1// Copyright 2014 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_LAYOUT_DESCRIPTOR_H_
6#define V8_LAYOUT_DESCRIPTOR_H_
7
8#include <iosfwd>
9
10#include "src/objects.h"
11
12namespace v8 {
13namespace internal {
14
15// LayoutDescriptor is a bit vector defining which fields contain non-tagged
16// values. It could either be a fixed typed array (slow form) or a Smi
17// if the length fits (fast form).
18// Each bit in the layout represents a FIELD. The bits are referenced by
19// field_index which is a field number. If the bit is set then the corresponding
20// field contains a non-tagged value and therefore must be skipped by GC.
21// Otherwise the field is considered tagged. If the queried bit lays "outside"
22// of the descriptor then the field is also considered tagged.
23// Once a layout descriptor is created it is allowed only to append properties
24// to it.
25class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
26 public:
27  V8_INLINE bool IsTagged(int field_index);
28
29  // Queries the contiguous region of fields that are either tagged or not.
30  // Returns true if the given field is tagged or false otherwise and writes
31  // the length of the contiguous region to |out_sequence_length|.
32  // If the sequence is longer than |max_sequence_length| then
33  // |out_sequence_length| is set to |max_sequence_length|.
34  bool IsTagged(int field_index, int max_sequence_length,
35                int* out_sequence_length);
36
37  // Returns true if this is a layout of the object having only tagged fields.
38  V8_INLINE bool IsFastPointerLayout();
39  V8_INLINE static bool IsFastPointerLayout(Object* layout_descriptor);
40
41  // Returns true if the layout descriptor is in non-Smi form.
42  V8_INLINE bool IsSlowLayout();
43
44  V8_INLINE static LayoutDescriptor* cast(Object* object);
45  V8_INLINE static const LayoutDescriptor* cast(const Object* object);
46
47  V8_INLINE static LayoutDescriptor* cast_gc_safe(Object* object);
48
49  // Builds layout descriptor optimized for given |map| by |num_descriptors|
50  // elements of given descriptors array. The |map|'s descriptors could be
51  // different.
52  static Handle<LayoutDescriptor> New(Handle<Map> map,
53                                      Handle<DescriptorArray> descriptors,
54                                      int num_descriptors);
55
56  // Modifies |map|'s layout descriptor or creates a new one if necessary by
57  // appending property with |details| to it.
58  static Handle<LayoutDescriptor> ShareAppend(Handle<Map> map,
59                                              PropertyDetails details);
60
61  // Creates new layout descriptor by appending property with |details| to
62  // |map|'s layout descriptor and if it is still fast then returns it.
63  // Otherwise the |full_layout_descriptor| is returned.
64  static Handle<LayoutDescriptor> AppendIfFastOrUseFull(
65      Handle<Map> map, PropertyDetails details,
66      Handle<LayoutDescriptor> full_layout_descriptor);
67
68  // Layout descriptor that corresponds to an object all fields of which are
69  // tagged (FastPointerLayout).
70  V8_INLINE static LayoutDescriptor* FastPointerLayout();
71
72  // Check that this layout descriptor corresponds to given map.
73  bool IsConsistentWithMap(Map* map, bool check_tail = false);
74
75  // Trims this layout descriptor to given number of descriptors. This happens
76  // only when corresponding descriptors array is trimmed.
77  // The layout descriptor could be trimmed if it was slow or it could
78  // become fast.
79  LayoutDescriptor* Trim(Heap* heap, Map* map, DescriptorArray* descriptors,
80                         int num_descriptors);
81
82#ifdef OBJECT_PRINT
83  // For our gdb macros, we should perhaps change these in the future.
84  void Print();
85
86  void Print(std::ostream& os);  // NOLINT
87#endif
88
89  // Capacity of layout descriptors in bits.
90  V8_INLINE int capacity();
91
92  static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length);
93  LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged);
94
95 private:
96  static const int kNumberOfBits = 32;
97
98  V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
99  V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);
100
101  V8_INLINE static bool InobjectUnboxedField(int inobject_properties,
102                                             PropertyDetails details);
103
104  // Calculates minimal layout descriptor capacity required for given
105  // |map|, |descriptors| and |num_descriptors|.
106  V8_INLINE static int CalculateCapacity(Map* map, DescriptorArray* descriptors,
107                                         int num_descriptors);
108
109  // Calculates the length of the slow-mode backing store array by given layout
110  // descriptor length.
111  V8_INLINE static int GetSlowModeBackingStoreLength(int length);
112
113  // Fills in clean |layout_descriptor| according to given |map|, |descriptors|
114  // and |num_descriptors|.
115  V8_INLINE static LayoutDescriptor* Initialize(
116      LayoutDescriptor* layout_descriptor, Map* map,
117      DescriptorArray* descriptors, int num_descriptors);
118
119  static Handle<LayoutDescriptor> EnsureCapacity(
120      Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
121      int new_capacity);
122
123  // Returns false if requested field_index is out of bounds.
124  V8_INLINE bool GetIndexes(int field_index, int* layout_word_index,
125                            int* layout_bit_index);
126
127  V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetRawData(int field_index);
128
129  V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetTagged(int field_index,
130                                                        bool tagged);
131};
132
133
134// LayoutDescriptorHelper is a helper class for querying layout descriptor
135// about whether the field at given offset is tagged or not.
136class LayoutDescriptorHelper {
137 public:
138  inline explicit LayoutDescriptorHelper(Map* map);
139
140  bool all_fields_tagged() { return all_fields_tagged_; }
141  inline bool IsTagged(int offset_in_bytes);
142
143  // Queries the contiguous region of fields that are either tagged or not.
144  // Returns true if fields starting at |offset_in_bytes| are tagged or false
145  // otherwise and writes the offset of the end of the contiguous region to
146  // |out_end_of_contiguous_region_offset|. The |end_offset| value is the
147  // upper bound for |out_end_of_contiguous_region_offset|.
148  bool IsTagged(int offset_in_bytes, int end_offset,
149                int* out_end_of_contiguous_region_offset);
150
151 private:
152  bool all_fields_tagged_;
153  int header_size_;
154  LayoutDescriptor* layout_descriptor_;
155};
156}  // namespace internal
157}  // namespace v8
158
159#endif  // V8_LAYOUT_DESCRIPTOR_H_
160