[analyzer] Let the checkers query upper and lower bounds on symbols (llvm#74141)

This commit extends the class `SValBuilder` with the methods
`getMinValue()` and `getMaxValue()` to that work like
`SValBuilder::getKnownValue()` but return the minimal/maximal possible
value the `SVal` is not perfectly constrained.

This extension of the ConstraintManager API is discussed at:
https://discourse.llvm.org/t/expose-the-inferred-range-information-in-warning-messages/75192

As a simple proof-of-concept application of this new API, this commit
extends a message from `core.BitwiseShift` with some range information
that reports the assumptions of the analyzer.

My main motivation for adding these methods is that I'll also want to
use them in `ArrayBoundCheckerV2` to make the error messages less
awkward, but I'm starting with this simpler and less important usecase
because I want to avoid merge conflicts with my other commit
llvm#72107 which is currently under
review.

The testcase `too_large_right_operand_compound()` shows a situation
where querying the range information does not work (and the extra
information is not added to the error message). This also affects the
debug utility `clang_analyzer_value()`, so the problem isn't in the
fresh code. I'll do some investigations to resolve this, but I think
that this commit is a step forward even with this limitation.

Author: NagyDonat

clang/include/clang/StaticAnalyzer/Core/PathSensitive/ConstraintManager.h

@@ -110,6 +110,22 @@ class ConstraintManager {
     return nullptr;
   }
 
+  /// Attempt to return the minimal possible value for a given symbol. Note
+  /// that a ConstraintManager is not obligated to return a lower bound, it may
+  /// also return nullptr.
+  virtual const llvm::APSInt *getSymMinVal(ProgramStateRef state,
+                                           SymbolRef sym) const {
+    return nullptr;
+  }
+
+  /// Attempt to return the minimal possible value for a given symbol. Note
+  /// that a ConstraintManager is not obligated to return a lower bound, it may
+  /// also return nullptr.
+  virtual const llvm::APSInt *getSymMaxVal(ProgramStateRef state,
+                                           SymbolRef sym) const {
+    return nullptr;
+  }
+
   /// Scan all symbols referenced by the constraints. If the symbol is not
   /// alive, remove it.
   virtual ProgramStateRef removeDeadBindings(ProgramStateRef state,

clang/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h

@@ -110,6 +110,14 @@ class SValBuilder {
   /// that value is returned. Otherwise, returns NULL.
   virtual const llvm::APSInt *getKnownValue(ProgramStateRef state, SVal val) = 0;
 
+  /// Tries to get the minimal possible (integer) value of a given SVal. If the
+  /// constraint manager cannot provide an useful answer, this returns NULL.
+  virtual const llvm::APSInt *getMinValue(ProgramStateRef state, SVal val) = 0;
+
+  /// Tries to get the maximal possible (integer) value of a given SVal. If the
+  /// constraint manager cannot provide an useful answer, this returns NULL.
+  virtual const llvm::APSInt *getMaxValue(ProgramStateRef state, SVal val) = 0;
+
   /// Simplify symbolic expressions within a given SVal. Return an SVal
   /// that represents the same value, but is hopefully easier to work with
   /// than the original SVal.

clang/lib/StaticAnalyzer/Checkers/BitwiseShiftChecker.cpp

@@ -172,18 +172,24 @@ BugReportPtr BitwiseShiftValidator::checkOvershift() {
 
   const SVal Right = Ctx.getSVal(operandExpr(OperandSide::Right));
 
-  std::string RightOpStr = "";
+  std::string RightOpStr = "", LowerBoundStr = "";
   if (auto ConcreteRight = Right.getAs<nonloc::ConcreteInt>())
     RightOpStr = formatv(" '{0}'", ConcreteRight->getValue());
+  else {
+    SValBuilder &SVB = Ctx.getSValBuilder();
+    if (const llvm::APSInt *MinRight = SVB.getMinValue(FoldedState, Right)) {
+      LowerBoundStr = formatv(" >= {0},", MinRight->getExtValue());
+    }
+  }
 
   std::string ShortMsg = formatv(
       "{0} shift{1}{2} overflows the capacity of '{3}'",
       isLeftShift() ? "Left" : "Right", RightOpStr.empty() ? "" : " by",
       RightOpStr, LHSTy.getAsString());
-  std::string Msg =
-      formatv("The result of {0} shift is undefined because the right "
-              "operand{1} is not smaller than {2}, the capacity of '{3}'",
-              shiftDir(), RightOpStr, LHSBitWidth, LHSTy.getAsString());
+  std::string Msg = formatv(
+      "The result of {0} shift is undefined because the right "
+      "operand{1} is{2} not smaller than {3}, the capacity of '{4}'",
+      shiftDir(), RightOpStr, LowerBoundStr, LHSBitWidth, LHSTy.getAsString());
   return createBugReport(ShortMsg, Msg);
 }
 

clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp

@@ -1876,6 +1876,12 @@ class RangeConstraintManager : public RangedConstraintManager {
   const llvm::APSInt *getSymVal(ProgramStateRef State,
                                 SymbolRef Sym) const override;
 
+  const llvm::APSInt *getSymMinVal(ProgramStateRef State,
+                                   SymbolRef Sym) const override;
+
+  const llvm::APSInt *getSymMaxVal(ProgramStateRef State,
+                                   SymbolRef Sym) const override;
+
   ProgramStateRef removeDeadBindings(ProgramStateRef State,
                                      SymbolReaper &SymReaper) override;
 
@@ -2863,6 +2869,22 @@ const llvm::APSInt *RangeConstraintManager::getSymVal(ProgramStateRef St,
   return T ? T->getConcreteValue() : nullptr;
 }
 
+const llvm::APSInt *RangeConstraintManager::getSymMinVal(ProgramStateRef St,
+                                                         SymbolRef Sym) const {
+  const RangeSet *T = getConstraint(St, Sym);
+  if (!T || T->isEmpty())
+    return nullptr;
+  return &T->getMinValue();
+}
+
+const llvm::APSInt *RangeConstraintManager::getSymMaxVal(ProgramStateRef St,
+                                                         SymbolRef Sym) const {
+  const RangeSet *T = getConstraint(St, Sym);
+  if (!T || T->isEmpty())
+    return nullptr;
+  return &T->getMaxValue();
+}
+
 //===----------------------------------------------------------------------===//
 //                Remove dead symbols from existing constraints
 //===----------------------------------------------------------------------===//

clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp

@@ -28,7 +28,11 @@ class SimpleSValBuilder : public SValBuilder {
   // returns NULL.
   // This is an implementation detail. Checkers should use `getKnownValue()`
   // instead.
-  const llvm::APSInt *getConstValue(ProgramStateRef state, SVal V);
+  static const llvm::APSInt *getConstValue(ProgramStateRef state, SVal V);
+
+  // Helper function that returns the value stored in a nonloc::ConcreteInt or
+  // loc::ConcreteInt.
+  static const llvm::APSInt *getConcreteValue(SVal V);
 
   // With one `simplifySValOnce` call, a compound symbols might collapse to
   // simpler symbol tree that is still possible to further simplify. Thus, we
@@ -76,6 +80,16 @@ class SimpleSValBuilder : public SValBuilder {
   /// (integer) value, that value is returned. Otherwise, returns NULL.
   const llvm::APSInt *getKnownValue(ProgramStateRef state, SVal V) override;
 
+  /// Evaluates a given SVal by recursively evaluating and simplifying the
+  /// children SVals, then returns its minimal possible (integer) value. If the
+  /// constraint manager cannot provide a meaningful answer, this returns NULL.
+  const llvm::APSInt *getMinValue(ProgramStateRef state, SVal V) override;
+
+  /// Evaluates a given SVal by recursively evaluating and simplifying the
+  /// children SVals, then returns its maximal possible (integer) value. If the
+  /// constraint manager cannot provide a meaningful answer, this returns NULL.
+  const llvm::APSInt *getMaxValue(ProgramStateRef state, SVal V) override;
+
   SVal simplifySVal(ProgramStateRef State, SVal V) override;
 
   SVal MakeSymIntVal(const SymExpr *LHS, BinaryOperator::Opcode op,
@@ -1182,18 +1196,22 @@ SVal SimpleSValBuilder::evalBinOpLN(ProgramStateRef state,
 
 const llvm::APSInt *SimpleSValBuilder::getConstValue(ProgramStateRef state,
                                                      SVal V) {
-  if (V.isUnknownOrUndef())
-    return nullptr;
+  if (const llvm::APSInt *Res = getConcreteValue(V))
+    return Res;
 
+  if (SymbolRef Sym = V.getAsSymbol())
+    return state->getConstraintManager().getSymVal(state, Sym);
+
+  return nullptr;
+}
+
+const llvm::APSInt *SimpleSValBuilder::getConcreteValue(SVal V) {
   if (std::optional<loc::ConcreteInt> X = V.getAs<loc::ConcreteInt>())
     return &X->getValue();
 
   if (std::optional<nonloc::ConcreteInt> X = V.getAs<nonloc::ConcreteInt>())
     return &X->getValue();
 
-  if (SymbolRef Sym = V.getAsSymbol())
-    return state->getConstraintManager().getSymVal(state, Sym);
-
   return nullptr;
 }
 
@@ -1202,6 +1220,32 @@ const llvm::APSInt *SimpleSValBuilder::getKnownValue(ProgramStateRef state,
   return getConstValue(state, simplifySVal(state, V));
 }
 
+const llvm::APSInt *SimpleSValBuilder::getMinValue(ProgramStateRef state,
+                                                   SVal V) {
+  V = simplifySVal(state, V);
+
+  if (const llvm::APSInt *Res = getConcreteValue(V))
+    return Res;
+
+  if (SymbolRef Sym = V.getAsSymbol())
+    return state->getConstraintManager().getSymMinVal(state, Sym);
+
+  return nullptr;
+}
+
+const llvm::APSInt *SimpleSValBuilder::getMaxValue(ProgramStateRef state,
+                                                   SVal V) {
+  V = simplifySVal(state, V);
+
+  if (const llvm::APSInt *Res = getConcreteValue(V))
+    return Res;
+
+  if (SymbolRef Sym = V.getAsSymbol())
+    return state->getConstraintManager().getSymMaxVal(state, Sym);
+
+  return nullptr;
+}
+
 SVal SimpleSValBuilder::simplifyUntilFixpoint(ProgramStateRef State, SVal Val) {
   SVal SimplifiedVal = simplifySValOnce(State, Val);
   while (SimplifiedVal != Val) {

clang/test/Analysis/bitwise-shift-common.c

@@ -1,11 +1,13 @@
 // RUN: %clang_analyze_cc1 -analyzer-checker=core.BitwiseShift \
+// RUN:    -analyzer-checker=debug.ExprInspection \
 // RUN:    -analyzer-output=text -verify \
 // RUN:    -triple x86_64-pc-linux-gnu -x c %s \
 // RUN:    -Wno-shift-count-negative -Wno-shift-negative-value \
 // RUN:    -Wno-shift-count-overflow -Wno-shift-overflow \
 // RUN:    -Wno-shift-sign-overflow
 //
 // RUN: %clang_analyze_cc1 -analyzer-checker=core.BitwiseShift \
+// RUN:    -analyzer-checker=debug.ExprInspection \
 // RUN:    -analyzer-config core.BitwiseShift:Pedantic=true \
 // RUN:    -analyzer-output=text -verify \
 // RUN:    -triple x86_64-pc-linux-gnu -x c++ -std=c++20 %s \
@@ -85,17 +87,23 @@ int too_large_right_operand_symbolic(int left, int right) {
     return 0;
   return left >> right;
   // expected-warning@-1 {{Right shift overflows the capacity of 'int'}}
-  // expected-note@-2 {{The result of right shift is undefined because the right operand is not smaller than 32, the capacity of 'int'}}
-  // NOTE: the messages of the checker are a bit vague in this case, but the
-  // tracking of the variables reveals our knowledge about them.
+  // expected-note@-2 {{The result of right shift is undefined because the right operand is >= 32, not smaller than 32, the capacity of 'int'}}
 }
 
+void clang_analyzer_value(int);
 int too_large_right_operand_compound(unsigned short arg) {
   // Note: this would be valid code with an 'unsigned int' because
   // unsigned addition is allowed to overflow.
+  clang_analyzer_value(32+arg);
+  // expected-warning@-1 {{32s:{ [-2147483648, 2147483647] }}
+  // expected-note@-2 {{32s:{ [-2147483648, 2147483647] }}
   return 1 << (32 + arg);
   // expected-warning@-1 {{Left shift overflows the capacity of 'int'}}
   // expected-note@-2 {{The result of left shift is undefined because the right operand is not smaller than 32, the capacity of 'int'}}
+  // FIXME: this message should be
+  //     {{The result of left shift is undefined because the right operand is >= 32, not smaller than 32, the capacity of 'int'}}
+  // but for some reason neither the new logic, nor debug.ExprInspection and
+  // clang_analyzer_value reports this range information.
 }
 
 // TEST STATE UPDATES