[llvm] [InstCombine] optimize unnecessary sext instruction with add + cmp (PR #152291)

[Gaurav Dhingra via llvm-commits]

gxyd wrote:

> Please see llvm.org/docs/InstCombineContributorGuide.html. Please add an alive2 proof to the PR description.

I've actually left a comment on the linked issue: https://github.com/llvm/llvm-project/issues/130088#issuecomment-3170208582, where I need help with the issue understanding currently.

https://github.com/llvm/llvm-project/pull/152291