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[VectorCombine] Fold bitwise operations of bitcasts into bitcast of bitwise operation #137322

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Merged
merged 3 commits into from
Jun 26, 2025
Merged

[VectorCombine] Fold bitwise operations of bitcasts into bitcast of bitwise operation #137322

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96ed7cb
[InstCombine] VectorCombine Pass
vortex73 Jun 15, 2025
03fc921
[InstCombine] Minor Tweaks
vortex73 Jun 16, 2025
e6ef896
Merge branch 'main' into pblendvb
RKSimon Jun 26, 2025
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58 changes: 58 additions & 0 deletions llvm/lib/Transforms/Vectorize/VectorCombine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,7 @@ class VectorCombine {
bool foldInsExtFNeg(Instruction &I);
bool foldInsExtBinop(Instruction &I);
bool foldInsExtVectorToShuffle(Instruction &I);
bool foldBitOpOfBitcasts(Instruction &I);
bool foldBitcastShuffle(Instruction &I);
bool scalarizeBinopOrCmp(Instruction &I);
bool scalarizeVPIntrinsic(Instruction &I);
Expand Down Expand Up @@ -801,6 +802,58 @@ bool VectorCombine::foldInsExtBinop(Instruction &I) {
return true;
}

bool VectorCombine::foldBitOpOfBitcasts(Instruction &I) {
// Match: bitop(bitcast(x), bitcast(y)) -> bitcast(bitop(x, y))
auto *BinOp = dyn_cast<BinaryOperator>(&I);
if (!BinOp || !BinOp->isBitwiseLogicOp())
return false;

Value *LHS = BinOp->getOperand(0);
Value *RHS = BinOp->getOperand(1);

// Both operands must be bitcasts
auto *LHSCast = dyn_cast<BitCastInst>(LHS);
auto *RHSCast = dyn_cast<BitCastInst>(RHS);
if (!LHSCast || !RHSCast)
return false;

Value *LHSSrc = LHSCast->getOperand(0);
Value *RHSSrc = RHSCast->getOperand(0);

// Source types must match
if (LHSSrc->getType() != RHSSrc->getType())
return false;

// Only handle vector types
auto *SrcVecTy = dyn_cast<FixedVectorType>(LHSSrc->getType());
auto *DstVecTy = dyn_cast<FixedVectorType>(I.getType());
if (!SrcVecTy || !DstVecTy)
return false;

// Same total bit width
if (SrcVecTy->getPrimitiveSizeInBits() != DstVecTy->getPrimitiveSizeInBits())
return false;

// Cost check: prefer operations on narrower element types
unsigned SrcEltBits = SrcVecTy->getScalarSizeInBits();
unsigned DstEltBits = DstVecTy->getScalarSizeInBits();

// Prefer smaller element sizes (more elements, finer granularity)
if (SrcEltBits > DstEltBits)
return false;

// Create the operation on the source type
Value *NewOp = Builder.CreateBinOp(BinOp->getOpcode(), LHSSrc, RHSSrc,
BinOp->getName() + ".inner");
if (auto *NewBinOp = dyn_cast<BinaryOperator>(NewOp))
NewBinOp->copyIRFlags(BinOp);

// Bitcast the result back
Value *Result = Builder.CreateBitCast(NewOp, I.getType());
replaceValue(I, *Result);
return true;
}

/// If this is a bitcast of a shuffle, try to bitcast the source vector to the
/// destination type followed by shuffle. This can enable further transforms by
/// moving bitcasts or shuffles together.
Expand Down Expand Up @@ -3562,6 +3615,11 @@ bool VectorCombine::run() {
case Instruction::BitCast:
MadeChange |= foldBitcastShuffle(I);
break;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
MadeChange |= foldBitOpOfBitcasts(I);
break;
default:
MadeChange |= shrinkType(I);
break;
Expand Down
30 changes: 11 additions & 19 deletions llvm/test/Transforms/PhaseOrdering/X86/blendv-select.ll
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Expand Up @@ -477,30 +477,22 @@ define <2 x i64> @PR66513(<2 x i64> %a, <2 x i64> %b, <2 x i64> %c, <2 x i64> %s
; CHECK-LABEL: @PR66513(
; CHECK-NEXT: [[I:%.*]] = bitcast <2 x i64> [[A:%.*]] to <4 x i32>
; CHECK-NEXT: [[CMP_I23:%.*]] = icmp sgt <4 x i32> [[I]], zeroinitializer
; CHECK-NEXT: [[SEXT_I24:%.*]] = sext <4 x i1> [[CMP_I23]] to <4 x i32>
; CHECK-NEXT: [[I1:%.*]] = bitcast <4 x i32> [[SEXT_I24]] to <2 x i64>
; CHECK-NEXT: [[I2:%.*]] = bitcast <2 x i64> [[B:%.*]] to <4 x i32>
; CHECK-NEXT: [[CMP_I21:%.*]] = icmp sgt <4 x i32> [[I2]], zeroinitializer
; CHECK-NEXT: [[SEXT_I22:%.*]] = sext <4 x i1> [[CMP_I21]] to <4 x i32>
; CHECK-NEXT: [[I3:%.*]] = bitcast <4 x i32> [[SEXT_I22]] to <2 x i64>
; CHECK-NEXT: [[I4:%.*]] = bitcast <2 x i64> [[C:%.*]] to <4 x i32>
; CHECK-NEXT: [[CMP_I:%.*]] = icmp sgt <4 x i32> [[I4]], zeroinitializer
; CHECK-NEXT: [[SEXT_I:%.*]] = sext <4 x i1> [[CMP_I]] to <4 x i32>
; CHECK-NEXT: [[NARROW:%.*]] = select <4 x i1> [[CMP_I21]], <4 x i1> [[CMP_I23]], <4 x i1> zeroinitializer
; CHECK-NEXT: [[XOR_I_INNER1:%.*]] = xor <4 x i1> [[NARROW]], [[CMP_I]]
; CHECK-NEXT: [[NARROW3:%.*]] = select <4 x i1> [[CMP_I23]], <4 x i1> [[XOR_I_INNER1]], <4 x i1> zeroinitializer
; CHECK-NEXT: [[AND_I25_INNER2:%.*]] = and <4 x i1> [[XOR_I_INNER1]], [[CMP_I21]]
; CHECK-NEXT: [[TMP1:%.*]] = bitcast <2 x i64> [[SRC:%.*]] to <4 x i32>
; CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[NARROW]], <4 x i32> [[TMP1]], <4 x i32> zeroinitializer
; CHECK-NEXT: [[TMP3:%.*]] = bitcast <2 x i64> [[A]] to <4 x i32>
; CHECK-NEXT: [[TMP4:%.*]] = select <4 x i1> [[NARROW3]], <4 x i32> [[TMP3]], <4 x i32> [[TMP2]]
; CHECK-NEXT: [[TMP5:%.*]] = bitcast <2 x i64> [[B]] to <4 x i32>
; CHECK-NEXT: [[SEXT_I:%.*]] = select <4 x i1> [[AND_I25_INNER2]], <4 x i32> [[TMP5]], <4 x i32> [[TMP4]]
; CHECK-NEXT: [[I5:%.*]] = bitcast <4 x i32> [[SEXT_I]] to <2 x i64>
; CHECK-NEXT: [[AND_I27:%.*]] = and <2 x i64> [[I3]], [[I1]]
; CHECK-NEXT: [[XOR_I:%.*]] = xor <2 x i64> [[AND_I27]], [[I5]]
; CHECK-NEXT: [[AND_I26:%.*]] = and <2 x i64> [[XOR_I]], [[I1]]
; CHECK-NEXT: [[AND_I25:%.*]] = and <2 x i64> [[XOR_I]], [[I3]]
; CHECK-NEXT: [[AND_I:%.*]] = and <2 x i64> [[AND_I27]], [[SRC:%.*]]
; CHECK-NEXT: [[I6:%.*]] = bitcast <2 x i64> [[AND_I]] to <16 x i8>
; CHECK-NEXT: [[I7:%.*]] = bitcast <2 x i64> [[A]] to <16 x i8>
; CHECK-NEXT: [[I8:%.*]] = bitcast <2 x i64> [[AND_I26]] to <16 x i8>
; CHECK-NEXT: [[I9:%.*]] = tail call <16 x i8> @llvm.x86.sse41.pblendvb(<16 x i8> [[I6]], <16 x i8> [[I7]], <16 x i8> [[I8]])
; CHECK-NEXT: [[I12:%.*]] = bitcast <2 x i64> [[B]] to <16 x i8>
; CHECK-NEXT: [[I13:%.*]] = bitcast <2 x i64> [[AND_I25]] to <16 x i8>
; CHECK-NEXT: [[I14:%.*]] = tail call <16 x i8> @llvm.x86.sse41.pblendvb(<16 x i8> [[I9]], <16 x i8> [[I12]], <16 x i8> [[I13]])
; CHECK-NEXT: [[I15:%.*]] = bitcast <16 x i8> [[I14]] to <2 x i64>
; CHECK-NEXT: ret <2 x i64> [[I15]]
; CHECK-NEXT: ret <2 x i64> [[I5]]
;
%i = bitcast <2 x i64> %a to <4 x i32>
%cmp.i23 = icmp sgt <4 x i32> %i, zeroinitializer
Expand Down
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