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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/214908">214908</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2017-04-04 15:37:51 -0700 (Tue, 04 Apr 2017)</dd>
</dl>
<h3>Log Message</h3>
<pre>B3::LowerToAir incorrectly selects BitXor(AtomicStrongCAS(...), $1)
https://bugs.webkit.org/show_bug.cgi?id=169867
Reviewed by Saam Barati.
The BitXor(AtomicWeakCAS(...), $1) optimization makes a lot of sense because we an fold the
BitXor into the CAS condition read-out. But there is no version of this that is profitable or
correct for AtomicStrongCAS. The inversion case is handled by Equal(AtomicStrongCAS(...), ...)
becoming NotEqual(AtomicStrongCAS(...), ...), and we alraedy handle that separately.
So, the fix here is to make the BitXor CAS pattern only recognize AtomicWeakCAS.
* b3/B3LowerToAir.cpp:
(JSC::B3::Air::LowerToAir::lower):
* b3/testb3.cpp:
(JSC::B3::testAtomicStrongCAS):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3B3LowerToAircpp">trunk/Source/JavaScriptCore/b3/B3LowerToAir.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3testb3cpp">trunk/Source/JavaScriptCore/b3/testb3.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (214907 => 214908)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2017-04-04 22:30:04 UTC (rev 214907)
+++ trunk/Source/JavaScriptCore/ChangeLog 2017-04-04 22:37:51 UTC (rev 214908)
</span><span class="lines">@@ -1,3 +1,22 @@
</span><ins>+2017-04-04 Filip Pizlo <fpizlo@apple.com>
+
+ B3::LowerToAir incorrectly selects BitXor(AtomicStrongCAS(...), $1)
+ https://bugs.webkit.org/show_bug.cgi?id=169867
+
+ Reviewed by Saam Barati.
+
+ The BitXor(AtomicWeakCAS(...), $1) optimization makes a lot of sense because we an fold the
+ BitXor into the CAS condition read-out. But there is no version of this that is profitable or
+ correct for AtomicStrongCAS. The inversion case is handled by Equal(AtomicStrongCAS(...), ...)
+ becoming NotEqual(AtomicStrongCAS(...), ...), and we alraedy handle that separately.
+
+ So, the fix here is to make the BitXor CAS pattern only recognize AtomicWeakCAS.
+
+ * b3/B3LowerToAir.cpp:
+ (JSC::B3::Air::LowerToAir::lower):
+ * b3/testb3.cpp:
+ (JSC::B3::testAtomicStrongCAS):
+
</ins><span class="cx"> 2017-04-04 Saam Barati <sbarati@apple.com>
</span><span class="cx">
</span><span class="cx"> WebAssembly: JSWebAssemblyCallee should not be a JSCell
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3B3LowerToAircpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/B3LowerToAir.cpp (214907 => 214908)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/B3LowerToAir.cpp 2017-04-04 22:30:04 UTC (rev 214907)
+++ trunk/Source/JavaScriptCore/b3/B3LowerToAir.cpp 2017-04-04 22:37:51 UTC (rev 214908)
</span><span class="lines">@@ -2597,10 +2597,8 @@
</span><span class="cx"> // This pattern is super useful on both x86 and ARM64, since the inversion of the CAS result
</span><span class="cx"> // can be done with zero cost on x86 (just flip the set from E to NE) and it's a progression
</span><span class="cx"> // on ARM64 (since STX returns 0 on success, so ordinarily we have to flip it).
</span><del>- // FIXME: This looks wrong for AtomicStrongCAS
- // https://bugs.webkit.org/show_bug.cgi?id=169867
</del><span class="cx"> if (m_value->child(1)->isInt(1)
</span><del>- && isAtomicCAS(m_value->child(0)->opcode())
</del><ins>+ && m_value->child(0)->opcode() == AtomicWeakCAS
</ins><span class="cx"> && canBeInternal(m_value->child(0))) {
</span><span class="cx"> commitInternal(m_value->child(0));
</span><span class="cx"> appendCAS(m_value->child(0), true);
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3testb3cpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/testb3.cpp (214907 => 214908)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/testb3.cpp 2017-04-04 22:30:04 UTC (rev 214907)
+++ trunk/Source/JavaScriptCore/b3/testb3.cpp 2017-04-04 22:37:51 UTC (rev 214908)
</span><span class="lines">@@ -14871,11 +14871,47 @@
</span><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> {
</span><ins>+ // Test for https://bugs.webkit.org/show_bug.cgi?id=169867.
+
</ins><span class="cx"> Procedure proc;
</span><span class="cx"> BasicBlock* root = proc.addBlock();
</span><span class="cx"> root->appendNew<Value>(
</span><span class="cx"> proc, Return, Origin(),
</span><span class="cx"> root->appendNew<Value>(
</span><ins>+ proc, BitXor, Origin(),
+ root->appendNew<AtomicValue>(
+ proc, AtomicStrongCAS, Origin(), width,
+ root->appendIntConstant(proc, Origin(), type, 42),
+ root->appendIntConstant(proc, Origin(), type, 0xbeef),
+ root->appendNew<ArgumentRegValue>(proc, Origin(), GPRInfo::argumentGPR0)),
+ root->appendIntConstant(proc, Origin(), type, 1)));
+
+ typename NativeTraits<T>::CanonicalType one = 1;
+
+ auto code = compileProc(proc);
+ T value[2];
+ value[0] = 42;
+ value[1] = 13;
+ CHECK_EQ(invoke<typename NativeTraits<T>::CanonicalType>(*code, value), 42 ^ one);
+ CHECK_EQ(value[0], static_cast<T>(0xbeef));
+ CHECK_EQ(value[1], 13);
+ value[0] = static_cast<T>(300);
+ CHECK_EQ(invoke<typename NativeTraits<T>::CanonicalType>(*code, value), static_cast<typename NativeTraits<T>::CanonicalType>(static_cast<T>(300)) ^ one);
+ CHECK_EQ(value[0], static_cast<T>(300));
+ CHECK_EQ(value[1], 13);
+ value[0] = static_cast<T>(-1);
+ CHECK_EQ(invoke<typename NativeTraits<T>::CanonicalType>(*code, value), static_cast<typename NativeTraits<T>::CanonicalType>(static_cast<T>(-1)) ^ one);
+ CHECK_EQ(value[0], static_cast<T>(-1));
+ CHECK_EQ(value[1], 13);
+ checkMyDisassembly(*code, true);
+ }
+
+ {
+ Procedure proc;
+ BasicBlock* root = proc.addBlock();
+ root->appendNew<Value>(
+ proc, Return, Origin(),
+ root->appendNew<Value>(
</ins><span class="cx"> proc, Equal, Origin(),
</span><span class="cx"> root->appendNew<AtomicValue>(
</span><span class="cx"> proc, AtomicStrongCAS, Origin(), width,
</span></span></pre>
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