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

[Florian Hahn via llvm-commits]

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@@ -9130,55 +9009,79 @@ 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 *OrigExitValue = PhiR->getBackedgeValue();
+    auto *ExitValue = OrigExitValue->getDefiningRecipe();
+    if (!PhiR->isInLoop() && CM.foldTailByMasking()) {
       VPValue *Cond =
           RecipeBuilder.createBlockInMask(OrigLoop->getHeader(), *Plan);
       VPValue *Red = PhiR->getBackedgeValue();
       assert(Red->getDefiningRecipe()->getParent() != LatchVPBB &&
              "reduction recipe must be defined before latch");
       FastMathFlags FMFs = RdxDesc.getFastMathFlags();
       Type *PhiTy = PhiR->getOperand(0)->getLiveInIRValue()->getType();
-      Result =
+      ExitValue =
           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); });
+      ExitValue->insertBefore(&*Builder.getInsertPoint());
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fhahn wrote:

Adjusted independently in 6dda74cc51dd33e266101bccd3647658e5ab3c35, will rebase and resolve the conflicts here once approved.

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