288 lines
16 KiB
HTML
288 lines
16 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2016 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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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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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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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>GNU Compiler Collection (GCC) Internals: Target Attributes</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals: Target Attributes">
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<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Target Attributes">
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<link href="index.html#Top" rel="start" title="Top">
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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="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
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<link href="Emulated-TLS.html#Emulated-TLS" rel="next" title="Emulated TLS">
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<link href="Mode-Switching.html#Mode-Switching" rel="prev" title="Mode Switching">
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Target-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="Emulated-TLS.html#Emulated-TLS" accesskey="n" rel="next">Emulated TLS</a>, Previous: <a href="Mode-Switching.html#Mode-Switching" accesskey="p" rel="prev">Mode Switching</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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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</div>
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<hr>
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<a name="Defining-target_002dspecific-uses-of-_005f_005fattribute_005f_005f"></a>
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<h3 class="section">17.24 Defining target-specific uses of <code>__attribute__</code></h3>
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<a name="index-target-attributes"></a>
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<a name="index-machine-attributes"></a>
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<a name="index-attributes_002c-target_002dspecific"></a>
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<p>Target-specific attributes may be defined for functions, data and types.
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These are described using the following target hooks; they also need to
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be documented in <samp>extend.texi</samp>.
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</p>
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<dl>
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<dt><a name="index-TARGET_005fATTRIBUTE_005fTABLE"></a>Target Hook: <em>const struct attribute_spec *</em> <strong>TARGET_ATTRIBUTE_TABLE</strong></dt>
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<dd><p>If defined, this target hook points to an array of ‘<samp>struct
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attribute_spec</samp>’ (defined in <samp>tree-core.h</samp>) specifying the machine
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specific attributes for this target and some of the restrictions on the
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entities to which these attributes are applied and the arguments they
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take.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fATTRIBUTE_005fTAKES_005fIDENTIFIER_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P</strong> <em>(const_tree <var>name</var>)</em></dt>
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<dd><p>If defined, this target hook is a function which returns true if the
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machine-specific attribute named <var>name</var> expects an identifier
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given as its first argument to be passed on as a plain identifier, not
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subjected to name lookup. If this is not defined, the default is
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false for all machine-specific attributes.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fCOMP_005fTYPE_005fATTRIBUTES"></a>Target Hook: <em>int</em> <strong>TARGET_COMP_TYPE_ATTRIBUTES</strong> <em>(const_tree <var>type1</var>, const_tree <var>type2</var>)</em></dt>
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<dd><p>If defined, this target hook is a function which returns zero if the attributes on
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<var>type1</var> and <var>type2</var> are incompatible, one if they are compatible,
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and two if they are nearly compatible (which causes a warning to be
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generated). If this is not defined, machine-specific attributes are
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supposed always to be compatible.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fSET_005fDEFAULT_005fTYPE_005fATTRIBUTES"></a>Target Hook: <em>void</em> <strong>TARGET_SET_DEFAULT_TYPE_ATTRIBUTES</strong> <em>(tree <var>type</var>)</em></dt>
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<dd><p>If defined, this target hook is a function which assigns default attributes to
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the newly defined <var>type</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMERGE_005fTYPE_005fATTRIBUTES"></a>Target Hook: <em>tree</em> <strong>TARGET_MERGE_TYPE_ATTRIBUTES</strong> <em>(tree <var>type1</var>, tree <var>type2</var>)</em></dt>
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<dd><p>Define this target hook if the merging of type attributes needs special
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handling. If defined, the result is a list of the combined
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<code>TYPE_ATTRIBUTES</code> of <var>type1</var> and <var>type2</var>. It is assumed
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that <code>comptypes</code> has already been called and returned 1. This
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function may call <code>merge_attributes</code> to handle machine-independent
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merging.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMERGE_005fDECL_005fATTRIBUTES"></a>Target Hook: <em>tree</em> <strong>TARGET_MERGE_DECL_ATTRIBUTES</strong> <em>(tree <var>olddecl</var>, tree <var>newdecl</var>)</em></dt>
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<dd><p>Define this target hook if the merging of decl attributes needs special
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handling. If defined, the result is a list of the combined
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<code>DECL_ATTRIBUTES</code> of <var>olddecl</var> and <var>newdecl</var>.
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<var>newdecl</var> is a duplicate declaration of <var>olddecl</var>. Examples of
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when this is needed are when one attribute overrides another, or when an
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attribute is nullified by a subsequent definition. This function may
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call <code>merge_attributes</code> to handle machine-independent merging.
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</p>
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<a name="index-TARGET_005fDLLIMPORT_005fDECL_005fATTRIBUTES"></a>
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<p>If the only target-specific handling you require is ‘<samp>dllimport</samp>’
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for Microsoft Windows targets, you should define the macro
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<code>TARGET_DLLIMPORT_DECL_ATTRIBUTES</code> to <code>1</code>. The compiler
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will then define a function called
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<code>merge_dllimport_decl_attributes</code> which can then be defined as
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the expansion of <code>TARGET_MERGE_DECL_ATTRIBUTES</code>. You can also
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add <code>handle_dll_attribute</code> in the attribute table for your port
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to perform initial processing of the ‘<samp>dllimport</samp>’ and
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‘<samp>dllexport</samp>’ attributes. This is done in <samp>i386/cygwin.h</samp> and
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<samp>i386/i386.c</samp>, for example.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fVALID_005fDLLIMPORT_005fATTRIBUTE_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_VALID_DLLIMPORT_ATTRIBUTE_P</strong> <em>(const_tree <var>decl</var>)</em></dt>
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<dd><p><var>decl</var> is a variable or function with <code>__attribute__((dllimport))</code> specified. Use this hook if the target needs to add extra validation checks to <code>handle_dll_attribute</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fDECLSPEC"></a>Macro: <strong>TARGET_DECLSPEC</strong></dt>
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<dd><p>Define this macro to a nonzero value if you want to treat
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<code>__declspec(X)</code> as equivalent to <code>__attribute((X))</code>. By
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default, this behavior is enabled only for targets that define
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<code>TARGET_DLLIMPORT_DECL_ATTRIBUTES</code>. The current implementation
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of <code>__declspec</code> is via a built-in macro, but you should not rely
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on this implementation detail.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fINSERT_005fATTRIBUTES"></a>Target Hook: <em>void</em> <strong>TARGET_INSERT_ATTRIBUTES</strong> <em>(tree <var>node</var>, tree *<var>attr_ptr</var>)</em></dt>
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<dd><p>Define this target hook if you want to be able to add attributes to a decl
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when it is being created. This is normally useful for back ends which
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wish to implement a pragma by using the attributes which correspond to
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the pragma’s effect. The <var>node</var> argument is the decl which is being
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created. The <var>attr_ptr</var> argument is a pointer to the attribute list
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for this decl. The list itself should not be modified, since it may be
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shared with other decls, but attributes may be chained on the head of
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the list and <code>*<var>attr_ptr</var></code> modified to point to the new
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attributes, or a copy of the list may be made if further changes are
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needed.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fFUNCTION_005fATTRIBUTE_005fINLINABLE_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P</strong> <em>(const_tree <var>fndecl</var>)</em></dt>
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<dd><a name="index-inlining"></a>
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<p>This target hook returns <code>true</code> if it is OK to inline <var>fndecl</var>
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into the current function, despite its having target-specific
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attributes, <code>false</code> otherwise. By default, if a function has a
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target specific attribute attached to it, it will not be inlined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fVALID_005fATTRIBUTE_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_OPTION_VALID_ATTRIBUTE_P</strong> <em>(tree <var>fndecl</var>, tree <var>name</var>, tree <var>args</var>, int <var>flags</var>)</em></dt>
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<dd><p>This hook is called to parse <code>attribute(target("..."))</code>, which
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allows setting target-specific options on individual functions.
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These function-specific options may differ
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from the options specified on the command line. The hook should return
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<code>true</code> if the options are valid.
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</p>
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<p>The hook should set the <code>DECL_FUNCTION_SPECIFIC_TARGET</code> field in
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the function declaration to hold a pointer to a target-specific
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<code>struct cl_target_option</code> structure.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fSAVE"></a>Target Hook: <em>void</em> <strong>TARGET_OPTION_SAVE</strong> <em>(struct cl_target_option *<var>ptr</var>, struct gcc_options *<var>opts</var>)</em></dt>
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<dd><p>This hook is called to save any additional target-specific information
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in the <code>struct cl_target_option</code> structure for function-specific
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options from the <code>struct gcc_options</code> structure.
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See <a href="Option-file-format.html#Option-file-format">Option file format</a>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fRESTORE"></a>Target Hook: <em>void</em> <strong>TARGET_OPTION_RESTORE</strong> <em>(struct gcc_options *<var>opts</var>, struct cl_target_option *<var>ptr</var>)</em></dt>
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<dd><p>This hook is called to restore any additional target-specific
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information in the <code>struct cl_target_option</code> structure for
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function-specific options to the <code>struct gcc_options</code> structure.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fPOST_005fSTREAM_005fIN"></a>Target Hook: <em>void</em> <strong>TARGET_OPTION_POST_STREAM_IN</strong> <em>(struct cl_target_option *<var>ptr</var>)</em></dt>
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<dd><p>This hook is called to update target-specific information in the
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<code>struct cl_target_option</code> structure after it is streamed in from
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LTO bytecode.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fPRINT"></a>Target Hook: <em>void</em> <strong>TARGET_OPTION_PRINT</strong> <em>(FILE *<var>file</var>, int <var>indent</var>, struct cl_target_option *<var>ptr</var>)</em></dt>
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<dd><p>This hook is called to print any additional target-specific
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information in the <code>struct cl_target_option</code> structure for
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function-specific options.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fPRAGMA_005fPARSE"></a>Target Hook: <em>bool</em> <strong>TARGET_OPTION_PRAGMA_PARSE</strong> <em>(tree <var>args</var>, tree <var>pop_target</var>)</em></dt>
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<dd><p>This target hook parses the options for <code>#pragma GCC target</code>, which
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sets the target-specific options for functions that occur later in the
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input stream. The options accepted should be the same as those handled by the
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<code>TARGET_OPTION_VALID_ATTRIBUTE_P</code> hook.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fOVERRIDE"></a>Target Hook: <em>void</em> <strong>TARGET_OPTION_OVERRIDE</strong> <em>(void)</em></dt>
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<dd><p>Sometimes certain combinations of command options do not make sense on
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a particular target machine. You can override the hook
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<code>TARGET_OPTION_OVERRIDE</code> to take account of this. This hooks is called
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once just after all the command options have been parsed.
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</p>
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<p>Don’t use this hook to turn on various extra optimizations for
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<samp>-O</samp>. That is what <code>TARGET_OPTION_OPTIMIZATION</code> is for.
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</p>
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<p>If you need to do something whenever the optimization level is
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changed via the optimize attribute or pragma, see
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<code>TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE</code>
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fOPTION_005fFUNCTION_005fVERSIONS"></a>Target Hook: <em>bool</em> <strong>TARGET_OPTION_FUNCTION_VERSIONS</strong> <em>(tree <var>decl1</var>, tree <var>decl2</var>)</em></dt>
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<dd><p>This target hook returns <code>true</code> if <var>DECL1</var> and <var>DECL2</var> are
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versions of the same function. <var>DECL1</var> and <var>DECL2</var> are function
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versions if and only if they have the same function signature and
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different target specific attributes, that is, they are compiled for
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different target machines.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fCAN_005fINLINE_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_CAN_INLINE_P</strong> <em>(tree <var>caller</var>, tree <var>callee</var>)</em></dt>
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<dd><p>This target hook returns <code>false</code> if the <var>caller</var> function
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cannot inline <var>callee</var>, based on target specific information. By
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default, inlining is not allowed if the callee function has function
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specific target options and the caller does not use the same options.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fRELAYOUT_005fFUNCTION"></a>Target Hook: <em>void</em> <strong>TARGET_RELAYOUT_FUNCTION</strong> <em>(tree <var>fndecl</var>)</em></dt>
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<dd><p>This target hook fixes function <var>fndecl</var> after attributes are processed. Default does nothing. On ARM, the default function’s alignment is updated with the attribute target.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Emulated-TLS.html#Emulated-TLS" accesskey="n" rel="next">Emulated TLS</a>, Previous: <a href="Mode-Switching.html#Mode-Switching" accesskey="p" rel="prev">Mode Switching</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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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</div>
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</body>
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</html>
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