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<a href="./Home">MLton 20201002</a>
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<h1>ToMachine</h1>
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<div class="paragraph"><p><a href="ToMachine">ToMachine</a> is a translation pass from the <a href="RSSA">RSSA</a>
<a href="IntermediateLanguage">IntermediateLanguage</a> to the <a href="Machine">Machine</a> <a href="IntermediateLanguage">IntermediateLanguage</a>.</p></div>
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<h2 id="_description">Description</h2>
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<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>
<div class="paragraph"><p>It uses <a href="AllocateVariables">AllocateVariables</a>, <a href="Chunkify">Chunkify</a>, and <a href="ParallelMove">ParallelMove</a>.</p></div>
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<h2 id="_implementation">Implementation</h2>
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<p>
<a href="https://github.com/MLton/mlton/blob/master/mlton/backend/backend.sig"><span class="monospaced">backend.sig</span></a>
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<a href="https://github.com/MLton/mlton/blob/master/mlton/backend/backend.fun"><span class="monospaced">backend.fun</span></a>
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<h2 id="_details_and_notes">Details and Notes</h2>
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<div class="paragraph"><p>Because the MLton runtime system is shared by all <a href="Codegen">codegens</a>, it is most
convenient to decide on stack layout <em>before</em> any <a href="Codegen">codegen</a> takes over.
In particular, we compute all the stack frame info for each <a href="RSSA">RSSA</a>
function, including stack size, <a href="GarbageCollection">garbage collector</a>
masks for each frame, etc.  To do so, the <a href="Machine">Machine</a>
<a href="IntermediateLanguage">IntermediateLanguage</a> imagines an abstract machine with an infinite
number of temporaries of every size.  A liveness analysis
determines, for each variable, whether or not it is live across a
point where the runtime system might take over (for example, any
garbage collection point) or a non-tail call to another <a href="RSSA">RSSA</a>
function.  Those that are live go on the stack, while those that
aren&#8217;t live go into temporaries.  From this information, we know
all we need to about each stack frame.  On the downside, nothing
further on is allowed to change this stack info; it is set in stone.</p></div>
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