[llvm] [AMDGPU] Fix waterfall inreg call args on gfx90a: hoist defs + avoid AGPR sources (PR #194890)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

This should be 2 separate changes. I also find the second part very suspect. This pass shouldn't need to do brute force searching through a loop, instruction reordering, or splicing 

https://github.com/llvm/llvm-project/pull/194890