| <!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> [<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> |
