[llvm] [LV][TTI] Calculate cost of extracting last index in a scalable vector (PR #144086)

[Paul Walker via llvm-commits]

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@@ -1512,6 +1512,14 @@ class TargetTransformInfo {
                                               TTI::TargetCostKind CostKind,
                                               unsigned Index = -1) const;
 
+  /// \return The expected cost of inserting or extracting a lane that is \p
+  /// Index from the end of a vector, i.e. the mathematical expression for
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paulwalker-arm wrote:

I think you want either `that is \p Index elements from the end of a vector` or `that is indexed from the end of a vector`?


https://github.com/llvm/llvm-project/pull/144086