Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 1 | // Copyright 2012 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_TRANSITIONS_H_ |
| 6 | #define V8_TRANSITIONS_H_ |
| 7 | |
| 8 | #include "src/checks.h" |
| 9 | #include "src/elements-kind.h" |
| 10 | #include "src/heap/heap.h" |
| 11 | #include "src/isolate.h" |
| 12 | #include "src/objects.h" |
| 13 | |
| 14 | namespace v8 { |
| 15 | namespace internal { |
| 16 | |
| 17 | |
| 18 | // TransitionArrays are fixed arrays used to hold map transitions for property, |
| 19 | // constant, and element changes. They can either be simple transition arrays |
| 20 | // that store a single property transition, or a full transition array that has |
| 21 | // prototype transitions and multiple property transitons. The details related |
| 22 | // to property transitions are accessed in the descriptor array of the target |
| 23 | // map. In the case of a simple transition, the key is also read from the |
| 24 | // descriptor array of the target map. |
| 25 | // |
| 26 | // The simple format of the these objects is: |
| 27 | // [0] Undefined or back pointer map |
| 28 | // [1] Single transition |
| 29 | // |
| 30 | // The full format is: |
| 31 | // [0] Undefined or back pointer map |
| 32 | // [1] Smi(0) or fixed array of prototype transitions |
| 33 | // [2] First transition |
| 34 | // [length() - kTransitionSize] Last transition |
| 35 | class TransitionArray: public FixedArray { |
| 36 | public: |
| 37 | // Accessors for fetching instance transition at transition number. |
| 38 | inline Name* GetKey(int transition_number); |
| 39 | inline void SetKey(int transition_number, Name* value); |
| 40 | inline Object** GetKeySlot(int transition_number); |
| 41 | int GetSortedKeyIndex(int transition_number) { return transition_number; } |
| 42 | |
| 43 | Name* GetSortedKey(int transition_number) { |
| 44 | return GetKey(transition_number); |
| 45 | } |
| 46 | |
| 47 | inline Map* GetTarget(int transition_number); |
| 48 | inline void SetTarget(int transition_number, Map* target); |
| 49 | |
| 50 | inline PropertyDetails GetTargetDetails(int transition_number); |
| 51 | |
| 52 | inline bool HasElementsTransition(); |
| 53 | |
| 54 | inline Object* back_pointer_storage(); |
| 55 | inline void set_back_pointer_storage( |
| 56 | Object* back_pointer, |
| 57 | WriteBarrierMode mode = UPDATE_WRITE_BARRIER); |
| 58 | |
| 59 | inline FixedArray* GetPrototypeTransitions(); |
| 60 | inline void SetPrototypeTransitions( |
| 61 | FixedArray* prototype_transitions, |
| 62 | WriteBarrierMode mode = UPDATE_WRITE_BARRIER); |
| 63 | inline Object** GetPrototypeTransitionsSlot(); |
| 64 | inline bool HasPrototypeTransitions(); |
| 65 | |
| 66 | // Returns the number of transitions in the array. |
| 67 | int number_of_transitions() { |
| 68 | if (IsSimpleTransition()) return 1; |
| 69 | int len = length(); |
| 70 | return len <= kFirstIndex ? 0 : (len - kFirstIndex) / kTransitionSize; |
| 71 | } |
| 72 | |
| 73 | inline int number_of_entries() { return number_of_transitions(); } |
| 74 | |
| 75 | // Creates a FullTransitionArray from a SimpleTransitionArray in |
| 76 | // containing_map. |
| 77 | static Handle<TransitionArray> ExtendToFullTransitionArray( |
| 78 | Handle<Map> containing_map); |
| 79 | |
| 80 | // Create a transition array, copying from the owning map if it already has |
| 81 | // one, otherwise creating a new one according to flag. |
| 82 | // TODO(verwaest): This should not cause an existing transition to be |
| 83 | // overwritten. |
| 84 | static Handle<TransitionArray> CopyInsert(Handle<Map> map, |
| 85 | Handle<Name> name, |
| 86 | Handle<Map> target, |
| 87 | SimpleTransitionFlag flag); |
| 88 | |
| 89 | // Search a transition for a given property name. |
| 90 | inline int Search(Name* name); |
| 91 | |
| 92 | // Allocates a TransitionArray. |
| 93 | static Handle<TransitionArray> Allocate( |
| 94 | Isolate* isolate, int number_of_transitions); |
| 95 | |
| 96 | bool IsSimpleTransition() { |
| 97 | return length() == kSimpleTransitionSize && |
| 98 | get(kSimpleTransitionTarget)->IsHeapObject() && |
| 99 | // The IntrusivePrototypeTransitionIterator may have set the map of the |
| 100 | // prototype transitions array to a smi. In that case, there are |
| 101 | // prototype transitions, hence this transition array is a full |
| 102 | // transition array. |
| 103 | HeapObject::cast(get(kSimpleTransitionTarget))->map()->IsMap() && |
| 104 | get(kSimpleTransitionTarget)->IsMap(); |
| 105 | } |
| 106 | |
| 107 | bool IsFullTransitionArray() { |
| 108 | return length() > kFirstIndex || |
| 109 | (length() == kFirstIndex && !IsSimpleTransition()); |
| 110 | } |
| 111 | |
| 112 | // Casting. |
| 113 | static inline TransitionArray* cast(Object* obj); |
| 114 | |
| 115 | // Constant for denoting key was not found. |
| 116 | static const int kNotFound = -1; |
| 117 | |
| 118 | static const int kBackPointerStorageIndex = 0; |
| 119 | |
| 120 | // Layout for full transition arrays. |
| 121 | static const int kPrototypeTransitionsIndex = 1; |
| 122 | static const int kFirstIndex = 2; |
| 123 | |
| 124 | // Layout for simple transition arrays. |
| 125 | static const int kSimpleTransitionTarget = 1; |
| 126 | static const int kSimpleTransitionSize = 2; |
| 127 | static const int kSimpleTransitionIndex = 0; |
| 128 | STATIC_ASSERT(kSimpleTransitionIndex != kNotFound); |
| 129 | |
| 130 | static const int kBackPointerStorageOffset = FixedArray::kHeaderSize; |
| 131 | |
| 132 | // Layout for the full transition array header. |
| 133 | static const int kPrototypeTransitionsOffset = kBackPointerStorageOffset + |
| 134 | kPointerSize; |
| 135 | |
| 136 | // Layout of map transition entries in full transition arrays. |
| 137 | static const int kTransitionKey = 0; |
| 138 | static const int kTransitionTarget = 1; |
| 139 | static const int kTransitionSize = 2; |
| 140 | |
| 141 | #ifdef OBJECT_PRINT |
| 142 | // Print all the transitions. |
| 143 | void PrintTransitions(OStream& os); // NOLINT |
| 144 | #endif |
| 145 | |
| 146 | #ifdef DEBUG |
| 147 | bool IsSortedNoDuplicates(int valid_entries = -1); |
| 148 | bool IsConsistentWithBackPointers(Map* current_map); |
| 149 | bool IsEqualTo(TransitionArray* other); |
| 150 | #endif |
| 151 | |
| 152 | // The maximum number of transitions we want in a transition array (should |
| 153 | // fit in a page). |
| 154 | static const int kMaxNumberOfTransitions = 1024 + 512; |
| 155 | |
| 156 | private: |
| 157 | // Conversion from transition number to array indices. |
| 158 | static int ToKeyIndex(int transition_number) { |
| 159 | return kFirstIndex + |
| 160 | (transition_number * kTransitionSize) + |
| 161 | kTransitionKey; |
| 162 | } |
| 163 | |
| 164 | static int ToTargetIndex(int transition_number) { |
| 165 | return kFirstIndex + |
| 166 | (transition_number * kTransitionSize) + |
| 167 | kTransitionTarget; |
| 168 | } |
| 169 | |
| 170 | static Handle<TransitionArray> AllocateSimple( |
| 171 | Isolate* isolate, Handle<Map> target); |
| 172 | |
| 173 | // Allocate a new transition array with a single entry. |
| 174 | static Handle<TransitionArray> NewWith(Handle<Map> map, |
| 175 | Handle<Name> name, |
| 176 | Handle<Map> target, |
| 177 | SimpleTransitionFlag flag); |
| 178 | |
| 179 | inline void NoIncrementalWriteBarrierSet(int transition_number, |
| 180 | Name* key, |
| 181 | Map* target); |
| 182 | |
| 183 | // Copy a single transition from the origin array. |
| 184 | inline void NoIncrementalWriteBarrierCopyFrom(TransitionArray* origin, |
| 185 | int origin_transition, |
| 186 | int target_transition); |
| 187 | |
| 188 | DISALLOW_IMPLICIT_CONSTRUCTORS(TransitionArray); |
| 189 | }; |
| 190 | |
| 191 | |
| 192 | } } // namespace v8::internal |
| 193 | |
| 194 | #endif // V8_TRANSITIONS_H_ |