[llvm] [VPlan] Implement VPExtendedReduction, VPMulAccumulateReductionRecipe and corresponding vplan transformations. (PR #137746)

[Elvis Wang via llvm-commits]

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@@ -273,6 +273,8 @@ Type *VPTypeAnalysis::inferScalarType(const VPValue *V) {
             // TODO: Use info from interleave group.
             return V->getUnderlyingValue()->getType();
           })
+          .Case<VPExtendedReductionRecipe, VPMulAccumulateReductionRecipe>(
+              [](const auto *R) { return R->getResultType(); })
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ElvisWang123 wrote:

No, IIUC there is no `RecurrenceDescriptor` in the `VPReductionRecipe`. 

Perhaps add a comment to explain why `VPMulAccumulateReductionRecipe` may not contains the result type if it doesn't contains extends?

https://github.com/llvm/llvm-project/pull/137746