Fix JSObject::EnsureCanContainElements to correctly iterate over Arguments

src/objects.cc

 // Copyright 2011 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 8737 matching lines @@
 
   heap->ClearInstanceofCache();
   ASSERT(size == Size());
   return value;
 }
 
 
 MaybeObject* JSObject::EnsureCanContainElements(Arguments* args,
                                                 uint32_t first_arg,
                                                 uint32_t arg_count) {
-  return EnsureCanContainElements(args->arguments() - first_arg, arg_count);
+  // Elements in |Arguments| are ordered backwards (because they're on the
+  // stack), but the method that's called here iterates over them in forward
+  // direction.
+  return EnsureCanContainElements(
+      args->arguments() - first_arg - (arg_count - 1),
+      arg_count);
 }
 
 
 bool JSObject::HasElementPostInterceptor(JSReceiver* receiver, uint32_t index) {
   switch (GetElementsKind()) {
     case FAST_SMI_ONLY_ELEMENTS:
     case FAST_ELEMENTS: {
       uint32_t length = IsJSArray() ?
           static_cast<uint32_t>
               (Smi::cast(JSArray::cast(this)->length())->value()) :
@@ skipping 3983 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single break point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 
 } }  // namespace v8::internal