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 5Copyright (C) 1991-2021 Free Software Foundation, Inc. 6 7Permission is granted to copy, distribute and/or modify this document 8under the terms of the GNU Free Documentation License, Version 1.3 9or any later version published by the Free Software Foundation; 10with no Invariant Sections, with no Front-Cover Texts, and with no 11Back-Cover Texts. A copy of the license is included in the 12section entitled "GNU Free Documentation License". 13 --> 14<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 15<head> 16<title>Using as: Xtensa Branch Relaxation</title> 17 18<meta name="description" content="Using as: Xtensa Branch Relaxation"> 19<meta name="keywords" content="Using as: Xtensa Branch Relaxation"> 20<meta name="resource-type" content="document"> 21<meta name="distribution" content="global"> 22<meta name="Generator" content="makeinfo"> 23<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 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-Relaxation.html#Xtensa-Relaxation" rel="up" title="Xtensa Relaxation"> 28<link href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" rel="next" title="Xtensa Call Relaxation"> 29<link href="Xtensa-Relaxation.html#Xtensa-Relaxation" rel="previous" title="Xtensa Relaxation"> 30<style type="text/css"> 31<!-- 32a.summary-letter {text-decoration: none} 33blockquote.smallquotation {font-size: smaller} 34div.display {margin-left: 3.2em} 35div.example {margin-left: 3.2em} 36div.indentedblock {margin-left: 3.2em} 37div.lisp {margin-left: 3.2em} 38div.smalldisplay {margin-left: 3.2em} 39div.smallexample {margin-left: 3.2em} 40div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 41div.smalllisp {margin-left: 3.2em} 42kbd {font-style:oblique} 43pre.display {font-family: inherit} 44pre.format {font-family: inherit} 45pre.menu-comment {font-family: serif} 46pre.menu-preformatted {font-family: serif} 47pre.smalldisplay {font-family: inherit; font-size: smaller} 48pre.smallexample {font-size: smaller} 49pre.smallformat {font-family: inherit; font-size: smaller} 50pre.smalllisp {font-size: smaller} 51span.nocodebreak {white-space:nowrap} 52span.nolinebreak {white-space:nowrap} 53span.roman {font-family:serif; font-weight:normal} 54span.sansserif {font-family:sans-serif; font-weight:normal} 55ul.no-bullet {list-style: none} 56--> 57</style> 58 59 60</head> 61 62<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 63<a name="Xtensa-Branch-Relaxation"></a> 64<div class="header"> 65<p> 66Next: <a href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" accesskey="n" rel="next">Xtensa Call 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> 67</div> 68<hr> 69<a name="Conditional-Branch-Relaxation"></a> 70<h4 class="subsubsection">9.55.4.1 Conditional Branch Relaxation</h4> 71<a name="index-relaxation-of-branch-instructions"></a> 72<a name="index-branch-instructions_002c-relaxation"></a> 73 74<p>When the target of a branch is too far away from the branch itself, 75i.e., when the offset from the branch to the target is too large to fit 76in the immediate field of the branch instruction, it may be necessary to 77replace the branch with a branch around a jump. For example, 78</p> 79<div class="smallexample"> 80<pre class="smallexample"> beqz a2, L 81</pre></div> 82 83<p>may result in: 84</p> 85<div class="smallexample"> 86<pre class="smallexample"> bnez.n a2, M 87 j L 88M: 89</pre></div> 90 91<p>(The <code>BNEZ.N</code> instruction would be used in this example only if the 92density option is available. Otherwise, <code>BNEZ</code> would be used.) 93</p> 94<p>This relaxation works well because the unconditional jump instruction 95has a much larger offset range than the various conditional branches. 96However, an error will occur if a branch target is beyond the range of a 97jump instruction. <code>as</code> cannot relax unconditional jumps. 98Similarly, an error will occur if the original input contains an 99unconditional jump to a target that is out of range. 100</p> 101<p>Branch relaxation is enabled by default. It can be disabled by using 102underscore prefixes (see <a href="Xtensa-Opcodes.html#Xtensa-Opcodes">Opcode Names</a>), the 103‘<samp>--no-transform</samp>’ command-line option (see <a href="Xtensa-Options.html#Xtensa-Options">Command-line Options</a>), or the <code>no-transform</code> directive 104(see <a href="Transform-Directive.html#Transform-Directive">transform</a>). 105</p> 106 107 108 109</body> 110</html> 111