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

[via llvm-commits]

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@@ -9130,36 +9008,34 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
     for (VPRecipeBase &R :
          Plan->getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
     VPReductionPHIRecipe *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);
-    if (!PhiR || PhiR->isInLoop())
+    if (!PhiR)
       continue;
 
     const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
-    auto *Result = PhiR->getBackedgeValue()->getDefiningRecipe();
     // If tail is folded by masking, introduce selects between the phi
     // and the live-out instruction of each reduction, at the beginning of the
     // dedicated latch block.
-    if (CM.foldTailByMasking()) {
+    auto *OrigExitingVPV = PhiR->getBackedgeValue();
+    auto *NewExitingRecipe = OrigExitingVPV->getDefiningRecipe();
+    if (!PhiR->isInLoop() && CM.foldTailByMasking()) {
       VPValue *Cond =
           RecipeBuilder.createBlockInMask(OrigLoop->getHeader(), *Plan);
-      VPValue *Red = PhiR->getBackedgeValue();
-      assert(Red->getDefiningRecipe()->getParent() != LatchVPBB &&
+      assert(OrigExitingVPV ->getDefiningRecipe()->getParent() != LatchVPBB &&
              "reduction recipe must be defined before latch");
       FastMathFlags FMFs = RdxDesc.getFastMathFlags();
       Type *PhiTy = PhiR->getOperand(0)->getLiveInIRValue()->getType();
-      Result =
+      NewExitingRecipe =
           PhiTy->isFloatingPointTy()
-              ? new VPInstruction(Instruction::Select, {Cond, Red, PhiR}, FMFs)
-              : new VPInstruction(Instruction::Select, {Cond, Red, PhiR});
-      Result->insertBefore(&*Builder.getInsertPoint());
-      Red->replaceUsesWithIf(
-          Result->getVPSingleValue(),
-          [](VPUser &U, unsigned) { return isa<VPLiveOut>(&U); });
+              ? new VPInstruction(Instruction::Select, {Cond, OrigExitingVPV, PhiR}, FMFs)
+              : new VPInstruction(Instruction::Select, {Cond, OrigExitingVPV, PhiR});
+      NewExitingRecipe->insertBefore(&*Builder.getInsertPoint());
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ayalz wrote:

nit (unrelated to this patch): call Builder.createSelect()?

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