131 lines
5.6 KiB
HTML
131 lines
5.6 KiB
HTML
<!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: Cleanups</title>
|
|
|
|
<meta name="description" content="GNU Compiler Collection (GCC) Internals: Cleanups">
|
|
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Cleanups">
|
|
<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="Statements.html#Statements" rel="up" title="Statements">
|
|
<link href="OpenMP.html#OpenMP" rel="next" title="OpenMP">
|
|
<link href="Jumps.html#Jumps" rel="prev" title="Jumps">
|
|
<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="Cleanups"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="OpenMP.html#OpenMP" accesskey="n" rel="next">OpenMP</a>, Previous: <a href="Jumps.html#Jumps" accesskey="p" rel="prev">Jumps</a>, Up: <a href="Statements.html#Statements" accesskey="u" rel="up">Statements</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="Cleanups-1"></a>
|
|
<h4 class="subsection">10.7.6 Cleanups</h4>
|
|
<a name="index-Cleanups"></a>
|
|
|
|
<p>Destructors for local C++ objects and similar dynamic cleanups are
|
|
represented in GIMPLE by a <code>TRY_FINALLY_EXPR</code>.
|
|
<code>TRY_FINALLY_EXPR</code> has two operands, both of which are a sequence
|
|
of statements to execute. The first sequence is executed. When it
|
|
completes the second sequence is executed.
|
|
</p>
|
|
<p>The first sequence may complete in the following ways:
|
|
</p>
|
|
<ol>
|
|
<li> Execute the last statement in the sequence and fall off the
|
|
end.
|
|
|
|
</li><li> Execute a goto statement (<code>GOTO_EXPR</code>) to an ordinary
|
|
label outside the sequence.
|
|
|
|
</li><li> Execute a return statement (<code>RETURN_EXPR</code>).
|
|
|
|
</li><li> Throw an exception. This is currently not explicitly represented in
|
|
GIMPLE.
|
|
|
|
</li></ol>
|
|
|
|
<p>The second sequence is not executed if the first sequence completes by
|
|
calling <code>setjmp</code> or <code>exit</code> or any other function that does
|
|
not return. The second sequence is also not executed if the first
|
|
sequence completes via a non-local goto or a computed goto (in general
|
|
the compiler does not know whether such a goto statement exits the
|
|
first sequence or not, so we assume that it doesn’t).
|
|
</p>
|
|
<p>After the second sequence is executed, if it completes normally by
|
|
falling off the end, execution continues wherever the first sequence
|
|
would have continued, by falling off the end, or doing a goto, etc.
|
|
</p>
|
|
<p><code>TRY_FINALLY_EXPR</code> complicates the flow graph, since the cleanup
|
|
needs to appear on every edge out of the controlled block; this
|
|
reduces the freedom to move code across these edges. Therefore, the
|
|
EH lowering pass which runs before most of the optimization passes
|
|
eliminates these expressions by explicitly adding the cleanup to each
|
|
edge. Rethrowing the exception is represented using <code>RESX_EXPR</code>.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="OpenMP.html#OpenMP" accesskey="n" rel="next">OpenMP</a>, Previous: <a href="Jumps.html#Jumps" accesskey="p" rel="prev">Jumps</a>, Up: <a href="Statements.html#Statements" accesskey="u" rel="up">Statements</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>
|