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

src/arm/macro-assembler-arm.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_ARM_MACRO_ASSEMBLER_ARM_H_
 #define V8_ARM_MACRO_ASSEMBLER_ARM_H_
 
 #include "assembler.h"
 #include "frames.h"
 #include "v8globals.h"
@@ skipping 1339 matching lines @@
                           LowDwVfpRegister double_scratch);
 
 
   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 >> shift) << kSmiTagSize;
+    static const int mask = Field::kMask >> shift;
     mov(reg, Operand(reg, LSR, shift));
     and_(reg, reg, Operand(mask));
   }
 
   // Activation support.
   void EnterFrame(StackFrame::Type type, bool load_constant_pool = false);
   // Returns the pc offset at which the frame ends.
   int LeaveFrame(StackFrame::Type type);
 
   // Expects object in r0 and returns map with validated enum cache
@@ skipping 205 matching lines @@
 #define __FILE_LINE__ __FILE__ ":" CODE_COVERAGE_TOSTRING(__LINE__)
 #define ACCESS_MASM(masm) masm->stop(__FILE_LINE__); masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_MACRO_ASSEMBLER_ARM_H_