<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="generator" content="AsciiDoc 8.6.10">
<title>RedundantTests</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 20201002</a>
</div>
</div>
<div id="header">
<h1>RedundantTests</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p><a href="RedundantTests">RedundantTests</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 simplifies conditionals whose results are implied by a
previous conditional test.</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/redundant-tests.fun"><span class="monospaced">redundant-tests.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>An additional test will sometimes eliminate the overflow test when
adding or subtracting 1.  In particular, it will eliminate it in the
following cases:</p></div>
<div class="listingblock">
<div class="content"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">&lt;</span><span class="w"> </span><span class="n">y</span><span class="w"></span>
<span class="w">  </span><span class="k">then</span><span class="w"> </span><span class="p">...</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">...</span><span class="w"></span>
<span class="k">else</span><span class="w"> </span><span class="p">...</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">...</span><span class="w"></span>
</pre></div></div></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>
