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 
11 namespace v8 {
12 namespace 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.
18 class 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:
ContextSlotCache()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 {
ValueValue60     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 
ValueValue75     explicit inline Value(uint32_t value) : value_(value) {}
76 
rawValue77     uint32_t raw() { return value_; }
78 
modeValue79     VariableMode mode() { return ModeField::decode(value_); }
80 
initialization_flagValue81     InitializationFlag initialization_flag() {
82       return InitField::decode(value_);
83     }
84 
maybe_assigned_flagValue85     MaybeAssignedFlag maybe_assigned_flag() {
86       return MaybeAssignedField::decode(value_);
87     }
88 
indexValue89     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