doc/guide/localhost/ToMachine

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  22 <a href="./Home">MLton 20180207</a>
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  26 <h1>ToMachine</h1>
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  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="paragraph"><p><a href="ToMachine">ToMachine</a> is a translation pass from the <a href="RSSA">RSSA</a>
  32 <a href="IntermediateLanguage">IntermediateLanguage</a> to the <a href="Machine">Machine</a> <a href="IntermediateLanguage">IntermediateLanguage</a>.</p></div>
  33 </div>
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  35 <div class="sect1">
  36 <h2 id="_description">Description</h2>
  37 <div class="sectionbody">
  38 <div class="paragraph"><p>This pass converts from a <a href="RSSA">RSSA</a> program into a <a href="Machine">Machine</a> program.</p></div>
  39 <div class="paragraph"><p>It uses <a href="AllocateRegisters">AllocateRegisters</a>, <a href="Chunkify">Chunkify</a>, and <a href="ParallelMove">ParallelMove</a>.</p></div>
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  42 <div class="sect1">
  43 <h2 id="_implementation">Implementation</h2>
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  45 <div class="ulist"><ul>
  46 <li>
  47 <p>
  48 <a href="https://github.com/MLton/mlton/blob/master/mlton/backend/backend.sig"><span class="monospaced">backend.sig</span></a>
  49 </p>
  50 </li>
  51 <li>
  52 <p>
  53 <a href="https://github.com/MLton/mlton/blob/master/mlton/backend/backend.fun"><span class="monospaced">backend.fun</span></a>
  54 </p>
  55 </li>
  56 </ul></div>
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  58 </div>
  59 <div class="sect1">
  60 <h2 id="_details_and_notes">Details and Notes</h2>
  61 <div class="sectionbody">
  62 <div class="paragraph"><p>Because the MLton runtime system is shared by all <a href="Codegen">codegens</a>, it is most
  63 convenient to decide on stack layout <em>before</em> any <a href="Codegen">codegen</a> takes over.
  64 In particular, we compute all the stack frame info for each <a href="RSSA">RSSA</a>
  65 function, including stack size, <a href="GarbageCollection">garbage collector</a>
  66 masks for each frame, etc.  To do so, the <a href="Machine">Machine</a>
  67 <a href="IntermediateLanguage">IntermediateLanguage</a> imagines an abstract machine with an infinite
  68 number of (pseudo-)registers of every size.  A liveness analysis
  69 determines, for each variable, whether or not it is live across a
  70 point where the runtime system might take over (for example, any
  71 garbage collection point) or a non-tail call to another <a href="RSSA">RSSA</a>
  72 function.  Those that are live go on the stack, while those that
  73 aren&#8217;t live go into psuedo-registers.  From this information, we know
  74 all we need to about each stack frame.  On the downside, nothing
  75 further on is allowed to change this stack info; it is set in stone.</p></div>
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