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110 lines
4.7 KiB
HTML
110 lines
4.7 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Constant Attributes (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Constant Attributes (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Constant Attributes (GNU Compiler Collection (GCC) Internals)">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Insn-Attributes.html#Insn-Attributes" rel="up" title="Insn Attributes">
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<link href="Mnemonic-Attribute.html#Mnemonic-Attribute" rel="next" title="Mnemonic Attribute">
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<link href="Insn-Lengths.html#Insn-Lengths" rel="prev" title="Insn Lengths">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Constant-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="Mnemonic-Attribute.html#Mnemonic-Attribute" accesskey="n" rel="next">Mnemonic Attribute</a>, Previous: <a href="Insn-Lengths.html#Insn-Lengths" accesskey="p" rel="prev">Insn Lengths</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Constant-Attributes-1"></a>
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<h4 class="subsection">17.19.6 Constant Attributes</h4>
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<a name="index-constant-attributes"></a>
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<p>A special form of <code>define_attr</code>, where the expression for the
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default value is a <code>const</code> expression, indicates an attribute that
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is constant for a given run of the compiler. Constant attributes may be
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used to specify which variety of processor is used. For example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">(define_attr "cpu" "m88100,m88110,m88000"
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(const
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(cond [(symbol_ref "TARGET_88100") (const_string "m88100")
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(symbol_ref "TARGET_88110") (const_string "m88110")]
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(const_string "m88000"))))
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(define_attr "memory" "fast,slow"
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(const
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(if_then_else (symbol_ref "TARGET_FAST_MEM")
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(const_string "fast")
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(const_string "slow"))))
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</pre></div>
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<p>The routine generated for constant attributes has no parameters as it
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does not depend on any particular insn. RTL expressions used to define
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the value of a constant attribute may use the <code>symbol_ref</code> form,
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but may not use either the <code>match_operand</code> form or <code>eq_attr</code>
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forms involving insn attributes.
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</p>
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</body>
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</html>
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