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Add information about the piece I forgot to write: parameterized tablegen classes 

llvm-svn: 11147
This commit is contained in:
Chris Lattner 2004-02-06 06:37:00 +00:00
parent 1215e32eb7
commit 55927236e8
1 changed files with 86 additions and 2 deletions
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88
llvm/docs/TableGenFundamentals.html
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@ -406,6 +406,13 @@ derive from the <tt>C</tt> class. Because of this, they both get the <tt>V</tt>
bit value. The <tt>Y</tt> definition also gets the Greeting member as well.
</p>
<p>
In general, classes are useful for collecting together the commonality between a
group of records, and isolating it in a single places. Also, classes permit the
specification of default values for their subclasses, allowing the subclasses to
override them as they wish.
</p>
</div>
<!----------------------------------------------------------------------------->
@ -456,7 +463,84 @@ because the <tt>D</tt> class overrode its value.
</div>
<div class="doc_text">
and default values...
<p>
TableGen permits the definition of parameterized classes as well as normal
concrete classes. Parameterized TableGen classes specify a list of variable
bindings (which may optionally have defaults) that are bound when used. Here is
a simple example:</p>
<p><pre>
<b>class</b> FPFormat&lt;<b>bits</b>&lt;3&gt; val&gt; {
<b>bits</b>&lt;3&gt; Value = val;
}
<b>def</b> NotFP : FPFormat&lt;0&gt;;
<b>def</b> ZeroArgFP : FPFormat&lt;1&gt;;
<b>def</b> OneArgFP : FPFormat&lt;2&gt;;
<b>def</b> OneArgFPRW : FPFormat&lt;3&gt;;
<b>def</b> TwoArgFP : FPFormat&lt;4&gt;;
<b>def</b> SpecialFP : FPFormat&lt;5&gt;;
</pre></p>
<p>
In this case, template arguments are used as a space efficient way to specify a
list of "enumeration values", each with a "Value" field set to the specified
integer.</p>
<p>The more esoteric forms of <a href="#values">TableGen expressions</a> are
useful in conjunction with template arguments. As an example:</p>
<p><pre>
<b>class</b> ModRefVal&lt;<b>bits</b>&lt;2&gt; val&gt; {
<b>bits</b>&lt;2&gt; Value = val;
}
<b>def</b> None : ModRefVal&lt;0&gt;;
<b>def</b> Mod : ModRefVal&lt;1&gt;;
<b>def</b> Ref : ModRefVal&lt;2&gt;;
<b>def</b> ModRef : ModRefVal&lt;3&gt;;
<b>class</b> Value&lt;ModRefVal MR&gt; {
<i>// decode some information into a more convenient format, while providing
// a nice interface to the user of the "Value" class.</i>
<b>bit</b> isMod = MR.Value{0};
<b>bit</b> isRef = MR.Value{1};
<i>// other stuff...</i>
}
<i>// Example uses</i>
<b>def</b> bork : Value&lt;Mod&gt;;
<b>def</b> zork : Value&lt;Ref&gt;;
<b>def</b> hork : Value&lt;ModRef&gt;;
</pre></p>
<p>
This is obviously a contrived example, but it shows how template arguments can
be used to decouple the interface provided to the user of the class from the
actual internal data representation expected by the class. In this case,
running <tt>tblgen</tt> on the example prints the following definitions:</p>
<p><pre>
<b>def</b> bork { <i>// Value</i>
bit isMod = 1;
bit isRef = 0;
}
<b>def</b> hork { <i>// Value</i>
bit isMod = 1;
bit isRef = 1;
}
<b>def</b> zork { <i>// Value</i>
bit isMod = 0;
bit isRef = 1;
}
</pre></p>
<p>
This shows that TableGen was able to dig into the argument and extract a piece
of information that was requested by the designer of the "Value" class. For
more realistic examples, please see existing users of TableGen, such as the X86
backend.</p>
</div>
@ -479,7 +563,7 @@ specified as a double quoted string immediately after the '<tt>include</tt>'
keyword. Example:
<p><pre>
<b>include</b> "foo.td"
<b>include</b> "foo.td"
</pre></p>
</div>