Distinguish slow from fast sloppy arguments

src/runtime/runtime-scopes.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/arguments.h"
 #include "src/frames-inl.h"
 #include "src/messages.h"
@@ skipping 365 matching lines @@
       isolate->factory()->NewArgumentsObject(callee, argument_count);
 
   // Allocate the elements if needed.
   int parameter_count = callee->shared()->internal_formal_parameter_count();
   if (argument_count > 0) {
     if (parameter_count > 0) {
       int mapped_count = Min(argument_count, parameter_count);
       Handle<FixedArray> parameter_map =
           isolate->factory()->NewFixedArray(mapped_count + 2, NOT_TENURED);
       parameter_map->set_map(isolate->heap()->sloppy_arguments_elements_map());
-
-      Handle<Map> map = Map::Copy(handle(result->map()), "NewSloppyArguments");
-      map->set_elements_kind(SLOPPY_ARGUMENTS_ELEMENTS);
-
-      result->set_map(*map);
+      result->set_map(isolate->native_context()->fast_aliased_arguments_map());
       result->set_elements(*parameter_map);
 
       // Store the context and the arguments array at the beginning of the
       // parameter map.
       Handle<Context> context(isolate->context());
       Handle<FixedArray> arguments =
           isolate->factory()->NewFixedArray(argument_count, NOT_TENURED);
       parameter_map->set(0, *context);
       parameter_map->set(1, *arguments);
 
@@ skipping 732 matching lines @@
   return Smi::FromInt(frame->GetArgumentsLength());
 }
 
 
 RUNTIME_FUNCTION(Runtime_Arguments) {
   SealHandleScope shs(isolate);
   return __RT_impl_Runtime_GetArgumentsProperty(args, isolate);
 }
 }  // namespace internal
 }  // namespace v8