType *
 CGDebugInfo::getOrCreateRecordFwdDecl(const RecordType *Ty,
                                       llvm::DIScope *Ctx) {
-  const RecordDecl *RD = Ty->getDecl();
-  if (llvm::DIType *T = getTypeOrNull(CGM.getContext().getRecordType(RD)))
+  const RecordDecl *RD = Ty->getOriginalDecl()->getDefinitionOrSelf();
+  if (llvm::DIType *T = getTypeOrNull(QualType(Ty, 0)))
     return cast<llvm::DICompositeType>(T);
   llvm::DIFile *DefUnit = getOrCreateFile(RD->getLocation());
   const unsigned Line =
@@ -2024,6 +2024,8 @@ void CGDebugInfo::CollectRecordNestedType(
     const TypeDecl *TD, SmallVectorImpl<llvm::Metadata *> &elements) {
   QualType Ty = CGM.getContext().getTypeDeclType(TD);
   // Injected class names are not considered nested records.
+  // FIXME: Is this supposed to be testing for injected class name declarations
+  // instead?
   if (isa<InjectedClassNameType>(Ty))
     return;
   SourceLocation Loc = TD->getLocation();
@@ -2365,7 +2367,9 @@ void CGDebugInfo::CollectCXXBasesAux(
   const ASTRecordLayout &RL = CGM.getContext().getASTRecordLayout(RD);
   for (const auto &BI : Bases) {
     const auto *Base =
-        cast<CXXRecordDecl>(BI.getType()->castAs<RecordType>()->getDecl());
+        cast<CXXRecordDecl>(
+            BI.getType()->castAs<RecordType>()->getOriginalDecl())
+            ->getDefinition();
     if (!SeenTypes.insert(Base).second)
       continue;
     auto *BaseTy = getOrCreateType(BI.getType(), Unit);
@@ -2831,12 +2835,12 @@ void CGDebugInfo::addHeapAllocSiteMetadata(llvm::CallBase *CI,
 void CGDebugInfo::completeType(const EnumDecl *ED) {
   if (DebugKind <= llvm::codegenoptions::DebugLineTablesOnly)
     return;
-  QualType Ty = CGM.getContext().getEnumType(ED);
+  CanQualType Ty = CGM.getContext().getCanonicalTagType(ED);
   void *TyPtr = Ty.getAsOpaquePtr();
   auto I = TypeCache.find(TyPtr);
   if (I == TypeCache.end() || !cast<llvm::DIType>(I->second)->isForwardDecl())
     return;
-  llvm::DIType *Res = CreateTypeDefinition(Ty->castAs<EnumType>());
+  llvm::DIType *Res = CreateTypeDefinition(dyn_cast<EnumType>(Ty));
   assert(!Res->isForwardDecl());
   TypeCache[TyPtr].reset(Res);
 }
@@ -2906,7 +2910,7 @@ void CGDebugInfo::completeClassData(const RecordDecl *RD) {
 void CGDebugInfo::completeClass(const RecordDecl *RD) {
   if (DebugKind <= llvm::codegenoptions::DebugLineTablesOnly)
     return;
-  QualType Ty = CGM.getContext().getRecordType(RD);
+  CanQualType Ty = CGM.getContext().getCanonicalTagType(RD);
   void *TyPtr = Ty.getAsOpaquePtr();
   auto I = TypeCache.find(TyPtr);
   if (I != TypeCache.end() && !cast<llvm::DIType>(I->second)->isForwardDecl())
@@ -2915,7 +2919,7 @@ void CGDebugInfo::completeClass(const RecordDecl *RD) {
   // We want the canonical definition of the structure to not
   // be the typedef. Since that would lead to circular typedef
   // metadata.
-  auto [Res, PrefRes] = CreateTypeDefinition(Ty->castAs<RecordType>());
+  auto [Res, PrefRes] = CreateTypeDefinition(dyn_cast<RecordType>(Ty));
   assert(!Res->isForwardDecl());
   TypeCache[TyPtr].reset(Res);
 }
@@ -3019,14 +3023,14 @@ void CGDebugInfo::completeRequiredType(const RecordDecl *RD) {
   if (shouldOmitDefinition(DebugKind, DebugTypeExtRefs, RD, CGM.getLangOpts()))
     return;
 
-  QualType Ty = CGM.getContext().getRecordType(RD);
+  CanQualType Ty = CGM.getContext().getCanonicalTagType(RD);
   llvm::DIType *T = getTypeOrNull(Ty);
   if (T && T->isForwardDecl())
     completeClassData(RD);
 }
 
 llvm::DIType *CGDebugInfo::CreateType(const RecordType *Ty) {
-  RecordDecl *RD = Ty->getDecl();
+  RecordDecl *RD = Ty->getOriginalDecl()->getDefinitionOrSelf();
   llvm::DIType *T = cast_or_null<llvm::DIType>(getTypeOrNull(QualType(Ty, 0)));
   if (T || shouldOmitDefinition(DebugKind, DebugTypeExtRefs, RD,
                                 CGM.getLangOpts())) {
@@ -3054,7 +3058,7 @@ llvm::DIType *CGDebugInfo::GetPreferredNameType(const CXXRecordDecl *RD,
 
 std::pair<llvm::DIType *, llvm::DIType *>
 CGDebugInfo::CreateTypeDefinition(const RecordType *Ty) {
-  RecordDecl *RD = Ty->getDecl();
+  RecordDecl *RD = Ty->getOriginalDecl()->getDefinitionOrSelf();
 
   // Get overall information about the record type for the debug info.
   llvm::DIFile *DefUnit = getOrCreateFile(RD->getLocation());
@@ -3076,7 +3080,7 @@ CGDebugInfo::CreateTypeDefinition(const RecordType *Ty) {
 
   // Push the struct on region stack.
   LexicalBlockStack.emplace_back(&*FwdDecl);
-  RegionMap[Ty->getDecl()].reset(FwdDecl);
+  RegionMap[RD].reset(FwdDecl);
 
   // Convert all the elements.
   SmallVector<llvm::Metadata *, 16> EltTys;
@@ -3098,7 +3102,7 @@ CGDebugInfo::CreateTypeDefinition(const RecordType *Ty) {
     CollectCXXMemberFunctions(CXXDecl, DefUnit, EltTys, FwdDecl);
 
   LexicalBlockStack.pop_back();
-  RegionMap.erase(Ty->getDecl());
+  RegionMap.erase(RD);
 
   llvm::DINodeArray Elements = DBuilder.getOrCreateArray(EltTys);
   DBuilder.replaceArrays(FwdDecl, Elements);
@@ -3107,7 +3111,7 @@ CGDebugInfo::CreateTypeDefinition(const RecordType *Ty) {
     FwdDecl =
         llvm::MDNode::replaceWithPermanent(llvm::TempDICompositeType(FwdDecl));
 
-  RegionMap[Ty->getDecl()].reset(FwdDecl);
+  RegionMap[RD].reset(FwdDecl);
 
   if (CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::LLDB)
     if (auto *PrefDI = GetPreferredNameType(CXXDecl, DefUnit))
@@ -3654,8 +3658,9 @@ llvm::DIType *CGDebugInfo::CreateType(const MemberPointerType *Ty,
     }
   }
 
-  llvm::DIType *ClassType = getOrCreateType(
-      QualType(Ty->getMostRecentCXXRecordDecl()->getTypeForDecl(), 0), U);
+  CanQualType T =
+      CGM.getContext().getCanonicalTagType(Ty->getMostRecentCXXRecordDecl());
+  llvm::DIType *ClassType = getOrCreateType(T, U);
   if (Ty->isMemberDataPointerType())
     return DBuilder.createMemberPointerType(
         getOrCreateType(Ty->getPointeeType(), U), ClassType, Size, /*Align=*/0,
@@ -3690,17 +3695,21 @@ llvm::DIType *CGDebugInfo::CreateType(const HLSLInlineSpirvType *Ty,
   return nullptr;
 }
 
-llvm::DIType *CGDebugInfo::CreateEnumType(const EnumType *Ty) {
-  const EnumDecl *ED = Ty->getDecl();
+static auto getEnumInfo(CodeGenModule &CGM, llvm::DICompileUnit *TheCU,
+                        const EnumType *Ty) {
+  const EnumDecl *ED = Ty->getOriginalDecl()->getDefinitionOrSelf();
 
   uint64_t Size = 0;
   uint32_t Align = 0;
-  if (!ED->getTypeForDecl()->isIncompleteType()) {
-    Size = CGM.getContext().getTypeSize(ED->getTypeForDecl());
+  if (ED->isComplete()) {
+    Size = CGM.getContext().getTypeSize(QualType(Ty, 0));
     Align = getDeclAlignIfRequired(ED, CGM.getContext());
   }
+  return std::make_tuple(ED, Size, Align, getTypeIdentifier(Ty, CGM, TheCU));
+}
 
-  SmallString<256> Identifier = getTypeIdentifier(Ty, CGM, TheCU);
+llvm::DIType *CGDebugInfo::CreateEnumType(const EnumType *Ty) {
+  auto [ED, Size, Align, Identifier] = getEnumInfo(CGM, TheCU, Ty);
 
   bool isImportedFromModule =
       DebugTypeExtRefs && ED->isFromASTFile() && ED->getDefinition();
@@ -3735,15 +3744,7 @@ llvm::DIType *CGDebugInfo::CreateEnumType(const EnumType *Ty) {
 }
 
 llvm::DIType *CGDebugInfo::CreateTypeDefinition(const EnumType *Ty) {
-  const EnumDecl *ED = Ty->getDecl();
-  uint64_t Size = 0;
-  uint32_t Align = 0;
-  if (!ED->getTypeForDecl()->isIncompleteType()) {
-    Size = CGM.getContext().getTypeSize(ED->getTypeForDecl());
-    Align = getDeclAlignIfRequired(ED, CGM.getContext());
-  }
-
-  SmallString<256> Identifier = getTypeIdentifier(Ty, CGM, TheCU);
+  auto [ED, Size, Align, Identifier] = getEnumInfo(CGM, TheCU, Ty);
 
   SmallVector<llvm::Metadata *, 16> Enumerators;
   ED = ED->getDefinition();
@@ -3818,6 +3819,11 @@ static QualType UnwrapTypeForDebugInfo(QualType T, const ASTContext &C) {
     switch (T->getTypeClass()) {
     default:
       return C.getQualifiedType(T.getTypePtr(), Quals);
+    case Type::Enum:
+    case Type::Record:
+    case Type::InjectedClassName:
+      return C.getQualifiedType(T->getCanonicalTypeUnqualified().getTypePtr(),
+                                Quals);
     case Type::TemplateSpecialization: {
       const auto *Spec = cast<TemplateSpecializationType>(T);
       if (Spec->isTypeAlias())
@@ -3846,11 +3852,8 @@ static QualType UnwrapTypeForDebugInfo(QualType T, const ASTContext &C) {
     case Type::CountAttributed:
       T = cast<CountAttributedType>(T)->desugar();
       break;
-    case Type::Elaborated:
-      T = cast<ElaboratedType>(T)->getNamedType();
-      break;
     case Type::Using:
-      T = cast<UsingType>(T)->getUnderlyingType();
+      T = cast<UsingType>(T)->desugar();
       break;
     case Type::Paren:
       T = cast<ParenType>(T)->getInnerType();
@@ -3909,7 +3912,8 @@ void CGDebugInfo::completeUnusedClass(const CXXRecordDecl &D) {
   completeClassData(&D);
   // In case this type has no member function definitions being emitted, ensure
   // it is retained
-  RetainedTypes.push_back(CGM.getContext().getRecordType(&D).getAsOpaquePtr());
+  RetainedTypes.push_back(
+      CGM.getContext().getCanonicalTagType(&D).getAsOpaquePtr());
 }
 
 llvm::DIType *CGDebugInfo::getOrCreateType(QualType Ty, llvm::DIFile *Unit) {
@@ -4053,7 +4057,6 @@ llvm::DIType *CGDebugInfo::CreateTypeNode(QualType Ty, llvm::DIFile *Unit) {
   case Type::Adjusted:
   case Type::Decayed:
   case Type::DeducedTemplateSpecialization:
-  case Type::Elaborated:
   case Type::Using:
   case Type::Paren:
   case Type::MacroQualified:
@@ -4096,7 +4099,7 @@ CGDebugInfo::getOrCreateLimitedType(const RecordType *Ty) {
 
 // TODO: Currently used for context chains when limiting debug info.
 llvm::DICompositeType *CGDebugInfo::CreateLimitedType(const RecordType *Ty) {
-  RecordDecl *RD = Ty->getDecl();
+  RecordDecl *RD = Ty->getOriginalDecl()->getDefinitionOrSelf();
 
   // Get overall information about the record type for the debug info.
   StringRef RDName = getClassName(RD);
@@ -4113,7 +4116,7 @@ llvm::DICompositeType *CGDebugInfo::CreateLimitedType(const RecordType *Ty) {
   // If we ended up creating the type during the context chain construction,
   // just return that.
   auto *T = cast_or_null<llvm::DICompositeType>(
-      getTypeOrNull(CGM.getContext().getRecordType(RD)));
+      getTypeOrNull(CGM.getContext().getCanonicalTagType(RD)));
   if (T && (!T->isForwardDecl() || !RD->getDefinition()))
     return T;
 
@@ -4183,7 +4186,7 @@ llvm::DICompositeType *CGDebugInfo::CreateLimitedType(const RecordType *Ty) {
     break;
   }
 
-  RegionMap[Ty->getDecl()].reset(RealDecl);
+  RegionMap[RD].reset(RealDecl);
   TypeCache[QualType(Ty, 0).getAsOpaquePtr()].reset(RealDecl);
 
   if (const auto *TSpecial = dyn_cast<ClassTemplateSpecializationDecl>(RD))
@@ -4207,8 +4210,8 @@ void CGDebugInfo::CollectContainingType(const CXXRecordDecl *RD,
       else
         break;
     }
-    ContainingType = getOrCreateType(QualType(PBase->getTypeForDecl(), 0),
-                                     getOrCreateFile(RD->getLocation()));
+    CanQualType T = CGM.getContext().getCanonicalTagType(PBase);
+    ContainingType = getOrCreateType(T, getOrCreateFile(RD->getLocation()));
   } else if (RD->isDynamicClass())
     ContainingType = RealDecl;
 
@@ -4414,9 +4417,10 @@ llvm::DINode *CGDebugInfo::getDeclarationOrDefinition(const Decl *D) {
   // we would otherwise do to get a type for a pointee. (forward declarations in
   // limited debug info, full definitions (if the type definition is available)
   // in unlimited debug info)
-  if (const auto *TD = dyn_cast<TypeDecl>(D))
-    return getOrCreateType(CGM.getContext().getTypeDeclType(TD),
-                           getOrCreateFile(TD->getLocation()));
+  if (const auto *TD = dyn_cast<TypeDecl>(D)) {
+    QualType Ty = CGM.getContext().getTypeDeclType(TD);
+    return getOrCreateType(Ty, getOrCreateFile(TD->getLocation()));
+  }
   auto I = DeclCache.find(D->getCanonicalDecl());
 
   if (I != DeclCache.end()) {
@@ -5074,7 +5078,7 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const VarDecl *VD,
   } else if (const auto *RT = dyn_cast<RecordType>(VD->getType())) {
     // If VD is an anonymous union then Storage represents value for
     // all union fields.
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->isUnion() && RD->isAnonymousStructOrUnion()) {
       // GDB has trouble finding local variables in anonymous unions, so we emit
       // artificial local variables for each of the members.
@@ -5531,7 +5535,7 @@ void CGDebugInfo::EmitDeclareOfBlockLiteralArgVariable(const CGBlockInfo &block,
               cast_or_null<CXXMethodDecl>(blockDecl->getNonClosureContext()))
         type = Method->getThisType();
       else if (auto *RDecl = dyn_cast<CXXRecordDecl>(blockDecl->getParent()))
-        type = QualType(RDecl->getTypeForDecl(), 0);
+        type = CGM.getContext().getCanonicalTagType(RDecl);
       else
         llvm_unreachable("unexpected block declcontext");
 
@@ -5620,8 +5624,9 @@ llvm::DIGlobalVariableExpression *CGDebugInfo::CollectAnonRecordDecls(
     // Ignore unnamed fields, but recurse into anonymous records.
     if (FieldName.empty()) {
       if (const auto *RT = dyn_cast<RecordType>(Field->getType()))
-        GVE = CollectAnonRecordDecls(RT->getDecl(), Unit, LineNo, LinkageName,
-                                     Var, DContext);
+        GVE =
+            CollectAnonRecordDecls(RT->getOriginalDecl()->getDefinitionOrSelf(),
+                                   Unit, LineNo, LinkageName, Var, DContext);
       continue;
     }
     // Use VarDecl's Tag, Scope and Line number.
@@ -5640,7 +5645,7 @@ static bool ReferencesAnonymousEntity(RecordType *RT) {
   // But so long as it's not one of those, it doesn't matter if some sub-type
   // of the record (a template parameter) can't be reconstituted - because the
   // un-reconstitutable type itself will carry its own name.
-  const auto *RD = dyn_cast<CXXRecordDecl>(RT->getDecl());
+  const auto *RD = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl());
   if (!RD)
     return false;
   if (!RD->getIdentifier())
@@ -5699,15 +5704,15 @@ struct ReconstitutableType : public RecursiveASTVisitor<ReconstitutableType> {
     }
     return true;
   }
-  bool TraverseEnumType(EnumType *ET) {
+  bool TraverseEnumType(EnumType *ET, bool = false) {
     // Unnamed enums can't be reconstituted due to a lack of column info we
     // produce in the DWARF, so we can't get Clang's full name back.
-    if (const auto *ED = dyn_cast<EnumDecl>(ET->getDecl())) {
+    if (const auto *ED = dyn_cast<EnumDecl>(ET->getOriginalDecl())) {
       if (!ED->getIdentifier()) {
         Reconstitutable = false;
         return false;
       }
-      if (!ED->isExternallyVisible()) {
+      if (!ED->getDefinitionOrSelf()->isExternallyVisible()) {
         Reconstitutable = false;
         return false;
       }
@@ -5720,7 +5725,7 @@ struct ReconstitutableType : public RecursiveASTVisitor<ReconstitutableType> {
     Reconstitutable &= !FT->getNoReturnAttr();
     return Reconstitutable;
   }
-  bool VisitRecordType(RecordType *RT) {
+  bool VisitRecordType(RecordType *RT, bool = false) {
     if (ReferencesAnonymousEntity(RT)) {
       Reconstitutable = false;
       return false;
@@ -5903,7 +5908,8 @@ void CGDebugInfo::EmitGlobalVariable(llvm::GlobalVariable *Var,
   // variable for each member of the anonymous union so that it's possible
   // to find the name of any field in the union.
   if (T->isUnionType() && DeclName.empty()) {
-    const RecordDecl *RD = T->castAs<RecordType>()->getDecl();
+    const RecordDecl *RD =
+        T->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
     assert(RD->isAnonymousStructOrUnion() &&
            "unnamed non-anonymous struct or union?");
     GVE = CollectAnonRecordDecls(RD, Unit, LineNo, LinkageName, Var, DContext);
@@ -5950,8 +5956,6 @@ void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
 
   if (const auto *ECD = dyn_cast<EnumConstantDecl>(VD)) {
     const auto *ED = cast<EnumDecl>(ECD->getDeclContext());
-    assert(isa<EnumType>(ED->getTypeForDecl()) && "Enum without EnumType?");
-
     if (CGM.getCodeGenOpts().EmitCodeView) {
       // If CodeView, emit enums as global variables, unless they are defined
       // inside a class. We do this because MSVC doesn't emit S_CONSTANTs for
@@ -5963,10 +5967,9 @@ void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
       // If not CodeView, emit DW_TAG_enumeration_type if necessary. For
       // example: for "enum { ZERO };", a DW_TAG_enumeration_type is created the
       // first time `ZERO` is referenced in a function.
-      llvm::DIType *EDTy =
-          getOrCreateType(QualType(ED->getTypeForDecl(), 0), Unit);
-      assert (EDTy->getTag() == llvm::dwarf::DW_TAG_enumeration_type);
-      (void)EDTy;
+      CanQualType T = CGM.getContext().getCanonicalTagType(ED);
+      [[maybe_unused]] llvm::DIType *EDTy = getOrCreateType(T, Unit);
+      assert(EDTy->getTag() == llvm::dwarf::DW_TAG_enumeration_type);
       return;
     }
   }
@@ -5985,7 +5988,7 @@ void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
     // FIXME: This is probably unnecessary, since Ty should reference RD
     // through its scope.
     RetainedTypes.push_back(
-        CGM.getContext().getRecordType(RD).getAsOpaquePtr());
+        CGM.getContext().getCanonicalTagType(RD).getAsOpaquePtr());
 
     return;
   }
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 04f13c7d7a6a3..55155ada9b9c7 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -113,12 +113,14 @@ void CodeGenFunction::EmitDecl(const Decl &D, bool EvaluateConditionDecl) {
   case Decl::CXXRecord: // struct/union/class X; [C++]
     if (CGDebugInfo *DI = getDebugInfo())
       if (cast<RecordDecl>(D).getDefinition())
-        DI->EmitAndRetainType(getContext().getRecordType(cast<RecordDecl>(&D)));
+        DI->EmitAndRetainType(
+            getContext().getCanonicalTagType(cast<RecordDecl>(&D)));
     return;
   case Decl::Enum:      // enum X;
     if (CGDebugInfo *DI = getDebugInfo())
       if (cast<EnumDecl>(D).getDefinition())
-        DI->EmitAndRetainType(getContext().getEnumType(cast<EnumDecl>(&D)));
+        DI->EmitAndRetainType(
+            getContext().getCanonicalTagType(cast<EnumDecl>(&D)));
     return;
   case Decl::Function:     // void X();
   case Decl::EnumConstant: // enum ? { X = ? }
@@ -1567,7 +1569,7 @@ CodeGenFunction::EmitAutoVarAlloca(const VarDecl &D) {
       ;
 
       if (const RecordType *RecordTy = Ty->getAs<RecordType>()) {
-        const auto *RD = RecordTy->getDecl();
+        const auto *RD = RecordTy->getOriginalDecl()->getDefinitionOrSelf();
         const auto *CXXRD = dyn_cast<CXXRecordDecl>(RD);
         if ((CXXRD && !CXXRD->hasTrivialDestructor()) ||
             RD->isNonTrivialToPrimitiveDestroy()) {
@@ -2727,7 +2729,10 @@ void CodeGenFunction::EmitParmDecl(const VarDecl &D, ParamValue Arg,
     // Don't push a cleanup in a thunk for a method that will also emit a
     // cleanup.
     if (Ty->isRecordType() && !CurFuncIsThunk &&
-        Ty->castAs<RecordType>()->getDecl()->isParamDestroyedInCallee()) {
+        Ty->castAs<RecordType>()
+            ->getOriginalDecl()
+            ->getDefinitionOrSelf()
+            ->isParamDestroyedInCallee()) {
       if (QualType::DestructionKind DtorKind =
               D.needsDestruction(getContext())) {
         assert((DtorKind == QualType::DK_cxx_destructor ||
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 85c768807572f..1b1f6a98988ef 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -397,9 +397,10 @@ pushTemporaryCleanup(CodeGenFunction &CGF, const MaterializeTemporaryExpr *M,
       if (const RecordType *RT =
               E->getType()->getBaseElementTypeUnsafe()->getAs<RecordType>()) {
         // Get the destructor for the reference temporary.
-        if (auto *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getDecl());
+        if (auto *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl());
             ClassDecl && !ClassDecl->hasTrivialDestructor())
-          ReferenceTemporaryDtor = ClassDecl->getDestructor();
+          ReferenceTemporaryDtor =
+              ClassDecl->getDefinitionOrSelf()->getDestructor();
       }
 
       if (!ReferenceTemporaryDtor)
@@ -1198,9 +1199,10 @@ llvm::Value *CodeGenFunction::GetCountedByFieldExprGEP(
     return nullptr;
 
   Indices.push_back(Builder.getInt32(0));
-  return Builder.CreateInBoundsGEP(
-      ConvertType(QualType(RD->getTypeForDecl(), 0)), Res,
-      RecIndicesTy(llvm::reverse(Indices)), "counted_by.gep");
+  CanQualType T = CGM.getContext().getCanonicalTagType(RD);
+  return Builder.CreateInBoundsGEP(ConvertType(T), Res,
+                                   RecIndicesTy(llvm::reverse(Indices)),
+                                   "counted_by.gep");
 }
 
 /// This method is typically called in contexts where we can't generate
@@ -1748,9 +1750,11 @@ static bool isConstantEmittableObjectType(QualType type) {
   // Otherwise, all object types satisfy this except C++ classes with
   // mutable subobjects or non-trivial copy/destroy behavior.
   if (const auto *RT = dyn_cast<RecordType>(type))
-    if (const auto *RD = dyn_cast<CXXRecordDecl>(RT->getDecl()))
+    if (const auto *RD = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl())) {
+      RD = RD->getDefinitionOrSelf();
       if (RD->hasMutableFields() || !RD->isTrivial())
         return false;
+    }
 
   return true;
 }
@@ -1911,8 +1915,10 @@ static bool getRangeForType(CodeGenFunction &CGF, QualType Ty,
                             llvm::APInt &Min, llvm::APInt &End,
                             bool StrictEnums, bool IsBool) {
   const EnumType *ET = Ty->getAs<EnumType>();
-  bool IsRegularCPlusPlusEnum = CGF.getLangOpts().CPlusPlus && StrictEnums &&
-                                ET && !ET->getDecl()->isFixed();
+  const EnumDecl *ED =
+      ET ? ET->getOriginalDecl()->getDefinitionOrSelf() : nullptr;
+  bool IsRegularCPlusPlusEnum =
+      CGF.getLangOpts().CPlusPlus && StrictEnums && ET && !ED->isFixed();
   if (!IsBool && !IsRegularCPlusPlusEnum)
     return false;
 
@@ -1920,7 +1926,6 @@ static bool getRangeForType(CodeGenFunction &CGF, QualType Ty,
     Min = llvm::APInt(CGF.getContext().getTypeSize(Ty), 0);
     End = llvm::APInt(CGF.getContext().getTypeSize(Ty), 2);
   } else {
-    const EnumDecl *ED = ET->getDecl();
     ED->getValueRange(End, Min);
   }
   return true;
@@ -4266,7 +4271,9 @@ static bool IsPreserveAIArrayBase(CodeGenFunction &CGF, const Expr *ArrayBase) {
     const auto *PointeeT = PtrT->getPointeeType()
                              ->getUnqualifiedDesugaredType();
     if (const auto *RecT = dyn_cast<RecordType>(PointeeT))
-      return RecT->getDecl()->hasAttr<BPFPreserveAccessIndexAttr>();
+      return RecT->getOriginalDecl()
+          ->getMostRecentDecl()
+          ->hasAttr<BPFPreserveAccessIndexAttr>();
     return false;
   }
 
@@ -5032,10 +5039,12 @@ LValue CodeGenFunction::EmitLValueForLambdaField(const FieldDecl *Field,
       Address Base = GetAddressOfBaseClass(
           LambdaLV.getAddress(), ThisTy, BasePathArray.begin(),
           BasePathArray.end(), /*NullCheckValue=*/false, SourceLocation());
-      LambdaLV = MakeAddrLValue(Base, QualType{LambdaTy->getTypeForDecl(), 0});
+      CanQualType T = getContext().getCanonicalTagType(LambdaTy);
+      LambdaLV = MakeAddrLValue(Base, T);
     }
   } else {
-    QualType LambdaTagType = getContext().getTagDeclType(Field->getParent());
+    CanQualType LambdaTagType =
+        getContext().getCanonicalTagType(Field->getParent());
     LambdaLV = MakeNaturalAlignAddrLValue(ThisValue, LambdaTagType);
   }
   return EmitLValueForField(LambdaLV, Field);
@@ -5160,7 +5169,7 @@ LValue CodeGenFunction::EmitLValueForField(LValue base, const FieldDecl *field,
         }
       } else {
         llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateRecordType(
-            getContext().getRecordType(rec), rec->getLocation());
+            getContext().getCanonicalTagType(rec), rec->getLocation());
         Addr = Builder.CreatePreserveStructAccessIndex(
             Addr, Idx, getDebugInfoFIndex(rec, field->getFieldIndex()),
             DbgInfo);
@@ -5622,7 +5631,9 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
   case CK_DerivedToBase: {
     const auto *DerivedClassTy =
         E->getSubExpr()->getType()->castAs<RecordType>();
-    auto *DerivedClassDecl = cast<CXXRecordDecl>(DerivedClassTy->getDecl());
+    auto *DerivedClassDecl =
+        cast<CXXRecordDecl>(DerivedClassTy->getOriginalDecl())
+            ->getDefinitionOrSelf();
 
     LValue LV = EmitLValue(E->getSubExpr());
     Address This = LV.getAddress();
@@ -5642,7 +5653,9 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
     return EmitAggExprToLValue(E);
   case CK_BaseToDerived: {
     const auto *DerivedClassTy = E->getType()->castAs<RecordType>();
-    auto *DerivedClassDecl = cast<CXXRecordDecl>(DerivedClassTy->getDecl());
+    auto *DerivedClassDecl =
+        cast<CXXRecordDecl>(DerivedClassTy->getOriginalDecl())
+            ->getDefinitionOrSelf();
 
     LValue LV = EmitLValue(E->getSubExpr());
 
@@ -6700,7 +6713,7 @@ void CodeGenFunction::FlattenAccessAndType(
         WorkList.emplace_back(CAT->getElementType(), IdxListCopy);
       }
     } else if (const auto *RT = dyn_cast<RecordType>(T)) {
-      const RecordDecl *Record = RT->getDecl();
+      const RecordDecl *Record = RT->getOriginalDecl()->getDefinitionOrSelf();
       assert(!Record->isUnion() && "Union types not supported in flat cast.");
 
       const CXXRecordDecl *CXXD = dyn_cast<CXXRecordDecl>(Record);
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index cad6731173700..2c1081d665231 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -272,7 +272,7 @@ bool AggExprEmitter::TypeRequiresGCollection(QualType T) {
   if (!RecordTy) return false;
 
   // Don't mess with non-trivial C++ types.
-  RecordDecl *Record = RecordTy->getDecl();
+  RecordDecl *Record = RecordTy->getOriginalDecl()->getDefinitionOrSelf();
   if (isa<CXXRecordDecl>(Record) &&
       (cast<CXXRecordDecl>(Record)->hasNonTrivialCopyConstructor() ||
        !cast<CXXRecordDecl>(Record)->hasTrivialDestructor()))
@@ -428,7 +428,10 @@ AggExprEmitter::VisitCXXStdInitializerListExpr(CXXStdInitializerListExpr *E) {
       Ctx.getAsConstantArrayType(E->getSubExpr()->getType());
   assert(ArrayType && "std::initializer_list constructed from non-array");
 
-  RecordDecl *Record = E->getType()->castAs<RecordType>()->getDecl();
+  RecordDecl *Record = E->getType()
+                           ->castAs<RecordType>()
+                           ->getOriginalDecl()
+                           ->getDefinitionOrSelf();
   RecordDecl::field_iterator Field = Record->field_begin();
   assert(Field != Record->field_end() &&
          Ctx.hasSameType(Field->getType()->getPointeeType(),
@@ -1810,7 +1813,10 @@ void AggExprEmitter::VisitCXXParenListOrInitListExpr(
   // the disadvantage is that the generated code is more difficult for
   // the optimizer, especially with bitfields.
   unsigned NumInitElements = InitExprs.size();
-  RecordDecl *record = ExprToVisit->getType()->castAs<RecordType>()->getDecl();
+  RecordDecl *record = ExprToVisit->getType()
+                           ->castAs<RecordType>()
+                           ->getOriginalDecl()
+                           ->getDefinitionOrSelf();
 
   // We'll need to enter cleanup scopes in case any of the element
   // initializers throws an exception.
@@ -2120,7 +2126,7 @@ static CharUnits GetNumNonZeroBytesInInit(const Expr *E, CodeGenFunction &CGF) {
   // referencee.  InitListExprs for unions and arrays can't have references.
   if (const RecordType *RT = E->getType()->getAs<RecordType>()) {
     if (!RT->isUnionType()) {
-      RecordDecl *SD = RT->getDecl();
+      RecordDecl *SD = RT->getOriginalDecl()->getDefinitionOrSelf();
       CharUnits NumNonZeroBytes = CharUnits::Zero();
 
       unsigned ILEElement = 0;
@@ -2172,7 +2178,7 @@ static void CheckAggExprForMemSetUse(AggValueSlot &Slot, const Expr *E,
   if (CGF.getLangOpts().CPlusPlus)
     if (const RecordType *RT = CGF.getContext()
                        .getBaseElementType(E->getType())->getAs<RecordType>()) {
-      const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+      const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getOriginalDecl());
       if (RD->hasUserDeclaredConstructor())
         return;
     }
@@ -2293,7 +2299,8 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
 
   if (getLangOpts().CPlusPlus) {
     if (const RecordType *RT = Ty->getAs<RecordType>()) {
-      CXXRecordDecl *Record = cast<CXXRecordDecl>(RT->getDecl());
+      auto *Record =
+          cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
       assert((Record->hasTrivialCopyConstructor() ||
               Record->hasTrivialCopyAssignment() ||
               Record->hasTrivialMoveConstructor() ||
@@ -2377,7 +2384,7 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
   if (CGM.getLangOpts().getGC() == LangOptions::NonGC) {
     // fall through
   } else if (const RecordType *RecordTy = Ty->getAs<RecordType>()) {
-    RecordDecl *Record = RecordTy->getDecl();
+    RecordDecl *Record = RecordTy->getOriginalDecl()->getDefinitionOrSelf();
     if (Record->hasObjectMember()) {
       CGM.getObjCRuntime().EmitGCMemmoveCollectable(*this, DestPtr, SrcPtr,
                                                     SizeVal);
@@ -2386,7 +2393,9 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
   } else if (Ty->isArrayType()) {
     QualType BaseType = getContext().getBaseElementType(Ty);
     if (const RecordType *RecordTy = BaseType->getAs<RecordType>()) {
-      if (RecordTy->getDecl()->hasObjectMember()) {
+      if (RecordTy->getOriginalDecl()
+              ->getDefinitionOrSelf()
+              ->hasObjectMember()) {
         CGM.getObjCRuntime().EmitGCMemmoveCollectable(*this, DestPtr, SrcPtr,
                                                       SizeVal);
         return;
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index 359e30cb8f5cd..a92b89def6433 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -181,7 +181,7 @@ static CXXRecordDecl *getCXXRecord(const Expr *E) {
   if (const PointerType *PTy = T->getAs<PointerType>())
     T = PTy->getPointeeType();
   const RecordType *Ty = T->castAs<RecordType>();
-  return cast<CXXRecordDecl>(Ty->getDecl());
+  return cast<CXXRecordDecl>(Ty->getOriginalDecl())->getDefinitionOrSelf();
 }
 
 // Note: This function also emit constructor calls to support a MSVC
@@ -206,7 +206,7 @@ RValue CodeGenFunction::EmitCXXMemberCallExpr(const CXXMemberCallExpr *CE,
   }
 
   bool HasQualifier = ME->hasQualifier();
-  NestedNameSpecifier *Qualifier = HasQualifier ? ME->getQualifier() : nullptr;
+  NestedNameSpecifier Qualifier = ME->getQualifier();
   bool IsArrow = ME->isArrow();
   const Expr *Base = ME->getBase();
 
@@ -217,7 +217,7 @@ RValue CodeGenFunction::EmitCXXMemberCallExpr(const CXXMemberCallExpr *CE,
 
 RValue CodeGenFunction::EmitCXXMemberOrOperatorMemberCallExpr(
     const CallExpr *CE, const CXXMethodDecl *MD, ReturnValueSlot ReturnValue,
-    bool HasQualifier, NestedNameSpecifier *Qualifier, bool IsArrow,
+    bool HasQualifier, NestedNameSpecifier Qualifier, bool IsArrow,
     const Expr *Base, llvm::CallBase **CallOrInvoke) {
   assert(isa<CXXMemberCallExpr>(CE) || isa<CXXOperatorCallExpr>(CE));
 
@@ -361,7 +361,7 @@ RValue CodeGenFunction::EmitCXXMemberOrOperatorMemberCallExpr(
   if (sanitizePerformTypeCheck())
     EmitTypeCheck(CodeGenFunction::TCK_MemberCall, CallLoc,
                   This.emitRawPointer(*this),
-                  C.getRecordType(CalleeDecl->getParent()),
+                  C.getCanonicalTagType(CalleeDecl->getParent()),
                   /*Alignment=*/CharUnits::Zero(), SkippedChecks);
 
   // C++ [class.virtual]p12:
@@ -461,9 +461,9 @@ CodeGenFunction::EmitCXXMemberPointerCallExpr(const CXXMemberCallExpr *E,
   else
     This = EmitLValue(BaseExpr, KnownNonNull).getAddress();
 
-  EmitTypeCheck(
-      TCK_MemberCall, E->getExprLoc(), This.emitRawPointer(*this),
-      QualType(MPT->getMostRecentCXXRecordDecl()->getTypeForDecl(), 0));
+  CanQualType ClassType = CGM.getContext().getCanonicalTagType(RD);
+  EmitTypeCheck(TCK_MemberCall, E->getExprLoc(), This.emitRawPointer(*this),
+                ClassType);
 
   // Get the member function pointer.
   llvm::Value *MemFnPtr = EmitScalarExpr(MemFnExpr);
@@ -476,8 +476,7 @@ CodeGenFunction::EmitCXXMemberPointerCallExpr(const CXXMemberCallExpr *E,
 
   CallArgList Args;
 
-  QualType ThisType =
-    getContext().getPointerType(getContext().getTagDeclType(RD));
+  QualType ThisType = getContext().getPointerType(ClassType);
 
   // Push the this ptr.
   Args.add(RValue::get(ThisPtrForCall), ThisType);
@@ -498,7 +497,7 @@ RValue CodeGenFunction::EmitCXXOperatorMemberCallExpr(
   assert(MD->isImplicitObjectMemberFunction() &&
          "Trying to emit a member call expr on a static method!");
   return EmitCXXMemberOrOperatorMemberCallExpr(
-      E, MD, ReturnValue, /*HasQualifier=*/false, /*Qualifier=*/nullptr,
+      E, MD, ReturnValue, /*HasQualifier=*/false, /*Qualifier=*/std::nullopt,
       /*IsArrow=*/false, E->getArg(0), CallOrInvoke);
 }
 
@@ -1237,11 +1236,12 @@ void CodeGenFunction::EmitNewArrayInitializer(
   // usually use memset.
   if (auto *ILE = dyn_cast<InitListExpr>(Init)) {
     if (const RecordType *RType = ILE->getType()->getAs<RecordType>()) {
-      if (RType->getDecl()->isStruct()) {
+      const RecordDecl *RD = RType->getOriginalDecl()->getDefinitionOrSelf();
+      if (RD->isStruct()) {
         unsigned NumElements = 0;
-        if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RType->getDecl()))
+        if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
           NumElements = CXXRD->getNumBases();
-        for (auto *Field : RType->getDecl()->fields())
+        for (auto *Field : RD->fields())
           if (!Field->isUnnamedBitField())
             ++NumElements;
         // FIXME: Recurse into nested InitListExprs.
@@ -1687,9 +1687,11 @@ llvm::Value *CodeGenFunction::EmitCXXNewExpr(const CXXNewExpr *E) {
       QualType AlignValT = sizeType;
       if (allocatorType->getNumParams() > IndexOfAlignArg) {
         AlignValT = allocatorType->getParamType(IndexOfAlignArg);
-        assert(getContext().hasSameUnqualifiedType(
-                   AlignValT->castAs<EnumType>()->getDecl()->getIntegerType(),
-                   sizeType) &&
+        assert(getContext().hasSameUnqualifiedType(AlignValT->castAs<EnumType>()
+                                                       ->getOriginalDecl()
+                                                       ->getDefinitionOrSelf()
+                                                       ->getIntegerType(),
+                                                   sizeType) &&
                "wrong type for alignment parameter");
         ++ParamsToSkip;
       } else {
@@ -1972,7 +1974,8 @@ static bool EmitObjectDelete(CodeGenFunction &CGF,
   // destructor is virtual, we'll just emit the vcall and return.
   const CXXDestructorDecl *Dtor = nullptr;
   if (const RecordType *RT = ElementType->getAs<RecordType>()) {
-    CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+    auto *RD =
+        cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
     if (RD->hasDefinition() && !RD->hasTrivialDestructor()) {
       Dtor = RD->getDestructor();
 
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 715bd392f59f7..a96c1518d2a1d 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -714,7 +714,10 @@ static bool EmitDesignatedInitUpdater(ConstantEmitter &Emitter,
 }
 
 bool ConstStructBuilder::Build(const InitListExpr *ILE, bool AllowOverwrite) {
-  RecordDecl *RD = ILE->getType()->castAs<RecordType>()->getDecl();
+  RecordDecl *RD = ILE->getType()
+                       ->castAs<RecordType>()
+                       ->getOriginalDecl()
+                       ->getDefinitionOrSelf();
   const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
 
   unsigned FieldNo = -1;
@@ -977,7 +980,8 @@ bool ConstStructBuilder::DoZeroInitPadding(const ASTRecordLayout &Layout,
 
 llvm::Constant *ConstStructBuilder::Finalize(QualType Type) {
   Type = Type.getNonReferenceType();
-  RecordDecl *RD = Type->castAs<RecordType>()->getDecl();
+  RecordDecl *RD =
+      Type->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
   llvm::Type *ValTy = CGM.getTypes().ConvertType(Type);
   return Builder.build(ValTy, RD->hasFlexibleArrayMember());
 }
@@ -1000,7 +1004,8 @@ llvm::Constant *ConstStructBuilder::BuildStruct(ConstantEmitter &Emitter,
   ConstantAggregateBuilder Const(Emitter.CGM);
   ConstStructBuilder Builder(Emitter, Const, CharUnits::Zero());
 
-  const RecordDecl *RD = ValTy->castAs<RecordType>()->getDecl();
+  const RecordDecl *RD =
+      ValTy->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
   const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD);
   if (!Builder.Build(Val, RD, false, CD, CharUnits::Zero()))
     return nullptr;
@@ -1506,7 +1511,9 @@ class ConstExprEmitter
     llvm::Type *ValTy = CGM.getTypes().ConvertType(destType);
     bool HasFlexibleArray = false;
     if (const auto *RT = destType->getAs<RecordType>())
-      HasFlexibleArray = RT->getDecl()->hasFlexibleArrayMember();
+      HasFlexibleArray = RT->getOriginalDecl()
+                             ->getDefinitionOrSelf()
+                             ->hasFlexibleArrayMember();
     return Const.build(ValTy, HasFlexibleArray);
   }
 
@@ -2640,7 +2647,9 @@ static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
       }
 
       const CXXRecordDecl *base =
-        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+          cast<CXXRecordDecl>(
+              I.getType()->castAs<RecordType>()->getOriginalDecl())
+              ->getDefinitionOrSelf();
 
       // Ignore empty bases.
       if (isEmptyRecordForLayout(CGM.getContext(), I.getType()) ||
@@ -2679,8 +2688,10 @@ static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
   // Fill in the virtual bases, if we're working with the complete object.
   if (CXXR && asCompleteObject) {
     for (const auto &I : CXXR->vbases()) {
-      const CXXRecordDecl *base =
-        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+      const auto *base =
+          cast<CXXRecordDecl>(
+              I.getType()->castAs<RecordType>()->getOriginalDecl())
+              ->getDefinitionOrSelf();
 
       // Ignore empty bases.
       if (isEmptyRecordForLayout(CGM.getContext(), I.getType()))
@@ -2746,7 +2757,9 @@ llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
   }
 
   if (const RecordType *RT = T->getAs<RecordType>())
-    return ::EmitNullConstant(*this, RT->getDecl(), /*complete object*/ true);
+    return ::EmitNullConstant(*this,
+                              RT->getOriginalDecl()->getDefinitionOrSelf(),
+                              /*complete object*/ true);
 
   assert(T->isMemberDataPointerType() &&
          "Should only see pointers to data members here!");
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 44931d0481e26..0318f85a344d7 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -3515,7 +3515,9 @@ Value *ScalarExprEmitter::VisitOffsetOfExpr(OffsetOfExpr *E) {
 
     case OffsetOfNode::Field: {
       FieldDecl *MemberDecl = ON.getField();
-      RecordDecl *RD = CurrentType->castAs<RecordType>()->getDecl();
+      RecordDecl *RD = CurrentType->castAs<RecordType>()
+                           ->getOriginalDecl()
+                           ->getDefinitionOrSelf();
       const ASTRecordLayout &RL = CGF.getContext().getASTRecordLayout(RD);
 
       // Compute the index of the field in its parent.
@@ -3548,15 +3550,16 @@ Value *ScalarExprEmitter::VisitOffsetOfExpr(OffsetOfExpr *E) {
         continue;
       }
 
-      RecordDecl *RD = CurrentType->castAs<RecordType>()->getDecl();
-      const ASTRecordLayout &RL = CGF.getContext().getASTRecordLayout(RD);
+      const ASTRecordLayout &RL = CGF.getContext().getASTRecordLayout(
+          CurrentType->castAs<RecordType>()->getOriginalDecl());
 
       // Save the element type.
       CurrentType = ON.getBase()->getType();
 
       // Compute the offset to the base.
       auto *BaseRT = CurrentType->castAs<RecordType>();
-      auto *BaseRD = cast<CXXRecordDecl>(BaseRT->getDecl());
+      auto *BaseRD =
+          cast<CXXRecordDecl>(BaseRT->getOriginalDecl())->getDefinitionOrSelf();
       CharUnits OffsetInt = RL.getBaseClassOffset(BaseRD);
       Offset = llvm::ConstantInt::get(ResultType, OffsetInt.getQuantity());
       break;
diff --git a/clang/lib/CodeGen/CGHLSLRuntime.cpp b/clang/lib/CodeGen/CGHLSLRuntime.cpp
index a47d1cc22980d..65c708022fc09 100644
--- a/clang/lib/CodeGen/CGHLSLRuntime.cpp
+++ b/clang/lib/CodeGen/CGHLSLRuntime.cpp
@@ -186,8 +186,7 @@ static const clang::HLSLAttributedResourceType *
 createBufferHandleType(const HLSLBufferDecl *BufDecl) {
   ASTContext &AST = BufDecl->getASTContext();
   QualType QT = AST.getHLSLAttributedResourceType(
-      AST.HLSLResourceTy,
-      QualType(BufDecl->getLayoutStruct()->getTypeForDecl(), 0),
+      AST.HLSLResourceTy, AST.getCanonicalTagType(BufDecl->getLayoutStruct()),
       HLSLAttributedResourceType::Attributes(ResourceClass::CBuffer));
   return cast<HLSLAttributedResourceType>(QT.getTypePtr());
 }
diff --git a/clang/lib/CodeGen/CGNonTrivialStruct.cpp b/clang/lib/CodeGen/CGNonTrivialStruct.cpp
index e0983ef256e71..1b941fff8b644 100644
--- a/clang/lib/CodeGen/CGNonTrivialStruct.cpp
+++ b/clang/lib/CodeGen/CGNonTrivialStruct.cpp
@@ -39,7 +39,8 @@ template <class Derived> struct StructVisitor {
 
   template <class... Ts>
   void visitStructFields(QualType QT, CharUnits CurStructOffset, Ts... Args) {
-    const RecordDecl *RD = QT->castAs<RecordType>()->getDecl();
+    const RecordDecl *RD =
+        QT->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
 
     // Iterate over the fields of the struct.
     for (const FieldDecl *FD : RD->fields()) {
@@ -464,7 +465,8 @@ template <class Derived> struct GenFuncBase {
 
       if (WrongType) {
         std::string FuncName = std::string(F->getName());
-        SourceLocation Loc = QT->castAs<RecordType>()->getDecl()->getLocation();
+        SourceLocation Loc =
+            QT->castAs<RecordType>()->getOriginalDecl()->getLocation();
         CGM.Error(Loc, "special function " + FuncName +
                            " for non-trivial C struct has incorrect type");
         return nullptr;
@@ -560,7 +562,8 @@ struct GenBinaryFunc : CopyStructVisitor<Derived, IsMove>,
       if (FD->isZeroLengthBitField())
         return;
 
-      QualType RT = QualType(FD->getParent()->getTypeForDecl(), 0);
+      CanQualType RT =
+          this->CGF->getContext().getCanonicalTagType(FD->getParent());
       llvm::Type *Ty = this->CGF->ConvertType(RT);
       Address DstAddr = this->getAddrWithOffset(Addrs[DstIdx], Offset);
       LValue DstBase =
diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index 6f87444d3f672..04b6d4fe29296 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -1000,7 +1000,9 @@ PropertyImplStrategy::PropertyImplStrategy(CodeGenModule &CGM,
   // Compute whether the ivar has strong members.
   if (CGM.getLangOpts().getGC())
     if (const RecordType *recordType = ivarType->getAs<RecordType>())
-      HasStrong = recordType->getDecl()->hasObjectMember();
+      HasStrong = recordType->getOriginalDecl()
+                      ->getDefinitionOrSelf()
+                      ->hasObjectMember();
 
   // We can never access structs with object members with a native
   // access, because we need to use write barriers.  This is what
diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index a52c92cdbc83b..adb5639e7289c 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -2493,7 +2493,7 @@ void CGObjCCommonMac::BuildRCBlockVarRecordLayout(const RecordType *RT,
                                                   CharUnits BytePos,
                                                   bool &HasUnion,
                                                   bool ByrefLayout) {
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   SmallVector<const FieldDecl *, 16> Fields(RD->fields());
   llvm::Type *Ty = CGM.getTypes().ConvertType(QualType(RT, 0));
   const llvm::StructLayout *RecLayout =
@@ -3352,7 +3352,8 @@ static bool hasWeakMember(QualType type) {
   }
 
   if (auto recType = type->getAs<RecordType>()) {
-    for (auto *field : recType->getDecl()->fields()) {
+    for (auto *field :
+         recType->getOriginalDecl()->getDefinitionOrSelf()->fields()) {
       if (hasWeakMember(field->getType()))
         return true;
     }
@@ -5174,7 +5175,7 @@ CGObjCCommonMac::GetIvarLayoutName(IdentifierInfo *Ident,
 }
 
 void IvarLayoutBuilder::visitRecord(const RecordType *RT, CharUnits offset) {
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
   // If this is a union, remember that we had one, because it might mess
   // up the ordering of layout entries.
@@ -5660,7 +5661,7 @@ ObjCCommonTypesHelper::ObjCCommonTypesHelper(CodeGen::CodeGenModule &cgm)
                                 nullptr, false, ICIS_NoInit));
   RD->completeDefinition();
 
-  SuperCTy = Ctx.getTagDeclType(RD);
+  SuperCTy = Ctx.getCanonicalTagType(RD);
   SuperPtrCTy = Ctx.getPointerType(SuperCTy);
 
   SuperTy = cast<llvm::StructType>(Types.ConvertType(SuperCTy));
@@ -6006,7 +6007,7 @@ ObjCNonFragileABITypesHelper::ObjCNonFragileABITypesHelper(
                                 false, ICIS_NoInit));
   RD->completeDefinition();
 
-  MessageRefCTy = Ctx.getTagDeclType(RD);
+  MessageRefCTy = Ctx.getCanonicalTagType(RD);
   MessageRefCPtrTy = Ctx.getPointerType(MessageRefCTy);
   MessageRefTy = cast<llvm::StructType>(Types.ConvertType(MessageRefCTy));
 
diff --git a/clang/lib/CodeGen/CGObjCRuntime.cpp b/clang/lib/CodeGen/CGObjCRuntime.cpp
index 6e2f32022a01e..cbf99534d2ce6 100644
--- a/clang/lib/CodeGen/CGObjCRuntime.cpp
+++ b/clang/lib/CodeGen/CGObjCRuntime.cpp
@@ -440,7 +440,9 @@ void CGObjCRuntime::destroyCalleeDestroyedArguments(CodeGenFunction &CGF,
     } else {
       QualType QT = param->getType();
       auto *RT = QT->getAs<RecordType>();
-      if (RT && RT->getDecl()->isParamDestroyedInCallee()) {
+      if (RT && RT->getOriginalDecl()
+                    ->getDefinitionOrSelf()
+                    ->isParamDestroyedInCallee()) {
         RValue RV = I->getRValue(CGF);
         QualType::DestructionKind DtorKind = QT.isDestructedType();
         switch (DtorKind) {
diff --git a/clang/lib/CodeGen/CGOpenMPRuntime.cpp b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
index a5f2f0efa2c3b..503c02f02cc6c 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntime.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -2915,7 +2915,7 @@ createKmpTaskTRecordDecl(CodeGenModule &CGM, OpenMPDirectiveKind Kind,
   addFieldToRecordDecl(C, UD, KmpInt32Ty);
   addFieldToRecordDecl(C, UD, KmpRoutineEntryPointerQTy);
   UD->completeDefinition();
-  QualType KmpCmplrdataTy = C.getRecordType(UD);
+  CanQualType KmpCmplrdataTy = C.getCanonicalTagType(UD);
   RecordDecl *RD = C.buildImplicitRecord("kmp_task_t");
   RD->startDefinition();
   addFieldToRecordDecl(C, RD, C.VoidPtrTy);
@@ -2950,7 +2950,7 @@ createKmpTaskTWithPrivatesRecordDecl(CodeGenModule &CGM, QualType KmpTaskTQTy,
   RD->startDefinition();
   addFieldToRecordDecl(C, RD, KmpTaskTQTy);
   if (const RecordDecl *PrivateRD = createPrivatesRecordDecl(CGM, Privates))
-    addFieldToRecordDecl(C, RD, C.getRecordType(PrivateRD));
+    addFieldToRecordDecl(C, RD, C.getCanonicalTagType(PrivateRD));
   RD->completeDefinition();
   return RD;
 }
@@ -3582,7 +3582,7 @@ static void getKmpAffinityType(ASTContext &C, QualType &KmpTaskAffinityInfoTy) {
     addFieldToRecordDecl(C, KmpAffinityInfoRD, C.getSizeType());
     addFieldToRecordDecl(C, KmpAffinityInfoRD, FlagsTy);
     KmpAffinityInfoRD->completeDefinition();
-    KmpTaskAffinityInfoTy = C.getRecordType(KmpAffinityInfoRD);
+    KmpTaskAffinityInfoTy = C.getCanonicalTagType(KmpAffinityInfoRD);
   }
 }
 
@@ -3640,7 +3640,7 @@ CGOpenMPRuntime::emitTaskInit(CodeGenFunction &CGF, SourceLocation Loc,
   // Build type kmp_task_t (if not built yet).
   if (isOpenMPTaskLoopDirective(D.getDirectiveKind())) {
     if (SavedKmpTaskloopTQTy.isNull()) {
-      SavedKmpTaskloopTQTy = C.getRecordType(createKmpTaskTRecordDecl(
+      SavedKmpTaskloopTQTy = C.getCanonicalTagType(createKmpTaskTRecordDecl(
           CGM, D.getDirectiveKind(), KmpInt32Ty, KmpRoutineEntryPtrQTy));
     }
     KmpTaskTQTy = SavedKmpTaskloopTQTy;
@@ -3650,7 +3650,7 @@ CGOpenMPRuntime::emitTaskInit(CodeGenFunction &CGF, SourceLocation Loc,
             isOpenMPTargetDataManagementDirective(D.getDirectiveKind())) &&
            "Expected taskloop, task or target directive");
     if (SavedKmpTaskTQTy.isNull()) {
-      SavedKmpTaskTQTy = C.getRecordType(createKmpTaskTRecordDecl(
+      SavedKmpTaskTQTy = C.getCanonicalTagType(createKmpTaskTRecordDecl(
           CGM, D.getDirectiveKind(), KmpInt32Ty, KmpRoutineEntryPtrQTy));
     }
     KmpTaskTQTy = SavedKmpTaskTQTy;
@@ -3659,7 +3659,8 @@ CGOpenMPRuntime::emitTaskInit(CodeGenFunction &CGF, SourceLocation Loc,
   // Build particular struct kmp_task_t for the given task.
   const RecordDecl *KmpTaskTWithPrivatesQTyRD =
       createKmpTaskTWithPrivatesRecordDecl(CGM, KmpTaskTQTy, Privates);
-  QualType KmpTaskTWithPrivatesQTy = C.getRecordType(KmpTaskTWithPrivatesQTyRD);
+  CanQualType KmpTaskTWithPrivatesQTy =
+      C.getCanonicalTagType(KmpTaskTWithPrivatesQTyRD);
   QualType KmpTaskTWithPrivatesPtrQTy =
       C.getPointerType(KmpTaskTWithPrivatesQTy);
   llvm::Type *KmpTaskTWithPrivatesPtrTy = CGF.Builder.getPtrTy(0);
@@ -3914,7 +3915,10 @@ CGOpenMPRuntime::emitTaskInit(CodeGenFunction &CGF, SourceLocation Loc,
   // Fill the data in the resulting kmp_task_t record.
   // Copy shareds if there are any.
   Address KmpTaskSharedsPtr = Address::invalid();
-  if (!SharedsTy->getAsStructureType()->getDecl()->field_empty()) {
+  if (!SharedsTy->getAsStructureType()
+           ->getOriginalDecl()
+           ->getDefinitionOrSelf()
+           ->field_empty()) {
     KmpTaskSharedsPtr = Address(
         CGF.EmitLoadOfScalar(
             CGF.EmitLValueForField(
@@ -3944,8 +3948,11 @@ CGOpenMPRuntime::emitTaskInit(CodeGenFunction &CGF, SourceLocation Loc,
   enum { Priority = 0, Destructors = 1 };
   // Provide pointer to function with destructors for privates.
   auto FI = std::next(KmpTaskTQTyRD->field_begin(), Data1);
-  const RecordDecl *KmpCmplrdataUD =
-      (*FI)->getType()->getAsUnionType()->getDecl();
+  const RecordDecl *KmpCmplrdataUD = (*FI)
+                                         ->getType()
+                                         ->getAsUnionType()
+                                         ->getOriginalDecl()
+                                         ->getDefinitionOrSelf();
   if (NeedsCleanup) {
     llvm::Value *DestructorFn = emitDestructorsFunction(
         CGM, Loc, KmpInt32Ty, KmpTaskTWithPrivatesPtrQTy,
@@ -4015,7 +4022,7 @@ static void getDependTypes(ASTContext &C, QualType &KmpDependInfoTy,
     addFieldToRecordDecl(C, KmpDependInfoRD, C.getSizeType());
     addFieldToRecordDecl(C, KmpDependInfoRD, FlagsTy);
     KmpDependInfoRD->completeDefinition();
-    KmpDependInfoTy = C.getRecordType(KmpDependInfoRD);
+    KmpDependInfoTy = C.getCanonicalTagType(KmpDependInfoRD);
   }
 }
 
@@ -5714,7 +5721,7 @@ llvm::Value *CGOpenMPRuntime::emitTaskReductionInit(
   const FieldDecl *FlagsFD = addFieldToRecordDecl(
       C, RD, C.getIntTypeForBitwidth(/*DestWidth=*/32, /*Signed=*/false));
   RD->completeDefinition();
-  QualType RDType = C.getRecordType(RD);
+  CanQualType RDType = C.getCanonicalTagType(RD);
   unsigned Size = Data.ReductionVars.size();
   llvm::APInt ArraySize(/*numBits=*/64, Size);
   QualType ArrayRDType =
@@ -10640,7 +10647,7 @@ static unsigned evaluateCDTSize(const FunctionDecl *FD,
     unsigned Offset = 0;
     if (const auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
       if (ParamAttrs[Offset].Kind == Vector)
-        CDT = C.getPointerType(C.getRecordType(MD->getParent()));
+        CDT = C.getPointerType(C.getCanonicalTagType(MD->getParent()));
       ++Offset;
     }
     if (CDT.isNull()) {
@@ -11222,7 +11229,7 @@ void CGOpenMPRuntime::emitDoacrossInit(CodeGenFunction &CGF,
     addFieldToRecordDecl(C, RD, Int64Ty);
     addFieldToRecordDecl(C, RD, Int64Ty);
     RD->completeDefinition();
-    KmpDimTy = C.getRecordType(RD);
+    KmpDimTy = C.getCanonicalTagType(RD);
   } else {
     RD = cast<RecordDecl>(KmpDimTy->getAsTagDecl());
   }
@@ -11718,7 +11725,7 @@ Address CGOpenMPRuntime::emitLastprivateConditionalInit(CodeGenFunction &CGF,
     VDField = addFieldToRecordDecl(C, RD, VD->getType().getNonReferenceType());
     FiredField = addFieldToRecordDecl(C, RD, C.CharTy);
     RD->completeDefinition();
-    NewType = C.getRecordType(RD);
+    NewType = C.getCanonicalTagType(RD);
     Address Addr = CGF.CreateMemTemp(NewType, C.getDeclAlign(VD), VD->getName());
     BaseLVal = CGF.MakeAddrLValue(Addr, NewType, AlignmentSource::Decl);
     I->getSecond().try_emplace(VD, NewType, VDField, FiredField, BaseLVal);
diff --git a/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp b/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
index e25b6948d30f8..0e746ddfe13a2 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
@@ -769,7 +769,7 @@ void CGOpenMPRuntimeGPU::emitKernelDeinit(CodeGenFunction &CGF,
       "_openmp_teams_reduction_type_$_", RecordDecl::TagKind::Union);
   StaticRD->startDefinition();
   for (const RecordDecl *TeamReductionRec : TeamsReductions) {
-    QualType RecTy = C.getRecordType(TeamReductionRec);
+    CanQualType RecTy = C.getCanonicalTagType(TeamReductionRec);
     auto *Field = FieldDecl::Create(
         C, StaticRD, SourceLocation(), SourceLocation(), nullptr, RecTy,
         C.getTrivialTypeSourceInfo(RecTy, SourceLocation()),
@@ -779,7 +779,7 @@ void CGOpenMPRuntimeGPU::emitKernelDeinit(CodeGenFunction &CGF,
     StaticRD->addDecl(Field);
   }
   StaticRD->completeDefinition();
-  QualType StaticTy = C.getRecordType(StaticRD);
+  CanQualType StaticTy = C.getCanonicalTagType(StaticRD);
   llvm::Type *LLVMReductionsBufferTy =
       CGM.getTypes().ConvertTypeForMem(StaticTy);
   const auto &DL = CGM.getModule().getDataLayout();
diff --git a/clang/lib/CodeGen/CGPointerAuth.cpp b/clang/lib/CodeGen/CGPointerAuth.cpp
index dcef01a5eb6d3..1a5ffb5eb33f8 100644
--- a/clang/lib/CodeGen/CGPointerAuth.cpp
+++ b/clang/lib/CodeGen/CGPointerAuth.cpp
@@ -531,7 +531,7 @@ llvm::Constant *CodeGenModule::getMemberFunctionPointer(llvm::Constant *Pointer,
 llvm::Constant *CodeGenModule::getMemberFunctionPointer(const FunctionDecl *FD,
                                                         llvm::Type *Ty) {
   QualType FT = FD->getType();
-  FT = getContext().getMemberPointerType(FT, /*Qualifier=*/nullptr,
+  FT = getContext().getMemberPointerType(FT, /*Qualifier=*/std::nullopt,
                                          cast<CXXMethodDecl>(FD)->getParent());
   return getMemberFunctionPointer(getRawFunctionPointer(FD, Ty), FT);
 }
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index e0650067b9547..28d518a52cfe7 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -3270,7 +3270,7 @@ void CodeGenFunction::EmitAsmStmt(const AsmStmt &S) {
 
 LValue CodeGenFunction::InitCapturedStruct(const CapturedStmt &S) {
   const RecordDecl *RD = S.getCapturedRecordDecl();
-  QualType RecordTy = getContext().getRecordType(RD);
+  CanQualType RecordTy = getContext().getCanonicalTagType(RD);
 
   // Initialize the captured struct.
   LValue SlotLV =
@@ -3350,7 +3350,7 @@ CodeGenFunction::GenerateCapturedStmtFunction(const CapturedStmt &S) {
 
   // Initialize variable-length arrays.
   LValue Base = MakeNaturalAlignRawAddrLValue(
-      CapturedStmtInfo->getContextValue(), Ctx.getTagDeclType(RD));
+      CapturedStmtInfo->getContextValue(), Ctx.getCanonicalTagType(RD));
   for (auto *FD : RD->fields()) {
     if (FD->hasCapturedVLAType()) {
       auto *ExprArg =
diff --git a/clang/lib/CodeGen/CGStmtOpenMP.cpp b/clang/lib/CodeGen/CGStmtOpenMP.cpp
index 5822e0f6db89a..f6a0ca574a191 100644
--- a/clang/lib/CodeGen/CGStmtOpenMP.cpp
+++ b/clang/lib/CodeGen/CGStmtOpenMP.cpp
@@ -5273,7 +5273,8 @@ void CodeGenFunction::EmitOMPTargetTaskBasedDirective(
   // Emit outlined function for task construct.
   const CapturedStmt *CS = S.getCapturedStmt(OMPD_task);
   Address CapturedStruct = GenerateCapturedStmtArgument(*CS);
-  QualType SharedsTy = getContext().getRecordType(CS->getCapturedRecordDecl());
+  CanQualType SharedsTy =
+      getContext().getCanonicalTagType(CS->getCapturedRecordDecl());
   auto I = CS->getCapturedDecl()->param_begin();
   auto PartId = std::next(I);
   auto TaskT = std::next(I, 4);
@@ -5507,7 +5508,8 @@ void CodeGenFunction::EmitOMPTaskDirective(const OMPTaskDirective &S) {
   // Emit outlined function for task construct.
   const CapturedStmt *CS = S.getCapturedStmt(OMPD_task);
   Address CapturedStruct = GenerateCapturedStmtArgument(*CS);
-  QualType SharedsTy = getContext().getRecordType(CS->getCapturedRecordDecl());
+  CanQualType SharedsTy =
+      getContext().getCanonicalTagType(CS->getCapturedRecordDecl());
   const Expr *IfCond = nullptr;
   for (const auto *C : S.getClausesOfKind<OMPIfClause>()) {
     if (C->getNameModifier() == OMPD_unknown ||
@@ -7890,7 +7892,8 @@ void CodeGenFunction::EmitOMPTaskLoopBasedDirective(const OMPLoopDirective &S) {
     OMPLexicalScope Scope(*this, S, OMPD_taskloop, /*EmitPreInitStmt=*/false);
     CapturedStruct = GenerateCapturedStmtArgument(*CS);
   }
-  QualType SharedsTy = getContext().getRecordType(CS->getCapturedRecordDecl());
+  CanQualType SharedsTy =
+      getContext().getCanonicalTagType(CS->getCapturedRecordDecl());
   const Expr *IfCond = nullptr;
   for (const auto *C : S.getClausesOfKind<OMPIfClause>()) {
     if (C->getNameModifier() == OMPD_unknown ||
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 0b6e830e0d557..e14e883a55ac5 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -971,7 +971,7 @@ llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
   VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 
   llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
-      CGM.getContext().getTagDeclType(Base.getBase()));
+      CGM.getContext().getCanonicalTagType(Base.getBase()));
 
   // Create and set the initializer.
   ConstantInitBuilder builder(CGM);
@@ -1382,8 +1382,8 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
                        AP.second.AddressPointIndex,
                    {}};
     llvm::raw_string_ostream Stream(N.TypeName);
-    getCXXABI().getMangleContext().mangleCanonicalTypeName(
-        QualType(N.Base->getTypeForDecl(), 0), Stream);
+    CanQualType T = getContext().getCanonicalTagType(N.Base);
+    getCXXABI().getMangleContext().mangleCanonicalTypeName(T, Stream);
     AddressPoints.push_back(std::move(N));
   }
 
@@ -1404,7 +1404,7 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
         continue;
       llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
           Context.getMemberPointerType(Comps[I].getFunctionDecl()->getType(),
-                                       /*Qualifier=*/nullptr, AP.Base));
+                                       /*Qualifier=*/std::nullopt, AP.Base));
       VTable->addTypeMetadata((ComponentWidth * I).getQuantity(), MD);
     }
   }
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 776a646ceb32f..3307e3fbd2196 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2224,7 +2224,9 @@ CodeGenFunction::EmitNullInitialization(Address DestPtr, QualType Ty) {
   // Ignore empty classes in C++.
   if (getLangOpts().CPlusPlus) {
     if (const RecordType *RT = Ty->getAs<RecordType>()) {
-      if (cast<CXXRecordDecl>(RT->getDecl())->isEmpty())
+      if (cast<CXXRecordDecl>(RT->getOriginalDecl())
+              ->getDefinitionOrSelf()
+              ->isEmpty())
         return;
     }
   }
@@ -2494,10 +2496,6 @@ void CodeGenFunction::EmitVariablyModifiedType(QualType type) {
     case Type::HLSLInlineSpirv:
       llvm_unreachable("type class is never variably-modified!");
 
-    case Type::Elaborated:
-      type = cast<ElaboratedType>(ty)->getNamedType();
-      break;
-
     case Type::Adjusted:
       type = cast<AdjustedType>(ty)->getAdjustedType();
       break;
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 6c32c98cec011..c33c215c03e01 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -2974,7 +2974,7 @@ class CodeGenFunction : public CodeGenTypeCache {
   /// member.
   bool hasVolatileMember(QualType T) {
     if (const RecordType *RT = T->getAs<RecordType>()) {
-      const RecordDecl *RD = cast<RecordDecl>(RT->getDecl());
+      const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
       return RD->hasVolatileMember();
     }
     return false;
@@ -4560,7 +4560,7 @@ class CodeGenFunction : public CodeGenTypeCache {
                                        ArrayRef<llvm::Value *> args);
 
   CGCallee BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
-                                     NestedNameSpecifier *Qual, llvm::Type *Ty);
+                                     NestedNameSpecifier Qual, llvm::Type *Ty);
 
   CGCallee BuildAppleKextVirtualDestructorCall(const CXXDestructorDecl *DD,
                                                CXXDtorType Type,
@@ -4665,7 +4665,7 @@ class CodeGenFunction : public CodeGenTypeCache {
                                llvm::CallBase **CallOrInvoke = nullptr);
   RValue EmitCXXMemberOrOperatorMemberCallExpr(
       const CallExpr *CE, const CXXMethodDecl *MD, ReturnValueSlot ReturnValue,
-      bool HasQualifier, NestedNameSpecifier *Qualifier, bool IsArrow,
+      bool HasQualifier, NestedNameSpecifier Qualifier, bool IsArrow,
       const Expr *Base, llvm::CallBase **CallOrInvoke);
   // Compute the object pointer.
   Address EmitCXXMemberDataPointerAddress(
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index c8866f15745c2..6fdb187b3a242 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2795,7 +2795,7 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
     for (const CXXRecordDecl *Base : getMostBaseClasses(MD->getParent())) {
       llvm::Metadata *Id =
           CreateMetadataIdentifierForType(Context.getMemberPointerType(
-              MD->getType(), /*Qualifier=*/nullptr, Base));
+              MD->getType(), /*Qualifier=*/std::nullopt, Base));
       F->addTypeMetadata(0, Id);
     }
   }
@@ -4154,9 +4154,11 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
 // Check if T is a class type with a destructor that's not dllimport.
 static bool HasNonDllImportDtor(QualType T) {
   if (const auto *RT = T->getBaseElementTypeUnsafe()->getAs<RecordType>())
-    if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(RT->getDecl()))
+    if (auto *RD = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl())) {
+      RD = RD->getDefinitionOrSelf();
       if (RD->getDestructor() && !RD->getDestructor()->hasAttr<DLLImportAttr>())
         return true;
+    }
 
   return false;
 }
@@ -6030,7 +6032,7 @@ static bool isVarDeclStrongDefinition(const ASTContext &Context,
       return true;
 
     if (const auto *RT = VarType->getAs<RecordType>()) {
-      const RecordDecl *RD = RT->getDecl();
+      const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
       for (const FieldDecl *FD : RD->fields()) {
         if (FD->isBitField())
           continue;
@@ -6737,7 +6739,7 @@ QualType CodeGenModule::getObjCFastEnumerationStateType() {
     }
 
     D->completeDefinition();
-    ObjCFastEnumerationStateType = Context.getTagDeclType(D);
+    ObjCFastEnumerationStateType = Context.getCanonicalTagType(D);
   }
 
   return ObjCFastEnumerationStateType;
@@ -7247,7 +7249,8 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
     CXXRecordDecl *CRD = cast<CXXRecordDecl>(D);
     if (CGDebugInfo *DI = getModuleDebugInfo()) {
       if (CRD->hasDefinition())
-        DI->EmitAndRetainType(getContext().getRecordType(cast<RecordDecl>(D)));
+        DI->EmitAndRetainType(
+            getContext().getCanonicalTagType(cast<RecordDecl>(D)));
       if (auto *ES = D->getASTContext().getExternalSource())
         if (ES->hasExternalDefinitions(D) == ExternalASTSource::EK_Never)
           DI->completeUnusedClass(*CRD);
@@ -7466,20 +7469,23 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
   case Decl::Typedef:
   case Decl::TypeAlias: // using foo = bar; [C++11]
     if (CGDebugInfo *DI = getModuleDebugInfo())
-      DI->EmitAndRetainType(
-          getContext().getTypedefType(cast<TypedefNameDecl>(D)));
+      DI->EmitAndRetainType(getContext().getTypedefType(
+          ElaboratedTypeKeyword::None, /*Qualifier=*/std::nullopt,
+          cast<TypedefNameDecl>(D)));
     break;
 
   case Decl::Record:
     if (CGDebugInfo *DI = getModuleDebugInfo())
       if (cast<RecordDecl>(D)->getDefinition())
-        DI->EmitAndRetainType(getContext().getRecordType(cast<RecordDecl>(D)));
+        DI->EmitAndRetainType(
+            getContext().getCanonicalTagType(cast<RecordDecl>(D)));
     break;
 
   case Decl::Enum:
     if (CGDebugInfo *DI = getModuleDebugInfo())
       if (cast<EnumDecl>(D)->getDefinition())
-        DI->EmitAndRetainType(getContext().getEnumType(cast<EnumDecl>(D)));
+        DI->EmitAndRetainType(
+            getContext().getCanonicalTagType(cast<EnumDecl>(D)));
     break;
 
   case Decl::HLSLBuffer:
@@ -7933,8 +7939,8 @@ bool CodeGenModule::NeedAllVtablesTypeId() const {
 void CodeGenModule::AddVTableTypeMetadata(llvm::GlobalVariable *VTable,
                                           CharUnits Offset,
                                           const CXXRecordDecl *RD) {
-  llvm::Metadata *MD =
-      CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
+  CanQualType T = getContext().getCanonicalTagType(RD);
+  llvm::Metadata *MD = CreateMetadataIdentifierForType(T);
   VTable->addTypeMetadata(Offset.getQuantity(), MD);
 
   if (CodeGenOpts.SanitizeCfiCrossDso)
diff --git a/clang/lib/CodeGen/CodeGenTBAA.cpp b/clang/lib/CodeGen/CodeGenTBAA.cpp
index a02a009158d12..3dc0859cc5d51 100644
--- a/clang/lib/CodeGen/CodeGenTBAA.cpp
+++ b/clang/lib/CodeGen/CodeGenTBAA.cpp
@@ -143,7 +143,7 @@ static bool TypeHasMayAlias(QualType QTy) {
 /// Check if the given type is a valid base type to be used in access tags.
 static bool isValidBaseType(QualType QTy) {
   if (const RecordType *TTy = QTy->getAs<RecordType>()) {
-    const RecordDecl *RD = TTy->getDecl()->getDefinition();
+    const RecordDecl *RD = TTy->getOriginalDecl()->getDefinition();
     // Incomplete types are not valid base access types.
     if (!RD)
       return false;
@@ -311,7 +311,7 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
       // This also covers anonymous structs and unions, which have a different
       // compatibility rule, but it doesn't matter because you can never have a
       // pointer to an anonymous struct or union.
-      if (!RT->getDecl()->getDeclName())
+      if (!RT->getOriginalDecl()->getDeclName())
         return getAnyPtr(PtrDepth);
 
       // For non-builtin types use the mangled name of the canonical type.
@@ -333,14 +333,15 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
   // Enum types are distinct types. In C++ they have "underlying types",
   // however they aren't related for TBAA.
   if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
+    const EnumDecl *ED = ETy->getOriginalDecl()->getDefinitionOrSelf();
     if (!Features.CPlusPlus)
-      return getTypeInfo(ETy->getDecl()->getIntegerType());
+      return getTypeInfo(ED->getIntegerType());
 
     // In C++ mode, types have linkage, so we can rely on the ODR and
     // on their mangled names, if they're external.
     // TODO: Is there a way to get a program-wide unique name for a
     // decl with local linkage or no linkage?
-    if (!ETy->getDecl()->isExternallyVisible())
+    if (!ED->isExternallyVisible())
       return getChar();
 
     SmallString<256> OutName;
@@ -433,7 +434,7 @@ CodeGenTBAA::CollectFields(uint64_t BaseOffset,
           llvm::MDBuilder::TBAAStructField(BaseOffset, Size, TBAATag));
       return true;
     }
-    const RecordDecl *RD = TTy->getDecl()->getDefinition();
+    const RecordDecl *RD = TTy->getOriginalDecl()->getDefinition();
     if (RD->hasFlexibleArrayMember())
       return false;
 
@@ -514,7 +515,7 @@ CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
 
 llvm::MDNode *CodeGenTBAA::getBaseTypeInfoHelper(const Type *Ty) {
   if (auto *TTy = dyn_cast<RecordType>(Ty)) {
-    const RecordDecl *RD = TTy->getDecl()->getDefinition();
+    const RecordDecl *RD = TTy->getOriginalDecl()->getDefinition();
     const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
     using TBAAStructField = llvm::MDBuilder::TBAAStructField;
     SmallVector<TBAAStructField, 4> Fields;
diff --git a/clang/lib/CodeGen/CodeGenTypes.cpp b/clang/lib/CodeGen/CodeGenTypes.cpp
index c98503e4bbd26..f2a0a649a88fd 100644
--- a/clang/lib/CodeGen/CodeGenTypes.cpp
+++ b/clang/lib/CodeGen/CodeGenTypes.cpp
@@ -229,12 +229,13 @@ bool CodeGenTypes::isFuncTypeConvertible(const FunctionType *FT) {
 /// UpdateCompletedType - When we find the full definition for a TagDecl,
 /// replace the 'opaque' type we previously made for it if applicable.
 void CodeGenTypes::UpdateCompletedType(const TagDecl *TD) {
+  CanQualType T = CGM.getContext().getCanonicalTagType(TD);
   // If this is an enum being completed, then we flush all non-struct types from
   // the cache.  This allows function types and other things that may be derived
   // from the enum to be recomputed.
   if (const EnumDecl *ED = dyn_cast<EnumDecl>(TD)) {
     // Only flush the cache if we've actually already converted this type.
-    if (TypeCache.count(ED->getTypeForDecl())) {
+    if (TypeCache.count(T->getTypePtr())) {
       // Okay, we formed some types based on this.  We speculated that the enum
       // would be lowered to i32, so we only need to flush the cache if this
       // didn't happen.
@@ -255,7 +256,7 @@ void CodeGenTypes::UpdateCompletedType(const TagDecl *TD) {
 
   // Only complete it if we converted it already.  If we haven't converted it
   // yet, we'll just do it lazily.
-  if (RecordDeclTypes.count(Context.getTagDeclType(RD).getTypePtr()))
+  if (RecordDeclTypes.count(T.getTypePtr()))
     ConvertRecordDeclType(RD);
 
   // If necessary, provide the full definition of a type only used with a
@@ -265,7 +266,7 @@ void CodeGenTypes::UpdateCompletedType(const TagDecl *TD) {
 }
 
 void CodeGenTypes::RefreshTypeCacheForClass(const CXXRecordDecl *RD) {
-  QualType T = Context.getRecordType(RD);
+  CanQualType T = Context.getCanonicalTagType(RD);
   T = Context.getCanonicalType(T);
 
   const Type *Ty = T.getTypePtr();
@@ -311,11 +312,11 @@ llvm::Type *CodeGenTypes::ConvertFunctionTypeInternal(QualType QFT) {
     // Force conversion of all the relevant record types, to make sure
     // we re-convert the FunctionType when appropriate.
     if (const RecordType *RT = FT->getReturnType()->getAs<RecordType>())
-      ConvertRecordDeclType(RT->getDecl());
+      ConvertRecordDeclType(RT->getOriginalDecl()->getDefinitionOrSelf());
     if (const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FT))
       for (unsigned i = 0, e = FPT->getNumParams(); i != e; i++)
         if (const RecordType *RT = FPT->getParamType(i)->getAs<RecordType>())
-          ConvertRecordDeclType(RT->getDecl());
+          ConvertRecordDeclType(RT->getOriginalDecl()->getDefinitionOrSelf());
 
     SkippedLayout = true;
 
@@ -373,7 +374,7 @@ llvm::Type *CodeGenTypes::ConvertType(QualType T) {
 
   // RecordTypes are cached and processed specially.
   if (const RecordType *RT = dyn_cast<RecordType>(Ty))
-    return ConvertRecordDeclType(RT->getDecl());
+    return ConvertRecordDeclType(RT->getOriginalDecl()->getDefinitionOrSelf());
 
   llvm::Type *CachedType = nullptr;
   auto TCI = TypeCache.find(Ty);
@@ -699,7 +700,8 @@ llvm::Type *CodeGenTypes::ConvertType(QualType T) {
     break;
 
   case Type::Enum: {
-    const EnumDecl *ED = cast<EnumType>(Ty)->getDecl();
+    const EnumDecl *ED =
+        cast<EnumType>(Ty)->getOriginalDecl()->getDefinitionOrSelf();
     if (ED->isCompleteDefinition() || ED->isFixed())
       return ConvertType(ED->getIntegerType());
     // Return a placeholder 'i32' type.  This can be changed later when the
@@ -725,8 +727,10 @@ llvm::Type *CodeGenTypes::ConvertType(QualType T) {
   case Type::MemberPointer: {
     auto *MPTy = cast<MemberPointerType>(Ty);
     if (!getCXXABI().isMemberPointerConvertible(MPTy)) {
-      auto *C = MPTy->getMostRecentCXXRecordDecl()->getTypeForDecl();
-      auto Insertion = RecordsWithOpaqueMemberPointers.try_emplace(C);
+      CanQualType T = CGM.getContext().getCanonicalTagType(
+          MPTy->getMostRecentCXXRecordDecl());
+      auto Insertion =
+          RecordsWithOpaqueMemberPointers.try_emplace(T.getTypePtr());
       if (Insertion.second)
         Insertion.first->second = llvm::StructType::create(getLLVMContext());
       ResultType = Insertion.first->second;
@@ -789,7 +793,7 @@ bool CodeGenModule::isPaddedAtomicType(const AtomicType *type) {
 llvm::StructType *CodeGenTypes::ConvertRecordDeclType(const RecordDecl *RD) {
   // TagDecl's are not necessarily unique, instead use the (clang)
   // type connected to the decl.
-  const Type *Key = Context.getTagDeclType(RD).getTypePtr();
+  const Type *Key = Context.getCanonicalTagType(RD).getTypePtr();
 
   llvm::StructType *&Entry = RecordDeclTypes[Key];
 
@@ -810,7 +814,10 @@ llvm::StructType *CodeGenTypes::ConvertRecordDeclType(const RecordDecl *RD) {
   if (const CXXRecordDecl *CRD = dyn_cast<CXXRecordDecl>(RD)) {
     for (const auto &I : CRD->bases()) {
       if (I.isVirtual()) continue;
-      ConvertRecordDeclType(I.getType()->castAs<RecordType>()->getDecl());
+      ConvertRecordDeclType(I.getType()
+                                ->castAs<RecordType>()
+                                ->getOriginalDecl()
+                                ->getDefinitionOrSelf());
     }
   }
 
@@ -830,7 +837,7 @@ llvm::StructType *CodeGenTypes::ConvertRecordDeclType(const RecordDecl *RD) {
 /// getCGRecordLayout - Return record layout info for the given record decl.
 const CGRecordLayout &
 CodeGenTypes::getCGRecordLayout(const RecordDecl *RD) {
-  const Type *Key = Context.getTagDeclType(RD).getTypePtr();
+  const Type *Key = Context.getCanonicalTagType(RD).getTypePtr();
 
   auto I = CGRecordLayouts.find(Key);
   if (I != CGRecordLayouts.end())
@@ -869,7 +876,7 @@ bool CodeGenTypes::isZeroInitializable(QualType T) {
   // Records are non-zero-initializable if they contain any
   // non-zero-initializable subobjects.
   if (const RecordType *RT = T->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     return isZeroInitializable(RD);
   }
 
diff --git a/clang/lib/CodeGen/HLSLBufferLayoutBuilder.cpp b/clang/lib/CodeGen/HLSLBufferLayoutBuilder.cpp
index 1ed33894b15aa..ac56dda74abb7 100644
--- a/clang/lib/CodeGen/HLSLBufferLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/HLSLBufferLayoutBuilder.cpp
@@ -101,7 +101,8 @@ llvm::TargetExtType *HLSLBufferLayoutBuilder::createLayoutType(
     const RecordType *RT = RecordTypes.back();
     RecordTypes.pop_back();
 
-    for (const auto *FD : RT->getDecl()->fields()) {
+    for (const auto *FD :
+         RT->getOriginalDecl()->getDefinitionOrSelf()->fields()) {
       assert((!PackOffsets || Index < PackOffsets->size()) &&
              "number of elements in layout struct does not match number of "
              "packoffset annotations");
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index f4a99467010af..f0f7b97c624f7 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -826,7 +826,7 @@ CGCallee ItaniumCXXABI::EmitLoadOfMemberFunctionPointer(
       for (const CXXRecordDecl *Base : CGM.getMostBaseClasses(RD)) {
         llvm::Metadata *MD = CGM.CreateMetadataIdentifierForType(
             getContext().getMemberPointerType(MPT->getPointeeType(),
-                                              /*Qualifier=*/nullptr,
+                                              /*Qualifier=*/std::nullopt,
                                               Base->getCanonicalDecl()));
         llvm::Value *TypeId =
             llvm::MetadataAsValue::get(CGF.getLLVMContext(), MD);
@@ -1236,7 +1236,7 @@ llvm::Constant *ItaniumCXXABI::EmitMemberPointer(const APValue &MP,
   if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(MPD)) {
     llvm::Constant *Src = BuildMemberPointer(MD, ThisAdjustment);
     QualType SrcType = getContext().getMemberPointerType(
-        MD->getType(), /*Qualifier=*/nullptr, MD->getParent());
+        MD->getType(), /*Qualifier=*/std::nullopt, MD->getParent());
     return pointerAuthResignMemberFunctionPointer(Src, MPType, SrcType, CGM);
   }
 
@@ -1392,8 +1392,9 @@ void ItaniumCXXABI::emitVirtualObjectDelete(CodeGenFunction &CGF,
     // to pass to the deallocation function.
 
     // Grab the vtable pointer as an intptr_t*.
-    auto *ClassDecl =
-        cast<CXXRecordDecl>(ElementType->castAs<RecordType>()->getDecl());
+    auto *ClassDecl = cast<CXXRecordDecl>(
+                          ElementType->castAs<RecordType>()->getOriginalDecl())
+                          ->getDefinitionOrSelf();
     llvm::Value *VTable = CGF.GetVTablePtr(Ptr, CGF.UnqualPtrTy, ClassDecl);
 
     // Track back to entry -2 and pull out the offset there.
@@ -1479,7 +1480,8 @@ void ItaniumCXXABI::emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) {
   // trivial destructor (or isn't a record), we just pass null.
   llvm::Constant *Dtor = nullptr;
   if (const RecordType *RecordTy = ThrowType->getAs<RecordType>()) {
-    CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordTy->getDecl());
+    CXXRecordDecl *Record =
+        cast<CXXRecordDecl>(RecordTy->getOriginalDecl())->getDefinitionOrSelf();
     if (!Record->hasTrivialDestructor()) {
       // __cxa_throw is declared to take its destructor as void (*)(void *). We
       // must match that if function pointers can be authenticated with a
@@ -1606,7 +1608,8 @@ llvm::Value *ItaniumCXXABI::EmitTypeid(CodeGenFunction &CGF,
                                        Address ThisPtr,
                                        llvm::Type *StdTypeInfoPtrTy) {
   auto *ClassDecl =
-      cast<CXXRecordDecl>(SrcRecordTy->castAs<RecordType>()->getDecl());
+      cast<CXXRecordDecl>(SrcRecordTy->castAs<RecordType>()->getOriginalDecl())
+          ->getDefinitionOrSelf();
   llvm::Value *Value = CGF.GetVTablePtr(ThisPtr, CGM.GlobalsInt8PtrTy,
                                         ClassDecl);
 
@@ -1763,7 +1766,8 @@ llvm::Value *ItaniumCXXABI::emitDynamicCastToVoid(CodeGenFunction &CGF,
                                                   Address ThisAddr,
                                                   QualType SrcRecordTy) {
   auto *ClassDecl =
-      cast<CXXRecordDecl>(SrcRecordTy->castAs<RecordType>()->getDecl());
+      cast<CXXRecordDecl>(SrcRecordTy->castAs<RecordType>()->getOriginalDecl())
+          ->getDefinitionOrSelf();
   llvm::Value *OffsetToTop;
   if (CGM.getItaniumVTableContext().isRelativeLayout()) {
     // Get the vtable pointer.
@@ -2016,7 +2020,7 @@ void ItaniumCXXABI::emitVTableDefinitions(CodeGenVTables &CGVT,
   const VTableLayout &VTLayout = VTContext.getVTableLayout(RD);
   llvm::GlobalVariable::LinkageTypes Linkage = CGM.getVTableLinkage(RD);
   llvm::Constant *RTTI =
-      CGM.GetAddrOfRTTIDescriptor(CGM.getContext().getTagDeclType(RD));
+      CGM.GetAddrOfRTTIDescriptor(CGM.getContext().getCanonicalTagType(RD));
 
   // Create and set the initializer.
   ConstantInitBuilder builder(CGM);
@@ -3755,7 +3759,8 @@ static bool ShouldUseExternalRTTIDescriptor(CodeGenModule &CGM,
   if (!Context.getLangOpts().RTTI) return false;
 
   if (const RecordType *RecordTy = dyn_cast<RecordType>(Ty)) {
-    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RecordTy->getDecl());
+    const CXXRecordDecl *RD =
+        cast<CXXRecordDecl>(RecordTy->getOriginalDecl())->getDefinitionOrSelf();
     if (!RD->hasDefinition())
       return false;
 
@@ -3789,7 +3794,9 @@ static bool ShouldUseExternalRTTIDescriptor(CodeGenModule &CGM,
 
 /// IsIncompleteClassType - Returns whether the given record type is incomplete.
 static bool IsIncompleteClassType(const RecordType *RecordTy) {
-  return !RecordTy->getDecl()->isCompleteDefinition();
+  return !RecordTy->getOriginalDecl()
+              ->getDefinitionOrSelf()
+              ->isCompleteDefinition();
 }
 
 /// ContainsIncompleteClassType - Returns whether the given type contains an
@@ -3815,9 +3822,7 @@ static bool ContainsIncompleteClassType(QualType Ty) {
   if (const MemberPointerType *MemberPointerTy =
       dyn_cast<MemberPointerType>(Ty)) {
     // Check if the class type is incomplete.
-    const auto *ClassType = cast<RecordType>(
-        MemberPointerTy->getMostRecentCXXRecordDecl()->getTypeForDecl());
-    if (IsIncompleteClassType(ClassType))
+    if (!MemberPointerTy->getMostRecentCXXRecordDecl()->hasDefinition())
       return true;
 
     return ContainsIncompleteClassType(MemberPointerTy->getPointeeType());
@@ -3846,8 +3851,9 @@ static bool CanUseSingleInheritance(const CXXRecordDecl *RD) {
     return false;
 
   // Check that the class is dynamic iff the base is.
-  auto *BaseDecl =
-      cast<CXXRecordDecl>(Base->getType()->castAs<RecordType>()->getDecl());
+  auto *BaseDecl = cast<CXXRecordDecl>(
+                       Base->getType()->castAs<RecordType>()->getOriginalDecl())
+                       ->getDefinitionOrSelf();
   if (!BaseDecl->isEmpty() &&
       BaseDecl->isDynamicClass() != RD->isDynamicClass())
     return false;
@@ -3926,7 +3932,8 @@ void ItaniumRTTIBuilder::BuildVTablePointer(const Type *Ty,
 
   case Type::Record: {
     const CXXRecordDecl *RD =
-      cast<CXXRecordDecl>(cast<RecordType>(Ty)->getDecl());
+        cast<CXXRecordDecl>(cast<RecordType>(Ty)->getOriginalDecl())
+            ->getDefinitionOrSelf();
 
     if (!RD->hasDefinition() || !RD->getNumBases()) {
       VTableName = ClassTypeInfo;
@@ -4048,7 +4055,8 @@ static llvm::GlobalVariable::LinkageTypes getTypeInfoLinkage(CodeGenModule &CGM,
       return llvm::GlobalValue::LinkOnceODRLinkage;
 
     if (const RecordType *Record = dyn_cast<RecordType>(Ty)) {
-      const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
+      const CXXRecordDecl *RD =
+          cast<CXXRecordDecl>(Record->getOriginalDecl())->getDefinitionOrSelf();
       if (RD->hasAttr<WeakAttr>())
         return llvm::GlobalValue::WeakODRLinkage;
       if (CGM.getTriple().isWindowsItaniumEnvironment())
@@ -4212,7 +4220,8 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(
 
   case Type::Record: {
     const CXXRecordDecl *RD =
-      cast<CXXRecordDecl>(cast<RecordType>(Ty)->getDecl());
+        cast<CXXRecordDecl>(cast<RecordType>(Ty)->getOriginalDecl())
+            ->getDefinitionOrSelf();
     if (!RD->hasDefinition() || !RD->getNumBases()) {
       // We don't need to emit any fields.
       break;
@@ -4259,7 +4268,8 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(
   if (CGM.getTarget().hasPS4DLLImportExport() &&
       GVDLLStorageClass != llvm::GlobalVariable::DLLExportStorageClass) {
     if (const RecordType *RecordTy = dyn_cast<RecordType>(Ty)) {
-      const CXXRecordDecl *RD = cast<CXXRecordDecl>(RecordTy->getDecl());
+      const CXXRecordDecl *RD = cast<CXXRecordDecl>(RecordTy->getOriginalDecl())
+                                    ->getDefinitionOrSelf();
       if (RD->hasAttr<DLLExportAttr>() ||
           CXXRecordNonInlineHasAttr<DLLExportAttr>(RD))
         GVDLLStorageClass = llvm::GlobalVariable::DLLExportStorageClass;
@@ -4363,8 +4373,9 @@ static unsigned ComputeVMIClassTypeInfoFlags(const CXXBaseSpecifier *Base,
 
   unsigned Flags = 0;
 
-  auto *BaseDecl =
-      cast<CXXRecordDecl>(Base->getType()->castAs<RecordType>()->getDecl());
+  auto *BaseDecl = cast<CXXRecordDecl>(
+                       Base->getType()->castAs<RecordType>()->getOriginalDecl())
+                       ->getDefinitionOrSelf();
 
   if (Base->isVirtual()) {
     // Mark the virtual base as seen.
@@ -4464,7 +4475,9 @@ void ItaniumRTTIBuilder::BuildVMIClassTypeInfo(const CXXRecordDecl *RD) {
     Fields.push_back(ItaniumRTTIBuilder(CXXABI).BuildTypeInfo(Base.getType()));
 
     auto *BaseDecl =
-        cast<CXXRecordDecl>(Base.getType()->castAs<RecordType>()->getDecl());
+        cast<CXXRecordDecl>(
+            Base.getType()->castAs<RecordType>()->getOriginalDecl())
+            ->getDefinitionOrSelf();
 
     int64_t OffsetFlags = 0;
 
@@ -4554,9 +4567,8 @@ ItaniumRTTIBuilder::BuildPointerToMemberTypeInfo(const MemberPointerType *Ty) {
   //   attributes of the type pointed to.
   unsigned Flags = extractPBaseFlags(CGM.getContext(), PointeeTy);
 
-  const auto *ClassType =
-      cast<RecordType>(Ty->getMostRecentCXXRecordDecl()->getTypeForDecl());
-  if (IsIncompleteClassType(ClassType))
+  const auto *RD = Ty->getMostRecentCXXRecordDecl();
+  if (!RD->hasDefinition())
     Flags |= PTI_ContainingClassIncomplete;
 
   llvm::Type *UnsignedIntLTy =
@@ -4574,8 +4586,8 @@ ItaniumRTTIBuilder::BuildPointerToMemberTypeInfo(const MemberPointerType *Ty) {
   //   __context is a pointer to an abi::__class_type_info corresponding to the
   //   class type containing the member pointed to
   //   (e.g., the "A" in "int A::*").
-  Fields.push_back(
-      ItaniumRTTIBuilder(CXXABI).BuildTypeInfo(QualType(ClassType, 0)));
+  CanQualType T = CGM.getContext().getCanonicalTagType(RD);
+  Fields.push_back(ItaniumRTTIBuilder(CXXABI).BuildTypeInfo(T));
 }
 
 llvm::Constant *ItaniumCXXABI::getAddrOfRTTIDescriptor(QualType Ty) {
@@ -5155,7 +5167,7 @@ ItaniumCXXABI::getSignedVirtualMemberFunctionPointer(const CXXMethodDecl *MD) {
                               .getDecl());
   llvm::Constant *thunk = getOrCreateVirtualFunctionPointerThunk(origMD);
   QualType funcType = CGM.getContext().getMemberPointerType(
-      MD->getType(), /*Qualifier=*/nullptr, MD->getParent());
+      MD->getType(), /*Qualifier=*/std::nullopt, MD->getParent());
   return CGM.getMemberFunctionPointer(thunk, funcType);
 }
 
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index a181559834296..977c9a27a6ad6 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -870,7 +870,8 @@ MicrosoftCXXABI::getRecordArgABI(const CXXRecordDecl *RD) const {
     // it indirectly. Prior to MSVC version 19.14, passing overaligned
     // arguments was not supported and resulted in a compiler error. In 19.14
     // and later versions, such arguments are now passed indirectly.
-    TypeInfo Info = getContext().getTypeInfo(RD->getTypeForDecl());
+    TypeInfo Info =
+        getContext().getTypeInfo(getContext().getCanonicalTagType(RD));
     if (Info.isAlignRequired() && Info.Align > 4)
       return RAA_Indirect;
 
@@ -2918,15 +2919,15 @@ llvm::Constant *MicrosoftCXXABI::EmitMemberPointer(const APValue &MP,
     if (!FD)
       FD = cast<FieldDecl>(*cast<IndirectFieldDecl>(MPD)->chain_begin());
     const CXXRecordDecl *RD = cast<CXXRecordDecl>(FD->getParent());
-    RD = RD->getMostRecentNonInjectedDecl();
+    RD = RD->getMostRecentDecl();
     C = EmitMemberDataPointer(RD, FieldOffset);
   }
 
   if (!MemberPointerPath.empty()) {
     const CXXRecordDecl *SrcRD = cast<CXXRecordDecl>(MPD->getDeclContext());
     const MemberPointerType *SrcTy =
-        Ctx.getMemberPointerType(DstTy->getPointeeType(), /*Qualifier=*/nullptr,
-                                 SrcRD)
+        Ctx.getMemberPointerType(DstTy->getPointeeType(),
+                                 /*Qualifier=*/std::nullopt, SrcRD)
             ->castAs<MemberPointerType>();
 
     bool DerivedMember = MP.isMemberPointerToDerivedMember();
@@ -2963,7 +2964,7 @@ MicrosoftCXXABI::EmitMemberFunctionPointer(const CXXMethodDecl *MD) {
   assert(MD->isInstance() && "Member function must not be static!");
 
   CharUnits NonVirtualBaseAdjustment = CharUnits::Zero();
-  const CXXRecordDecl *RD = MD->getParent()->getMostRecentNonInjectedDecl();
+  const CXXRecordDecl *RD = MD->getParent()->getMostRecentDecl();
   CodeGenTypes &Types = CGM.getTypes();
 
   unsigned VBTableIndex = 0;
@@ -3684,7 +3685,7 @@ struct MSRTTIBuilder {
   MSRTTIBuilder(MicrosoftCXXABI &ABI, const CXXRecordDecl *RD)
       : CGM(ABI.CGM), Context(CGM.getContext()),
         VMContext(CGM.getLLVMContext()), Module(CGM.getModule()), RD(RD),
-        Linkage(getLinkageForRTTI(CGM.getContext().getTagDeclType(RD))),
+        Linkage(getLinkageForRTTI(CGM.getContext().getCanonicalTagType(RD))),
         ABI(ABI) {}
 
   llvm::GlobalVariable *getBaseClassDescriptor(const MSRTTIClass &Classes);
@@ -3858,7 +3859,7 @@ MSRTTIBuilder::getBaseClassDescriptor(const MSRTTIClass &Class) {
   // Initialize the BaseClassDescriptor.
   llvm::Constant *Fields[] = {
       ABI.getImageRelativeConstant(
-          ABI.getAddrOfRTTIDescriptor(Context.getTypeDeclType(Class.RD))),
+          ABI.getAddrOfRTTIDescriptor(Context.getCanonicalTagType(Class.RD))),
       llvm::ConstantInt::get(CGM.IntTy, Class.NumBases),
       llvm::ConstantInt::get(CGM.IntTy, Class.OffsetInVBase),
       llvm::ConstantInt::get(CGM.IntTy, VBPtrOffset),
@@ -3905,7 +3906,7 @@ MSRTTIBuilder::getCompleteObjectLocator(const VPtrInfo &Info) {
       llvm::ConstantInt::get(CGM.IntTy, OffsetToTop),
       llvm::ConstantInt::get(CGM.IntTy, VFPtrOffset),
       ABI.getImageRelativeConstant(
-          CGM.GetAddrOfRTTIDescriptor(Context.getTypeDeclType(RD))),
+          CGM.GetAddrOfRTTIDescriptor(Context.getCanonicalTagType(RD))),
       ABI.getImageRelativeConstant(getClassHierarchyDescriptor()),
       ABI.getImageRelativeConstant(COL),
   };
@@ -4076,7 +4077,7 @@ MicrosoftCXXABI::getAddrOfCXXCtorClosure(const CXXConstructorDecl *CD,
   const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeMSCtorClosure(CD, CT);
   llvm::FunctionType *ThunkTy = CGM.getTypes().GetFunctionType(FnInfo);
   const CXXRecordDecl *RD = CD->getParent();
-  QualType RecordTy = getContext().getRecordType(RD);
+  CanQualType RecordTy = getContext().getCanonicalTagType(RD);
   llvm::Function *ThunkFn = llvm::Function::Create(
       ThunkTy, getLinkageForRTTI(RecordTy), ThunkName.str(), &CGM.getModule());
   ThunkFn->setCallingConv(static_cast<llvm::CallingConv::ID>(
@@ -4312,7 +4313,7 @@ llvm::GlobalVariable *MicrosoftCXXABI::getCatchableTypeArray(QualType T) {
 
       // Turn our record back into a pointer if the exception object is a
       // pointer.
-      QualType RTTITy = QualType(Class.RD->getTypeForDecl(), 0);
+      CanQualType RTTITy = Context.getCanonicalTagType(Class.RD);
       if (IsPointer)
         RTTITy = Context.getPointerType(RTTITy);
       CatchableTypes.insert(getCatchableType(RTTITy, Class.OffsetInVBase,
@@ -4463,8 +4464,8 @@ void MicrosoftCXXABI::emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) {
 std::pair<llvm::Value *, const CXXRecordDecl *>
 MicrosoftCXXABI::LoadVTablePtr(CodeGenFunction &CGF, Address This,
                                const CXXRecordDecl *RD) {
-  std::tie(This, std::ignore, RD) =
-      performBaseAdjustment(CGF, This, QualType(RD->getTypeForDecl(), 0));
+  CanQualType T = CGF.getContext().getCanonicalTagType(RD);
+  std::tie(This, std::ignore, RD) = performBaseAdjustment(CGF, This, T);
   return {CGF.GetVTablePtr(This, CGM.Int8PtrTy, RD), RD};
 }
 
diff --git a/clang/lib/CodeGen/SwiftCallingConv.cpp b/clang/lib/CodeGen/SwiftCallingConv.cpp
index 10f9f20bca313..de58e0d95a866 100644
--- a/clang/lib/CodeGen/SwiftCallingConv.cpp
+++ b/clang/lib/CodeGen/SwiftCallingConv.cpp
@@ -66,9 +66,9 @@ void SwiftAggLowering::addTypedData(QualType type, CharUnits begin) {
 
   // Record types.
   if (auto recType = type->getAs<RecordType>()) {
-    addTypedData(recType->getDecl(), begin);
+    addTypedData(recType->getOriginalDecl(), begin);
 
-  // Array types.
+    // Array types.
   } else if (type->isArrayType()) {
     // Incomplete array types (flexible array members?) don't provide
     // data to lay out, and the other cases shouldn't be possible.
@@ -814,7 +814,7 @@ static ABIArgInfo classifyType(CodeGenModule &CGM, CanQualType type,
                                bool forReturn) {
   unsigned IndirectAS = CGM.getDataLayout().getAllocaAddrSpace();
   if (auto recordType = dyn_cast<RecordType>(type)) {
-    auto record = recordType->getDecl();
+    auto record = recordType->getOriginalDecl();
     auto &layout = CGM.getContext().getASTRecordLayout(record);
 
     if (mustPassRecordIndirectly(CGM, record))
@@ -822,7 +822,8 @@ static ABIArgInfo classifyType(CodeGenModule &CGM, CanQualType type,
                                      /*AddrSpace=*/IndirectAS, /*byval=*/false);
 
     SwiftAggLowering lowering(CGM);
-    lowering.addTypedData(recordType->getDecl(), CharUnits::Zero(), layout);
+    lowering.addTypedData(recordType->getOriginalDecl(), CharUnits::Zero(),
+                          layout);
     lowering.finish();
 
     return classifyExpandedType(lowering, forReturn, layout.getAlignment(),
diff --git a/clang/lib/CodeGen/Targets/AArch64.cpp b/clang/lib/CodeGen/Targets/AArch64.cpp
index b82c46966cf0b..289f8a9dcf211 100644
--- a/clang/lib/CodeGen/Targets/AArch64.cpp
+++ b/clang/lib/CodeGen/Targets/AArch64.cpp
@@ -375,7 +375,7 @@ ABIArgInfo AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadicFn,
   if (!passAsAggregateType(Ty)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     if (const auto *EIT = Ty->getAs<BitIntType>())
       if (EIT->getNumBits() > 128)
@@ -496,7 +496,7 @@ ABIArgInfo AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadicFn,
       const RecordType *RT = Ty->getAs<RecordType>();
       if (!RT)
         return false;
-      const RecordDecl *RD = RT->getDecl();
+      const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
       if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
         for (const auto &I : CXXRD->bases())
           if (!Self(Self, I.getType()))
@@ -548,7 +548,8 @@ ABIArgInfo AArch64ABIInfo::classifyReturnType(QualType RetTy,
   if (!passAsAggregateType(RetTy)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-      RetTy = EnumTy->getDecl()->getIntegerType();
+      RetTy =
+          EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     if (const auto *EIT = RetTy->getAs<BitIntType>())
       if (EIT->getNumBits() > 128)
@@ -744,7 +745,7 @@ bool AArch64ABIInfo::passAsPureScalableType(
       return false;
 
     // Pure scalable types are never unions and never contain unions.
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->isUnion())
       return false;
 
diff --git a/clang/lib/CodeGen/Targets/AMDGPU.cpp b/clang/lib/CodeGen/Targets/AMDGPU.cpp
index 47a552a7bf495..41bccbb5721b2 100644
--- a/clang/lib/CodeGen/Targets/AMDGPU.cpp
+++ b/clang/lib/CodeGen/Targets/AMDGPU.cpp
@@ -96,7 +96,7 @@ unsigned AMDGPUABIInfo::numRegsForType(QualType Ty) const {
   }
 
   if (const RecordType *RT = Ty->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     assert(!RD->hasFlexibleArrayMember());
 
     for (const FieldDecl *Field : RD->fields()) {
@@ -153,7 +153,7 @@ ABIArgInfo AMDGPUABIInfo::classifyReturnType(QualType RetTy) const {
         return ABIArgInfo::getDirect(CGT.ConvertType(QualType(SeltTy, 0)));
 
       if (const RecordType *RT = RetTy->getAs<RecordType>()) {
-        const RecordDecl *RD = RT->getDecl();
+        const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
         if (RD->hasFlexibleArrayMember())
           return DefaultABIInfo::classifyReturnType(RetTy);
       }
@@ -246,7 +246,7 @@ ABIArgInfo AMDGPUABIInfo::classifyArgumentType(QualType Ty, bool Variadic,
       return ABIArgInfo::getDirect(CGT.ConvertType(QualType(SeltTy, 0)));
 
     if (const RecordType *RT = Ty->getAs<RecordType>()) {
-      const RecordDecl *RD = RT->getDecl();
+      const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
       if (RD->hasFlexibleArrayMember())
         return DefaultABIInfo::classifyArgumentType(Ty);
     }
diff --git a/clang/lib/CodeGen/Targets/ARC.cpp b/clang/lib/CodeGen/Targets/ARC.cpp
index c8db7e8f9706e..ace524e1976d9 100644
--- a/clang/lib/CodeGen/Targets/ARC.cpp
+++ b/clang/lib/CodeGen/Targets/ARC.cpp
@@ -106,13 +106,14 @@ ABIArgInfo ARCABIInfo::classifyArgumentType(QualType Ty,
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   auto SizeInRegs = llvm::alignTo(getContext().getTypeSize(Ty), 32) / 32;
 
   if (isAggregateTypeForABI(Ty)) {
     // Structures with flexible arrays are always indirect.
-    if (RT && RT->getDecl()->hasFlexibleArrayMember())
+    if (RT &&
+        RT->getOriginalDecl()->getDefinitionOrSelf()->hasFlexibleArrayMember())
       return getIndirectByValue(Ty);
 
     // Ignore empty structs/unions.
diff --git a/clang/lib/CodeGen/Targets/ARM.cpp b/clang/lib/CodeGen/Targets/ARM.cpp
index 68f9e01856486..532ba4cead244 100644
--- a/clang/lib/CodeGen/Targets/ARM.cpp
+++ b/clang/lib/CodeGen/Targets/ARM.cpp
@@ -383,7 +383,7 @@ ABIArgInfo ARMABIInfo::classifyArgumentType(QualType Ty, bool isVariadic,
   if (!isAggregateTypeForABI(Ty)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>()) {
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
     }
 
     if (const auto *EIT = Ty->getAs<BitIntType>())
@@ -516,7 +516,7 @@ static bool isIntegerLikeType(QualType Ty, ASTContext &Context,
   if (!RT) return false;
 
   // Ignore records with flexible arrays.
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   if (RD->hasFlexibleArrayMember())
     return false;
 
@@ -593,7 +593,8 @@ ABIArgInfo ARMABIInfo::classifyReturnType(QualType RetTy, bool isVariadic,
   if (!isAggregateTypeForABI(RetTy)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-      RetTy = EnumTy->getDecl()->getIntegerType();
+      RetTy =
+          EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     if (const auto *EIT = RetTy->getAs<BitIntType>())
       if (EIT->getNumBits() > 64)
@@ -718,7 +719,7 @@ bool ARMABIInfo::containsAnyFP16Vectors(QualType Ty) const {
       return false;
     return containsAnyFP16Vectors(AT->getElementType());
   } else if (const RecordType *RT = Ty->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
     // If this is a C++ record, check the bases first.
     if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
diff --git a/clang/lib/CodeGen/Targets/BPF.cpp b/clang/lib/CodeGen/Targets/BPF.cpp
index 880a891083c3a..87d50e671d251 100644
--- a/clang/lib/CodeGen/Targets/BPF.cpp
+++ b/clang/lib/CodeGen/Targets/BPF.cpp
@@ -48,7 +48,7 @@ class BPFABIInfo : public DefaultABIInfo {
     }
 
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     ASTContext &Context = getContext();
     if (const auto *EIT = Ty->getAs<BitIntType>())
@@ -70,7 +70,8 @@ class BPFABIInfo : public DefaultABIInfo {
 
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-      RetTy = EnumTy->getDecl()->getIntegerType();
+      RetTy =
+          EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     ASTContext &Context = getContext();
     if (const auto *EIT = RetTy->getAs<BitIntType>())
diff --git a/clang/lib/CodeGen/Targets/CSKY.cpp b/clang/lib/CodeGen/Targets/CSKY.cpp
index ef26d483a180a..7e5a16f30727f 100644
--- a/clang/lib/CodeGen/Targets/CSKY.cpp
+++ b/clang/lib/CodeGen/Targets/CSKY.cpp
@@ -116,7 +116,7 @@ ABIArgInfo CSKYABIInfo::classifyArgumentType(QualType Ty, int &ArgGPRsLeft,
   if (!isAggregateTypeForABI(Ty)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     // All integral types are promoted to XLen width, unless passed on the
     // stack.
diff --git a/clang/lib/CodeGen/Targets/Hexagon.cpp b/clang/lib/CodeGen/Targets/Hexagon.cpp
index 2976657360650..0c423429eda4f 100644
--- a/clang/lib/CodeGen/Targets/Hexagon.cpp
+++ b/clang/lib/CodeGen/Targets/Hexagon.cpp
@@ -98,7 +98,7 @@ ABIArgInfo HexagonABIInfo::classifyArgumentType(QualType Ty,
   if (!isAggregateTypeForABI(Ty)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     uint64_t Size = getContext().getTypeSize(Ty);
     if (Size <= 64)
@@ -161,7 +161,8 @@ ABIArgInfo HexagonABIInfo::classifyReturnType(QualType RetTy) const {
   if (!isAggregateTypeForABI(RetTy)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-      RetTy = EnumTy->getDecl()->getIntegerType();
+      RetTy =
+          EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     if (Size > 64 && RetTy->isBitIntType())
       return getNaturalAlignIndirect(
diff --git a/clang/lib/CodeGen/Targets/Lanai.cpp b/clang/lib/CodeGen/Targets/Lanai.cpp
index 6f75bd54a8ef2..08cb36034f6fd 100644
--- a/clang/lib/CodeGen/Targets/Lanai.cpp
+++ b/clang/lib/CodeGen/Targets/Lanai.cpp
@@ -102,7 +102,8 @@ ABIArgInfo LanaiABIInfo::classifyArgumentType(QualType Ty,
 
   if (isAggregateTypeForABI(Ty)) {
     // Structures with flexible arrays are always indirect.
-    if (RT && RT->getDecl()->hasFlexibleArrayMember())
+    if (RT &&
+        RT->getOriginalDecl()->getDefinitionOrSelf()->hasFlexibleArrayMember())
       return getIndirectResult(Ty, /*ByVal=*/true, State);
 
     // Ignore empty structs/unions.
@@ -125,7 +126,7 @@ ABIArgInfo LanaiABIInfo::classifyArgumentType(QualType Ty,
 
   // Treat an enum type as its underlying type.
   if (const auto *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   bool InReg = shouldUseInReg(Ty, State);
 
diff --git a/clang/lib/CodeGen/Targets/LoongArch.cpp b/clang/lib/CodeGen/Targets/LoongArch.cpp
index 7640f3779816a..af863e6101e2c 100644
--- a/clang/lib/CodeGen/Targets/LoongArch.cpp
+++ b/clang/lib/CodeGen/Targets/LoongArch.cpp
@@ -150,7 +150,7 @@ bool LoongArchABIInfo::detectFARsEligibleStructHelper(
     // Non-zero-length arrays of empty records make the struct ineligible to be
     // passed via FARs in C++.
     if (const auto *RTy = EltTy->getAs<RecordType>()) {
-      if (ArraySize != 0 && isa<CXXRecordDecl>(RTy->getDecl()) &&
+      if (ArraySize != 0 && isa<CXXRecordDecl>(RTy->getOriginalDecl()) &&
           isEmptyRecord(getContext(), EltTy, true, true))
         return false;
     }
@@ -169,7 +169,7 @@ bool LoongArchABIInfo::detectFARsEligibleStructHelper(
     // copy constructor are not eligible for the FP calling convention.
     if (getRecordArgABI(Ty, CGT.getCXXABI()))
       return false;
-    const RecordDecl *RD = RTy->getDecl();
+    const RecordDecl *RD = RTy->getOriginalDecl()->getDefinitionOrSelf();
     if (isEmptyRecord(getContext(), Ty, true, true) &&
         (!RD->isUnion() || !isa<CXXRecordDecl>(RD)))
       return true;
@@ -181,7 +181,9 @@ bool LoongArchABIInfo::detectFARsEligibleStructHelper(
     if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
       for (const CXXBaseSpecifier &B : CXXRD->bases()) {
         const auto *BDecl =
-            cast<CXXRecordDecl>(B.getType()->castAs<RecordType>()->getDecl());
+            cast<CXXRecordDecl>(
+                B.getType()->castAs<RecordType>()->getOriginalDecl())
+                ->getDefinitionOrSelf();
         if (!detectFARsEligibleStructHelper(
                 B.getType(), CurOff + Layout.getBaseClassOffset(BDecl),
                 Field1Ty, Field1Off, Field2Ty, Field2Off))
@@ -369,7 +371,7 @@ ABIArgInfo LoongArchABIInfo::classifyArgumentType(QualType Ty, bool IsFixed,
   if (!isAggregateTypeForABI(Ty) && !Ty->isVectorType()) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     // All integral types are promoted to GRLen width.
     if (Size < GRLen && Ty->isIntegralOrEnumerationType())
diff --git a/clang/lib/CodeGen/Targets/Mips.cpp b/clang/lib/CodeGen/Targets/Mips.cpp
index c025f7312959c..e12a34ce07bbe 100644
--- a/clang/lib/CodeGen/Targets/Mips.cpp
+++ b/clang/lib/CodeGen/Targets/Mips.cpp
@@ -161,7 +161,7 @@ llvm::Type* MipsABIInfo::HandleAggregates(QualType Ty, uint64_t TySize) const {
     return llvm::StructType::get(getVMContext(), ArgList);
   }
 
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
   assert(!(TySize % 8) && "Size of structure must be multiple of 8.");
 
@@ -242,7 +242,7 @@ MipsABIInfo::classifyArgumentType(QualType Ty, uint64_t &Offset) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Make sure we pass indirectly things that are too large.
   if (const auto *EIT = Ty->getAs<BitIntType>())
@@ -265,7 +265,7 @@ MipsABIInfo::returnAggregateInRegs(QualType RetTy, uint64_t Size) const {
   SmallVector<llvm::Type*, 8> RTList;
 
   if (RT && RT->isStructureOrClassType()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
     unsigned FieldCnt = Layout.getFieldCount();
 
@@ -333,7 +333,7 @@ ABIArgInfo MipsABIInfo::classifyReturnType(QualType RetTy) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-    RetTy = EnumTy->getDecl()->getIntegerType();
+    RetTy = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Make sure we pass indirectly things that are too large.
   if (const auto *EIT = RetTy->getAs<BitIntType>())
diff --git a/clang/lib/CodeGen/Targets/NVPTX.cpp b/clang/lib/CodeGen/Targets/NVPTX.cpp
index 82bdfe2666b52..e874617796f86 100644
--- a/clang/lib/CodeGen/Targets/NVPTX.cpp
+++ b/clang/lib/CodeGen/Targets/NVPTX.cpp
@@ -133,7 +133,7 @@ bool NVPTXABIInfo::isUnsupportedType(QualType T) const {
   const auto *RT = T->getAs<RecordType>();
   if (!RT)
     return false;
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
   // If this is a C++ record, check the bases first.
   if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
@@ -174,7 +174,7 @@ ABIArgInfo NVPTXABIInfo::classifyReturnType(QualType RetTy) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-    RetTy = EnumTy->getDecl()->getIntegerType();
+    RetTy = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   return (isPromotableIntegerTypeForABI(RetTy) ? ABIArgInfo::getExtend(RetTy)
                                                : ABIArgInfo::getDirect());
@@ -183,7 +183,7 @@ ABIArgInfo NVPTXABIInfo::classifyReturnType(QualType RetTy) const {
 ABIArgInfo NVPTXABIInfo::classifyArgumentType(QualType Ty) const {
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Return aggregates type as indirect by value
   if (isAggregateTypeForABI(Ty)) {
diff --git a/clang/lib/CodeGen/Targets/PNaCl.cpp b/clang/lib/CodeGen/Targets/PNaCl.cpp
index 358010785850e..a2610950f24be 100644
--- a/clang/lib/CodeGen/Targets/PNaCl.cpp
+++ b/clang/lib/CodeGen/Targets/PNaCl.cpp
@@ -68,7 +68,7 @@ ABIArgInfo PNaClABIInfo::classifyArgumentType(QualType Ty) const {
     return getNaturalAlignIndirect(Ty, getDataLayout().getAllocaAddrSpace());
   } else if (const EnumType *EnumTy = Ty->getAs<EnumType>()) {
     // Treat an enum type as its underlying type.
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
   } else if (Ty->isFloatingType()) {
     // Floating-point types don't go inreg.
     return ABIArgInfo::getDirect();
@@ -102,7 +102,7 @@ ABIArgInfo PNaClABIInfo::classifyReturnType(QualType RetTy) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-    RetTy = EnumTy->getDecl()->getIntegerType();
+    RetTy = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   return (isPromotableIntegerTypeForABI(RetTy) ? ABIArgInfo::getExtend(RetTy)
                                                : ABIArgInfo::getDirect());
diff --git a/clang/lib/CodeGen/Targets/PPC.cpp b/clang/lib/CodeGen/Targets/PPC.cpp
index 4df4c9f3c3475..38e76399299ec 100644
--- a/clang/lib/CodeGen/Targets/PPC.cpp
+++ b/clang/lib/CodeGen/Targets/PPC.cpp
@@ -154,7 +154,7 @@ class AIXTargetCodeGenInfo : public TargetCodeGenInfo {
 bool AIXABIInfo::isPromotableTypeForABI(QualType Ty) const {
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Promotable integer types are required to be promoted by the ABI.
   if (getContext().isPromotableIntegerType(Ty))
@@ -295,7 +295,9 @@ void AIXTargetCodeGenInfo::setTargetAttributes(
     unsigned Alignment = Context.toBits(Context.getDeclAlign(D)) / 8;
     const auto *Ty = VarD->getType().getTypePtr();
     const RecordDecl *RDecl =
-        Ty->isRecordType() ? Ty->getAs<RecordType>()->getDecl() : nullptr;
+        Ty->isRecordType()
+            ? Ty->getAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf()
+            : nullptr;
 
     bool EmitDiagnostic = UserSpecifiedTOC && GV->hasExternalLinkage();
     auto reportUnsupportedWarning = [&](bool ShouldEmitWarning, StringRef Msg) {
@@ -707,7 +709,7 @@ bool
 PPC64_SVR4_ABIInfo::isPromotableTypeForABI(QualType Ty) const {
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Promotable integer types are required to be promoted by the ABI.
   if (isPromotableIntegerTypeForABI(Ty))
diff --git a/clang/lib/CodeGen/Targets/RISCV.cpp b/clang/lib/CodeGen/Targets/RISCV.cpp
index e3232b61a693c..1fab9e402ee7f 100644
--- a/clang/lib/CodeGen/Targets/RISCV.cpp
+++ b/clang/lib/CodeGen/Targets/RISCV.cpp
@@ -228,7 +228,7 @@ bool RISCVABIInfo::detectFPCCEligibleStructHelper(QualType Ty, CharUnits CurOff,
     // Non-zero-length arrays of empty records make the struct ineligible for
     // the FP calling convention in C++.
     if (const auto *RTy = EltTy->getAs<RecordType>()) {
-      if (ArraySize != 0 && isa<CXXRecordDecl>(RTy->getDecl()) &&
+      if (ArraySize != 0 && isa<CXXRecordDecl>(RTy->getOriginalDecl()) &&
           isEmptyRecord(getContext(), EltTy, true, true))
         return false;
     }
@@ -250,7 +250,7 @@ bool RISCVABIInfo::detectFPCCEligibleStructHelper(QualType Ty, CharUnits CurOff,
       return false;
     if (isEmptyRecord(getContext(), Ty, true, true))
       return true;
-    const RecordDecl *RD = RTy->getDecl();
+    const RecordDecl *RD = RTy->getOriginalDecl()->getDefinitionOrSelf();
     // Unions aren't eligible unless they're empty (which is caught above).
     if (RD->isUnion())
       return false;
@@ -259,7 +259,9 @@ bool RISCVABIInfo::detectFPCCEligibleStructHelper(QualType Ty, CharUnits CurOff,
     if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
       for (const CXXBaseSpecifier &B : CXXRD->bases()) {
         const auto *BDecl =
-            cast<CXXRecordDecl>(B.getType()->castAs<RecordType>()->getDecl());
+            cast<CXXRecordDecl>(
+                B.getType()->castAs<RecordType>()->getOriginalDecl())
+                ->getDefinitionOrSelf();
         CharUnits BaseOff = Layout.getBaseClassOffset(BDecl);
         bool Ret = detectFPCCEligibleStructHelper(B.getType(), CurOff + BaseOff,
                                                   Field1Ty, Field1Off, Field2Ty,
@@ -673,7 +675,7 @@ ABIArgInfo RISCVABIInfo::classifyArgumentType(QualType Ty, bool IsFixed,
   if (!isAggregateTypeForABI(Ty) && !Ty->isVectorType()) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     // All integral types are promoted to XLen width
     if (Size < XLen && Ty->isIntegralOrEnumerationType()) {
diff --git a/clang/lib/CodeGen/Targets/SPIR.cpp b/clang/lib/CodeGen/Targets/SPIR.cpp
index d952c6e117607..237aea755fa29 100644
--- a/clang/lib/CodeGen/Targets/SPIR.cpp
+++ b/clang/lib/CodeGen/Targets/SPIR.cpp
@@ -119,7 +119,7 @@ ABIArgInfo SPIRVABIInfo::classifyReturnType(QualType RetTy) const {
     return DefaultABIInfo::classifyReturnType(RetTy);
 
   if (const RecordType *RT = RetTy->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->hasFlexibleArrayMember())
       return DefaultABIInfo::classifyReturnType(RetTy);
   }
@@ -187,7 +187,7 @@ ABIArgInfo SPIRVABIInfo::classifyArgumentType(QualType Ty) const {
                                    RAA == CGCXXABI::RAA_DirectInMemory);
 
   if (const RecordType *RT = Ty->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->hasFlexibleArrayMember())
       return DefaultABIInfo::classifyArgumentType(Ty);
   }
@@ -432,7 +432,7 @@ static llvm::Type *getInlineSpirvType(CodeGenModule &CGM,
     case SpirvOperandKind::TypeId: {
       QualType TypeOperand = Operand.getResultType();
       if (auto *RT = TypeOperand->getAs<RecordType>()) {
-        auto *RD = RT->getDecl();
+        auto *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
         assert(RD->isCompleteDefinition() &&
                "Type completion should have been required in Sema");
 
diff --git a/clang/lib/CodeGen/Targets/Sparc.cpp b/clang/lib/CodeGen/Targets/Sparc.cpp
index 9642196b78c63..1547bed7ea8b2 100644
--- a/clang/lib/CodeGen/Targets/Sparc.cpp
+++ b/clang/lib/CodeGen/Targets/Sparc.cpp
@@ -238,7 +238,7 @@ SparcV9ABIInfo::classifyType(QualType Ty, unsigned SizeLimit) const {
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Integer types smaller than a register are extended.
   if (Size < 64 && Ty->isIntegerType())
diff --git a/clang/lib/CodeGen/Targets/SystemZ.cpp b/clang/lib/CodeGen/Targets/SystemZ.cpp
index 6ea6c7a546436..38cc4d39126be 100644
--- a/clang/lib/CodeGen/Targets/SystemZ.cpp
+++ b/clang/lib/CodeGen/Targets/SystemZ.cpp
@@ -146,7 +146,7 @@ class SystemZTargetCodeGenInfo : public TargetCodeGenInfo {
 bool SystemZABIInfo::isPromotableIntegerTypeForABI(QualType Ty) const {
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   // Promotable integer types are required to be promoted by the ABI.
   if (ABIInfo::isPromotableIntegerTypeForABI(Ty))
@@ -211,7 +211,7 @@ QualType SystemZABIInfo::GetSingleElementType(QualType Ty) const {
   const RecordType *RT = Ty->getAs<RecordType>();
 
   if (RT && RT->isStructureOrClassType()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     QualType Found;
 
     // If this is a C++ record, check the bases first.
@@ -455,7 +455,7 @@ ABIArgInfo SystemZABIInfo::classifyArgumentType(QualType Ty) const {
   if (const RecordType *RT = Ty->getAs<RecordType>()) {
     // Structures with flexible arrays have variable length, so really
     // fail the size test above.
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->hasFlexibleArrayMember())
       return getNaturalAlignIndirect(Ty, getDataLayout().getAllocaAddrSpace(),
                                      /*ByVal=*/false);
@@ -526,7 +526,7 @@ bool SystemZTargetCodeGenInfo::isVectorTypeBased(const Type *Ty,
       return true;
 
   if (const auto *RecordTy = Ty->getAs<RecordType>()) {
-    const RecordDecl *RD = RecordTy->getDecl();
+    const RecordDecl *RD = RecordTy->getOriginalDecl()->getDefinitionOrSelf();
     if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
       if (CXXRD->hasDefinition())
         for (const auto &I : CXXRD->bases())
diff --git a/clang/lib/CodeGen/Targets/WebAssembly.cpp b/clang/lib/CodeGen/Targets/WebAssembly.cpp
index 9217c78a540a3..ac8dcd2a0540a 100644
--- a/clang/lib/CodeGen/Targets/WebAssembly.cpp
+++ b/clang/lib/CodeGen/Targets/WebAssembly.cpp
@@ -118,7 +118,8 @@ ABIArgInfo WebAssemblyABIInfo::classifyArgumentType(QualType Ty) const {
       const RecordType *RT = Ty->getAs<RecordType>();
       assert(RT);
       bool HasBitField = false;
-      for (auto *Field : RT->getDecl()->fields()) {
+      for (auto *Field :
+           RT->getOriginalDecl()->getDefinitionOrSelf()->fields()) {
         if (Field->isBitField()) {
           HasBitField = true;
           break;
diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp
index 0f59caac2323e..51d144e2f223a 100644
--- a/clang/lib/CodeGen/Targets/X86.cpp
+++ b/clang/lib/CodeGen/Targets/X86.cpp
@@ -359,7 +359,8 @@ bool X86_32ABIInfo::shouldReturnTypeInRegister(QualType Ty,
 
   // Structure types are passed in register if all fields would be
   // passed in a register.
-  for (const auto *FD : RT->getDecl()->fields()) {
+  for (const auto *FD :
+       RT->getOriginalDecl()->getDefinitionOrSelf()->fields()) {
     // Empty fields are ignored.
     if (isEmptyField(Context, FD, true))
       continue;
@@ -429,9 +430,9 @@ bool X86_32ABIInfo::canExpandIndirectArgument(QualType Ty) const {
   const RecordType *RT = Ty->getAs<RecordType>();
   if (!RT)
     return false;
-  const RecordDecl *RD = RT->getDecl();
   uint64_t Size = 0;
-  if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
+  if (const auto *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
     if (!IsWin32StructABI) {
       // On non-Windows, we have to conservatively match our old bitcode
       // prototypes in order to be ABI-compatible at the bitcode level.
@@ -509,7 +510,9 @@ ABIArgInfo X86_32ABIInfo::classifyReturnType(QualType RetTy,
   if (isAggregateTypeForABI(RetTy)) {
     if (const RecordType *RT = RetTy->getAs<RecordType>()) {
       // Structures with flexible arrays are always indirect.
-      if (RT->getDecl()->hasFlexibleArrayMember())
+      if (RT->getOriginalDecl()
+              ->getDefinitionOrSelf()
+              ->hasFlexibleArrayMember())
         return getIndirectReturnResult(RetTy, State);
     }
 
@@ -554,7 +557,7 @@ ABIArgInfo X86_32ABIInfo::classifyReturnType(QualType RetTy,
 
   // Treat an enum type as its underlying type.
   if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-    RetTy = EnumTy->getDecl()->getIntegerType();
+    RetTy = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   if (const auto *EIT = RetTy->getAs<BitIntType>())
     if (EIT->getNumBits() > 64)
@@ -796,7 +799,8 @@ ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty, CCState &State,
   if (isAggregateTypeForABI(Ty)) {
     // Structures with flexible arrays are always indirect.
     // FIXME: This should not be byval!
-    if (RT && RT->getDecl()->hasFlexibleArrayMember())
+    if (RT &&
+        RT->getOriginalDecl()->getDefinitionOrSelf()->hasFlexibleArrayMember())
       return getIndirectResult(Ty, true, State);
 
     // Ignore empty structs/unions on non-Windows.
@@ -831,7 +835,7 @@ ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty, CCState &State,
       unsigned AlignInBits = 0;
       if (RT) {
         const ASTRecordLayout &Layout =
-          getContext().getASTRecordLayout(RT->getDecl());
+            getContext().getASTRecordLayout(RT->getOriginalDecl());
         AlignInBits = getContext().toBits(Layout.getRequiredAlignment());
       } else if (TI.isAlignRequired()) {
         AlignInBits = TI.Align;
@@ -883,7 +887,7 @@ ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty, CCState &State,
 
 
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   bool InReg = shouldPrimitiveUseInReg(Ty, State);
 
@@ -1847,7 +1851,8 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase, Class &Lo,
 
   if (const EnumType *ET = Ty->getAs<EnumType>()) {
     // Classify the underlying integer type.
-    classify(ET->getDecl()->getIntegerType(), OffsetBase, Lo, Hi, isNamedArg);
+    classify(ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType(),
+             OffsetBase, Lo, Hi, isNamedArg);
     return;
   }
 
@@ -2053,7 +2058,7 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase, Class &Lo,
     if (getRecordArgABI(RT, getCXXABI()))
       return;
 
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
     // Assume variable sized types are passed in memory.
     if (RD->hasFlexibleArrayMember())
@@ -2070,7 +2075,9 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase, Class &Lo,
         assert(!I.isVirtual() && !I.getType()->isDependentType() &&
                "Unexpected base class!");
         const auto *Base =
-            cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+            cast<CXXRecordDecl>(
+                I.getType()->castAs<RecordType>()->getOriginalDecl())
+                ->getDefinitionOrSelf();
 
         // Classify this field.
         //
@@ -2184,7 +2191,7 @@ ABIArgInfo X86_64ABIInfo::getIndirectReturnResult(QualType Ty) const {
   if (!isAggregateTypeForABI(Ty)) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     if (Ty->isBitIntType())
       return getNaturalAlignIndirect(Ty, getDataLayout().getAllocaAddrSpace());
@@ -2226,7 +2233,7 @@ ABIArgInfo X86_64ABIInfo::getIndirectResult(QualType Ty,
       !Ty->isBitIntType()) {
     // Treat an enum type as its underlying type.
     if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-      Ty = EnumTy->getDecl()->getIntegerType();
+      Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
     return (isPromotableIntegerTypeForABI(Ty) ? ABIArgInfo::getExtend(Ty)
                                               : ABIArgInfo::getDirect());
@@ -2347,7 +2354,7 @@ static bool BitsContainNoUserData(QualType Ty, unsigned StartBit,
   }
 
   if (const RecordType *RT = Ty->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
 
     // If this is a C++ record, check the bases first.
@@ -2356,7 +2363,9 @@ static bool BitsContainNoUserData(QualType Ty, unsigned StartBit,
         assert(!I.isVirtual() && !I.getType()->isDependentType() &&
                "Unexpected base class!");
         const auto *Base =
-            cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+            cast<CXXRecordDecl>(
+                I.getType()->castAs<RecordType>()->getOriginalDecl())
+                ->getDefinitionOrSelf();
 
         // If the base is after the span we care about, ignore it.
         unsigned BaseOffset = Context.toBits(Layout.getBaseClassOffset(Base));
@@ -2633,7 +2642,8 @@ classifyReturnType(QualType RetTy) const {
     if (Hi == NoClass && isa<llvm::IntegerType>(ResType)) {
       // Treat an enum type as its underlying type.
       if (const EnumType *EnumTy = RetTy->getAs<EnumType>())
-        RetTy = EnumTy->getDecl()->getIntegerType();
+        RetTy =
+            EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
       if (RetTy->isIntegralOrEnumerationType() &&
           isPromotableIntegerTypeForABI(RetTy))
@@ -2777,7 +2787,7 @@ X86_64ABIInfo::classifyArgumentType(QualType Ty, unsigned freeIntRegs,
     if (Hi == NoClass && isa<llvm::IntegerType>(ResType)) {
       // Treat an enum type as its underlying type.
       if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-        Ty = EnumTy->getDecl()->getIntegerType();
+        Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
       if (Ty->isIntegralOrEnumerationType() &&
           isPromotableIntegerTypeForABI(Ty))
@@ -2851,14 +2861,15 @@ ABIArgInfo
 X86_64ABIInfo::classifyRegCallStructTypeImpl(QualType Ty, unsigned &NeededInt,
                                              unsigned &NeededSSE,
                                              unsigned &MaxVectorWidth) const {
-  auto RT = Ty->getAs<RecordType>();
-  assert(RT && "classifyRegCallStructType only valid with struct types");
+  auto *RD = cast<RecordType>(Ty.getCanonicalType())
+                 ->getOriginalDecl()
+                 ->getDefinitionOrSelf();
 
-  if (RT->getDecl()->hasFlexibleArrayMember())
+  if (RD->hasFlexibleArrayMember())
     return getIndirectReturnResult(Ty);
 
   // Sum up bases
-  if (auto CXXRD = dyn_cast<CXXRecordDecl>(RT->getDecl())) {
+  if (auto CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
     if (CXXRD->isDynamicClass()) {
       NeededInt = NeededSSE = 0;
       return getIndirectReturnResult(Ty);
@@ -2874,7 +2885,7 @@ X86_64ABIInfo::classifyRegCallStructTypeImpl(QualType Ty, unsigned &NeededInt,
   }
 
   // Sum up members
-  for (const auto *FD : RT->getDecl()->fields()) {
+  for (const auto *FD : RD->fields()) {
     QualType MTy = FD->getType();
     if (MTy->isRecordType() && !MTy->isUnionType()) {
       if (classifyRegCallStructTypeImpl(MTy, NeededInt, NeededSSE,
@@ -3298,7 +3309,7 @@ ABIArgInfo WinX86_64ABIInfo::classify(QualType Ty, unsigned &FreeSSERegs,
     return ABIArgInfo::getIgnore();
 
   if (const EnumType *EnumTy = Ty->getAs<EnumType>())
-    Ty = EnumTy->getDecl()->getIntegerType();
+    Ty = EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   TypeInfo Info = getContext().getTypeInfo(Ty);
   uint64_t Width = Info.Width;
@@ -3312,7 +3323,7 @@ ABIArgInfo WinX86_64ABIInfo::classify(QualType Ty, unsigned &FreeSSERegs,
                                        RAA == CGCXXABI::RAA_DirectInMemory);
     }
 
-    if (RT->getDecl()->hasFlexibleArrayMember())
+    if (RT->getOriginalDecl()->getDefinitionOrSelf()->hasFlexibleArrayMember())
       return getNaturalAlignIndirect(Ty, getDataLayout().getAllocaAddrSpace(),
                                      /*ByVal=*/false);
   }
diff --git a/clang/lib/CodeGen/Targets/XCore.cpp b/clang/lib/CodeGen/Targets/XCore.cpp
index b7824bde5f55a..aa6947b1d956b 100644
--- a/clang/lib/CodeGen/Targets/XCore.cpp
+++ b/clang/lib/CodeGen/Targets/XCore.cpp
@@ -379,7 +379,7 @@ static bool appendRecordType(SmallStringEnc &Enc, const RecordType *RT,
 
   // We collect all encoded fields and order as necessary.
   bool IsRecursive = false;
-  const RecordDecl *RD = RT->getDecl()->getDefinition();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinition();
   if (RD && !RD->field_empty()) {
     // An incomplete TypeString stub is placed in the cache for this RecordType
     // so that recursive calls to this RecordType will use it whilst building a
@@ -428,7 +428,7 @@ static bool appendEnumType(SmallStringEnc &Enc, const EnumType *ET,
   Enc += "){";
 
   // We collect all encoded enumerations and order them alphanumerically.
-  if (const EnumDecl *ED = ET->getDecl()->getDefinition()) {
+  if (const EnumDecl *ED = ET->getOriginalDecl()->getDefinition()) {
     SmallVector<FieldEncoding, 16> FE;
     for (auto I = ED->enumerator_begin(), E = ED->enumerator_end(); I != E;
          ++I) {
diff --git a/clang/lib/ExtractAPI/DeclarationFragments.cpp b/clang/lib/ExtractAPI/DeclarationFragments.cpp
index 791afc1a97575..d3d549c0127bf 100644
--- a/clang/lib/ExtractAPI/DeclarationFragments.cpp
+++ b/clang/lib/ExtractAPI/DeclarationFragments.cpp
@@ -205,54 +205,39 @@ DeclarationFragments::getStructureTypeFragment(const RecordDecl *Record) {
 // Build declaration fragments for NNS recursively so that we have the USR for
 // every part in a qualified name, and also leaves the actual underlying type
 // cleaner for its own fragment.
-DeclarationFragments
-DeclarationFragmentsBuilder::getFragmentsForNNS(const NestedNameSpecifier *NNS,
-                                                ASTContext &Context,
-                                                DeclarationFragments &After) {
+DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForNNS(
+    NestedNameSpecifier NNS, ASTContext &Context, DeclarationFragments &After) {
   DeclarationFragments Fragments;
-  if (NNS->getPrefix())
-    Fragments.append(getFragmentsForNNS(NNS->getPrefix(), Context, After));
-
-  switch (NNS->getKind()) {
-  case NestedNameSpecifier::Identifier:
-    Fragments.append(NNS->getAsIdentifier()->getName(),
-                     DeclarationFragments::FragmentKind::Identifier);
-    break;
+  switch (NNS.getKind()) {
+  case NestedNameSpecifier::Kind::Null:
+    return Fragments;
 
-  case NestedNameSpecifier::Namespace: {
-    const NamespaceDecl *NS = NNS->getAsNamespace();
-    if (NS->isAnonymousNamespace())
+  case NestedNameSpecifier::Kind::Namespace: {
+    auto [Namespace, Prefix] = NNS.getAsNamespaceAndPrefix();
+    Fragments.append(getFragmentsForNNS(Prefix, Context, After));
+    if (const auto *NS = dyn_cast<NamespaceDecl>(Namespace);
+        NS && NS->isAnonymousNamespace())
       return Fragments;
     SmallString<128> USR;
-    index::generateUSRForDecl(NS, USR);
-    Fragments.append(NS->getName(),
-                     DeclarationFragments::FragmentKind::Identifier, USR, NS);
-    break;
-  }
-
-  case NestedNameSpecifier::NamespaceAlias: {
-    const NamespaceAliasDecl *Alias = NNS->getAsNamespaceAlias();
-    SmallString<128> USR;
-    index::generateUSRForDecl(Alias, USR);
-    Fragments.append(Alias->getName(),
+    index::generateUSRForDecl(Namespace, USR);
+    Fragments.append(Namespace->getName(),
                      DeclarationFragments::FragmentKind::Identifier, USR,
-                     Alias);
+                     Namespace);
     break;
   }
 
-  case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Kind::Global:
     // The global specifier `::` at the beginning. No stored value.
     break;
 
-  case NestedNameSpecifier::Super:
+  case NestedNameSpecifier::Kind::Super:
     // Microsoft's `__super` specifier.
     Fragments.append("__super", DeclarationFragments::FragmentKind::Keyword);
     break;
 
-  case NestedNameSpecifier::TypeSpec: {
-    const Type *T = NNS->getAsType();
+  case NestedNameSpecifier::Kind::Type: {
     // FIXME: Handle C++ template specialization type
-    Fragments.append(getFragmentsForType(T, Context, After));
+    Fragments.append(getFragmentsForType(NNS.getAsType(), Context, After));
     break;
   }
   }
@@ -282,26 +267,6 @@ DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForType(
     return Fragments;
   }
 
-  // An ElaboratedType is a sugar for types that are referred to using an
-  // elaborated keyword, e.g., `struct S`, `enum E`, or (in C++) via a
-  // qualified name, e.g., `N::M::type`, or both.
-  if (const ElaboratedType *ET = dyn_cast<ElaboratedType>(T)) {
-    ElaboratedTypeKeyword Keyword = ET->getKeyword();
-    if (Keyword != ElaboratedTypeKeyword::None) {
-      Fragments
-          .append(ElaboratedType::getKeywordName(Keyword),
-                  DeclarationFragments::FragmentKind::Keyword)
-          .appendSpace();
-    }
-
-    if (const NestedNameSpecifier *NNS = ET->getQualifier())
-      Fragments.append(getFragmentsForNNS(NNS, Context, After));
-
-    // After handling the elaborated keyword or qualified name, build
-    // declaration fragments for the desugared underlying type.
-    return Fragments.append(getFragmentsForType(ET->desugar(), Context, After));
-  }
-
   // If the type is a typedefed type, get the underlying TypedefNameDecl for a
   // direct reference to the typedef instead of the wrapped type.
 
@@ -312,7 +277,18 @@ DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForType(
     TypedefUnderlyingTypeResolver TypedefResolver(Context);
     std::string USR = TypedefResolver.getUSRForType(QualType(T, 0));
 
-    if (T->isObjCIdType()) {
+    if (ElaboratedTypeKeyword Keyword = TypedefTy->getKeyword();
+        Keyword != ElaboratedTypeKeyword::None) {
+      Fragments
+          .append(KeywordHelpers::getKeywordName(Keyword),
+                  DeclarationFragments::FragmentKind::Keyword)
+          .appendSpace();
+    }
+
+    Fragments.append(
+        getFragmentsForNNS(TypedefTy->getQualifier(), Context, After));
+
+    if (TypedefTy->isObjCIdType()) {
       return Fragments.append(Decl->getName(),
                               DeclarationFragments::FragmentKind::Keyword);
     }
@@ -405,14 +381,26 @@ DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForType(
 
   if (const TemplateSpecializationType *TemplSpecTy =
           dyn_cast<TemplateSpecializationType>(T)) {
-    const auto TemplName = TemplSpecTy->getTemplateName();
+    if (ElaboratedTypeKeyword Keyword = TemplSpecTy->getKeyword();
+        Keyword != ElaboratedTypeKeyword::None)
+      Fragments
+          .append(KeywordHelpers::getKeywordName(Keyword),
+                  DeclarationFragments::FragmentKind::Keyword)
+          .appendSpace();
+
+    auto TemplName = TemplSpecTy->getTemplateName();
     std::string Str;
     raw_string_ostream Stream(Str);
     TemplName.print(Stream, Context.getPrintingPolicy(),
                     TemplateName::Qualified::AsWritten);
     SmallString<64> USR("");
+    if (const auto *QTN = TemplName.getAsQualifiedTemplateName()) {
+      Fragments.append(getFragmentsForNNS(QTN->getQualifier(), Context, After));
+      TemplName = QTN->getUnderlyingTemplate();
+    }
     if (const auto *TemplDecl = TemplName.getAsTemplateDecl())
       index::generateUSRForDecl(TemplDecl, USR);
+    // FIXME: Handle other kinds of TemplateNames.
 
     return Fragments
         .append(Str, DeclarationFragments::FragmentKind::TypeIdentifier, USR)
@@ -422,14 +410,19 @@ DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForType(
         .append(">", DeclarationFragments::FragmentKind::Text);
   }
 
-  // Everything we care about has been handled now, reduce to the canonical
-  // unqualified base type.
-  QualType Base = T->getCanonicalTypeUnqualified();
-
   // If the base type is a TagType (struct/interface/union/class/enum), let's
   // get the underlying Decl for better names and USRs.
-  if (const TagType *TagTy = dyn_cast<TagType>(Base)) {
-    const TagDecl *Decl = TagTy->getDecl();
+  if (const TagType *TagTy = dyn_cast<TagType>(T)) {
+    if (ElaboratedTypeKeyword Keyword = TagTy->getKeyword();
+        Keyword != ElaboratedTypeKeyword::None)
+      Fragments
+          .append(KeywordHelpers::getKeywordName(Keyword),
+                  DeclarationFragments::FragmentKind::Keyword)
+          .appendSpace();
+
+    Fragments.append(getFragmentsForNNS(TagTy->getQualifier(), Context, After));
+
+    const TagDecl *Decl = TagTy->getOriginalDecl();
     // Anonymous decl, skip this fragment.
     if (Decl->getName().empty())
       return Fragments.append("{ ... }",
@@ -441,6 +434,10 @@ DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForType(
                             TagUSR, Decl);
   }
 
+  // Everything we care about has been handled now, reduce to the canonical
+  // unqualified base type.
+  QualType Base = T->getCanonicalTypeUnqualified();
+
   // If the base type is an ObjCInterfaceType, use the underlying
   // ObjCInterfaceDecl for the true USR.
   if (const auto *ObjCIT = dyn_cast<ObjCInterfaceType>(Base)) {
diff --git a/clang/lib/ExtractAPI/TypedefUnderlyingTypeResolver.cpp b/clang/lib/ExtractAPI/TypedefUnderlyingTypeResolver.cpp
index 41e4e0cf1795f..5adbbc6d1c34c 100644
--- a/clang/lib/ExtractAPI/TypedefUnderlyingTypeResolver.cpp
+++ b/clang/lib/ExtractAPI/TypedefUnderlyingTypeResolver.cpp
@@ -26,7 +26,7 @@ TypedefUnderlyingTypeResolver::getUnderlyingTypeDecl(QualType Type) const {
   if (TypedefTy)
     TypeDecl = TypedefTy->getDecl();
   if (const TagType *TagTy = Type->getAs<TagType>()) {
-    TypeDecl = TagTy->getDecl();
+    TypeDecl = TagTy->getOriginalDecl();
   } else if (const ObjCInterfaceType *ObjCITy =
                  Type->getAs<ObjCInterfaceType>()) {
     TypeDecl = ObjCITy->getDecl();
diff --git a/clang/lib/Frontend/ASTConsumers.cpp b/clang/lib/Frontend/ASTConsumers.cpp
index ab8a35a189250..67c8761511e0c 100644
--- a/clang/lib/Frontend/ASTConsumers.cpp
+++ b/clang/lib/Frontend/ASTConsumers.cpp
@@ -97,6 +97,7 @@ namespace {
           Out << "Not a DeclContext\n";
       } else if (OutputKind == Print) {
         PrintingPolicy Policy(D->getASTContext().getLangOpts());
+        Policy.IncludeTagDefinition = true;
         D->print(Out, Policy, /*Indentation=*/0, /*PrintInstantiation=*/true);
       } else if (OutputKind != None) {
         D->dump(Out, OutputKind == DumpFull, OutputFormat);
@@ -112,8 +113,10 @@ namespace {
         // FIXME: Support combining -ast-dump-decl-types with -ast-dump-lookups.
         if (auto *VD = dyn_cast<ValueDecl>(InnerD))
           VD->getType().dump(Out, VD->getASTContext());
-        if (auto *TD = dyn_cast<TypeDecl>(InnerD))
-          TD->getTypeForDecl()->dump(Out, TD->getASTContext());
+        if (auto *TD = dyn_cast<TypeDecl>(InnerD)) {
+          const ASTContext &Ctx = TD->getASTContext();
+          Ctx.getTypeDeclType(TD)->dump(Out, Ctx);
+        }
       }
     }
 
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index b7f52fd224ab5..689a32fbb3999 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -395,7 +395,7 @@ void ASTUnit::CacheCodeCompletionResults() {
 
       // Keep track of the type of this completion in an ASTContext-agnostic
       // way.
-      QualType UsageType = getDeclUsageType(*Ctx, R.Declaration);
+      QualType UsageType = getDeclUsageType(*Ctx, R.Qualifier, R.Declaration);
       if (UsageType.isNull()) {
         CachedResult.TypeClass = STC_Void;
         CachedResult.Type = 0;
diff --git a/clang/lib/Index/IndexTypeSourceInfo.cpp b/clang/lib/Index/IndexTypeSourceInfo.cpp
index 98b5513128fbe..8868aea53f10b 100644
--- a/clang/lib/Index/IndexTypeSourceInfo.cpp
+++ b/clang/lib/Index/IndexTypeSourceInfo.cpp
@@ -59,7 +59,7 @@ class TypeIndexer : public RecursiveASTVisitor<TypeIndexer> {
 
   bool VisitTypedefTypeLoc(TypedefTypeLoc TL) {
     SourceLocation Loc = TL.getNameLoc();
-    TypedefNameDecl *ND = TL.getTypedefNameDecl();
+    TypedefNameDecl *ND = TL.getDecl();
     if (ND->isTransparentTag()) {
       TagDecl *Underlying = ND->getUnderlyingType()->getAsTagDecl();
       return IndexCtx.handleReference(Underlying, Loc, Parent,
@@ -117,7 +117,7 @@ class TypeIndexer : public RecursiveASTVisitor<TypeIndexer> {
   }
 
   bool VisitTagTypeLoc(TagTypeLoc TL) {
-    TagDecl *D = TL.getDecl();
+    TagDecl *D = TL.getOriginalDecl();
     if (!IndexCtx.shouldIndexFunctionLocalSymbols() &&
         D->getParentFunctionOrMethod())
       return true;
@@ -172,7 +172,8 @@ class TypeIndexer : public RecursiveASTVisitor<TypeIndexer> {
     return true;
   }
 
-  bool TraverseTemplateSpecializationTypeLoc(TemplateSpecializationTypeLoc TL) {
+  bool TraverseTemplateSpecializationTypeLoc(TemplateSpecializationTypeLoc TL,
+                                             bool TraverseQualifier) {
     if (!WalkUpFromTemplateSpecializationTypeLoc(TL))
       return false;
     if (!TraverseTemplateName(TL.getTypePtr()->getTemplateName()))
@@ -202,11 +203,6 @@ class TypeIndexer : public RecursiveASTVisitor<TypeIndexer> {
     return true;
   }
 
-  bool VisitInjectedClassNameTypeLoc(InjectedClassNameTypeLoc TL) {
-    return IndexCtx.handleReference(TL.getDecl(), TL.getNameLoc(), Parent,
-                                    ParentDC, SymbolRoleSet(), Relations);
-  }
-
   bool VisitDependentNameTypeLoc(DependentNameTypeLoc TL) {
     std::vector<const NamedDecl *> Symbols =
         IndexCtx.getResolver()->resolveDependentNameType(TL.getTypePtr());
@@ -248,36 +244,28 @@ void IndexingContext::indexTypeLoc(TypeLoc TL,
   TypeIndexer(*this, Parent, DC, isBase, isIBType).TraverseTypeLoc(TL);
 }
 
-void IndexingContext::indexNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS,
-                                                  const NamedDecl *Parent,
-                                                  const DeclContext *DC) {
-  if (!NNS)
-    return;
-
-  if (NestedNameSpecifierLoc Prefix = NNS.getPrefix())
-    indexNestedNameSpecifierLoc(Prefix, Parent, DC);
-
+void IndexingContext::indexNestedNameSpecifierLoc(
+    NestedNameSpecifierLoc QualifierLoc, const NamedDecl *Parent,
+    const DeclContext *DC) {
   if (!DC)
     DC = Parent->getLexicalDeclContext();
-  SourceLocation Loc = NNS.getLocalBeginLoc();
-
-  switch (NNS.getNestedNameSpecifier()->getKind()) {
-  case NestedNameSpecifier::Identifier:
-  case NestedNameSpecifier::Global:
-  case NestedNameSpecifier::Super:
+  switch (NestedNameSpecifier Qualifier = QualifierLoc.getNestedNameSpecifier();
+          Qualifier.getKind()) {
+  case NestedNameSpecifier::Kind::Null:
+  case NestedNameSpecifier::Kind::Global:
+  case NestedNameSpecifier::Kind::Super:
     break;
 
-  case NestedNameSpecifier::Namespace:
-    handleReference(NNS.getNestedNameSpecifier()->getAsNamespace(),
-                    Loc, Parent, DC, SymbolRoleSet());
-    break;
-  case NestedNameSpecifier::NamespaceAlias:
-    handleReference(NNS.getNestedNameSpecifier()->getAsNamespaceAlias(),
-                    Loc, Parent, DC, SymbolRoleSet());
+  case NestedNameSpecifier::Kind::Namespace: {
+    auto [Namespace, Prefix] = QualifierLoc.castAsNamespaceAndPrefix();
+    indexNestedNameSpecifierLoc(Prefix, Parent, DC);
+    handleReference(Namespace, QualifierLoc.getLocalBeginLoc(), Parent, DC,
+                    SymbolRoleSet());
     break;
+  }
 
-  case NestedNameSpecifier::TypeSpec:
-    indexTypeLoc(NNS.getTypeLoc(), Parent, DC);
+  case NestedNameSpecifier::Kind::Type:
+    indexTypeLoc(QualifierLoc.castAsTypeLoc(), Parent, DC);
     break;
   }
 }
diff --git a/clang/lib/Index/USRGeneration.cpp b/clang/lib/Index/USRGeneration.cpp
index 6a884f7be00e1..9e69ca567e80c 100644
--- a/clang/lib/Index/USRGeneration.cpp
+++ b/clang/lib/Index/USRGeneration.cpp
@@ -653,14 +653,14 @@ bool USRGenerator::GenLoc(const Decl *D, bool IncludeOffset) {
 }
 
 static void printQualifier(llvm::raw_ostream &Out, const LangOptions &LangOpts,
-                           NestedNameSpecifier *NNS) {
+                           NestedNameSpecifier NNS) {
   // FIXME: Encode the qualifier, don't just print it.
   PrintingPolicy PO(LangOpts);
   PO.SuppressTagKeyword = true;
   PO.SuppressUnwrittenScope = true;
   PO.ConstantArraySizeAsWritten = false;
   PO.AnonymousTagLocations = false;
-  NNS->print(Out, PO);
+  NNS.print(Out, PO);
 }
 
 void USRGenerator::VisitType(QualType T) {
@@ -910,9 +910,13 @@ void USRGenerator::VisitType(QualType T) {
       continue;
     }
     if (const TagType *TT = T->getAs<TagType>()) {
-      Out << '$';
-      VisitTagDecl(TT->getDecl());
-      return;
+      if (const auto *ICNT = dyn_cast<InjectedClassNameType>(TT)) {
+        T = ICNT->getCanonicalInjectedTST();
+      } else {
+        Out << '$';
+        VisitTagDecl(TT->getOriginalDecl());
+        return;
+      }
     }
     if (const ObjCInterfaceType *OIT = T->getAs<ObjCInterfaceType>()) {
       Out << '$';
@@ -945,10 +949,6 @@ void USRGenerator::VisitType(QualType T) {
       Out << ':' << DNT->getIdentifier()->getName();
       return;
     }
-    if (const InjectedClassNameType *InjT = T->getAs<InjectedClassNameType>()) {
-      T = InjT->getInjectedSpecializationType();
-      continue;
-    }
     if (const auto *VT = T->getAs<VectorType>()) {
       Out << (T->isExtVectorType() ? ']' : '[');
       Out << VT->getNumElements();
diff --git a/clang/lib/InstallAPI/Visitor.cpp b/clang/lib/InstallAPI/Visitor.cpp
index 487be2c300887..f12e04069817b 100644
--- a/clang/lib/InstallAPI/Visitor.cpp
+++ b/clang/lib/InstallAPI/Visitor.cpp
@@ -424,7 +424,7 @@ std::string
 InstallAPIVisitor::getMangledCXXRTTIName(const CXXRecordDecl *D) const {
   SmallString<256> Name;
   raw_svector_ostream NameStream(Name);
-  MC->mangleCXXRTTIName(QualType(D->getTypeForDecl(), 0), NameStream);
+  MC->mangleCXXRTTIName(MC->getASTContext().getCanonicalTagType(D), NameStream);
 
   return getBackendMangledName(Name);
 }
@@ -432,7 +432,7 @@ InstallAPIVisitor::getMangledCXXRTTIName(const CXXRecordDecl *D) const {
 std::string InstallAPIVisitor::getMangledCXXRTTI(const CXXRecordDecl *D) const {
   SmallString<256> Name;
   raw_svector_ostream NameStream(Name);
-  MC->mangleCXXRTTI(QualType(D->getTypeForDecl(), 0), NameStream);
+  MC->mangleCXXRTTI(MC->getASTContext().getCanonicalTagType(D), NameStream);
 
   return getBackendMangledName(Name);
 }
@@ -543,8 +543,8 @@ void InstallAPIVisitor::emitVTableSymbols(const CXXRecordDecl *D,
   }
 
   for (const auto &It : D->bases()) {
-    const CXXRecordDecl *Base =
-        cast<CXXRecordDecl>(It.getType()->castAs<RecordType>()->getDecl());
+    const CXXRecordDecl *Base = cast<CXXRecordDecl>(
+        It.getType()->castAs<RecordType>()->getOriginalDecl());
     const auto BaseAccess = getAccessForDecl(Base);
     if (!BaseAccess)
       continue;
diff --git a/clang/lib/Interpreter/InterpreterValuePrinter.cpp b/clang/lib/Interpreter/InterpreterValuePrinter.cpp
index 3e7e32b2e8557..00f9a7a631e36 100644
--- a/clang/lib/Interpreter/InterpreterValuePrinter.cpp
+++ b/clang/lib/Interpreter/InterpreterValuePrinter.cpp
@@ -324,7 +324,7 @@ extern "C" void REPL_EXTERNAL_VISIBILITY __clang_Interpreter_SetValueNoAlloc(
     VRef.setPtr(va_arg(args, void *));
   } else {
     if (const auto *ET = QT->getAs<EnumType>())
-      QT = ET->getDecl()->getIntegerType();
+      QT = ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
     switch (QT->castAs<BuiltinType>()->getKind()) {
     default:
       llvm_unreachable("unknown type kind!");
diff --git a/clang/lib/Interpreter/Value.cpp b/clang/lib/Interpreter/Value.cpp
index afdf406b37253..526cca80a983a 100644
--- a/clang/lib/Interpreter/Value.cpp
+++ b/clang/lib/Interpreter/Value.cpp
@@ -99,7 +99,7 @@ static Value::Kind ConvertQualTypeToKind(const ASTContext &Ctx, QualType QT) {
     return Value::K_Void;
 
   if (const auto *ET = QT->getAs<EnumType>())
-    QT = ET->getDecl()->getIntegerType();
+    QT = ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   const auto *BT = QT->getAs<BuiltinType>();
   if (!BT || BT->isNullPtrType())
@@ -145,9 +145,9 @@ Value::Value(Interpreter *In, void *Ty) : Interp(In), OpaqueType(Ty) {
       }
       if (const auto *RT = DtorTy->getAs<RecordType>()) {
         if (CXXRecordDecl *CXXRD =
-                llvm::dyn_cast<CXXRecordDecl>(RT->getDecl())) {
+                llvm::dyn_cast<CXXRecordDecl>(RT->getOriginalDecl())) {
           if (llvm::Expected<llvm::orc::ExecutorAddr> Addr =
-                  Interp.CompileDtorCall(CXXRD))
+                  Interp.CompileDtorCall(CXXRD->getDefinitionOrSelf()))
             DtorF = reinterpret_cast<void *>(Addr->getValue());
           else
             llvm::logAllUnhandledErrors(Addr.takeError(), llvm::errs());
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 9fe18b0dbcedb..bc54d590e3b80 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -591,8 +591,7 @@ bool Parser::ParseUsingDeclarator(DeclaratorContext Context,
        NextToken().isRegularKeywordAttribute() ||
        NextToken().is(tok::kw___attribute)) &&
       D.SS.isNotEmpty() && LastII == Tok.getIdentifierInfo() &&
-      !D.SS.getScopeRep()->getAsNamespace() &&
-      !D.SS.getScopeRep()->getAsNamespaceAlias()) {
+      D.SS.getScopeRep().getKind() != NestedNameSpecifier::Kind::Namespace) {
     SourceLocation IdLoc = ConsumeToken();
     ParsedType Type =
         Actions.getInheritingConstructorName(D.SS, IdLoc, *LastII);
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 8dce2268082d9..8605ba2cdb49b 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -195,9 +195,10 @@ bool Parser::ParseOptionalCXXScopeSpecifier(
     if (DS.getTypeSpecType() == DeclSpec::TST_error)
       return false;
 
-    QualType Type = Actions.ActOnPackIndexingType(
-        DS.getRepAsType().get(), DS.getPackIndexingExpr(), DS.getBeginLoc(),
-        DS.getEllipsisLoc());
+    QualType Pattern = Sema::GetTypeFromParser(DS.getRepAsType());
+    QualType Type =
+        Actions.ActOnPackIndexingType(Pattern, DS.getPackIndexingExpr(),
+                                      DS.getBeginLoc(), DS.getEllipsisLoc());
 
     if (Type.isNull())
       return false;
@@ -2355,8 +2356,10 @@ bool Parser::ParseUnqualifiedIdTemplateId(
 
   // Constructor and destructor names.
   TypeResult Type = Actions.ActOnTemplateIdType(
-      getCurScope(), SS, TemplateKWLoc, Template, Name, NameLoc, LAngleLoc,
-      TemplateArgsPtr, RAngleLoc, /*IsCtorOrDtorName=*/true);
+      getCurScope(), ElaboratedTypeKeyword::None,
+      /*ElaboratedKeywordLoc=*/SourceLocation(), SS, TemplateKWLoc, Template,
+      Name, NameLoc, LAngleLoc, TemplateArgsPtr, RAngleLoc,
+      /*IsCtorOrDtorName=*/true);
   if (Type.isInvalid())
     return true;
 
diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
index 9a04bf298c0ac..004cb40445eab 100644
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -1109,12 +1109,14 @@ bool Parser::AnnotateTemplateIdToken(TemplateTy Template, TemplateNameKind TNK,
 
   // Build the annotation token.
   if (TNK == TNK_Type_template && AllowTypeAnnotation) {
-    TypeResult Type = ArgsInvalid
-                          ? TypeError()
-                          : Actions.ActOnTemplateIdType(
-                                getCurScope(), SS, TemplateKWLoc, Template,
-                                TemplateName.Identifier, TemplateNameLoc,
-                                LAngleLoc, TemplateArgsPtr, RAngleLoc);
+    TypeResult Type =
+        ArgsInvalid
+            ? TypeError()
+            : Actions.ActOnTemplateIdType(
+                  getCurScope(), ElaboratedTypeKeyword::None,
+                  /*ElaboratedKeywordLoc=*/SourceLocation(), SS, TemplateKWLoc,
+                  Template, TemplateName.Identifier, TemplateNameLoc, LAngleLoc,
+                  TemplateArgsPtr, RAngleLoc);
 
     Tok.setKind(tok::annot_typename);
     setTypeAnnotation(Tok, Type);
@@ -1175,10 +1177,11 @@ void Parser::AnnotateTemplateIdTokenAsType(
       TemplateId->isInvalid()
           ? TypeError()
           : Actions.ActOnTemplateIdType(
-                getCurScope(), SS, TemplateId->TemplateKWLoc,
-                TemplateId->Template, TemplateId->Name,
-                TemplateId->TemplateNameLoc, TemplateId->LAngleLoc,
-                TemplateArgsPtr, TemplateId->RAngleLoc,
+                getCurScope(), ElaboratedTypeKeyword::None,
+                /*ElaboratedKeywordLoc=*/SourceLocation(), SS,
+                TemplateId->TemplateKWLoc, TemplateId->Template,
+                TemplateId->Name, TemplateId->TemplateNameLoc,
+                TemplateId->LAngleLoc, TemplateArgsPtr, TemplateId->RAngleLoc,
                 /*IsCtorOrDtorName=*/false, IsClassName, AllowImplicitTypename);
   // Create the new "type" annotation token.
   Tok.setKind(tok::annot_typename);
@@ -1243,7 +1246,8 @@ ParsedTemplateArgument Parser::ParseTemplateTemplateArgument() {
           Actions.ActOnTemplateName(getCurScope(), SS, TemplateKWLoc, Name,
                                     /*ObjectType=*/nullptr,
                                     /*EnteringContext=*/false, Template))
-        Result = ParsedTemplateArgument(SS, Template, Name.StartLocation);
+        Result = ParsedTemplateArgument(TemplateKWLoc, SS, Template,
+                                        Name.StartLocation);
     }
   } else if (Tok.is(tok::identifier)) {
     // We may have a (non-dependent) template name.
@@ -1264,7 +1268,8 @@ ParsedTemplateArgument Parser::ParseTemplateTemplateArgument() {
       if (TNK == TNK_Dependent_template_name || TNK == TNK_Type_template) {
         // We have an id-expression that refers to a class template or
         // (C++0x) alias template.
-        Result = ParsedTemplateArgument(SS, Template, Name.StartLocation);
+        Result = ParsedTemplateArgument(/*TemplateKwLoc=*/SourceLocation(), SS,
+                                        Template, Name.StartLocation);
       }
     }
   }
diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
index b58100c635677..6cbc48102bf73 100644
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -1328,7 +1328,7 @@ Parser::isCXXDeclarationSpecifier(ImplicitTypenameContext AllowImplicitTypename,
         Actions.RestoreNestedNameSpecifierAnnotation(Tok.getAnnotationValue(),
                                                      Tok.getAnnotationRange(),
                                                      SS);
-        if (SS.getScopeRep() && SS.getScopeRep()->isDependent()) {
+        if (SS.getScopeRep().isDependent()) {
           RevertingTentativeParsingAction PA(*this);
           ConsumeAnnotationToken();
           ConsumeToken();
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index 8834bf80c4016..1ddc59a5b6fe3 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1774,9 +1774,9 @@ Parser::TryAnnotateName(CorrectionCandidateCallback *CCC,
     /// An Objective-C object type followed by '<' is a specialization of
     /// a parameterized class type or a protocol-qualified type.
     ParsedType Ty = Classification.getType();
+    QualType T = Actions.GetTypeFromParser(Ty);
     if (getLangOpts().ObjC && NextToken().is(tok::less) &&
-        (Ty.get()->isObjCObjectType() ||
-         Ty.get()->isObjCObjectPointerType())) {
+        (T->isObjCObjectType() || T->isObjCObjectPointerType())) {
       // Consume the name.
       SourceLocation IdentifierLoc = ConsumeToken();
       SourceLocation NewEndLoc;
@@ -2031,11 +2031,12 @@ bool Parser::TryAnnotateTypeOrScopeTokenAfterScopeSpec(
       if (SS.isNotEmpty()) // it was a C++ qualified type name.
         BeginLoc = SS.getBeginLoc();
 
+      QualType T = Actions.GetTypeFromParser(Ty);
+
       /// An Objective-C object type followed by '<' is a specialization of
       /// a parameterized class type or a protocol-qualified type.
       if (getLangOpts().ObjC && NextToken().is(tok::less) &&
-          (Ty.get()->isObjCObjectType() ||
-           Ty.get()->isObjCObjectPointerType())) {
+          (T->isObjCObjectType() || T->isObjCObjectPointerType())) {
         // Consume the name.
         SourceLocation IdentifierLoc = ConsumeToken();
         SourceLocation NewEndLoc;
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index ec8acbdff3b49..c863568b699ac 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -225,14 +225,11 @@ static bool hasRecursiveCallInPath(const FunctionDecl *FD, CFGBlock &Block) {
 
     // Skip function calls which are qualified with a templated class.
     if (const DeclRefExpr *DRE =
-            dyn_cast<DeclRefExpr>(CE->getCallee()->IgnoreParenImpCasts())) {
-      if (NestedNameSpecifier *NNS = DRE->getQualifier()) {
-        if (NNS->getKind() == NestedNameSpecifier::TypeSpec &&
-            isa<TemplateSpecializationType>(NNS->getAsType())) {
+            dyn_cast<DeclRefExpr>(CE->getCallee()->IgnoreParenImpCasts()))
+      if (NestedNameSpecifier NNS = DRE->getQualifier();
+          NNS.getKind() == NestedNameSpecifier::Kind::Type)
+        if (isa_and_nonnull<TemplateSpecializationType>(NNS.getAsType()))
           continue;
-        }
-      }
-    }
 
     const CXXMemberCallExpr *MCE = dyn_cast<CXXMemberCallExpr>(CE);
     if (!MCE || isa<CXXThisExpr>(MCE->getImplicitObjectArgument()) ||
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
index ee5a862c32509..cc385abc3059d 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -48,9 +48,9 @@ void UnqualifiedId::setConstructorTemplateId(TemplateIdAnnotation *TemplateId) {
   EndLocation = TemplateId->RAngleLoc;
 }
 
-void CXXScopeSpec::Extend(ASTContext &Context, TypeLoc TL,
-                          SourceLocation ColonColonLoc) {
-  Builder.Extend(Context, TL, ColonColonLoc);
+void CXXScopeSpec::Make(ASTContext &Context, TypeLoc TL,
+                        SourceLocation ColonColonLoc) {
+  Builder.Make(Context, TL, ColonColonLoc);
   if (Range.getBegin().isInvalid())
     Range.setBegin(TL.getBeginLoc());
   Range.setEnd(ColonColonLoc);
@@ -59,20 +59,7 @@ void CXXScopeSpec::Extend(ASTContext &Context, TypeLoc TL,
          "NestedNameSpecifierLoc range computation incorrect");
 }
 
-void CXXScopeSpec::Extend(ASTContext &Context, IdentifierInfo *Identifier,
-                          SourceLocation IdentifierLoc,
-                          SourceLocation ColonColonLoc) {
-  Builder.Extend(Context, Identifier, IdentifierLoc, ColonColonLoc);
-
-  if (Range.getBegin().isInvalid())
-    Range.setBegin(IdentifierLoc);
-  Range.setEnd(ColonColonLoc);
-
-  assert(Range == Builder.getSourceRange() &&
-         "NestedNameSpecifierLoc range computation incorrect");
-}
-
-void CXXScopeSpec::Extend(ASTContext &Context, NamespaceDecl *Namespace,
+void CXXScopeSpec::Extend(ASTContext &Context, NamespaceBaseDecl *Namespace,
                           SourceLocation NamespaceLoc,
                           SourceLocation ColonColonLoc) {
   Builder.Extend(Context, Namespace, NamespaceLoc, ColonColonLoc);
@@ -85,19 +72,6 @@ void CXXScopeSpec::Extend(ASTContext &Context, NamespaceDecl *Namespace,
          "NestedNameSpecifierLoc range computation incorrect");
 }
 
-void CXXScopeSpec::Extend(ASTContext &Context, NamespaceAliasDecl *Alias,
-                          SourceLocation AliasLoc,
-                          SourceLocation ColonColonLoc) {
-  Builder.Extend(Context, Alias, AliasLoc, ColonColonLoc);
-
-  if (Range.getBegin().isInvalid())
-    Range.setBegin(AliasLoc);
-  Range.setEnd(ColonColonLoc);
-
-  assert(Range == Builder.getSourceRange() &&
-         "NestedNameSpecifierLoc range computation incorrect");
-}
-
 void CXXScopeSpec::MakeGlobal(ASTContext &Context,
                               SourceLocation ColonColonLoc) {
   Builder.MakeGlobal(Context, ColonColonLoc);
@@ -121,7 +95,7 @@ void CXXScopeSpec::MakeSuper(ASTContext &Context, CXXRecordDecl *RD,
 }
 
 void CXXScopeSpec::MakeTrivial(ASTContext &Context,
-                               NestedNameSpecifier *Qualifier, SourceRange R) {
+                               NestedNameSpecifier Qualifier, SourceRange R) {
   Builder.MakeTrivial(Context, Qualifier, R);
   Range = R;
 }
diff --git a/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.cpp b/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.cpp
index 87f9ae07550c2..806800cb7b213 100644
--- a/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.cpp
+++ b/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.cpp
@@ -313,9 +313,6 @@ TemplateParameterListBuilder::finalizeTemplateArgs(ConceptDecl *CD) {
   Builder.Record->getDeclContext()->addDecl(Builder.Template);
   Params.clear();
 
-  QualType T = Builder.Template->getInjectedClassNameSpecialization();
-  T = AST.getInjectedClassNameType(Builder.Record, T);
-
   return Builder;
 }
 
@@ -351,7 +348,7 @@ BuiltinTypeMethodBuilder::BuiltinTypeMethodBuilder(BuiltinTypeDeclBuilder &DB,
   ASTContext &AST = DB.SemaRef.getASTContext();
   if (IsCtor) {
     Name = AST.DeclarationNames.getCXXConstructorName(
-        DB.Record->getTypeForDecl()->getCanonicalTypeUnqualified());
+        AST.getCanonicalTagType(DB.Record));
   } else {
     const IdentifierInfo &II =
         AST.Idents.get(NameStr, tok::TokenKind::identifier);
@@ -553,9 +550,9 @@ BuiltinTypeDeclBuilder::BuiltinTypeDeclBuilder(Sema &SemaRef,
     return;
   }
 
-  Record = CXXRecordDecl::Create(AST, TagDecl::TagKind::Class, HLSLNamespace,
-                                 SourceLocation(), SourceLocation(), &II,
-                                 PrevDecl, true);
+  Record =
+      CXXRecordDecl::Create(AST, TagDecl::TagKind::Class, HLSLNamespace,
+                            SourceLocation(), SourceLocation(), &II, PrevDecl);
   Record->setImplicit(true);
   Record->setLexicalDeclContext(HLSLNamespace);
   Record->setHasExternalLexicalStorage();
@@ -570,18 +567,6 @@ BuiltinTypeDeclBuilder::~BuiltinTypeDeclBuilder() {
     HLSLNamespace->addDecl(Record);
 }
 
-CXXRecordDecl *BuiltinTypeDeclBuilder::finalizeForwardDeclaration() {
-  // Force the QualType to be generated for the record declaration. In most
-  // cases this will happen naturally when something uses the type the
-  // QualType gets lazily created. Unfortunately, with our injected types if a
-  // type isn't used in a translation unit the QualType may not get
-  // automatically generated before a PCH is generated. To resolve this we
-  // just force that the QualType is generated after we create a forward
-  // declaration.
-  (void)Record->getASTContext().getRecordType(Record);
-  return Record;
-}
-
 BuiltinTypeDeclBuilder &
 BuiltinTypeDeclBuilder::addMemberVariable(StringRef Name, QualType Type,
                                           llvm::ArrayRef<Attr *> Attrs,
diff --git a/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.h b/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.h
index 36c4add20b225..098b72692bd3a 100644
--- a/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.h
+++ b/clang/lib/Sema/HLSLBuiltinTypeDeclBuilder.h
@@ -64,7 +64,7 @@ class BuiltinTypeDeclBuilder {
 
   BuiltinTypeDeclBuilder &addSimpleTemplateParams(ArrayRef<StringRef> Names,
                                                   ConceptDecl *CD);
-  CXXRecordDecl *finalizeForwardDeclaration();
+  CXXRecordDecl *finalizeForwardDeclaration() { return Record; }
   BuiltinTypeDeclBuilder &completeDefinition();
 
   BuiltinTypeDeclBuilder &
diff --git a/clang/lib/Sema/HeuristicResolver.cpp b/clang/lib/Sema/HeuristicResolver.cpp
index 6874d30516f8f..9c56dd356421e 100644
--- a/clang/lib/Sema/HeuristicResolver.cpp
+++ b/clang/lib/Sema/HeuristicResolver.cpp
@@ -44,7 +44,7 @@ class HeuristicResolverImpl {
   resolveDependentNameType(const DependentNameType *DNT);
   std::vector<const NamedDecl *> resolveTemplateSpecializationType(
       const DependentTemplateSpecializationType *DTST);
-  QualType resolveNestedNameSpecifierToType(const NestedNameSpecifier *NNS);
+  QualType resolveNestedNameSpecifierToType(NestedNameSpecifier NNS);
   QualType getPointeeType(QualType T);
   std::vector<const NamedDecl *>
   lookupDependentName(CXXRecordDecl *RD, DeclarationName Name,
@@ -101,9 +101,8 @@ QualType resolveDeclsToType(const std::vector<const NamedDecl *> &Decls,
                             ASTContext &Ctx) {
   if (Decls.size() != 1) // Names an overload set -- just bail.
     return QualType();
-  if (const auto *TD = dyn_cast<TypeDecl>(Decls[0])) {
-    return Ctx.getTypeDeclType(TD);
-  }
+  if (const auto *TD = dyn_cast<TypeDecl>(Decls[0]))
+    return Ctx.getCanonicalTypeDeclType(TD);
   if (const auto *VD = dyn_cast<ValueDecl>(Decls[0])) {
     return VD->getType();
   }
@@ -139,8 +138,7 @@ TagDecl *HeuristicResolverImpl::resolveTypeToTagDecl(QualType QT) {
     T = T->getCanonicalTypeInternal().getTypePtr();
   }
 
-  if (auto *TT = T->getAs<TagType>()) {
-    TagDecl *TD = TT->getDecl();
+  if (auto *TD = T->getAsTagDecl()) {
     // Template might not be instantiated yet, fall back to primary template
     // in such cases.
     if (const auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(TD)) {
@@ -151,11 +149,6 @@ TagDecl *HeuristicResolverImpl::resolveTypeToTagDecl(QualType QT) {
     return TD;
   }
 
-  if (const auto *ICNT = T->getAs<InjectedClassNameType>())
-    T = ICNT->getInjectedSpecializationType().getTypePtrOrNull();
-  if (!T)
-    return nullptr;
-
   TemplateName TN = getReferencedTemplateName(T);
   if (TN.isNull())
     return nullptr;
@@ -292,7 +285,7 @@ std::vector<const NamedDecl *> HeuristicResolverImpl::resolveMemberExpr(
   //      an instance method, it's represented as a CXXDependentScopeMemberExpr
   //      with `this` as the base expression as `X` as the qualifier
   //      (which could be valid if `X` names a base class after instantiation).
-  if (NestedNameSpecifier *NNS = ME->getQualifier()) {
+  if (NestedNameSpecifier NNS = ME->getQualifier()) {
     if (QualType QualifierType = resolveNestedNameSpecifierToType(NNS);
         !QualifierType.isNull()) {
       auto Decls =
@@ -348,7 +341,10 @@ HeuristicResolverImpl::resolveCalleeOfCallExpr(const CallExpr *CE) {
 
 std::vector<const NamedDecl *> HeuristicResolverImpl::resolveUsingValueDecl(
     const UnresolvedUsingValueDecl *UUVD) {
-  return resolveDependentMember(QualType(UUVD->getQualifier()->getAsType(), 0),
+  NestedNameSpecifier Qualifier = UUVD->getQualifier();
+  if (Qualifier.getKind() != NestedNameSpecifier::Kind::Type)
+    return {};
+  return resolveDependentMember(QualType(Qualifier.getAsType(), 0),
                                 UUVD->getNameInfo().getName(), ValueFilter);
 }
 
@@ -399,23 +395,23 @@ QualType HeuristicResolverImpl::resolveExprToType(const Expr *E) {
 }
 
 QualType HeuristicResolverImpl::resolveNestedNameSpecifierToType(
-    const NestedNameSpecifier *NNS) {
-  if (!NNS)
-    return QualType();
-
+    NestedNameSpecifier NNS) {
   // The purpose of this function is to handle the dependent (Kind ==
   // Identifier) case, but we need to recurse on the prefix because
   // that may be dependent as well, so for convenience handle
   // the TypeSpec cases too.
-  switch (NNS->getKind()) {
-  case NestedNameSpecifier::TypeSpec:
-    return QualType(NNS->getAsType(), 0);
-  case NestedNameSpecifier::Identifier: {
-    return resolveDeclsToType(
-        resolveDependentMember(
-            resolveNestedNameSpecifierToType(NNS->getPrefix()),
-            NNS->getAsIdentifier(), TypeFilter),
-        Ctx);
+  switch (NNS.getKind()) {
+  case NestedNameSpecifier::Kind::Type: {
+    const auto *T = NNS.getAsType();
+    // FIXME: Should this handle the DependentTemplateSpecializationType as
+    // well?
+    if (const auto *DTN = dyn_cast<DependentNameType>(T))
+      return resolveDeclsToType(
+          resolveDependentMember(
+              resolveNestedNameSpecifierToType(DTN->getQualifier()),
+              DTN->getIdentifier(), TypeFilter),
+          Ctx);
+    return QualType(T, 0);
   }
   default:
     break;
@@ -590,7 +586,7 @@ HeuristicResolver::resolveTemplateSpecializationType(
   return HeuristicResolverImpl(Ctx).resolveTemplateSpecializationType(DTST);
 }
 QualType HeuristicResolver::resolveNestedNameSpecifierToType(
-    const NestedNameSpecifier *NNS) const {
+    NestedNameSpecifier NNS) const {
   return HeuristicResolverImpl(Ctx).resolveNestedNameSpecifierToType(NNS);
 }
 std::vector<const NamedDecl *> HeuristicResolver::lookupDependentName(
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 56608e990fd50..48ec4a48b9e63 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -1882,9 +1882,10 @@ class DeferredDiagnosticsEmitter
     for (const FieldDecl *FD : RD->fields()) {
       QualType FT = FD->getType();
       if (const auto *RT = FT->getAs<RecordType>())
-        if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getDecl()))
-          if (ClassDecl->hasDefinition())
-            if (CXXDestructorDecl *MemberDtor = ClassDecl->getDestructor())
+        if (const auto *ClassDecl =
+                dyn_cast<CXXRecordDecl>(RT->getOriginalDecl()))
+          if (const auto *Def = ClassDecl->getDefinition())
+            if (CXXDestructorDecl *MemberDtor = Def->getDestructor())
               asImpl().visitUsedDecl(MemberDtor->getLocation(), MemberDtor);
     }
 
@@ -1892,9 +1893,10 @@ class DeferredDiagnosticsEmitter
     for (const auto &Base : RD->bases()) {
       QualType BaseType = Base.getType();
       if (const auto *RT = BaseType->getAs<RecordType>())
-        if (const auto *BaseDecl = dyn_cast<CXXRecordDecl>(RT->getDecl()))
-          if (BaseDecl->hasDefinition())
-            if (CXXDestructorDecl *BaseDtor = BaseDecl->getDestructor())
+        if (const auto *BaseDecl =
+                dyn_cast<CXXRecordDecl>(RT->getOriginalDecl()))
+          if (const auto *Def = BaseDecl->getDefinition())
+            if (CXXDestructorDecl *BaseDtor = Def->getDestructor())
               asImpl().visitUsedDecl(BaseDtor->getLocation(), BaseDtor);
     }
   }
@@ -1907,9 +1909,10 @@ class DeferredDiagnosticsEmitter
             VD->needsDestruction(S.Context)) {
           QualType VT = VD->getType();
           if (const auto *RT = VT->getAs<RecordType>())
-            if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getDecl()))
-              if (ClassDecl->hasDefinition())
-                if (CXXDestructorDecl *Dtor = ClassDecl->getDestructor())
+            if (const auto *ClassDecl =
+                    dyn_cast<CXXRecordDecl>(RT->getOriginalDecl()))
+              if (const auto *Def = ClassDecl->getDefinition())
+                if (CXXDestructorDecl *Dtor = Def->getDestructor())
                   asImpl().visitUsedDecl(Dtor->getLocation(), Dtor);
         }
 
diff --git a/clang/lib/Sema/SemaAccess.cpp b/clang/lib/Sema/SemaAccess.cpp
index 83a07a23f3414..ba560d3c52340 100644
--- a/clang/lib/Sema/SemaAccess.cpp
+++ b/clang/lib/Sema/SemaAccess.cpp
@@ -318,11 +318,8 @@ static AccessResult IsDerivedFromInclusive(const CXXRecordDecl *Derived,
       const CXXRecordDecl *RD;
 
       QualType T = I.getType();
-      if (const RecordType *RT = T->getAs<RecordType>()) {
-        RD = cast<CXXRecordDecl>(RT->getDecl());
-      } else if (const InjectedClassNameType *IT
-                   = T->getAs<InjectedClassNameType>()) {
-        RD = IT->getDecl();
+      if (CXXRecordDecl *Rec = T->getAsCXXRecordDecl()) {
+        RD = Rec;
       } else {
         assert(T->isDependentType() && "non-dependent base wasn't a record?");
         OnFailure = AR_dependent;
@@ -443,7 +440,9 @@ static AccessResult MatchesFriend(Sema &S,
                                   const EffectiveContext &EC,
                                   CanQualType Friend) {
   if (const RecordType *RT = Friend->getAs<RecordType>())
-    return MatchesFriend(S, EC, cast<CXXRecordDecl>(RT->getDecl()));
+    return MatchesFriend(
+        S, EC,
+        cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf());
 
   // TODO: we can do better than this
   if (Friend->isDependentType())
@@ -671,11 +670,8 @@ struct ProtectedFriendContext {
       const CXXRecordDecl *RD;
 
       QualType T = I.getType();
-      if (const RecordType *RT = T->getAs<RecordType>()) {
-        RD = cast<CXXRecordDecl>(RT->getDecl());
-      } else if (const InjectedClassNameType *IT
-                   = T->getAs<InjectedClassNameType>()) {
-        RD = IT->getDecl();
+      if (CXXRecordDecl *Rec = T->getAsCXXRecordDecl()) {
+        RD = Rec;
       } else {
         assert(T->isDependentType() && "non-dependent base wasn't a record?");
         EverDependent = true;
@@ -1072,7 +1068,7 @@ static bool TryDiagnoseProtectedAccess(Sema &S, const EffectiveContext &EC,
       // TODO: it would be great to have a fixit here, since this is
       // such an obvious error.
       S.Diag(D->getLocation(), diag::note_access_protected_restricted_noobject)
-        << S.Context.getTypeDeclType(ECRecord);
+          << S.Context.getCanonicalTagType(ECRecord);
       return true;
     }
 
@@ -1101,7 +1097,7 @@ static bool TryDiagnoseProtectedAccess(Sema &S, const EffectiveContext &EC,
     // Otherwise, use the generic diagnostic.
     return S.Diag(D->getLocation(),
                   diag::note_access_protected_restricted_object)
-           << S.Context.getTypeDeclType(ECRecord);
+           << S.Context.getCanonicalTagType(ECRecord);
   }
 
   return false;
@@ -1129,7 +1125,7 @@ static void diagnoseBadDirectAccess(Sema &S,
     else if (TypedefNameDecl *TND = dyn_cast<TypedefNameDecl>(D))
       PrevDecl = TND->getPreviousDecl();
     else if (TagDecl *TD = dyn_cast<TagDecl>(D)) {
-      if (auto *RD = dyn_cast<CXXRecordDecl>(D);
+      if (const auto *RD = dyn_cast<CXXRecordDecl>(TD);
           RD && RD->isInjectedClassName())
         break;
       PrevDecl = TD->getPreviousDecl();
@@ -1284,10 +1280,10 @@ static void DiagnoseBadAccess(Sema &S, SourceLocation Loc,
   NamedDecl *D = (Entity.isMemberAccess() ? Entity.getTargetDecl() : nullptr);
 
   S.Diag(Loc, Entity.getDiag())
-    << (Entity.getAccess() == AS_protected)
-    << (D ? D->getDeclName() : DeclarationName())
-    << S.Context.getTypeDeclType(NamingClass)
-    << S.Context.getTypeDeclType(DeclaringClass);
+      << (Entity.getAccess() == AS_protected)
+      << (D ? D->getDeclName() : DeclarationName())
+      << S.Context.getCanonicalTagType(NamingClass)
+      << S.Context.getCanonicalTagType(DeclaringClass);
   DiagnoseAccessPath(S, EC, Entity);
 }
 
@@ -1640,7 +1636,8 @@ Sema::AccessResult Sema::CheckDestructorAccess(SourceLocation Loc,
     return AR_accessible;
 
   CXXRecordDecl *NamingClass = Dtor->getParent();
-  if (ObjectTy.isNull()) ObjectTy = Context.getTypeDeclType(NamingClass);
+  if (ObjectTy.isNull())
+    ObjectTy = Context.getCanonicalTagType(NamingClass);
 
   AccessTarget Entity(Context, AccessTarget::Member, NamingClass,
                       DeclAccessPair::make(Dtor, Access),
@@ -1728,7 +1725,7 @@ Sema::AccessResult Sema::CheckConstructorAccess(SourceLocation UseLoc,
   AccessTarget AccessEntity(
       Context, AccessTarget::Member, NamingClass,
       DeclAccessPair::make(Constructor, Found.getAccess()),
-      Context.getTypeDeclType(ObjectClass));
+      Context.getCanonicalTagType(ObjectClass));
   AccessEntity.setDiag(PD);
 
   return CheckAccess(*this, UseLoc, AccessEntity);
@@ -1776,7 +1773,7 @@ Sema::CheckStructuredBindingMemberAccess(SourceLocation UseLoc,
     return AR_accessible;
 
   AccessTarget Entity(Context, AccessTarget::Member, DecomposedClass, Field,
-                      Context.getRecordType(DecomposedClass));
+                      Context.getCanonicalTagType(DecomposedClass));
   Entity.setDiag(diag::err_decomp_decl_inaccessible_field);
 
   return CheckAccess(*this, UseLoc, Entity);
@@ -1790,7 +1787,8 @@ Sema::AccessResult Sema::CheckMemberOperatorAccess(SourceLocation OpLoc,
     return AR_accessible;
 
   const RecordType *RT = ObjectExpr->getType()->castAs<RecordType>();
-  CXXRecordDecl *NamingClass = cast<CXXRecordDecl>(RT->getDecl());
+  CXXRecordDecl *NamingClass =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
 
   AccessTarget Entity(Context, AccessTarget::Member, NamingClass, Found,
                       ObjectExpr->getType());
diff --git a/clang/lib/Sema/SemaAvailability.cpp b/clang/lib/Sema/SemaAvailability.cpp
index 8c6a17301fba6..778941c128bdd 100644
--- a/clang/lib/Sema/SemaAvailability.cpp
+++ b/clang/lib/Sema/SemaAvailability.cpp
@@ -102,7 +102,7 @@ Sema::ShouldDiagnoseAvailabilityOfDecl(const NamedDecl *D, std::string *Message,
       break;
     for (const Type *T = TD->getUnderlyingType().getTypePtr(); /**/; /**/) {
       if (auto *TT = dyn_cast<TagType>(T)) {
-        D = TT->getDecl();
+        D = TT->getOriginalDecl()->getDefinitionOrSelf();
       } else if (isa<SubstTemplateTypeParmType>(T)) {
         // A Subst* node represents a use through a template.
         // Any uses of the underlying declaration happened through it's template
@@ -1011,7 +1011,7 @@ bool DiagnoseUnguardedAvailability::VisitTypeLoc(TypeLoc Ty) {
     return true;
 
   if (const auto *TT = dyn_cast<TagType>(TyPtr)) {
-    TagDecl *TD = TT->getDecl();
+    TagDecl *TD = TT->getOriginalDecl()->getDefinitionOrSelf();
     DiagnoseDeclAvailability(TD, Range);
 
   } else if (const auto *TD = dyn_cast<TypedefType>(TyPtr)) {
diff --git a/clang/lib/Sema/SemaBPF.cpp b/clang/lib/Sema/SemaBPF.cpp
index 7c00084d62dd9..6428435ed9d2a 100644
--- a/clang/lib/Sema/SemaBPF.cpp
+++ b/clang/lib/Sema/SemaBPF.cpp
@@ -58,10 +58,10 @@ static bool isValidPreserveTypeInfoArg(Expr *Arg) {
   // Record type or Enum type.
   const Type *Ty = ArgType->getUnqualifiedDesugaredType();
   if (const auto *RT = Ty->getAs<RecordType>()) {
-    if (!RT->getDecl()->getDeclName().isEmpty())
+    if (!RT->getOriginalDecl()->getDeclName().isEmpty())
       return true;
   } else if (const auto *ET = Ty->getAs<EnumType>()) {
-    if (!ET->getDecl()->getDeclName().isEmpty())
+    if (!ET->getOriginalDecl()->getDeclName().isEmpty())
       return true;
   }
 
@@ -105,7 +105,7 @@ static bool isValidPreserveEnumValueArg(Expr *Arg) {
     return false;
 
   // The enum value must be supported.
-  return llvm::is_contained(ET->getDecl()->enumerators(), Enumerator);
+  return llvm::is_contained(ET->getOriginalDecl()->enumerators(), Enumerator);
 }
 
 bool SemaBPF::CheckBPFBuiltinFunctionCall(unsigned BuiltinID,
diff --git a/clang/lib/Sema/SemaCUDA.cpp b/clang/lib/Sema/SemaCUDA.cpp
index 24cb8c369790b..fbf64d3d57050 100644
--- a/clang/lib/Sema/SemaCUDA.cpp
+++ b/clang/lib/Sema/SemaCUDA.cpp
@@ -426,7 +426,8 @@ bool SemaCUDA::inferTargetForImplicitSpecialMember(CXXRecordDecl *ClassDecl,
       continue;
     }
 
-    CXXRecordDecl *BaseClassDecl = cast<CXXRecordDecl>(BaseType->getDecl());
+    CXXRecordDecl *BaseClassDecl =
+        cast<CXXRecordDecl>(BaseType->getOriginalDecl())->getDefinitionOrSelf();
     Sema::SpecialMemberOverloadResult SMOR =
         SemaRef.LookupSpecialMember(BaseClassDecl, CSM,
                                     /* ConstArg */ ConstRHS,
@@ -471,7 +472,9 @@ bool SemaCUDA::inferTargetForImplicitSpecialMember(CXXRecordDecl *ClassDecl,
       continue;
     }
 
-    CXXRecordDecl *FieldRecDecl = cast<CXXRecordDecl>(FieldType->getDecl());
+    CXXRecordDecl *FieldRecDecl =
+        cast<CXXRecordDecl>(FieldType->getOriginalDecl())
+            ->getDefinitionOrSelf();
     Sema::SpecialMemberOverloadResult SMOR =
         SemaRef.LookupSpecialMember(FieldRecDecl, CSM,
                                     /* ConstArg */ ConstRHS && !F->isMutable(),
diff --git a/clang/lib/Sema/SemaCXXScopeSpec.cpp b/clang/lib/Sema/SemaCXXScopeSpec.cpp
index ab83f625d2849..fefcfdcdb3fd4 100644
--- a/clang/lib/Sema/SemaCXXScopeSpec.cpp
+++ b/clang/lib/Sema/SemaCXXScopeSpec.cpp
@@ -28,24 +28,21 @@ static CXXRecordDecl *getCurrentInstantiationOf(QualType T,
   if (T.isNull())
     return nullptr;
 
-  const Type *Ty = T->getCanonicalTypeInternal().getTypePtr();
-  if (const RecordType *RecordTy = dyn_cast<RecordType>(Ty)) {
-    CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordTy->getDecl());
-    if (Record->isCurrentInstantiation(CurContext))
-      return Record;
-
-    return nullptr;
-  } else if (isa<InjectedClassNameType>(Ty))
-    return cast<InjectedClassNameType>(Ty)->getDecl();
-  else
+  const TagType *TagTy = dyn_cast<TagType>(T->getCanonicalTypeInternal());
+  if (!isa_and_present<RecordType, InjectedClassNameType>(TagTy))
     return nullptr;
+  auto *RD =
+      cast<CXXRecordDecl>(TagTy->getOriginalDecl())->getDefinitionOrSelf();
+  if (isa<InjectedClassNameType>(TagTy) ||
+      RD->isCurrentInstantiation(CurContext))
+    return RD;
+  return nullptr;
 }
 
 DeclContext *Sema::computeDeclContext(QualType T) {
   if (!T->isDependentType())
-    if (const TagType *Tag = T->getAs<TagType>())
-      return Tag->getDecl();
-
+    if (auto *D = T->getAsTagDecl())
+      return D;
   return ::getCurrentInstantiationOf(T, CurContext);
 }
 
@@ -54,18 +51,17 @@ DeclContext *Sema::computeDeclContext(const CXXScopeSpec &SS,
   if (!SS.isSet() || SS.isInvalid())
     return nullptr;
 
-  NestedNameSpecifier *NNS = SS.getScopeRep();
-  if (NNS->isDependent()) {
+  NestedNameSpecifier NNS = SS.getScopeRep();
+  if (NNS.isDependent()) {
     // If this nested-name-specifier refers to the current
     // instantiation, return its DeclContext.
     if (CXXRecordDecl *Record = getCurrentInstantiationOf(NNS))
       return Record;
 
     if (EnteringContext) {
-      const Type *NNSType = NNS->getAsType();
-      if (!NNSType) {
+      if (NNS.getKind() != NestedNameSpecifier::Kind::Type)
         return nullptr;
-      }
+      const Type *NNSType = NNS.getAsType();
 
       // Look through type alias templates, per C++0x [temp.dep.type]p1.
       NNSType = Context.getCanonicalType(NNSType);
@@ -118,41 +114,39 @@ DeclContext *Sema::computeDeclContext(const CXXScopeSpec &SS,
           // If the type of the nested name specifier is the same as the
           // injected class name of the named class template, we're entering
           // into that class template definition.
-          QualType Injected =
-              ClassTemplate->getInjectedClassNameSpecialization();
+          CanQualType Injected =
+              ClassTemplate->getCanonicalInjectedSpecializationType(Context);
           if (Context.hasSameType(Injected, QualType(SpecType, 0)))
             return ClassTemplate->getTemplatedDecl();
         }
-      } else if (const RecordType *RecordT = NNSType->getAs<RecordType>()) {
+      } else if (const auto *RecordT = dyn_cast<RecordType>(NNSType)) {
         // The nested name specifier refers to a member of a class template.
-        return RecordT->getDecl();
+        return RecordT->getOriginalDecl()->getDefinitionOrSelf();
       }
     }
 
     return nullptr;
   }
 
-  switch (NNS->getKind()) {
-  case NestedNameSpecifier::Identifier:
-    llvm_unreachable("Dependent nested-name-specifier has no DeclContext");
-
-  case NestedNameSpecifier::Namespace:
-    return NNS->getAsNamespace();
-
-  case NestedNameSpecifier::NamespaceAlias:
-    return NNS->getAsNamespaceAlias()->getNamespace();
+  switch (NNS.getKind()) {
+  case NestedNameSpecifier::Kind::Namespace:
+    return const_cast<NamespaceDecl *>(
+        NNS.getAsNamespaceAndPrefix().Namespace->getNamespace());
 
-  case NestedNameSpecifier::TypeSpec: {
-    const TagType *Tag = NNS->getAsType()->getAs<TagType>();
-    assert(Tag && "Non-tag type in nested-name-specifier");
-    return Tag->getDecl();
+  case NestedNameSpecifier::Kind::Type: {
+    auto *TD = NNS.getAsType()->getAsTagDecl();
+    assert(TD && "Non-tag type in nested-name-specifier");
+    return TD;
   }
 
-  case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Kind::Global:
     return Context.getTranslationUnitDecl();
 
-  case NestedNameSpecifier::Super:
-    return NNS->getAsRecordDecl();
+  case NestedNameSpecifier::Kind::Super:
+    return NNS.getAsSuper();
+
+  case NestedNameSpecifier::Kind::Null:
+    llvm_unreachable("unexpected null nested name specifier");
   }
 
   llvm_unreachable("Invalid NestedNameSpecifier::Kind!");
@@ -162,17 +156,17 @@ bool Sema::isDependentScopeSpecifier(const CXXScopeSpec &SS) {
   if (!SS.isSet() || SS.isInvalid())
     return false;
 
-  return SS.getScopeRep()->isDependent();
+  return SS.getScopeRep().isDependent();
 }
 
-CXXRecordDecl *Sema::getCurrentInstantiationOf(NestedNameSpecifier *NNS) {
+CXXRecordDecl *Sema::getCurrentInstantiationOf(NestedNameSpecifier NNS) {
   assert(getLangOpts().CPlusPlus && "Only callable in C++");
-  assert(NNS->isDependent() && "Only dependent nested-name-specifier allowed");
+  assert(NNS.isDependent() && "Only dependent nested-name-specifier allowed");
 
-  if (!NNS->getAsType())
+  if (NNS.getKind() != NestedNameSpecifier::Kind::Type)
     return nullptr;
 
-  QualType T = QualType(NNS->getAsType(), 0);
+  QualType T = QualType(NNS.getAsType(), 0);
   return ::getCurrentInstantiationOf(T, CurContext);
 }
 
@@ -198,8 +192,7 @@ bool Sema::RequireCompleteDeclContext(CXXScopeSpec &SS,
     return false;
 
   // Grab the tag definition, if there is one.
-  QualType type = Context.getTypeDeclType(tag);
-  tag = type->getAsTagDecl();
+  tag = tag->getDefinitionOrSelf();
 
   // If we're currently defining this type, then lookup into the
   // type is okay: don't complain that it isn't complete yet.
@@ -210,7 +203,8 @@ bool Sema::RequireCompleteDeclContext(CXXScopeSpec &SS,
   if (loc.isInvalid()) loc = SS.getRange().getBegin();
 
   // The type must be complete.
-  if (RequireCompleteType(loc, type, diag::err_incomplete_nested_name_spec,
+  if (RequireCompleteType(loc, Context.getCanonicalTagType(tag),
+                          diag::err_incomplete_nested_name_spec,
                           SS.getRange())) {
     SS.SetInvalid(SS.getRange());
     return true;
@@ -262,10 +256,10 @@ bool Sema::RequireCompleteEnumDecl(EnumDecl *EnumD, SourceLocation L,
 
   if (SS) {
     Diag(L, diag::err_incomplete_nested_name_spec)
-        << QualType(EnumD->getTypeForDecl(), 0) << SS->getRange();
+        << Context.getCanonicalTagType(EnumD) << SS->getRange();
     SS->SetInvalid(SS->getRange());
   } else {
-    Diag(L, diag::err_incomplete_enum) << QualType(EnumD->getTypeForDecl(), 0);
+    Diag(L, diag::err_incomplete_enum) << Context.getCanonicalTagType(EnumD);
     Diag(EnumD->getLocation(), diag::note_declared_at);
   }
 
@@ -327,9 +321,6 @@ bool Sema::isAcceptableNestedNameSpecifier(const NamedDecl *SD,
 
   // Determine whether we have a class (or, in C++11, an enum) or
   // a typedef thereof. If so, build the nested-name-specifier.
-  QualType T = Context.getTypeDeclType(cast<TypeDecl>(SD));
-  if (T->isDependentType())
-    return true;
   if (const TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(SD)) {
     if (TD->getUnderlyingType()->isRecordType())
       return true;
@@ -347,32 +338,42 @@ bool Sema::isAcceptableNestedNameSpecifier(const NamedDecl *SD,
     if (IsExtension)
       *IsExtension = true;
   }
+  if (auto *TD = dyn_cast<TagDecl>(SD)) {
+    if (TD->isDependentType())
+      return true;
+  } else if (Context.getCanonicalTypeDeclType(cast<TypeDecl>(SD))
+                 ->isDependentType()) {
+    return true;
+  }
 
   return false;
 }
 
-NamedDecl *Sema::FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS) {
-  if (!S || !NNS)
+NamedDecl *Sema::FindFirstQualifierInScope(Scope *S, NestedNameSpecifier NNS) {
+  if (!S)
     return nullptr;
 
-  while (NNS->getPrefix())
-    NNS = NNS->getPrefix();
-
-  if (NNS->getKind() != NestedNameSpecifier::Identifier)
-    return nullptr;
+  while (NNS.getKind() == NestedNameSpecifier::Kind::Type) {
+    const Type *T = NNS.getAsType();
+    if ((NNS = T->getPrefix()))
+      continue;
 
-  LookupResult Found(*this, NNS->getAsIdentifier(), SourceLocation(),
-                     LookupNestedNameSpecifierName);
-  LookupName(Found, S);
-  assert(!Found.isAmbiguous() && "Cannot handle ambiguities here yet");
+    const auto *DNT = dyn_cast<DependentNameType>(T);
+    if (!DNT)
+      break;
 
-  if (!Found.isSingleResult())
-    return nullptr;
+    LookupResult Found(*this, DNT->getIdentifier(), SourceLocation(),
+                       LookupNestedNameSpecifierName);
+    LookupName(Found, S);
+    assert(!Found.isAmbiguous() && "Cannot handle ambiguities here yet");
 
-  NamedDecl *Result = Found.getFoundDecl();
-  if (isAcceptableNestedNameSpecifier(Result))
-    return Result;
+    if (!Found.isSingleResult())
+      return nullptr;
 
+    NamedDecl *Result = Found.getFoundDecl();
+    if (isAcceptableNestedNameSpecifier(Result))
+      return Result;
+  }
   return nullptr;
 }
 
@@ -496,7 +497,18 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
     // base object type or prior nested-name-specifier, so this
     // nested-name-specifier refers to an unknown specialization. Just build
     // a dependent nested-name-specifier.
-    SS.Extend(Context, IdInfo.Identifier, IdInfo.IdentifierLoc, IdInfo.CCLoc);
+
+    TypeLocBuilder TLB;
+
+    QualType DTN = Context.getDependentNameType(
+        ElaboratedTypeKeyword::None, SS.getScopeRep(), IdInfo.Identifier);
+    auto DTNL = TLB.push<DependentNameTypeLoc>(DTN);
+    DTNL.setElaboratedKeywordLoc(SourceLocation());
+    DTNL.setNameLoc(IdInfo.IdentifierLoc);
+    DTNL.setQualifierLoc(SS.getWithLocInContext(Context));
+
+    SS.clear();
+    SS.Make(Context, TLB.getTypeLocInContext(Context, DTN), IdInfo.CCLoc);
     return false;
   }
 
@@ -602,8 +614,8 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
           OuterDecl->getCanonicalDecl() != SD->getCanonicalDecl() &&
           (!isa<TypeDecl>(OuterDecl) || !isa<TypeDecl>(SD) ||
            !Context.hasSameType(
-                            Context.getTypeDeclType(cast<TypeDecl>(OuterDecl)),
-                               Context.getTypeDeclType(cast<TypeDecl>(SD))))) {
+               Context.getCanonicalTypeDeclType(cast<TypeDecl>(OuterDecl)),
+               Context.getCanonicalTypeDeclType(cast<TypeDecl>(SD))))) {
         if (ErrorRecoveryLookup)
           return true;
 
@@ -616,7 +628,7 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
 
          // Fall through so that we'll pick the name we found in the object
          // type, since that's probably what the user wanted anyway.
-       }
+      }
     }
 
     if (auto *TD = dyn_cast_or_null<TypedefNameDecl>(SD))
@@ -640,50 +652,44 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
       return false;
     }
 
-    QualType T =
-        Context.getTypeDeclType(cast<TypeDecl>(SD->getUnderlyingDecl()));
-
-    if (T->isEnumeralType())
+    const auto *TD = cast<TypeDecl>(SD->getUnderlyingDecl());
+    if (isa<EnumDecl>(TD))
       Diag(IdInfo.IdentifierLoc, diag::warn_cxx98_compat_enum_nested_name_spec);
 
+    QualType T;
     TypeLocBuilder TLB;
     if (const auto *USD = dyn_cast<UsingShadowDecl>(SD)) {
-      T = Context.getUsingType(USD, T);
-      TLB.pushTypeSpec(T).setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<InjectedClassNameType>(T)) {
-      InjectedClassNameTypeLoc InjectedTL
-        = TLB.push<InjectedClassNameTypeLoc>(T);
-      InjectedTL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<RecordType>(T)) {
-      RecordTypeLoc RecordTL = TLB.push<RecordTypeLoc>(T);
-      RecordTL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<TypedefType>(T)) {
-      TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(T);
-      TypedefTL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<EnumType>(T)) {
-      EnumTypeLoc EnumTL = TLB.push<EnumTypeLoc>(T);
-      EnumTL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<TemplateTypeParmType>(T)) {
-      TemplateTypeParmTypeLoc TemplateTypeTL
-        = TLB.push<TemplateTypeParmTypeLoc>(T);
-      TemplateTypeTL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<UnresolvedUsingType>(T)) {
-      UnresolvedUsingTypeLoc UnresolvedTL
-        = TLB.push<UnresolvedUsingTypeLoc>(T);
-      UnresolvedTL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<SubstTemplateTypeParmType>(T)) {
-      SubstTemplateTypeParmTypeLoc TL
-        = TLB.push<SubstTemplateTypeParmTypeLoc>(T);
-      TL.setNameLoc(IdInfo.IdentifierLoc);
-    } else if (isa<SubstTemplateTypeParmPackType>(T)) {
-      SubstTemplateTypeParmPackTypeLoc TL
-        = TLB.push<SubstTemplateTypeParmPackTypeLoc>(T);
-      TL.setNameLoc(IdInfo.IdentifierLoc);
+      T = Context.getUsingType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
+                               USD);
+      TLB.push<UsingTypeLoc>(T).set(/*ElaboratedKeywordLoc=*/SourceLocation(),
+                                    SS.getWithLocInContext(Context),
+                                    IdInfo.IdentifierLoc);
+    } else if (const auto *Tag = dyn_cast<TagDecl>(TD)) {
+      T = Context.getTagType(ElaboratedTypeKeyword::None, SS.getScopeRep(), Tag,
+                             /*OwnsTag=*/false);
+      auto TTL = TLB.push<TagTypeLoc>(T);
+      TTL.setElaboratedKeywordLoc(SourceLocation());
+      TTL.setQualifierLoc(SS.getWithLocInContext(SemaRef.Context));
+      TTL.setNameLoc(IdInfo.IdentifierLoc);
+    } else if (auto *TN = dyn_cast<TypedefNameDecl>(TD)) {
+      T = Context.getTypedefType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
+                                 TN);
+      TLB.push<TypedefTypeLoc>(T).set(/*ElaboratedKeywordLoc=*/SourceLocation(),
+                                      SS.getWithLocInContext(SemaRef.Context),
+                                      IdInfo.IdentifierLoc);
+    } else if (auto *UD = dyn_cast<UnresolvedUsingTypenameDecl>(TD)) {
+      T = Context.getUnresolvedUsingType(ElaboratedTypeKeyword::None,
+                                         SS.getScopeRep(), UD);
+      TLB.push<UnresolvedUsingTypeLoc>(T).set(
+          /*ElaboratedKeywordLoc=*/SourceLocation(),
+          SS.getWithLocInContext(SemaRef.Context), IdInfo.IdentifierLoc);
     } else {
-      llvm_unreachable("Unhandled TypeDecl node in nested-name-specifier");
+      assert(SS.isEmpty());
+      T = Context.getTypeDeclType(TD);
+      TLB.pushTypeSpec(T).setNameLoc(IdInfo.IdentifierLoc);
     }
-
-    SS.Extend(Context, TLB.getTypeLocInContext(Context, T), IdInfo.CCLoc);
+    SS.clear();
+    SS.Make(Context, TLB.getTypeLocInContext(Context, T), IdInfo.CCLoc);
     return false;
   }
 
@@ -725,16 +731,34 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
         Diag(IdInfo.IdentifierLoc,
              diag::ext_undeclared_unqual_id_with_dependent_base)
             << IdInfo.Identifier << ContainingClass;
+
+        TypeLocBuilder TLB;
+
         // Fake up a nested-name-specifier that starts with the
         // injected-class-name of the enclosing class.
-        QualType T = Context.getTypeDeclType(ContainingClass);
-        TypeLocBuilder TLB;
-        TLB.pushTrivial(Context, T, IdInfo.IdentifierLoc);
-        SS.Extend(Context, TLB.getTypeLocInContext(Context, T),
-                  IdInfo.IdentifierLoc);
-        // Add the identifier to form a dependent name.
-        SS.Extend(Context, IdInfo.Identifier, IdInfo.IdentifierLoc,
-                  IdInfo.CCLoc);
+        // FIXME: This should be done as part of an adjustment, so that this
+        // doesn't get confused with something written in source.
+        QualType Result =
+            Context.getTagType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
+                               ContainingClass, /*OwnsTag=*/false);
+        auto TTL = TLB.push<TagTypeLoc>(Result);
+        TTL.setElaboratedKeywordLoc(SourceLocation());
+        TTL.setQualifierLoc(SS.getWithLocInContext(Context));
+        TTL.setNameLoc(IdInfo.IdentifierLoc);
+        SS.Make(Context, TLB.getTypeLocInContext(Context, Result),
+                SourceLocation());
+
+        TLB.clear();
+
+        // Form a DependentNameType.
+        QualType DTN = Context.getDependentNameType(
+            ElaboratedTypeKeyword::None, SS.getScopeRep(), IdInfo.Identifier);
+        auto DTNL = TLB.push<DependentNameTypeLoc>(DTN);
+        DTNL.setElaboratedKeywordLoc(SourceLocation());
+        DTNL.setNameLoc(IdInfo.IdentifierLoc);
+        DTNL.setQualifierLoc(SS.getWithLocInContext(Context));
+        SS.clear();
+        SS.Make(Context, TLB.getTypeLocInContext(Context, DTN), IdInfo.CCLoc);
         return false;
       }
     }
@@ -742,8 +766,19 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
 
   if (!Found.empty()) {
     if (TypeDecl *TD = Found.getAsSingle<TypeDecl>()) {
+      QualType T;
+      if (auto *TN = dyn_cast<TypedefNameDecl>(TD)) {
+        T = Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                   SS.getScopeRep(), TN);
+      } else {
+        // FIXME: Enumerate the possibilities here.
+        assert(!isa<TagDecl>(TD));
+        assert(SS.isEmpty());
+        T = Context.getTypeDeclType(TD);
+      }
+
       Diag(IdInfo.IdentifierLoc, diag::err_expected_class_or_namespace)
-          << Context.getTypeDeclType(TD) << getLangOpts().CPlusPlus;
+          << T << getLangOpts().CPlusPlus;
     } else if (Found.getAsSingle<TemplateDecl>()) {
       ParsedType SuggestedType;
       DiagnoseUnknownTypeName(IdInfo.Identifier, IdInfo.IdentifierLoc, S, &SS,
@@ -789,17 +824,19 @@ bool Sema::ActOnCXXNestedNameSpecifierDecltype(CXXScopeSpec &SS,
   if (T.isNull())
     return true;
 
-  if (!T->isDependentType() && !T->getAs<TagType>()) {
+  if (!T->isDependentType() && !isa<TagType>(T.getCanonicalType())) {
     Diag(DS.getTypeSpecTypeLoc(), diag::err_expected_class_or_namespace)
       << T << getLangOpts().CPlusPlus;
     return true;
   }
 
+  assert(SS.isEmpty());
+
   TypeLocBuilder TLB;
   DecltypeTypeLoc DecltypeTL = TLB.push<DecltypeTypeLoc>(T);
   DecltypeTL.setDecltypeLoc(DS.getTypeSpecTypeLoc());
   DecltypeTL.setRParenLoc(DS.getTypeofParensRange().getEnd());
-  SS.Extend(Context, TLB.getTypeLocInContext(Context, T), ColonColonLoc);
+  SS.Make(Context, TLB.getTypeLocInContext(Context, T), ColonColonLoc);
   return false;
 }
 
@@ -815,13 +852,15 @@ bool Sema::ActOnCXXNestedNameSpecifierIndexedPack(CXXScopeSpec &SS,
   if (Type.isNull())
     return true;
 
+  assert(SS.isEmpty());
+
   TypeLocBuilder TLB;
   TLB.pushTrivial(getASTContext(),
                   cast<PackIndexingType>(Type.getTypePtr())->getPattern(),
                   DS.getBeginLoc());
   PackIndexingTypeLoc PIT = TLB.push<PackIndexingTypeLoc>(Type);
   PIT.setEllipsisLoc(DS.getEllipsisLoc());
-  SS.Extend(Context, TLB.getTypeLocInContext(Context, Type), ColonColonLoc);
+  SS.Make(Context, TLB.getTypeLocInContext(Context, Type), ColonColonLoc);
   return false;
 }
 
@@ -861,7 +900,7 @@ bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
     assert(DTN->getQualifier() == SS.getScopeRep());
     QualType T = Context.getDependentTemplateSpecializationType(
         ElaboratedTypeKeyword::None,
-        {/*Qualifier=*/nullptr, DTN->getName().getIdentifier(),
+        {SS.getScopeRep(), DTN->getName().getIdentifier(),
          TemplateKWLoc.isValid()},
         TemplateArgs.arguments());
 
@@ -870,7 +909,7 @@ bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
     DependentTemplateSpecializationTypeLoc SpecTL
       = Builder.push<DependentTemplateSpecializationTypeLoc>(T);
     SpecTL.setElaboratedKeywordLoc(SourceLocation());
-    SpecTL.setQualifierLoc(NestedNameSpecifierLoc());
+    SpecTL.setQualifierLoc(SS.getWithLocInContext(Context));
     SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
     SpecTL.setTemplateNameLoc(TemplateNameLoc);
     SpecTL.setLAngleLoc(LAngleLoc);
@@ -878,7 +917,8 @@ bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
     for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
       SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
 
-    SS.Extend(Context, Builder.getTypeLocInContext(Context, T), CCLoc);
+    SS.clear();
+    SS.Make(Context, Builder.getTypeLocInContext(Context, T), CCLoc);
     return false;
   }
 
@@ -903,30 +943,28 @@ bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,
 
   // We were able to resolve the template name to an actual template.
   // Build an appropriate nested-name-specifier.
-  QualType T = CheckTemplateIdType(Template, TemplateNameLoc, TemplateArgs);
+  QualType T = CheckTemplateIdType(ElaboratedTypeKeyword::None, Template,
+                                   TemplateNameLoc, TemplateArgs);
   if (T.isNull())
     return true;
 
   // Alias template specializations can produce types which are not valid
   // nested name specifiers.
-  if (!T->isDependentType() && !T->getAs<TagType>()) {
+  if (!T->isDependentType() && !isa<TagType>(T.getCanonicalType())) {
     Diag(TemplateNameLoc, diag::err_nested_name_spec_non_tag) << T;
     NoteAllFoundTemplates(Template);
     return true;
   }
 
   // Provide source-location information for the template specialization type.
-  TypeLocBuilder Builder;
-  TemplateSpecializationTypeLoc SpecTL
-    = Builder.push<TemplateSpecializationTypeLoc>(T);
-  SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
-  SpecTL.setTemplateNameLoc(TemplateNameLoc);
-  SpecTL.setLAngleLoc(LAngleLoc);
-  SpecTL.setRAngleLoc(RAngleLoc);
-  for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
-    SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
-
-  SS.Extend(Context, Builder.getTypeLocInContext(Context, T), CCLoc);
+  TypeLocBuilder TLB;
+  TLB.push<TemplateSpecializationTypeLoc>(T).set(
+      /*ElaboratedKeywordLoc=*/SourceLocation(),
+      SS.getWithLocInContext(Context), TemplateKWLoc, TemplateNameLoc,
+      TemplateArgs);
+
+  SS.clear();
+  SS.Make(Context, TLB.getTypeLocInContext(Context, T), CCLoc);
   return false;
 }
 
@@ -934,7 +972,7 @@ namespace {
   /// A structure that stores a nested-name-specifier annotation,
   /// including both the nested-name-specifier
   struct NestedNameSpecifierAnnotation {
-    NestedNameSpecifier *NNS;
+    NestedNameSpecifier NNS = std::nullopt;
   };
 }
 
@@ -973,8 +1011,6 @@ bool Sema::ShouldEnterDeclaratorScope(Scope *S, const CXXScopeSpec &SS) {
   if (isa<ObjCContainerDecl>(CurContext) || isa<ObjCMethodDecl>(CurContext))
     return false;
 
-  NestedNameSpecifier *Qualifier = SS.getScopeRep();
-
   // There are only two places a well-formed program may qualify a
   // declarator: first, when defining a namespace or class member
   // out-of-line, and second, when naming an explicitly-qualified
@@ -989,19 +1025,20 @@ bool Sema::ShouldEnterDeclaratorScope(Scope *S, const CXXScopeSpec &SS) {
   //   granting friendship.
   // i.e. we don't push a scope unless it's a class member.
 
-  switch (Qualifier->getKind()) {
-  case NestedNameSpecifier::Global:
-  case NestedNameSpecifier::Namespace:
-  case NestedNameSpecifier::NamespaceAlias:
+  switch (SS.getScopeRep().getKind()) {
+  case NestedNameSpecifier::Kind::Global:
+  case NestedNameSpecifier::Kind::Namespace:
     // These are always namespace scopes.  We never want to enter a
     // namespace scope from anything but a file context.
     return CurContext->getRedeclContext()->isFileContext();
 
-  case NestedNameSpecifier::Identifier:
-  case NestedNameSpecifier::TypeSpec:
-  case NestedNameSpecifier::Super:
+  case NestedNameSpecifier::Kind::Type:
+  case NestedNameSpecifier::Kind::Super:
     // These are never namespace scopes.
     return true;
+
+  case NestedNameSpecifier::Kind::Null:
+    llvm_unreachable("unexpected null nested name specifier");
   }
 
   llvm_unreachable("Invalid NestedNameSpecifier::Kind!");
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 01252a4bc69c6..da43848a1a7d0 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -964,7 +964,7 @@ void CastOperation::CheckDynamicCast() {
   }
 
   // C++ 5.2.7p6: Otherwise, v shall be [polymorphic].
-  const RecordDecl *SrcDecl = SrcRecord->getDecl()->getDefinition();
+  const RecordDecl *SrcDecl = SrcRecord->getOriginalDecl()->getDefinition();
   assert(SrcDecl && "Definition missing");
   if (!cast<CXXRecordDecl>(SrcDecl)->isPolymorphic()) {
     Self.Diag(OpRange.getBegin(), diag::err_bad_dynamic_cast_not_polymorphic)
@@ -1455,7 +1455,7 @@ static TryCastResult TryStaticCast(Sema &Self, ExprResult &SrcExpr,
   // converted to an integral type. [...] A value of a scoped enumeration type
   // can also be explicitly converted to a floating-point type [...].
   if (const EnumType *Enum = SrcType->getAs<EnumType>()) {
-    if (Enum->getDecl()->isScoped()) {
+    if (Enum->getOriginalDecl()->isScoped()) {
       if (DestType->isBooleanType()) {
         Kind = CK_IntegralToBoolean;
         return TC_Success;
@@ -1487,8 +1487,8 @@ static TryCastResult TryStaticCast(Sema &Self, ExprResult &SrcExpr,
       // [expr.static.cast]p10 If the enumeration type has a fixed underlying
       // type, the value is first converted to that type by integral conversion
       const EnumType *Enum = DestType->castAs<EnumType>();
-      Kind = Enum->getDecl()->isFixed() &&
-                     Enum->getDecl()->getIntegerType()->isBooleanType()
+      const EnumDecl *ED = Enum->getOriginalDecl()->getDefinitionOrSelf();
+      Kind = ED->isFixed() && ED->getIntegerType()->isBooleanType()
                  ? CK_IntegralToBoolean
                  : CK_IntegralCast;
       return TC_Success;
@@ -1856,7 +1856,7 @@ TryCastResult TryStaticMemberPointerUpcast(Sema &Self, ExprResult &SrcExpr,
                                                     FoundOverload)) {
       CXXMethodDecl *M = cast<CXXMethodDecl>(Fn);
       SrcType = Self.Context.getMemberPointerType(
-          Fn->getType(), /*Qualifier=*/nullptr, M->getParent());
+          Fn->getType(), /*Qualifier=*/std::nullopt, M->getParent());
       WasOverloadedFunction = true;
     }
   }
@@ -2102,9 +2102,9 @@ void Sema::CheckCompatibleReinterpretCast(QualType SrcType, QualType DestType,
     return;
   }
   // or one of the types is a tag type.
-  if (SrcTy->getAs<TagType>() || DestTy->getAs<TagType>()) {
+  if (isa<TagType>(SrcTy.getCanonicalType()) ||
+      isa<TagType>(DestTy.getCanonicalType()))
     return;
-  }
 
   // FIXME: Scoped enums?
   if ((SrcTy->isUnsignedIntegerType() && DestTy->isSignedIntegerType()) ||
@@ -3097,27 +3097,26 @@ void CastOperation::CheckCStyleCast() {
 
   if (!DestType->isScalarType() && !DestType->isVectorType() &&
       !DestType->isMatrixType()) {
-    const RecordType *DestRecordTy = DestType->getAs<RecordType>();
-
-    if (DestRecordTy && Self.Context.hasSameUnqualifiedType(DestType, SrcType)){
-      // GCC struct/union extension: allow cast to self.
-      Self.Diag(OpRange.getBegin(), diag::ext_typecheck_cast_nonscalar)
-        << DestType << SrcExpr.get()->getSourceRange();
-      Kind = CK_NoOp;
-      return;
-    }
-
-    // GCC's cast to union extension.
-    if (DestRecordTy && DestRecordTy->getDecl()->isUnion()) {
-      RecordDecl *RD = DestRecordTy->getDecl();
-      if (CastExpr::getTargetFieldForToUnionCast(RD, SrcType)) {
-        Self.Diag(OpRange.getBegin(), diag::ext_typecheck_cast_to_union)
-          << SrcExpr.get()->getSourceRange();
-        Kind = CK_ToUnion;
+    if (const RecordType *DestRecordTy = DestType->getAs<RecordType>()) {
+      if (Self.Context.hasSameUnqualifiedType(DestType, SrcType)) {
+        // GCC struct/union extension: allow cast to self.
+        Self.Diag(OpRange.getBegin(), diag::ext_typecheck_cast_nonscalar)
+            << DestType << SrcExpr.get()->getSourceRange();
+        Kind = CK_NoOp;
         return;
-      } else {
+      }
+
+      // GCC's cast to union extension.
+      if (RecordDecl *RD = DestRecordTy->getOriginalDecl(); RD->isUnion()) {
+        if (CastExpr::getTargetFieldForToUnionCast(RD->getDefinitionOrSelf(),
+                                                   SrcType)) {
+          Self.Diag(OpRange.getBegin(), diag::ext_typecheck_cast_to_union)
+              << SrcExpr.get()->getSourceRange();
+          Kind = CK_ToUnion;
+          return;
+        }
         Self.Diag(OpRange.getBegin(), diag::err_typecheck_cast_to_union_no_type)
-          << SrcType << SrcExpr.get()->getSourceRange();
+            << SrcType << SrcExpr.get()->getSourceRange();
         SrcExpr = ExprError();
         return;
       }
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index dd5b710d7e1d4..f4daa8f506ccf 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -603,7 +603,7 @@ struct BuiltinDumpStructGenerator {
 
   bool dumpUnnamedRecord(const RecordDecl *RD, Expr *E, unsigned Depth) {
     Expr *IndentLit = getIndentString(Depth);
-    Expr *TypeLit = getTypeString(S.Context.getRecordType(RD));
+    Expr *TypeLit = getTypeString(S.Context.getCanonicalTagType(RD));
     if (IndentLit ? callPrintFunction("%s%s", {IndentLit, TypeLit})
                   : callPrintFunction("%s", {TypeLit}))
       return true;
@@ -2288,7 +2288,7 @@ static ExprResult BuiltinInvoke(Sema &S, CallExpr *TheCall) {
       return ExprError();
     }
 
-    const Type *MemPtrClass = MPT->getQualifier()->getAsType();
+    const Type *MemPtrClass = MPT->getQualifier().getAsType();
     QualType ObjectT = Args[1]->getType();
 
     if (MPT->isMemberDataPointer() && S.checkArgCount(TheCall, 2))
@@ -3315,7 +3315,9 @@ static bool CheckNonNullExpr(Sema &S, const Expr *Expr) {
   // As a special case, transparent unions initialized with zero are
   // considered null for the purposes of the nonnull attribute.
   if (const RecordType *UT = Expr->getType()->getAsUnionType();
-      UT && UT->getDecl()->hasAttr<TransparentUnionAttr>()) {
+      UT && UT->getOriginalDecl()
+                ->getMostRecentDecl()
+                ->hasAttr<TransparentUnionAttr>()) {
     if (const auto *CLE = dyn_cast<CompoundLiteralExpr>(Expr))
       if (const auto *ILE = dyn_cast<InitListExpr>(CLE->getInitializer()))
         Expr = ILE->getInit(0);
@@ -5172,7 +5174,9 @@ bool Sema::BuiltinVAStart(unsigned BuiltinID, CallExpr *TheCall) {
                return false;
              if (!Type->isEnumeralType())
                return true;
-             const EnumDecl *ED = Type->castAs<EnumType>()->getDecl();
+             const EnumDecl *ED = Type->castAs<EnumType>()
+                                      ->getOriginalDecl()
+                                      ->getDefinitionOrSelf();
              return !(ED &&
                       Context.typesAreCompatible(ED->getPromotionType(), Type));
            }()) {
@@ -7786,8 +7790,11 @@ CXXRecordMembersNamed(StringRef Name, Sema &S, QualType Ty) {
 
   if (!RT)
     return Results;
-  const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(RT->getDecl());
-  if (!RD || !RD->getDefinition())
+  CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl());
+  if (!RD)
+    return Results;
+  RD = RD->getDefinition();
+  if (!RD)
     return Results;
 
   LookupResult R(S, &S.Context.Idents.get(Name), SourceLocation(),
@@ -7796,7 +7803,7 @@ CXXRecordMembersNamed(StringRef Name, Sema &S, QualType Ty) {
 
   // We just need to include all members of the right kind turned up by the
   // filter, at this point.
-  if (S.LookupQualifiedName(R, RT->getDecl()))
+  if (S.LookupQualifiedName(R, RD))
     for (LookupResult::iterator I = R.begin(), E = R.end(); I != E; ++I) {
       NamedDecl *decl = (*I)->getUnderlyingDecl();
       if (MemberKind *FK = dyn_cast<MemberKind>(decl))
@@ -8323,7 +8330,8 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
   bool IsScopedEnum = false;
   QualType IntendedTy = ExprTy;
   if (auto EnumTy = ExprTy->getAs<EnumType>()) {
-    IntendedTy = EnumTy->getDecl()->getIntegerType();
+    IntendedTy =
+        EnumTy->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
     if (EnumTy->isUnscopedEnumerationType()) {
       ExprTy = IntendedTy;
       // This controls whether we're talking about the underlying type or not,
@@ -8359,7 +8367,9 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
         NamedDecl *ND = Result.getFoundDecl();
         if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(ND))
           if (TD->getUnderlyingType() == IntendedTy)
-            IntendedTy = S.Context.getTypedefType(TD);
+            IntendedTy =
+                S.Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                         /*Qualifier=*/std::nullopt, TD);
       }
     }
   }
@@ -9617,7 +9627,10 @@ struct SearchNonTrivialToInitializeField
     S.DiagRuntimeBehavior(SL, E, S.PDiag(diag::note_nontrivial_field) << 1);
   }
   void visitStruct(QualType FT, SourceLocation SL) {
-    for (const FieldDecl *FD : FT->castAs<RecordType>()->getDecl()->fields())
+    for (const FieldDecl *FD : FT->castAs<RecordType>()
+                                   ->getOriginalDecl()
+                                   ->getDefinitionOrSelf()
+                                   ->fields())
       visit(FD->getType(), FD->getLocation());
   }
   void visitArray(QualType::PrimitiveDefaultInitializeKind PDIK,
@@ -9662,7 +9675,10 @@ struct SearchNonTrivialToCopyField
     S.DiagRuntimeBehavior(SL, E, S.PDiag(diag::note_nontrivial_field) << 0);
   }
   void visitStruct(QualType FT, SourceLocation SL) {
-    for (const FieldDecl *FD : FT->castAs<RecordType>()->getDecl()->fields())
+    for (const FieldDecl *FD : FT->castAs<RecordType>()
+                                   ->getOriginalDecl()
+                                   ->getDefinitionOrSelf()
+                                   ->fields())
       visit(FD->getType(), FD->getLocation());
   }
   void visitArray(QualType::PrimitiveCopyKind PCK, const ArrayType *AT,
@@ -9943,8 +9959,9 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
           getLangOpts().CPlusPlus && !RT->isIncompleteType() &&
           !RT->desugar().isTriviallyCopyableType(Context);
 
+      const auto *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
       if ((BId == Builtin::BImemset || BId == Builtin::BIbzero) &&
-          RT->getDecl()->isNonTrivialToPrimitiveDefaultInitialize()) {
+          RD->isNonTrivialToPrimitiveDefaultInitialize()) {
         DiagRuntimeBehavior(Dest->getExprLoc(), Dest,
                             PDiag(diag::warn_cstruct_memaccess)
                                 << ArgIdx << FnName << PointeeTy << 0);
@@ -9957,7 +9974,7 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
                             PDiag(diag::warn_cxxstruct_memaccess)
                                 << FnName << PointeeTy);
       } else if ((BId == Builtin::BImemcpy || BId == Builtin::BImemmove) &&
-                 RT->getDecl()->isNonTrivialToPrimitiveCopy()) {
+                 RD->isNonTrivialToPrimitiveCopy()) {
         DiagRuntimeBehavior(Dest->getExprLoc(), Dest,
                             PDiag(diag::warn_cstruct_memaccess)
                                 << ArgIdx << FnName << PointeeTy << 1);
@@ -10463,10 +10480,14 @@ struct IntRange {
     if (!C.getLangOpts().CPlusPlus) {
       // For enum types in C code, use the underlying datatype.
       if (const auto *ET = dyn_cast<EnumType>(T))
-        T = ET->getDecl()->getIntegerType().getDesugaredType(C).getTypePtr();
+        T = ET->getOriginalDecl()
+                ->getDefinitionOrSelf()
+                ->getIntegerType()
+                .getDesugaredType(C)
+                .getTypePtr();
     } else if (const auto *ET = dyn_cast<EnumType>(T)) {
       // For enum types in C++, use the known bit width of the enumerators.
-      EnumDecl *Enum = ET->getDecl();
+      EnumDecl *Enum = ET->getOriginalDecl()->getDefinitionOrSelf();
       // In C++11, enums can have a fixed underlying type. Use this type to
       // compute the range.
       if (Enum->isFixed()) {
@@ -10508,7 +10529,9 @@ struct IntRange {
     if (const AtomicType *AT = dyn_cast<AtomicType>(T))
       T = AT->getValueType().getTypePtr();
     if (const EnumType *ET = dyn_cast<EnumType>(T))
-      T = C.getCanonicalType(ET->getDecl()->getIntegerType()).getTypePtr();
+      T = C.getCanonicalType(
+               ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType())
+              .getTypePtr();
 
     if (const auto *EIT = dyn_cast<BitIntType>(T))
       return IntRange(EIT->getNumBits(), EIT->isUnsigned());
@@ -11480,7 +11503,9 @@ static bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init,
      return false;
 
   if (BitfieldType->isEnumeralType()) {
-    EnumDecl *BitfieldEnumDecl = BitfieldType->castAs<EnumType>()->getDecl();
+    EnumDecl *BitfieldEnumDecl = BitfieldType->castAs<EnumType>()
+                                     ->getOriginalDecl()
+                                     ->getDefinitionOrSelf();
     // If the underlying enum type was not explicitly specified as an unsigned
     // type and the enum contain only positive values, MSVC++ will cause an
     // inconsistency by storing this as a signed type.
@@ -11517,7 +11542,7 @@ static bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init,
         EnumTy = PTAttr->getType()->getAs<EnumType>();
     }
     if (EnumTy) {
-      EnumDecl *ED = EnumTy->getDecl();
+      EnumDecl *ED = EnumTy->getOriginalDecl()->getDefinitionOrSelf();
       bool SignedBitfield = BitfieldType->isSignedIntegerOrEnumerationType();
 
       // Enum types are implicitly signed on Windows, so check if there are any
@@ -12583,8 +12608,8 @@ void Sema::CheckImplicitConversion(Expr *E, QualType T, SourceLocation CC,
 
   if (const EnumType *SourceEnum = Source->getAs<EnumType>())
     if (const EnumType *TargetEnum = Target->getAs<EnumType>())
-      if (SourceEnum->getDecl()->hasNameForLinkage() &&
-          TargetEnum->getDecl()->hasNameForLinkage() &&
+      if (SourceEnum->getOriginalDecl()->hasNameForLinkage() &&
+          TargetEnum->getOriginalDecl()->hasNameForLinkage() &&
           SourceEnum != TargetEnum) {
         if (SourceMgr.isInSystemMacro(CC))
           return;
@@ -15108,10 +15133,9 @@ static bool isLayoutCompatible(const ASTContext &C, const EnumDecl *ED1,
 static bool isLayoutCompatible(const ASTContext &C, const FieldDecl *Field1,
                                const FieldDecl *Field2,
                                bool AreUnionMembers = false) {
-  [[maybe_unused]] const Type *Field1Parent =
-      Field1->getParent()->getTypeForDecl();
-  [[maybe_unused]] const Type *Field2Parent =
-      Field2->getParent()->getTypeForDecl();
+#ifndef NDEBUG
+  CanQualType Field1Parent = C.getCanonicalTagType(Field1->getParent());
+  CanQualType Field2Parent = C.getCanonicalTagType(Field2->getParent());
   assert(((Field1Parent->isStructureOrClassType() &&
            Field2Parent->isStructureOrClassType()) ||
           (Field1Parent->isUnionType() && Field2Parent->isUnionType())) &&
@@ -15120,6 +15144,7 @@ static bool isLayoutCompatible(const ASTContext &C, const FieldDecl *Field1,
   assert(((!AreUnionMembers && Field1Parent->isStructureOrClassType()) ||
           (AreUnionMembers && Field1Parent->isUnionType())) &&
          "AreUnionMembers should be 'true' for union fields (only).");
+#endif
 
   if (!isLayoutCompatible(C, Field1->getType(), Field2->getType()))
     return false;
@@ -15224,16 +15249,16 @@ static bool isLayoutCompatible(const ASTContext &C, QualType T1, QualType T2) {
     return false;
 
   if (TC1 == Type::Enum) {
-    return isLayoutCompatible(C,
-                              cast<EnumType>(T1)->getDecl(),
-                              cast<EnumType>(T2)->getDecl());
+    return isLayoutCompatible(
+        C, cast<EnumType>(T1)->getOriginalDecl()->getDefinitionOrSelf(),
+        cast<EnumType>(T2)->getOriginalDecl()->getDefinitionOrSelf());
   } else if (TC1 == Type::Record) {
     if (!T1->isStandardLayoutType() || !T2->isStandardLayoutType())
       return false;
 
-    return isLayoutCompatible(C,
-                              cast<RecordType>(T1)->getDecl(),
-                              cast<RecordType>(T2)->getDecl());
+    return isLayoutCompatible(
+        C, cast<RecordType>(T1)->getOriginalDecl()->getDefinitionOrSelf(),
+        cast<RecordType>(T2)->getOriginalDecl()->getDefinitionOrSelf());
   }
 
   return false;
@@ -15587,7 +15612,9 @@ void Sema::RefersToMemberWithReducedAlignment(
       return;
     if (ME->isArrow())
       BaseType = BaseType->getPointeeType();
-    RecordDecl *RD = BaseType->castAs<RecordType>()->getDecl();
+    RecordDecl *RD = BaseType->castAs<RecordType>()
+                         ->getOriginalDecl()
+                         ->getDefinitionOrSelf();
     if (RD->isInvalidDecl())
       return;
 
@@ -15632,7 +15659,7 @@ void Sema::RefersToMemberWithReducedAlignment(
 
   // Compute the CompleteObjectAlignment as the alignment of the whole chain.
   CharUnits CompleteObjectAlignment = Context.getTypeAlignInChars(
-      ReverseMemberChain.back()->getParent()->getTypeForDecl());
+      Context.getCanonicalTagType(ReverseMemberChain.back()->getParent()));
 
   // The base expression of the innermost MemberExpr may give
   // stronger guarantees than the class containing the member.
@@ -15662,9 +15689,9 @@ void Sema::RefersToMemberWithReducedAlignment(
       if (FDI->hasAttr<PackedAttr>() ||
           FDI->getParent()->hasAttr<PackedAttr>()) {
         FD = FDI;
-        Alignment = std::min(
-            Context.getTypeAlignInChars(FD->getType()),
-            Context.getTypeAlignInChars(FD->getParent()->getTypeForDecl()));
+        Alignment = std::min(Context.getTypeAlignInChars(FD->getType()),
+                             Context.getTypeAlignInChars(
+                                 Context.getCanonicalTagType(FD->getParent())));
         break;
       }
     }
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index a43ac9eb7610d..99492cea4e6c2 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -732,7 +732,7 @@ ResultBuilder::ShadowMapEntry::end() const {
 ///
 /// \returns a nested name specifier that refers into the target context, or
 /// NULL if no qualification is needed.
-static NestedNameSpecifier *
+static NestedNameSpecifier
 getRequiredQualification(ASTContext &Context, const DeclContext *CurContext,
                          const DeclContext *TargetContext) {
   SmallVector<const DeclContext *, 4> TargetParents;
@@ -747,7 +747,7 @@ getRequiredQualification(ASTContext &Context, const DeclContext *CurContext,
     TargetParents.push_back(CommonAncestor);
   }
 
-  NestedNameSpecifier *Result = nullptr;
+  NestedNameSpecifier Result = std::nullopt;
   while (!TargetParents.empty()) {
     const DeclContext *Parent = TargetParents.pop_back_val();
 
@@ -755,10 +755,12 @@ getRequiredQualification(ASTContext &Context, const DeclContext *CurContext,
       if (!Namespace->getIdentifier())
         continue;
 
-      Result = NestedNameSpecifier::Create(Context, Result, Namespace);
-    } else if (const auto *TD = dyn_cast<TagDecl>(Parent))
-      Result = NestedNameSpecifier::Create(
-          Context, Result, Context.getTypeDeclType(TD).getTypePtr());
+      Result = NestedNameSpecifier(Context, Namespace, Result);
+    } else if (const auto *TD = dyn_cast<TagDecl>(Parent)) {
+      QualType TT = Context.getTagType(ElaboratedTypeKeyword::None, Result, TD,
+                                       /*OwnsTag=*/false);
+      Result = NestedNameSpecifier(TT.getTypePtr());
+    }
   }
   return Result;
 }
@@ -937,11 +939,12 @@ SimplifiedTypeClass clang::getSimplifiedTypeClass(CanQualType T) {
 
 /// Get the type that a given expression will have if this declaration
 /// is used as an expression in its "typical" code-completion form.
-QualType clang::getDeclUsageType(ASTContext &C, const NamedDecl *ND) {
+QualType clang::getDeclUsageType(ASTContext &C, NestedNameSpecifier Qualifier,
+                                 const NamedDecl *ND) {
   ND = ND->getUnderlyingDecl();
 
   if (const auto *Type = dyn_cast<TypeDecl>(ND))
-    return C.getTypeDeclType(Type);
+    return C.getTypeDeclType(ElaboratedTypeKeyword::None, Qualifier, Type);
   if (const auto *Iface = dyn_cast<ObjCInterfaceDecl>(ND))
     return C.getObjCInterfaceType(Iface);
 
@@ -951,7 +954,9 @@ QualType clang::getDeclUsageType(ASTContext &C, const NamedDecl *ND) {
   else if (const auto *Method = dyn_cast<ObjCMethodDecl>(ND))
     T = Method->getSendResultType();
   else if (const auto *Enumerator = dyn_cast<EnumConstantDecl>(ND))
-    T = C.getTypeDeclType(cast<EnumDecl>(Enumerator->getDeclContext()));
+    T = C.getTagType(ElaboratedTypeKeyword::None, Qualifier,
+                     cast<EnumDecl>(Enumerator->getDeclContext()),
+                     /*OwnsTag=*/false);
   else if (const auto *Property = dyn_cast<ObjCPropertyDecl>(ND))
     T = Property->getType();
   else if (const auto *Value = dyn_cast<ValueDecl>(ND))
@@ -1053,7 +1058,7 @@ void ResultBuilder::AdjustResultPriorityForDecl(Result &R) {
   // If we have a preferred type, adjust the priority for results with exactly-
   // matching or nearly-matching types.
   if (!PreferredType.isNull()) {
-    QualType T = getDeclUsageType(SemaRef.Context, R.Declaration);
+    QualType T = getDeclUsageType(SemaRef.Context, R.Qualifier, R.Declaration);
     if (!T.isNull()) {
       CanQualType TC = SemaRef.Context.getCanonicalType(T);
       // Check for exactly-matching types (modulo qualifiers).
@@ -1070,10 +1075,9 @@ void ResultBuilder::AdjustResultPriorityForDecl(Result &R) {
 
 static DeclContext::lookup_result getConstructors(ASTContext &Context,
                                                   const CXXRecordDecl *Record) {
-  QualType RecordTy = Context.getTypeDeclType(Record);
+  CanQualType RecordTy = Context.getCanonicalTagType(Record);
   DeclarationName ConstructorName =
-      Context.DeclarationNames.getCXXConstructorName(
-          Context.getCanonicalType(RecordTy));
+      Context.DeclarationNames.getCXXConstructorName(RecordTy);
   return Record->lookup(ConstructorName);
 }
 
@@ -1216,11 +1220,13 @@ void ResultBuilder::MaybeAddResult(Result R, DeclContext *CurContext) {
     const DeclContext *Ctx = R.Declaration->getDeclContext();
     if (const NamespaceDecl *Namespace = dyn_cast<NamespaceDecl>(Ctx))
       R.Qualifier =
-          NestedNameSpecifier::Create(SemaRef.Context, nullptr, Namespace);
+          NestedNameSpecifier(SemaRef.Context, Namespace, std::nullopt);
     else if (const TagDecl *Tag = dyn_cast<TagDecl>(Ctx))
-      R.Qualifier = NestedNameSpecifier::Create(
-          SemaRef.Context, nullptr,
-          SemaRef.Context.getTypeDeclType(Tag).getTypePtr());
+      R.Qualifier = NestedNameSpecifier(
+          SemaRef.Context
+              .getTagType(ElaboratedTypeKeyword::None,
+                          /*Qualifier=*/std::nullopt, Tag, /*OwnsTag=*/false)
+              .getTypePtr());
     else
       R.QualifierIsInformative = false;
   }
@@ -1405,11 +1411,13 @@ void ResultBuilder::AddResult(Result R, DeclContext *CurContext,
     const DeclContext *Ctx = R.Declaration->getDeclContext();
     if (const auto *Namespace = dyn_cast<NamespaceDecl>(Ctx))
       R.Qualifier =
-          NestedNameSpecifier::Create(SemaRef.Context, nullptr, Namespace);
+          NestedNameSpecifier(SemaRef.Context, Namespace, std::nullopt);
     else if (const auto *Tag = dyn_cast<TagDecl>(Ctx))
-      R.Qualifier = NestedNameSpecifier::Create(
-          SemaRef.Context, nullptr,
-          SemaRef.Context.getTypeDeclType(Tag).getTypePtr());
+      R.Qualifier = NestedNameSpecifier(
+          SemaRef.Context
+              .getTagType(ElaboratedTypeKeyword::None,
+                          /*Qualifier=*/std::nullopt, Tag, /*OwnsTag=*/false)
+              .getTypePtr());
     else
       R.QualifierIsInformative = false;
   }
@@ -1664,7 +1672,8 @@ static bool isObjCReceiverType(ASTContext &C, QualType T) {
 }
 
 bool ResultBuilder::IsObjCMessageReceiver(const NamedDecl *ND) const {
-  QualType T = getDeclUsageType(SemaRef.Context, ND);
+  QualType T =
+      getDeclUsageType(SemaRef.Context, /*Qualifier=*/std::nullopt, ND);
   if (T.isNull())
     return false;
 
@@ -1689,7 +1698,8 @@ bool ResultBuilder::IsObjCCollection(const NamedDecl *ND) const {
       (!SemaRef.getLangOpts().CPlusPlus && !IsOrdinaryNonTypeName(ND)))
     return false;
 
-  QualType T = getDeclUsageType(SemaRef.Context, ND);
+  QualType T =
+      getDeclUsageType(SemaRef.Context, /*Qualifier=*/std::nullopt, ND);
   if (T.isNull())
     return false;
 
@@ -1745,8 +1755,10 @@ class CodeCompletionDeclConsumer : public VisibleDeclConsumer {
 
   void FoundDecl(NamedDecl *ND, NamedDecl *Hiding, DeclContext *Ctx,
                  bool InBaseClass) override {
-    ResultBuilder::Result Result(ND, Results.getBasePriority(ND), nullptr,
-                                 false, IsAccessible(ND, Ctx), FixIts);
+    ResultBuilder::Result Result(ND, Results.getBasePriority(ND),
+                                 /*Qualifier=*/std::nullopt,
+                                 /*QualifierIsInformative=*/false,
+                                 IsAccessible(ND, Ctx), FixIts);
     Results.AddResult(Result, InitialLookupCtx, Hiding, InBaseClass, BaseType);
   }
 
@@ -2010,7 +2022,6 @@ static PrintingPolicy getCompletionPrintingPolicy(const ASTContext &Context,
   Policy.AnonymousTagLocations = false;
   Policy.SuppressStrongLifetime = true;
   Policy.SuppressUnwrittenScope = true;
-  Policy.SuppressScope = true;
   Policy.CleanUglifiedParameters = true;
   return Policy;
 }
@@ -2035,7 +2046,7 @@ static const char *GetCompletionTypeString(QualType T, ASTContext &Context,
 
     // Anonymous tag types are constant strings.
     if (const TagType *TagT = dyn_cast<TagType>(T))
-      if (TagDecl *Tag = TagT->getDecl())
+      if (TagDecl *Tag = TagT->getOriginalDecl())
         if (!Tag->hasNameForLinkage()) {
           switch (Tag->getTagKind()) {
           case TagTypeKind::Struct:
@@ -2925,8 +2936,8 @@ static void AddResultTypeChunk(ASTContext &Context,
     else
       T = Method->getReturnType();
   } else if (const auto *Enumerator = dyn_cast<EnumConstantDecl>(ND)) {
-    T = Context.getTypeDeclType(cast<TypeDecl>(Enumerator->getDeclContext()));
-    T = clang::TypeName::getFullyQualifiedType(T, Context);
+    T = Context.getCanonicalTagType(
+        cast<EnumDecl>(Enumerator->getDeclContext()));
   } else if (isa<UnresolvedUsingValueDecl>(ND)) {
     /* Do nothing: ignore unresolved using declarations*/
   } else if (const auto *Ivar = dyn_cast<ObjCIvarDecl>(ND)) {
@@ -3021,7 +3032,7 @@ static void findTypeLocationForBlockDecl(const TypeSourceInfo *TSInfo,
     if (!SuppressBlock) {
       if (TypedefTypeLoc TypedefTL = TL.getAsAdjusted<TypedefTypeLoc>()) {
         if (TypeSourceInfo *InnerTSInfo =
-                TypedefTL.getTypedefNameDecl()->getTypeSourceInfo()) {
+                TypedefTL.getDecl()->getTypeSourceInfo()) {
           TL = InnerTSInfo->getTypeLoc().getUnqualifiedLoc();
           continue;
         }
@@ -3381,7 +3392,7 @@ static void AddTemplateParameterChunks(
 /// Add a qualifier to the given code-completion string, if the
 /// provided nested-name-specifier is non-NULL.
 static void AddQualifierToCompletionString(CodeCompletionBuilder &Result,
-                                           NestedNameSpecifier *Qualifier,
+                                           NestedNameSpecifier Qualifier,
                                            bool QualifierIsInformative,
                                            ASTContext &Context,
                                            const PrintingPolicy &Policy) {
@@ -3391,7 +3402,7 @@ static void AddQualifierToCompletionString(CodeCompletionBuilder &Result,
   std::string PrintedNNS;
   {
     llvm::raw_string_ostream OS(PrintedNNS);
-    Qualifier->print(OS, Policy);
+    Qualifier.print(OS, Policy);
   }
   if (QualifierIsInformative)
     Result.AddInformativeChunk(Result.getAllocator().CopyString(PrintedNNS));
@@ -3520,11 +3531,9 @@ static void AddTypedNameChunk(ASTContext &Context, const PrintingPolicy &Policy,
   case DeclarationName::CXXConstructorName: {
     CXXRecordDecl *Record = nullptr;
     QualType Ty = Name.getCXXNameType();
-    if (const auto *RecordTy = Ty->getAs<RecordType>())
-      Record = cast<CXXRecordDecl>(RecordTy->getDecl());
-    else if (const auto *InjectedTy = Ty->getAs<InjectedClassNameType>())
-      Record = InjectedTy->getDecl();
-    else {
+    if (auto *RD = Ty->getAsCXXRecordDecl()) {
+      Record = RD;
+    } else {
       Result.AddTypedTextChunk(
           Result.getAllocator().CopyString(ND->getNameAsString()));
       break;
@@ -4498,12 +4507,12 @@ static void MaybeAddOverrideCalls(Sema &S, DeclContext *InContext,
 
     // If we need a nested-name-specifier, add one now.
     if (!InContext) {
-      NestedNameSpecifier *NNS = getRequiredQualification(
+      NestedNameSpecifier NNS = getRequiredQualification(
           S.Context, CurContext, Overridden->getDeclContext());
       if (NNS) {
         std::string Str;
         llvm::raw_string_ostream OS(Str);
-        NNS->print(OS, Policy);
+        NNS.print(OS, Policy);
         Builder.AddTextChunk(Results.getAllocator().CopyString(Str));
       }
     } else if (!InContext->Equals(Overridden->getDeclContext()))
@@ -4912,14 +4921,14 @@ namespace {
 /// Information that allows to avoid completing redundant enumerators.
 struct CoveredEnumerators {
   llvm::SmallPtrSet<EnumConstantDecl *, 8> Seen;
-  NestedNameSpecifier *SuggestedQualifier = nullptr;
+  NestedNameSpecifier SuggestedQualifier = std::nullopt;
 };
 } // namespace
 
 static void AddEnumerators(ResultBuilder &Results, ASTContext &Context,
                            EnumDecl *Enum, DeclContext *CurContext,
                            const CoveredEnumerators &Enumerators) {
-  NestedNameSpecifier *Qualifier = Enumerators.SuggestedQualifier;
+  NestedNameSpecifier Qualifier = Enumerators.SuggestedQualifier;
   if (Context.getLangOpts().CPlusPlus && !Qualifier && Enumerators.Seen.empty()) {
     // If there are no prior enumerators in C++, check whether we have to
     // qualify the names of the enumerators that we suggest, because they
@@ -5051,9 +5060,9 @@ void SemaCodeCompletion::CodeCompleteExpression(
                              Data.PreferredType->isMemberPointerType() ||
                              Data.PreferredType->isBlockPointerType();
     if (Data.PreferredType->isEnumeralType()) {
-      EnumDecl *Enum = Data.PreferredType->castAs<EnumType>()->getDecl();
-      if (auto *Def = Enum->getDefinition())
-        Enum = Def;
+      EnumDecl *Enum = Data.PreferredType->castAs<EnumType>()
+                           ->getOriginalDecl()
+                           ->getDefinitionOrSelf();
       // FIXME: collect covered enumerators in cases like:
       //        if (x == my_enum::one) { ... } else if (x == ^) {}
       AddEnumerators(Results, getASTContext(), Enum, SemaRef.CurContext,
@@ -5177,7 +5186,8 @@ AddObjCProperties(const CodeCompletionContext &CCContext,
     // expressions.
     if (!P->getType().getTypePtr()->isBlockPointerType() ||
         !IsBaseExprStatement) {
-      Result R = Result(P, Results.getBasePriority(P), nullptr);
+      Result R =
+          Result(P, Results.getBasePriority(P), /*Qualifier=*/std::nullopt);
       if (!InOriginalClass)
         setInBaseClass(R);
       Results.MaybeAddResult(R, CurContext);
@@ -5191,7 +5201,8 @@ AddObjCProperties(const CodeCompletionContext &CCContext,
     findTypeLocationForBlockDecl(P->getTypeSourceInfo(), BlockLoc,
                                  BlockProtoLoc);
     if (!BlockLoc) {
-      Result R = Result(P, Results.getBasePriority(P), nullptr);
+      Result R =
+          Result(P, Results.getBasePriority(P), /*Qualifier=*/std::nullopt);
       if (!InOriginalClass)
         setInBaseClass(R);
       Results.MaybeAddResult(R, CurContext);
@@ -5603,15 +5614,18 @@ class ConceptInfo {
 
     // In T::foo, `foo` is a static member function/variable.
     bool VisitDependentScopeDeclRefExpr(DependentScopeDeclRefExpr *E) override {
-      if (E->getQualifier() && isApprox(E->getQualifier()->getAsType(), T))
+      NestedNameSpecifier Qualifier = E->getQualifier();
+      if (Qualifier.getKind() == NestedNameSpecifier::Kind::Type &&
+          isApprox(Qualifier.getAsType(), T))
         addValue(E, E->getDeclName(), Member::Colons);
       return true;
     }
 
     // In T::typename foo, `foo` is a type.
     bool VisitDependentNameType(DependentNameType *DNT) override {
-      const auto *Q = DNT->getQualifier();
-      if (Q && isApprox(Q->getAsType(), T))
+      NestedNameSpecifier Q = DNT->getQualifier();
+      if (Q.getKind() == NestedNameSpecifier::Kind::Type &&
+          isApprox(Q.getAsType(), T))
         addType(DNT->getIdentifier());
       return true;
     }
@@ -5620,10 +5634,15 @@ class ConceptInfo {
     // VisitNNS() doesn't exist, and TraverseNNS isn't always called :-(
     bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc NNSL) override {
       if (NNSL) {
-        NestedNameSpecifier *NNS = NNSL.getNestedNameSpecifier();
-        const auto *Q = NNS->getPrefix();
-        if (Q && isApprox(Q->getAsType(), T))
-          addType(NNS->getAsIdentifier());
+        NestedNameSpecifier NNS = NNSL.getNestedNameSpecifier();
+        if (NNS.getKind() == NestedNameSpecifier::Kind::Type) {
+          const Type *NNST = NNS.getAsType();
+          if (NestedNameSpecifier Q = NNST->getPrefix();
+              Q.getKind() == NestedNameSpecifier::Kind::Type &&
+              isApprox(Q.getAsType(), T))
+            if (const auto *DNT = dyn_cast_or_null<DependentNameType>(NNST))
+              addType(DNT->getIdentifier());
+        }
       }
       // FIXME: also handle T::foo<X>::bar
       return DynamicRecursiveASTVisitor::TraverseNestedNameSpecifierLoc(NNSL);
@@ -5769,7 +5788,7 @@ QualType getApproximateType(const Expr *E, HeuristicResolver &Resolver) {
     if (auto Decls = Resolver.resolveDependentNameType(DNT);
         Decls.size() == 1) {
       if (const auto *TD = dyn_cast<TypeDecl>(Decls[0]))
-        return QualType(TD->getTypeForDecl(), 0);
+        return TD->getASTContext().getTypeDeclType(TD);
     }
   }
   // We only resolve DependentTy, or undeduced autos (including auto* etc).
@@ -6176,9 +6195,8 @@ void SemaCodeCompletion::CodeCompleteCase(Scope *S) {
 
   // Code-complete the cases of a switch statement over an enumeration type
   // by providing the list of
-  EnumDecl *Enum = type->castAs<EnumType>()->getDecl();
-  if (EnumDecl *Def = Enum->getDefinition())
-    Enum = Def;
+  EnumDecl *Enum =
+      type->castAs<EnumType>()->getOriginalDecl()->getDefinitionOrSelf();
 
   // Determine which enumerators we have already seen in the switch statement.
   // FIXME: Ideally, we would also be able to look *past* the code-completion
@@ -6879,8 +6897,8 @@ void SemaCodeCompletion::CodeCompleteQualifiedId(Scope *S, CXXScopeSpec &SS,
 
   // Try to instantiate any non-dependent declaration contexts before
   // we look in them. Bail out if we fail.
-  NestedNameSpecifier *NNS = SS.getScopeRep();
-  if (NNS != nullptr && SS.isValid() && !NNS->isDependent()) {
+  NestedNameSpecifier NNS = SS.getScopeRep();
+  if (NNS && !NNS.isDependent()) {
     if (Ctx == nullptr || SemaRef.RequireCompleteDeclContext(SS, Ctx))
       return;
   }
@@ -6894,14 +6912,13 @@ void SemaCodeCompletion::CodeCompleteQualifiedId(Scope *S, CXXScopeSpec &SS,
   // The "template" keyword can follow "::" in the grammar, but only
   // put it into the grammar if the nested-name-specifier is dependent.
   // FIXME: results is always empty, this appears to be dead.
-  if (!Results.empty() && NNS && NNS->isDependent())
+  if (!Results.empty() && NNS.isDependent())
     Results.AddResult("template");
 
   // If the scope is a concept-constrained type parameter, infer nested
   // members based on the constraints.
-  if (NNS) {
-    if (const auto *TTPT =
-            dyn_cast_or_null<TemplateTypeParmType>(NNS->getAsType())) {
+  if (NNS.getKind() == NestedNameSpecifier::Kind::Type) {
+    if (const auto *TTPT = dyn_cast<TemplateTypeParmType>(NNS.getAsType())) {
       for (const auto &R : ConceptInfo(*TTPT, S).members()) {
         if (R.Operator != ConceptInfo::Member::Colons)
           continue;
@@ -7026,7 +7043,7 @@ void SemaCodeCompletion::CodeCompleteNamespaceDecl(Scope *S) {
          NS != NSEnd; ++NS)
       Results.AddResult(
           CodeCompletionResult(NS->second, Results.getBasePriority(NS->second),
-                               nullptr),
+                               /*Qualifier=*/std::nullopt),
           SemaRef.CurContext, nullptr, false);
     Results.ExitScope();
   }
@@ -7813,7 +7830,8 @@ static void AddObjCMethods(ObjCContainerDecl *Container,
       if (!Selectors.insert(M->getSelector()).second)
         continue;
 
-      Result R = Result(M, Results.getBasePriority(M), nullptr);
+      Result R =
+          Result(M, Results.getBasePriority(M), /*Qualifier=*/std::nullopt);
       R.StartParameter = SelIdents.size();
       R.AllParametersAreInformative = (WantKind != MK_Any);
       if (!InOriginalClass)
@@ -8404,7 +8422,8 @@ AddClassMessageCompletions(Sema &SemaRef, Scope *S, ParsedType Receiver,
           continue;
 
         Result R(MethList->getMethod(),
-                 Results.getBasePriority(MethList->getMethod()), nullptr);
+                 Results.getBasePriority(MethList->getMethod()),
+                 /*Qualifier=*/std::nullopt);
         R.StartParameter = SelIdents.size();
         R.AllParametersAreInformative = false;
         Results.MaybeAddResult(R, SemaRef.CurContext);
@@ -8580,7 +8599,8 @@ void SemaCodeCompletion::CodeCompleteObjCInstanceMessage(
           continue;
 
         Result R(MethList->getMethod(),
-                 Results.getBasePriority(MethList->getMethod()), nullptr);
+                 Results.getBasePriority(MethList->getMethod()),
+                 /*Qualifier=*/std::nullopt);
         R.StartParameter = SelIdents.size();
         R.AllParametersAreInformative = false;
         Results.MaybeAddResult(R, SemaRef.CurContext);
@@ -8696,9 +8716,9 @@ static void AddProtocolResults(DeclContext *Ctx, DeclContext *CurContext,
     // Record any protocols we find.
     if (const auto *Proto = dyn_cast<ObjCProtocolDecl>(D))
       if (!OnlyForwardDeclarations || !Proto->hasDefinition())
-        Results.AddResult(
-            Result(Proto, Results.getBasePriority(Proto), nullptr), CurContext,
-            nullptr, false);
+        Results.AddResult(Result(Proto, Results.getBasePriority(Proto),
+                                 /*Qualifier=*/std::nullopt),
+                          CurContext, nullptr, false);
   }
 }
 
@@ -8764,9 +8784,9 @@ static void AddInterfaceResults(DeclContext *Ctx, DeclContext *CurContext,
     if (const auto *Class = dyn_cast<ObjCInterfaceDecl>(D))
       if ((!OnlyForwardDeclarations || !Class->hasDefinition()) &&
           (!OnlyUnimplemented || !Class->getImplementation()))
-        Results.AddResult(
-            Result(Class, Results.getBasePriority(Class), nullptr), CurContext,
-            nullptr, false);
+        Results.AddResult(Result(Class, Results.getBasePriority(Class),
+                                 /*Qualifier=*/std::nullopt),
+                          CurContext, nullptr, false);
   }
 }
 
@@ -8878,9 +8898,9 @@ void SemaCodeCompletion::CodeCompleteObjCInterfaceCategory(
   for (const auto *D : TU->decls())
     if (const auto *Category = dyn_cast<ObjCCategoryDecl>(D))
       if (CategoryNames.insert(Category->getIdentifier()).second)
-        Results.AddResult(
-            Result(Category, Results.getBasePriority(Category), nullptr),
-            SemaRef.CurContext, nullptr, false);
+        Results.AddResult(Result(Category, Results.getBasePriority(Category),
+                                 /*Qualifier=*/std::nullopt),
+                          SemaRef.CurContext, nullptr, false);
   Results.ExitScope();
 
   HandleCodeCompleteResults(&SemaRef, CodeCompleter,
@@ -8915,7 +8935,8 @@ void SemaCodeCompletion::CodeCompleteObjCImplementationCategory(
     for (const auto *Cat : Class->visible_categories()) {
       if ((!IgnoreImplemented || !Cat->getImplementation()) &&
           CategoryNames.insert(Cat->getIdentifier()).second)
-        Results.AddResult(Result(Cat, Results.getBasePriority(Cat), nullptr),
+        Results.AddResult(Result(Cat, Results.getBasePriority(Cat),
+                                 /*Qualifier=*/std::nullopt),
                           SemaRef.CurContext, nullptr, false);
     }
 
@@ -9015,7 +9036,8 @@ void SemaCodeCompletion::CodeCompleteObjCPropertySynthesizeIvar(
   for (; Class; Class = Class->getSuperClass()) {
     for (ObjCIvarDecl *Ivar = Class->all_declared_ivar_begin(); Ivar;
          Ivar = Ivar->getNextIvar()) {
-      Results.AddResult(Result(Ivar, Results.getBasePriority(Ivar), nullptr),
+      Results.AddResult(Result(Ivar, Results.getBasePriority(Ivar),
+                               /*Qualifier=*/std::nullopt),
                         SemaRef.CurContext, nullptr, false);
 
       // Determine whether we've seen an ivar with a name similar to the
@@ -10031,7 +10053,8 @@ void SemaCodeCompletion::CodeCompleteObjCMethodDeclSelector(
       }
 
       Result R(MethList->getMethod(),
-               Results.getBasePriority(MethList->getMethod()), nullptr);
+               Results.getBasePriority(MethList->getMethod()),
+               /*Qualifier=*/std::nullopt);
       R.StartParameter = SelIdents.size();
       R.AllParametersAreInformative = false;
       R.DeclaringEntity = true;
diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index d193a33f22393..cc03616e0dfe1 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -89,8 +89,8 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
     AddArg(T);
 
   // Build the template-id.
-  QualType CoroTrait =
-      S.CheckTemplateIdType(TemplateName(CoroTraits), KwLoc, Args);
+  QualType CoroTrait = S.CheckTemplateIdType(
+      ElaboratedTypeKeyword::None, TemplateName(CoroTraits), KwLoc, Args);
   if (CoroTrait.isNull())
     return QualType();
   if (S.RequireCompleteType(KwLoc, CoroTrait,
@@ -111,23 +111,18 @@ static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
         << RD;
     return QualType();
   }
-  // The promise type is required to be a class type.
-  QualType PromiseType = S.Context.getTypeDeclType(Promise);
-
-  auto buildElaboratedType = [&]() {
-    auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, S.getStdNamespace());
-    NNS = NestedNameSpecifier::Create(S.Context, NNS, CoroTrait.getTypePtr());
-    return S.Context.getElaboratedType(ElaboratedTypeKeyword::None, NNS,
-                                       PromiseType);
-  };
 
+  NestedNameSpecifier Qualifier(CoroTrait.getTypePtr());
+  QualType PromiseType = S.Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                                   Qualifier, Promise);
+  // The promise type is required to be a class type.
   if (!PromiseType->getAsCXXRecordDecl()) {
     S.Diag(FuncLoc,
            diag::err_implied_std_coroutine_traits_promise_type_not_class)
-        << buildElaboratedType();
+        << PromiseType;
     return QualType();
   }
-  if (S.RequireCompleteType(FuncLoc, buildElaboratedType(),
+  if (S.RequireCompleteType(FuncLoc, PromiseType,
                             diag::err_coroutine_promise_type_incomplete))
     return QualType();
 
@@ -167,8 +162,8 @@ static QualType lookupCoroutineHandleType(Sema &S, QualType PromiseType,
       S.Context.getTrivialTypeSourceInfo(PromiseType, Loc)));
 
   // Build the template-id.
-  QualType CoroHandleType =
-      S.CheckTemplateIdType(TemplateName(CoroHandle), Loc, Args);
+  QualType CoroHandleType = S.CheckTemplateIdType(
+      ElaboratedTypeKeyword::None, TemplateName(CoroHandle), Loc, Args);
   if (CoroHandleType.isNull())
     return QualType();
   if (S.RequireCompleteType(Loc, CoroHandleType,
@@ -643,7 +638,9 @@ static void checkNoThrow(Sema &S, const Stmt *E,
         QualType::DestructionKind::DK_cxx_destructor) {
       const auto *T =
           cast<RecordType>(ReturnType.getCanonicalType().getTypePtr());
-      checkDeclNoexcept(cast<CXXRecordDecl>(T->getDecl())->getDestructor(),
+      checkDeclNoexcept(cast<CXXRecordDecl>(T->getOriginalDecl())
+                            ->getDefinition()
+                            ->getDestructor(),
                         /*IsDtor=*/true);
     }
   } else
@@ -1083,9 +1080,9 @@ static Expr *buildStdNoThrowDeclRef(Sema &S, SourceLocation Loc) {
 
 static TypeSourceInfo *getTypeSourceInfoForStdAlignValT(Sema &S,
                                                         SourceLocation Loc) {
-  EnumDecl *StdAlignValT = S.getStdAlignValT();
-  QualType StdAlignValDecl = S.Context.getTypeDeclType(StdAlignValT);
-  return S.Context.getTrivialTypeSourceInfo(StdAlignValDecl);
+  EnumDecl *StdAlignValDecl = S.getStdAlignValT();
+  CanQualType StdAlignValT = S.Context.getCanonicalTagType(StdAlignValDecl);
+  return S.Context.getTrivialTypeSourceInfo(StdAlignValT);
 }
 
 // When searching for custom allocators on the PromiseType we want to
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d7234e269f645..c610c26979bb0 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -140,8 +140,8 @@ class TypeNameValidatorCCC final : public CorrectionCandidateCallback {
 
 } // end anonymous namespace
 
-QualType Sema::getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
-                               TypeDecl *TD, SourceLocation NameLoc) {
+void Sema::checkTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
+                             TypeDecl *TD, SourceLocation NameLoc) {
   auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
   auto *FoundRD = dyn_cast<CXXRecordDecl>(TD);
   if (DCK != DiagCtorKind::None && LookupRD && FoundRD &&
@@ -157,7 +157,6 @@ QualType Sema::getTypeDeclType(DeclContext *LookupCtx, DiagCtorKind DCK,
 
   DiagnoseUseOfDecl(TD, NameLoc);
   MarkAnyDeclReferenced(TD->getLocation(), TD, /*OdrUse=*/false);
-  return Context.getTypeDeclType(TD);
 }
 
 namespace {
@@ -182,13 +181,13 @@ lookupUnqualifiedTypeNameInBase(Sema &S, const IdentifierInfo &II,
   UnqualifiedTypeNameLookupResult FoundTypeDecl =
       UnqualifiedTypeNameLookupResult::NotFound;
   for (const auto &Base : RD->bases()) {
-    const CXXRecordDecl *BaseRD = nullptr;
-    if (auto *BaseTT = Base.getType()->getAs<TagType>())
-      BaseRD = BaseTT->getAsCXXRecordDecl();
-    else if (auto *TST = Base.getType()->getAs<TemplateSpecializationType>()) {
+    const CXXRecordDecl *BaseRD = Base.getType()->getAsCXXRecordDecl();
+    if (BaseRD) {
+    } else if (auto *TST = dyn_cast<TemplateSpecializationType>(
+                   Base.getType().getCanonicalType())) {
       // Look for type decls in dependent base classes that have known primary
       // templates.
-      if (!TST || !TST->isDependentType())
+      if (!TST->isDependentType())
         continue;
       auto *TD = TST->getTemplateName().getAsTemplateDecl();
       if (!TD)
@@ -253,8 +252,7 @@ static ParsedType recoverFromTypeInKnownDependentBase(Sema &S,
   S.Diag(NameLoc, diag::ext_found_in_dependent_base) << &II;
 
   ASTContext &Context = S.Context;
-  auto *NNS = NestedNameSpecifier::Create(
-      Context, nullptr, cast<Type>(Context.getRecordType(RD)));
+  NestedNameSpecifier NNS(Context.getCanonicalTagType(RD).getTypePtr());
   QualType T =
       Context.getDependentNameType(ElaboratedTypeKeyword::None, NNS, &II);
 
@@ -269,45 +267,6 @@ static ParsedType recoverFromTypeInKnownDependentBase(Sema &S,
   return S.CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
 }
 
-/// Build a ParsedType for a simple-type-specifier with a nested-name-specifier.
-static ParsedType buildNamedType(Sema &S, const CXXScopeSpec *SS, QualType T,
-                                 SourceLocation NameLoc,
-                                 bool WantNontrivialTypeSourceInfo = true) {
-  switch (T->getTypeClass()) {
-  case Type::DeducedTemplateSpecialization:
-  case Type::Enum:
-  case Type::InjectedClassName:
-  case Type::Record:
-  case Type::Typedef:
-  case Type::UnresolvedUsing:
-  case Type::Using:
-    break;
-  // These can never be qualified so an ElaboratedType node
-  // would carry no additional meaning.
-  case Type::ObjCInterface:
-  case Type::ObjCTypeParam:
-  case Type::TemplateTypeParm:
-    return ParsedType::make(T);
-  default:
-    llvm_unreachable("Unexpected Type Class");
-  }
-
-  if (!SS || SS->isEmpty())
-    return ParsedType::make(S.Context.getElaboratedType(
-        ElaboratedTypeKeyword::None, nullptr, T, nullptr));
-
-  QualType ElTy = S.getElaboratedType(ElaboratedTypeKeyword::None, *SS, T);
-  if (!WantNontrivialTypeSourceInfo)
-    return ParsedType::make(ElTy);
-
-  TypeLocBuilder Builder;
-  Builder.pushTypeSpec(T).setNameLoc(NameLoc);
-  ElaboratedTypeLoc ElabTL = Builder.push<ElaboratedTypeLoc>(ElTy);
-  ElabTL.setElaboratedKeywordLoc(SourceLocation());
-  ElabTL.setQualifierLoc(SS->getWithLocInContext(S.Context));
-  return S.CreateParsedType(ElTy, Builder.getTypeSourceInfo(S.Context, ElTy));
-}
-
 ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
                              Scope *S, CXXScopeSpec *SS, bool isClassName,
                              bool HasTrailingDot, ParsedType ObjectTypePtr,
@@ -348,9 +307,10 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
           if (AllowImplicitTypename == ImplicitTypenameContext::No)
             return nullptr;
           SourceLocation QualifiedLoc = SS->getRange().getBegin();
-          auto DB =
-              DiagCompat(QualifiedLoc, diag_compat::implicit_typename)
-              << NestedNameSpecifier::Create(Context, SS->getScopeRep(), &II);
+          // FIXME: Defer the diagnostic after we build the type and use it.
+          auto DB = DiagCompat(QualifiedLoc, diag_compat::implicit_typename)
+                    << Context.getDependentNameType(ElaboratedTypeKeyword::None,
+                                                    SS->getScopeRep(), &II);
           if (!getLangOpts().CPlusPlus20)
             DB << FixItHint::CreateInsertion(QualifiedLoc, "typename ");
         }
@@ -430,7 +390,7 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
       bool MemberOfUnknownSpecialization;
       UnqualifiedId TemplateName;
       TemplateName.setIdentifier(NewII, NameLoc);
-      NestedNameSpecifier *NNS = Correction.getCorrectionSpecifier();
+      NestedNameSpecifier NNS = Correction.getCorrectionSpecifier();
       CXXScopeSpec NewSS, *NewSSPtr = SS;
       if (SS && NNS) {
         NewSS.MakeTrivial(Context, NNS, SourceRange(NameLoc));
@@ -530,20 +490,78 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
 
   assert(IIDecl && "Didn't find decl");
 
-  QualType T;
+  TypeLocBuilder TLB;
   if (TypeDecl *TD = dyn_cast<TypeDecl>(IIDecl)) {
-    // C++ [class.qual]p2: A lookup that would find the injected-class-name
-    // instead names the constructors of the class, except when naming a class.
-    // This is ill-formed when we're not actually forming a ctor or dtor name.
-    T = getTypeDeclType(LookupCtx,
-                        IsImplicitTypename ? DiagCtorKind::Implicit
-                                           : DiagCtorKind::None,
-                        TD, NameLoc);
-  } else if (ObjCInterfaceDecl *IDecl = dyn_cast<ObjCInterfaceDecl>(IIDecl)) {
+    checkTypeDeclType(LookupCtx,
+                      IsImplicitTypename ? DiagCtorKind::Implicit
+                                         : DiagCtorKind::None,
+                      TD, NameLoc);
+    QualType T;
+    if (FoundUsingShadow) {
+      T = Context.getUsingType(ElaboratedTypeKeyword::None,
+                               SS ? SS->getScopeRep() : std::nullopt,
+                               FoundUsingShadow);
+      if (!WantNontrivialTypeSourceInfo)
+        return ParsedType::make(T);
+      TLB.push<UsingTypeLoc>(T).set(/*ElaboratedKeywordLoc=*/SourceLocation(),
+                                    SS ? SS->getWithLocInContext(Context)
+                                       : NestedNameSpecifierLoc(),
+                                    NameLoc);
+    } else if (auto *Tag = dyn_cast<TagDecl>(TD)) {
+      T = Context.getTagType(ElaboratedTypeKeyword::None,
+                             SS ? SS->getScopeRep() : std::nullopt, Tag,
+                             /*OwnsTag=*/false);
+      if (!WantNontrivialTypeSourceInfo)
+        return ParsedType::make(T);
+      auto TL = TLB.push<TagTypeLoc>(T);
+      TL.setElaboratedKeywordLoc(SourceLocation());
+      TL.setQualifierLoc(SS ? SS->getWithLocInContext(Context)
+                            : NestedNameSpecifierLoc());
+      TL.setNameLoc(NameLoc);
+    } else if (auto *TN = dyn_cast<TypedefNameDecl>(TD);
+               TN && !isa<ObjCTypeParamDecl>(TN)) {
+      T = Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                 SS ? SS->getScopeRep() : std::nullopt, TN);
+      if (!WantNontrivialTypeSourceInfo)
+        return ParsedType::make(T);
+      TLB.push<TypedefTypeLoc>(T).set(
+          /*ElaboratedKeywordLoc=*/SourceLocation(),
+          SS ? SS->getWithLocInContext(Context) : NestedNameSpecifierLoc(),
+          NameLoc);
+    } else if (auto *UD = dyn_cast<UnresolvedUsingTypenameDecl>(TD)) {
+      T = Context.getUnresolvedUsingType(ElaboratedTypeKeyword::None,
+                                         SS ? SS->getScopeRep() : std::nullopt,
+                                         UD);
+      if (!WantNontrivialTypeSourceInfo)
+        return ParsedType::make(T);
+      TLB.push<UnresolvedUsingTypeLoc>(T).set(
+          /*ElaboratedKeywordLoc=*/SourceLocation(),
+          SS ? SS->getWithLocInContext(Context) : NestedNameSpecifierLoc(),
+          NameLoc);
+    } else {
+      T = Context.getTypeDeclType(TD);
+      if (!WantNontrivialTypeSourceInfo)
+        return ParsedType::make(T);
+      if (isa<ObjCTypeParamType>(T))
+        TLB.push<ObjCTypeParamTypeLoc>(T).setNameLoc(NameLoc);
+      else
+        TLB.pushTypeSpec(T).setNameLoc(NameLoc);
+    }
+    return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
+  }
+  if (ObjCInterfaceDecl *IDecl = dyn_cast<ObjCInterfaceDecl>(IIDecl)) {
     (void)DiagnoseUseOfDecl(IDecl, NameLoc);
-    if (!HasTrailingDot)
-      T = Context.getObjCInterfaceType(IDecl);
-    FoundUsingShadow = nullptr; // FIXME: Target must be a TypeDecl.
+    if (!HasTrailingDot) {
+      // FIXME: Support UsingType for this case.
+      QualType T = Context.getObjCInterfaceType(IDecl);
+      if (!WantNontrivialTypeSourceInfo)
+        return ParsedType::make(T);
+      auto TL = TLB.push<ObjCInterfaceTypeLoc>(T);
+      TL.setNameLoc(NameLoc);
+      // FIXME: Pass in this source location.
+      TL.setNameEndLoc(NameLoc);
+      return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
+    }
   } else if (auto *UD = dyn_cast<UnresolvedUsingIfExistsDecl>(IIDecl)) {
     (void)DiagnoseUseOfDecl(UD, NameLoc);
     // Recover with 'int'
@@ -551,41 +569,38 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
   } else if (AllowDeducedTemplate) {
     if (auto *TD = getAsTypeTemplateDecl(IIDecl)) {
       assert(!FoundUsingShadow || FoundUsingShadow->getTargetDecl() == TD);
+      // FIXME: Support UsingType here.
       TemplateName Template = Context.getQualifiedTemplateName(
-          SS ? SS->getScopeRep() : nullptr, /*TemplateKeyword=*/false,
+          SS ? SS->getScopeRep() : std::nullopt, /*TemplateKeyword=*/false,
           FoundUsingShadow ? TemplateName(FoundUsingShadow) : TemplateName(TD));
-      T = Context.getDeducedTemplateSpecializationType(Template, QualType(),
-                                                       false);
-      // Don't wrap in a further UsingType.
-      FoundUsingShadow = nullptr;
+      QualType T = Context.getDeducedTemplateSpecializationType(
+          ElaboratedTypeKeyword::None, Template, QualType(), false);
+      auto TL = TLB.push<DeducedTemplateSpecializationTypeLoc>(T);
+      TL.setElaboratedKWLoc(SourceLocation());
+      TL.setNameLoc(NameLoc);
+      TL.setQualifierLoc(SS ? SS->getWithLocInContext(Context)
+                            : NestedNameSpecifierLoc());
+      return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
     }
   }
 
-  if (T.isNull()) {
-    // If it's not plausibly a type, suppress diagnostics.
-    Result.suppressDiagnostics();
-    return nullptr;
-  }
-
-  if (FoundUsingShadow)
-    T = Context.getUsingType(FoundUsingShadow, T);
-
-  return buildNamedType(*this, SS, T, NameLoc, WantNontrivialTypeSourceInfo);
+  // As it's not plausibly a type, suppress diagnostics.
+  Result.suppressDiagnostics();
+  return nullptr;
 }
 
 // Builds a fake NNS for the given decl context.
-static NestedNameSpecifier *
+static NestedNameSpecifier
 synthesizeCurrentNestedNameSpecifier(ASTContext &Context, DeclContext *DC) {
   for (;; DC = DC->getLookupParent()) {
     DC = DC->getPrimaryContext();
     auto *ND = dyn_cast<NamespaceDecl>(DC);
     if (ND && !ND->isInline() && !ND->isAnonymousNamespace())
-      return NestedNameSpecifier::Create(Context, nullptr, ND);
+      return NestedNameSpecifier(Context, ND, std::nullopt);
     if (auto *RD = dyn_cast<CXXRecordDecl>(DC))
-      return NestedNameSpecifier::Create(Context, nullptr,
-                                         RD->getTypeForDecl());
+      return NestedNameSpecifier(Context.getCanonicalTagType(RD)->getTypePtr());
     if (isa<TranslationUnitDecl>(DC))
-      return NestedNameSpecifier::GlobalSpecifier(Context);
+      return NestedNameSpecifier::getGlobal();
   }
   llvm_unreachable("something isn't in TU scope?");
 }
@@ -610,7 +625,7 @@ ParsedType Sema::ActOnMSVCUnknownTypeName(const IdentifierInfo &II,
                                           bool IsTemplateTypeArg) {
   assert(getLangOpts().MSVCCompat && "shouldn't be called in non-MSVC mode");
 
-  NestedNameSpecifier *NNS = nullptr;
+  NestedNameSpecifier NNS = std::nullopt;
   if (IsTemplateTypeArg && getCurScope()->isTemplateParamScope()) {
     // If we weren't able to parse a default template argument, delay lookup
     // until instantiation time by making a non-dependent DependentTypeName. We
@@ -625,7 +640,7 @@ ParsedType Sema::ActOnMSVCUnknownTypeName(const IdentifierInfo &II,
                  findRecordWithDependentBasesOfEnclosingMethod(CurContext)) {
     // Build a DependentNameType that will perform lookup into RD at
     // instantiation time.
-    NNS = NestedNameSpecifier::Create(Context, nullptr, RD->getTypeForDecl());
+    NNS = NestedNameSpecifier(Context.getCanonicalTagType(RD)->getTypePtr());
 
     // Diagnose that this identifier was undeclared, and retry the lookup during
     // template instantiation.
@@ -678,19 +693,22 @@ DeclSpec::TST Sema::isTagName(IdentifierInfo &II, Scope *S) {
 }
 
 bool Sema::isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S) {
-  if (CurContext->isRecord()) {
-    if (SS->getScopeRep()->getKind() == NestedNameSpecifier::Super)
-      return true;
-
-    const Type *Ty = SS->getScopeRep()->getAsType();
+  if (!CurContext->isRecord())
+    return CurContext->isFunctionOrMethod() || S->isFunctionPrototypeScope();
 
-    CXXRecordDecl *RD = cast<CXXRecordDecl>(CurContext);
-    for (const auto &Base : RD->bases())
-      if (Ty && Context.hasSameUnqualifiedType(QualType(Ty, 1), Base.getType()))
+  switch (SS->getScopeRep().getKind()) {
+  case NestedNameSpecifier::Kind::Super:
+    return true;
+  case NestedNameSpecifier::Kind::Type: {
+    QualType T(SS->getScopeRep().getAsType(), 0);
+    for (const auto &Base : cast<CXXRecordDecl>(CurContext)->bases())
+      if (Context.hasSameUnqualifiedType(T, Base.getType()))
         return true;
+    [[fallthrough]];
+  }
+  default:
     return S->isFunctionPrototypeScope();
   }
-  return CurContext->isFunctionOrMethod() || S->isFunctionPrototypeScope();
 }
 
 void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
@@ -786,7 +804,7 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
     Diag(IILoc, IsTemplateName ? diag::err_no_member_template
                                : diag::err_typename_nested_not_found)
         << II << DC << SS->getRange();
-  else if (SS->isValid() && SS->getScopeRep()->containsErrors()) {
+  else if (SS->isValid() && SS->getScopeRep().containsErrors()) {
     SuggestedType =
         ActOnTypenameType(S, SourceLocation(), *SS, *II, IILoc).get();
   } else if (isDependentScopeSpecifier(*SS)) {
@@ -794,12 +812,13 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
     if (getLangOpts().MSVCCompat && isMicrosoftMissingTypename(SS, S))
       DiagID = diag::ext_typename_missing;
 
+    SuggestedType =
+        ActOnTypenameType(S, SourceLocation(), *SS, *II, IILoc).get();
+
     Diag(SS->getRange().getBegin(), DiagID)
-        << NestedNameSpecifier::Create(Context, SS->getScopeRep(), II)
+        << GetTypeFromParser(SuggestedType)
         << SourceRange(SS->getRange().getBegin(), IILoc)
         << FixItHint::CreateInsertion(SS->getRange().getBegin(), "typename ");
-    SuggestedType = ActOnTypenameType(S, SourceLocation(),
-                                      *SS, *II, IILoc).get();
   } else {
     assert(SS && SS->isInvalid() &&
            "Invalid scope specifier has already been diagnosed");
@@ -1156,10 +1175,34 @@ Sema::NameClassification Sema::ClassifyName(Scope *S, CXXScopeSpec &SS,
   }
 
   auto BuildTypeFor = [&](TypeDecl *Type, NamedDecl *Found) {
-    QualType T = Context.getTypeDeclType(Type);
-    if (const auto *USD = dyn_cast<UsingShadowDecl>(Found))
-      T = Context.getUsingType(USD, T);
-    return buildNamedType(*this, &SS, T, NameLoc);
+    QualType T;
+    TypeLocBuilder TLB;
+    if (const auto *USD = dyn_cast<UsingShadowDecl>(Found)) {
+      T = Context.getUsingType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
+                               USD);
+      TLB.push<UsingTypeLoc>(T).set(/*ElaboratedKeywordLoc=*/SourceLocation(),
+                                    SS.getWithLocInContext(Context), NameLoc);
+    } else {
+      T = Context.getTypeDeclType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
+                                  Type);
+      if (isa<TagType>(T)) {
+        auto TTL = TLB.push<TagTypeLoc>(T);
+        TTL.setElaboratedKeywordLoc(SourceLocation());
+        TTL.setQualifierLoc(SS.getWithLocInContext(Context));
+        TTL.setNameLoc(NameLoc);
+      } else if (isa<TypedefType>(T)) {
+        TLB.push<TypedefTypeLoc>(T).set(
+            /*ElaboratedKeywordLoc=*/SourceLocation(),
+            SS.getWithLocInContext(Context), NameLoc);
+      } else if (isa<UnresolvedUsingType>(T)) {
+        TLB.push<UnresolvedUsingTypeLoc>(T).set(
+            /*ElaboratedKeywordLoc=*/SourceLocation(),
+            SS.getWithLocInContext(Context), NameLoc);
+      } else {
+        TLB.pushTypeSpec(T).setNameLoc(NameLoc);
+      }
+    }
+    return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
   };
 
   NamedDecl *FirstDecl = (*Result.begin())->getUnderlyingDecl();
@@ -2009,8 +2052,7 @@ static bool ShouldDiagnoseUnusedDecl(const LangOptions &LangOpts,
     // consistent for both scalars and arrays.
     Ty = Ty->getBaseElementTypeUnsafe();
 
-    if (const TagType *TT = Ty->getAs<TagType>()) {
-      const TagDecl *Tag = TT->getDecl();
+    if (const TagDecl *Tag = Ty->getAsTagDecl()) {
       if (Tag->hasAttr<UnusedAttr>())
         return false;
 
@@ -2070,7 +2112,7 @@ void Sema::DiagnoseUnusedNestedTypedefs(const RecordDecl *D) {
 
 void Sema::DiagnoseUnusedNestedTypedefs(const RecordDecl *D,
                                         DiagReceiverTy DiagReceiver) {
-  if (D->getTypeForDecl()->isDependentType())
+  if (D->isDependentType())
     return;
 
   for (auto *TmpD : D->decls()) {
@@ -2128,8 +2170,7 @@ void Sema::DiagnoseUnusedButSetDecl(const VarDecl *VD,
   if (Ty->isReferenceType() || Ty->isDependentType())
     return;
 
-  if (const TagType *TT = Ty->getAs<TagType>()) {
-    const TagDecl *Tag = TT->getDecl();
+  if (const TagDecl *Tag = Ty->getAsTagDecl()) {
     if (Tag->hasAttr<UnusedAttr>())
       return;
     // In C++, don't warn for record types that don't have WarnUnusedAttr, to
@@ -2508,7 +2549,8 @@ void Sema::MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
         }
         Context.setObjCIdRedefinitionType(T);
         // Install the built-in type for 'id', ignoring the current definition.
-        New->setTypeForDecl(Context.getObjCIdType().getTypePtr());
+        New->setModedTypeSourceInfo(New->getTypeSourceInfo(),
+                                    Context.getObjCIdType());
         return;
       }
     case 5:
@@ -2516,14 +2558,16 @@ void Sema::MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
         break;
       Context.setObjCClassRedefinitionType(New->getUnderlyingType());
       // Install the built-in type for 'Class', ignoring the current definition.
-      New->setTypeForDecl(Context.getObjCClassType().getTypePtr());
+      New->setModedTypeSourceInfo(New->getTypeSourceInfo(),
+                                  Context.getObjCClassType());
       return;
     case 3:
       if (!TypeID->isStr("SEL"))
         break;
       Context.setObjCSelRedefinitionType(New->getUnderlyingType());
       // Install the built-in type for 'SEL', ignoring the current definition.
-      New->setTypeForDecl(Context.getObjCSelType().getTypePtr());
+      New->setModedTypeSourceInfo(New->getTypeSourceInfo(),
+                                  Context.getObjCSelType());
       return;
     }
     // Fall through - the typedef name was not a builtin type.
@@ -2555,7 +2599,6 @@ void Sema::MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
         !hasVisibleDefinition(OldTag, &Hidden)) {
       // There is a definition of this tag, but it is not visible. Use it
       // instead of our tag.
-      New->setTypeForDecl(OldTD->getTypeForDecl());
       if (OldTD->isModed())
         New->setModedTypeSourceInfo(OldTD->getTypeSourceInfo(),
                                     OldTD->getUnderlyingType());
@@ -2742,7 +2785,7 @@ static bool mergeAlignedAttrs(Sema &S, NamedDecl *New, Decl *Old) {
       if (ValueDecl *VD = dyn_cast<ValueDecl>(New))
         Ty = VD->getType();
       else
-        Ty = S.Context.getTagDeclType(cast<TagDecl>(New));
+        Ty = S.Context.getCanonicalTagType(cast<TagDecl>(New));
 
       if (OldAlign == 0)
         OldAlign = S.Context.getTypeAlign(Ty);
@@ -2913,8 +2956,11 @@ static bool mergeDeclAttribute(Sema &S, NamedDecl *D,
 }
 
 static const NamedDecl *getDefinition(const Decl *D) {
-  if (const TagDecl *TD = dyn_cast<TagDecl>(D))
-    return TD->getDefinition();
+  if (const TagDecl *TD = dyn_cast<TagDecl>(D)) {
+    if (const auto *Def = TD->getDefinition(); Def && !Def->isBeingDefined())
+      return Def;
+    return nullptr;
+  }
   if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
     const VarDecl *Def = VD->getDefinition();
     if (Def)
@@ -5016,7 +5062,7 @@ void Sema::setTagNameForLinkagePurposes(TagDecl *TagFromDeclSpec,
 
   // The type must match the tag exactly;  no qualifiers allowed.
   if (!Context.hasSameType(NewTD->getUnderlyingType(),
-                           Context.getTagDeclType(TagFromDeclSpec))) {
+                           Context.getCanonicalTagType(TagFromDeclSpec))) {
     if (getLangOpts().CPlusPlus)
       Context.addTypedefNameForUnnamedTagDecl(TagFromDeclSpec, NewTD);
     return;
@@ -5224,9 +5270,9 @@ Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
         Record = dyn_cast<RecordDecl>(Tag);
       else if (const RecordType *RT =
                    DS.getRepAsType().get()->getAsStructureType())
-        Record = RT->getDecl();
+        Record = RT->getOriginalDecl()->getDefinitionOrSelf();
       else if (const RecordType *UT = DS.getRepAsType().get()->getAsUnionType())
-        Record = UT->getDecl();
+        Record = UT->getOriginalDecl()->getDefinitionOrSelf();
 
       if (Record && getLangOpts().MicrosoftExt) {
         Diag(DS.getBeginLoc(), diag::ext_ms_anonymous_record)
@@ -5754,7 +5800,7 @@ Decl *Sema::BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
   if (RecordDecl *OwningClass = dyn_cast<RecordDecl>(Owner)) {
     Anon = FieldDecl::Create(
         Context, OwningClass, DS.getBeginLoc(), Record->getLocation(),
-        /*IdentifierInfo=*/nullptr, Context.getTypeDeclType(Record), TInfo,
+        /*IdentifierInfo=*/nullptr, Context.getCanonicalTagType(Record), TInfo,
         /*BitWidth=*/nullptr, /*Mutable=*/false,
         /*InitStyle=*/ICIS_NoInit);
     Anon->setAccess(AS);
@@ -5774,7 +5820,7 @@ Decl *Sema::BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
 
     Anon = VarDecl::Create(Context, Owner, DS.getBeginLoc(),
                            Record->getLocation(), /*IdentifierInfo=*/nullptr,
-                           Context.getTypeDeclType(Record), TInfo, SC);
+                           Context.getCanonicalTagType(Record), TInfo, SC);
     if (Invalid)
       Anon->setInvalidDecl();
 
@@ -5837,7 +5883,7 @@ Decl *Sema::BuildMicrosoftCAnonymousStruct(Scope *S, DeclSpec &DS,
   assert(TInfo && "couldn't build declarator info for anonymous struct");
 
   auto *ParentDecl = cast<RecordDecl>(CurContext);
-  QualType RecTy = Context.getTypeDeclType(Record);
+  CanQualType RecTy = Context.getCanonicalTagType(Record);
 
   // Create a declaration for this anonymous struct.
   NamedDecl *Anon =
@@ -5956,14 +6002,14 @@ Sema::GetNameFromUnqualifiedId(const UnqualifiedId &Name) {
       return DeclarationNameInfo();
 
     // Determine the type of the class being constructed.
-    QualType CurClassType = Context.getTypeDeclType(CurClass);
+    CanQualType CurClassType = Context.getCanonicalTagType(CurClass);
 
     // FIXME: Check two things: that the template-id names the same type as
     // CurClassType, and that the template-id does not occur when the name
     // was qualified.
 
-    NameInfo.setName(Context.DeclarationNames.getCXXConstructorName(
-                                    Context.getCanonicalType(CurClassType)));
+    NameInfo.setName(
+        Context.DeclarationNames.getCXXConstructorName(CurClassType));
     // FIXME: should we retrieve TypeSourceInfo?
     NameInfo.setNamedTypeInfo(nullptr);
     return NameInfo;
@@ -6251,8 +6297,9 @@ bool Sema::diagnoseQualifiedDeclaration(CXXScopeSpec &SS, DeclContext *DC,
     // that's the case, then drop this declaration entirely.
     if ((Name.getNameKind() == DeclarationName::CXXConstructorName ||
          Name.getNameKind() == DeclarationName::CXXDestructorName) &&
-        !Context.hasSameType(Name.getCXXNameType(),
-                             Context.getTypeDeclType(cast<CXXRecordDecl>(Cur))))
+        !Context.hasSameType(
+            Name.getCXXNameType(),
+            Context.getCanonicalTagType(cast<CXXRecordDecl>(Cur))))
       return true;
 
     return false;
@@ -6272,36 +6319,48 @@ bool Sema::diagnoseQualifiedDeclaration(CXXScopeSpec &SS, DeclContext *DC,
         << FixItHint::CreateRemoval(TemplateId->TemplateKWLoc);
 
   NestedNameSpecifierLoc SpecLoc(SS.getScopeRep(), SS.location_data());
-  do {
-    if (TypeLoc TL = SpecLoc.getTypeLoc()) {
-      if (SourceLocation TemplateKeywordLoc = TL.getTemplateKeywordLoc();
-          TemplateKeywordLoc.isValid())
-        Diag(Loc, diag::ext_template_after_declarative_nns)
-            << FixItHint::CreateRemoval(TemplateKeywordLoc);
-    }
-
-    if (const Type *T = SpecLoc.getNestedNameSpecifier()->getAsType()) {
-      if (const auto *TST = T->getAsAdjusted<TemplateSpecializationType>()) {
-        // C++23 [expr.prim.id.qual]p3:
-        //   [...] If a nested-name-specifier N is declarative and has a
-        //   simple-template-id with a template argument list A that involves a
-        //   template parameter, let T be the template nominated by N without A.
-        //   T shall be a class template.
-        if (TST->isDependentType() && TST->isTypeAlias())
-          Diag(Loc, diag::ext_alias_template_in_declarative_nns)
-              << SpecLoc.getLocalSourceRange();
-      } else if (T->isDecltypeType() || T->getAsAdjusted<PackIndexingType>()) {
-        // C++23 [expr.prim.id.qual]p2:
-        //   [...] A declarative nested-name-specifier shall not have a
-        //   computed-type-specifier.
-        //
-        // CWG2858 changed this from 'decltype-specifier' to
-        // 'computed-type-specifier'.
-        Diag(Loc, diag::err_computed_type_in_declarative_nns)
-            << T->isDecltypeType() << SpecLoc.getTypeLoc().getSourceRange();
-      }
+  for (TypeLoc TL = SpecLoc.getAsTypeLoc(), NextTL; TL;
+       TL = std::exchange(NextTL, TypeLoc())) {
+    SourceLocation TemplateKeywordLoc;
+    switch (TL.getTypeLocClass()) {
+    case TypeLoc::TemplateSpecialization: {
+      auto TST = TL.castAs<TemplateSpecializationTypeLoc>();
+      TemplateKeywordLoc = TST.getTemplateKeywordLoc();
+      if (auto *T = TST.getTypePtr(); T->isDependentType() && T->isTypeAlias())
+        Diag(Loc, diag::ext_alias_template_in_declarative_nns)
+            << TST.getLocalSourceRange();
+      break;
+    }
+    case TypeLoc::Decltype:
+    case TypeLoc::PackIndexing: {
+      const Type *T = TL.getTypePtr();
+      // C++23 [expr.prim.id.qual]p2:
+      //   [...] A declarative nested-name-specifier shall not have a
+      //   computed-type-specifier.
+      //
+      // CWG2858 changed this from 'decltype-specifier' to
+      // 'computed-type-specifier'.
+      Diag(Loc, diag::err_computed_type_in_declarative_nns)
+          << T->isDecltypeType() << TL.getSourceRange();
+      break;
     }
-  } while ((SpecLoc = SpecLoc.getPrefix()));
+    case TypeLoc::DependentName:
+      NextTL =
+          TL.castAs<DependentNameTypeLoc>().getQualifierLoc().getAsTypeLoc();
+      break;
+    case TypeLoc::DependentTemplateSpecialization: {
+      auto TST = TL.castAs<DependentTemplateSpecializationTypeLoc>();
+      TemplateKeywordLoc = TST.getTemplateKeywordLoc();
+      NextTL = TST.getQualifierLoc().getAsTypeLoc();
+      break;
+    }
+    default:
+      break;
+    }
+    if (TemplateKeywordLoc.isValid())
+      Diag(Loc, diag::ext_template_after_declarative_nns)
+          << FixItHint::CreateRemoval(TemplateKeywordLoc);
+  }
 
   return false;
 }
@@ -9040,9 +9099,8 @@ bool Sema::AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD) {
 
     if (Name.getNameKind() == DeclarationName::CXXDestructorName) {
       // We really want to find the base class destructor here.
-      QualType T = Context.getTypeDeclType(BaseRecord);
-      CanQualType CT = Context.getCanonicalType(T);
-      Name = Context.DeclarationNames.getCXXDestructorName(CT);
+      Name = Context.DeclarationNames.getCXXDestructorName(
+          Context.getCanonicalTagType(BaseRecord));
     }
 
     for (NamedDecl *BaseND : BaseRecord->lookup(Name)) {
@@ -9728,7 +9786,8 @@ static void checkIsValidOpenCLKernelParameter(
 
   // At this point we already handled everything except of a RecordType.
   assert(PT->isRecordType() && "Unexpected type.");
-  const RecordDecl *PD = PT->castAs<RecordType>()->getDecl();
+  const RecordDecl *PD =
+      PT->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
   VisitStack.push_back(PD);
   assert(VisitStack.back() && "First decl null?");
 
@@ -9756,7 +9815,9 @@ static void checkIsValidOpenCLKernelParameter(
              "Unexpected type.");
       const Type *FieldRecTy = FieldTy->getPointeeOrArrayElementType();
 
-      RD = FieldRecTy->castAs<RecordType>()->getDecl();
+      RD = FieldRecTy->castAs<RecordType>()
+               ->getOriginalDecl()
+               ->getDefinitionOrSelf();
     } else {
       RD = cast<RecordDecl>(Next);
     }
@@ -10763,7 +10824,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
         // redeclaration lookup found nothing at all. Diagnose that now;
         // nothing will diagnose that error later.
         if (isFriend &&
-            (D.getCXXScopeSpec().getScopeRep()->isDependent() ||
+            (D.getCXXScopeSpec().getScopeRep().isDependent() ||
              (!Previous.empty() && CurContext->isDependentContext()))) {
           // ignore these
         } else if (NewFD->isCPUDispatchMultiVersion() ||
@@ -12267,11 +12328,11 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
       // template struct A<B>;
       if (NewFD->getFriendObjectKind() == Decl::FriendObjectKind::FOK_None ||
           !Destructor->getFunctionObjectParameterType()->isDependentType()) {
-        CXXRecordDecl *Record = Destructor->getParent();
-        QualType ClassType = Context.getTypeDeclType(Record);
+        CanQualType ClassType =
+            Context.getCanonicalTagType(Destructor->getParent());
 
-        DeclarationName Name = Context.DeclarationNames.getCXXDestructorName(
-            Context.getCanonicalType(ClassType));
+        DeclarationName Name =
+            Context.DeclarationNames.getCXXDestructorName(ClassType);
         if (NewFD->getDeclName() != Name) {
           Diag(NewFD->getLocation(), diag::err_destructor_name);
           NewFD->setInvalidDecl();
@@ -13275,7 +13336,8 @@ struct DiagNonTrivalCUnionDefaultInitializeVisitor
   }
 
   void visitStruct(QualType QT, const FieldDecl *FD, bool InNonTrivialUnion) {
-    const RecordDecl *RD = QT->castAs<RecordType>()->getDecl();
+    const RecordDecl *RD =
+        QT->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->isUnion()) {
       if (OrigLoc.isValid()) {
         bool IsUnion = false;
@@ -13341,7 +13403,8 @@ struct DiagNonTrivalCUnionDestructedTypeVisitor
   }
 
   void visitStruct(QualType QT, const FieldDecl *FD, bool InNonTrivialUnion) {
-    const RecordDecl *RD = QT->castAs<RecordType>()->getDecl();
+    const RecordDecl *RD =
+        QT->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->isUnion()) {
       if (OrigLoc.isValid()) {
         bool IsUnion = false;
@@ -13406,7 +13469,8 @@ struct DiagNonTrivalCUnionCopyVisitor
   }
 
   void visitStruct(QualType QT, const FieldDecl *FD, bool InNonTrivialUnion) {
-    const RecordDecl *RD = QT->castAs<RecordType>()->getDecl();
+    const RecordDecl *RD =
+        QT->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
     if (RD->isUnion()) {
       if (OrigLoc.isValid()) {
         bool IsUnion = false;
@@ -14379,7 +14443,9 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
     if (getLangOpts().CPlusPlus && Var->hasLocalStorage()) {
       if (const RecordType *Record
             = Context.getBaseElementType(Type)->getAs<RecordType>()) {
-        CXXRecordDecl *CXXRecord = cast<CXXRecordDecl>(Record->getDecl());
+        CXXRecordDecl *CXXRecord =
+            cast<CXXRecordDecl>(Record->getOriginalDecl())
+                ->getDefinitionOrSelf();
         // Mark the function (if we're in one) for further checking even if the
         // looser rules of C++11 do not require such checks, so that we can
         // diagnose incompatibilities with C++98.
@@ -17478,6 +17544,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
 
   // FIXME: Check member specializations more carefully.
   bool isMemberSpecialization = false;
+  bool IsInjectedClassName = false;
   bool Invalid = false;
 
   // We only need to do this matching if we have template parameters
@@ -17943,8 +18010,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
     // see http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#407
     if (getLangOpts().CPlusPlus) {
       if (TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(PrevDecl)) {
-        if (const TagType *TT = TD->getUnderlyingType()->getAs<TagType>()) {
-          TagDecl *Tag = TT->getDecl();
+        if (TagDecl *Tag = TD->getUnderlyingType()->getAsTagDecl()) {
           if (Tag->getDeclName() == Name &&
               Tag->getDeclContext()->getRedeclContext()
                           ->Equals(TD->getDeclContext()->getRedeclContext())) {
@@ -17954,6 +18020,15 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
             Previous.resolveKind();
           }
         }
+      } else if (auto *RD = dyn_cast<CXXRecordDecl>(PrevDecl);
+                 RD && RD->isInjectedClassName()) {
+        // If lookup found the injected class name, the previous declaration is
+        // the class being injected into.
+        PrevDecl = cast<TagDecl>(RD->getDeclContext());
+        Previous.clear();
+        Previous.addDecl(PrevDecl);
+        Previous.resolveKind();
+        IsInjectedClassName = true;
       }
     }
 
@@ -18077,78 +18152,79 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
 
           // Diagnose attempts to redefine a tag.
           if (TUK == TagUseKind::Definition) {
-            if (NamedDecl *Def = PrevTagDecl->getDefinition()) {
-              // If we're defining a specialization and the previous definition
-              // is from an implicit instantiation, don't emit an error
-              // here; we'll catch this in the general case below.
-              bool IsExplicitSpecializationAfterInstantiation = false;
-              if (isMemberSpecialization) {
-                if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Def))
-                  IsExplicitSpecializationAfterInstantiation =
-                    RD->getTemplateSpecializationKind() !=
-                    TSK_ExplicitSpecialization;
-                else if (EnumDecl *ED = dyn_cast<EnumDecl>(Def))
-                  IsExplicitSpecializationAfterInstantiation =
-                    ED->getTemplateSpecializationKind() !=
-                    TSK_ExplicitSpecialization;
-              }
-
-              // Note that clang allows ODR-like semantics for ObjC/C, i.e., do
-              // not keep more that one definition around (merge them). However,
-              // ensure the decl passes the structural compatibility check in
-              // C11 6.2.7/1 (or 6.1.2.6/1 in C89).
-              NamedDecl *Hidden = nullptr;
-              if (SkipBody &&
-                  (!hasVisibleDefinition(Def, &Hidden) || getLangOpts().C23)) {
-                // There is a definition of this tag, but it is not visible. We
-                // explicitly make use of C++'s one definition rule here, and
-                // assume that this definition is identical to the hidden one
-                // we already have. Make the existing definition visible and
-                // use it in place of this one.
-                if (!getLangOpts().CPlusPlus) {
-                  // Postpone making the old definition visible until after we
-                  // complete parsing the new one and do the structural
-                  // comparison.
-                  SkipBody->CheckSameAsPrevious = true;
-                  SkipBody->New = createTagFromNewDecl();
-                  SkipBody->Previous = Def;
-
-                  ProcessDeclAttributeList(S, SkipBody->New, Attrs);
-                  return Def;
-                } else {
-                  SkipBody->ShouldSkip = true;
-                  SkipBody->Previous = Def;
-                  makeMergedDefinitionVisible(Hidden);
-                  // Carry on and handle it like a normal definition. We'll
-                  // skip starting the definition later.
-                }
-              } else if (!IsExplicitSpecializationAfterInstantiation) {
-                // A redeclaration in function prototype scope in C isn't
-                // visible elsewhere, so merely issue a warning.
-                if (!getLangOpts().CPlusPlus && S->containedInPrototypeScope())
-                  Diag(NameLoc, diag::warn_redefinition_in_param_list) << Name;
-                else
-                  Diag(NameLoc, diag::err_redefinition) << Name;
-                notePreviousDefinition(Def,
-                                       NameLoc.isValid() ? NameLoc : KWLoc);
-                // If this is a redefinition, recover by making this
-                // struct be anonymous, which will make any later
-                // references get the previous definition.
-                Name = nullptr;
-                Previous.clear();
-                Invalid = true;
-              }
-            } else {
+            if (TagDecl *Def = PrevTagDecl->getDefinition()) {
               // If the type is currently being defined, complain
               // about a nested redefinition.
-              auto *TD = Context.getTagDeclType(PrevTagDecl)->getAsTagDecl();
-              if (TD->isBeingDefined()) {
+              if (Def->isBeingDefined()) {
                 Diag(NameLoc, diag::err_nested_redefinition) << Name;
                 Diag(PrevTagDecl->getLocation(),
                      diag::note_previous_definition);
                 Name = nullptr;
                 Previous.clear();
                 Invalid = true;
+              } else {
+                // If we're defining a specialization and the previous
+                // definition is from an implicit instantiation, don't emit an
+                // error here; we'll catch this in the general case below.
+                bool IsExplicitSpecializationAfterInstantiation = false;
+                if (isMemberSpecialization) {
+                  if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Def))
+                    IsExplicitSpecializationAfterInstantiation =
+                        RD->getTemplateSpecializationKind() !=
+                        TSK_ExplicitSpecialization;
+                  else if (EnumDecl *ED = dyn_cast<EnumDecl>(Def))
+                    IsExplicitSpecializationAfterInstantiation =
+                        ED->getTemplateSpecializationKind() !=
+                        TSK_ExplicitSpecialization;
+                }
+
+                // Note that clang allows ODR-like semantics for ObjC/C, i.e.,
+                // do not keep more that one definition around (merge them).
+                // However, ensure the decl passes the structural compatibility
+                // check in C11 6.2.7/1 (or 6.1.2.6/1 in C89).
+                NamedDecl *Hidden = nullptr;
+                if (SkipBody && (!hasVisibleDefinition(Def, &Hidden) ||
+                                 getLangOpts().C23)) {
+                  // There is a definition of this tag, but it is not visible.
+                  // We explicitly make use of C++'s one definition rule here,
+                  // and assume that this definition is identical to the hidden
+                  // one we already have. Make the existing definition visible
+                  // and use it in place of this one.
+                  if (!getLangOpts().CPlusPlus) {
+                    // Postpone making the old definition visible until after we
+                    // complete parsing the new one and do the structural
+                    // comparison.
+                    SkipBody->CheckSameAsPrevious = true;
+                    SkipBody->New = createTagFromNewDecl();
+                    SkipBody->Previous = Def;
+
+                    ProcessDeclAttributeList(S, SkipBody->New, Attrs);
+                    return Def;
+                  } else {
+                    SkipBody->ShouldSkip = true;
+                    SkipBody->Previous = Def;
+                    makeMergedDefinitionVisible(Hidden);
+                    // Carry on and handle it like a normal definition. We'll
+                    // skip starting the definition later.
+                  }
+                } else if (!IsExplicitSpecializationAfterInstantiation) {
+                  // A redeclaration in function prototype scope in C isn't
+                  // visible elsewhere, so merely issue a warning.
+                  if (!getLangOpts().CPlusPlus &&
+                      S->containedInPrototypeScope())
+                    Diag(NameLoc, diag::warn_redefinition_in_param_list)
+                        << Name;
+                  else
+                    Diag(NameLoc, diag::err_redefinition) << Name;
+                  notePreviousDefinition(Def,
+                                         NameLoc.isValid() ? NameLoc : KWLoc);
+                  // If this is a redefinition, recover by making this
+                  // struct be anonymous, which will make any later
+                  // references get the previous definition.
+                  Name = nullptr;
+                  Previous.clear();
+                  Invalid = true;
+                }
               }
             }
 
@@ -18319,14 +18395,14 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       (IsTypeSpecifier || IsTemplateParamOrArg) &&
       TUK == TagUseKind::Definition) {
     Diag(New->getLocation(), diag::err_type_defined_in_type_specifier)
-      << Context.getTagDeclType(New);
+        << Context.getCanonicalTagType(New);
     Invalid = true;
   }
 
   if (!Invalid && getLangOpts().CPlusPlus && TUK == TagUseKind::Definition &&
       DC->getDeclKind() == Decl::Enum) {
     Diag(New->getLocation(), diag::err_type_defined_in_enum)
-      << Context.getTagDeclType(New);
+        << Context.getCanonicalTagType(New);
     Invalid = true;
   }
 
@@ -18407,7 +18483,8 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       // In C23 mode, if the declaration is complete, we do not want to
       // diagnose.
       if (!getLangOpts().C23 || TUK != TagUseKind::Definition)
-        Diag(Loc, diag::warn_decl_in_param_list) << Context.getTagDeclType(New);
+        Diag(Loc, diag::warn_decl_in_param_list)
+            << Context.getCanonicalTagType(New);
     }
   }
 
@@ -18439,7 +18516,7 @@ Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
   AddPragmaAttributes(S, New);
 
   // If this has an identifier, add it to the scope stack.
-  if (TUK == TagUseKind::Friend) {
+  if (TUK == TagUseKind::Friend || IsInjectedClassName) {
     // We might be replacing an existing declaration in the lookup tables;
     // if so, borrow its access specifier.
     if (PrevDecl)
@@ -18555,14 +18632,12 @@ void Sema::ActOnStartCXXMemberDeclarations(
   //   as if it were a public member name.
   CXXRecordDecl *InjectedClassName = CXXRecordDecl::Create(
       Context, Record->getTagKind(), CurContext, Record->getBeginLoc(),
-      Record->getLocation(), Record->getIdentifier(),
-      /*PrevDecl=*/nullptr,
-      /*DelayTypeCreation=*/true);
-  Context.getTypeDeclType(InjectedClassName, Record);
+      Record->getLocation(), Record->getIdentifier());
   InjectedClassName->setImplicit();
   InjectedClassName->setAccess(AS_public);
   if (ClassTemplateDecl *Template = Record->getDescribedClassTemplate())
       InjectedClassName->setDescribedClassTemplate(Template);
+
   PushOnScopeChains(InjectedClassName, S);
   assert(InjectedClassName->isInjectedClassName() &&
          "Broken injected-class-name");
@@ -18992,7 +19067,7 @@ FieldDecl *Sema::CheckFieldDecl(DeclarationName Name, QualType T,
   if (!InvalidDecl && getLangOpts().CPlusPlus) {
     if (Record->isUnion()) {
       if (const RecordType *RT = EltTy->getAs<RecordType>()) {
-        CXXRecordDecl* RDecl = cast<CXXRecordDecl>(RT->getDecl());
+        CXXRecordDecl *RDecl = cast<CXXRecordDecl>(RT->getOriginalDecl());
         if (RDecl->getDefinition()) {
           // C++ [class.union]p1: An object of a class with a non-trivial
           // constructor, a non-trivial copy constructor, a non-trivial
@@ -19058,7 +19133,8 @@ bool Sema::CheckNontrivialField(FieldDecl *FD) {
 
   QualType EltTy = Context.getBaseElementType(FD->getType());
   if (const RecordType *RT = EltTy->getAs<RecordType>()) {
-    CXXRecordDecl *RDecl = cast<CXXRecordDecl>(RT->getDecl());
+    CXXRecordDecl *RDecl =
+        cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
     if (RDecl->getDefinition()) {
       // We check for copy constructors before constructors
       // because otherwise we'll never get complaints about
@@ -19381,7 +19457,7 @@ bool Sema::EntirelyFunctionPointers(const RecordDecl *Record) {
     }
     // If a member is a struct entirely of function pointers, that counts too.
     if (const RecordType *RT = FieldType->getAs<RecordType>()) {
-      const RecordDecl *Record = RT->getDecl();
+      const RecordDecl *Record = RT->getOriginalDecl()->getDefinitionOrSelf();
       if (Record->isStruct() && EntirelyFunctionPointers(Record))
         return true;
     }
@@ -19539,7 +19615,9 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
       EnclosingDecl->setInvalidDecl();
       continue;
     } else if (const RecordType *FDTTy = FDTy->getAs<RecordType>()) {
-      if (Record && FDTTy->getDecl()->hasFlexibleArrayMember()) {
+      if (Record && FDTTy->getOriginalDecl()
+                        ->getDefinitionOrSelf()
+                        ->hasFlexibleArrayMember()) {
         // A type which contains a flexible array member is considered to be a
         // flexible array member.
         Record->setHasFlexibleArrayMember(true);
@@ -19565,9 +19643,10 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
         // Ivars can not have abstract class types
         FD->setInvalidDecl();
       }
-      if (Record && FDTTy->getDecl()->hasObjectMember())
+      const RecordDecl *RD = FDTTy->getOriginalDecl()->getDefinitionOrSelf();
+      if (Record && RD->hasObjectMember())
         Record->setHasObjectMember(true);
-      if (Record && FDTTy->getDecl()->hasVolatileMember())
+      if (Record && RD->hasVolatileMember())
         Record->setHasVolatileMember(true);
     } else if (FDTy->isObjCObjectType()) {
       /// A field cannot be an Objective-c object
@@ -19598,8 +19677,10 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
         Record->setHasObjectMember(true);
       else if (Context.getAsArrayType(FD->getType())) {
         QualType BaseType = Context.getBaseElementType(FD->getType());
-        if (BaseType->isRecordType() &&
-            BaseType->castAs<RecordType>()->getDecl()->hasObjectMember())
+        if (BaseType->isRecordType() && BaseType->castAs<RecordType>()
+                                            ->getOriginalDecl()
+                                            ->getDefinitionOrSelf()
+                                            ->hasObjectMember())
           Record->setHasObjectMember(true);
         else if (BaseType->isObjCObjectPointerType() ||
                  BaseType.isObjCGCStrong())
@@ -19632,7 +19713,9 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
       }
 
       if (const auto *RT = FT->getAs<RecordType>()) {
-        if (RT->getDecl()->getArgPassingRestrictions() ==
+        if (RT->getOriginalDecl()
+                ->getDefinitionOrSelf()
+                ->getArgPassingRestrictions() ==
             RecordArgPassingKind::CanNeverPassInRegs)
           Record->setArgPassingRestrictions(
               RecordArgPassingKind::CanNeverPassInRegs);
@@ -20398,7 +20481,7 @@ void Sema::ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
                          Decl *EnumDeclX, ArrayRef<Decl *> Elements, Scope *S,
                          const ParsedAttributesView &Attrs) {
   EnumDecl *Enum = cast<EnumDecl>(EnumDeclX);
-  QualType EnumType = Context.getTypeDeclType(Enum);
+  CanQualType EnumType = Context.getCanonicalTagType(Enum);
 
   ProcessDeclAttributeList(S, Enum, Attrs);
   ProcessAPINotes(Enum);
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 099207727c8c8..1a7de725b000b 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -177,7 +177,7 @@ static bool threadSafetyCheckIsSmartPointer(Sema &S, const RecordType* RT) {
     return !Result.empty();
   };
 
-  const RecordDecl *Record = RT->getDecl();
+  const RecordDecl *Record = RT->getOriginalDecl()->getDefinitionOrSelf();
   bool foundStarOperator = IsOverloadedOperatorPresent(Record, OO_Star);
   bool foundArrowOperator = IsOverloadedOperatorPresent(Record, OO_Arrow);
   if (foundStarOperator && foundArrowOperator)
@@ -271,7 +271,8 @@ static bool checkRecordTypeForCapability(Sema &S, QualType Ty) {
   if (threadSafetyCheckIsSmartPointer(S, RT))
     return true;
 
-  return checkRecordDeclForAttr<CapabilityAttr>(RT->getDecl());
+  return checkRecordDeclForAttr<CapabilityAttr>(
+      RT->getOriginalDecl()->getDefinitionOrSelf());
 }
 
 static bool checkRecordTypeForScopedCapability(Sema &S, QualType Ty) {
@@ -284,7 +285,8 @@ static bool checkRecordTypeForScopedCapability(Sema &S, QualType Ty) {
   if (RT->isIncompleteType())
     return true;
 
-  return checkRecordDeclForAttr<ScopedLockableAttr>(RT->getDecl());
+  return checkRecordDeclForAttr<ScopedLockableAttr>(
+      RT->getOriginalDecl()->getDefinitionOrSelf());
 }
 
 static bool checkTypedefTypeForCapability(QualType Ty) {
@@ -1254,8 +1256,8 @@ bool Sema::isValidPointerAttrType(QualType T, bool RefOkay) {
   // The nonnull attribute, and other similar attributes, can be applied to a
   // transparent union that contains a pointer type.
   if (const RecordType *UT = T->getAsUnionType()) {
-    if (UT && UT->getDecl()->hasAttr<TransparentUnionAttr>()) {
-      RecordDecl *UD = UT->getDecl();
+    RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
+    if (UD->hasAttr<TransparentUnionAttr>()) {
       for (const auto *I : UD->fields()) {
         QualType QT = I->getType();
         if (QT->isAnyPointerType() || QT->isBlockPointerType())
@@ -3757,7 +3759,9 @@ static void handleFormatArgAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   }
   Ty = getFunctionOrMethodResultType(D);
   // replace instancetype with the class type
-  auto Instancetype = S.Context.getObjCInstanceTypeDecl()->getTypeForDecl();
+  auto *Instancetype = cast<TypedefType>(S.Context.getTypedefType(
+      ElaboratedTypeKeyword::None, /*Qualifier=*/std::nullopt,
+      S.Context.getObjCInstanceTypeDecl()));
   if (Ty->getAs<TypedefType>() == Instancetype)
     if (auto *OMD = dyn_cast<ObjCMethodDecl>(D))
       if (auto *Interface = OMD->getClassInterface())
@@ -4351,7 +4355,10 @@ static void handleTransparentUnionAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   RecordDecl *RD = nullptr;
   const auto *TD = dyn_cast<TypedefNameDecl>(D);
   if (TD && TD->getUnderlyingType()->isUnionType())
-    RD = TD->getUnderlyingType()->getAsUnionType()->getDecl();
+    RD = TD->getUnderlyingType()
+             ->getAsUnionType()
+             ->getOriginalDecl()
+             ->getDefinitionOrSelf();
   else
     RD = dyn_cast<RecordDecl>(D);
 
@@ -4704,7 +4711,7 @@ void Sema::CheckAlignasUnderalignment(Decl *D) {
   if (const auto *VD = dyn_cast<ValueDecl>(D)) {
     UnderlyingTy = DiagTy = VD->getType();
   } else {
-    UnderlyingTy = DiagTy = Context.getTagDeclType(cast<TagDecl>(D));
+    UnderlyingTy = DiagTy = Context.getCanonicalTagType(cast<TagDecl>(D));
     if (const auto *ED = dyn_cast<EnumDecl>(D))
       UnderlyingTy = ED->getIntegerType();
   }
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 5cc92ebb0171f..919331f27ce63 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "TypeLocBuilder.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTMutationListener.h"
@@ -1101,15 +1102,13 @@ static std::string printTemplateArgs(const PrintingPolicy &PrintingPolicy,
   return std::string(OS.str());
 }
 
-static bool lookupStdTypeTraitMember(Sema &S, LookupResult &TraitMemberLookup,
-                                     SourceLocation Loc, StringRef Trait,
-                                     TemplateArgumentListInfo &Args,
-                                     unsigned DiagID) {
+static QualType getStdTrait(Sema &S, SourceLocation Loc, StringRef Trait,
+                            TemplateArgumentListInfo &Args, unsigned DiagID) {
   auto DiagnoseMissing = [&] {
     if (DiagID)
       S.Diag(Loc, DiagID) << printTemplateArgs(S.Context.getPrintingPolicy(),
                                                Args, /*Params*/ nullptr);
-    return true;
+    return QualType();
   };
 
   // FIXME: Factor out duplication with lookupPromiseType in SemaCoroutine.
@@ -1122,12 +1121,12 @@ static bool lookupStdTypeTraitMember(Sema &S, LookupResult &TraitMemberLookup,
   // missing specialization, because this can only fail if the user has been
   // declaring their own names in namespace std or we don't support the
   // standard library implementation in use.
-  LookupResult Result(S, &S.PP.getIdentifierTable().get(Trait),
-                      Loc, Sema::LookupOrdinaryName);
+  LookupResult Result(S, &S.PP.getIdentifierTable().get(Trait), Loc,
+                      Sema::LookupOrdinaryName);
   if (!S.LookupQualifiedName(Result, Std))
     return DiagnoseMissing();
   if (Result.isAmbiguous())
-    return true;
+    return QualType();
 
   ClassTemplateDecl *TraitTD = Result.getAsSingle<ClassTemplateDecl>();
   if (!TraitTD) {
@@ -1135,28 +1134,31 @@ static bool lookupStdTypeTraitMember(Sema &S, LookupResult &TraitMemberLookup,
     NamedDecl *Found = *Result.begin();
     S.Diag(Loc, diag::err_std_type_trait_not_class_template) << Trait;
     S.Diag(Found->getLocation(), diag::note_declared_at);
-    return true;
+    return QualType();
   }
 
   // Build the template-id.
-  QualType TraitTy = S.CheckTemplateIdType(TemplateName(TraitTD), Loc, Args);
+  QualType TraitTy = S.CheckTemplateIdType(ElaboratedTypeKeyword::None,
+                                           TemplateName(TraitTD), Loc, Args);
   if (TraitTy.isNull())
-    return true;
+    return QualType();
+
   if (!S.isCompleteType(Loc, TraitTy)) {
     if (DiagID)
       S.RequireCompleteType(
           Loc, TraitTy, DiagID,
           printTemplateArgs(S.Context.getPrintingPolicy(), Args,
                             TraitTD->getTemplateParameters()));
-    return true;
+    return QualType();
   }
+  return TraitTy;
+}
 
-  CXXRecordDecl *RD = TraitTy->getAsCXXRecordDecl();
+static bool lookupMember(Sema &S, CXXRecordDecl *RD,
+                         LookupResult &MemberLookup) {
   assert(RD && "specialization of class template is not a class?");
-
-  // Look up the member of the trait type.
-  S.LookupQualifiedName(TraitMemberLookup, RD);
-  return TraitMemberLookup.isAmbiguous();
+  S.LookupQualifiedName(MemberLookup, RD);
+  return MemberLookup.isAmbiguous();
 }
 
 static TemplateArgumentLoc
@@ -1178,17 +1180,20 @@ static IsTupleLike isTupleLike(Sema &S, SourceLocation Loc, QualType T,
   EnterExpressionEvaluationContext ContextRAII(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
-  DeclarationName Value = S.PP.getIdentifierInfo("value");
-  LookupResult R(S, Value, Loc, Sema::LookupOrdinaryName);
-
   // Form template argument list for tuple_size<T>.
   TemplateArgumentListInfo Args(Loc, Loc);
   Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
 
+  QualType TraitTy = getStdTrait(S, Loc, "tuple_size", Args, /*DiagID=*/0);
+  if (TraitTy.isNull())
+    return IsTupleLike::NotTupleLike;
+
+  DeclarationName Value = S.PP.getIdentifierInfo("value");
+  LookupResult R(S, Value, Loc, Sema::LookupOrdinaryName);
+
   // If there's no tuple_size specialization or the lookup of 'value' is empty,
   // it's not tuple-like.
-  if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/ 0) ||
-      R.empty())
+  if (lookupMember(S, TraitTy->getAsCXXRecordDecl(), R) || R.empty())
     return IsTupleLike::NotTupleLike;
 
   // If we get this far, we've committed to the tuple interpretation, but
@@ -1228,11 +1233,15 @@ static QualType getTupleLikeElementType(Sema &S, SourceLocation Loc,
       getTrivialIntegralTemplateArgument(S, Loc, S.Context.getSizeType(), I));
   Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
 
+  QualType TraitTy =
+      getStdTrait(S, Loc, "tuple_element", Args,
+                  diag::err_decomp_decl_std_tuple_element_not_specialized);
+  if (TraitTy.isNull())
+    return QualType();
+
   DeclarationName TypeDN = S.PP.getIdentifierInfo("type");
   LookupResult R(S, TypeDN, Loc, Sema::LookupOrdinaryName);
-  if (lookupStdTypeTraitMember(
-          S, R, Loc, "tuple_element", Args,
-          diag::err_decomp_decl_std_tuple_element_not_specialized))
+  if (lookupMember(S, TraitTy->getAsCXXRecordDecl(), R))
     return QualType();
 
   auto *TD = R.getAsSingle<TypeDecl>();
@@ -1246,7 +1255,8 @@ static QualType getTupleLikeElementType(Sema &S, SourceLocation Loc,
     return QualType();
   }
 
-  return S.Context.getTypeDeclType(TD);
+  NestedNameSpecifier Qualifier(TraitTy.getTypePtr());
+  return S.Context.getTypeDeclType(ElaboratedTypeKeyword::None, Qualifier, TD);
 }
 
 namespace {
@@ -1452,7 +1462,7 @@ static DeclAccessPair findDecomposableBaseClass(Sema &S, SourceLocation Loc,
     }
 
     //   ... [accessible, implied by other rules] base class of E.
-    S.CheckBaseClassAccess(Loc, BaseType, S.Context.getRecordType(RD),
+    S.CheckBaseClassAccess(Loc, BaseType, S.Context.getCanonicalTagType(RD),
                            *BestPath, diag::err_decomp_decl_inaccessible_base);
     AS = BestPath->Access;
 
@@ -1528,8 +1538,8 @@ static bool checkMemberDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
   const auto *RD = cast_or_null<CXXRecordDecl>(BasePair.getDecl());
   if (!RD)
     return true;
-  QualType BaseType = S.Context.getQualifiedType(S.Context.getRecordType(RD),
-                                                 DecompType.getQualifiers());
+  QualType BaseType = S.Context.getQualifiedType(
+      S.Context.getCanonicalTagType(RD), DecompType.getQualifiers());
 
   auto *DD = cast<DecompositionDecl>(Src);
   unsigned NumFields = llvm::count_if(
@@ -2174,7 +2184,10 @@ static bool CheckConstexprCtorInitializer(Sema &SemaRef,
       return false;
     }
   } else if (Field->isAnonymousStructOrUnion()) {
-    const RecordDecl *RD = Field->getType()->castAs<RecordType>()->getDecl();
+    const RecordDecl *RD = Field->getType()
+                               ->castAs<RecordType>()
+                               ->getOriginalDecl()
+                               ->getDefinitionOrSelf();
     for (auto *I : RD->fields())
       // If an anonymous union contains an anonymous struct of which any member
       // is initialized, all members must be initialized.
@@ -2666,7 +2679,9 @@ void Sema::DiagnoseImmediateEscalatingReason(FunctionDecl *FD) {
       return DynamicRecursiveASTVisitor::TraverseCXXConstructorDecl(Ctr);
     }
 
-    bool TraverseType(QualType T) override { return true; }
+    bool TraverseType(QualType T, bool TraverseQualifier) override {
+      return true;
+    }
     bool VisitBlockExpr(BlockExpr *T) override { return true; }
 
   } Visitor(*this, FD);
@@ -2969,7 +2984,8 @@ bool Sema::AttachBaseSpecifiers(CXXRecordDecl *Class,
         NoteIndirectBases(Context, IndirectBaseTypes, NewBaseType);
 
       if (const RecordType *Record = NewBaseType->getAs<RecordType>()) {
-        const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
+        const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getOriginalDecl())
+                                      ->getDefinitionOrSelf();
         if (Class->isInterface() &&
               (!RD->isInterfaceLike() ||
                KnownBase->getAccessSpecifier() != AS_public)) {
@@ -3050,7 +3066,7 @@ bool Sema::IsDerivedFrom(SourceLocation Loc, CXXRecordDecl *Derived,
 
   // FIXME: In a modules build, do we need the entire path to be visible for us
   // to be able to use the inheritance relationship?
-  if (!isCompleteType(Loc, Context.getTypeDeclType(Derived)) &&
+  if (!isCompleteType(Loc, Context.getCanonicalTagType(Derived)) &&
       !Derived->isBeingDefined())
     return false;
 
@@ -3205,7 +3221,8 @@ std::string Sema::getAmbiguousPathsDisplayString(CXXBasePaths &Paths) {
       // We haven't displayed a path to this particular base
       // class subobject yet.
       PathDisplayStr += "\n    ";
-      PathDisplayStr += Context.getTypeDeclType(Paths.getOrigin()).getAsString();
+      PathDisplayStr += QualType(Context.getCanonicalTagType(Paths.getOrigin()))
+                            .getAsString();
       for (CXXBasePath::const_iterator Element = Path->begin();
            Element != Path->end(); ++Element)
         PathDisplayStr += " -> " + Element->Base->getType().getAsString();
@@ -4245,7 +4262,7 @@ static bool FindBaseInitializer(Sema &SemaRef,
     CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
                        /*DetectVirtual=*/false);
     if (SemaRef.IsDerivedFrom(ClassDecl->getLocation(),
-                              SemaRef.Context.getTypeDeclType(ClassDecl),
+                              SemaRef.Context.getCanonicalTagType(ClassDecl),
                               BaseType, Paths)) {
       for (CXXBasePaths::paths_iterator Path = Paths.begin();
            Path != Paths.end(); ++Path) {
@@ -4481,7 +4498,7 @@ Sema::BuildMemInitializer(Decl *ConstructorD,
       if (getLangOpts().MSVCCompat && !getLangOpts().CPlusPlus20) {
         if (auto UnqualifiedBase = R.getAsSingle<ClassTemplateDecl>()) {
           auto *TempSpec = cast<TemplateSpecializationType>(
-              UnqualifiedBase->getInjectedClassNameSpecialization());
+              UnqualifiedBase->getCanonicalInjectedSpecializationType(Context));
           TemplateName TN = TempSpec->getTemplateName();
           for (auto const &Base : ClassDecl->bases()) {
             auto BaseTemplate =
@@ -4545,14 +4562,29 @@ Sema::BuildMemInitializer(Decl *ConstructorD,
     }
 
     if (BaseType.isNull()) {
-      BaseType = getElaboratedType(ElaboratedTypeKeyword::None, SS,
-                                   Context.getTypeDeclType(TyD));
       MarkAnyDeclReferenced(TyD->getLocation(), TyD, /*OdrUse=*/false);
-      TInfo = Context.CreateTypeSourceInfo(BaseType);
-      ElaboratedTypeLoc TL = TInfo->getTypeLoc().castAs<ElaboratedTypeLoc>();
-      TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IdLoc);
-      TL.setElaboratedKeywordLoc(SourceLocation());
-      TL.setQualifierLoc(SS.getWithLocInContext(Context));
+
+      TypeLocBuilder TLB;
+      if (const auto *TD = dyn_cast<TagDecl>(TyD)) {
+        BaseType = Context.getTagType(ElaboratedTypeKeyword::None,
+                                      SS.getScopeRep(), TD, /*OwnsTag=*/false);
+        auto TL = TLB.push<TagTypeLoc>(BaseType);
+        TL.setElaboratedKeywordLoc(SourceLocation());
+        TL.setQualifierLoc(SS.getWithLocInContext(Context));
+        TL.setNameLoc(IdLoc);
+      } else if (auto *TN = dyn_cast<TypedefNameDecl>(TyD)) {
+        BaseType = Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                          SS.getScopeRep(), TN);
+        TLB.push<TypedefTypeLoc>(BaseType).set(
+            /*ElaboratedKeywordLoc=*/SourceLocation(),
+            SS.getWithLocInContext(Context), IdLoc);
+      } else {
+        // FIXME: What else can appear here?
+        assert(SS.isEmpty());
+        BaseType = Context.getTypeDeclType(TyD);
+        TLB.pushTypeSpec(BaseType).setNameLoc(IdLoc);
+      }
+      TInfo = TLB.getTypeSourceInfo(Context, BaseType);
     }
   }
 
@@ -4661,10 +4693,12 @@ Sema::BuildDelegatingInitializer(TypeSourceInfo *TInfo, Expr *Init,
     Args = MultiExprArg(ParenList->getExprs(), ParenList->getNumExprs());
   }
 
+  CanQualType ClassType = Context.getCanonicalTagType(ClassDecl);
+
   SourceRange InitRange = Init->getSourceRange();
   // Initialize the object.
-  InitializedEntity DelegationEntity = InitializedEntity::InitializeDelegation(
-                                     QualType(ClassDecl->getTypeForDecl(), 0));
+  InitializedEntity DelegationEntity =
+      InitializedEntity::InitializeDelegation(ClassType);
   InitializationKind Kind =
       InitList ? InitializationKind::CreateDirectList(
                      NameLoc, Init->getBeginLoc(), Init->getEndLoc())
@@ -4686,9 +4720,8 @@ Sema::BuildDelegatingInitializer(TypeSourceInfo *TInfo, Expr *Init,
   }
 
   if (DelegationInit.isInvalid()) {
-    DelegationInit =
-        CreateRecoveryExpr(InitRange.getBegin(), InitRange.getEnd(), Args,
-                           QualType(ClassDecl->getTypeForDecl(), 0));
+    DelegationInit = CreateRecoveryExpr(InitRange.getBegin(),
+                                        InitRange.getEnd(), Args, ClassType);
     if (DelegationInit.isInvalid())
       return true;
   } else {
@@ -4753,8 +4786,7 @@ Sema::BuildBaseInitializer(QualType BaseType, TypeSourceInfo *BaseTInfo,
   const CXXBaseSpecifier *DirectBaseSpec = nullptr;
   const CXXBaseSpecifier *VirtualBaseSpec = nullptr;
   if (!Dependent) {
-    if (Context.hasSameUnqualifiedType(QualType(ClassDecl->getTypeForDecl(),0),
-                                       BaseType))
+    if (declaresSameEntity(ClassDecl, BaseType->getAsCXXRecordDecl()))
       return BuildDelegatingInitializer(BaseTInfo, Init, ClassDecl);
 
     FindBaseInitializer(*this, ClassDecl, BaseType, DirectBaseSpec,
@@ -4774,7 +4806,7 @@ Sema::BuildBaseInitializer(QualType BaseType, TypeSourceInfo *BaseTInfo,
         Dependent = true;
       else
         return Diag(BaseLoc, diag::err_not_direct_base_or_virtual)
-               << BaseType << Context.getTypeDeclType(ClassDecl)
+               << BaseType << Context.getCanonicalTagType(ClassDecl)
                << BaseTInfo->getTypeLoc().getSourceRange();
     }
   }
@@ -5078,9 +5110,9 @@ BuildImplicitMemberInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
     if (FieldBaseElementType->isReferenceType()) {
       SemaRef.Diag(Constructor->getLocation(),
                    diag::err_uninitialized_member_in_ctor)
-      << (int)Constructor->isImplicit()
-      << SemaRef.Context.getTagDeclType(Constructor->getParent())
-      << 0 << Field->getDeclName();
+          << (int)Constructor->isImplicit()
+          << SemaRef.Context.getCanonicalTagType(Constructor->getParent()) << 0
+          << Field->getDeclName();
       SemaRef.Diag(Field->getLocation(), diag::note_declared_at);
       return true;
     }
@@ -5088,9 +5120,9 @@ BuildImplicitMemberInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
     if (FieldBaseElementType.isConstQualified()) {
       SemaRef.Diag(Constructor->getLocation(),
                    diag::err_uninitialized_member_in_ctor)
-      << (int)Constructor->isImplicit()
-      << SemaRef.Context.getTagDeclType(Constructor->getParent())
-      << 1 << Field->getDeclName();
+          << (int)Constructor->isImplicit()
+          << SemaRef.Context.getCanonicalTagType(Constructor->getParent()) << 1
+          << Field->getDeclName();
       SemaRef.Diag(Field->getLocation(), diag::note_declared_at);
       return true;
     }
@@ -5391,7 +5423,7 @@ static void MarkBaseDestructorsReferenced(Sema &S, SourceLocation Location,
     S.CheckDestructorAccess(Base.getBeginLoc(), Dtor,
                             S.PDiag(diag::err_access_dtor_base)
                                 << Base.getType() << Base.getSourceRange(),
-                            S.Context.getTypeDeclType(ClassDecl));
+                            S.Context.getCanonicalTagType(ClassDecl));
 
     S.MarkFunctionReferenced(Location, Dtor);
     S.DiagnoseUseOfDecl(Dtor, Location);
@@ -5594,9 +5626,9 @@ bool Sema::SetCtorInitializers(CXXConstructorDecl *Constructor, bool AnyErrors,
 
 static void PopulateKeysForFields(FieldDecl *Field, SmallVectorImpl<const void*> &IdealInits) {
   if (const RecordType *RT = Field->getType()->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl();
     if (RD->isAnonymousStructOrUnion()) {
-      for (auto *Field : RD->fields())
+      for (auto *Field : RD->getDefinitionOrSelf()->fields())
         PopulateKeysForFields(Field, IdealInits);
       return;
     }
@@ -5928,16 +5960,14 @@ void Sema::MarkVirtualBaseDestructorsReferenced(
     if (!Dtor)
       continue;
 
-    if (CheckDestructorAccess(
-            ClassDecl->getLocation(), Dtor,
-            PDiag(diag::err_access_dtor_vbase)
-                << Context.getTypeDeclType(ClassDecl) << VBase.getType(),
-            Context.getTypeDeclType(ClassDecl)) ==
-        AR_accessible) {
+    CanQualType CT = Context.getCanonicalTagType(ClassDecl);
+    if (CheckDestructorAccess(ClassDecl->getLocation(), Dtor,
+                              PDiag(diag::err_access_dtor_vbase)
+                                  << CT << VBase.getType(),
+                              CT) == AR_accessible) {
       CheckDerivedToBaseConversion(
-          Context.getTypeDeclType(ClassDecl), VBase.getType(),
-          diag::err_access_dtor_vbase, 0, ClassDecl->getLocation(),
-          SourceRange(), DeclarationName(), nullptr);
+          CT, VBase.getType(), diag::err_access_dtor_vbase, 0,
+          ClassDecl->getLocation(), SourceRange(), DeclarationName(), nullptr);
     }
 
     MarkFunctionReferenced(Location, Dtor);
@@ -6052,10 +6082,8 @@ struct AbstractUsageInfo {
   bool Invalid;
 
   AbstractUsageInfo(Sema &S, CXXRecordDecl *Record)
-    : S(S), Record(Record),
-      AbstractType(S.Context.getCanonicalType(
-                   S.Context.getTypeDeclType(Record))),
-      Invalid(false) {}
+      : S(S), Record(Record),
+        AbstractType(S.Context.getCanonicalTagType(Record)), Invalid(false) {}
 
   void DiagnoseAbstractType() {
     if (Invalid) return;
@@ -6868,8 +6896,8 @@ static bool canPassInRegisters(Sema &S, CXXRecordDecl *D,
     bool isAArch64 = S.Context.getTargetInfo().getTriple().isAArch64();
     uint64_t TypeSize = isAArch64 ? 128 : 64;
 
-    if (CopyCtorIsTrivial &&
-        S.getASTContext().getTypeSize(D->getTypeForDecl()) <= TypeSize)
+    if (CopyCtorIsTrivial && S.getASTContext().getTypeSize(
+                                 S.Context.getCanonicalTagType(D)) <= TypeSize)
       return true;
     return false;
   }
@@ -7000,7 +7028,8 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
     if ((!dtor || (!dtor->isVirtual() && dtor->getAccess() == AS_public)) &&
         !Record->hasAttr<FinalAttr>())
       Diag(dtor ? dtor->getLocation() : Record->getLocation(),
-           diag::warn_non_virtual_dtor) << Context.getRecordType(Record);
+           diag::warn_non_virtual_dtor)
+          << Context.getCanonicalTagType(Record);
   }
 
   if (Record->isAbstract()) {
@@ -7022,7 +7051,7 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
                    (FA->isSpelledAsSealed() ? " sealed" : " final"));
         Diag(Record->getLocation(),
              diag::note_final_dtor_non_final_class_silence)
-            << Context.getRecordType(Record) << FA->isSpelledAsSealed();
+            << Context.getCanonicalTagType(Record) << FA->isSpelledAsSealed();
       }
     }
   }
@@ -7177,7 +7206,7 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
         return true;
       };
       EffectivelyConstexprDestructor =
-          Check(QualType(Record->getTypeForDecl(), 0), Check);
+          Check(Context.getCanonicalTagType(Record), Check);
     }
 
     // Define defaulted constexpr virtual functions that override a base class
@@ -7333,7 +7362,7 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
                 NewDecls.empty() ? NewKind : DeleteKind);
         Diag(Record->getLocation(),
              diag::err_type_aware_allocator_missing_matching_operator)
-            << FoundOperator << Context.getRecordType(Record)
+            << FoundOperator << Context.getCanonicalTagType(Record)
             << MissingOperator;
         for (auto MD : NewDecls)
           Diag(MD->getLocation(),
@@ -7572,7 +7601,9 @@ static bool defaultedSpecialMemberIsConstexpr(
       const RecordType *BaseType = B.getType()->getAs<RecordType>();
       if (!BaseType)
         continue;
-      CXXRecordDecl *BaseClassDecl = cast<CXXRecordDecl>(BaseType->getDecl());
+      CXXRecordDecl *BaseClassDecl =
+          cast<CXXRecordDecl>(BaseType->getOriginalDecl())
+              ->getDefinitionOrSelf();
       if (!specialMemberIsConstexpr(S, BaseClassDecl, CSM, 0, ConstArg,
                                     InheritedCtor, Inherited))
         return false;
@@ -7595,7 +7626,9 @@ static bool defaultedSpecialMemberIsConstexpr(
         continue;
       QualType BaseType = S.Context.getBaseElementType(F->getType());
       if (const RecordType *RecordTy = BaseType->getAs<RecordType>()) {
-        CXXRecordDecl *FieldRecDecl = cast<CXXRecordDecl>(RecordTy->getDecl());
+        CXXRecordDecl *FieldRecDecl =
+            cast<CXXRecordDecl>(RecordTy->getOriginalDecl())
+                ->getDefinitionOrSelf();
         if (!specialMemberIsConstexpr(S, FieldRecDecl, CSM,
                                       BaseType.getCVRQualifiers(),
                                       ConstArg && !F->isMutable()))
@@ -7782,9 +7815,9 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
     ReturnType = Type->getReturnType();
     QualType ThisType = MD->getFunctionObjectParameterType();
 
-    QualType DeclType = Context.getTypeDeclType(RD);
-    DeclType = Context.getElaboratedType(ElaboratedTypeKeyword::None, nullptr,
-                                         DeclType, nullptr);
+    QualType DeclType =
+        Context.getTagType(ElaboratedTypeKeyword::None,
+                           /*Qualifier=*/std::nullopt, RD, /*OwnsTag=*/false);
     DeclType = Context.getAddrSpaceQualType(
         DeclType, ThisType.getQualifiers().getAddressSpace());
     QualType ExpectedReturnType = Context.getLValueReferenceType(DeclType);
@@ -7819,7 +7852,7 @@ bool Sema::CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
     if (!ExplicitObjectParameter.isNull() &&
         (!ExplicitObjectParameter->isReferenceType() ||
          !Context.hasSameType(ExplicitObjectParameter.getNonReferenceType(),
-                              Context.getRecordType(RD)))) {
+                              Context.getCanonicalTagType(RD)))) {
       if (DeleteOnTypeMismatch)
         ShouldDeleteForTypeMismatch = true;
       else {
@@ -8278,7 +8311,7 @@ class DefaultedComparisonAnalyzer
           Best->FoundDecl.getDecl()->isCXXClassMember()) {
         QualType ObjectType = Subobj.Kind == Subobject::Member
                                   ? Args[0]->getType()
-                                  : S.Context.getRecordType(RD);
+                                  : S.Context.getCanonicalTagType(RD);
         if (!S.isMemberAccessibleForDeletion(
                 ArgClass, Best->FoundDecl, ObjectType, Subobj.Loc,
                 Diagnose == ExplainDeleted
@@ -8979,7 +9012,7 @@ bool Sema::CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *FD,
       bool Ok = !IsMethod || FD->hasCXXExplicitFunctionObjectParameter();
       QualType ExpectedTy;
       if (RD)
-        ExpectedTy = Context.getRecordType(RD);
+        ExpectedTy = Context.getCanonicalTagType(RD);
       if (auto *Ref = CTy->getAs<LValueReferenceType>()) {
         CTy = Ref->getPointeeType();
         if (RD)
@@ -9002,7 +9035,7 @@ bool Sema::CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *FD,
         // corresponding defaulted 'operator<=>' already.
         if (!FD->isImplicit()) {
           if (RD) {
-            QualType PlainTy = Context.getRecordType(RD);
+            CanQualType PlainTy = Context.getCanonicalTagType(RD);
             QualType RefTy =
                 Context.getLValueReferenceType(PlainTy.withConst());
             Diag(FD->getLocation(), diag::err_defaulted_comparison_param)
@@ -9033,7 +9066,7 @@ bool Sema::CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *FD,
   } else {
     // Out of class, require the defaulted comparison to be a friend (of a
     // complete type, per CWG2547).
-    if (RequireCompleteType(FD->getLocation(), Context.getRecordType(RD),
+    if (RequireCompleteType(FD->getLocation(), Context.getCanonicalTagType(RD),
                             diag::err_defaulted_comparison_not_friend, int(DCK),
                             int(1)))
       return true;
@@ -9486,15 +9519,15 @@ bool SpecialMemberDeletionInfo::isAccessible(Subobject Subobj,
                                              CXXMethodDecl *target) {
   /// If we're operating on a base class, the object type is the
   /// type of this special member.
-  QualType objectTy;
+  CanQualType objectTy;
   AccessSpecifier access = target->getAccess();
   if (CXXBaseSpecifier *base = Subobj.dyn_cast<CXXBaseSpecifier*>()) {
-    objectTy = S.Context.getTypeDeclType(MD->getParent());
+    objectTy = S.Context.getCanonicalTagType(MD->getParent());
     access = CXXRecordDecl::MergeAccess(base->getAccessSpecifier(), access);
 
   // If we're operating on a field, the object type is the type of the field.
   } else {
-    objectTy = S.Context.getTypeDeclType(target->getParent());
+    objectTy = S.Context.getCanonicalTagType(target->getParent());
   }
 
   return S.isMemberAccessibleForDeletion(
@@ -9912,7 +9945,7 @@ bool Sema::ShouldDeleteSpecialMember(CXXMethodDecl *MD,
   //    results in an ambiguity or in a function that is deleted or inaccessible
   if (CSM == CXXSpecialMemberKind::Destructor && MD->isVirtual()) {
     FunctionDecl *OperatorDelete = nullptr;
-    QualType DeallocType = Context.getRecordType(RD);
+    CanQualType DeallocType = Context.getCanonicalTagType(RD);
     DeclarationName Name =
       Context.DeclarationNames.getCXXOperatorName(OO_Delete);
     ImplicitDeallocationParameters IDP = {
@@ -10245,7 +10278,7 @@ static bool checkTrivialClassMembers(Sema &S, CXXRecordDecl *RD,
 
 void Sema::DiagnoseNontrivial(const CXXRecordDecl *RD,
                               CXXSpecialMemberKind CSM) {
-  QualType Ty = Context.getRecordType(RD);
+  CanQualType Ty = Context.getCanonicalTagType(RD);
 
   bool ConstArg = (CSM == CXXSpecialMemberKind::CopyConstructor ||
                    CSM == CXXSpecialMemberKind::CopyAssignment);
@@ -10293,9 +10326,9 @@ bool Sema::SpecialMemberIsTrivial(CXXMethodDecl *MD, CXXSpecialMemberKind CSM,
          ClangABICompat14)) {
       if (Diagnose)
         Diag(Param0->getLocation(), diag::note_nontrivial_param_type)
-          << Param0->getSourceRange() << Param0->getType()
-          << Context.getLValueReferenceType(
-               Context.getRecordType(RD).withConst());
+            << Param0->getSourceRange() << Param0->getType()
+            << Context.getLValueReferenceType(
+                   Context.getCanonicalTagType(RD).withConst());
       return false;
     }
 
@@ -10312,8 +10345,8 @@ bool Sema::SpecialMemberIsTrivial(CXXMethodDecl *MD, CXXSpecialMemberKind CSM,
     if (!RT || RT->getPointeeType().getCVRQualifiers()) {
       if (Diagnose)
         Diag(Param0->getLocation(), diag::note_nontrivial_param_type)
-          << Param0->getSourceRange() << Param0->getType()
-          << Context.getRValueReferenceType(Context.getRecordType(RD));
+            << Param0->getSourceRange() << Param0->getType()
+            << Context.getRValueReferenceType(Context.getCanonicalTagType(RD));
       return false;
     }
     break;
@@ -10432,8 +10465,10 @@ struct FindHiddenVirtualMethod {
   /// method overloads virtual methods in a base class without overriding any,
   /// to be used with CXXRecordDecl::lookupInBases().
   bool operator()(const CXXBaseSpecifier *Specifier, CXXBasePath &Path) {
-    RecordDecl *BaseRecord =
-        Specifier->getType()->castAs<RecordType>()->getDecl();
+    RecordDecl *BaseRecord = Specifier->getType()
+                                 ->castAs<RecordType>()
+                                 ->getOriginalDecl()
+                                 ->getDefinitionOrSelf();
 
     DeclarationName Name = Method->getDeclName();
     assert(Name.getNameKind() == DeclarationName::Identifier);
@@ -10591,7 +10626,8 @@ void Sema::checkIllFormedTrivialABIStruct(CXXRecordDecl &RD) {
 
     if (const auto *RT = FT->getBaseElementTypeUnsafe()->getAs<RecordType>())
       if (!RT->isDependentType() &&
-          !cast<CXXRecordDecl>(RT->getDecl())->canPassInRegisters()) {
+          !cast<CXXRecordDecl>(RT->getOriginalDecl()->getDefinitionOrSelf())
+               ->canPassInRegisters()) {
         PrintDiagAndRemoveAttr(5);
         return;
       }
@@ -10626,7 +10662,7 @@ void Sema::checkIllFormedTrivialABIStruct(CXXRecordDecl &RD) {
 
 void Sema::checkIncorrectVTablePointerAuthenticationAttribute(
     CXXRecordDecl &RD) {
-  if (RequireCompleteType(RD.getLocation(), Context.getRecordType(&RD),
+  if (RequireCompleteType(RD.getLocation(), Context.getCanonicalTagType(&RD),
                           diag::err_incomplete_type_vtable_pointer_auth))
     return;
 
@@ -11056,9 +11092,10 @@ void Sema::CheckConstructor(CXXConstructorDecl *Constructor) {
   if (!Constructor->isInvalidDecl() &&
       Constructor->hasOneParamOrDefaultArgs() &&
       !Constructor->isFunctionTemplateSpecialization()) {
-    QualType ParamType = Constructor->getParamDecl(0)->getType();
-    QualType ClassTy = Context.getTagDeclType(ClassDecl);
-    if (Context.getCanonicalType(ParamType).getUnqualifiedType() == ClassTy) {
+    CanQualType ParamType =
+        Constructor->getParamDecl(0)->getType()->getCanonicalTypeUnqualified();
+    CanQualType ClassTy = Context.getCanonicalTagType(ClassDecl);
+    if (ParamType == ClassTy) {
       SourceLocation ParamLoc = Constructor->getParamDecl(0)->getLocation();
       const char *ConstRef
         = Constructor->getParamDecl(0)->getIdentifier() ? "const &"
@@ -11429,8 +11466,7 @@ Decl *Sema::ActOnConversionDeclarator(CXXConversionDecl *Conversion) {
   //   same object type (or a reference to it), to a (possibly
   //   cv-qualified) base class of that type (or a reference to it),
   //   or to (possibly cv-qualified) void.
-  QualType ClassType
-    = Context.getCanonicalType(Context.getTypeDeclType(ClassDecl));
+  CanQualType ClassType = Context.getCanonicalTagType(ClassDecl);
   if (const ReferenceType *ConvTypeRef = ConvType->getAs<ReferenceType>())
     ConvType = ConvTypeRef->getPointeeType();
   if (Conversion->getTemplateSpecializationKind() != TSK_Undeclared &&
@@ -11698,8 +11734,8 @@ bool Sema::CheckDeductionGuideDeclarator(Declarator &D, QualType &R,
       const QualifiedTemplateName *Qualifiers =
           SpecifiedName.getAsQualifiedTemplateName();
       assert(Qualifiers && "expected QualifiedTemplate");
-      bool SimplyWritten = !Qualifiers->hasTemplateKeyword() &&
-                           Qualifiers->getQualifier() == nullptr;
+      bool SimplyWritten =
+          !Qualifiers->hasTemplateKeyword() && !Qualifiers->getQualifier();
       if (SimplyWritten && TemplateMatches)
         AcceptableReturnType = true;
       else {
@@ -11930,7 +11966,7 @@ Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
 
 /// getNamespaceDecl - Returns the namespace a decl represents. If the decl
 /// is a namespace alias, returns the namespace it points to.
-static inline NamespaceDecl *getNamespaceDecl(NamedDecl *D) {
+static inline NamespaceDecl *getNamespaceDecl(NamespaceBaseDecl *D) {
   if (NamespaceAliasDecl *AD = dyn_cast_or_null<NamespaceAliasDecl>(D))
     return AD->getNamespace();
   return dyn_cast_or_null<NamespaceDecl>(D);
@@ -12004,10 +12040,11 @@ QualType Sema::CheckComparisonCategoryType(ComparisonCategoryType Kind,
   // Use an elaborated type for diagnostics which has a name containing the
   // prepended 'std' namespace but not any inline namespace names.
   auto TyForDiags = [&](ComparisonCategoryInfo *Info) {
-    auto *NNS =
-        NestedNameSpecifier::Create(Context, nullptr, getStdNamespace());
-    return Context.getElaboratedType(ElaboratedTypeKeyword::None, NNS,
-                                     Info->getType());
+    NestedNameSpecifier Qualifier(Context, getStdNamespace(),
+                                  /*Prefix=*/std::nullopt);
+    return Context.getTagType(ElaboratedTypeKeyword::None, Qualifier,
+                              Info->Record,
+                              /*OwnsTag=*/false);
   };
 
   // Check if we've already successfully checked the comparison category type
@@ -12143,26 +12180,14 @@ static bool isStdClassTemplate(Sema &S, QualType SugaredType, QualType *TypeArg,
 
   ClassTemplateDecl *Template = nullptr;
   ArrayRef<TemplateArgument> Arguments;
-  {
-    const TemplateSpecializationType *TST =
-        SugaredType->getAsNonAliasTemplateSpecializationType();
-    if (!TST)
-      if (const auto *ICN = SugaredType->getAs<InjectedClassNameType>())
-        TST = ICN->getInjectedTST();
-    if (TST) {
-      Template = dyn_cast_or_null<ClassTemplateDecl>(
-          TST->getTemplateName().getAsTemplateDecl());
-      Arguments = TST->template_arguments();
-    } else if (const RecordType *RT = SugaredType->getAs<RecordType>()) {
-      ClassTemplateSpecializationDecl *Specialization =
-          dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl());
-      if (!Specialization) {
-        ReportMatchingNameAsMalformed(RT->getDecl());
-        return false;
-      }
-      Template = Specialization->getSpecializedTemplate();
-      Arguments = Specialization->getTemplateArgs().asArray();
-    }
+  if (const TemplateSpecializationType *TST =
+          SugaredType->getAsNonAliasTemplateSpecializationType()) {
+    Template = dyn_cast_or_null<ClassTemplateDecl>(
+        TST->getTemplateName().getAsTemplateDecl());
+    Arguments = TST->template_arguments();
+  } else if (const auto *TT = SugaredType->getAs<TagType>()) {
+    Template = TT->getTemplateDecl();
+    Arguments = TT->getTemplateArgs(S.Context);
   }
 
   if (!Template) {
@@ -12288,13 +12313,8 @@ static QualType BuildStdClassTemplate(Sema &S, ClassTemplateDecl *CTD,
   auto TSI = S.Context.getTrivialTypeSourceInfo(TypeParam, Loc);
   Args.addArgument(TemplateArgumentLoc(TemplateArgument(TypeParam), TSI));
 
-  QualType T = S.CheckTemplateIdType(TemplateName(CTD), Loc, Args);
-  if (T.isNull())
-    return QualType();
-
-  return S.Context.getElaboratedType(
-      ElaboratedTypeKeyword::None,
-      NestedNameSpecifier::Create(S.Context, nullptr, S.getStdNamespace()), T);
+  return S.CheckTemplateIdType(ElaboratedTypeKeyword::None, TemplateName(CTD),
+                               Loc, Args);
 }
 
 QualType Sema::BuildStdInitializerList(QualType Element, SourceLocation Loc) {
@@ -12436,9 +12456,7 @@ Decl *Sema::ActOnUsingDirective(Scope *S, SourceLocation UsingLoc,
   S = S->getDeclParent();
 
   UsingDirectiveDecl *UDir = nullptr;
-  NestedNameSpecifier *Qualifier = nullptr;
-  if (SS.isSet())
-    Qualifier = SS.getScopeRep();
+  NestedNameSpecifier Qualifier = SS.getScopeRep();
 
   // Lookup namespace name.
   LookupResult R(*this, NamespcName, IdentLoc, LookupNamespaceName);
@@ -12450,14 +12468,16 @@ Decl *Sema::ActOnUsingDirective(Scope *S, SourceLocation UsingLoc,
     R.clear();
     // Allow "using namespace std;" or "using namespace ::std;" even if
     // "std" hasn't been defined yet, for GCC compatibility.
-    if ((!Qualifier || Qualifier->getKind() == NestedNameSpecifier::Global) &&
+    if ((!Qualifier ||
+         Qualifier.getKind() == NestedNameSpecifier::Kind::Global) &&
         NamespcName->isStr("std")) {
       Diag(IdentLoc, diag::ext_using_undefined_std);
       R.addDecl(getOrCreateStdNamespace());
       R.resolveKind();
     }
     // Otherwise, attempt typo correction.
-    else TryNamespaceTypoCorrection(*this, R, S, SS, IdentLoc, NamespcName);
+    else
+      TryNamespaceTypoCorrection(*this, R, S, SS, IdentLoc, NamespcName);
   }
 
   if (!R.empty()) {
@@ -12584,7 +12604,7 @@ Decl *Sema::ActOnUsingDeclaration(Scope *S, AccessSpecifier AS,
         DiagnoseUnexpandedParameterPack(TargetNameInfo, UPPC_UsingDeclaration))
       return nullptr;
   } else {
-    if (!SS.getScopeRep()->containsUnexpandedParameterPack() &&
+    if (!SS.getScopeRep().containsUnexpandedParameterPack() &&
         !TargetNameInfo.containsUnexpandedParameterPack()) {
       Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
         << SourceRange(SS.getBeginLoc(), TargetNameInfo.getEndLoc());
@@ -12869,7 +12889,7 @@ UsingShadowDecl *Sema::BuildUsingShadowDecl(Scope *S, BaseUsingDecl *BUD,
     UsingDecl *Using = cast<UsingDecl>(BUD);
     bool IsVirtualBase =
         isVirtualDirectBase(cast<CXXRecordDecl>(CurContext),
-                            Using->getQualifier()->getAsRecordDecl());
+                            Using->getQualifier().getAsRecordDecl());
     Shadow = ConstructorUsingShadowDecl::Create(
         Context, CurContext, Using->getLocation(), Using, Orig, IsVirtualBase);
   } else {
@@ -12935,7 +12955,7 @@ namespace {
 class UsingValidatorCCC final : public CorrectionCandidateCallback {
 public:
   UsingValidatorCCC(bool HasTypenameKeyword, bool IsInstantiation,
-                    NestedNameSpecifier *NNS, CXXRecordDecl *RequireMemberOf)
+                    NestedNameSpecifier NNS, CXXRecordDecl *RequireMemberOf)
       : HasTypenameKeyword(HasTypenameKeyword),
         IsInstantiation(IsInstantiation), OldNNS(NNS),
         RequireMemberOf(RequireMemberOf) {}
@@ -12962,24 +12982,23 @@ class UsingValidatorCCC final : public CorrectionCandidateCallback {
         ASTContext &Ctx = ND->getASTContext();
         if (!Ctx.getLangOpts().CPlusPlus11)
           return false;
-        QualType FoundType = Ctx.getRecordType(FoundRecord);
+        CanQualType FoundType = Ctx.getCanonicalTagType(FoundRecord);
 
         // Check that the injected-class-name is named as a member of its own
         // type; we don't want to suggest 'using Derived::Base;', since that
         // means something else.
-        NestedNameSpecifier *Specifier =
-            Candidate.WillReplaceSpecifier()
-                ? Candidate.getCorrectionSpecifier()
-                : OldNNS;
-        if (!Specifier->getAsType() ||
-            !Ctx.hasSameType(QualType(Specifier->getAsType(), 0), FoundType))
+        NestedNameSpecifier Specifier = Candidate.WillReplaceSpecifier()
+                                            ? Candidate.getCorrectionSpecifier()
+                                            : OldNNS;
+        if (Specifier.getKind() != NestedNameSpecifier::Kind::Type ||
+            !Ctx.hasSameType(QualType(Specifier.getAsType(), 0), FoundType))
           return false;
 
         // Check that this inheriting constructor declaration actually names a
         // direct base class of the current class.
         bool AnyDependentBases = false;
         if (!findDirectBaseWithType(RequireMemberOf,
-                                    Ctx.getRecordType(FoundRecord),
+                                    Ctx.getCanonicalTagType(FoundRecord),
                                     AnyDependentBases) &&
             !AnyDependentBases)
           return false;
@@ -13009,7 +13028,7 @@ class UsingValidatorCCC final : public CorrectionCandidateCallback {
 private:
   bool HasTypenameKeyword;
   bool IsInstantiation;
-  NestedNameSpecifier *OldNNS;
+  NestedNameSpecifier OldNNS;
   CXXRecordDecl *RequireMemberOf;
 };
 } // end anonymous namespace
@@ -13051,7 +13070,7 @@ NamedDecl *Sema::BuildUsingDeclaration(
   if (UsingName.getName().getNameKind() == DeclarationName::CXXConstructorName)
     if (auto *RD = dyn_cast<CXXRecordDecl>(CurContext))
       UsingName.setName(Context.DeclarationNames.getCXXConstructorName(
-          Context.getCanonicalType(Context.getRecordType(RD))));
+          Context.getCanonicalTagType(RD)));
 
   // Do the redeclaration lookup in the current scope.
   LookupResult Previous(*this, UsingName, LookupUsingDeclName,
@@ -13154,7 +13173,7 @@ NamedDecl *Sema::BuildUsingDeclaration(
   // equal to that of the current context.
   if (CurContext->isRecord()) {
     R.setBaseObjectType(
-                   Context.getTypeDeclType(cast<CXXRecordDecl>(CurContext)));
+        Context.getCanonicalTagType(cast<CXXRecordDecl>(CurContext)));
   }
 
   LookupQualifiedName(R, LookupContext);
@@ -13220,7 +13239,7 @@ NamedDecl *Sema::BuildUsingDeclaration(
         // constructor.
         auto *CurClass = cast<CXXRecordDecl>(CurContext);
         UsingName.setName(Context.DeclarationNames.getCXXConstructorName(
-            Context.getCanonicalType(Context.getRecordType(CurClass))));
+            Context.getCanonicalTagType(CurClass)));
         UsingName.setNamedTypeInfo(nullptr);
         for (auto *Ctor : LookupConstructors(RD))
           R.addDecl(Ctor);
@@ -13366,20 +13385,16 @@ NamedDecl *Sema::BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
 bool Sema::CheckInheritingConstructorUsingDecl(UsingDecl *UD) {
   assert(!UD->hasTypename() && "expecting a constructor name");
 
-  const Type *SourceType = UD->getQualifier()->getAsType();
-  assert(SourceType &&
-         "Using decl naming constructor doesn't have type in scope spec.");
+  QualType SourceType(UD->getQualifier().getAsType(), 0);
   CXXRecordDecl *TargetClass = cast<CXXRecordDecl>(CurContext);
 
   // Check whether the named type is a direct base class.
   bool AnyDependentBases = false;
-  auto *Base = findDirectBaseWithType(TargetClass, QualType(SourceType, 0),
-                                      AnyDependentBases);
+  auto *Base =
+      findDirectBaseWithType(TargetClass, SourceType, AnyDependentBases);
   if (!Base && !AnyDependentBases) {
-    Diag(UD->getUsingLoc(),
-         diag::err_using_decl_constructor_not_in_direct_base)
-      << UD->getNameInfo().getSourceRange()
-      << QualType(SourceType, 0) << TargetClass;
+    Diag(UD->getUsingLoc(), diag::err_using_decl_constructor_not_in_direct_base)
+        << UD->getNameInfo().getSourceRange() << SourceType << TargetClass;
     UD->setInvalidDecl();
     return true;
   }
@@ -13395,7 +13410,7 @@ bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
                                        const CXXScopeSpec &SS,
                                        SourceLocation NameLoc,
                                        const LookupResult &Prev) {
-  NestedNameSpecifier *Qual = SS.getScopeRep();
+  NestedNameSpecifier Qual = SS.getScopeRep();
 
   // C++03 [namespace.udecl]p8:
   // C++0x [namespace.udecl]p10:
@@ -13410,7 +13425,7 @@ bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
     // declaration in the same scope.
     // FIXME: How should we check for dependent type-type conflicts at block
     // scope?
-    if (Qual->isDependent() && !HasTypenameKeyword) {
+    if (Qual.isDependent() && !HasTypenameKeyword) {
       for (auto *D : Prev) {
         if (!isa<TypeDecl>(D) && !isa<UsingDecl>(D) && !isa<UsingPackDecl>(D)) {
           bool OldCouldBeEnumerator =
@@ -13427,13 +13442,12 @@ bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
     return false;
   }
 
-  const NestedNameSpecifier *CNNS =
-      Context.getCanonicalNestedNameSpecifier(Qual);
+  NestedNameSpecifier CNNS = Qual.getCanonical();
   for (LookupResult::iterator I = Prev.begin(), E = Prev.end(); I != E; ++I) {
     NamedDecl *D = *I;
 
     bool DTypename;
-    NestedNameSpecifier *DQual;
+    NestedNameSpecifier DQual = std::nullopt;
     if (UsingDecl *UD = dyn_cast<UsingDecl>(D)) {
       DTypename = UD->hasTypename();
       DQual = UD->getQualifier();
@@ -13454,7 +13468,7 @@ bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
     // using decls differ if they name different scopes (but note that
     // template instantiation can cause this check to trigger when it
     // didn't before instantiation).
-    if (CNNS != Context.getCanonicalNestedNameSpecifier(DQual))
+    if (CNNS != DQual.getCanonical())
       continue;
 
     Diag(NameLoc, diag::err_using_decl_redeclaration) << SS.getRange();
@@ -13829,7 +13843,7 @@ Decl *Sema::ActOnNamespaceAliasDef(Scope *S, SourceLocation NamespaceLoc,
     }
   }
   assert(!R.isAmbiguous() && !R.empty());
-  NamedDecl *ND = R.getRepresentativeDecl();
+  auto *ND = cast<NamespaceBaseDecl>(R.getRepresentativeDecl());
 
   // Check if we have a previous declaration with the same name.
   LookupResult PrevR(*this, Alias, AliasLoc, LookupOrdinaryName,
@@ -13914,7 +13928,8 @@ bool SpecialMemberExceptionSpecInfo::visitBase(CXXBaseSpecifier *Base) {
   if (!RT)
     return false;
 
-  auto *BaseClass = cast<CXXRecordDecl>(RT->getDecl());
+  auto *BaseClass =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
   Sema::SpecialMemberOverloadResult SMOR = lookupInheritedCtor(BaseClass);
   if (auto *BaseCtor = SMOR.getMethod()) {
     visitSubobjectCall(Base, BaseCtor);
@@ -13940,8 +13955,9 @@ bool SpecialMemberExceptionSpecInfo::visitField(FieldDecl *FD) {
       ExceptSpec.CalledExpr(E);
   } else if (auto *RT = S.Context.getBaseElementType(FD->getType())
                             ->getAs<RecordType>()) {
-    visitClassSubobject(cast<CXXRecordDecl>(RT->getDecl()), FD,
-                        FD->getType().getCVRQualifiers());
+    visitClassSubobject(
+        cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf(), FD,
+        FD->getType().getCVRQualifiers());
   }
   return false;
 }
@@ -14003,7 +14019,7 @@ ComputeDefaultedSpecialMemberExceptionSpec(
   // attempting to resolve an exception specification before it's known
   // at a higher level.
   if (S.RequireCompleteType(MD->getLocation(),
-                            S.Context.getRecordType(ClassDecl),
+                            S.Context.getCanonicalTagType(ClassDecl),
                             diag::err_exception_spec_incomplete_type))
     return Info.ExceptSpec;
 
@@ -14134,8 +14150,7 @@ CXXConstructorDecl *Sema::DeclareImplicitDefaultConstructor(
       *this, ClassDecl, CXXSpecialMemberKind::DefaultConstructor, false);
 
   // Create the actual constructor declaration.
-  CanQualType ClassType
-    = Context.getCanonicalType(Context.getTypeDeclType(ClassDecl));
+  CanQualType ClassType = Context.getCanonicalTagType(ClassDecl);
   SourceLocation ClassLoc = ClassDecl->getLocation();
   DeclarationName Name
     = Context.DeclarationNames.getCXXConstructorName(ClassType);
@@ -14420,8 +14435,7 @@ CXXDestructorDecl *Sema::DeclareImplicitDestructor(CXXRecordDecl *ClassDecl) {
       *this, ClassDecl, CXXSpecialMemberKind::Destructor, false);
 
   // Create the actual destructor declaration.
-  CanQualType ClassType
-    = Context.getCanonicalType(Context.getTypeDeclType(ClassDecl));
+  CanQualType ClassType = Context.getCanonicalTagType(ClassDecl);
   SourceLocation ClassLoc = ClassDecl->getLocation();
   DeclarationName Name
     = Context.DeclarationNames.getCXXDestructorName(ClassType);
@@ -14759,9 +14773,10 @@ buildMemcpyForAssignmentOp(Sema &S, SourceLocation Loc, QualType T,
       VK_PRValue, OK_Ordinary, Loc, false, S.CurFPFeatureOverrides());
 
   const Type *E = T->getBaseElementTypeUnsafe();
-  bool NeedsCollectableMemCpy =
-      E->isRecordType() &&
-      E->castAs<RecordType>()->getDecl()->hasObjectMember();
+  bool NeedsCollectableMemCpy = E->isRecordType() && E->castAs<RecordType>()
+                                                         ->getOriginalDecl()
+                                                         ->getDefinitionOrSelf()
+                                                         ->hasObjectMember();
 
   // Create a reference to the __builtin_objc_memmove_collectable function
   StringRef MemCpyName = NeedsCollectableMemCpy ?
@@ -14838,7 +14853,8 @@ buildSingleCopyAssignRecursively(Sema &S, SourceLocation Loc, QualType T,
   //       ignoring any possible virtual overriding functions in more derived
   //       classes);
   if (const RecordType *RecordTy = T->getAs<RecordType>()) {
-    CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(RecordTy->getDecl());
+    CXXRecordDecl *ClassDecl =
+        cast<CXXRecordDecl>(RecordTy->getOriginalDecl())->getDefinitionOrSelf();
 
     // Look for operator=.
     DeclarationName Name
@@ -14885,10 +14901,9 @@ buildSingleCopyAssignRecursively(Sema &S, SourceLocation Loc, QualType T,
     // reference to operator=; this is required to suppress the virtual
     // call mechanism.
     CXXScopeSpec SS;
+    // FIXME: Don't canonicalize this.
     const Type *CanonicalT = S.Context.getCanonicalType(T.getTypePtr());
-    SS.MakeTrivial(S.Context,
-                   NestedNameSpecifier::Create(S.Context, nullptr, CanonicalT),
-                   Loc);
+    SS.MakeTrivial(S.Context, NestedNameSpecifier(CanonicalT), Loc);
 
     // Create the reference to operator=.
     ExprResult OpEqualRef
@@ -15042,9 +15057,9 @@ CXXMethodDecl *Sema::DeclareImplicitCopyAssignment(CXXRecordDecl *ClassDecl) {
   if (DSM.isAlreadyBeingDeclared())
     return nullptr;
 
-  QualType ArgType = Context.getTypeDeclType(ClassDecl);
-  ArgType = Context.getElaboratedType(ElaboratedTypeKeyword::None, nullptr,
-                                      ArgType, nullptr);
+  QualType ArgType = Context.getTagType(ElaboratedTypeKeyword::None,
+                                        /*Qualifier=*/std::nullopt, ClassDecl,
+                                        /*OwnsTag=*/false);
   LangAS AS = getDefaultCXXMethodAddrSpace();
   if (AS != LangAS::Default)
     ArgType = Context.getAddrSpaceQualType(ArgType, AS);
@@ -15303,7 +15318,8 @@ void Sema::DefineImplicitCopyAssignment(SourceLocation CurrentLocation,
     // Check for members of reference type; we can't copy those.
     if (Field->getType()->isReferenceType()) {
       Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
-        << Context.getTagDeclType(ClassDecl) << 0 << Field->getDeclName();
+          << Context.getCanonicalTagType(ClassDecl) << 0
+          << Field->getDeclName();
       Diag(Field->getLocation(), diag::note_declared_at);
       Invalid = true;
       continue;
@@ -15313,7 +15329,8 @@ void Sema::DefineImplicitCopyAssignment(SourceLocation CurrentLocation,
     QualType BaseType = Context.getBaseElementType(Field->getType());
     if (!BaseType->getAs<RecordType>() && BaseType.isConstQualified()) {
       Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
-        << Context.getTagDeclType(ClassDecl) << 1 << Field->getDeclName();
+          << Context.getCanonicalTagType(ClassDecl) << 1
+          << Field->getDeclName();
       Diag(Field->getLocation(), diag::note_declared_at);
       Invalid = true;
       continue;
@@ -15398,9 +15415,9 @@ CXXMethodDecl *Sema::DeclareImplicitMoveAssignment(CXXRecordDecl *ClassDecl) {
   // Note: The following rules are largely analoguous to the move
   // constructor rules.
 
-  QualType ArgType = Context.getTypeDeclType(ClassDecl);
-  ArgType = Context.getElaboratedType(ElaboratedTypeKeyword::None, nullptr,
-                                      ArgType, nullptr);
+  QualType ArgType = Context.getTagType(ElaboratedTypeKeyword::None,
+                                        /*Qualifier=*/std::nullopt, ClassDecl,
+                                        /*OwnsTag=*/false);
   LangAS AS = getDefaultCXXMethodAddrSpace();
   if (AS != LangAS::Default)
     ArgType = Context.getAddrSpaceQualType(ArgType, AS);
@@ -15690,7 +15707,8 @@ void Sema::DefineImplicitMoveAssignment(SourceLocation CurrentLocation,
     // Check for members of reference type; we can't move those.
     if (Field->getType()->isReferenceType()) {
       Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
-        << Context.getTagDeclType(ClassDecl) << 0 << Field->getDeclName();
+          << Context.getCanonicalTagType(ClassDecl) << 0
+          << Field->getDeclName();
       Diag(Field->getLocation(), diag::note_declared_at);
       Invalid = true;
       continue;
@@ -15700,7 +15718,8 @@ void Sema::DefineImplicitMoveAssignment(SourceLocation CurrentLocation,
     QualType BaseType = Context.getBaseElementType(Field->getType());
     if (!BaseType->getAs<RecordType>() && BaseType.isConstQualified()) {
       Diag(ClassDecl->getLocation(), diag::err_uninitialized_member_for_assign)
-        << Context.getTagDeclType(ClassDecl) << 1 << Field->getDeclName();
+          << Context.getCanonicalTagType(ClassDecl) << 1
+          << Field->getDeclName();
       Diag(Field->getLocation(), diag::note_declared_at);
       Invalid = true;
       continue;
@@ -15791,10 +15810,10 @@ CXXConstructorDecl *Sema::DeclareImplicitCopyConstructor(
   if (DSM.isAlreadyBeingDeclared())
     return nullptr;
 
-  QualType ClassType = Context.getTypeDeclType(ClassDecl);
+  QualType ClassType = Context.getTagType(ElaboratedTypeKeyword::None,
+                                          /*Qualifier=*/std::nullopt, ClassDecl,
+                                          /*OwnsTag=*/false);
   QualType ArgType = ClassType;
-  ArgType = Context.getElaboratedType(ElaboratedTypeKeyword::None, nullptr,
-                                      ArgType, nullptr);
   bool Const = ClassDecl->implicitCopyConstructorHasConstParam();
   if (Const)
     ArgType = ArgType.withConst();
@@ -15938,11 +15957,11 @@ CXXConstructorDecl *Sema::DeclareImplicitMoveConstructor(
   if (DSM.isAlreadyBeingDeclared())
     return nullptr;
 
-  QualType ClassType = Context.getTypeDeclType(ClassDecl);
+  QualType ClassType = Context.getTagType(ElaboratedTypeKeyword::None,
+                                          /*Qualifier=*/std::nullopt, ClassDecl,
+                                          /*OwnsTag=*/false);
 
   QualType ArgType = ClassType;
-  ArgType = Context.getElaboratedType(ElaboratedTypeKeyword::None, nullptr,
-                                      ArgType, nullptr);
   LangAS AS = getDefaultCXXMethodAddrSpace();
   if (AS != LangAS::Default)
     ArgType = Context.getAddrSpaceQualType(ClassType, AS);
@@ -16297,7 +16316,8 @@ void Sema::FinalizeVarWithDestructor(VarDecl *VD, const RecordType *Record) {
   if (VD->getInit() && VD->getInit()->containsErrors())
     return;
 
-  CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(Record->getDecl());
+  CXXRecordDecl *ClassDecl =
+      cast<CXXRecordDecl>(Record->getOriginalDecl())->getDefinitionOrSelf();
   if (ClassDecl->isInvalidDecl()) return;
   if (ClassDecl->hasIrrelevantDestructor()) return;
   if (ClassDecl->isDependentContext()) return;
@@ -16643,10 +16663,10 @@ static inline bool CheckOperatorNewDeleteTypes(
 
   if (CheckType(SizeParameterIndex, SemaRef.Context.getSizeType(), "size_t"))
     return true;
-  TypeDecl *StdAlignValTDecl = SemaRef.getStdAlignValT();
-  QualType StdAlignValT =
-      StdAlignValTDecl ? SemaRef.Context.getTypeDeclType(StdAlignValTDecl)
-                       : QualType();
+  TagDecl *StdAlignValTDecl = SemaRef.getStdAlignValT();
+  CanQualType StdAlignValT =
+      StdAlignValTDecl ? SemaRef.Context.getCanonicalTagType(StdAlignValTDecl)
+                       : CanQualType();
   if (CheckType(SizeParameterIndex + 1, StdAlignValT, "std::align_val_t"))
     return true;
 
@@ -16686,8 +16706,8 @@ CheckOperatorDeleteDeclaration(Sema &SemaRef, FunctionDecl *FnDecl) {
   auto *MD = dyn_cast<CXXMethodDecl>(FnDecl);
   auto ConstructDestroyingDeleteAddressType = [&]() {
     assert(MD);
-    return SemaRef.Context.getCanonicalType(SemaRef.Context.getPointerType(
-        SemaRef.Context.getRecordType(MD->getParent())));
+    return SemaRef.Context.getPointerType(
+        SemaRef.Context.getCanonicalTagType(MD->getParent()));
   };
 
   // C++ P2719: A destroying operator delete cannot be type aware
@@ -16726,8 +16746,8 @@ CheckOperatorDeleteDeclaration(Sema &SemaRef, FunctionDecl *FnDecl) {
   //   function shall be of type void *.
   CanQualType ExpectedAddressParamType =
       MD && IsPotentiallyDestroyingOperatorDelete(SemaRef, MD)
-          ? SemaRef.Context.getCanonicalType(SemaRef.Context.getPointerType(
-                SemaRef.Context.getRecordType(MD->getParent())))
+          ? SemaRef.Context.getPointerType(
+                SemaRef.Context.getCanonicalTagType(MD->getParent()))
           : SemaRef.Context.VoidPtrTy;
 
   // C++ [basic.stc.dynamic.deallocation]p2:
@@ -17958,27 +17978,14 @@ DeclResult Sema::ActOnTemplatedFriendTag(
                       /*OOK=*/OffsetOfKind::Outside);
     }
 
+    TypeSourceInfo *TSI = nullptr;
     ElaboratedTypeKeyword Keyword
       = TypeWithKeyword::getKeywordForTagTypeKind(Kind);
-    QualType T = CheckTypenameType(Keyword, TagLoc, QualifierLoc,
-                                   *Name, NameLoc);
+    QualType T = CheckTypenameType(Keyword, TagLoc, QualifierLoc, *Name,
+                                   NameLoc, &TSI, /*DeducedTSTContext=*/true);
     if (T.isNull())
       return true;
 
-    TypeSourceInfo *TSI = Context.CreateTypeSourceInfo(T);
-    if (isa<DependentNameType>(T)) {
-      DependentNameTypeLoc TL =
-          TSI->getTypeLoc().castAs<DependentNameTypeLoc>();
-      TL.setElaboratedKeywordLoc(TagLoc);
-      TL.setQualifierLoc(QualifierLoc);
-      TL.setNameLoc(NameLoc);
-    } else {
-      ElaboratedTypeLoc TL = TSI->getTypeLoc().castAs<ElaboratedTypeLoc>();
-      TL.setElaboratedKeywordLoc(TagLoc);
-      TL.setQualifierLoc(QualifierLoc);
-      TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(NameLoc);
-    }
-
     FriendDecl *Friend =
         FriendDecl::Create(Context, CurContext, NameLoc, TSI, FriendLoc,
                            EllipsisLoc, TempParamLists);
@@ -18290,7 +18297,7 @@ NamedDecl *Sema::ActOnFriendFunctionDecl(Scope *S, Declarator &D,
   //   - There's a non-dependent scope specifier, in which case we
   //     compute it and do a previous lookup there for a function
   //     or function template.
-  } else if (!SS.getScopeRep()->isDependent()) {
+  } else if (!SS.getScopeRep().isDependent()) {
     DC = computeDeclContext(SS);
     if (!DC) return nullptr;
 
@@ -18789,7 +18796,7 @@ bool Sema::CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
     //   complete at the point of declaration of D::f or shall be the class
     //   type D.
     if (const RecordType *RT = NewClassTy->getAs<RecordType>()) {
-      if (!RT->isBeingDefined() &&
+      if (!RT->getOriginalDecl()->isEntityBeingDefined() &&
           RequireCompleteType(New->getLocation(), NewClassTy,
                               diag::err_covariant_return_incomplete,
                               New->getDeclName()))
@@ -19144,8 +19151,9 @@ void Sema::MarkVirtualMembersReferenced(SourceLocation Loc,
     return;
 
   for (const auto &I : RD->bases()) {
-    const auto *Base =
-        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+    const auto *Base = cast<CXXRecordDecl>(
+                           I.getType()->castAs<RecordType>()->getOriginalDecl())
+                           ->getDefinitionOrSelf();
     if (Base->getNumVBases() == 0)
       continue;
     MarkVirtualMembersReferenced(Loc, Base);
diff --git a/clang/lib/Sema/SemaDeclObjC.cpp b/clang/lib/Sema/SemaDeclObjC.cpp
index 9dbc3efbca405..4614cf766b19c 100644
--- a/clang/lib/Sema/SemaDeclObjC.cpp
+++ b/clang/lib/Sema/SemaDeclObjC.cpp
@@ -591,12 +591,13 @@ void SemaObjC::ActOnSuperClassOfClassInterface(
       // The previous declaration was not a class decl. Check if we have a
       // typedef. If we do, get the underlying class type.
       if (const TypedefNameDecl *TDecl =
-          dyn_cast_or_null<TypedefNameDecl>(PrevDecl)) {
+              dyn_cast_or_null<TypedefNameDecl>(PrevDecl)) {
         QualType T = TDecl->getUnderlyingType();
         if (T->isObjCObjectType()) {
           if (NamedDecl *IDecl = T->castAs<ObjCObjectType>()->getInterface()) {
             SuperClassDecl = dyn_cast<ObjCInterfaceDecl>(IDecl);
-            SuperClassType = Context.getTypeDeclType(TDecl);
+            SuperClassType = Context.getTypeDeclType(
+                ElaboratedTypeKeyword::None, /*Qualifier=*/std::nullopt, TDecl);
 
             // This handles the following case:
             // @interface NewI @end
@@ -1389,11 +1390,9 @@ class ObjCTypeArgOrProtocolValidatorCCC final
 
         // Make sure the type is something we would accept as a type
         // argument.
-        auto type = Context.getTypeDeclType(typeDecl);
-        if (type->isObjCObjectPointerType() ||
-            type->isBlockPointerType() ||
+        if (CanQualType type = Context.getCanonicalTypeDeclType(typeDecl);
             type->isDependentType() ||
-            type->isObjCObjectType())
+            isa<ObjCObjectPointerType, BlockPointerType, ObjCObjectType>(type))
           return true;
 
         return false;
@@ -1589,7 +1588,9 @@ void SemaObjC::actOnObjCTypeArgsOrProtocolQualifiers(
     unsigned diagID; // unused
     QualType type;
     if (auto *actualTypeDecl = dyn_cast<TypeDecl *>(typeDecl))
-      type = Context.getTypeDeclType(actualTypeDecl);
+      type =
+          Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                  /*Qualifier=*/std::nullopt, actualTypeDecl);
     else
       type = Context.getObjCInterfaceType(cast<ObjCInterfaceDecl *>(typeDecl));
     TypeSourceInfo *parsedTSInfo = Context.getTrivialTypeSourceInfo(type, loc);
@@ -3231,8 +3232,10 @@ static bool tryMatchRecordTypes(ASTContext &Context,
   assert(lt && rt && lt != rt);
 
   if (!isa<RecordType>(lt) || !isa<RecordType>(rt)) return false;
-  RecordDecl *left = cast<RecordType>(lt)->getDecl();
-  RecordDecl *right = cast<RecordType>(rt)->getDecl();
+  RecordDecl *left =
+      cast<RecordType>(lt)->getOriginalDecl()->getDefinitionOrSelf();
+  RecordDecl *right =
+      cast<RecordType>(rt)->getOriginalDecl()->getDefinitionOrSelf();
 
   // Require union-hood to match.
   if (left->isUnion() != right->isUnion()) return false;
@@ -3846,7 +3849,9 @@ static bool IsVariableSizedType(QualType T) {
   if (T->isIncompleteArrayType())
     return true;
   const auto *RecordTy = T->getAs<RecordType>();
-  return (RecordTy && RecordTy->getDecl()->hasFlexibleArrayMember());
+  return (RecordTy && RecordTy->getOriginalDecl()
+                          ->getDefinitionOrSelf()
+                          ->hasFlexibleArrayMember());
 }
 
 static void DiagnoseVariableSizedIvars(Sema &S, ObjCContainerDecl *OCD) {
@@ -3892,7 +3897,9 @@ static void DiagnoseVariableSizedIvars(Sema &S, ObjCContainerDecl *OCD) {
           << TagTypeKind::Class; // Use "class" for Obj-C.
       IsInvalidIvar = true;
     } else if (const RecordType *RecordTy = IvarTy->getAs<RecordType>()) {
-      if (RecordTy->getDecl()->hasFlexibleArrayMember()) {
+      if (RecordTy->getOriginalDecl()
+              ->getDefinitionOrSelf()
+              ->hasFlexibleArrayMember()) {
         S.Diag(ivar->getLocation(),
                diag::err_objc_variable_sized_type_not_at_end)
             << ivar->getDeclName() << IvarTy;
@@ -5537,7 +5544,8 @@ void SemaObjC::SetIvarInitializers(ObjCImplementationDecl *ObjCImplementation) {
       if (const RecordType *RecordTy =
               Context.getBaseElementType(Field->getType())
                   ->getAs<RecordType>()) {
-        CXXRecordDecl *RD = cast<CXXRecordDecl>(RecordTy->getDecl());
+        CXXRecordDecl *RD = cast<CXXRecordDecl>(RecordTy->getOriginalDecl())
+                                ->getDefinitionOrSelf();
         if (CXXDestructorDecl *Destructor = SemaRef.LookupDestructor(RD)) {
           SemaRef.MarkFunctionReferenced(Field->getLocation(), Destructor);
           SemaRef.CheckDestructorAccess(
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index 0a6cea8869c14..94413b5b92d22 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -163,8 +163,9 @@ bool Sema::CheckSpecifiedExceptionType(QualType &T, SourceRange Range) {
     DiagID = diag::ext_incomplete_in_exception_spec;
     ReturnValueOnError = false;
   }
-  if (!(PointeeT->isRecordType() &&
-        PointeeT->castAs<RecordType>()->isBeingDefined()) &&
+  if (!(PointeeT->isRecordType() && PointeeT->castAs<RecordType>()
+                                        ->getOriginalDecl()
+                                        ->isEntityBeingDefined()) &&
       RequireCompleteType(Range.getBegin(), PointeeT, DiagID, Kind, Range))
     return ReturnValueOnError;
 
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 728ada33e2e63..40e742a826d3d 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -1528,8 +1528,8 @@ void Sema::checkEnumArithmeticConversions(Expr *LHS, Expr *RHS,
     // are ill-formed.
     if (getLangOpts().CPlusPlus26)
       DiagID = diag::warn_conv_mixed_enum_types_cxx26;
-    else if (!L->castAs<EnumType>()->getDecl()->hasNameForLinkage() ||
-             !R->castAs<EnumType>()->getDecl()->hasNameForLinkage()) {
+    else if (!L->castAs<EnumType>()->getOriginalDecl()->hasNameForLinkage() ||
+             !R->castAs<EnumType>()->getOriginalDecl()->hasNameForLinkage()) {
       // If either enumeration type is unnamed, it's less likely that the
       // user cares about this, but this situation is still deprecated in
       // C++2a. Use a different warning group.
@@ -2531,7 +2531,7 @@ bool Sema::DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
     if (isa<CXXRecordDecl>(DC)) {
       if (ExplicitTemplateArgs) {
         if (LookupTemplateName(
-                R, S, SS, Context.getRecordType(cast<CXXRecordDecl>(DC)),
+                R, S, SS, Context.getCanonicalTagType(cast<CXXRecordDecl>(DC)),
                 /*EnteringContext*/ false, TemplateNameIsRequired,
                 /*RequiredTemplateKind*/ nullptr, /*AllowTypoCorrection*/ true))
           return true;
@@ -2607,11 +2607,8 @@ bool Sema::DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
       }
       R.addDecl(ND);
       if (getLangOpts().CPlusPlus && ND->isCXXClassMember()) {
-        CXXRecordDecl *Record = nullptr;
-        if (Corrected.getCorrectionSpecifier()) {
-          const Type *Ty = Corrected.getCorrectionSpecifier()->getAsType();
-          Record = Ty->getAsCXXRecordDecl();
-        }
+        CXXRecordDecl *Record =
+            Corrected.getCorrectionSpecifier().getAsRecordDecl();
         if (!Record)
           Record = cast<CXXRecordDecl>(
               ND->getDeclContext()->getRedeclContext());
@@ -2707,8 +2704,7 @@ recoverFromMSUnqualifiedLookup(Sema &S, ASTContext &Context,
   // Synthesize a fake NNS that points to the derived class.  This will
   // perform name lookup during template instantiation.
   CXXScopeSpec SS;
-  auto *NNS =
-      NestedNameSpecifier::Create(Context, nullptr, RD->getTypeForDecl());
+  NestedNameSpecifier NNS(Context.getCanonicalTagType(RD)->getTypePtr());
   SS.MakeTrivial(Context, NNS, SourceRange(Loc, Loc));
   return DependentScopeDeclRefExpr::Create(
       Context, SS.getWithLocInContext(Context), TemplateKWLoc, NameInfo,
@@ -2831,8 +2827,7 @@ Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
 
     // If this name wasn't predeclared and if this is not a function
     // call, diagnose the problem.
-    DefaultFilterCCC DefaultValidator(II, SS.isValid() ? SS.getScopeRep()
-                                                       : nullptr);
+    DefaultFilterCCC DefaultValidator(II, SS.getScopeRep());
     DefaultValidator.IsAddressOfOperand = IsAddressOfOperand;
     assert((!CCC || CCC->IsAddressOfOperand == IsAddressOfOperand) &&
            "Typo correction callback misconfigured");
@@ -2942,8 +2937,28 @@ ExprResult Sema::BuildQualifiedDeclarationNameExpr(
   }
 
   if (const TypeDecl *TD = R.getAsSingle<TypeDecl>()) {
-    QualType Ty = Context.getTypeDeclType(TD);
-    QualType ET = getElaboratedType(ElaboratedTypeKeyword::None, SS, Ty);
+    QualType ET;
+    TypeLocBuilder TLB;
+    if (auto *TagD = dyn_cast<TagDecl>(TD)) {
+      ET = SemaRef.Context.getTagType(ElaboratedTypeKeyword::None,
+                                      SS.getScopeRep(), TagD,
+                                      /*OwnsTag=*/false);
+      auto TL = TLB.push<TagTypeLoc>(ET);
+      TL.setElaboratedKeywordLoc(SourceLocation());
+      TL.setQualifierLoc(SS.getWithLocInContext(Context));
+      TL.setNameLoc(NameInfo.getLoc());
+    } else if (auto *TypedefD = dyn_cast<TypedefNameDecl>(TD)) {
+      ET = SemaRef.Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                          SS.getScopeRep(), TypedefD);
+      TLB.push<TypedefTypeLoc>(ET).set(
+          /*ElaboratedKeywordLoc=*/SourceLocation(),
+          SS.getWithLocInContext(Context), NameInfo.getLoc());
+    } else {
+      // FIXME: What else can appear here?
+      ET = SemaRef.Context.getTypeDeclType(TD);
+      TLB.pushTypeSpec(ET).setNameLoc(NameInfo.getLoc());
+      assert(SS.isEmpty());
+    }
 
     // Diagnose a missing typename if this resolved unambiguously to a type in
     // a dependent context.  If we can recover with a type, downgrade this to
@@ -2964,13 +2979,6 @@ ExprResult Sema::BuildQualifiedDeclarationNameExpr(
     D << FixItHint::CreateInsertion(Loc, "typename ");
 
     // Recover by pretending this was an elaborated type.
-    TypeLocBuilder TLB;
-    TLB.pushTypeSpec(Ty).setNameLoc(NameInfo.getLoc());
-
-    ElaboratedTypeLoc QTL = TLB.push<ElaboratedTypeLoc>(ET);
-    QTL.setElaboratedKeywordLoc(SourceLocation());
-    QTL.setQualifierLoc(SS.getWithLocInContext(Context));
-
     *RecoveryTSI = TLB.getTypeSourceInfo(Context, ET);
 
     return ExprEmpty();
@@ -2986,11 +2994,10 @@ ExprResult Sema::BuildQualifiedDeclarationNameExpr(
   return BuildDeclarationNameExpr(SS, R, /*ADL=*/false);
 }
 
-ExprResult
-Sema::PerformObjectMemberConversion(Expr *From,
-                                    NestedNameSpecifier *Qualifier,
-                                    NamedDecl *FoundDecl,
-                                    NamedDecl *Member) {
+ExprResult Sema::PerformObjectMemberConversion(Expr *From,
+                                               NestedNameSpecifier Qualifier,
+                                               NamedDecl *FoundDecl,
+                                               NamedDecl *Member) {
   const auto *RD = dyn_cast<CXXRecordDecl>(Member->getDeclContext());
   if (!RD)
     return From;
@@ -3001,7 +3008,7 @@ Sema::PerformObjectMemberConversion(Expr *From,
   QualType FromType = From->getType();
   bool PointerConversions = false;
   if (isa<FieldDecl>(Member)) {
-    DestRecordType = Context.getCanonicalType(Context.getTypeDeclType(RD));
+    DestRecordType = Context.getCanonicalTagType(RD);
     auto FromPtrType = FromType->getAs<PointerType>();
     DestRecordType = Context.getAddrSpaceQualType(
         DestRecordType, FromPtrType
@@ -3079,8 +3086,8 @@ Sema::PerformObjectMemberConversion(Expr *From,
   //     x = 17; // error: ambiguous base subobjects
   //     Derived1::x = 17; // okay, pick the Base subobject of Derived1
   //   }
-  if (Qualifier && Qualifier->getAsType()) {
-    QualType QType = QualType(Qualifier->getAsType(), 0);
+  if (Qualifier.getKind() == NestedNameSpecifier::Kind::Type) {
+    QualType QType = QualType(Qualifier.getAsType(), 0);
     assert(QType->isRecordType() && "lookup done with non-record type");
 
     QualType QRecordType = QualType(QType->castAs<RecordType>(), 0);
@@ -4482,9 +4489,6 @@ static void captureVariablyModifiedType(ASTContext &Context, QualType T,
     case Type::BitInt:
     case Type::HLSLInlineSpirv:
       llvm_unreachable("type class is never variably-modified!");
-    case Type::Elaborated:
-      T = cast<ElaboratedType>(Ty)->getNamedType();
-      break;
     case Type::Adjusted:
       T = cast<AdjustedType>(Ty)->getOriginalType();
       break;
@@ -5873,7 +5877,7 @@ static bool isParenthetizedAndQualifiedAddressOfExpr(Expr *Fn) {
     return DRE->hasQualifier();
   }
   if (auto *OVL = dyn_cast<OverloadExpr>(UO->getSubExpr()->IgnoreParens()))
-    return OVL->getQualifier();
+    return bool(OVL->getQualifier());
   return false;
 }
 
@@ -7073,7 +7077,7 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
     for (unsigned i = 0, e = Args.size(); i != e; i++) {
       if (const auto *RT =
               dyn_cast<RecordType>(Args[i]->getType().getCanonicalType())) {
-        if (RT->getDecl()->isOrContainsUnion())
+        if (RT->getOriginalDecl()->isOrContainsUnion())
           Diag(Args[i]->getBeginLoc(), diag::warn_cmse_nonsecure_union)
               << 0 << i;
       }
@@ -8602,7 +8606,8 @@ QualType Sema::CheckConditionalOperands(ExprResult &Cond, ExprResult &LHS,
   // type.
   if (const RecordType *LHSRT = LHSTy->getAs<RecordType>()) {    // C99 6.5.15p3
     if (const RecordType *RHSRT = RHSTy->getAs<RecordType>())
-      if (LHSRT->getDecl() == RHSRT->getDecl())
+      if (declaresSameEntity(LHSRT->getOriginalDecl(),
+                             RHSRT->getOriginalDecl()))
         // "If both the operands have structure or union type, the result has
         // that type."  This implies that CV qualifiers are dropped.
         return Context.getCommonSugaredType(LHSTy.getUnqualifiedType(),
@@ -9671,11 +9676,14 @@ Sema::CheckTransparentUnionArgumentConstraints(QualType ArgType,
   // If the ArgType is a Union type, we want to handle a potential
   // transparent_union GCC extension.
   const RecordType *UT = ArgType->getAsUnionType();
-  if (!UT || !UT->getDecl()->hasAttr<TransparentUnionAttr>())
+  if (!UT)
+    return AssignConvertType::Incompatible;
+
+  RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
+  if (!UD->hasAttr<TransparentUnionAttr>())
     return AssignConvertType::Incompatible;
 
   // The field to initialize within the transparent union.
-  RecordDecl *UD = UT->getDecl();
   FieldDecl *InitField = nullptr;
   // It's compatible if the expression matches any of the fields.
   for (auto *it : UD->fields()) {
@@ -11398,7 +11406,7 @@ QualType Sema::CheckSubtractionOperands(ExprResult &LHS, ExprResult &RHS,
 
 static bool isScopedEnumerationType(QualType T) {
   if (const EnumType *ET = T->getAs<EnumType>())
-    return ET->getDecl()->isScoped();
+    return ET->getOriginalDecl()->isScoped();
   return false;
 }
 
@@ -12287,8 +12295,10 @@ static QualType checkArithmeticOrEnumeralThreeWayCompare(Sema &S,
       S.InvalidOperands(Loc, LHS, RHS);
       return QualType();
     }
-    QualType IntType =
-        LHSStrippedType->castAs<EnumType>()->getDecl()->getIntegerType();
+    QualType IntType = LHSStrippedType->castAs<EnumType>()
+                           ->getOriginalDecl()
+                           ->getDefinitionOrSelf()
+                           ->getIntegerType();
     assert(IntType->isArithmeticType());
 
     // We can't use `CK_IntegralCast` when the underlying type is 'bool', so we
@@ -12454,7 +12464,7 @@ QualType Sema::CheckCompareOperands(ExprResult &LHS, ExprResult &RHS,
 
   auto computeResultTy = [&]() {
     if (Opc != BO_Cmp)
-      return Context.getLogicalOperationType();
+      return QualType(Context.getLogicalOperationType());
     assert(getLangOpts().CPlusPlus);
     assert(Context.hasSameType(LHS.get()->getType(), RHS.get()->getType()));
 
@@ -13691,8 +13701,10 @@ static void DiagnoseRecursiveConstFields(Sema &S, const ValueDecl *VD,
   // diagnostics in field nesting order.
   while (RecordTypeList.size() > NextToCheckIndex) {
     bool IsNested = NextToCheckIndex > 0;
-    for (const FieldDecl *Field :
-         RecordTypeList[NextToCheckIndex]->getDecl()->fields()) {
+    for (const FieldDecl *Field : RecordTypeList[NextToCheckIndex]
+                                      ->getOriginalDecl()
+                                      ->getDefinitionOrSelf()
+                                      ->fields()) {
       // First, check every field for constness.
       QualType FieldTy = Field->getType();
       if (FieldTy.isConstQualified()) {
@@ -16147,7 +16159,7 @@ ExprResult Sema::BuildBuiltinOffsetOf(SourceLocation BuiltinLoc,
     if (!RC)
       return ExprError(Diag(OC.LocEnd, diag::err_offsetof_record_type)
                        << CurrentType);
-    RecordDecl *RD = RC->getDecl();
+    RecordDecl *RD = RC->getOriginalDecl()->getDefinitionOrSelf();
 
     // C++ [lib.support.types]p5:
     //   The macro offsetof accepts a restricted set of type arguments in this
@@ -16208,8 +16220,8 @@ ExprResult Sema::BuildBuiltinOffsetOf(SourceLocation BuiltinLoc,
     // If the member was found in a base class, introduce OffsetOfNodes for
     // the base class indirections.
     CXXBasePaths Paths;
-    if (IsDerivedFrom(OC.LocStart, CurrentType, Context.getTypeDeclType(Parent),
-                      Paths)) {
+    if (IsDerivedFrom(OC.LocStart, CurrentType,
+                      Context.getCanonicalTagType(Parent), Paths)) {
       if (Paths.getDetectedVirtual()) {
         Diag(OC.LocEnd, diag::err_offsetof_field_of_virtual_base)
           << MemberDecl->getDeclName()
@@ -16774,7 +16786,8 @@ ExprResult Sema::BuildVAArgExpr(SourceLocation BuiltinLoc,
       // that.
       QualType UnderlyingType = TInfo->getType();
       if (const auto *ET = UnderlyingType->getAs<EnumType>())
-        UnderlyingType = ET->getDecl()->getIntegerType();
+        UnderlyingType =
+            ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
       if (Context.typesAreCompatible(PromoteType, UnderlyingType,
                                      /*CompareUnqualified*/ true))
         PromoteType = QualType();
@@ -16920,7 +16933,7 @@ ExprResult Sema::ActOnSourceLocExpr(SourceLocIdentKind Kind,
         return ExprError();
     }
     ResultTy = Context.getPointerType(
-        Context.getRecordType(StdSourceLocationImplDecl).withConst());
+        Context.getCanonicalTagType(StdSourceLocationImplDecl).withConst());
     break;
   }
 
@@ -18769,7 +18782,9 @@ static bool isVariableCapturable(CapturingScopeInfo *CSI, ValueDecl *Var,
   // Prohibit structs with flexible array members too.
   // We cannot capture what is in the tail end of the struct.
   if (const RecordType *VTTy = Var->getType()->getAs<RecordType>()) {
-    if (VTTy->getDecl()->hasFlexibleArrayMember()) {
+    if (VTTy->getOriginalDecl()
+            ->getDefinitionOrSelf()
+            ->hasFlexibleArrayMember()) {
       if (Diagnose) {
         if (IsBlock)
           S.Diag(Loc, diag::err_ref_flexarray_type);
@@ -21210,7 +21225,7 @@ ExprResult Sema::CheckPlaceholderExpr(Expr *E) {
     NamedDecl *Temp = *ULE->decls_begin();
     const bool IsTypeAliasTemplateDecl = isa<TypeAliasTemplateDecl>(Temp);
 
-    NestedNameSpecifier *NNS = ULE->getQualifierLoc().getNestedNameSpecifier();
+    NestedNameSpecifier NNS = ULE->getQualifierLoc().getNestedNameSpecifier();
     // FIXME: AssumedTemplate is not very appropriate for error recovery here,
     // as it models only the unqualified-id case, where this case can clearly be
     // qualified. Thus we can't just qualify an assumed template.
@@ -21236,16 +21251,16 @@ ExprResult Sema::CheckPlaceholderExpr(Expr *E) {
     QualType TST;
     {
       SFINAETrap Trap(*this);
-      TST = CheckTemplateIdType(TN, NameInfo.getBeginLoc(), TAL);
+      TST = CheckTemplateIdType(ElaboratedTypeKeyword::None, TN,
+                                NameInfo.getBeginLoc(), TAL);
     }
     if (TST.isNull())
       TST = Context.getTemplateSpecializationType(
-          TN, ULE->template_arguments(), /*CanonicalArgs=*/{},
+          ElaboratedTypeKeyword::None, TN, ULE->template_arguments(),
+          /*CanonicalArgs=*/{},
           HasAnyDependentTA ? Context.DependentTy : Context.IntTy);
-    QualType ET =
-        Context.getElaboratedType(ElaboratedTypeKeyword::None, NNS, TST);
     return CreateRecoveryExpr(NameInfo.getBeginLoc(), NameInfo.getEndLoc(), {},
-                              ET);
+                              TST);
   }
 
   // Overloaded expressions.
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 5e232fbbd590c..8614c473c402f 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -57,11 +57,11 @@ using namespace sema;
 ParsedType Sema::getInheritingConstructorName(CXXScopeSpec &SS,
                                               SourceLocation NameLoc,
                                               const IdentifierInfo &Name) {
-  NestedNameSpecifier *NNS = SS.getScopeRep();
-  if ([[maybe_unused]] const IdentifierInfo *II = NNS->getAsIdentifier())
-    assert(II == &Name && "not a constructor name");
+  NestedNameSpecifier NNS = SS.getScopeRep();
+  QualType Type(NNS.getAsType(), 0);
+  if ([[maybe_unused]] const auto *DNT = dyn_cast<DependentNameType>(Type))
+    assert(DNT->getIdentifier() == &Name && "not a constructor name");
 
-  QualType Type(NNS->translateToType(Context), 0);
   // This reference to the type is located entirely at the location of the
   // final identifier in the qualified-id.
   return CreateParsedType(Type,
@@ -111,10 +111,8 @@ ParsedType Sema::getConstructorName(const IdentifierInfo &II,
     return ParsedType();
   }
 
-  QualType T = Context.getTypeDeclType(InjectedClassName);
-  DiagnoseUseOfDecl(InjectedClassName, NameLoc);
-  MarkAnyDeclReferenced(NameLoc, InjectedClassName, /*OdrUse=*/false);
-
+  QualType T = Context.getTagType(ElaboratedTypeKeyword::None, SS.getScopeRep(),
+                                  InjectedClassName, /*OwnsTag=*/false);
   return ParsedType::make(T);
 }
 
@@ -175,7 +173,7 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
       if (SearchType.isNull() || SearchType->isDependentType())
         return true;
 
-      QualType T = Context.getTypeDeclType(Type);
+      CanQualType T = Context.getCanonicalTypeDeclType(Type);
       return Context.hasSameUnqualifiedType(T, SearchType);
     };
 
@@ -207,7 +205,8 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
         NamedDecl *D = F.next();
         if (auto *TD = dyn_cast<TypeDecl>(D->getUnderlyingDecl()))
           Diag(D->getLocation(), diag::note_destructor_type_here)
-              << Context.getTypeDeclType(TD);
+              << Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                         /*Qualifier=*/std::nullopt, TD);
         else
           Diag(D->getLocation(), diag::note_destructor_nontype_here);
 
@@ -222,11 +221,11 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
 
     if (TypeDecl *Type = Found.getAsSingle<TypeDecl>()) {
       if (IsAcceptableResult(Type)) {
-        QualType T = Context.getTypeDeclType(Type);
+        QualType T = Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                             /*Qualifier=*/std::nullopt, Type);
         MarkAnyDeclReferenced(Type->getLocation(), Type, /*OdrUse=*/false);
-        return CreateParsedType(
-            Context.getElaboratedType(ElaboratedTypeKeyword::None, nullptr, T),
-            Context.getTrivialTypeSourceInfo(T, NameLoc));
+        return CreateParsedType(T,
+                                Context.getTrivialTypeSourceInfo(T, NameLoc));
       }
     }
 
@@ -311,15 +310,23 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
   // If both lookups succeed and find a dependent result, which result should
   // we retain? (Same question for p->~type-name().)
 
-  if (NestedNameSpecifier *Prefix =
-      SS.isSet() ? SS.getScopeRep()->getPrefix() : nullptr) {
+  auto Prefix = [&]() -> NestedNameSpecifierLoc {
+    NestedNameSpecifierLoc NNS = SS.getWithLocInContext(Context);
+    if (!NNS)
+      return NestedNameSpecifierLoc();
+    if (auto TL = NNS.getAsTypeLoc())
+      return TL.getPrefix();
+    return NNS.getAsNamespaceAndPrefix().Prefix;
+  }();
+
+  if (Prefix) {
     // This is
     //
     //   nested-name-specifier type-name :: ~ type-name
     //
     // Look for the second type-name in the nested-name-specifier.
     CXXScopeSpec PrefixSS;
-    PrefixSS.Adopt(NestedNameSpecifierLoc(Prefix, SS.location_data()));
+    PrefixSS.Adopt(Prefix);
     if (ParsedType T = LookupInNestedNameSpec(PrefixSS))
       return T;
   } else {
@@ -374,7 +381,7 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
     //
     // also looks for type-name in the scope. Unfortunately, we can't
     // reasonably apply this fallback for dependent nested-name-specifiers.
-    if (SS.isValid() && SS.getScopeRep()->getPrefix()) {
+    if (Prefix) {
       if (ParsedType T = LookupInScope()) {
         Diag(SS.getEndLoc(), diag::ext_qualified_dtor_named_in_lexical_scope)
             << FixItHint::CreateRemoval(SS.getRange());
@@ -419,9 +426,10 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
     if (auto *TD = dyn_cast<TypeDecl>(FoundDecls[0]->getUnderlyingDecl())) {
       assert(!SearchType.isNull() &&
              "should only reject a type result if we have a search type");
-      QualType T = Context.getTypeDeclType(TD);
       Diag(NameLoc, diag::err_destructor_expr_type_mismatch)
-          << T << SearchType << MakeFixItHint();
+          << Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                     /*Qualifier=*/std::nullopt, TD)
+          << SearchType << MakeFixItHint();
     } else {
       Diag(NameLoc, diag::err_destructor_expr_nontype)
           << &II << MakeFixItHint();
@@ -435,7 +443,8 @@ ParsedType Sema::getDestructorName(const IdentifierInfo &II,
   for (NamedDecl *FoundD : FoundDecls) {
     if (auto *TD = dyn_cast<TypeDecl>(FoundD->getUnderlyingDecl()))
       Diag(FoundD->getLocation(), diag::note_destructor_type_here)
-          << Context.getTypeDeclType(TD);
+          << Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                     /*Qualifier=*/std::nullopt, TD);
     else
       Diag(FoundD->getLocation(), diag::note_destructor_nontype_here)
           << FoundD;
@@ -501,12 +510,8 @@ bool Sema::checkLiteralOperatorId(const CXXScopeSpec &SS,
           << II << static_cast<int>(Status) << Hint;
   }
 
-  if (!SS.isValid())
-    return false;
-
-  switch (SS.getScopeRep()->getKind()) {
-  case NestedNameSpecifier::Identifier:
-  case NestedNameSpecifier::TypeSpec:
+  switch (SS.getScopeRep().getKind()) {
+  case NestedNameSpecifier::Kind::Type:
     // Per C++11 [over.literal]p2, literal operators can only be declared at
     // namespace scope. Therefore, this unqualified-id cannot name anything.
     // Reject it early, because we have no AST representation for this in the
@@ -515,10 +520,10 @@ bool Sema::checkLiteralOperatorId(const CXXScopeSpec &SS,
         << SS.getScopeRep();
     return true;
 
-  case NestedNameSpecifier::Global:
-  case NestedNameSpecifier::Super:
-  case NestedNameSpecifier::Namespace:
-  case NestedNameSpecifier::NamespaceAlias:
+  case NestedNameSpecifier::Kind::Null:
+  case NestedNameSpecifier::Kind::Global:
+  case NestedNameSpecifier::Kind::Super:
+  case NestedNameSpecifier::Kind::Namespace:
     return false;
   }
 
@@ -566,7 +571,8 @@ ExprResult Sema::BuildCXXTypeId(QualType TypeInfoType,
 
     QualType T = E->getType();
     if (const RecordType *RecordT = T->getAs<RecordType>()) {
-      CXXRecordDecl *RecordD = cast<CXXRecordDecl>(RecordT->getDecl());
+      CXXRecordDecl *RecordD = cast<CXXRecordDecl>(RecordT->getOriginalDecl())
+                                   ->getDefinitionOrSelf();
       // C++ [expr.typeid]p3:
       //   [...] If the type of the expression is a class type, the class
       //   shall be completely-defined.
@@ -660,7 +666,7 @@ Sema::ActOnCXXTypeid(SourceLocation OpLoc, SourceLocation LParenLoc,
     return ExprError(Diag(OpLoc, diag::err_no_typeid_with_fno_rtti));
   }
 
-  QualType TypeInfoType = Context.getTypeDeclType(CXXTypeInfoDecl);
+  CanQualType TypeInfoType = Context.getCanonicalTagType(CXXTypeInfoDecl);
 
   if (isType) {
     // The operand is a type; handle it as such.
@@ -1215,7 +1221,7 @@ QualType Sema::getCurrentThisType() {
     // This is a lambda call operator that is being instantiated as a default
     // initializer. DC must point to the enclosing class type, so we can recover
     // the 'this' type from it.
-    QualType ClassTy = Context.getTypeDeclType(cast<CXXRecordDecl>(DC));
+    CanQualType ClassTy = Context.getCanonicalTagType(cast<CXXRecordDecl>(DC));
     // There are no cv-qualifiers for 'this' within default initializers,
     // per [expr.prim.general]p4.
     ThisTy = Context.getPointerType(ClassTy);
@@ -1245,7 +1251,7 @@ Sema::CXXThisScopeRAII::CXXThisScopeRAII(Sema &S,
   else
     Record = cast<CXXRecordDecl>(ContextDecl);
 
-  QualType T = S.Context.getRecordType(Record);
+  QualType T = S.Context.getCanonicalTagType(Record);
   T = S.getASTContext().getQualifiedType(T, CXXThisTypeQuals);
 
   S.CXXThisTypeOverride =
@@ -1733,7 +1739,7 @@ static bool isNonPlacementDeallocationFunction(Sema &S, FunctionDecl *FD) {
   if (S.getLangOpts().AlignedAllocation && UsualParams < FD->getNumParams() &&
       S.Context.hasSameUnqualifiedType(
           FD->getParamDecl(UsualParams)->getType(),
-          S.Context.getTypeDeclType(S.getStdAlignValT())))
+          S.Context.getCanonicalTagType(S.getStdAlignValT())))
     ++UsualParams;
 
   return UsualParams == FD->getNumParams();
@@ -1861,8 +1867,8 @@ namespace {
           if (FunctionTemplateDecl *Best = S.getMoreSpecializedTemplate(
                   PrimaryTemplate, OtherPrimaryTemplate, SourceLocation(),
                   TPOC_Call, ImplicitArgCount,
-                  DC ? QualType(DC->getTypeForDecl(), 0) : QualType{},
-                  OtherDC ? QualType(OtherDC->getTypeForDecl(), 0) : QualType{},
+                  DC ? S.Context.getCanonicalTagType(DC) : QualType{},
+                  OtherDC ? S.Context.getCanonicalTagType(OtherDC) : QualType{},
                   false)) {
             return Best == PrimaryTemplate ? 1 : -1;
           }
@@ -1978,7 +1984,7 @@ static bool doesUsualArrayDeleteWantSize(Sema &S, SourceLocation loc,
   DeclarationName deleteName =
     S.Context.DeclarationNames.getCXXOperatorName(OO_Array_Delete);
   LookupResult ops(S, deleteName, loc, Sema::LookupOrdinaryName);
-  S.LookupQualifiedName(ops, record->getDecl());
+  S.LookupQualifiedName(ops, record->getOriginalDecl()->getDefinitionOrSelf());
 
   // We're just doing this for information.
   ops.suppressDiagnostics();
@@ -2506,7 +2512,7 @@ ExprResult Sema::BuildCXXNew(SourceRange Range, bool UseGlobal,
     // because there might not be a `std::align_val_t` type.
     EnumDecl *StdAlignValT = getStdAlignValT();
     QualType AlignValT =
-        StdAlignValT ? Context.getTypeDeclType(StdAlignValT) : SizeTy;
+        StdAlignValT ? Context.getCanonicalTagType(StdAlignValT) : SizeTy;
     IntegerLiteral AlignmentLiteral(
         Context,
         llvm::APInt(Context.getTypeSize(SizeTy),
@@ -2967,7 +2973,7 @@ bool Sema::FindAllocationFunctions(
                            isTypeAwareAllocation(IAP.PassTypeIdentity);
   if (IncludeAlignParam) {
     DeclareGlobalNewDelete();
-    AlignValT = Context.getTypeDeclType(getStdAlignValT());
+    AlignValT = Context.getCanonicalTagType(getStdAlignValT());
   }
   CXXScalarValueInitExpr Align(AlignValT, nullptr, SourceLocation());
   if (IncludeAlignParam)
@@ -3049,8 +3055,9 @@ bool Sema::FindAllocationFunctions(
   LookupResult FoundDelete(*this, DeleteName, StartLoc, LookupOrdinaryName);
   if (AllocElemType->isRecordType() &&
       DeleteScope != AllocationFunctionScope::Global) {
-    auto *RD =
-        cast<CXXRecordDecl>(AllocElemType->castAs<RecordType>()->getDecl());
+    auto *RD = cast<CXXRecordDecl>(
+                   AllocElemType->castAs<RecordType>()->getOriginalDecl())
+                   ->getDefinitionOrSelf();
     LookupQualifiedName(FoundDelete, RD);
   }
   if (FoundDelete.isAmbiguous())
@@ -3427,7 +3434,7 @@ void Sema::DeclareGlobalNewDelete() {
 
       for (int Aligned = 0; Aligned < NumAlignVariants; ++Aligned) {
         if (Aligned)
-          Params.push_back(Context.getTypeDeclType(getStdAlignValT()));
+          Params.push_back(Context.getCanonicalTagType(getStdAlignValT()));
 
         DeclareGlobalAllocationFunction(
             Context.DeclarationNames.getCXXOperatorName(Kind), Return, Params);
@@ -3484,7 +3491,7 @@ void Sema::DeclareGlobalAllocationFunction(DeclarationName Name,
   bool HasBadAllocExceptionSpec = Name.isAnyOperatorNew();
   if (HasBadAllocExceptionSpec) {
     if (!getLangOpts().CPlusPlus11) {
-      BadAllocType = Context.getTypeDeclType(getStdBadAlloc());
+      BadAllocType = Context.getCanonicalTagType(getStdBadAlloc());
       assert(StdBadAlloc && "Must have std::bad_alloc declared");
       EPI.ExceptionSpec.Type = EST_Dynamic;
       EPI.ExceptionSpec.Exceptions = llvm::ArrayRef(BadAllocType);
@@ -3594,7 +3601,7 @@ FunctionDecl *Sema::FindDeallocationFunctionForDestructor(SourceLocation Loc,
   DeclarationName Name = Context.DeclarationNames.getCXXOperatorName(OO_Delete);
 
   FunctionDecl *OperatorDelete = nullptr;
-  QualType DeallocType = Context.getRecordType(RD);
+  CanQualType DeallocType = Context.getCanonicalTagType(RD);
   ImplicitDeallocationParameters IDP = {
       DeallocType, ShouldUseTypeAwareOperatorNewOrDelete(),
       AlignedAllocationMode::No, SizedDeallocationMode::No};
@@ -3628,7 +3635,7 @@ bool Sema::FindDeallocationFunction(SourceLocation StartLoc, CXXRecordDecl *RD,
   Found.suppressDiagnostics();
 
   if (!isAlignedAllocation(IDP.PassAlignment) &&
-      hasNewExtendedAlignment(*this, Context.getRecordType(RD)))
+      hasNewExtendedAlignment(*this, Context.getCanonicalTagType(RD)))
     IDP.PassAlignment = AlignedAllocationMode::Yes;
 
   // C++17 [expr.delete]p10:
@@ -4051,7 +4058,8 @@ Sema::ActOnCXXDelete(SourceLocation StartLoc, bool UseGlobal,
                                    : diag::warn_delete_incomplete,
                                Ex.get())) {
         if (const RecordType *RT = PointeeElem->getAs<RecordType>())
-          PointeeRD = cast<CXXRecordDecl>(RT->getDecl());
+          PointeeRD =
+              cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
       }
     }
 
@@ -4576,7 +4584,7 @@ Sema::PerformImplicitConversion(Expr *From, QualType ToType,
         // If the user-defined conversion is specified by a conversion function,
         // the initial standard conversion sequence converts the source type to
         // the implicit object parameter of the conversion function.
-        BeforeToType = Context.getTagDeclType(Conv->getParent());
+        BeforeToType = Context.getCanonicalTagType(Conv->getParent());
       } else {
         const CXXConstructorDecl *Ctor = cast<CXXConstructorDecl>(FD);
         CastKind = CK_ConstructorConversion;
@@ -4820,7 +4828,10 @@ Sema::PerformImplicitConversion(Expr *From, QualType ToType,
     if (FromType->isVectorType() || ToType->isVectorType())
       StepTy = adjustVectorType(Context, FromType, ToType, &ElTy);
     if (ElTy->isBooleanType()) {
-      assert(FromType->castAs<EnumType>()->getDecl()->isFixed() &&
+      assert(FromType->castAs<EnumType>()
+                 ->getOriginalDecl()
+                 ->getDefinitionOrSelf()
+                 ->isFixed() &&
              SCS.Second == ICK_Integral_Promotion &&
              "only enums with fixed underlying type can promote to bool");
       From = ImpCastExprToType(From, StepTy, CK_IntegralToBoolean, VK_PRValue,
@@ -5372,16 +5383,18 @@ QualType Sema::CheckPointerToMemberOperands(ExprResult &LHS, ExprResult &RHS,
       return QualType();
     }
 
+    // FIXME: use sugared type from member pointer.
+    CanQualType RHSClassType = Context.getCanonicalTagType(RHSClass);
     CXXCastPath BasePath;
     if (CheckDerivedToBaseConversion(
-            LHSType, QualType(RHSClass->getTypeForDecl(), 0), Loc,
+            LHSType, RHSClassType, Loc,
             SourceRange(LHS.get()->getBeginLoc(), RHS.get()->getEndLoc()),
             &BasePath))
       return QualType();
 
     // Cast LHS to type of use.
-    QualType UseType = Context.getQualifiedType(RHSClass->getTypeForDecl(),
-                                                LHSType.getQualifiers());
+    QualType UseType =
+        Context.getQualifiedType(RHSClassType, LHSType.getQualifiers());
     if (isIndirect)
       UseType = Context.getPointerType(UseType);
     ExprValueKind VK = isIndirect ? VK_PRValue : LHS.get()->getValueKind();
@@ -6186,7 +6199,7 @@ QualType Sema::FindCompositePointerType(SourceLocation Loc,
       case Pointer:
         return Ctx.getPointerType(T);
       case MemberPointer:
-        return Ctx.getMemberPointerType(T, /*Qualifier=*/nullptr,
+        return Ctx.getMemberPointerType(T, /*Qualifier=*/std::nullopt,
                                         ClassOrBound->getAsCXXRecordDecl());
       case ObjCPointer:
         return Ctx.getObjCObjectPointerType(T);
@@ -6359,7 +6372,7 @@ QualType Sema::FindCompositePointerType(SourceLocation Loc,
         return QualType();
 
       Steps.emplace_back(Step::MemberPointer,
-                         Context.getTypeDeclType(Cls).getTypePtr());
+                         Context.getCanonicalTagType(Cls).getTypePtr());
       continue;
     }
 
@@ -6638,7 +6651,8 @@ ExprResult Sema::MaybeBindToTemporary(Expr *E) {
 
   // That should be enough to guarantee that this type is complete, if we're
   // not processing a decltype expression.
-  CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+  CXXRecordDecl *RD =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
   if (RD->isInvalidDecl() || RD->isDependentContext())
     return E;
 
@@ -7245,16 +7259,13 @@ ExprResult Sema::ActOnPseudoDestructorExpr(Scope *S, Expr *Base,
     TemplateIdAnnotation *TemplateId = SecondTypeName.TemplateId;
     ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
                                        TemplateId->NumArgs);
-    TypeResult T = ActOnTemplateIdType(S,
-                                       SS,
-                                       TemplateId->TemplateKWLoc,
-                                       TemplateId->Template,
-                                       TemplateId->Name,
-                                       TemplateId->TemplateNameLoc,
-                                       TemplateId->LAngleLoc,
-                                       TemplateArgsPtr,
-                                       TemplateId->RAngleLoc,
-                                       /*IsCtorOrDtorName*/true);
+    TypeResult T = ActOnTemplateIdType(
+        S, ElaboratedTypeKeyword::None,
+        /*ElaboratedKeywordLoc=*/SourceLocation(), SS,
+        TemplateId->TemplateKWLoc, TemplateId->Template, TemplateId->Name,
+        TemplateId->TemplateNameLoc, TemplateId->LAngleLoc, TemplateArgsPtr,
+        TemplateId->RAngleLoc,
+        /*IsCtorOrDtorName*/ true);
     if (T.isInvalid() || !T.get()) {
       // Recover by assuming we had the right type all along.
       DestructedType = ObjectType;
@@ -7298,16 +7309,13 @@ ExprResult Sema::ActOnPseudoDestructorExpr(Scope *S, Expr *Base,
       TemplateIdAnnotation *TemplateId = FirstTypeName.TemplateId;
       ASTTemplateArgsPtr TemplateArgsPtr(TemplateId->getTemplateArgs(),
                                          TemplateId->NumArgs);
-      TypeResult T = ActOnTemplateIdType(S,
-                                         SS,
-                                         TemplateId->TemplateKWLoc,
-                                         TemplateId->Template,
-                                         TemplateId->Name,
-                                         TemplateId->TemplateNameLoc,
-                                         TemplateId->LAngleLoc,
-                                         TemplateArgsPtr,
-                                         TemplateId->RAngleLoc,
-                                         /*IsCtorOrDtorName*/true);
+      TypeResult T = ActOnTemplateIdType(
+          S, ElaboratedTypeKeyword::None,
+          /*ElaboratedKeywordLoc=*/SourceLocation(), SS,
+          TemplateId->TemplateKWLoc, TemplateId->Template, TemplateId->Name,
+          TemplateId->TemplateNameLoc, TemplateId->LAngleLoc, TemplateArgsPtr,
+          TemplateId->RAngleLoc,
+          /*IsCtorOrDtorName*/ true);
       if (T.isInvalid() || !T.get()) {
         // Recover by dropping this type.
         ScopeType = QualType();
@@ -7507,7 +7515,7 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
 
   // GCC seems to also exclude expressions of incomplete enum type.
   if (const EnumType *T = E->getType()->getAs<EnumType>()) {
-    if (!T->getDecl()->isComplete()) {
+    if (!T->getOriginalDecl()->getDefinitionOrSelf()->isComplete()) {
       // FIXME: stupid workaround for a codegen bug!
       E = ImpCastExprToType(E, Context.VoidTy, CK_ToVoid).get();
       return E;
diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 5dca509d46fdb..4a31a139eaf4f 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -492,13 +492,14 @@ CheckExtVectorComponent(Sema &S, QualType baseType, ExprValueKind &VK,
 
   QualType VT = S.Context.getExtVectorType(vecType->getElementType(), CompSize);
   // Now look up the TypeDefDecl from the vector type. Without this,
-  // diagostics look bad. We want extended vector types to appear built-in.
+  // diagnostics look bad. We want extended vector types to appear built-in.
   for (Sema::ExtVectorDeclsType::iterator
          I = S.ExtVectorDecls.begin(S.getExternalSource()),
          E = S.ExtVectorDecls.end();
        I != E; ++I) {
     if ((*I)->getUnderlyingType() == VT)
-      return S.Context.getTypedefType(*I);
+      return S.Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                      /*Qualifier=*/std::nullopt, *I);
   }
 
   return VT; // should never get here (a typedef type should always be found).
@@ -881,7 +882,7 @@ Sema::BuildMemberReferenceExpr(Expr *BaseExpr, QualType BaseExprType,
   // build a CXXDependentScopeMemberExpr.
   if (R.wasNotFoundInCurrentInstantiation() ||
       (R.getLookupName().getCXXOverloadedOperator() == OO_Equal &&
-       (SS.isSet() ? SS.getScopeRep()->isDependent()
+       (SS.isSet() ? SS.getScopeRep().isDependent()
                    : BaseExprType->isDependentType())))
     return ActOnDependentMemberExpr(BaseExpr, BaseExprType, IsArrow, OpLoc, SS,
                                     TemplateKWLoc, FirstQualifierInScope,
diff --git a/clang/lib/Sema/SemaExprObjC.cpp b/clang/lib/Sema/SemaExprObjC.cpp
index e0662d82914f4..03b5c79cf70e3 100644
--- a/clang/lib/Sema/SemaExprObjC.cpp
+++ b/clang/lib/Sema/SemaExprObjC.cpp
@@ -639,14 +639,14 @@ ExprResult SemaObjC::BuildObjCBoxedExpr(SourceRange SR, Expr *ValueExpr) {
     BoxingMethod = getNSNumberFactoryMethod(*this, Loc, ValueType);
     BoxedType = NSNumberPointer;
   } else if (const EnumType *ET = ValueType->getAs<EnumType>()) {
-    if (!ET->getDecl()->isComplete()) {
+    const EnumDecl *ED = ET->getOriginalDecl()->getDefinitionOrSelf();
+    if (!ED->isComplete()) {
       Diag(Loc, diag::err_objc_incomplete_boxed_expression_type)
         << ValueType << ValueExpr->getSourceRange();
       return ExprError();
     }
 
-    BoxingMethod = getNSNumberFactoryMethod(*this, Loc,
-                                            ET->getDecl()->getIntegerType());
+    BoxingMethod = getNSNumberFactoryMethod(*this, Loc, ED->getIntegerType());
     BoxedType = NSNumberPointer;
   } else if (ValueType->isObjCBoxableRecordType()) {
     // Support for structure types, that marked as objc_boxable
@@ -2337,10 +2337,10 @@ SemaObjC::getObjCMessageKind(Scope *S, IdentifierInfo *Name,
     if (ObjCInterfaceDecl *Class = dyn_cast<ObjCInterfaceDecl>(ND))
       T = Context.getObjCInterfaceType(Class);
     else if (TypeDecl *Type = dyn_cast<TypeDecl>(ND)) {
-      T = Context.getTypeDeclType(Type);
       SemaRef.DiagnoseUseOfDecl(Type, NameLoc);
-    }
-    else
+      T = Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                  /*Qualifier=*/std::nullopt, Type);
+    } else
       return ObjCInstanceMessage;
 
     //  We have a class message, and T is the type we're
@@ -3847,7 +3847,8 @@ static inline T *getObjCBridgeAttr(const TypedefType *TD) {
   if (QT->isPointerType()) {
     QT = QT->getPointeeType();
     if (const RecordType *RT = QT->getAs<RecordType>()) {
-      for (auto *Redecl : RT->getDecl()->getMostRecentDecl()->redecls()) {
+      for (auto *Redecl :
+           RT->getOriginalDecl()->getMostRecentDecl()->redecls()) {
         if (auto *attr = Redecl->getAttr<T>())
           return attr;
       }
diff --git a/clang/lib/Sema/SemaFunctionEffects.cpp b/clang/lib/Sema/SemaFunctionEffects.cpp
index 1592862416bf9..8590ee831084f 100644
--- a/clang/lib/Sema/SemaFunctionEffects.cpp
+++ b/clang/lib/Sema/SemaFunctionEffects.cpp
@@ -1352,11 +1352,15 @@ class Analyzer {
       return true;
     }
 
-    bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc Node) override {
+    bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc Node,
+                                   bool TraverseQualifier) override {
       return true;
     }
 
-    bool TraverseDecltypeTypeLoc(DecltypeTypeLoc Node) override { return true; }
+    bool TraverseDecltypeTypeLoc(DecltypeTypeLoc Node,
+                                 bool TraverseQualifier) override {
+      return true;
+    }
 
     bool TraverseCXXNoexceptExpr(CXXNoexceptExpr *Node) override {
       return true;
diff --git a/clang/lib/Sema/SemaHLSL.cpp b/clang/lib/Sema/SemaHLSL.cpp
index 9af32138f9385..c68c5f61ba423 100644
--- a/clang/lib/Sema/SemaHLSL.cpp
+++ b/clang/lib/Sema/SemaHLSL.cpp
@@ -231,7 +231,7 @@ static unsigned calculateLegacyCbufferSize(const ASTContext &Context,
   constexpr unsigned CBufferAlign = 16;
   if (const RecordType *RT = T->getAs<RecordType>()) {
     unsigned Size = 0;
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     for (const FieldDecl *Field : RD->fields()) {
       QualType Ty = Field->getType();
       unsigned FieldSize = calculateLegacyCbufferSize(Context, Ty);
@@ -370,7 +370,7 @@ static bool isInvalidConstantBufferLeafElementType(const Type *Ty) {
 // needs to be created for HLSL Buffer use that will exclude these unwanted
 // declarations (see createHostLayoutStruct function).
 static bool requiresImplicitBufferLayoutStructure(const CXXRecordDecl *RD) {
-  if (RD->getTypeForDecl()->isHLSLIntangibleType() || RD->isEmpty())
+  if (RD->isHLSLIntangible() || RD->isEmpty())
     return true;
   // check fields
   for (const FieldDecl *Field : RD->fields()) {
@@ -455,7 +455,7 @@ static FieldDecl *createFieldForHostLayoutStruct(Sema &S, const Type *Ty,
       RD = createHostLayoutStruct(S, RD);
       if (!RD)
         return nullptr;
-      Ty = RD->getTypeForDecl();
+      Ty = S.Context.getCanonicalTagType(RD)->getTypePtr();
     }
   }
 
@@ -505,8 +505,8 @@ static CXXRecordDecl *createHostLayoutStruct(Sema &S,
     if (requiresImplicitBufferLayoutStructure(BaseDecl)) {
       BaseDecl = createHostLayoutStruct(S, BaseDecl);
       if (BaseDecl) {
-        TypeSourceInfo *TSI = AST.getTrivialTypeSourceInfo(
-            QualType(BaseDecl->getTypeForDecl(), 0));
+        TypeSourceInfo *TSI =
+            AST.getTrivialTypeSourceInfo(AST.getCanonicalTagType(BaseDecl));
         Base = CXXBaseSpecifier(SourceRange(), false, StructDecl->isClass(),
                                 AS_none, TSI, SourceLocation());
       }
@@ -1717,7 +1717,7 @@ SemaHLSL::TakeLocForHLSLAttribute(const HLSLAttributedResourceType *RT) {
 // requirements and adds them to Bindings
 void SemaHLSL::collectResourceBindingsOnUserRecordDecl(const VarDecl *VD,
                                                        const RecordType *RT) {
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   for (FieldDecl *FD : RD->fields()) {
     const Type *Ty = FD->getType()->getUnqualifiedDesugaredType();
 
@@ -3270,7 +3270,7 @@ bool SemaHLSL::ContainsBitField(QualType BaseTy) {
       continue;
     }
     if (const auto *RT = dyn_cast<RecordType>(T)) {
-      const RecordDecl *RD = RT->getDecl();
+      const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
       if (RD->isUnion())
         continue;
 
@@ -3786,7 +3786,8 @@ class InitListTransformer {
       }
       while (!RecordTypes.empty()) {
         const RecordType *RT = RecordTypes.pop_back_val();
-        for (auto *FD : RT->getDecl()->fields()) {
+        for (auto *FD :
+             RT->getOriginalDecl()->getDefinitionOrSelf()->fields()) {
           DeclAccessPair Found = DeclAccessPair::make(FD, FD->getAccess());
           DeclarationNameInfo NameInfo(FD->getDeclName(), E->getBeginLoc());
           ExprResult Res = S.BuildFieldReferenceExpr(
@@ -3834,7 +3835,8 @@ class InitListTransformer {
       }
       while (!RecordTypes.empty()) {
         const RecordType *RT = RecordTypes.pop_back_val();
-        for (auto *FD : RT->getDecl()->fields()) {
+        for (auto *FD :
+             RT->getOriginalDecl()->getDefinitionOrSelf()->fields()) {
           Inits.push_back(generateInitListsImpl(FD->getType()));
         }
       }
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 95746b35f71ef..92aeab892e7b1 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -446,7 +446,6 @@ class InitListChecker {
                                    unsigned ExpectedNumInits);
   int numArrayElements(QualType DeclType);
   int numStructUnionElements(QualType DeclType);
-  static RecordDecl *getRecordDecl(QualType DeclType);
 
   ExprResult PerformEmptyInit(SourceLocation Loc,
                               const InitializedEntity &Entity);
@@ -776,7 +775,7 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
 
   if (Init >= NumInits || !ILE->getInit(Init)) {
     if (const RecordType *RType = ILE->getType()->getAs<RecordType>())
-      if (!RType->getDecl()->isUnion())
+      if (!RType->getOriginalDecl()->isUnion())
         assert((Init < NumInits || VerifyOnly) &&
                "This ILE should have been expanded");
 
@@ -923,7 +922,7 @@ InitListChecker::FillInEmptyInitializations(const InitializedEntity &Entity,
     return;
 
   if (const RecordType *RType = ILE->getType()->getAs<RecordType>()) {
-    const RecordDecl *RDecl = RType->getDecl();
+    const RecordDecl *RDecl = RType->getOriginalDecl()->getDefinitionOrSelf();
     if (RDecl->isUnion() && ILE->getInitializedFieldInUnion()) {
       FillInEmptyInitForField(0, ILE->getInitializedFieldInUnion(), Entity, ILE,
                               RequiresSecondPass, FillWithNoInit);
@@ -1127,7 +1126,8 @@ int InitListChecker::numArrayElements(QualType DeclType) {
 }
 
 int InitListChecker::numStructUnionElements(QualType DeclType) {
-  RecordDecl *structDecl = DeclType->castAs<RecordType>()->getDecl();
+  RecordDecl *structDecl =
+      DeclType->castAs<RecordType>()->getOriginalDecl()->getDefinitionOrSelf();
   int InitializableMembers = 0;
   if (auto *CXXRD = dyn_cast<CXXRecordDecl>(structDecl))
     InitializableMembers += CXXRD->getNumBases();
@@ -1140,14 +1140,6 @@ int InitListChecker::numStructUnionElements(QualType DeclType) {
   return InitializableMembers - structDecl->hasFlexibleArrayMember();
 }
 
-RecordDecl *InitListChecker::getRecordDecl(QualType DeclType) {
-  if (const auto *RT = DeclType->getAs<RecordType>())
-    return RT->getDecl();
-  if (const auto *Inject = DeclType->getAs<InjectedClassNameType>())
-    return Inject->getDecl();
-  return nullptr;
-}
-
 /// Determine whether Entity is an entity for which it is idiomatic to elide
 /// the braces in aggregate initialization.
 static bool isIdiomaticBraceElisionEntity(const InitializedEntity &Entity) {
@@ -1164,16 +1156,22 @@ static bool isIdiomaticBraceElisionEntity(const InitializedEntity &Entity) {
 
   // Allows elide brace initialization for aggregates with empty base.
   if (Entity.getKind() == InitializedEntity::EK_Base) {
-    auto *ParentRD =
-        Entity.getParent()->getType()->castAs<RecordType>()->getDecl();
+    auto *ParentRD = Entity.getParent()
+                         ->getType()
+                         ->castAs<RecordType>()
+                         ->getOriginalDecl()
+                         ->getDefinitionOrSelf();
     CXXRecordDecl *CXXRD = cast<CXXRecordDecl>(ParentRD);
     return CXXRD->getNumBases() == 1 && CXXRD->field_empty();
   }
 
   // Allow brace elision if the only subobject is a field.
   if (Entity.getKind() == InitializedEntity::EK_Member) {
-    auto *ParentRD =
-        Entity.getParent()->getType()->castAs<RecordType>()->getDecl();
+    auto *ParentRD = Entity.getParent()
+                         ->getType()
+                         ->castAs<RecordType>()
+                         ->getOriginalDecl()
+                         ->getDefinitionOrSelf();
     if (CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(ParentRD)) {
       if (CXXRD->getNumBases()) {
         return false;
@@ -1442,7 +1440,7 @@ void InitListChecker::CheckListElementTypes(const InitializedEntity &Entity,
   } else if (DeclType->isVectorType()) {
     CheckVectorType(Entity, IList, DeclType, Index,
                     StructuredList, StructuredIndex);
-  } else if (const RecordDecl *RD = getRecordDecl(DeclType)) {
+  } else if (const RecordDecl *RD = DeclType->getAsRecordDecl()) {
     auto Bases =
         CXXRecordDecl::base_class_const_range(CXXRecordDecl::base_class_const_iterator(),
                                         CXXRecordDecl::base_class_const_iterator());
@@ -2320,7 +2318,7 @@ void InitListChecker::CheckStructUnionTypes(
     bool SubobjectIsDesignatorContext, unsigned &Index,
     InitListExpr *StructuredList, unsigned &StructuredIndex,
     bool TopLevelObject) {
-  const RecordDecl *RD = getRecordDecl(DeclType);
+  const RecordDecl *RD = DeclType->getAsRecordDecl();
 
   // If the record is invalid, some of it's members are invalid. To avoid
   // confusion, we forgo checking the initializer for the entire record.
@@ -2889,7 +2887,7 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
     //   then the current object (defined below) shall have
     //   structure or union type and the identifier shall be the
     //   name of a member of that type.
-    RecordDecl *RD = getRecordDecl(CurrentObjectType);
+    RecordDecl *RD = CurrentObjectType->getAsRecordDecl();
     if (!RD) {
       SourceLocation Loc = D->getDotLoc();
       if (Loc.isInvalid())
@@ -4337,8 +4335,8 @@ static bool hasCopyOrMoveCtorParam(ASTContext &Ctx,
 
   QualType ParmT =
       Info.Constructor->getParamDecl(0)->getType().getNonReferenceType();
-  QualType ClassT =
-      Ctx.getRecordType(cast<CXXRecordDecl>(Info.FoundDecl->getDeclContext()));
+  CanQualType ClassT = Ctx.getCanonicalTagType(
+      cast<CXXRecordDecl>(Info.FoundDecl->getDeclContext()));
 
   return Ctx.hasSameUnqualifiedType(ParmT, ClassT);
 }
@@ -4537,8 +4535,8 @@ static void TryConstructorInitialization(Sema &S,
 
   const RecordType *DestRecordType = DestType->getAs<RecordType>();
   assert(DestRecordType && "Constructor initialization requires record type");
-  CXXRecordDecl *DestRecordDecl
-    = cast<CXXRecordDecl>(DestRecordType->getDecl());
+  auto *DestRecordDecl = cast<CXXRecordDecl>(DestRecordType->getOriginalDecl())
+                             ->getDefinitionOrSelf();
 
   // Build the candidate set directly in the initialization sequence
   // structure, so that it will persist if we fail.
@@ -5059,8 +5057,8 @@ static void TryListInitialization(Sema &S,
     //     the underlying type of T, the program is ill-formed.
     auto *ET = DestType->getAs<EnumType>();
     if (S.getLangOpts().CPlusPlus17 &&
-        Kind.getKind() == InitializationKind::IK_DirectList &&
-        ET && ET->getDecl()->isFixed() &&
+        Kind.getKind() == InitializationKind::IK_DirectList && ET &&
+        ET->getOriginalDecl()->getDefinitionOrSelf()->isFixed() &&
         !S.Context.hasSameUnqualifiedType(E->getType(), DestType) &&
         (E->getType()->isIntegralOrUnscopedEnumerationType() ||
          E->getType()->isFloatingType())) {
@@ -5170,7 +5168,8 @@ static OverloadingResult TryRefInitWithConversionFunction(
       S.isCompleteType(Kind.getLocation(), T1)) {
     // The type we're converting to is a class type. Enumerate its constructors
     // to see if there is a suitable conversion.
-    CXXRecordDecl *T1RecordDecl = cast<CXXRecordDecl>(T1RecordType->getDecl());
+    auto *T1RecordDecl = cast<CXXRecordDecl>(T1RecordType->getOriginalDecl())
+                             ->getDefinitionOrSelf();
 
     for (NamedDecl *D : S.LookupConstructors(T1RecordDecl)) {
       auto Info = getConstructorInfo(D);
@@ -5193,7 +5192,8 @@ static OverloadingResult TryRefInitWithConversionFunction(
       }
     }
   }
-  if (T1RecordType && T1RecordType->getDecl()->isInvalidDecl())
+  if (T1RecordType &&
+      T1RecordType->getOriginalDecl()->getDefinitionOrSelf()->isInvalidDecl())
     return OR_No_Viable_Function;
 
   const RecordType *T2RecordType = nullptr;
@@ -5201,7 +5201,8 @@ static OverloadingResult TryRefInitWithConversionFunction(
       S.isCompleteType(Kind.getLocation(), T2)) {
     // The type we're converting from is a class type, enumerate its conversion
     // functions.
-    CXXRecordDecl *T2RecordDecl = cast<CXXRecordDecl>(T2RecordType->getDecl());
+    auto *T2RecordDecl = cast<CXXRecordDecl>(T2RecordType->getOriginalDecl())
+                             ->getDefinitionOrSelf();
 
     const auto &Conversions = T2RecordDecl->getVisibleConversionFunctions();
     for (auto I = Conversions.begin(), E = Conversions.end(); I != E; ++I) {
@@ -5237,7 +5238,8 @@ static OverloadingResult TryRefInitWithConversionFunction(
       }
     }
   }
-  if (T2RecordType && T2RecordType->getDecl()->isInvalidDecl())
+  if (T2RecordType &&
+      T2RecordType->getOriginalDecl()->getDefinitionOrSelf()->isInvalidDecl())
     return OR_No_Viable_Function;
 
   SourceLocation DeclLoc = Initializer->getBeginLoc();
@@ -5715,7 +5717,9 @@ static void TryValueInitialization(Sema &S,
   T = S.Context.getBaseElementType(T);
 
   if (const RecordType *RT = T->getAs<RecordType>()) {
-    if (CXXRecordDecl *ClassDecl = dyn_cast<CXXRecordDecl>(RT->getDecl())) {
+    if (CXXRecordDecl *ClassDecl =
+            dyn_cast<CXXRecordDecl>(RT->getOriginalDecl())) {
+      ClassDecl = ClassDecl->getDefinitionOrSelf();
       bool NeedZeroInitialization = true;
       // C++98:
       // -- if T is a class type (clause 9) with a user-declared constructor
@@ -5913,7 +5917,8 @@ static void TryOrBuildParenListInitialization(
     }
   } else if (auto *RT = Entity.getType()->getAs<RecordType>()) {
     bool IsUnion = RT->isUnionType();
-    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+    const auto *RD =
+        cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
     if (RD->isInvalidDecl()) {
       // Exit early to avoid confusion when processing members.
       // We do the same for braced list initialization in
@@ -6102,8 +6107,9 @@ static void TryUserDefinedConversion(Sema &S,
   if (const RecordType *DestRecordType = DestType->getAs<RecordType>()) {
     // The type we're converting to is a class type. Enumerate its constructors
     // to see if there is a suitable conversion.
-    CXXRecordDecl *DestRecordDecl
-      = cast<CXXRecordDecl>(DestRecordType->getDecl());
+    auto *DestRecordDecl =
+        cast<CXXRecordDecl>(DestRecordType->getOriginalDecl())
+            ->getDefinitionOrSelf();
 
     // Try to complete the type we're converting to.
     if (S.isCompleteType(Kind.getLocation(), DestType)) {
@@ -6139,8 +6145,9 @@ static void TryUserDefinedConversion(Sema &S,
     // We can only enumerate the conversion functions for a complete type; if
     // the type isn't complete, simply skip this step.
     if (S.isCompleteType(DeclLoc, SourceType)) {
-      CXXRecordDecl *SourceRecordDecl
-        = cast<CXXRecordDecl>(SourceRecordType->getDecl());
+      auto *SourceRecordDecl =
+          cast<CXXRecordDecl>(SourceRecordType->getOriginalDecl())
+              ->getDefinitionOrSelf();
 
       const auto &Conversions =
           SourceRecordDecl->getVisibleConversionFunctions();
@@ -7173,7 +7180,8 @@ static ExprResult CopyObject(Sema &S,
   Expr *CurInitExpr = (Expr *)CurInit.get();
   CXXRecordDecl *Class = nullptr;
   if (const RecordType *Record = T->getAs<RecordType>())
-    Class = cast<CXXRecordDecl>(Record->getDecl());
+    Class =
+        cast<CXXRecordDecl>(Record->getOriginalDecl())->getDefinitionOrSelf();
   if (!Class)
     return CurInit;
 
@@ -7328,8 +7336,8 @@ static void CheckCXX98CompatAccessibleCopy(Sema &S,
 
   // Find constructors which would have been considered.
   OverloadCandidateSet CandidateSet(Loc, OverloadCandidateSet::CSK_Normal);
-  DeclContext::lookup_result Ctors =
-      S.LookupConstructors(cast<CXXRecordDecl>(Record->getDecl()));
+  DeclContext::lookup_result Ctors = S.LookupConstructors(
+      cast<CXXRecordDecl>(Record->getOriginalDecl())->getDefinitionOrSelf());
 
   // Perform overload resolution.
   OverloadCandidateSet::iterator Best;
@@ -8160,8 +8168,9 @@ ExprResult InitializationSequence::Perform(Sema &S,
         // regardless of how we initialized the entity.
         QualType T = CurInit.get()->getType();
         if (const RecordType *Record = T->getAs<RecordType>()) {
-          CXXDestructorDecl *Destructor
-            = S.LookupDestructor(cast<CXXRecordDecl>(Record->getDecl()));
+          CXXDestructorDecl *Destructor =
+              S.LookupDestructor(cast<CXXRecordDecl>(Record->getOriginalDecl())
+                                     ->getDefinitionOrSelf());
           S.CheckDestructorAccess(CurInit.get()->getBeginLoc(), Destructor,
                                   S.PDiag(diag::err_access_dtor_temp) << T);
           S.MarkFunctionReferenced(CurInit.get()->getBeginLoc(), Destructor);
@@ -8808,8 +8817,8 @@ static void emitBadConversionNotes(Sema &S, const InitializedEntity &entity,
       destPointeeType.getQualifiers().compatiblyIncludes(
           fromPointeeType.getQualifiers(), S.getASTContext()))
     S.Diag(fromDecl->getLocation(), diag::note_forward_class_conversion)
-        << S.getASTContext().getTagDeclType(fromDecl)
-        << S.getASTContext().getTagDeclType(destDecl);
+        << S.getASTContext().getCanonicalTagType(fromDecl)
+        << S.getASTContext().getCanonicalTagType(destDecl);
 }
 
 static void diagnoseListInit(Sema &S, const InitializedEntity &Entity,
@@ -9208,32 +9217,34 @@ bool InitializationSequence::Diagnose(Sema &S,
             InheritedFrom = Inherited.getShadowDecl()->getNominatedBaseClass();
           if (Entity.getKind() == InitializedEntity::EK_Base) {
             S.Diag(Kind.getLocation(), diag::err_missing_default_ctor)
-              << (InheritedFrom ? 2 : Constructor->isImplicit() ? 1 : 0)
-              << S.Context.getTypeDeclType(Constructor->getParent())
-              << /*base=*/0
-              << Entity.getType()
-              << InheritedFrom;
-
-            RecordDecl *BaseDecl
-              = Entity.getBaseSpecifier()->getType()->castAs<RecordType>()
-                                                                  ->getDecl();
+                << (InheritedFrom               ? 2
+                    : Constructor->isImplicit() ? 1
+                                                : 0)
+                << S.Context.getCanonicalTagType(Constructor->getParent())
+                << /*base=*/0 << Entity.getType() << InheritedFrom;
+
+            RecordDecl *BaseDecl = Entity.getBaseSpecifier()
+                                       ->getType()
+                                       ->castAs<RecordType>()
+                                       ->getOriginalDecl()
+                                       ->getDefinitionOrSelf();
             S.Diag(BaseDecl->getLocation(), diag::note_previous_decl)
-              << S.Context.getTagDeclType(BaseDecl);
+                << S.Context.getCanonicalTagType(BaseDecl);
           } else {
             S.Diag(Kind.getLocation(), diag::err_missing_default_ctor)
-              << (InheritedFrom ? 2 : Constructor->isImplicit() ? 1 : 0)
-              << S.Context.getTypeDeclType(Constructor->getParent())
-              << /*member=*/1
-              << Entity.getName()
-              << InheritedFrom;
+                << (InheritedFrom               ? 2
+                    : Constructor->isImplicit() ? 1
+                                                : 0)
+                << S.Context.getCanonicalTagType(Constructor->getParent())
+                << /*member=*/1 << Entity.getName() << InheritedFrom;
             S.Diag(Entity.getDecl()->getLocation(),
                    diag::note_member_declared_at);
 
             if (const RecordType *Record
                                  = Entity.getType()->getAs<RecordType>())
-              S.Diag(Record->getDecl()->getLocation(),
+              S.Diag(Record->getOriginalDecl()->getLocation(),
                      diag::note_previous_decl)
-                << S.Context.getTagDeclType(Record->getDecl());
+                  << S.Context.getCanonicalTagType(Record->getOriginalDecl());
           }
           break;
         }
@@ -9300,11 +9311,11 @@ bool InitializationSequence::Diagnose(Sema &S,
       // initialized.
       CXXConstructorDecl *Constructor = cast<CXXConstructorDecl>(S.CurContext);
       S.Diag(Kind.getLocation(), diag::err_uninitialized_member_in_ctor)
-        << (Constructor->getInheritedConstructor() ? 2 :
-            Constructor->isImplicit() ? 1 : 0)
-        << S.Context.getTypeDeclType(Constructor->getParent())
-        << /*const=*/1
-        << Entity.getName();
+          << (Constructor->getInheritedConstructor() ? 2
+              : Constructor->isImplicit()            ? 1
+                                                     : 0)
+          << S.Context.getCanonicalTagType(Constructor->getParent())
+          << /*const=*/1 << Entity.getName();
       S.Diag(Entity.getDecl()->getLocation(), diag::note_previous_decl)
         << Entity.getName();
     } else if (const auto *VD = dyn_cast_if_present<VarDecl>(Entity.getDecl());
@@ -10157,7 +10168,7 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
       auto *RD = cast<CXXRecordDecl>(Pattern->getTemplatedDecl());
       if (!(RD->getDefinition() && RD->isAggregate()))
         return;
-      QualType Ty = Context.getRecordType(RD);
+      QualType Ty = Context.getCanonicalTagType(RD);
       SmallVector<QualType, 8> ElementTypes;
 
       InitListChecker CheckInitList(*this, Entity, ListInit, Ty, ElementTypes);
@@ -10297,8 +10308,8 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
   case OR_No_Viable_Function: {
     CXXRecordDecl *Primary =
         cast<ClassTemplateDecl>(Template)->getTemplatedDecl();
-    bool Complete =
-        isCompleteType(Kind.getLocation(), Context.getTypeDeclType(Primary));
+    bool Complete = isCompleteType(Kind.getLocation(),
+                                   Context.getCanonicalTagType(Primary));
     Candidates.NoteCandidates(
         PartialDiagnosticAt(
             Kind.getLocation(),
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index bc3c4b0addeba..0d891fc08c207 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -425,7 +425,7 @@ bool Sema::DiagnoseInvalidExplicitObjectParameterInLambda(
                                              .getNonReferenceType()
                                              .getUnqualifiedType()
                                              .getDesugaredType(getASTContext());
-  QualType LambdaType = getASTContext().getRecordType(RD);
+  CanQualType LambdaType = getASTContext().getCanonicalTagType(RD);
   if (LambdaType == ExplicitObjectParameterType)
     return false;
 
@@ -457,7 +457,7 @@ bool Sema::DiagnoseInvalidExplicitObjectParameterInLambda(
     return true;
   }
 
-  if (Paths.isAmbiguous(LambdaType->getCanonicalTypeUnqualified())) {
+  if (Paths.isAmbiguous(LambdaType)) {
     std::string PathsDisplay = getAmbiguousPathsDisplayString(Paths);
     Diag(CallLoc, diag::err_explicit_object_lambda_ambiguous_base)
         << LambdaType << PathsDisplay;
@@ -642,7 +642,7 @@ static EnumDecl *findEnumForBlockReturn(Expr *E) {
 
   //   - it is an expression of that formal enum type.
   if (const EnumType *ET = E->getType()->getAs<EnumType>()) {
-    return ET->getDecl();
+    return ET->getOriginalDecl()->getDefinitionOrSelf();
   }
 
   // Otherwise, nope.
@@ -759,7 +759,7 @@ void Sema::deduceClosureReturnType(CapturingScopeInfo &CSI) {
     assert(isa<BlockScopeInfo>(CSI));
     const EnumDecl *ED = findCommonEnumForBlockReturns(CSI.Returns);
     if (ED) {
-      CSI.ReturnType = Context.getTypeDeclType(ED);
+      CSI.ReturnType = Context.getCanonicalTagType(ED);
       adjustBlockReturnsToEnum(*this, CSI.Returns, CSI.ReturnType);
       return;
     }
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index aa7191d2814fe..9299500e430f3 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -562,9 +562,8 @@ void LookupResult::resolveKind() {
     // no ambiguity if they all refer to the same type, so unique based on the
     // canonical type.
     if (const auto *TD = dyn_cast<TypeDecl>(D)) {
-      QualType T = getSema().Context.getTypeDeclType(TD);
       auto UniqueResult = UniqueTypes.insert(
-          std::make_pair(getSema().Context.getCanonicalType(T), I));
+          std::make_pair(getSema().Context.getCanonicalTypeDeclType(TD), I));
       if (!UniqueResult.second) {
         // The type is not unique.
         ExistingI = UniqueResult.first->second;
@@ -716,7 +715,7 @@ static QualType getOpenCLEnumType(Sema &S, llvm::StringRef Name) {
   EnumDecl *Decl = Result.getAsSingle<EnumDecl>();
   if (!Decl)
     return diagOpenCLBuiltinTypeError(S, "enum", Name);
-  return S.Context.getEnumType(Decl);
+  return S.Context.getCanonicalTagType(Decl);
 }
 
 /// Lookup an OpenCL typedef type.
@@ -729,7 +728,8 @@ static QualType getOpenCLTypedefType(Sema &S, llvm::StringRef Name) {
   TypedefNameDecl *Decl = Result.getAsSingle<TypedefNameDecl>();
   if (!Decl)
     return diagOpenCLBuiltinTypeError(S, "typedef", Name);
-  return S.Context.getTypedefType(Decl);
+  return S.Context.getTypedefType(ElaboratedTypeKeyword::None,
+                                  /*Qualifier=*/std::nullopt, Decl);
 }
 
 /// Get the QualType instances of the return type and arguments for an OpenCL
@@ -1000,7 +1000,7 @@ static void LookupPredefedObjCSuperType(Sema &Sema, Scope *S) {
   Sema.LookupName(Result, S);
   if (Result.getResultKind() == LookupResultKind::Found)
     if (const TagDecl *TD = Result.getAsSingle<TagDecl>())
-      Context.setObjCSuperType(Context.getTagDeclType(TD));
+      Context.setObjCSuperType(Context.getCanonicalTagType(TD));
 }
 
 void Sema::LookupNecessaryTypesForBuiltin(Scope *S, unsigned ID) {
@@ -2434,12 +2434,12 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
   if (!R.getLookupName())
     return false;
 
+#ifndef NDEBUG
   // Make sure that the declaration context is complete.
-  assert((!isa<TagDecl>(LookupCtx) ||
-          LookupCtx->isDependentContext() ||
-          cast<TagDecl>(LookupCtx)->isCompleteDefinition() ||
-          cast<TagDecl>(LookupCtx)->isBeingDefined()) &&
-         "Declaration context must already be complete!");
+  if (const auto *TD = dyn_cast<TagDecl>(LookupCtx);
+      TD && !TD->isDependentType() && TD->getDefinition() == nullptr)
+    llvm_unreachable("Declaration context must already be complete!");
+#endif
 
   struct QualifiedLookupInScope {
     bool oldVal;
@@ -2595,10 +2595,8 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
         // C++ [class.member.lookup]p3:
         //   type declarations (including injected-class-names) are replaced by
         //   the types they designate
-        if (const TypeDecl *TD = dyn_cast<TypeDecl>(ND->getUnderlyingDecl())) {
-          QualType T = Context.getTypeDeclType(TD);
-          return T.getCanonicalType().getAsOpaquePtr();
-        }
+        if (const TypeDecl *TD = dyn_cast<TypeDecl>(ND->getUnderlyingDecl()))
+          return Context.getCanonicalTypeDeclType(TD).getAsOpaquePtr();
 
         return ND->getUnderlyingDecl()->getCanonicalDecl();
       }
@@ -2703,12 +2701,10 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
 
 bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                                CXXScopeSpec &SS) {
-  auto *NNS = SS.getScopeRep();
-  if (NNS && NNS->getKind() == NestedNameSpecifier::Super)
-    return LookupInSuper(R, NNS->getAsRecordDecl());
-  else
-
-    return LookupQualifiedName(R, LookupCtx);
+  NestedNameSpecifier Qualifier = SS.getScopeRep();
+  if (Qualifier.getKind() == NestedNameSpecifier::Kind::Super)
+    return LookupInSuper(R, Qualifier.getAsSuper());
+  return LookupQualifiedName(R, LookupCtx);
 }
 
 bool Sema::LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
@@ -2730,7 +2726,9 @@ bool Sema::LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
     IsDependent = !DC && ObjectType->isDependentType();
     assert(((!DC && ObjectType->isDependentType()) ||
             !ObjectType->isIncompleteType() || !ObjectType->getAs<TagType>() ||
-            ObjectType->castAs<TagType>()->isBeingDefined()) &&
+            ObjectType->castAs<TagType>()
+                ->getOriginalDecl()
+                ->isEntityBeingDefined()) &&
            "Caller should have completed object type");
   } else if (SS && SS->isNotEmpty()) {
     // This nested-name-specifier occurs after another nested-name-specifier,
@@ -2743,9 +2741,9 @@ bool Sema::LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
       // FIXME: '__super' lookup semantics could be implemented by a
       // LookupResult::isSuperLookup flag which skips the initial search of
       // the lookup context in LookupQualified.
-      if (NestedNameSpecifier *NNS = SS->getScopeRep();
-          NNS->getKind() == NestedNameSpecifier::Super)
-        return LookupInSuper(R, NNS->getAsRecordDecl());
+      if (NestedNameSpecifier Qualifier = SS->getScopeRep();
+          Qualifier.getKind() == NestedNameSpecifier::Kind::Super)
+        return LookupInSuper(R, Qualifier.getAsSuper());
     }
     IsDependent = !DC && isDependentScopeSpecifier(*SS);
   } else {
@@ -2771,10 +2769,12 @@ bool Sema::LookupInSuper(LookupResult &R, CXXRecordDecl *Class) {
   // members of Class itself.  That is, the naming class is Class, and the
   // access includes the access of the base.
   for (const auto &BaseSpec : Class->bases()) {
-    CXXRecordDecl *RD = cast<CXXRecordDecl>(
-        BaseSpec.getType()->castAs<RecordType>()->getDecl());
+    CXXRecordDecl *RD =
+        cast<CXXRecordDecl>(
+            BaseSpec.getType()->castAs<RecordType>()->getOriginalDecl())
+            ->getDefinitionOrSelf();
     LookupResult Result(*this, R.getLookupNameInfo(), R.getLookupKind());
-    Result.setBaseObjectType(Context.getRecordType(Class));
+    Result.setBaseObjectType(Context.getCanonicalTagType(Class));
     LookupQualifiedName(Result, RD);
 
     // Copy the lookup results into the target, merging the base's access into
@@ -3100,7 +3100,7 @@ addAssociatedClassesAndNamespaces(AssociatedLookup &Result,
 
   // Only recurse into base classes for complete types.
   if (!Result.S.isCompleteType(Result.InstantiationLoc,
-                               Result.S.Context.getRecordType(Class)))
+                               Result.S.Context.getCanonicalTagType(Class)))
     return;
 
   // Add direct and indirect base classes along with their associated
@@ -3122,7 +3122,8 @@ addAssociatedClassesAndNamespaces(AssociatedLookup &Result,
       // the classes and namespaces of known non-dependent arguments.
       if (!BaseType)
         continue;
-      CXXRecordDecl *BaseDecl = cast<CXXRecordDecl>(BaseType->getDecl());
+      CXXRecordDecl *BaseDecl = cast<CXXRecordDecl>(BaseType->getOriginalDecl())
+                                    ->getDefinitionOrSelf();
       if (Result.addClassTransitive(BaseDecl)) {
         // Find the associated namespace for this base class.
         DeclContext *BaseCtx = BaseDecl->getDeclContext();
@@ -3193,8 +3194,10 @@ addAssociatedClassesAndNamespaces(AssociatedLookup &Result, QualType Ty) {
     //        Its associated namespaces are the innermost enclosing
     //        namespaces of its associated classes.
     case Type::Record: {
+      // FIXME: This should use the original decl.
       CXXRecordDecl *Class =
-          cast<CXXRecordDecl>(cast<RecordType>(T)->getDecl());
+          cast<CXXRecordDecl>(cast<RecordType>(T)->getOriginalDecl())
+              ->getDefinitionOrSelf();
       addAssociatedClassesAndNamespaces(Result, Class);
       break;
     }
@@ -3204,7 +3207,9 @@ addAssociatedClassesAndNamespaces(AssociatedLookup &Result, QualType Ty) {
     //        If it is a class member, its associated class is the
     //        member’s class; else it has no associated class.
     case Type::Enum: {
-      EnumDecl *Enum = cast<EnumType>(T)->getDecl();
+      // FIXME: This should use the original decl.
+      EnumDecl *Enum =
+          cast<EnumType>(T)->getOriginalDecl()->getDefinitionOrSelf();
 
       DeclContext *Ctx = Enum->getDeclContext();
       if (CXXRecordDecl *EnclosingClass = dyn_cast<CXXRecordDecl>(Ctx))
@@ -3437,7 +3442,7 @@ Sema::LookupSpecialMember(CXXRecordDecl *RD, CXXSpecialMemberKind SM,
 
   // Prepare for overload resolution. Here we construct a synthetic argument
   // if necessary and make sure that implicit functions are declared.
-  CanQualType CanTy = Context.getCanonicalType(Context.getTagDeclType(RD));
+  CanQualType CanTy = Context.getCanonicalTagType(RD);
   DeclarationName Name;
   Expr *Arg = nullptr;
   unsigned NumArgs;
@@ -3644,7 +3649,7 @@ DeclContext::lookup_result Sema::LookupConstructors(CXXRecordDecl *Class) {
     });
   }
 
-  CanQualType T = Context.getCanonicalType(Context.getTypeDeclType(Class));
+  CanQualType T = Context.getCanonicalTagType(Class);
   DeclarationName Name = Context.DeclarationNames.getCXXConstructorName(T);
   return Class->lookup(Name);
 }
@@ -4259,7 +4264,7 @@ class LookupVisibleHelper {
           const auto *Record = BaseType->getAs<RecordType>();
           if (!Record)
             continue;
-          RD = Record->getDecl();
+          RD = Record->getOriginalDecl()->getDefinitionOrSelf();
         }
 
         // FIXME: It would be nice to be able to determine whether referencing
@@ -4545,41 +4550,101 @@ static void checkCorrectionVisibility(Sema &SemaRef, TypoCorrection &TC) {
 // the given NestedNameSpecifier (i.e. given a NestedNameSpecifier "foo::bar::",
 // fill the vector with the IdentifierInfo pointers for "foo" and "bar").
 static void getNestedNameSpecifierIdentifiers(
-    NestedNameSpecifier *NNS,
-    SmallVectorImpl<const IdentifierInfo*> &Identifiers) {
-  if (NestedNameSpecifier *Prefix = NNS->getPrefix())
-    getNestedNameSpecifierIdentifiers(Prefix, Identifiers);
-  else
+    NestedNameSpecifier NNS,
+    SmallVectorImpl<const IdentifierInfo *> &Identifiers) {
+  switch (NNS.getKind()) {
+  case NestedNameSpecifier::Kind::Null:
     Identifiers.clear();
+    return;
 
-  const IdentifierInfo *II = nullptr;
-
-  switch (NNS->getKind()) {
-  case NestedNameSpecifier::Identifier:
-    II = NNS->getAsIdentifier();
-    break;
-
-  case NestedNameSpecifier::Namespace:
-    if (NNS->getAsNamespace()->isAnonymousNamespace())
+  case NestedNameSpecifier::Kind::Namespace: {
+    auto [Namespace, Prefix] = NNS.getAsNamespaceAndPrefix();
+    getNestedNameSpecifierIdentifiers(Prefix, Identifiers);
+    if (const auto *NS = dyn_cast<NamespaceDecl>(Namespace);
+        NS && NS->isAnonymousNamespace())
       return;
-    II = NNS->getAsNamespace()->getIdentifier();
-    break;
-
-  case NestedNameSpecifier::NamespaceAlias:
-    II = NNS->getAsNamespaceAlias()->getIdentifier();
-    break;
+    Identifiers.push_back(Namespace->getIdentifier());
+    return;
+  }
 
-  case NestedNameSpecifier::TypeSpec:
-    II = QualType(NNS->getAsType(), 0).getBaseTypeIdentifier();
+  case NestedNameSpecifier::Kind::Type: {
+    for (const Type *T = NNS.getAsType(); /**/; /**/) {
+      switch (T->getTypeClass()) {
+      case Type::DependentName: {
+        auto *DT = cast<DependentNameType>(T);
+        getNestedNameSpecifierIdentifiers(DT->getQualifier(), Identifiers);
+        Identifiers.push_back(DT->getIdentifier());
+        return;
+      }
+      case Type::TemplateSpecialization: {
+        TemplateName Name =
+            cast<TemplateSpecializationType>(T)->getTemplateName();
+        if (const QualifiedTemplateName *QTN =
+                Name.getAsAdjustedQualifiedTemplateName()) {
+          getNestedNameSpecifierIdentifiers(QTN->getQualifier(), Identifiers);
+          Name = QTN->getUnderlyingTemplate();
+        }
+        if (const auto *TD = Name.getAsTemplateDecl(/*IgnoreDeduced=*/true))
+          Identifiers.push_back(TD->getIdentifier());
+        return;
+      }
+      case Type::DependentTemplateSpecialization: {
+        const DependentTemplateStorage &S =
+            cast<DependentTemplateSpecializationType>(T)
+                ->getDependentTemplateName();
+        getNestedNameSpecifierIdentifiers(S.getQualifier(), Identifiers);
+        // FIXME: Should this dig into the Name as well?
+        // Identifiers.push_back(S.getName().getIdentifier());
+        return;
+      }
+      case Type::SubstTemplateTypeParm:
+        T = cast<SubstTemplateTypeParmType>(T)
+                ->getReplacementType()
+                .getTypePtr();
+        continue;
+      case Type::TemplateTypeParm:
+        Identifiers.push_back(cast<TemplateTypeParmType>(T)->getIdentifier());
+        return;
+      case Type::Decltype:
+        return;
+      case Type::Enum:
+      case Type::Record:
+      case Type::InjectedClassName: {
+        auto *TT = cast<TagType>(T);
+        getNestedNameSpecifierIdentifiers(TT->getQualifier(), Identifiers);
+        Identifiers.push_back(TT->getOriginalDecl()->getIdentifier());
+        return;
+      }
+      case Type::Typedef: {
+        auto *TT = cast<TypedefType>(T);
+        getNestedNameSpecifierIdentifiers(TT->getQualifier(), Identifiers);
+        Identifiers.push_back(TT->getDecl()->getIdentifier());
+        return;
+      }
+      case Type::Using: {
+        auto *TT = cast<UsingType>(T);
+        getNestedNameSpecifierIdentifiers(TT->getQualifier(), Identifiers);
+        Identifiers.push_back(TT->getDecl()->getIdentifier());
+        return;
+      }
+      case Type::UnresolvedUsing: {
+        auto *TT = cast<UnresolvedUsingType>(T);
+        getNestedNameSpecifierIdentifiers(TT->getQualifier(), Identifiers);
+        Identifiers.push_back(TT->getDecl()->getIdentifier());
+        return;
+      }
+      default:
+        Identifiers.push_back(QualType(T, 0).getBaseTypeIdentifier());
+        return;
+      }
+    }
     break;
+  }
 
-  case NestedNameSpecifier::Global:
-  case NestedNameSpecifier::Super:
+  case NestedNameSpecifier::Kind::Global:
+  case NestedNameSpecifier::Kind::Super:
     return;
   }
-
-  if (II)
-    Identifiers.push_back(II);
 }
 
 void TypoCorrectionConsumer::FoundDecl(NamedDecl *ND, NamedDecl *Hiding,
@@ -4612,11 +4677,11 @@ void TypoCorrectionConsumer::FoundName(StringRef Name) {
 void TypoCorrectionConsumer::addKeywordResult(StringRef Keyword) {
   // Compute the edit distance between the typo and this keyword,
   // and add the keyword to the list of results.
-  addName(Keyword, nullptr, nullptr, true);
+  addName(Keyword, /*ND=*/nullptr, /*NNS=*/std::nullopt, /*isKeyword=*/true);
 }
 
 void TypoCorrectionConsumer::addName(StringRef Name, NamedDecl *ND,
-                                     NestedNameSpecifier *NNS, bool isKeyword) {
+                                     NestedNameSpecifier NNS, bool isKeyword) {
   // Use a simple length-based heuristic to determine the minimum possible
   // edit distance. If the minimum isn't good enough, bail out early.
   StringRef TypoStr = Typo->getName();
@@ -4708,10 +4773,10 @@ void TypoCorrectionConsumer::addNamespaces(
     Namespaces.addNameSpecifier(KNPair.first);
 
   bool SSIsTemplate = false;
-  if (NestedNameSpecifier *NNS =
-          (SS && SS->isValid()) ? SS->getScopeRep() : nullptr) {
-    if (const Type *T = NNS->getAsType())
-      SSIsTemplate = T->getTypeClass() == Type::TemplateSpecialization;
+  if (NestedNameSpecifier NNS = (SS ? SS->getScopeRep() : std::nullopt)) {
+    if (NNS.getKind() == NestedNameSpecifier::Kind::Type)
+      SSIsTemplate =
+          NNS.getAsType()->getTypeClass() == Type::TemplateSpecialization;
   }
   // Do not transform this into an iterator-based loop. The loop body can
   // trigger the creation of further types (through lazy deserialization) and
@@ -4813,17 +4878,15 @@ void TypoCorrectionConsumer::performQualifiedLookups() {
   for (const TypoCorrection &QR : QualifiedResults) {
     for (const auto &NSI : Namespaces) {
       DeclContext *Ctx = NSI.DeclCtx;
-      const Type *NSType = NSI.NameSpecifier->getAsType();
+      CXXRecordDecl *NamingClass = NSI.NameSpecifier.getAsRecordDecl();
 
       // If the current NestedNameSpecifier refers to a class and the
       // current correction candidate is the name of that class, then skip
       // it as it is unlikely a qualified version of the class' constructor
       // is an appropriate correction.
-      if (CXXRecordDecl *NSDecl = NSType ? NSType->getAsCXXRecordDecl() :
-                                           nullptr) {
-        if (NSDecl->getIdentifier() == QR.getCorrectionAsIdentifierInfo())
-          continue;
-      }
+      if (NamingClass &&
+          NamingClass->getIdentifier() == QR.getCorrectionAsIdentifierInfo())
+        continue;
 
       TypoCorrection TC(QR);
       TC.ClearCorrectionDecls();
@@ -4853,7 +4916,7 @@ void TypoCorrectionConsumer::performQualifiedLookups() {
           std::string NewQualified = TC.getAsString(SemaRef.getLangOpts());
           std::string OldQualified;
           llvm::raw_string_ostream OldOStream(OldQualified);
-          SS->getScopeRep()->print(OldOStream, SemaRef.getPrintingPolicy());
+          SS->getScopeRep().print(OldOStream, SemaRef.getPrintingPolicy());
           OldOStream << Typo->getName();
           // If correction candidate would be an identical written qualified
           // identifier, then the existing CXXScopeSpec probably included a
@@ -4864,8 +4927,7 @@ void TypoCorrectionConsumer::performQualifiedLookups() {
         for (LookupResult::iterator TRD = Result.begin(), TRDEnd = Result.end();
              TRD != TRDEnd; ++TRD) {
           if (SemaRef.CheckMemberAccess(TC.getCorrectionRange().getBegin(),
-                                        NSType ? NSType->getAsCXXRecordDecl()
-                                               : nullptr,
+                                        NamingClass,
                                         TRD.getPair()) == Sema::AR_accessible)
             TC.addCorrectionDecl(*TRD);
         }
@@ -4889,10 +4951,10 @@ void TypoCorrectionConsumer::performQualifiedLookups() {
 TypoCorrectionConsumer::NamespaceSpecifierSet::NamespaceSpecifierSet(
     ASTContext &Context, DeclContext *CurContext, CXXScopeSpec *CurScopeSpec)
     : Context(Context), CurContextChain(buildContextChain(CurContext)) {
-  if (NestedNameSpecifier *NNS =
-          CurScopeSpec ? CurScopeSpec->getScopeRep() : nullptr) {
+  if (NestedNameSpecifier NNS =
+          CurScopeSpec ? CurScopeSpec->getScopeRep() : std::nullopt) {
     llvm::raw_string_ostream SpecifierOStream(CurNameSpecifier);
-    NNS->print(SpecifierOStream, Context.getPrintingPolicy());
+    NNS.print(SpecifierOStream, Context.getPrintingPolicy());
 
     getNestedNameSpecifierIdentifiers(NNS, CurNameSpecifierIdentifiers);
   }
@@ -4906,7 +4968,7 @@ TypoCorrectionConsumer::NamespaceSpecifierSet::NamespaceSpecifierSet(
 
   // Add the global context as a NestedNameSpecifier
   SpecifierInfo SI = {cast<DeclContext>(Context.getTranslationUnitDecl()),
-                      NestedNameSpecifier::GlobalSpecifier(Context), 1};
+                      NestedNameSpecifier::getGlobal(), 1};
   DistanceMap[1].push_back(SI);
 }
 
@@ -4926,14 +4988,16 @@ auto TypoCorrectionConsumer::NamespaceSpecifierSet::buildContextChain(
 
 unsigned
 TypoCorrectionConsumer::NamespaceSpecifierSet::buildNestedNameSpecifier(
-    DeclContextList &DeclChain, NestedNameSpecifier *&NNS) {
+    DeclContextList &DeclChain, NestedNameSpecifier &NNS) {
   unsigned NumSpecifiers = 0;
   for (DeclContext *C : llvm::reverse(DeclChain)) {
     if (auto *ND = dyn_cast_or_null<NamespaceDecl>(C)) {
-      NNS = NestedNameSpecifier::Create(Context, NNS, ND);
+      NNS = NestedNameSpecifier(Context, ND, NNS);
       ++NumSpecifiers;
     } else if (auto *RD = dyn_cast_or_null<RecordDecl>(C)) {
-      NNS = NestedNameSpecifier::Create(Context, NNS, RD->getTypeForDecl());
+      QualType T = Context.getTagType(ElaboratedTypeKeyword::None, NNS, RD,
+                                      /*OwnsTag=*/false);
+      NNS = NestedNameSpecifier(T.getTypePtr());
       ++NumSpecifiers;
     }
   }
@@ -4942,7 +5006,7 @@ TypoCorrectionConsumer::NamespaceSpecifierSet::buildNestedNameSpecifier(
 
 void TypoCorrectionConsumer::NamespaceSpecifierSet::addNameSpecifier(
     DeclContext *Ctx) {
-  NestedNameSpecifier *NNS = nullptr;
+  NestedNameSpecifier NNS = std::nullopt;
   unsigned NumSpecifiers = 0;
   DeclContextList NamespaceDeclChain(buildContextChain(Ctx));
   DeclContextList FullNamespaceDeclChain(NamespaceDeclChain);
@@ -4960,7 +5024,7 @@ void TypoCorrectionConsumer::NamespaceSpecifierSet::addNameSpecifier(
   // Add an explicit leading '::' specifier if needed.
   if (NamespaceDeclChain.empty()) {
     // Rebuild the NestedNameSpecifier as a globally-qualified specifier.
-    NNS = NestedNameSpecifier::GlobalSpecifier(Context);
+    NNS = NestedNameSpecifier::getGlobal();
     NumSpecifiers =
         buildNestedNameSpecifier(FullNamespaceDeclChain, NNS);
   } else if (NamedDecl *ND =
@@ -4972,12 +5036,12 @@ void TypoCorrectionConsumer::NamespaceSpecifierSet::addNameSpecifier(
       llvm::raw_string_ostream SpecifierOStream(NewNameSpecifier);
       SmallVector<const IdentifierInfo *, 4> NewNameSpecifierIdentifiers;
       getNestedNameSpecifierIdentifiers(NNS, NewNameSpecifierIdentifiers);
-      NNS->print(SpecifierOStream, Context.getPrintingPolicy());
+      NNS.print(SpecifierOStream, Context.getPrintingPolicy());
       SameNameSpecifier = NewNameSpecifier == CurNameSpecifier;
     }
     if (SameNameSpecifier || llvm::is_contained(CurContextIdentifiers, Name)) {
       // Rebuild the NestedNameSpecifier as a globally-qualified specifier.
-      NNS = NestedNameSpecifier::GlobalSpecifier(Context);
+      NNS = NestedNameSpecifier::getGlobal();
       NumSpecifiers =
           buildNestedNameSpecifier(FullNamespaceDeclChain, NNS);
     }
@@ -5463,7 +5527,7 @@ std::string TypoCorrection::getAsString(const LangOptions &LO) const {
   if (CorrectionNameSpec) {
     std::string tmpBuffer;
     llvm::raw_string_ostream PrefixOStream(tmpBuffer);
-    CorrectionNameSpec->print(PrefixOStream, PrintingPolicy(LO));
+    CorrectionNameSpec.print(PrefixOStream, PrintingPolicy(LO));
     PrefixOStream << CorrectionName;
     return PrefixOStream.str();
   }
diff --git a/clang/lib/Sema/SemaObjC.cpp b/clang/lib/Sema/SemaObjC.cpp
index 0f39a9817ce7f..27951c9105411 100644
--- a/clang/lib/Sema/SemaObjC.cpp
+++ b/clang/lib/Sema/SemaObjC.cpp
@@ -1407,7 +1407,8 @@ SemaObjC::ObjCSubscriptKind SemaObjC::CheckSubscriptingKind(Expr *FromE) {
   int NoIntegrals = 0, NoObjCIdPointers = 0;
   SmallVector<CXXConversionDecl *, 4> ConversionDecls;
 
-  for (NamedDecl *D : cast<CXXRecordDecl>(RecordTy->getDecl())
+  for (NamedDecl *D : cast<CXXRecordDecl>(RecordTy->getOriginalDecl())
+                          ->getDefinitionOrSelf()
                           ->getVisibleConversionFunctions()) {
     if (CXXConversionDecl *Conversion =
             dyn_cast<CXXConversionDecl>(D->getUnderlyingDecl())) {
@@ -1510,7 +1511,7 @@ bool SemaObjC::isCFStringType(QualType T) {
   if (!RT)
     return false;
 
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl();
   if (RD->getTagKind() != TagTypeKind::Struct)
     return false;
 
diff --git a/clang/lib/Sema/SemaObjCProperty.cpp b/clang/lib/Sema/SemaObjCProperty.cpp
index 9d5106805892a..3dbce070e0e18 100644
--- a/clang/lib/Sema/SemaObjCProperty.cpp
+++ b/clang/lib/Sema/SemaObjCProperty.cpp
@@ -1312,7 +1312,9 @@ Decl *SemaObjC::ActOnPropertyImplDecl(
       }
       if (!CompleteTypeErr) {
         const RecordType *RecordTy = PropertyIvarType->getAs<RecordType>();
-        if (RecordTy && RecordTy->getDecl()->hasFlexibleArrayMember()) {
+        if (RecordTy && RecordTy->getOriginalDecl()
+                            ->getDefinitionOrSelf()
+                            ->hasFlexibleArrayMember()) {
           Diag(PropertyIvarLoc, diag::err_synthesize_variable_sized_ivar)
             << PropertyIvarType;
           CompleteTypeErr = true; // suppress later diagnostics about the ivar
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index 4ecc9b0d4c5c8..ac108221683ea 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -7358,7 +7358,9 @@ SemaOpenMP::checkOpenMPDeclareVariantFunction(SemaOpenMP::DeclGroupPtrTy DG,
       Diag(SR.getBegin(), diag::err_omp_interop_type_not_found) << SR;
       return std::nullopt;
     }
-    QualType InteropType = Context.getTypeDeclType(TD);
+    QualType InteropType =
+        Context.getTypeDeclType(ElaboratedTypeKeyword::None,
+                                /*Qualifier=*/std::nullopt, TD);
     if (PTy->isVariadic()) {
       Diag(FD->getLocation(), diag::err_omp_append_args_with_varargs) << SR;
       return std::nullopt;
@@ -7378,7 +7380,7 @@ SemaOpenMP::checkOpenMPDeclareVariantFunction(SemaOpenMP::DeclGroupPtrTy DG,
     auto *Method = dyn_cast<CXXMethodDecl>(FD);
     if (Method && !Method->isStatic()) {
       FnPtrType = Context.getMemberPointerType(
-          AdjustedFnType, /*Qualifier=*/nullptr, Method->getParent());
+          AdjustedFnType, /*Qualifier=*/std::nullopt, Method->getParent());
       ExprResult ER;
       {
         // Build addr_of unary op to correctly handle type checks for member
@@ -18612,10 +18614,11 @@ buildDeclareReductionRef(Sema &SemaRef, SourceLocation Loc, SourceRange Range,
   if (const auto *TyRec = Ty->getAs<RecordType>()) {
     // Complete the type if it can be completed.
     // If the type is neither complete nor being defined, bail out now.
-    if (SemaRef.isCompleteType(Loc, Ty) || TyRec->isBeingDefined() ||
-        TyRec->getDecl()->getDefinition()) {
+    bool IsComplete = SemaRef.isCompleteType(Loc, Ty);
+    RecordDecl *RD = TyRec->getOriginalDecl()->getDefinition();
+    if (IsComplete || RD) {
       Lookup.clear();
-      SemaRef.LookupQualifiedName(Lookup, TyRec->getDecl());
+      SemaRef.LookupQualifiedName(Lookup, RD);
       if (Lookup.empty()) {
         Lookups.emplace_back();
         Lookups.back().append(Lookup.begin(), Lookup.end());
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 1b54628c5e564..c336866c3ba4b 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -370,7 +370,7 @@ NarrowingKind StandardConversionSequence::getNarrowingKind(
   // the underlying type is narrowing. This only arises for expressions of
   // the form 'Enum{init}'.
   if (auto *ET = ToType->getAs<EnumType>())
-    ToType = ET->getDecl()->getIntegerType();
+    ToType = ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   switch (Second) {
   // 'bool' is an integral type; dispatch to the right place to handle it.
@@ -1063,7 +1063,8 @@ static bool shouldAddReversedEqEq(Sema &S, SourceLocation OpLoc,
       return true;
     LookupResult Members(S, NotEqOp, OpLoc,
                          Sema::LookupNameKind::LookupMemberName);
-    S.LookupQualifiedName(Members, RHSRec->getDecl());
+    S.LookupQualifiedName(Members,
+                          RHSRec->getOriginalDecl()->getDefinitionOrSelf());
     Members.suppressAccessDiagnostics();
     for (NamedDecl *Op : Members)
       if (FunctionsCorrespond(S.Context, EqFD, Op->getAsFunction()))
@@ -1268,7 +1269,7 @@ OverloadKind Sema::CheckOverload(Scope *S, FunctionDecl *New,
       //
       // Exception: if the scope is dependent and this is not a class
       // member, the using declaration can only introduce an enumerator.
-      if (UUD->getQualifier()->isDependent() && !UUD->isCXXClassMember()) {
+      if (UUD->getQualifier().isDependent() && !UUD->isCXXClassMember()) {
         Match = *I;
         return OverloadKind::NonFunction;
       }
@@ -1471,9 +1472,8 @@ static bool IsOverloadOrOverrideImpl(Sema &SemaRef, FunctionDecl *New,
 
     if (OldMethod->isImplicitObjectMemberFunction() &&
         OldMethod->getParent() != NewMethod->getParent()) {
-      QualType ParentType =
-          SemaRef.Context.getTypeDeclType(OldMethod->getParent())
-              .getCanonicalType();
+      CanQualType ParentType =
+          SemaRef.Context.getCanonicalTagType(OldMethod->getParent());
       if (ParentType.getTypePtr() != BS.Ty)
         return false;
       BS.Ty = DS.Ty;
@@ -2293,7 +2293,7 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
                == UO_AddrOf &&
                "Non-address-of operator on non-static member address");
         FromType = S.Context.getMemberPointerType(
-            FromType, /*Qualifier=*/nullptr, Method->getParent());
+            FromType, /*Qualifier=*/std::nullopt, Method->getParent());
       } else if (isa<UnaryOperator>(From->IgnoreParens())) {
         assert(cast<UnaryOperator>(From->IgnoreParens())->getOpcode() ==
                UO_AddrOf &&
@@ -2602,10 +2602,12 @@ IsTransparentUnionStandardConversion(Sema &S, Expr* From,
                                      bool CStyle) {
 
   const RecordType *UT = ToType->getAsUnionType();
-  if (!UT || !UT->getDecl()->hasAttr<TransparentUnionAttr>())
+  if (!UT)
     return false;
   // The field to initialize within the transparent union.
-  RecordDecl *UD = UT->getDecl();
+  const RecordDecl *UD = UT->getOriginalDecl()->getDefinitionOrSelf();
+  if (!UD->hasAttr<TransparentUnionAttr>())
+    return false;
   // It's compatible if the expression matches any of the fields.
   for (const auto *it : UD->fields()) {
     if (IsStandardConversion(S, From, it->getType(), InOverloadResolution, SCS,
@@ -2663,15 +2665,17 @@ bool Sema::IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType) {
   if (const EnumType *FromEnumType = FromType->getAs<EnumType>()) {
     // C++0x 7.2p9: Note that this implicit enum to int conversion is not
     // provided for a scoped enumeration.
-    if (FromEnumType->getDecl()->isScoped())
+    const EnumDecl *FromED =
+        FromEnumType->getOriginalDecl()->getDefinitionOrSelf();
+    if (FromED->isScoped())
       return false;
 
     // We can perform an integral promotion to the underlying type of the enum,
     // even if that's not the promoted type. Note that the check for promoting
     // the underlying type is based on the type alone, and does not consider
     // the bitfield-ness of the actual source expression.
-    if (FromEnumType->getDecl()->isFixed()) {
-      QualType Underlying = FromEnumType->getDecl()->getIntegerType();
+    if (FromED->isFixed()) {
+      QualType Underlying = FromED->getIntegerType();
       return Context.hasSameUnqualifiedType(Underlying, ToType) ||
              IsIntegralPromotion(nullptr, Underlying, ToType);
     }
@@ -2679,8 +2683,7 @@ bool Sema::IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType) {
     // We have already pre-calculated the promotion type, so this is trivial.
     if (ToType->isIntegerType() &&
         isCompleteType(From->getBeginLoc(), FromType))
-      return Context.hasSameUnqualifiedType(
-          ToType, FromEnumType->getDecl()->getPromotionType());
+      return Context.hasSameUnqualifiedType(ToType, FromED->getPromotionType());
 
     // C++ [conv.prom]p5:
     //   If the bit-field has an enumerated type, it is treated as any other
@@ -3347,12 +3350,12 @@ void Sema::HandleFunctionTypeMismatch(PartialDiagnostic &PDiag,
                             ToMember->getMostRecentCXXRecordDecl())) {
       PDiag << ft_different_class;
       if (ToMember->isSugared())
-        PDiag << Context.getTypeDeclType(
+        PDiag << Context.getCanonicalTagType(
             ToMember->getMostRecentCXXRecordDecl());
       else
         PDiag << ToMember->getQualifier();
       if (FromMember->isSugared())
-        PDiag << Context.getTypeDeclType(
+        PDiag << Context.getCanonicalTagType(
             FromMember->getMostRecentCXXRecordDecl());
       else
         PDiag << FromMember->getQualifier();
@@ -3636,12 +3639,12 @@ Sema::MemberPointerConversionResult Sema::CheckMemberPointerConversion(
   CXXRecordDecl *FromClass = FromPtrType->getMostRecentCXXRecordDecl(),
                 *ToClass = ToPtrType->getMostRecentCXXRecordDecl();
 
-  auto DiagCls = [](PartialDiagnostic &PD, NestedNameSpecifier *Qual,
-                    const CXXRecordDecl *Cls) {
-    if (declaresSameEntity(Qual->getAsRecordDecl(), Cls))
+  auto DiagCls = [&](PartialDiagnostic &PD, NestedNameSpecifier Qual,
+                     const CXXRecordDecl *Cls) {
+    if (declaresSameEntity(Qual.getAsRecordDecl(), Cls))
       PD << Qual;
     else
-      PD << QualType(Cls->getTypeForDecl(), 0);
+      PD << Context.getCanonicalTagType(Cls);
   };
   auto DiagFromTo = [&](PartialDiagnostic &PD) -> PartialDiagnostic & {
     DiagCls(PD, FromPtrType->getQualifier(), FromClass);
@@ -3658,8 +3661,7 @@ Sema::MemberPointerConversionResult Sema::CheckMemberPointerConversion(
   if (!IsDerivedFrom(OpRange.getBegin(), Derived, Base, Paths))
     return MemberPointerConversionResult::NotDerived;
 
-  if (Paths.isAmbiguous(
-          Base->getTypeForDecl()->getCanonicalTypeUnqualified())) {
+  if (Paths.isAmbiguous(Context.getCanonicalTagType(Base))) {
     PartialDiagnostic PD = PDiag(diag::err_ambiguous_memptr_conv);
     PD << int(Direction);
     DiagFromTo(PD) << getAmbiguousPathsDisplayString(Paths) << OpRange;
@@ -3687,8 +3689,8 @@ Sema::MemberPointerConversionResult Sema::CheckMemberPointerConversion(
             ? diag::err_upcast_to_inaccessible_base
             : diag::err_downcast_from_inaccessible_base,
         [&](PartialDiagnostic &PD) {
-          NestedNameSpecifier *BaseQual = FromPtrType->getQualifier(),
-                              *DerivedQual = ToPtrType->getQualifier();
+          NestedNameSpecifier BaseQual = FromPtrType->getQualifier(),
+                              DerivedQual = ToPtrType->getQualifier();
           if (Direction == MemberPointerConversionDirection::Upcast)
             std::swap(BaseQual, DerivedQual);
           DiagCls(PD, DerivedQual, Derived);
@@ -3983,8 +3985,9 @@ IsUserDefinedConversion(Sema &S, Expr *From, QualType ToType,
 
     if (!S.isCompleteType(From->getExprLoc(), ToType)) {
       // We're not going to find any constructors.
-    } else if (CXXRecordDecl *ToRecordDecl
-                 = dyn_cast<CXXRecordDecl>(ToRecordType->getDecl())) {
+    } else if (auto *ToRecordDecl =
+                   dyn_cast<CXXRecordDecl>(ToRecordType->getOriginalDecl())) {
+      ToRecordDecl = ToRecordDecl->getDefinitionOrSelf();
 
       Expr **Args = &From;
       unsigned NumArgs = 1;
@@ -4057,8 +4060,9 @@ IsUserDefinedConversion(Sema &S, Expr *From, QualType ToType,
     // No conversion functions from incomplete types.
   } else if (const RecordType *FromRecordType =
                  From->getType()->getAs<RecordType>()) {
-    if (CXXRecordDecl *FromRecordDecl
-         = dyn_cast<CXXRecordDecl>(FromRecordType->getDecl())) {
+    if (auto *FromRecordDecl =
+            dyn_cast<CXXRecordDecl>(FromRecordType->getOriginalDecl())) {
+      FromRecordDecl = FromRecordDecl->getDefinitionOrSelf();
       // Add all of the conversion functions as candidates.
       const auto &Conversions = FromRecordDecl->getVisibleConversionFunctions();
       for (auto I = Conversions.begin(), E = Conversions.end(); I != E; ++I) {
@@ -4509,7 +4513,8 @@ getFixedEnumPromtion(Sema &S, const StandardConversionSequence &SCS) {
   if (!FromType->isEnumeralType())
     return FixedEnumPromotion::None;
 
-  EnumDecl *Enum = FromType->castAs<EnumType>()->getDecl();
+  EnumDecl *Enum =
+      FromType->castAs<EnumType>()->getOriginalDecl()->getDefinitionOrSelf();
   if (!Enum->isFixed())
     return FixedEnumPromotion::None;
 
@@ -5145,7 +5150,9 @@ FindConversionForRefInit(Sema &S, ImplicitConversionSequence &ICS,
                          Expr *Init, QualType T2, bool AllowRvalues,
                          bool AllowExplicit) {
   assert(T2->isRecordType() && "Can only find conversions of record types.");
-  auto *T2RecordDecl = cast<CXXRecordDecl>(T2->castAs<RecordType>()->getDecl());
+  auto *T2RecordDecl =
+      cast<CXXRecordDecl>(T2->castAs<RecordType>()->getOriginalDecl())
+          ->getDefinitionOrSelf();
 
   OverloadCandidateSet CandidateSet(
       DeclLoc, OverloadCandidateSet::CSK_InitByUserDefinedConversion);
@@ -5934,7 +5941,7 @@ static ImplicitConversionSequence TryObjectArgumentInitialization(
 
   assert(FromType->isRecordType());
 
-  QualType ClassType = S.Context.getTypeDeclType(ActingContext);
+  CanQualType ClassType = S.Context.getCanonicalTagType(ActingContext);
   // C++98 [class.dtor]p2:
   //   A destructor can be invoked for a const, volatile or const volatile
   //   object.
@@ -6055,7 +6062,7 @@ static ImplicitConversionSequence TryObjectArgumentInitialization(
 /// the implicit object parameter for the given Method with the given
 /// expression.
 ExprResult Sema::PerformImplicitObjectArgumentInitialization(
-    Expr *From, NestedNameSpecifier *Qualifier, NamedDecl *FoundDecl,
+    Expr *From, NestedNameSpecifier Qualifier, NamedDecl *FoundDecl,
     CXXMethodDecl *Method) {
   QualType FromRecordType, DestType;
   QualType ImplicitParamRecordType = Method->getFunctionObjectParameterType();
@@ -6840,8 +6847,9 @@ ExprResult Sema::PerformContextualImplicitConversion(
   UnresolvedSet<4>
       ViableConversions; // These are *potentially* viable in C++1y.
   UnresolvedSet<4> ExplicitConversions;
-  const auto &Conversions =
-      cast<CXXRecordDecl>(RecordTy->getDecl())->getVisibleConversionFunctions();
+  const auto &Conversions = cast<CXXRecordDecl>(RecordTy->getOriginalDecl())
+                                ->getDefinitionOrSelf()
+                                ->getVisibleConversionFunctions();
 
   bool HadMultipleCandidates =
       (std::distance(Conversions.begin(), Conversions.end()) > 1);
@@ -7160,7 +7168,8 @@ void Sema::AddOverloadCandidate(
     // C++ [class.copy]p3:
     //   A member function template is never instantiated to perform the copy
     //   of a class object to an object of its class type.
-    QualType ClassType = Context.getTypeDeclType(Constructor->getParent());
+    CanQualType ClassType =
+        Context.getCanonicalTagType(Constructor->getParent());
     if (Args.size() == 1 && Constructor->isSpecializationCopyingObject() &&
         (Context.hasSameUnqualifiedType(ClassType, Args[0]->getType()) ||
          IsDerivedFrom(Args[0]->getBeginLoc(), Args[0]->getType(),
@@ -7181,8 +7190,8 @@ void Sema::AddOverloadCandidate(
     if (Shadow && Args.size() == 1 && Constructor->getNumParams() >= 1 &&
         Constructor->getParamDecl(0)->getType()->isReferenceType()) {
       QualType P = Constructor->getParamDecl(0)->getType()->getPointeeType();
-      QualType C = Context.getRecordType(Constructor->getParent());
-      QualType D = Context.getRecordType(Shadow->getParent());
+      CanQualType C = Context.getCanonicalTagType(Constructor->getParent());
+      CanQualType D = Context.getCanonicalTagType(Shadow->getParent());
       SourceLocation Loc = Args.front()->getExprLoc();
       if ((Context.hasSameUnqualifiedType(P, C) || IsDerivedFrom(Loc, P, C)) &&
           (Context.hasSameUnqualifiedType(D, P) || IsDerivedFrom(Loc, D, P))) {
@@ -7403,7 +7412,7 @@ static bool convertArgsForAvailabilityChecks(
            "Shouldn't have `this` for ctors!");
     assert(!Method->isStatic() && "Shouldn't have `this` for static methods!");
     ExprResult R = S.PerformImplicitObjectArgumentInitialization(
-        ThisArg, /*Qualifier=*/nullptr, Method, Method);
+        ThisArg, /*Qualifier=*/std::nullopt, Method, Method);
     if (R.isInvalid())
       return false;
     ConvertedThis = R.get();
@@ -8159,29 +8168,24 @@ bool Sema::CheckNonDependentConversions(
       ArgType = ArgType->getPointeeType();
     }
 
-    if (auto *RT = ParamType->getAs<RecordType>())
-      if (auto *RD = dyn_cast<CXXRecordDecl>(RT->getDecl());
-          RD && RD->hasDefinition()) {
-        if (llvm::any_of(LookupConstructors(RD), [](NamedDecl *ND) {
-              auto Info = getConstructorInfo(ND);
-              if (!Info)
-                return false;
-              CXXConstructorDecl *Ctor = Info.Constructor;
-              /// isConvertingConstructor takes copy/move constructors into
-              /// account!
-              return !Ctor->isCopyOrMoveConstructor() &&
-                     Ctor->isConvertingConstructor(
-                         /*AllowExplicit=*/true);
-            }))
-          return true;
-      }
-
-    if (auto *RT = ArgType->getAs<RecordType>())
-      if (auto *RD = dyn_cast<CXXRecordDecl>(RT->getDecl());
-          RD && RD->hasDefinition() &&
-          !RD->getVisibleConversionFunctions().empty()) {
-        return true;
-      }
+    if (auto *RD = ParamType->getAsCXXRecordDecl();
+        RD && RD->hasDefinition() &&
+        llvm::any_of(LookupConstructors(RD), [](NamedDecl *ND) {
+          auto Info = getConstructorInfo(ND);
+          if (!Info)
+            return false;
+          CXXConstructorDecl *Ctor = Info.Constructor;
+          /// isConvertingConstructor takes copy/move constructors into
+          /// account!
+          return !Ctor->isCopyOrMoveConstructor() &&
+                 Ctor->isConvertingConstructor(
+                     /*AllowExplicit=*/true);
+        }))
+      return true;
+    if (auto *RD = ArgType->getAsCXXRecordDecl();
+        RD && RD->hasDefinition() &&
+        !RD->getVisibleConversionFunctions().empty())
+      return true;
 
     return false;
   };
@@ -8336,7 +8340,8 @@ void Sema::AddConversionCandidate(
   if (const auto *FromPtrType = ObjectType->getAs<PointerType>())
     ObjectType = FromPtrType->getPointeeType();
   const auto *ConversionContext =
-      cast<CXXRecordDecl>(ObjectType->castAs<RecordType>()->getDecl());
+      cast<CXXRecordDecl>(ObjectType->castAs<RecordType>()->getOriginalDecl())
+          ->getDefinitionOrSelf();
 
   // C++23 [over.best.ics.general]
   // However, if the target is [...]
@@ -8736,15 +8741,16 @@ void Sema::AddMemberOperatorCandidates(OverloadedOperatorKind Op,
   //        qualified lookup of T1::operator@ (13.3.1.1.1); otherwise,
   //        the set of member candidates is empty.
   if (const RecordType *T1Rec = T1->getAs<RecordType>()) {
+    bool IsComplete = isCompleteType(OpLoc, T1);
+    CXXRecordDecl *T1RD =
+        cast<CXXRecordDecl>(T1Rec->getOriginalDecl())->getDefinition();
     // Complete the type if it can be completed.
-    if (!isCompleteType(OpLoc, T1) && !T1Rec->isBeingDefined())
-      return;
     // If the type is neither complete nor being defined, bail out now.
-    if (!T1Rec->getDecl()->getDefinition())
+    if (!T1RD || (!IsComplete && !T1RD->isBeingDefined()))
       return;
 
     LookupResult Operators(*this, OpName, OpLoc, LookupOrdinaryName);
-    LookupQualifiedName(Operators, T1Rec->getDecl());
+    LookupQualifiedName(Operators, T1RD);
     Operators.suppressAccessDiagnostics();
 
     for (LookupResult::iterator Oper = Operators.begin(),
@@ -9009,8 +9015,8 @@ BuiltinCandidateTypeSet::AddMemberPointerWithMoreQualifiedTypeVariants(
     if ((CVR | BaseCVR) != CVR) continue;
 
     QualType QPointeeTy = Context.getCVRQualifiedType(PointeeTy, CVR);
-    MemberPointerTypes.insert(
-        Context.getMemberPointerType(QPointeeTy, /*Qualifier=*/nullptr, Cls));
+    MemberPointerTypes.insert(Context.getMemberPointerType(
+        QPointeeTy, /*Qualifier=*/std::nullopt, Cls));
   }
 
   return true;
@@ -9087,7 +9093,8 @@ BuiltinCandidateTypeSet::AddTypesConvertedFrom(QualType Ty,
     if (!SemaRef.isCompleteType(Loc, Ty))
       return;
 
-    CXXRecordDecl *ClassDecl = cast<CXXRecordDecl>(TyRec->getDecl());
+    auto *ClassDecl =
+        cast<CXXRecordDecl>(TyRec->getOriginalDecl())->getDefinitionOrSelf();
     for (NamedDecl *D : ClassDecl->getVisibleConversionFunctions()) {
       if (isa<UsingShadowDecl>(D))
         D = cast<UsingShadowDecl>(D)->getTargetDecl();
@@ -10199,7 +10206,7 @@ class BuiltinOperatorOverloadBuilder {
 
       if (S.getLangOpts().CPlusPlus11) {
         for (QualType EnumTy : CandidateTypes[ArgIdx].enumeration_types()) {
-          if (!EnumTy->castAs<EnumType>()->getDecl()->isScoped())
+          if (!EnumTy->castAs<EnumType>()->getOriginalDecl()->isScoped())
             continue;
 
           if (!AddedTypes.insert(S.Context.getCanonicalType(EnumTy)).second)
@@ -10955,9 +10962,9 @@ bool clang::isBetterOverloadCandidate(
             isa<CXXConversionDecl>(Cand1.Function) ? TPOC_Conversion
                                                    : TPOC_Call,
             Cand1.ExplicitCallArguments,
-            Obj1Context ? QualType(Obj1Context->getTypeForDecl(), 0)
+            Obj1Context ? S.Context.getCanonicalTagType(Obj1Context)
                         : QualType{},
-            Obj2Context ? QualType(Obj2Context->getTypeForDecl(), 0)
+            Obj2Context ? S.Context.getCanonicalTagType(Obj2Context)
                         : QualType{},
             Cand1.isReversed() ^ Cand2.isReversed(), PartialOverloading)) {
       return BetterTemplate == Cand1.Function->getPrimaryTemplate();
@@ -14900,8 +14907,8 @@ ExprResult Sema::BuildCXXMemberCallExpr(Expr *E, NamedDecl *FoundDecl,
   if (Method->isExplicitObjectMemberFunction())
     Exp = InitializeExplicitObjectArgument(*this, E, Method);
   else
-    Exp = PerformImplicitObjectArgumentInitialization(E, /*Qualifier=*/nullptr,
-                                                      FoundDecl, Method);
+    Exp = PerformImplicitObjectArgumentInitialization(
+        E, /*Qualifier=*/std::nullopt, FoundDecl, Method);
   if (Exp.isInvalid())
     return true;
 
@@ -15062,7 +15069,7 @@ Sema::CreateOverloadedUnaryOp(SourceLocation OpLoc, UnaryOperatorKind Opc,
           InputInit = InitializeExplicitObjectArgument(*this, Input, Method);
         else
           InputInit = PerformImplicitObjectArgumentInitialization(
-              Input, /*Qualifier=*/nullptr, Best->FoundDecl, Method);
+              Input, /*Qualifier=*/std::nullopt, Best->FoundDecl, Method);
         if (InputInit.isInvalid())
           return ExprError();
         Base = Input = InputInit.get();
@@ -15445,7 +15452,7 @@ ExprResult Sema::CreateOverloadedBinOp(SourceLocation OpLoc,
             ParamIdx = 1;
           } else {
             Arg0 = PerformImplicitObjectArgumentInitialization(
-                Args[0], /*Qualifier=*/nullptr, Best->FoundDecl, Method);
+                Args[0], /*Qualifier=*/std::nullopt, Best->FoundDecl, Method);
           }
           Arg1 = PerformCopyInitialization(
               InitializedEntity::InitializeParameter(
@@ -15915,7 +15922,7 @@ ExprResult Sema::CreateOverloadedArraySubscriptExpr(SourceLocation LLoc,
           ArgExpr = Args;
         } else {
           ExprResult Arg0 = PerformImplicitObjectArgumentInitialization(
-              Args[0], /*Qualifier=*/nullptr, Best->FoundDecl, Method);
+              Args[0], /*Qualifier=*/std::nullopt, Best->FoundDecl, Method);
           if (Arg0.isInvalid())
             return ExprError();
 
@@ -16111,7 +16118,7 @@ ExprResult Sema::BuildCallToMemberFunction(Scope *S, Expr *MemExprE,
   CXXMethodDecl *Method = nullptr;
   bool HadMultipleCandidates = false;
   DeclAccessPair FoundDecl = DeclAccessPair::make(nullptr, AS_public);
-  NestedNameSpecifier *Qualifier = nullptr;
+  NestedNameSpecifier Qualifier = std::nullopt;
   if (isa<MemberExpr>(NakedMemExpr)) {
     MemExpr = cast<MemberExpr>(NakedMemExpr);
     Method = cast<CXXMethodDecl>(MemExpr->getMemberDecl());
@@ -16383,7 +16390,7 @@ Sema::BuildCallToObjectOfClassType(Scope *S, Expr *Obj,
 
   const auto *Record = Object.get()->getType()->castAs<RecordType>();
   LookupResult R(*this, OpName, LParenLoc, LookupOrdinaryName);
-  LookupQualifiedName(R, Record->getDecl());
+  LookupQualifiedName(R, Record->getOriginalDecl()->getDefinitionOrSelf());
   R.suppressAccessDiagnostics();
 
   for (LookupResult::iterator Oper = R.begin(), OperEnd = R.end();
@@ -16427,8 +16434,9 @@ Sema::BuildCallToObjectOfClassType(Scope *S, Expr *Obj,
   //   functions for each conversion function declared in an
   //   accessible base class provided the function is not hidden
   //   within T by another intervening declaration.
-  const auto &Conversions =
-      cast<CXXRecordDecl>(Record->getDecl())->getVisibleConversionFunctions();
+  const auto &Conversions = cast<CXXRecordDecl>(Record->getOriginalDecl())
+                                ->getDefinitionOrSelf()
+                                ->getVisibleConversionFunctions();
   for (auto I = Conversions.begin(), E = Conversions.end();
        !IgnoreSurrogateFunctions && I != E; ++I) {
     NamedDecl *D = *I;
@@ -16578,7 +16586,7 @@ Sema::BuildCallToObjectOfClassType(Scope *S, Expr *Obj,
     IsError |= PrepareExplicitObjectArgument(*this, Method, Obj, Args, NewArgs);
   } else {
     ExprResult ObjRes = PerformImplicitObjectArgumentInitialization(
-        Object.get(), /*Qualifier=*/nullptr, Best->FoundDecl, Method);
+        Object.get(), /*Qualifier=*/std::nullopt, Best->FoundDecl, Method);
     if (ObjRes.isInvalid())
       IsError = true;
     else
@@ -16649,7 +16657,10 @@ ExprResult Sema::BuildOverloadedArrowExpr(Scope *S, Expr *Base,
     return ExprError();
 
   LookupResult R(*this, OpName, OpLoc, LookupOrdinaryName);
-  LookupQualifiedName(R, Base->getType()->castAs<RecordType>()->getDecl());
+  LookupQualifiedName(R, Base->getType()
+                             ->castAs<RecordType>()
+                             ->getOriginalDecl()
+                             ->getDefinitionOrSelf());
   R.suppressAccessDiagnostics();
 
   for (LookupResult::iterator Oper = R.begin(), OperEnd = R.end();
@@ -16723,7 +16734,7 @@ ExprResult Sema::BuildOverloadedArrowExpr(Scope *S, Expr *Base,
     Base = R.get();
   } else {
     ExprResult BaseResult = PerformImplicitObjectArgumentInitialization(
-        Base, /*Qualifier=*/nullptr, Best->FoundDecl, Method);
+        Base, /*Qualifier=*/std::nullopt, Best->FoundDecl, Method);
     if (BaseResult.isInvalid())
       return ExprError();
     Base = BaseResult.get();
@@ -16977,7 +16988,7 @@ ExprResult Sema::FixOverloadedFunctionReference(Expr *E, DeclAccessPair Found,
 
         assert(isa<DeclRefExpr>(SubExpr.get()) &&
                "fixed to something other than a decl ref");
-        NestedNameSpecifier *Qualifier =
+        NestedNameSpecifier Qualifier =
             cast<DeclRefExpr>(SubExpr.get())->getQualifier();
         assert(Qualifier &&
                "fixed to a member ref with no nested name qualifier");
diff --git a/clang/lib/Sema/SemaPPC.cpp b/clang/lib/Sema/SemaPPC.cpp
index d5c83aedb3008..7c82e540a9194 100644
--- a/clang/lib/Sema/SemaPPC.cpp
+++ b/clang/lib/Sema/SemaPPC.cpp
@@ -41,8 +41,10 @@ void SemaPPC::checkAIXMemberAlignment(SourceLocation Loc, const Expr *Arg) {
     return;
 
   QualType ArgType = Arg->getType();
-  for (const FieldDecl *FD :
-       ArgType->castAs<RecordType>()->getDecl()->fields()) {
+  for (const FieldDecl *FD : ArgType->castAs<RecordType>()
+                                 ->getOriginalDecl()
+                                 ->getDefinitionOrSelf()
+                                 ->fields()) {
     if (const auto *AA = FD->getAttr<AlignedAttr>()) {
       CharUnits Alignment = getASTContext().toCharUnitsFromBits(
           AA->getAlignment(getASTContext()));
diff --git a/clang/lib/Sema/SemaSYCL.cpp b/clang/lib/Sema/SemaSYCL.cpp
index 3e03cb4bd5f99..76b705e7ad4a2 100644
--- a/clang/lib/Sema/SemaSYCL.cpp
+++ b/clang/lib/Sema/SemaSYCL.cpp
@@ -221,7 +221,7 @@ static SourceLocation SourceLocationForUserDeclaredType(QualType QT) {
   SourceLocation Loc;
   const Type *T = QT->getUnqualifiedDesugaredType();
   if (const TagType *TT = dyn_cast<TagType>(T))
-    Loc = TT->getDecl()->getLocation();
+    Loc = TT->getOriginalDecl()->getLocation();
   else if (const ObjCInterfaceType *ObjCIT = dyn_cast<ObjCInterfaceType>(T))
     Loc = ObjCIT->getDecl()->getLocation();
   return Loc;
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index f85826aecadf3..8bfb9f8b1b99b 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -801,7 +801,7 @@ bool Sema::checkMustTailAttr(const Stmt *St, const Attr &MTA) {
     const auto *MPT =
         CalleeBinOp->getRHS()->getType()->castAs<MemberPointerType>();
     CalleeType.This =
-        Context.getTypeDeclType(MPT->getMostRecentCXXRecordDecl());
+        Context.getCanonicalTagType(MPT->getMostRecentCXXRecordDecl());
     CalleeType.Func = MPT->getPointeeType()->castAs<FunctionProtoType>();
     CalleeType.MemberType = FuncType::ft_pointer_to_member;
   } else if (isa<CXXPseudoDestructorExpr>(CalleeExpr)) {
@@ -1257,7 +1257,7 @@ static bool ShouldDiagnoseSwitchCaseNotInEnum(const Sema &S,
           dyn_cast<DeclRefExpr>(CaseExpr->IgnoreParenImpCasts())) {
     if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
       QualType VarType = VD->getType();
-      QualType EnumType = S.Context.getTypeDeclType(ED);
+      CanQualType EnumType = S.Context.getCanonicalTagType(ED);
       if (VD->hasGlobalStorage() && VarType.isConstQualified() &&
           S.Context.hasSameUnqualifiedType(EnumType, VarType))
         return false;
@@ -1287,11 +1287,11 @@ static void checkEnumTypesInSwitchStmt(Sema &S, const Expr *Cond,
     return;
 
   // Ignore anonymous enums.
-  if (!CondEnumType->getDecl()->getIdentifier() &&
-      !CondEnumType->getDecl()->getTypedefNameForAnonDecl())
+  if (!CondEnumType->getOriginalDecl()->getIdentifier() &&
+      !CondEnumType->getOriginalDecl()->getTypedefNameForAnonDecl())
     return;
-  if (!CaseEnumType->getDecl()->getIdentifier() &&
-      !CaseEnumType->getDecl()->getTypedefNameForAnonDecl())
+  if (!CaseEnumType->getOriginalDecl()->getIdentifier() &&
+      !CaseEnumType->getOriginalDecl()->getTypedefNameForAnonDecl())
     return;
 
   if (S.Context.hasSameUnqualifiedType(CondType, CaseType))
@@ -1604,9 +1604,11 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
 
     // If switch has default case, then ignore it.
     if (!CaseListIsErroneous && !CaseListIsIncomplete && !HasConstantCond &&
-        ET && ET->getDecl()->isCompleteDefinition() &&
-        !ET->getDecl()->enumerators().empty()) {
-      const EnumDecl *ED = ET->getDecl();
+        ET) {
+      const EnumDecl *ED = ET->getOriginalDecl()->getDefinitionOrSelf();
+      if (!ED->isCompleteDefinition() || ED->enumerators().empty())
+        goto enum_out;
+
       EnumValsTy EnumVals;
 
       // Gather all enum values, set their type and sort them,
@@ -1719,6 +1721,7 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
       if (!hasCasesNotInSwitch)
         SS->setAllEnumCasesCovered();
     }
+  enum_out:;
   }
 
   if (BodyStmt)
@@ -1748,7 +1751,7 @@ Sema::DiagnoseAssignmentEnum(QualType DstType, QualType SrcType,
   if (SrcExpr->isTypeDependent() || SrcExpr->isValueDependent())
     return;
 
-  const EnumDecl *ED = ET->getDecl();
+  const EnumDecl *ED = ET->getOriginalDecl()->getDefinitionOrSelf();
   if (!ED->isClosed())
     return;
 
@@ -3709,7 +3712,7 @@ class LocalTypedefNameReferencer : public DynamicRecursiveASTVisitor {
   Sema &S;
 };
 bool LocalTypedefNameReferencer::VisitRecordType(RecordType *RT) {
-  auto *R = dyn_cast<CXXRecordDecl>(RT->getDecl());
+  auto *R = dyn_cast<CXXRecordDecl>(RT->getOriginalDecl());
   if (!R || !R->isLocalClass() || !R->isLocalClass()->isExternallyVisible() ||
       R->isDependentType())
     return true;
@@ -3928,7 +3931,7 @@ StmtResult Sema::BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
             << RetValExp->getSourceRange();
     if (FD->hasAttr<CmseNSEntryAttr>() && RetValExp) {
       if (const auto *RT = dyn_cast<RecordType>(FnRetType.getCanonicalType())) {
-        if (RT->getDecl()->isOrContainsUnion())
+        if (RT->getOriginalDecl()->isOrContainsUnion())
           Diag(RetValExp->getBeginLoc(), diag::warn_cmse_nonsecure_union) << 1;
       }
     }
@@ -4619,7 +4622,8 @@ void Sema::ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
   // Build the context parameter
   DeclContext *DC = CapturedDecl::castToDeclContext(CD);
   IdentifierInfo *ParamName = &Context.Idents.get("__context");
-  QualType ParamType = Context.getPointerType(Context.getTagDeclType(RD));
+  CanQualType ParamType =
+      Context.getPointerType(Context.getCanonicalTagType(RD));
   auto *Param =
       ImplicitParamDecl::Create(Context, DC, Loc, ParamName, ParamType,
                                 ImplicitParamKind::CapturedContext);
@@ -4661,9 +4665,10 @@ void Sema::ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
       assert(!ContextIsFound &&
              "null type has been found already for '__context' parameter");
       IdentifierInfo *ParamName = &Context.Idents.get("__context");
-      QualType ParamType = Context.getPointerType(Context.getTagDeclType(RD))
-                               .withConst()
-                               .withRestrict();
+      QualType ParamType =
+          Context.getPointerType(Context.getCanonicalTagType(RD))
+              .withConst()
+              .withRestrict();
       auto *Param =
           ImplicitParamDecl::Create(Context, DC, Loc, ParamName, ParamType,
                                     ImplicitParamKind::CapturedContext);
@@ -4683,7 +4688,8 @@ void Sema::ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
   if (!ContextIsFound) {
     // Add __context implicitly if it is not specified.
     IdentifierInfo *ParamName = &Context.Idents.get("__context");
-    QualType ParamType = Context.getPointerType(Context.getTagDeclType(RD));
+    CanQualType ParamType =
+        Context.getPointerType(Context.getCanonicalTagType(RD));
     auto *Param =
         ImplicitParamDecl::Create(Context, DC, Loc, ParamName, ParamType,
                                   ImplicitParamKind::CapturedContext);
diff --git a/clang/lib/Sema/SemaStmtAsm.cpp b/clang/lib/Sema/SemaStmtAsm.cpp
index 4507a21a4c111..cd8b98c7444eb 100644
--- a/clang/lib/Sema/SemaStmtAsm.cpp
+++ b/clang/lib/Sema/SemaStmtAsm.cpp
@@ -894,7 +894,7 @@ bool Sema::LookupInlineAsmField(StringRef Base, StringRef Member,
         QT = PT->getPointeeType();
       RT = QT->getAs<RecordType>();
     } else if (TypeDecl *TD = dyn_cast<TypeDecl>(FoundDecl))
-      RT = TD->getTypeForDecl()->getAs<RecordType>();
+      RT = Context.getTypeDeclType(TD)->getAs<RecordType>();
     else if (FieldDecl *TD = dyn_cast<FieldDecl>(FoundDecl))
       RT = TD->getType()->getAs<RecordType>();
     if (!RT)
@@ -907,7 +907,8 @@ bool Sema::LookupInlineAsmField(StringRef Base, StringRef Member,
     LookupResult FieldResult(*this, &Context.Idents.get(NextMember),
                              SourceLocation(), LookupMemberName);
 
-    if (!LookupQualifiedName(FieldResult, RT->getDecl()))
+    RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
+    if (!LookupQualifiedName(FieldResult, RD))
       return true;
 
     if (!FieldResult.isSingleResult())
@@ -919,7 +920,7 @@ bool Sema::LookupInlineAsmField(StringRef Base, StringRef Member,
     if (!FD)
       return true;
 
-    const ASTRecordLayout &RL = Context.getASTRecordLayout(RT->getDecl());
+    const ASTRecordLayout &RL = Context.getASTRecordLayout(RD);
     unsigned i = FD->getFieldIndex();
     CharUnits Result = Context.toCharUnitsFromBits(RL.getFieldOffset(i));
     Offset += (unsigned)Result.getQuantity();
@@ -951,7 +952,8 @@ Sema::LookupInlineAsmVarDeclField(Expr *E, StringRef Member,
   LookupResult FieldResult(*this, &Context.Idents.get(Member), AsmLoc,
                            LookupMemberName);
 
-  if (!LookupQualifiedName(FieldResult, RT->getDecl()))
+  if (!LookupQualifiedName(FieldResult,
+                           RT->getOriginalDecl()->getDefinitionOrSelf()))
     return ExprResult();
 
   // Only normal and indirect field results will work.
diff --git a/clang/lib/Sema/SemaSwift.cpp b/clang/lib/Sema/SemaSwift.cpp
index 4000beff7dc49..a99222c5ed55f 100644
--- a/clang/lib/Sema/SemaSwift.cpp
+++ b/clang/lib/Sema/SemaSwift.cpp
@@ -130,7 +130,7 @@ static bool isErrorParameter(Sema &S, QualType QT) {
   // Check for CFError**.
   if (const auto *PT = Pointee->getAs<PointerType>())
     if (const auto *RT = PT->getPointeeType()->getAs<RecordType>())
-      if (S.ObjC().isCFError(RT->getDecl()))
+      if (S.ObjC().isCFError(RT->getOriginalDecl()->getDefinitionOrSelf()))
         return true;
 
   return false;
@@ -272,7 +272,8 @@ static void checkSwiftAsyncErrorBlock(Sema &S, Decl *D,
       // Check for CFError *.
       if (const auto *PtrTy = Param->getAs<PointerType>()) {
         if (const auto *RT = PtrTy->getPointeeType()->getAs<RecordType>()) {
-          if (S.ObjC().isCFError(RT->getDecl())) {
+          if (S.ObjC().isCFError(
+                  RT->getOriginalDecl()->getDefinitionOrSelf())) {
             AnyErrorParams = true;
             break;
           }
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index b76619fc50268..4cff3a443ae5f 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -291,7 +291,7 @@ TemplateNameKind Sema::isTemplateName(Scope *S,
         FoundUsingShadow ? TemplateName(FoundUsingShadow) : TemplateName(TD);
     assert(!FoundUsingShadow || FoundUsingShadow->getTargetDecl() == TD);
     if (!SS.isInvalid()) {
-      NestedNameSpecifier *Qualifier = SS.getScopeRep();
+      NestedNameSpecifier Qualifier = SS.getScopeRep();
       Template = Context.getQualifiedTemplateName(Qualifier, hasTemplateKeyword,
                                                   Template);
     }
@@ -363,9 +363,8 @@ bool Sema::DiagnoseUnknownTemplateName(const IdentifierInfo &II,
 
   // The code is missing a 'template' keyword prior to the dependent template
   // name.
-  NestedNameSpecifier *Qualifier = (NestedNameSpecifier *)SS->getScopeRep();
   SuggestedTemplate = TemplateTy::make(Context.getDependentTemplateName(
-      {Qualifier, &II, /*HasTemplateKeyword=*/false}));
+      {SS->getScopeRep(), &II, /*HasTemplateKeyword=*/false}));
   Diag(IILoc, diag::err_template_kw_missing)
       << SuggestedTemplate.get()
       << FixItHint::CreateInsertion(IILoc, "template ");
@@ -397,7 +396,9 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
     IsDependent = !LookupCtx && ObjectType->isDependentType();
     assert((IsDependent || !ObjectType->isIncompleteType() ||
             !ObjectType->getAs<TagType>() ||
-            ObjectType->castAs<TagType>()->isBeingDefined()) &&
+            ObjectType->castAs<TagType>()
+                ->getOriginalDecl()
+                ->isEntityBeingDefined()) &&
            "Caller should have completed object type");
 
     // Template names cannot appear inside an Objective-C class or object type
@@ -797,9 +798,9 @@ bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
   if (!Complain || (PatternDef && PatternDef->isInvalidDecl()))
     return true;
 
-  QualType InstantiationTy;
+  CanQualType InstantiationTy;
   if (TagDecl *TD = dyn_cast<TagDecl>(Instantiation))
-    InstantiationTy = Context.getTypeDeclType(TD);
+    InstantiationTy = Context.getCanonicalTagType(TD);
   if (PatternDef) {
     Diag(PointOfInstantiation,
          diag::err_template_instantiate_within_definition)
@@ -907,7 +908,7 @@ static TemplateArgumentLoc translateTemplateArgument(Sema &SemaRef,
     TypeSourceInfo *DI;
     QualType T = SemaRef.GetTypeFromParser(Arg.getAsType(), &DI);
     if (!DI)
-      DI = SemaRef.Context.getTrivialTypeSourceInfo(T, Arg.getLocation());
+      DI = SemaRef.Context.getTrivialTypeSourceInfo(T, Arg.getNameLoc());
     return TemplateArgumentLoc(TemplateArgument(T), DI);
   }
 
@@ -924,9 +925,9 @@ static TemplateArgumentLoc translateTemplateArgument(Sema &SemaRef,
     else
       TArg = Template;
     return TemplateArgumentLoc(
-        SemaRef.Context, TArg,
+        SemaRef.Context, TArg, Arg.getTemplateKwLoc(),
         Arg.getScopeSpec().getWithLocInContext(SemaRef.Context),
-        Arg.getLocation(), Arg.getEllipsisLoc());
+        Arg.getNameLoc(), Arg.getEllipsisLoc());
   }
   }
 
@@ -967,15 +968,12 @@ ParsedTemplateArgument Sema::ActOnTemplateTypeArgument(TypeResult ParsedType) {
       TL = PET.getPatternLoc();
     }
 
-    CXXScopeSpec SS;
-    if (auto ET = TL.getAs<ElaboratedTypeLoc>()) {
-      SS.Adopt(ET.getQualifierLoc());
-      TL = ET.getNamedTypeLoc();
-    }
-
     if (auto DTST = TL.getAs<DeducedTemplateSpecializationTypeLoc>()) {
       TemplateName Name = DTST.getTypePtr()->getTemplateName();
-      ParsedTemplateArgument Result(SS, TemplateTy::make(Name),
+      CXXScopeSpec SS;
+      SS.Adopt(DTST.getQualifierLoc());
+      ParsedTemplateArgument Result(/*TemplateKwLoc=*/SourceLocation(), SS,
+                                    TemplateTy::make(Name),
                                     DTST.getTemplateNameLoc());
       if (EllipsisLoc.isValid())
         Result = Result.getTemplatePackExpansion(EllipsisLoc);
@@ -2106,11 +2104,11 @@ DeclResult Sema::CheckClassTemplate(
   bool ShouldAddRedecl =
       !(TUK == TagUseKind::Friend && CurContext->isDependentContext());
 
-  CXXRecordDecl *NewClass =
-    CXXRecordDecl::Create(Context, Kind, SemanticContext, KWLoc, NameLoc, Name,
-                          PrevClassTemplate && ShouldAddRedecl ?
-                            PrevClassTemplate->getTemplatedDecl() : nullptr,
-                          /*DelayTypeCreation=*/true);
+  CXXRecordDecl *NewClass = CXXRecordDecl::Create(
+      Context, Kind, SemanticContext, KWLoc, NameLoc, Name,
+      PrevClassTemplate && ShouldAddRedecl
+          ? PrevClassTemplate->getTemplatedDecl()
+          : nullptr);
   SetNestedNameSpecifier(*this, NewClass, SS);
   if (NumOuterTemplateParamLists > 0)
     NewClass->setTemplateParameterListsInfo(
@@ -2139,12 +2137,6 @@ DeclResult Sema::CheckClassTemplate(
   if (ModulePrivateLoc.isValid())
     NewTemplate->setModulePrivate();
 
-  // Build the type for the class template declaration now.
-  QualType T = NewTemplate->getInjectedClassNameSpecialization();
-  T = Context.getInjectedClassNameType(NewClass, T);
-  assert(T->isDependentType() && "Class template type is not dependent?");
-  (void)T;
-
   // If we are providing an explicit specialization of a member that is a
   // class template, make a note of that.
   if (PrevClassTemplate &&
@@ -2635,11 +2627,11 @@ struct DependencyChecker : DynamicRecursiveASTVisitor {
     return DynamicRecursiveASTVisitor::TraverseStmt(S);
   }
 
-  bool TraverseTypeLoc(TypeLoc TL) override {
+  bool TraverseTypeLoc(TypeLoc TL, bool TraverseQualifier = true) override {
     if (IgnoreNonTypeDependent && !TL.isNull() &&
         !TL.getType()->isDependentType())
       return true;
-    return DynamicRecursiveASTVisitor::TraverseTypeLoc(TL);
+    return DynamicRecursiveASTVisitor::TraverseTypeLoc(TL, TraverseQualifier);
   }
 
   bool VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TL) override {
@@ -2676,8 +2668,12 @@ struct DependencyChecker : DynamicRecursiveASTVisitor {
     return TraverseTemplateArgument(T->getArgumentPack());
   }
 
-  bool TraverseInjectedClassNameType(InjectedClassNameType *T) override {
-    return TraverseType(T->getInjectedSpecializationType());
+  bool TraverseInjectedClassNameType(InjectedClassNameType *T,
+                                     bool TraverseQualifier) override {
+    // An InjectedClassNameType will never have a dependent template name,
+    // so no need to traverse it.
+    return TraverseTemplateArguments(
+        T->getTemplateArgs(T->getOriginalDecl()->getASTContext()));
   }
 };
 } // end anonymous namespace
@@ -2700,14 +2696,14 @@ static SourceRange getRangeOfTypeInNestedNameSpecifier(ASTContext &Context,
                                                        QualType T,
                                                        const CXXScopeSpec &SS) {
   NestedNameSpecifierLoc NNSLoc(SS.getScopeRep(), SS.location_data());
-  while (NestedNameSpecifier *NNS = NNSLoc.getNestedNameSpecifier()) {
-    if (const Type *CurType = NNS->getAsType()) {
-      if (Context.hasSameUnqualifiedType(T, QualType(CurType, 0)))
-        return NNSLoc.getTypeLoc().getSourceRange();
-    } else
+  for (;;) {
+    NestedNameSpecifier NNS = NNSLoc.getNestedNameSpecifier();
+    if (NNS.getKind() != NestedNameSpecifier::Kind::Type)
       break;
-
-    NNSLoc = NNSLoc.getPrefix();
+    if (Context.hasSameUnqualifiedType(T, QualType(NNS.getAsType(), 0)))
+      return NNSLoc.castAsTypeLoc().getSourceRange();
+    // FIXME: This will always be empty.
+    NNSLoc = NNSLoc.getAsNamespaceAndPrefix().Prefix;
   }
 
   return SourceRange();
@@ -2726,12 +2722,13 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
   // by the nested-name-specifier and walking out until we run out of types.
   SmallVector<QualType, 4> NestedTypes;
   QualType T;
-  if (SS.getScopeRep()) {
-    if (CXXRecordDecl *Record
-              = dyn_cast_or_null<CXXRecordDecl>(computeDeclContext(SS, true)))
-      T = Context.getTypeDeclType(Record);
+  if (NestedNameSpecifier Qualifier = SS.getScopeRep();
+      Qualifier.getKind() == NestedNameSpecifier::Kind::Type) {
+    if (CXXRecordDecl *Record =
+            dyn_cast_or_null<CXXRecordDecl>(computeDeclContext(SS, true)))
+      T = Context.getCanonicalTagType(Record);
     else
-      T = QualType(SS.getScopeRep()->getAsType(), 0);
+      T = QualType(Qualifier.getAsType(), 0);
   }
 
   // If we found an explicit specialization that prevents us from needing
@@ -2779,9 +2776,10 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
     // Look one step prior in a dependent template specialization type.
     if (const DependentTemplateSpecializationType *DependentTST
                           = T->getAs<DependentTemplateSpecializationType>()) {
-      if (NestedNameSpecifier *NNS =
-              DependentTST->getDependentTemplateName().getQualifier())
-        T = QualType(NNS->getAsType(), 0);
+      if (NestedNameSpecifier NNS =
+              DependentTST->getDependentTemplateName().getQualifier();
+          NNS.getKind() == NestedNameSpecifier::Kind::Type)
+        T = QualType(NNS.getAsType(), 0);
       else
         T = QualType();
       continue;
@@ -2789,8 +2787,9 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
 
     // Look one step prior in a dependent name type.
     if (const DependentNameType *DependentName = T->getAs<DependentNameType>()){
-      if (NestedNameSpecifier *NNS = DependentName->getQualifier())
-        T = QualType(NNS->getAsType(), 0);
+      if (NestedNameSpecifier NNS = DependentName->getQualifier();
+          NNS.getKind() == NestedNameSpecifier::Kind::Type)
+        T = QualType(NNS.getAsType(), 0);
       else
         T = QualType();
       continue;
@@ -2800,7 +2799,7 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
     if (const EnumType *EnumT = T->getAs<EnumType>()) {
       // FIXME: Forward-declared enums require a TSK_ExplicitSpecialization
       // check here.
-      EnumDecl *Enum = EnumT->getDecl();
+      EnumDecl *Enum = EnumT->getOriginalDecl();
 
       // Get to the parent type.
       if (TypeDecl *Parent = dyn_cast<TypeDecl>(Enum->getParent()))
@@ -3100,7 +3099,8 @@ void Sema::NoteAllFoundTemplates(TemplateName Name) {
   }
 }
 
-static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
+static QualType builtinCommonTypeImpl(Sema &S, ElaboratedTypeKeyword Keyword,
+                                      TemplateName BaseTemplate,
                                       SourceLocation TemplateLoc,
                                       ArrayRef<TemplateArgument> Ts) {
   auto lookUpCommonType = [&](TemplateArgument T1,
@@ -3108,7 +3108,8 @@ static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
     // Don't bother looking for other specializations if both types are
     // builtins - users aren't allowed to specialize for them
     if (T1.getAsType()->isBuiltinType() && T2.getAsType()->isBuiltinType())
-      return builtinCommonTypeImpl(S, BaseTemplate, TemplateLoc, {T1, T2});
+      return builtinCommonTypeImpl(S, Keyword, BaseTemplate, TemplateLoc,
+                                   {T1, T2});
 
     TemplateArgumentListInfo Args;
     Args.addArgument(TemplateArgumentLoc(
@@ -3122,7 +3123,7 @@ static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
     Sema::ContextRAII TUContext(S, S.Context.getTranslationUnitDecl());
 
     QualType BaseTemplateInst =
-        S.CheckTemplateIdType(BaseTemplate, TemplateLoc, Args);
+        S.CheckTemplateIdType(Keyword, BaseTemplate, TemplateLoc, Args);
 
     if (SFINAE.hasErrorOccurred())
       return QualType();
@@ -3235,7 +3236,7 @@ static QualType builtinCommonTypeImpl(Sema &S, TemplateName BaseTemplate,
 }
 
 static bool isInVkNamespace(const RecordType *RT) {
-  DeclContext *DC = RT->getDecl()->getDeclContext();
+  DeclContext *DC = RT->getOriginalDecl()->getDeclContext();
   if (!DC)
     return false;
 
@@ -3252,8 +3253,9 @@ static SpirvOperand checkHLSLSpirvTypeOperand(Sema &SemaRef,
   if (auto *RT = OperandArg->getAs<RecordType>()) {
     bool Literal = false;
     SourceLocation LiteralLoc;
-    if (isInVkNamespace(RT) && RT->getDecl()->getName() == "Literal") {
-      auto SpecDecl = dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl());
+    if (isInVkNamespace(RT) && RT->getOriginalDecl()->getName() == "Literal") {
+      auto SpecDecl =
+          dyn_cast<ClassTemplateSpecializationDecl>(RT->getOriginalDecl());
       assert(SpecDecl);
 
       const TemplateArgumentList &LiteralArgs = SpecDecl->getTemplateArgs();
@@ -3264,8 +3266,9 @@ static SpirvOperand checkHLSLSpirvTypeOperand(Sema &SemaRef,
     }
 
     if (RT && isInVkNamespace(RT) &&
-        RT->getDecl()->getName() == "integral_constant") {
-      auto SpecDecl = dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl());
+        RT->getOriginalDecl()->getName() == "integral_constant") {
+      auto SpecDecl =
+          dyn_cast<ClassTemplateSpecializationDecl>(RT->getOriginalDecl());
       assert(SpecDecl);
 
       const TemplateArgumentList &ConstantArgs = SpecDecl->getTemplateArgs();
@@ -3287,11 +3290,10 @@ static SpirvOperand checkHLSLSpirvTypeOperand(Sema &SemaRef,
   return SpirvOperand::createType(OperandArg);
 }
 
-static QualType
-checkBuiltinTemplateIdType(Sema &SemaRef, BuiltinTemplateDecl *BTD,
-                           ArrayRef<TemplateArgument> Converted,
-                           SourceLocation TemplateLoc,
-                           TemplateArgumentListInfo &TemplateArgs) {
+static QualType checkBuiltinTemplateIdType(
+    Sema &SemaRef, ElaboratedTypeKeyword Keyword, BuiltinTemplateDecl *BTD,
+    ArrayRef<TemplateArgument> Converted, SourceLocation TemplateLoc,
+    TemplateArgumentListInfo &TemplateArgs) {
   ASTContext &Context = SemaRef.getASTContext();
 
   switch (BTD->getBuiltinTemplateKind()) {
@@ -3338,7 +3340,7 @@ checkBuiltinTemplateIdType(Sema &SemaRef, BuiltinTemplateDecl *BTD,
 
     // The first template argument will be reused as the template decl that
     // our synthetic template arguments will be applied to.
-    return SemaRef.CheckTemplateIdType(Converted[0].getAsTemplate(),
+    return SemaRef.CheckTemplateIdType(Keyword, Converted[0].getAsTemplate(),
                                        TemplateLoc, SyntheticTemplateArgs);
   }
 
@@ -3375,14 +3377,16 @@ checkBuiltinTemplateIdType(Sema &SemaRef, BuiltinTemplateDecl *BTD,
 
     TemplateName BaseTemplate = Converted[0].getAsTemplate();
     ArrayRef<TemplateArgument> Ts = Converted[3].getPackAsArray();
-    if (auto CT = builtinCommonTypeImpl(SemaRef, BaseTemplate, TemplateLoc, Ts);
+    if (auto CT = builtinCommonTypeImpl(SemaRef, Keyword, BaseTemplate,
+                                        TemplateLoc, Ts);
         !CT.isNull()) {
       TemplateArgumentListInfo TAs;
       TAs.addArgument(TemplateArgumentLoc(
           TemplateArgument(CT), SemaRef.Context.getTrivialTypeSourceInfo(
                                     CT, TemplateArgs[1].getLocation())));
       TemplateName HasTypeMember = Converted[1].getAsTemplate();
-      return SemaRef.CheckTemplateIdType(HasTypeMember, TemplateLoc, TAs);
+      return SemaRef.CheckTemplateIdType(Keyword, HasTypeMember, TemplateLoc,
+                                         TAs);
     }
     QualType HasNoTypeMember = Converted[2].getAsType();
     return HasNoTypeMember;
@@ -3494,7 +3498,7 @@ class FailedBooleanConditionPrinterHelper : public PrinterHelper {
     if (DR && DR->getQualifier()) {
       // If this is a qualified name, expand the template arguments in nested
       // qualifiers.
-      DR->getQualifier()->print(OS, Policy, true);
+      DR->getQualifier().print(OS, Policy, true);
       // Then print the decl itself.
       const ValueDecl *VD = DR->getDecl();
       OS << VD->getName();
@@ -3559,7 +3563,8 @@ Sema::findFailedBooleanCondition(Expr *Cond) {
   return { FailedCond, Description };
 }
 
-QualType Sema::CheckTemplateIdType(TemplateName Name,
+QualType Sema::CheckTemplateIdType(ElaboratedTypeKeyword Keyword,
+                                   TemplateName Name,
                                    SourceLocation TemplateLoc,
                                    TemplateArgumentListInfo &TemplateArgs) {
   // FIXME: 'getUnderlying' loses SubstTemplateTemplateParm nodes from alias
@@ -3610,6 +3615,18 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
   } else if (TypeAliasTemplateDecl *AliasTemplate =
                  dyn_cast<TypeAliasTemplateDecl>(Template)) {
 
+    // C++0x [dcl.type.elab]p2:
+    //   If the identifier resolves to a typedef-name or the simple-template-id
+    //   resolves to an alias template specialization, the
+    //   elaborated-type-specifier is ill-formed.
+    if (Keyword != ElaboratedTypeKeyword::None &&
+        Keyword != ElaboratedTypeKeyword::Typename) {
+      SemaRef.Diag(TemplateLoc, diag::err_tag_reference_non_tag)
+          << AliasTemplate << NonTagKind::TypeAliasTemplate
+          << KeywordHelpers::getTagTypeKindForKeyword(Keyword);
+      SemaRef.Diag(AliasTemplate->getLocation(), diag::note_declared_at);
+    }
+
     // Find the canonical type for this type alias template specialization.
     TypeAliasDecl *Pattern = AliasTemplate->getTemplatedDecl();
     if (Pattern->isInvalidDecl())
@@ -3677,8 +3694,8 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
       return QualType();
     }
   } else if (auto *BTD = dyn_cast<BuiltinTemplateDecl>(Template)) {
-    CanonType = checkBuiltinTemplateIdType(*this, BTD, CTAI.SugaredConverted,
-                                           TemplateLoc, TemplateArgs);
+    CanonType = checkBuiltinTemplateIdType(
+        *this, Keyword, BTD, CTAI.SugaredConverted, TemplateLoc, TemplateArgs);
   } else if (Name.isDependent() ||
              TemplateSpecializationType::anyDependentTemplateArguments(
                  TemplateArgs, CTAI.CanonicalConverted)) {
@@ -3717,16 +3734,15 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
 
         // Fetch the injected class name type and check whether its
         // injected type is equal to the type we just built.
-        QualType ICNT = Context.getTypeDeclType(Record);
-        QualType Injected = cast<InjectedClassNameType>(ICNT)
-          ->getInjectedSpecializationType();
+        CanQualType ICNT = Context.getCanonicalTagType(Record);
+        CanQualType Injected =
+            cast<InjectedClassNameType>(ICNT)->getCanonicalInjectedTST();
 
-        if (CanonType != Injected->getCanonicalTypeInternal())
+        if (CanonType != Injected)
           continue;
 
         // If so, the canonical type of this TST is the injected
         // class name type of the record we just found.
-        assert(ICNT.isCanonical());
         CanonType = ICNT;
         break;
       }
@@ -3768,7 +3784,7 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
     // Diagnose uses of this specialization.
     (void)DiagnoseUseOfDecl(Decl, TemplateLoc);
 
-    CanonType = Context.getTypeDeclType(Decl);
+    CanonType = Context.getCanonicalTagType(Decl);
     assert(isa<RecordType>(CanonType) &&
            "type of non-dependent specialization is not a RecordType");
   } else {
@@ -3779,7 +3795,8 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
   // specialization, which refers back to the class template
   // specialization we created or found.
   return Context.getTemplateSpecializationType(
-      Name, TemplateArgs.arguments(), CTAI.CanonicalConverted, CanonType);
+      Keyword, Name, TemplateArgs.arguments(), CTAI.CanonicalConverted,
+      CanonType);
 }
 
 void Sema::ActOnUndeclaredTypeTemplateName(Scope *S, TemplateTy &ParsedName,
@@ -3827,7 +3844,7 @@ bool Sema::resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
     diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest)
                                 << ATN->getDeclName());
     Name = Context.getQualifiedTemplateName(
-        /*NNS=*/nullptr, /*TemplateKeyword=*/false,
+        /*Qualifier=*/std::nullopt, /*TemplateKeyword=*/false,
         TemplateName(Corrected.getCorrectionDeclAs<TemplateDecl>()));
     return false;
   }
@@ -3838,11 +3855,12 @@ bool Sema::resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
 }
 
 TypeResult Sema::ActOnTemplateIdType(
-    Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
-    TemplateTy TemplateD, const IdentifierInfo *TemplateII,
-    SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
-    ASTTemplateArgsPtr TemplateArgsIn, SourceLocation RAngleLoc,
-    bool IsCtorOrDtorName, bool IsClassName,
+    Scope *S, ElaboratedTypeKeyword ElaboratedKeyword,
+    SourceLocation ElaboratedKeywordLoc, CXXScopeSpec &SS,
+    SourceLocation TemplateKWLoc, TemplateTy TemplateD,
+    const IdentifierInfo *TemplateII, SourceLocation TemplateIILoc,
+    SourceLocation LAngleLoc, ASTTemplateArgsPtr TemplateArgsIn,
+    SourceLocation RAngleLoc, bool IsCtorOrDtorName, bool IsClassName,
     ImplicitTypenameContext AllowImplicitTypename) {
   if (SS.isInvalid())
     return true;
@@ -3858,8 +3876,9 @@ TypeResult Sema::ActOnTemplateIdType(
     //   elaborated-type-specifier (7.1.5.3).
     if (!LookupCtx && isDependentScopeSpecifier(SS)) {
       // C++2a relaxes some of those restrictions in [temp.res]p5.
-      NestedNameSpecifier *NNS =
-          NestedNameSpecifier::Create(Context, SS.getScopeRep(), TemplateII);
+      QualType DNT = Context.getDependentNameType(ElaboratedTypeKeyword::None,
+                                                  SS.getScopeRep(), TemplateII);
+      NestedNameSpecifier NNS(DNT.getTypePtr());
       if (AllowImplicitTypename == ImplicitTypenameContext::Yes) {
         auto DB = DiagCompat(SS.getBeginLoc(), diag_compat::implicit_typename)
                   << NNS;
@@ -3903,12 +3922,12 @@ TypeResult Sema::ActOnTemplateIdType(
   if (DependentTemplateName *DTN = Template.getAsDependentTemplateName()) {
     assert(SS.getScopeRep() == DTN->getQualifier());
     QualType T = Context.getDependentTemplateSpecializationType(
-        ElaboratedTypeKeyword::None, *DTN, TemplateArgs.arguments());
+        ElaboratedKeyword, *DTN, TemplateArgs.arguments());
     // Build type-source information.
     TypeLocBuilder TLB;
     DependentTemplateSpecializationTypeLoc SpecTL
       = TLB.push<DependentTemplateSpecializationTypeLoc>(T);
-    SpecTL.setElaboratedKeywordLoc(SourceLocation());
+    SpecTL.setElaboratedKeywordLoc(ElaboratedKeywordLoc);
     SpecTL.setQualifierLoc(SS.getWithLocInContext(Context));
     SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
     SpecTL.setTemplateNameLoc(TemplateIILoc);
@@ -3919,30 +3938,17 @@ TypeResult Sema::ActOnTemplateIdType(
     return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
   }
 
-  QualType SpecTy = CheckTemplateIdType(Template, TemplateIILoc, TemplateArgs);
+  QualType SpecTy = CheckTemplateIdType(ElaboratedKeyword, Template,
+                                        TemplateIILoc, TemplateArgs);
   if (SpecTy.isNull())
     return true;
 
   // Build type-source information.
   TypeLocBuilder TLB;
-  TemplateSpecializationTypeLoc SpecTL =
-      TLB.push<TemplateSpecializationTypeLoc>(SpecTy);
-  SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
-  SpecTL.setTemplateNameLoc(TemplateIILoc);
-  SpecTL.setLAngleLoc(LAngleLoc);
-  SpecTL.setRAngleLoc(RAngleLoc);
-  for (unsigned i = 0, e = SpecTL.getNumArgs(); i != e; ++i)
-    SpecTL.setArgLocInfo(i, TemplateArgs[i].getLocInfo());
-
-  // Create an elaborated-type-specifier containing the nested-name-specifier.
-  QualType ElTy =
-      getElaboratedType(ElaboratedTypeKeyword::None,
-                        !IsCtorOrDtorName ? SS : CXXScopeSpec(), SpecTy);
-  ElaboratedTypeLoc ElabTL = TLB.push<ElaboratedTypeLoc>(ElTy);
-  ElabTL.setElaboratedKeywordLoc(SourceLocation());
-  if (!ElabTL.isEmpty())
-    ElabTL.setQualifierLoc(SS.getWithLocInContext(Context));
-  return CreateParsedType(ElTy, TLB.getTypeSourceInfo(Context, ElTy));
+  TLB.push<TemplateSpecializationTypeLoc>(SpecTy).set(
+      ElaboratedKeywordLoc, SS.getWithLocInContext(Context), TemplateKWLoc,
+      TemplateIILoc, TemplateArgs);
+  return CreateParsedType(SpecTy, TLB.getTypeSourceInfo(Context, SpecTy));
 }
 
 TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
@@ -3989,24 +3995,14 @@ TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
     return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
   }
 
-  if (TypeAliasTemplateDecl *TAT =
-        dyn_cast_or_null<TypeAliasTemplateDecl>(Template.getAsTemplateDecl())) {
-    // C++0x [dcl.type.elab]p2:
-    //   If the identifier resolves to a typedef-name or the simple-template-id
-    //   resolves to an alias template specialization, the
-    //   elaborated-type-specifier is ill-formed.
-    Diag(TemplateLoc, diag::err_tag_reference_non_tag)
-        << TAT << NonTagKind::TypeAliasTemplate << TagKind;
-    Diag(TAT->getLocation(), diag::note_declared_at);
-  }
-
-  QualType Result = CheckTemplateIdType(Template, TemplateLoc, TemplateArgs);
+  QualType Result =
+      CheckTemplateIdType(Keyword, Template, TemplateLoc, TemplateArgs);
   if (Result.isNull())
     return TypeResult(true);
 
   // Check the tag kind
   if (const RecordType *RT = Result->getAs<RecordType>()) {
-    RecordDecl *D = RT->getDecl();
+    RecordDecl *D = RT->getOriginalDecl()->getDefinitionOrSelf();
 
     IdentifierInfo *Id = D->getIdentifier();
     assert(Id && "templated class must have an identifier");
@@ -4022,21 +4018,9 @@ TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
 
   // Provide source-location information for the template specialization.
   TypeLocBuilder TLB;
-  TemplateSpecializationTypeLoc SpecTL
-    = TLB.push<TemplateSpecializationTypeLoc>(Result);
-  SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
-  SpecTL.setTemplateNameLoc(TemplateLoc);
-  SpecTL.setLAngleLoc(LAngleLoc);
-  SpecTL.setRAngleLoc(RAngleLoc);
-  for (unsigned i = 0, e = SpecTL.getNumArgs(); i != e; ++i)
-    SpecTL.setArgLocInfo(i, TemplateArgs[i].getLocInfo());
-
-  // Construct an elaborated type containing the nested-name-specifier (if any)
-  // and tag keyword.
-  Result = Context.getElaboratedType(Keyword, SS.getScopeRep(), Result);
-  ElaboratedTypeLoc ElabTL = TLB.push<ElaboratedTypeLoc>(Result);
-  ElabTL.setElaboratedKeywordLoc(TagLoc);
-  ElabTL.setQualifierLoc(SS.getWithLocInContext(Context));
+  TLB.push<TemplateSpecializationTypeLoc>(Result).set(
+      TagLoc, SS.getWithLocInContext(Context), TemplateKWLoc, TemplateLoc,
+      TemplateArgs);
   return CreateParsedType(Result, TLB.getTypeSourceInfo(Context, Result));
 }
 
@@ -4958,7 +4942,7 @@ TemplateNameKind Sema::ActOnTemplateName(Scope *S,
     return TNK_Non_template;
   }
 
-  NestedNameSpecifier *Qualifier = SS.getScopeRep();
+  NestedNameSpecifier Qualifier = SS.getScopeRep();
 
   switch (Name.getKind()) {
   case UnqualifiedIdKind::IK_Identifier:
@@ -5246,8 +5230,9 @@ static bool SubstDefaultTemplateArgument(
 ///
 /// \returns the substituted template argument, or NULL if an error occurred.
 static TemplateName SubstDefaultTemplateArgument(
-    Sema &SemaRef, TemplateDecl *Template, SourceLocation TemplateLoc,
-    SourceLocation RAngleLoc, TemplateTemplateParmDecl *Param,
+    Sema &SemaRef, TemplateDecl *Template, SourceLocation TemplateKWLoc,
+    SourceLocation TemplateLoc, SourceLocation RAngleLoc,
+    TemplateTemplateParmDecl *Param,
     ArrayRef<TemplateArgument> SugaredConverted,
     ArrayRef<TemplateArgument> CanonicalConverted,
     NestedNameSpecifierLoc &QualifierLoc) {
@@ -5264,25 +5249,17 @@ static TemplateName SubstDefaultTemplateArgument(
     TemplateArgLists.addOuterTemplateArguments(std::nullopt);
 
   Sema::ContextRAII SavedContext(SemaRef, Template->getDeclContext());
-  // Substitute into the nested-name-specifier first,
-  QualifierLoc = Param->getDefaultArgument().getTemplateQualifierLoc();
-  if (QualifierLoc) {
-    QualifierLoc =
-        SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc, TemplateArgLists);
-    if (!QualifierLoc)
-      return TemplateName();
-  }
 
-  return SemaRef.SubstTemplateName(
-             QualifierLoc,
-             Param->getDefaultArgument().getArgument().getAsTemplate(),
-             Param->getDefaultArgument().getTemplateNameLoc(),
-             TemplateArgLists);
+  const TemplateArgumentLoc &A = Param->getDefaultArgument();
+  QualifierLoc = A.getTemplateQualifierLoc();
+  return SemaRef.SubstTemplateName(TemplateKWLoc, QualifierLoc,
+                                   A.getArgument().getAsTemplate(),
+                                   A.getTemplateNameLoc(), TemplateArgLists);
 }
 
 TemplateArgumentLoc Sema::SubstDefaultTemplateArgumentIfAvailable(
-    TemplateDecl *Template, SourceLocation TemplateLoc,
-    SourceLocation RAngleLoc, Decl *Param,
+    TemplateDecl *Template, SourceLocation TemplateKWLoc,
+    SourceLocation TemplateNameLoc, SourceLocation RAngleLoc, Decl *Param,
     ArrayRef<TemplateArgument> SugaredConverted,
     ArrayRef<TemplateArgument> CanonicalConverted, bool &HasDefaultArg) {
   HasDefaultArg = false;
@@ -5293,8 +5270,8 @@ TemplateArgumentLoc Sema::SubstDefaultTemplateArgumentIfAvailable(
 
     HasDefaultArg = true;
     TemplateArgumentLoc Output;
-    if (SubstDefaultTemplateArgument(*this, Template, TemplateLoc, RAngleLoc,
-                                     TypeParm, SugaredConverted,
+    if (SubstDefaultTemplateArgument(*this, Template, TemplateNameLoc,
+                                     RAngleLoc, TypeParm, SugaredConverted,
                                      CanonicalConverted, Output))
       return TemplateArgumentLoc();
     return Output;
@@ -5307,8 +5284,8 @@ TemplateArgumentLoc Sema::SubstDefaultTemplateArgumentIfAvailable(
 
     HasDefaultArg = true;
     TemplateArgumentLoc Output;
-    if (SubstDefaultTemplateArgument(*this, Template, TemplateLoc, RAngleLoc,
-                                     NonTypeParm, SugaredConverted,
+    if (SubstDefaultTemplateArgument(*this, Template, TemplateNameLoc,
+                                     RAngleLoc, NonTypeParm, SugaredConverted,
                                      CanonicalConverted, Output))
       return TemplateArgumentLoc();
     return Output;
@@ -5320,17 +5297,16 @@ TemplateArgumentLoc Sema::SubstDefaultTemplateArgumentIfAvailable(
     return TemplateArgumentLoc();
 
   HasDefaultArg = true;
+  const TemplateArgumentLoc &A = TempTempParm->getDefaultArgument();
   NestedNameSpecifierLoc QualifierLoc;
   TemplateName TName = SubstDefaultTemplateArgument(
-      *this, Template, TemplateLoc, RAngleLoc, TempTempParm, SugaredConverted,
-      CanonicalConverted, QualifierLoc);
+      *this, Template, TemplateKWLoc, TemplateNameLoc, RAngleLoc, TempTempParm,
+      SugaredConverted, CanonicalConverted, QualifierLoc);
   if (TName.isNull())
     return TemplateArgumentLoc();
 
-  return TemplateArgumentLoc(
-      Context, TemplateArgument(TName),
-      TempTempParm->getDefaultArgument().getTemplateQualifierLoc(),
-      TempTempParm->getDefaultArgument().getTemplateNameLoc());
+  return TemplateArgumentLoc(Context, TemplateArgument(TName), TemplateKWLoc,
+                             QualifierLoc, A.getTemplateNameLoc());
 }
 
 /// Convert a template-argument that we parsed as a type into a template, if
@@ -5338,33 +5314,24 @@ TemplateArgumentLoc Sema::SubstDefaultTemplateArgumentIfAvailable(
 /// template template arguments and as template type arguments.
 static TemplateArgumentLoc
 convertTypeTemplateArgumentToTemplate(ASTContext &Context, TypeLoc TLoc) {
-  // Extract and step over any surrounding nested-name-specifier.
-  NestedNameSpecifierLoc QualLoc;
-  if (auto ETLoc = TLoc.getAs<ElaboratedTypeLoc>()) {
-    if (ETLoc.getTypePtr()->getKeyword() != ElaboratedTypeKeyword::None)
-      return TemplateArgumentLoc();
+  auto TagLoc = TLoc.getAs<TagTypeLoc>();
+  if (!TagLoc)
+    return TemplateArgumentLoc();
 
-    QualLoc = ETLoc.getQualifierLoc();
-    TLoc = ETLoc.getNamedTypeLoc();
-  }
   // If this type was written as an injected-class-name, it can be used as a
   // template template argument.
-  if (auto InjLoc = TLoc.getAs<InjectedClassNameTypeLoc>())
-    return TemplateArgumentLoc(Context, InjLoc.getTypePtr()->getTemplateName(),
-                               QualLoc, InjLoc.getNameLoc());
-
   // If this type was written as an injected-class-name, it may have been
   // converted to a RecordType during instantiation. If the RecordType is
   // *not* wrapped in a TemplateSpecializationType and denotes a class
   // template specialization, it must have come from an injected-class-name.
-  if (auto RecLoc = TLoc.getAs<RecordTypeLoc>())
-    if (auto *CTSD =
-            dyn_cast<ClassTemplateSpecializationDecl>(RecLoc.getDecl()))
-      return TemplateArgumentLoc(Context,
-                                 TemplateName(CTSD->getSpecializedTemplate()),
-                                 QualLoc, RecLoc.getNameLoc());
 
-  return TemplateArgumentLoc();
+  TemplateName Name = TagLoc.getTypePtr()->getTemplateName(Context);
+  if (Name.isNull())
+    return TemplateArgumentLoc();
+
+  return TemplateArgumentLoc(Context, Name,
+                             /*TemplateKWLoc=*/SourceLocation(),
+                             TagLoc.getQualifierLoc(), TagLoc.getNameLoc());
 }
 
 bool Sema::CheckTemplateArgument(NamedDecl *Param, TemplateArgumentLoc &ArgLoc,
@@ -5897,8 +5864,8 @@ bool Sema::CheckTemplateArgumentList(
     // (when the template parameter was part of a nested template) into
     // the default argument.
     TemplateArgumentLoc Arg = SubstDefaultTemplateArgumentIfAvailable(
-        Template, TemplateLoc, RAngleLoc, *Param, CTAI.SugaredConverted,
-        CTAI.CanonicalConverted, HasDefaultArg);
+        Template, /*TemplateKWLoc=*/SourceLocation(), TemplateLoc, RAngleLoc,
+        *Param, CTAI.SugaredConverted, CTAI.CanonicalConverted, HasDefaultArg);
 
     if (Arg.getArgument().isNull()) {
       if (!HasDefaultArg) {
@@ -6042,7 +6009,7 @@ namespace {
 #include "clang/AST/TypeNodes.inc"
 
     bool VisitTagDecl(const TagDecl *Tag);
-    bool VisitNestedNameSpecifier(NestedNameSpecifier *NNS);
+    bool VisitNestedNameSpecifier(NestedNameSpecifier NNS);
   };
 } // end anonymous namespace
 
@@ -6187,11 +6154,11 @@ bool UnnamedLocalNoLinkageFinder::VisitDeducedTemplateSpecializationType(
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitRecordType(const RecordType* T) {
-  return VisitTagDecl(T->getDecl());
+  return VisitTagDecl(T->getOriginalDecl()->getDefinitionOrSelf());
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitEnumType(const EnumType* T) {
-  return VisitTagDecl(T->getDecl());
+  return VisitTagDecl(T->getOriginalDecl()->getDefinitionOrSelf());
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitTemplateTypeParmType(
@@ -6211,7 +6178,7 @@ bool UnnamedLocalNoLinkageFinder::VisitTemplateSpecializationType(
 
 bool UnnamedLocalNoLinkageFinder::VisitInjectedClassNameType(
                                               const InjectedClassNameType* T) {
-  return VisitTagDecl(T->getDecl());
+  return VisitTagDecl(T->getOriginalDecl()->getDefinitionOrSelf());
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitDependentNameType(
@@ -6221,10 +6188,7 @@ bool UnnamedLocalNoLinkageFinder::VisitDependentNameType(
 
 bool UnnamedLocalNoLinkageFinder::VisitDependentTemplateSpecializationType(
                                  const DependentTemplateSpecializationType* T) {
-  if (auto *Q = T->getDependentTemplateName().getQualifier())
-    return VisitNestedNameSpecifier(Q);
-
-  return false;
+  return VisitNestedNameSpecifier(T->getDependentTemplateName().getQualifier());
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitPackExpansionType(
@@ -6270,11 +6234,10 @@ bool UnnamedLocalNoLinkageFinder::VisitDependentBitIntType(
 
 bool UnnamedLocalNoLinkageFinder::VisitTagDecl(const TagDecl *Tag) {
   if (Tag->getDeclContext()->isFunctionOrMethod()) {
-    S.Diag(SR.getBegin(),
-           S.getLangOpts().CPlusPlus11 ?
-             diag::warn_cxx98_compat_template_arg_local_type :
-             diag::ext_template_arg_local_type)
-      << S.Context.getTypeDeclType(Tag) << SR;
+    S.Diag(SR.getBegin(), S.getLangOpts().CPlusPlus11
+                              ? diag::warn_cxx98_compat_template_arg_local_type
+                              : diag::ext_template_arg_local_type)
+        << S.Context.getCanonicalTagType(Tag) << SR;
     return true;
   }
 
@@ -6291,21 +6254,15 @@ bool UnnamedLocalNoLinkageFinder::VisitTagDecl(const TagDecl *Tag) {
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitNestedNameSpecifier(
-                                                    NestedNameSpecifier *NNS) {
-  assert(NNS);
-  if (NNS->getPrefix() && VisitNestedNameSpecifier(NNS->getPrefix()))
-    return true;
-
-  switch (NNS->getKind()) {
-  case NestedNameSpecifier::Identifier:
-  case NestedNameSpecifier::Namespace:
-  case NestedNameSpecifier::NamespaceAlias:
-  case NestedNameSpecifier::Global:
-  case NestedNameSpecifier::Super:
+    NestedNameSpecifier NNS) {
+  switch (NNS.getKind()) {
+  case NestedNameSpecifier::Kind::Null:
+  case NestedNameSpecifier::Kind::Namespace:
+  case NestedNameSpecifier::Kind::Global:
+  case NestedNameSpecifier::Kind::Super:
     return false;
-
-  case NestedNameSpecifier::TypeSpec:
-    return Visit(QualType(NNS->getAsType(), 0));
+  case NestedNameSpecifier::Kind::Type:
+    return Visit(QualType(NNS.getAsType(), 0));
   }
   llvm_unreachable("Invalid NestedNameSpecifier::Kind!");
 }
@@ -7266,7 +7223,8 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
       // that case, this may extend the argument from 1 bit to 8 bits.
       QualType IntegerType = ParamType;
       if (const EnumType *Enum = IntegerType->getAs<EnumType>())
-        IntegerType = Enum->getDecl()->getIntegerType();
+        IntegerType =
+            Enum->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
       Value = Value.extOrTrunc(IntegerType->isBitIntType()
                                    ? Context.getIntWidth(IntegerType)
                                    : Context.getTypeSize(IntegerType));
@@ -7364,7 +7322,8 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
 
     QualType IntegerType = ParamType;
     if (const EnumType *Enum = IntegerType->getAs<EnumType>()) {
-      IntegerType = Enum->getDecl()->getIntegerType();
+      IntegerType =
+          Enum->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
     }
 
     if (ParamType->isBooleanType()) {
@@ -7727,10 +7686,9 @@ ExprResult Sema::BuildExpressionFromDeclTemplateArgument(
     assert(VD->getDeclContext()->isRecord() &&
            (isa<CXXMethodDecl>(VD) || isa<FieldDecl>(VD) ||
             isa<IndirectFieldDecl>(VD)));
-    QualType ClassType
-      = Context.getTypeDeclType(cast<RecordDecl>(VD->getDeclContext()));
-    NestedNameSpecifier *Qualifier =
-        NestedNameSpecifier::Create(Context, nullptr, ClassType.getTypePtr());
+    CanQualType ClassType =
+        Context.getCanonicalTagType(cast<RecordDecl>(VD->getDeclContext()));
+    NestedNameSpecifier Qualifier(ClassType.getTypePtr());
     SS.MakeTrivial(Context, Qualifier, Loc);
   }
 
@@ -7822,7 +7780,7 @@ static Expr *BuildExpressionFromIntegralTemplateArgumentValue(
   // type of literal for it.
   QualType T = OrigT;
   if (const EnumType *ET = OrigT->getAs<EnumType>())
-    T = ET->getDecl()->getIntegerType();
+    T = ET->getOriginalDecl()->getDefinitionOrSelf()->getIntegerType();
 
   Expr *E;
   if (T->isAnyCharacterType()) {
@@ -8691,7 +8649,6 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
                                        isPartialSpecialization))
     return true;
 
-  QualType CanonType;
   if (!isPartialSpecialization) {
     // Create a new class template specialization declaration node for
     // this explicit specialization or friend declaration.
@@ -8707,18 +8664,14 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
 
     if (!PrevDecl)
       ClassTemplate->AddSpecialization(Specialization, InsertPos);
-
-    if (!CurContext->isDependentContext())
-      CanonType = Context.getTypeDeclType(Specialization);
-  }
-
-  TypeSourceInfo *WrittenTy = Context.getTemplateSpecializationTypeInfo(
-      Name, TemplateNameLoc, TemplateArgs, CTAI.CanonicalConverted, CanonType);
-
-  if (isPartialSpecialization) {
+  } else {
+    CanQualType CanonType = CanQualType::CreateUnsafe(
+        Context.getCanonicalTemplateSpecializationType(
+            TemplateName(ClassTemplate->getCanonicalDecl()),
+            CTAI.CanonicalConverted));
     if (Context.hasSameType(
-            WrittenTy->getType(),
-            ClassTemplate->getInjectedClassNameSpecialization()) &&
+            CanonType,
+            ClassTemplate->getCanonicalInjectedSpecializationType(Context)) &&
         (!Context.getLangOpts().CPlusPlus20 ||
          !TemplateParams->hasAssociatedConstraints())) {
       // C++ [temp.class.spec]p9b3:
@@ -8740,13 +8693,12 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
     }
 
     // Create a new class template partial specialization declaration node.
-    ClassTemplatePartialSpecializationDecl *PrevPartial
-      = cast_or_null<ClassTemplatePartialSpecializationDecl>(PrevDecl);
+    ClassTemplatePartialSpecializationDecl *PrevPartial =
+        cast_or_null<ClassTemplatePartialSpecializationDecl>(PrevDecl);
     ClassTemplatePartialSpecializationDecl *Partial =
         ClassTemplatePartialSpecializationDecl::Create(
             Context, Kind, DC, KWLoc, TemplateNameLoc, TemplateParams,
-            ClassTemplate, CTAI.CanonicalConverted, WrittenTy->getType(),
-            PrevPartial);
+            ClassTemplate, CTAI.CanonicalConverted, CanonType, PrevPartial);
     Partial->setTemplateArgsAsWritten(TemplateArgs);
     SetNestedNameSpecifier(*this, Partial, SS);
     if (TemplateParameterLists.size() > 1 && SS.isSet()) {
@@ -8785,7 +8737,7 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
     if (!Okay) {
       SourceRange Range(TemplateNameLoc, RAngleLoc);
       Diag(TemplateNameLoc, diag::err_specialization_after_instantiation)
-        << Context.getTypeDeclType(Specialization) << Range;
+          << Context.getCanonicalTagType(Specialization) << Range;
 
       Diag(PrevDecl->getPointOfInstantiation(),
            diag::note_instantiation_required_here)
@@ -8848,6 +8800,13 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
     Specialization->startDefinition();
 
   if (TUK == TagUseKind::Friend) {
+    CanQualType CanonType = Context.getCanonicalTagType(Specialization);
+    TypeSourceInfo *WrittenTy = Context.getTemplateSpecializationTypeInfo(
+        ElaboratedTypeKeyword::None, /*ElaboratedKeywordLoc=*/SourceLocation(),
+        SS.getWithLocInContext(Context),
+        /*TemplateKeywordLoc=*/SourceLocation(), Name, TemplateNameLoc,
+        TemplateArgs, CTAI.CanonicalConverted, CanonType);
+
     // Build the fully-sugared type for this class template
     // specialization as the user wrote in the specialization
     // itself. This means that we'll pretty-print the type retrieved
@@ -9886,9 +9845,6 @@ static bool CheckExplicitInstantiation(Sema &S, NamedDecl *D,
 
 /// Determine whether the given scope specifier has a template-id in it.
 static bool ScopeSpecifierHasTemplateId(const CXXScopeSpec &SS) {
-  if (!SS.isSet())
-    return false;
-
   // C++11 [temp.explicit]p3:
   //   If the explicit instantiation is for a member function, a member class
   //   or a static data member of a class template specialization, the name of
@@ -9896,12 +9852,14 @@ static bool ScopeSpecifierHasTemplateId(const CXXScopeSpec &SS) {
   //   name shall be a simple-template-id.
   //
   // C++98 has the same restriction, just worded differently.
-  for (NestedNameSpecifier *NNS = SS.getScopeRep(); NNS;
-       NNS = NNS->getPrefix())
-    if (const Type *T = NNS->getAsType())
-      if (isa<TemplateSpecializationType>(T))
-        return true;
-
+  for (NestedNameSpecifier NNS = SS.getScopeRep();
+       NNS.getKind() == NestedNameSpecifier::Kind::Type;
+       /**/) {
+    const Type *T = NNS.getAsType();
+    if (isa<TemplateSpecializationType>(T))
+      return true;
+    NNS = T->getPrefix();
+  }
   return false;
 }
 
@@ -10256,7 +10214,7 @@ Sema::ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
   CXXRecordDecl *Pattern = Record->getInstantiatedFromMemberClass();
   if (!Pattern) {
     Diag(TemplateLoc, diag::err_explicit_instantiation_nontemplate_type)
-      << Context.getTypeDeclType(Record);
+        << Context.getCanonicalTagType(Record);
     Diag(Record->getLocation(), diag::note_nontemplate_decl_here);
     return true;
   }
@@ -10803,7 +10761,7 @@ TypeResult Sema::ActOnDependentTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
   // This has to hold, because SS is expected to be defined.
   assert(Name && "Expected a name in a dependent tag");
 
-  NestedNameSpecifier *NNS = SS.getScopeRep();
+  NestedNameSpecifier NNS = SS.getScopeRep();
   if (!NNS)
     return true;
 
@@ -10915,7 +10873,10 @@ Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
     return CreateParsedType(T, Builder.getTypeSourceInfo(Context, T));
   }
 
-  QualType T = CheckTemplateIdType(Template, TemplateIILoc, TemplateArgs);
+  QualType T = CheckTemplateIdType(TypenameLoc.isValid()
+                                       ? ElaboratedTypeKeyword::Typename
+                                       : ElaboratedTypeKeyword::None,
+                                   Template, TemplateIILoc, TemplateArgs);
   if (T.isNull())
     return true;
 
@@ -10923,18 +10884,8 @@ Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
   TypeLocBuilder Builder;
   TemplateSpecializationTypeLoc SpecTL
     = Builder.push<TemplateSpecializationTypeLoc>(T);
-  SpecTL.setTemplateKeywordLoc(TemplateKWLoc);
-  SpecTL.setTemplateNameLoc(TemplateIILoc);
-  SpecTL.setLAngleLoc(LAngleLoc);
-  SpecTL.setRAngleLoc(RAngleLoc);
-  for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
-    SpecTL.setArgLocInfo(I, TemplateArgs[I].getLocInfo());
-
-  T = Context.getElaboratedType(Keyword, SS.getScopeRep(), T);
-  ElaboratedTypeLoc TL = Builder.push<ElaboratedTypeLoc>(T);
-  TL.setElaboratedKeywordLoc(TypenameLoc);
-  TL.setQualifierLoc(SS.getWithLocInContext(Context));
-
+  SpecTL.set(TypenameLoc, SS.getWithLocInContext(Context), TemplateKWLoc,
+             TemplateIILoc, TemplateArgs);
   TypeSourceInfo *TSI = Builder.getTypeSourceInfo(Context, T);
   return CreateParsedType(T, TSI);
 }
@@ -10948,11 +10899,12 @@ static bool isEnableIf(NestedNameSpecifierLoc NNS, const IdentifierInfo &II,
     return false;
 
   // ... within an explicitly-written template specialization...
-  if (!NNS || !NNS.getNestedNameSpecifier()->getAsType())
+  if (NNS.getNestedNameSpecifier().getKind() != NestedNameSpecifier::Kind::Type)
     return false;
-  TypeLoc EnableIfTy = NNS.getTypeLoc();
-  TemplateSpecializationTypeLoc EnableIfTSTLoc =
-      EnableIfTy.getAs<TemplateSpecializationTypeLoc>();
+
+  // FIXME: Look through sugar.
+  auto EnableIfTSTLoc =
+      NNS.castAsTypeLoc().getAs<TemplateSpecializationTypeLoc>();
   if (!EnableIfTSTLoc || EnableIfTSTLoc.getNumArgs() == 0)
     return false;
   const TemplateSpecializationType *EnableIfTST = EnableIfTSTLoc.getTypePtr();
@@ -11000,19 +10952,33 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
   if (T.isNull())
     return QualType();
 
-  *TSI = Context.CreateTypeSourceInfo(T);
+  TypeLocBuilder TLB;
   if (isa<DependentNameType>(T)) {
-    DependentNameTypeLoc TL =
-        (*TSI)->getTypeLoc().castAs<DependentNameTypeLoc>();
+    auto TL = TLB.push<DependentNameTypeLoc>(T);
     TL.setElaboratedKeywordLoc(KeywordLoc);
     TL.setQualifierLoc(QualifierLoc);
     TL.setNameLoc(IILoc);
-  } else {
-    ElaboratedTypeLoc TL = (*TSI)->getTypeLoc().castAs<ElaboratedTypeLoc>();
+  } else if (isa<DeducedTemplateSpecializationType>(T)) {
+    auto TL = TLB.push<DeducedTemplateSpecializationTypeLoc>(T);
+    TL.setElaboratedKWLoc(KeywordLoc);
+    TL.setQualifierLoc(QualifierLoc);
+    TL.setNameLoc(IILoc);
+  } else if (isa<TemplateTypeParmType>(T)) {
+    // FIXME: There might be a 'typename' keyword here, but we just drop it
+    // as it can't be represented.
+    assert(!QualifierLoc);
+    TLB.pushTypeSpec(T).setNameLoc(IILoc);
+  } else if (isa<TagType>(T)) {
+    auto TL = TLB.push<TagTypeLoc>(T);
     TL.setElaboratedKeywordLoc(KeywordLoc);
     TL.setQualifierLoc(QualifierLoc);
-    TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IILoc);
+    TL.setNameLoc(IILoc);
+  } else if (isa<TypedefType>(T)) {
+    TLB.push<TypedefTypeLoc>(T).set(KeywordLoc, QualifierLoc, IILoc);
+  } else {
+    TLB.push<UnresolvedUsingTypeLoc>(T).set(KeywordLoc, QualifierLoc, IILoc);
   }
+  *TSI = TLB.getTypeSourceInfo(Context, T);
   return T;
 }
 
@@ -11035,7 +11001,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
     if (!Ctx) {
       // If the nested-name-specifier is dependent and couldn't be
       // resolved to a type, build a typename type.
-      assert(QualifierLoc.getNestedNameSpecifier()->isDependent());
+      assert(QualifierLoc.getNestedNameSpecifier().isDependent());
       return Context.getDependentNameType(Keyword,
                                           QualifierLoc.getNestedNameSpecifier(),
                                           &II);
@@ -11117,6 +11083,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
                                         &II);
 
   case LookupResultKind::Found:
+    // FXIME: Missing support for UsingShadowDecl on this path?
     if (TypeDecl *Type = dyn_cast<TypeDecl>(Result.getFoundDecl())) {
       // C++ [class.qual]p2:
       //   In a lookup in which function names are not ignored and the
@@ -11132,15 +11099,20 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
       //
       // FIXME: That's not strictly true: mem-initializer-id lookup does not
       // ignore functions, but that appears to be an oversight.
-      QualType T = getTypeDeclType(Ctx,
-                                   Keyword == ElaboratedTypeKeyword::Typename
-                                       ? DiagCtorKind::Typename
-                                       : DiagCtorKind::None,
-                                   Type, IILoc);
-      // We found a type. Build an ElaboratedType, since the
-      // typename-specifier was just sugar.
-      return Context.getElaboratedType(
-          Keyword, QualifierLoc.getNestedNameSpecifier(), T);
+      checkTypeDeclType(Ctx,
+                        Keyword == ElaboratedTypeKeyword::Typename
+                            ? DiagCtorKind::Typename
+                            : DiagCtorKind::None,
+                        Type, IILoc);
+      // FIXME: This appears to be the only case where a template type parameter
+      // can have an elaborated keyword. We should preserve it somehow.
+      if (isa<TemplateTypeParmDecl>(Type)) {
+        assert(Keyword == ElaboratedTypeKeyword::Typename);
+        assert(!QualifierLoc);
+        Keyword = ElaboratedTypeKeyword::None;
+      }
+      return Context.getTypeDeclType(
+          Keyword, QualifierLoc.getNestedNameSpecifier(), Type);
     }
 
     // C++ [dcl.type.simple]p2:
@@ -11150,22 +11122,22 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
     if (getLangOpts().CPlusPlus17) {
       if (auto *TD = getAsTypeTemplateDecl(Result.getFoundDecl())) {
         if (!DeducedTSTContext) {
-          QualType T(QualifierLoc
-                         ? QualifierLoc.getNestedNameSpecifier()->getAsType()
-                         : nullptr, 0);
-          if (!T.isNull())
+          NestedNameSpecifier Qualifier = QualifierLoc.getNestedNameSpecifier();
+          if (Qualifier.getKind() == NestedNameSpecifier::Kind::Type)
             Diag(IILoc, diag::err_dependent_deduced_tst)
-              << (int)getTemplateNameKindForDiagnostics(TemplateName(TD)) << T;
+                << (int)getTemplateNameKindForDiagnostics(TemplateName(TD))
+                << QualType(Qualifier.getAsType(), 0);
           else
             Diag(IILoc, diag::err_deduced_tst)
               << (int)getTemplateNameKindForDiagnostics(TemplateName(TD));
           NoteTemplateLocation(*TD);
           return QualType();
         }
-        return Context.getElaboratedType(
-            Keyword, QualifierLoc.getNestedNameSpecifier(),
-            Context.getDeducedTemplateSpecializationType(TemplateName(TD),
-                                                         QualType(), false));
+        TemplateName Name = Context.getQualifiedTemplateName(
+            QualifierLoc.getNestedNameSpecifier(), /*TemplateKeyword=*/false,
+            TemplateName(TD));
+        return Context.getDeducedTemplateSpecializationType(
+            Keyword, Name, /*DeducedType=*/QualType(), /*IsDependent=*/false);
       }
     }
 
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index d09a72b71b805..9e46c0da8736c 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -613,38 +613,29 @@ DeduceTemplateSpecArguments(Sema &S, TemplateParameterList *TemplateParams,
                             TemplateDeductionInfo &Info, bool PartialOrdering,
                             SmallVectorImpl<DeducedTemplateArgument> &Deduced,
                             bool *HasDeducedAnyParam) {
-  QualType UP = P;
-  if (const auto *IP = P->getAs<InjectedClassNameType>())
-    UP = IP->getInjectedSpecializationType();
-
-  assert(isa<TemplateSpecializationType>(UP.getCanonicalType()));
-  const TemplateSpecializationType *TP = ::getLastTemplateSpecType(UP);
-  TemplateName TNP = TP->getTemplateName();
+  TemplateName TNP;
+  ArrayRef<TemplateArgument> PResolved;
+  if (isa<TemplateSpecializationType>(P.getCanonicalType())) {
+    const TemplateSpecializationType *TP = ::getLastTemplateSpecType(P);
+    TNP = TP->getTemplateName();
+    // FIXME: To preserve sugar, the TST needs to carry sugared resolved
+    // arguments.
+    PResolved = TP->getCanonicalTypeInternal()
+                    ->castAs<TemplateSpecializationType>()
+                    ->template_arguments();
+  } else {
+    const auto *TT = P->castAs<InjectedClassNameType>();
+    TNP = TT->getTemplateName(S.Context);
+    PResolved = TT->getTemplateArgs(S.Context);
+  }
 
   // If the parameter is an alias template, there is nothing to deduce.
   if (const auto *TD = TNP.getAsTemplateDecl(); TD && TD->isTypeAlias())
     return TemplateDeductionResult::Success;
 
-  // FIXME: To preserve sugar, the TST needs to carry sugared resolved
-  // arguments.
-  ArrayRef<TemplateArgument> PResolved =
-      TP->getCanonicalTypeInternal()
-          ->castAs<TemplateSpecializationType>()
-          ->template_arguments();
-
-  QualType UA = A;
-  std::optional<NestedNameSpecifier *> NNS;
-  // Treat an injected-class-name as its underlying template-id.
-  if (const auto *Elaborated = A->getAs<ElaboratedType>()) {
-    NNS = Elaborated->getQualifier();
-  } else if (const auto *Injected = A->getAs<InjectedClassNameType>()) {
-    UA = Injected->getInjectedSpecializationType();
-    NNS = nullptr;
-  }
-
   // Check whether the template argument is a dependent template-id.
-  if (isa<TemplateSpecializationType>(UA.getCanonicalType())) {
-    const TemplateSpecializationType *SA = ::getLastTemplateSpecType(UA);
+  if (isa<TemplateSpecializationType>(A.getCanonicalType())) {
+    const TemplateSpecializationType *SA = ::getLastTemplateSpecType(A);
     TemplateName TNA = SA->getTemplateName();
 
     // If the argument is an alias template, there is nothing to deduce.
@@ -678,34 +669,36 @@ DeduceTemplateSpecArguments(Sema &S, TemplateParameterList *TemplateParams,
   // If the argument type is a class template specialization, we
   // perform template argument deduction using its template
   // arguments.
-  const auto *RA = UA->getAs<RecordType>();
-  const auto *SA =
-      RA ? dyn_cast<ClassTemplateSpecializationDecl>(RA->getDecl()) : nullptr;
-  if (!SA) {
+  const auto *TA = A->getAs<TagType>();
+  TemplateName TNA;
+  if (TA) {
+    // FIXME: Can't use the template arguments from this TST, as they are not
+    // resolved.
+    if (const auto *TST = A->getAsNonAliasTemplateSpecializationType())
+      TNA = TST->getTemplateName();
+    else
+      TNA = TA->getTemplateName(S.Context);
+  }
+  if (TNA.isNull()) {
     Info.FirstArg = TemplateArgument(P);
     Info.SecondArg = TemplateArgument(A);
     return TemplateDeductionResult::NonDeducedMismatch;
   }
 
-  TemplateName TNA = TemplateName(SA->getSpecializedTemplate());
-  if (NNS)
-    TNA = S.Context.getQualifiedTemplateName(
-        *NNS, false, TemplateName(SA->getSpecializedTemplate()));
-
+  ArrayRef<TemplateArgument> AResolved = TA->getTemplateArgs(S.Context);
   // Perform template argument deduction for the template name.
-  if (auto Result = DeduceTemplateArguments(
-          S, TemplateParams, TNP, TNA, Info,
-          /*DefaultArguments=*/SA->getTemplateArgs().asArray(), PartialOrdering,
-          Deduced, HasDeducedAnyParam);
+  if (auto Result =
+          DeduceTemplateArguments(S, TemplateParams, TNP, TNA, Info,
+                                  /*DefaultArguments=*/AResolved,
+                                  PartialOrdering, Deduced, HasDeducedAnyParam);
       Result != TemplateDeductionResult::Success)
     return Result;
 
   // Perform template argument deduction for the template arguments.
-  return DeduceTemplateArguments(S, TemplateParams, PResolved,
-                                 SA->getTemplateArgs().asArray(), Info, Deduced,
-                                 /*NumberOfArgumentsMustMatch=*/true,
-                                 PartialOrdering, PackFold::ParameterToArgument,
-                                 HasDeducedAnyParam);
+  return DeduceTemplateArguments(
+      S, TemplateParams, PResolved, AResolved, Info, Deduced,
+      /*NumberOfArgumentsMustMatch=*/true, PartialOrdering,
+      PackFold::ParameterToArgument, HasDeducedAnyParam);
 }
 
 static bool IsPossiblyOpaquelyQualifiedTypeInternal(const Type *T) {
@@ -2110,26 +2103,19 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch(
           Result != TemplateDeductionResult::Success)
         return Result;
 
-      QualType TP;
-      if (MPP->isSugared()) {
-        TP = S.Context.getTypeDeclType(MPP->getMostRecentCXXRecordDecl());
-      } else {
-        NestedNameSpecifier *QP = MPP->getQualifier();
-        if (QP->getKind() == NestedNameSpecifier::Identifier)
-          // Skip translation if it's a non-deduced context anyway.
-          return TemplateDeductionResult::Success;
-        TP = QualType(QP->translateToType(S.Context), 0);
-      }
+      QualType TP =
+          MPP->isSugared()
+              ? S.Context.getCanonicalTagType(MPP->getMostRecentCXXRecordDecl())
+              : QualType(MPP->getQualifier().getAsType(), 0);
       assert(!TP.isNull() && "member pointer with non-type class");
 
-      QualType TA;
-      if (MPA->isSugared()) {
-        TA = S.Context.getTypeDeclType(MPA->getMostRecentCXXRecordDecl());
-      } else {
-        NestedNameSpecifier *QA = MPA->getQualifier();
-        TA = QualType(QA->translateToType(S.Context), 0).getUnqualifiedType();
-      }
+      QualType TA =
+          MPA->isSugared()
+              ? S.Context.getCanonicalTagType(MPA->getMostRecentCXXRecordDecl())
+              : QualType(MPA->getQualifier().getAsType(), 0)
+                    .getUnqualifiedType();
       assert(!TA.isNull() && "member pointer with non-type class");
+
       return DeduceTemplateArgumentsByTypeMatch(
           S, TemplateParams, TP, TA, Info, Deduced, SubTDF,
           degradeCallPartialOrderingKind(POK),
@@ -2853,13 +2839,11 @@ Sema::getTrivialTemplateArgumentLoc(const TemplateArgument &Arg,
       else if (QualifiedTemplateName *QTN =
                    Template.getAsQualifiedTemplateName())
         Builder.MakeTrivial(Context, QTN->getQualifier(), Loc);
-
-      if (Arg.getKind() == TemplateArgument::Template)
-        return TemplateArgumentLoc(Context, Arg,
-                                   Builder.getWithLocInContext(Context), Loc);
-
       return TemplateArgumentLoc(
-          Context, Arg, Builder.getWithLocInContext(Context), Loc, Loc);
+          Context, Arg, Loc, Builder.getWithLocInContext(Context), Loc,
+          /*EllipsisLoc=*/Arg.getKind() == TemplateArgument::TemplateExpansion
+              ? Loc
+              : SourceLocation());
     }
 
   case TemplateArgument::Expression:
@@ -3077,8 +3061,9 @@ static TemplateDeductionResult ConvertDeducedTemplateArguments(
                                        S.getLangOpts().CPlusPlus17);
 
       DefArg = S.SubstDefaultTemplateArgumentIfAvailable(
-          TD, TD->getLocation(), TD->getSourceRange().getEnd(), Param,
-          CTAI.SugaredConverted, CTAI.CanonicalConverted, HasDefaultArg);
+          TD, /*TemplateKWLoc=*/SourceLocation(), TD->getLocation(),
+          TD->getSourceRange().getEnd(), Param, CTAI.SugaredConverted,
+          CTAI.CanonicalConverted, HasDefaultArg);
     }
 
     // If there was no default argument, deduction is incomplete.
@@ -3437,7 +3422,7 @@ Sema::DeduceTemplateArgumentsFromType(TemplateDecl *TD, QualType FromType,
   QualType PType;
   if (const auto *CTD = dyn_cast<ClassTemplateDecl>(TD)) {
     // Use the InjectedClassNameType.
-    PType = Context.getTypeDeclType(CTD->getTemplatedDecl());
+    PType = Context.getCanonicalTagType(CTD->getTemplatedDecl());
   } else if (const auto *AliasTemplate = dyn_cast<TypeAliasTemplateDecl>(TD)) {
     PType = AliasTemplate->getTemplatedDecl()->getUnderlyingType();
   } else {
@@ -4107,7 +4092,7 @@ static QualType GetTypeOfFunction(Sema &S, const OverloadExpr::FindResult &R,
         return {};
 
       return S.Context.getMemberPointerType(
-          Fn->getType(), /*Qualifier=*/nullptr, Method->getParent());
+          Fn->getType(), /*Qualifier=*/std::nullopt, Method->getParent());
     }
 
   if (!R.IsAddressOfOperand) return Fn->getType();
@@ -5063,10 +5048,12 @@ namespace {
         return TransformDesugared(TLB, TL);
 
       QualType Result = SemaRef.Context.getDeducedTemplateSpecializationType(
-          TL.getTypePtr()->getTemplateName(),
+          TL.getTypePtr()->getKeyword(), TL.getTypePtr()->getTemplateName(),
           Replacement, Replacement.isNull());
       auto NewTL = TLB.push<DeducedTemplateSpecializationTypeLoc>(Result);
+      NewTL.setElaboratedKWLoc(TL.getElaboratedKWLoc());
       NewTL.setNameLoc(TL.getNameLoc());
+      NewTL.setQualifierLoc(TL.getQualifierLoc());
       return Result;
     }
 
@@ -6381,8 +6368,8 @@ Sema::getMoreSpecializedPartialSpecialization(
                                   ClassTemplatePartialSpecializationDecl *PS1,
                                   ClassTemplatePartialSpecializationDecl *PS2,
                                               SourceLocation Loc) {
-  QualType PT1 = PS1->getInjectedSpecializationType().getCanonicalType();
-  QualType PT2 = PS2->getInjectedSpecializationType().getCanonicalType();
+  QualType PT1 = PS1->getCanonicalInjectedSpecializationType(Context);
+  QualType PT2 = PS2->getCanonicalInjectedSpecializationType(Context);
 
   TemplateDeductionInfo Info(Loc);
   return getMoreSpecialized(*this, PT1, PT2, PS1, PS2, Info);
@@ -6391,9 +6378,8 @@ Sema::getMoreSpecializedPartialSpecialization(
 bool Sema::isMoreSpecializedThanPrimary(
     ClassTemplatePartialSpecializationDecl *Spec, TemplateDeductionInfo &Info) {
   ClassTemplateDecl *Primary = Spec->getSpecializedTemplate();
-  QualType PrimaryT =
-      Primary->getInjectedClassNameSpecialization().getCanonicalType();
-  QualType PartialT = Spec->getInjectedSpecializationType().getCanonicalType();
+  QualType PrimaryT = Primary->getCanonicalInjectedSpecializationType(Context);
+  QualType PartialT = Spec->getCanonicalInjectedSpecializationType(Context);
 
   ClassTemplatePartialSpecializationDecl *MaybeSpec =
       getMoreSpecialized(*this, PartialT, PrimaryT, Spec, Primary, Info);
@@ -6677,19 +6663,13 @@ MarkUsedTemplateParameters(ASTContext &Ctx,
 
 /// Mark the template parameters that are used by the given
 /// nested name specifier.
-static void
-MarkUsedTemplateParameters(ASTContext &Ctx,
-                           NestedNameSpecifier *NNS,
-                           bool OnlyDeduced,
-                           unsigned Depth,
-                           llvm::SmallBitVector &Used) {
-  if (!NNS)
+static void MarkUsedTemplateParameters(ASTContext &Ctx, NestedNameSpecifier NNS,
+                                       bool OnlyDeduced, unsigned Depth,
+                                       llvm::SmallBitVector &Used) {
+  if (NNS.getKind() != NestedNameSpecifier::Kind::Type)
     return;
-
-  MarkUsedTemplateParameters(Ctx, NNS->getPrefix(), OnlyDeduced, Depth,
-                             Used);
-  MarkUsedTemplateParameters(Ctx, QualType(NNS->getAsType(), 0),
-                             OnlyDeduced, Depth, Used);
+  MarkUsedTemplateParameters(Ctx, QualType(NNS.getAsType(), 0), OnlyDeduced,
+                             Depth, Used);
 }
 
 /// Mark the template parameters that are used by the given
@@ -6763,7 +6743,7 @@ MarkUsedTemplateParameters(ASTContext &Ctx, QualType T,
     MarkUsedTemplateParameters(Ctx, MemPtr->getPointeeType(), OnlyDeduced,
                                Depth, Used);
     MarkUsedTemplateParameters(Ctx,
-                               QualType(MemPtr->getQualifier()->getAsType(), 0),
+                               QualType(MemPtr->getQualifier().getAsType(), 0),
                                OnlyDeduced, Depth, Used);
     break;
   }
@@ -6881,7 +6861,7 @@ MarkUsedTemplateParameters(ASTContext &Ctx, QualType T,
   }
 
   case Type::InjectedClassName:
-    T = cast<InjectedClassNameType>(T)->getInjectedSpecializationType();
+    T = cast<InjectedClassNameType>(T)->getCanonicalInjectedTST();
     [[fallthrough]];
 
   case Type::TemplateSpecialization: {
diff --git a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
index bdc46a0115a45..4a7b31a942f31 100644
--- a/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
+++ b/clang/lib/Sema/SemaTemplateDeductionGuide.cpp
@@ -105,22 +105,21 @@ class ExtractTypeForDeductionGuide
     return false;
   }
 
-  QualType
-  RebuildTemplateSpecializationType(TemplateName Template,
-                                    SourceLocation TemplateNameLoc,
-                                    TemplateArgumentListInfo &TemplateArgs) {
+  QualType RebuildTemplateSpecializationType(
+      ElaboratedTypeKeyword Keyword, TemplateName Template,
+      SourceLocation TemplateNameLoc, TemplateArgumentListInfo &TemplateArgs) {
     if (!OuterInstantiationArgs ||
         !isa_and_present<TypeAliasTemplateDecl>(Template.getAsTemplateDecl()))
-      return Base::RebuildTemplateSpecializationType(Template, TemplateNameLoc,
-                                                     TemplateArgs);
+      return Base::RebuildTemplateSpecializationType(
+          Keyword, Template, TemplateNameLoc, TemplateArgs);
 
     auto *TATD = cast<TypeAliasTemplateDecl>(Template.getAsTemplateDecl());
     auto *Pattern = TATD;
     while (Pattern->getInstantiatedFromMemberTemplate())
       Pattern = Pattern->getInstantiatedFromMemberTemplate();
     if (!mightReferToOuterTemplateParameters(Pattern->getTemplatedDecl()))
-      return Base::RebuildTemplateSpecializationType(Template, TemplateNameLoc,
-                                                     TemplateArgs);
+      return Base::RebuildTemplateSpecializationType(
+          Keyword, Template, TemplateNameLoc, TemplateArgs);
 
     Decl *NewD =
         TypedefNameInstantiator->InstantiateTypeAliasTemplateDecl(TATD);
@@ -131,13 +130,14 @@ class ExtractTypeForDeductionGuide
     MaterializedTypedefs.push_back(NewTATD->getTemplatedDecl());
 
     return Base::RebuildTemplateSpecializationType(
-        TemplateName(NewTATD), TemplateNameLoc, TemplateArgs);
+        Keyword, TemplateName(NewTATD), TemplateNameLoc, TemplateArgs);
   }
 
   QualType TransformTypedefType(TypeLocBuilder &TLB, TypedefTypeLoc TL) {
     ASTContext &Context = SemaRef.getASTContext();
-    TypedefNameDecl *OrigDecl = TL.getTypedefNameDecl();
+    TypedefNameDecl *OrigDecl = TL.getDecl();
     TypedefNameDecl *Decl = OrigDecl;
+    const TypedefType *T = TL.getTypePtr();
     // Transform the underlying type of the typedef and clone the Decl only if
     // the typedef has a dependent context.
     bool InDependentContext = OrigDecl->getDeclContext()->isDependentContext();
@@ -155,7 +155,7 @@ class ExtractTypeForDeductionGuide
     //     };
     //   };
     if (OuterInstantiationArgs && InDependentContext &&
-        TL.getTypePtr()->isInstantiationDependentType()) {
+        T->isInstantiationDependentType()) {
       Decl = cast_if_present<TypedefNameDecl>(
           TypedefNameInstantiator->InstantiateTypedefNameDecl(
               OrigDecl, /*IsTypeAlias=*/isa<TypeAliasDecl>(OrigDecl)));
@@ -180,10 +180,17 @@ class ExtractTypeForDeductionGuide
       MaterializedTypedefs.push_back(Decl);
     }
 
-    QualType TDTy = Context.getTypedefType(Decl);
-    TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(TDTy);
-    TypedefTL.setNameLoc(TL.getNameLoc());
+    NestedNameSpecifierLoc QualifierLoc = TL.getQualifierLoc();
+    if (QualifierLoc) {
+      QualifierLoc = getDerived().TransformNestedNameSpecifierLoc(QualifierLoc);
+      if (!QualifierLoc)
+        return QualType();
+    }
 
+    QualType TDTy = Context.getTypedefType(
+        T->getKeyword(), QualifierLoc.getNestedNameSpecifier(), Decl);
+    TLB.push<TypedefTypeLoc>(TDTy).set(TL.getElaboratedKeywordLoc(),
+                                       QualifierLoc, TL.getNameLoc());
     return TDTy;
   }
 };
@@ -327,7 +334,7 @@ struct ConvertConstructorToDeductionGuideTransform {
   DeclarationName DeductionGuideName =
       SemaRef.Context.DeclarationNames.getCXXDeductionGuideName(Template);
 
-  QualType DeducedType = SemaRef.Context.getTypeDeclType(Primary);
+  QualType DeducedType = SemaRef.Context.getCanonicalTagType(Primary);
 
   // Index adjustment to apply to convert depth-1 template parameters into
   // depth-0 template parameters.
@@ -593,7 +600,10 @@ struct ConvertConstructorToDeductionGuideTransform {
     // context of the template), so implicit deduction guides can never collide
     // with explicit ones.
     QualType ReturnType = DeducedType;
-    TLB.pushTypeSpec(ReturnType).setNameLoc(Primary->getLocation());
+    auto TTL = TLB.push<TagTypeLoc>(ReturnType);
+    TTL.setElaboratedKeywordLoc(SourceLocation());
+    TTL.setQualifierLoc(NestedNameSpecifierLoc());
+    TTL.setNameLoc(Primary->getLocation());
 
     // Resolving a wording defect, we also inherit the variadicness of the
     // constructor.
@@ -954,7 +964,8 @@ Expr *buildIsDeducibleConstraint(Sema &SemaRef,
   SmallVector<TypeSourceInfo *> IsDeducibleTypeTraitArgs = {
       Context.getTrivialTypeSourceInfo(
           Context.getDeducedTemplateSpecializationType(
-              TemplateName(AliasTemplate), /*DeducedType=*/QualType(),
+              ElaboratedTypeKeyword::None, TemplateName(AliasTemplate),
+              /*DeducedType=*/QualType(),
               /*IsDependent=*/true),
           AliasTemplate->getLocation()), // template specialization type whose
                                          // arguments will be deduced.
@@ -970,10 +981,7 @@ Expr *buildIsDeducibleConstraint(Sema &SemaRef,
 
 std::pair<TemplateDecl *, llvm::ArrayRef<TemplateArgument>>
 getRHSTemplateDeclAndArgs(Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate) {
-  // Unwrap the sugared ElaboratedType.
-  auto RhsType = AliasTemplate->getTemplatedDecl()
-                     ->getUnderlyingType()
-                     .getSingleStepDesugaredType(SemaRef.Context);
+  auto RhsType = AliasTemplate->getTemplatedDecl()->getUnderlyingType();
   TemplateDecl *Template = nullptr;
   llvm::ArrayRef<TemplateArgument> AliasRhsTemplateArgs;
   if (const auto *TST = RhsType->getAs<TemplateSpecializationType>()) {
@@ -1029,12 +1037,10 @@ BuildDeductionGuideForTypeAlias(Sema &SemaRef,
   // The (trailing) return type of the deduction guide.
   const TemplateSpecializationType *FReturnType =
       RType->getAs<TemplateSpecializationType>();
-  if (const auto *InjectedCNT = RType->getAs<InjectedClassNameType>())
+  if (const auto *ICNT = RType->getAs<InjectedClassNameType>())
     // implicitly-generated deduction guide.
-    FReturnType = InjectedCNT->getInjectedTST();
-  else if (const auto *ET = RType->getAs<ElaboratedType>())
-    // explicit deduction guide.
-    FReturnType = ET->getNamedType()->getAs<TemplateSpecializationType>();
+    FReturnType =
+        cast<TemplateSpecializationType>(ICNT->getCanonicalInjectedTST());
   assert(FReturnType && "expected to see a return type");
   // Deduce template arguments of the deduction guide f from the RHS of
   // the alias.
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index f04b01f64b960..0423b7002e883 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -353,45 +353,50 @@ Response HandleFunctionTemplateDecl(Sema &SemaRef,
             SemaRef.Context),
         /*Final=*/false);
 
-    NestedNameSpecifier *NNS = FTD->getTemplatedDecl()->getQualifier();
-
-    while (const Type *Ty = NNS ? NNS->getAsType() : nullptr) {
-      if (NNS->isInstantiationDependent()) {
-        if (const auto *TSTy = Ty->getAs<TemplateSpecializationType>()) {
-          ArrayRef<TemplateArgument> Arguments = TSTy->template_arguments();
-          // Prefer template arguments from the injected-class-type if possible.
-          // For example,
-          // ```cpp
-          // template <class... Pack> struct S {
-          //   template <class T> void foo();
-          // };
-          // template <class... Pack> template <class T>
-          //           ^^^^^^^^^^^^^ InjectedTemplateArgs
-          //           They're of kind TemplateArgument::Pack, not of
-          //           TemplateArgument::Type.
-          // void S<Pack...>::foo() {}
-          //        ^^^^^^^
-          //        TSTy->template_arguments() (which are of PackExpansionType)
-          // ```
-          // This meets the contract in
-          // TreeTransform::TryExpandParameterPacks that the template arguments
-          // for unexpanded parameters should be of a Pack kind.
-          if (TSTy->isCurrentInstantiation()) {
-            auto *RD = TSTy->getCanonicalTypeInternal()->getAsCXXRecordDecl();
-            if (ClassTemplateDecl *CTD = RD->getDescribedClassTemplate())
-              Arguments = CTD->getInjectedTemplateArgs(SemaRef.Context);
-            else if (auto *Specialization =
-                         dyn_cast<ClassTemplateSpecializationDecl>(RD))
-              Arguments =
-                  Specialization->getTemplateInstantiationArgs().asArray();
-          }
-          Result.addOuterTemplateArguments(
-              TSTy->getTemplateName().getAsTemplateDecl(), Arguments,
-              /*Final=*/false);
-        }
-      }
+    NestedNameSpecifier NNS = FTD->getTemplatedDecl()->getQualifier();
+
+    for (const Type *Ty = NNS.getKind() == NestedNameSpecifier::Kind::Type
+                              ? NNS.getAsType()
+                              : nullptr,
+                    *NextTy = nullptr;
+         Ty && Ty->isInstantiationDependentType();
+         Ty = std::exchange(NextTy, nullptr)) {
+      if (NestedNameSpecifier P = Ty->getPrefix();
+          P.getKind() == NestedNameSpecifier::Kind::Type)
+        NextTy = P.getAsType();
+      const auto *TSTy = dyn_cast<TemplateSpecializationType>(Ty);
+      if (!TSTy)
+        continue;
 
-      NNS = NNS->getPrefix();
+      ArrayRef<TemplateArgument> Arguments = TSTy->template_arguments();
+      // Prefer template arguments from the injected-class-type if possible.
+      // For example,
+      // ```cpp
+      // template <class... Pack> struct S {
+      //   template <class T> void foo();
+      // };
+      // template <class... Pack> template <class T>
+      //           ^^^^^^^^^^^^^ InjectedTemplateArgs
+      //           They're of kind TemplateArgument::Pack, not of
+      //           TemplateArgument::Type.
+      // void S<Pack...>::foo() {}
+      //        ^^^^^^^
+      //        TSTy->template_arguments() (which are of PackExpansionType)
+      // ```
+      // This meets the contract in
+      // TreeTransform::TryExpandParameterPacks that the template arguments
+      // for unexpanded parameters should be of a Pack kind.
+      if (TSTy->isCurrentInstantiation()) {
+        auto *RD = TSTy->getCanonicalTypeInternal()->getAsCXXRecordDecl();
+        if (ClassTemplateDecl *CTD = RD->getDescribedClassTemplate())
+          Arguments = CTD->getInjectedTemplateArgs(SemaRef.Context);
+        else if (auto *Specialization =
+                     dyn_cast<ClassTemplateSpecializationDecl>(RD))
+          Arguments = Specialization->getTemplateInstantiationArgs().asArray();
+      }
+      Result.addOuterTemplateArguments(
+          TSTy->getTemplateName().getAsTemplateDecl(), Arguments,
+          /*Final=*/false);
     }
   }
 
@@ -1165,7 +1170,7 @@ void Sema::PrintInstantiationStack(InstantiationContextDiagFuncRef DiagFunc) {
         DiagFunc(Active->PointOfInstantiation,
                  PDiag(diag::note_member_synthesized_at)
                      << MD->isExplicitlyDefaulted() << DFK.asSpecialMember()
-                     << Context.getTagDeclType(MD->getParent()));
+                     << Context.getCanonicalTagType(MD->getParent()));
       } else if (DFK.isComparison()) {
         QualType RecordType = FD->getParamDecl(0)
                                   ->getType()
@@ -1595,15 +1600,9 @@ namespace {
     VarDecl *RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
                                       TypeSourceInfo *TSInfo, QualType T);
 
-    /// Check for tag mismatches when instantiating an
-    /// elaborated type.
-    QualType RebuildElaboratedType(SourceLocation KeywordLoc,
-                                   ElaboratedTypeKeyword Keyword,
-                                   NestedNameSpecifierLoc QualifierLoc,
-                                   QualType T);
-
     TemplateName
-    TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
+    TransformTemplateName(NestedNameSpecifierLoc &QualifierLoc,
+                          SourceLocation TemplateKWLoc, TemplateName Name,
                           SourceLocation NameLoc,
                           QualType ObjectType = QualType(),
                           NamedDecl *FirstQualifierInScope = nullptr,
@@ -1649,22 +1648,18 @@ namespace {
       return inherited::TransformFunctionProtoType(TLB, TL);
     }
 
-    QualType TransformInjectedClassNameType(TypeLocBuilder &TLB,
-                                            InjectedClassNameTypeLoc TL) {
-      auto Type = inherited::TransformInjectedClassNameType(TLB, TL);
+    QualType TransformTagType(TypeLocBuilder &TLB, TagTypeLoc TL) {
+      auto Type = inherited::TransformTagType(TLB, TL);
+      if (!Type.isNull())
+        return Type;
       // Special case for transforming a deduction guide, we return a
       // transformed TemplateSpecializationType.
-      if (Type.isNull() &&
-          SemaRef.CodeSynthesisContexts.back().Kind ==
-              Sema::CodeSynthesisContext::BuildingDeductionGuides) {
-        // Return a TemplateSpecializationType for transforming a deduction
-        // guide.
-        if (auto *ICT = TL.getType()->getAs<InjectedClassNameType>()) {
-          auto Type =
-              inherited::TransformType(ICT->getInjectedSpecializationType());
-          TLB.pushTrivial(SemaRef.Context, Type, TL.getNameLoc());
-          return Type;
-        }
+      // FIXME: Why is this hack necessary?
+      if (const auto *ICNT = dyn_cast<InjectedClassNameType>(TL.getTypePtr());
+          ICNT && SemaRef.CodeSynthesisContexts.back().Kind ==
+                      Sema::CodeSynthesisContext::BuildingDeductionGuides) {
+        Type = inherited::TransformType(ICNT->getCanonicalInjectedTST());
+        TLB.pushTrivial(SemaRef.Context, Type, TL.getNameLoc());
       }
       return Type;
     }
@@ -2050,7 +2045,7 @@ TemplateInstantiator::TransformFirstQualifierInScope(NamedDecl *D,
         return cast_or_null<NamedDecl>(TransformDecl(Loc, D));
 
       if (const TagType *Tag = T->getAs<TagType>())
-        return Tag->getDecl();
+        return Tag->getOriginalDecl();
 
       // The resulting type is not a tag; complain.
       getSema().Diag(Loc, diag::err_nested_name_spec_non_tag) << T;
@@ -2083,41 +2078,10 @@ VarDecl *TemplateInstantiator::RebuildObjCExceptionDecl(VarDecl *ExceptionDecl,
   return Var;
 }
 
-QualType
-TemplateInstantiator::RebuildElaboratedType(SourceLocation KeywordLoc,
-                                            ElaboratedTypeKeyword Keyword,
-                                            NestedNameSpecifierLoc QualifierLoc,
-                                            QualType T) {
-  if (const TagType *TT = T->getAs<TagType>()) {
-    TagDecl* TD = TT->getDecl();
-
-    SourceLocation TagLocation = KeywordLoc;
-
-    IdentifierInfo *Id = TD->getIdentifier();
-
-    // TODO: should we even warn on struct/class mismatches for this?  Seems
-    // like it's likely to produce a lot of spurious errors.
-    if (Id && Keyword != ElaboratedTypeKeyword::None &&
-        Keyword != ElaboratedTypeKeyword::Typename) {
-      TagTypeKind Kind = TypeWithKeyword::getTagTypeKindForKeyword(Keyword);
-      if (!SemaRef.isAcceptableTagRedeclaration(TD, Kind, /*isDefinition*/false,
-                                                TagLocation, Id)) {
-        SemaRef.Diag(TagLocation, diag::err_use_with_wrong_tag)
-          << Id
-          << FixItHint::CreateReplacement(SourceRange(TagLocation),
-                                          TD->getKindName());
-        SemaRef.Diag(TD->getLocation(), diag::note_previous_use);
-      }
-    }
-  }
-
-  return inherited::RebuildElaboratedType(KeywordLoc, Keyword, QualifierLoc, T);
-}
-
 TemplateName TemplateInstantiator::TransformTemplateName(
-    CXXScopeSpec &SS, TemplateName Name, SourceLocation NameLoc,
-    QualType ObjectType, NamedDecl *FirstQualifierInScope,
-    bool AllowInjectedClassName) {
+    NestedNameSpecifierLoc &QualifierLoc, SourceLocation TemplateKWLoc,
+    TemplateName Name, SourceLocation NameLoc, QualType ObjectType,
+    NamedDecl *FirstQualifierInScope, bool AllowInjectedClassName) {
   if (TemplateTemplateParmDecl *TTP
        = dyn_cast_or_null<TemplateTemplateParmDecl>(Name.getAsTemplateDecl())) {
     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
@@ -2164,6 +2128,12 @@ TemplateName TemplateInstantiator::TransformTemplateName(
       TemplateName Template = Arg.getAsTemplate();
       assert(!Template.isNull() && "Null template template argument");
 
+      if (NestedNameSpecifier Qualifier = Template.getQualifier()) {
+        NestedNameSpecifierLocBuilder Builder;
+        Builder.MakeTrivial(SemaRef.Context, Qualifier, NameLoc);
+        QualifierLoc = Builder.getWithLocInContext(SemaRef.Context);
+      }
+
       return getSema().Context.getSubstTemplateTemplateParm(
           Template, AssociatedDecl, TTP->getIndex(), PackIndex, Final);
     }
@@ -2182,9 +2152,9 @@ TemplateName TemplateInstantiator::TransformTemplateName(
         getPackIndex(Pack), SubstPack->getFinal());
   }
 
-  return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,
-                                          FirstQualifierInScope,
-                                          AllowInjectedClassName);
+  return inherited::TransformTemplateName(
+      QualifierLoc, TemplateKWLoc, Name, NameLoc, ObjectType,
+      FirstQualifierInScope, AllowInjectedClassName);
 }
 
 ExprResult
@@ -3160,10 +3130,6 @@ namespace {
     // Only these types can contain 'auto' types, and subsequently be replaced
     // by references to invented parameters.
 
-    TemplateTypeParmDecl *VisitElaboratedType(const ElaboratedType *T) {
-      return Visit(T->getNamedType());
-    }
-
     TemplateTypeParmDecl *VisitPointerType(const PointerType *T) {
       return Visit(T->getPointeeType());
     }
@@ -4554,14 +4520,14 @@ Sema::SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
 }
 
 TemplateName
-Sema::SubstTemplateName(NestedNameSpecifierLoc QualifierLoc,
-                        TemplateName Name, SourceLocation Loc,
+Sema::SubstTemplateName(SourceLocation TemplateKWLoc,
+                        NestedNameSpecifierLoc &QualifierLoc, TemplateName Name,
+                        SourceLocation NameLoc,
                         const MultiLevelTemplateArgumentList &TemplateArgs) {
-  TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
+  TemplateInstantiator Instantiator(*this, TemplateArgs, NameLoc,
                                     DeclarationName());
-  CXXScopeSpec SS;
-  SS.Adopt(QualifierLoc);
-  return Instantiator.TransformTemplateName(SS, Name, Loc);
+  return Instantiator.TransformTemplateName(QualifierLoc, TemplateKWLoc, Name,
+                                            NameLoc);
 }
 
 static const Decl *getCanonicalParmVarDecl(const Decl *D) {
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index e2c3cdcd536bc..755cbb6e4547d 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1483,9 +1483,9 @@ Decl *TemplateDeclInstantiator::InstantiateTypedefNameDecl(TypedefNameDecl *D,
   // If the old typedef was the name for linkage purposes of an anonymous
   // tag decl, re-establish that relationship for the new typedef.
   if (const TagType *oldTagType = D->getUnderlyingType()->getAs<TagType>()) {
-    TagDecl *oldTag = oldTagType->getDecl();
+    TagDecl *oldTag = oldTagType->getOriginalDecl();
     if (oldTag->getTypedefNameForAnonDecl() == D && !Invalid) {
-      TagDecl *newTag = DI->getType()->castAs<TagType>()->getDecl();
+      TagDecl *newTag = DI->getType()->castAs<TagType>()->getOriginalDecl();
       assert(!newTag->hasNameForLinkage());
       newTag->setTypedefNameForAnonDecl(Typedef);
     }
@@ -2250,8 +2250,7 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
 
   CXXRecordDecl *RecordInst = CXXRecordDecl::Create(
       SemaRef.Context, Pattern->getTagKind(), DC, Pattern->getBeginLoc(),
-      Pattern->getLocation(), Pattern->getIdentifier(), PrevDecl,
-      /*DelayTypeCreation=*/true);
+      Pattern->getLocation(), Pattern->getIdentifier(), PrevDecl);
   if (QualifierLoc)
     RecordInst->setQualifierInfo(QualifierLoc);
 
@@ -2271,8 +2270,6 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
 
     if (PrevClassTemplate) {
       Inst->setCommonPtr(PrevClassTemplate->getCommonPtr());
-      RecordInst->setTypeForDecl(
-          PrevClassTemplate->getTemplatedDecl()->getTypeForDecl());
       const ClassTemplateDecl *MostRecentPrevCT =
           PrevClassTemplate->getMostRecentDecl();
       TemplateParameterList *PrevParams =
@@ -2306,10 +2303,6 @@ Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
 
   Inst->setPreviousDecl(PrevClassTemplate);
 
-  // Trigger creation of the type for the instantiation.
-  SemaRef.Context.getInjectedClassNameType(
-      RecordInst, Inst->getInjectedClassNameSpecialization());
-
   // Finish handling of friends.
   if (isFriend) {
     DC->makeDeclVisibleInContext(Inst);
@@ -2515,11 +2508,9 @@ Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
   else
     Record = CXXRecordDecl::Create(SemaRef.Context, D->getTagKind(), Owner,
                                    D->getBeginLoc(), D->getLocation(),
-                                   D->getIdentifier(), PrevDecl,
-                                   /*DelayTypeCreation=*/IsInjectedClassName);
-  // Link the type of the injected-class-name to that of the outer class.
-  if (IsInjectedClassName)
-    (void)SemaRef.Context.getTypeDeclType(Record, cast<CXXRecordDecl>(Owner));
+                                   D->getIdentifier(), PrevDecl);
+
+  Record->setImplicit(D->isImplicit());
 
   // Substitute the nested name specifier, if any.
   if (SubstQualifier(D, Record))
@@ -2528,7 +2519,6 @@ Decl *TemplateDeclInstantiator::VisitCXXRecordDecl(CXXRecordDecl *D) {
   SemaRef.InstantiateAttrsForDecl(TemplateArgs, D, Record, LateAttrs,
                                                               StartingScope);
 
-  Record->setImplicit(D->isImplicit());
   // FIXME: Check against AS_none is an ugly hack to work around the issue that
   // the tag decls introduced by friend class declarations don't have an access
   // specifier. Remove once this area of the code gets sorted out.
@@ -3164,8 +3154,8 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
     Method->setIneligibleOrNotSelected(true);
     Method->setRangeEnd(Destructor->getEndLoc());
     Method->setDeclName(SemaRef.Context.DeclarationNames.getCXXDestructorName(
-        SemaRef.Context.getCanonicalType(
-            SemaRef.Context.getTypeDeclType(Record))));
+
+        SemaRef.Context.getCanonicalTagType(Record)));
   } else if (CXXConversionDecl *Conversion = dyn_cast<CXXConversionDecl>(D)) {
     Method = CXXConversionDecl::Create(
         SemaRef.Context, Record, StartLoc, NameInfo, T, TInfo,
@@ -3793,19 +3783,18 @@ TemplateDeclInstantiator::VisitTemplateTemplateParmDecl(
         D->getPosition(), D->isParameterPack(), D->getIdentifier(),
         D->wasDeclaredWithTypename(), InstParams);
   if (D->hasDefaultArgument() && !D->defaultArgumentWasInherited()) {
-    NestedNameSpecifierLoc QualifierLoc =
-        D->getDefaultArgument().getTemplateQualifierLoc();
-    QualifierLoc =
-        SemaRef.SubstNestedNameSpecifierLoc(QualifierLoc, TemplateArgs);
+    const TemplateArgumentLoc &A = D->getDefaultArgument();
+    NestedNameSpecifierLoc QualifierLoc = A.getTemplateQualifierLoc();
+    // FIXME: Pass in the template keyword location.
     TemplateName TName = SemaRef.SubstTemplateName(
-        QualifierLoc, D->getDefaultArgument().getArgument().getAsTemplate(),
-        D->getDefaultArgument().getTemplateNameLoc(), TemplateArgs);
+        A.getTemplateKWLoc(), QualifierLoc, A.getArgument().getAsTemplate(),
+        A.getTemplateNameLoc(), TemplateArgs);
     if (!TName.isNull())
       Param->setDefaultArgument(
           SemaRef.Context,
           TemplateArgumentLoc(SemaRef.Context, TemplateArgument(TName),
-                              D->getDefaultArgument().getTemplateQualifierLoc(),
-                              D->getDefaultArgument().getTemplateNameLoc()));
+                              A.getTemplateKWLoc(), QualifierLoc,
+                              A.getTemplateNameLoc()));
   }
   Param->setAccess(AS_public);
   Param->setImplicit(D->isImplicit());
@@ -3907,7 +3896,7 @@ Decl *TemplateDeclInstantiator::VisitUsingDecl(UsingDecl *D) {
   if (NameInfo.getName().getNameKind() == DeclarationName::CXXConstructorName)
     if (auto *RD = dyn_cast<CXXRecordDecl>(SemaRef.CurContext))
       NameInfo.setName(SemaRef.Context.DeclarationNames.getCXXConstructorName(
-          SemaRef.Context.getCanonicalType(SemaRef.Context.getRecordType(RD))));
+          SemaRef.Context.getCanonicalTagType(RD)));
 
   // We only need to do redeclaration lookups if we're in a class scope (in
   // fact, it's not really even possible in non-class scopes).
@@ -4819,18 +4808,13 @@ TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(
       ClassTemplate->findPartialSpecialization(CTAI.CanonicalConverted,
                                                InstParams, InsertPos);
 
-  // Build the type that describes the converted template arguments of the class
-  // template partial specialization.
-  TypeSourceInfo *WrittenTy = SemaRef.Context.getTemplateSpecializationTypeInfo(
-      TemplateName(ClassTemplate), TemplArgInfo->getLAngleLoc(),
-      InstTemplateArgs, CTAI.CanonicalConverted);
-
   // Create the class template partial specialization declaration.
   ClassTemplatePartialSpecializationDecl *InstPartialSpec =
       ClassTemplatePartialSpecializationDecl::Create(
           SemaRef.Context, PartialSpec->getTagKind(), Owner,
           PartialSpec->getBeginLoc(), PartialSpec->getLocation(), InstParams,
-          ClassTemplate, CTAI.CanonicalConverted, WrittenTy->getType(),
+          ClassTemplate, CTAI.CanonicalConverted,
+          /*CanonInjectedTST=*/CanQualType(),
           /*PrevDecl=*/nullptr);
 
   InstPartialSpec->setTemplateArgsAsWritten(InstTemplateArgs);
@@ -4861,7 +4845,7 @@ TemplateDeclInstantiator::InstantiateClassTemplatePartialSpecialization(
                  diag::err_partial_spec_redeclared)
         << InstPartialSpec;
     SemaRef.Diag(PrevDecl->getLocation(), diag::note_prev_partial_spec_here)
-      << SemaRef.Context.getTypeDeclType(PrevDecl);
+        << SemaRef.Context.getCanonicalTagType(PrevDecl);
     return nullptr;
   }
 
@@ -5750,15 +5734,19 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
       QualType TransformRecordType(TypeLocBuilder &TLB, RecordTypeLoc TL) {
         const RecordType *T = TL.getTypePtr();
         RecordDecl *Record = cast_or_null<RecordDecl>(
-            getDerived().TransformDecl(TL.getNameLoc(), T->getDecl()));
+            getDerived().TransformDecl(TL.getNameLoc(), T->getOriginalDecl()));
         if (Record != OldDecl)
           return Base::TransformRecordType(TLB, TL);
 
-        QualType Result = getDerived().RebuildRecordType(NewDecl);
+        // FIXME: transform the rest of the record type.
+        QualType Result = getDerived().RebuildTagType(
+            ElaboratedTypeKeyword::None, /*Qualifier=*/std::nullopt, NewDecl);
         if (Result.isNull())
           return QualType();
 
-        RecordTypeLoc NewTL = TLB.push<RecordTypeLoc>(Result);
+        TagTypeLoc NewTL = TLB.push<RecordTypeLoc>(Result);
+        NewTL.setElaboratedKeywordLoc(SourceLocation());
+        NewTL.setQualifierLoc(NestedNameSpecifierLoc());
         NewTL.setNameLoc(TL.getNameLoc());
         return Result;
       }
@@ -6920,7 +6908,8 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
               Args.addArgument(
                   getTrivialTemplateArgumentLoc(UnpackedArg, QualType(), Loc));
           }
-          QualType T = CheckTemplateIdType(TemplateName(TD), Loc, Args);
+          QualType T = CheckTemplateIdType(ElaboratedTypeKeyword::None,
+                                           TemplateName(TD), Loc, Args);
           // We may get a non-null type with errors, in which case
           // `getAsCXXRecordDecl` will return `nullptr`. For instance, this
           // happens when one of the template arguments is an invalid
@@ -6986,16 +6975,17 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
     bool IsBeingInstantiated = false;
     if (CXXRecordDecl *Spec = dyn_cast<CXXRecordDecl>(ParentDC)) {
       if (!Spec->isDependentContext()) {
-        QualType T = Context.getTypeDeclType(Spec);
+        CanQualType T = Context.getCanonicalTagType(Spec);
         const RecordType *Tag = T->getAs<RecordType>();
         assert(Tag && "type of non-dependent record is not a RecordType");
-        if (Tag->isBeingDefined())
+        auto *TagDecl =
+            cast<CXXRecordDecl>(Tag->getOriginalDecl())->getDefinitionOrSelf();
+        if (TagDecl->isBeingDefined())
           IsBeingInstantiated = true;
-        if (!Tag->isBeingDefined() &&
-            RequireCompleteType(Loc, T, diag::err_incomplete_type))
+        else if (RequireCompleteType(Loc, T, diag::err_incomplete_type))
           return nullptr;
 
-        ParentDC = Tag->getDecl();
+        ParentDC = TagDecl;
       }
     }
 
@@ -7041,8 +7031,8 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
         // of member classes, and introduces ordering dependencies via
         // template instantiation.
         Diag(Loc, diag::err_member_not_yet_instantiated)
-          << D->getDeclName()
-          << Context.getTypeDeclType(cast<CXXRecordDecl>(ParentDC));
+            << D->getDeclName()
+            << Context.getCanonicalTagType(cast<CXXRecordDecl>(ParentDC));
         Diag(D->getLocation(), diag::note_non_instantiated_member_here);
       } else if (EnumConstantDecl *ED = dyn_cast<EnumConstantDecl>(D)) {
         // This enumeration constant was found when the template was defined,
@@ -7057,7 +7047,7 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
           << D->getDeclName()
           << Context.getTypeDeclType(cast<TypeDecl>(Spec->getDeclContext()));
         Diag(Spec->getLocation(), diag::note_enum_specialized_here)
-          << Context.getTypeDeclType(Spec);
+            << Context.getCanonicalTagType(Spec);
       } else {
         // We should have found something, but didn't.
         llvm_unreachable("Unable to find instantiation of declaration!");
diff --git a/clang/lib/Sema/SemaTemplateVariadic.cpp b/clang/lib/Sema/SemaTemplateVariadic.cpp
index 572dbf2e7393f..b518400b60c7e 100644
--- a/clang/lib/Sema/SemaTemplateVariadic.cpp
+++ b/clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -155,21 +155,22 @@ class CollectUnexpandedParameterPacksVisitor
 
     /// Suppress traversal into types that do not contain
     /// unexpanded parameter packs.
-    bool TraverseType(QualType T) override {
+    bool TraverseType(QualType T, bool TraverseQualifier = true) override {
       if ((!T.isNull() && T->containsUnexpandedParameterPack()) ||
           InLambdaOrBlock)
-        return DynamicRecursiveASTVisitor::TraverseType(T);
+        return DynamicRecursiveASTVisitor::TraverseType(T, TraverseQualifier);
 
       return true;
     }
 
     /// Suppress traversal into types with location information
     /// that do not contain unexpanded parameter packs.
-    bool TraverseTypeLoc(TypeLoc TL) override {
+    bool TraverseTypeLoc(TypeLoc TL, bool TraverseQualifier = true) override {
       if ((!TL.getType().isNull() &&
            TL.getType()->containsUnexpandedParameterPack()) ||
           InLambdaOrBlock)
-        return DynamicRecursiveASTVisitor::TraverseTypeLoc(TL);
+        return DynamicRecursiveASTVisitor::TraverseTypeLoc(TL,
+                                                           TraverseQualifier);
 
       return true;
     }
@@ -195,10 +196,12 @@ class CollectUnexpandedParameterPacksVisitor
 
     /// Suppress traversal of pack expansion expressions and types.
     ///@{
-    bool TraversePackExpansionType(PackExpansionType *T) override {
+    bool TraversePackExpansionType(PackExpansionType *T,
+                                   bool TraverseQualifier) override {
       return true;
     }
-    bool TraversePackExpansionTypeLoc(PackExpansionTypeLoc TL) override {
+    bool TraversePackExpansionTypeLoc(PackExpansionTypeLoc TL,
+                                      bool TraverseQualifier) override {
       return true;
     }
     bool TraversePackExpansionExpr(PackExpansionExpr *E) override {
@@ -208,10 +211,12 @@ class CollectUnexpandedParameterPacksVisitor
     bool TraversePackIndexingExpr(PackIndexingExpr *E) override {
       return DynamicRecursiveASTVisitor::TraverseStmt(E->getIndexExpr());
     }
-    bool TraversePackIndexingType(PackIndexingType *E) override {
+    bool TraversePackIndexingType(PackIndexingType *E,
+                                  bool TraverseQualifier) override {
       return DynamicRecursiveASTVisitor::TraverseStmt(E->getIndexExpr());
     }
-    bool TraversePackIndexingTypeLoc(PackIndexingTypeLoc TL) override {
+    bool TraversePackIndexingTypeLoc(PackIndexingTypeLoc TL,
+                                     bool TraverseQualifier) override {
       return DynamicRecursiveASTVisitor::TraverseStmt(TL.getIndexExpr());
     }
 
@@ -515,8 +520,7 @@ bool Sema::DiagnoseUnexpandedParameterPack(const CXXScopeSpec &SS,
   // C++0x [temp.variadic]p5:
   //   An appearance of a name of a parameter pack that is not expanded is
   //   ill-formed.
-  if (!SS.getScopeRep() ||
-      !SS.getScopeRep()->containsUnexpandedParameterPack())
+  if (!SS.getScopeRep().containsUnexpandedParameterPack())
     return false;
 
   SmallVector<UnexpandedParameterPack, 2> Unexpanded;
@@ -644,7 +648,7 @@ Sema::ActOnPackExpansion(const ParsedTemplateArgument &Arg,
       return ParsedTemplateArgument();
 
     return ParsedTemplateArgument(Arg.getKind(), Result.get().getAsOpaquePtr(),
-                                  Arg.getLocation());
+                                  Arg.getNameLoc());
   }
 
   case ParsedTemplateArgument::NonType: {
@@ -653,12 +657,12 @@ Sema::ActOnPackExpansion(const ParsedTemplateArgument &Arg,
       return ParsedTemplateArgument();
 
     return ParsedTemplateArgument(Arg.getKind(), Result.get(),
-                                  Arg.getLocation());
+                                  Arg.getNameLoc());
   }
 
   case ParsedTemplateArgument::Template:
     if (!Arg.getAsTemplate().get().containsUnexpandedParameterPack()) {
-      SourceRange R(Arg.getLocation());
+      SourceRange R(Arg.getNameLoc());
       if (Arg.getScopeSpec().isValid())
         R.setBegin(Arg.getScopeSpec().getBeginLoc());
       Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
@@ -1105,8 +1109,7 @@ bool Sema::containsUnexpandedParameterPacks(Declarator &D) {
       break;
 
     case DeclaratorChunk::MemberPointer:
-      if (Chunk.Mem.Scope().getScopeRep() &&
-          Chunk.Mem.Scope().getScopeRep()->containsUnexpandedParameterPack())
+      if (Chunk.Mem.Scope().getScopeRep().containsUnexpandedParameterPack())
         return true;
       break;
     }
@@ -1290,9 +1293,9 @@ TemplateArgumentLoc Sema::getTemplateArgumentPackExpansionPattern(
   case TemplateArgument::TemplateExpansion:
     Ellipsis = OrigLoc.getTemplateEllipsisLoc();
     NumExpansions = Argument.getNumTemplateExpansions();
-    return TemplateArgumentLoc(Context, Argument.getPackExpansionPattern(),
-                               OrigLoc.getTemplateQualifierLoc(),
-                               OrigLoc.getTemplateNameLoc());
+    return TemplateArgumentLoc(
+        Context, Argument.getPackExpansionPattern(), OrigLoc.getTemplateKWLoc(),
+        OrigLoc.getTemplateQualifierLoc(), OrigLoc.getTemplateNameLoc());
 
   case TemplateArgument::Declaration:
   case TemplateArgument::NullPtr:
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 88aa63d3b9e83..b96592f5cb48e 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -1211,14 +1211,11 @@ static QualType ConvertDeclSpecToType(TypeProcessingState &state) {
            DS.getTypeSpecSign() == TypeSpecifierSign::Unspecified &&
            "No qualifiers on tag names!");
 
+    ElaboratedTypeKeyword Keyword =
+        KeywordHelpers::getKeywordForTypeSpec(DS.getTypeSpecType());
     // TypeQuals handled by caller.
-    Result = Context.getTypeDeclType(D);
-
-    // In both C and C++, make an ElaboratedType.
-    ElaboratedTypeKeyword Keyword
-      = ElaboratedType::getKeywordForTypeSpec(DS.getTypeSpecType());
-    Result = S.getElaboratedType(Keyword, DS.getTypeSpecScope(), Result,
-                                 DS.isTypeSpecOwned() ? D : nullptr);
+    Result = Context.getTagType(Keyword, DS.getTypeSpecScope().getScopeRep(), D,
+                                DS.isTypeSpecOwned());
     break;
   }
   case DeclSpec::TST_typename: {
@@ -1241,7 +1238,7 @@ static QualType ConvertDeclSpecToType(TypeProcessingState &state) {
     assert(!Result.isNull() && "Didn't get a type for typeof?");
     if (!Result->isDependentType())
       if (const TagType *TT = Result->getAs<TagType>())
-        S.DiagnoseUseOfDecl(TT->getDecl(), DS.getTypeSpecTypeLoc());
+        S.DiagnoseUseOfDecl(TT->getOriginalDecl(), DS.getTypeSpecTypeLoc());
     // TypeQuals handled by caller.
     Result = Context.getTypeOfType(
         Result, DS.getTypeSpecType() == DeclSpec::TST_typeof_unqualType
@@ -2085,7 +2082,7 @@ QualType Sema::BuildArrayType(QualType T, ArraySizeModifier ASM,
     // an inheritance model, even if it's inside an unused typedef.
     if (Context.getTargetInfo().getCXXABI().isMicrosoft())
       if (const MemberPointerType *MPTy = T->getAs<MemberPointerType>())
-        if (!MPTy->getQualifier()->isDependent())
+        if (!MPTy->getQualifier().isDependent())
           (void)isCompleteType(Loc, T);
 
   } else {
@@ -2120,7 +2117,9 @@ QualType Sema::BuildArrayType(QualType T, ArraySizeModifier ASM,
   if (const RecordType *EltTy = T->getAs<RecordType>()) {
     // If the element type is a struct or union that contains a variadic
     // array, accept it as a GNU extension: C99 6.7.2.1p2.
-    if (EltTy->getDecl()->hasFlexibleArrayMember())
+    if (EltTy->getOriginalDecl()
+            ->getDefinitionOrSelf()
+            ->hasFlexibleArrayMember())
       Diag(Loc, diag::ext_flexible_array_in_array) << T;
   } else if (T->isObjCObjectType()) {
     Diag(Loc, diag::err_objc_array_of_interfaces) << T;
@@ -3462,7 +3461,7 @@ static QualType GetDeclSpecTypeForDeclarator(TypeProcessingState &state,
 
     if (DiagID != 0) {
       SemaRef.Diag(OwnedTagDecl->getLocation(), DiagID)
-          << SemaRef.Context.getTypeDeclType(OwnedTagDecl);
+          << SemaRef.Context.getCanonicalTagType(OwnedTagDecl);
       D.setInvalidType(true);
     }
   }
@@ -3655,11 +3654,22 @@ static void warnAboutRedundantParens(Sema &S, Declarator &D, QualType T) {
     // here: even (e.g.) "int ::x" is visually ambiguous even though it's
     // formally unambiguous.
     if (StartsWithDeclaratorId && D.getCXXScopeSpec().isValid()) {
-      for (NestedNameSpecifier *NNS = D.getCXXScopeSpec().getScopeRep(); NNS;
-           NNS = NNS->getPrefix()) {
-        if (NNS->getKind() == NestedNameSpecifier::Global)
+      NestedNameSpecifier NNS = D.getCXXScopeSpec().getScopeRep();
+      for (;;) {
+        switch (NNS.getKind()) {
+        case NestedNameSpecifier::Kind::Global:
           return;
+        case NestedNameSpecifier::Kind::Type:
+          NNS = NNS.getAsType()->getPrefix();
+          continue;
+        case NestedNameSpecifier::Kind::Namespace:
+          NNS = NNS.getAsNamespaceAndPrefix().Prefix;
+          continue;
+        default:
+          goto out;
+        }
       }
+    out:;
     }
 
     S.Diag(Paren.Loc, diag::warn_redundant_parens_around_declarator)
@@ -3967,7 +3977,8 @@ classifyPointerDeclarator(Sema &S, QualType type, Declarator &declarator,
       return PointerDeclaratorKind::NonPointer;
 
     if (auto recordType = type->getAs<RecordType>()) {
-      RecordDecl *recordDecl = recordType->getDecl();
+      RecordDecl *recordDecl =
+          recordType->getOriginalDecl()->getDefinitionOrSelf();
 
       // If this is CFErrorRef*, report it as such.
       if (numNormalPointers == 2 && numTypeSpecifierPointers < 2 &&
@@ -5101,7 +5112,7 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
         //   Types shall not be defined in return or parameter types.
         TagDecl *Tag = cast<TagDecl>(D.getDeclSpec().getRepAsDecl());
         S.Diag(Tag->getLocation(), diag::err_type_defined_in_result_type)
-          << Context.getTypeDeclType(Tag);
+            << Context.getCanonicalTagType(Tag);
       }
 
       // Exception specs are not allowed in typedefs. Complain, but add it
@@ -5319,7 +5330,7 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
                   state.getDeclarator()
                           .getCXXScopeSpec()
                           .getScopeRep()
-                          ->getKind() == NestedNameSpecifier::TypeSpec) ||
+                          .getKind() == NestedNameSpecifier::Kind::Type) ||
                  state.getDeclarator().getContext() ==
                      DeclaratorContext::Member ||
                  state.getDeclarator().getContext() ==
@@ -5898,7 +5909,49 @@ namespace {
     //   int __attr * __attr * __attr *p;
     void VisitPointerTypeLoc(PointerTypeLoc TL) { Visit(TL.getNextTypeLoc()); }
     void VisitTypedefTypeLoc(TypedefTypeLoc TL) {
-      TL.setNameLoc(DS.getTypeSpecTypeLoc());
+      if (DS.getTypeSpecType() == TST_typename) {
+        TypeSourceInfo *TInfo = nullptr;
+        Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
+        if (TInfo) {
+          TL.copy(TInfo->getTypeLoc().castAs<TypedefTypeLoc>());
+          return;
+        }
+      }
+      TL.set(TL.getTypePtr()->getKeyword() != ElaboratedTypeKeyword::None
+                 ? DS.getTypeSpecTypeLoc()
+                 : SourceLocation(),
+             DS.getTypeSpecScope().getWithLocInContext(Context),
+             DS.getTypeSpecTypeNameLoc());
+    }
+    void VisitUnresolvedUsingTypeLoc(UnresolvedUsingTypeLoc TL) {
+      if (DS.getTypeSpecType() == TST_typename) {
+        TypeSourceInfo *TInfo = nullptr;
+        Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
+        if (TInfo) {
+          TL.copy(TInfo->getTypeLoc().castAs<UnresolvedUsingTypeLoc>());
+          return;
+        }
+      }
+      TL.set(TL.getTypePtr()->getKeyword() != ElaboratedTypeKeyword::None
+                 ? DS.getTypeSpecTypeLoc()
+                 : SourceLocation(),
+             DS.getTypeSpecScope().getWithLocInContext(Context),
+             DS.getTypeSpecTypeNameLoc());
+    }
+    void VisitUsingTypeLoc(UsingTypeLoc TL) {
+      if (DS.getTypeSpecType() == TST_typename) {
+        TypeSourceInfo *TInfo = nullptr;
+        Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
+        if (TInfo) {
+          TL.copy(TInfo->getTypeLoc().castAs<UsingTypeLoc>());
+          return;
+        }
+      }
+      TL.set(TL.getTypePtr()->getKeyword() != ElaboratedTypeKeyword::None
+                 ? DS.getTypeSpecTypeLoc()
+                 : SourceLocation(),
+             DS.getTypeSpecScope().getWithLocInContext(Context),
+             DS.getTypeSpecTypeNameLoc());
     }
     void VisitObjCInterfaceTypeLoc(ObjCInterfaceTypeLoc TL) {
       TL.setNameLoc(DS.getTypeSpecTypeLoc());
@@ -5929,16 +5982,9 @@ namespace {
       }
 
       TypeLoc OldTL = TInfo->getTypeLoc();
-      if (TInfo->getType()->getAs<ElaboratedType>()) {
-        ElaboratedTypeLoc ElabTL = OldTL.castAs<ElaboratedTypeLoc>();
-        TemplateSpecializationTypeLoc NamedTL = ElabTL.getNamedTypeLoc()
-            .castAs<TemplateSpecializationTypeLoc>();
-        TL.copy(NamedTL);
-      } else {
-        TL.copy(OldTL.castAs<TemplateSpecializationTypeLoc>());
-        assert(TL.getRAngleLoc() == OldTL.castAs<TemplateSpecializationTypeLoc>().getRAngleLoc());
-      }
-
+      TL.copy(OldTL.castAs<TemplateSpecializationTypeLoc>());
+      assert(TL.getRAngleLoc() ==
+             OldTL.castAs<TemplateSpecializationTypeLoc>().getRAngleLoc());
     }
     void VisitTypeOfExprTypeLoc(TypeOfExprTypeLoc TL) {
       assert(DS.getTypeSpecType() == DeclSpec::TST_typeofExpr ||
@@ -5987,24 +6033,6 @@ namespace {
           TL.expandBuiltinRange(DS.getTypeSpecWidthRange());
       }
     }
-    void VisitElaboratedTypeLoc(ElaboratedTypeLoc TL) {
-      if (DS.getTypeSpecType() == TST_typename) {
-        TypeSourceInfo *TInfo = nullptr;
-        Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
-        if (TInfo)
-          if (auto ETL = TInfo->getTypeLoc().getAs<ElaboratedTypeLoc>()) {
-            TL.copy(ETL);
-            return;
-          }
-      }
-      const ElaboratedType *T = TL.getTypePtr();
-      TL.setElaboratedKeywordLoc(T->getKeyword() != ElaboratedTypeKeyword::None
-                                     ? DS.getTypeSpecTypeLoc()
-                                     : SourceLocation());
-      const CXXScopeSpec& SS = DS.getTypeSpecScope();
-      TL.setQualifierLoc(SS.getWithLocInContext(Context));
-      Visit(TL.getNextTypeLoc().getUnqualifiedLoc());
-    }
     void VisitDependentNameTypeLoc(DependentNameTypeLoc TL) {
       assert(DS.getTypeSpecType() == TST_typename);
       TypeSourceInfo *TInfo = nullptr;
@@ -6063,7 +6091,29 @@ namespace {
           ASTTemplateArgumentListInfo::Create(Context, TemplateArgsInfo));
       TL.setConceptReference(CR);
     }
+    void VisitDeducedTemplateSpecializationTypeLoc(
+        DeducedTemplateSpecializationTypeLoc TL) {
+      assert(DS.getTypeSpecType() == TST_typename);
+      TypeSourceInfo *TInfo = nullptr;
+      Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
+      assert(TInfo);
+      TL.copy(
+          TInfo->getTypeLoc().castAs<DeducedTemplateSpecializationTypeLoc>());
+    }
     void VisitTagTypeLoc(TagTypeLoc TL) {
+      if (DS.getTypeSpecType() == TST_typename) {
+        TypeSourceInfo *TInfo = nullptr;
+        Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
+        if (TInfo) {
+          TL.copy(TInfo->getTypeLoc().castAs<TagTypeLoc>());
+          return;
+        }
+      }
+      TL.setElaboratedKeywordLoc(TL.getTypePtr()->getKeyword() !=
+                                         ElaboratedTypeKeyword::None
+                                     ? DS.getTypeSpecTypeLoc()
+                                     : SourceLocation());
+      TL.setQualifierLoc(DS.getTypeSpecScope().getWithLocInContext(Context));
       TL.setNameLoc(DS.getTypeSpecTypeNameLoc());
     }
     void VisitAtomicTypeLoc(AtomicTypeLoc TL) {
@@ -7029,9 +7079,6 @@ static bool handleMSPointerTypeQualifierAttr(TypeProcessingState &State,
     if (const TypedefType *TT = dyn_cast<TypedefType>(Desugared)) {
       Desugared = TT->desugar();
       continue;
-    } else if (const ElaboratedType *ET = dyn_cast<ElaboratedType>(Desugared)) {
-      Desugared = ET->desugar();
-      continue;
     }
     const AttributedType *AT = dyn_cast<AttributedType>(Desugared);
     if (!AT)
@@ -9170,11 +9217,9 @@ bool Sema::RequireCompleteType(SourceLocation Loc, QualType T,
                                TypeDiagnoser &Diagnoser) {
   if (RequireCompleteTypeImpl(Loc, T, Kind, &Diagnoser))
     return true;
-  if (const TagType *Tag = T->getAs<TagType>()) {
-    if (!Tag->getDecl()->isCompleteDefinitionRequired()) {
-      Tag->getDecl()->setCompleteDefinitionRequired();
-      Consumer.HandleTagDeclRequiredDefinition(Tag->getDecl());
-    }
+  if (auto *TD = T->getAsTagDecl(); TD && !TD->isCompleteDefinitionRequired()) {
+    TD->setCompleteDefinitionRequired();
+    Consumer.HandleTagDeclRequiredDefinition(TD);
   }
   return false;
 }
@@ -9312,7 +9357,7 @@ bool Sema::hasReachableDefinition(NamedDecl *D, NamedDecl **Suggested,
 
 /// Locks in the inheritance model for the given class and all of its bases.
 static void assignInheritanceModel(Sema &S, CXXRecordDecl *RD) {
-  RD = RD->getMostRecentNonInjectedDecl();
+  RD = RD->getMostRecentDecl();
   if (!RD->hasAttr<MSInheritanceAttr>()) {
     MSInheritanceModel IM;
     bool BestCase = false;
@@ -9352,10 +9397,10 @@ bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
   //  assert(!T->isDependentType() &&
   //         "Can't ask whether a dependent type is complete");
 
-  if (const MemberPointerType *MPTy = T->getAs<MemberPointerType>()) {
+  if (const auto *MPTy = dyn_cast<MemberPointerType>(T.getCanonicalType())) {
     if (CXXRecordDecl *RD = MPTy->getMostRecentCXXRecordDecl();
         RD && !RD->isDependentType()) {
-      QualType T = Context.getTypeDeclType(RD);
+      CanQualType T = Context.getCanonicalTagType(RD);
       if (getLangOpts().CompleteMemberPointers && !RD->isBeingDefined() &&
           RequireCompleteType(Loc, T, Kind, diag::err_memptr_incomplete))
         return true;
@@ -9492,10 +9537,10 @@ bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
   // If the type was a forward declaration of a class/struct/union
   // type, produce a note.
   if (Tag && !Tag->isInvalidDecl() && !Tag->getLocation().isInvalid())
-    Diag(Tag->getLocation(),
-         Tag->isBeingDefined() ? diag::note_type_being_defined
-                               : diag::note_forward_declaration)
-      << Context.getTagDeclType(Tag);
+    Diag(Tag->getLocation(), Tag->isBeingDefined()
+                                 ? diag::note_type_being_defined
+                                 : diag::note_forward_declaration)
+        << Context.getCanonicalTagType(Tag);
 
   // If the Objective-C class was a forward declaration, produce a note.
   if (IFace && !IFace->isInvalidDecl() && !IFace->getLocation().isInvalid())
@@ -9550,7 +9595,8 @@ bool Sema::RequireLiteralType(SourceLocation Loc, QualType T,
   if (!RT)
     return true;
 
-  const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+  const CXXRecordDecl *RD =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
 
   // A partially-defined class type can't be a literal type, because a literal
   // class type must have a trivial destructor (which can't be checked until
@@ -9628,15 +9674,6 @@ bool Sema::RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID) {
   return RequireLiteralType(Loc, T, Diagnoser);
 }
 
-QualType Sema::getElaboratedType(ElaboratedTypeKeyword Keyword,
-                                 const CXXScopeSpec &SS, QualType T,
-                                 TagDecl *OwnedTagDecl) {
-  if (T.isNull())
-    return T;
-  return Context.getElaboratedType(
-      Keyword, SS.isValid() ? SS.getScopeRep() : nullptr, T, OwnedTagDecl);
-}
-
 QualType Sema::BuildTypeofExprType(Expr *E, TypeOfKind Kind) {
   assert(!E->hasPlaceholderType() && "unexpected placeholder");
 
@@ -9647,7 +9684,7 @@ QualType Sema::BuildTypeofExprType(Expr *E, TypeOfKind Kind) {
   if (!E->isTypeDependent()) {
     QualType T = E->getType();
     if (const TagType *TT = T->getAs<TagType>())
-      DiagnoseUseOfDecl(TT->getDecl(), E->getExprLoc());
+      DiagnoseUseOfDecl(TT->getOriginalDecl(), E->getExprLoc());
   }
   return Context.getTypeOfExprType(E, Kind);
 }
@@ -9813,8 +9850,7 @@ QualType Sema::BuildPackIndexingType(QualType Pattern, Expr *IndexExpr,
 static QualType GetEnumUnderlyingType(Sema &S, QualType BaseType,
                                       SourceLocation Loc) {
   assert(BaseType->isEnumeralType());
-  EnumDecl *ED = BaseType->castAs<EnumType>()->getDecl();
-  assert(ED && "EnumType has no EnumDecl");
+  EnumDecl *ED = BaseType->castAs<EnumType>()->getOriginalDecl();
 
   S.DiagnoseUseOfDecl(ED, Loc);
 
diff --git a/clang/lib/Sema/SemaTypeTraits.cpp b/clang/lib/Sema/SemaTypeTraits.cpp
index 1d8687e4bf1c1..9b9dd172003a0 100644
--- a/clang/lib/Sema/SemaTypeTraits.cpp
+++ b/clang/lib/Sema/SemaTypeTraits.cpp
@@ -32,8 +32,7 @@ static CXXMethodDecl *LookupSpecialMemberFromXValue(Sema &SemaRef,
   RD = RD->getDefinition();
   SourceLocation LookupLoc = RD->getLocation();
 
-  CanQualType CanTy = SemaRef.getASTContext().getCanonicalType(
-      SemaRef.getASTContext().getTagDeclType(RD));
+  CanQualType CanTy = SemaRef.getASTContext().getCanonicalTagType(RD);
   DeclarationName Name;
   Expr *Arg = nullptr;
   unsigned NumArgs;
@@ -562,7 +561,8 @@ static bool HasNoThrowOperator(const RecordType *RT, OverloadedOperatorKind Op,
                                bool (CXXRecordDecl::*HasTrivial)() const,
                                bool (CXXRecordDecl::*HasNonTrivial)() const,
                                bool (CXXMethodDecl::*IsDesiredOp)() const) {
-  CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+  CXXRecordDecl *RD =
+      cast<CXXRecordDecl>(RT->getOriginalDecl())->getDefinitionOrSelf();
   if ((RD->*HasTrivial)() && !(RD->*HasNonTrivial)())
     return true;
 
@@ -599,6 +599,7 @@ static bool HasNonDeletedDefaultedEqualityComparison(Sema &S,
   if (Decl->isLambda())
     return Decl->isCapturelessLambda();
 
+  CanQualType T = S.Context.getCanonicalTagType(Decl);
   {
     EnterExpressionEvaluationContext UnevaluatedContext(
         S, Sema::ExpressionEvaluationContext::Unevaluated);
@@ -606,10 +607,7 @@ static bool HasNonDeletedDefaultedEqualityComparison(Sema &S,
     Sema::ContextRAII TUContext(S, S.Context.getTranslationUnitDecl());
 
     // const ClassT& obj;
-    OpaqueValueExpr Operand(
-        KeyLoc,
-        Decl->getTypeForDecl()->getCanonicalTypeUnqualified().withConst(),
-        ExprValueKind::VK_LValue);
+    OpaqueValueExpr Operand(KeyLoc, T.withConst(), ExprValueKind::VK_LValue);
     UnresolvedSet<16> Functions;
     // obj == obj;
     S.LookupBinOp(S.TUScope, {}, BinaryOperatorKind::BO_EQ, Functions);
@@ -628,8 +626,7 @@ static bool HasNonDeletedDefaultedEqualityComparison(Sema &S,
       return false;
     if (!ParamT->isReferenceType() && !Decl->isTriviallyCopyable())
       return false;
-    if (ParamT.getNonReferenceType()->getUnqualifiedDesugaredType() !=
-        Decl->getTypeForDecl())
+    if (!S.Context.hasSameUnqualifiedType(ParamT.getNonReferenceType(), T))
       return false;
   }
 
@@ -1613,9 +1610,9 @@ bool Sema::BuiltinIsBaseOf(SourceLocation RhsTLoc, QualType LhsT,
 
   // Unions are never base classes, and never have base classes.
   // It doesn't matter if they are complete or not. See PR#41843
-  if (lhsRecord && lhsRecord->getDecl()->isUnion())
+  if (lhsRecord && lhsRecord->getOriginalDecl()->isUnion())
     return false;
-  if (rhsRecord && rhsRecord->getDecl()->isUnion())
+  if (rhsRecord && rhsRecord->getOriginalDecl()->isUnion())
     return false;
 
   if (lhsRecord == rhsRecord)
@@ -1629,8 +1626,8 @@ bool Sema::BuiltinIsBaseOf(SourceLocation RhsTLoc, QualType LhsT,
                           diag::err_incomplete_type_used_in_type_trait_expr))
     return false;
 
-  return cast<CXXRecordDecl>(rhsRecord->getDecl())
-      ->isDerivedFrom(cast<CXXRecordDecl>(lhsRecord->getDecl()));
+  return cast<CXXRecordDecl>(rhsRecord->getOriginalDecl())
+      ->isDerivedFrom(cast<CXXRecordDecl>(lhsRecord->getOriginalDecl()));
 }
 
 static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT,
@@ -1670,8 +1667,9 @@ static bool EvaluateBinaryTypeTrait(Sema &Self, TypeTrait BTT,
                                  diag::err_incomplete_type))
       return false;
 
-    return cast<CXXRecordDecl>(DerivedRecord->getDecl())
-        ->isVirtuallyDerivedFrom(cast<CXXRecordDecl>(BaseRecord->getDecl()));
+    return cast<CXXRecordDecl>(DerivedRecord->getOriginalDecl())
+        ->isVirtuallyDerivedFrom(
+            cast<CXXRecordDecl>(BaseRecord->getOriginalDecl()));
   }
   case BTT_IsSame:
     return Self.Context.hasSameType(LhsT, RhsT);
@@ -2018,11 +2016,10 @@ static ExtractedTypeTraitInfo ExtractTypeTraitFromExpression(const Expr *E) {
   // std::is_xxx<>::value
   if (const auto *VD = dyn_cast<VarDecl>(Ref->getDecl());
       Ref->hasQualifier() && VD && VD->getIdentifier()->isStr("value")) {
-    const Type *T = Ref->getQualifier()->getAsType();
-    if (!T)
+    NestedNameSpecifier Qualifier = Ref->getQualifier();
+    if (Qualifier.getKind() != NestedNameSpecifier::Kind::Type)
       return std::nullopt;
-    const TemplateSpecializationType *Ts =
-        T->getAs<TemplateSpecializationType>();
+    const auto *Ts = Qualifier.getAsType()->getAs<TemplateSpecializationType>();
     if (!Ts)
       return std::nullopt;
     const TemplateDecl *D = Ts->getTemplateName().getAsTemplateDecl();
diff --git a/clang/lib/Sema/UsedDeclVisitor.h b/clang/lib/Sema/UsedDeclVisitor.h
index 580d702f96fe5..ad475ab0f42ae 100644
--- a/clang/lib/Sema/UsedDeclVisitor.h
+++ b/clang/lib/Sema/UsedDeclVisitor.h
@@ -71,9 +71,10 @@ class UsedDeclVisitor : public EvaluatedExprVisitor<Derived> {
     if (!DestroyedOrNull.isNull()) {
       QualType Destroyed = S.Context.getBaseElementType(DestroyedOrNull);
       if (const RecordType *DestroyedRec = Destroyed->getAs<RecordType>()) {
-        CXXRecordDecl *Record = cast<CXXRecordDecl>(DestroyedRec->getDecl());
-        if (Record->getDefinition())
-          asImpl().visitUsedDecl(E->getBeginLoc(), S.LookupDestructor(Record));
+        CXXRecordDecl *Record =
+            cast<CXXRecordDecl>(DestroyedRec->getOriginalDecl());
+        if (auto *Def = Record->getDefinition())
+          asImpl().visitUsedDecl(E->getBeginLoc(), S.LookupDestructor(Def));
       }
     }
 
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 30e0973149594..353560fab6692 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -5413,7 +5413,7 @@ void ASTReader::InitializeContext() {
             Error("Invalid FILE type in AST file");
             return;
           }
-          Context.setFILEDecl(Tag->getDecl());
+          Context.setFILEDecl(Tag->getOriginalDecl());
         }
       }
     }
@@ -5434,7 +5434,7 @@ void ASTReader::InitializeContext() {
             Error("Invalid jmp_buf type in AST file");
             return;
           }
-          Context.setjmp_bufDecl(Tag->getDecl());
+          Context.setjmp_bufDecl(Tag->getOriginalDecl());
         }
       }
     }
@@ -5452,7 +5452,7 @@ void ASTReader::InitializeContext() {
         else {
           const TagType *Tag = Sigjmp_bufType->getAs<TagType>();
           assert(Tag && "Invalid sigjmp_buf type in AST file");
-          Context.setsigjmp_bufDecl(Tag->getDecl());
+          Context.setsigjmp_bufDecl(Tag->getOriginalDecl());
         }
       }
     }
@@ -5487,7 +5487,7 @@ void ASTReader::InitializeContext() {
         else {
           const TagType *Tag = Ucontext_tType->getAs<TagType>();
           assert(Tag && "Invalid ucontext_t type in AST file");
-          Context.setucontext_tDecl(Tag->getDecl());
+          Context.setucontext_tDecl(Tag->getOriginalDecl());
         }
       }
     }
@@ -7107,6 +7107,7 @@ class TypeLocReader : public TypeLocVisitor<TypeLocReader> {
 
   void VisitFunctionTypeLoc(FunctionTypeLoc);
   void VisitArrayTypeLoc(ArrayTypeLoc);
+  void VisitTagTypeLoc(TagTypeLoc TL);
 };
 
 } // namespace clang
@@ -7253,15 +7254,24 @@ void TypeLocReader::VisitFunctionNoProtoTypeLoc(FunctionNoProtoTypeLoc TL) {
 }
 
 void TypeLocReader::VisitUnresolvedUsingTypeLoc(UnresolvedUsingTypeLoc TL) {
-  TL.setNameLoc(readSourceLocation());
+  SourceLocation ElaboratedKeywordLoc = readSourceLocation();
+  NestedNameSpecifierLoc QualifierLoc = ReadNestedNameSpecifierLoc();
+  SourceLocation NameLoc = readSourceLocation();
+  TL.set(ElaboratedKeywordLoc, QualifierLoc, NameLoc);
 }
 
 void TypeLocReader::VisitUsingTypeLoc(UsingTypeLoc TL) {
-  TL.setNameLoc(readSourceLocation());
+  SourceLocation ElaboratedKeywordLoc = readSourceLocation();
+  NestedNameSpecifierLoc QualifierLoc = ReadNestedNameSpecifierLoc();
+  SourceLocation NameLoc = readSourceLocation();
+  TL.set(ElaboratedKeywordLoc, QualifierLoc, NameLoc);
 }
 
 void TypeLocReader::VisitTypedefTypeLoc(TypedefTypeLoc TL) {
-  TL.setNameLoc(readSourceLocation());
+  SourceLocation ElaboratedKeywordLoc = readSourceLocation();
+  NestedNameSpecifierLoc QualifierLoc = ReadNestedNameSpecifierLoc();
+  SourceLocation NameLoc = readSourceLocation();
+  TL.set(ElaboratedKeywordLoc, QualifierLoc, NameLoc);
 }
 
 void TypeLocReader::VisitTypeOfExprTypeLoc(TypeOfExprTypeLoc TL) {
@@ -7315,17 +7325,27 @@ void TypeLocReader::VisitAutoTypeLoc(AutoTypeLoc TL) {
 
 void TypeLocReader::VisitDeducedTemplateSpecializationTypeLoc(
     DeducedTemplateSpecializationTypeLoc TL) {
+  TL.setElaboratedKWLoc(readSourceLocation());
+  TL.setQualifierLoc(ReadNestedNameSpecifierLoc());
   TL.setTemplateNameLoc(readSourceLocation());
 }
 
-void TypeLocReader::VisitRecordTypeLoc(RecordTypeLoc TL) {
+void TypeLocReader::VisitTagTypeLoc(TagTypeLoc TL) {
+  TL.setElaboratedKeywordLoc(readSourceLocation());
+  TL.setQualifierLoc(ReadNestedNameSpecifierLoc());
   TL.setNameLoc(readSourceLocation());
 }
 
-void TypeLocReader::VisitEnumTypeLoc(EnumTypeLoc TL) {
-  TL.setNameLoc(readSourceLocation());
+void TypeLocReader::VisitRecordTypeLoc(RecordTypeLoc TL) {
+  VisitTagTypeLoc(TL);
 }
 
+void TypeLocReader::VisitInjectedClassNameTypeLoc(InjectedClassNameTypeLoc TL) {
+  VisitTagTypeLoc(TL);
+}
+
+void TypeLocReader::VisitEnumTypeLoc(EnumTypeLoc TL) { VisitTagTypeLoc(TL); }
+
 void TypeLocReader::VisitAttributedTypeLoc(AttributedTypeLoc TL) {
   TL.setAttr(ReadAttr());
 }
@@ -7363,14 +7383,18 @@ void TypeLocReader::VisitSubstTemplateTypeParmPackTypeLoc(
 
 void TypeLocReader::VisitTemplateSpecializationTypeLoc(
                                            TemplateSpecializationTypeLoc TL) {
-  TL.setTemplateKeywordLoc(readSourceLocation());
-  TL.setTemplateNameLoc(readSourceLocation());
-  TL.setLAngleLoc(readSourceLocation());
-  TL.setRAngleLoc(readSourceLocation());
-  for (unsigned i = 0, e = TL.getNumArgs(); i != e; ++i)
-    TL.setArgLocInfo(i,
-                     Reader.readTemplateArgumentLocInfo(
-                         TL.getTypePtr()->template_arguments()[i].getKind()));
+  SourceLocation ElaboratedKeywordLoc = readSourceLocation();
+  NestedNameSpecifierLoc QualifierLoc = ReadNestedNameSpecifierLoc();
+  SourceLocation TemplateKeywordLoc = readSourceLocation();
+  SourceLocation NameLoc = readSourceLocation();
+  SourceLocation LAngleLoc = readSourceLocation();
+  SourceLocation RAngleLoc = readSourceLocation();
+  TL.set(ElaboratedKeywordLoc, QualifierLoc, TemplateKeywordLoc, NameLoc,
+         LAngleLoc, RAngleLoc);
+  MutableArrayRef<TemplateArgumentLocInfo> Args = TL.getArgLocInfos();
+  for (unsigned I = 0, E = TL.getNumArgs(); I != E; ++I)
+    Args[I] = Reader.readTemplateArgumentLocInfo(
+        TL.getTypePtr()->template_arguments()[I].getKind());
 }
 
 void TypeLocReader::VisitParenTypeLoc(ParenTypeLoc TL) {
@@ -7378,15 +7402,6 @@ void TypeLocReader::VisitParenTypeLoc(ParenTypeLoc TL) {
   TL.setRParenLoc(readSourceLocation());
 }
 
-void TypeLocReader::VisitElaboratedTypeLoc(ElaboratedTypeLoc TL) {
-  TL.setElaboratedKeywordLoc(readSourceLocation());
-  TL.setQualifierLoc(ReadNestedNameSpecifierLoc());
-}
-
-void TypeLocReader::VisitInjectedClassNameTypeLoc(InjectedClassNameTypeLoc TL) {
-  TL.setNameLoc(readSourceLocation());
-}
-
 void TypeLocReader::VisitDependentNameTypeLoc(DependentNameTypeLoc TL) {
   TL.setElaboratedKeywordLoc(readSourceLocation());
   TL.setQualifierLoc(ReadNestedNameSpecifierLoc());
@@ -7838,18 +7853,15 @@ ASTRecordReader::readTemplateArgumentLocInfo(TemplateArgument::ArgKind Kind) {
     return readExpr();
   case TemplateArgument::Type:
     return readTypeSourceInfo();
-  case TemplateArgument::Template: {
-    NestedNameSpecifierLoc QualifierLoc =
-      readNestedNameSpecifierLoc();
-    SourceLocation TemplateNameLoc = readSourceLocation();
-    return TemplateArgumentLocInfo(getASTContext(), QualifierLoc,
-                                   TemplateNameLoc, SourceLocation());
-  }
+  case TemplateArgument::Template:
   case TemplateArgument::TemplateExpansion: {
+    SourceLocation TemplateKWLoc = readSourceLocation();
     NestedNameSpecifierLoc QualifierLoc = readNestedNameSpecifierLoc();
     SourceLocation TemplateNameLoc = readSourceLocation();
-    SourceLocation EllipsisLoc = readSourceLocation();
-    return TemplateArgumentLocInfo(getASTContext(), QualifierLoc,
+    SourceLocation EllipsisLoc = Kind == TemplateArgument::TemplateExpansion
+                                     ? readSourceLocation()
+                                     : SourceLocation();
+    return TemplateArgumentLocInfo(getASTContext(), TemplateKWLoc, QualifierLoc,
                                    TemplateNameLoc, EllipsisLoc);
   }
   case TemplateArgument::Null:
@@ -9458,12 +9470,6 @@ void ASTReader::AssignedLambdaNumbering(CXXRecordDecl *Lambda) {
     CXXRecordDecl *Previous =
         cast<CXXRecordDecl>(Iter->second)->getMostRecentDecl();
     Lambda->setPreviousDecl(Previous);
-    // FIXME: It will be best to use the Previous type when we creating the
-    // lambda directly. But that requires us to get the lambda context decl and
-    // lambda index before creating the lambda, which needs a drastic change in
-    // the parser.
-    const_cast<QualType &>(Lambda->TypeForDecl->CanonicalType) =
-        Previous->TypeForDecl->CanonicalType;
     return;
   }
 
@@ -9979,48 +9985,37 @@ ASTRecordReader::readNestedNameSpecifierLoc() {
   for (unsigned I = 0; I != N; ++I) {
     auto Kind = readNestedNameSpecifierKind();
     switch (Kind) {
-    case NestedNameSpecifier::Identifier: {
-      IdentifierInfo *II = readIdentifier();
-      SourceRange Range = readSourceRange();
-      Builder.Extend(Context, II, Range.getBegin(), Range.getEnd());
-      break;
-    }
-
-    case NestedNameSpecifier::Namespace: {
-      NamespaceDecl *NS = readDeclAs<NamespaceDecl>();
+    case NestedNameSpecifier::Kind::Namespace: {
+      auto *NS = readDeclAs<NamespaceBaseDecl>();
       SourceRange Range = readSourceRange();
       Builder.Extend(Context, NS, Range.getBegin(), Range.getEnd());
       break;
     }
 
-    case NestedNameSpecifier::NamespaceAlias: {
-      NamespaceAliasDecl *Alias = readDeclAs<NamespaceAliasDecl>();
-      SourceRange Range = readSourceRange();
-      Builder.Extend(Context, Alias, Range.getBegin(), Range.getEnd());
-      break;
-    }
-
-    case NestedNameSpecifier::TypeSpec: {
+    case NestedNameSpecifier::Kind::Type: {
       TypeSourceInfo *T = readTypeSourceInfo();
       if (!T)
         return NestedNameSpecifierLoc();
       SourceLocation ColonColonLoc = readSourceLocation();
-      Builder.Extend(Context, T->getTypeLoc(), ColonColonLoc);
+      Builder.Make(Context, T->getTypeLoc(), ColonColonLoc);
       break;
     }
 
-    case NestedNameSpecifier::Global: {
+    case NestedNameSpecifier::Kind::Global: {
       SourceLocation ColonColonLoc = readSourceLocation();
       Builder.MakeGlobal(Context, ColonColonLoc);
       break;
     }
 
-    case NestedNameSpecifier::Super: {
+    case NestedNameSpecifier::Kind::Super: {
       CXXRecordDecl *RD = readDeclAs<CXXRecordDecl>();
       SourceRange Range = readSourceRange();
       Builder.MakeSuper(Context, RD, Range.getBegin(), Range.getEnd());
       break;
     }
+
+    case NestedNameSpecifier::Kind::Null:
+      llvm_unreachable("unexpected null nested name specifier");
     }
   }
 
@@ -10416,12 +10411,7 @@ void ASTReader::finishPendingActions() {
   // happen now, after the redeclaration chains have been fully wired.
   for (Decl *D : PendingDefinitions) {
     if (TagDecl *TD = dyn_cast<TagDecl>(D)) {
-      if (const TagType *TagT = dyn_cast<TagType>(TD->getTypeForDecl())) {
-        // Make sure that the TagType points at the definition.
-        const_cast<TagType*>(TagT)->decl = TD;
-      }
-
-      if (auto RD = dyn_cast<CXXRecordDecl>(D)) {
+      if (auto *RD = dyn_cast<CXXRecordDecl>(TD)) {
         for (auto *R = getMostRecentExistingDecl(RD); R;
              R = R->getPreviousDecl()) {
           assert((R == D) ==
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index b918bfbd549c3..922440e949756 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -538,7 +538,11 @@ void ASTDeclReader::Visit(Decl *D) {
 
   if (auto *TD = dyn_cast<TypeDecl>(D)) {
     // We have a fully initialized TypeDecl. Read its type now.
-    TD->setTypeForDecl(Reader.GetType(DeferredTypeID).getTypePtrOrNull());
+    if (isa<TagDecl, TypedefDecl, TypeAliasDecl>(TD))
+      assert(DeferredTypeID == 0 &&
+             "Deferred type not used for TagDecls and Typedefs");
+    else
+      TD->setTypeForDecl(Reader.GetType(DeferredTypeID).getTypePtrOrNull());
 
     // If this is a tag declaration with a typedef name for linkage, it's safe
     // to load that typedef now.
@@ -695,7 +699,8 @@ void ASTDeclReader::VisitTypeDecl(TypeDecl *TD) {
   VisitNamedDecl(TD);
   TD->setLocStart(readSourceLocation());
   // Delay type reading until after we have fully initialized the decl.
-  DeferredTypeID = Record.getGlobalTypeID(Record.readInt());
+  if (!isa<TagDecl, TypedefDecl, TypeAliasDecl>(TD))
+    DeferredTypeID = Record.getGlobalTypeID(Record.readInt());
 }
 
 RedeclarableResult ASTDeclReader::VisitTypedefNameDecl(TypedefNameDecl *TD) {
@@ -1889,7 +1894,7 @@ void ASTDeclReader::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
   D->NamespaceLoc = readSourceLocation();
   D->IdentLoc = readSourceLocation();
   D->QualifierLoc = Record.readNestedNameSpecifierLoc();
-  D->Namespace = readDeclAs<NamedDecl>();
+  D->Namespace = readDeclAs<NamespaceBaseDecl>();
   mergeRedeclarable(D, Redecl);
 }
 
@@ -2236,15 +2241,6 @@ RedeclarableResult ASTDeclReader::VisitCXXRecordDeclImpl(CXXRecordDecl *D) {
     // Merged when we merge the template.
     auto *Template = readDeclAs<ClassTemplateDecl>();
     D->TemplateOrInstantiation = Template;
-    if (!Template->getTemplatedDecl()) {
-      // We've not actually loaded the ClassTemplateDecl yet, because we're
-      // currently being loaded as its pattern. Rely on it to set up our
-      // TypeForDecl (see VisitClassTemplateDecl).
-      //
-      // Beware: we do not yet know our canonical declaration, and may still
-      // get merged once the surrounding class template has got off the ground.
-      DeferredTypeID = 0;
-    }
     break;
   }
   case CXXRecMemberSpecialization: {
@@ -2478,14 +2474,6 @@ void ASTDeclReader::VisitClassTemplateDecl(ClassTemplateDecl *D) {
     ReadSpecializations(*Loc.F, D, Loc.F->DeclsCursor, /*IsPartial=*/false);
     ReadSpecializations(*Loc.F, D, Loc.F->DeclsCursor, /*IsPartial=*/true);
   }
-
-  if (D->getTemplatedDecl()->TemplateOrInstantiation) {
-    // We were loaded before our templated declaration was. We've not set up
-    // its corresponding type yet (see VisitCXXRecordDeclImpl), so reconstruct
-    // it now.
-    Reader.getContext().getInjectedClassNameType(
-        D->getTemplatedDecl(), D->getInjectedClassNameSpecialization());
-  }
 }
 
 void ASTDeclReader::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 1a20fc9595dce..2d41482327c15 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -345,6 +345,7 @@ class TypeLocWriter : public TypeLocVisitor<TypeLocWriter> {
 
   void VisitArrayTypeLoc(ArrayTypeLoc TyLoc);
   void VisitFunctionTypeLoc(FunctionTypeLoc TyLoc);
+  void VisitTagTypeLoc(TagTypeLoc TL);
 };
 
 } // namespace
@@ -490,14 +491,20 @@ void TypeLocWriter::VisitFunctionNoProtoTypeLoc(FunctionNoProtoTypeLoc TL) {
 }
 
 void TypeLocWriter::VisitUnresolvedUsingTypeLoc(UnresolvedUsingTypeLoc TL) {
+  addSourceLocation(TL.getElaboratedKeywordLoc());
+  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
   addSourceLocation(TL.getNameLoc());
 }
 
 void TypeLocWriter::VisitUsingTypeLoc(UsingTypeLoc TL) {
+  addSourceLocation(TL.getElaboratedKeywordLoc());
+  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
   addSourceLocation(TL.getNameLoc());
 }
 
 void TypeLocWriter::VisitTypedefTypeLoc(TypedefTypeLoc TL) {
+  addSourceLocation(TL.getElaboratedKeywordLoc());
+  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
   addSourceLocation(TL.getNameLoc());
 }
 
@@ -564,17 +571,27 @@ void TypeLocWriter::VisitAutoTypeLoc(AutoTypeLoc TL) {
 
 void TypeLocWriter::VisitDeducedTemplateSpecializationTypeLoc(
     DeducedTemplateSpecializationTypeLoc TL) {
+  addSourceLocation(TL.getElaboratedKWLoc());
+  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
   addSourceLocation(TL.getTemplateNameLoc());
 }
 
-void TypeLocWriter::VisitRecordTypeLoc(RecordTypeLoc TL) {
+void TypeLocWriter::VisitTagTypeLoc(TagTypeLoc TL) {
+  addSourceLocation(TL.getElaboratedKeywordLoc());
+  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
   addSourceLocation(TL.getNameLoc());
 }
 
-void TypeLocWriter::VisitEnumTypeLoc(EnumTypeLoc TL) {
-  addSourceLocation(TL.getNameLoc());
+void TypeLocWriter::VisitRecordTypeLoc(RecordTypeLoc TL) {
+  VisitTagTypeLoc(TL);
+}
+
+void TypeLocWriter::VisitInjectedClassNameTypeLoc(InjectedClassNameTypeLoc TL) {
+  VisitTagTypeLoc(TL);
 }
 
+void TypeLocWriter::VisitEnumTypeLoc(EnumTypeLoc TL) { VisitTagTypeLoc(TL); }
+
 void TypeLocWriter::VisitAttributedTypeLoc(AttributedTypeLoc TL) {
   Record.AddAttr(TL.getAttr());
 }
@@ -612,13 +629,14 @@ void TypeLocWriter::VisitSubstTemplateTypeParmPackTypeLoc(
 
 void TypeLocWriter::VisitTemplateSpecializationTypeLoc(
                                            TemplateSpecializationTypeLoc TL) {
+  addSourceLocation(TL.getElaboratedKeywordLoc());
+  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
   addSourceLocation(TL.getTemplateKeywordLoc());
   addSourceLocation(TL.getTemplateNameLoc());
   addSourceLocation(TL.getLAngleLoc());
   addSourceLocation(TL.getRAngleLoc());
   for (unsigned i = 0, e = TL.getNumArgs(); i != e; ++i)
-    Record.AddTemplateArgumentLocInfo(TL.getArgLoc(i).getArgument().getKind(),
-                                      TL.getArgLoc(i).getLocInfo());
+    Record.AddTemplateArgumentLocInfo(TL.getArgLoc(i));
 }
 
 void TypeLocWriter::VisitParenTypeLoc(ParenTypeLoc TL) {
@@ -630,15 +648,6 @@ void TypeLocWriter::VisitMacroQualifiedTypeLoc(MacroQualifiedTypeLoc TL) {
   addSourceLocation(TL.getExpansionLoc());
 }
 
-void TypeLocWriter::VisitElaboratedTypeLoc(ElaboratedTypeLoc TL) {
-  addSourceLocation(TL.getElaboratedKeywordLoc());
-  Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
-}
-
-void TypeLocWriter::VisitInjectedClassNameTypeLoc(InjectedClassNameTypeLoc TL) {
-  addSourceLocation(TL.getNameLoc());
-}
-
 void TypeLocWriter::VisitDependentNameTypeLoc(DependentNameTypeLoc TL) {
   addSourceLocation(TL.getElaboratedKeywordLoc());
   Record.AddNestedNameSpecifierLoc(TL.getQualifierLoc());
@@ -654,8 +663,7 @@ void TypeLocWriter::VisitDependentTemplateSpecializationTypeLoc(
   addSourceLocation(TL.getLAngleLoc());
   addSourceLocation(TL.getRAngleLoc());
   for (unsigned I = 0, E = TL.getNumArgs(); I != E; ++I)
-    Record.AddTemplateArgumentLocInfo(TL.getArgLoc(I).getArgument().getKind(),
-                                      TL.getArgLoc(I).getLocInfo());
+    Record.AddTemplateArgumentLocInfo(TL.getArgLoc(I));
 }
 
 void TypeLocWriter::VisitPackExpansionTypeLoc(PackExpansionTypeLoc TL) {
@@ -1033,7 +1041,6 @@ void ASTWriter::WriteBlockInfoBlock() {
   RECORD(TYPE_OBJC_INTERFACE);
   RECORD(TYPE_OBJC_OBJECT_POINTER);
   RECORD(TYPE_DECLTYPE);
-  RECORD(TYPE_ELABORATED);
   RECORD(TYPE_SUBST_TEMPLATE_TYPE_PARM);
   RECORD(TYPE_UNRESOLVED_USING);
   RECORD(TYPE_INJECTED_CLASS_NAME);
@@ -6749,22 +6756,22 @@ void ASTRecordWriter::AddCXXTemporary(const CXXTemporary *Temp) {
 }
 
 void ASTRecordWriter::AddTemplateArgumentLocInfo(
-    TemplateArgument::ArgKind Kind, const TemplateArgumentLocInfo &Arg) {
-  switch (Kind) {
+    const TemplateArgumentLoc &Arg) {
+  const TemplateArgumentLocInfo &Info = Arg.getLocInfo();
+  switch (auto K = Arg.getArgument().getKind()) {
   case TemplateArgument::Expression:
-    AddStmt(Arg.getAsExpr());
+    AddStmt(Info.getAsExpr());
     break;
   case TemplateArgument::Type:
-    AddTypeSourceInfo(Arg.getAsTypeSourceInfo());
+    AddTypeSourceInfo(Info.getAsTypeSourceInfo());
     break;
   case TemplateArgument::Template:
-    AddNestedNameSpecifierLoc(Arg.getTemplateQualifierLoc());
-    AddSourceLocation(Arg.getTemplateNameLoc());
-    break;
   case TemplateArgument::TemplateExpansion:
+    AddSourceLocation(Arg.getTemplateKWLoc());
     AddNestedNameSpecifierLoc(Arg.getTemplateQualifierLoc());
     AddSourceLocation(Arg.getTemplateNameLoc());
-    AddSourceLocation(Arg.getTemplateEllipsisLoc());
+    if (K == TemplateArgument::TemplateExpansion)
+      AddSourceLocation(Arg.getTemplateEllipsisLoc());
     break;
   case TemplateArgument::Null:
   case TemplateArgument::Integral:
@@ -6787,7 +6794,7 @@ void ASTRecordWriter::AddTemplateArgumentLoc(const TemplateArgumentLoc &Arg) {
     if (InfoHasSameExpr)
       return; // Avoid storing the same expr twice.
   }
-  AddTemplateArgumentLocInfo(Arg.getArgument().getKind(), Arg.getLocInfo());
+  AddTemplateArgumentLocInfo(Arg);
 }
 
 void ASTRecordWriter::AddTypeSourceInfo(TypeSourceInfo *TInfo) {
@@ -7045,54 +7052,50 @@ void ASTRecordWriter::AddQualifierInfo(const QualifierInfo &Info) {
     AddTemplateParameterList(Info.TemplParamLists[i]);
 }
 
-void ASTRecordWriter::AddNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS) {
+void ASTRecordWriter::AddNestedNameSpecifierLoc(
+    NestedNameSpecifierLoc QualifierLoc) {
   // Nested name specifiers usually aren't too long. I think that 8 would
   // typically accommodate the vast majority.
   SmallVector<NestedNameSpecifierLoc , 8> NestedNames;
 
   // Push each of the nested-name-specifiers's onto a stack for
   // serialization in reverse order.
-  while (NNS) {
-    NestedNames.push_back(NNS);
-    NNS = NNS.getPrefix();
+  while (QualifierLoc) {
+    NestedNames.push_back(QualifierLoc);
+    QualifierLoc = QualifierLoc.getAsNamespaceAndPrefix().Prefix;
   }
 
   Record->push_back(NestedNames.size());
   while(!NestedNames.empty()) {
-    NNS = NestedNames.pop_back_val();
-    NestedNameSpecifier::SpecifierKind Kind
-      = NNS.getNestedNameSpecifier()->getKind();
-    Record->push_back(Kind);
+    QualifierLoc = NestedNames.pop_back_val();
+    NestedNameSpecifier Qualifier = QualifierLoc.getNestedNameSpecifier();
+    NestedNameSpecifier::Kind Kind = Qualifier.getKind();
+    Record->push_back(llvm::to_underlying(Kind));
     switch (Kind) {
-    case NestedNameSpecifier::Identifier:
-      AddIdentifierRef(NNS.getNestedNameSpecifier()->getAsIdentifier());
-      AddSourceRange(NNS.getLocalSourceRange());
+    case NestedNameSpecifier::Kind::Namespace:
+      AddDeclRef(Qualifier.getAsNamespaceAndPrefix().Namespace);
+      AddSourceRange(QualifierLoc.getLocalSourceRange());
       break;
 
-    case NestedNameSpecifier::Namespace:
-      AddDeclRef(NNS.getNestedNameSpecifier()->getAsNamespace());
-      AddSourceRange(NNS.getLocalSourceRange());
-      break;
-
-    case NestedNameSpecifier::NamespaceAlias:
-      AddDeclRef(NNS.getNestedNameSpecifier()->getAsNamespaceAlias());
-      AddSourceRange(NNS.getLocalSourceRange());
+    case NestedNameSpecifier::Kind::Type: {
+      TypeLoc TL = QualifierLoc.castAsTypeLoc();
+      AddTypeRef(TL.getType());
+      AddTypeLoc(TL);
+      AddSourceLocation(QualifierLoc.getLocalSourceRange().getEnd());
       break;
+    }
 
-    case NestedNameSpecifier::TypeSpec:
-      AddTypeRef(NNS.getTypeLoc().getType());
-      AddTypeLoc(NNS.getTypeLoc());
-      AddSourceLocation(NNS.getLocalSourceRange().getEnd());
+    case NestedNameSpecifier::Kind::Global:
+      AddSourceLocation(QualifierLoc.getLocalSourceRange().getEnd());
       break;
 
-    case NestedNameSpecifier::Global:
-      AddSourceLocation(NNS.getLocalSourceRange().getEnd());
+    case NestedNameSpecifier::Kind::Super:
+      AddDeclRef(Qualifier.getAsSuper());
+      AddSourceRange(QualifierLoc.getLocalSourceRange());
       break;
 
-    case NestedNameSpecifier::Super:
-      AddDeclRef(NNS.getNestedNameSpecifier()->getAsRecordDecl());
-      AddSourceRange(NNS.getLocalSourceRange());
-      break;
+    case NestedNameSpecifier::Kind::Null:
+      llvm_unreachable("unexpected null nested name specifier");
     }
   }
 }
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index e414910469a64..1ce75eba525b1 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -524,7 +524,7 @@ void ASTDeclWriter::VisitDecl(Decl *D) {
   // bits actually. However, if we changed the order to be 0x0f, then we can
   // store it as 0b001111, which takes 6 bits only now.
   DeclBits.addBits((uint64_t)D->getModuleOwnershipKind(), /*BitWidth=*/3);
-  DeclBits.addBit(D->isReferenced());
+  DeclBits.addBit(D->isThisDeclarationReferenced());
   DeclBits.addBit(D->isUsed(false));
   DeclBits.addBits(D->getAccess(), /*BitWidth=*/2);
   DeclBits.addBit(D->isImplicit());
@@ -601,7 +601,8 @@ void ASTDeclWriter::VisitNamedDecl(NamedDecl *D) {
 void ASTDeclWriter::VisitTypeDecl(TypeDecl *D) {
   VisitNamedDecl(D);
   Record.AddSourceLocation(D->getBeginLoc());
-  Record.AddTypeRef(QualType(D->getTypeForDecl(), 0));
+  if (!isa<TagDecl, TypedefDecl, TypeAliasDecl>(D))
+    Record.AddTypeRef(QualType(D->getTypeForDecl(), 0));
 }
 
 void ASTDeclWriter::VisitTypedefNameDecl(TypedefNameDecl *D) {
@@ -2560,7 +2561,6 @@ void ASTWriter::WriteDeclAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(0));                       // AnonDeclNumber
   // TypeDecl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Source Location
-  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Type Ref
   // TagDecl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // IdentifierNamespace
   Abv->Add(BitCodeAbbrevOp(
@@ -2606,7 +2606,6 @@ void ASTWriter::WriteDeclAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(0));                       // AnonDeclNumber
   // TypeDecl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Source Location
-  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Type Ref
   // TagDecl
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // IdentifierNamespace
   Abv->Add(BitCodeAbbrevOp(
diff --git a/clang/lib/Serialization/TemplateArgumentHasher.cpp b/clang/lib/Serialization/TemplateArgumentHasher.cpp
index c56138e8893c1..3e8ffea78c2f1 100644
--- a/clang/lib/Serialization/TemplateArgumentHasher.cpp
+++ b/clang/lib/Serialization/TemplateArgumentHasher.cpp
@@ -320,7 +320,7 @@ class TypeVisitorHelper : public TypeVisitor<TypeVisitorHelper> {
 
   void VisitMemberPointerType(const MemberPointerType *T) {
     AddQualType(T->getPointeeType());
-    AddType(T->getQualifier()->getAsType());
+    AddType(T->getQualifier().getAsType());
     if (auto *RD = T->getMostRecentCXXRecordDecl())
       AddDecl(RD->getCanonicalDecl());
   }
@@ -358,7 +358,7 @@ class TypeVisitorHelper : public TypeVisitor<TypeVisitorHelper> {
     AddQualType(T->getReplacementType());
   }
 
-  void VisitTagType(const TagType *T) { AddDecl(T->getDecl()); }
+  void VisitTagType(const TagType *T) { AddDecl(T->getOriginalDecl()); }
 
   void VisitRecordType(const RecordType *T) { VisitTagType(T); }
   void VisitEnumType(const EnumType *T) { VisitTagType(T); }
@@ -379,10 +379,6 @@ class TypeVisitorHelper : public TypeVisitor<TypeVisitorHelper> {
 
   void VisitTypedefType(const TypedefType *T) { AddDecl(T->getDecl()); }
 
-  void VisitElaboratedType(const ElaboratedType *T) {
-    AddQualType(T->getNamedType());
-  }
-
   void VisitUnaryTransformType(const UnaryTransformType *T) {
     AddQualType(T->getUnderlyingType());
     AddQualType(T->getBaseType());
diff --git a/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
index 23935647a5826..731e506a5d259 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
@@ -250,7 +250,7 @@ class FindUninitializedField {
   bool Find(const TypedValueRegion *R) {
     QualType T = R->getValueType();
     if (const RecordType *RT = T->getAsStructureType()) {
-      const RecordDecl *RD = RT->getDecl()->getDefinition();
+      const RecordDecl *RD = RT->getOriginalDecl()->getDefinition();
       assert(RD && "Referred record has no definition");
       for (const auto *I : RD->fields()) {
         if (I->isUnnamedBitField())
diff --git a/clang/lib/StaticAnalyzer/Checkers/CastSizeChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/CastSizeChecker.cpp
index 0b52c9bd8ac2a..90c6537d71d9d 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CastSizeChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CastSizeChecker.cpp
@@ -53,7 +53,7 @@ static bool evenFlexibleArraySize(ASTContext &Ctx, CharUnits RegionSize,
   if (!RT)
     return false;
 
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
   RecordDecl::field_iterator Iter(RD->field_begin());
   RecordDecl::field_iterator End(RD->field_end());
   const FieldDecl *Last = nullptr;
diff --git a/clang/lib/StaticAnalyzer/Checkers/DynamicTypePropagation.cpp b/clang/lib/StaticAnalyzer/Checkers/DynamicTypePropagation.cpp
index 4982cd59b0a4a..cee744aecb686 100644
--- a/clang/lib/StaticAnalyzer/Checkers/DynamicTypePropagation.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/DynamicTypePropagation.cpp
@@ -245,7 +245,7 @@ static void recordFixedType(const MemRegion *Region, const CXXMethodDecl *MD,
   assert(MD);
 
   ASTContext &Ctx = C.getASTContext();
-  QualType Ty = Ctx.getPointerType(Ctx.getRecordType(MD->getParent()));
+  CanQualType Ty = Ctx.getPointerType(Ctx.getCanonicalTagType(MD->getParent()));
 
   ProgramStateRef State = C.getState();
   State = setDynamicTypeInfo(State, Region, Ty, /*CanBeSubClassed=*/false);
diff --git a/clang/lib/StaticAnalyzer/Checkers/EnumCastOutOfRangeChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/EnumCastOutOfRangeChecker.cpp
index 355e82e465e82..054b2e96bd13b 100644
--- a/clang/lib/StaticAnalyzer/Checkers/EnumCastOutOfRangeChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/EnumCastOutOfRangeChecker.cpp
@@ -148,7 +148,8 @@ void EnumCastOutOfRangeChecker::checkPreStmt(const CastExpr *CE,
   // If the isEnumeralType() returned true, then the declaration must exist
   // even if it is a stub declaration. It is up to the getDeclValuesForEnum()
   // function to handle this.
-  const EnumDecl *ED = T->castAs<EnumType>()->getDecl();
+  const EnumDecl *ED =
+      T->castAs<EnumType>()->getOriginalDecl()->getDefinitionOrSelf();
 
   // [[clang::flag_enum]] annotated enums are by definition should be ignored.
   if (ED->hasAttr<FlagEnumAttr>())
diff --git a/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
index 1cb3848cfed2a..828b6f91d81c2 100644
--- a/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
@@ -47,9 +47,6 @@ static bool InNamespace(const Decl *D, StringRef NS) {
 }
 
 static bool IsStdString(QualType T) {
-  if (const ElaboratedType *QT = T->getAs<ElaboratedType>())
-    T = QT->getNamedType();
-
   const TypedefType *TT = T->getAs<TypedefType>();
   if (!TT)
     return false;
@@ -201,7 +198,7 @@ static bool IsPartOfAST(const CXXRecordDecl *R) {
   for (const auto &BS : R->bases()) {
     QualType T = BS.getType();
     if (const RecordType *baseT = T->getAs<RecordType>()) {
-      CXXRecordDecl *baseD = cast<CXXRecordDecl>(baseT->getDecl());
+      CXXRecordDecl *baseD = cast<CXXRecordDecl>(baseT->getOriginalDecl());
       if (IsPartOfAST(baseD))
         return true;
     }
@@ -247,7 +244,7 @@ void ASTFieldVisitor::Visit(FieldDecl *D) {
     ReportError(T);
 
   if (const RecordType *RT = T->getAs<RecordType>()) {
-    const RecordDecl *RD = RT->getDecl()->getDefinition();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinition();
     for (auto *I : RD->fields())
       Visit(I);
   }
diff --git a/clang/lib/StaticAnalyzer/Checkers/NonNullParamChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/NonNullParamChecker.cpp
index 0aea981252259..b1a7cd7620424 100644
--- a/clang/lib/StaticAnalyzer/Checkers/NonNullParamChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/NonNullParamChecker.cpp
@@ -148,7 +148,9 @@ void NonNullParamChecker::checkPreCall(const CallEvent &Call,
 
       QualType T = ArgE->getType();
       const RecordType *UT = T->getAsUnionType();
-      if (!UT || !UT->getDecl()->hasAttr<TransparentUnionAttr>())
+      if (!UT || !UT->getOriginalDecl()
+                      ->getMostRecentDecl()
+                      ->hasAttr<TransparentUnionAttr>())
         continue;
 
       auto CSV = DV->getAs<nonloc::CompoundVal>();
diff --git a/clang/lib/StaticAnalyzer/Checkers/NonnullGlobalConstantsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/NonnullGlobalConstantsChecker.cpp
index 7927967093dcb..b5e32495235aa 100644
--- a/clang/lib/StaticAnalyzer/Checkers/NonnullGlobalConstantsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/NonnullGlobalConstantsChecker.cpp
@@ -114,10 +114,7 @@ bool NonnullGlobalConstantsChecker::isGlobalConstString(SVal V) const {
       if (AT->getAttrKind() == attr::TypeNonNull)
         return true;
       Ty = AT->getModifiedType();
-    } else if (const auto *ET = dyn_cast<ElaboratedType>(T)) {
-      const auto *TT = dyn_cast<TypedefType>(ET->getNamedType());
-      if (!TT)
-        return false;
+    } else if (const auto *TT = dyn_cast<TypedefType>(T)) {
       Ty = TT->getDecl()->getUnderlyingType();
       // It is sufficient for any intermediate typedef
       // to be classified const.
diff --git a/clang/lib/StaticAnalyzer/Checkers/NumberObjectConversionChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/NumberObjectConversionChecker.cpp
index f217520d8f4a0..68ab22a44e7b6 100644
--- a/clang/lib/StaticAnalyzer/Checkers/NumberObjectConversionChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/NumberObjectConversionChecker.cpp
@@ -197,9 +197,9 @@ void NumberObjectConversionChecker::checkASTCodeBody(const Decl *D,
                                                      BugReporter &BR) const {
   // Currently this matches CoreFoundation opaque pointer typedefs.
   auto CSuspiciousNumberObjectExprM = expr(ignoringParenImpCasts(
-      expr(hasType(elaboratedType(namesType(typedefType(
+      expr(hasType(typedefType(
                hasDeclaration(anyOf(typedefDecl(hasName("CFNumberRef")),
-                                    typedefDecl(hasName("CFBooleanRef")))))))))
+                                    typedefDecl(hasName("CFBooleanRef")))))))
           .bind("c_object")));
 
   // Currently this matches XNU kernel number-object pointers.
@@ -238,8 +238,7 @@ void NumberObjectConversionChecker::checkASTCodeBody(const Decl *D,
 
   // The .bind here is in order to compose the error message more accurately.
   auto ObjCSuspiciousScalarBooleanTypeM =
-      qualType(elaboratedType(namesType(
-                   typedefType(hasDeclaration(typedefDecl(hasName("BOOL")))))))
+      qualType(typedefType(hasDeclaration(typedefDecl(hasName("BOOL")))))
           .bind("objc_bool_type");
 
   // The .bind here is in order to compose the error message more accurately.
@@ -252,8 +251,8 @@ void NumberObjectConversionChecker::checkASTCodeBody(const Decl *D,
   // for storing pointers.
   auto SuspiciousScalarNumberTypeM =
       qualType(hasCanonicalType(isInteger()),
-               unless(elaboratedType(namesType(typedefType(hasDeclaration(
-                   typedefDecl(matchesName("^::u?intptr_t$"))))))))
+               unless(typedefType(
+                   hasDeclaration(typedefDecl(matchesName("^::u?intptr_t$"))))))
           .bind("int_type");
 
   auto SuspiciousScalarTypeM =
diff --git a/clang/lib/StaticAnalyzer/Checkers/PaddingChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
index d4efbdd54fc22..7ef659518ab1b 100644
--- a/clang/lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
@@ -104,7 +104,7 @@ class PaddingChecker : public Checker<check::ASTDecl<TranslationUnitDecl>> {
       // There is not enough excess padding to trigger a warning.
       return;
     }
-    reportRecord(RD, BaselinePad, OptimalPad, OptimalFieldsOrder);
+    reportRecord(ASTContext, RD, BaselinePad, OptimalPad, OptimalFieldsOrder);
   }
 
   /// Look for arrays of overly padded types. If the padding of the
@@ -123,7 +123,7 @@ class PaddingChecker : public Checker<check::ASTDecl<TranslationUnitDecl>> {
       return;
 
     // TODO: Recurse into the fields to see if they have excess padding.
-    visitRecord(RT->getDecl(), Elts);
+    visitRecord(RT->getOriginalDecl()->getDefinitionOrSelf(), Elts);
   }
 
   bool shouldSkipDecl(const RecordDecl *RD) const {
@@ -159,9 +159,7 @@ class PaddingChecker : public Checker<check::ASTDecl<TranslationUnitDecl>> {
         return true;
       // Can't layout a template, so skip it. We do still layout the
       // instantiations though.
-      if (CXXRD->getTypeForDecl()->isDependentType())
-        return true;
-      if (CXXRD->getTypeForDecl()->isInstantiationDependentType())
+      if (CXXRD->isDependentType())
         return true;
     }
     // How do you reorder fields if you haven't got any?
@@ -306,14 +304,14 @@ class PaddingChecker : public Checker<check::ASTDecl<TranslationUnitDecl>> {
   }
 
   void reportRecord(
-      const RecordDecl *RD, CharUnits BaselinePad, CharUnits OptimalPad,
+      const ASTContext &Ctx, const RecordDecl *RD, CharUnits BaselinePad,
+      CharUnits OptimalPad,
       const SmallVector<const FieldDecl *, 20> &OptimalFieldsOrder) const {
     SmallString<100> Buf;
     llvm::raw_svector_ostream Os(Buf);
     Os << "Excessive padding in '";
-    Os << QualType::getAsString(RD->getTypeForDecl(), Qualifiers(),
-                                LangOptions())
-       << "'";
+    QualType(Ctx.getCanonicalTagType(RD)).print(Os, LangOptions());
+    Os << "'";
 
     if (auto *TSD = dyn_cast<ClassTemplateSpecializationDecl>(RD)) {
       // TODO: make this show up better in the console output and in
diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
index 1c748f9bc1828..c82618fc7a3fb 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
@@ -1589,7 +1589,7 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
       // and we have a TypedefDecl with the name 'FILE'.
       for (Decl *D : LookupRes)
         if (auto *TD = dyn_cast<TypedefNameDecl>(D))
-          return ACtx.getTypeDeclType(TD).getCanonicalType();
+          return ACtx.getCanonicalTypeDeclType(TD);
 
       // Find the first TypeDecl.
       // There maybe cases when a function has the same name as a struct.
@@ -1597,7 +1597,7 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
       //   int stat(const char *restrict path, struct stat *restrict buf);
       for (Decl *D : LookupRes)
         if (auto *TD = dyn_cast<TypeDecl>(D))
-          return ACtx.getTypeDeclType(TD).getCanonicalType();
+          return ACtx.getCanonicalTypeDeclType(TD);
       return std::nullopt;
     }
   } lookupTy(ACtx);
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
index 72199af2f80a5..36c12582a5787 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
@@ -181,10 +181,6 @@ template <typename Predicate>
 static bool isPtrOfType(const clang::QualType T, Predicate Pred) {
   QualType type = T;
   while (!type.isNull()) {
-    if (auto *elaboratedT = type->getAs<ElaboratedType>()) {
-      type = elaboratedT->desugar();
-      continue;
-    }
     if (auto *SpecialT = type->getAs<TemplateSpecializationType>()) {
       auto *Decl = SpecialT->getTemplateName().getAsTemplateDecl();
       return Decl && Pred(Decl->getNameAsString());
@@ -248,13 +244,15 @@ void RetainTypeChecker::visitTypedef(const TypedefDecl *TD) {
   const RecordType *RT = PointeeQT->getAs<RecordType>();
   if (!RT) {
     if (TD->hasAttr<ObjCBridgeAttr>() || TD->hasAttr<ObjCBridgeMutableAttr>()) {
-      if (auto *Type = TD->getTypeForDecl())
-        RecordlessTypes.insert(Type);
+      RecordlessTypes.insert(TD->getASTContext()
+                                 .getTypedefType(ElaboratedTypeKeyword::None,
+                                                 /*Qualifier=*/std::nullopt, TD)
+                                 .getTypePtr());
     }
     return;
   }
 
-  for (auto *Redecl : RT->getDecl()->getMostRecentDecl()->redecls()) {
+  for (auto *Redecl : RT->getOriginalDecl()->getMostRecentDecl()->redecls()) {
     if (Redecl->getAttr<ObjCBridgeAttr>() ||
         Redecl->getAttr<ObjCBridgeMutableAttr>()) {
       CFPointees.insert(RT);
@@ -266,21 +264,10 @@ void RetainTypeChecker::visitTypedef(const TypedefDecl *TD) {
 bool RetainTypeChecker::isUnretained(const QualType QT, bool ignoreARC) {
   if (ento::cocoa::isCocoaObjectRef(QT) && (!IsARCEnabled || ignoreARC))
     return true;
-  auto CanonicalType = QT.getCanonicalType();
-  auto PointeeType = CanonicalType->getPointeeType();
-  auto *RT = dyn_cast_or_null<RecordType>(PointeeType.getTypePtrOrNull());
-  if (!RT) {
-    auto *Type = QT.getTypePtrOrNull();
-    while (Type) {
-      if (RecordlessTypes.contains(Type))
-        return true;
-      auto *ET = dyn_cast_or_null<ElaboratedType>(Type);
-      if (!ET)
-        break;
-      Type = ET->desugar().getTypePtrOrNull();
-    }
-  }
-  return RT && CFPointees.contains(RT);
+  if (auto *RT = dyn_cast_or_null<RecordType>(
+          QT.getCanonicalType()->getPointeeType().getTypePtrOrNull()))
+    return CFPointees.contains(RT);
+  return RecordlessTypes.contains(QT.getTypePtr());
 }
 
 std::optional<bool> isUnretained(const QualType T, bool IsARCEnabled) {
@@ -306,7 +293,7 @@ std::optional<bool> isUnretained(const QualType T, bool IsARCEnabled) {
   auto *Record = PointeeType->getAsStructureType();
   if (!Record)
     return false;
-  auto *Decl = Record->getDecl();
+  auto *Decl = Record->getOriginalDecl();
   if (!Decl)
     return false;
   auto TypeName = Decl->getName();
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp
index 98c587d62978b..6f3a280971cb8 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp
@@ -113,10 +113,6 @@ class DerefFuncDeleteExprVisitor
         auto CastType = Cast->getType();
         if (auto *PtrType = dyn_cast<PointerType>(CastType)) {
           auto PointeeType = PtrType->getPointeeType();
-          while (auto *ET = dyn_cast<ElaboratedType>(PointeeType)) {
-            if (ET->isSugared())
-              PointeeType = ET->desugar();
-          }
           if (auto *ParmType = dyn_cast<TemplateTypeParmType>(PointeeType)) {
             if (ArgList) {
               auto ParmIndex = ParmType->getIndex();
@@ -125,13 +121,13 @@ class DerefFuncDeleteExprVisitor
                 return true;
             }
           } else if (auto *RD = dyn_cast<RecordType>(PointeeType)) {
-            if (RD->getDecl() == ClassDecl)
+            if (declaresSameEntity(RD->getOriginalDecl(), ClassDecl))
               return true;
           } else if (auto *ST =
                          dyn_cast<SubstTemplateTypeParmType>(PointeeType)) {
             auto Type = ST->getReplacementType();
             if (auto *RD = dyn_cast<RecordType>(Type)) {
-              if (RD->getDecl() == ClassDecl)
+              if (declaresSameEntity(RD->getOriginalDecl(), ClassDecl))
                 return true;
             }
           }
diff --git a/clang/lib/StaticAnalyzer/Core/CallEvent.cpp b/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
index 34fcb9b64d555..180056cf68b64 100644
--- a/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
+++ b/clang/lib/StaticAnalyzer/Core/CallEvent.cpp
@@ -89,7 +89,7 @@ static bool isCallback(QualType T) {
     T = T->getPointeeType();
 
   if (const RecordType *RT = T->getAsStructureType()) {
-    const RecordDecl *RD = RT->getDecl();
+    const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
     for (const auto *I : RD->fields()) {
       QualType FieldT = I->getType();
       if (FieldT->isBlockPointerType() || FieldT->isFunctionPointerType())
@@ -391,7 +391,9 @@ bool CallEvent::isVariadic(const Decl *D) {
 
 static bool isTransparentUnion(QualType T) {
   const RecordType *UT = T->getAsUnionType();
-  return UT && UT->getDecl()->hasAttr<TransparentUnionAttr>();
+  return UT && UT->getOriginalDecl()
+                   ->getMostRecentDecl()
+                   ->hasAttr<TransparentUnionAttr>();
 }
 
 // In some cases, symbolic cases should be transformed before we associate
@@ -843,7 +845,7 @@ void CXXInstanceCall::getInitialStackFrameContents(
     if (MD->getCanonicalDecl() != getDecl()->getCanonicalDecl()) {
       ASTContext &Ctx = SVB.getContext();
       const CXXRecordDecl *Class = MD->getParent();
-      QualType Ty = Ctx.getPointerType(Ctx.getRecordType(Class));
+      CanQualType Ty = Ctx.getPointerType(Ctx.getCanonicalTagType(Class));
 
       // FIXME: CallEvent maybe shouldn't be directly accessing StoreManager.
       std::optional<SVal> V =
@@ -854,7 +856,8 @@ void CXXInstanceCall::getInitialStackFrameContents(
         // Fall back to a generic pointer cast for this-value.
         const CXXMethodDecl *StaticMD = cast<CXXMethodDecl>(getDecl());
         const CXXRecordDecl *StaticClass = StaticMD->getParent();
-        QualType StaticTy = Ctx.getPointerType(Ctx.getRecordType(StaticClass));
+        CanQualType StaticTy =
+            Ctx.getPointerType(Ctx.getCanonicalTagType(StaticClass));
         ThisVal = SVB.evalCast(ThisVal, Ty, StaticTy);
       } else
         ThisVal = *V;
diff --git a/clang/lib/StaticAnalyzer/Core/MemRegion.cpp b/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
index 63ad567ab7151..68bf97e43f3c1 100644
--- a/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
+++ b/clang/lib/StaticAnalyzer/Core/MemRegion.cpp
@@ -192,11 +192,11 @@ QualType ObjCIvarRegion::getValueType() const {
 }
 
 QualType CXXBaseObjectRegion::getValueType() const {
-  return QualType(getDecl()->getTypeForDecl(), 0);
+  return getContext().getCanonicalTagType(getDecl());
 }
 
 QualType CXXDerivedObjectRegion::getValueType() const {
-  return QualType(getDecl()->getTypeForDecl(), 0);
+  return getContext().getCanonicalTagType(getDecl());
 }
 
 QualType ParamVarRegion::getValueType() const {
diff --git a/clang/lib/StaticAnalyzer/Core/RegionStore.cpp b/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
index 388034b087789..02375b0c3469a 100644
--- a/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
@@ -2453,7 +2453,8 @@ NonLoc RegionStoreManager::createLazyBinding(RegionBindingsConstRef B,
 
 SVal RegionStoreManager::getBindingForStruct(RegionBindingsConstRef B,
                                              const TypedValueRegion *R) {
-  const RecordDecl *RD = R->getValueType()->castAs<RecordType>()->getDecl();
+  const RecordDecl *RD =
+      R->getValueType()->castAs<RecordType>()->getOriginalDecl();
   if (!RD->getDefinition())
     return UnknownVal();
 
@@ -2844,7 +2845,7 @@ RegionStoreManager::bindStruct(LimitedRegionBindingsConstRef B,
   assert(T->isStructureOrClassType());
 
   const RecordType* RT = T->castAs<RecordType>();
-  const RecordDecl *RD = RT->getDecl();
+  const RecordDecl *RD = RT->getOriginalDecl()->getDefinitionOrSelf();
 
   if (!RD->isCompleteDefinition())
     return B;
diff --git a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
index 2276c452cce76..a6f4463852a9b 100644
--- a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
+++ b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
@@ -320,8 +320,8 @@ loc::MemRegionVal SValBuilder::getCXXThis(const CXXMethodDecl *D,
 /// Return a memory region for the 'this' object reference.
 loc::MemRegionVal SValBuilder::getCXXThis(const CXXRecordDecl *D,
                                           const StackFrameContext *SFC) {
-  const Type *T = D->getTypeForDecl();
-  QualType PT = getContext().getPointerType(QualType(T, 0));
+  CanQualType PT =
+      getContext().getPointerType(getContext().getCanonicalTagType(D));
   return loc::MemRegionVal(getRegionManager().getCXXThisRegion(PT, SFC));
 }
 
diff --git a/clang/lib/Tooling/ASTDiff/ASTDiff.cpp b/clang/lib/Tooling/ASTDiff/ASTDiff.cpp
index 5f7153cd53ac2..d70a679cc8dd0 100644
--- a/clang/lib/Tooling/ASTDiff/ASTDiff.cpp
+++ b/clang/lib/Tooling/ASTDiff/ASTDiff.cpp
@@ -246,7 +246,7 @@ struct PreorderVisitor : public RecursiveASTVisitor<PreorderVisitor> {
     PostTraverse(SavedState);
     return true;
   }
-  bool TraverseType(QualType T) { return true; }
+  bool TraverseType(QualType T, bool TraverseQualifier = true) { return true; }
   bool TraverseConstructorInitializer(CXXCtorInitializer *Init) {
     if (isNodeExcluded(Tree.AST.getSourceManager(), Init))
       return true;
@@ -428,11 +428,12 @@ std::string SyntaxTree::Impl::getDeclValue(const Decl *D) const {
     Value += getRelativeName(N) + ";";
   if (auto *T = dyn_cast<TypedefNameDecl>(D))
     return Value + T->getUnderlyingType().getAsString(TypePP) + ";";
-  if (auto *T = dyn_cast<TypeDecl>(D))
-    if (T->getTypeForDecl())
-      Value +=
-          T->getTypeForDecl()->getCanonicalTypeInternal().getAsString(TypePP) +
-          ";";
+  if (auto *T = dyn_cast<TypeDecl>(D)) {
+    const ASTContext &Ctx = T->getASTContext();
+    Value +=
+        Ctx.getTypeDeclType(T)->getCanonicalTypeInternal().getAsString(TypePP) +
+        ";";
+  }
   if (auto *U = dyn_cast<UsingDirectiveDecl>(D))
     return std::string(U->getNominatedNamespace()->getName());
   if (auto *A = dyn_cast<AccessSpecDecl>(D)) {
diff --git a/clang/lib/Tooling/Refactoring/Lookup.cpp b/clang/lib/Tooling/Refactoring/Lookup.cpp
index 757fba0404e62..dedde860516ab 100644
--- a/clang/lib/Tooling/Refactoring/Lookup.cpp
+++ b/clang/lib/Tooling/Refactoring/Lookup.cpp
@@ -108,16 +108,6 @@ static StringRef getBestNamespaceSubstr(const DeclContext *DeclA,
   }
 }
 
-/// Check if the name specifier begins with a written "::".
-static bool isFullyQualified(const NestedNameSpecifier *NNS) {
-  while (NNS) {
-    if (NNS->getKind() == NestedNameSpecifier::Global)
-      return true;
-    NNS = NNS->getPrefix();
-  }
-  return false;
-}
-
 // Adds more scope specifier to the spelled name until the spelling is not
 // ambiguous. A spelling is ambiguous if the resolution of the symbol is
 // ambiguous. For example, if QName is "::y::bar", the spelling is "y::bar", and
@@ -182,7 +172,7 @@ static std::string disambiguateSpellingInScope(StringRef Spelling,
   return Disambiguated;
 }
 
-std::string tooling::replaceNestedName(const NestedNameSpecifier *Use,
+std::string tooling::replaceNestedName(NestedNameSpecifier Use,
                                        SourceLocation UseLoc,
                                        const DeclContext *UseContext,
                                        const NamedDecl *FromDecl,
@@ -217,7 +207,7 @@ std::string tooling::replaceNestedName(const NestedNameSpecifier *Use,
   // We work backwards (from most specific possible namespace to least
   // specific).
   StringRef Suggested = getBestNamespaceSubstr(UseContext, ReplacementString,
-                                               isFullyQualified(Use));
+                                               Use.isFullyQualified());
 
   return disambiguateSpellingInScope(Suggested, ReplacementString, *UseContext,
                                      UseLoc);
diff --git a/clang/lib/Tooling/Refactoring/Rename/USRLocFinder.cpp b/clang/lib/Tooling/Refactoring/Rename/USRLocFinder.cpp
index 8eff77861f753..d9444110d421c 100644
--- a/clang/lib/Tooling/Refactoring/Rename/USRLocFinder.cpp
+++ b/clang/lib/Tooling/Refactoring/Rename/USRLocFinder.cpp
@@ -107,45 +107,83 @@ class USRLocFindingASTVisitor
 };
 
 SourceLocation StartLocationForType(TypeLoc TL) {
+  if (auto QTL = TL.getAs<QualifiedTypeLoc>())
+    TL = QTL.getUnqualifiedLoc();
+
   // For elaborated types (e.g. `struct a::A`) we want the portion after the
-  // `struct` but including the namespace qualifier, `a::`.
-  if (auto ElaboratedTypeLoc = TL.getAs<clang::ElaboratedTypeLoc>()) {
-    NestedNameSpecifierLoc NestedNameSpecifier =
-        ElaboratedTypeLoc.getQualifierLoc();
-    if (NestedNameSpecifier.getNestedNameSpecifier())
-      return NestedNameSpecifier.getBeginLoc();
-    TL = TL.getNextTypeLoc();
+  // `struct`, including the namespace qualifier, `a::`.
+  switch (TL.getTypeLocClass()) {
+  case TypeLoc::Record:
+  case TypeLoc::InjectedClassName:
+  case TypeLoc::Enum: {
+    auto TTL = TL.castAs<TagTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getNameLoc();
+  }
+  case TypeLoc::Typedef: {
+    auto TTL = TL.castAs<TypedefTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getNameLoc();
+  }
+  case TypeLoc::UnresolvedUsing: {
+    auto TTL = TL.castAs<UnresolvedUsingTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getNameLoc();
+  }
+  case TypeLoc::Using: {
+    auto TTL = TL.castAs<UsingTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getNameLoc();
+  }
+  case TypeLoc::TemplateSpecialization: {
+    auto TTL = TL.castAs<TemplateSpecializationTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getTemplateNameLoc();
+  }
+  case TypeLoc::DeducedTemplateSpecialization: {
+    auto DTL = TL.castAs<clang::DeducedTemplateSpecializationTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = DTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return DTL.getTemplateNameLoc();
+  }
+  case TypeLoc::DependentName: {
+    auto TTL = TL.castAs<DependentNameTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getNameLoc();
+  }
+  case TypeLoc::DependentTemplateSpecialization: {
+    auto TTL = TL.castAs<DependentTemplateSpecializationTypeLoc>();
+    if (NestedNameSpecifierLoc QualifierLoc = TTL.getQualifierLoc())
+      return QualifierLoc.getBeginLoc();
+    return TTL.getTemplateNameLoc();
+  }
+  default:
+    llvm_unreachable("unhandled TypeLoc class");
   }
-  return TL.getBeginLoc();
 }
 
 SourceLocation EndLocationForType(TypeLoc TL) {
-  // Dig past any namespace or keyword qualifications.
-  while (TL.getTypeLocClass() == TypeLoc::Elaborated ||
-         TL.getTypeLocClass() == TypeLoc::Qualified)
-    TL = TL.getNextTypeLoc();
+  if (auto QTL = TL.getAs<QualifiedTypeLoc>())
+    TL = QTL.getUnqualifiedLoc();
 
   // The location for template specializations (e.g. Foo<int>) includes the
   // templated types in its location range.  We want to restrict this to just
   // before the `<` character.
-  if (TL.getTypeLocClass() == TypeLoc::TemplateSpecialization) {
-    return TL.castAs<TemplateSpecializationTypeLoc>()
-        .getLAngleLoc()
-        .getLocWithOffset(-1);
-  }
+  if (auto TTL = TL.getAs<TemplateSpecializationTypeLoc>())
+    return TTL.getLAngleLoc().getLocWithOffset(-1);
   return TL.getEndLoc();
 }
 
-NestedNameSpecifier *GetNestedNameForType(TypeLoc TL) {
-  // Dig past any keyword qualifications.
-  while (TL.getTypeLocClass() == TypeLoc::Qualified)
-    TL = TL.getNextTypeLoc();
-
-  // For elaborated types (e.g. `struct a::A`) we want the portion after the
-  // `struct` but including the namespace qualifier, `a::`.
-  if (auto ElaboratedTypeLoc = TL.getAs<clang::ElaboratedTypeLoc>())
-    return ElaboratedTypeLoc.getQualifierLoc().getNestedNameSpecifier();
-  return nullptr;
+NestedNameSpecifier GetNestedNameForType(TypeLoc TL) {
+  if (auto QTL = TL.getAs<QualifiedTypeLoc>())
+    TL = QTL.getUnqualifiedLoc();
+  return TL.getPrefix().getNestedNameSpecifier();
 }
 
 // Find all locations identified by the given USRs for rename.
@@ -168,14 +206,14 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
     const NamedDecl *FromDecl;
     // The declaration in which the nested name is contained (can be nullptr).
     const Decl *Context;
-    // The nested name being replaced (can be nullptr).
-    const NestedNameSpecifier *Specifier;
+    // The nested name being replaced.
+    NestedNameSpecifier Specifier;
     // Determine whether the prefix qualifiers of the NewName should be ignored.
     // Normally, we set it to true for the symbol declaration and definition to
     // avoid adding prefix qualifiers.
     // For example, if it is true and NewName is "a::b::foo", then the symbol
     // occurrence which the RenameInfo points to will be renamed to "foo".
-    bool IgnorePrefixQualifers;
+    bool IgnorePrefixQualifiers;
   };
 
   bool VisitNamedDecl(const NamedDecl *Decl) {
@@ -203,8 +241,8 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
                            EndLoc,
                            /*FromDecl=*/nullptr,
                            /*Context=*/nullptr,
-                           /*Specifier=*/nullptr,
-                           /*IgnorePrefixQualifers=*/true};
+                           /*Specifier=*/std::nullopt,
+                           /*IgnorePrefixQualifiers=*/true};
         RenameInfos.push_back(Info);
       }
     }
@@ -217,10 +255,10 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
     auto EndLoc = Expr->getMemberLoc();
     if (isInUSRSet(Decl)) {
       RenameInfos.push_back({StartLoc, EndLoc,
-                            /*FromDecl=*/nullptr,
-                            /*Context=*/nullptr,
-                            /*Specifier=*/nullptr,
-                            /*IgnorePrefixQualifiers=*/true});
+                             /*FromDecl=*/nullptr,
+                             /*Context=*/nullptr,
+                             /*Specifier=*/std::nullopt,
+                             /*IgnorePrefixQualifiers=*/true});
     }
     return true;
   }
@@ -235,7 +273,7 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
             RenameInfos.push_back({StartLoc, EndLoc,
                                    /*FromDecl=*/nullptr,
                                    /*Context=*/nullptr,
-                                   /*Specifier=*/nullptr,
+                                   /*Specifier=*/std::nullopt,
                                    /*IgnorePrefixQualifiers=*/true});
           }
         }
@@ -257,7 +295,7 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
           RenameInfos.push_back({Loc, Loc,
                                  /*FromDecl=*/nullptr,
                                  /*Context=*/nullptr,
-                                 /*Specifier=*/nullptr,
+                                 /*Specifier=*/std::nullopt,
                                  /*IgnorePrefixQualifiers=*/true});
         }
       }
@@ -288,7 +326,7 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
         RenameInfos.push_back({EndLoc, EndLoc,
                                /*FromDecl=*/nullptr,
                                /*Context=*/nullptr,
-                               /*Specifier=*/nullptr,
+                               /*Specifier=*/std::nullopt,
                                /*IgnorePrefixQualifiers=*/true});
         return true;
       }
@@ -332,7 +370,7 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
                          Decl,
                          getClosestAncestorDecl(*Expr),
                          Expr->getQualifier(),
-                         /*IgnorePrefixQualifers=*/false};
+                         /*IgnorePrefixQualifiers=*/false};
       RenameInfos.push_back(Info);
     }
 
@@ -350,18 +388,18 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
   }
 
   bool VisitNestedNameSpecifierLocations(NestedNameSpecifierLoc NestedLoc) {
-    if (!NestedLoc.getNestedNameSpecifier()->getAsType())
+    TypeLoc TL = NestedLoc.getAsTypeLoc();
+    if (!TL)
       return true;
 
-    if (const auto *TargetDecl =
-            getSupportedDeclFromTypeLoc(NestedLoc.getTypeLoc())) {
+    if (const auto *TargetDecl = getSupportedDeclFromTypeLoc(TL)) {
       if (isInUSRSet(TargetDecl)) {
         RenameInfo Info = {NestedLoc.getBeginLoc(),
-                           EndLocationForType(NestedLoc.getTypeLoc()),
+                           EndLocationForType(TL),
                            TargetDecl,
                            getClosestAncestorDecl(NestedLoc),
-                           NestedLoc.getNestedNameSpecifier()->getPrefix(),
-                           /*IgnorePrefixQualifers=*/false};
+                           /*Specifier=*/std::nullopt,
+                           /*IgnorePrefixQualifiers=*/false};
         RenameInfos.push_back(Info);
       }
     }
@@ -411,7 +449,7 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
                              TargetDecl,
                              getClosestAncestorDecl(Loc),
                              GetNestedNameForType(Loc),
-                             /*IgnorePrefixQualifers=*/false};
+                             /*IgnorePrefixQualifiers=*/false};
           RenameInfos.push_back(Info);
         }
         return true;
@@ -421,33 +459,17 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
     // Handle specific template class specialiation cases.
     if (const auto *TemplateSpecType =
             dyn_cast<TemplateSpecializationType>(Loc.getType())) {
-      TypeLoc TargetLoc = Loc;
-      if (!ParentTypeLoc.isNull()) {
-        if (llvm::isa<ElaboratedType>(ParentTypeLoc.getType()))
-          TargetLoc = ParentTypeLoc;
-      }
-
       if (isInUSRSet(TemplateSpecType->getTemplateName().getAsTemplateDecl())) {
-        TypeLoc TargetLoc = Loc;
-        // FIXME: Find a better way to handle this case.
-        // For the qualified template class specification type like
-        // "ns::Foo<int>" in "ns::Foo<int>& f();", we want the parent typeLoc
-        // (ElaboratedType) of the TemplateSpecializationType in order to
-        // catch the prefix qualifiers "ns::".
-        if (!ParentTypeLoc.isNull() &&
-            llvm::isa<ElaboratedType>(ParentTypeLoc.getType()))
-          TargetLoc = ParentTypeLoc;
-
-        auto StartLoc = StartLocationForType(TargetLoc);
-        auto EndLoc = EndLocationForType(TargetLoc);
+        auto StartLoc = StartLocationForType(Loc);
+        auto EndLoc = EndLocationForType(Loc);
         if (IsValidEditLoc(Context.getSourceManager(), StartLoc)) {
           RenameInfo Info = {
               StartLoc,
               EndLoc,
               TemplateSpecType->getTemplateName().getAsTemplateDecl(),
-              getClosestAncestorDecl(DynTypedNode::create(TargetLoc)),
-              GetNestedNameForType(TargetLoc),
-              /*IgnorePrefixQualifers=*/false};
+              getClosestAncestorDecl(DynTypedNode::create(Loc)),
+              GetNestedNameForType(Loc),
+              /*IgnorePrefixQualifiers=*/false};
           RenameInfos.push_back(Info);
         }
       }
@@ -469,12 +491,7 @@ class RenameLocFinder : public RecursiveASTVisitor<RenameLocFinder> {
   const NamedDecl *getSupportedDeclFromTypeLoc(TypeLoc Loc) {
     if (const auto* TT = Loc.getType()->getAs<clang::TypedefType>())
       return TT->getDecl();
-    if (const auto *RD = Loc.getType()->getAsCXXRecordDecl())
-      return RD;
-    if (const auto *ED =
-            llvm::dyn_cast_or_null<EnumDecl>(Loc.getType()->getAsTagDecl()))
-      return ED;
-    return nullptr;
+    return Loc.getType()->getAsTagDecl();
   }
 
   // Get the closest ancester which is a declaration of a given AST node.
@@ -549,7 +566,7 @@ createRenameAtomicChanges(llvm::ArrayRef<std::string> USRs,
 
   for (const auto &RenameInfo : Finder.getRenameInfos()) {
     std::string ReplacedName = NewName.str();
-    if (RenameInfo.IgnorePrefixQualifers) {
+    if (RenameInfo.IgnorePrefixQualifiers) {
       // Get the name without prefix qualifiers from NewName.
       size_t LastColonPos = NewName.find_last_of(':');
       if (LastColonPos != std::string::npos)
diff --git a/clang/lib/Tooling/Syntax/BuildTree.cpp b/clang/lib/Tooling/Syntax/BuildTree.cpp
index caac719caf8e8..546161cee33f4 100644
--- a/clang/lib/Tooling/Syntax/BuildTree.cpp
+++ b/clang/lib/Tooling/Syntax/BuildTree.cpp
@@ -918,98 +918,91 @@ class BuildTreeVisitor : public RecursiveASTVisitor<BuildTreeVisitor> {
     return true;
   }
 
-  // FIXME: Fix `NestedNameSpecifierLoc::getLocalSourceRange` for the
-  // `DependentTemplateSpecializationType` case.
-  /// Given a nested-name-specifier return the range for the last name
-  /// specifier.
-  ///
-  /// e.g. `std::T::template X<U>::` => `template X<U>::`
-  SourceRange getLocalSourceRange(const NestedNameSpecifierLoc &NNSLoc) {
-    auto SR = NNSLoc.getLocalSourceRange();
-
-    // The method `NestedNameSpecifierLoc::getLocalSourceRange` *should*
-    // return the desired `SourceRange`, but there is a corner case. For a
-    // `DependentTemplateSpecializationType` this method returns its
-    // qualifiers as well, in other words in the example above this method
-    // returns `T::template X<U>::` instead of only `template X<U>::`
-    if (auto TL = NNSLoc.getTypeLoc()) {
-      if (auto DependentTL =
-              TL.getAs<DependentTemplateSpecializationTypeLoc>()) {
-        // The 'template' keyword is always present in dependent template
-        // specializations. Except in the case of incorrect code
-        // TODO: Treat the case of incorrect code.
-        SR.setBegin(DependentTL.getTemplateKeywordLoc());
-      }
-    }
-
-    return SR;
-  }
-
-  syntax::NodeKind getNameSpecifierKind(const NestedNameSpecifier &NNS) {
-    switch (NNS.getKind()) {
-    case NestedNameSpecifier::Global:
-      return syntax::NodeKind::GlobalNameSpecifier;
-    case NestedNameSpecifier::Namespace:
-    case NestedNameSpecifier::NamespaceAlias:
-    case NestedNameSpecifier::Identifier:
-      return syntax::NodeKind::IdentifierNameSpecifier;
-    case NestedNameSpecifier::TypeSpec: {
-      const auto *NNSType = NNS.getAsType();
-      assert(NNSType);
-      if (isa<DecltypeType>(NNSType))
-        return syntax::NodeKind::DecltypeNameSpecifier;
-      if (isa<TemplateSpecializationType, DependentTemplateSpecializationType>(
-              NNSType))
-        return syntax::NodeKind::SimpleTemplateNameSpecifier;
-      return syntax::NodeKind::IdentifierNameSpecifier;
-    }
-    default:
-      // FIXME: Support Microsoft's __super
-      llvm::report_fatal_error("We don't yet support the __super specifier",
-                               true);
-    }
+  syntax::NameSpecifier *buildIdentifier(SourceRange SR,
+                                         bool DropBack = false) {
+    auto NameSpecifierTokens = Builder.getRange(SR).drop_back(DropBack);
+    assert(NameSpecifierTokens.size() == 1);
+    Builder.markChildToken(NameSpecifierTokens.begin(),
+                           syntax::NodeRole::Unknown);
+    auto *NS = new (allocator()) syntax::IdentifierNameSpecifier;
+    Builder.foldNode(NameSpecifierTokens, NS, nullptr);
+    return NS;
+  }
+
+  syntax::NameSpecifier *buildSimpleTemplateName(SourceRange SR) {
+    auto NameSpecifierTokens = Builder.getRange(SR);
+    // TODO: Build `SimpleTemplateNameSpecifier` children and implement
+    // accessors to them.
+    // Be aware, we cannot do that simply by calling `TraverseTypeLoc`,
+    // some `TypeLoc`s have inside them the previous name specifier and
+    // we want to treat them independently.
+    auto *NS = new (allocator()) syntax::SimpleTemplateNameSpecifier;
+    Builder.foldNode(NameSpecifierTokens, NS, nullptr);
+    return NS;
   }
 
   syntax::NameSpecifier *
   buildNameSpecifier(const NestedNameSpecifierLoc &NNSLoc) {
     assert(NNSLoc.hasQualifier());
-    auto NameSpecifierTokens =
-        Builder.getRange(getLocalSourceRange(NNSLoc)).drop_back();
-    switch (getNameSpecifierKind(*NNSLoc.getNestedNameSpecifier())) {
-    case syntax::NodeKind::GlobalNameSpecifier:
+    switch (NNSLoc.getNestedNameSpecifier().getKind()) {
+    case NestedNameSpecifier::Kind::Global:
       return new (allocator()) syntax::GlobalNameSpecifier;
-    case syntax::NodeKind::IdentifierNameSpecifier: {
-      assert(NameSpecifierTokens.size() == 1);
-      Builder.markChildToken(NameSpecifierTokens.begin(),
-                             syntax::NodeRole::Unknown);
-      auto *NS = new (allocator()) syntax::IdentifierNameSpecifier;
-      Builder.foldNode(NameSpecifierTokens, NS, nullptr);
-      return NS;
-    }
-    case syntax::NodeKind::SimpleTemplateNameSpecifier: {
-      // TODO: Build `SimpleTemplateNameSpecifier` children and implement
-      // accessors to them.
-      // Be aware, we cannot do that simply by calling `TraverseTypeLoc`,
-      // some `TypeLoc`s have inside them the previous name specifier and
-      // we want to treat them independently.
-      auto *NS = new (allocator()) syntax::SimpleTemplateNameSpecifier;
-      Builder.foldNode(NameSpecifierTokens, NS, nullptr);
-      return NS;
-    }
-    case syntax::NodeKind::DecltypeNameSpecifier: {
-      const auto TL = NNSLoc.getTypeLoc().castAs<DecltypeTypeLoc>();
-      if (!RecursiveASTVisitor::TraverseDecltypeTypeLoc(TL))
-        return nullptr;
-      auto *NS = new (allocator()) syntax::DecltypeNameSpecifier;
-      // TODO: Implement accessor to `DecltypeNameSpecifier` inner
-      // `DecltypeTypeLoc`.
-      // For that add mapping from `TypeLoc` to `syntax::Node*` then:
-      // Builder.markChild(TypeLoc, syntax::NodeRole);
-      Builder.foldNode(NameSpecifierTokens, NS, nullptr);
-      return NS;
+
+    case NestedNameSpecifier::Kind::Namespace:
+      return buildIdentifier(NNSLoc.getLocalSourceRange(), /*DropBack=*/true);
+
+    case NestedNameSpecifier::Kind::Type: {
+      TypeLoc TL = NNSLoc.castAsTypeLoc();
+      switch (TL.getTypeLocClass()) {
+      case TypeLoc::Record:
+      case TypeLoc::InjectedClassName:
+      case TypeLoc::Enum:
+        return buildIdentifier(TL.castAs<TagTypeLoc>().getNameLoc());
+      case TypeLoc::Typedef:
+        return buildIdentifier(TL.castAs<TypedefTypeLoc>().getNameLoc());
+      case TypeLoc::UnresolvedUsing:
+        return buildIdentifier(
+            TL.castAs<UnresolvedUsingTypeLoc>().getNameLoc());
+      case TypeLoc::Using:
+        return buildIdentifier(TL.castAs<UsingTypeLoc>().getNameLoc());
+      case TypeLoc::DependentName:
+        return buildIdentifier(TL.castAs<DependentNameTypeLoc>().getNameLoc());
+      case TypeLoc::TemplateSpecialization: {
+        auto TST = TL.castAs<TemplateSpecializationTypeLoc>();
+        SourceLocation BeginLoc = TST.getTemplateKeywordLoc();
+        if (BeginLoc.isInvalid())
+          BeginLoc = TST.getTemplateNameLoc();
+        return buildSimpleTemplateName({BeginLoc, TST.getEndLoc()});
+      }
+      case TypeLoc::DependentTemplateSpecialization: {
+        auto DT = TL.castAs<DependentTemplateSpecializationTypeLoc>();
+        SourceLocation BeginLoc = DT.getTemplateKeywordLoc();
+        if (BeginLoc.isInvalid())
+          BeginLoc = DT.getTemplateNameLoc();
+        return buildSimpleTemplateName({BeginLoc, DT.getEndLoc()});
+      }
+      case TypeLoc::Decltype: {
+        const auto DTL = TL.castAs<DecltypeTypeLoc>();
+        if (!RecursiveASTVisitor::TraverseDecltypeTypeLoc(
+                DTL, /*TraverseQualifier=*/true))
+          return nullptr;
+        auto *NS = new (allocator()) syntax::DecltypeNameSpecifier;
+        // TODO: Implement accessor to `DecltypeNameSpecifier` inner
+        // `DecltypeTypeLoc`.
+        // For that add mapping from `TypeLoc` to `syntax::Node*` then:
+        // Builder.markChild(TypeLoc, syntax::NodeRole);
+        Builder.foldNode(Builder.getRange(DTL.getLocalSourceRange()), NS,
+                         nullptr);
+        return NS;
+      }
+      default:
+        return buildIdentifier(TL.getLocalSourceRange());
+      }
     }
     default:
-      llvm_unreachable("getChildKind() does not return this value");
+      // FIXME: Support Microsoft's __super
+      llvm::report_fatal_error("We don't yet support the __super specifier",
+                               true);
     }
   }
 
@@ -1020,12 +1013,16 @@ class BuildTreeVisitor : public RecursiveASTVisitor<BuildTreeVisitor> {
   bool TraverseNestedNameSpecifierLoc(NestedNameSpecifierLoc QualifierLoc) {
     if (!QualifierLoc)
       return true;
-    for (auto It = QualifierLoc; It; It = It.getPrefix()) {
+    for (auto It = QualifierLoc; It; /**/) {
       auto *NS = buildNameSpecifier(It);
       if (!NS)
         return false;
       Builder.markChild(NS, syntax::NodeRole::ListElement);
       Builder.markChildToken(It.getEndLoc(), syntax::NodeRole::ListDelimiter);
+      if (TypeLoc TL = It.getAsTypeLoc())
+        It = TL.getPrefix();
+      else
+        It = It.getAsNamespaceAndPrefix().Prefix;
     }
     Builder.foldNode(Builder.getRange(QualifierLoc.getSourceRange()),
                      new (allocator()) syntax::NestedNameSpecifier,
@@ -1329,7 +1326,7 @@ class BuildTreeVisitor : public RecursiveASTVisitor<BuildTreeVisitor> {
 
   // FIXME: Deleting the `TraverseParenTypeLoc` override doesn't change test
   // results. Find test coverage or remove it.
-  bool TraverseParenTypeLoc(ParenTypeLoc L) {
+  bool TraverseParenTypeLoc(ParenTypeLoc L, bool TraverseQualifier) {
     // We reverse order of traversal to get the proper syntax structure.
     if (!WalkUpFromParenTypeLoc(L))
       return false;
@@ -1392,7 +1389,8 @@ class BuildTreeVisitor : public RecursiveASTVisitor<BuildTreeVisitor> {
     return WalkUpFromFunctionTypeLoc(L);
   }
 
-  bool TraverseMemberPointerTypeLoc(MemberPointerTypeLoc L) {
+  bool TraverseMemberPointerTypeLoc(MemberPointerTypeLoc L,
+                                    bool TraverseQualifier) {
     // In the source code "void (Y::*mp)()" `MemberPointerTypeLoc` corresponds
     // to "Y::*" but it points to a `ParenTypeLoc` that corresponds to
     // "(Y::*mp)" We thus reverse the order of traversal to get the proper
diff --git a/clang/lib/Tooling/Transformer/RangeSelector.cpp b/clang/lib/Tooling/Transformer/RangeSelector.cpp
index 00f4611ddb5d4..171c786bc366f 100644
--- a/clang/lib/Tooling/Transformer/RangeSelector.cpp
+++ b/clang/lib/Tooling/Transformer/RangeSelector.cpp
@@ -222,14 +222,10 @@ RangeSelector transformer::name(std::string ID) {
       return CharSourceRange::getTokenRange(L, L);
     }
     if (const auto *T = Node.get<TypeLoc>()) {
-      TypeLoc Loc = *T;
-      auto ET = Loc.getAs<ElaboratedTypeLoc>();
-      if (!ET.isNull())
-        Loc = ET.getNamedTypeLoc();
-      if (auto SpecLoc = Loc.getAs<TemplateSpecializationTypeLoc>();
+      if (auto SpecLoc = T->getAs<TemplateSpecializationTypeLoc>();
           !SpecLoc.isNull())
         return CharSourceRange::getTokenRange(SpecLoc.getTemplateNameLoc());
-      return CharSourceRange::getTokenRange(Loc.getSourceRange());
+      return CharSourceRange::getTokenRange(T->getSourceRange());
     }
     return typeError(ID, Node.getNodeKind(),
                      "DeclRefExpr, NamedDecl, CXXCtorInitializer, TypeLoc");
diff --git a/clang/tools/libclang/CIndex.cpp b/clang/tools/libclang/CIndex.cpp
index 9089984fa4a54..08e34d7261626 100644
--- a/clang/tools/libclang/CIndex.cpp
+++ b/clang/tools/libclang/CIndex.cpp
@@ -1420,90 +1420,25 @@ bool CursorVisitor::VisitDeclarationNameInfo(DeclarationNameInfo Name) {
   llvm_unreachable("Invalid DeclarationName::Kind!");
 }
 
-bool CursorVisitor::VisitNestedNameSpecifier(NestedNameSpecifier *NNS,
-                                             SourceRange Range) {
-  // FIXME: This whole routine is a hack to work around the lack of proper
-  // source information in nested-name-specifiers (PR5791). Since we do have
-  // a beginning source location, we can visit the first component of the
-  // nested-name-specifier, if it's a single-token component.
-  if (!NNS)
-    return false;
-
-  // Get the first component in the nested-name-specifier.
-  while (NestedNameSpecifier *Prefix = NNS->getPrefix())
-    NNS = Prefix;
-
-  switch (NNS->getKind()) {
-  case NestedNameSpecifier::Namespace:
-    return Visit(
-        MakeCursorNamespaceRef(NNS->getAsNamespace(), Range.getBegin(), TU));
-
-  case NestedNameSpecifier::NamespaceAlias:
-    return Visit(MakeCursorNamespaceRef(NNS->getAsNamespaceAlias(),
-                                        Range.getBegin(), TU));
-
-  case NestedNameSpecifier::TypeSpec: {
-    // If the type has a form where we know that the beginning of the source
-    // range matches up with a reference cursor. Visit the appropriate reference
-    // cursor.
-    const Type *T = NNS->getAsType();
-    if (const TypedefType *Typedef = dyn_cast<TypedefType>(T))
-      return Visit(MakeCursorTypeRef(Typedef->getDecl(), Range.getBegin(), TU));
-    if (const TagType *Tag = dyn_cast<TagType>(T))
-      return Visit(MakeCursorTypeRef(Tag->getDecl(), Range.getBegin(), TU));
-    if (const TemplateSpecializationType *TST =
-            dyn_cast<TemplateSpecializationType>(T))
-      return VisitTemplateName(TST->getTemplateName(), Range.getBegin());
-    break;
-  }
-
-  case NestedNameSpecifier::Global:
-  case NestedNameSpecifier::Identifier:
-  case NestedNameSpecifier::Super:
-    break;
-  }
-
-  return false;
-}
-
 bool CursorVisitor::VisitNestedNameSpecifierLoc(
     NestedNameSpecifierLoc Qualifier) {
-  SmallVector<NestedNameSpecifierLoc, 4> Qualifiers;
-  for (; Qualifier; Qualifier = Qualifier.getPrefix())
-    Qualifiers.push_back(Qualifier);
-
-  while (!Qualifiers.empty()) {
-    NestedNameSpecifierLoc Q = Qualifiers.pop_back_val();
-    NestedNameSpecifier *NNS = Q.getNestedNameSpecifier();
-    switch (NNS->getKind()) {
-    case NestedNameSpecifier::Namespace:
-      if (Visit(MakeCursorNamespaceRef(NNS->getAsNamespace(),
-                                       Q.getLocalBeginLoc(), TU)))
-        return true;
-
-      break;
-
-    case NestedNameSpecifier::NamespaceAlias:
-      if (Visit(MakeCursorNamespaceRef(NNS->getAsNamespaceAlias(),
-                                       Q.getLocalBeginLoc(), TU)))
-        return true;
-
-      break;
-
-    case NestedNameSpecifier::TypeSpec:
-      if (Visit(Q.getTypeLoc()))
-        return true;
-
-      break;
-
-    case NestedNameSpecifier::Global:
-    case NestedNameSpecifier::Identifier:
-    case NestedNameSpecifier::Super:
-      break;
-    }
+  NestedNameSpecifier NNS = Qualifier.getNestedNameSpecifier();
+  switch (NNS.getKind()) {
+  case NestedNameSpecifier::Kind::Namespace: {
+    auto [Namespace, Prefix] = Qualifier.castAsNamespaceAndPrefix();
+    if (VisitNestedNameSpecifierLoc(Prefix))
+      return true;
+    return Visit(
+        MakeCursorNamespaceRef(Namespace, Qualifier.getLocalBeginLoc(), TU));
   }
-
-  return false;
+  case NestedNameSpecifier::Kind::Type:
+    return Visit(Qualifier.castAsTypeLoc());
+  case NestedNameSpecifier::Kind::Null:
+  case NestedNameSpecifier::Kind::Global:
+  case NestedNameSpecifier::Kind::Super:
+    return false;
+  }
+  llvm_unreachable("unexpected nested name specifier kind");
 }
 
 bool CursorVisitor::VisitTemplateParameters(
@@ -1526,16 +1461,23 @@ bool CursorVisitor::VisitTemplateParameters(
   return false;
 }
 
-bool CursorVisitor::VisitTemplateName(TemplateName Name, SourceLocation Loc) {
+bool CursorVisitor::VisitTemplateName(TemplateName Name, SourceLocation NameLoc,
+                                      NestedNameSpecifierLoc NNS) {
   switch (Name.getKind()) {
+  case TemplateName::QualifiedTemplate: {
+    const QualifiedTemplateName *QTN = Name.getAsQualifiedTemplateName();
+    assert(QTN->getQualifier() == NNS.getNestedNameSpecifier());
+    if (VisitNestedNameSpecifierLoc(NNS))
+      return true;
+    return VisitTemplateName(QTN->getUnderlyingTemplate(), NameLoc, /*NNS=*/{});
+  }
   case TemplateName::Template:
   case TemplateName::UsingTemplate:
-  case TemplateName::QualifiedTemplate: // FIXME: Visit nested-name-specifier.
-    return Visit(MakeCursorTemplateRef(Name.getAsTemplateDecl(), Loc, TU));
+    return Visit(MakeCursorTemplateRef(Name.getAsTemplateDecl(), NameLoc, TU));
 
   case TemplateName::OverloadedTemplate:
     // Visit the overloaded template set.
-    if (Visit(MakeCursorOverloadedDeclRef(Name, Loc, TU)))
+    if (Visit(MakeCursorOverloadedDeclRef(Name, NameLoc, TU)))
       return true;
 
     return false;
@@ -1544,17 +1486,19 @@ bool CursorVisitor::VisitTemplateName(TemplateName Name, SourceLocation Loc) {
     // FIXME: Visit DeclarationName?
     return false;
 
-  case TemplateName::DependentTemplate:
-    // FIXME: Visit nested-name-specifier.
-    return false;
+  case TemplateName::DependentTemplate: {
+    assert(Name.getAsDependentTemplateName()->getQualifier() ==
+           NNS.getNestedNameSpecifier());
+    return VisitNestedNameSpecifierLoc(NNS);
+  }
 
   case TemplateName::SubstTemplateTemplateParm:
     return Visit(MakeCursorTemplateRef(
-        Name.getAsSubstTemplateTemplateParm()->getParameter(), Loc, TU));
+        Name.getAsSubstTemplateTemplateParm()->getParameter(), NameLoc, TU));
 
   case TemplateName::SubstTemplateTemplateParmPack:
     return Visit(MakeCursorTemplateRef(
-        Name.getAsSubstTemplateTemplateParmPack()->getParameterPack(), Loc,
+        Name.getAsSubstTemplateTemplateParmPack()->getParameterPack(), NameLoc,
         TU));
 
   case TemplateName::DeducedTemplate:
@@ -1598,11 +1542,9 @@ bool CursorVisitor::VisitTemplateArgumentLoc(const TemplateArgumentLoc &TAL) {
 
   case TemplateArgument::Template:
   case TemplateArgument::TemplateExpansion:
-    if (VisitNestedNameSpecifierLoc(TAL.getTemplateQualifierLoc()))
-      return true;
-
     return VisitTemplateName(TAL.getArgument().getAsTemplateOrTemplatePattern(),
-                             TAL.getTemplateNameLoc());
+                             TAL.getTemplateNameLoc(),
+                             TAL.getTemplateQualifierLoc());
   }
 
   llvm_unreachable("Invalid TemplateArgument::Kind!");
@@ -1680,18 +1622,27 @@ bool CursorVisitor::VisitBuiltinTypeLoc(BuiltinTypeLoc TL) {
 }
 
 bool CursorVisitor::VisitTypedefTypeLoc(TypedefTypeLoc TL) {
-  return Visit(MakeCursorTypeRef(TL.getTypedefNameDecl(), TL.getNameLoc(), TU));
+  if (VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
+    return true;
+
+  return Visit(MakeCursorTypeRef(TL.getDecl(), TL.getNameLoc(), TU));
 }
 
 bool CursorVisitor::VisitUnresolvedUsingTypeLoc(UnresolvedUsingTypeLoc TL) {
+  if (VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
+    return true;
+
   return Visit(MakeCursorTypeRef(TL.getDecl(), TL.getNameLoc(), TU));
 }
 
 bool CursorVisitor::VisitTagTypeLoc(TagTypeLoc TL) {
+  if (VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
+    return true;
+
   if (TL.isDefinition())
-    return Visit(MakeCXCursor(TL.getDecl(), TU, RegionOfInterest));
+    return Visit(MakeCXCursor(TL.getOriginalDecl(), TU, RegionOfInterest));
 
-  return Visit(MakeCursorTypeRef(TL.getDecl(), TL.getNameLoc(), TU));
+  return Visit(MakeCursorTypeRef(TL.getOriginalDecl(), TL.getNameLoc(), TU));
 }
 
 bool CursorVisitor::VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TL) {
@@ -1770,7 +1721,10 @@ bool CursorVisitor::VisitRValueReferenceTypeLoc(RValueReferenceTypeLoc TL) {
 }
 
 bool CursorVisitor::VisitUsingTypeLoc(UsingTypeLoc TL) {
-  auto *underlyingDecl = TL.getUnderlyingType()->getAsTagDecl();
+  if (VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
+    return true;
+
+  auto *underlyingDecl = TL.getTypePtr()->desugar()->getAsTagDecl();
   if (underlyingDecl) {
     return Visit(MakeCursorTypeRef(underlyingDecl, TL.getNameLoc(), TU));
   }
@@ -1833,7 +1787,7 @@ bool CursorVisitor::VisitAdjustedTypeLoc(AdjustedTypeLoc TL) {
 bool CursorVisitor::VisitDeducedTemplateSpecializationTypeLoc(
     DeducedTemplateSpecializationTypeLoc TL) {
   if (VisitTemplateName(TL.getTypePtr()->getTemplateName(),
-                        TL.getTemplateNameLoc()))
+                        TL.getTemplateNameLoc(), TL.getQualifierLoc()))
     return true;
 
   return false;
@@ -1843,7 +1797,7 @@ bool CursorVisitor::VisitTemplateSpecializationTypeLoc(
     TemplateSpecializationTypeLoc TL) {
   // Visit the template name.
   if (VisitTemplateName(TL.getTypePtr()->getTemplateName(),
-                        TL.getTemplateNameLoc()))
+                        TL.getTemplateNameLoc(), TL.getQualifierLoc()))
     return true;
 
   // Visit the template arguments.
@@ -1878,8 +1832,7 @@ bool CursorVisitor::VisitDependentNameTypeLoc(DependentNameTypeLoc TL) {
 
 bool CursorVisitor::VisitDependentTemplateSpecializationTypeLoc(
     DependentTemplateSpecializationTypeLoc TL) {
-  // Visit the nested-name-specifier, if there is one.
-  if (TL.getQualifierLoc() && VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
+  if (VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
     return true;
 
   // Visit the template arguments.
@@ -1890,13 +1843,6 @@ bool CursorVisitor::VisitDependentTemplateSpecializationTypeLoc(
   return false;
 }
 
-bool CursorVisitor::VisitElaboratedTypeLoc(ElaboratedTypeLoc TL) {
-  if (VisitNestedNameSpecifierLoc(TL.getQualifierLoc()))
-    return true;
-
-  return Visit(TL.getNamedTypeLoc());
-}
-
 bool CursorVisitor::VisitPackExpansionTypeLoc(PackExpansionTypeLoc TL) {
   return Visit(TL.getPatternLoc());
 }
@@ -1915,7 +1861,7 @@ bool CursorVisitor::VisitPackIndexingTypeLoc(PackIndexingTypeLoc TL) {
 }
 
 bool CursorVisitor::VisitInjectedClassNameTypeLoc(InjectedClassNameTypeLoc TL) {
-  return Visit(MakeCursorTypeRef(TL.getDecl(), TL.getNameLoc(), TU));
+  return Visit(MakeCursorTypeRef(TL.getOriginalDecl(), TL.getNameLoc(), TU));
 }
 
 bool CursorVisitor::VisitAtomicTypeLoc(AtomicTypeLoc TL) {
@@ -2072,7 +2018,7 @@ class NestedNameSpecifierLocVisit : public VisitorJob {
 public:
   NestedNameSpecifierLocVisit(NestedNameSpecifierLoc Qualifier, CXCursor parent)
       : VisitorJob(parent, VisitorJob::NestedNameSpecifierLocVisitKind,
-                   Qualifier.getNestedNameSpecifier(),
+                   Qualifier.getNestedNameSpecifier().getAsVoidPointer(),
                    Qualifier.getOpaqueData()) {}
 
   static bool classof(const VisitorJob *VJ) {
@@ -2081,8 +2027,7 @@ class NestedNameSpecifierLocVisit : public VisitorJob {
 
   NestedNameSpecifierLoc get() const {
     return NestedNameSpecifierLoc(
-        const_cast<NestedNameSpecifier *>(
-            static_cast<const NestedNameSpecifier *>(data[0])),
+        NestedNameSpecifier::getFromVoidPointer(data[0]),
         const_cast<void *>(data[1]));
   }
 };
@@ -5367,9 +5312,13 @@ CXString clang_getCursorSpelling(CXCursor C) {
     case CXCursor_TypeRef: {
       const TypeDecl *Type = getCursorTypeRef(C).first;
       assert(Type && "Missing type decl");
+      const ASTContext &Ctx = getCursorContext(C);
+      QualType T = Ctx.getTypeDeclType(Type);
 
-      return cxstring::createDup(
-          getCursorContext(C).getTypeDeclType(Type).getAsString());
+      PrintingPolicy Policy = Ctx.getPrintingPolicy();
+      Policy.FullyQualifiedName = true;
+      Policy.SuppressTagKeyword = false;
+      return cxstring::createDup(T.getAsString(Policy));
     }
     case CXCursor_TemplateRef: {
       const TemplateDecl *Template = getCursorTemplateRef(C).first;
diff --git a/clang/tools/libclang/CIndexCodeCompletion.cpp b/clang/tools/libclang/CIndexCodeCompletion.cpp
index 8f6729b83ffa0..1636e1e5e0a7b 100644
--- a/clang/tools/libclang/CIndexCodeCompletion.cpp
+++ b/clang/tools/libclang/CIndexCodeCompletion.cpp
@@ -616,7 +616,7 @@ namespace {
       if (!baseType.isNull()) {
         // Get the declaration for a class/struct/union/enum type
         if (const TagType *Tag = baseType->getAs<TagType>())
-          D = Tag->getDecl();
+          D = Tag->getOriginalDecl();
         // Get the @interface declaration for a (possibly-qualified) Objective-C
         // object pointer type, e.g., NSString*
         else if (const ObjCObjectPointerType *ObjPtr = 
@@ -628,7 +628,7 @@ namespace {
         // Get the class for a C++ injected-class-name
         else if (const InjectedClassNameType *Injected =
                  baseType->getAs<InjectedClassNameType>())
-          D = Injected->getDecl();
+          D = Injected->getOriginalDecl();
       }
 
       if (D != nullptr) {
diff --git a/clang/tools/libclang/CXCursor.cpp b/clang/tools/libclang/CXCursor.cpp
index a6301daa672c3..3c4062410eac1 100644
--- a/clang/tools/libclang/CXCursor.cpp
+++ b/clang/tools/libclang/CXCursor.cpp
@@ -1332,16 +1332,10 @@ CXCursor cxcursor::getTypeRefCursor(CXCursor cursor) {
   TypeLoc TL = Type->getTypeLoc();
   SourceLocation Loc = TL.getBeginLoc();
 
-  if (const ElaboratedType *ElabT = Ty->getAs<ElaboratedType>()) {
-    Ty = ElabT->getNamedType();
-    ElaboratedTypeLoc ElabTL = TL.castAs<ElaboratedTypeLoc>();
-    Loc = ElabTL.getNamedTypeLoc().getBeginLoc();
-  }
-
   if (const TypedefType *Typedef = Ty->getAs<TypedefType>())
     return MakeCursorTypeRef(Typedef->getDecl(), Loc, TU);
   if (const TagType *Tag = Ty->getAs<TagType>())
-    return MakeCursorTypeRef(Tag->getDecl(), Loc, TU);
+    return MakeCursorTypeRef(Tag->getOriginalDecl(), Loc, TU);
   if (const TemplateTypeParmType *TemplP = Ty->getAs<TemplateTypeParmType>())
     return MakeCursorTypeRef(TemplP->getDecl(), Loc, TU);
 
diff --git a/clang/tools/libclang/CXIndexDataConsumer.cpp b/clang/tools/libclang/CXIndexDataConsumer.cpp
index f0d92e8c40124..941e39a582758 100644
--- a/clang/tools/libclang/CXIndexDataConsumer.cpp
+++ b/clang/tools/libclang/CXIndexDataConsumer.cpp
@@ -357,7 +357,7 @@ CXIndexDataConsumer::CXXBasesListInfo::CXXBasesListInfo(const CXXRecordDecl *D,
           TST = T->getAs<TemplateSpecializationType>()) {
       BaseD = TST->getTemplateName().getAsTemplateDecl();
     } else if (const RecordType *RT = T->getAs<RecordType>()) {
-      BaseD = RT->getDecl();
+      BaseD = RT->getOriginalDecl();
     }
 
     if (BaseD)
@@ -389,13 +389,22 @@ SourceLocation CXIndexDataConsumer::CXXBasesListInfo::getBaseLoc(
   if (QualifiedTypeLoc QL = TL.getAs<QualifiedTypeLoc>())
     TL = QL.getUnqualifiedLoc();
 
-  if (ElaboratedTypeLoc EL = TL.getAs<ElaboratedTypeLoc>())
-    return EL.getNamedTypeLoc().getBeginLoc();
-  if (DependentNameTypeLoc DL = TL.getAs<DependentNameTypeLoc>())
-    return DL.getNameLoc();
-  if (DependentTemplateSpecializationTypeLoc DTL =
-          TL.getAs<DependentTemplateSpecializationTypeLoc>())
-    return DTL.getTemplateNameLoc();
+  // FIXME: Factor this out, a lot of TypeLoc users seem to need a generic
+  // TypeLoc::getNameLoc()
+  if (auto TTL = TL.getAs<DependentNameTypeLoc>())
+    return TTL.getNameLoc();
+  if (auto TTL = TL.getAs<DependentTemplateSpecializationTypeLoc>())
+    return TTL.getTemplateNameLoc();
+  if (auto TTL = TL.getAs<TemplateSpecializationTypeLoc>())
+    return TTL.getTemplateNameLoc();
+  if (auto TTL = TL.getAs<TagTypeLoc>())
+    return TTL.getNameLoc();
+  if (auto TTL = TL.getAs<TypedefTypeLoc>())
+    return TTL.getNameLoc();
+  if (auto TTL = TL.getAs<UnresolvedUsingTypeLoc>())
+    return TTL.getNameLoc();
+  if (auto TTL = TL.getAs<UsingTypeLoc>())
+    return TTL.getNameLoc();
 
   return Loc;
 }
diff --git a/clang/tools/libclang/CXType.cpp b/clang/tools/libclang/CXType.cpp
index e7864e6d62e4d..11d02d8088918 100644
--- a/clang/tools/libclang/CXType.cpp
+++ b/clang/tools/libclang/CXType.cpp
@@ -118,7 +118,6 @@ static CXTypeKind GetTypeKind(QualType T) {
     TKCASE(ExtVector);
     TKCASE(MemberPointer);
     TKCASE(Auto);
-    TKCASE(Elaborated);
     TKCASE(Pipe);
     TKCASE(Attributed);
     TKCASE(BTFTagAttributed);
@@ -225,6 +224,11 @@ FindTemplateArgumentTypeAt(ArrayRef<TemplateArgument> TA, unsigned index) {
   return std::nullopt;
 }
 
+static CXType getTypeDeclType(const ASTContext &Context, CXTranslationUnit TU,
+                              const TypeDecl *TD) {
+  return MakeCXType(Context.getTypeDeclType(TD), TU);
+}
+
 CXType clang_getCursorType(CXCursor C) {
   using namespace cxcursor;
 
@@ -244,7 +248,7 @@ CXType clang_getCursorType(CXCursor C) {
       return MakeCXType(QualType(), TU);
 
     if (const TypeDecl *TD = dyn_cast<TypeDecl>(D))
-      return MakeCXType(Context.getTypeDeclType(TD), TU);
+      return getTypeDeclType(Context, TU, TD);
     if (const ObjCInterfaceDecl *ID = dyn_cast<ObjCInterfaceDecl>(D))
       return MakeCXType(Context.getObjCInterfaceType(ID), TU);
     if (const DeclaratorDecl *DD = dyn_cast<DeclaratorDecl>(D))
@@ -271,11 +275,8 @@ CXType clang_getCursorType(CXCursor C) {
       return MakeCXType(T, TU);
     }
 
-    case CXCursor_TypeRef: {
-      QualType T = Context.getTypeDeclType(getCursorTypeRef(C).first);
-      return MakeCXType(T, TU);
-
-    }
+    case CXCursor_TypeRef:
+      return getTypeDeclType(Context, TU, getCursorTypeRef(C).first);
 
     case CXCursor_CXXBaseSpecifier:
       return cxtype::MakeCXType(getCursorCXXBaseSpecifier(C)->getType(), TU);
@@ -545,11 +546,11 @@ CXCursor clang_getTypeDeclaration(CXType CT) {
     break;
   case Type::Record:
   case Type::Enum:
-    D = cast<TagType>(TP)->getDecl();
+    D = cast<TagType>(TP)->getOriginalDecl();
     break;
   case Type::TemplateSpecialization:
     if (const RecordType *Record = TP->getAs<RecordType>())
-      D = Record->getDecl();
+      D = Record->getOriginalDecl();
     else
       D = cast<TemplateSpecializationType>(TP)->getTemplateName()
                                                          .getAsTemplateDecl();
@@ -563,14 +564,10 @@ CXCursor clang_getTypeDeclaration(CXType CT) {
     break;
 
   case Type::InjectedClassName:
-    D = cast<InjectedClassNameType>(TP)->getDecl();
+    D = cast<InjectedClassNameType>(TP)->getOriginalDecl();
     break;
 
-  // FIXME: Template type parameters!      
-
-  case Type::Elaborated:
-    TP = cast<ElaboratedType>(TP)->getNamedType().getTypePtrOrNull();
-    goto try_again;
+    // FIXME: Template type parameters!
 
   default:
     break;
@@ -990,7 +987,7 @@ CXType clang_Type_getClassType(CXType CT) {
   const Type *TP = T.getTypePtrOrNull();
 
   if (TP && TP->getTypeClass() == Type::MemberPointer) {
-    ET = Ctx.getTypeDeclType(
+    ET = Ctx.getCanonicalTagType(
         cast<MemberPointerType>(TP)->getMostRecentCXXRecordDecl());
   }
   return MakeCXType(ET, GetTU(CT));
@@ -1040,7 +1037,7 @@ static long long visitRecordForValidation(const RecordDecl *RD) {
       return CXTypeLayoutError_Dependent;
     // recurse
     if (const RecordType *ChildType = I->getType()->getAs<RecordType>()) {
-      if (const RecordDecl *Child = ChildType->getDecl()) {
+      if (const RecordDecl *Child = ChildType->getOriginalDecl()) {
         long long ret = visitRecordForValidation(Child);
         if (ret < 0)
           return ret;
@@ -1390,10 +1387,9 @@ unsigned clang_Cursor_isInlineNamespace(CXCursor C) {
 
 CXType clang_Type_getNamedType(CXType CT){
   QualType T = GetQualType(CT);
-  const Type *TP = T.getTypePtrOrNull();
 
-  if (TP && TP->getTypeClass() == Type::Elaborated)
-    return MakeCXType(cast<ElaboratedType>(TP)->getNamedType(), GetTU(CT));
+  if (!T.isNull() && T->getPrefix())
+    return MakeCXType(T, GetTU(CT));
 
   return MakeCXType(QualType(), GetTU(CT));
 }
diff --git a/clang/tools/libclang/CursorVisitor.h b/clang/tools/libclang/CursorVisitor.h
index 949b73908c315..d5ab699756988 100644
--- a/clang/tools/libclang/CursorVisitor.h
+++ b/clang/tools/libclang/CursorVisitor.h
@@ -255,12 +255,12 @@ class CursorVisitor : public DeclVisitor<CursorVisitor, bool>,
 
   // Name visitor
   bool VisitDeclarationNameInfo(DeclarationNameInfo Name);
-  bool VisitNestedNameSpecifier(NestedNameSpecifier *NNS, SourceRange Range);
   bool VisitNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS);
 
   // Template visitors
   bool VisitTemplateParameters(const TemplateParameterList *Params);
-  bool VisitTemplateName(TemplateName Name, SourceLocation Loc);
+  bool VisitTemplateName(TemplateName Name, SourceLocation NameLoc,
+                         NestedNameSpecifierLoc NNS);
   bool VisitTemplateArgumentLoc(const TemplateArgumentLoc &TAL);
 
   // Type visitors