You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
134 lines
6.3 KiB
HTML
134 lines
6.3 KiB
HTML
4 years ago
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1988-2018 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 6.4, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>loop-iv (GNU Compiler Collection (GCC) Internals)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="loop-iv (GNU Compiler Collection (GCC) Internals)">
|
||
|
|
<meta name="keywords" content="loop-iv (GNU Compiler Collection (GCC) Internals)">
|
||
|
|
<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="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation" rel="up" title="Loop Analysis and Representation">
|
||
|
|
<link href="Number-of-iterations.html#Number-of-iterations" rel="next" title="Number of iterations">
|
||
|
|
<link href="Scalar-evolutions.html#Scalar-evolutions" rel="prev" title="Scalar evolutions">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
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.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<a name="loop_002div"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Number-of-iterations.html#Number-of-iterations" accesskey="n" rel="next">Number of iterations</a>, Previous: <a href="Scalar-evolutions.html#Scalar-evolutions" accesskey="p" rel="prev">Scalar evolutions</a>, Up: <a href="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation" accesskey="u" rel="up">Loop Analysis and Representation</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="IV-analysis-on-RTL"></a>
|
||
|
|
<h3 class="section">16.6 IV analysis on RTL</h3>
|
||
|
|
<a name="index-IV-analysis-on-RTL"></a>
|
||
|
|
|
||
|
|
<p>The induction variable on RTL is simple and only allows analysis of
|
||
|
|
affine induction variables, and only in one loop at once. The interface
|
||
|
|
is declared in <samp>cfgloop.h</samp>. Before analyzing induction variables
|
||
|
|
in a loop L, <code>iv_analysis_loop_init</code> function must be called on L.
|
||
|
|
After the analysis (possibly calling <code>iv_analysis_loop_init</code> for
|
||
|
|
several loops) is finished, <code>iv_analysis_done</code> should be called.
|
||
|
|
The following functions can be used to access the results of the
|
||
|
|
analysis:
|
||
|
|
</p>
|
||
|
|
<ul>
|
||
|
|
<li> <code>iv_analyze</code>: Analyzes a single register used in the given
|
||
|
|
insn. If no use of the register in this insn is found, the following
|
||
|
|
insns are scanned, so that this function can be called on the insn
|
||
|
|
returned by get_condition.
|
||
|
|
</li><li> <code>iv_analyze_result</code>: Analyzes result of the assignment in the
|
||
|
|
given insn.
|
||
|
|
</li><li> <code>iv_analyze_expr</code>: Analyzes a more complicated expression.
|
||
|
|
All its operands are analyzed by <code>iv_analyze</code>, and hence they must
|
||
|
|
be used in the specified insn or one of the following insns.
|
||
|
|
</li></ul>
|
||
|
|
|
||
|
|
<p>The description of the induction variable is provided in <code>struct
|
||
|
|
rtx_iv</code>. In order to handle subregs, the representation is a bit
|
||
|
|
complicated; if the value of the <code>extend</code> field is not
|
||
|
|
<code>UNKNOWN</code>, the value of the induction variable in the i-th
|
||
|
|
iteration is
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">delta + mult * extend_{extend_mode} (subreg_{mode} (base + i * step)),
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>with the following exception: if <code>first_special</code> is true, then the
|
||
|
|
value in the first iteration (when <code>i</code> is zero) is <code>delta +
|
||
|
|
mult * base</code>. However, if <code>extend</code> is equal to <code>UNKNOWN</code>,
|
||
|
|
then <code>first_special</code> must be false, <code>delta</code> 0, <code>mult</code> 1
|
||
|
|
and the value in the i-th iteration is
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">subreg_{mode} (base + i * step)
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>The function <code>get_iv_value</code> can be used to perform these
|
||
|
|
calculations.
|
||
|
|
</p>
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Number-of-iterations.html#Number-of-iterations" accesskey="n" rel="next">Number of iterations</a>, Previous: <a href="Scalar-evolutions.html#Scalar-evolutions" accesskey="p" rel="prev">Scalar evolutions</a>, Up: <a href="Loop-Analysis-and-Representation.html#Loop-Analysis-and-Representation" accesskey="u" rel="up">Loop Analysis and Representation</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>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|