[llvm] [AMDGPU] SIFixSgprCopies should not process twice VGPR to SGPR copies inserted by PHI preprocessing. (PR #134153)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

lgtm with some test cleanups, you don't need most of the stuff in the mir 

https://github.com/llvm/llvm-project/pull/134153