Merging ContentArray into DescriptorArray

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index cb87c71fb1193c38953701a88ffac4e1f465d9cd..d04518c8021bd011a5cd8453a05380ab19e36bfb 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -4889,39 +4889,39 @@ class IntrusiveMapTransitionIterator {
 
   void Start() {
     ASSERT(!IsIterating());
-    if (HasContentArray()) *ContentHeader() = Smi::FromInt(0);
+    if (HasDescriptors()) *DescriptorArrayHeader() = Smi::FromInt(0);
   }
 
   bool IsIterating() {
-    return HasContentArray() && (*ContentHeader())->IsSmi();
+    return HasDescriptors() && (*DescriptorArrayHeader())->IsSmi();
   }
 
   Map* Next() {
     ASSERT(IsIterating());
-    FixedArray* contents = ContentArray();
-    // Attention, tricky index manipulation ahead: Every entry in the contents
-    // array consists of a value/details pair, so the index is typically even.
-    // An exception is made for CALLBACKS entries: An even index means we look
-    // at its getter, and an odd index means we look at its setter.
-    int index = Smi::cast(*ContentHeader())->value();
-    while (index < contents->length()) {
-      PropertyDetails details(Smi::cast(contents->get(index | 1)));
+    // Attention, tricky index manipulation ahead: Two two consecutive indices
+    // are assigned to each descriptor. Most descriptors directly advance to the
+    // next descriptor by adding 2 to the index. The exceptions are the
+    // CALLBACKS entries: An even index means we look at its getter, and an odd
+    // index means we look at its setter.
+    int index = Smi::cast(*DescriptorArrayHeader())->value();
+    while ((index / 2) < descriptor_array_->number_of_descriptors()) {
+      PropertyDetails details(descriptor_array_->GetDetails(index / 2));
       switch (details.type()) {
         case MAP_TRANSITION:
         case CONSTANT_TRANSITION:
         case ELEMENTS_TRANSITION:
           // We definitely have a map transition.
-          *ContentHeader() = Smi::FromInt(index + 2);
-          return static_cast<Map*>(contents->get(index));
+          *DescriptorArrayHeader() = Smi::FromInt(index + 2);
+          return static_cast<Map*>(descriptor_array_->GetValue(index / 2));
         case CALLBACKS: {
           // We might have a map transition in a getter or in a setter.
           AccessorPair* accessors =
-              static_cast<AccessorPair*>(contents->get(index & ~1));
+              static_cast<AccessorPair*>(descriptor_array_->GetValue(index / 2));

[Florian Schneider, 2012/05/22 16:53:09]

Long line.

           Object* accessor =
               ((index & 1) == 0) ? accessors->getter() : accessors->setter();
           index++;
           if (accessor->IsMap()) {
-            *ContentHeader() = Smi::FromInt(index);
+            *DescriptorArrayHeader() = Smi::FromInt(index);
             return static_cast<Map*>(accessor);
           }
           break;
@@ -4937,22 +4937,17 @@ class IntrusiveMapTransitionIterator {
           break;
       }
     }
-    *ContentHeader() = descriptor_array_->GetHeap()->fixed_array_map();
+    *DescriptorArrayHeader() = descriptor_array_->GetHeap()->fixed_array_map();
     return NULL;
   }
 
  private:
-  bool HasContentArray() {
-    return descriptor_array_-> length() > DescriptorArray::kContentArrayIndex;
+  bool HasDescriptors() {
+    return !descriptor_array_->IsEmpty();
   }
 
-  FixedArray* ContentArray() {
-    Object* array = descriptor_array_->get(DescriptorArray::kContentArrayIndex);
-    return static_cast<FixedArray*>(array);
-  }
-
-  Object** ContentHeader() {
-    return HeapObject::RawField(ContentArray(), DescriptorArray::kMapOffset);
+  Object** DescriptorArrayHeader() {
+    return HeapObject::RawField(descriptor_array_, DescriptorArray::kMapOffset);
   }
 
   DescriptorArray* descriptor_array_;
@@ -5053,6 +5048,20 @@ class TraversableMap : public Map {
     return old_parent;
   }
 
+  // Can either be Smi (no instance descriptors), or a descriptor array with the
+  // header overwritten as a Smi (thus iterating).
+  DescriptorArray* MutatedInstanceDescriptors() {
+    Object* object = *HeapObject::RawField(this, kInstanceDescriptorsOrBitField3Offset);

[Florian Schneider, 2012/05/22 16:53:09]

Long line.

+    if (object->IsSmi()) {
+      return GetHeap()->empty_descriptor_array();
+    } else {
+      DescriptorArray* descriptor_array = static_cast<DescriptorArray*>(object);
+      ASSERT((*HeapObject::RawField(descriptor_array,
+                                    DescriptorArray::kMapOffset))->IsSmi());
+      return descriptor_array;
+    }
+  }
+
   // Start iterating over this map's children, possibly destroying a FixedArray
   // map (see explanation above).
   void ChildIteratorStart() {
@@ -5064,17 +5073,17 @@ class TraversableMap : public Map {
   // If we have an unvisited child map, return that one and advance. If we have
   // none, return NULL and reset any destroyed FixedArray maps.
   TraversableMap* ChildIteratorNext() {
-    IntrusiveMapTransitionIterator descriptor_iterator(instance_descriptors());
-    if (descriptor_iterator.IsIterating()) {
-      Map* next = descriptor_iterator.Next();
-      if (next != NULL) return static_cast<TraversableMap*>(next);
-    }
     IntrusivePrototypeTransitionIterator
         proto_iterator(unchecked_prototype_transitions());
     if (proto_iterator.IsIterating()) {
       Map* next = proto_iterator.Next();
       if (next != NULL) return static_cast<TraversableMap*>(next);
     }
+    IntrusiveMapTransitionIterator descriptor_iterator(MutatedInstanceDescriptors());

[Florian Schneider, 2012/05/22 16:53:09]

Long line.

+    if (descriptor_iterator.IsIterating()) {
+      Map* next = descriptor_iterator.Next();
+      if (next != NULL) return static_cast<TraversableMap*>(next);
+    }
     return NULL;
   }
 };
@@ -5638,13 +5647,7 @@ MaybeObject* DescriptorArray::Allocate(int number_of_descriptors) {
   // Do not use DescriptorArray::cast on incomplete object.
   FixedArray* result = FixedArray::cast(array);
 
-  // Allocate the content array and set it in the descriptor array.
-  { MaybeObject* maybe_array =
-        heap->AllocateFixedArray(number_of_descriptors << 1);
-    if (!maybe_array->ToObject(&array)) return maybe_array;
-  }
   result->set(kBitField3StorageIndex, Smi::FromInt(0));
-  result->set(kContentArrayIndex, array);
   result->set(kEnumerationIndexIndex,
               Smi::FromInt(PropertyDetails::kInitialIndex));
   return result;
@@ -5829,7 +5832,11 @@ MaybeObject* DescriptorArray::RemoveTransitions() {
   return new_descriptors;
 }
 
-
+// The whiteness witness is needed since sort will reshuffle the entries in the
+// descriptor array. If the descriptor array were to be gray, the sort would
+// potentially swap a black and a white member. This would result in
+// accidentally reclaiming the white member if the descriptor array owned the
+// unique pointer.
 void DescriptorArray::SortUnchecked(const WhitenessWitness& witness) {
   // In-place heap sort.
   int len = number_of_descriptors();
@@ -5974,9 +5981,9 @@ bool DescriptorArray::IsEqualTo(DescriptorArray* other) {
   if (other->IsEmpty()) return false;
   if (length() != other->length()) return false;
   for (int i = 0; i < length(); ++i) {
-    if (get(i) != other->get(i) && i != kContentArrayIndex) return false;
+    if (get(i) != other->get(i)) return false;
   }
-  return GetContentArray()->IsEqualTo(other->GetContentArray());
+  return true;
 }
 #endif
 
@@ -7198,23 +7205,20 @@ void Map::ClearNonLiveTransitions(Heap* heap) {
   if (d->IsEmpty()) return;
   Smi* NullDescriptorDetails =
     PropertyDetails(NONE, NULL_DESCRIPTOR).AsSmi();
-  FixedArray* contents = FixedArray::cast(
-      d->get(DescriptorArray::kContentArrayIndex));
-  ASSERT(contents->length() >= 2);
-  for (int i = 0; i < contents->length(); i += 2) {
+  for (int i = 0; i < d->number_of_descriptors(); ++i) {
     // If the pair (value, details) is a map transition, 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 that non-live map.
     bool keep_entry = false;
-    PropertyDetails details(Smi::cast(contents->get(i + 1)));
+    PropertyDetails details(d->GetDetails(i));
     switch (details.type()) {
       case MAP_TRANSITION:
       case CONSTANT_TRANSITION:
-        ClearBackPointer(heap, contents->get(i), &keep_entry);
+        ClearBackPointer(heap, d->GetValue(i), &keep_entry);
         break;
       case ELEMENTS_TRANSITION: {
-        Object* object = contents->get(i);
+        Object* object = d->GetValue(i);
         if (object->IsMap()) {
           ClearBackPointer(heap, object, &keep_entry);
         } else {
@@ -7228,7 +7232,7 @@ void Map::ClearNonLiveTransitions(Heap* heap) {
         break;
       }
       case CALLBACKS: {
-        Object* object = contents->get(i);
+        Object* object = d->GetValue(i);
         if (object->IsAccessorPair()) {
           AccessorPair* accessors = AccessorPair::cast(object);
           if (ClearBackPointer(heap, accessors->getter(), &keep_entry)) {
@@ -7255,8 +7259,8 @@ void Map::ClearNonLiveTransitions(Heap* heap) {
     // What we *really* want to do here is removing this entry completely, but
     // for technical reasons we can't do this, so we zero it out instead.
     if (!keep_entry) {
-      contents->set_unchecked(i + 1, NullDescriptorDetails);
-      contents->set_null_unchecked(heap, i);
+      d->SetDetailsUnchecked(i, NullDescriptorDetails);
+      d->SetNullValueUnchecked(i, heap);
     }
   }
 }