Use a special EnumLength field to indicate number of valid enum cache values.

src/arm/macro-assembler-arm.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1254 matching lines @@
   void ClampUint8(Register output_reg, Register input_reg);
 
   void ClampDoubleToUint8(Register result_reg,
                           DoubleRegister input_reg,
                           DoubleRegister temp_double_reg);
 
 
   void LoadInstanceDescriptors(Register map,
                                Register descriptors,
                                Register scratch);
+  void EnumLength(Register dst, Register map);
 
   // Activation support.
   void EnterFrame(StackFrame::Type type);
   void LeaveFrame(StackFrame::Type type);
 
   // Expects object in r0 and returns map with validated enum cache
   // in r0.  Assumes that any other register can be used as a scratch.
   void CheckEnumCache(Register null_value, Label* call_runtime);
 
  private:
@@ skipping 104 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_