<html lang="en"> <head> <title>Constant Attributes - GNU Compiler Collection (GCC) Internals</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="GNU Compiler Collection (GCC) Internals"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Insn-Attributes.html#Insn-Attributes" title="Insn Attributes"> <link rel="prev" href="Insn-Lengths.html#Insn-Lengths" title="Insn Lengths"> <link rel="next" href="Mnemonic-Attribute.html#Mnemonic-Attribute" title="Mnemonic Attribute"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- Copyright (C) 1988-2015 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``Funding Free Software'', the Front-Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled ``GNU Free Documentation License''. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.--> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="Constant-Attributes"></a> <p> Next: <a rel="next" accesskey="n" href="Mnemonic-Attribute.html#Mnemonic-Attribute">Mnemonic Attribute</a>, Previous: <a rel="previous" accesskey="p" href="Insn-Lengths.html#Insn-Lengths">Insn Lengths</a>, Up: <a rel="up" accesskey="u" href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a> <hr> </div> <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. </body></html>