[PATCH] D48768: [X86] When have BMI2, prefer shifts to clear low/high bits, rather than variable mask.

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

This implements what was suggested. The BMI2 case looks like a win because it can save an instruction. I'm still not sure about the base case. @craig.topper or @RKSimon probably have a better sense for how that compares on various uarch. We could argue that this patch is just restoring the previous behavior, so that's the least risky and preferred way to go.


Repository:
  rL LLVM

https://reviews.llvm.org/D48768