[PATCH] D38637: [InstSimplify] don't let poison inhibit an easy fold

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D38637#891147, @efriedma wrote:

> The exact definition of poison is still getting refined, but it's different from undef.  undef is a bit-wise property, which is why ComputeKnownBits has to be careful around it.  poison works differently; essentially, any arithmetic or logical operation which has poison as an input produces poison, no matter what the other input is.  So it doesn't matter what ComputeKnownBits returns for a known poison value.


Thanks! Then, it seems clear I can abandon the InstCombine fix, and I'll redo this one to work in value tracking directly.


https://reviews.llvm.org/D38637