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

[via llvm-commits]

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@@ -344,6 +344,16 @@ class LoopVectorizationPlanner {
   /// A builder used to construct the current plan.
   VPBuilder Builder;
 
+  /// Computes the cost of \p Plan for vectorization factor \p VF.
+  ///
+  /// The current implementation requires access to the
+  /// LoopVectorizationLegality to handle inductions and reductions, which is
+  /// why it is kept separate from the VPlan-only cost infrastructure.
+  ///
+  /// TODO: Move to VPlan::computeCost once the use of the legacy cost model
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ayalz wrote:

```suggestion
  /// TODO: Move to VPlan::computeCost once the use of Legal
```


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