[llvm] [InstCombine] fold (Binop phi(a, b) phi(b, a)) -> (Binop a, b) while Binop is commutative. (PR #75765)

[Nikita Popov via llvm-commits]

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@@ -1096,6 +1096,50 @@ Value *InstCombinerImpl::foldUsingDistributiveLaws(BinaryOperator &I) {
   return SimplifySelectsFeedingBinaryOp(I, LHS, RHS);
 }
 
+bool InstCombinerImpl::matchSymmetricPhiNodesPair(PHINode *LHS, PHINode *RHS) {
+
+  if (LHS->getNumIncomingValues() != 2 || RHS->getNumIncomingValues() != 2)
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nikic wrote:

I don't think we really need this restriction. We just need all pairs of phi operands to have the same two values (in either order). The number of pairs doesn't matter.

https://github.com/llvm/llvm-project/pull/75765