[PATCH] D47891: [InstSimplify] shl nuw %x, %y -> %x iff KnownBits says %x is negative.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

If you use the generic instruction simplify entry point, we literally do call computeKnownBits on every input. It's the last thing we do if no simplications are found. If you call the individual instruction entry points like InstCombine does we don't do this. InstCombine itself will try to do something similar in main worklist processing code, but only when ExpensiveCombines is true. I've never understood why InstSimplify was more aggressive here.


Repository:
  rL LLVM

https://reviews.llvm.org/D47891