Emit slightly more compact code in untag double.

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 35 matching lines @@
 
 // -----------------------------------------------------------------------------
 // Common double constants.
 
 class DoubleConstant: public AllStatic {
  public:
   static const double min_int;
   static const double one_half;
   static const double minus_zero;
   static const double negative_infinity;
+  static const double nan;
 };
 
 
 // -----------------------------------------------------------------------------
 // Labels represent pc locations; they are typically jump or call targets.
 // After declaration, a label can be freely used to denote known or (yet)
 // unknown pc location. Assembler::bind() is used to bind a label to the
 // current pc. A label can be bound only once.
 
 class Label BASE_EMBEDDED {
@@ skipping 517 matching lines @@
   static ExternalReference handle_scope_limit_address();
   static ExternalReference handle_scope_level_address();
 
   static ExternalReference scheduled_exception_address();
 
   // Static variables containing common double constants.
   static ExternalReference address_of_min_int();
   static ExternalReference address_of_one_half();
   static ExternalReference address_of_minus_zero();
   static ExternalReference address_of_negative_infinity();
+  static ExternalReference address_of_nan();
 
   static ExternalReference math_sin_double_function();
   static ExternalReference math_cos_double_function();
   static ExternalReference math_log_double_function();
 
   Address address() const {return reinterpret_cast<Address>(address_);}
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
   // Function Debug::Break()
   static ExternalReference debug_break();
@@ skipping 179 matching lines @@
   return num_bits_set;
 }
 
 // Computes pow(x, y) with the special cases in the spec for Math.pow.
 double power_double_int(double x, int y);
 double power_double_double(double x, double y);
 
 } }  // namespace v8::internal
 
 #endif  // V8_ASSEMBLER_H_