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// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/base/functional.h"
#include "src/compiler/graph-reducer.h"
#include "src/compiler/js-graph.h"
#include "src/compiler/persistent-map.h"
#include "src/globals.h"
#include "src/objects/name.h"
namespace v8 {
namespace internal {
namespace compiler {
class CommonOperatorBuilder;
class VariableTracker;
class EscapeAnalysisTracker;
// {EffectGraphReducer} reduces up to a fixed point. It distinguishes changes to
// the effect output of a node from changes to the value output to reduce the
// number of revisitations.
class EffectGraphReducer {
class Reduction {
bool value_changed() const { return value_changed_; }
void set_value_changed() { value_changed_ = true; }
bool effect_changed() const { return effect_changed_; }
void set_effect_changed() { effect_changed_ = true; }
bool value_changed_ = false;
bool effect_changed_ = false;
EffectGraphReducer(Graph* graph,
std::function<void(Node*, Reduction*)> reduce, Zone* zone);
void ReduceGraph() { ReduceFrom(graph_->end()); }
// Mark node for revisitation.
void Revisit(Node* node);
// Add a new root node to start reduction from. This is useful if the reducer
// adds nodes that are not yet reachable, but should already be considered
// part of the graph.
void AddRoot(Node* node) {
DCHECK_EQ(State::kUnvisited, state_.Get(node));
state_.Set(node, State::kRevisit);
bool Complete() { return stack_.empty() && revisit_.empty(); }
struct NodeState {
Node* node;
int input_index;
void ReduceFrom(Node* node);
enum class State : uint8_t { kUnvisited = 0, kRevisit, kOnStack, kVisited };
const uint8_t kNumStates = static_cast<uint8_t>(State::kVisited) + 1;
Graph* graph_;
NodeMarker<State> state_;
ZoneStack<Node*> revisit_;
ZoneStack<NodeState> stack_;
std::function<void(Node*, Reduction*)> reduce_;
// A variable is an abstract storage location, which is lowered to SSA values
// and phi nodes by {VariableTracker}.
class Variable {
Variable() : id_(kInvalid) {}
bool operator==(Variable other) const { return id_ == other.id_; }
bool operator!=(Variable other) const { return id_ != other.id_; }
bool operator<(Variable other) const { return id_ < other.id_; }
static Variable Invalid() { return Variable(kInvalid); }
friend V8_INLINE size_t hash_value(Variable v) {
return base::hash_value(v.id_);
friend std::ostream& operator<<(std::ostream& os, Variable var) {
return os << var.id_;
typedef int Id;
explicit Variable(Id id) : id_(id) {}
Id id_;
static const Id kInvalid = -1;
friend class VariableTracker;
// An object that can track the nodes in the graph whose current reduction
// depends on the value of the object.
class Dependable : public ZoneObject {
explicit Dependable(Zone* zone) : dependants_(zone) {}
void AddDependency(Node* node) { dependants_.push_back(node); }
void RevisitDependants(EffectGraphReducer* reducer) {
for (Node* node : dependants_) {
ZoneVector<Node*> dependants_;
// A virtual object represents an allocation site and tracks the Variables
// associated with its fields as well as its global escape status.
class VirtualObject : public Dependable {
typedef uint32_t Id;
typedef ZoneVector<Variable>::const_iterator const_iterator;
VirtualObject(VariableTracker* var_states, Id id, int size);
Maybe<Variable> FieldAt(int offset) const {
if (offset % kPointerSize != 0) {
// We do not support fields that are not word-aligned. Bail out by
// treating the object as escaping. This can only happen for
// {Name::kHashFieldOffset} on 64bit big endian architectures.
DCHECK_EQ(Name::kHashFieldOffset, offset);
return Nothing<Variable>();
if (offset >= size()) {
// TODO(tebbi): Reading out-of-bounds can only happen in unreachable
// code. In this case, we have to mark the object as escaping to avoid
// dead nodes in the graph. This is a workaround that should be removed
// once we can handle dead nodes everywhere.
return Nothing<Variable>();
return Just( / kPointerSize));
Id id() const { return id_; }
int size() const { return static_cast<int>(kPointerSize * fields_.size()); }
// Escaped might mean that the object escaped to untracked memory or that it
// is used in an operation that requires materialization.
void SetEscaped() { escaped_ = true; }
bool HasEscaped() const { return escaped_; }
const_iterator begin() const { return fields_.begin(); }
const_iterator end() const { return fields_.end(); }
bool escaped_ = false;
Id id_;
ZoneVector<Variable> fields_;
class EscapeAnalysisResult {
explicit EscapeAnalysisResult(EscapeAnalysisTracker* tracker)
: tracker_(tracker) {}
const VirtualObject* GetVirtualObject(Node* node);
Node* GetVirtualObjectField(const VirtualObject* vobject, int field,
Node* effect);
Node* GetReplacementOf(Node* node);
EscapeAnalysisTracker* tracker_;
class V8_EXPORT_PRIVATE EscapeAnalysis final
: public NON_EXPORTED_BASE(EffectGraphReducer) {
EscapeAnalysis(JSGraph* jsgraph, Zone* zone);
EscapeAnalysisResult analysis_result() {
return EscapeAnalysisResult(tracker_);
void Reduce(Node* node, Reduction* reduction);
JSGraph* jsgraph() { return jsgraph_; }
EscapeAnalysisTracker* tracker_;
JSGraph* jsgraph_;
} // namespace compiler
} // namespace internal
} // namespace v8