[PATCH] D68811: [CVP] Remove a masking operation if range information implies it's a noop

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: apilipenko, nikic, lebedev.ri.
Herald added subscribers: bollu, mcrosier.
Herald added a project: LLVM.

This is really a known bits style transformation, but known bits isn't context sensitive.  The particular case which comes up happens to involve a range which allows range based reasoning to eliminate the mask pattern, so handle that case specifically in CVP.

InstCombine likes to generate the mask-by-low-bits pattern when widening an arithmetic expression which includes a zext in the middle.


Repository:
  rL LLVM

https://reviews.llvm.org/D68811

Files:
  lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
  test/Transforms/CorrelatedValuePropagation/and.ll

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