// Copyright 2014 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. #include "src/layout-descriptor.h" #include <sstream> #include "src/base/bits.h" #include "src/handles-inl.h" #include "src/objects-inl.h" namespace v8 { namespace internal { Handle<LayoutDescriptor> LayoutDescriptor::New( Isolate* isolate, Handle<Map> map, Handle<DescriptorArray> descriptors, int num_descriptors) { if (!FLAG_unbox_double_fields) return handle(FastPointerLayout(), isolate); int layout_descriptor_length = CalculateCapacity(*map, *descriptors, num_descriptors); if (layout_descriptor_length == 0) { // No double fields were found, use fast pointer layout. return handle(FastPointerLayout(), isolate); } // Initially, layout descriptor corresponds to an object with all fields // tagged. Handle<LayoutDescriptor> layout_descriptor_handle = LayoutDescriptor::New(isolate, layout_descriptor_length); LayoutDescriptor layout_descriptor = Initialize( *layout_descriptor_handle, *map, *descriptors, num_descriptors); return handle(layout_descriptor, isolate); } Handle<LayoutDescriptor> LayoutDescriptor::ShareAppend( Isolate* isolate, Handle<Map> map, PropertyDetails details) { DCHECK(map->owns_descriptors()); Handle<LayoutDescriptor> layout_descriptor(map->GetLayoutDescriptor(), isolate); if (!InobjectUnboxedField(map->GetInObjectProperties(), details)) { DCHECK(details.location() != kField || layout_descriptor->IsTagged(details.field_index())); return layout_descriptor; } int field_index = details.field_index(); layout_descriptor = LayoutDescriptor::EnsureCapacity( isolate, layout_descriptor, field_index + details.field_width_in_words()); DisallowHeapAllocation no_allocation; LayoutDescriptor layout_desc = *layout_descriptor; layout_desc = layout_desc->SetRawData(field_index); if (details.field_width_in_words() > 1) { layout_desc = layout_desc->SetRawData(field_index + 1); } return handle(layout_desc, isolate); } Handle<LayoutDescriptor> LayoutDescriptor::AppendIfFastOrUseFull( Isolate* isolate, Handle<Map> map, PropertyDetails details, Handle<LayoutDescriptor> full_layout_descriptor) { DisallowHeapAllocation no_allocation; LayoutDescriptor layout_descriptor = map->layout_descriptor(); if (layout_descriptor->IsSlowLayout()) { return full_layout_descriptor; } if (!InobjectUnboxedField(map->GetInObjectProperties(), details)) { DCHECK(details.location() != kField || layout_descriptor->IsTagged(details.field_index())); return handle(layout_descriptor, isolate); } int field_index = details.field_index(); int new_capacity = field_index + details.field_width_in_words(); if (new_capacity > layout_descriptor->capacity()) { // Current map's layout descriptor runs out of space, so use the full // layout descriptor. return full_layout_descriptor; } layout_descriptor = layout_descriptor->SetRawData(field_index); if (details.field_width_in_words() > 1) { layout_descriptor = layout_descriptor->SetRawData(field_index + 1); } return handle(layout_descriptor, isolate); } Handle<LayoutDescriptor> LayoutDescriptor::EnsureCapacity( Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor, int new_capacity) { int old_capacity = layout_descriptor->capacity(); if (new_capacity <= old_capacity) { return layout_descriptor; } Handle<LayoutDescriptor> new_layout_descriptor = LayoutDescriptor::New(isolate, new_capacity); DCHECK(new_layout_descriptor->IsSlowLayout()); if (layout_descriptor->IsSlowLayout()) { memcpy(new_layout_descriptor->GetDataStartAddress(), layout_descriptor->GetDataStartAddress(), layout_descriptor->DataSize()); return new_layout_descriptor; } else { // Fast layout. uint32_t value = static_cast<uint32_t>(Smi::ToInt(*layout_descriptor)); new_layout_descriptor->set_layout_word(0, value); return new_layout_descriptor; } } bool LayoutDescriptor::IsTagged(int field_index, int max_sequence_length, int* out_sequence_length) { DCHECK_GT(max_sequence_length, 0); if (IsFastPointerLayout()) { *out_sequence_length = max_sequence_length; return true; } int layout_word_index; int layout_bit_index; if (!GetIndexes(field_index, &layout_word_index, &layout_bit_index)) { // Out of bounds queries are considered tagged. *out_sequence_length = max_sequence_length; return true; } uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index; uint32_t value = IsSlowLayout() ? get_layout_word(layout_word_index) : static_cast<uint32_t>(Smi::ToInt(*this)); bool is_tagged = (value & layout_mask) == 0; if (!is_tagged) value = ~value; // Count set bits instead of cleared bits. value = value & ~(layout_mask - 1); // Clear bits we are not interested in. int sequence_length; if (IsSlowLayout()) { sequence_length = base::bits::CountTrailingZeros(value) - layout_bit_index; if (layout_bit_index + sequence_length == kBitsPerLayoutWord) { // This is a contiguous sequence till the end of current word, proceed // counting in the subsequent words. ++layout_word_index; int num_words = number_of_layout_words(); for (; layout_word_index < num_words; layout_word_index++) { value = get_layout_word(layout_word_index); bool cur_is_tagged = (value & 1) == 0; if (cur_is_tagged != is_tagged) break; if (!is_tagged) value = ~value; // Count set bits instead. int cur_sequence_length = base::bits::CountTrailingZeros(value); sequence_length += cur_sequence_length; if (sequence_length >= max_sequence_length) break; if (cur_sequence_length != kBitsPerLayoutWord) break; } if (is_tagged && (field_index + sequence_length == capacity())) { // The contiguous sequence of tagged fields lasts till the end of the // layout descriptor which means that all the fields starting from // field_index are tagged. sequence_length = std::numeric_limits<int>::max(); } } } else { // Fast layout. sequence_length = Min(base::bits::CountTrailingZeros(value), static_cast<unsigned>(kBitsInSmiLayout)) - layout_bit_index; if (is_tagged && (field_index + sequence_length == capacity())) { // The contiguous sequence of tagged fields lasts till the end of the // layout descriptor which means that all the fields starting from // field_index are tagged. sequence_length = std::numeric_limits<int>::max(); } } *out_sequence_length = Min(sequence_length, max_sequence_length); return is_tagged; } Handle<LayoutDescriptor> LayoutDescriptor::NewForTesting(Isolate* isolate, int length) { return New(isolate, length); } LayoutDescriptor LayoutDescriptor::SetTaggedForTesting(int field_index, bool tagged) { return SetTagged(field_index, tagged); } bool LayoutDescriptorHelper::IsTagged( int offset_in_bytes, int end_offset, int* out_end_of_contiguous_region_offset) { DCHECK(IsAligned(offset_in_bytes, kTaggedSize)); DCHECK(IsAligned(end_offset, kTaggedSize)); DCHECK(offset_in_bytes < end_offset); if (all_fields_tagged_) { *out_end_of_contiguous_region_offset = end_offset; DCHECK(offset_in_bytes < *out_end_of_contiguous_region_offset); return true; } int max_sequence_length = (end_offset - offset_in_bytes) / kTaggedSize; int field_index = Max(0, (offset_in_bytes - header_size_) / kTaggedSize); int sequence_length; bool tagged = layout_descriptor_->IsTagged(field_index, max_sequence_length, &sequence_length); DCHECK_GT(sequence_length, 0); if (offset_in_bytes < header_size_) { // Object headers do not contain non-tagged fields. Check if the contiguous // region continues after the header. if (tagged) { // First field is tagged, calculate end offset from there. *out_end_of_contiguous_region_offset = header_size_ + sequence_length * kTaggedSize; } else { *out_end_of_contiguous_region_offset = header_size_; } DCHECK(offset_in_bytes < *out_end_of_contiguous_region_offset); return true; } *out_end_of_contiguous_region_offset = offset_in_bytes + sequence_length * kTaggedSize; DCHECK(offset_in_bytes < *out_end_of_contiguous_region_offset); return tagged; } LayoutDescriptor LayoutDescriptor::Trim(Heap* heap, Map map, DescriptorArray descriptors, int num_descriptors) { DisallowHeapAllocation no_allocation; // Fast mode descriptors are never shared and therefore always fully // correspond to their map. if (!IsSlowLayout()) return *this; int layout_descriptor_length = CalculateCapacity(map, descriptors, num_descriptors); // It must not become fast-mode descriptor here, because otherwise it has to // be fast pointer layout descriptor already but it's is slow mode now. DCHECK_LT(kBitsInSmiLayout, layout_descriptor_length); // Trim, clean and reinitialize this slow-mode layout descriptor. int new_backing_store_length = GetSlowModeBackingStoreLength(layout_descriptor_length); int backing_store_length = length(); if (new_backing_store_length != backing_store_length) { DCHECK_LT(new_backing_store_length, backing_store_length); int delta = backing_store_length - new_backing_store_length; heap->RightTrimFixedArray(*this, delta); } memset(GetDataStartAddress(), 0, DataSize()); LayoutDescriptor layout_descriptor = Initialize(*this, map, descriptors, num_descriptors); DCHECK_EQ(*this, layout_descriptor); return layout_descriptor; } bool LayoutDescriptor::IsConsistentWithMap(Map map, bool check_tail) { if (FLAG_unbox_double_fields) { DescriptorArray descriptors = map->instance_descriptors(); int nof_descriptors = map->NumberOfOwnDescriptors(); int last_field_index = 0; for (int i = 0; i < nof_descriptors; i++) { PropertyDetails details = descriptors->GetDetails(i); if (details.location() != kField) continue; FieldIndex field_index = FieldIndex::ForDescriptor(map, i); bool tagged_expected = !field_index.is_inobject() || !details.representation().IsDouble(); for (int bit = 0; bit < details.field_width_in_words(); bit++) { bool tagged_actual = IsTagged(details.field_index() + bit); DCHECK_EQ(tagged_expected, tagged_actual); if (tagged_actual != tagged_expected) return false; } last_field_index = Max(last_field_index, details.field_index() + details.field_width_in_words()); } if (check_tail) { int n = capacity(); for (int i = last_field_index; i < n; i++) { DCHECK(IsTagged(i)); } } } return true; } } // namespace internal } // namespace v8