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| <a name="Aggregate-Return"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Caller-Saves.html#Caller-Saves" accesskey="n" rel="next">Caller Saves</a>, Previous: <a href="Scalar-Return.html#Scalar-Return" accesskey="p" rel="prev">Scalar Return</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</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="How-Large-Values-Are-Returned"></a> |
| <h4 class="subsection">17.10.9 How Large Values Are Returned</h4> |
| <a name="index-aggregates-as-return-values"></a> |
| <a name="index-large-return-values"></a> |
| <a name="index-returning-aggregate-values"></a> |
| <a name="index-structure-value-address"></a> |
| |
| <p>When a function value’s mode is <code>BLKmode</code> (and in some other |
| cases), the value is not returned according to |
| <code>TARGET_FUNCTION_VALUE</code> (see <a href="Scalar-Return.html#Scalar-Return">Scalar Return</a>). Instead, the |
| caller passes the address of a block of memory in which the value |
| should be stored. This address is called the <em>structure value |
| address</em>. |
| </p> |
| <p>This section describes how to control returning structure values in |
| memory. |
| </p> |
| <dl> |
| <dt><a name="index-TARGET_005fRETURN_005fIN_005fMEMORY"></a>Target Hook: <em>bool</em> <strong>TARGET_RETURN_IN_MEMORY</strong> <em>(const_tree <var>type</var>, const_tree <var>fntype</var>)</em></dt> |
| <dd><p>This target hook should return a nonzero value to say to return the |
| function value in memory, just as large structures are always returned. |
| Here <var>type</var> will be the data type of the value, and <var>fntype</var> |
| will be the type of the function doing the returning, or <code>NULL</code> for |
| libcalls. |
| </p> |
| <p>Note that values of mode <code>BLKmode</code> must be explicitly handled |
| by this function. Also, the option <samp>-fpcc-struct-return</samp> |
| takes effect regardless of this macro. On most systems, it is |
| possible to leave the hook undefined; this causes a default |
| definition to be used, whose value is the constant 1 for <code>BLKmode</code> |
| values, and 0 otherwise. |
| </p> |
| <p>Do not use this hook to indicate that structures and unions should always |
| be returned in memory. You should instead use <code>DEFAULT_PCC_STRUCT_RETURN</code> |
| to indicate this. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-DEFAULT_005fPCC_005fSTRUCT_005fRETURN"></a>Macro: <strong>DEFAULT_PCC_STRUCT_RETURN</strong></dt> |
| <dd><p>Define this macro to be 1 if all structure and union return values must be |
| in memory. Since this results in slower code, this should be defined |
| only if needed for compatibility with other compilers or with an ABI. |
| If you define this macro to be 0, then the conventions used for structure |
| and union return values are decided by the <code>TARGET_RETURN_IN_MEMORY</code> |
| target hook. |
| </p> |
| <p>If not defined, this defaults to the value 1. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fSTRUCT_005fVALUE_005fRTX"></a>Target Hook: <em>rtx</em> <strong>TARGET_STRUCT_VALUE_RTX</strong> <em>(tree <var>fndecl</var>, int <var>incoming</var>)</em></dt> |
| <dd><p>This target hook should return the location of the structure value |
| address (normally a <code>mem</code> or <code>reg</code>), or 0 if the address is |
| passed as an “invisible” first argument. Note that <var>fndecl</var> may |
| be <code>NULL</code>, for libcalls. You do not need to define this target |
| hook if the address is always passed as an “invisible” first |
| argument. |
| </p> |
| <p>On some architectures the place where the structure value address |
| is found by the called function is not the same place that the |
| caller put it. This can be due to register windows, or it could |
| be because the function prologue moves it to a different place. |
| <var>incoming</var> is <code>1</code> or <code>2</code> when the location is needed in |
| the context of the called function, and <code>0</code> in the context of |
| the caller. |
| </p> |
| <p>If <var>incoming</var> is nonzero and the address is to be found on the |
| stack, return a <code>mem</code> which refers to the frame pointer. If |
| <var>incoming</var> is <code>2</code>, the result is being used to fetch the |
| structure value address at the beginning of a function. If you need |
| to emit adjusting code, you should do it at this point. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-PCC_005fSTATIC_005fSTRUCT_005fRETURN"></a>Macro: <strong>PCC_STATIC_STRUCT_RETURN</strong></dt> |
| <dd><p>Define this macro if the usual system convention on the target machine |
| for returning structures and unions is for the called function to return |
| the address of a static variable containing the value. |
| </p> |
| <p>Do not define this if the usual system convention is for the caller to |
| pass an address to the subroutine. |
| </p> |
| <p>This macro has effect in <samp>-fpcc-struct-return</samp> mode, but it does |
| nothing when you use <samp>-freg-struct-return</samp> mode. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fGET_005fRAW_005fRESULT_005fMODE"></a>Target Hook: <em>enum machine_mode</em> <strong>TARGET_GET_RAW_RESULT_MODE</strong> <em>(int <var>regno</var>)</em></dt> |
| <dd><p>This target hook returns the mode to be used when accessing raw return registers in <code>__builtin_return</code>. Define this macro if the value in <var>reg_raw_mode</var> is not correct. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fGET_005fRAW_005fARG_005fMODE"></a>Target Hook: <em>enum machine_mode</em> <strong>TARGET_GET_RAW_ARG_MODE</strong> <em>(int <var>regno</var>)</em></dt> |
| <dd><p>This target hook returns the mode to be used when accessing raw argument registers in <code>__builtin_apply_args</code>. Define this macro if the value in <var>reg_raw_mode</var> is not correct. |
| </p></dd></dl> |
| |
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| Next: <a href="Caller-Saves.html#Caller-Saves" accesskey="n" rel="next">Caller Saves</a>, Previous: <a href="Scalar-Return.html#Scalar-Return" accesskey="p" rel="prev">Scalar Return</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</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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