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[AArch64] Update cost model for extracting halves from 128+ bit vectors #155601

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Merged
merged 6 commits into from
Sep 3, 2025
Merged

[AArch64] Update cost model for extracting halves from 128+ bit vectors #155601

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dc66670
Precommit CostModel tests for 128+ bits extract shuffles
gbossu Jun 23, 2025
b020391
[AArch64] Update cost model for extracting halves from 128+ bit vectors
gbossu Aug 26, 2025
92a3083
Replace SVEBitsPerBlock with plain 128
gbossu Aug 28, 2025
8d57a65
Restore NEON shuffle-extract.ll test
gbossu Sep 1, 2025
8d32485
Add SVE-specific cost test for VLS
gbossu Sep 1, 2025
e0d3f2d
Fix typo
gbossu Sep 1, 2025
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11 changes: 7 additions & 4 deletions llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
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Expand Up @@ -5750,11 +5750,14 @@ AArch64TTIImpl::getShuffleCost(TTI::ShuffleKind Kind, VectorType *DstTy,

Kind = improveShuffleKindFromMask(Kind, Mask, SrcTy, Index, SubTp);
bool IsExtractSubvector = Kind == TTI::SK_ExtractSubvector;
// A subvector extract can be implemented with an ext (or trivial extract, if
// from lane 0). This currently only handles low or high extracts to prevent
// SLP vectorizer regressions.
// A subvector extract can be implemented with a NEON/SVE ext (or trivial
// extract, if from lane 0) for 128-bit NEON vectors or legal SVE vectors.
// This currently only handles low or high extracts to prevent SLP vectorizer
// regressions.
// Note that SVE's ext instruction is destructive, but it can be fused with
// a movprfx to act like a constructive instruction.
if (IsExtractSubvector && LT.second.isFixedLengthVector()) {
if (LT.second.is128BitVector() &&
if (LT.second.getFixedSizeInBits() >= 128 &&
cast<FixedVectorType>(SubTp)->getNumElements() ==
LT.second.getVectorNumElements() / 2) {
if (Index == 0)
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3 changes: 3 additions & 0 deletions llvm/test/Analysis/CostModel/AArch64/shuffle-extract.ll
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@@ -1,6 +1,9 @@
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
; RUN: opt < %s -mtriple=aarch64--linux-gnu -passes="print<cost-model>" -cost-kind=all 2>&1 -disable-output | FileCheck %s

; This tests the cost of fixed-length subvector extracts for NEON.
; For the SVE equivalent test, see sve-vls-shuffle-extract.ll

target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"

define void @extract_half() {
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