[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 commented:

In terms of high-level approach, an alternative I'd like to consider is to instead add support for the ctz/abs poison flag to hasPoisonGeneratingAnnotations / dropPoisonGeneratingAnnotations. I believe that way we'll automatically handle this through the select equivalence fold.

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