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

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> 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.
> 
> (I think that may allow removing this special case fold in InstCombine entirely?)

Do you mean we can perform this fold in `simplifyWithOpReplaced`?


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