Move LayoutObject to satellite NodeLayoutData that hangs from a Node.

third_party/WebKit/Source/core/dom/Node.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004-2011, 2014 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 39 matching lines @@
 class Event;
 class ExceptionState;
 class GetRootNodeOptions;
 class HTMLQualifiedName;
 class HTMLSlotElement;
 class IntRect;
 class EventDispatchHandlingState;
 class NodeList;
 class NodeListsNodeData;
 class NodeOrString;
+class NodeLayoutData;
 class NodeRareData;
 class QualifiedName;
 class RegisteredEventListener;
 class LayoutBox;
 class LayoutBoxModelObject;
 class LayoutObject;
 class ComputedStyle;
 class SVGQualifiedName;
 class ShadowRoot;
 template <typename NodeType>
@@ skipping 21 matching lines @@
   kFailed = 3 << kNodeCustomElementShift,
 
   kNotDefinedFlag = 2 << kNodeCustomElementShift,
 };
 
 enum class SlotChangeType {
   kInitial,
   kChained,
 };
 
+class NodeLayoutData {
+ public:
+  explicit NodeLayoutData(LayoutObject* layout_object)
+      : layout_object_(layout_object) {}
+  LayoutObject* GetLayoutObject() const { return layout_object_; }
+  void SetLayoutObject(LayoutObject* layout_object) {
+    DCHECK_NE(&SharedEmptyData(), this);
+    layout_object_ = layout_object;
+  }
+  static NodeLayoutData& SharedEmptyData() {
+    static NodeLayoutData& shared_empty_data_ = *new NodeLayoutData(nullptr);

[esprehn, 2017/04/13 18:41:08]

DEFINE_STATIC_LOCAL(NodeLayoutData, shared_empty_data, (nullptr));

Also no underscore at the end, it's not a member variable.

[nainar, 2017/04/13 20:21:03]

Done.

+    return shared_empty_data_;
+  }
+  bool IsSharedEmptyData() { return this == &SharedEmptyData(); }
+
+ private:
+  LayoutObject* layout_object_;
+};
+
 class NodeRareDataBase {
  public:
-  LayoutObject* GetLayoutObject() const { return layout_object_; }
-  void SetLayoutObject(LayoutObject* layout_object) {
-    layout_object_ = layout_object;
+  NodeLayoutData* GetNodeLayoutData() const { return node_layout_data_; }
+  void SetNodeLayoutData(NodeLayoutData* node_layout_data) {
+    DCHECK(node_layout_data);
+    node_layout_data_ = node_layout_data;
   }
 
  protected:
-  NodeRareDataBase(LayoutObject* layout_object)
-      : layout_object_(layout_object) {}
+  NodeRareDataBase(NodeLayoutData* node_layout_data)
+      : node_layout_data_(node_layout_data) {}
+  ~NodeRareDataBase() {
+    if (node_layout_data_ && !node_layout_data_->IsSharedEmptyData())
+      delete node_layout_data_;
+  }
 
  protected:
-  // LayoutObjects are fully owned by their DOM node. See LayoutObject's
-  // LIFETIME documentation section.
-  LayoutObject* layout_object_;
+  NodeLayoutData* node_layout_data_;
 };
 
 class Node;
 WILL_NOT_BE_EAGERLY_TRACED_CLASS(Node);
 
 // This class represents a DOM node in the DOM tree.
 // https://dom.spec.whatwg.org/#interface-node
 class CORE_EXPORT Node : public EventTarget {
   DEFINE_WRAPPERTYPEINFO();
   friend class TreeScope;
@@ skipping 435 matching lines @@
   virtual bool CanStartSelection() const;
 
   // -----------------------------------------------------------------------------
   // Integration with layout tree
 
   // As layoutObject() includes a branch you should avoid calling it repeatedly
   // in hot code paths.
   // Note that if a Node has a layoutObject, it's parentNode is guaranteed to
   // have one as well.
   LayoutObject* GetLayoutObject() const {
-    return HasRareData() ? data_.rare_data_->GetLayoutObject()
-                         : data_.layout_object_;
+    return HasRareData()
+               ? data_.rare_data_->GetNodeLayoutData()->GetLayoutObject()
+               : data_.node_layout_data_->GetLayoutObject();
   }
-  void SetLayoutObject(LayoutObject* layout_object) {
-    if (HasRareData())
-      data_.rare_data_->SetLayoutObject(layout_object);
-    else
-      data_.layout_object_ = layout_object;
-  }
-
+  void SetLayoutObject(LayoutObject*);
   // Use these two methods with caution.
   LayoutBox* GetLayoutBox() const;
   LayoutBoxModelObject* GetLayoutBoxModelObject() const;
 
   struct AttachContext {
     STACK_ALLOCATED();
     ComputedStyle* resolved_style = nullptr;
     bool performing_reattach = false;
     bool clear_invalidation = false;
 
@@ skipping 332 matching lines @@
   const HeapHashSet<TraceWrapperMember<MutationObserverRegistration>>*
   TransientMutationObserverRegistry();
 
   uint32_t node_flags_;
   Member<ContainerNode> parent_or_shadow_host_node_;
   Member<TreeScope> tree_scope_;
   Member<Node> previous_;
   Member<Node> next_;
   // When a node has rare data we move the layoutObject into the rare data.
   union DataUnion {
-    DataUnion() : layout_object_(nullptr) {}
+    DataUnion() : node_layout_data_(&NodeLayoutData::SharedEmptyData()) {}
     // LayoutObjects are fully owned by their DOM node. See LayoutObject's
     // LIFETIME documentation section.
-    LayoutObject* layout_object_;
+    NodeLayoutData* node_layout_data_;
     NodeRareDataBase* rare_data_;
   } data_;
 };
 
 inline void Node::SetParentOrShadowHostNode(ContainerNode* parent) {
   DCHECK(IsMainThread());
   parent_or_shadow_host_node_ = parent;
   ScriptWrappableVisitor::WriteBarrier(
       this, reinterpret_cast<Node*>(parent_or_shadow_host_node_.Get()));
 }
@@ skipping 52 matching lines @@
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showNode(const blink::Node*);
 void showTree(const blink::Node*);
 void showNodePath(const blink::Node*);
 #endif
 
 #endif  // Node_h