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| <a name="Constant-Attributes-1"></a> |
| <h4 class="subsection">16.19.6 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 "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></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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