[llvm] [AMDGPU] Fix SIFoldOperands miscompiling values that leave a divergent loop (PR #203256)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I'd also like to see an end to end test, and another similar test for peephole-opt. It doesn't make sense to me that we would hit this kind of issue first here, rather than there 

https://github.com/llvm/llvm-project/pull/203256