<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>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection"><a name="running">Basic concepts</a></div>
+<div class="doc_subsection"><a name="concepts">Basic concepts</a></div>
<div class="doc_text">
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>
<!-- ======================================================================= -->
<li><tt>(DEF a, b)</tt> - a dag value. The first element is required to be a
record definition, the remaining elements in the list may be arbitrary other
values, including nested `<tt>dag</tt>' values.</li>
+<li><tt>!strconcat(a, b)</tt> - A string value that is the result of
+ concatenating the 'a' and 'b' strings.</li>
</ul>
<p>Note that all of the values have rules specifying how they convert to values
<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>
</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<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>;
+
+<b>multiclass</b> ri_inst<<b>int</b> opc, <b>string</b> asmstr> {
+ def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
+ def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
+}
+
+// Instantiations of the ri_inst multiclass.
+<b>defm</b> ADD : ri_inst<0b111, "add">;
+<b>defm</b> SUB : ri_inst<0b101, "sub">;
+<b>defm</b> MUL : ri_inst<0b100, "mul">;
+...
+</pre>
+
+<p>The name of the resultant 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<<b>int</b> opc, <b>string</b> asmstr, <b>dag</b> operandlist>;
+
+<b>class</b> rrinst<<b>int</b> opc, <b>string</b> asmstr>
+ : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, GPR:$src2)>;
+
+<b>class</b> riinst<<b>int</b> opc, <b>string</b> asmstr>
+ : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
+ (ops GPR:$dst, GPR:$src1, Imm:$src2)>;
+
+// Instantiations of the ri_inst multiclass.
+<b>def</b> ADD_rr : rrinst<0b111, "add">;
+<b>def</b> ADD_ri : riinst<0b111, "add">;
+<b>def</b> SUB_rr : rrinst<0b101, "sub">;
+<b>def</b> SUB_ri : riinst<0b101, "sub">;
+<b>def</b> MUL_rr : rrinst<0b100, "mul">;
+<b>def</b> MUL_ri : riinst<0b100, "mul">;
+...
+</pre>
+
+</div>
+
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="filescope">File scope entities</a>
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
projects / oota-llvm.git / blobdiff