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82 lines
3.6 KiB
HTML
82 lines
3.6 KiB
HTML
4 years ago
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<title>Memory model - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Tree-SSA.html#Tree-SSA" title="Tree SSA">
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<link rel="prev" href="Alias-analysis.html#Alias-analysis" title="Alias analysis">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 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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</head>
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<body>
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<div class="node">
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<a name="Memory-model"></a>
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<p>
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Previous: <a rel="previous" accesskey="p" href="Alias-analysis.html#Alias-analysis">Alias analysis</a>,
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Up: <a rel="up" accesskey="u" href="Tree-SSA.html#Tree-SSA">Tree SSA</a>
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<hr>
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</div>
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<h3 class="section">12.5 Memory model</h3>
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<p><a name="index-memory-model-2533"></a>
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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>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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<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>
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<!-- Copyright (C) 1988-2015 Free Software Foundation, Inc. -->
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<!-- This is part of the GCC manual. -->
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<!-- For copying conditions, see the file gcc.texi. -->
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</body></html>
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