Line data Source code
1 : // Copyright 2017 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_MAP_RECONFIGURER_H_
6 : #define V8_MAP_RECONFIGURER_H_
7 :
8 : #include "src/elements-kind.h"
9 : #include "src/globals.h"
10 : #include "src/handles.h"
11 : #include "src/objects.h"
12 : #include "src/property-details.h"
13 :
14 : namespace v8 {
15 : namespace internal {
16 :
17 : // The |MapUpdater| class implements all sorts of map reconfigurations
18 : // including changes of elements kind, property attributes, property kind,
19 : // property location and field representations/type changes. It ensures that
20 : // the reconfigured map and all the intermediate maps are properly integrated
21 : // into the exising transition tree.
22 : //
23 : // To avoid high degrees over polymorphism, and to stabilize quickly, on every
24 : // rewrite the new type is deduced by merging the current type with any
25 : // potential new (partial) version of the type in the transition tree.
26 : // To do this, on each rewrite:
27 : // - Search the root of the transition tree using FindRootMap.
28 : // - Find/create a |root_map| with requested |new_elements_kind|.
29 : // - Find |target_map|, the newest matching version of this map using the
30 : // "updated" |old_map|'s descriptor array (i.e. whose entry at |modify_index|
31 : // is considered to be of |new_kind| and having |new_attributes|) to walk
32 : // the transition tree.
33 : // - Merge/generalize the "updated" descriptor array of the |old_map| and
34 : // descriptor array of the |target_map|.
35 : // - Generalize the |modify_index| descriptor using |new_representation| and
36 : // |new_field_type|.
37 : // - Walk the tree again starting from the root towards |target_map|. Stop at
38 : // |split_map|, the first map who's descriptor array does not match the merged
39 : // descriptor array.
40 : // - If |target_map| == |split_map|, |target_map| is in the expected state.
41 : // Return it.
42 : // - Otherwise, invalidate the outdated transition target from |target_map|, and
43 : // replace its transition tree with a new branch for the updated descriptors.
44 : class MapUpdater {
45 : public:
46 1846740 : MapUpdater(Isolate* isolate, Handle<Map> old_map)
47 : : isolate_(isolate),
48 : old_map_(old_map),
49 : old_descriptors_(old_map->instance_descriptors(), isolate_),
50 : old_nof_(old_map_->NumberOfOwnDescriptors()),
51 5540220 : new_elements_kind_(old_map_->elements_kind()) {
52 : // We shouldn't try to update remote objects.
53 : DCHECK(!old_map->FindRootMap()->GetConstructor()->IsFunctionTemplateInfo());
54 1846740 : }
55 :
56 : // Prepares for reconfiguring of a property at |descriptor| to data field
57 : // with given |attributes| and |representation|/|field_type| and
58 : // performs the steps 1-5.
59 : Handle<Map> ReconfigureToDataField(int descriptor,
60 : PropertyAttributes attributes,
61 : PropertyConstness constness,
62 : Representation representation,
63 : Handle<FieldType> field_type);
64 :
65 : // Prepares for reconfiguring elements kind and performs the steps 1-5.
66 : Handle<Map> ReconfigureElementsKind(ElementsKind elements_kind);
67 :
68 : // Prepares for updating deprecated map to most up-to-date non-deprecated
69 : // version and performs the steps 1-5.
70 : Handle<Map> Update();
71 :
72 : private:
73 : enum State { kInitialized, kAtRootMap, kAtTargetMap, kEnd };
74 :
75 : // Try to reconfigure property in-place without rebuilding transition tree
76 : // and creating new maps. See implementation for details.
77 : State TryRecofigureToDataFieldInplace();
78 :
79 : // Step 1.
80 : // - Search the root of the transition tree using FindRootMap.
81 : // - Find/create a |root_map_| with requested |new_elements_kind_|.
82 : State FindRootMap();
83 :
84 : // Step 2.
85 : // - Find |target_map_|, the newest matching version of this map using the
86 : // "updated" |old_map|'s descriptor array (i.e. whose entry at
87 : // |modified_descriptor_| is considered to be of |new_kind| and having
88 : // |new_attributes|) to walk the transition tree.
89 : State FindTargetMap();
90 :
91 : // Step 3.
92 : // - Merge/generalize the "updated" descriptor array of the |old_map_| and
93 : // descriptor array of the |target_map_|.
94 : // - Generalize the |modified_descriptor_| using |new_representation| and
95 : // |new_field_type_|.
96 : Handle<DescriptorArray> BuildDescriptorArray();
97 :
98 : // Step 4.
99 : // - Walk the tree again starting from the root towards |target_map|. Stop at
100 : // |split_map|, the first map who's descriptor array does not match the
101 : // merged descriptor array.
102 : Handle<Map> FindSplitMap(Handle<DescriptorArray> descriptors);
103 :
104 : // Step 5.
105 : // - If |target_map| == |split_map|, |target_map| is in the expected state.
106 : // Return it.
107 : // - Otherwise, invalidate the outdated transition target from |target_map|,
108 : // and replace its transition tree with a new branch for the updated
109 : // descriptors.
110 : State ConstructNewMap();
111 :
112 : // When a requested reconfiguration can not be done the result is a copy
113 : // of |old_map_| where every field has |Tagged| representation and |Any|
114 : // field type. This map is disconnected from the transition tree.
115 : State CopyGeneralizeAllFields(const char* reason);
116 :
117 : // Returns name of a |descriptor| property.
118 : inline Name* GetKey(int descriptor) const;
119 :
120 : // Returns property details of a |descriptor| in "updated" |old_descrtiptors_|
121 : // array.
122 : inline PropertyDetails GetDetails(int descriptor) const;
123 :
124 : // Returns value of a |descriptor| with kDescriptor location in "updated"
125 : // |old_descrtiptors_| array.
126 : inline Object* GetValue(int descriptor) const;
127 :
128 : // Returns field type for a |descriptor| with kField location in "updated"
129 : // |old_descrtiptors_| array.
130 : inline FieldType* GetFieldType(int descriptor) const;
131 :
132 : // If a |descriptor| property in "updated" |old_descriptors_| has kField
133 : // location then returns it's field type otherwise computes optimal field
134 : // type for the descriptor's value and |representation|. The |location|
135 : // value must be a pre-fetched location for |descriptor|.
136 : inline Handle<FieldType> GetOrComputeFieldType(
137 : int descriptor, PropertyLocation location,
138 : Representation representation) const;
139 :
140 : // If a |descriptor| property in given |descriptors| array has kField
141 : // location then returns it's field type otherwise computes optimal field
142 : // type for the descriptor's value and |representation|.
143 : // The |location| value must be a pre-fetched location for |descriptor|.
144 : inline Handle<FieldType> GetOrComputeFieldType(
145 : Handle<DescriptorArray> descriptors, int descriptor,
146 : PropertyLocation location, Representation representation);
147 :
148 : void GeneralizeField(Handle<Map> map, int modify_index,
149 : PropertyConstness new_constness,
150 : Representation new_representation,
151 : Handle<FieldType> new_field_type);
152 :
153 : Isolate* isolate_;
154 : Handle<Map> old_map_;
155 : Handle<DescriptorArray> old_descriptors_;
156 : Handle<Map> root_map_;
157 : Handle<Map> target_map_;
158 : Handle<Map> result_map_;
159 : int old_nof_;
160 :
161 : State state_ = kInitialized;
162 : ElementsKind new_elements_kind_;
163 :
164 : // If |modified_descriptor_| is not equal to -1 them the fields below form
165 : // an "update" of the |old_map_|'s descriptors.
166 : int modified_descriptor_ = -1;
167 : PropertyKind new_kind_ = kData;
168 : PropertyAttributes new_attributes_ = NONE;
169 : PropertyConstness new_constness_ = kMutable;
170 : PropertyLocation new_location_ = kField;
171 : Representation new_representation_ = Representation::None();
172 :
173 : // Data specific to kField location.
174 : Handle<FieldType> new_field_type_;
175 :
176 : // Data specific to kDescriptor location.
177 : Handle<Object> new_value_;
178 : };
179 :
180 : } // namespace internal
181 : } // namespace v8
182 :
183 : #endif // V8_MAP_RECONFIGURER_H_
|
