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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/169316">169316</a></dd>
<dt>Author</dt> <dd>akling@apple.com</dd>
<dt>Date</dt> <dd>2014-05-24 20:50:43 -0700 (Sat, 24 May 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Object.prototype.toString() should use cached strings for null/undefined.
<https://webkit.org/b/133261>
Normally, when calling Object.prototype.toString() on a regular object,
we'd cache the result of the stringification on the object's structure,
making repeated calls fast.
For null and undefined, we were not as smart. We'd instead construct a
new string with either "[object Null]" or "[object Undefined]" each time.
This was exposed by Dromaeo's JS library tests, where some prototype.js
subtests generate millions of strings this way.
This patch adds two VM-permanent cached strings to the SmallStrings.
Looks like ~10% speed-up on Dromaeo/jslib-traverse-prototype.html
Reviewed by Darin Adler.
* runtime/ObjectPrototype.cpp:
(JSC::objectProtoFuncToString):
* runtime/SmallStrings.cpp:
(JSC::SmallStrings::SmallStrings):
(JSC::SmallStrings::initializeCommonStrings):
(JSC::SmallStrings::visitStrongReferences):
* runtime/SmallStrings.h:
(JSC::SmallStrings::nullObjectString):
(JSC::SmallStrings::undefinedObjectString):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeObjectPrototypecpp">trunk/Source/JavaScriptCore/runtime/ObjectPrototype.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeSmallStringscpp">trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeSmallStringsh">trunk/Source/JavaScriptCore/runtime/SmallStrings.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (169315 => 169316)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-05-25 03:30:56 UTC (rev 169315)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-05-25 03:50:43 UTC (rev 169316)
</span><span class="lines">@@ -1,3 +1,33 @@
</span><ins>+2014-05-24 Andreas Kling <akling@apple.com>
+
+ Object.prototype.toString() should use cached strings for null/undefined.
+ <https://webkit.org/b/133261>
+
+ Normally, when calling Object.prototype.toString() on a regular object,
+ we'd cache the result of the stringification on the object's structure,
+ making repeated calls fast.
+
+ For null and undefined, we were not as smart. We'd instead construct a
+ new string with either "[object Null]" or "[object Undefined]" each time.
+
+ This was exposed by Dromaeo's JS library tests, where some prototype.js
+ subtests generate millions of strings this way.
+
+ This patch adds two VM-permanent cached strings to the SmallStrings.
+ Looks like ~10% speed-up on Dromaeo/jslib-traverse-prototype.html
+
+ Reviewed by Darin Adler.
+
+ * runtime/ObjectPrototype.cpp:
+ (JSC::objectProtoFuncToString):
+ * runtime/SmallStrings.cpp:
+ (JSC::SmallStrings::SmallStrings):
+ (JSC::SmallStrings::initializeCommonStrings):
+ (JSC::SmallStrings::visitStrongReferences):
+ * runtime/SmallStrings.h:
+ (JSC::SmallStrings::nullObjectString):
+ (JSC::SmallStrings::undefinedObjectString):
+
</ins><span class="cx"> 2014-05-23 Mark Hahnenberg <mhahnenberg@apple.com>
</span><span class="cx">
</span><span class="cx"> Remove operationCallGetter
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeObjectPrototypecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/ObjectPrototype.cpp (169315 => 169316)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/ObjectPrototype.cpp 2014-05-25 03:30:56 UTC (rev 169315)
+++ trunk/Source/JavaScriptCore/runtime/ObjectPrototype.cpp 2014-05-25 03:50:43 UTC (rev 169316)
</span><span class="lines">@@ -215,7 +215,7 @@
</span><span class="cx"> VM& vm = exec->vm();
</span><span class="cx"> JSValue thisValue = exec->thisValue().toThis(exec, StrictMode);
</span><span class="cx"> if (thisValue.isUndefinedOrNull())
</span><del>- return JSValue::encode(jsNontrivialString(&vm, String(thisValue.isUndefined() ? ASCIILiteral("[object Undefined]") : ASCIILiteral("[object Null]"))));
</del><ins>+ return JSValue::encode(thisValue.isUndefined() ? vm.smallStrings.undefinedObjectString() : vm.smallStrings.nullObjectString());
</ins><span class="cx"> JSObject* thisObject = thisValue.toObject(exec);
</span><span class="cx">
</span><span class="cx"> JSString* result = thisObject->structure(vm)->objectToStringValue();
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeSmallStringscpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp (169315 => 169316)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp 2014-05-25 03:30:56 UTC (rev 169315)
+++ trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp 2014-05-25 03:50:43 UTC (rev 169316)
</span><span class="lines">@@ -67,6 +67,8 @@
</span><span class="cx"> #define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) , m_##name(0)
</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><ins>+ , m_nullObjectString(nullptr)
+ , m_undefinedObjectString(nullptr)
</ins><span class="cx"> {
</span><span class="cx"> COMPILE_ASSERT(singleCharacterStringCount == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
</span><span class="cx">
</span><span class="lines">@@ -82,6 +84,8 @@
</span><span class="cx"> #define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) initialize(&vm, m_##name, #name);
</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><ins>+ initialize(&vm, m_nullObjectString, "[object Null]");
+ initialize(&vm, m_undefinedObjectString, "[object Undefined]");
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void SmallStrings::visitStrongReferences(SlotVisitor& visitor)
</span><span class="lines">@@ -92,6 +96,8 @@
</span><span class="cx"> #define JSC_COMMON_STRINGS_ATTRIBUTE_VISIT(name) visitor.appendUnbarrieredPointer(&m_##name);
</span><span class="cx"> JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_VISIT)
</span><span class="cx"> #undef JSC_COMMON_STRINGS_ATTRIBUTE_VISIT
</span><ins>+ visitor.appendUnbarrieredPointer(&m_nullObjectString);
+ visitor.appendUnbarrieredPointer(&m_undefinedObjectString);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> SmallStrings::~SmallStrings()
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeSmallStringsh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/SmallStrings.h (169315 => 169316)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/SmallStrings.h 2014-05-25 03:30:56 UTC (rev 169315)
+++ trunk/Source/JavaScriptCore/runtime/SmallStrings.h 2014-05-25 03:50:43 UTC (rev 169316)
</span><span class="lines">@@ -86,6 +86,9 @@
</span><span class="cx"> JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ACCESSOR_DEFINITION)
</span><span class="cx"> #undef JSC_COMMON_STRINGS_ACCESSOR_DEFINITION
</span><span class="cx">
</span><ins>+ JSString* nullObjectString() const { return m_nullObjectString; }
+ JSString* undefinedObjectString() const { return m_undefinedObjectString; }
+
</ins><span class="cx"> private:
</span><span class="cx"> static const unsigned singleCharacterStringCount = maxSingleCharacterString + 1;
</span><span class="cx">
</span><span class="lines">@@ -98,6 +101,8 @@
</span><span class="cx"> #define JSC_COMMON_STRINGS_ATTRIBUTE_DECLARATION(name) JSString* m_##name;
</span><span class="cx"> JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_DECLARATION)
</span><span class="cx"> #undef JSC_COMMON_STRINGS_ATTRIBUTE_DECLARATION
</span><ins>+ JSString* m_nullObjectString;
+ JSString* m_undefinedObjectString;
</ins><span class="cx"> JSString* m_singleCharacterStrings[singleCharacterStringCount];
</span><span class="cx"> OwnPtr<SmallStringsStorage> m_storage;
</span><span class="cx"> };
</span></span></pre>
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