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Document multiclasses and defm's 

llvm-svn: 30030
This commit is contained in:
Chris Lattner 2006-09-01 21:44:18 +00:00
parent aec1af2239
commit f01a85bdf2
1 changed files with 83 additions and 6 deletions
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llvm/docs/TableGenFundamentals.html
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@ -30,6 +30,7 @@
<li><a href="#valuedef">Value definitions</a></li>
<li><a href="#recordlet">'let' expressions</a></li>
<li><a href="#templateargs">Class template arguments</a></li>
<li><a href="#multiclass">Multiclass definitions and instances</a></li>
</ol></li>
<li><a href="#filescope">File scope entities</a>
<ol>
@ -102,6 +103,10 @@ TableGen keeps track of all of the classes that are used to build up a
definition, so the backend can find all definitions of a particular class, such
as "Instruction".</p>
<p><b>TableGen multiclasses</b> are groups of abstract records that are
instantiated all at once. Each instantiation can result in multiple TableGen
definitions.</p>
</div>
<!-- ======================================================================= -->
@ -463,16 +468,16 @@ running <tt>tblgen</tt> on the example prints the following definitions:</p>
<pre>
<b>def</b> bork { <i>// Value</i>
bit isMod = 1;
bit isRef = 0;
<b>bit</b> isMod = 1;
<b>bit</b> isRef = 0;
}
<b>def</b> hork { <i>// Value</i>
bit isMod = 1;
bit isRef = 1;
<b>bit</b> isMod = 1;
<b>bit</b> isRef = 1;
}
<b>def</b> zork { <i>// Value</i>
bit isMod = 0;
bit isRef = 1;
<b>bit</b> isMod = 0;
<b>bit</b> isRef = 1;
}
</pre>
@ -483,6 +488,78 @@ X86 backend.</p>
</div>
<!-- -------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="multiclass">Multiclass definitions and instances</a>
</div>
<div class="doc_text">
<p>
While classes with template arguments are a good way to factor commonality
between two instances of a definition, multiclasses allow a convenient notation
for defining multiple definitions at once (instances of implicitly constructed
classes). For example, consider an 3-address instruction set whose instructions
come in two forms: "reg = reg op reg" and "reg = reg op imm" (e.g. SPARC). In
this case, you'd like to specify in one place that this commonality exists, then
in a separate place indicate what all the ops are.
</p>
<p>
Here is an example TableGen fragment that shows this idea:
</p>
<pre>
<b>def</b> ops;
<b>def</b> GPR;
<b>def</b> Imm;
<b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
<b>multiclass</b> ri_inst&lt;<b>int</b> opc, <b>string</b> asmstr&gt; {
def _rr : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
def _ri : inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
}
// Instantiations of the ri_inst multiclass.
<b>defm</b> ADD : ri_inst&lt;0b111, "add"&gt;;
<b>defm</b> SUB : ri_inst&lt;0b101, "sub"&gt;;
<b>defm</b> MUL : ri_inst&lt;0b100, "mul"&gt;;
...
</pre>
<p>The name of the resuntant definitions has the multidef fragment names
appended to them, so this defines ADD_rr, ADD_ri, SUB_rr, etc. Using a
multiclass this way is exactly equivalent to instantiating the
classes multiple times yourself, e.g. by writing:</p>
<pre>
<b>def</b> ops;
<b>def</b> GPR;
<b>def</b> Imm;
<b>class</b> inst&lt;<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist&gt;;
<b>class</b> rrinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
: inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, GPR:$src2)&gt;;
<b>class</b> riinst&lt;<b>int</b> opc, <b>string</b> asmstr&gt;
: inst&lt;opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, Imm:$src2)&gt;;
// Instantiations of the ri_inst multiclass.
<b>def</b> ADD_rr : rrinst&lt;0b111, "add"&gt;;
<b>def</b> ADD_ri : riinst&lt;0b111, "add"&gt;;
<b>def</b> SUB_rr : rrinst&lt;0b101, "sub"&gt;;
<b>def</b> SUB_ri : riinst&lt;0b101, "sub"&gt;;
<b>def</b> MUL_rr : rrinst&lt;0b100, "mul"&gt;;
<b>def</b> MUL_ri : riinst&lt;0b100, "mul"&gt;;
...
</pre>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="filescope">File scope entities</a>