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[AArch64][TTI] Reduce cost for splatting whole first vector segment (SVE) #145701

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[AArch64][TTI] Reduce cost for splatting whole first vector segment (SVE) #145701

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3285bc9
Test precommit
huntergr-arm Jun 25, 2025
0bea665
Match first segment splat
huntergr-arm Jun 25, 2025
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15 changes: 15 additions & 0 deletions llvm/lib/Target/AArch64/AArch64PerfectShuffle.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6750,6 +6750,21 @@ inline std::optional<unsigned> isDUPQMask(ArrayRef<int> Mask, unsigned Segments,
return std::nullopt;
}

/// isDUPFirstSegmentMask - matches a splat of the first 128b segment.
inline bool isDUPFirstSegmentMask(ArrayRef<int> Mask, unsigned Segments,
unsigned SegmentSize) {
// Make sure there's no size changes.
if (SegmentSize * Segments != Mask.size())
return false;

// Check that all lanes refer to the equivalent lane in the first segment.
// Undef/poison lanes (<0) are also accepted.
return all_of(enumerate(Mask), [&](auto P) {
const unsigned IndexWithinSegment = P.index() % SegmentSize;
return P.value() < 0 || unsigned(P.value()) == IndexWithinSegment;
});
}

} // namespace llvm

#endif
13 changes: 9 additions & 4 deletions llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
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Expand Up @@ -5600,9 +5600,8 @@ AArch64TTIImpl::getShuffleCost(TTI::ShuffleKind Kind, VectorType *DstTy,
}

// Segmented shuffle matching.
if ((ST->hasSVE2p1() || ST->hasSME2p1()) &&
ST->isSVEorStreamingSVEAvailable() && Kind == TTI::SK_PermuteSingleSrc &&
isa<FixedVectorType>(SrcTy) && !Mask.empty() &&
if (Kind == TTI::SK_PermuteSingleSrc && isa<FixedVectorType>(SrcTy) &&
!Mask.empty() &&
SrcTy->getPrimitiveSizeInBits().isKnownMultipleOf(
AArch64::SVEBitsPerBlock)) {

Expand All @@ -5612,7 +5611,13 @@ AArch64TTIImpl::getShuffleCost(TTI::ShuffleKind Kind, VectorType *DstTy,
unsigned SegmentElts = VTy->getNumElements() / Segments;

// dupq zd.t, zn.t[idx]
if (isDUPQMask(Mask, Segments, SegmentElts))
if ((ST->hasSVE2p1() || ST->hasSME2p1()) &&
ST->isSVEorStreamingSVEAvailable() &&
isDUPQMask(Mask, Segments, SegmentElts))
return LT.first;

// mov zd.q, vn
if (isDUPFirstSegmentMask(Mask, Segments, SegmentElts))
return LT.first;
}

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48 changes: 48 additions & 0 deletions llvm/test/Analysis/CostModel/AArch64/segmented-shufflevector-patterns.ll
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Expand Up @@ -49,5 +49,53 @@ define void @dup_within_each_segment_512b() #1 {
ret void
}

define void @dup_whole_segment_256b() #0 {
; CHECK-LABEL: 'dup_whole_segment_256b'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_b = shufflevector <32 x i8> poison, <32 x i8> poison, <32 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_h = shufflevector <16 x i16> poison, <16 x i16> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_s = shufflevector <8 x i32> poison, <8 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_d = shufflevector <4 x i64> poison, <4 x i64> poison, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_512b_d = shufflevector <8 x double> poison, <8 x double> poison, <8 x i32> <i32 0, i32 1, i32 0, i32 1, i32 0, i32 1, i32 0, i32 1>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_s_with_poison = shufflevector <8 x float> poison, <8 x float> poison, <8 x i32> <i32 0, i32 1, i32 poison, i32 3, i32 poison, i32 1, i32 2, i32 3>
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%dup_seg_b = shufflevector <32 x i8> poison, <32 x i8> poison, <32 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15,
i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
%dup_seg_h = shufflevector <16 x i16> poison, <16 x i16> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7,
i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
%dup_seg_s = shufflevector <8 x i32> poison, <8 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3,
i32 0, i32 1, i32 2, i32 3>
%dup_seg_d = shufflevector <4 x i64> poison, <4 x i64> poison, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
%dup_seg_512b_d = shufflevector <8 x double> poison, <8 x double> poison, <8 x i32> <i32 0, i32 1, i32 0, i32 1,
i32 0, i32 1, i32 0, i32 1>
%dup_seg_s_with_poison = shufflevector <8 x float> poison, <8 x float> poison, <8 x i32> <i32 0, i32 1, i32 poison, i32 3,
i32 poison, i32 1, i32 2, i32 3>
ret void
}

define void @dup_whole_segment_512b() #1 {
; CHECK-LABEL: 'dup_whole_segment_512b'
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_b = shufflevector <32 x i8> poison, <32 x i8> poison, <32 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_h = shufflevector <16 x i16> poison, <16 x i16> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_s = shufflevector <8 x i32> poison, <8 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_d = shufflevector <4 x i64> poison, <4 x i64> poison, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_512b_d = shufflevector <8 x double> poison, <8 x double> poison, <8 x i32> <i32 0, i32 1, i32 0, i32 1, i32 0, i32 1, i32 0, i32 1>
; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction: %dup_seg_s_with_poison = shufflevector <8 x float> poison, <8 x float> poison, <8 x i32> <i32 0, i32 1, i32 poison, i32 3, i32 poison, i32 1, i32 2, i32 3>
; CHECK-NEXT: Cost Model: Found an estimated cost of 0 for instruction: ret void
;
%dup_seg_b = shufflevector <32 x i8> poison, <32 x i8> poison, <32 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15,
i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
%dup_seg_h = shufflevector <16 x i16> poison, <16 x i16> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7,
i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
%dup_seg_s = shufflevector <8 x i32> poison, <8 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3,
i32 0, i32 1, i32 2, i32 3>
%dup_seg_d = shufflevector <4 x i64> poison, <4 x i64> poison, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
%dup_seg_512b_d = shufflevector <8 x double> poison, <8 x double> poison, <8 x i32> <i32 0, i32 1, i32 0, i32 1,
i32 0, i32 1, i32 0, i32 1>
%dup_seg_s_with_poison = shufflevector <8 x float> poison, <8 x float> poison, <8 x i32> <i32 0, i32 1, i32 poison, i32 3,
i32 poison, i32 1, i32 2, i32 3>
ret void
}

attributes #0 = { noinline vscale_range(2,2) }
attributes #1 = { noinline vscale_range(4,4) }
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