1// Copyright 2016 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#ifndef V8_AST_CONTEXT_SLOT_CACHE_H_
6#define V8_AST_CONTEXT_SLOT_CACHE_H_
7
8#include "src/allocation.h"
9#include "src/ast/modules.h"
10
11namespace v8 {
12namespace internal {
13
14// Cache for mapping (data, property name) into context slot index.
15// The cache contains both positive and negative results.
16// Slot index equals -1 means the property is absent.
17// Cleared at startup and prior to mark sweep collection.
18class ContextSlotCache {
19 public:
20  // Lookup context slot index for (data, name).
21  // If absent, kNotFound is returned.
22  int Lookup(Object* data, String* name, VariableMode* mode,
23             InitializationFlag* init_flag,
24             MaybeAssignedFlag* maybe_assigned_flag);
25
26  // Update an element in the cache.
27  void Update(Handle<Object> data, Handle<String> name, VariableMode mode,
28              InitializationFlag init_flag,
29              MaybeAssignedFlag maybe_assigned_flag, int slot_index);
30
31  // Clear the cache.
32  void Clear();
33
34  static const int kNotFound = -2;
35
36 private:
37  ContextSlotCache() {
38    for (int i = 0; i < kLength; ++i) {
39      keys_[i].data = NULL;
40      keys_[i].name = NULL;
41      values_[i] = kNotFound;
42    }
43  }
44
45  inline static int Hash(Object* data, String* name);
46
47#ifdef DEBUG
48  void ValidateEntry(Handle<Object> data, Handle<String> name,
49                     VariableMode mode, InitializationFlag init_flag,
50                     MaybeAssignedFlag maybe_assigned_flag, int slot_index);
51#endif
52
53  static const int kLength = 256;
54  struct Key {
55    Object* data;
56    String* name;
57  };
58
59  struct Value {
60    Value(VariableMode mode, InitializationFlag init_flag,
61          MaybeAssignedFlag maybe_assigned_flag, int index) {
62      DCHECK(ModeField::is_valid(mode));
63      DCHECK(InitField::is_valid(init_flag));
64      DCHECK(MaybeAssignedField::is_valid(maybe_assigned_flag));
65      DCHECK(IndexField::is_valid(index));
66      value_ = ModeField::encode(mode) | IndexField::encode(index) |
67               InitField::encode(init_flag) |
68               MaybeAssignedField::encode(maybe_assigned_flag);
69      DCHECK(mode == this->mode());
70      DCHECK(init_flag == this->initialization_flag());
71      DCHECK(maybe_assigned_flag == this->maybe_assigned_flag());
72      DCHECK(index == this->index());
73    }
74
75    explicit inline Value(uint32_t value) : value_(value) {}
76
77    uint32_t raw() { return value_; }
78
79    VariableMode mode() { return ModeField::decode(value_); }
80
81    InitializationFlag initialization_flag() {
82      return InitField::decode(value_);
83    }
84
85    MaybeAssignedFlag maybe_assigned_flag() {
86      return MaybeAssignedField::decode(value_);
87    }
88
89    int index() { return IndexField::decode(value_); }
90
91    // Bit fields in value_ (type, shift, size). Must be public so the
92    // constants can be embedded in generated code.
93    class ModeField : public BitField<VariableMode, 0, 4> {};
94    class InitField : public BitField<InitializationFlag, 4, 1> {};
95    class MaybeAssignedField : public BitField<MaybeAssignedFlag, 5, 1> {};
96    class IndexField : public BitField<int, 6, 32 - 6> {};
97
98   private:
99    uint32_t value_;
100  };
101
102  Key keys_[kLength];
103  uint32_t values_[kLength];
104
105  friend class Isolate;
106  DISALLOW_COPY_AND_ASSIGN(ContextSlotCache);
107};
108
109}  // namespace internal
110}  // namespace v8
111
112#endif  // V8_AST_CONTEXT_SLOT_CACHE_H_
113