[llvm] [VPlan] First step towards VPlan cost modeling (LegacyCM in CostCtx) (PR #92555)

[via llvm-commits]

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@@ -1621,6 +1622,12 @@ class LoopVectorizationCostModel {
   /// \p VF is the vectorization factor chosen for the original loop.
   bool isEpilogueVectorizationProfitable(const ElementCount VF) const;
 
+  /// Return the cost of instructions in an inloop reduction pattern, if I is
+  /// part of that pattern.
+  std::optional<InstructionCost>
+  getReductionPatternCost(Instruction *I, ElementCount VF, Type *VectorTy,
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ayalz wrote:

> Will adjust separately.

Very well. Another suggestion is to use Invalid cost for "no cost" instead of optional.

https://github.com/llvm/llvm-project/pull/92555