Micro-optimizations to pop() and shift()

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 @@
 // Returns empty handle if not applicable.
 MUST_USE_RESULT
 static inline MaybeHandle<FixedArrayBase> EnsureJSArrayWithWritableFastElements(
     Isolate* isolate,
     Handle<Object> receiver,
     Arguments* args,
     int first_added_arg) {
   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 (array->map()->DictionaryElementsInPrototypeChainOnly()) {
+  // cannot be used if there arguments to add to the array.
+  if (args != NULL && array->map()->DictionaryElementsInPrototypeChainOnly()) {
     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);
   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()) {
@@ skipping 196 matching lines @@
   }
 
   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;
-  MaybeHandle<Object> maybe_element;
-  if (accessor->HasElement(array, array, new_length, elms_obj)) {
-    maybe_element = accessor->Get(array, array, new_length, elms_obj);
-  } else {
-    Handle<Object> proto(array->GetPrototype(), isolate);
-    maybe_element = Object::GetElement(isolate, proto, len - 1);
+  Handle<Object> element =
+      accessor->Get(array, array, new_length, elms_obj).ToHandleChecked();
+  if (element->IsTheHole()) {
+    return CallJsBuiltin(isolate, "ArrayPop", args);
   }
-  Handle<Object> element;
-  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, element, maybe_element);
   RETURN_IF_EMPTY_HANDLE(
       isolate,
       accessor->SetLength(array, handle(Smi::FromInt(new_length), isolate)));
   return *element;
 }
 
 
 BUILTIN(ArrayShift) {
   HandleScope scope(isolate);
   Heap* heap = isolate->heap();
   Handle<Object> receiver = args.receiver();
   MaybeHandle<FixedArrayBase> maybe_elms_obj =
       EnsureJSArrayWithWritableFastElements(isolate, receiver, NULL, 0);
   Handle<FixedArrayBase> elms_obj;
   if (!maybe_elms_obj.ToHandle(&elms_obj) ||
       !IsJSArrayFastElementMovingAllowed(heap,
                                          *Handle<JSArray>::cast(receiver))) {
     return CallJsBuiltin(isolate, "ArrayShift", args);
   }
   Handle<JSArray> array = Handle<JSArray>::cast(receiver);
   ASSERT(!array->map()->is_observed());
 
   int len = Smi::cast(array->length())->value();
   if (len == 0) return heap->undefined_value();
 
   // Get first element
   ElementsAccessor* accessor = array->GetElementsAccessor();
-  Handle<Object> first;
-  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
-      isolate, first, accessor->Get(receiver, array, 0, elms_obj));
+  Handle<Object> first =
+    accessor->Get(array, array, 0, elms_obj).ToHandleChecked();
   if (first->IsTheHole()) {
-    first = isolate->factory()->undefined_value();
+    return CallJsBuiltin(isolate, "ArrayShift", args);
   }
 
   if (heap->CanMoveObjectStart(*elms_obj)) {
     array->set_elements(LeftTrimFixedArray(heap, *elms_obj, 1));
   } else {
     // Shift the elements.
     if (elms_obj->IsFixedArray()) {
       Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
       DisallowHeapAllocation no_gc;
       heap->MoveElements(*elms, 0, 1, len - 1);
@@ skipping 1160 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