[clang] [llvm] [AMDGPU] Add initial support for VGPR as memory (PR #205435)

[Diana Picus via cfe-commits]

https://github.com/rovka commented:

I think it would be good to add some PEI-directed tests to make sure we don't spill any of these registers if they end up in the callee-saved area.

https://github.com/llvm/llvm-project/pull/205435