[llvm] [InstCombine] Fold ((X + AddC) & Mask) ^ Mask to ((Mask - AddC) - X) & Mask (PR #174278)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

>  I think the %sub = subnsw i32 0, %x syntax alone breaks the alive2 verification, as in the example shown by

But the tgt function was directly extracted from the IR diff, right? I cannot reproduce this when I run `opt -passes=instcombine` with your patch (excluding the nsw inference). I guess there is some missing context in the alive2 proof. Both your patch and the rest of InstCombine are fine.


https://github.com/llvm/llvm-project/pull/174278