<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
<html>
|
<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
|
|
Permission is granted to copy, distribute and/or modify this document
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
any later version published by the Free Software Foundation; with the
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
(see below). A copy of the license is included in the section entitled
|
"GNU Free Documentation License".
|
|
(a) The FSF's Front-Cover Text is:
|
|
A GNU Manual
|
|
(b) The FSF's Back-Cover Text is:
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
software. Copies published by the Free Software Foundation raise
|
funds for GNU development. -->
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
<head>
|
<title>GNU Compiler Collection (GCC) Internals: Aggregate Return</title>
|
|
<meta name="description" content="GNU Compiler Collection (GCC) Internals: Aggregate Return">
|
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Aggregate Return">
|
<meta name="resource-type" content="document">
|
<meta name="distribution" content="global">
|
<meta name="Generator" content="makeinfo">
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
<link href="index.html#Top" rel="start" title="Top">
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
<link href="Stack-and-Calling.html#Stack-and-Calling" rel="up" title="Stack and Calling">
|
<link href="Caller-Saves.html#Caller-Saves" rel="next" title="Caller Saves">
|
<link href="Scalar-Return.html#Scalar-Return" rel="prev" title="Scalar Return">
|
<style type="text/css">
|
<!--
|
a.summary-letter {text-decoration: none}
|
blockquote.smallquotation {font-size: smaller}
|
div.display {margin-left: 3.2em}
|
div.example {margin-left: 3.2em}
|
div.indentedblock {margin-left: 3.2em}
|
div.lisp {margin-left: 3.2em}
|
div.smalldisplay {margin-left: 3.2em}
|
div.smallexample {margin-left: 3.2em}
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
div.smalllisp {margin-left: 3.2em}
|
kbd {font-style:oblique}
|
pre.display {font-family: inherit}
|
pre.format {font-family: inherit}
|
pre.menu-comment {font-family: serif}
|
pre.menu-preformatted {font-family: serif}
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
pre.smallexample {font-size: smaller}
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
pre.smalllisp {font-size: smaller}
|
span.nocodebreak {white-space:nowrap}
|
span.nolinebreak {white-space:nowrap}
|
span.roman {font-family:serif; font-weight:normal}
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
ul.no-bullet {list-style: none}
|
-->
|
</style>
|
|
|
</head>
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
<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>
|
</div>
|
<hr>
|
<a name="How-Large-Values-Are-Returned"></a>
|
<h4 class="subsection">17.9.9 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>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>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>
|
|
<hr>
|
<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>
|
</div>
|
|
|
|
</body>
|
</html>
|
