[PATCH] D102698: [InstCombine] Relaxed constraints of uses for exp(X) * exp(Y) -> exp(X + Y) and exp2(X) * exp2(Y) -> exp2(X + Y)

[Daniil Seredkin via Phabricator via llvm-commits]

vdsered added a comment.

As I understand it

  if (match(Op0, m_Intrinsic<Intrinsic::exp2>(m_Value(X))) &&
          match(Op1, m_Intrinsic<Intrinsic::exp2>(m_Value(Y))) &&
          isOnlyUserOfAnyOperand(&I))

will be

  if (match(Op0, m_Intrinsic<Intrinsic::exp2>(m_Value(X))) &&
          match(Op1, m_Intrinsic<Intrinsic::exp2>(m_Value(Y))) &&
          (X->hasOneUser() || Y -> hasOneUser()))

The difference between them is that isOnlyUserOfAnyOperand depends on how many operands an instruction has (a known count, we use it for mul now where it is 2). On the other, hasOneUser depends on the total number of uses of each operand (can be an arbitrary number). I'm not sure, but there can theoretically be situations when a number of uses is more than a number of ops, right?

@lebedev.ri, we could implement isOnlyUserOfAnyOperand like this

  bool llvm::isOnlyUserOfAnyOperand(Instruction *I) {
      return llvm::any_of(I->operands(), [](Value *V) { return V->hasOneUser(); })
  }

This solution would be good too especially because it is easier to understand, but I'd leave it as-is without hasOneUser in case there are no any performance/logical issues with it.


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  https://reviews.llvm.org/D102698/new/

https://reviews.llvm.org/D102698