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<title>[202512] trunk/Source/JavaScriptCore</title>
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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/202512">202512</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2016-06-27 14:36:19 -0700 (Mon, 27 Jun 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>B3::Procedure::resetReachability() can create dangling references from Upsilons to Phis
https://bugs.webkit.org/show_bug.cgi?id=159165
Reviewed by Mark Lam.
You can delete an unreachable block that has a Phi but some prior block may still have an
Upsilon pointing to that Phi. This can happen if the Upsilon precedes a Check that always
exits or it can happen if we remove some successor of a block and this block had an Upsilon
for one of the removed successors. These things are valid IR even if they are not canonical.
Our policy for not-canonical-but-valid IR is that the compiler should still emit valid code
in the end.
The solution is to have Procedure::resetReachability() turn those Upsilons into Nops.
* b3/B3Procedure.cpp:
(JSC::B3::Procedure::resetReachability): Fix the bug.
* b3/B3Validate.h:
* b3/testb3.cpp:
(JSC::B3::testResetReachabilityDanglingReference): Add a test. This always crashes prior to this change.
* dfg/DFGGraph.cpp:
(JSC::DFG::Graph::killUnreachableBlocks): Add a FIXME about a possible similar bug.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3B3Procedurecpp">trunk/Source/JavaScriptCore/b3/B3Procedure.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3B3Validateh">trunk/Source/JavaScriptCore/b3/B3Validate.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3testb3cpp">trunk/Source/JavaScriptCore/b3/testb3.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGGraphcpp">trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (202511 => 202512)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-06-27 20:59:27 UTC (rev 202511)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-06-27 21:36:19 UTC (rev 202512)
</span><span class="lines">@@ -1,3 +1,27 @@
</span><ins>+2016-06-27 Filip Pizlo <fpizlo@apple.com>
+
+ B3::Procedure::resetReachability() can create dangling references from Upsilons to Phis
+ https://bugs.webkit.org/show_bug.cgi?id=159165
+
+ Reviewed by Mark Lam.
+
+ You can delete an unreachable block that has a Phi but some prior block may still have an
+ Upsilon pointing to that Phi. This can happen if the Upsilon precedes a Check that always
+ exits or it can happen if we remove some successor of a block and this block had an Upsilon
+ for one of the removed successors. These things are valid IR even if they are not canonical.
+ Our policy for not-canonical-but-valid IR is that the compiler should still emit valid code
+ in the end.
+
+ The solution is to have Procedure::resetReachability() turn those Upsilons into Nops.
+
+ * b3/B3Procedure.cpp:
+ (JSC::B3::Procedure::resetReachability): Fix the bug.
+ * b3/B3Validate.h:
+ * b3/testb3.cpp:
+ (JSC::B3::testResetReachabilityDanglingReference): Add a test. This always crashes prior to this change.
+ * dfg/DFGGraph.cpp:
+ (JSC::DFG::Graph::killUnreachableBlocks): Add a FIXME about a possible similar bug.
+
</ins><span class="cx"> 2016-06-27 Keith Miller <keith_miller@apple.com>
</span><span class="cx">
</span><span class="cx"> Add comment to Module feature in features.json
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3B3Procedurecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/B3Procedure.cpp (202511 => 202512)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/B3Procedure.cpp 2016-06-27 20:59:27 UTC (rev 202511)
+++ trunk/Source/JavaScriptCore/b3/B3Procedure.cpp 2016-06-27 21:36:19 UTC (rev 202512)
</span><span class="lines">@@ -36,6 +36,7 @@
</span><span class="cx"> #include "B3DataSection.h"
</span><span class="cx"> #include "B3Dominators.h"
</span><span class="cx"> #include "B3OpaqueByproducts.h"
</span><ins>+#include "B3PhiChildren.h"
</ins><span class="cx"> #include "B3StackSlot.h"
</span><span class="cx"> #include "B3ValueInlines.h"
</span><span class="cx"> #include "B3Variable.h"
</span><span class="lines">@@ -172,13 +173,31 @@
</span><span class="cx"> }
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ IndexSet<Value> valuesToDelete;
+
</ins><span class="cx"> B3::resetReachability(
</span><span class="cx"> m_blocks,
</span><span class="cx"> [&] (BasicBlock* deleted) {
</span><span class="cx"> // Gotta delete the values in this block.
</span><span class="cx"> for (Value* value : *deleted)
</span><del>- deleteValue(value);
</del><ins>+ valuesToDelete.add(value);
</ins><span class="cx"> });
</span><ins>+
+ if (valuesToDelete.isEmpty())
+ return;
+
+ for (BasicBlock* block : *this) {
+ for (Value* value : *block) {
+ ASSERT(!valuesToDelete.contains(value)); // The block should have been deleted already.
+ if (UpsilonValue* upsilon = value->as<UpsilonValue>()) {
+ if (valuesToDelete.contains(upsilon->phi()))
+ upsilon->replaceWithNop();
+ }
+ }
+ }
+
+ for (Value* value : valuesToDelete.values(values()))
+ deleteValue(value);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void Procedure::invalidateCFG()
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3B3Validateh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/B3Validate.h (202511 => 202512)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/B3Validate.h 2016-06-27 20:59:27 UTC (rev 202511)
+++ trunk/Source/JavaScriptCore/b3/B3Validate.h 2016-06-27 21:36:19 UTC (rev 202512)
</span><span class="lines">@@ -32,7 +32,7 @@
</span><span class="cx">
</span><span class="cx"> class Procedure;
</span><span class="cx">
</span><del>-void validate(Procedure&, const char* dumpBefore = nullptr);
</del><ins>+JS_EXPORT_PRIVATE void validate(Procedure&, const char* dumpBefore = nullptr);
</ins><span class="cx">
</span><span class="cx"> } } // namespace JSC::B3
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3testb3cpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/testb3.cpp (202511 => 202512)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/testb3.cpp 2016-06-27 20:59:27 UTC (rev 202511)
+++ trunk/Source/JavaScriptCore/b3/testb3.cpp 2016-06-27 21:36:19 UTC (rev 202512)
</span><span class="lines">@@ -44,6 +44,7 @@
</span><span class="cx"> #include "B3StackmapGenerationParams.h"
</span><span class="cx"> #include "B3SwitchValue.h"
</span><span class="cx"> #include "B3UpsilonValue.h"
</span><ins>+#include "B3Validate.h"
</ins><span class="cx"> #include "B3ValueInlines.h"
</span><span class="cx"> #include "CCallHelpers.h"
</span><span class="cx"> #include "InitializeThreading.h"
</span><span class="lines">@@ -12084,6 +12085,25 @@
</span><span class="cx"> reduceStrength(proc);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+void testResetReachabilityDanglingReference()
+{
+ Procedure proc;
+
+ BasicBlock* one = proc.addBlock();
+ BasicBlock* two = proc.addBlock();
+
+ UpsilonValue* upsilon = one->appendNew<UpsilonValue>(
+ proc, Origin(), one->appendNew<Const32Value>(proc, Origin(), 42));
+ one->appendNew<ControlValue>(proc, Oops, Origin());
+
+ Value* phi = two->appendNew<Value>(proc, Phi, Int32, Origin());
+ upsilon->setPhi(phi);
+ two->appendNew<ControlValue>(proc, Oops, Origin());
+
+ proc.resetReachability();
+ validate(proc);
+}
+
</ins><span class="cx"> // Make sure the compiler does not try to optimize anything out.
</span><span class="cx"> NEVER_INLINE double zero()
</span><span class="cx"> {
</span><span class="lines">@@ -13487,6 +13507,7 @@
</span><span class="cx"> RUN(testSpillUseLargerThanDef());
</span><span class="cx"> RUN(testLateRegister());
</span><span class="cx"> RUN(testReduceStrengthCheckBottomUseInAnotherBlock());
</span><ins>+ RUN(testResetReachabilityDanglingReference());
</ins><span class="cx">
</span><span class="cx"> if (tasks.isEmpty())
</span><span class="cx"> usage();
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGGraphcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp (202511 => 202512)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp 2016-06-27 20:59:27 UTC (rev 202511)
+++ trunk/Source/JavaScriptCore/dfg/DFGGraph.cpp 2016-06-27 21:36:19 UTC (rev 202512)
</span><span class="lines">@@ -754,6 +754,9 @@
</span><span class="cx">
</span><span class="cx"> void Graph::killUnreachableBlocks()
</span><span class="cx"> {
</span><ins>+ // FIXME: This probably creates dangling references from Upsilons to Phis in SSA.
+ // https://bugs.webkit.org/show_bug.cgi?id=159164
+
</ins><span class="cx"> for (BlockIndex blockIndex = 0; blockIndex < numBlocks(); ++blockIndex) {
</span><span class="cx"> BasicBlock* block = this->block(blockIndex);
</span><span class="cx"> if (!block)
</span></span></pre>
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