- Revision
- 186986
- Author
- [email protected]
- Date
- 2015-07-17 22:51:06 -0700 (Fri, 17 Jul 2015)
Log Message
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:
Modified Paths
Diff
Modified: trunk/Source/_javascript_Core/ChangeLog (186985 => 186986)
--- trunk/Source/_javascript_Core/ChangeLog 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/_javascript_Core/ChangeLog 2015-07-18 05:51:06 UTC (rev 186986)
@@ -1,3 +1,40 @@
+2015-07-17 Filip Pizlo <[email protected]>
+
+ 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:
+
2015-07-16 Filip Pizlo <[email protected]>
Remove DFG::DesiredWriteBarriers because it's just a very difficult way of saying "please barrier the machine code block owner"
Modified: trunk/Source/_javascript_Core/bytecode/Watchpoint.h (186985 => 186986)
--- trunk/Source/_javascript_Core/bytecode/Watchpoint.h 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/_javascript_Core/bytecode/Watchpoint.h 2015-07-18 05:51:06 UTC (rev 186986)
@@ -188,6 +188,11 @@
invalidate(StringFireDetail(reason));
}
+ bool isBeingWatched() const
+ {
+ return m_setIsNotEmpty;
+ }
+
int8_t* addressOfState() { return &m_state; }
int8_t* addressOfSetIsNotEmpty() { return &m_setIsNotEmpty; }
@@ -331,6 +336,13 @@
touch(StringFireDetail(reason));
}
+ bool isBeingWatched() const
+ {
+ if (isFat())
+ return fat()->isBeingWatched();
+ return false;
+ }
+
private:
static const uintptr_t IsThinFlag = 1;
static const uintptr_t StateMask = 6;
Modified: trunk/Source/_javascript_Core/runtime/JSGlobalObject.h (186985 => 186986)
--- trunk/Source/_javascript_Core/runtime/JSGlobalObject.h 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/_javascript_Core/runtime/JSGlobalObject.h 2015-07-18 05:51:06 UTC (rev 186986)
@@ -613,7 +613,9 @@
static Structure* createStructure(VM& vm, JSValue prototype)
{
- return Structure::create(vm, 0, prototype, TypeInfo(GlobalObjectType, StructureFlags), info());
+ Structure* result = Structure::create(vm, 0, prototype, TypeInfo(GlobalObjectType, StructureFlags), info());
+ result->setTransitionWatchpointIsLikelyToBeFired(true);
+ return result;
}
void registerWeakMap(OpaqueJSWeakObjectMap* map)
Modified: trunk/Source/_javascript_Core/runtime/Structure.cpp (186985 => 186986)
--- trunk/Source/_javascript_Core/runtime/Structure.cpp 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/_javascript_Core/runtime/Structure.cpp 2015-07-18 05:51:06 UTC (rev 186986)
@@ -171,6 +171,7 @@
setDidTransition(false);
setStaticFunctionsReified(false);
setHasRareData(false);
+ setTransitionWatchpointIsLikelyToBeFired(false);
ASSERT(inlineCapacity <= JSFinalObject::maxInlineCapacity());
ASSERT(static_cast<PropertyOffset>(inlineCapacity) < firstOutOfLineOffset);
@@ -201,6 +202,7 @@
setDidTransition(false);
setStaticFunctionsReified(false);
setHasRareData(false);
+ setTransitionWatchpointIsLikelyToBeFired(false);
TypeInfo typeInfo = TypeInfo(CellType, StructureFlags);
m_blob = StructureIDBlob(vm.heap.structureIDTable().allocateID(this), 0, typeInfo);
@@ -239,6 +241,10 @@
setPreviousID(vm, previous);
previous->didTransitionFromThisStructure(deferred);
+
+ // Copy this bit now, in case previous was being watched.
+ setTransitionWatchpointIsLikelyToBeFired(previous->transitionWatchpointIsLikelyToBeFired());
+
if (previous->m_globalObject)
m_globalObject.set(vm, this, previous->m_globalObject.get());
ASSERT(hasReadOnlyOrGetterSetterPropertiesExcludingProto() || !m_classInfo->hasStaticSetterOrReadonlyProperties());
@@ -495,6 +501,7 @@
transition->m_offset = structure->m_offset;
transition->setDictionaryKind(kind);
transition->pin();
+ transition->setTransitionWatchpointIsLikelyToBeFired(true);
transition->checkOffsetConsistency();
return transition;
@@ -975,6 +982,12 @@
void Structure::didTransitionFromThisStructure(DeferredStructureTransitionWatchpointFire* deferred) const
{
+ // 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);
+
if (deferred)
deferred->add(this);
else
Modified: trunk/Source/_javascript_Core/runtime/Structure.h (186985 => 186986)
--- trunk/Source/_javascript_Core/runtime/Structure.h 2015-07-18 05:49:32 UTC (rev 186985)
+++ trunk/Source/_javascript_Core/runtime/Structure.h 2015-07-18 05:51:06 UTC (rev 186986)
@@ -413,6 +413,13 @@
// watching it. We should come up with a comprehensive story for not watching things that
// aren't profitable to watch.
// https://bugs.webkit.org/show_bug.cgi?id=133625
+
+ // - 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;
+
return true;
}
@@ -502,6 +509,7 @@
DEFINE_BITFIELD(bool, hasBeenFlattenedBefore, HasBeenFlattenedBefore, 1, 24);
DEFINE_BITFIELD(bool, hasCustomGetterSetterProperties, HasCustomGetterSetterProperties, 1, 25);
DEFINE_BITFIELD(bool, didWatchInternalProperties, DidWatchInternalProperties, 1, 26);
+ DEFINE_BITFIELD(bool, transitionWatchpointIsLikelyToBeFired, TransitionWatchpointIsLikelyToBeFired, 1, 27);
private:
friend class LLIntOffsetsExtractor;
