<!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>
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