Implement explicit back pointers in transition tree.

src/objects-debug.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 285 matching lines @@
 
 
 void Map::MapVerify() {
   ASSERT(!HEAP->InNewSpace(this));
   ASSERT(FIRST_TYPE <= instance_type() && instance_type() <= LAST_TYPE);
   ASSERT(instance_size() == kVariableSizeSentinel ||
          (kPointerSize <= instance_size() &&
           instance_size() < HEAP->Capacity()));
   VerifyHeapPointer(prototype());
   VerifyHeapPointer(instance_descriptors());
+  SLOW_ASSERT(instance_descriptors()->IsSortedNoDuplicates());
+  SLOW_ASSERT(instance_descriptors()->IsConsistentWithBackPointers(this));
 }
 
 
 void Map::SharedMapVerify() {
   MapVerify();
   ASSERT(is_shared());
   ASSERT(instance_descriptors()->IsEmpty());
   ASSERT_EQ(0, pre_allocated_property_fields());
   ASSERT_EQ(0, unused_property_fields());
   ASSERT_EQ(StaticVisitorBase::GetVisitorId(instance_type(), instance_size()),
@@ skipping 571 matching lines @@
     if (hash < current) {
       PrintDescriptors();
       return false;
     }
     current = hash;
   }
   return true;
 }
 
 
+static bool CheckOneBackPointer(Map* current_map, Object* target) {
+  return !target->IsMap() || Map::cast(target)->GetBackPointer() == current_map;
+}
+
+
+bool DescriptorArray::IsConsistentWithBackPointers(Map* current_map) {
+  for (int i = 0; i < number_of_descriptors(); ++i) {
+    switch (GetType(i)) {
+      case MAP_TRANSITION:
+      case CONSTANT_TRANSITION:
+        if (!CheckOneBackPointer(current_map, GetValue(i))) {
+          return false;
+        }
+        break;
+      case ELEMENTS_TRANSITION: {
+        Object* object = GetValue(i);
+        if (!CheckOneBackPointer(current_map, object)) {
+          return false;
+        }
+        if (object->IsFixedArray()) {
+          FixedArray* array = FixedArray::cast(object);
+          for (int i = 0; i < array->length(); ++i) {
+            if (!CheckOneBackPointer(current_map, array->get(i))) {
+              return false;
+            }
+          }
+        }
+        break;
+      }
+      case CALLBACKS: {
+        Object* object = GetValue(i);
+        if (object->IsAccessorPair()) {
+          AccessorPair* accessors = AccessorPair::cast(object);
+          if (!CheckOneBackPointer(current_map, accessors->getter())) {
+            return false;
+          }
+          if (!CheckOneBackPointer(current_map, accessors->setter())) {
+            return false;
+          }
+        }
+        break;
+      }
+      case NORMAL:
+      case FIELD:
+      case CONSTANT_FUNCTION:
+      case HANDLER:
+      case INTERCEPTOR:
+      case NULL_DESCRIPTOR:
+        break;
+    }
+  }
+  return true;
+}
+
+
 void JSFunctionResultCache::JSFunctionResultCacheVerify() {
   JSFunction::cast(get(kFactoryIndex))->Verify();
 
   int size = Smi::cast(get(kCacheSizeIndex))->value();
   ASSERT(kEntriesIndex <= size);
   ASSERT(size <= length());
   ASSERT_EQ(0, size % kEntrySize);
 
   int finger = Smi::cast(get(kFingerIndex))->value();
   ASSERT(kEntriesIndex <= finger);
@@ skipping 24 matching lines @@
         ASSERT(e->IsUndefined());
       }
     }
   }
 }
 
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal