[C++20] Fix a crash with spaceship and vector types

[AaronBallman]

Vector types cannot be directly compared, you get an error when you try to do so. This patch causes the explicitly defaulted spaceship operator to be implicitly deleted.

Fixes #137452

[llvmbot]

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

Vector types cannot be directly compared, you get an error when you try to do so. This patch causes the explicitly defaulted spaceship operator to be implicitly deleted.

Fixes #137452

---

Full diff: https://github.com/llvm/llvm-project/pull/139767.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+3)
• (modified) clang/lib/Sema/SemaDeclCXX.cpp (+5)
• (modified) clang/test/SemaCXX/cxx2a-three-way-comparison.cpp (+8)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index bc13d02e2d20b..3941eb51b00d7 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -118,6 +118,9 @@ C++23 Feature Support
 
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
+- Fixed a crash with a defaulted spaceship (``<=>``) operator when the class
+  contains a member declaration of vector type. Vector types cannot yet be
+  compared directly, so this causes the operator to be deleted. (#GH137452)
 
 C++17 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index cbccb567e2adf..2f2ff2d471c71 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -8651,6 +8651,11 @@ class DefaultedComparisonAnalyzer
         assert(Best->BuiltinParamTypes[2].isNull() &&
                "invalid builtin comparison");
 
+        // FIXME: If the type we deduced is a vector type, we mark the
+        // comparison as deleted because we don't yet support this.
+        if (isa<VectorType>(T))
+          return Result::deleted();
+
         if (NeedsDeducing) {
           std::optional<ComparisonCategoryType> Cat =
               getComparisonCategoryForBuiltinCmp(T);
diff --git a/clang/test/SemaCXX/cxx2a-three-way-comparison.cpp b/clang/test/SemaCXX/cxx2a-three-way-comparison.cpp
index b94225274fffb..36b603e4f7660 100644
--- a/clang/test/SemaCXX/cxx2a-three-way-comparison.cpp
+++ b/clang/test/SemaCXX/cxx2a-three-way-comparison.cpp
@@ -58,3 +58,11 @@ namespace PR44325 {
   // implicit rewrite rules, not for explicit use by programs.
   bool c = cmp_cat() < 0; // expected-warning {{zero as null pointer constant}}
 }
+
+namespace GH137452 {
+struct comparable_t {
+    __attribute__((vector_size(32))) double numbers;
+    auto operator<=>(const comparable_t& rhs) const = default; // expected-warning {{explicitly defaulted three-way comparison operator is implicitly deleted}} \
+                                                                  expected-note {{replace 'default' with 'delete'}}
+};
+} // namespace GH137452

[erichkeane]

The other versions of 'deleted' all seem to diagnose first, is there a reason to not do so here?

[AaronBallman]

Oh, I missed the "explain deleted" code paths entirely. I'll address that.

[Sirraide]

Do we want to issue a diagnostic for this? I would imagine that users could get confused about this if they don’t know why the operator is marked as deleted.

[Sirraide]

GCC does print a note explaining that this is not implemented apparently.

[AaronBallman]

Do we want to issue a diagnostic for this? I would imagine that users could get confused about this if they don’t know why the operator is marked as deleted.

Yeah, I missed that part of the patch. More changes coming.