Make BitField3 a raw uint32 field, and move to the start of the map.

src/objects.h

 // Copyright 2012 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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include "allocation.h"
 #include "assert-scope.h"
 #include "builtins.h"
@@ skipping 6463 matching lines @@
   // and the values are the maps the are transitioned to.
   static const int kMaxCachedPrototypeTransitions = 256;
   static Handle<Map> TransitionToPrototype(Handle<Map> map,
                                            Handle<Object> prototype);
 
   static const int kMaxPreAllocatedPropertyFields = 255;
 
   // Layout description.
   static const int kInstanceSizesOffset = HeapObject::kHeaderSize;
   static const int kInstanceAttributesOffset = kInstanceSizesOffset + kIntSize;
-  static const int kPrototypeOffset = kInstanceAttributesOffset + kIntSize;
+  static const int kBitField3Offset = kInstanceAttributesOffset + kIntSize;
+  static const int kPrototypeOffset = kBitField3Offset + kPointerSize;
   static const int kConstructorOffset = kPrototypeOffset + kPointerSize;
   // Storage for the transition array is overloaded to directly contain a back
   // pointer if unused. When the map has transitions, the back pointer is
   // transferred to the transition array and accessed through an extra
   // indirection.
   static const int kTransitionsOrBackPointerOffset =
       kConstructorOffset + kPointerSize;
   static const int kDescriptorsOffset =
       kTransitionsOrBackPointerOffset + kPointerSize;
   static const int kCodeCacheOffset = kDescriptorsOffset + kPointerSize;
   static const int kDependentCodeOffset = kCodeCacheOffset + kPointerSize;
-  static const int kBitField3Offset = kDependentCodeOffset + kPointerSize;
-  static const int kSize = kBitField3Offset + kPointerSize;
+  static const int kSize = kDependentCodeOffset + kPointerSize;
 
   // Layout of pointer fields. Heap iteration code relies on them
   // being continuously allocated.
   static const int kPointerFieldsBeginOffset = Map::kPrototypeOffset;
-  static const int kPointerFieldsEndOffset = kBitField3Offset + kPointerSize;
+  static const int kPointerFieldsEndOffset = kSize;
 
   // Byte offsets within kInstanceSizesOffset.
   static const int kInstanceSizeOffset = kInstanceSizesOffset + 0;
   static const int kInObjectPropertiesByte = 1;
   static const int kInObjectPropertiesOffset =
       kInstanceSizesOffset + kInObjectPropertiesByte;
   static const int kPreAllocatedPropertyFieldsByte = 2;
   static const int kPreAllocatedPropertyFieldsOffset =
       kInstanceSizesOffset + kPreAllocatedPropertyFieldsByte;
   static const int kVisitorIdByte = 3;
@@ skipping 4607 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_