<!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: Pass manager</title>

<meta name="description" content="GNU Compiler Collection (GCC) Internals: Pass manager">
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Pass manager">
<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="Passes.html#Passes" rel="up" title="Passes">
<link href="Tree-SSA-passes.html#Tree-SSA-passes" rel="next" title="Tree SSA passes">
<link href="Gimplification-pass.html#Gimplification-pass" rel="prev" title="Gimplification pass">
<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="Pass-manager"></a>
<div class="header">
<p>
Next: <a href="Tree-SSA-passes.html#Tree-SSA-passes" accesskey="n" rel="next">Tree SSA passes</a>, Previous: <a href="Gimplification-pass.html#Gimplification-pass" accesskey="p" rel="prev">Gimplification pass</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</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="Pass-manager-1"></a>
<h3 class="section">9.4 Pass manager</h3>

<p>The pass manager is located in <samp>passes.c</samp>, <samp>tree-optimize.c</samp>
and <samp>tree-pass.h</samp>.
It processes passes as described in <samp>passes.def</samp>.
Its job is to run all of the individual passes in the correct order,
and take care of standard bookkeeping that applies to every pass.
</p>
<p>The theory of operation is that each pass defines a structure that
represents everything we need to know about that pass&mdash;when it
should be run, how it should be run, what intermediate language
form or on-the-side data structures it needs.  We register the pass
to be run in some particular order, and the pass manager arranges
for everything to happen in the correct order.
</p>
<p>The actuality doesn&rsquo;t completely live up to the theory at present.
Command-line switches and <code>timevar_id_t</code> enumerations must still
be defined elsewhere.  The pass manager validates constraints but does
not attempt to (re-)generate data structures or lower intermediate
language form based on the requirements of the next pass.  Nevertheless,
what is present is useful, and a far sight better than nothing at all.
</p>
<p>Each pass should have a unique name.
Each pass may have its own dump file (for GCC debugging purposes).
Passes with a name starting with a star do not dump anything.
Sometimes passes are supposed to share a dump file / option name.
To still give these unique names, you can use a prefix that is delimited
by a space from the part that is used for the dump file / option name.
E.g. When the pass name is &quot;ud dce&quot;, the name used for dump file/options
is &quot;dce&quot;.
</p>
<p>TODO: describe the global variables set up by the pass manager,
and a brief description of how a new pass should use it.
I need to look at what info RTL passes use first<small class="enddots">...</small>
</p>
<hr>
<div class="header">
<p>
Next: <a href="Tree-SSA-passes.html#Tree-SSA-passes" accesskey="n" rel="next">Tree SSA passes</a>, Previous: <a href="Gimplification-pass.html#Gimplification-pass" accesskey="p" rel="prev">Gimplification pass</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</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>


</body>
</html>