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Document Multidefs

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Provide documentation for multidefs, explaining in detail how they
work.

llvm-svn: 141236
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David Greene 2011-10-05 22:42:49 +00:00
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docs/TableGenFundamentals.html
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@ -769,6 +769,65 @@ before them.
</pre>
</div>
<p>
A special "multidef" may be used inside a multiclass to generate
several defs given a list of values.
</p>
<div class="doc_code">
<pre>
<b>class</b> Base&lt;int i&gt; {
int value = i;
}
<b>multiclass</b> Multi&lt;list&lt;int&gt; values&gt; {
<b>def</b> ONE : Base&lt;values[0]&gt;;
<b>def</b> TWO : Base&lt;values[1]&gt;;
<b>multidef</b> COUNT&lt;values, int v, 2&gt; : Base&lt:v&gt;;
}
<b>defm</b> List : Multi&lt;[1, 2, 3, 4, 5, 6]&lt;;
...
<i>// Results</i>
<b>def</b> ListCOUNT {
int v = ?;
int value = v;
list<int> Multi::values = [1, 2, 3, 4, 5, 6];
}
<b>def</b> ListONE {
int value = 1;
}
<b>def</b> ListTWO {
int value = 2;
}
<b>def</b> MD2.ListCOUNT {
int value = 3;
}
<b>def</b> MD3.ListCOUNT {
int value = 4;
}
<b>def</b> MD4.ListCOUNT {
int value = 5;
}
<b>def</b> MD5.ListCOUNT {
int value = 6;
}
</pre>
</div>
<p>
A multidef takes three "arguments" in the &lt;&gt; notation after the multidef
name. The first is a list of items to process. The second is a declaration.
This declaration creates a temporary name used as an iterator. It picks up the
value of each processed list item as TableGen generates defs from the multidef.
This temporary may be named and passed into the multidef body as shown in the
example above. This provides a powerful way to generate defs with various
values from a single multidef. The final "argument" is an integer value
indicating where in the list to begin processing. In the above example we
chose to begin list processing with the third item (index 2).
</p>
</div>
</div>