4497ec293a
This is a follow-up from the conversation starting at https://github.com/llvm/llvm-project/pull/93809#issuecomment-2173729801 The root problem that motivated the change are external AST sources that compute `ASTRecordLayout`s themselves instead of letting Clang compute them from the AST. One such example is LLDB using DWARF to get the definitive offsets and sizes of C++ structures. Such layouts should be considered correct (modulo buggy DWARF), but various assertions and lowering logic around the `CGRecordLayoutBuilder` relies on the AST having `[[no_unique_address]]` attached to them. This is a layout-altering attribute which is not encoded in DWARF. This causes us LLDB to trip over the various LLVM<->Clang layout consistency checks. There has been precedent for avoiding such layout-altering attributes from affecting lowering with externally-provided layouts (e.g., packed structs). This patch proposes to replace the `isZeroSize` checks in `CGRecordLayoutBuilder` (which roughly means "empty field with [[no_unique_address]]") with checks for `CodeGen::isEmptyField`/`CodeGen::isEmptyRecord`. **Details** The main strategy here was to change the `isZeroSize` check in `CGRecordLowering::accumulateFields` and `CGRecordLowering::accumulateBases` to use the `isEmptyXXX` APIs instead, preventing empty fields from being added to the `Members` and `Bases` structures. The rest of the changes fall out from here, to prevent lookups into these structures (for field numbers or base indices) from failing. Added `isEmptyRecordForLayout` and `isEmptyFieldForLayout` (open to better naming suggestions). The main difference to the existing `isEmptyRecord`/`isEmptyField` APIs, is that the `isEmptyXXXForLayout` counterparts don't have special treatment for `unnamed bitfields`/arrays and also treat fields of empty types as if they had `[[no_unique_address]]` (i.e., just like the `AsIfNoUniqueAddr` in `isEmptyField` does).
54 KiB
54 KiB