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GlobalISel: Fix mishandling vector-as-scalar in return values #175780

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Merged
arsenm merged 4 commits into from
Jan 22, 2026
Merged

GlobalISel: Fix mishandling vector-as-scalar in return values #175780

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9232a0b
GlobalISel: Fix mishandling vector-as-scalar in return values
arsenm Jan 13, 2026
a6418f0
suggestion
arsenm Jan 22, 2026
0fec035
Suggestion with TypeSize
arsenm Jan 22, 2026
85d881b
suggestion cleanup
arsenm Jan 22, 2026
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36 changes: 28 additions & 8 deletions llvm/lib/CodeGen/GlobalISel/CallLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -568,6 +568,13 @@ static void buildCopyToRegs(MachineIRBuilder &B, ArrayRef<Register> DstRegs,

const TypeSize PartSize = PartTy.getSizeInBits();

if (PartSize == SrcTy.getSizeInBits() && DstRegs.size() == 1) {
// TODO: Handle int<->ptr casts. It just happens the ABI lowering
// assignments are not pointer aware.
B.buildBitcast(DstRegs[0], SrcReg);
return;
}

if (PartTy.isVector() == SrcTy.isVector() &&
PartTy.getScalarSizeInBits() > SrcTy.getScalarSizeInBits()) {
assert(DstRegs.size() == 1);
Expand All @@ -576,7 +583,8 @@ static void buildCopyToRegs(MachineIRBuilder &B, ArrayRef<Register> DstRegs,
}

if (SrcTy.isVector() && !PartTy.isVector() &&
TypeSize::isKnownGT(PartSize, SrcTy.getElementType().getSizeInBits())) {
TypeSize::isKnownGT(PartSize, SrcTy.getElementType().getSizeInBits()) &&
SrcTy.getElementCount() == ElementCount::getFixed(DstRegs.size())) {
// Vector was scalarized, and the elements extended.
auto UnmergeToEltTy = B.buildUnmerge(SrcTy.getElementType(), SrcReg);
for (int i = 0, e = DstRegs.size(); i != e; ++i)
Expand Down Expand Up @@ -614,21 +622,33 @@ static void buildCopyToRegs(MachineIRBuilder &B, ArrayRef<Register> DstRegs,

MachineRegisterInfo &MRI = *B.getMRI();
LLT DstTy = MRI.getType(DstRegs[0]);
LLT LCMTy = getCoverTy(SrcTy, PartTy);
LLT CoverTy = getCoverTy(SrcTy, PartTy);
if (SrcTy.isVector() && DstRegs.size() > 1) {
TypeSize FullCoverSize =
DstTy.getSizeInBits().multiplyCoefficientBy(DstRegs.size());

LLT EltTy = SrcTy.getElementType();
TypeSize EltSize = EltTy.getSizeInBits();
if (FullCoverSize.isKnownMultipleOf(EltSize)) {
TypeSize VecSize = FullCoverSize.divideCoefficientBy(EltSize);
CoverTy =
LLT::vector(ElementCount::get(VecSize, VecSize.isScalable()), EltTy);
}
}

if (PartTy.isVector() && LCMTy == PartTy) {
if (PartTy.isVector() && CoverTy == PartTy) {
assert(DstRegs.size() == 1);
B.buildPadVectorWithUndefElements(DstRegs[0], SrcReg);
return;
}

const unsigned DstSize = DstTy.getSizeInBits();
const unsigned SrcSize = SrcTy.getSizeInBits();
unsigned CoveringSize = LCMTy.getSizeInBits();
unsigned CoveringSize = CoverTy.getSizeInBits();

Register UnmergeSrc = SrcReg;

if (!LCMTy.isVector() && CoveringSize != SrcSize) {
if (!CoverTy.isVector() && CoveringSize != SrcSize) {
// For scalars, it's common to be able to use a simple extension.
if (SrcTy.isScalar() && DstTy.isScalar()) {
CoveringSize = alignTo(SrcSize, DstSize);
Expand All @@ -641,12 +661,12 @@ static void buildCopyToRegs(MachineIRBuilder &B, ArrayRef<Register> DstRegs,
SmallVector<Register, 8> MergeParts(1, SrcReg);
for (unsigned Size = SrcSize; Size != CoveringSize; Size += SrcSize)
MergeParts.push_back(Undef);
UnmergeSrc = B.buildMergeLikeInstr(LCMTy, MergeParts).getReg(0);
UnmergeSrc = B.buildMergeLikeInstr(CoverTy, MergeParts).getReg(0);
}
}

if (LCMTy.isVector() && CoveringSize != SrcSize)
UnmergeSrc = B.buildPadVectorWithUndefElements(LCMTy, SrcReg).getReg(0);
if (CoverTy.isVector() && CoveringSize != SrcSize)
UnmergeSrc = B.buildPadVectorWithUndefElements(CoverTy, SrcReg).getReg(0);

B.buildUnmerge(DstRegs, UnmergeSrc);
}
Expand Down
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