[llvm-branch-commits] [clang] [HLSL] Use memcpy for HLSL buffer copies that don't have padding (PR #173093)

[Justin Bogner via llvm-branch-commits]

bogner wrote:

> I think this can cause issues in the spirv backend. I believe some optimizations will replace short memcopy with a load and store of integers regardless of the actual type of the memory. That does not translate well to spirv.

I guess you're referring to the buggy logic in InstCombinerImpl::SimplifyAnyMemTransfer that assumes all integer types are appropriate to replace small memcpys with. We had an attempt to (partially) fix that in #169966 that was rejected by upstream in preference to wait for the [byte type](https://blog.llvm.org/posts/2025-08-29-gsoc-byte-type/) which will nominally resolve this. I guess that means we should block the issue here like we did with #165753 and wait for the byte type stuff to be finished before cleaning this up.

https://github.com/llvm/llvm-project/pull/173093