[llvm] [RISCV][TTI] Add shuffle costing for masked slide lowering (PR #128537)

[Alexey Bataev via llvm-commits]

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@@ -203,6 +203,15 @@ bool getShuffleDemandedElts(int SrcWidth, ArrayRef<int> Mask,
                             const APInt &DemandedElts, APInt &DemandedLHS,
                             APInt &DemandedRHS, bool AllowUndefElts = false);
 
+/// Does this shuffle mask represent either one slide shuffle or a pair of
+/// two slide shuffles, combined with a select on some constant vector mask?
+/// A slide is a shuffle masks which shifts some set of elements up or down
+/// the vector, with all other elements being undefined.  An identity shuffle
+/// will be matched a slide by 0.  The output parameter provides the source
+/// (-1 means no source), and slide direction for each slide.
+bool isMaskedSlidePair(ArrayRef<int> Mask, int NumElts,
+                       std::pair<int, int> SrcInfo[2]);
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alexey-bataev wrote:

```suggestion
                      std::array<std::pair<int, int>, 2> &SrcInfo);
```
Preferred way of passing arrays in C++

https://github.com/llvm/llvm-project/pull/128537