<!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> <a href = "TitleIndex">Index</a> </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>