doc/guide/localhost/SSA2

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  26 <h1>SSA2</h1>
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  28 <div id="content">
  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p><a href="SSA2">SSA2</a> is an <a href="IntermediateLanguage">IntermediateLanguage</a>, translated from <a href="SSA">SSA</a> by
  32 <a href="ToSSA2">ToSSA2</a>, optimized by <a href="SSA2Simplify">SSA2Simplify</a>, and translated by
  33 <a href="ToRSSA">ToRSSA</a> to <a href="RSSA">RSSA</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="SSA2">SSA2</a> is a <a href="FirstOrder">FirstOrder</a>, <a href="SimplyTyped">SimplyTyped</a>
  40 <a href="IntermediateLanguage">IntermediateLanguage</a>, a slight variant of the <a href="SSA">SSA</a>
  41 <a href="IntermediateLanguage">IntermediateLanguage</a>,</p></div>
  42 <div class="paragraph"><p>Like <a href="SSA">SSA</a>, an <a href="SSA2">SSA2</a> program consists of a collection of datatype
  43 declarations, a sequence of global statements, and a collection of
  44 functions, along with a distinguished "main" function.  Each function
  45 consists of a collection of basic blocks, where each basic block is a
  46 sequence of statements ending with some control transfer.</p></div>
  47 <div class="paragraph"><p>Unlike <a href="SSA">SSA</a>, <a href="SSA2">SSA2</a> includes mutable fields in objects and makes
  48 the vector type constructor n-ary instead of unary.  This allows
  49 optimizations like <a href="RefFlatten">RefFlatten</a> and <a href="DeepFlatten">DeepFlatten</a> to be expressed.</p></div>
  50 </div>
  51 </div>
  52 <div class="sect1">
  53 <h2 id="_implementation">Implementation</h2>
  54 <div class="sectionbody">
  55 <div class="ulist"><ul>
  56 <li>
  57 <p>
  58 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa2.sig"><span class="monospaced">ssa2.sig</span></a>
  59 </p>
  60 </li>
  61 <li>
  62 <p>
  63 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa2.fun"><span class="monospaced">ssa2.fun</span></a>
  64 </p>
  65 </li>
  66 <li>
  67 <p>
  68 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree2.sig"><span class="monospaced">ssa-tree2.sig</span></a>
  69 </p>
  70 </li>
  71 <li>
  72 <p>
  73 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/ssa-tree2.fun"><span class="monospaced">ssa-tree2.fun</span></a>
  74 </p>
  75 </li>
  76 </ul></div>
  77 </div>
  78 </div>
  79 <div class="sect1">
  80 <h2 id="_type_checking">Type Checking</h2>
  81 <div class="sectionbody">
  82 <div class="paragraph"><p>Type checking (<a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/type-check2.sig"><span class="monospaced">type-check2.sig</span></a>,
  83 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/type-check2.fun"><span class="monospaced">type-check2.fun</span></a>) of a <a href="SSA2">SSA2</a>
  84 program verifies the following:</p></div>
  85 <div class="ulist"><ul>
  86 <li>
  87 <p>
  88 no duplicate definitions (tycons, cons, vars, labels, funcs)
  89 </p>
  90 </li>
  91 <li>
  92 <p>
  93 no out of scope references (tycons, cons, vars, labels, funcs)
  94 </p>
  95 </li>
  96 <li>
  97 <p>
  98 variable definitions dominate variable uses
  99 </p>
 100 </li>
 101 <li>
 102 <p>
 103 case transfers are exhaustive and irredundant
 104 </p>
 105 </li>
 106 <li>
 107 <p>
 108 <span class="monospaced">Enter</span>/<span class="monospaced">Leave</span> profile statements match
 109 </p>
 110 </li>
 111 <li>
 112 <p>
 113 "traditional" well-typedness
 114 </p>
 115 </li>
 116 </ul></div>
 117 </div>
 118 </div>
 119 <div class="sect1">
 120 <h2 id="_details_and_notes">Details and Notes</h2>
 121 <div class="sectionbody">
 122 <div class="paragraph"><p>SSA is an abbreviation for Static Single Assignment.</p></div>
 123 </div>
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