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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 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/Delay-Slots.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
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diff --git a/share/doc/gccint/Delay-Slots.html b/share/doc/gccint/Delay-Slots.html new file mode 100644 index 0000000..4a0e59c --- /dev/null +++ b/share/doc/gccint/Delay-Slots.html @@ -0,0 +1,160 @@ +<!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: Delay Slots</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Delay Slots"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Delay Slots"> +<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="Insn-Attributes.html#Insn-Attributes" rel="up" title="Insn Attributes"> +<link href="Processor-pipeline-description.html#Processor-pipeline-description" rel="next" title="Processor pipeline description"> +<link href="Mnemonic-Attribute.html#Mnemonic-Attribute" rel="previous" title="Mnemonic Attribute"> +<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="Delay-Slots"></a> +<div class="header"> +<p> +Next: <a href="Processor-pipeline-description.html#Processor-pipeline-description" accesskey="n" rel="next">Processor pipeline description</a>, Previous: <a href="Mnemonic-Attribute.html#Mnemonic-Attribute" accesskey="p" rel="previous">Mnemonic Attribute</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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="Delay-Slot-Scheduling"></a> +<h4 class="subsection">17.19.8 Delay Slot Scheduling</h4> +<a name="index-delay-slots_002c-defining"></a> + +<p>The insn attribute mechanism can be used to specify the requirements for +delay slots, if any, on a target machine. An instruction is said to +require a <em>delay slot</em> if some instructions that are physically +after the instruction are executed as if they were located before it. +Classic examples are branch and call instructions, which often execute +the following instruction before the branch or call is performed. +</p> +<p>On some machines, conditional branch instructions can optionally +<em>annul</em> instructions in the delay slot. This means that the +instruction will not be executed for certain branch outcomes. Both +instructions that annul if the branch is true and instructions that +annul if the branch is false are supported. +</p> +<p>Delay slot scheduling differs from instruction scheduling in that +determining whether an instruction needs a delay slot is dependent only +on the type of instruction being generated, not on data flow between the +instructions. See the next section for a discussion of data-dependent +instruction scheduling. +</p> +<a name="index-define_005fdelay"></a> +<p>The requirement of an insn needing one or more delay slots is indicated +via the <code>define_delay</code> expression. It has the following form: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_delay <var>test</var> + [<var>delay-1</var> <var>annul-true-1</var> <var>annul-false-1</var> + <var>delay-2</var> <var>annul-true-2</var> <var>annul-false-2</var> + …]) +</pre></div> + +<p><var>test</var> is an attribute test that indicates whether this +<code>define_delay</code> applies to a particular insn. If so, the number of +required delay slots is determined by the length of the vector specified +as the second argument. An insn placed in delay slot <var>n</var> must +satisfy attribute test <var>delay-n</var>. <var>annul-true-n</var> is an +attribute test that specifies which insns may be annulled if the branch +is true. Similarly, <var>annul-false-n</var> specifies which insns in the +delay slot may be annulled if the branch is false. If annulling is not +supported for that delay slot, <code>(nil)</code> should be coded. +</p> +<p>For example, in the common case where branch and call insns require +a single delay slot, which may contain any insn other than a branch or +call, the following would be placed in the <samp>md</samp> file: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_delay (eq_attr "type" "branch,call") + [(eq_attr "type" "!branch,call") (nil) (nil)]) +</pre></div> + +<p>Multiple <code>define_delay</code> expressions may be specified. In this +case, each such expression specifies different delay slot requirements +and there must be no insn for which tests in two <code>define_delay</code> +expressions are both true. +</p> +<p>For example, if we have a machine that requires one delay slot for branches +but two for calls, no delay slot can contain a branch or call insn, +and any valid insn in the delay slot for the branch can be annulled if the +branch is true, we might represent this as follows: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_delay (eq_attr "type" "branch") + [(eq_attr "type" "!branch,call") + (eq_attr "type" "!branch,call") + (nil)]) + +(define_delay (eq_attr "type" "call") + [(eq_attr "type" "!branch,call") (nil) (nil) + (eq_attr "type" "!branch,call") (nil) (nil)]) +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Processor-pipeline-description.html#Processor-pipeline-description" accesskey="n" rel="next">Processor pipeline description</a>, Previous: <a href="Mnemonic-Attribute.html#Mnemonic-Attribute" accesskey="p" rel="previous">Mnemonic Attribute</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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> |