<html lang="en">
<head>
<title>Subst Iterators - 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="Iterators.html#Iterators" title="Iterators">
<link rel="prev" href="Int-Iterators.html#Int-Iterators" title="Int Iterators">
<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="Subst-Iterators"></a>
<p>
Previous: <a rel="previous" accesskey="p" href="Int-Iterators.html#Int-Iterators">Int Iterators</a>,
Up: <a rel="up" accesskey="u" href="Iterators.html#Iterators">Iterators</a>
<hr>
</div>
<h4 class="subsection">16.23.4 Subst Iterators</h4>
<p><a name="index-subst-iterators-in-_0040file_007b_002emd_007d-files-3846"></a><a name="index-define_005fsubst-3847"></a><a name="index-define_005fsubst_005fattr-3848"></a>
Subst iterators are special type of iterators with the following
restrictions: they could not be declared explicitly, they always have
only two values, and they do not have explicit dedicated name.
Subst-iterators are triggered only when corresponding subst-attribute is
used in RTL-pattern.
<p>Subst iterators transform templates in the following way: the templates
are duplicated, the subst-attributes in these templates are replaced
with the corresponding values, and a new attribute is implicitly added
to the given <code>define_insn</code>/<code>define_expand</code>. The name of the
added attribute matches the name of <code>define_subst</code>. Such
attributes are declared implicitly, and it is not allowed to have a
<code>define_attr</code> named as a <code>define_subst</code>.
<p>Each subst iterator is linked to a <code>define_subst</code>. It is declared
implicitly by the first appearance of the corresponding
<code>define_subst_attr</code>, and it is not allowed to define it explicitly.
<p>Declarations of subst-attributes have the following syntax:
<p><a name="index-define_005fsubst_005fattr-3849"></a>
<pre class="smallexample"> (define_subst_attr "<var>name</var>"
"<var>subst-name</var>"
"<var>no-subst-value</var>"
"<var>subst-applied-value</var>")
</pre>
<p><var>name</var> is a string with which the given subst-attribute could be
referred to.
<p><var>subst-name</var> shows which <code>define_subst</code> should be applied to an
RTL-template if the given subst-attribute is present in the
RTL-template.
<p><var>no-subst-value</var> is a value with which subst-attribute would be
replaced in the first copy of the original RTL-template.
<p><var>subst-applied-value</var> is a value with which subst-attribute would be
replaced in the second copy of the original RTL-template.
<!-- Copyright (C) 1988-2015 Free Software Foundation, Inc. -->
<!-- This is part of the GCC manual. -->
<!-- For copying conditions, see the file gcc.texi. -->
</body></html>