126 lines
5.6 KiB
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126 lines
5.6 KiB
HTML
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<title>GNU Compiler Collection (GCC) Internals: Defining Mode Iterators</title>
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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="Mode-Iterators.html#Mode-Iterators" rel="up" title="Mode Iterators">
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<a name="Defining-Mode-Iterators"></a>
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<p>
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Next: <a href="Substitutions.html#Substitutions" accesskey="n" rel="next">Substitutions</a>, Up: <a href="Mode-Iterators.html#Mode-Iterators" accesskey="u" rel="up">Mode 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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<a name="Defining-Mode-Iterators-1"></a>
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<h4 class="subsubsection">16.23.1.1 Defining Mode Iterators</h4>
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<a name="index-define_005fmode_005fiterator"></a>
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<p>The syntax for defining a mode iterator is:
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</p>
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<div class="smallexample">
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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></div>
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<p>This allows subsequent <samp>.md</samp> file constructs to use the mode suffix
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<code>:<var>name</var></code>. Every construct that does so will be expanded
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<var>n</var> times, once with every use of <code>:<var>name</var></code> replaced by
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<code>:<var>mode1</var></code>, once with every use replaced by <code>:<var>mode2</var></code>,
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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>
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<p>For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(define_mode_iterator P [(SI "Pmode == SImode") (DI "Pmode == DImode")])
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</pre></div>
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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>
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<p>As with other <samp>.md</samp> conditions, an empty string is treated
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as “always true”. <code>(<var>mode</var> "")</code> can also be abbreviated
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to <code><var>mode</var></code>. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(define_mode_iterator GPR [SI (DI "TARGET_64BIT")])
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</pre></div>
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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>
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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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</p>
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