doc/guide/localhost/DeepFlatten

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  26 <h1>DeepFlatten</h1>
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  28 <div id="content">
  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p><a href="DeepFlatten">DeepFlatten</a> is an optimization pass for the <a href="SSA2">SSA2</a>
  32 <a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSA2Simplify">SSA2Simplify</a>.</p></div>
  33 </div>
  34 </div>
  35 <div class="sect1">
  36 <h2 id="_description">Description</h2>
  37 <div class="sectionbody">
  38 <div class="paragraph"><p>This pass flattens into mutable fields of objects and into vectors.</p></div>
  39 <div class="paragraph"><p>For example, an <span class="monospaced">(int * int) ref</span> is represented by a 2 word
  40 object, and an <span class="monospaced">(int * int) array</span> contains pairs of <span class="monospaced">int</span>-s,
  41 rather than pointers to pairs of <span class="monospaced">int</span>-s.</p></div>
  42 </div>
  43 </div>
  44 <div class="sect1">
  45 <h2 id="_implementation">Implementation</h2>
  46 <div class="sectionbody">
  47 <div class="ulist"><ul>
  48 <li>
  49 <p>
  50 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/deep-flatten.fun"><span class="monospaced">deep-flatten.fun</span></a>
  51 </p>
  52 </li>
  53 </ul></div>
  54 </div>
  55 </div>
  56 <div class="sect1">
  57 <h2 id="_details_and_notes">Details and Notes</h2>
  58 <div class="sectionbody">
  59 <div class="paragraph"><p>There are some performance issues with the deep flatten pass, where it
  60 consumes an excessive amount of memory.</p></div>
  61 <div class="ulist"><ul>
  62 <li>
  63 <p>
  64 <a href="http://www.mlton.org/pipermail/mlton/2005-April/026990.html">http://www.mlton.org/pipermail/mlton/2005-April/026990.html</a>
  65 </p>
  66 </li>
  67 <li>
  68 <p>
  69 <a href="http://www.mlton.org/pipermail/mlton-user/2010-June/001626.html">http://www.mlton.org/pipermail/mlton-user/2010-June/001626.html</a>
  70 </p>
  71 </li>
  72 <li>
  73 <p>
  74 <a href="http://www.mlton.org/pipermail/mlton/2010-December/030876.html">http://www.mlton.org/pipermail/mlton/2010-December/030876.html</a>
  75 </p>
  76 </li>
  77 </ul></div>
  78 <div class="paragraph"><p>A number of applications require compilation with
  79 <span class="monospaced">-disable-pass deepFlatten</span> to avoid exceeding available memory.  It is
  80 often asked whether the deep flatten pass usually has a significant
  81 impact on performance.  The standard benchmark suite was run with and
  82 without the deep flatten pass enabled when the pass was first
  83 introduced:</p></div>
  84 <div class="ulist"><ul>
  85 <li>
  86 <p>
  87 <a href="http://www.mlton.org/pipermail/mlton/2004-August/025760.html">http://www.mlton.org/pipermail/mlton/2004-August/025760.html</a>
  88 </p>
  89 </li>
  90 </ul></div>
  91 <div class="paragraph"><p>The conclusion is that it does not have a significant impact.
  92 However, these are micro benchmarks; other applications may derive
  93 greater benefit from the pass.</p></div>
  94 </div>
  95 </div>
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