[PATCH] D30311: [ValueTracking] Don't do an unchecked shift in ComputeNumSignBits

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> why not be maximally aggressive?

This is not how undef works... unlike poison, you can't assert sign bits you don't actually have.


https://reviews.llvm.org/D30311