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128 lines
5.0 KiB
HTML
128 lines
5.0 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>Example (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Example (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Example (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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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="Machine-Desc.html#Machine-Desc" rel="up" title="Machine Desc">
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<link href="RTL-Template.html#RTL-Template" rel="next" title="RTL Template">
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<link href="Patterns.html#Patterns" rel="prev" title="Patterns">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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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="Example"></a>
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<div class="header">
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<p>
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Next: <a href="RTL-Template.html#RTL-Template" accesskey="n" rel="next">RTL Template</a>, Previous: <a href="Patterns.html#Patterns" accesskey="p" rel="prev">Patterns</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</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="Example-of-define_005finsn"></a>
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<h3 class="section">17.3 Example of <code>define_insn</code></h3>
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<a name="index-define_005finsn-example"></a>
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<p>Here is an example of an instruction pattern, taken from the machine
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description for the 68000/68020.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(define_insn "tstsi"
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[(set (cc0)
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(match_operand:SI 0 "general_operand" "rm"))]
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""
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"*
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{
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if (TARGET_68020 || ! ADDRESS_REG_P (operands[0]))
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return \"tstl %0\";
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return \"cmpl #0,%0\";
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}")
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</pre></div>
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<p>This can also be written using braced strings:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(define_insn "tstsi"
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[(set (cc0)
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(match_operand:SI 0 "general_operand" "rm"))]
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""
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{
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if (TARGET_68020 || ! ADDRESS_REG_P (operands[0]))
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return "tstl %0";
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return "cmpl #0,%0";
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})
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</pre></div>
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<p>This describes an instruction which sets the condition codes based on the
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value of a general operand. It has no condition, so any insn with an RTL
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description of the form shown may be matched to this pattern. The name
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‘<samp>tstsi</samp>’ means “test a <code>SImode</code> value” and tells the RTL
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generation pass that, when it is necessary to test such a value, an insn
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to do so can be constructed using this pattern.
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</p>
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<p>The output control string is a piece of C code which chooses which
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output template to return based on the kind of operand and the specific
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type of CPU for which code is being generated.
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</p>
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<p>‘<samp>"rm"</samp>’ is an operand constraint. Its meaning is explained below.
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</p>
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</body>
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</html>
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