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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/201622">201622</a></dd>
<dt>Author</dt> <dd>sbarati@apple.com</dd>
<dt>Date</dt> <dd>2016-06-02 15:18:27 -0700 (Thu, 02 Jun 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>Teach bytecode liveness about the debugger
https://bugs.webkit.org/show_bug.cgi?id=158288
Reviewed by Filip Pizlo.
There was a bug where we wouldn't always keep the scope register
on the stack when the debugger is enabled. The debugger always assumes
it can read from the scope. The bug happened in OSR exit from the FTL.
The FTL uses bytecode liveness for OSR exit. Bytecode liveness proved
that the scope register was dead, so the FTL OSR exit wrote `undefined`
into the scope's stack slot when OSR exiting to the baseline.
To fix this, I taught bytecode liveness' computeUsesForBytecodeOffset() that the
scope is used by every instruction except op_enter. This causes the
scope to be live-in at every instruction except op_enter.
* bytecode/BytecodeLivenessAnalysis.cpp:
(JSC::blockContainsBytecodeOffset):
(JSC::addAlwaysLiveLocals):
(JSC::findBasicBlockForBytecodeOffset):
(JSC::stepOverInstruction):
(JSC::computeLocalLivenessForBytecodeOffset):
(JSC::BytecodeLivenessAnalysis::runLivenessFixpoint):
* bytecode/UnlinkedCodeBlock.cpp:
(JSC::UnlinkedCodeBlock::UnlinkedCodeBlock):
* tests/stress/shadow-chicken-reading-from-scope-after-ftl-osr-exit-bytecode-liveness.js: Added.
(foo):
(catch):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecodeBytecodeUseDefh">trunk/Source/JavaScriptCore/bytecode/BytecodeUseDef.h</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecodeUnlinkedCodeBlockcpp">trunk/Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.cpp</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoretestsstressshadowchickenreadingfromscopeafterftlosrexitbytecodelivenessjs">trunk/Source/JavaScriptCore/tests/stress/shadow-chicken-reading-from-scope-after-ftl-osr-exit-bytecode-liveness.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (201621 => 201622)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-06-02 22:15:08 UTC (rev 201621)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-06-02 22:18:27 UTC (rev 201622)
</span><span class="lines">@@ -1,3 +1,34 @@
</span><ins>+2016-06-02 Saam Barati <sbarati@apple.com>
+
+ Teach bytecode liveness about the debugger
+ https://bugs.webkit.org/show_bug.cgi?id=158288
+
+ Reviewed by Filip Pizlo.
+
+ There was a bug where we wouldn't always keep the scope register
+ on the stack when the debugger is enabled. The debugger always assumes
+ it can read from the scope. The bug happened in OSR exit from the FTL.
+ The FTL uses bytecode liveness for OSR exit. Bytecode liveness proved
+ that the scope register was dead, so the FTL OSR exit wrote `undefined`
+ into the scope's stack slot when OSR exiting to the baseline.
+
+ To fix this, I taught bytecode liveness' computeUsesForBytecodeOffset() that the
+ scope is used by every instruction except op_enter. This causes the
+ scope to be live-in at every instruction except op_enter.
+
+ * bytecode/BytecodeLivenessAnalysis.cpp:
+ (JSC::blockContainsBytecodeOffset):
+ (JSC::addAlwaysLiveLocals):
+ (JSC::findBasicBlockForBytecodeOffset):
+ (JSC::stepOverInstruction):
+ (JSC::computeLocalLivenessForBytecodeOffset):
+ (JSC::BytecodeLivenessAnalysis::runLivenessFixpoint):
+ * bytecode/UnlinkedCodeBlock.cpp:
+ (JSC::UnlinkedCodeBlock::UnlinkedCodeBlock):
+ * tests/stress/shadow-chicken-reading-from-scope-after-ftl-osr-exit-bytecode-liveness.js: Added.
+ (foo):
+ (catch):
+
</ins><span class="cx"> 2016-06-02 Michael Saboff <msaboff@apple.com>
</span><span class="cx">
</span><span class="cx"> REGRESSION(r200694): %ThrowTypeError% is not unique
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecodeBytecodeUseDefh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecode/BytecodeUseDef.h (201621 => 201622)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecode/BytecodeUseDef.h 2016-06-02 22:15:08 UTC (rev 201621)
+++ trunk/Source/JavaScriptCore/bytecode/BytecodeUseDef.h 2016-06-02 22:18:27 UTC (rev 201622)
</span><span class="lines">@@ -38,6 +38,10 @@
</span><span class="cx"> Instruction* instructionsBegin = codeBlock->instructions().begin();
</span><span class="cx"> Instruction* instruction = &instructionsBegin[bytecodeOffset];
</span><span class="cx"> OpcodeID opcodeID = interpreter->getOpcodeID(instruction->u.opcode);
</span><ins>+
+ if (opcodeID != op_enter && codeBlock->wasCompiledWithDebuggingOpcodes() && codeBlock->scopeRegister().isValid())
+ functor(codeBlock, instruction, opcodeID, codeBlock->scopeRegister().offset());
+
</ins><span class="cx"> switch (opcodeID) {
</span><span class="cx"> // No uses.
</span><span class="cx"> case op_new_regexp:
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecodeUnlinkedCodeBlockcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.cpp (201621 => 201622)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.cpp 2016-06-02 22:15:08 UTC (rev 201621)
+++ trunk/Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.cpp 2016-06-02 22:18:27 UTC (rev 201622)
</span><span class="lines">@@ -68,7 +68,7 @@
</span><span class="cx"> , m_evalContextType(static_cast<unsigned>(info.evalContextType()))
</span><span class="cx"> , m_isArrowFunctionContext(info.isArrowFunctionContext())
</span><span class="cx"> , m_isClassContext(info.isClassContext())
</span><del>- , m_wasCompiledWithDebuggingOpcodes(debuggerMode == DebuggerMode::DebuggerOn)
</del><ins>+ , m_wasCompiledWithDebuggingOpcodes(debuggerMode == DebuggerMode::DebuggerOn || Options::forceDebuggerBytecodeGeneration())
</ins><span class="cx"> , m_firstLine(0)
</span><span class="cx"> , m_lineCount(0)
</span><span class="cx"> , m_endColumn(UINT_MAX)
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoretestsstressshadowchickenreadingfromscopeafterftlosrexitbytecodelivenessjs"></a>
<div class="addfile"><h4>Added: trunk/Source/JavaScriptCore/tests/stress/shadow-chicken-reading-from-scope-after-ftl-osr-exit-bytecode-liveness.js (0 => 201622)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/tests/stress/shadow-chicken-reading-from-scope-after-ftl-osr-exit-bytecode-liveness.js (rev 0)
+++ trunk/Source/JavaScriptCore/tests/stress/shadow-chicken-reading-from-scope-after-ftl-osr-exit-bytecode-liveness.js 2016-06-02 22:18:27 UTC (rev 201622)
</span><span class="lines">@@ -0,0 +1,17 @@
</span><ins>+//@ runMiscNoCJITTest("--forceDebuggerBytecodeGeneration=true", "--alwaysUseShadowChicken=true")
+
+"use strict";
+
+function foo(b) {
+ if (b)
+ throw "foo";
+ return b;
+}
+noInline(foo);
+
+for (let i = 0; i < 10000; i++)
+ foo(false);
+
+try {
+ foo(true);
+} catch(e) { }
</ins></span></pre>
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