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<title>[201738] trunk/Source/WTF</title>
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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/201738">201738</a></dd>
<dt>Author</dt> <dd>sbarati@apple.com</dd>
<dt>Date</dt> <dd>2016-06-06 20:24:54 -0700 (Mon, 06 Jun 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>equal(StringView, StringView) for strings should have a fast path for pointer equality
https://bugs.webkit.org/show_bug.cgi?id=158452
Reviewed by Andreas Kling.
JSBench does a lot of StringView::operator== on StringViews that have
the same underlying characters pointer. This becomes hot inside JSBench
because JSBench heavily stresses JSC's UnlinkedCodeCache with a high
hit rate. This means that when we get a hit in the cache, we used to
do the long form of string compare. However, we were often comparing
two StringViews that had the same underlying buffer and length.
This patch speeds this case up to run in constant time instead of
linear time.
* wtf/text/StringCommon.h:
(WTF::equalCommon):
* wtf/text/StringImpl.h:
(WTF::StringImpl::StringImpl):
(WTF::StringImpl::data):
* wtf/text/StringView.h:
(WTF::StringView::data):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtftextStringViewh">trunk/Source/WTF/wtf/text/StringView.h</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (201737 => 201738)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog 2016-06-07 03:02:06 UTC (rev 201737)
+++ trunk/Source/WTF/ChangeLog 2016-06-07 03:24:54 UTC (rev 201738)
</span><span class="lines">@@ -1,3 +1,27 @@
</span><ins>+2016-06-06 Saam Barati <sbarati@apple.com>
+
+ equal(StringView, StringView) for strings should have a fast path for pointer equality
+ https://bugs.webkit.org/show_bug.cgi?id=158452
+
+ Reviewed by Andreas Kling.
+
+ JSBench does a lot of StringView::operator== on StringViews that have
+ the same underlying characters pointer. This becomes hot inside JSBench
+ because JSBench heavily stresses JSC's UnlinkedCodeCache with a high
+ hit rate. This means that when we get a hit in the cache, we used to
+ do the long form of string compare. However, we were often comparing
+ two StringViews that had the same underlying buffer and length.
+ This patch speeds this case up to run in constant time instead of
+ linear time.
+
+ * wtf/text/StringCommon.h:
+ (WTF::equalCommon):
+ * wtf/text/StringImpl.h:
+ (WTF::StringImpl::StringImpl):
+ (WTF::StringImpl::data):
+ * wtf/text/StringView.h:
+ (WTF::StringView::data):
+
</ins><span class="cx"> 2016-06-04 Anders Carlsson <andersca@apple.com>
</span><span class="cx">
</span><span class="cx"> Get rid of WorkItemWin
</span></span></pre></div>
<a id="trunkSourceWTFwtftextStringViewh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/text/StringView.h (201737 => 201738)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/text/StringView.h 2016-06-07 03:02:06 UTC (rev 201737)
+++ trunk/Source/WTF/wtf/text/StringView.h 2016-06-07 03:24:54 UTC (rev 201738)
</span><span class="lines">@@ -135,6 +135,8 @@
</span><span class="cx"> struct UnderlyingString;
</span><span class="cx">
</span><span class="cx"> private:
</span><ins>+ friend bool equal(StringView, StringView);
+
</ins><span class="cx"> void initialize(const LChar*, unsigned length);
</span><span class="cx"> void initialize(const UChar*, unsigned length);
</span><span class="cx">
</span><span class="lines">@@ -525,6 +527,11 @@
</span><span class="cx">
</span><span class="cx"> inline bool equal(StringView a, StringView b)
</span><span class="cx"> {
</span><ins>+ if (a.m_characters == b.m_characters) {
+ ASSERT(a.is8Bit() == b.is8Bit());
+ return a.length() == b.length();
+ }
+
</ins><span class="cx"> return equalCommon(a, b);
</span><span class="cx"> }
</span><span class="cx">
</span></span></pre>
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