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 12 namespace v8 { 13 namespace 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. 25 class 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. 136 class LayoutDescriptorHelper { 137 public: 138 inline explicit LayoutDescriptorHelper(Map* map); 139 all_fields_tagged()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