[llvm] [VPlan] Introduce ComputeReductionResult VPInstruction opcode. (PR #70253)

[Florian Hahn via llvm-commits]

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@@ -7719,6 +7542,27 @@ SCEV2ValueTy LoopVectorizationPlanner::executePlan(
 
   BestVPlan.execute(&State);
 
+  DenseMap<const RecurrenceDescriptor *, Value *> ReductionResumeValues;
+  for (VPRecipeBase &R : *cast<VPBasicBlock>(
+           BestVPlan.getVectorLoopRegion()->getSingleSuccessor())) {
+
+    auto *Red = dyn_cast<VPInstruction>(&R);
+    if (!Red || Red->getOpcode() != VPInstruction::ComputeReductionResult)
+      continue;
+
+    Value *FinalValue = State.get(
+        Red, VPIteration(State.UF - 1, VPLane::getLastLaneForVF(State.VF)));
+    auto *PhiR = cast<VPReductionPHIRecipe>(Red->getOperand(0));
+    assert(FinalValue->hasOneUse() || PhiR->isInLoop() ||
+           PhiR->getRecurrenceDescriptor().IntermediateStore);
+
+    PHINode *MergePhi = nullptr;
+    for (Value *U : FinalValue->users())
+      if (auto *P = dyn_cast<PHINode>(U))
+        MergePhi = P;
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fhahn wrote:

Adjusted thanks! There actually can be multiple phi users (one could be the phi node in the vector loop), refined to check that the phi is in the original scalar PH.

https://github.com/llvm/llvm-project/pull/70253