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

[via llvm-commits]

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@@ -664,6 +676,9 @@ class VPBlockBase {
   /// the cloned recipes, including all blocks in the single-entry single-exit
   /// region for VPRegionBlocks.
   virtual VPBlockBase *clone() = 0;
+
+  /// Compute the cost of the block.
+  virtual InstructionCost cost(ElementCount VF, VPCostContext &Ctx) = 0;
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ayalz wrote:

nit: better place all `cost()` methods next to `execute()`, as done in VPRecipeBase.

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