[left-trimming] Avoid creating duplicate handles in builtins.cc

src/builtins.cc

 // Copyright 2012 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/builtins.h"
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
@@ skipping 233 matching lines @@
   PrototypeIterator iter(isolate, receiver);
   return PrototypeHasNoElements(&iter);
 }
 
 
 // Returns empty handle if not applicable.
 MUST_USE_RESULT
 inline MaybeHandle<FixedArrayBase> EnsureJSArrayWithWritableFastElements(
     Isolate* isolate, Handle<Object> receiver, Arguments* args,
     int first_added_arg) {
+  // We explicitly add a HandleScope to avoid creating several copies of the
+  // same handle which would otherwise cause issue when left-trimming later-on.
+  HandleScope scope(isolate);
   if (!receiver->IsJSArray()) return MaybeHandle<FixedArrayBase>();
   Handle<JSArray> array = Handle<JSArray>::cast(receiver);
   // If there may be elements accessors in the prototype chain, the fast path
   // cannot be used if there arguments to add to the array.
   Heap* heap = isolate->heap();
   if (args != NULL && !IsJSArrayFastElementMovingAllowed(isolate, *array)) {
     return MaybeHandle<FixedArrayBase>();
   }
   if (array->map()->is_observed()) return MaybeHandle<FixedArrayBase>();
   if (!array->map()->is_extensible()) return MaybeHandle<FixedArrayBase>();
   Handle<FixedArrayBase> elms(array->elements(), isolate);
   Map* map = elms->map();
   if (map == heap->fixed_array_map()) {
     if (args == NULL || array->HasFastObjectElements()) return elms;

[ulan, 2016/02/15 15:33:09]

I think CloseAndEscape should be used here and in other return paths.

   } else if (map == heap->fixed_cow_array_map()) {
     elms = JSObject::EnsureWritableFastElements(array);
     if (args == NULL || array->HasFastObjectElements()) return elms;
   } else if (map == heap->fixed_double_array_map()) {
     if (args == NULL) return elms;
   } else {
     return MaybeHandle<FixedArrayBase>();
   }
 
   // Adding elements to the array prototype would break code that makes sure
@@ skipping 4099 matching lines @@
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 }  // namespace internal
 }  // namespace v8