[llvm] [VPlan] Implement VPReductionRecipe::computeCost(). NFC (PR #107790)

[Elvis Wang via llvm-commits]

================
@@ -1999,6 +1999,27 @@ void VPReductionEVLRecipe::execute(VPTransformState &State) {
   State.set(this, NewRed, 0, /*IsScalar*/ true);
 }
 
+InstructionCost VPReductionRecipe::computeCost(ElementCount VF,
+                                               VPCostContext &Ctx) const {
+  RecurKind RdxKind = RdxDesc.getRecurrenceKind();
----------------
ElvisWang123 wrote:

Sure, I will open another PR to address in-loop reduction.

https://github.com/llvm/llvm-project/pull/107790