Partial recover from performance degradation after handlification of ElementsAccessor::CopyElements…

src/builtins.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 284 matching lines @@
 MUST_USE_RESULT
 static inline Handle<FixedArrayBase> EnsureJSArrayWithWritableFastElements(
     Isolate* isolate,
     Handle<Object> receiver,
     Arguments* args,
     int first_added_arg) {
   if (!receiver->IsJSArray()) return Handle<FixedArrayBase>::null();
   Handle<JSArray> array = Handle<JSArray>::cast(receiver);
   if (array->map()->is_observed()) return Handle<FixedArrayBase>::null();
   if (!array->map()->is_extensible()) return Handle<FixedArrayBase>::null();
-  Handle<FixedArrayBase> elms(array->elements());
+  Handle<FixedArrayBase> elms(array->elements(), isolate);
   Heap* heap = isolate->heap();
   Map* map = elms->map();
   if (map == heap->fixed_array_map()) {
     if (args == NULL || array->HasFastObjectElements()) return elms;
   } 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 Handle<FixedArrayBase>::null();
   }
 
   // Need to ensure that the arguments passed in args can be contained in
   // the array.
   int args_length = args->length();
-  if (first_added_arg >= args_length) return handle(array->elements());
+  if (first_added_arg >= args_length) return handle(array->elements(), isolate);
 
   ElementsKind origin_kind = array->map()->elements_kind();
   ASSERT(!IsFastObjectElementsKind(origin_kind));
   ElementsKind target_kind = origin_kind;
   int arg_count = args->length() - first_added_arg;
   Object** arguments = args->arguments() - first_added_arg - (arg_count - 1);
   for (int i = 0; i < arg_count; i++) {
     Object* arg = arguments[i];
     if (arg->IsHeapObject()) {
       if (arg->IsHeapNumber()) {
         target_kind = FAST_DOUBLE_ELEMENTS;
       } else {
         target_kind = FAST_ELEMENTS;
         break;
       }
     }
   }
   if (target_kind != origin_kind) {
     JSObject::TransitionElementsKind(array, target_kind);
-    return handle(array->elements());
+    return handle(array->elements(), isolate);
   }
   return elms;
 }
 
 
 // TODO(ishell): Handlify when all Array* builtins are handlified.
 static inline bool IsJSArrayFastElementMovingAllowed(Heap* heap,
                                                      JSArray* receiver) {
   if (!FLAG_clever_optimizations) return false;
   Context* native_context = heap->isolate()->context()->native_context();
   JSObject* array_proto =
       JSObject::cast(native_context->array_function()->prototype());
   return receiver->GetPrototype() == array_proto &&
          ArrayPrototypeHasNoElements(heap, native_context, array_proto);
 }
 
 
 MUST_USE_RESULT static MaybeObject* CallJsBuiltin(
     Isolate* isolate,
     const char* name,
     BuiltinArguments<NO_EXTRA_ARGUMENTS> args) {
+  AllowHeapAllocation allow_allocation;

[Yang, 2014/04/03 08:10:43]

Add a comment that the callees return immediately afterwards

[Igor Sheludko, 2014/04/03 09:01:00]

As discussed offline, it is safer to put explicit AllowAllocationScope before
each affected call of CallJsBuiltin().

   HandleScope handleScope(isolate);
 
   Handle<Object> js_builtin =
       GetProperty(Handle<JSObject>(isolate->native_context()->builtins()),
                   name);
   Handle<JSFunction> function = Handle<JSFunction>::cast(js_builtin);
   int argc = args.length() - 1;
   ScopedVector<Handle<Object> > argv(argc);
   for (int i = 0; i < argc; ++i) {
     argv[i] = args.at<Object>(i + 1);
@@ skipping 37 matching lines @@
     int new_length = len + to_add;
 
     if (new_length > elms->length()) {
       // New backing storage is needed.
       int capacity = new_length + (new_length >> 1) + 16;
       Handle<FixedArray> new_elms =
           isolate->factory()->NewUninitializedFixedArray(capacity);
 
       ElementsAccessor* accessor = array->GetElementsAccessor();
       accessor->CopyElements(
-          Handle<JSObject>::null(), 0, kind, new_elms, 0,
-          ElementsAccessor::kCopyToEndAndInitializeToHole, elms_obj);
+          elms_obj, 0, kind, new_elms, 0,
+          ElementsAccessor::kCopyToEndAndInitializeToHole);
 
       elms = new_elms;
     }
 
     // Add the provided values.
     DisallowHeapAllocation no_gc;
     WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
     for (int index = 0; index < to_add; index++) {
       elms->set(index + len, args[index + 1], mode);
     }
@@ skipping 21 matching lines @@
 
     Handle<FixedDoubleArray> new_elms;
 
     if (new_length > elms_len) {
       // New backing storage is needed.
       int capacity = new_length + (new_length >> 1) + 16;
       new_elms = isolate->factory()->NewFixedDoubleArray(capacity);
 
       ElementsAccessor* accessor = array->GetElementsAccessor();
       accessor->CopyElements(
-          Handle<JSObject>::null(), 0, kind, new_elms, 0,
-          ElementsAccessor::kCopyToEndAndInitializeToHole, elms_obj);
+          elms_obj, 0, kind, new_elms, 0,
+          ElementsAccessor::kCopyToEndAndInitializeToHole);
 
     } else {
       // to_add is > 0 and new_length <= elms_len, so elms_obj cannot be the
       // empty_fixed_array.
       new_elms = Handle<FixedDoubleArray>::cast(elms_obj);
     }
 
     // Add the provided values.
     DisallowHeapAllocation no_gc;
     int index;
     for (index = 0; index < to_add; index++) {
       Object* arg = args[index + 1];
       new_elms->set(index + len, arg->Number());
     }
 
     if (*new_elms != array->elements()) {
       array->set_elements(*new_elms);
     }
 
     // Set the length.
     array->set_length(Smi::FromInt(new_length));
     return Smi::FromInt(new_length);
   }
 }
 
 
-// TODO(ishell): Temporary wrapper until handlified.
-static bool ElementsAccessorHasElementWrapper(
-    ElementsAccessor* accessor,
-    Handle<Object> receiver,
-    Handle<JSObject> holder,
-    uint32_t key,
-    Handle<FixedArrayBase> backing_store = Handle<FixedArrayBase>::null()) {
-  return accessor->HasElement(*receiver, *holder, key,
-                              backing_store.is_null() ? NULL : *backing_store);
-}
-
-
 BUILTIN(ArrayPop) {
   HandleScope scope(isolate);
   Handle<Object> receiver = args.receiver();
   Handle<FixedArrayBase> elms_obj =
       EnsureJSArrayWithWritableFastElements(isolate, receiver, NULL, 0);
   if (elms_obj.is_null()) return CallJsBuiltin(isolate, "ArrayPop", args);
 
   Handle<JSArray> array = Handle<JSArray>::cast(receiver);
   ASSERT(!array->map()->is_observed());
 
   int len = Smi::cast(array->length())->value();
   if (len == 0) return isolate->heap()->undefined_value();
 
   ElementsAccessor* accessor = array->GetElementsAccessor();
   int new_length = len - 1;
   Handle<Object> element;
-  if (ElementsAccessorHasElementWrapper(
-      accessor, array, array, new_length, elms_obj)) {
+  if (accessor->HasElement(*array, *array, new_length, *elms_obj)) {
     element = accessor->Get(
         array, array, new_length, elms_obj);
   } else {
     Handle<Object> proto(array->GetPrototype(), isolate);
     element = Object::GetElement(isolate, proto, len - 1);
   }
   RETURN_IF_EMPTY_HANDLE(isolate, element);
   RETURN_IF_EMPTY_HANDLE(isolate,
                          accessor->SetLength(
                              array, handle(Smi::FromInt(new_length), isolate)));
@@ skipping 79 matching lines @@
 
   if (new_length > elms->length()) {
     // New backing storage is needed.
     int capacity = new_length + (new_length >> 1) + 16;
     Handle<FixedArray> new_elms =
         isolate->factory()->NewUninitializedFixedArray(capacity);
 
     ElementsKind kind = array->GetElementsKind();
     ElementsAccessor* accessor = array->GetElementsAccessor();
     accessor->CopyElements(
-        Handle<JSObject>::null(), 0, kind, new_elms, to_add,
-        ElementsAccessor::kCopyToEndAndInitializeToHole, elms);
+        elms, 0, kind, new_elms, to_add,
+        ElementsAccessor::kCopyToEndAndInitializeToHole);
 
     elms = new_elms;
     array->set_elements(*elms);
   } else {
     DisallowHeapAllocation no_gc;
     heap->MoveElements(*elms, to_add, 0, len);
   }
 
   // Add the provided values.
   DisallowHeapAllocation no_gc;
   WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < to_add; i++) {
     elms->set(i, args[i + 1], mode);
   }
 
   // Set the length.
   array->set_length(Smi::FromInt(new_length));
   return Smi::FromInt(new_length);
 }
 
 
 BUILTIN(ArraySlice) {
   HandleScope scope(isolate);
   Heap* heap = isolate->heap();
   Handle<Object> receiver = args.receiver();
-  Handle<FixedArrayBase> elms;
   int len = -1;
+  DisallowHeapAllocation no_allocations_before_creating_result;

[Yang, 2014/04/03 08:10:43]

I would prefer if you still use scopes instead of interchanging Disallow/Allow
whenever possible. That would improve readability a lot imo.

For example, scope this to go from line 637 to 714.

[Igor Sheludko, 2014/04/03 09:01:00]

Done.

+
   if (receiver->IsJSArray()) {
-    Handle<JSArray> array = Handle<JSArray>::cast(receiver);
-    if (!IsJSArrayFastElementMovingAllowed(heap, *array)) {
+    JSArray* array = JSArray::cast(*receiver);
+    if (!IsJSArrayFastElementMovingAllowed(heap, array)) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
 
-    if (array->HasFastElements()) {
-      elms = handle(array->elements());
-    } else {
+    if (!array->HasFastElements()) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
 
     len = Smi::cast(array->length())->value();
   } else {
     // Array.slice(arguments, ...) is quite a common idiom (notably more
     // than 50% of invocations in Web apps).  Treat it in C++ as well.
-    Handle<Map> arguments_map(isolate->context()->native_context()->
-        sloppy_arguments_boilerplate()->map());
+    Map* arguments_map = isolate->context()->native_context()->
+        sloppy_arguments_boilerplate()->map();
 
     bool is_arguments_object_with_fast_elements =
         receiver->IsJSObject() &&
-        Handle<JSObject>::cast(receiver)->map() == *arguments_map;
+        JSObject::cast(*receiver)->map() == arguments_map;
     if (!is_arguments_object_with_fast_elements) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
-    Handle<JSObject> object = Handle<JSObject>::cast(receiver);
+    JSObject* object = JSObject::cast(*receiver);
 
-    if (object->HasFastElements()) {
-      elms = handle(object->elements());
-    } else {
+    if (!object->HasFastElements()) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
-    Handle<Object> len_obj(
-        object->InObjectPropertyAt(Heap::kArgumentsLengthIndex), isolate);
+
+    Object* len_obj = object->InObjectPropertyAt(Heap::kArgumentsLengthIndex);
     if (!len_obj->IsSmi()) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
-    len = Handle<Smi>::cast(len_obj)->value();
-    if (len > elms->length()) {
+    len = Smi::cast(len_obj)->value();
+    if (len > object->elements()->length()) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
   }
 
-  Handle<JSObject> object = Handle<JSObject>::cast(receiver);
-
   ASSERT(len >= 0);
   int n_arguments = args.length() - 1;
 
   // Note carefully choosen defaults---if argument is missing,
   // it's undefined which gets converted to 0 for relative_start
   // and to len for relative_end.
   int relative_start = 0;
   int relative_end = len;
   if (n_arguments > 0) {
-    Handle<Object> arg1 = args.at<Object>(1);
+    Object* arg1 = args[1];
     if (arg1->IsSmi()) {
-      relative_start = Handle<Smi>::cast(arg1)->value();
+      relative_start = Smi::cast(arg1)->value();
     } else if (arg1->IsHeapNumber()) {
-      double start = Handle<HeapNumber>::cast(arg1)->value();
+      double start = HeapNumber::cast(arg1)->value();
       if (start < kMinInt || start > kMaxInt) {
         return CallJsBuiltin(isolate, "ArraySlice", args);
       }
       relative_start = std::isnan(start) ? 0 : static_cast<int>(start);
     } else if (!arg1->IsUndefined()) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
     if (n_arguments > 1) {
-      Handle<Object> arg2 = args.at<Object>(2);
+      Object* arg2 = args[2];
       if (arg2->IsSmi()) {
-        relative_end = Handle<Smi>::cast(arg2)->value();
+        relative_end = Smi::cast(arg2)->value();
       } else if (arg2->IsHeapNumber()) {
-        double end = Handle<HeapNumber>::cast(arg2)->value();
+        double end = HeapNumber::cast(arg2)->value();
         if (end < kMinInt || end > kMaxInt) {
           return CallJsBuiltin(isolate, "ArraySlice", args);
         }
         relative_end = std::isnan(end) ? 0 : static_cast<int>(end);
       } else if (!arg2->IsUndefined()) {
         return CallJsBuiltin(isolate, "ArraySlice", args);
       }
     }
   }
 
   // ECMAScript 232, 3rd Edition, Section 15.4.4.10, step 6.
   int k = (relative_start < 0) ? Max(len + relative_start, 0)
                                : Min(relative_start, len);
 
   // ECMAScript 232, 3rd Edition, Section 15.4.4.10, step 8.
   int final = (relative_end < 0) ? Max(len + relative_end, 0)
                                  : Min(relative_end, len);
 
   // Calculate the length of result array.
   int result_len = Max(final - k, 0);
 
+  Handle<JSObject> object = Handle<JSObject>::cast(receiver);
+  Handle<FixedArrayBase> elms(object->elements(), isolate);
+
   ElementsKind kind = object->GetElementsKind();
   if (IsHoleyElementsKind(kind)) {

[Yang, 2014/04/03 08:10:43]

Then add a DisallowHeapAllocation scope here.

[Igor Sheludko, 2014/04/03 09:01:00]

Done.

     bool packed = true;
     ElementsAccessor* accessor = ElementsAccessor::ForKind(kind);
     for (int i = k; i < final; i++) {
-      if (!ElementsAccessorHasElementWrapper(
-          accessor, object, object, i, elms)) {
+      if (!accessor->HasElement(*object, *object, i, *elms)) {
         packed = false;
         break;
       }
     }
     if (packed) {
       kind = GetPackedElementsKind(kind);
     } else if (!receiver->IsJSArray()) {
       return CallJsBuiltin(isolate, "ArraySlice", args);
     }
   }
 
+  AllowHeapAllocation allow_allocation_to_create_a_result;

[Yang, 2014/04/03 08:10:43]

This is now unnecessary.

[Igor Sheludko, 2014/04/03 09:01:00]

Done.

   Handle<JSArray> result_array =
       isolate->factory()->NewJSArray(kind, result_len, result_len);
 
-  DisallowHeapAllocation no_gc;
+  DisallowHeapAllocation no_more_allocations_allowed;
   if (result_len == 0) return *result_array;
 
   ElementsAccessor* accessor = object->GetElementsAccessor();
-  accessor->CopyElements(Handle<JSObject>::null(), k, kind,
-                         handle(result_array->elements()), 0, result_len, elms);
+  accessor->CopyElements(
+      elms, k, kind, handle(result_array->elements(), isolate), 0, result_len);
   return *result_array;
 }
 
 
 BUILTIN(ArraySplice) {
   HandleScope scope(isolate);
   Heap* heap = isolate->heap();
   Handle<Object> receiver = args.receiver();
   Handle<FixedArrayBase> elms_obj =
       EnsureJSArrayWithWritableFastElements(isolate, receiver, &args, 3);
   if (elms_obj.is_null() ||
       !IsJSArrayFastElementMovingAllowed(heap,
                                          *Handle<JSArray>::cast(receiver))) {
     return CallJsBuiltin(isolate, "ArraySplice", args);
   }
   Handle<JSArray> array = Handle<JSArray>::cast(receiver);
   ASSERT(!array->map()->is_observed());
 
   int len = Smi::cast(array->length())->value();
 
   int n_arguments = args.length() - 1;
 
   int relative_start = 0;
   if (n_arguments > 0) {
-    Handle<Object> arg1 = args.at<Object>(1);
+    Object* arg1 = args[1];
     if (arg1->IsSmi()) {
-      relative_start = Handle<Smi>::cast(arg1)->value();
+      relative_start = Smi::cast(arg1)->value();
     } else if (arg1->IsHeapNumber()) {
-      double start = Handle<HeapNumber>::cast(arg1)->value();
+      double start = HeapNumber::cast(arg1)->value();
       if (start < kMinInt || start > kMaxInt) {
         return CallJsBuiltin(isolate, "ArraySplice", args);
       }
       relative_start = std::isnan(start) ? 0 : static_cast<int>(start);
     } else if (!arg1->IsUndefined()) {
       return CallJsBuiltin(isolate, "ArraySplice", args);
     }
   }
   int actual_start = (relative_start < 0) ? Max(len + relative_start, 0)
                                           : Min(relative_start, len);
@@ skipping 40 matching lines @@
 
   Handle<JSArray> result_array =
       isolate->factory()->NewJSArray(elements_kind,
                                      actual_delete_count,
                                      actual_delete_count);
 
   if (actual_delete_count > 0) {
     DisallowHeapAllocation no_gc;
     ElementsAccessor* accessor = array->GetElementsAccessor();
     accessor->CopyElements(
-        Handle<JSObject>::null(), actual_start, elements_kind,
-        handle(result_array->elements()), 0, actual_delete_count, elms_obj);
+        elms_obj, actual_start, elements_kind,
+        handle(result_array->elements(), isolate), 0, actual_delete_count);
   }
 
   bool elms_changed = false;
   if (item_count < actual_delete_count) {
     // Shrink the array.
     const bool trim_array = !heap->lo_space()->Contains(*elms_obj) &&
       ((actual_start + item_count) <
           (len - actual_delete_count - actual_start));
     if (trim_array) {
       const int delta = actual_delete_count - item_count;
 
       if (elms_obj->IsFixedDoubleArray()) {
         Handle<FixedDoubleArray> elms =
             Handle<FixedDoubleArray>::cast(elms_obj);
         MoveDoubleElements(*elms, delta, *elms, 0, actual_start);
       } else {
         Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
         DisallowHeapAllocation no_gc;
         heap->MoveElements(*elms, delta, 0, actual_start);
       }
 
       if (heap->CanMoveObjectStart(*elms_obj)) {
         // On the fast path we move the start of the object in memory.
-        elms_obj = handle(LeftTrimFixedArray(heap, *elms_obj, delta));
+        elms_obj = handle(LeftTrimFixedArray(heap, *elms_obj, delta), isolate);
       } else {
         // This is the slow path. We are going to move the elements to the left
         // by copying them. For trimmed values we store the hole.
         if (elms_obj->IsFixedDoubleArray()) {
           Handle<FixedDoubleArray> elms =
               Handle<FixedDoubleArray>::cast(elms_obj);
           MoveDoubleElements(*elms, 0, *elms, delta, len - delta);
           elms->FillWithHoles(len - delta, len);
         } else {
           Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
@@ skipping 33 matching lines @@
       Handle<FixedArray> new_elms =
           isolate->factory()->NewUninitializedFixedArray(capacity);
 
       DisallowHeapAllocation no_gc;
 
       ElementsKind kind = array->GetElementsKind();
       ElementsAccessor* accessor = array->GetElementsAccessor();
       if (actual_start > 0) {
         // Copy the part before actual_start as is.
         accessor->CopyElements(
-            Handle<JSObject>::null(), 0, kind, new_elms, 0, actual_start, elms);
+            elms, 0, kind, new_elms, 0, actual_start);
       }
       accessor->CopyElements(
-          Handle<JSObject>::null(), actual_start + actual_delete_count, kind,
+          elms, actual_start + actual_delete_count, kind,
           new_elms, actual_start + item_count,
-          ElementsAccessor::kCopyToEndAndInitializeToHole, elms);
+          ElementsAccessor::kCopyToEndAndInitializeToHole);
 
       elms_obj = new_elms;
       elms_changed = true;
     } else {
       DisallowHeapAllocation no_gc;
       heap->MoveElements(*elms, actual_start + item_count,
                          actual_start + actual_delete_count,
                          (len - actual_delete_count - actual_start));
     }
   }
@@ skipping 23 matching lines @@
   // Set the length.
   array->set_length(Smi::FromInt(new_length));
 
   return *result_array;
 }
 
 
 BUILTIN(ArrayConcat) {
   HandleScope scope(isolate);
   Heap* heap = isolate->heap();
-  Handle<Context> native_context(isolate->context()->native_context());
+  Handle<Context> native_context(isolate->context()->native_context(), isolate);
   Handle<JSObject> array_proto(
-      JSObject::cast(native_context->array_function()->prototype()));
+      JSObject::cast(native_context->array_function()->prototype()), isolate);
   if (!ArrayPrototypeHasNoElements(heap, *native_context, *array_proto)) {
     return CallJsBuiltin(isolate, "ArrayConcat", args);
   }
 
   // Iterate through all the arguments performing checks
   // and calculating total length.
   int n_arguments = args.length();
   int result_len = 0;
   ElementsKind elements_kind = GetInitialFastElementsKind();
   bool has_double = false;
   bool is_holey = false;
   for (int i = 0; i < n_arguments; i++) {
-    Handle<Object> arg = args.at<Object>(i);
+    DisallowHeapAllocation no_gc;
+    Object* arg = args[i];
     if (!arg->IsJSArray() ||
-        !Handle<JSArray>::cast(arg)->HasFastElements() ||
-        Handle<JSArray>::cast(arg)->GetPrototype() != *array_proto) {
+        !JSArray::cast(arg)->HasFastElements() ||
+        JSArray::cast(arg)->GetPrototype() != *array_proto) {
       return CallJsBuiltin(isolate, "ArrayConcat", args);
     }
-    int len = Smi::cast(Handle<JSArray>::cast(arg)->length())->value();
+    int len = Smi::cast(JSArray::cast(arg)->length())->value();
 
     // We shouldn't overflow when adding another len.
     const int kHalfOfMaxInt = 1 << (kBitsPerInt - 2);
     STATIC_ASSERT(FixedArray::kMaxLength < kHalfOfMaxInt);
     USE(kHalfOfMaxInt);
     result_len += len;
     ASSERT(result_len >= 0);
 
     if (result_len > FixedDoubleArray::kMaxLength) {
       return CallJsBuiltin(isolate, "ArrayConcat", args);
     }
 
-    ElementsKind arg_kind = Handle<JSArray>::cast(arg)->map()->elements_kind();
+    ElementsKind arg_kind = JSArray::cast(arg)->map()->elements_kind();
     has_double = has_double || IsFastDoubleElementsKind(arg_kind);
     is_holey = is_holey || IsFastHoleyElementsKind(arg_kind);
     if (IsMoreGeneralElementsKindTransition(elements_kind, arg_kind)) {
       elements_kind = arg_kind;
     }
   }
 
   if (is_holey) elements_kind = GetHoleyElementsKind(elements_kind);
 
   // If a double array is concatted into a fast elements array, the fast
   // elements array needs to be initialized to contain proper holes, since
   // boxing doubles may cause incremental marking.
   ArrayStorageAllocationMode mode =
       has_double && IsFastObjectElementsKind(elements_kind)
       ? INITIALIZE_ARRAY_ELEMENTS_WITH_HOLE : DONT_INITIALIZE_ARRAY_ELEMENTS;
   Handle<JSArray> result_array =
       isolate->factory()->NewJSArray(elements_kind,
                                      result_len,
                                      result_len,
                                      mode);
   if (result_len == 0) return *result_array;
 
   int j = 0;
-  Handle<FixedArrayBase> storage(result_array->elements());
+  Handle<FixedArrayBase> storage(result_array->elements(), isolate);
   ElementsAccessor* accessor = ElementsAccessor::ForKind(elements_kind);
   for (int i = 0; i < n_arguments; i++) {
-    Handle<JSArray> array = args.at<JSArray>(i);
+    // It is crucial to keep |array| as a raw pointer to avoid performance
+    // degradation.
+    JSArray* array = JSArray::cast(args[i]);
     int len = Smi::cast(array->length())->value();
     ElementsKind from_kind = array->GetElementsKind();
     if (len > 0) {
       accessor->CopyElements(array, 0, from_kind, storage, j, len);
       j += len;
     }
   }
 
   ASSERT(j == result_len);
 
@@ skipping 660 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 v8::internal