[llvm] [AArch64] Add costs for LD3/LD4 shuffles. (PR #89268)

[Simon Pilgrim via llvm-commits]

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@@ -3815,6 +3815,27 @@ InstructionCost AArch64TTIImpl::getSpliceCost(VectorType *Tp, int Index) {
   return LegalizationCost * LT.first;
 }
 
+/// Check if the mask is a DE-interleave mask of the given factor
+/// \p Factor like:
+///     <Index, Index+Factor, ..., Index+(NumElts-1)*Factor>
+static bool isDeInterleaveMaskOfFactor(ArrayRef<int> Mask, unsigned Factor) {
+  // Check all potential start indices from 0 to (Factor - 1).
+  for (unsigned Index = 0; Index < Factor; Index++) {
+    unsigned i = 0;
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RKSimon wrote:

`unsigned I = 0;`

https://github.com/llvm/llvm-project/pull/89268