[clang] [llvm] [opt][AMDGPU] Add pass to handle AMDGCN pseudo-intrinsics target specific info), start with `llvm.amdgcn.wavefrontsize` (PR #114481)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Just adding this to the pass pipeline where it is is no better than just doing it in instcombine, which is the natural place to do this. This patch, like instcombine, still has the problem that we don't know if we're producing the final code.

Yeah that was my concern, it could go in the backend passes but then that would be pretty late. However, this is probably legal in general if the function has `wavefrontsize` attrs.

https://github.com/llvm/llvm-project/pull/114481