65 lines
3.1 KiB
HTML
65 lines
3.1 KiB
HTML
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<html lang="en">
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<head>
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<title>Density Instructions - Using as</title>
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<meta name="description" content="Using as">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Xtensa-Optimizations.html#Xtensa-Optimizations" title="Xtensa Optimizations">
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<link rel="next" href="Xtensa-Automatic-Alignment.html#Xtensa-Automatic-Alignment" title="Xtensa Automatic Alignment">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 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 1.1
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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--></style>
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</head>
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<body>
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<div class="node">
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<p>
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<a name="Density-Instructions"></a>Next: <a rel="next" accesskey="n" href="Xtensa-Automatic-Alignment.html#Xtensa-Automatic-Alignment">Xtensa Automatic Alignment</a>,
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Up: <a rel="up" accesskey="u" href="Xtensa-Optimizations.html#Xtensa-Optimizations">Xtensa Optimizations</a>
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<hr><br>
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</div>
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<h5 class="subsubsection">9.36.3.1 Using Density Instructions</h5>
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<p><a name="index-density-instructions-1858"></a>
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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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<span class="samp">--no-transform</span> command-line option (see <a href="Xtensa-Options.html#Xtensa-Options">Command 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>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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</body></html>
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