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<title>[163737] trunk/Source/JavaScriptCore</title>
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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/163737">163737</a></dd>
<dt>Author</dt> <dd>andersca@apple.com</dd>
<dt>Date</dt> <dd>2014-02-08 19:51:46 -0800 (Sat, 08 Feb 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Simplify single character substrings in JSC
https://bugs.webkit.org/show_bug.cgi?id=128483
Reviewed by Andreas Kling.
With the recent work to make StringImpl occupy less space, it is actually more
efficient to allocate a single character string that it is to use createSubstringSharingImpl!
* runtime/JSString.h:
(JSC::jsSingleCharacterString):
(JSC::jsSingleCharacterSubstring):
(JSC::jsString):
(JSC::jsSubstring8):
* runtime/SmallStrings.cpp:
(JSC::SmallStringsStorage::SmallStringsStorage):
(JSC::SmallStrings::SmallStrings):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSStringh">trunk/Source/JavaScriptCore/runtime/JSString.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeSmallStringscpp">trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (163736 => 163737)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-02-09 03:36:56 UTC (rev 163736)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-02-09 03:51:46 UTC (rev 163737)
</span><span class="lines">@@ -1,3 +1,22 @@
</span><ins>+2014-02-08 Anders Carlsson <andersca@apple.com>
+
+ Simplify single character substrings in JSC
+ https://bugs.webkit.org/show_bug.cgi?id=128483
+
+ Reviewed by Andreas Kling.
+
+ With the recent work to make StringImpl occupy less space, it is actually more
+ efficient to allocate a single character string that it is to use createSubstringSharingImpl!
+
+ * runtime/JSString.h:
+ (JSC::jsSingleCharacterString):
+ (JSC::jsSingleCharacterSubstring):
+ (JSC::jsString):
+ (JSC::jsSubstring8):
+ * runtime/SmallStrings.cpp:
+ (JSC::SmallStringsStorage::SmallStringsStorage):
+ (JSC::SmallStrings::SmallStrings):
+
</ins><span class="cx"> 2014-02-08 Mark Hahnenberg <mhahnenberg@apple.com>
</span><span class="cx">
</span><span class="cx"> Baseline JIT uses the wrong version of checkMarkWord in emitWriteBarrier
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSStringh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSString.h (163736 => 163737)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSString.h 2014-02-09 03:36:56 UTC (rev 163736)
+++ trunk/Source/JavaScriptCore/runtime/JSString.h 2014-02-09 03:51:46 UTC (rev 163737)
</span><span class="lines">@@ -350,7 +350,7 @@
</span><span class="cx"> {
</span><span class="cx"> if (c <= maxSingleCharacterString)
</span><span class="cx"> return vm->smallStrings.singleCharacterString(c);
</span><del>- return JSString::create(*vm, String(&c, 1).impl());
</del><ins>+ return JSString::create(*vm, StringImpl::create(&c, 1));
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> ALWAYS_INLINE JSString* jsSingleCharacterSubstring(ExecState* exec, const String& s, unsigned offset)
</span><span class="lines">@@ -358,9 +358,8 @@
</span><span class="cx"> VM* vm = &exec->vm();
</span><span class="cx"> ASSERT(offset < static_cast<unsigned>(s.length()));
</span><span class="cx"> UChar c = s.characterAt(offset);
</span><del>- if (c <= maxSingleCharacterString)
- return vm->smallStrings.singleCharacterString(c);
- return JSString::create(*vm, StringImpl::createSubstringSharingImpl(s.impl(), offset, 1));
</del><ins>+
+ return jsSingleCharacterString(vm, c);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> inline JSString* jsNontrivialString(VM* vm, const String& s)
</span><span class="lines">@@ -399,8 +398,7 @@
</span><span class="cx"> return vm->smallStrings.emptyString();
</span><span class="cx"> if (size == 1) {
</span><span class="cx"> UChar c = s.characterAt(0);
</span><del>- if (c <= maxSingleCharacterString)
- return vm->smallStrings.singleCharacterString(c);
</del><ins>+ return jsSingleCharacterString(vm, c);
</ins><span class="cx"> }
</span><span class="cx"> return JSString::create(*vm, s.impl());
</span><span class="cx"> }
</span><span class="lines">@@ -425,8 +423,7 @@
</span><span class="cx"> return vm->smallStrings.emptyString();
</span><span class="cx"> if (length == 1) {
</span><span class="cx"> UChar c = s.characterAt(offset);
</span><del>- if (c <= maxSingleCharacterString)
- return vm->smallStrings.singleCharacterString(c);
</del><ins>+ return jsSingleCharacterString(vm, c);
</ins><span class="cx"> }
</span><span class="cx"> return JSString::createHasOtherOwner(*vm, StringImpl::createSubstringSharingImpl8(s.impl(), offset, length));
</span><span class="cx"> }
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeSmallStringscpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp (163736 => 163737)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp 2014-02-09 03:36:56 UTC (rev 163736)
+++ trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp 2014-02-09 03:51:46 UTC (rev 163737)
</span><span class="lines">@@ -54,11 +54,9 @@
</span><span class="cx">
</span><span class="cx"> SmallStringsStorage::SmallStringsStorage()
</span><span class="cx"> {
</span><del>- LChar* characterBuffer = 0;
- RefPtr<StringImpl> baseString = StringImpl::createUninitialized(singleCharacterStringCount, characterBuffer);
</del><span class="cx"> for (unsigned i = 0; i < singleCharacterStringCount; ++i) {
</span><del>- characterBuffer[i] = i;
- m_reps[i] = StringImpl::createSubstringSharingImpl(baseString, i, 1);
</del><ins>+ LChar character = i;
+ m_reps[i] = StringImpl::create(&character, 1);
</ins><span class="cx"> }
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -68,10 +66,10 @@
</span><span class="cx"> JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
</span><span class="cx"> #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
</span><span class="cx"> {
</span><del>- COMPILE_ASSERT(singleCharacterStringCount == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
</del><ins>+ static_assert(singleCharacterStringCount == WTF_ARRAY_LENGTH(m_singleCharacterStrings), "");
</ins><span class="cx">
</span><span class="cx"> for (unsigned i = 0; i < singleCharacterStringCount; ++i)
</span><del>- m_singleCharacterStrings[i] = 0;
</del><ins>+ m_singleCharacterStrings[i] = nullptr;
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void SmallStrings::initializeCommonStrings(VM& vm)
</span></span></pre>
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