<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta name="robots" content="index,nofollow"> <title>Useless - MLton Standard ML Compiler (SML Compiler)</title> <link rel="stylesheet" type="text/css" charset="iso-8859-1" media="all" href="common.css"> <link rel="stylesheet" type="text/css" charset="iso-8859-1" media="screen" href="screen.css"> <link rel="stylesheet" type="text/css" charset="iso-8859-1" media="print" href="print.css"> <link rel="Start" href="Home"> </head> <body lang="en" dir="ltr"> <script src="http://www.google-analytics.com/urchin.js" type="text/javascript"> </script> <script type="text/javascript"> _uacct = "UA-833377-1"; urchinTracker(); </script> <table bgcolor = lightblue cellspacing = 0 style = "border: 0px;" width = 100%> <tr> <td style = " border: 0px; color: darkblue; font-size: 150%; text-align: left;"> <a class = mltona href="Home">MLton MLTONWIKIVERSION</a> <td style = " border: 0px; font-size: 150%; text-align: center; width: 50%;"> Useless <td style = " border: 0px; text-align: right;"> <table cellspacing = 0 style = "border: 0px"> <tr style = "vertical-align: middle;"> </table> <tr style = "background-color: white;"> <td colspan = 3 style = " border: 0px; font-size:70%; text-align: right;"> <a href = "Home">Home</a> <a href = "TitleIndex">Index</a> </table> <div id="content" lang="en" dir="ltr"> Useless is an optimization pass for the <a href="SSA">SSA</a> <a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSASimplify">SSASimplify</a>. <h2 id="head-55f8ebc805e65b5b71ddafdae390e3be2bcd69af">Description</h2> <p> This pass: </p> <ul> <li> <p> removes components of tuples that are constants (use unification) </p> </li> <li> <p> removes function arguments that are constants </p> </li> <li> <p> builds some kind of dependence graph where </p> </li> <ul> - a value of ground type is useful if it is an arg to a primitive - a tuple is useful if it contains a useful component - a constructor is useful if it contains a useful component or is used in a <tt>Case</tt> transfer </ul> </ul> <p> If a useful tuple is coerced to another useful tuple, then all of their components must agree (exactly). It is trivial to convert a useful value to a useless one. </p> <h2 id="head-8781d615fd77be9578225c40ac67b9471394cced">Implementation</h2> <p> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/useless.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">useless.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/useless.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">useless.fun</a> </p> <h2 id="head-35ec00231a68203708e39f0e2cc10b50c6bf62de">Details and Notes</h2> <p> It is also trivial to convert a useful tuple to one of its useful components -- but this seems hard. </p> <p> Suppose that you have a <tt>ref</tt>/<tt>array</tt>/<tt>vector</tt> that is useful, but the components aren't -- then the components are converted to type <tt>unit</tt>, and any primitive args must be as well. </p> <p> Unify all handler arguments so that <tt>raise</tt>/<tt>handle</tt> has a consistent calling convention. </p> </div> <p> <hr> Last edited on 2006-11-02 17:56:21 by <span title="76.16.241.4"><a href="MatthewFluet">MatthewFluet</a></span>. </body></html>