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DeepFlatten
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Deep flatten is an optimization pass for the <a href="SSA2">SSA2</a> <a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSA2Simplify">SSA2Simplify</a>. <h2 id="head-55f8ebc805e65b5b71ddafdae390e3be2bcd69af">Description</h2>
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This pass flattens into mutable fields of objects and into vectors.
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For example, an <tt>(int * int) ref</tt> is represented by a 2 word object, and an <tt>(int * int) array</tt> contains pairs of <tt>int</tt>s, rather than pointers to pairs of <tt>int</tt>s.
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<h2 id="head-8781d615fd77be9578225c40ac67b9471394cced">Implementation</h2>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/deep-flatten.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">deep-flatten.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/deep-flatten.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">deep-flatten.fun</a> <h2 id="head-35ec00231a68203708e39f0e2cc10b50c6bf62de">Details and Notes</h2>
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There are some performance issues with the deep flatten pass, where it consumes an excessive amount of memory.
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<a href="http://mlton.org/pipermail/mlton/2005-April/026990.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">http://mlton.org/pipermail/mlton/2005-April/026990.html</a>
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<a href="http://mlton.org/pipermail/mlton-user/2010-June/001626.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">http://mlton.org/pipermail/mlton-user/2010-June/001626.html</a>
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<p>
A number of applications require compilation with <tt>-drop-pass deepFlatten</tt> to avoid exceeding available memory. It is often asked whether the deep flatten pass usually has a significant impact on performance. The standard benchmark suite was run with and without the deep flatten pass enabled when the pass was first introduced:
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<a href="http://mlton.org/pipermail/mlton/2004-August/025760.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">http://mlton.org/pipermail/mlton/2004-August/025760.html</a>
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<p>
The conclusion is that it does not have a significant impact. However, these are micro benchmarks; other applications may derive greater benefit from the pass.
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Last edited on 2010-06-01 17:13:13 by <span title="fenrir.cs.rit.edu"><a href="MatthewFluet">MatthewFluet</a></span>.
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