130 lines
5.9 KiB
HTML
130 lines
5.9 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>GNU Compiler Collection (GCC) Internals: GIMPLE Exception Handling</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals: GIMPLE Exception Handling">
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<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: GIMPLE Exception Handling">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="GIMPLE.html#GIMPLE" rel="up" title="GIMPLE">
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<link href="Temporaries.html#Temporaries" rel="next" title="Temporaries">
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<link href="GIMPLE-instruction-set.html#GIMPLE-instruction-set" rel="prev" title="GIMPLE instruction set">
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="GIMPLE-Exception-Handling"></a>
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<div class="header">
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<p>
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Next: <a href="Temporaries.html#Temporaries" accesskey="n" rel="next">Temporaries</a>, Previous: <a href="GIMPLE-instruction-set.html#GIMPLE-instruction-set" accesskey="p" rel="prev">GIMPLE instruction set</a>, Up: <a href="GIMPLE.html#GIMPLE" accesskey="u" rel="up">GIMPLE</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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</div>
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<hr>
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<a name="Exception-Handling-1"></a>
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<h3 class="section">11.4 Exception Handling</h3>
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<a name="index-GIMPLE-Exception-Handling"></a>
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<p>Other exception handling constructs are represented using
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<code>GIMPLE_TRY_CATCH</code>. <code>GIMPLE_TRY_CATCH</code> has two operands. The
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first operand is a sequence of statements to execute. If executing
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these statements does not throw an exception, then the second operand
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is ignored. Otherwise, if an exception is thrown, then the second
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operand of the <code>GIMPLE_TRY_CATCH</code> is checked. The second
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operand may have the following forms:
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</p>
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<ol>
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<li> A sequence of statements to execute. When an exception occurs,
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these statements are executed, and then the exception is rethrown.
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</li><li> A sequence of <code>GIMPLE_CATCH</code> statements. Each
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<code>GIMPLE_CATCH</code> has a list of applicable exception types and
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handler code. If the thrown exception matches one of the caught
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types, the associated handler code is executed. If the handler
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code falls off the bottom, execution continues after the original
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<code>GIMPLE_TRY_CATCH</code>.
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</li><li> A <code>GIMPLE_EH_FILTER</code> statement. This has a list of
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permitted exception types, and code to handle a match failure. If the
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thrown exception does not match one of the allowed types, the
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associated match failure code is executed. If the thrown exception
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does match, it continues unwinding the stack looking for the next
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handler.
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</li></ol>
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<p>Currently throwing an exception is not directly represented in
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GIMPLE, since it is implemented by calling a function. At some
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point in the future we will want to add some way to express that
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the call will throw an exception of a known type.
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</p>
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<p>Just before running the optimizers, the compiler lowers the
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high-level EH constructs above into a set of ‘<samp>goto</samp>’s, magic
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labels, and EH regions. Continuing to unwind at the end of a
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cleanup is represented with a <code>GIMPLE_RESX</code>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Temporaries.html#Temporaries" accesskey="n" rel="next">Temporaries</a>, Previous: <a href="GIMPLE-instruction-set.html#GIMPLE-instruction-set" accesskey="p" rel="prev">GIMPLE instruction set</a>, Up: <a href="GIMPLE.html#GIMPLE" accesskey="u" rel="up">GIMPLE</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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</div>
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</body>
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</html>
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