Add initial hydrogenized NewStringAddStub.

src/x64/code-stubs-x64.cc

 // Copyright 2013 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 284 matching lines @@
     Isolate* isolate,
     CodeStubInterfaceDescriptor* descriptor) {
   static Register registers[] = { rax, rbx, rcx, rdx };
   descriptor->register_param_count_ = 4;
   descriptor->register_params_ = registers;
   descriptor->deoptimization_handler_ =
       FUNCTION_ADDR(ElementsTransitionAndStoreIC_Miss);
 }
 
 
+void NewStringAddStub::InitializeInterfaceDescriptor(
+    Isolate* isolate,
+    CodeStubInterfaceDescriptor* descriptor) {
+  static Register registers[] = { rdx, rax };
+  descriptor->register_param_count_ = 2;
+  descriptor->register_params_ = registers;
+  descriptor->deoptimization_handler_ =
+      Runtime::FunctionForId(Runtime::kStringAdd)->entry;
+}
+
+
 #define __ ACCESS_MASM(masm)
 
 
 void HydrogenCodeStub::GenerateLightweightMiss(MacroAssembler* masm) {
   // Update the static counter each time a new code stub is generated.
   Isolate* isolate = masm->isolate();
   isolate->counters()->code_stubs()->Increment();
 
   CodeStubInterfaceDescriptor* descriptor = GetInterfaceDescriptor(isolate);
   int param_count = descriptor->register_param_count_;
@@ skipping 5496 matching lines @@
   __ bind(&fast_elements_case);
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64