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129 lines
5.3 KiB
HTML
129 lines
5.3 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>Subst Iterators (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Subst Iterators (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Subst Iterators (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="Iterators.html#Iterators" rel="up" title="Iterators">
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<link href="Target-Macros.html#Target-Macros" rel="next" title="Target Macros">
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<link href="Int-Iterators.html#Int-Iterators" rel="prev" title="Int Iterators">
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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="Subst-Iterators"></a>
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<div class="header">
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<p>
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Previous: <a href="Int-Iterators.html#Int-Iterators" accesskey="p" rel="prev">Int Iterators</a>, Up: <a href="Iterators.html#Iterators" accesskey="u" rel="up">Iterators</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="Subst-Iterators-1"></a>
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<h4 class="subsection">17.23.4 Subst Iterators</h4>
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<a name="index-subst-iterators-in-_002emd-files"></a>
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<a name="index-define_005fsubst-5"></a>
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<a name="index-define_005fsubst_005fattr"></a>
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<p>Subst iterators are special type of iterators with the following
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restrictions: they could not be declared explicitly, they always have
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only two values, and they do not have explicit dedicated name.
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Subst-iterators are triggered only when corresponding subst-attribute is
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used in RTL-pattern.
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</p>
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<p>Subst iterators transform templates in the following way: the templates
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are duplicated, the subst-attributes in these templates are replaced
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with the corresponding values, and a new attribute is implicitly added
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to the given <code>define_insn</code>/<code>define_expand</code>. The name of the
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added attribute matches the name of <code>define_subst</code>. Such
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attributes are declared implicitly, and it is not allowed to have a
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<code>define_attr</code> named as a <code>define_subst</code>.
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</p>
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<p>Each subst iterator is linked to a <code>define_subst</code>. It is declared
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implicitly by the first appearance of the corresponding
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<code>define_subst_attr</code>, and it is not allowed to define it explicitly.
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</p>
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<p>Declarations of subst-attributes have the following syntax:
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</p>
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<a name="index-define_005fsubst_005fattr-1"></a>
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<div class="smallexample">
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<pre class="smallexample">(define_subst_attr "<var>name</var>"
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"<var>subst-name</var>"
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"<var>no-subst-value</var>"
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"<var>subst-applied-value</var>")
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</pre></div>
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<p><var>name</var> is a string with which the given subst-attribute could be
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referred to.
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</p>
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<p><var>subst-name</var> shows which <code>define_subst</code> should be applied to an
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RTL-template if the given subst-attribute is present in the
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RTL-template.
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</p>
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<p><var>no-subst-value</var> is a value with which subst-attribute would be
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replaced in the first copy of the original RTL-template.
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</p>
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<p><var>subst-applied-value</var> is a value with which subst-attribute would be
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replaced in the second copy of the original RTL-template.
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</p>
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</body>
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</html>
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