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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/37627">37627</a></dd>
<dt>Author</dt> <dd>cwzwarich@webkit.org</dd>
<dt>Date</dt> <dd>2008-10-15 21:36:12 -0700 (Wed, 15 Oct 2008)</dd>
</dl>

<h3>Log Message</h3>
<pre>2008-10-15  Cameron Zwarich  &lt;zwarich@apple.com&gt;

        Reviewed by Maciej Stachowiak.

        Bug 21633: Avoid using a HashMap when there is only a single transition
        &lt;https://bugs.webkit.org/show_bug.cgi?id=21633&gt;

        This is a 0.8% speedup on SunSpider and between a 0.5% and 1.0% speedup
        on the V8 benchmark suite, depending on which harness we use. It will
        also slightly reduce the memory footprint of a StructureID.

        * kjs/StructureID.cpp:
        (JSC::StructureID::StructureID):
        (JSC::StructureID::~StructureID):
        (JSC::StructureID::addPropertyTransition):
        * kjs/StructureID.h:
        (JSC::StructureID::):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkJavaScriptCoreChangeLog">trunk/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkJavaScriptCorekjsStructureIDcpp">trunk/JavaScriptCore/kjs/StructureID.cpp</a></li>
<li><a href="#trunkJavaScriptCorekjsStructureIDh">trunk/JavaScriptCore/kjs/StructureID.h</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/JavaScriptCore/ChangeLog (37626 => 37627)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JavaScriptCore/ChangeLog        2008-10-16 03:09:37 UTC (rev 37626)
+++ trunk/JavaScriptCore/ChangeLog        2008-10-16 04:36:12 UTC (rev 37627)
</span><span class="lines">@@ -1,3 +1,21 @@
</span><ins>+2008-10-15  Cameron Zwarich  &lt;zwarich@apple.com&gt;
+
+        Reviewed by Maciej Stachowiak.
+
+        Bug 21633: Avoid using a HashMap when there is only a single transition
+        &lt;https://bugs.webkit.org/show_bug.cgi?id=21633&gt;
+
+        This is a 0.8% speedup on SunSpider and between a 0.5% and 1.0% speedup
+        on the V8 benchmark suite, depending on which harness we use. It will
+        also slightly reduce the memory footprint of a StructureID.
+
+        * kjs/StructureID.cpp:
+        (JSC::StructureID::StructureID):
+        (JSC::StructureID::~StructureID):
+        (JSC::StructureID::addPropertyTransition):
+        * kjs/StructureID.h:
+        (JSC::StructureID::):
+
</ins><span class="cx"> 2008-10-15  Csaba Osztrogonac  &lt;oszi@inf.u-szeged.hu&gt;
</span><span class="cx"> 
</span><span class="cx">         Reviewed by Geoffrey Garen.
</span></span></pre></div>
<a id="trunkJavaScriptCorekjsStructureIDcpp"></a>
<div class="modfile"><h4>Modified: trunk/JavaScriptCore/kjs/StructureID.cpp (37626 => 37627)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JavaScriptCore/kjs/StructureID.cpp        2008-10-16 03:09:37 UTC (rev 37626)
+++ trunk/JavaScriptCore/kjs/StructureID.cpp        2008-10-16 04:36:12 UTC (rev 37627)
</span><span class="lines">@@ -53,12 +53,15 @@
</span><span class="cx">     , m_previous(0)
</span><span class="cx">     , m_nameInPrevious(0)
</span><span class="cx">     , m_transitionCount(0)
</span><ins>+    , m_usingSingleTransitionSlot(true)
</ins><span class="cx">     , m_propertyStorageCapacity(JSObject::inlineStorageCapacity)
</span><span class="cx">     , m_cachedTransistionOffset(WTF::notFound)
</span><span class="cx"> {
</span><span class="cx">     ASSERT(m_prototype);
</span><span class="cx">     ASSERT(m_prototype-&gt;isObject() || m_prototype-&gt;isNull());
</span><span class="cx"> 
</span><ins>+    m_transitions.singleTransition = 0;
+
</ins><span class="cx"> #ifndef NDEBUG
</span><span class="cx">     if (shouldIgnoreLeaks)
</span><span class="cx">         ignoreSet.add(this);
</span><span class="lines">@@ -70,13 +73,24 @@
</span><span class="cx"> StructureID::~StructureID()
</span><span class="cx"> {
</span><span class="cx">     if (m_previous) {
</span><del>-        ASSERT(m_previous-&gt;m_transitionTable.contains(make_pair(m_nameInPrevious, m_attributesInPrevious)));
-        m_previous-&gt;m_transitionTable.remove(make_pair(m_nameInPrevious, m_attributesInPrevious));
</del><ins>+        if (m_previous-&gt;m_usingSingleTransitionSlot) {
+            m_previous-&gt;m_transitions.singleTransition-&gt;deref();
+            m_previous-&gt;m_transitions.singleTransition = 0;
+        } else {
+            ASSERT(m_previous-&gt;m_transitions.table-&gt;contains(make_pair(m_nameInPrevious, m_attributesInPrevious)));
+            m_previous-&gt;m_transitions.table-&gt;remove(make_pair(m_nameInPrevious, m_attributesInPrevious));
+        }
</ins><span class="cx">     }
</span><span class="cx"> 
</span><span class="cx">     if (m_cachedPropertyNameArrayData)
</span><span class="cx">         m_cachedPropertyNameArrayData-&gt;setCachedStructureID(0);
</span><span class="cx"> 
</span><ins>+    if (m_usingSingleTransitionSlot) {
+        if (m_transitions.singleTransition)
+            m_transitions.singleTransition-&gt;deref();
+    } else
+        delete m_transitions.table;
+
</ins><span class="cx"> #ifndef NDEBUG
</span><span class="cx">     HashSet&lt;StructureID*&gt;::iterator it = ignoreSet.find(this);
</span><span class="cx">     if (it != ignoreSet.end())
</span><span class="lines">@@ -168,10 +182,19 @@
</span><span class="cx">     ASSERT(!structureID-&gt;m_isDictionary);
</span><span class="cx">     ASSERT(structureID-&gt;typeInfo().type() == ObjectType);
</span><span class="cx"> 
</span><del>-    if (StructureID* existingTransition = structureID-&gt;m_transitionTable.get(make_pair(propertyName.ustring().rep(), attributes))) {
-        offset = existingTransition-&gt;cachedTransistionOffset();
-        ASSERT(offset != WTF::notFound);
-        return existingTransition;
</del><ins>+    if (structureID-&gt;m_usingSingleTransitionSlot) {
+        StructureID* existingTransition = structureID-&gt;m_transitions.singleTransition;
+        if (existingTransition &amp;&amp; existingTransition-&gt;m_nameInPrevious == propertyName.ustring().rep() &amp;&amp; existingTransition-&gt;m_attributesInPrevious == attributes) {
+            offset = structureID-&gt;m_transitions.singleTransition-&gt;cachedTransistionOffset();
+            ASSERT(offset != WTF::notFound);
+            return existingTransition;
+        }
+    } else {
+        if (StructureID* existingTransition = structureID-&gt;m_transitions.table-&gt;get(make_pair(propertyName.ustring().rep(), attributes))) {
+            offset = existingTransition-&gt;cachedTransistionOffset();
+            ASSERT(offset != WTF::notFound);
+            return existingTransition;
+        }        
</ins><span class="cx">     }
</span><span class="cx"> 
</span><span class="cx">     if (structureID-&gt;m_transitionCount &gt; s_maxTransitionLength) {
</span><span class="lines">@@ -198,7 +221,21 @@
</span><span class="cx"> 
</span><span class="cx">     transition-&gt;setCachedTransistionOffset(offset);
</span><span class="cx"> 
</span><del>-    structureID-&gt;m_transitionTable.add(make_pair(propertyName.ustring().rep(), attributes), transition.get());
</del><ins>+    if (structureID-&gt;m_usingSingleTransitionSlot) {
+        if (!structureID-&gt;m_transitions.singleTransition) {
+            structureID-&gt;m_transitions.singleTransition = transition.get();
+            transition-&gt;ref();
+            return transition.release();
+        }
+
+        StructureID* existingTransition = structureID-&gt;m_transitions.singleTransition;
+        structureID-&gt;m_usingSingleTransitionSlot = false;
+        TransitionTable* transitionTable = new TransitionTable;
+        structureID-&gt;m_transitions.table = transitionTable;
+        transitionTable-&gt;add(make_pair(existingTransition-&gt;m_nameInPrevious, existingTransition-&gt;m_attributesInPrevious), existingTransition);
+        existingTransition-&gt;deref();
+    }
+    structureID-&gt;m_transitions.table-&gt;add(make_pair(propertyName.ustring().rep(), attributes), transition.get());
</ins><span class="cx">     return transition.release();
</span><span class="cx"> }
</span><span class="cx"> 
</span></span></pre></div>
<a id="trunkJavaScriptCorekjsStructureIDh"></a>
<div class="modfile"><h4>Modified: trunk/JavaScriptCore/kjs/StructureID.h (37626 => 37627)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JavaScriptCore/kjs/StructureID.h        2008-10-16 03:09:37 UTC (rev 37626)
+++ trunk/JavaScriptCore/kjs/StructureID.h        2008-10-16 04:36:12 UTC (rev 37627)
</span><span class="lines">@@ -152,7 +152,11 @@
</span><span class="cx">         unsigned m_attributesInPrevious;
</span><span class="cx"> 
</span><span class="cx">         size_t m_transitionCount;
</span><del>-        TransitionTable m_transitionTable;
</del><ins>+        bool m_usingSingleTransitionSlot;
+        union {
+            StructureID* singleTransition;
+            TransitionTable* table;
+        } m_transitions;
</ins><span class="cx"> 
</span><span class="cx">         RefPtr&lt;PropertyNameArrayData&gt; m_cachedPropertyNameArrayData;
</span><span class="cx"> 
</span></span></pre>
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