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

src/objects-inl.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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 4735 matching lines @@
   int len = descriptors->number_of_descriptors();
   set_instance_descriptors(descriptors);
   SetNumberOfOwnDescriptors(len);
 }
 
 
 ACCESSORS(Map, instance_descriptors, DescriptorArray, kDescriptorsOffset)
 
 
 void Map::set_bit_field3(uint32_t bits) {
-  // Ensure the upper 2 bits have the same value by sign extending it. This is
-  // necessary to be able to use the 31st bit.
-  int value = bits << 1;
-  WRITE_FIELD(this, kBitField3Offset, Smi::FromInt(value >> 1));
+  if (kInt32Size != kPointerSize) {
+    WRITE_UINT32_FIELD(this, kBitField3Offset + kInt32Size, 0);
+  }
+  WRITE_UINT32_FIELD(this, kBitField3Offset, bits);
 }
 
 
 uint32_t Map::bit_field3() {
-  Object* value = READ_FIELD(this, kBitField3Offset);
-  return Smi::cast(value)->value();
+  return READ_UINT32_FIELD(this, kBitField3Offset);
 }
 
 
 void Map::AppendDescriptor(Descriptor* desc) {
   DescriptorArray* descriptors = instance_descriptors();
   int number_of_own_descriptors = NumberOfOwnDescriptors();
   ASSERT(descriptors->number_of_descriptors() == number_of_own_descriptors);
   descriptors->Append(desc);
   SetNumberOfOwnDescriptors(number_of_own_descriptors + 1);
 }
@@ skipping 2080 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_