[llvm] [AArch64][CostModel] Lower cost of dupq (SVE2.1) (PR #144918)

[David Green via llvm-commits]

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@@ -5583,6 +5583,26 @@ InstructionCost AArch64TTIImpl::getShuffleCost(
     Kind = TTI::SK_PermuteSingleSrc;
   }
 
+  // Segmented shuffle matching.
+  if (ST->hasSVE2p1() && CostKind == TTI::TCK_RecipThroughput &&
+      Kind == TTI::SK_PermuteSingleSrc && isa<FixedVectorType>(Tp) &&
+      Tp->getPrimitiveSizeInBits().isKnownMultipleOf(128)) {
+
+    FixedVectorType *VTy = cast<FixedVectorType>(Tp);
+    unsigned Segments = VTy->getPrimitiveSizeInBits() / 128;
+    unsigned SegmentElts = VTy->getNumElements() / Segments;
+
+    // dupq zd.t, zn.t[idx]
+    unsigned Lane = (unsigned)Mask[0];
+    if (SegmentElts * Segments == Mask.size() && Lane < SegmentElts) {
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davemgreen wrote:

Can this re-use the isDUPQMask method added recently?

https://github.com/llvm/llvm-project/pull/144918