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[LVI][SCCP] Avoid copying ValueLatticeElement #163901

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Merged
merged 3 commits into from
Oct 18, 2025
Merged

[LVI][SCCP] Avoid copying ValueLatticeElement #163901

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6a67889
[LVI][SCCP] Avoid copying ValueLatticeElement
dtcxzyw Oct 17, 2025
6b08eeb
[SCCP] Avoid implicit reallocation
dtcxzyw Oct 17, 2025
4ea449b
[SCCP] Address review comments
dtcxzyw Oct 18, 2025
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10 changes: 4 additions & 6 deletions llvm/lib/Analysis/LazyValueInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -947,9 +947,8 @@ LazyValueInfoImpl::solveBlockValueSelect(SelectInst *SI, BasicBlock *BB) {
/*UseBlockValue*/ false));
}

ValueLatticeElement Result = TrueVal;
Result.mergeIn(FalseVal);
return Result;
TrueVal.mergeIn(FalseVal);
return TrueVal;
}

std::optional<ConstantRange>
Expand Down Expand Up @@ -1778,9 +1777,8 @@ ValueLatticeElement LazyValueInfoImpl::getValueInBlock(Value *V, BasicBlock *BB,
assert(OptResult && "Value not available after solving");
}

ValueLatticeElement Result = *OptResult;
LLVM_DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
LLVM_DEBUG(dbgs() << " Result = " << *OptResult << "\n");
return *OptResult;
}

ValueLatticeElement LazyValueInfoImpl::getValueAt(Value *V, Instruction *CxtI) {
Expand Down
47 changes: 25 additions & 22 deletions llvm/lib/Transforms/Utils/SCCPSolver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -634,11 +634,11 @@ class SCCPInstVisitor : public InstVisitor<SCCPInstVisitor> {
/// Merge \p MergeWithV into \p IV and push \p V to the worklist, if \p IV
/// changes.
bool mergeInValue(ValueLatticeElement &IV, Value *V,
ValueLatticeElement MergeWithV,
const ValueLatticeElement &MergeWithV,
ValueLatticeElement::MergeOptions Opts = {
/*MayIncludeUndef=*/false, /*CheckWiden=*/false});

bool mergeInValue(Value *V, ValueLatticeElement MergeWithV,
bool mergeInValue(Value *V, const ValueLatticeElement &MergeWithV,
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I'm not sure this one is always safe. For example in https://github.com/dtcxzyw/llvm-project/blob/6a67889a728f410074d12ccfdf46bdf54bf9f56b/llvm/lib/Transforms/Utils/SCCPSolver.cpp#L1630 MergeWithV is the result of getValueState(). In that case ValueState[V] is known to be initialized already due to the previous ValueState[&I].isOverdefined() check, but it seems easy to cause reference invalidation here.

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I have removed the helper function to avoid implicit invalidations. Hopefully it makes the implementation cleaner.

ValueLatticeElement::MergeOptions Opts = {
/*MayIncludeUndef=*/false, /*CheckWiden=*/false}) {
assert(!V->getType()->isStructTy() &&
Expand Down Expand Up @@ -1128,8 +1128,7 @@ bool SCCPInstVisitor::isStructLatticeConstant(Function *F, StructType *STy) {
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
const auto &It = TrackedMultipleRetVals.find(std::make_pair(F, i));
assert(It != TrackedMultipleRetVals.end());
ValueLatticeElement LV = It->second;
if (!SCCPSolver::isConstant(LV))
if (!SCCPSolver::isConstant(It->second))
return false;
}
return true;
Expand Down Expand Up @@ -1160,7 +1159,7 @@ Constant *SCCPInstVisitor::getConstantOrNull(Value *V) const {
std::vector<Constant *> ConstVals;
auto *ST = cast<StructType>(V->getType());
for (unsigned I = 0, E = ST->getNumElements(); I != E; ++I) {
ValueLatticeElement LV = LVs[I];
const ValueLatticeElement &LV = LVs[I];
ConstVals.push_back(SCCPSolver::isConstant(LV)
? getConstant(LV, ST->getElementType(I))
: UndefValue::get(ST->getElementType(I)));
Expand Down Expand Up @@ -1225,7 +1224,7 @@ void SCCPInstVisitor::visitInstruction(Instruction &I) {
}

bool SCCPInstVisitor::mergeInValue(ValueLatticeElement &IV, Value *V,
ValueLatticeElement MergeWithV,
const ValueLatticeElement &MergeWithV,
ValueLatticeElement::MergeOptions Opts) {
if (IV.mergeIn(MergeWithV, Opts)) {
pushUsersToWorkList(V);
Expand Down Expand Up @@ -1264,7 +1263,7 @@ void SCCPInstVisitor::getFeasibleSuccessors(Instruction &TI,
return;
}

ValueLatticeElement BCValue = getValueState(BI->getCondition());
const ValueLatticeElement &BCValue = getValueState(BI->getCondition());
ConstantInt *CI = getConstantInt(BCValue, BI->getCondition()->getType());
if (!CI) {
// Overdefined condition variables, and branches on unfoldable constant
Expand Down Expand Up @@ -1326,7 +1325,7 @@ void SCCPInstVisitor::getFeasibleSuccessors(Instruction &TI,
// the target as executable.
if (auto *IBR = dyn_cast<IndirectBrInst>(&TI)) {
// Casts are folded by visitCastInst.
ValueLatticeElement IBRValue = getValueState(IBR->getAddress());
const ValueLatticeElement &IBRValue = getValueState(IBR->getAddress());
BlockAddress *Addr = dyn_cast_or_null<BlockAddress>(
getConstant(IBRValue, IBR->getAddress()->getType()));
if (!Addr) { // Overdefined or unknown condition?
Expand Down Expand Up @@ -1408,7 +1407,7 @@ void SCCPInstVisitor::visitPHINode(PHINode &PN) {
if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
continue;

ValueLatticeElement IV = getValueState(PN.getIncomingValue(i));
const ValueLatticeElement &IV = getValueState(PN.getIncomingValue(i));
PhiState.mergeIn(IV);
NumActiveIncoming++;
if (PhiState.isOverdefined())
Expand Down Expand Up @@ -1481,7 +1480,7 @@ void SCCPInstVisitor::visitCastInst(CastInst &I) {
}
}

ValueLatticeElement OpSt = getValueState(I.getOperand(0));
const ValueLatticeElement &OpSt = getValueState(I.getOperand(0));
if (OpSt.isUnknownOrUndef())
return;

Expand All @@ -1496,9 +1495,9 @@ void SCCPInstVisitor::visitCastInst(CastInst &I) {
if (I.getDestTy()->isIntOrIntVectorTy() &&
I.getSrcTy()->isIntOrIntVectorTy() &&
I.getOpcode() != Instruction::BitCast) {
auto &LV = getValueState(&I);
ConstantRange OpRange =
OpSt.asConstantRange(I.getSrcTy(), /*UndefAllowed=*/false);
auto &LV = getValueState(&I);

Type *DestTy = I.getDestTy();
ConstantRange Res = ConstantRange::getEmpty(DestTy->getScalarSizeInBits());
Expand All @@ -1516,15 +1515,20 @@ void SCCPInstVisitor::handleExtractOfWithOverflow(ExtractValueInst &EVI,
const WithOverflowInst *WO,
unsigned Idx) {
Value *LHS = WO->getLHS(), *RHS = WO->getRHS();
ValueLatticeElement L = getValueState(LHS);
ValueLatticeElement R = getValueState(RHS);
Type *Ty = LHS->getType();

addAdditionalUser(LHS, &EVI);
addAdditionalUser(RHS, &EVI);
if (L.isUnknownOrUndef() || R.isUnknownOrUndef())
return; // Wait to resolve.

Type *Ty = LHS->getType();
const ValueLatticeElement &L = getValueState(LHS);
if (L.isUnknownOrUndef())
return; // Wait to resolve.
ConstantRange LR = L.asConstantRange(Ty, /*UndefAllowed=*/false);

const ValueLatticeElement &R = getValueState(RHS);
if (R.isUnknownOrUndef())
return; // Wait to resolve.

ConstantRange RR = R.asConstantRange(Ty, /*UndefAllowed=*/false);
if (Idx == 0) {
ConstantRange Res = LR.binaryOp(WO->getBinaryOp(), RR);
Expand Down Expand Up @@ -1616,7 +1620,7 @@ void SCCPInstVisitor::visitSelectInst(SelectInst &I) {
if (ValueState[&I].isOverdefined())
return (void)markOverdefined(&I);

ValueLatticeElement CondValue = getValueState(I.getCondition());
const ValueLatticeElement &CondValue = getValueState(I.getCondition());
if (CondValue.isUnknownOrUndef())
return;

Expand Down Expand Up @@ -1802,7 +1806,7 @@ void SCCPInstVisitor::visitGetElementPtrInst(GetElementPtrInst &I) {
Operands.reserve(I.getNumOperands());

for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
ValueLatticeElement State = getValueState(I.getOperand(i));
const ValueLatticeElement &State = getValueState(I.getOperand(i));
if (State.isUnknownOrUndef())
return; // Operands are not resolved yet.

Expand Down Expand Up @@ -1881,14 +1885,13 @@ void SCCPInstVisitor::visitLoadInst(LoadInst &I) {
if (ValueState[&I].isOverdefined())
return (void)markOverdefined(&I);

ValueLatticeElement PtrVal = getValueState(I.getOperand(0));
const ValueLatticeElement &PtrVal = getValueState(I.getOperand(0));
if (PtrVal.isUnknownOrUndef())
return; // The pointer is not resolved yet!

ValueLatticeElement &IV = ValueState[&I];

if (SCCPSolver::isConstant(PtrVal)) {
Constant *Ptr = getConstant(PtrVal, I.getOperand(0)->getType());
ValueLatticeElement &IV = ValueState[&I];

// load null is undefined.
if (isa<ConstantPointerNull>(Ptr)) {
Expand Down Expand Up @@ -1944,7 +1947,7 @@ void SCCPInstVisitor::handleCallOverdefined(CallBase &CB) {
return markOverdefined(&CB); // Can't handle struct args.
if (A.get()->getType()->isMetadataTy())
continue; // Carried in CB, not allowed in Operands.
ValueLatticeElement State = getValueState(A);
const ValueLatticeElement &State = getValueState(A);

if (State.isUnknownOrUndef())
return; // Operands are not resolved yet.
Expand Down