<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2015 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: Memory model</title>

<meta name="description" content="GNU Compiler Collection (GCC) Internals: Memory model">
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Memory model">
<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="Tree-SSA.html#Tree-SSA" rel="up" title="Tree SSA">
<link href="RTL.html#RTL" rel="next" title="RTL">
<link href="Alias-analysis.html#Alias-analysis" rel="prev" title="Alias analysis">
<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="Memory-model"></a>
<div class="header">
<p>
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> &nbsp; [<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="Memory-model-1"></a>
<h3 class="section">12.5 Memory model</h3>
<a name="index-memory-model"></a>

<p>The memory model used by the middle-end models that of the C/C++
languages.  The middle-end has the notion of an effective type
of a memory region which is used for type-based alias analysis.
</p>
<p>The following is a refinement of ISO C99 6.5/6, clarifying the block copy case
to follow common sense and extending the concept of a dynamic effective
type to objects with a declared type as required for C++.
</p>
<div class="smallexample">
<pre class="smallexample">The effective type of an object for an access to its stored value is
the declared type of the object or the effective type determined by
a previous store to it.  If a value is stored into an object through
an lvalue having a type that is not a character type, then the
type of the lvalue becomes the effective type of the object for that
access and for subsequent accesses that do not modify the stored value.
If a value is copied into an object using <code>memcpy</code> or <code>memmove</code>,
or is copied as an array of character type, then the effective type
of the modified object for that access and for subsequent accesses that
do not modify the value is undetermined.  For all other accesses to an
object, the effective type of the object is simply the type of the
lvalue used for the access.
</pre></div>


</body>
</html>