[PATCH] D58475: [X86] Improve detection of unneeded shift amount masking to also handle the case that the LHS has known zeroes in it

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: RKSimon, spatel.
Herald added a subscriber: jdoerfert.

If the LHS has known zeros, the RHS immediate will have had bits removed. So call computeKnownBits to get the known zeroes so we can handle this case.


https://reviews.llvm.org/D58475

Files:
  lib/Target/X86/X86ISelDAGToDAG.cpp
  lib/Target/X86/X86InstrCompiler.td
  test/CodeGen/X86/btc_bts_btr.ll
  test/CodeGen/X86/rotate4.ll

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