<!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>SSA</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>SSA</h1> </div> <div id="content"> <div id="preamble"> <div class="sectionbody"> <div class="paragraph"><p><a href="SSA">SSA</a> is an <a href="IntermediateLanguage">IntermediateLanguage</a>, translated from <a href="SXML">SXML</a> by <a href="ClosureConvert">ClosureConvert</a>, optimized by <a href="SSASimplify">SSASimplify</a>, and translated by <a href="ToSSA2">ToSSA2</a> to <a href="SSA2">SSA2</a>.</p></div> </div> </div> <div class="sect1"> <h2 id="_description">Description</h2> <div class="sectionbody"> <div class="paragraph"><p><a href="SSA">SSA</a> is a <a href="FirstOrder">FirstOrder</a>, <a href="SimplyTyped">SimplyTyped</a> <a href="IntermediateLanguage">IntermediateLanguage</a>. It is the main <a href="IntermediateLanguage">IntermediateLanguage</a> used for optimizations.</p></div> <div class="paragraph"><p>An <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></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/ssa.sig"><span class="monospaced">ssa.sig</span></a> </p> </li> <li> <p> <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa.fun"><span class="monospaced">ssa.fun</span></a> </p> </li> <li> <p> <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree.sig"><span class="monospaced">ssa-tree.sig</span></a> </p> </li> <li> <p> <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree.fun"><span class="monospaced">ssa-tree.fun</span></a> </p> </li> </ul></div> </div> </div> <div class="sect1"> <h2 id="_type_checking">Type Checking</h2> <div class="sectionbody"> <div class="paragraph"><p>Type checking (<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/type-check.sig"><span class="monospaced">type-check.sig</span></a>, <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/type-check.fun"><span class="monospaced">type-check.fun</span></a>) of a <a href="SSA">SSA</a> program verifies the following:</p></div> <div class="ulist"><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> <span class="monospaced">Enter</span>/<span class="monospaced">Leave</span> profile statements match </p> </li> <li> <p> "traditional" well-typedness </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>SSA is an abbreviation for Static Single Assignment.</p></div> <div class="paragraph"><p>For some initial design discussion, see the thread at:</p></div> <div class="ulist"><ul> <li> <p> <a href="http://mlton.org/pipermail/mlton/2001-August/019689.html">http://mlton.org/pipermail/mlton/2001-August/019689.html</a> </p> </li> </ul></div> <div class="paragraph"><p>For a retrospective, see the thread at:</p></div> <div class="ulist"><ul> <li> <p> <a href="http://mlton.org/pipermail/mlton/2007-February/029597.html">http://mlton.org/pipermail/mlton/2007-February/029597.html</a> </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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