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author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/loop_002div.html |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gccint/loop_002div.html b/share/doc/gccint/loop_002div.html new file mode 100644 index 0000000..735c4d3 --- /dev/null +++ b/share/doc/gccint/loop_002div.html @@ -0,0 +1,134 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>GNU Compiler Collection (GCC) Internals: loop-iv</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: loop-iv"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: loop-iv"> +<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="previous" title="Scalar evolutions"> +<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="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="previous">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="previous">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> |