[llvm] [InstCombine] Fold `X!=Y ? ctz(X^Y, true) : BW -> ctz(X^Y, false)` (PR #128483)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

LGTM. I think the patch is simple enough that we can land this for now, and generalize later.

https://github.com/llvm/llvm-project/pull/128483