[llvm] [VPlan] Use ResumePhi to create reduction resume phis. (PR #110004)

[via llvm-commits]

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@@ -7561,67 +7561,53 @@ static void addRuntimeUnrollDisableMetaData(Loop *L) {
   }
 }
 
-// Check if \p RedResult is a ComputeReductionResult instruction, and if it is
-// create a merge phi node for it.
-static void createAndCollectMergePhiForReduction(
-    VPInstruction *RedResult,
-    VPTransformState &State, Loop *OrigLoop, BasicBlock *LoopMiddleBlock,
-    bool VectorizingEpilogue) {
+// If \p R is a ComputeReductionResult when vectorizing the epilog loop,
+// update the reduction's scalar PHI node by adding the incoming value from the
+// main vector loop.
+static void updateMergePhiForReductionForEpilogueVectorization(
+    VPRecipeBase *R, VPTransformState &State, Loop *OrigLoop,
+    BasicBlock *LoopMiddleBlock) {
+  auto *RedResult = dyn_cast<VPInstruction>(R);
   if (!RedResult ||
       RedResult->getOpcode() != VPInstruction::ComputeReductionResult)
     return;
 
   auto *PhiR = cast<VPReductionPHIRecipe>(RedResult->getOperand(0));
   const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
-
-  Value *FinalValue = State.get(RedResult, VPLane(VPLane::getFirstLane()));
-  auto *ResumePhi =
-      dyn_cast<PHINode>(PhiR->getStartValue()->getUnderlyingValue());
-  if (VectorizingEpilogue && RecurrenceDescriptor::isAnyOfRecurrenceKind(
-                                 RdxDesc.getRecurrenceKind())) {
+  PHINode *MainResumePhi;
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ayalz wrote:

Wonder if Reduction MainResumePhi could be recorded similar to the way Induction resume value of main loop is recorded and retrieved for epilog loop to continue from. Instead of searching for it from epilog through main loop via ComputeResult->HeaderPhi->ResumePhi recipes.

https://github.com/llvm/llvm-project/pull/110004