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<title>Using the GNU Compiler Collection (GCC): Label Attributes</title>
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<a name="Label-Attributes"></a>
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<p>
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Next: <a href="Enumerator-Attributes.html#Enumerator-Attributes" accesskey="n" rel="next">Enumerator Attributes</a>, Previous: <a href="Type-Attributes.html#Type-Attributes" accesskey="p" rel="prev">Type Attributes</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</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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<hr>
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<a name="Label-Attributes-1"></a>
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<h3 class="section">6.34 Label Attributes</h3>
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<a name="index-Label-Attributes"></a>
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<p>GCC allows attributes to be set on C labels. See <a href="Attribute-Syntax.html#Attribute-Syntax">Attribute Syntax</a>, for
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details of the exact syntax for using attributes. Other attributes are
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available for functions (see <a href="Function-Attributes.html#Function-Attributes">Function Attributes</a>), variables
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(see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>), enumerators (see <a href="Enumerator-Attributes.html#Enumerator-Attributes">Enumerator Attributes</a>),
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and for types (see <a href="Type-Attributes.html#Type-Attributes">Type Attributes</a>).
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</p>
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<p>This example uses the <code>cold</code> label attribute to indicate the
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<code>ErrorHandling</code> branch is unlikely to be taken and that the
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<code>ErrorHandling</code> label is unused:
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</p>
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<div class="smallexample">
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<pre class="smallexample">
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asm goto ("some asm" : : : : NoError);
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/* This branch (the fall-through from the asm) is less commonly used */
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ErrorHandling:
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__attribute__((cold, unused)); /* Semi-colon is required here */
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printf("error\n");
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return 0;
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NoError:
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printf("no error\n");
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return 1;
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</pre></div>
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<dl compact="compact">
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<dt><code>unused</code></dt>
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<dd><a name="index-unused-label-attribute"></a>
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<p>This feature is intended for program-generated code that may contain
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unused labels, but which is compiled with <samp>-Wall</samp>. It is
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not normally appropriate to use in it human-written code, though it
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could be useful in cases where the code that jumps to the label is
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contained within an <code>#ifdef</code> conditional.
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</p>
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</dd>
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<dt><code>hot</code></dt>
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<dd><a name="index-hot-label-attribute"></a>
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<p>The <code>hot</code> attribute on a label is used to inform the compiler that
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the path following the label is more likely than paths that are not so
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annotated. This attribute is used in cases where <code>__builtin_expect</code>
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cannot be used, for instance with computed goto or <code>asm goto</code>.
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</p>
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</dd>
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<dt><code>cold</code></dt>
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<dd><a name="index-cold-label-attribute"></a>
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<p>The <code>cold</code> attribute on labels is used to inform the compiler that
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the path following the label is unlikely to be executed. This attribute
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is used in cases where <code>__builtin_expect</code> cannot be used, for instance
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with computed goto or <code>asm goto</code>.
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</p>
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</dd>
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</dl>
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Next: <a href="Enumerator-Attributes.html#Enumerator-Attributes" accesskey="n" rel="next">Enumerator Attributes</a>, Previous: <a href="Type-Attributes.html#Type-Attributes" accesskey="p" rel="prev">Type Attributes</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</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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