173 lines
7.5 KiB
HTML
173 lines
7.5 KiB
HTML
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<!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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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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-->
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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: Xtensa Immediate Relaxation</title>
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<meta name="description" content="Using as: Xtensa Immediate Relaxation">
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<meta name="keywords" content="Using as: Xtensa Immediate Relaxation">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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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-Relaxation.html#Xtensa-Relaxation" rel="up" title="Xtensa Relaxation">
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<link href="Xtensa-Directives.html#Xtensa-Directives" rel="next" title="Xtensa Directives">
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<link href="Xtensa-Jump-Relaxation.html#Xtensa-Jump-Relaxation" rel="prev" title="Xtensa Jump Relaxation">
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Xtensa-Immediate-Relaxation"></a>
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<div class="header">
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<p>
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Previous: <a href="Xtensa-Jump-Relaxation.html#Xtensa-Jump-Relaxation" accesskey="p" rel="prev">Xtensa Jump Relaxation</a>, Up: <a href="Xtensa-Relaxation.html#Xtensa-Relaxation" accesskey="u" rel="up">Xtensa Relaxation</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="Other-Immediate-Field-Relaxation"></a>
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<h4 class="subsubsection">9.52.4.4 Other Immediate Field Relaxation</h4>
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<a name="index-immediate-fields_002c-relaxation"></a>
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<a name="index-relaxation-of-immediate-fields"></a>
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<p>The assembler normally performs the following other relaxations. They
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can be disabled by using underscore prefixes (see <a href="Xtensa-Opcodes.html#Xtensa-Opcodes">Opcode Names</a>), the ‘<samp>--no-transform</samp>’ command-line option
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(see <a href="Xtensa-Options.html#Xtensa-Options">Command Line Options</a>), or the
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<code>no-transform</code> directive (see <a href="Transform-Directive.html#Transform-Directive">transform</a>).
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</p>
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<a name="index-MOVI-instructions_002c-relaxation"></a>
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<a name="index-relaxation-of-MOVI-instructions"></a>
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<p>The <code>MOVI</code> machine instruction can only materialize values in the
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range from -2048 to 2047. Values outside this range are best
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materialized with <code>L32R</code> instructions. Thus:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> movi a0, 100000
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</pre></div>
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<p>is assembled into the following machine code:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> .literal .L1, 100000
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l32r a0, .L1
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</pre></div>
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<a name="index-L8UI-instructions_002c-relaxation"></a>
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<a name="index-L16SI-instructions_002c-relaxation"></a>
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<a name="index-L16UI-instructions_002c-relaxation"></a>
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<a name="index-L32I-instructions_002c-relaxation"></a>
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<a name="index-relaxation-of-L8UI-instructions"></a>
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<a name="index-relaxation-of-L16SI-instructions"></a>
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<a name="index-relaxation-of-L16UI-instructions"></a>
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<a name="index-relaxation-of-L32I-instructions"></a>
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<p>The <code>L8UI</code> machine instruction can only be used with immediate
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offsets in the range from 0 to 255. The <code>L16SI</code> and <code>L16UI</code>
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machine instructions can only be used with offsets from 0 to 510. The
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<code>L32I</code> machine instruction can only be used with offsets from 0 to
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1020. A load offset outside these ranges can be materialized with
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an <code>L32R</code> instruction if the destination register of the load
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is different than the source address register. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> l32i a1, a0, 2040
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</pre></div>
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<p>is translated to:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> .literal .L1, 2040
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l32r a1, .L1
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</pre><pre class="smallexample"> add a1, a0, a1
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l32i a1, a1, 0
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</pre></div>
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<p>If the load destination and source address register are the same, an
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out-of-range offset causes an error.
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</p>
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<a name="index-ADDI-instructions_002c-relaxation"></a>
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<a name="index-relaxation-of-ADDI-instructions"></a>
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<p>The Xtensa <code>ADDI</code> instruction only allows immediate operands in the
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range from -128 to 127. There are a number of alternate instruction
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sequences for the <code>ADDI</code> operation. First, if the
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immediate is 0, the <code>ADDI</code> will be turned into a <code>MOV.N</code>
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instruction (or the equivalent <code>OR</code> instruction if the code density
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option is not available). If the <code>ADDI</code> immediate is outside of
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the range -128 to 127, but inside the range -32896 to 32639, an
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<code>ADDMI</code> instruction or <code>ADDMI</code>/<code>ADDI</code> sequence will be
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used. Finally, if the immediate is outside of this range and a free
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register is available, an <code>L32R</code>/<code>ADD</code> sequence will be used
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with a literal allocated from the literal pool.
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</p>
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<p>For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> addi a5, a6, 0
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addi a5, a6, 512
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</pre><pre class="smallexample"> addi a5, a6, 513
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addi a5, a6, 50000
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</pre></div>
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<p>is assembled into the following:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> .literal .L1, 50000
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mov.n a5, a6
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</pre><pre class="smallexample"> addmi a5, a6, 0x200
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addmi a5, a6, 0x200
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addi a5, a5, 1
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</pre><pre class="smallexample"> l32r a5, .L1
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add a5, a6, a5
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</pre></div>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Xtensa-Jump-Relaxation.html#Xtensa-Jump-Relaxation" accesskey="p" rel="prev">Xtensa Jump Relaxation</a>, Up: <a href="Xtensa-Relaxation.html#Xtensa-Relaxation" accesskey="u" rel="up">Xtensa Relaxation</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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</body>
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</html>
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