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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/169816">169816</a></dd>
<dt>Author</dt> <dd>rniwa@webkit.org</dd>
<dt>Date</dt> <dd>2014-06-11 12:29:51 -0700 (Wed, 11 Jun 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Structure::get should instantiate DeferGC only when materializing property map
https://bugs.webkit.org/show_bug.cgi?id=133727
Reviewed by Geoffrey Garen.
DeferGC instances in Structure::get was added in http://trac.webkit.org/<a href="http://trac.webkit.org/projects/webkit/changeset/157539">r157539</a> in order to avoid
collecting the property table newly created by materializePropertyMapIfNecessary since GC can happen
when GCSafeConcurrentJITLocker goes out of scope.
However, always instantiating DeferGC inside Structure::get introduced a new performance bottleneck
in JSObject::getPropertySlot because frequently incrementing and decrementing a counter in vm.m_heap
and running a release assertion inside Heap::incrementDeferralDepth() is expensive.
Work around this by instantiating DeferGC only when we're actually calling materializePropertyMap,
and immediately storing a pointer to the newly created property table in the stack before DeferGC
goes out of scope so that the property table will be marked.
This shows 13-16% improvement on the microbenchmark attached in the bug.
* runtime/JSCJSValue.cpp:
* runtime/JSObject.h:
(JSC::JSObject::fastGetOwnPropertySlot):
* runtime/Structure.h:
(JSC::Structure::materializePropertyMapIfNecessary):
* runtime/StructureInlines.h:
(JSC::Structure::get):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSCJSValuecpp">trunk/Source/JavaScriptCore/runtime/JSCJSValue.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSObjecth">trunk/Source/JavaScriptCore/runtime/JSObject.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeStructureh">trunk/Source/JavaScriptCore/runtime/Structure.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeStructureInlinesh">trunk/Source/JavaScriptCore/runtime/StructureInlines.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (169815 => 169816)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-06-11 18:40:13 UTC (rev 169815)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-06-11 19:29:51 UTC (rev 169816)
</span><span class="lines">@@ -1,3 +1,32 @@
</span><ins>+2014-06-11 Ryosuke Niwa <rniwa@webkit.org>
+
+ Structure::get should instantiate DeferGC only when materializing property map
+ https://bugs.webkit.org/show_bug.cgi?id=133727
+
+ Reviewed by Geoffrey Garen.
+
+ DeferGC instances in Structure::get was added in http://trac.webkit.org/r157539 in order to avoid
+ collecting the property table newly created by materializePropertyMapIfNecessary since GC can happen
+ when GCSafeConcurrentJITLocker goes out of scope.
+
+ However, always instantiating DeferGC inside Structure::get introduced a new performance bottleneck
+ in JSObject::getPropertySlot because frequently incrementing and decrementing a counter in vm.m_heap
+ and running a release assertion inside Heap::incrementDeferralDepth() is expensive.
+
+ Work around this by instantiating DeferGC only when we're actually calling materializePropertyMap,
+ and immediately storing a pointer to the newly created property table in the stack before DeferGC
+ goes out of scope so that the property table will be marked.
+
+ This shows 13-16% improvement on the microbenchmark attached in the bug.
+
+ * runtime/JSCJSValue.cpp:
+ * runtime/JSObject.h:
+ (JSC::JSObject::fastGetOwnPropertySlot):
+ * runtime/Structure.h:
+ (JSC::Structure::materializePropertyMapIfNecessary):
+ * runtime/StructureInlines.h:
+ (JSC::Structure::get):
+
</ins><span class="cx"> 2014-06-11 Andreas Kling <akling@apple.com>
</span><span class="cx">
</span><span class="cx"> Some JSValue::get() micro-optimzations.
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSCJSValuecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSCJSValue.cpp (169815 => 169816)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSCJSValue.cpp 2014-06-11 18:40:13 UTC (rev 169815)
+++ trunk/Source/JavaScriptCore/runtime/JSCJSValue.cpp 2014-06-11 19:29:51 UTC (rev 169816)
</span><span class="lines">@@ -34,6 +34,7 @@
</span><span class="cx"> #include "JSGlobalObject.h"
</span><span class="cx"> #include "JSNotAnObject.h"
</span><span class="cx"> #include "NumberObject.h"
</span><ins>+#include "StructureInlines.h"
</ins><span class="cx"> #include <wtf/MathExtras.h>
</span><span class="cx"> #include <wtf/StringExtras.h>
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSObjecth"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSObject.h (169815 => 169816)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSObject.h 2014-06-11 18:40:13 UTC (rev 169815)
+++ trunk/Source/JavaScriptCore/runtime/JSObject.h 2014-06-11 19:29:51 UTC (rev 169816)
</span><span class="lines">@@ -1256,7 +1256,7 @@
</span><span class="cx">
</span><span class="cx"> ALWAYS_INLINE bool JSObject::fastGetOwnPropertySlot(ExecState* exec, VM& vm, Structure& structure, PropertyName propertyName, PropertySlot& slot)
</span><span class="cx"> {
</span><del>- if (!TypeInfo::overridesGetOwnPropertySlot(inlineTypeFlags()))
</del><ins>+ if (LIKELY(!TypeInfo::overridesGetOwnPropertySlot(inlineTypeFlags())))
</ins><span class="cx"> return asObject(this)->inlineGetOwnPropertySlot(vm, structure, propertyName, slot);
</span><span class="cx"> return structure.classInfo()->methodTable.getOwnPropertySlot(this, exec, propertyName, slot);
</span><span class="cx"> }
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeStructureh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/Structure.h (169815 => 169816)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/Structure.h 2014-06-11 18:40:13 UTC (rev 169815)
+++ trunk/Source/JavaScriptCore/runtime/Structure.h 2014-06-11 19:29:51 UTC (rev 169816)
</span><span class="lines">@@ -434,6 +434,18 @@
</span><span class="cx"> if (!propertyTable() && previousID())
</span><span class="cx"> materializePropertyMap(vm);
</span><span class="cx"> }
</span><ins>+ void materializePropertyMapIfNecessary(VM& vm, PropertyTable*& table)
+ {
+ ASSERT(!isCompilationThread());
+ ASSERT(structure()->classInfo() == info());
+ ASSERT(checkOffsetConsistency());
+ table = propertyTable().get();
+ if (!table && previousID()) {
+ DeferGC deferGC(vm.heap);
+ materializePropertyMap(vm);
+ table = propertyTable().get();
+ }
+ }
</ins><span class="cx"> void materializePropertyMapIfNecessaryForPinning(VM& vm, DeferGC&)
</span><span class="cx"> {
</span><span class="cx"> ASSERT(structure()->classInfo() == info());
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeStructureInlinesh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/StructureInlines.h (169815 => 169816)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/StructureInlines.h 2014-06-11 18:40:13 UTC (rev 169815)
+++ trunk/Source/JavaScriptCore/runtime/StructureInlines.h 2014-06-11 19:29:51 UTC (rev 169816)
</span><span class="lines">@@ -77,12 +77,12 @@
</span><span class="cx"> {
</span><span class="cx"> ASSERT(!isCompilationThread());
</span><span class="cx"> ASSERT(structure()->classInfo() == info());
</span><del>- DeferGC deferGC(vm.heap);
- materializePropertyMapIfNecessary(vm, deferGC);
- if (!propertyTable())
</del><ins>+ PropertyTable* propertyTable;
+ materializePropertyMapIfNecessary(vm, propertyTable);
+ if (!propertyTable)
</ins><span class="cx"> return invalidOffset;
</span><span class="cx">
</span><del>- PropertyMapEntry* entry = propertyTable()->get(propertyName.uid());
</del><ins>+ PropertyMapEntry* entry = propertyTable->get(propertyName.uid());
</ins><span class="cx"> return entry ? entry->offset : invalidOffset;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -90,12 +90,12 @@
</span><span class="cx"> {
</span><span class="cx"> ASSERT(!isCompilationThread());
</span><span class="cx"> ASSERT(structure()->classInfo() == info());
</span><del>- DeferGC deferGC(vm.heap);
- materializePropertyMapIfNecessary(vm, deferGC);
- if (!propertyTable())
</del><ins>+ PropertyTable* propertyTable;
+ materializePropertyMapIfNecessary(vm, propertyTable);
+ if (!propertyTable)
</ins><span class="cx"> return invalidOffset;
</span><span class="cx">
</span><del>- PropertyMapEntry* entry = propertyTable()->findWithString(name.impl()).first;
</del><ins>+ PropertyMapEntry* entry = propertyTable->findWithString(name.impl()).first;
</ins><span class="cx"> return entry ? entry->offset : invalidOffset;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -104,12 +104,12 @@
</span><span class="cx"> ASSERT(!isCompilationThread());
</span><span class="cx"> ASSERT(structure()->classInfo() == info());
</span><span class="cx">
</span><del>- DeferGC deferGC(vm.heap);
- materializePropertyMapIfNecessary(vm, deferGC);
- if (!propertyTable())
</del><ins>+ PropertyTable* propertyTable;
+ materializePropertyMapIfNecessary(vm, propertyTable);
+ if (!propertyTable)
</ins><span class="cx"> return invalidOffset;
</span><span class="cx">
</span><del>- PropertyMapEntry* entry = propertyTable()->get(propertyName.uid());
</del><ins>+ PropertyMapEntry* entry = propertyTable->get(propertyName.uid());
</ins><span class="cx"> if (!entry)
</span><span class="cx"> return invalidOffset;
</span><span class="cx">
</span></span></pre>
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