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PolyEqual is an optimization pass for the <a href="SSA">SSA</a> <a href="IntermediateLanguage">IntermediateLanguage</a>, invoked from <a href="SSASimplify">SSASimplify</a>. <h2 id="head-55f8ebc805e65b5b71ddafdae390e3be2bcd69af">Description</h2>
<p>
This pass implements polymorphic equality.
</p>
<h2 id="head-8781d615fd77be9578225c40ac67b9471394cced">Implementation</h2>
<a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/poly-equal.sig?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">poly-equal.sig</a> <a href = "http://mlton.org/cgi-bin/viewsvn.cgi/mlton/tags/on-MLTONWIKIVERSION-release/mlton/ssa/poly-equal.fun?view=markup"><img src="moin-www.png" alt="[WWW]" height="11" width="11">poly-equal.fun</a> <h2 id="head-35ec00231a68203708e39f0e2cc10b50c6bf62de">Details and Notes</h2>
<p>
For each datatype, tycon, and vector type, it builds and equality function and translates calls to <tt>MLton_equal</tt> into calls to that function.
</p>
<p>
Also generates calls to <tt>IntInf_equal</tt> and <tt>Word_equal</tt>.
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<p>
For tuples, it does the equality test inline; i.e., it does not create a separate equality function for each tuple type.
</p>
<p>
All equality functions are created only if necessary, i.e., if equality is actually used at a type.
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<p>
Optimizations:
</p>
<ul>
<li>
<p>
for datatypes that are enumerations, do not build a case dispatch, just use <tt>MLton_eq</tt>, as the backend will represent these as ints
</p>
</li>
<li class="gap">
<p>
deep equality always does an <tt>MLton_eq</tt> test first
</p>
</li>
<li class="gap">
<p>
If one argument to <tt>=</tt> is a constant and the type will get translated to an <tt>IntOrPointer</tt>, then just use <tt>eq</tt> instead of the full equality. This is important for implementing code like the following efficiently:
<pre>if x = 0 ... (where x is an IntInf.int)
</pre>
</p>
</li>
<li class="gap">
<p>
Also convert pointer equality on scalar types to type specific primitives.
</p>
</li>
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<hr>
Last edited on 2009-07-11 17:10:54 by <span title="c-67-165-143-160.hsd1.il.comcast.net"><a href="MatthewFluet">MatthewFluet</a></span>.
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