[llvm] [SimplifyCFG] Add support for hoisting commutative instructions (PR #104805)

[Nikita Popov via llvm-commits]

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@@ -1583,6 +1583,26 @@ static void hoistLockstepIdenticalDbgVariableRecords(
   }
 }
 
+static bool areIdenticalUpToCommutativity(const Instruction *I1,
+                                          const Instruction *I2) {
+  if (I1->isIdenticalToWhenDefined(I2))
+    return true;
+
+  if (auto *Cmp1 = dyn_cast<CmpInst>(I1))
+    if (auto *Cmp2 = dyn_cast<CmpInst>(I2))
+      return Cmp1->getPredicate() == Cmp2->getSwappedPredicate() &&
+             Cmp1->getOperand(0) == Cmp2->getOperand(1) &&
+             Cmp1->getOperand(1) == Cmp2->getOperand(0);
+
+  if (I1->isCommutative() && I1->isSameOperationAs(I2)) {
+    return I1->getOperand(0) == I2->getOperand(1) &&
+           I1->getOperand(1) == I2->getOperand(0) &&
+           equal(drop_begin(I1->operands(), 2), drop_begin(I2->operands(), 2));
+  }
+
+  return false;
+}
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nikic wrote:

You mean where the select operands are swapped with an inverted icmp? I don't think we can easily handle this here, because we hoist instructions one by one, so the icmp needs to be hoistable independently. It's not impossible, but a lot more complex than just changing the comparison logic.

https://github.com/llvm/llvm-project/pull/104805