[PATCH] D145852: [Clang][AST] Fix __has_unique_object_representations computation for unnamed bitfields.

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: clang/lib/AST/ASTContext.cpp:2817
+    // unique representation.
+    if (Field->isUnnamedBitfield() && BitfieldSize > 0)
+      return std::nullopt;
----------------
I think the check for a non-zero bit-field width might not be completely correct in cases where it's used to split an allocation unit. I suggested a test case below.


================
Comment at: clang/test/SemaCXX/type-traits.cpp:2886-2889
+struct UnnamedEmptyBitfield {
+  int named;
+  int : 0;
+};
----------------
I think there's one more test to add:
```
struct UnnamedEmptyBitfieldSplit {
  short named;
  int : 0;
  short also_named;
};
static_assert(sizeof(UnnamedEmptyBitfieldSplit) != (sizeof(short) * 2));
static_assert(!has_unique_object_representations<UnnamedEmptyBitfieldSplit>::value, "Bitfield padding");
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D145852/new/

https://reviews.llvm.org/D145852