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

[Florian Hahn via llvm-commits]

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@@ -7494,67 +7494,49 @@ 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 RedResult 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(
+    VPInstruction *RedResult, VPTransformState &State, Loop *OrigLoop,
+    BasicBlock *LoopMiddleBlock) {
   if (!RedResult ||
       RedResult->getOpcode() != VPInstruction::ComputeReductionResult)
     return;
 
+  using namespace VPlanPatternMatch;
+  VPValue *ResumePhiVPV =
+      cast<VPInstruction>(*find_if(RedResult->users(), [](VPUser *U) {
+        return match(U, m_VPInstruction<VPInstruction::ResumePhi>(m_VPValue(),
+                                                                  m_VPValue()));
+      }));
+  assert(ResumePhiVPV->getNumUsers() == 1 &&
+         "ResumePhi must have a single user");
+  auto *BCBlockPhi = cast<PHINode>(State.get(ResumePhiVPV, true));
   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())) {
+  if (RecurrenceDescriptor::isAnyOfRecurrenceKind(
+          RdxDesc.getRecurrenceKind())) {
     auto *Cmp = cast<ICmpInst>(PhiR->getStartValue()->getUnderlyingValue());
     assert(Cmp->getPredicate() == CmpInst::ICMP_NE);
     assert(Cmp->getOperand(1) == RdxDesc.getRecurrenceStartValue());
     ResumePhi = cast<PHINode>(Cmp->getOperand(0));
   }
-  assert((!VectorizingEpilogue || ResumePhi) &&
+  assert(ResumePhi &&
          "when vectorizing the epilogue loop, we need a resume phi from main "
          "vector loop");
 
-  // TODO: bc.merge.rdx should not be created here, instead it should be
-  // modeled in VPlan.
   BasicBlock *LoopScalarPreHeader = OrigLoop->getLoopPreheader();
-  // Create a phi node that merges control-flow from the backedge-taken check
-  // block and the middle block.
-  auto *BCBlockPhi =
-      PHINode::Create(FinalValue->getType(), 2, "bc.merge.rdx",
-                      LoopScalarPreHeader->getTerminator()->getIterator());
-
-  // If we are fixing reductions in the epilogue loop then we should already
-  // have created a bc.merge.rdx Phi after the main vector body. Ensure that
-  // we carry over the incoming values correctly.
+  // When fixing reductions in the epilogue loop then we should already have
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fhahn wrote:

Updated, thanks!

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