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

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

If I understand correctly, the reason computeKnownBits can't handle this is that it doesn't know what to do with a known poison value?  We could just solve the issue in computeKnownBits: currently, it says there are no known bits when it detects a shift overflow, but it could just say, for example, that all the bits are known zero (since the result of computeKnownBits is only meaningful if the value isn't poison).


https://reviews.llvm.org/D38637