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diff --git a/share/doc/gccint/Condition-Code.html b/share/doc/gccint/Condition-Code.html new file mode 100644 index 0000000..51b93c7 --- /dev/null +++ b/share/doc/gccint/Condition-Code.html @@ -0,0 +1,126 @@ +<!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: Condition Code</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Condition Code"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Condition Code"> +<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="Target-Macros.html#Target-Macros" rel="up" title="Target Macros"> +<link href="MODE_005fCC-Condition-Codes.html#MODE_005fCC-Condition-Codes" rel="next" title="MODE_CC Condition Codes"> +<link href="Anchored-Addresses.html#Anchored-Addresses" rel="previous" title="Anchored Addresses"> +<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="Condition-Code"></a> +<div class="header"> +<p> +Next: <a href="Costs.html#Costs" accesskey="n" rel="next">Costs</a>, Previous: <a href="Anchored-Addresses.html#Anchored-Addresses" accesskey="p" rel="previous">Anchored Addresses</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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="Condition-Code-Status"></a> +<h3 class="section">18.15 Condition Code Status</h3> +<a name="index-condition-code-status"></a> + +<p>Condition codes in GCC are represented as registers, +which provides better schedulability for +architectures that do have a condition code register, but on which +most instructions do not affect it. The latter category includes +most RISC machines. +</p> +<p>Implicit clobbering would pose a strong restriction on the placement of +the definition and use of the condition code. In the past the definition +and use were always adjacent. However, recent changes to support trapping +arithmetic may result in the definition and user being in different blocks. +Thus, there may be a <code>NOTE_INSN_BASIC_BLOCK</code> between them. Additionally, +the definition may be the source of exception handling edges. +</p> +<p>These restrictions can prevent important +optimizations on some machines. For example, on the IBM RS/6000, there +is a delay for taken branches unless the condition code register is set +three instructions earlier than the conditional branch. The instruction +scheduler cannot perform this optimization if it is not permitted to +separate the definition and use of the condition code register. +</p> +<p>If there is a specific +condition code register in the machine, use a hard register. If the +condition code or comparison result can be placed in any general register, +or if there are multiple condition registers, use a pseudo register. +Registers used to store the condition code value will usually have a mode +that is in class <code>MODE_CC</code>. +</p> +<p>Alternatively, you can use <code>BImode</code> if the comparison operator is +specified already in the compare instruction. In this case, you are not +interested in most macros in this section. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="MODE_005fCC-Condition-Codes.html#MODE_005fCC-Condition-Codes" accesskey="1">MODE_CC Condition Codes</a>:</td><td> </td><td align="left" valign="top">Modern representation of condition codes. +</td></tr> +</table> + +<hr> +<div class="header"> +<p> +Next: <a href="Costs.html#Costs" accesskey="n" rel="next">Costs</a>, Previous: <a href="Anchored-Addresses.html#Anchored-Addresses" accesskey="p" rel="previous">Anchored Addresses</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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> |