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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/198018">198018</a></dd>
<dt>Author</dt> <dd>carlosgc@webkit.org</dd>
<dt>Date</dt> <dd>2016-03-11 06:45:14 -0800 (Fri, 11 Mar 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>Merge - 197688 - [JSC] Simplify the overflow check of ArithAbs
https://bugs.webkit.org/show_bug.cgi?id=155063
Reviewed by Geoffrey Garen.
The only integer that overflow abs(int32) is INT_MIN.
For some reason, our code testing for that case
was checking the top bit of the result specifically.
The code required a large immediate on x86 and an extra
register on ARM64.
This patch turns the overflow check into a branch on
the sign of the result.
* dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* ftl/FTLLowerDFGToB3.cpp:
(JSC::FTL::DFG::LowerDFGToB3::compileArithAbs):
* jit/ThunkGenerators.cpp:
(JSC::absThunkGenerator):
* tests/stress/arith-abs-overflow.js: Added.
(opaqueAbs):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit212SourceJavaScriptCoreChangeLog">releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#releasesWebKitGTKwebkit212SourceJavaScriptCoredfgDFGSpeculativeJIT32_64cpp">releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp</a></li>
<li><a href="#releasesWebKitGTKwebkit212SourceJavaScriptCoredfgDFGSpeculativeJIT64cpp">releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp</a></li>
<li><a href="#releasesWebKitGTKwebkit212SourceJavaScriptCoreftlFTLLowerDFGToB3cpp">releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp</a></li>
<li><a href="#releasesWebKitGTKwebkit212SourceJavaScriptCorejitThunkGeneratorscpp">releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/jit/ThunkGenerators.cpp</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit212SourceJavaScriptCoretestsstressarithabsoverflowjs">releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/tests/stress/arith-abs-overflow.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="releasesWebKitGTKwebkit212SourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ChangeLog (198017 => 198018)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ChangeLog 2016-03-11 14:37:34 UTC (rev 198017)
+++ releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ChangeLog 2016-03-11 14:45:14 UTC (rev 198018)
</span><span class="lines">@@ -1,3 +1,31 @@
</span><ins>+2016-03-07 Benjamin Poulain <benjamin@webkit.org>
+
+ [JSC] Simplify the overflow check of ArithAbs
+ https://bugs.webkit.org/show_bug.cgi?id=155063
+
+ Reviewed by Geoffrey Garen.
+
+ The only integer that overflow abs(int32) is INT_MIN.
+ For some reason, our code testing for that case
+ was checking the top bit of the result specifically.
+
+ The code required a large immediate on x86 and an extra
+ register on ARM64.
+
+ This patch turns the overflow check into a branch on
+ the sign of the result.
+
+ * dfg/DFGSpeculativeJIT32_64.cpp:
+ (JSC::DFG::SpeculativeJIT::compile):
+ * dfg/DFGSpeculativeJIT64.cpp:
+ (JSC::DFG::SpeculativeJIT::compile):
+ * ftl/FTLLowerDFGToB3.cpp:
+ (JSC::FTL::DFG::LowerDFGToB3::compileArithAbs):
+ * jit/ThunkGenerators.cpp:
+ (JSC::absThunkGenerator):
+ * tests/stress/arith-abs-overflow.js: Added.
+ (opaqueAbs):
+
</ins><span class="cx"> 2016-03-07 Csaba Osztrogonác <ossy@webkit.org>
</span><span class="cx">
</span><span class="cx"> Fix the ARM build after r197687
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit212SourceJavaScriptCoredfgDFGSpeculativeJIT32_64cpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp (198017 => 198018)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp 2016-03-11 14:37:34 UTC (rev 198017)
+++ releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp 2016-03-11 14:45:14 UTC (rev 198018)
</span><span class="lines">@@ -2187,7 +2187,7 @@
</span><span class="cx"> m_jit.rshift32(result.gpr(), MacroAssembler::TrustedImm32(31), scratch.gpr());
</span><span class="cx"> m_jit.add32(scratch.gpr(), result.gpr());
</span><span class="cx"> m_jit.xor32(scratch.gpr(), result.gpr());
</span><del>- speculationCheck(Overflow, JSValueRegs(), 0, m_jit.branch32(MacroAssembler::Equal, result.gpr(), MacroAssembler::TrustedImm32(1 << 31)));
</del><ins>+ speculationCheck(Overflow, JSValueRegs(), 0, m_jit.branchTest32(MacroAssembler::Signed, result.gpr()));
</ins><span class="cx"> int32Result(result.gpr(), node);
</span><span class="cx"> break;
</span><span class="cx"> }
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit212SourceJavaScriptCoredfgDFGSpeculativeJIT64cpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp (198017 => 198018)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp 2016-03-11 14:37:34 UTC (rev 198017)
+++ releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp 2016-03-11 14:45:14 UTC (rev 198018)
</span><span class="lines">@@ -2335,7 +2335,7 @@
</span><span class="cx"> m_jit.add32(scratch.gpr(), result.gpr());
</span><span class="cx"> m_jit.xor32(scratch.gpr(), result.gpr());
</span><span class="cx"> if (shouldCheckOverflow(node->arithMode()))
</span><del>- speculationCheck(Overflow, JSValueRegs(), 0, m_jit.branch32(MacroAssembler::Equal, result.gpr(), MacroAssembler::TrustedImm32(1 << 31)));
</del><ins>+ speculationCheck(Overflow, JSValueRegs(), 0, m_jit.branchTest32(MacroAssembler::Signed, result.gpr()));
</ins><span class="cx"> int32Result(result.gpr(), node);
</span><span class="cx"> break;
</span><span class="cx"> }
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit212SourceJavaScriptCoreftlFTLLowerDFGToB3cpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp (198017 => 198018)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp 2016-03-11 14:37:34 UTC (rev 198017)
+++ releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp 2016-03-11 14:45:14 UTC (rev 198018)
</span><span class="lines">@@ -1774,7 +1774,7 @@
</span><span class="cx"> LValue result = m_out.bitXor(mask, m_out.add(mask, value));
</span><span class="cx">
</span><span class="cx"> if (shouldCheckOverflow(m_node->arithMode()))
</span><del>- speculate(Overflow, noValue(), 0, m_out.equal(result, m_out.constInt32(1 << 31)));
</del><ins>+ speculate(Overflow, noValue(), 0, m_out.lessThan(result, m_out.int32Zero));
</ins><span class="cx">
</span><span class="cx"> setInt32(result);
</span><span class="cx"> break;
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit212SourceJavaScriptCorejitThunkGeneratorscpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/jit/ThunkGenerators.cpp (198017 => 198018)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/jit/ThunkGenerators.cpp 2016-03-11 14:37:34 UTC (rev 198017)
+++ releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/jit/ThunkGenerators.cpp 2016-03-11 14:45:14 UTC (rev 198018)
</span><span class="lines">@@ -910,7 +910,7 @@
</span><span class="cx"> jit.rshift32(SpecializedThunkJIT::regT0, MacroAssembler::TrustedImm32(31), SpecializedThunkJIT::regT1);
</span><span class="cx"> jit.add32(SpecializedThunkJIT::regT1, SpecializedThunkJIT::regT0);
</span><span class="cx"> jit.xor32(SpecializedThunkJIT::regT1, SpecializedThunkJIT::regT0);
</span><del>- jit.appendFailure(jit.branch32(MacroAssembler::Equal, SpecializedThunkJIT::regT0, MacroAssembler::TrustedImm32(1 << 31)));
</del><ins>+ jit.appendFailure(jit.branchTest32(MacroAssembler::Signed, SpecializedThunkJIT::regT0));
</ins><span class="cx"> jit.returnInt32(SpecializedThunkJIT::regT0);
</span><span class="cx"> nonIntJump.link(&jit);
</span><span class="cx"> // Shame about the double int conversion here.
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit212SourceJavaScriptCoretestsstressarithabsoverflowjs"></a>
<div class="addfile"><h4>Added: releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/tests/stress/arith-abs-overflow.js (0 => 198018)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/tests/stress/arith-abs-overflow.js (rev 0)
+++ releases/WebKitGTK/webkit-2.12/Source/JavaScriptCore/tests/stress/arith-abs-overflow.js 2016-03-11 14:45:14 UTC (rev 198018)
</span><span class="lines">@@ -0,0 +1,22 @@
</span><ins>+function opaqueAbs(value)
+{
+ return Math.abs(value);
+}
+noInline(opaqueAbs);
+
+// Warmup.
+for (let i = 0; i < 1e4; ++i) {
+ var positiveResult = opaqueAbs(i);
+ if (positiveResult !== i)
+ throw "Incorrect positive result at i = " + i + " result = " + positiveResult;
+ var negativeResult = opaqueAbs(-i);
+ if (negativeResult !== i)
+ throw "Incorrect negative result at -i = " + -i + " result = " + negativeResult;
+}
+
+// Overflow.
+for (let i = 0; i < 1e4; ++i) {
+ var overflowResult = opaqueAbs(-2147483648);
+ if (overflowResult !== 2147483648)
+ throw "Incorrect overflow result at i = " + i + " result = " + overflowResult;
+}
</ins></span></pre>
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