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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

  3. <!-- This file documents the GNU Assembler "as".

  4. 

  5. Copyright (C) 1991-2020 Free Software Foundation, Inc.

  6. 

  7. Permission is granted to copy, distribute and/or modify this document

  8. under the terms of the GNU Free Documentation License, Version 1.3

  9. or any later version published by the Free Software Foundation;

  10. with no Invariant Sections, with no Front-Cover Texts, and with no

  11. Back-Cover Texts.  A copy of the license is included in the

  12. section entitled "GNU Free Documentation License".

  13.  -->

  14. <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->

  15. <head>

  16. <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

  17. <title>Density Instructions (Using as)</title>

  18. 

  19. <meta name="description" content="Density Instructions (Using as)">

  20. <meta name="keywords" content="Density Instructions (Using as)">

  21. <meta name="resource-type" content="document">

  22. <meta name="distribution" content="global">

  23. <meta name="Generator" content="makeinfo">

  24. <link href="index.html#Top" rel="start" title="Top">

  25. <link href="AS-Index.html#AS-Index" rel="index" title="AS Index">

  26. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  27. <link href="Xtensa-Optimizations.html#Xtensa-Optimizations" rel="up" title="Xtensa Optimizations">

  28. <link href="Xtensa-Automatic-Alignment.html#Xtensa-Automatic-Alignment" rel="next" title="Xtensa Automatic Alignment">

  29. <link href="Xtensa-Optimizations.html#Xtensa-Optimizations" rel="prev" title="Xtensa Optimizations">

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  59. </head>

  60. 

  61. <body lang="en">

  62. <a name="Density-Instructions"></a>

  63. <div class="header">

  64. <p>

  65. 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> &nbsp; [<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>

  66. </div>

  67. <hr>

  68. <a name="Using-Density-Instructions"></a>

  69. <h4 class="subsubsection">9.55.3.1 Using Density Instructions</h4>

  70. <a name="index-density-instructions"></a>

  71. 

  72. <p>The Xtensa instruction set has a code density option that provides

  73. 16-bit versions of some of the most commonly used opcodes.  Use of these

  74. opcodes can significantly reduce code size.  When possible, the

  75. assembler automatically translates instructions from the core

  76. Xtensa instruction set into equivalent instructions from the Xtensa code

  77. density option.  This translation can be disabled by using underscore

  78. prefixes (see <a href="Xtensa-Opcodes.html#Xtensa-Opcodes">Opcode Names</a>), by using the

  79. &lsquo;<samp>--no-transform</samp>&rsquo; command-line option (see <a href="Xtensa-Options.html#Xtensa-Options">Command

  80. Line Options</a>), or by using the <code>no-transform</code> directive

  81. (see <a href="Transform-Directive.html#Transform-Directive">transform</a>).

  82. </p>

  83. <p>It is a good idea <em>not</em> to use the density instructions directly.

  84. The assembler will automatically select dense instructions where

  85. possible.  If you later need to use an Xtensa processor without the code

  86. density option, the same assembly code will then work without modification.

  87. </p>

  88. 

  89. 

  90. 

  91. </body>

  92. </html>