bool foldConstants(BasicBlock* block)
{
bool changed = false;
m_state.beginBasicBlock(block);
for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
if (!m_state.isValid())
break;
Node* node = block->at(indexInBlock);
bool alreadyHandled = false;
bool eliminated = false;
switch (node->op()) {
case BooleanToNumber: {
if (node->child1().useKind() == UntypedUse
&& !m_interpreter.needsTypeCheck(node->child1(), SpecBoolean))
node->child1().setUseKind(BooleanUse);
break;
}
case CheckArgumentsNotCreated: {
if (!isEmptySpeculation(
m_state.variables().operand(
m_graph.argumentsRegisterFor(node->origin.semantic)).m_type))
break;
node->convertToPhantom();
eliminated = true;
break;
}
case CheckStructure:
case ArrayifyToStructure: {
AbstractValue& value = m_state.forNode(node->child1());
StructureSet set;
if (node->op() == ArrayifyToStructure)
set = node->structure();
else
set = node->structureSet();
if (value.m_structure.isSubsetOf(set)) {
m_interpreter.execute(indexInBlock); // Catch the fact that we may filter on cell.
node->convertToPhantom();
eliminated = true;
break;
}
break;
}
case CheckArray:
case Arrayify: {
if (!node->arrayMode().alreadyChecked(m_graph, node, m_state.forNode(node->child1())))
break;
node->convertToPhantom();
eliminated = true;
break;
}
case PutStructure: {
if (m_state.forNode(node->child1()).m_structure.onlyStructure() != node->transition()->next)
break;
node->convertToPhantom();
eliminated = true;
break;
}
case CheckFunction: {
if (m_state.forNode(node->child1()).value() != node->function()->value())
break;
node->convertToPhantom();
eliminated = true;
break;
}
case CheckInBounds: {
JSValue left = m_state.forNode(node->child1()).value();
JSValue right = m_state.forNode(node->child2()).value();
if (left && right && left.isInt32() && right.isInt32()
&& static_cast<uint32_t>(left.asInt32()) < static_cast<uint32_t>(right.asInt32())) {
node->convertToPhantom();
eliminated = true;
break;
}
break;
}
case MultiGetByOffset: {
Edge baseEdge = node->child1();
Node* base = baseEdge.node();
MultiGetByOffsetData& data = node->multiGetByOffsetData();
// First prune the variants, then check if the MultiGetByOffset can be
// strength-reduced to a GetByOffset.
AbstractValue baseValue = m_state.forNode(base);
m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
alreadyHandled = true; // Don't allow the default constant folder to do things to this.
for (unsigned i = 0; i < data.variants.size(); ++i) {
GetByIdVariant& variant = data.variants[i];
variant.structureSet().filter(baseValue);
if (variant.structureSet().isEmpty()) {
data.variants[i--] = data.variants.last();
data.variants.removeLast();
changed = true;
}
}
if (data.variants.size() != 1)
break;
emitGetByOffset(
indexInBlock, node, baseValue, data.variants[0], data.identifierNumber);
changed = true;
break;
}
case MultiPutByOffset: {
Edge baseEdge = node->child1();
Node* base = baseEdge.node();
MultiPutByOffsetData& data = node->multiPutByOffsetData();
AbstractValue baseValue = m_state.forNode(base);
m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
alreadyHandled = true; // Don't allow the default constant folder to do things to this.
for (unsigned i = 0; i < data.variants.size(); ++i) {
PutByIdVariant& variant = data.variants[i];
variant.oldStructure().filter(baseValue);
if (variant.oldStructure().isEmpty()) {
data.variants[i--] = data.variants.last();
data.variants.removeLast();
changed = true;
continue;
}
if (variant.kind() == PutByIdVariant::Transition
&& variant.oldStructure().onlyStructure() == variant.newStructure()) {
variant = PutByIdVariant::replace(
variant.oldStructure(),
variant.offset());
changed = true;
}
}
if (data.variants.size() != 1)
break;
emitPutByOffset(
indexInBlock, node, baseValue, data.variants[0], data.identifierNumber);
changed = true;
break;
}
case GetById:
case GetByIdFlush: {
Edge childEdge = node->child1();
Node* child = childEdge.node();
unsigned identifierNumber = node->identifierNumber();
AbstractValue baseValue = m_state.forNode(child);
m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
alreadyHandled = true; // Don't allow the default constant folder to do things to this.
if (baseValue.m_structure.isTop() || baseValue.m_structure.isClobbered()
|| (node->child1().useKind() == UntypedUse || (baseValue.m_type & ~SpecCell)))
break;
GetByIdStatus status = GetByIdStatus::computeFor(
vm(), baseValue.m_structure.set(), m_graph.identifiers()[identifierNumber]);
if (!status.isSimple())
break;
for (unsigned i = status.numVariants(); i--;) {
if (!status[i].constantChecks().isEmpty()
|| status[i].alternateBase()) {
// FIXME: We could handle prototype cases.
// https://bugs.webkit.org/show_bug.cgi?id=110386
break;
}
}
if (status.numVariants() == 1) {
emitGetByOffset(indexInBlock, node, baseValue, status[0], identifierNumber);
changed = true;
break;
}
if (!isFTL(m_graph.m_plan.mode))
break;
MultiGetByOffsetData* data = m_graph.m_multiGetByOffsetData.add();
data->variants = status.variants();
data->identifierNumber = identifierNumber;
node->convertToMultiGetByOffset(data);
changed = true;
break;
}
case PutById:
case PutByIdDirect:
case PutByIdFlush: {
NodeOrigin origin = node->origin;
Edge childEdge = node->child1();
Node* child = childEdge.node();
unsigned identifierNumber = node->identifierNumber();
ASSERT(childEdge.useKind() == CellUse);
AbstractValue baseValue = m_state.forNode(child);
m_interpreter.execute(indexInBlock); // Push CFA over this node after we get the state before.
alreadyHandled = true; // Don't allow the default constant folder to do things to this.
if (baseValue.m_structure.isTop() || baseValue.m_structure.isClobbered())
break;
PutByIdStatus status = PutByIdStatus::computeFor(
vm(),
m_graph.globalObjectFor(origin.semantic),
baseValue.m_structure.set(),
m_graph.identifiers()[identifierNumber],
node->op() == PutByIdDirect);
if (!status.isSimple())
break;
ASSERT(status.numVariants());
if (status.numVariants() > 1 && !isFTL(m_graph.m_plan.mode))
break;
changed = true;
for (unsigned i = status.numVariants(); i--;)
addChecks(origin, indexInBlock, status[i].constantChecks());
if (status.numVariants() == 1) {
emitPutByOffset(indexInBlock, node, baseValue, status[0], identifierNumber);
break;
}
ASSERT(isFTL(m_graph.m_plan.mode));
MultiPutByOffsetData* data = m_graph.m_multiPutByOffsetData.add();
data->variants = status.variants();
data->identifierNumber = identifierNumber;
node->convertToMultiPutByOffset(data);
break;
}
case ToPrimitive: {
if (m_state.forNode(node->child1()).m_type & ~(SpecFullNumber | SpecBoolean | SpecString))
break;
node->convertToIdentity();
changed = true;
break;
}
case GetMyArgumentByVal: {
InlineCallFrame* inlineCallFrame = node->origin.semantic.inlineCallFrame;
JSValue value = m_state.forNode(node->child1()).m_value;
if (inlineCallFrame && value && value.isInt32()) {
int32_t index = value.asInt32();
if (index >= 0
&& static_cast<size_t>(index + 1) < inlineCallFrame->arguments.size()) {
// Roll the interpreter over this.
m_interpreter.execute(indexInBlock);
eliminated = true;
int operand =
inlineCallFrame->stackOffset +
m_graph.baselineCodeBlockFor(inlineCallFrame)->argumentIndexAfterCapture(index);
m_insertionSet.insertNode(
indexInBlock, SpecNone, CheckArgumentsNotCreated, node->origin);
m_insertionSet.insertNode(
indexInBlock, SpecNone, Phantom, node->origin, node->children);
node->convertToGetLocalUnlinked(VirtualRegister(operand));
break;
}
}
break;
}
case Check: {
alreadyHandled = true;
m_interpreter.execute(indexInBlock);
for (unsigned i = 0; i < AdjacencyList::Size; ++i) {
Edge edge = node->children.child(i);
if (!edge)
break;
if (edge.isProved() || edge.willNotHaveCheck()) {
node->children.removeEdge(i--);
changed = true;
}
}
break;
}
default:
break;
}
if (eliminated) {
changed = true;
continue;
}
if (alreadyHandled)
continue;
m_interpreter.execute(indexInBlock);
if (!m_state.isValid()) {
// If we invalidated then we shouldn't attempt to constant-fold. Here's an
// example:
//
// c: JSConstant(4.2)
// x: ValueToInt32(Check:Int32:@const)
//
// It would be correct for an analysis to assume that execution cannot
// proceed past @x. Therefore, constant-folding @x could be rather bad. But,
// the CFA may report that it found a constant even though it also reported
// that everything has been invalidated. This will only happen in a couple of
// the constant folding cases; most of them are also separately defensive
// about such things.
break;
}
if (!node->shouldGenerate() || m_state.didClobber() || node->hasConstant())
continue;
// Interesting fact: this freezing that we do right here may turn an fragile value into
// a weak value. See DFGValueStrength.h.
FrozenValue* value = m_graph.freeze(m_state.forNode(node).value());
if (!*value)
continue;
NodeOrigin origin = node->origin;
AdjacencyList children = node->children;
m_graph.convertToConstant(node, value);
if (!children.isEmpty()) {
m_insertionSet.insertNode(
indexInBlock, SpecNone, Phantom, origin, children);
}
changed = true;
}
m_state.reset();
m_insertionSet.execute(block);
return changed;
}
bool foldConstants(BasicBlock* block)
{
bool changed = false;
m_state.beginBasicBlock(block);
for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
if (!m_state.isValid())
break;
Node* node = block->at(indexInBlock);
bool eliminated = false;
switch (node->op()) {
case BooleanToNumber: {
if (node->child1().useKind() == UntypedUse
&& !m_interpreter.needsTypeCheck(node->child1(), SpecBoolean))
node->child1().setUseKind(BooleanUse);
break;
}
case CheckArgumentsNotCreated: {
if (!isEmptySpeculation(
m_state.variables().operand(
m_graph.argumentsRegisterFor(node->origin.semantic)).m_type))
break;
node->convertToPhantom();
eliminated = true;
break;
}
case CheckStructure:
case ArrayifyToStructure: {
AbstractValue& value = m_state.forNode(node->child1());
StructureSet set;
if (node->op() == ArrayifyToStructure)
set = node->structure();
else
set = node->structureSet();
if (value.m_currentKnownStructure.isSubsetOf(set)) {
m_interpreter.execute(indexInBlock); // Catch the fact that we may filter on cell.
node->convertToPhantom();
eliminated = true;
break;
}
StructureAbstractValue& structureValue = value.m_futurePossibleStructure;
if (structureValue.isSubsetOf(set)
&& structureValue.hasSingleton()) {
Structure* structure = structureValue.singleton();
m_interpreter.execute(indexInBlock); // Catch the fact that we may filter on cell.
AdjacencyList children = node->children;
children.removeEdge(0);
if (!!children.child1())
m_insertionSet.insertNode(indexInBlock, SpecNone, Phantom, node->origin, children);
node->children.setChild2(Edge());
node->children.setChild3(Edge());
node->convertToStructureTransitionWatchpoint(structure);
eliminated = true;
break;
}
break;
}
case CheckArray:
case Arrayify: {
if (!node->arrayMode().alreadyChecked(m_graph, node, m_state.forNode(node->child1())))
break;
node->convertToPhantom();
eliminated = true;
break;
}
case CheckFunction: {
if (m_state.forNode(node->child1()).value() != node->function())
break;
node->convertToPhantom();
eliminated = true;
break;
}
case CheckInBounds: {
JSValue left = m_state.forNode(node->child1()).value();
JSValue right = m_state.forNode(node->child2()).value();
if (left && right && left.isInt32() && right.isInt32()
&& static_cast<uint32_t>(left.asInt32()) < static_cast<uint32_t>(right.asInt32())) {
node->convertToPhantom();
eliminated = true;
break;
}
break;
}
case MultiGetByOffset: {
Edge childEdge = node->child1();
Node* child = childEdge.node();
MultiGetByOffsetData& data = node->multiGetByOffsetData();
Structure* structure = m_state.forNode(child).bestProvenStructure();
if (!structure)
break;
for (unsigned i = data.variants.size(); i--;) {
const GetByIdVariant& variant = data.variants[i];
if (!variant.structureSet().contains(structure))
continue;
if (variant.chain())
break;
emitGetByOffset(indexInBlock, node, structure, variant, data.identifierNumber);
eliminated = true;
break;
}
break;
}
case MultiPutByOffset: {
Edge childEdge = node->child1();
Node* child = childEdge.node();
MultiPutByOffsetData& data = node->multiPutByOffsetData();
Structure* structure = m_state.forNode(child).bestProvenStructure();
if (!structure)
break;
for (unsigned i = data.variants.size(); i--;) {
const PutByIdVariant& variant = data.variants[i];
if (variant.oldStructure() != structure)
continue;
emitPutByOffset(indexInBlock, node, structure, variant, data.identifierNumber);
eliminated = true;
break;
}
break;
}
case GetById:
case GetByIdFlush: {
Edge childEdge = node->child1();
Node* child = childEdge.node();
unsigned identifierNumber = node->identifierNumber();
if (childEdge.useKind() != CellUse)
break;
Structure* structure = m_state.forNode(child).bestProvenStructure();
if (!structure)
break;
GetByIdStatus status = GetByIdStatus::computeFor(
vm(), structure, m_graph.identifiers()[identifierNumber]);
if (!status.isSimple() || status.numVariants() != 1) {
// FIXME: We could handle prototype cases.
// https://bugs.webkit.org/show_bug.cgi?id=110386
break;
}
emitGetByOffset(indexInBlock, node, structure, status[0], identifierNumber);
eliminated = true;
break;
}
case PutById:
case PutByIdDirect: {
NodeOrigin origin = node->origin;
Edge childEdge = node->child1();
Node* child = childEdge.node();
unsigned identifierNumber = node->identifierNumber();
ASSERT(childEdge.useKind() == CellUse);
Structure* structure = m_state.forNode(child).bestProvenStructure();
if (!structure)
break;
PutByIdStatus status = PutByIdStatus::computeFor(
vm(),
m_graph.globalObjectFor(origin.semantic),
structure,
m_graph.identifiers()[identifierNumber],
node->op() == PutByIdDirect);
if (!status.isSimple())
break;
if (status.numVariants() != 1)
break;
emitPutByOffset(indexInBlock, node, structure, status[0], identifierNumber);
eliminated = true;
break;
}
case ToPrimitive: {
if (m_state.forNode(node->child1()).m_type & ~(SpecFullNumber | SpecBoolean | SpecString))
break;
node->convertToIdentity();
break;
}
default:
break;
}
if (eliminated) {
changed = true;
continue;
}
m_interpreter.execute(indexInBlock);
if (!m_state.isValid()) {
// If we invalidated then we shouldn't attempt to constant-fold. Here's an
// example:
//
// c: JSConstant(4.2)
// x: ValueToInt32(Check:Int32:@const)
//
// It would be correct for an analysis to assume that execution cannot
// proceed past @x. Therefore, constant-folding @x could be rather bad. But,
// the CFA may report that it found a constant even though it also reported
// that everything has been invalidated. This will only happen in a couple of
// the constant folding cases; most of them are also separately defensive
// about such things.
break;
}
if (!node->shouldGenerate() || m_state.didClobber() || node->hasConstant())
continue;
JSValue value = m_state.forNode(node).value();
if (!value)
continue;
// Check if merging the abstract value of the constant into the abstract value
// we've proven for this node wouldn't widen the proof. If it widens the proof
// (i.e. says that the set contains more things in it than it previously did)
// then we refuse to fold.
AbstractValue oldValue = m_state.forNode(node);
AbstractValue constantValue;
constantValue.set(m_graph, value);
constantValue.fixTypeForRepresentation(node);
if (oldValue.merge(constantValue))
continue;
NodeOrigin origin = node->origin;
AdjacencyList children = node->children;
if (node->op() == GetLocal)
m_graph.dethread();
else
ASSERT(!node->hasVariableAccessData(m_graph));
m_graph.convertToConstant(node, value);
m_insertionSet.insertNode(
indexInBlock, SpecNone, Phantom, origin, children);
changed = true;
}
m_state.reset();
m_insertionSet.execute(block);
return changed;
}