Object.observe: prevent observed objects from using fast elements.

src/objects.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 9411 matching lines @@
 #endif  // ENABLE_DISASSEMBLER
 
 
 MaybeObject* JSObject::SetFastElementsCapacityAndLength(
     int capacity,
     int length,
     SetFastElementsCapacitySmiMode smi_mode) {
   Heap* heap = GetHeap();
   // We should never end in here with a pixel or external array.
   ASSERT(!HasExternalArrayElements());
+  ASSERT(!map()->is_observed());
 
   // Allocate a new fast elements backing store.
   FixedArray* new_elements;
   MaybeObject* maybe = heap->AllocateUninitializedFixedArray(capacity);
   if (!maybe->To(&new_elements)) return maybe;
 
   ElementsKind elements_kind = GetElementsKind();
   ElementsKind new_elements_kind;
   // The resized array has FAST_*_SMI_ELEMENTS if the capacity mode forces it,
   // or if it's allowed and the old elements array contained only SMIs.
@@ skipping 44 matching lines @@
   return new_elements;
 }
 
 
 MaybeObject* JSObject::SetFastDoubleElementsCapacityAndLength(
     int capacity,
     int length) {
   Heap* heap = GetHeap();
   // We should never end in here with a pixel or external array.
   ASSERT(!HasExternalArrayElements());
+  ASSERT(!map()->is_observed());
 
   FixedArrayBase* elems;
   { MaybeObject* maybe_obj =
         heap->AllocateUninitializedFixedDoubleArray(capacity);
     if (!maybe_obj->To(&elems)) return maybe_obj;
   }
 
   ElementsKind elements_kind = GetElementsKind();
   ElementsKind new_elements_kind = elements_kind;
   if (IsHoleyElementsKind(elements_kind)) {
@@ skipping 1123 matching lines @@
 
 Handle<Object> JSObject::TransitionElementsKind(Handle<JSObject> object,
                                                 ElementsKind to_kind) {
   CALL_HEAP_FUNCTION(object->GetIsolate(),
                      object->TransitionElementsKind(to_kind),
                      Object);
 }
 
 
 MaybeObject* JSObject::TransitionElementsKind(ElementsKind to_kind) {
+  ASSERT(!map()->is_observed());
   ElementsKind from_kind = map()->elements_kind();
 
   if (IsFastHoleyElementsKind(from_kind)) {
     to_kind = GetHoleyElementsKind(to_kind);
   }
 
   if (from_kind == to_kind) return this;
 
   Isolate* isolate = GetIsolate();
   if (elements() == isolate->heap()->empty_fixed_array() ||
@@ skipping 236 matching lines @@
 }
 
 
 bool JSObject::ShouldConvertToFastElements() {
   ASSERT(HasDictionaryElements() || HasDictionaryArgumentsElements());
   // If the elements are sparse, we should not go back to fast case.
   if (!HasDenseElements()) return false;
   // An object requiring access checks is never allowed to have fast
   // elements.  If it had fast elements we would skip security checks.
   if (IsAccessCheckNeeded()) return false;
+  // Observed objects may not go to fast mode because they rely on map checks,
+  // and for fast elements we sometimes check element kinds only.
+  if (FLAG_harmony_observation && map()->is_observed()) return false;
 
   FixedArray* elements = FixedArray::cast(this->elements());
   SeededNumberDictionary* dictionary = NULL;
   if (elements->map() == GetHeap()->non_strict_arguments_elements_map()) {
     dictionary = SeededNumberDictionary::cast(elements->get(1));
   } else {
     dictionary = SeededNumberDictionary::cast(elements);
   }
   // If an element has been added at a very high index in the elements
   // dictionary, we cannot go back to fast case.
@@ skipping 3126 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal