[clang] [llvm] [LLVM] Fix incorrect alignment on AMDGPU variadics (PR #96370)

[Jon Chesterfield via llvm-commits]

JonChesterfield wrote:

This PR is invalid.

First, the alignment on the eight byte pointer is supposed to be four. Increasing it to 8 makes things worse.

Second, I can't see any support for the claim that the code is incrementing by the alignment of the value, as opposed to the size.

The frame is setup as a struct instance with explicit padding by Int8Tys and the calculation there is correct.

The va_arg increment is done in CodeGen:emitVoidPtrVAArg, where DirectSize is ValueInfo.Width, aligned to the 4 byte slot size, then stored. It does not increment the iterator by the alignment of the type.

The lowering pass is doing exactly what was intended.


https://github.com/llvm/llvm-project/pull/96370