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[VectorCombine] foldShuffleOfCastops - handle unary shuffles #160009

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Merged
merged 7 commits into from
Sep 29, 2025
Merged

[VectorCombine] foldShuffleOfCastops - handle unary shuffles #160009

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ed4c1df
[VectorCombine] foldShuffleOfCastops - handle unary shuffles
ckoparkar Sep 21, 2025
1e2aaf4
Merge branch 'main' into ckoparkar/156853
ckoparkar Sep 21, 2025
8ae9816
Fix shuffletoidentity test
ckoparkar Sep 23, 2025
8c27278
Break loop with foldBitcastOfShuffle
ckoparkar Sep 24, 2025
e4b329f
Add tests, remove comment
ckoparkar Sep 25, 2025
4f5f5da
Remove test that uses undef
ckoparkar Sep 25, 2025
00fa20d
Merge branch 'main' into ckoparkar/156853
ckoparkar Sep 25, 2025
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67 changes: 44 additions & 23 deletions llvm/lib/Transforms/Vectorize/VectorCombine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2487,21 +2487,28 @@ bool VectorCombine::foldShuffleOfCastops(Instruction &I) {
if (!match(&I, m_Shuffle(m_Value(V0), m_Value(V1), m_Mask(OldMask))))
return false;

// Check whether this is a unary shuffle.
// TODO: check if this can be extended to match undef or unused values,
// perhaps using ShuffleVectorInst::isSingleSource.
bool IsBinaryShuffle = !isa<PoisonValue>(V1);

auto *C0 = dyn_cast<CastInst>(V0);
auto *C1 = dyn_cast<CastInst>(V1);
if (!C0 || !C1)
if (!C0 || (IsBinaryShuffle && !C1))
return false;

Instruction::CastOps Opcode = C0->getOpcode();
if (C0->getSrcTy() != C1->getSrcTy())
return false;

// Handle shuffle(zext_nneg(x), sext(y)) -> sext(shuffle(x,y)) folds.
if (Opcode != C1->getOpcode()) {
if (match(C0, m_SExtLike(m_Value())) && match(C1, m_SExtLike(m_Value())))
Opcode = Instruction::SExt;
else
if (IsBinaryShuffle) {
if (C0->getSrcTy() != C1->getSrcTy())
return false;
// Handle shuffle(zext_nneg(x), sext(y)) -> sext(shuffle(x,y)) folds.
if (Opcode != C1->getOpcode()) {
if (match(C0, m_SExtLike(m_Value())) && match(C1, m_SExtLike(m_Value())))
Opcode = Instruction::SExt;
else
return false;
}
}

auto *ShuffleDstTy = dyn_cast<FixedVectorType>(I.getType());
Expand Down Expand Up @@ -2544,38 +2551,52 @@ bool VectorCombine::foldShuffleOfCastops(Instruction &I) {
InstructionCost CostC0 =
TTI.getCastInstrCost(C0->getOpcode(), CastDstTy, CastSrcTy,
TTI::CastContextHint::None, CostKind);
InstructionCost CostC1 =
TTI.getCastInstrCost(C1->getOpcode(), CastDstTy, CastSrcTy,
TTI::CastContextHint::None, CostKind);
InstructionCost OldCost = CostC0 + CostC1;
OldCost +=
TTI.getShuffleCost(TargetTransformInfo::SK_PermuteTwoSrc, ShuffleDstTy,
CastDstTy, OldMask, CostKind, 0, nullptr, {}, &I);

InstructionCost NewCost =
TTI.getShuffleCost(TargetTransformInfo::SK_PermuteTwoSrc, NewShuffleDstTy,
CastSrcTy, NewMask, CostKind);
TargetTransformInfo::ShuffleKind ShuffleKind;
if (IsBinaryShuffle)
ShuffleKind = TargetTransformInfo::SK_PermuteTwoSrc;
else
ShuffleKind = TargetTransformInfo::SK_PermuteSingleSrc;

InstructionCost OldCost = CostC0;
OldCost += TTI.getShuffleCost(ShuffleKind, ShuffleDstTy, CastDstTy, OldMask,
CostKind, 0, nullptr, {}, &I);

InstructionCost NewCost = TTI.getShuffleCost(ShuffleKind, NewShuffleDstTy,
CastSrcTy, NewMask, CostKind);
NewCost += TTI.getCastInstrCost(Opcode, ShuffleDstTy, NewShuffleDstTy,
TTI::CastContextHint::None, CostKind);
if (!C0->hasOneUse())
NewCost += CostC0;
if (!C1->hasOneUse())
NewCost += CostC1;
if (IsBinaryShuffle) {
InstructionCost CostC1 =
TTI.getCastInstrCost(C1->getOpcode(), CastDstTy, CastSrcTy,
TTI::CastContextHint::None, CostKind);
OldCost += CostC1;
if (!C1->hasOneUse())
NewCost += CostC1;
}

LLVM_DEBUG(dbgs() << "Found a shuffle feeding two casts: " << I
<< "\n OldCost: " << OldCost << " vs NewCost: " << NewCost
<< "\n");
if (NewCost > OldCost)
return false;

Value *Shuf = Builder.CreateShuffleVector(C0->getOperand(0),
C1->getOperand(0), NewMask);
Value *Shuf;
if (IsBinaryShuffle)
Shuf = Builder.CreateShuffleVector(C0->getOperand(0), C1->getOperand(0),
NewMask);
else
Shuf = Builder.CreateShuffleVector(C0->getOperand(0), NewMask);

Value *Cast = Builder.CreateCast(Opcode, Shuf, ShuffleDstTy);

// Intersect flags from the old casts.
if (auto *NewInst = dyn_cast<Instruction>(Cast)) {
NewInst->copyIRFlags(C0);
NewInst->andIRFlags(C1);
if (IsBinaryShuffle)
NewInst->andIRFlags(C1);
}

Worklist.pushValue(Shuf);
Expand Down
17 changes: 8 additions & 9 deletions llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -205,8 +205,8 @@ define <8 x i8> @abs_different(<8 x i8> %a) {
define <4 x i32> @poison_intrinsic(<2 x i16> %l256) {
; CHECK-LABEL: @poison_intrinsic(
; CHECK-NEXT: [[L266:%.*]] = call <2 x i16> @llvm.abs.v2i16(<2 x i16> [[L256:%.*]], i1 false)
; CHECK-NEXT: [[L267:%.*]] = zext <2 x i16> [[L266]] to <2 x i32>
; CHECK-NEXT: [[L271:%.*]] = shufflevector <2 x i32> [[L267]], <2 x i32> poison, <4 x i32> <i32 0, i32 1, i32 poison, i32 poison>
; CHECK-NEXT: [[L267:%.*]] = shufflevector <2 x i16> [[L266]], <2 x i16> poison, <4 x i32> <i32 0, i32 1, i32 poison, i32 poison>
; CHECK-NEXT: [[L271:%.*]] = zext <4 x i16> [[L267]] to <4 x i32>
; CHECK-NEXT: ret <4 x i32> [[L271]]
;
%l266 = call <2 x i16> @llvm.abs.v2i16(<2 x i16> %l256, i1 false)
Expand Down Expand Up @@ -534,9 +534,9 @@ define <4 x i64> @single_zext(<4 x i32> %x) {

define <4 x i64> @not_zext(<4 x i32> %x) {
; CHECK-LABEL: @not_zext(
; CHECK-NEXT: [[ZEXT:%.*]] = zext <4 x i32> [[X:%.*]] to <4 x i64>
; CHECK-NEXT: [[REVSHUF:%.*]] = shufflevector <4 x i64> [[ZEXT]], <4 x i64> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
; CHECK-NEXT: ret <4 x i64> [[REVSHUF]]
; CHECK-NEXT: [[REVSHUF:%.*]] = shufflevector <4 x i32> [[X]], <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
; CHECK-NEXT: [[ZEXT:%.*]] = zext <4 x i32> [[REVSHUF:%.*]] to <4 x i64>
; CHECK-NEXT: ret <4 x i64> [[ZEXT]]
;
%zext = zext <4 x i32> %x to <4 x i64>
%revshuf = shufflevector <4 x i64> %zext, <4 x i64> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
Expand Down Expand Up @@ -922,10 +922,9 @@ define <4 x i8> @singleop(<4 x i8> %a, <4 x i8> %b) {

define <4 x i64> @cast_mismatched_types(<4 x i32> %x) {
; CHECK-LABEL: @cast_mismatched_types(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <4 x i32> [[X:%.*]], <4 x i32> poison, <2 x i32> <i32 0, i32 2>
; CHECK-NEXT: [[ZEXT:%.*]] = zext <2 x i32> [[SHUF]] to <2 x i64>
; CHECK-NEXT: [[EXTSHUF:%.*]] = shufflevector <2 x i64> [[ZEXT]], <2 x i64> poison, <4 x i32> <i32 0, i32 2, i32 1, i32 3>
; CHECK-NEXT: ret <4 x i64> [[EXTSHUF]]
; CHECK-SAME: <4 x i32> [[X:%.*]]) {
; CHECK-NEXT: [[ZEXT:%.*]] = zext <4 x i32> [[X]] to <4 x i64>
; CHECK-NEXT: ret <4 x i64> [[ZEXT]]
;
%shuf = shufflevector <4 x i32> %x, <4 x i32> poison, <2 x i32> <i32 0, i32 2>
%zext = zext <2 x i32> %shuf to <2 x i64>
Expand Down
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