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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/186986">186986</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2015-07-17 22:51:06 -0700 (Fri, 17 Jul 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>DFG should have some obvious mitigations against watching structures that are unprofitable to watch
https://bugs.webkit.org/show_bug.cgi?id=147034
Reviewed by Mark Lam and Michael Saboff.
This implements two guards against the DFG watching structures that are likely to fire
their watchpoints:
- Don't watch dictionaries or any structure that had a dictionary in its past. Dictionaries
can be flattened, and then they can transform back to dictionaries.
- Don't watch structures whose past structures were transitioned-away from while their
transition watchpoints were being watched. This property gives us monotonicity: if we
recompile because we watched structure S1 of object O, then we won't make the same mistake
again when object O has structure S2, S3, and so on.
This is a 1.5% speed-up on Kraken. It does penalize some Octane tests, but it also seems to
help some of them, so on Octane it's basically neutral.
* bytecode/Watchpoint.h:
(JSC::WatchpointSet::invalidate):
(JSC::WatchpointSet::isBeingWatched):
(JSC::WatchpointSet::addressOfState):
(JSC::WatchpointSet::addressOfSetIsNotEmpty):
(JSC::InlineWatchpointSet::touch):
(JSC::InlineWatchpointSet::isBeingWatched):
* runtime/JSGlobalObject.h:
(JSC::JSGlobalObject::createStructure):
(JSC::JSGlobalObject::registerWeakMap):
* runtime/Structure.cpp:
(JSC::Structure::Structure):
(JSC::Structure::toDictionaryTransition):
(JSC::Structure::didTransitionFromThisStructure):
* runtime/Structure.h:</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecodeWatchpointh">trunk/Source/JavaScriptCore/bytecode/Watchpoint.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSGlobalObjecth">trunk/Source/JavaScriptCore/runtime/JSGlobalObject.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeStructurecpp">trunk/Source/JavaScriptCore/runtime/Structure.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeStructureh">trunk/Source/JavaScriptCore/runtime/Structure.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (186985 => 186986)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/JavaScriptCore/ChangeLog 2015-07-18 05:51:06 UTC (rev 186986)
</span><span class="lines">@@ -1,3 +1,40 @@
</span><ins>+2015-07-17 Filip Pizlo <fpizlo@apple.com>
+
+ DFG should have some obvious mitigations against watching structures that are unprofitable to watch
+ https://bugs.webkit.org/show_bug.cgi?id=147034
+
+ Reviewed by Mark Lam and Michael Saboff.
+
+ This implements two guards against the DFG watching structures that are likely to fire
+ their watchpoints:
+
+ - Don't watch dictionaries or any structure that had a dictionary in its past. Dictionaries
+ can be flattened, and then they can transform back to dictionaries.
+
+ - Don't watch structures whose past structures were transitioned-away from while their
+ transition watchpoints were being watched. This property gives us monotonicity: if we
+ recompile because we watched structure S1 of object O, then we won't make the same mistake
+ again when object O has structure S2, S3, and so on.
+
+ This is a 1.5% speed-up on Kraken. It does penalize some Octane tests, but it also seems to
+ help some of them, so on Octane it's basically neutral.
+
+ * bytecode/Watchpoint.h:
+ (JSC::WatchpointSet::invalidate):
+ (JSC::WatchpointSet::isBeingWatched):
+ (JSC::WatchpointSet::addressOfState):
+ (JSC::WatchpointSet::addressOfSetIsNotEmpty):
+ (JSC::InlineWatchpointSet::touch):
+ (JSC::InlineWatchpointSet::isBeingWatched):
+ * runtime/JSGlobalObject.h:
+ (JSC::JSGlobalObject::createStructure):
+ (JSC::JSGlobalObject::registerWeakMap):
+ * runtime/Structure.cpp:
+ (JSC::Structure::Structure):
+ (JSC::Structure::toDictionaryTransition):
+ (JSC::Structure::didTransitionFromThisStructure):
+ * runtime/Structure.h:
+
</ins><span class="cx"> 2015-07-16 Filip Pizlo <fpizlo@apple.com>
</span><span class="cx">
</span><span class="cx"> Remove DFG::DesiredWriteBarriers because it's just a very difficult way of saying "please barrier the machine code block owner"
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecodeWatchpointh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecode/Watchpoint.h (186985 => 186986)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecode/Watchpoint.h 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/JavaScriptCore/bytecode/Watchpoint.h 2015-07-18 05:51:06 UTC (rev 186986)
</span><span class="lines">@@ -188,6 +188,11 @@
</span><span class="cx"> invalidate(StringFireDetail(reason));
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ bool isBeingWatched() const
+ {
+ return m_setIsNotEmpty;
+ }
+
</ins><span class="cx"> int8_t* addressOfState() { return &m_state; }
</span><span class="cx"> int8_t* addressOfSetIsNotEmpty() { return &m_setIsNotEmpty; }
</span><span class="cx">
</span><span class="lines">@@ -331,6 +336,13 @@
</span><span class="cx"> touch(StringFireDetail(reason));
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ bool isBeingWatched() const
+ {
+ if (isFat())
+ return fat()->isBeingWatched();
+ return false;
+ }
+
</ins><span class="cx"> private:
</span><span class="cx"> static const uintptr_t IsThinFlag = 1;
</span><span class="cx"> static const uintptr_t StateMask = 6;
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSGlobalObjecth"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSGlobalObject.h (186985 => 186986)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSGlobalObject.h 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/JavaScriptCore/runtime/JSGlobalObject.h 2015-07-18 05:51:06 UTC (rev 186986)
</span><span class="lines">@@ -613,7 +613,9 @@
</span><span class="cx">
</span><span class="cx"> static Structure* createStructure(VM& vm, JSValue prototype)
</span><span class="cx"> {
</span><del>- return Structure::create(vm, 0, prototype, TypeInfo(GlobalObjectType, StructureFlags), info());
</del><ins>+ Structure* result = Structure::create(vm, 0, prototype, TypeInfo(GlobalObjectType, StructureFlags), info());
+ result->setTransitionWatchpointIsLikelyToBeFired(true);
+ return result;
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void registerWeakMap(OpaqueJSWeakObjectMap* map)
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeStructurecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/Structure.cpp (186985 => 186986)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/Structure.cpp 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/JavaScriptCore/runtime/Structure.cpp 2015-07-18 05:51:06 UTC (rev 186986)
</span><span class="lines">@@ -171,6 +171,7 @@
</span><span class="cx"> setDidTransition(false);
</span><span class="cx"> setStaticFunctionsReified(false);
</span><span class="cx"> setHasRareData(false);
</span><ins>+ setTransitionWatchpointIsLikelyToBeFired(false);
</ins><span class="cx">
</span><span class="cx"> ASSERT(inlineCapacity <= JSFinalObject::maxInlineCapacity());
</span><span class="cx"> ASSERT(static_cast<PropertyOffset>(inlineCapacity) < firstOutOfLineOffset);
</span><span class="lines">@@ -201,6 +202,7 @@
</span><span class="cx"> setDidTransition(false);
</span><span class="cx"> setStaticFunctionsReified(false);
</span><span class="cx"> setHasRareData(false);
</span><ins>+ setTransitionWatchpointIsLikelyToBeFired(false);
</ins><span class="cx">
</span><span class="cx"> TypeInfo typeInfo = TypeInfo(CellType, StructureFlags);
</span><span class="cx"> m_blob = StructureIDBlob(vm.heap.structureIDTable().allocateID(this), 0, typeInfo);
</span><span class="lines">@@ -239,6 +241,10 @@
</span><span class="cx"> setPreviousID(vm, previous);
</span><span class="cx">
</span><span class="cx"> previous->didTransitionFromThisStructure(deferred);
</span><ins>+
+ // Copy this bit now, in case previous was being watched.
+ setTransitionWatchpointIsLikelyToBeFired(previous->transitionWatchpointIsLikelyToBeFired());
+
</ins><span class="cx"> if (previous->m_globalObject)
</span><span class="cx"> m_globalObject.set(vm, this, previous->m_globalObject.get());
</span><span class="cx"> ASSERT(hasReadOnlyOrGetterSetterPropertiesExcludingProto() || !m_classInfo->hasStaticSetterOrReadonlyProperties());
</span><span class="lines">@@ -495,6 +501,7 @@
</span><span class="cx"> transition->m_offset = structure->m_offset;
</span><span class="cx"> transition->setDictionaryKind(kind);
</span><span class="cx"> transition->pin();
</span><ins>+ transition->setTransitionWatchpointIsLikelyToBeFired(true);
</ins><span class="cx">
</span><span class="cx"> transition->checkOffsetConsistency();
</span><span class="cx"> return transition;
</span><span class="lines">@@ -975,6 +982,12 @@
</span><span class="cx">
</span><span class="cx"> void Structure::didTransitionFromThisStructure(DeferredStructureTransitionWatchpointFire* deferred) const
</span><span class="cx"> {
</span><ins>+ // If the structure is being watched, and this is the kind of structure that the DFG would
+ // like to watch, then make sure to note for all future versions of this structure that it's
+ // unwise to watch it.
+ if (m_transitionWatchpointSet.isBeingWatched())
+ const_cast<Structure*>(this)->setTransitionWatchpointIsLikelyToBeFired(true);
+
</ins><span class="cx"> if (deferred)
</span><span class="cx"> deferred->add(this);
</span><span class="cx"> else
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeStructureh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/Structure.h (186985 => 186986)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/Structure.h 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/JavaScriptCore/runtime/Structure.h 2015-07-18 05:51:06 UTC (rev 186986)
</span><span class="lines">@@ -413,6 +413,13 @@
</span><span class="cx"> // watching it. We should come up with a comprehensive story for not watching things that
</span><span class="cx"> // aren't profitable to watch.
</span><span class="cx"> // https://bugs.webkit.org/show_bug.cgi?id=133625
</span><ins>+
+ // - We don't watch Structures that either decided not to be watched, or whose predecessors
+ // decided not to be watched. This happens either when a transition is fired while being
+ // watched, or if a dictionary transition occurs.
+ if (transitionWatchpointIsLikelyToBeFired())
+ return false;
+
</ins><span class="cx"> return true;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -502,6 +509,7 @@
</span><span class="cx"> DEFINE_BITFIELD(bool, hasBeenFlattenedBefore, HasBeenFlattenedBefore, 1, 24);
</span><span class="cx"> DEFINE_BITFIELD(bool, hasCustomGetterSetterProperties, HasCustomGetterSetterProperties, 1, 25);
</span><span class="cx"> DEFINE_BITFIELD(bool, didWatchInternalProperties, DidWatchInternalProperties, 1, 26);
</span><ins>+ DEFINE_BITFIELD(bool, transitionWatchpointIsLikelyToBeFired, TransitionWatchpointIsLikelyToBeFired, 1, 27);
</ins><span class="cx">
</span><span class="cx"> private:
</span><span class="cx"> friend class LLIntOffsetsExtractor;
</span></span></pre>
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