[llvm] [VPlan] Remove single-operand dead VPPhi (PR #156438)

[Florian Hahn via llvm-commits]

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@@ -561,17 +561,23 @@ void VPlanTransforms::removeDeadRecipes(VPlan &Plan) {
         continue;
       }
 
-      // Check if R is a dead VPPhi <-> update cycle and remove it.
+      // Remove dead VPPhi <-> update cycles.
       auto *PhiR = dyn_cast<VPPhi>(&R);
-      if (!PhiR || PhiR->getNumOperands() != 2 || PhiR->getNumUsers() != 1)
+      if (!PhiR)
         continue;
-      VPValue *Incoming = PhiR->getOperand(1);
-      if (*PhiR->user_begin() != Incoming->getDefiningRecipe() ||
-          Incoming->getNumUsers() != 1)
-        continue;
-      PhiR->replaceAllUsesWith(PhiR->getOperand(0));
-      PhiR->eraseFromParent();
-      Incoming->getDefiningRecipe()->eraseFromParent();
+      if (PhiR->getNumOperands() == 1) {
+        PhiR->replaceAllUsesWith(PhiR->getOperand(0));
+        PhiR->eraseFromParent();
+      }
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fhahn wrote:

Sure, for the improvements, it looks like we get those because all incoming values are the same, right? If that's the case, perhaps what is missing is s generalization of the fold in simplifyRecipes: instead of checking for single incoming value it could check if all incoming values are the same?

https://github.com/llvm/llvm-project/pull/156438