<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="generator" content="AsciiDoc 8.6.8">
<title>PolyEqual</title>
<link rel="stylesheet" href="./asciidoc.css" type="text/css">
<link rel="stylesheet" href="./pygments.css" type="text/css">


<script type="text/javascript" src="./asciidoc.js"></script>
<script type="text/javascript">
/*<![CDATA[*/
asciidoc.install();
/*]]>*/
</script>
<link rel="stylesheet" href="./mlton.css" type="text/css"/>
</head>
<body class="article">
<div id="banner">
<div id="banner-home">
<a href="./Home">MLton 20130715</a>
</div>
</div>
<div id="header">
<h1>PolyEqual</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p><a href="PolyEqual">PolyEqual</a> is an optimization pass for the <a href="SSA">SSA</a>
<a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSASimplify">SSASimplify</a>.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">Description</h2>
<div class="sectionbody">
<div class="paragraph"><p>This pass implements polymorphic equality.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_implementation">Implementation</h2>
<div class="sectionbody">
<div class="ulist"><ul>
<li>
<p>
<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/poly-equal.fun"><span class="monospaced">poly-equal.fun</span></a>
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_details_and_notes">Details and Notes</h2>
<div class="sectionbody">
<div class="paragraph"><p>For each datatype, tycon, and vector type, it builds and equality
function and translates calls to <span class="monospaced">MLton_equal</span> into calls to that
function.</p></div>
<div class="paragraph"><p>Also generates calls to <span class="monospaced">IntInf_equal</span> and <span class="monospaced">Word_equal</span>.</p></div>
<div class="paragraph"><p>For tuples, it does the equality test inline; i.e., it does not create
a separate equality function for each tuple type.</p></div>
<div class="paragraph"><p>All equality functions are created only if necessary, i.e., if
equality is actually used at a type.</p></div>
<div class="paragraph"><p>Optimizations:</p></div>
<div class="ulist"><ul>
<li>
<p>
for datatypes that are enumerations, do not build a case dispatch,
just use <span class="monospaced">MLton_eq</span>, as the backend will represent these as ints
</p>
</li>
<li>
<p>
deep equality always does an <span class="monospaced">MLton_eq</span> test first
</p>
</li>
<li>
<p>
If one argument to <span class="monospaced">=</span> is a constant and the type will get
translated to an <span class="monospaced">IntOrPointer</span>, then just use <span class="monospaced">eq</span> instead of the
full equality.  This is important for implementing code like the
following efficiently:
</p>
<div class="listingblock">
<div class="content monospaced">
<pre>if x = 0  ...    (where x is of type IntInf.int)</pre>
</div></div>
</li>
<li>
<p>
Also convert pointer equality on scalar types to type specific
primitives.
</p>
</li>
</ul></div>
</div>
</div>
</div>
<div id="footnotes"><hr></div>
<div id="footer">
<div id="footer-text">
</div>
<div id="footer-badges">
</div>
</div>
</body>
</html>
