RFC: Try to be much more careful with where we skip the write barrier by:...

src/objects.cc

 // Copyright 2006-2009 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 3182 matching lines @@
     Object* value = other->get(y);
     if (!value->IsTheHole() && !HasKey(this, value)) extra++;
   }
 
   if (extra == 0) return this;
 
   // Allocate the result
   Object* obj = Heap::AllocateFixedArray(len0 + extra);
   if (obj->IsFailure()) return obj;
   // Fill in the content
+  AssertNoAllocation no_gc;
   FixedArray* result = FixedArray::cast(obj);
-  WriteBarrierMode mode = result->GetWriteBarrierMode();
+  WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < len0; i++) {
     result->set(i, get(i), mode);
   }
   // Fill in the extra keys.
   int index = 0;
   for (int y = 0; y < len1; y++) {
     Object* value = other->get(y);
     if (!value->IsTheHole() && !HasKey(this, value)) {
       result->set(len0 + index, other->get(y), mode);
       index++;
     }
   }
   ASSERT(extra == index);
   return result;
 }
 
 
 Object* FixedArray::CopySize(int new_length) {
   if (new_length == 0) return Heap::empty_fixed_array();
   Object* obj = Heap::AllocateFixedArray(new_length);
   if (obj->IsFailure()) return obj;
   FixedArray* result = FixedArray::cast(obj);
   // Copy the content
+  AssertNoAllocation no_gc;
   int len = length();
   if (new_length < len) len = new_length;
   result->set_map(map());
-  WriteBarrierMode mode = result->GetWriteBarrierMode();
+  WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < len; i++) {
     result->set(i, get(i), mode);
   }
   return result;
 }
 
 
 void FixedArray::CopyTo(int pos, FixedArray* dest, int dest_pos, int len) {
-  WriteBarrierMode mode = dest->GetWriteBarrierMode();
+  AssertNoAllocation no_gc;
+  WriteBarrierMode mode = dest->GetWriteBarrierMode(no_gc);
   for (int index = 0; index < len; index++) {
     dest->set(dest_pos+index, get(pos+index), mode);
   }
 }
 
 
 #ifdef DEBUG
 bool FixedArray::IsEqualTo(FixedArray* other) {
   if (length() != other->length()) return false;
   for (int i = 0 ; i < length(); ++i) {
@@ skipping 13 matching lines @@
       Heap::AllocateFixedArray(ToKeyIndex(number_of_descriptors));
   if (array->IsFailure()) return array;
   // Do not use DescriptorArray::cast on incomplete object.
   FixedArray* result = FixedArray::cast(array);
 
   // Allocate the content array and set it in the descriptor array.
   array = Heap::AllocateFixedArray(number_of_descriptors << 1);
   if (array->IsFailure()) return array;
   result->set(kContentArrayIndex, array);
   result->set(kEnumerationIndexIndex,
-              Smi::FromInt(PropertyDetails::kInitialIndex),
-              SKIP_WRITE_BARRIER);
+              Smi::FromInt(PropertyDetails::kInitialIndex));
   return result;
 }
 
 
 void DescriptorArray::SetEnumCache(FixedArray* bridge_storage,
                                    FixedArray* new_cache) {
   ASSERT(bridge_storage->length() >= kEnumCacheBridgeLength);
   if (HasEnumCache()) {
     FixedArray::cast(get(kEnumerationIndexIndex))->
       set(kEnumCacheBridgeCacheIndex, new_cache);
@@ skipping 1407 matching lines @@
     // check if the target is live.  If not, null the descriptor.
     // Also drop the back pointer for that map transition, so that this
     // map is not reached again by following a back pointer from a
     // non-live object.
     PropertyDetails details(Smi::cast(contents->get(i + 1)));
     if (details.type() == MAP_TRANSITION) {
       Map* target = reinterpret_cast<Map*>(contents->get(i));
       ASSERT(target->IsHeapObject());
       if (!target->IsMarked()) {
         ASSERT(target->IsMap());
-        contents->set(i + 1, NullDescriptorDetails, SKIP_WRITE_BARRIER);
-        contents->set(i, Heap::null_value(), SKIP_WRITE_BARRIER);
+        contents->set(i + 1, NullDescriptorDetails);
+        contents->set_null(i);
         ASSERT(target->prototype() == this ||
                target->prototype() == real_prototype);
         // Getter prototype() is read-only, set_prototype() has side effects.
         *RawField(target, Map::kPrototypeOffset) = real_prototype;
       }
     }
   }
 }
 
 
@@ skipping 439 matching lines @@
 
 
 void JSObject::SetFastElements(FixedArray* elems) {
   // We should never end in here with a pixel or external array.
   ASSERT(!HasPixelElements() && !HasExternalArrayElements());
 #ifdef DEBUG
   // Check the provided array is filled with the_hole.
   uint32_t len = static_cast<uint32_t>(elems->length());
   for (uint32_t i = 0; i < len; i++) ASSERT(elems->get(i)->IsTheHole());
 #endif
-  WriteBarrierMode mode = elems->GetWriteBarrierMode();
+  AssertNoAllocation no_gc;
+  WriteBarrierMode mode = elems->GetWriteBarrierMode(no_gc);
   switch (GetElementsKind()) {
     case FAST_ELEMENTS: {
       FixedArray* old_elements = FixedArray::cast(elements());
       uint32_t old_length = static_cast<uint32_t>(old_elements->length());
       // Fill out the new array with this content and array holes.
       for (uint32_t i = 0; i < old_length; i++) {
         elems->set(i, old_elements->get(i), mode);
       }
       break;
     }
@@ skipping 46 matching lines @@
     default:
       UNREACHABLE();
       break;
   }
   return this;
 }
 
 
 Object* JSArray::Initialize(int capacity) {
   ASSERT(capacity >= 0);
-  set_length(Smi::FromInt(0), SKIP_WRITE_BARRIER);
+  set_length(Smi::FromInt(0));
   FixedArray* new_elements;
   if (capacity == 0) {
     new_elements = Heap::empty_fixed_array();
   } else {
     Object* obj = Heap::AllocateFixedArrayWithHoles(capacity);
     if (obj->IsFailure()) return obj;
     new_elements = FixedArray::cast(obj);
   }
   set_elements(new_elements);
   return this;
@@ skipping 39 matching lines @@
         int old_capacity = FixedArray::cast(elements())->length();
         if (value <= old_capacity) {
           if (IsJSArray()) {
             int old_length = FastD2I(JSArray::cast(this)->length()->Number());
             // NOTE: We may be able to optimize this by removing the
             // last part of the elements backing storage array and
             // setting the capacity to the new size.
             for (int i = value; i < old_length; i++) {
               FixedArray::cast(elements())->set_the_hole(i);
             }
-            JSArray::cast(this)->set_length(smi_length, SKIP_WRITE_BARRIER);
+            JSArray::cast(this)->set_length(Smi::cast(smi_length));
           }
           return this;
         }
         int min = NewElementsCapacity(old_capacity);
         int new_capacity = value > min ? value : min;
         if (new_capacity <= kMaxFastElementsLength ||
             !ShouldConvertToSlowElements(new_capacity)) {
           Object* obj = Heap::AllocateFixedArrayWithHoles(new_capacity);
           if (obj->IsFailure()) return obj;
-          if (IsJSArray()) JSArray::cast(this)->set_length(smi_length,
-                                                           SKIP_WRITE_BARRIER);
+          if (IsJSArray()) {
+            JSArray::cast(this)->set_length(Smi::cast(smi_length));
+          }
           SetFastElements(FixedArray::cast(obj));
           return this;
         }
         break;
       }
       case DICTIONARY_ELEMENTS: {
         if (IsJSArray()) {
           if (value == 0) {
             // If the length of a slow array is reset to zero, we clear
             // the array and flush backing storage. This has the added
             // benefit that the array returns to fast mode.
             initialize_elements();
           } else {
             // Remove deleted elements.
             uint32_t old_length =
             static_cast<uint32_t>(JSArray::cast(this)->length()->Number());
             element_dictionary()->RemoveNumberEntries(value, old_length);
           }
-          JSArray::cast(this)->set_length(smi_length, SKIP_WRITE_BARRIER);
+          JSArray::cast(this)->set_length(Smi::cast(smi_length));
         }
         return this;
       }
       default:
         UNREACHABLE();
         break;
     }
   }
 
   // General slow case.
   if (len->IsNumber()) {
     uint32_t length;
     if (Array::IndexFromObject(len, &length)) {
       return SetSlowElements(len);
     } else {
       return ArrayLengthRangeError();
     }
   }
 
   // len is not a number so make the array size one and
   // set only element to len.
   Object* obj = Heap::AllocateFixedArray(1);
   if (obj->IsFailure()) return obj;
   FixedArray::cast(obj)->set(0, len);
-  if (IsJSArray()) JSArray::cast(this)->set_length(Smi::FromInt(1),
-                                                   SKIP_WRITE_BARRIER);
+  if (IsJSArray()) JSArray::cast(this)->set_length(Smi::FromInt(1));
   set_elements(FixedArray::cast(obj));
   return this;
 }
 
 
 bool JSObject::HasElementPostInterceptor(JSObject* receiver, uint32_t index) {
   switch (GetElementsKind()) {
     case FAST_ELEMENTS: {
       uint32_t length = IsJSArray() ?
           static_cast<uint32_t>
@@ skipping 249 matching lines @@
 
   // Check whether there is extra space in fixed array..
   if (index < elms_length) {
     elms->set(index, value);
     if (IsJSArray()) {
       // Update the length of the array if needed.
       uint32_t array_length = 0;
       CHECK(Array::IndexFromObject(JSArray::cast(this)->length(),
                                    &array_length));
       if (index >= array_length) {
-        JSArray::cast(this)->set_length(Smi::FromInt(index + 1),
-                                        SKIP_WRITE_BARRIER);
+        JSArray::cast(this)->set_length(Smi::FromInt(index + 1));
       }
     }
     return value;
   }
 
   // Allow gap in fast case.
   if ((index - elms_length) < kMaxGap) {
     // Try allocating extra space.
     int new_capacity = NewElementsCapacity(index+1);
     if (new_capacity <= kMaxFastElementsLength ||
         !ShouldConvertToSlowElements(new_capacity)) {
       ASSERT(static_cast<uint32_t>(new_capacity) > index);
       Object* obj = Heap::AllocateFixedArrayWithHoles(new_capacity);
       if (obj->IsFailure()) return obj;
       SetFastElements(FixedArray::cast(obj));
-      if (IsJSArray()) JSArray::cast(this)->set_length(Smi::FromInt(index + 1),
-                                                       SKIP_WRITE_BARRIER);
+      if (IsJSArray()) {
+        JSArray::cast(this)->set_length(Smi::FromInt(index + 1));
+      }
       FixedArray::cast(elements())->set(index, value);
       return value;
     }
   }
 
   // Otherwise default to slow case.
   Object* obj = NormalizeElements();
   if (obj->IsFailure()) return obj;
   ASSERT(HasDictionaryElements());
   return SetElement(index, value);
@@ skipping 476 matching lines @@
     }
   }
 }
 #endif
 
 
 template<typename Shape, typename Key>
 void Dictionary<Shape, Key>::CopyValuesTo(FixedArray* elements) {
   int pos = 0;
   int capacity = HashTable<Shape, Key>::Capacity();
-  WriteBarrierMode mode = elements->GetWriteBarrierMode();
+  AssertNoAllocation no_gc;
+  WriteBarrierMode mode = elements->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < capacity; i++) {
     Object* k =  Dictionary<Shape, Key>::KeyAt(i);
     if (Dictionary<Shape, Key>::IsKey(k)) {
       elements->set(pos++, ValueAt(i), mode);
     }
   }
   ASSERT(pos == elements->length());
 }
 
 
@@ skipping 350 matching lines @@
                                   PropertyAttributes filter) {
   int counter = 0;
   switch (GetElementsKind()) {
     case FAST_ELEMENTS: {
       int length = IsJSArray() ?
           Smi::cast(JSArray::cast(this)->length())->value() :
           FixedArray::cast(elements())->length();
       for (int i = 0; i < length; i++) {
         if (!FixedArray::cast(elements())->get(i)->IsTheHole()) {
           if (storage != NULL) {
-            storage->set(counter, Smi::FromInt(i), SKIP_WRITE_BARRIER);
+            storage->set(counter, Smi::FromInt(i));
           }
           counter++;
         }
       }
       ASSERT(!storage || storage->length() >= counter);
       break;
     }
     case PIXEL_ELEMENTS: {
       int length = PixelArray::cast(elements())->length();
       while (counter < length) {
         if (storage != NULL) {
-          storage->set(counter, Smi::FromInt(counter), SKIP_WRITE_BARRIER);
+          storage->set(counter, Smi::FromInt(counter));
         }
         counter++;
       }
       ASSERT(!storage || storage->length() >= counter);
       break;
     }
     case EXTERNAL_BYTE_ELEMENTS:
     case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
     case EXTERNAL_SHORT_ELEMENTS:
     case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
     case EXTERNAL_INT_ELEMENTS:
     case EXTERNAL_UNSIGNED_INT_ELEMENTS:
     case EXTERNAL_FLOAT_ELEMENTS: {
       int length = ExternalArray::cast(elements())->length();
       while (counter < length) {
         if (storage != NULL) {
-          storage->set(counter, Smi::FromInt(counter), SKIP_WRITE_BARRIER);
+          storage->set(counter, Smi::FromInt(counter));
         }
         counter++;
       }
       ASSERT(!storage || storage->length() >= counter);
       break;
     }
     case DICTIONARY_ELEMENTS: {
       if (storage != NULL) {
         element_dictionary()->CopyKeysTo(storage, filter);
       }
       counter = element_dictionary()->NumberOfElementsFilterAttributes(filter);
       break;
     }
     default:
       UNREACHABLE();
       break;
   }
 
   if (this->IsJSValue()) {
     Object* val = JSValue::cast(this)->value();
     if (val->IsString()) {
       String* str = String::cast(val);
       if (storage) {
         for (int i = 0; i < str->length(); i++) {
-          storage->set(counter + i, Smi::FromInt(i), SKIP_WRITE_BARRIER);
+          storage->set(counter + i, Smi::FromInt(i));
         }
       }
       counter += str->length();
     }
   }
   ASSERT(!storage || storage->length() == counter);
   return counter;
 }
 
 
@@ skipping 311 matching lines @@
   int nof = NumberOfElements() + n;
   int nod = NumberOfDeletedElements();
   // Return if:
   //   50% is still free after adding n elements and
   //   at most 50% of the free elements are deleted elements.
   if ((nof + (nof >> 1) <= capacity) &&
       (nod <= (capacity - nof) >> 1)) return this;
 
   Object* obj = Allocate(nof * 2);
   if (obj->IsFailure()) return obj;
+
+  AssertNoAllocation no_gc;
   HashTable* table = HashTable::cast(obj);
-  WriteBarrierMode mode = table->GetWriteBarrierMode();
+  WriteBarrierMode mode = table->GetWriteBarrierMode(no_gc);
 
   // Copy prefix to new array.
   for (int i = kPrefixStartIndex;
        i < kPrefixStartIndex + Shape::kPrefixSize;
        i++) {
     table->set(i, get(i), mode);
   }
   // Rehash the elements.
   for (int i = 0; i < capacity; i++) {
     uint32_t from_index = EntryToIndex(i);
@@ skipping 226 matching lines @@
     // we start mutating the array.
     Object* new_double = Heap::AllocateHeapNumber(0.0);
     if (new_double->IsFailure()) return new_double;
     result_double = HeapNumber::cast(new_double);
   }
 
   AssertNoAllocation no_alloc;
 
   // Split elements into defined, undefined and the_hole, in that order.
   // Only count locations for undefined and the hole, and fill them afterwards.
-  WriteBarrierMode write_barrier = elements->GetWriteBarrierMode();
+  WriteBarrierMode write_barrier = elements->GetWriteBarrierMode(no_alloc);
   unsigned int undefs = limit;
   unsigned int holes = limit;
   // Assume most arrays contain no holes and undefined values, so minimize the
   // number of stores of non-undefined, non-the-hole values.
   for (unsigned int i = 0; i < undefs; i++) {
     Object* current = elements->get(i);
     if (current->IsTheHole()) {
       holes--;
       undefs--;
     } else if (current->IsUndefined()) {
@@ skipping 474 matching lines @@
 
 template<typename Shape, typename Key>
 Object* Dictionary<Shape, Key>::GenerateNewEnumerationIndices() {
   int length = HashTable<Shape, Key>::NumberOfElements();
 
   // Allocate and initialize iteration order array.
   Object* obj = Heap::AllocateFixedArray(length);
   if (obj->IsFailure()) return obj;
   FixedArray* iteration_order = FixedArray::cast(obj);
   for (int i = 0; i < length; i++) {
-    iteration_order->set(i, Smi::FromInt(i), SKIP_WRITE_BARRIER);
+    iteration_order->set(i, Smi::FromInt(i));
   }
 
   // Allocate array with enumeration order.
   obj = Heap::AllocateFixedArray(length);
   if (obj->IsFailure()) return obj;
   FixedArray* enumeration_order = FixedArray::cast(obj);
 
   // Fill the enumeration order array with property details.
   int capacity = HashTable<Shape, Key>::Capacity();
   int pos = 0;
   for (int i = 0; i < capacity; i++) {
     if (Dictionary<Shape, Key>::IsKey(Dictionary<Shape, Key>::KeyAt(i))) {
-      enumeration_order->set(pos++,
-                             Smi::FromInt(DetailsAt(i).index()),
-                             SKIP_WRITE_BARRIER);
+      enumeration_order->set(pos++, Smi::FromInt(DetailsAt(i).index()));
     }
   }
 
   // Sort the arrays wrt. enumeration order.
   iteration_order->SortPairs(enumeration_order, enumeration_order->length());
 
   // Overwrite the enumeration_order with the enumeration indices.
   for (int i = 0; i < length; i++) {
     int index = Smi::cast(iteration_order->get(i))->value();
     int enum_index = PropertyDetails::kInitialIndex + i;
-    enumeration_order->set(index,
-                           Smi::FromInt(enum_index),
-                           SKIP_WRITE_BARRIER);
+    enumeration_order->set(index, Smi::FromInt(enum_index));
   }
 
   // Update the dictionary with new indices.
   capacity = HashTable<Shape, Key>::Capacity();
   pos = 0;
   for (int i = 0; i < capacity; i++) {
     if (Dictionary<Shape, Key>::IsKey(Dictionary<Shape, Key>::KeyAt(i))) {
       int enum_index = Smi::cast(enumeration_order->get(pos++))->value();
       PropertyDetails details = DetailsAt(i);
       PropertyDetails new_details =
@@ skipping 127 matching lines @@
   // Check if this index is high enough that we should require slow
   // elements.
   if (key > kRequiresSlowElementsLimit) {
     set_requires_slow_elements();
     return;
   }
   // Update max key value.
   Object* max_index_object = get(kMaxNumberKeyIndex);
   if (!max_index_object->IsSmi() || max_number_key() < key) {
     FixedArray::set(kMaxNumberKeyIndex,
-                    Smi::FromInt(key << kRequiresSlowElementsTagSize),
-                    SKIP_WRITE_BARRIER);
+                    Smi::FromInt(key << kRequiresSlowElementsTagSize));
   }
 }
 
 
 Object* NumberDictionary::AddNumberEntry(uint32_t key,
                                          Object* value,
                                          PropertyDetails details) {
   UpdateMaxNumberKey(key);
   SLOW_ASSERT(FindEntry(key) == kNotFound);
   return Add(key, value, details);
@@ skipping 70 matching lines @@
                                       FixedArray* sort_array) {
   ASSERT(storage->length() >= NumberOfEnumElements());
   int capacity = Capacity();
   int index = 0;
   for (int i = 0; i < capacity; i++) {
      Object* k = KeyAt(i);
      if (IsKey(k)) {
        PropertyDetails details = DetailsAt(i);
        if (details.IsDeleted() || details.IsDontEnum()) continue;
        storage->set(index, k);
-       sort_array->set(index,
-                       Smi::FromInt(details.index()),
-                       SKIP_WRITE_BARRIER);
+       sort_array->set(index, Smi::FromInt(details.index()));
        index++;
      }
   }
   storage->SortPairs(sort_array, sort_array->length());
   ASSERT(storage->length() >= index);
 }
 
 
 template<typename Shape, typename Key>
 void Dictionary<Shape, Key>::CopyKeysTo(FixedArray* storage) {
@@ skipping 388 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single beak point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif
 
 
 } }  // namespace v8::internal