Use linear backing store for hidden properties to save memory.

src/objects-inl.h

 // 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 502 matching lines @@
 TYPE_CHECKER(JSFunctionProxy, JS_FUNCTION_PROXY_TYPE)
 TYPE_CHECKER(JSSet, JS_SET_TYPE)
 TYPE_CHECKER(JSMap, JS_MAP_TYPE)
 TYPE_CHECKER(JSWeakMap, JS_WEAK_MAP_TYPE)
 TYPE_CHECKER(JSContextExtensionObject, JS_CONTEXT_EXTENSION_OBJECT_TYPE)
 TYPE_CHECKER(Map, MAP_TYPE)
 TYPE_CHECKER(FixedArray, FIXED_ARRAY_TYPE)
 TYPE_CHECKER(FixedDoubleArray, FIXED_DOUBLE_ARRAY_TYPE)
 
 
+bool Object::IsHiddenPropertiesArray() {
+  return IsFixedArray();
+}
+
+
 bool Object::IsDescriptorArray() {
   return IsFixedArray();
 }
 
 
 bool Object::IsTransitionArray() {
   return IsFixedArray();
 }
 
 
@@ skipping 1339 matching lines @@
   ASSERT(!heap->InNewSpace(heap->null_value()));
   WRITE_FIELD(this, kHeaderSize + index * kPointerSize, heap->null_value());
 }
 
 
 Object** FixedArray::data_start() {
   return HeapObject::RawField(this, kHeaderSize);
 }
 
 
+MaybeObject* HiddenPropertiesArray::Allocate() {
+  static const int initial_size = 2;
+  ASSERT(IS_POWER_OF_TWO(initial_size));
+  return Isolate::Current()->heap()->AllocateFixedArrayWithHoles(initial_size);
+}
+
+
+MaybeObject* HiddenPropertiesArray::Set(String* key, Object* value) {
+  for (int i = 0; i < length(); i += 2) {
+    if (is_the_hole(i) || String::cast(get(i))->Equals(key)) {
+      set(i, key);
+      set(i + 1, value);
+      return this;
+    }
+  }
+  // Need to extend the backing store.
+  int old_size = length();
+  int new_size = old_size << 1;
+  ASSERT(IS_POWER_OF_TWO(new_size));
+  FixedArray* new_array;
+  { MaybeObject* maybe_obj = GetHeap()->AllocateFixedArrayWithHoles(new_size);
+    if (!maybe_obj->To<FixedArray>(&new_array)) return maybe_obj;
+  }
+  CopyTo(0, new_array, 0, old_size);
+  new_array->set(old_size, key);
+  new_array->set(old_size + 1, value);
+  return new_array;
+}
+
+
+void HiddenPropertiesArray::Delete(String* key) {
+  // Linear search to find the key and delete the entry.
+  for (int i = 0; i < length(); i += 2) {
+    if (is_the_hole(i)) {
+      if (is_the_hole(i + 1)) {
+        // Both key and value are holes.  This is the end of the list.
+        return;
+      }
+    } else if (String::cast(get(i))->Equals(key)) {
+      // Set the value field to undefined (not the hole) to signal that the
+      // list may not end here.
+      set_the_hole(i);
+      set_undefined(i + 1);
+      return;
+    }
+  }
+}
+
+
+Object* HiddenPropertiesArray::Get(String* key) {
+  // Linear search to find the key and return the value.
+  for (int i = 0; i < length(); i += 2) {
+    if (is_the_hole(i)) {
+      if (is_the_hole(i + 1)) {
+        // Both key and value are holes.  This is the end of the list.
+        break;
+      }
+    } else if (String::cast(get(i))->Equals(key)) {
+      return get(i + 1);
+    }
+  }
+  // Not found, return undefined.
+  return GetHeap()->undefined_value();
+}
+
+
 bool DescriptorArray::IsEmpty() {
   ASSERT(length() >= kFirstIndex ||
          this == HEAP->empty_descriptor_array());
   return length() < kFirstIndex;
 }
 
 
 bool DescriptorArray::MayContainTransitions() {
   return !IsEmpty();
 }
@@ skipping 320 matching lines @@
   set(kMaxNumberKeyIndex, Smi::FromInt(kRequiresSlowElementsMask));
 }
 
 
 // ------------------------------------
 // Cast operations
 
 
 CAST_ACCESSOR(FixedArray)
 CAST_ACCESSOR(FixedDoubleArray)
+CAST_ACCESSOR(HiddenPropertiesArray)
 CAST_ACCESSOR(DescriptorArray)
 CAST_ACCESSOR(DeoptimizationInputData)
 CAST_ACCESSOR(DeoptimizationOutputData)
 CAST_ACCESSOR(TypeFeedbackCells)
 CAST_ACCESSOR(SymbolTable)
 CAST_ACCESSOR(JSFunctionResultCache)
 CAST_ACCESSOR(NormalizedMapCache)
 CAST_ACCESSOR(ScopeInfo)
 CAST_ACCESSOR(CompilationCacheTable)
 CAST_ACCESSOR(CodeCacheHashTable)
@@ skipping 3158 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_