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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/202795">202795</a></dd>
<dt>Author</dt> <dd>sbarati@apple.com</dd>
<dt>Date</dt> <dd>2016-07-03 14:36:48 -0700 (Sun, 03 Jul 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>BytecodeGenerator::getVariablesUnderTDZ is too conservative
https://bugs.webkit.org/show_bug.cgi?id=159387
Reviewed by Filip Pizlo.
Source/JavaScriptCore:
We were too conservative in the following type of programs:
```
{
{
let x;
...
}
let x;
}
```
We used to report "x" as under TDZ when calling getVariablesUnderTDZ at the
"...", even though "x" is not under TDZ. This patch removes this conservatism
and makes the algorithm precise.
* bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::getVariablesUnderTDZ):
* bytecompiler/BytecodeGenerator.h:
Source/WTF:
I've templatized SmallPtrSet on its SmallArraySize instead
of it always being 8.
* wtf/SmallPtrSet.h:
(WTF::SmallPtrSet::SmallPtrSet):
(WTF::SmallPtrSet::add):
(WTF::SmallPtrSet::iterator::operator!=):
(WTF::SmallPtrSet::bucket):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecompilerBytecodeGeneratorcpp">trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp</a></li>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtfSmallPtrSeth">trunk/Source/WTF/wtf/SmallPtrSet.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (202794 => 202795)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-07-03 20:01:20 UTC (rev 202794)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-07-03 21:36:48 UTC (rev 202795)
</span><span class="lines">@@ -1,3 +1,28 @@
</span><ins>+2016-07-03 Saam Barati <sbarati@apple.com>
+
+ BytecodeGenerator::getVariablesUnderTDZ is too conservative
+ https://bugs.webkit.org/show_bug.cgi?id=159387
+
+ Reviewed by Filip Pizlo.
+
+ We were too conservative in the following type of programs:
+ ```
+ {
+ {
+ let x;
+ ...
+ }
+ let x;
+ }
+ ```
+ We used to report "x" as under TDZ when calling getVariablesUnderTDZ at the
+ "...", even though "x" is not under TDZ. This patch removes this conservatism
+ and makes the algorithm precise.
+
+ * bytecompiler/BytecodeGenerator.cpp:
+ (JSC::BytecodeGenerator::getVariablesUnderTDZ):
+ * bytecompiler/BytecodeGenerator.h:
+
</ins><span class="cx"> 2016-07-03 Filip Pizlo <fpizlo@apple.com>
</span><span class="cx">
</span><span class="cx"> FTL should refer to B3 types directly
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecompilerBytecodeGeneratorcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp (202794 => 202795)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp 2016-07-03 20:01:20 UTC (rev 202794)
+++ trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp 2016-07-03 21:36:48 UTC (rev 202795)
</span><span class="lines">@@ -46,6 +46,7 @@
</span><span class="cx"> #include "UnlinkedCodeBlock.h"
</span><span class="cx"> #include "UnlinkedInstructionStream.h"
</span><span class="cx"> #include <wtf/CommaPrinter.h>
</span><ins>+#include <wtf/SmallPtrSet.h>
</ins><span class="cx"> #include <wtf/StdLibExtras.h>
</span><span class="cx"> #include <wtf/text/WTFString.h>
</span><span class="cx">
</span><span class="lines">@@ -2791,7 +2792,8 @@
</span><span class="cx">
</span><span class="cx"> void BytecodeGenerator::getVariablesUnderTDZ(VariableEnvironment& result)
</span><span class="cx"> {
</span><del>- // NOTE: This is conservative. If called at "...", it will report "x" as being under TDZ:
</del><ins>+ // We keep track of variablesThatDontNeedTDZ in this algorithm to prevent
+ // reporting that "x" is under TDZ if this function is called at "...".
</ins><span class="cx"> //
</span><span class="cx"> // {
</span><span class="cx"> // {
</span><span class="lines">@@ -2801,11 +2803,15 @@
</span><span class="cx"> // let x;
</span><span class="cx"> // }
</span><span class="cx"> //
</span><del>- // FIXME: https://bugs.webkit.org/show_bug.cgi?id=159387
- for (auto& map : m_TDZStack) {
</del><ins>+ SmallPtrSet<UniquedStringImpl*, 16> variablesThatDontNeedTDZ;
+ for (unsigned i = m_TDZStack.size(); i--; ) {
+ auto& map = m_TDZStack[i];
</ins><span class="cx"> for (auto& entry : map) {
</span><del>- if (entry.value != TDZNecessityLevel::NotNeeded)
- result.add(entry.key.get());
</del><ins>+ if (entry.value != TDZNecessityLevel::NotNeeded) {
+ if (!variablesThatDontNeedTDZ.contains(entry.key.get()))
+ result.add(entry.key.get());
+ } else
+ variablesThatDontNeedTDZ.add(entry.key.get());
</ins><span class="cx"> }
</span><span class="cx"> }
</span><span class="cx"> }
</span></span></pre></div>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (202794 => 202795)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog 2016-07-03 20:01:20 UTC (rev 202794)
+++ trunk/Source/WTF/ChangeLog 2016-07-03 21:36:48 UTC (rev 202795)
</span><span class="lines">@@ -1,3 +1,19 @@
</span><ins>+2016-07-03 Saam Barati <sbarati@apple.com>
+
+ BytecodeGenerator::getVariablesUnderTDZ is too conservative
+ https://bugs.webkit.org/show_bug.cgi?id=159387
+
+ Reviewed by Filip Pizlo.
+
+ I've templatized SmallPtrSet on its SmallArraySize instead
+ of it always being 8.
+
+ * wtf/SmallPtrSet.h:
+ (WTF::SmallPtrSet::SmallPtrSet):
+ (WTF::SmallPtrSet::add):
+ (WTF::SmallPtrSet::iterator::operator!=):
+ (WTF::SmallPtrSet::bucket):
+
</ins><span class="cx"> 2016-07-03 Filip Pizlo <fpizlo@apple.com>
</span><span class="cx">
</span><span class="cx"> Ugh. Once again, unreviewed, roll out unintentional commit in r202790.
</span></span></pre></div>
<a id="trunkSourceWTFwtfSmallPtrSeth"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/SmallPtrSet.h (202794 => 202795)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/SmallPtrSet.h 2016-07-03 20:01:20 UTC (rev 202794)
+++ trunk/Source/WTF/wtf/SmallPtrSet.h 2016-07-03 21:36:48 UTC (rev 202795)
</span><span class="lines">@@ -33,11 +33,12 @@
</span><span class="cx">
</span><span class="cx"> namespace WTF {
</span><span class="cx">
</span><del>-template<typename PtrType>
</del><ins>+template<typename PtrType, unsigned SmallArraySize = 8>
</ins><span class="cx"> class SmallPtrSet {
</span><span class="cx"> WTF_MAKE_NONCOPYABLE(SmallPtrSet);
</span><span class="cx"> static_assert(std::is_trivially_destructible<PtrType>::value, "We currently don't support non-trivially destructible pointer types.");
</span><span class="cx"> static_assert(sizeof(PtrType) == sizeof(void*), "Only support pointer sized things.");
</span><ins>+ static_assert(!(SmallArraySize & (SmallArraySize - 1)), "Inline size must be a power of two.");
</ins><span class="cx">
</span><span class="cx"> public:
</span><span class="cx"> SmallPtrSet()
</span><span class="lines">@@ -90,7 +91,7 @@
</span><span class="cx"> return;
</span><span class="cx"> }
</span><span class="cx">
</span><del>- grow(64);
</del><ins>+ grow(std::max(64u, SmallArraySize * 2));
</ins><span class="cx"> // Fall through. We're no longer small :(
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -138,7 +139,7 @@
</span><span class="cx"> bool operator!=(const iterator& other) const { ASSERT(m_buffer == other.m_buffer); return !(*this == other); }
</span><span class="cx">
</span><span class="cx"> private:
</span><del>- template<typename U> friend class WTF::SmallPtrSet;
</del><ins>+ template<typename U, unsigned S> friend class WTF::SmallPtrSet;
</ins><span class="cx"> unsigned m_index;
</span><span class="cx"> unsigned m_capacity;
</span><span class="cx"> void** m_buffer;
</span><span class="lines">@@ -239,8 +240,6 @@
</span><span class="cx"> }
</span><span class="cx"> }
</span><span class="cx">
</span><del>- static const unsigned SmallArraySize = 8;
-
</del><span class="cx"> unsigned m_size;
</span><span class="cx"> unsigned m_capacity;
</span><span class="cx"> void** m_buffer;
</span></span></pre>
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