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<h4 class="subsection">16.19.6 Constant Attributes</h4>
<p><a name="index-constant-attributes-3776"></a>
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,
<pre class="smallexample"> (define_attr "cpu" "m88100,m88110,m88000"
(const
(cond [(symbol_ref "TARGET_88100") (const_string "m88100")
(symbol_ref "TARGET_88110") (const_string "m88110")]
(const_string "m88000"))))
(define_attr "memory" "fast,slow"
(const
(if_then_else (symbol_ref "TARGET_FAST_MEM")
(const_string "fast")
(const_string "slow"))))
</pre>
<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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