[llvm] [AMDGPU] Inplace FI elimination during PEI for scalar copy instruction (PR #99556)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> It would still be good if we had an IR test that hit these cases

I think I've managed to craft one that will need some adjustment to hit the various cases 

https://github.com/llvm/llvm-project/pull/99556