[PATCH] D103424: [IndVars] Don't forget value when inferring nowrap flags

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added a comment.

Did you try a lightweight (and absolutely NFCish) approach of dropping SCEV 1 time instead of 2? Like

  if (!BO->hasNoUnsignedWrap() &&
      willNotOverflow(SE, BO->getOpcode(), /* Signed */ false, LHS, RHS)) {
    BO->setHasNoUnsignedWrap();
    Changed = true;
  }
  
  if (!BO->hasNoSignedWrap() &&
      willNotOverflow(SE, BO->getOpcode(), /* Signed */ true, LHS, RHS)) {
    BO->setHasNoSignedWrap();
    Changed = true;
  }
  if (Changed)
    SE->forgetValue(BO);

? Curious if it improves the situation.

As for this patch, I don't have a strong opinion. To me it looks that dropping SCEV here can be useful to infer nsw/nuw for some AddRec involving BO, and, consequently, prove iteration count of some loop that depends on it. Not sure how often does it happen and how useful it is, though.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D103424/new/

https://reviews.llvm.org/D103424