[PATCH] D99674: [InstCombine] Conditionally fold select i1 into and/or

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

Apart from being unsafe, this pair of transforms also goes against the usual rule of not creating more instructions than we started with:

  // select a, false, b -> select !a, b, false
  if (match(TrueVal, m_Zero())) {
    Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
    return SelectInst::Create(NotCond, FalseVal, Zero);
  }
  // select a, b, true -> select !a, true, b
  if (match(FalseVal, m_One())) {
    Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
    return SelectInst::Create(NotCond, One, TrueVal);
  }

I think we should just delete those (either with or without reverting this patch). We can add a safe transform for "select i1 %x, i1 0, i1 1 --> xor i1 %x, -1" to avoid a regression:
https://alive2.llvm.org/ce/z/Bhdy-Y


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D99674