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

[Florian Hahn via llvm-commits]

================
@@ -2189,6 +2277,172 @@ void VPlanTransforms::handleUncountableEarlyExit(
   LatchExitingBranch->eraseFromParent();
 }
 
+/// 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.
+static VPExtendedReductionRecipe *
+tryToMatchAndCreateExtendedReduction(VPReductionRecipe *Red, VPCostContext &Ctx,
+                                     VFRange &Range) {
+  using namespace VPlanPatternMatch;
+
+  Type *RedTy = Ctx.Types.inferScalarType(Red);
+  VPValue *VecOp = Red->getVecOp();
+
+  // Test if using extended-reduction is beneficial and clamp the range.
----------------
fhahn wrote:

```suggestion
  // Test if using extended-reduction is profitable and clamp the range.
```

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