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

src/layout-descriptor.h

+// 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.
+
+#ifndef V8_LAYOUT_DESCRIPTOR_H_
+#define V8_LAYOUT_DESCRIPTOR_H_
+
+#include <iosfwd>
+
+#include "src/objects.h"
+
+namespace v8 {
+namespace internal {
+
+// LayoutDescriptor is a bit vector defining which fields contain non-tagged
+// values. It could either be a fixed typed array (slow form) or a Smi
+// if the length fits (fast form).
+// Each bit in the layout represents a FIELD. The bits are referenced by
+// field_index which is a field number. If the bit is set then corresponding
+// field contains non tagged value and therefore must be skipped by GC.

[Hannes Payer (out of office), 2014/11/06 12:29:46]

... *the* corresponding field contains *a* non-tagged value and ...

[Igor Sheludko, 2014/11/07 08:03:52]

Done.

+// Otherwise the field is considered tagged. If the queried bit lays "outside"
+// of the descriptor then the field is also considered tagged.
+// Once a layout descriptor is created it is allowed only to append properties
+// to it.
+class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
+ public:
+  V8_INLINE bool IsTagged(int field_index);
+
+  // Returns true if this is a layout of the object having only tagged fields.
+  V8_INLINE bool IsFastPointerLayout();
+
+  // Returns true if the layout descriptor is in non-Smi form.
+  V8_INLINE bool IsSlowLayout();
+
+  V8_INLINE static LayoutDescriptor* cast(Object* object);
+  V8_INLINE static const LayoutDescriptor* cast(const Object* object);
+
+  V8_INLINE static LayoutDescriptor* cast_gc_safe(Object* object);
+
+  // Builds layout descriptor optimized for given |map| by |num_descriptors|
+  // elements of given descriptors array. The |map|'s descriptors could be
+  // different.
+  static Handle<LayoutDescriptor> New(Handle<Map> map,
+                                      Handle<DescriptorArray> descriptors,
+                                      int num_descriptors);
+
+  // Creates new layout descriptor by appending property with |details| to
+  // |map|'s layout descriptor.
+  static Handle<LayoutDescriptor> Append(Handle<Map> map,
+                                         PropertyDetails details);
+
+  // Creates new layout descriptor by appending property with |details| to
+  // |map|'s layout descriptor and if it is still fast then returns it.
+  // Otherwise the |full_layout_descriptor| is returned.
+  static Handle<LayoutDescriptor> AppendIfFastOrUseFull(
+      Handle<Map> map, PropertyDetails details,
+      Handle<LayoutDescriptor> full_layout_descriptor);
+
+  // Layout descriptor that corresponds to an object all fields of which are
+  // tagged (FastPointerLayout).
+  V8_INLINE static LayoutDescriptor* FastPointerLayout();
+
+#ifdef DEBUG
+  // Check that this layout descriptor corresponds to given map.
+  bool IsConsistentWithMap(Map* map);
+#endif
+
+#ifdef OBJECT_PRINT
+  // For our gdb macros, we should perhaps change these in the future.
+  void Print();
+
+  void Print(std::ostream& os);  // NOLINT
+#endif
+
+ private:
+  static const int kNumberOfBits = 32;
+
+  V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
+  V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);
+
+  V8_INLINE static bool InobjectUnboxedField(int inobject_properties,
+                                             PropertyDetails details);
+
+  static Handle<LayoutDescriptor> EnsureCapacity(
+      Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
+      int new_capacity);
+
+  // Returns false if requested field_index is out of bounds.
+  V8_INLINE bool GetIndexes(int field_index, int* layout_word_index,
+                            uint32_t* layout_mask);
+
+  V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetRawData(int field_index) {
+    return SetTagged(field_index, false);
+  }
+
+  V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetTagged(int field_index,
+                                                        bool tagged);
+  // Capacity of layout descriptors in bits.
+  V8_INLINE int capacity();
+
+  friend class TestAccessor;
+};
+
+
+// InobjectPropertiesHelper is a helper class for querying layout descriptor
+// about whether the field at given offset is tagged or not.
+class InobjectPropertiesHelper {
+ public:
+  inline explicit InobjectPropertiesHelper(Map* map);
+
+  bool all_fields_tagged() { return all_fields_tagged_; }
+  inline bool IsTagged(int offset_in_bytes);
+
+ private:
+  bool all_fields_tagged_;
+  int header_size_;
+  int inobject_properties_count_;
+  LayoutDescriptor* layout_descriptor_;
+};
+}
+}  // namespace v8::internal
+
+#endif  // V8_LAYOUT_DESCRIPTOR_H_