[llvm] [ConstraintElim] Teach checkAndReplaceCondition about samesign (PR #128168)

[Marina Taylor via llvm-commits]

citymarina wrote:

Thanks, I've updated the description. If this is good to go, I could use some help to land as I don't yet have write access (I'll probably have enough commits to request it after this).

https://github.com/llvm/llvm-project/pull/128168