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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/243686">243686</a></dd>
<dt>Author</dt> <dd>rniwa@webkit.org</dd>
<dt>Date</dt> <dd>2019-03-31 19:03:14 -0700 (Sun, 31 Mar 2019)</dd>
</dl>

<h3>Log Message</h3>
<pre>Reduce the size of Node::deref by eliminating an explicit parentNode check
https://bugs.webkit.org/show_bug.cgi?id=195776

Reviewed by Darin Adler.

Address post-commit review comments.

* dom/Document.cpp:
(WebCore::Document::removedLastRef):
* dom/Node.cpp:
(WebCore::Node::~Node):
(WebCore::Node::removedLastRef):
* dom/Node.h:
(WebCore::Node::deref):
(WebCore::Node::setParentNode):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoredomDocumentcpp">trunk/Source/WebCore/dom/Document.cpp</a></li>
<li><a href="#trunkSourceWebCoredomNodecpp">trunk/Source/WebCore/dom/Node.cpp</a></li>
<li><a href="#trunkSourceWebCoredomNodeh">trunk/Source/WebCore/dom/Node.h</a></li>
</ul>

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<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (243685 => 243686)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog   2019-04-01 01:38:09 UTC (rev 243685)
+++ trunk/Source/WebCore/ChangeLog      2019-04-01 02:03:14 UTC (rev 243686)
</span><span class="lines">@@ -1,3 +1,21 @@
</span><ins>+2019-03-31  Ryosuke Niwa  <rniwa@webkit.org>
+
+        Reduce the size of Node::deref by eliminating an explicit parentNode check
+        https://bugs.webkit.org/show_bug.cgi?id=195776
+
+        Reviewed by Darin Adler.
+
+        Address post-commit review comments.
+
+        * dom/Document.cpp:
+        (WebCore::Document::removedLastRef):
+        * dom/Node.cpp:
+        (WebCore::Node::~Node):
+        (WebCore::Node::removedLastRef):
+        * dom/Node.h:
+        (WebCore::Node::deref):
+        (WebCore::Node::setParentNode):
+
</ins><span class="cx"> 2019-03-31  Sam Weinig  <weinig@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Remove more i386 specific configurations
</span></span></pre></div>
<a id="trunkSourceWebCoredomDocumentcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/dom/Document.cpp (243685 => 243686)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/dom/Document.cpp    2019-04-01 01:38:09 UTC (rev 243685)
+++ trunk/Source/WebCore/dom/Document.cpp       2019-04-01 02:03:14 UTC (rev 243686)
</span><span class="lines">@@ -668,7 +668,7 @@
</span><span class="cx">     ASSERT(!m_deletionHasBegun);
</span><span class="cx">     if (m_referencingNodeCount) {
</span><span class="cx">         // Node::removedLastRef doesn't set refCount() to zero because it's not observable.
</span><del>-        // But we need to remember that our refCount reached zero in subsequent calls to decrementReferencingNodeCount()
</del><ins>+        // But we need to remember that our refCount reached zero in subsequent calls to decrementReferencingNodeCount().
</ins><span class="cx">         m_refCountAndParentBit = 0;
</span><span class="cx"> 
</span><span class="cx">         // If removing a child removes the last node reference, we don't want the scope to be destroyed
</span></span></pre></div>
<a id="trunkSourceWebCoredomNodecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/dom/Node.cpp (243685 => 243686)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/dom/Node.cpp        2019-04-01 01:38:09 UTC (rev 243685)
+++ trunk/Source/WebCore/dom/Node.cpp   2019-04-01 02:03:14 UTC (rev 243686)
</span><span class="lines">@@ -332,8 +332,6 @@
</span><span class="cx"> Node::~Node()
</span><span class="cx"> {
</span><span class="cx">     ASSERT(isMainThread());
</span><del>-    // We set m_refCount to 2 before calling delete to avoid double destruction through use of Ref<T>/RefPtr<T>.
-    // This is a security mitigation in case of programmer errorm (caught by a debug assertion).
</del><span class="cx">     ASSERT(m_refCountAndParentBit == s_refCountIncrement);
</span><span class="cx">     ASSERT(m_deletionHasBegun);
</span><span class="cx">     ASSERT(!m_adoptionIsRequired);
</span><span class="lines">@@ -2514,8 +2512,6 @@
</span><span class="cx"> // delete a Node at each deref call site.
</span><span class="cx"> void Node::removedLastRef()
</span><span class="cx"> {
</span><del>-    // This avoids double destruction even when there is a programming error to use Ref<T> / RefPtr<T> on this node.
-    // There are debug assertions in Node::ref() / Node::deref() to catch such a programming error.
</del><span class="cx">     ASSERT(m_refCountAndParentBit == s_refCountIncrement);
</span><span class="cx"> 
</span><span class="cx">     // An explicit check for Document here is better than a virtual function since it is
</span></span></pre></div>
<a id="trunkSourceWebCoredomNodeh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/dom/Node.h (243685 => 243686)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/dom/Node.h  2019-04-01 01:38:09 UTC (rev 243685)
+++ trunk/Source/WebCore/dom/Node.h     2019-04-01 02:03:14 UTC (rev 243686)
</span><span class="lines">@@ -618,7 +618,7 @@
</span><span class="cx">     Node(Document&, ConstructionType);
</span><span class="cx"> 
</span><span class="cx">     static constexpr uint32_t s_refCountIncrement = 2;
</span><del>-    static constexpr uint32_t s_refCountMask = ~static_cast<uint32_t>(0x1);
</del><ins>+    static constexpr uint32_t s_refCountMask = ~static_cast<uint32_t>(1);
</ins><span class="cx"> 
</span><span class="cx">     virtual void addSubresourceAttributeURLs(ListHashSet<URL>&) const { }
</span><span class="cx"> 
</span><span class="lines">@@ -707,8 +707,10 @@
</span><span class="cx">     ASSERT(!m_deletionHasBegun);
</span><span class="cx">     ASSERT(!m_inRemovedLastRefFunction);
</span><span class="cx">     ASSERT(!m_adoptionIsRequired);
</span><del>-    auto tempRefCount = m_refCountAndParentBit - s_refCountIncrement;
-    if (!tempRefCount) {
</del><ins>+    auto updatedRefCount = m_refCountAndParentBit - s_refCountIncrement;
+    if (!updatedRefCount) {
+        // Don't update m_refCountAndParentBit to avoid double destruction through use of Ref<T>/RefPtr<T>.
+        // (This is a security mitigation in case of programmer error. It will ASSERT in debug builds.)
</ins><span class="cx"> #ifndef NDEBUG
</span><span class="cx">         m_inRemovedLastRefFunction = true;
</span><span class="cx"> #endif
</span><span class="lines">@@ -715,7 +717,7 @@
</span><span class="cx">         removedLastRef();
</span><span class="cx">         return;
</span><span class="cx">     }
</span><del>-    m_refCountAndParentBit = tempRefCount;
</del><ins>+    m_refCountAndParentBit = updatedRefCount;
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> ALWAYS_INLINE bool Node::hasOneRef() const
</span><span class="lines">@@ -741,8 +743,7 @@
</span><span class="cx"> {
</span><span class="cx">     ASSERT(isMainThread());
</span><span class="cx">     m_parentNode = parent;
</span><del>-    auto refCountWithoutParentBit = m_refCountAndParentBit & s_refCountMask;
-    m_refCountAndParentBit = refCountWithoutParentBit | !!parent;
</del><ins>+    m_refCountAndParentBit = (m_refCountAndParentBit & s_refCountMask) | !!parent;
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> inline ContainerNode* Node::parentNode() const
</span></span></pre>
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