Turn the NumberToStringStub into a hydrogen stub.

src/x64/full-codegen-x64.cc

 // 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 3489 matching lines @@
 
   __ bind(&done);
   context()->Plug(rax);
 }
 
 
 void FullCodeGenerator::EmitNumberToString(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   ASSERT_EQ(args->length(), 1);
 
-  // Load the argument on the stack and call the stub.
-  VisitForStackValue(args->at(0));
+  // Load the argument into rax and call the stub.
+  VisitForAccumulatorValue(args->at(0));
 
   NumberToStringStub stub;
   __ CallStub(&stub);
   context()->Plug(rax);
 }
 
 
 void FullCodeGenerator::EmitStringCharFromCode(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   ASSERT(args->length() == 1);
@@ skipping 1433 matching lines @@
     ASSERT_EQ(kJnsOffset,       *(call_target_address - 2));
     return INTERRUPT;
   }
 }
 #endif  // DEBUG
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64