You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
151 lines
6.9 KiB
HTML
151 lines
6.9 KiB
HTML
4 years ago
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1988-2018 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 6.4, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Calls (GNU Compiler Collection (GCC) Internals)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Calls (GNU Compiler Collection (GCC) Internals)">
|
||
|
|
<meta name="keywords" content="Calls (GNU Compiler Collection (GCC) Internals)">
|
||
|
|
<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="RTL.html#RTL" rel="up" title="RTL">
|
||
|
|
<link href="Sharing.html#Sharing" rel="next" title="Sharing">
|
||
|
|
<link href="Insns.html#Insns" rel="prev" title="Insns">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
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.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<a name="Calls"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Sharing.html#Sharing" accesskey="n" rel="next">Sharing</a>, Previous: <a href="Insns.html#Insns" accesskey="p" rel="prev">Insns</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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="RTL-Representation-of-Function_002dCall-Insns"></a>
|
||
|
|
<h3 class="section">14.20 RTL Representation of Function-Call Insns</h3>
|
||
|
|
<a name="index-calling-functions-in-RTL"></a>
|
||
|
|
<a name="index-RTL-function_002dcall-insns"></a>
|
||
|
|
<a name="index-function_002dcall-insns"></a>
|
||
|
|
|
||
|
|
<p>Insns that call subroutines have the RTL expression code <code>call_insn</code>.
|
||
|
|
These insns must satisfy special rules, and their bodies must use a special
|
||
|
|
RTL expression code, <code>call</code>.
|
||
|
|
</p>
|
||
|
|
<a name="index-call-usage"></a>
|
||
|
|
<p>A <code>call</code> expression has two operands, as follows:
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">(call (mem:<var>fm</var> <var>addr</var>) <var>nbytes</var>)
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>Here <var>nbytes</var> is an operand that represents the number of bytes of
|
||
|
|
argument data being passed to the subroutine, <var>fm</var> is a machine mode
|
||
|
|
(which must equal as the definition of the <code>FUNCTION_MODE</code> macro in
|
||
|
|
the machine description) and <var>addr</var> represents the address of the
|
||
|
|
subroutine.
|
||
|
|
</p>
|
||
|
|
<p>For a subroutine that returns no value, the <code>call</code> expression as
|
||
|
|
shown above is the entire body of the insn, except that the insn might
|
||
|
|
also contain <code>use</code> or <code>clobber</code> expressions.
|
||
|
|
</p>
|
||
|
|
<a name="index-BLKmode_002c-and-function-return-values"></a>
|
||
|
|
<p>For a subroutine that returns a value whose mode is not <code>BLKmode</code>,
|
||
|
|
the value is returned in a hard register. If this register’s number is
|
||
|
|
<var>r</var>, then the body of the call insn looks like this:
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">(set (reg:<var>m</var> <var>r</var>)
|
||
|
|
(call (mem:<var>fm</var> <var>addr</var>) <var>nbytes</var>))
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>This RTL expression makes it clear (to the optimizer passes) that the
|
||
|
|
appropriate register receives a useful value in this insn.
|
||
|
|
</p>
|
||
|
|
<p>When a subroutine returns a <code>BLKmode</code> value, it is handled by
|
||
|
|
passing to the subroutine the address of a place to store the value.
|
||
|
|
So the call insn itself does not “return” any value, and it has the
|
||
|
|
same RTL form as a call that returns nothing.
|
||
|
|
</p>
|
||
|
|
<p>On some machines, the call instruction itself clobbers some register,
|
||
|
|
for example to contain the return address. <code>call_insn</code> insns
|
||
|
|
on these machines should have a body which is a <code>parallel</code>
|
||
|
|
that contains both the <code>call</code> expression and <code>clobber</code>
|
||
|
|
expressions that indicate which registers are destroyed. Similarly,
|
||
|
|
if the call instruction requires some register other than the stack
|
||
|
|
pointer that is not explicitly mentioned in its RTL, a <code>use</code>
|
||
|
|
subexpression should mention that register.
|
||
|
|
</p>
|
||
|
|
<p>Functions that are called are assumed to modify all registers listed in
|
||
|
|
the configuration macro <code>CALL_USED_REGISTERS</code> (see <a href="Register-Basics.html#Register-Basics">Register Basics</a>) and, with the exception of <code>const</code> functions and library
|
||
|
|
calls, to modify all of memory.
|
||
|
|
</p>
|
||
|
|
<p>Insns containing just <code>use</code> expressions directly precede the
|
||
|
|
<code>call_insn</code> insn to indicate which registers contain inputs to the
|
||
|
|
function. Similarly, if registers other than those in
|
||
|
|
<code>CALL_USED_REGISTERS</code> are clobbered by the called function, insns
|
||
|
|
containing a single <code>clobber</code> follow immediately after the call to
|
||
|
|
indicate which registers.
|
||
|
|
</p>
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Sharing.html#Sharing" accesskey="n" rel="next">Sharing</a>, Previous: <a href="Insns.html#Insns" accesskey="p" rel="prev">Insns</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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>
|