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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/204360">204360</a></dd>
<dt>Author</dt> <dd>mark.lam@apple.com</dd>
<dt>Date</dt> <dd>2016-08-10 16:19:49 -0700 (Wed, 10 Aug 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>DFG's flushForTerminal() needs to add PhantomLocals for bytecode live locals.
https://bugs.webkit.org/show_bug.cgi?id=160755
<rdar://problem/27488507>
Reviewed by Filip Pizlo.
JSTests:
* stress/need-bytecode-liveness-for-unreachable-blocks-at-dfg-time.js: Added.
Source/JavaScriptCore:
If the DFG sees that an inlined function will result in an OSR exit every time,
it will treat all downstream blocks as dead. However, it still needs to keep
locals that are alive in the bytecode alive for the compiled function so that
those locals are properly written to the stack by the OSR exit ramp.
The existing code neglected to do this. This patch remedies this issue.
* dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::flushDirect):
(JSC::DFG::ByteCodeParser::addFlushOrPhantomLocal):
(JSC::DFG::ByteCodeParser::phantomLocalDirect):
(JSC::DFG::ByteCodeParser::flushForTerminal):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkJSTestsChangeLog">trunk/JSTests/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGByteCodeParsercpp">trunk/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkJSTestsstressneedbytecodelivenessforunreachableblocksatdfgtimejs">trunk/JSTests/stress/need-bytecode-liveness-for-unreachable-blocks-at-dfg-time.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkJSTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/JSTests/ChangeLog (204359 => 204360)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/ChangeLog 2016-08-10 22:37:47 UTC (rev 204359)
+++ trunk/JSTests/ChangeLog 2016-08-10 23:19:49 UTC (rev 204360)
</span><span class="lines">@@ -1,3 +1,13 @@
</span><ins>+2016-08-10 Mark Lam <mark.lam@apple.com>
+
+ DFG's flushForTerminal() needs to add PhantomLocals for bytecode live locals.
+ https://bugs.webkit.org/show_bug.cgi?id=160755
+ <rdar://problem/27488507>
+
+ Reviewed by Filip Pizlo.
+
+ * stress/need-bytecode-liveness-for-unreachable-blocks-at-dfg-time.js: Added.
+
</ins><span class="cx"> 2016-08-09 Skachkov Oleksandr <gskachkov@gmail.com>
</span><span class="cx">
</span><span class="cx"> [ES2016] Implement Object.values
</span></span></pre></div>
<a id="trunkJSTestsstressneedbytecodelivenessforunreachableblocksatdfgtimejs"></a>
<div class="addfile"><h4>Added: trunk/JSTests/stress/need-bytecode-liveness-for-unreachable-blocks-at-dfg-time.js (0 => 204360)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/JSTests/stress/need-bytecode-liveness-for-unreachable-blocks-at-dfg-time.js (rev 0)
+++ trunk/JSTests/stress/need-bytecode-liveness-for-unreachable-blocks-at-dfg-time.js 2016-08-10 23:19:49 UTC (rev 204360)
</span><span class="lines">@@ -0,0 +1,31 @@
</span><ins>+//@ run("--useConcurrentJIT=false")
+
+// This test is set up delicately to:
+// 1. cause the test() function to DFG compile with just the right amount of profiling
+// so that ...
+// 2. the DFG identifies the "return Function()" path as dead, and ...
+// 3. the DFG compiled function doesn't OSR exit too many times before ...
+// 4. we change the implementation of the inlined foo() and execute test() again.
+//
+// This test should not crash.
+
+eval("\"use strict\"; var w;");
+foo = function() { throw 0; }
+var x;
+
+(function() {
+ eval("test = function() { ~foo(~(0 ? ~x : x) ? 0 : 0); return Function(); }");
+})();
+
+// This loop count of 2000 was empirically determined to be the right amount to get this
+// this issue to manifest. Dropping or raising it may mask the issue and prevent it from
+// manifesting.
+for (var i = 0; i < 2000; ++i) {
+ try {
+ test();
+ } catch(e) {
+ }
+}
+
+foo = function() { };
+test();
</ins></span></pre></div>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (204359 => 204360)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-08-10 22:37:47 UTC (rev 204359)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-08-10 23:19:49 UTC (rev 204360)
</span><span class="lines">@@ -1,3 +1,24 @@
</span><ins>+2016-08-10 Mark Lam <mark.lam@apple.com>
+
+ DFG's flushForTerminal() needs to add PhantomLocals for bytecode live locals.
+ https://bugs.webkit.org/show_bug.cgi?id=160755
+ <rdar://problem/27488507>
+
+ Reviewed by Filip Pizlo.
+
+ If the DFG sees that an inlined function will result in an OSR exit every time,
+ it will treat all downstream blocks as dead. However, it still needs to keep
+ locals that are alive in the bytecode alive for the compiled function so that
+ those locals are properly written to the stack by the OSR exit ramp.
+
+ The existing code neglected to do this. This patch remedies this issue.
+
+ * dfg/DFGByteCodeParser.cpp:
+ (JSC::DFG::ByteCodeParser::flushDirect):
+ (JSC::DFG::ByteCodeParser::addFlushOrPhantomLocal):
+ (JSC::DFG::ByteCodeParser::phantomLocalDirect):
+ (JSC::DFG::ByteCodeParser::flushForTerminal):
+
</ins><span class="cx"> 2016-08-09 Skachkov Oleksandr <gskachkov@gmail.com>
</span><span class="cx">
</span><span class="cx"> [ES2016] Implement Object.values
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGByteCodeParsercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp (204359 => 204360)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp 2016-08-10 22:37:47 UTC (rev 204359)
+++ trunk/Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp 2016-08-10 23:19:49 UTC (rev 204360)
</span><span class="lines">@@ -573,9 +573,15 @@
</span><span class="cx"> {
</span><span class="cx"> flushDirect(operand, findArgumentPosition(operand));
</span><span class="cx"> }
</span><del>-
</del><ins>+
</ins><span class="cx"> void flushDirect(VirtualRegister operand, ArgumentPosition* argumentPosition)
</span><span class="cx"> {
</span><ins>+ addFlushOrPhantomLocal<Flush>(operand, argumentPosition);
+ }
+
+ template<NodeType nodeType>
+ void addFlushOrPhantomLocal(VirtualRegister operand, ArgumentPosition* argumentPosition)
+ {
</ins><span class="cx"> ASSERT(!operand.isConstant());
</span><span class="cx">
</span><span class="cx"> Node* node = m_currentBlock->variablesAtTail.operand(operand);
</span><span class="lines">@@ -587,12 +593,17 @@
</span><span class="cx"> else
</span><span class="cx"> variable = newVariableAccessData(operand);
</span><span class="cx">
</span><del>- node = addToGraph(Flush, OpInfo(variable));
</del><ins>+ node = addToGraph(nodeType, OpInfo(variable));
</ins><span class="cx"> m_currentBlock->variablesAtTail.operand(operand) = node;
</span><span class="cx"> if (argumentPosition)
</span><span class="cx"> argumentPosition->addVariable(variable);
</span><span class="cx"> }
</span><del>-
</del><ins>+
+ void phantomLocalDirect(VirtualRegister operand)
+ {
+ addFlushOrPhantomLocal<PhantomLocal>(operand, findArgumentPosition(operand));
+ }
+
</ins><span class="cx"> void flush(InlineStackEntry* inlineStackEntry)
</span><span class="cx"> {
</span><span class="cx"> int numArguments;
</span><span class="lines">@@ -615,8 +626,32 @@
</span><span class="cx">
</span><span class="cx"> void flushForTerminal()
</span><span class="cx"> {
</span><del>- for (InlineStackEntry* inlineStackEntry = m_inlineStackTop; inlineStackEntry; inlineStackEntry = inlineStackEntry->m_caller)
</del><ins>+ CodeOrigin origin = currentCodeOrigin();
+ unsigned bytecodeIndex = origin.bytecodeIndex;
+
+ for (InlineStackEntry* inlineStackEntry = m_inlineStackTop; inlineStackEntry; inlineStackEntry = inlineStackEntry->m_caller) {
</ins><span class="cx"> flush(inlineStackEntry);
</span><ins>+
+ ASSERT(origin.inlineCallFrame == inlineStackEntry->m_inlineCallFrame);
+ InlineCallFrame* inlineCallFrame = inlineStackEntry->m_inlineCallFrame;
+ CodeBlock* codeBlock = m_graph.baselineCodeBlockFor(inlineCallFrame);
+ FullBytecodeLiveness& fullLiveness = m_graph.livenessFor(codeBlock);
+ const FastBitVector& livenessAtBytecode = fullLiveness.getLiveness(bytecodeIndex);
+
+ for (unsigned local = codeBlock->m_numCalleeLocals; local--;) {
+ if (livenessAtBytecode.get(local)) {
+ VirtualRegister reg = virtualRegisterForLocal(local);
+ if (inlineCallFrame)
+ reg = inlineStackEntry->remapOperand(reg);
+ phantomLocalDirect(reg);
+ }
+ }
+
+ if (inlineCallFrame) {
+ bytecodeIndex = inlineCallFrame->directCaller.bytecodeIndex;
+ origin = inlineCallFrame->directCaller;
+ }
+ }
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void flushForReturn()
</span></span></pre>
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