[llvm] [VPlan] Replace PhiR operand of ComputeRdxResult with VPIRFlags. (PR #174026)

[via llvm-commits]

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@@ -8790,8 +8792,8 @@ void LoopVectorizationPlanner::addReductionResultComputation(
         PhiR->setOperand(1, Extnd->getVPSingleValue());
 
       // Update ComputeReductionResult with the truncated exiting value and
-      // extend its result.
-      FinalReductionResult->setOperand(1, Trunc);
+      // extend its result. Operand 0 provides the value to be reduced.
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ayalz wrote:

Maybe clearer:
```suggestion
      // extend its result. Operand 0 provides the values to be reduced.
```

https://github.com/llvm/llvm-project/pull/174026