[PATCH] D132333: [DAG] Strip poison generating flags in freeze(op()) -> op(freeze()) fold

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
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This patch follows the InstCombine approach of stripping poison generating flags (nsw/nuw from add/sub etc.) to allow us to push a freeze() through the op. It's coaser than InstCombine as it doesn't retain any flags, but we have plenty of DAG folds that do the same thing already. We assert that the newly generated op isGuaranteedNotToBeUndefOrPoison.

Similar to the ValueTracking approach, isGuaranteedNotToBeUndefOrPoison has been updated to confirm that if an op can't create undef/poison and its operands are guaranteed to be undef/poison - then its not undef/poison. This is just for the generic opcodes . - target specific opcodes will need to do this manually just in case they have some special cases.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D132333

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  llvm/test/CodeGen/X86/freeze-binary.ll

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