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_INL_H_ 6 #define V8_LAYOUT_DESCRIPTOR_INL_H_ 7 8 #include "src/layout-descriptor.h" 9 10 namespace v8 { 11 namespace internal { 12 13 LayoutDescriptor* LayoutDescriptor::FromSmi(Smi* smi) { 14 return LayoutDescriptor::cast(smi); 15 } 16 17 18 Handle<LayoutDescriptor> LayoutDescriptor::New(Isolate* isolate, int length) { 19 if (length <= kSmiValueSize) { 20 // The whole bit vector fits into a smi. 21 return handle(LayoutDescriptor::FromSmi(Smi::kZero), isolate); 22 } 23 length = GetSlowModeBackingStoreLength(length); 24 return Handle<LayoutDescriptor>::cast(isolate->factory()->NewFixedTypedArray( 25 length, kExternalUint32Array, true)); 26 } 27 28 29 bool LayoutDescriptor::InobjectUnboxedField(int inobject_properties, 30 PropertyDetails details) { 31 if (details.location() != kField || !details.representation().IsDouble()) { 32 return false; 33 } 34 // We care only about in-object properties. 35 return details.field_index() < inobject_properties; 36 } 37 38 39 LayoutDescriptor* LayoutDescriptor::FastPointerLayout() { 40 return LayoutDescriptor::FromSmi(Smi::kZero); 41 } 42 43 44 bool LayoutDescriptor::GetIndexes(int field_index, int* layout_word_index, 45 int* layout_bit_index) { 46 if (static_cast<unsigned>(field_index) >= static_cast<unsigned>(capacity())) { 47 return false; 48 } 49 50 *layout_word_index = field_index / kNumberOfBits; 51 CHECK((!IsSmi() && (*layout_word_index < length())) || 52 (IsSmi() && (*layout_word_index < 1))); 53 54 *layout_bit_index = field_index % kNumberOfBits; 55 return true; 56 } 57 58 59 LayoutDescriptor* LayoutDescriptor::SetRawData(int field_index) { 60 return SetTagged(field_index, false); 61 } 62 63 64 LayoutDescriptor* LayoutDescriptor::SetTagged(int field_index, bool tagged) { 65 int layout_word_index = 0; 66 int layout_bit_index = 0; 67 68 if (!GetIndexes(field_index, &layout_word_index, &layout_bit_index)) { 69 CHECK(false); 70 return this; 71 } 72 uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index; 73 74 if (IsSlowLayout()) { 75 uint32_t value = get_scalar(layout_word_index); 76 if (tagged) { 77 value &= ~layout_mask; 78 } else { 79 value |= layout_mask; 80 } 81 set(layout_word_index, value); 82 return this; 83 } else { 84 uint32_t value = static_cast<uint32_t>(Smi::cast(this)->value()); 85 if (tagged) { 86 value &= ~layout_mask; 87 } else { 88 value |= layout_mask; 89 } 90 return LayoutDescriptor::FromSmi(Smi::FromInt(static_cast<int>(value))); 91 } 92 } 93 94 95 bool LayoutDescriptor::IsTagged(int field_index) { 96 if (IsFastPointerLayout()) return true; 97 98 int layout_word_index; 99 int layout_bit_index; 100 101 if (!GetIndexes(field_index, &layout_word_index, &layout_bit_index)) { 102 // All bits after Out of bounds queries 103 return true; 104 } 105 uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index; 106 107 if (IsSlowLayout()) { 108 uint32_t value = get_scalar(layout_word_index); 109 return (value & layout_mask) == 0; 110 } else { 111 uint32_t value = static_cast<uint32_t>(Smi::cast(this)->value()); 112 return (value & layout_mask) == 0; 113 } 114 } 115 116 117 bool LayoutDescriptor::IsFastPointerLayout() { 118 return this == FastPointerLayout(); 119 } 120 121 122 bool LayoutDescriptor::IsFastPointerLayout(Object* layout_descriptor) { 123 return layout_descriptor == FastPointerLayout(); 124 } 125 126 127 bool LayoutDescriptor::IsSlowLayout() { return !IsSmi(); } 128 129 130 int LayoutDescriptor::capacity() { 131 return IsSlowLayout() ? (length() * kNumberOfBits) : kSmiValueSize; 132 } 133 134 135 LayoutDescriptor* LayoutDescriptor::cast_gc_safe(Object* object) { 136 if (object->IsSmi()) { 137 // Fast mode layout descriptor. 138 return reinterpret_cast<LayoutDescriptor*>(object); 139 } 140 141 // This is a mixed descriptor which is a fixed typed array. 142 MapWord map_word = reinterpret_cast<HeapObject*>(object)->map_word(); 143 if (map_word.IsForwardingAddress()) { 144 // Mark-compact has already moved layout descriptor. 145 object = map_word.ToForwardingAddress(); 146 } 147 return LayoutDescriptor::cast(object); 148 } 149 150 151 int LayoutDescriptor::GetSlowModeBackingStoreLength(int length) { 152 length = (length + kNumberOfBits - 1) / kNumberOfBits; 153 DCHECK_LT(0, length); 154 155 if (SmiValuesAre32Bits() && (length & 1)) { 156 // On 64-bit systems if the length is odd then the half-word space would be 157 // lost anyway (due to alignment and the fact that we are allocating 158 // uint32-typed array), so we increase the length of allocated array 159 // to utilize that "lost" space which could also help to avoid layout 160 // descriptor reallocations. 161 ++length; 162 } 163 return length; 164 } 165 166 167 int LayoutDescriptor::CalculateCapacity(Map* map, DescriptorArray* descriptors, 168 int num_descriptors) { 169 int inobject_properties = map->GetInObjectProperties(); 170 if (inobject_properties == 0) return 0; 171 172 DCHECK_LE(num_descriptors, descriptors->number_of_descriptors()); 173 174 int layout_descriptor_length; 175 const int kMaxWordsPerField = kDoubleSize / kPointerSize; 176 177 if (num_descriptors <= kSmiValueSize / kMaxWordsPerField) { 178 // Even in the "worst" case (all fields are doubles) it would fit into 179 // a Smi, so no need to calculate length. 180 layout_descriptor_length = kSmiValueSize; 181 182 } else { 183 layout_descriptor_length = 0; 184 185 for (int i = 0; i < num_descriptors; i++) { 186 PropertyDetails details = descriptors->GetDetails(i); 187 if (!InobjectUnboxedField(inobject_properties, details)) continue; 188 int field_index = details.field_index(); 189 int field_width_in_words = details.field_width_in_words(); 190 layout_descriptor_length = 191 Max(layout_descriptor_length, field_index + field_width_in_words); 192 } 193 } 194 layout_descriptor_length = Min(layout_descriptor_length, inobject_properties); 195 return layout_descriptor_length; 196 } 197 198 199 LayoutDescriptor* LayoutDescriptor::Initialize( 200 LayoutDescriptor* layout_descriptor, Map* map, DescriptorArray* descriptors, 201 int num_descriptors) { 202 DisallowHeapAllocation no_allocation; 203 int inobject_properties = map->GetInObjectProperties(); 204 205 for (int i = 0; i < num_descriptors; i++) { 206 PropertyDetails details = descriptors->GetDetails(i); 207 if (!InobjectUnboxedField(inobject_properties, details)) { 208 DCHECK(details.location() != kField || 209 layout_descriptor->IsTagged(details.field_index())); 210 continue; 211 } 212 int field_index = details.field_index(); 213 layout_descriptor = layout_descriptor->SetRawData(field_index); 214 if (details.field_width_in_words() > 1) { 215 layout_descriptor = layout_descriptor->SetRawData(field_index + 1); 216 } 217 } 218 return layout_descriptor; 219 } 220 221 222 // LayoutDescriptorHelper is a helper class for querying whether inobject 223 // property at offset is Double or not. 224 LayoutDescriptorHelper::LayoutDescriptorHelper(Map* map) 225 : all_fields_tagged_(true), 226 header_size_(0), 227 layout_descriptor_(LayoutDescriptor::FastPointerLayout()) { 228 if (!FLAG_unbox_double_fields) return; 229 230 layout_descriptor_ = map->layout_descriptor_gc_safe(); 231 if (layout_descriptor_->IsFastPointerLayout()) { 232 return; 233 } 234 235 int inobject_properties = map->GetInObjectProperties(); 236 DCHECK(inobject_properties > 0); 237 header_size_ = map->instance_size() - (inobject_properties * kPointerSize); 238 DCHECK(header_size_ >= 0); 239 240 all_fields_tagged_ = false; 241 } 242 243 244 bool LayoutDescriptorHelper::IsTagged(int offset_in_bytes) { 245 DCHECK(IsAligned(offset_in_bytes, kPointerSize)); 246 if (all_fields_tagged_) return true; 247 // Object headers do not contain non-tagged fields. 248 if (offset_in_bytes < header_size_) return true; 249 int field_index = (offset_in_bytes - header_size_) / kPointerSize; 250 251 return layout_descriptor_->IsTagged(field_index); 252 } 253 } // namespace internal 254 } // namespace v8 255 256 #endif // V8_LAYOUT_DESCRIPTOR_INL_H_ 257
