1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
|
// 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.
#ifndef V8_OBJECTS_MAP_UPDATER_H_
#define V8_OBJECTS_MAP_UPDATER_H_
#include "src/common/globals.h"
#include "src/handles/handles.h"
#include "src/objects/elements-kind.h"
#include "src/objects/field-type.h"
#include "src/objects/map.h"
#include "src/objects/property-details.h"
namespace v8 {
namespace internal {
// The |MapUpdater| class implements all sorts of map reconfigurations
// including changes of elements kind, property attributes, property kind,
// property location and field representations/type changes. It ensures that
// the reconfigured map and all the intermediate maps are properly integrated
// into the exising transition tree.
//
// To avoid high degrees over polymorphism, and to stabilize quickly, on every
// rewrite the new type is deduced by merging the current type with any
// potential new (partial) version of the type in the transition tree.
// To do this, on each rewrite:
// - Search the root of the transition tree using FindRootMap, remember
// the integrity level (preventExtensions/seal/freeze) transitions.
// - Find/create a |root_map| with requested |new_elements_kind|.
// - Find |target_map|, the newest matching version of this map using the
// "updated" |old_map|'s descriptor array (i.e. whose entry at |modify_index|
// is considered to be of |new_kind| and having |new_attributes|) to walk
// the transition tree. If there was an integrity level transition on the path
// to the old map, use the descriptor array of the map preceding the first
// integrity level transition (|integrity_source_map|), and try to replay
// the integrity level transition afterwards.
// - Merge/generalize the "updated" descriptor array of the |old_map| and
// descriptor array of the |target_map|.
// - Generalize the |modify_index| descriptor using |new_representation| and
// |new_field_type|.
// - Walk the tree again starting from the root towards |target_map|. Stop at
// |split_map|, the first map who's descriptor array does not match the merged
// descriptor array.
// - If |target_map| == |split_map|, and there are no integrity level
// transitions, |target_map| is in the expected state. Return it.
// - Otherwise, invalidate the outdated transition target from |target_map|, and
// replace its transition tree with a new branch for the updated descriptors.
// - If the |old_map| had integrity level transition, create the new map for it.
class MapUpdater {
public:
MapUpdater(Isolate* isolate, Handle<Map> old_map);
// Prepares for reconfiguring of a property at |descriptor| to data field
// with given |attributes| and |representation|/|field_type| and
// performs the steps 1-5.
Handle<Map> ReconfigureToDataField(int descriptor,
PropertyAttributes attributes,
PropertyConstness constness,
Representation representation,
Handle<FieldType> field_type);
// Prepares for reconfiguring elements kind and performs the steps 1-5.
Handle<Map> ReconfigureElementsKind(ElementsKind elements_kind);
// Prepares for updating deprecated map to most up-to-date non-deprecated
// version and performs the steps 1-5.
Handle<Map> Update();
private:
enum State {
kInitialized,
kAtRootMap,
kAtTargetMap,
kAtIntegrityLevelSource,
kEnd
};
// Try to reconfigure property in-place without rebuilding transition tree
// and creating new maps. See implementation for details.
State TryReconfigureToDataFieldInplace();
// Step 1.
// - Search the root of the transition tree using FindRootMap.
// - Find/create a |root_map_| with requested |new_elements_kind_|.
State FindRootMap();
// Step 2.
// - Find |target_map|, the newest matching version of this map using the
// "updated" |old_map|'s descriptor array (i.e. whose entry at
// |modify_index| is considered to be of |new_kind| and having
// |new_attributes|) to walk the transition tree. If there was an integrity
// level transition on the path to the old map, use the descriptor array
// of the map preceding the first integrity level transition
// (|integrity_source_map|), and try to replay the integrity level
// transition afterwards.
State FindTargetMap();
// Step 3.
// - Merge/generalize the "updated" descriptor array of the |old_map_| and
// descriptor array of the |target_map_|.
// - Generalize the |modified_descriptor_| using |new_representation| and
// |new_field_type_|.
Handle<DescriptorArray> BuildDescriptorArray();
// Step 4.
// - Walk the tree again starting from the root towards |target_map|. Stop at
// |split_map|, the first map who's descriptor array does not match the
// merged descriptor array.
Handle<Map> FindSplitMap(Handle<DescriptorArray> descriptors);
// Step 5.
// - If |target_map| == |split_map|, |target_map| is in the expected state.
// Return it.
// - Otherwise, invalidate the outdated transition target from |target_map|,
// and replace its transition tree with a new branch for the updated
// descriptors.
State ConstructNewMap();
// Step 6 (if there was
// - If the |old_map| had integrity level transition, create the new map
// for it.
State ConstructNewMapWithIntegrityLevelTransition();
// When a requested reconfiguration can not be done the result is a copy
// of |old_map_| in dictionary mode.
State Normalize(const char* reason);
// Returns name of a |descriptor| property.
inline Name GetKey(int descriptor) const;
// Returns property details of a |descriptor| in "updated" |old_descrtiptors_|
// array.
inline PropertyDetails GetDetails(int descriptor) const;
// Returns value of a |descriptor| with kDescriptor location in "updated"
// |old_descrtiptors_| array.
inline Object GetValue(int descriptor) const;
// Returns field type for a |descriptor| with kField location in "updated"
// |old_descrtiptors_| array.
inline FieldType GetFieldType(int descriptor) const;
// If a |descriptor| property in "updated" |old_descriptors_| has kField
// location then returns it's field type otherwise computes optimal field
// type for the descriptor's value and |representation|. The |location|
// value must be a pre-fetched location for |descriptor|.
inline Handle<FieldType> GetOrComputeFieldType(
int descriptor, PropertyLocation location,
Representation representation) const;
// If a |descriptor| property in given |descriptors| array has kField
// location then returns it's field type otherwise computes optimal field
// type for the descriptor's value and |representation|.
// The |location| value must be a pre-fetched location for |descriptor|.
inline Handle<FieldType> GetOrComputeFieldType(
Handle<DescriptorArray> descriptors, int descriptor,
PropertyLocation location, Representation representation);
void GeneralizeField(Handle<Map> map, int modify_index,
PropertyConstness new_constness,
Representation new_representation,
Handle<FieldType> new_field_type);
bool TrySaveIntegrityLevelTransitions();
Isolate* isolate_;
Handle<Map> old_map_;
Handle<DescriptorArray> old_descriptors_;
Handle<Map> root_map_;
Handle<Map> target_map_;
Handle<Map> result_map_;
int old_nof_;
// Information about integrity level transitions.
bool has_integrity_level_transition_ = false;
PropertyAttributes integrity_level_ = NONE;
Handle<Symbol> integrity_level_symbol_;
Handle<Map> integrity_source_map_;
State state_ = kInitialized;
ElementsKind new_elements_kind_;
bool is_transitionable_fast_elements_kind_;
// If |modified_descriptor_| is not equal to -1 then the fields below form
// an "update" of the |old_map_|'s descriptors.
int modified_descriptor_ = -1;
PropertyKind new_kind_ = kData;
PropertyAttributes new_attributes_ = NONE;
PropertyConstness new_constness_ = PropertyConstness::kMutable;
PropertyLocation new_location_ = kField;
Representation new_representation_ = Representation::None();
// Data specific to kField location.
Handle<FieldType> new_field_type_;
// Data specific to kDescriptor location.
Handle<Object> new_value_;
};
} // namespace internal
} // namespace v8
#endif // V8_OBJECTS_MAP_UPDATER_H_
|
