[llvm] [VPlan] Impl VPlan-based pattern match for ExtendedRed and MulAccRed (PR #113903)

[Florian Hahn via llvm-commits]

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@@ -2185,6 +2273,172 @@ void VPlanTransforms::handleUncountableEarlyExit(
   LatchExitingBranch->eraseFromParent();
 }
 
+/// This function tries to match following pattern to create
+/// VPExtendedReductionRecipe and clamp the \p Range if it is beneficial and
+/// valid. The created VPExtendedReductionRecipe will lower to concrete recipes
+/// before execution.
+///   reduce(ext(...)).
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fhahn wrote:

```suggestion
/// This function tries convert extended in-loop reductions to VPExtendedReductionRecipe and clamp the \p Range if it is beneficial and
/// valid. The created VPExtendedReductionRecipe must be lower to concrete recipes before execution.
```

https://github.com/llvm/llvm-project/pull/113903