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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/195882">195882</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2016-01-29 21:14:23 -0800 (Fri, 29 Jan 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>B3 should reduce Mod(value, constant) to Div and Mul so that our Div optimizations can do things
https://bugs.webkit.org/show_bug.cgi?id=153693
Reviewed by Saam Barati.
The most efficient way to handle Mod(value, constant) is to reduce it to
Sub(value, Mul(Div(value, constant), constant)) and then let the Div optimizations do their
thing.
In the future we could add special handling of Mod(value, 1 << constant), but it's not
obvious that this would produce better code than reducing through Div, if we also make sure
that we have great optimizations for Mul and Div.
* b3/B3ReduceStrength.cpp:</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreb3B3ReduceStrengthcpp">trunk/Source/JavaScriptCore/b3/B3ReduceStrength.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (195881 => 195882)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-01-30 03:31:32 UTC (rev 195881)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-01-30 05:14:23 UTC (rev 195882)
</span><span class="lines">@@ -1,3 +1,20 @@
</span><ins>+2016-01-29 Filip Pizlo <fpizlo@apple.com>
+
+ B3 should reduce Mod(value, constant) to Div and Mul so that our Div optimizations can do things
+ https://bugs.webkit.org/show_bug.cgi?id=153693
+
+ Reviewed by Saam Barati.
+
+ The most efficient way to handle Mod(value, constant) is to reduce it to
+ Sub(value, Mul(Div(value, constant), constant)) and then let the Div optimizations do their
+ thing.
+
+ In the future we could add special handling of Mod(value, 1 << constant), but it's not
+ obvious that this would produce better code than reducing through Div, if we also make sure
+ that we have great optimizations for Mul and Div.
+
+ * b3/B3ReduceStrength.cpp:
+
</ins><span class="cx"> 2016-01-29 Keith Miller <keith_miller@apple.com>
</span><span class="cx">
</span><span class="cx"> Array.prototype native functions should use Symbol.species to construct the result
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreb3B3ReduceStrengthcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/b3/B3ReduceStrength.cpp (195881 => 195882)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/b3/B3ReduceStrength.cpp 2016-01-30 03:31:32 UTC (rev 195881)
+++ trunk/Source/JavaScriptCore/b3/B3ReduceStrength.cpp 2016-01-30 05:14:23 UTC (rev 195882)
</span><span class="lines">@@ -662,14 +662,12 @@
</span><span class="cx"> // We can do this because it's precisely correct for ChillDiv and for Div we
</span><span class="cx"> // are allowed to do whatever we want.
</span><span class="cx"> m_value->replaceWithIdentity(m_value->child(1));
</span><del>- m_changed = true;
</del><span class="cx"> break;
</span><span class="cx">
</span><span class="cx"> case 1:
</span><span class="cx"> // Turn this: Div(value, 1)
</span><span class="cx"> // Into this: value
</span><span class="cx"> m_value->replaceWithIdentity(m_value->child(0));
</span><del>- m_changed = true;
</del><span class="cx"> break;
</span><span class="cx">
</span><span class="cx"> default:
</span><span class="lines">@@ -722,12 +720,11 @@
</span><span class="cx"> m_index, ZShr, m_value->origin(), magicQuotient,
</span><span class="cx"> m_insertionSet.insert<Const32Value>(
</span><span class="cx"> m_index, m_value->origin(), 31))));
</span><del>- m_changed = true;
</del><span class="cx"> break;
</span><span class="cx"> }
</span><span class="cx">
</span><del>- if (m_value->opcode() != ChillDiv && m_value->opcode() != Div)
- break;
</del><ins>+ m_changed = true;
+ break;
</ins><span class="cx"> }
</span><span class="cx"> break;
</span><span class="cx">
</span><span class="lines">@@ -737,6 +734,68 @@
</span><span class="cx"> // Into this: constant1 / constant2
</span><span class="cx"> // Note that this uses ChillMod semantics.
</span><span class="cx"> replaceWithNewValue(m_value->child(0)->modConstant(m_proc, m_value->child(1)));
</span><ins>+
+ // Modulo by constant is more efficient if we turn it into Div, and then let Div get
+ // optimized.
+ if (m_value->child(1)->hasInt()) {
+ switch (m_value->child(1)->asInt()) {
+ case 0:
+ // Turn this: Mod(value, 0)
+ // Into this: 0
+ // This is correct according to ChillMod semantics.
+ m_value->replaceWithIdentity(m_value->child(1));
+ break;
+
+ default:
+ // Turn this: Mod(N, D)
+ // Into this: Sub(N, Mul(Div(N, D), D))
+ //
+ // This is a speed-up because we use our existing Div optimizations.
+ //
+ // Here's an easier way to look at it:
+ // N % D = N - N / D * D
+ //
+ // Note that this does not work for D = 0 and ChillMod. The expected result is 0.
+ // That's why we have a special-case above.
+ // X % 0 = X - X / 0 * 0 = X (should be 0)
+ //
+ // This does work for the D = -1 special case.
+ // -2^31 % -1 = -2^31 - -2^31 / -1 * -1
+ // = -2^31 - -2^31 * -1
+ // = -2^31 - -2^31
+ // = 0
+
+ Opcode divOpcode;
+ switch (m_value->opcode()) {
+ case Mod:
+ divOpcode = Div;
+ break;
+ case ChillMod:
+ divOpcode = ChillDiv;
+ break;
+ default:
+ divOpcode = Oops;
+ RELEASE_ASSERT_NOT_REACHED();
+ break;
+ }
+
+ m_value->replaceWithIdentity(
+ m_insertionSet.insert<Value>(
+ m_index, Sub, m_value->origin(),
+ m_value->child(0),
+ m_insertionSet.insert<Value>(
+ m_index, Mul, m_value->origin(),
+ m_insertionSet.insert<Value>(
+ m_index, divOpcode, m_value->origin(),
+ m_value->child(0), m_value->child(1)),
+ m_value->child(1))));
+ break;
+ }
+
+ m_changed = true;
+ break;
+ }
+
</ins><span class="cx"> break;
</span><span class="cx">
</span><span class="cx"> case BitAnd:
</span></span></pre>
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