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

[via llvm-commits]

LU-JOHN wrote:

Is it possible to hit this issue, but the COPY and use do not fall inside/outside of a loop?
@aobolensk and I discussed this privately, but we were not able to come up with a conclusion.

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