doc/guide/localhost/SSA

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  26 <h1>SSA</h1>
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  28 <div id="content">
  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p><a href="SSA">SSA</a> is an <a href="IntermediateLanguage">IntermediateLanguage</a>, translated from <a href="SXML">SXML</a> by
  32 <a href="ClosureConvert">ClosureConvert</a>, optimized by <a href="SSASimplify">SSASimplify</a>, and translated by
  33 <a href="ToSSA2">ToSSA2</a> to <a href="SSA2">SSA2</a>.</p></div>
  34 </div>
  35 </div>
  36 <div class="sect1">
  37 <h2 id="_description">Description</h2>
  38 <div class="sectionbody">
  39 <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>.
  40 It is the main <a href="IntermediateLanguage">IntermediateLanguage</a> used for optimizations.</p></div>
  41 <div class="paragraph"><p>An <a href="SSA">SSA</a> program consists of a collection of datatype declarations,
  42 a sequence of global statements, and a collection of functions, along
  43 with a distinguished "main" function.  Each function consists of a
  44 collection of basic blocks, where each basic block is a sequence of
  45 statements ending with some control transfer.</p></div>
  46 </div>
  47 </div>
  48 <div class="sect1">
  49 <h2 id="_implementation">Implementation</h2>
  50 <div class="sectionbody">
  51 <div class="ulist"><ul>
  52 <li>
  53 <p>
  54 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa.sig"><span class="monospaced">ssa.sig</span></a>
  55 </p>
  56 </li>
  57 <li>
  58 <p>
  59 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa.fun"><span class="monospaced">ssa.fun</span></a>
  60 </p>
  61 </li>
  62 <li>
  63 <p>
  64 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree.sig"><span class="monospaced">ssa-tree.sig</span></a>
  65 </p>
  66 </li>
  67 <li>
  68 <p>
  69 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree.fun"><span class="monospaced">ssa-tree.fun</span></a>
  70 </p>
  71 </li>
  72 </ul></div>
  73 </div>
  74 </div>
  75 <div class="sect1">
  76 <h2 id="_type_checking">Type Checking</h2>
  77 <div class="sectionbody">
  78 <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>,
  79 <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
  80 verifies the following:</p></div>
  81 <div class="ulist"><ul>
  82 <li>
  83 <p>
  84 no duplicate definitions (tycons, cons, vars, labels, funcs)
  85 </p>
  86 </li>
  87 <li>
  88 <p>
  89 no out of scope references (tycons, cons, vars, labels, funcs)
  90 </p>
  91 </li>
  92 <li>
  93 <p>
  94 variable definitions dominate variable uses
  95 </p>
  96 </li>
  97 <li>
  98 <p>
  99 case transfers are exhaustive and irredundant
 100 </p>
 101 </li>
 102 <li>
 103 <p>
 104 <span class="monospaced">Enter</span>/<span class="monospaced">Leave</span> profile statements match
 105 </p>
 106 </li>
 107 <li>
 108 <p>
 109 "traditional" well-typedness
 110 </p>
 111 </li>
 112 </ul></div>
 113 </div>
 114 </div>
 115 <div class="sect1">
 116 <h2 id="_details_and_notes">Details and Notes</h2>
 117 <div class="sectionbody">
 118 <div class="paragraph"><p>SSA is an abbreviation for Static Single Assignment.</p></div>
 119 <div class="paragraph"><p>For some initial design discussion, see the thread at:</p></div>
 120 <div class="ulist"><ul>
 121 <li>
 122 <p>
 123 <a href="http://mlton.org/pipermail/mlton/2001-August/019689.html">http://mlton.org/pipermail/mlton/2001-August/019689.html</a>
 124 </p>
 125 </li>
 126 </ul></div>
 127 <div class="paragraph"><p>For some retrospectives, see the threads at:</p></div>
 128 <div class="ulist"><ul>
 129 <li>
 130 <p>
 131 <a href="http://mlton.org/pipermail/mlton/2003-January/023054.html">http://mlton.org/pipermail/mlton/2003-January/023054.html</a>
 132 </p>
 133 </li>
 134 <li>
 135 <p>
 136 <a href="http://mlton.org/pipermail/mlton/2007-February/029597.html">http://mlton.org/pipermail/mlton/2007-February/029597.html</a>
 137 </p>
 138 </li>
 139 </ul></div>
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