doc/guide/localhost/RedundantTests

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  26 <h1>RedundantTests</h1>
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  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p><a href="RedundantTests">RedundantTests</a> is an optimization pass for the <a href="SSA">SSA</a>
  32 <a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSASimplify">SSASimplify</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 simplifies conditionals whose results are implied by a
  39 previous conditional test.</p></div>
  40 </div>
  41 </div>
  42 <div class="sect1">
  43 <h2 id="_implementation">Implementation</h2>
  44 <div class="sectionbody">
  45 <div class="ulist"><ul>
  46 <li>
  47 <p>
  48 <a href="https://github.com/MLton/mlton/blob/master/mlton/ssa/redundant-tests.fun"><span class="monospaced">redundant-tests.fun</span></a>
  49 </p>
  50 </li>
  51 </ul></div>
  52 </div>
  53 </div>
  54 <div class="sect1">
  55 <h2 id="_details_and_notes">Details and Notes</h2>
  56 <div class="sectionbody">
  57 <div class="paragraph"><p>An additional test will sometimes eliminate the overflow test when
  58 adding or subtracting 1.  In particular, it will eliminate it in the
  59 following cases:</p></div>
  60 <div class="listingblock">
  61 <div class="content"><div class="highlight"><pre><span class="k">if</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">&lt;</span><span class="w"> </span><span class="n">y</span><span class="w"></span>
  62 <span class="w">  </span><span class="k">then</span><span class="w"> </span><span class="p">...</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">...</span><span class="w"></span>
  63 <span class="k">else</span><span class="w"> </span><span class="p">...</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">...</span><span class="w"></span>
  64 </pre></div></div></div>
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