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<title>GNU Compiler Collection (GCC) Internals: Target Attributes</title>

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<a name="Target-Attributes"></a>
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<p>
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<hr>
<a name="Defining-target_002dspecific-uses-of-_005f_005fattribute_005f_005f"></a>
<h3 class="section">17.24 Defining target-specific uses of <code>__attribute__</code></h3>
<a name="index-target-attributes"></a>
<a name="index-machine-attributes"></a>
<a name="index-attributes_002c-target_002dspecific"></a>

<p>Target-specific attributes may be defined for functions, data and types.
These are described using the following target hooks; they also need to
be documented in <samp>extend.texi</samp>.
</p>
<dl>
<dt><a name="index-TARGET_005fATTRIBUTE_005fTABLE"></a>Target Hook: <em>const struct attribute_spec *</em> <strong>TARGET_ATTRIBUTE_TABLE</strong></dt>
<dd><p>If defined, this target hook points to an array of &lsquo;<samp>struct
attribute_spec</samp>&rsquo; (defined in <samp>tree-core.h</samp>) specifying the machine
specific attributes for this target and some of the restrictions on the
entities to which these attributes are applied and the arguments they
take.
</p></dd></dl>

<dl>
<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>
<dd><p>If defined, this target hook is a function which returns true if the
machine-specific attribute named <var>name</var> expects an identifier
given as its first argument to be passed on as a plain identifier, not
subjected to name lookup.  If this is not defined, the default is
false for all machine-specific attributes.
</p></dd></dl>

<dl>
<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>
<dd><p>If defined, this target hook is a function which returns zero if the attributes on
<var>type1</var> and <var>type2</var> are incompatible, one if they are compatible,
and two if they are nearly compatible (which causes a warning to be
generated).  If this is not defined, machine-specific attributes are
supposed always to be compatible.
</p></dd></dl>

<dl>
<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>
<dd><p>If defined, this target hook is a function which assigns default attributes to
the newly defined <var>type</var>.
</p></dd></dl>

<dl>
<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>
<dd><p>Define this target hook if the merging of type attributes needs special
handling.  If defined, the result is a list of the combined
<code>TYPE_ATTRIBUTES</code> of <var>type1</var> and <var>type2</var>.  It is assumed
that <code>comptypes</code> has already been called and returned 1.  This
function may call <code>merge_attributes</code> to handle machine-independent
merging.
</p></dd></dl>

<dl>
<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>
<dd><p>Define this target hook if the merging of decl attributes needs special
handling.  If defined, the result is a list of the combined
<code>DECL_ATTRIBUTES</code> of <var>olddecl</var> and <var>newdecl</var>.
<var>newdecl</var> is a duplicate declaration of <var>olddecl</var>.  Examples of
when this is needed are when one attribute overrides another, or when an
attribute is nullified by a subsequent definition.  This function may
call <code>merge_attributes</code> to handle machine-independent merging.
</p>
<a name="index-TARGET_005fDLLIMPORT_005fDECL_005fATTRIBUTES"></a>
<p>If the only target-specific handling you require is &lsquo;<samp>dllimport</samp>&rsquo;
for Microsoft Windows targets, you should define the macro
<code>TARGET_DLLIMPORT_DECL_ATTRIBUTES</code> to <code>1</code>.  The compiler
will then define a function called
<code>merge_dllimport_decl_attributes</code> which can then be defined as
the expansion of <code>TARGET_MERGE_DECL_ATTRIBUTES</code>.  You can also
add <code>handle_dll_attribute</code> in the attribute table for your port
to perform initial processing of the &lsquo;<samp>dllimport</samp>&rsquo; and
&lsquo;<samp>dllexport</samp>&rsquo; attributes.  This is done in <samp>i386/cygwin.h</samp> and
<samp>i386/i386.c</samp>, for example.
</p></dd></dl>

<dl>
<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>
<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>.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fDECLSPEC"></a>Macro: <strong>TARGET_DECLSPEC</strong></dt>
<dd><p>Define this macro to a nonzero value if you want to treat
<code>__declspec(X)</code> as equivalent to <code>__attribute((X))</code>.  By
default, this behavior is enabled only for targets that define
<code>TARGET_DLLIMPORT_DECL_ATTRIBUTES</code>.  The current implementation
of <code>__declspec</code> is via a built-in macro, but you should not rely
on this implementation detail.
</p></dd></dl>

<dl>
<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>
<dd><p>Define this target hook if you want to be able to add attributes to a decl
when it is being created.  This is normally useful for back ends which
wish to implement a pragma by using the attributes which correspond to
the pragma&rsquo;s effect.  The <var>node</var> argument is the decl which is being
created.  The <var>attr_ptr</var> argument is a pointer to the attribute list
for this decl.  The list itself should not be modified, since it may be
shared with other decls, but attributes may be chained on the head of
the list and <code>*<var>attr_ptr</var></code> modified to point to the new
attributes, or a copy of the list may be made if further changes are
needed.
</p></dd></dl>

<dl>
<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>
<dd><a name="index-inlining"></a>
<p>This target hook returns <code>true</code> if it is OK to inline <var>fndecl</var>
into the current function, despite its having target-specific
attributes, <code>false</code> otherwise.  By default, if a function has a
target specific attribute attached to it, it will not be inlined.
</p></dd></dl>

<dl>
<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>
<dd><p>This hook is called to parse <code>attribute(target(&quot;...&quot;))</code>, which
allows setting target-specific options on individual functions.
These function-specific options may differ
from the options specified on the command line.  The hook should return
<code>true</code> if the options are valid.
</p>
<p>The hook should set the <code>DECL_FUNCTION_SPECIFIC_TARGET</code> field in
the function declaration to hold a pointer to a target-specific
<code>struct cl_target_option</code> structure.
</p></dd></dl>

<dl>
<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>
<dd><p>This hook is called to save any additional target-specific information
in the <code>struct cl_target_option</code> structure for function-specific
options from the <code>struct gcc_options</code> structure.
See <a href="Option-file-format.html#Option-file-format">Option file format</a>.
</p></dd></dl>

<dl>
<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>
<dd><p>This hook is called to restore any additional target-specific
information in the <code>struct cl_target_option</code> structure for
function-specific options to the <code>struct gcc_options</code> structure.
</p></dd></dl>

<dl>
<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>
<dd><p>This hook is called to update target-specific information in the
<code>struct cl_target_option</code> structure after it is streamed in from
LTO bytecode.
</p></dd></dl>

<dl>
<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>
<dd><p>This hook is called to print any additional target-specific
information in the <code>struct cl_target_option</code> structure for
function-specific options.
</p></dd></dl>

<dl>
<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>
<dd><p>This target hook parses the options for <code>#pragma GCC target</code>, which
sets the target-specific options for functions that occur later in the
input stream.  The options accepted should be the same as those handled by the
<code>TARGET_OPTION_VALID_ATTRIBUTE_P</code> hook.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fOPTION_005fOVERRIDE"></a>Target Hook: <em>void</em> <strong>TARGET_OPTION_OVERRIDE</strong> <em>(void)</em></dt>
<dd><p>Sometimes certain combinations of command options do not make sense on
a particular target machine.  You can override the hook
<code>TARGET_OPTION_OVERRIDE</code> to take account of this.  This hooks is called
once just after all the command options have been parsed.
</p>
<p>Don&rsquo;t use this hook to turn on various extra optimizations for
<samp>-O</samp>.  That is what <code>TARGET_OPTION_OPTIMIZATION</code> is for.
</p>
<p>If you need to do something whenever the optimization level is
changed via the optimize attribute or pragma, see
<code>TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE</code>
</p></dd></dl>

<dl>
<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>
<dd><p>This target hook returns <code>true</code> if <var>DECL1</var> and <var>DECL2</var> are
versions of the same function.  <var>DECL1</var> and <var>DECL2</var> are function
versions if and only if they have the same function signature and
different target specific attributes, that is, they are compiled for
different target machines.
</p></dd></dl>

<dl>
<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>
<dd><p>This target hook returns <code>false</code> if the <var>caller</var> function
cannot inline <var>callee</var>, based on target specific information.  By
default, inlining is not allowed if the callee function has function
specific target options and the caller does not use the same options.
</p></dd></dl>

<dl>
<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>
<dd><p>This target hook fixes function <var>fndecl</var> after attributes are processed. Default does nothing. On ARM, the default function&rsquo;s alignment is updated with the attribute target.
</p></dd></dl>

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