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109 lines
4.6 KiB
HTML
109 lines
4.6 KiB
HTML
4 years ago
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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) 1988-2018 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 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Memory model (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Memory model (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Memory model (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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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="Tree-SSA.html#Tree-SSA" rel="up" title="Tree SSA">
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<link href="RTL.html#RTL" rel="next" title="RTL">
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<link href="Alias-analysis.html#Alias-analysis" rel="prev" title="Alias analysis">
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<style type="text/css">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Memory-model"></a>
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<div class="header">
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<p>
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Previous: <a href="Alias-analysis.html#Alias-analysis" accesskey="p" rel="prev">Alias analysis</a>, Up: <a href="Tree-SSA.html#Tree-SSA" accesskey="u" rel="up">Tree SSA</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="Memory-model-1"></a>
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<h3 class="section">13.5 Memory model</h3>
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<a name="index-memory-model"></a>
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<p>The memory model used by the middle-end models that of the C/C++
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languages. The middle-end has the notion of an effective type
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of a memory region which is used for type-based alias analysis.
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</p>
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<p>The following is a refinement of ISO C99 6.5/6, clarifying the block copy case
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to follow common sense and extending the concept of a dynamic effective
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type to objects with a declared type as required for C++.
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</p>
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<div class="smallexample">
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<pre class="smallexample">The effective type of an object for an access to its stored value is
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the declared type of the object or the effective type determined by
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a previous store to it. If a value is stored into an object through
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an lvalue having a type that is not a character type, then the
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type of the lvalue becomes the effective type of the object for that
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access and for subsequent accesses that do not modify the stored value.
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If a value is copied into an object using <code>memcpy</code> or <code>memmove</code>,
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or is copied as an array of character type, then the effective type
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of the modified object for that access and for subsequent accesses that
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do not modify the value is undetermined. For all other accesses to an
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object, the effective type of the object is simply the type of the
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lvalue used for the access.
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</pre></div>
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</body>
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</html>
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