<html lang="en">
<head>
<title>Defining Mode 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="Mode-Iterators.html#Mode-Iterators" title="Mode Iterators">
<link rel="next" href="Substitutions.html#Substitutions" title="Substitutions">
<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="Defining-Mode-Iterators"></a>
<p>
Next: <a rel="next" accesskey="n" href="Substitutions.html#Substitutions">Substitutions</a>,
Up: <a rel="up" accesskey="u" href="Mode-Iterators.html#Mode-Iterators">Mode Iterators</a>
<hr>
</div>
<h5 class="subsubsection">16.23.1.1 Defining Mode Iterators</h5>
<p><a name="index-define_005fmode_005fiterator-3838"></a>
The syntax for defining a mode iterator is:
<pre class="smallexample"> (define_mode_iterator <var>name</var> [(<var>mode1</var> "<var>cond1</var>") ... (<var>moden</var> "<var>condn</var>")])
</pre>
<p>This allows subsequent <samp><span class="file">.md</span></samp> file constructs to use the mode suffix
<code>:</code><var>name</var>. Every construct that does so will be expanded
<var>n</var> times, once with every use of <code>:</code><var>name</var> replaced by
<code>:</code><var>mode1</var>, once with every use replaced by <code>:</code><var>mode2</var>,
and so on. In the expansion for a particular <var>modei</var>, every
C condition will also require that <var>condi</var> be true.
<p>For example:
<pre class="smallexample"> (define_mode_iterator P [(SI "Pmode == SImode") (DI "Pmode == DImode")])
</pre>
<p>defines a new mode suffix <code>:P</code>. Every construct that uses
<code>:P</code> will be expanded twice, once with every <code>:P</code> replaced
by <code>:SI</code> and once with every <code>:P</code> replaced by <code>:DI</code>.
The <code>:SI</code> version will only apply if <code>Pmode == SImode</code> and
the <code>:DI</code> version will only apply if <code>Pmode == DImode</code>.
<p>As with other <samp><span class="file">.md</span></samp> conditions, an empty string is treated
as “always true”. <code>(</code><var>mode</var><code> "")</code> can also be abbreviated
to <var>mode</var>. For example:
<pre class="smallexample"> (define_mode_iterator GPR [SI (DI "TARGET_64BIT")])
</pre>
<p>means that the <code>:DI</code> expansion only applies if <code>TARGET_64BIT</code>
but that the <code>:SI</code> expansion has no such constraint.
<p>Iterators are applied in the order they are defined. This can be
significant if two iterators are used in a construct that requires
substitutions. See <a href="Substitutions.html#Substitutions">Substitutions</a>.
</body></html>