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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/203851">203851</a></dd>
<dt>Author</dt> <dd>msaboff@apple.com</dd>
<dt>Date</dt> <dd>2016-07-28 17:30:32 -0700 (Thu, 28 Jul 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>ARM64: Fused left shift with a right shift can create NaNs from integers
https://bugs.webkit.org/show_bug.cgi?id=160329
Reviewed by Geoffrey Garen.
When we fuse a left shift and a right shift of integers where the shift amounts
are the same and the size of the quantity being shifted is 8 bits, we rightly
generate a sign extend byte instruction. On ARM64, we were sign extending
to a 64 bit quantity, when we really wanted to sign extend to a 32 bit quantity.
Checking the ARM64 marco assembler and we were extending to 64 bits for all
four combinations of zero / sign and 8 / 16 bits.
* assembler/MacroAssemblerARM64.h:
(JSC::MacroAssemblerARM64::zeroExtend16To32):
(JSC::MacroAssemblerARM64::signExtend16To32):
(JSC::MacroAssemblerARM64::zeroExtend8To32):
(JSC::MacroAssemblerARM64::signExtend8To32):
* tests/stress/regress-160329.js: New test added.
(narrow):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreassemblerMacroAssemblerARM64h">trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.h</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoretestsstressregress160329js">trunk/Source/JavaScriptCore/tests/stress/regress-160329.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (203850 => 203851)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-07-28 23:52:42 UTC (rev 203850)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-07-29 00:30:32 UTC (rev 203851)
</span><span class="lines">@@ -1,3 +1,26 @@
</span><ins>+2016-07-28 Michael Saboff <msaboff@apple.com>
+
+ ARM64: Fused left shift with a right shift can create NaNs from integers
+ https://bugs.webkit.org/show_bug.cgi?id=160329
+
+ Reviewed by Geoffrey Garen.
+
+ When we fuse a left shift and a right shift of integers where the shift amounts
+ are the same and the size of the quantity being shifted is 8 bits, we rightly
+ generate a sign extend byte instruction. On ARM64, we were sign extending
+ to a 64 bit quantity, when we really wanted to sign extend to a 32 bit quantity.
+
+ Checking the ARM64 marco assembler and we were extending to 64 bits for all
+ four combinations of zero / sign and 8 / 16 bits.
+
+ * assembler/MacroAssemblerARM64.h:
+ (JSC::MacroAssemblerARM64::zeroExtend16To32):
+ (JSC::MacroAssemblerARM64::signExtend16To32):
+ (JSC::MacroAssemblerARM64::zeroExtend8To32):
+ (JSC::MacroAssemblerARM64::signExtend8To32):
+ * tests/stress/regress-160329.js: New test added.
+ (narrow):
+
</ins><span class="cx"> 2016-07-28 Mark Lam <mark.lam@apple.com>
</span><span class="cx">
</span><span class="cx"> StringView should have an explicit m_is8Bit field.
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreassemblerMacroAssemblerARM64h"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.h (203850 => 203851)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.h 2016-07-28 23:52:42 UTC (rev 203850)
+++ trunk/Source/JavaScriptCore/assembler/MacroAssemblerARM64.h 2016-07-29 00:30:32 UTC (rev 203851)
</span><span class="lines">@@ -1125,12 +1125,12 @@
</span><span class="cx">
</span><span class="cx"> void zeroExtend16To32(RegisterID src, RegisterID dest)
</span><span class="cx"> {
</span><del>- m_assembler.uxth<64>(dest, src);
</del><ins>+ m_assembler.uxth<32>(dest, src);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void signExtend16To32(RegisterID src, RegisterID dest)
</span><span class="cx"> {
</span><del>- m_assembler.sxth<64>(dest, src);
</del><ins>+ m_assembler.sxth<32>(dest, src);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void load8(ImplicitAddress address, RegisterID dest)
</span><span class="lines">@@ -1190,12 +1190,12 @@
</span><span class="cx">
</span><span class="cx"> void zeroExtend8To32(RegisterID src, RegisterID dest)
</span><span class="cx"> {
</span><del>- m_assembler.uxtb<64>(dest, src);
</del><ins>+ m_assembler.uxtb<32>(dest, src);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void signExtend8To32(RegisterID src, RegisterID dest)
</span><span class="cx"> {
</span><del>- m_assembler.sxtb<64>(dest, src);
</del><ins>+ m_assembler.sxtb<32>(dest, src);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void store64(RegisterID src, ImplicitAddress address)
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoretestsstressregress160329js"></a>
<div class="addfile"><h4>Added: trunk/Source/JavaScriptCore/tests/stress/regress-160329.js (0 => 203851)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/tests/stress/regress-160329.js (rev 0)
+++ trunk/Source/JavaScriptCore/tests/stress/regress-160329.js 2016-07-29 00:30:32 UTC (rev 203851)
</span><span class="lines">@@ -0,0 +1,17 @@
</span><ins>+// Regression test for 160329. This test should not crash or throw an exception.
+
+function narrow(x) {
+ return x << 24 >> 24;
+}
+
+noInline(narrow);
+
+for (var i = 0; i < 1000000; i++) {
+ let expected = i << 24;
+ let got = narrow(i);
+ expected = expected >> 24;
+
+ if (expected != got)
+ throw "FAILURE, expected:" + expected + ", got:" + got;
+}
+
</ins></span></pre>
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