<!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>SSA2 - 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%;">
      SSA2
    <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>
      &nbsp;<a href = "Index">Index</a>
      &nbsp;
</table>
<div id="content" lang="en" dir="ltr">
SSA2 is an <a href="IntermediateLanguage">IntermediateLanguage</a>,  translated from <a href="SSA">SSA</a> by <a href="ToSSA2">ToSSA2</a>,  optimized by <a href="SSA2Simplify">SSA2Simplify</a>, and  translated by <a href="ToRSSA">ToRSSA</a> to <a href="RSSA">RSSA</a>. <h2 id="head-55f8ebc805e65b5b71ddafdae390e3be2bcd69af">Description</h2>
<p>
SSA2 is a <a class="nonexistent" href="FirstOrder">FirstOrder</a>, <a class="nonexistent" href="SimplyTyped">SimplyTyped</a> <a href="IntermediateLanguage">IntermediateLanguage</a>, a slight variant of the <a href="SSA">SSA</a> <a href="IntermediateLanguage">IntermediateLanguage</a>, 
</p>
<p>
Like <a href="SSA">SSA</a>, a <a href="SSA">SSA</a> program consists of a collection of datatype declarations, a sequence of global statements, and a collection of functions, along with a distinguished "main" function.  Each function consists of a collection of basic blocks, where each basic block is a sequence of statements ending with some control transfer. 
</p>
<p>
Unlike <a href="SSA">SSA</a>, SSA2 includes mutable fields in objects and makes the vector type constructor n-ary instead of unary.  This allows optimizations like <a href="RefFlatten">RefFlatten</a> and <a href="DeepFlatten">DeepFlatten</a> to be expressed. 
</p>
<h2 id="head-8781d615fd77be9578225c40ac67b9471394cced">Implementation</h2>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/ssa2.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa2.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/ssa2.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa2.fun</a><br>
 <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/ssa-tree2.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa-tree2.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/ssa-tree2.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">ssa-tree2.fun</a> <h2 id="head-a6de4b535fedeaa8890bd890b60fe09f87b5f96a">Type Checking</h2>
<p>
Type checking of a SSA2 program verifies the following: 
</p>

    <ul>

    <li>
<p>
 no duplicate definitions (tycons, cons, vars, labels, funcs) 
</p>
</li>
    <li>
<p>
 no out of scope references (tycons, cons, vars, labels, funcs) 
</p>
</li>
    <li>
<p>
 variable definitions dominate variable uses 
</p>
</li>
    <li>
<p>
 case transfers are exhaustive and irredundant 
</p>
</li>
    <li>
<p>
 <tt>Enter</tt>/<tt>Leave</tt> profile statements match 
</p>
</li>
    <li>
<p>
 "traditional" well-typedness 
</p>
</li>

    </ul>


<p>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/type-check2.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">type-check2.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/type-check2.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">type-check2.fun</a> 
</p>
<h2 id="head-35ec00231a68203708e39f0e2cc10b50c6bf62de">Details and Notes</h2>
<p>
SSA is an abbreviation for Static Single Assignment.   
</p>
</div>



<p>
<hr>
Last edited on 2007-08-15 22:07:25 by <span title="fenrir.uchicago.edu"><a href="MatthewFluet">MatthewFluet</a></span>.
</body></html>
