94 lines
4.3 KiB
HTML
94 lines
4.3 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using as: Density Instructions</title>
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<meta name="description" content="Using as: Density Instructions">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Xtensa-Optimizations.html#Xtensa-Optimizations" rel="up" title="Xtensa Optimizations">
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<link href="Xtensa-Automatic-Alignment.html#Xtensa-Automatic-Alignment" rel="next" title="Xtensa Automatic Alignment">
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Density-Instructions"></a>
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<div class="header">
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<p>
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Next: <a href="Xtensa-Automatic-Alignment.html#Xtensa-Automatic-Alignment" accesskey="n" rel="next">Xtensa Automatic Alignment</a>, Up: <a href="Xtensa-Optimizations.html#Xtensa-Optimizations" accesskey="u" rel="up">Xtensa Optimizations</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Using-Density-Instructions"></a>
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<h4 class="subsubsection">9.52.3.1 Using Density Instructions</h4>
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<a name="index-density-instructions"></a>
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<p>The Xtensa instruction set has a code density option that provides
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16-bit versions of some of the most commonly used opcodes. Use of these
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opcodes can significantly reduce code size. When possible, the
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assembler automatically translates instructions from the core
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Xtensa instruction set into equivalent instructions from the Xtensa code
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density option. This translation can be disabled by using underscore
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prefixes (see <a href="Xtensa-Opcodes.html#Xtensa-Opcodes">Opcode Names</a>), by using the
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‘<samp>--no-transform</samp>’ command-line option (see <a href="Xtensa-Options.html#Xtensa-Options">Command
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Line Options</a>), or by using the <code>no-transform</code> directive
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(see <a href="Transform-Directive.html#Transform-Directive">transform</a>).
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</p>
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<p>It is a good idea <em>not</em> to use the density instructions directly.
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The assembler will automatically select dense instructions where
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possible. If you later need to use an Xtensa processor without the code
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density option, the same assembly code will then work without modification.
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</p>
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</body>
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</html>
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