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

[via llvm-commits]

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@@ -3081,6 +3130,9 @@ class VPRegionBlock : public VPBlockBase {
   /// this VPRegionBlock, thereby "executing" the VPlan.
   void execute(VPTransformState *State) override;
 
+  // Compute the cost of this region.
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ayalz wrote:

```suggestion
  // Return the cost of this region.
```

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