Perform string add in generated code on IA-32 platforms...

src/x64/codegen-x64.h

 // Copyright 2009 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 526 matching lines @@
 
   // Fast support for Math.random().
   void GenerateRandomPositiveSmi(ZoneList<Expression*>* args);
 
   // Fast support for Math.sin and Math.cos.
   enum MathOp { SIN, COS };
   void GenerateFastMathOp(MathOp op, ZoneList<Expression*>* args);
   inline void GenerateMathSin(ZoneList<Expression*>* args);
   inline void GenerateMathCos(ZoneList<Expression*>* args);
 
+  // Fast support for StringAdd.
+  void GenerateStringAdd(ZoneList<Expression*>* args);
+
   // Simple condition analysis.
   enum ConditionAnalysis {
     ALWAYS_TRUE,
     ALWAYS_FALSE,
     DONT_KNOW
   };
   ConditionAnalysis AnalyzeCondition(Expression* cond);
 
   // Methods used to indicate which source code is generated for. Source
   // positions are collected by the assembler and emitted with the relocation
@@ skipping 181 matching lines @@
   void SetArgsReversed() { args_reversed_ = true; }
   bool HasSmiCodeInStub() { return (flags_ & NO_SMI_CODE_IN_STUB) == 0; }
   bool HasArgumentsInRegisters() { return args_in_registers_; }
   bool HasArgumentsReversed() { return args_reversed_; }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODEGEN_X64_H_