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<a name="Assembler-Instructions-as-Expressions"></a>
<h3 class="section">13.17 Assembler Instructions as Expressions</h3>
<a name="index-assembler-instructions-in-RTL"></a>

<a name="index-asm_005foperands_002c-usage"></a>
<p>The RTX code <code>asm_operands</code> represents a value produced by a
user-specified assembler instruction.  It is used to represent
an <code>asm</code> statement with arguments.  An <code>asm</code> statement with
a single output operand, like this:
</p>
<div class="smallexample">
<pre class="smallexample">asm (&quot;foo %1,%2,%0&quot; : &quot;=a&quot; (outputvar) : &quot;g&quot; (x + y), &quot;di&quot; (*z));
</pre></div>

<p>is represented using a single <code>asm_operands</code> RTX which represents
the value that is stored in <code>outputvar</code>:
</p>
<div class="smallexample">
<pre class="smallexample">(set <var>rtx-for-outputvar</var>
     (asm_operands &quot;foo %1,%2,%0&quot; &quot;a&quot; 0
                   [<var>rtx-for-addition-result</var> <var>rtx-for-*z</var>]
                   [(asm_input:<var>m1</var> &quot;g&quot;)
                    (asm_input:<var>m2</var> &quot;di&quot;)]))
</pre></div>

<p>Here the operands of the <code>asm_operands</code> RTX are the assembler
template string, the output-operand&rsquo;s constraint, the index-number of the
output operand among the output operands specified, a vector of input
operand RTX&rsquo;s, and a vector of input-operand modes and constraints.  The
mode <var>m1</var> is the mode of the sum <code>x+y</code>; <var>m2</var> is that of
<code>*z</code>.
</p>
<p>When an <code>asm</code> statement has multiple output values, its insn has
several such <code>set</code> RTX&rsquo;s inside of a <code>parallel</code>.  Each <code>set</code>
contains an <code>asm_operands</code>; all of these share the same assembler
template and vectors, but each contains the constraint for the respective
output operand.  They are also distinguished by the output-operand index
number, which is 0, 1, &hellip; for successive output operands.
</p>


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