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

src/ia32/macro-assembler-ia32.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_IA32_MACRO_ASSEMBLER_IA32_H_
 #define V8_IA32_MACRO_ASSEMBLER_IA32_H_
 
 #include "assembler.h"
 #include "frames.h"
 #include "v8globals.h"
@@ skipping 482 matching lines @@
     j(not_zero, not_smi_label, distance);
   }
 
   void LoadInstanceDescriptors(Register map, Register descriptors);
   void EnumLength(Register dst, Register map);
   void NumberOfOwnDescriptors(Register dst, Register map);
 
   template<typename Field>
   void DecodeField(Register reg) {
     static const int shift = Field::kShift;
-    static const int mask = (Field::kMask >> Field::kShift) << kSmiTagSize;
+    static const int mask = Field::kMask >> Field::kShift;
     sar(reg, shift);
     and_(reg, Immediate(mask));
   }
   void LoadPowerOf2(XMMRegister dst, Register scratch, int power);
 
   // Abort execution if argument is not a number, enabled via --debug-code.
   void AssertNumber(Register object);
 
   // Abort execution if argument is not a smi, enabled via --debug-code.
   void AssertSmi(Register object);
@@ skipping 576 matching lines @@
   }                                                                       \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_MACRO_ASSEMBLER_IA32_H_