You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
115 lines
5.9 KiB
HTML
115 lines
5.9 KiB
HTML
15 years ago
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>Xtensa Immediate Relaxation - Using as</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="Using as">
|
||
|
|
<meta name="generator" content="makeinfo 4.7">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="up" href="Xtensa-Relaxation.html#Xtensa-Relaxation" title="Xtensa Relaxation">
|
||
|
|
<link rel="prev" href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" title="Xtensa Call Relaxation">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
This file documents the GNU Assembler "as".
|
||
|
|
|
||
|
|
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
|
||
|
|
2006, 2007 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 1.1
|
||
|
|
or any later version published by the Free Software Foundation;
|
||
|
|
with no Invariant Sections, with no Front-Cover Texts, and with no
|
||
|
|
Back-Cover Texts. A copy of the license is included in the
|
||
|
|
section entitled ``GNU Free Documentation License''.
|
||
|
|
|
||
|
|
man end-->
|
||
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
||
|
|
<style type="text/css"><!--
|
||
|
|
pre.display { font-family:inherit }
|
||
|
|
pre.format { font-family:inherit }
|
||
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallexample { font-size:smaller }
|
||
|
|
pre.smalllisp { font-size:smaller }
|
||
|
|
span.sc { font-variant:small-caps }
|
||
|
|
span.roman { font-family: serif; font-weight: normal; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div class="node">
|
||
|
|
<p>
|
||
|
|
<a name="Xtensa-Immediate-Relaxation"></a>Previous: <a rel="previous" accesskey="p" href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation">Xtensa Call Relaxation</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="Xtensa-Relaxation.html#Xtensa-Relaxation">Xtensa Relaxation</a>
|
||
|
|
<hr><br>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h5 class="subsubsection">9.36.4.3 Other Immediate Field Relaxation</h5>
|
||
|
|
|
||
|
|
<p><a name="index-immediate-fields_002c-relaxation-1868"></a><a name="index-relaxation-of-immediate-fields-1869"></a>
|
||
|
|
The assembler normally performs the following other relaxations. They
|
||
|
|
can be disabled by using underscore prefixes (see <a href="Xtensa-Opcodes.html#Xtensa-Opcodes">Opcode Names</a>), the <span class="samp">--no-transform</span> command-line option
|
||
|
|
(see <a href="Xtensa-Options.html#Xtensa-Options">Command Line Options</a>), or the
|
||
|
|
<code>no-transform</code> directive (see <a href="Transform-Directive.html#Transform-Directive">transform</a>).
|
||
|
|
|
||
|
|
<p><a name="index-_0040code_007bMOVI_007d-instructions_002c-relaxation-1870"></a><a name="index-relaxation-of-_0040code_007bMOVI_007d-instructions-1871"></a>The <code>MOVI</code> machine instruction can only materialize values in the
|
||
|
|
range from -2048 to 2047. Values outside this range are best
|
||
|
|
materialized with <code>L32R</code> instructions. Thus:
|
||
|
|
|
||
|
|
<pre class="smallexample"> movi a0, 100000
|
||
|
|
</pre>
|
||
|
|
<p>is assembled into the following machine code:
|
||
|
|
|
||
|
|
<pre class="smallexample"> .literal .L1, 100000
|
||
|
|
l32r a0, .L1
|
||
|
|
</pre>
|
||
|
|
<p><a name="index-_0040code_007bL8UI_007d-instructions_002c-relaxation-1872"></a><a name="index-_0040code_007bL16SI_007d-instructions_002c-relaxation-1873"></a><a name="index-_0040code_007bL16UI_007d-instructions_002c-relaxation-1874"></a><a name="index-_0040code_007bL32I_007d-instructions_002c-relaxation-1875"></a><a name="index-relaxation-of-_0040code_007bL8UI_007d-instructions-1876"></a><a name="index-relaxation-of-_0040code_007bL16SI_007d-instructions-1877"></a><a name="index-relaxation-of-_0040code_007bL16UI_007d-instructions-1878"></a><a name="index-relaxation-of-_0040code_007bL32I_007d-instructions-1879"></a>The <code>L8UI</code> machine instruction can only be used with immediate
|
||
|
|
offsets in the range from 0 to 255. The <code>L16SI</code> and <code>L16UI</code>
|
||
|
|
machine instructions can only be used with offsets from 0 to 510. The
|
||
|
|
<code>L32I</code> machine instruction can only be used with offsets from 0 to
|
||
|
|
1020. A load offset outside these ranges can be materialized with
|
||
|
|
an <code>L32R</code> instruction if the destination register of the load
|
||
|
|
is different than the source address register. For example:
|
||
|
|
|
||
|
|
<pre class="smallexample"> l32i a1, a0, 2040
|
||
|
|
</pre>
|
||
|
|
<p>is translated to:
|
||
|
|
|
||
|
|
<pre class="smallexample"> .literal .L1, 2040
|
||
|
|
l32r a1, .L1
|
||
|
|
add a1, a0, a1
|
||
|
|
l32i a1, a1, 0
|
||
|
|
</pre>
|
||
|
|
<p class="noindent">If the load destination and source address register are the same, an
|
||
|
|
out-of-range offset causes an error.
|
||
|
|
|
||
|
|
<p><a name="index-_0040code_007bADDI_007d-instructions_002c-relaxation-1880"></a><a name="index-relaxation-of-_0040code_007bADDI_007d-instructions-1881"></a>The Xtensa <code>ADDI</code> instruction only allows immediate operands in the
|
||
|
|
range from -128 to 127. There are a number of alternate instruction
|
||
|
|
sequences for the <code>ADDI</code> operation. First, if the
|
||
|
|
immediate is 0, the <code>ADDI</code> will be turned into a <code>MOV.N</code>
|
||
|
|
instruction (or the equivalent <code>OR</code> instruction if the code density
|
||
|
|
option is not available). If the <code>ADDI</code> immediate is outside of
|
||
|
|
the range -128 to 127, but inside the range -32896 to 32639, an
|
||
|
|
<code>ADDMI</code> instruction or <code>ADDMI</code>/<code>ADDI</code> sequence will be
|
||
|
|
used. Finally, if the immediate is outside of this range and a free
|
||
|
|
register is available, an <code>L32R</code>/<code>ADD</code> sequence will be used
|
||
|
|
with a literal allocated from the literal pool.
|
||
|
|
|
||
|
|
<p>For example:
|
||
|
|
|
||
|
|
<pre class="smallexample"> addi a5, a6, 0
|
||
|
|
addi a5, a6, 512
|
||
|
|
addi a5, a6, 513
|
||
|
|
addi a5, a6, 50000
|
||
|
|
</pre>
|
||
|
|
<p>is assembled into the following:
|
||
|
|
|
||
|
|
<pre class="smallexample"> .literal .L1, 50000
|
||
|
|
mov.n a5, a6
|
||
|
|
addmi a5, a6, 0x200
|
||
|
|
addmi a5, a6, 0x200
|
||
|
|
addi a5, a5, 1
|
||
|
|
l32r a5, .L1
|
||
|
|
add a5, a6, a5
|
||
|
|
</pre>
|
||
|
|
</body></html>
|
||
|
|
|