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<a name="Constant-Attributes-1"></a>
<h4 class="subsection">17.19.6 Constant Attributes</h4>
<a name="index-constant-attributes"></a>

<p>A special form of <code>define_attr</code>, where the expression for the
default value is a <code>const</code> expression, indicates an attribute that
is constant for a given run of the compiler.  Constant attributes may be
used to specify which variety of processor is used.  For example,
</p>
<div class="smallexample">
<pre class="smallexample">(define_attr &quot;cpu&quot; &quot;m88100,m88110,m88000&quot;
 (const
  (cond [(symbol_ref &quot;TARGET_88100&quot;) (const_string &quot;m88100&quot;)
         (symbol_ref &quot;TARGET_88110&quot;) (const_string &quot;m88110&quot;)]
        (const_string &quot;m88000&quot;))))

(define_attr &quot;memory&quot; &quot;fast,slow&quot;
 (const
  (if_then_else (symbol_ref &quot;TARGET_FAST_MEM&quot;)
                (const_string &quot;fast&quot;)
                (const_string &quot;slow&quot;))))
</pre></div>

<p>The routine generated for constant attributes has no parameters as it
does not depend on any particular insn.  RTL expressions used to define
the value of a constant attribute may use the <code>symbol_ref</code> form,
but may not use either the <code>match_operand</code> form or <code>eq_attr</code>
forms involving insn attributes.
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