[llvm] [VPlan] Truncate/Extend ComputeReductionResult at construction (NFC). (PR #141860)

[David Sherwood via llvm-commits]

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@@ -7270,6 +7270,13 @@ static void fixReductionScalarResumeWhenVectorizingEpilog(
   // created a bc.merge.rdx Phi after the main vector body. Ensure that we carry
   // over the incoming values correctly.
   using namespace VPlanPatternMatch;
+  if (EpiRedResult->getNumUsers() == 1 &&
+      isa<VPInstructionWithType>(*EpiRedResult->user_begin())) {
+    EpiRedResult = cast<VPInstructionWithType>(*EpiRedResult->user_begin());
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david-arm wrote:

Do you know why we don't just pass in the sext/zext as the `R` argument to `fixReductionScalarResumeWhenVectorizingEpilog` and then look through the sext/zext?

https://github.com/llvm/llvm-project/pull/141860