1 // Copyright 2018 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "src/compiler/constant-folding-reducer.h"
6
7 #include "src/compiler/js-graph.h"
8 #include "src/compiler/js-heap-broker.h"
9 #include "src/objects/objects-inl.h"
10
11 namespace v8 {
12 namespace internal {
13 namespace compiler {
14
15 namespace {
TryGetConstant(JSGraph * jsgraph,Node * node)16 Node* TryGetConstant(JSGraph* jsgraph, Node* node) {
17 Type type = NodeProperties::GetType(node);
18 Node* result;
19 if (type.IsNone()) {
20 result = nullptr;
21 } else if (type.Is(Type::Null())) {
22 result = jsgraph->NullConstant();
23 } else if (type.Is(Type::Undefined())) {
24 result = jsgraph->UndefinedConstant();
25 } else if (type.Is(Type::MinusZero())) {
26 result = jsgraph->MinusZeroConstant();
27 } else if (type.Is(Type::NaN())) {
28 result = jsgraph->NaNConstant();
29 } else if (type.Is(Type::Hole())) {
30 result = jsgraph->TheHoleConstant();
31 } else if (type.IsHeapConstant()) {
32 result = jsgraph->Constant(type.AsHeapConstant()->Ref());
33 } else if (type.Is(Type::PlainNumber()) && type.Min() == type.Max()) {
34 result = jsgraph->Constant(type.Min());
35 } else {
36 result = nullptr;
37 }
38 DCHECK_EQ(result != nullptr, type.IsSingleton());
39 DCHECK_IMPLIES(result != nullptr,
40 type.Equals(NodeProperties::GetType(result)));
41 return result;
42 }
43
IsAlreadyBeingFolded(Node * node)44 bool IsAlreadyBeingFolded(Node* node) {
45 DCHECK(FLAG_assert_types);
46 if (node->opcode() == IrOpcode::kFoldConstant) return true;
47 for (Edge edge : node->use_edges()) {
48 if (NodeProperties::IsValueEdge(edge) &&
49 edge.from()->opcode() == IrOpcode::kFoldConstant) {
50 // Note: {node} may have gained new value uses since the time it was
51 // "constant-folded", and theses uses should ideally be rewritten as well.
52 // For simplicity, we ignore them here.
53 return true;
54 }
55 }
56 return false;
57 }
58 } // namespace
59
ConstantFoldingReducer(Editor * editor,JSGraph * jsgraph,JSHeapBroker * broker)60 ConstantFoldingReducer::ConstantFoldingReducer(Editor* editor, JSGraph* jsgraph,
61 JSHeapBroker* broker)
62 : AdvancedReducer(editor), jsgraph_(jsgraph), broker_(broker) {}
63
64 ConstantFoldingReducer::~ConstantFoldingReducer() = default;
65
Reduce(Node * node)66 Reduction ConstantFoldingReducer::Reduce(Node* node) {
67 if (!NodeProperties::IsConstant(node) && NodeProperties::IsTyped(node) &&
68 node->op()->HasProperty(Operator::kEliminatable) &&
69 node->opcode() != IrOpcode::kFinishRegion) {
70 Node* constant = TryGetConstant(jsgraph(), node);
71 if (constant != nullptr) {
72 DCHECK(NodeProperties::IsTyped(constant));
73 if (!FLAG_assert_types) {
74 DCHECK_EQ(node->op()->ControlOutputCount(), 0);
75 ReplaceWithValue(node, constant);
76 return Replace(constant);
77 } else if (!IsAlreadyBeingFolded(node)) {
78 // Delay the constant folding (by inserting a FoldConstant operation
79 // instead) in order to keep type assertions meaningful.
80 Node* fold_constant = jsgraph()->graph()->NewNode(
81 jsgraph()->common()->FoldConstant(), node, constant);
82 DCHECK(NodeProperties::IsTyped(fold_constant));
83 ReplaceWithValue(node, fold_constant, node, node);
84 fold_constant->ReplaceInput(0, node);
85 DCHECK(IsAlreadyBeingFolded(node));
86 DCHECK(IsAlreadyBeingFolded(fold_constant));
87 return Changed(node);
88 }
89 }
90 }
91 return NoChange();
92 }
93
94 } // namespace compiler
95 } // namespace internal
96 } // namespace v8
97