[llvm] [VPlan] Create casts before ComputeReductionResult (NFC). (PR #199372)

[Florian Hahn via llvm-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/199372

This ensures ComputeReductionResult is created with operands that have their correct types set at construction.

>From 4051be95522267082a33464ce0801a97a28dfebf Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Sat, 23 May 2026 10:43:07 +0100
Subject: [PATCH] [VPlan] Create casts before ComputeReductionResult (NFC).

This ensures ComputeReductionResult is created with operands that have
their correct types set at construction.
---
 .../Transforms/Vectorize/LoopVectorize.cpp    | 64 +++++++++----------
 1 file changed, 30 insertions(+), 34 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 14677427bfdda..40e3eaf319bde 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7118,42 +7118,38 @@ void LoopVectorizationPlanner::addReductionResultComputation(
       FinalReductionResult =
           Builder.createAnyOfReduction(NewExiting, NewVal, Start, ExitDL);
     } else {
-      VPIRFlags Flags(RecurrenceKind, PhiR->isOrdered(), PhiR->isInLoop(),
-                      PhiR->getFastMathFlags());
-      FinalReductionResult =
-          Builder.createNaryOp(VPInstruction::ComputeReductionResult,
-                               {NewExitingVPV}, Flags, ExitDL);
-    }
-    // If the vector reduction can be performed in a smaller type, we truncate
-    // then extend the loop exit value to enable InstCombine to evaluate the
-    // entire expression in the smaller type.
-    if (MinVF.isVector() && PhiTy != RdxDesc.getRecurrenceType() &&
-        !RecurrenceDescriptor::isAnyOfRecurrenceKind(RecurrenceKind)) {
-      assert(!PhiR->isInLoop() && "Unexpected truncated inloop reduction!");
-      assert(!RecurrenceDescriptor::isMinMaxRecurrenceKind(RecurrenceKind) &&
-             "Unexpected truncated min-max recurrence!");
-      Type *RdxTy = RdxDesc.getRecurrenceType();
-      VPWidenCastRecipe *Trunc;
-      Instruction::CastOps ExtendOpc =
-          RdxDesc.isSigned() ? Instruction::SExt : Instruction::ZExt;
-      VPWidenCastRecipe *Extnd;
-      {
-        VPBuilder::InsertPointGuard Guard(Builder);
-        Builder.setInsertPoint(
-            NewExitingVPV->getDefiningRecipe()->getParent(),
-            std::next(NewExitingVPV->getDefiningRecipe()->getIterator()));
-        Trunc =
-            Builder.createWidenCast(Instruction::Trunc, NewExitingVPV, RdxTy);
-        Extnd = Builder.createWidenCast(ExtendOpc, Trunc, PhiTy);
+      // If the vector reduction can be performed in a smaller type, we
+      // truncate then extend the loop exit value to enable InstCombine to
+      // evaluate the entire expression in the smaller type.
+      VPValue *ReductionOp = NewExitingVPV;
+      Instruction::CastOps ExtendOpc = Instruction::CastOpsEnd;
+      if (MinVF.isVector() && PhiTy != RdxDesc.getRecurrenceType()) {
+        assert(!PhiR->isInLoop() && "Unexpected truncated inloop reduction!");
+        assert(!RecurrenceDescriptor::isMinMaxRecurrenceKind(RecurrenceKind) &&
+               "Unexpected truncated min-max recurrence!");
+        Type *RdxTy = RdxDesc.getRecurrenceType();
+        ExtendOpc = RdxDesc.isSigned() ? Instruction::SExt : Instruction::ZExt;
+        {
+          VPBuilder::InsertPointGuard Guard(Builder);
+          Builder.setInsertPoint(
+              NewExitingVPV->getDefiningRecipe()->getParent(),
+              std::next(NewExitingVPV->getDefiningRecipe()->getIterator()));
+          ReductionOp =
+              Builder.createWidenCast(Instruction::Trunc, NewExitingVPV, RdxTy);
+          VPWidenCastRecipe *Extnd =
+              Builder.createWidenCast(ExtendOpc, ReductionOp, PhiTy);
+          if (PhiR->getOperand(1) == NewExitingVPV)
+            PhiR->setOperand(1, Extnd);
+        }
       }
-      if (PhiR->getOperand(1) == NewExitingVPV)
-        PhiR->setOperand(1, Extnd->getVPSingleValue());
 
-      // Update ComputeReductionResult with the truncated exiting value and
-      // extend its result. Operand 0 provides the values to be reduced.
-      FinalReductionResult->setOperand(0, Trunc);
-      FinalReductionResult =
-          Builder.createScalarCast(ExtendOpc, FinalReductionResult, PhiTy, {});
+      VPIRFlags Flags(RecurrenceKind, PhiR->isOrdered(), PhiR->isInLoop(),
+                      PhiR->getFastMathFlags());
+      FinalReductionResult = Builder.createNaryOp(
+          VPInstruction::ComputeReductionResult, {ReductionOp}, Flags, ExitDL);
+      if (ExtendOpc != Instruction::CastOpsEnd)
+        FinalReductionResult = Builder.createScalarCast(
+            ExtendOpc, FinalReductionResult, PhiTy, {});
     }
 
     // Update all users outside the vector region. Also replace redundant