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92 lines
4.2 KiB
HTML
92 lines
4.2 KiB
HTML
4 years ago
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<title>Defining Mode Iterators - GNU Compiler Collection (GCC) Internals</title>
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Mode-Iterators.html#Mode-Iterators" title="Mode Iterators">
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<link rel="next" href="Substitutions.html#Substitutions" title="Substitutions">
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Copyright (C) 1988-2015 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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(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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</head>
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<body>
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<div class="node">
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<a name="Defining-Mode-Iterators"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Substitutions.html#Substitutions">Substitutions</a>,
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Up: <a rel="up" accesskey="u" href="Mode-Iterators.html#Mode-Iterators">Mode Iterators</a>
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<hr>
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</div>
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<h5 class="subsubsection">16.23.1.1 Defining Mode Iterators</h5>
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<p><a name="index-define_005fmode_005fiterator-3838"></a>
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The syntax for defining a mode iterator is:
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<pre class="smallexample"> (define_mode_iterator <var>name</var> [(<var>mode1</var> "<var>cond1</var>") ... (<var>moden</var> "<var>condn</var>")])
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</pre>
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<p>This allows subsequent <samp><span class="file">.md</span></samp> file constructs to use the mode suffix
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<code>:</code><var>name</var>. Every construct that does so will be expanded
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<var>n</var> times, once with every use of <code>:</code><var>name</var> replaced by
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<code>:</code><var>mode1</var>, once with every use replaced by <code>:</code><var>mode2</var>,
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and so on. In the expansion for a particular <var>modei</var>, every
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C condition will also require that <var>condi</var> be true.
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<p>For example:
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<pre class="smallexample"> (define_mode_iterator P [(SI "Pmode == SImode") (DI "Pmode == DImode")])
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</pre>
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<p>defines a new mode suffix <code>:P</code>. Every construct that uses
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<code>:P</code> will be expanded twice, once with every <code>:P</code> replaced
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by <code>:SI</code> and once with every <code>:P</code> replaced by <code>:DI</code>.
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The <code>:SI</code> version will only apply if <code>Pmode == SImode</code> and
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the <code>:DI</code> version will only apply if <code>Pmode == DImode</code>.
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<p>As with other <samp><span class="file">.md</span></samp> conditions, an empty string is treated
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as “always true”. <code>(</code><var>mode</var><code> "")</code> can also be abbreviated
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to <var>mode</var>. For example:
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<pre class="smallexample"> (define_mode_iterator GPR [SI (DI "TARGET_64BIT")])
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</pre>
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<p>means that the <code>:DI</code> expansion only applies if <code>TARGET_64BIT</code>
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but that the <code>:SI</code> expansion has no such constraint.
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<p>Iterators are applied in the order they are defined. This can be
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significant if two iterators are used in a construct that requires
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substitutions. See <a href="Substitutions.html#Substitutions">Substitutions</a>.
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</body></html>
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