[llvm] [InstCombine] Simplify demanded elements of vector intrinsics (PR #229498)

[Rudrajeet Pal via llvm-commits]

KineticTactic wrote:

I have read the policies and documented the AI usage. I have added a proof for the test I changed in `minmax-fold.ll`, but I am not fully sure how to provide a general proof for the transformation that my code does

https://github.com/llvm/llvm-project/pull/229498