In-object double fields unboxing (for 64-bit only).

src/layout-descriptor.cc

+// 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 <sstream>
+
+#include "src/v8.h"
+
+#include "src/layout-descriptor.h"
+
+namespace v8 {
+namespace internal {
+
+Handle<LayoutDescriptor> LayoutDescriptor::New(
+    Handle<Map> map, Handle<DescriptorArray> descriptors, int num_descriptors) {
+  Isolate* isolate = descriptors->GetIsolate();
+  if (!FLAG_unbox_double_fields) return handle(FastPointerLayout(), isolate);
+
+  int inobject_properties = map->inobject_properties();
+  if (inobject_properties == 0) return handle(FastPointerLayout(), isolate);
+
+  DCHECK(num_descriptors <= descriptors->number_of_descriptors());
+
+  int layout_descriptor_length;
+  const int kMaxWordsPerField = kDoubleSize / kPointerSize;
+
+  if (num_descriptors <= kSmiValueSize / kMaxWordsPerField) {
+    // Even in the "worst" case (all fields are doubles) it would fit into
+    // a Smi, so no need to calculate length.
+    layout_descriptor_length = kSmiValueSize;
+
+  } else {
+    layout_descriptor_length = 0;
+
+    for (int i = 0; i < num_descriptors; i++) {
+      PropertyDetails details = descriptors->GetDetails(i);
+      if (!InobjectUnboxedField(inobject_properties, details)) continue;
+      int field_index = details.field_index();
+      int field_width_in_words = details.field_width_in_words();
+      layout_descriptor_length =
+          Max(layout_descriptor_length, field_index + field_width_in_words);
+    }
+
+    if (layout_descriptor_length == 0) {
+      // No double fields were found, use fast pointer layout.
+      return handle(FastPointerLayout(), isolate);
+    }
+  }
+  layout_descriptor_length = Min(layout_descriptor_length, inobject_properties);
+
+  // Initially, layout descriptor corresponds to an object with all fields
+  // tagged.
+  Handle<LayoutDescriptor> layout_descriptor_handle =
+      LayoutDescriptor::New(isolate, layout_descriptor_length);
+
+  DisallowHeapAllocation no_allocation;
+  LayoutDescriptor* layout_descriptor = *layout_descriptor_handle;
+
+  for (int i = 0; i < num_descriptors; i++) {
+    PropertyDetails details = descriptors->GetDetails(i);
+    if (!InobjectUnboxedField(inobject_properties, details)) continue;
+    int field_index = details.field_index();
+    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::Append(Handle<Map> map,
+                                                  PropertyDetails details) {
+  Handle<LayoutDescriptor> layout_descriptor = map->GetLayoutDescriptor();
+
+  if (!InobjectUnboxedField(map->inobject_properties(), details)) {
+    return layout_descriptor;
+  }
+  Isolate* isolate = map->GetIsolate();
+  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(
+    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->inobject_properties(), details)) {
+    return handle(layout_descriptor, map->GetIsolate());
+  }
+  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, map->GetIsolate());
+}
+
+
+Handle<LayoutDescriptor> LayoutDescriptor::EnsureCapacity(
+    Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
+    int new_capacity) {
+  int old_capacity = layout_descriptor->capacity();
+  if (new_capacity <= old_capacity) {
+    // Nothing to do with layout in Smi-form.
+    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->DataPtr(), layout_descriptor->DataPtr(),
+           layout_descriptor->DataSize());
+    return new_layout_descriptor;
+  } else {
+    // Fast layout.
+    uint32_t value =
+        static_cast<uint32_t>(Smi::cast(*layout_descriptor)->value());
+    new_layout_descriptor->set(0, value);
+    return new_layout_descriptor;
+  }
+}
+}
+}  // namespace v8::internal