[PATCH] D48987: [InstCombine] drop poison flags for shuffle transforms with undefs

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D48987#1153565, @lebedev.ri wrote:

> So my concerns weren't unfounded :/
>  Do we want to also do such kind of fixup in `VisitShl()` in instcombine, for every `shl` we visit?


Do you have an example of the problem you're thinking of? AFAIK, we won't hit this problem with scalars or general transforms because they don't modify constants like we're doing here. We do have a related foldShuffledBinop() function that I will review/fix if this patch looks right.


https://reviews.llvm.org/D48987