Storage of ComputedStyle separate from LayoutObject.

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
  * License as published by the Free Software Foundation; either
@@ skipping 72 matching lines @@
 class ComputedStyle;
 class SVGQualifiedName;
 class ShadowRoot;
 template <typename NodeType> class StaticNodeTypeList;
 using StaticNodeList = StaticNodeTypeList<Node>;
 class StyleChangeReasonForTracing;
 class TagCollection;
 class Text;
 class TouchEvent;
 
-const int nodeStyleChangeShift = 19;
+const int nodeStyleChangeShift = 20;
 
 enum StyleChangeType {
     NoStyleChange = 0,
     LocalStyleChange = 1 << nodeStyleChangeShift,
     SubtreeStyleChange = 2 << nodeStyleChangeShift,
     NeedsReattachStyleChange = 3 << nodeStyleChangeShift,
 };
 
 enum class CustomElementState {
     Uncustomized = 0,
@@ skipping 408 matching lines @@
     virtual int maxCharacterOffset() const;
 
     // Whether or not a selection can be started in this object
     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* layoutObject() const { return hasRareData() ? m_data.m_rareData->layoutObject() : m_data.m_layoutObject; }
+    LayoutObject* layoutObject() const
+    {
+        if (hasRareData())
+            return m_data.m_rareData->layoutObject();
+        return hasLayoutObject() ? m_data.m_layoutObject : nullptr;
+    }
     void setLayoutObject(LayoutObject* layoutObject)
     {
         if (hasRareData())
             m_data.m_rareData->setLayoutObject(layoutObject);
         else
             m_data.m_layoutObject = layoutObject;
+        if (layoutObject)
+            setFlag(HasLayoutObjectFlag);
+        else
+            clearFlag(HasLayoutObjectFlag);
     }
 
     // Use these two methods with caution.
     LayoutBox* layoutBox() const;
     LayoutBoxModelObject* layoutBoxModelObject() const;
 
     struct AttachContext {
         STACK_ALLOCATED();
         ComputedStyle* resolvedStyle = nullptr;
         bool performingReattach = false;
@@ skipping 147 matching lines @@
 
     DECLARE_VIRTUAL_TRACE_WRAPPERS();
 
     unsigned lengthOfContents() const;
 
     v8::Local<v8::Object> wrap(v8::Isolate*, v8::Local<v8::Object> creationContext) override;
     v8::Local<v8::Object> associateWithWrapper(v8::Isolate*, const WrapperTypeInfo*, v8::Local<v8::Object> wrapper) override WARN_UNUSED_RETURN;
 
 private:
     enum NodeFlags {
-        HasRareDataFlag = 1,
+        HasLayoutObjectFlag = 1,
+        HasRareDataFlag = 1 << 1,
 
         // Node type flags. These never change once created.
-        IsTextFlag = 1 << 1,
-        IsContainerFlag = 1 << 2,
-        IsElementFlag = 1 << 3,
-        IsHTMLFlag = 1 << 4,
-        IsSVGFlag = 1 << 5,
-        IsDocumentFragmentFlag = 1 << 6,
-        IsInsertionPointFlag = 1 << 7,
+        IsTextFlag = 1 << 2,
+        IsContainerFlag = 1 << 3,
+        IsElementFlag = 1 << 4,
+        IsHTMLFlag = 1 << 5,
+        IsSVGFlag = 1 << 6,
+        IsDocumentFragmentFlag = 1 << 7,
+        IsInsertionPointFlag = 1 << 8,
 
         // Changes based on if the element should be treated like a link,
         // ex. When setting the href attribute on an <a>.
-        IsLinkFlag = 1 << 8,
+        IsLinkFlag = 1 << 9,
 
         // Changes based on :hover, :active and :focus state.
-        IsUserActionElementFlag = 1 << 9,
+        IsUserActionElementFlag = 1 << 10,
 
         // Tree state flags. These change when the element is added/removed
         // from a DOM tree.
-        InDocumentFlag = 1 << 10,
-        IsInShadowTreeFlag = 1 << 11,
+        InDocumentFlag = 1 << 11,
+        IsInShadowTreeFlag = 1 << 12,
 
         // Set by the parser when the children are done parsing.
-        IsFinishedParsingChildrenFlag = 1 << 12,
+        IsFinishedParsingChildrenFlag = 1 << 13,
 
         // Flags related to recalcStyle.
-        SVGFilterNeedsLayerUpdateFlag = 1 << 13,
-        HasCustomStyleCallbacksFlag = 1 << 14,
-        ChildNeedsStyleInvalidationFlag = 1 << 15,
-        NeedsStyleInvalidationFlag = 1 << 16,
-        ChildNeedsDistributionRecalcFlag = 1 << 17,
-        ChildNeedsStyleRecalcFlag = 1 << 18,
+        SVGFilterNeedsLayerUpdateFlag = 1 << 14,
+        HasCustomStyleCallbacksFlag = 1 << 15,
+        ChildNeedsStyleInvalidationFlag = 1 << 16,
+        NeedsStyleInvalidationFlag = 1 << 17,
+        ChildNeedsDistributionRecalcFlag = 1 << 18,
+        ChildNeedsStyleRecalcFlag = 1 << 19,
         StyleChangeMask = 1 << nodeStyleChangeShift | 1 << (nodeStyleChangeShift + 1),
 
-        CustomElementFlag = 1 << 21,
-        CustomElementCustomFlag = 1 << 22,
+        CustomElementFlag = 1 << 22,
+        CustomElementCustomFlag = 1 << 23,
 
-        HasNameOrIsEditingTextFlag = 1 << 23,
-        HasWeakReferencesFlag = 1 << 24,
-        V8CollectableDuringMinorGCFlag = 1 << 25,
-        HasEventTargetDataFlag = 1 << 26,
-        AlreadySpellCheckedFlag = 1 << 27,
+        HasNameOrIsEditingTextFlag = 1 << 24,
+        HasWeakReferencesFlag = 1 << 25,
+        V8CollectableDuringMinorGCFlag = 1 << 26,
+        HasEventTargetDataFlag = 1 << 27,
+        AlreadySpellCheckedFlag = 1 << 28,
 
-        V0CustomElementFlag = 1 << 28,
-        V0CustomElementUpgradedFlag = 1 << 29,
+        V0CustomElementFlag = 1 << 29,
+        V0CustomElementUpgradedFlag = 1 << 30,
 
         DefaultNodeFlags = IsFinishedParsingChildrenFlag | NeedsReattachStyleChange
     };
 
-    // 3 bits remaining.
+    // 1 bit remaining.
 
     bool getFlag(NodeFlags mask) const { return m_nodeFlags & mask; }
     void setFlag(bool f, NodeFlags mask) { m_nodeFlags = (m_nodeFlags & ~mask) | (-(int32_t)f & mask); }
     void setFlag(NodeFlags mask) { m_nodeFlags |= mask; }
     void clearFlag(NodeFlags mask) { m_nodeFlags &= ~mask; }
 
 protected:
     enum ConstructionType {
         CreateOther = DefaultNodeFlags,
         CreateText = DefaultNodeFlags | IsTextFlag,
@@ skipping 11 matching lines @@
     Node(TreeScope*, ConstructionType);
 
     virtual void didMoveToNewDocument(Document& oldDocument);
 
     void addedEventListener(const AtomicString& eventType, RegisteredEventListener&) override;
     void removedEventListener(const AtomicString& eventType, const RegisteredEventListener&) override;
     DispatchEventResult dispatchEventInternal(Event*) override;
 
     static void reattachWhitespaceSiblingsIfNeeded(Text* start);
 
+    bool hasLayoutObject() const { return getFlag(HasLayoutObjectFlag); }
     bool hasRareData() const { return getFlag(HasRareDataFlag); }
 
     NodeRareData* rareData() const;
     NodeRareData& ensureRareData();
 
     void setHasCustomStyleCallbacks() { setFlag(true, HasCustomStyleCallbacksFlag); }
 
     void setTreeScope(TreeScope* scope) { m_treeScope = scope; }
 
     // isTreeScopeInitialized() can be false
@@ skipping 37 matching lines @@
     HeapVector<Member<MutationObserverRegistration>>* mutationObserverRegistry();
     HeapHashSet<Member<MutationObserverRegistration>>* transientMutationObserverRegistry();
 
     uint32_t m_nodeFlags;
     Member<ContainerNode> m_parentOrShadowHostNode;
     Member<TreeScope> m_treeScope;
     Member<Node> m_previous;
     Member<Node> m_next;
     // When a node has rare data we move the layoutObject into the rare data.
     union DataUnion {
-        DataUnion() : m_layoutObject(nullptr) { }
+        DataUnion() : m_computedStyle(nullptr) { }

[Timothy Loh, 2016/06/23 23:58:02]

I'd leave this as initializing the LayoutObject (it makes no difference to what
the compiler will do, but the main thing stored here will be the LayoutObject)

+        ComputedStyle* m_computedStyle;
         // LayoutObjects are fully owned by their DOM node. See LayoutObject's
         // LIFETIME documentation section.
         LayoutObject* m_layoutObject;
         NodeRareDataBase* m_rareData;
     } m_data;
 };
 
 inline void Node::setParentOrShadowHostNode(ContainerNode* parent)
 {
     DCHECK(isMainThread());
@@ skipping 74 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