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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/186215">186215</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2015-07-01 18:30:28 -0700 (Wed, 01 Jul 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>DFG::freezeFragile should register the frozen value's structure
https://bugs.webkit.org/show_bug.cgi?id=136055
rdar://problem/21042120
Reviewed by Mark Lam and Geoffrey Garen.
This fixes weird concurrency bugs where the constant folding phase tries to convert
something to a constant but then crashes because the constant's structure wasn't
registered. The AI was registering the structure of any value it saw, but constant folding
wasn't - and that's fine so long as there ain't no concurrency.
The best fix is to just make it impossible to introduce a constant into the IR without
registering its structure. That's what this change does. This is not only a great
concurrency fix - it also makes the compiler somewhat easier to hack on because it's one
less case of structure registering that you have to remember about.
* dfg/DFGAbstractValue.cpp:
(JSC::DFG::AbstractValue::setOSREntryValue): No need to register.
(JSC::DFG::AbstractValue::set): We still call register, but just to get the watchpoint state.
* dfg/DFGGraph.cpp:
(JSC::DFG::Graph::freezeFragile): Register the structure.
* dfg/DFGStructureRegistrationPhase.cpp:
(JSC::DFG::StructureRegistrationPhase::run): Assert that these are all registered.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGAbstractValuecpp">trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGGraphcpp">trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGStructureRegistrationPhasecpp">trunk/Source/JavaScriptCore/dfg/DFGStructureRegistrationPhase.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (186214 => 186215)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2015-07-02 00:51:15 UTC (rev 186214)
+++ trunk/Source/JavaScriptCore/ChangeLog 2015-07-02 01:30:28 UTC (rev 186215)
</span><span class="lines">@@ -1,3 +1,29 @@
</span><ins>+2015-06-30 Filip Pizlo <fpizlo@apple.com>
+
+ DFG::freezeFragile should register the frozen value's structure
+ https://bugs.webkit.org/show_bug.cgi?id=136055
+ rdar://problem/21042120
+
+ Reviewed by Mark Lam and Geoffrey Garen.
+
+ This fixes weird concurrency bugs where the constant folding phase tries to convert
+ something to a constant but then crashes because the constant's structure wasn't
+ registered. The AI was registering the structure of any value it saw, but constant folding
+ wasn't - and that's fine so long as there ain't no concurrency.
+
+ The best fix is to just make it impossible to introduce a constant into the IR without
+ registering its structure. That's what this change does. This is not only a great
+ concurrency fix - it also makes the compiler somewhat easier to hack on because it's one
+ less case of structure registering that you have to remember about.
+
+ * dfg/DFGAbstractValue.cpp:
+ (JSC::DFG::AbstractValue::setOSREntryValue): No need to register.
+ (JSC::DFG::AbstractValue::set): We still call register, but just to get the watchpoint state.
+ * dfg/DFGGraph.cpp:
+ (JSC::DFG::Graph::freezeFragile): Register the structure.
+ * dfg/DFGStructureRegistrationPhase.cpp:
+ (JSC::DFG::StructureRegistrationPhase::run): Assert that these are all registered.
+
</ins><span class="cx"> 2015-07-01 Matthew Mirman <mmirman@apple.com>
</span><span class="cx">
</span><span class="cx"> Unreviewed, rolling out r185889
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGAbstractValuecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp (186214 => 186215)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp 2015-07-02 00:51:15 UTC (rev 186214)
+++ trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp 2015-07-02 01:30:28 UTC (rev 186215)
</span><span class="lines">@@ -51,7 +51,6 @@
</span><span class="cx"> {
</span><span class="cx"> if (!!value && value.value().isCell()) {
</span><span class="cx"> Structure* structure = value.structure();
</span><del>- graph.registerStructure(structure);
</del><span class="cx"> m_structure = structure;
</span><span class="cx"> m_arrayModes = asArrayModes(structure->indexingType());
</span><span class="cx"> } else {
</span><span class="lines">@@ -70,9 +69,6 @@
</span><span class="cx"> {
</span><span class="cx"> if (!!value && value.value().isCell()) {
</span><span class="cx"> Structure* structure = value.structure();
</span><del>- // FIXME: This check may not be necessary since any frozen value should have its structure
- // watched already.
- // https://bugs.webkit.org/show_bug.cgi?id=136055
</del><span class="cx"> if (graph.registerStructure(structure) == StructureRegisteredAndWatched) {
</span><span class="cx"> m_structure = structure;
</span><span class="cx"> if (clobberState == StructuresAreClobbered) {
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGGraphcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp (186214 => 186215)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp 2015-07-02 00:51:15 UTC (rev 186214)
+++ trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp 2015-07-02 01:30:28 UTC (rev 186215)
</span><span class="lines">@@ -1214,7 +1214,11 @@
</span><span class="cx"> if (value.isUInt32())
</span><span class="cx"> m_uint32ValuesInUse.append(value.asUInt32());
</span><span class="cx">
</span><del>- return result.iterator->value = m_frozenValues.add(FrozenValue::freeze(value));
</del><ins>+ FrozenValue frozenValue = FrozenValue::freeze(value);
+ if (Structure* structure = frozenValue.structure())
+ registerStructure(structure);
+
+ return result.iterator->value = m_frozenValues.add(frozenValue);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> FrozenValue* Graph::freeze(JSValue value)
</span><span class="lines">@@ -1258,6 +1262,10 @@
</span><span class="cx">
</span><span class="cx"> void Graph::assertIsRegistered(Structure* structure)
</span><span class="cx"> {
</span><ins>+ // It's convenient to be able to call this with a maybe-null structure.
+ if (!structure)
+ return;
+
</ins><span class="cx"> if (m_structureRegistrationState == HaveNotStartedRegistering)
</span><span class="cx"> return;
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGStructureRegistrationPhasecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGStructureRegistrationPhase.cpp (186214 => 186215)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGStructureRegistrationPhase.cpp 2015-07-02 00:51:15 UTC (rev 186214)
+++ trunk/Source/JavaScriptCore/dfg/DFGStructureRegistrationPhase.cpp 2015-07-02 01:30:28 UTC (rev 186215)
</span><span class="lines">@@ -44,6 +44,11 @@
</span><span class="cx">
</span><span class="cx"> bool run()
</span><span class="cx"> {
</span><ins>+ // We need to set this before this phase finishes. This phase doesn't do anything
+ // conditioned on this field, except for assertIsRegistered() below. We intend for that
+ // method to behave as if the phase was already finished. So, we set this up here.
+ m_graph.m_structureRegistrationState = AllStructuresAreRegistered;
+
</ins><span class="cx"> // These are pretty dumb, but needed to placate subsequent assertions. We don't actually
</span><span class="cx"> // have to watch these because there is no way to transition away from it, but they are
</span><span class="cx"> // watchable and so we will assert if they aren't watched.
</span><span class="lines">@@ -52,7 +57,7 @@
</span><span class="cx"> registerStructure(m_graph.m_vm.getterSetterStructure.get());
</span><span class="cx">
</span><span class="cx"> for (FrozenValue* value : m_graph.m_frozenValues)
</span><del>- registerStructure(value->structure());
</del><ins>+ m_graph.assertIsRegistered(value->structure());
</ins><span class="cx">
</span><span class="cx"> for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
</span><span class="cx"> BasicBlock* block = m_graph.block(blockIndex);
</span><span class="lines">@@ -141,8 +146,6 @@
</span><span class="cx"> }
</span><span class="cx"> }
</span><span class="cx">
</span><del>- m_graph.m_structureRegistrationState = AllStructuresAreRegistered;
-
</del><span class="cx"> return true;
</span><span class="cx"> }
</span><span class="cx">
</span></span></pre>
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