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 <a name="Xtensa-Jump-Relaxation"></a>
 <div class="header">
 <p>
 Next: <a href="Xtensa-Immediate-Relaxation.html#Xtensa-Immediate-Relaxation" accesskey="n" rel="next">Xtensa Immediate Relaxation</a>, Previous: <a href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" accesskey="p" rel="prev">Xtensa Call Relaxation</a>, Up: <a href="Xtensa-Relaxation.html#Xtensa-Relaxation" accesskey="u" rel="up">Xtensa Relaxation</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>
 </div>
 <hr>
 <a name="Jump-Relaxation"></a>
 <h4 class="subsubsection">9.52.4.3 Jump Relaxation</h4>
 <a name="index-relaxation-of-jump-instructions"></a>
 <a name="index-jump-instructions_002c-relaxation"></a>

 <p>Jump instruction may require relaxation because the Xtensa jump instruction
 (<code>J</code>) provide a PC-relative offset of only 128 Kbytes in either
 direction.  One option is to use jump long (<code>J.L</code>) instruction, which
 depending on jump distance may be assembled as jump (<code>J</code>) or indirect
 jump (<code>JX</code>).  However it needs a free register.  When there&rsquo;s no spare
 register it is possible to plant intermediate jump sites (trampolines)
 between the jump instruction and its target.  These sites may be located in
 areas unreachable by normal code execution flow, in that case they only
 contain intermediate jumps, or they may be inserted in the middle of code
 block, in which case there&rsquo;s an additional jump from the beginning of the
 trampoline to the instruction past its end.  So, for example:
 </p>
 <div class="smallexample">
 <pre class="smallexample">    j 1f
     ...
     retw
     ...
     mov a10, a2
     call8 func
     ...
 1:
     ...
 </pre></div>

 <p>might be relaxed to:
 </p>
 <div class="smallexample">
 <pre class="smallexample">    j .L0_TR_1
     ...
     retw
 .L0_TR_1:
     j 1f
     ...
     mov a10, a2
     call8 func
     ...
 1:
     ...
 </pre></div>

 <p>or to:
 </p>
 <div class="smallexample">
 <pre class="smallexample">    j .L0_TR_1
     ...
     retw
     ...
     mov a10, a2
     j .L0_TR_0
 .L0_TR_1:
     j 1f
 .L0_TR_0:
     call8 func
     ...
 1:
     ...
 </pre></div>

 <p>The Xtensa assempler uses trampolines with jump around only when it cannot
 find suitable unreachable trampoline.  There may be multiple trampolines
 between the jump instruction and its target.
 </p>
 <p>This relaxation does not apply to jumps to undefined symbols, assuming they
 will reach their targets once resolved.
 </p>
 <p>Jump relaxation is enabled by default because it does not affect code size
 or performance while the code itself is small.  This relaxation may be
 disabled completely with &lsquo;<samp>--no-trampolines</samp>&rsquo; or &lsquo;<samp>--no-transform</samp>&rsquo;
 command-line options (see <a href="Xtensa-Options.html#Xtensa-Options">Command Line Options</a>).
 </p>
 <hr>
 <div class="header">
 <p>
 Next: <a href="Xtensa-Immediate-Relaxation.html#Xtensa-Immediate-Relaxation" accesskey="n" rel="next">Xtensa Immediate Relaxation</a>, Previous: <a href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" accesskey="p" rel="prev">Xtensa Call Relaxation</a>, Up: <a href="Xtensa-Relaxation.html#Xtensa-Relaxation" accesskey="u" rel="up">Xtensa Relaxation</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>
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	<a name="Xtensa-Jump-Relaxation"></a>
	<div class="header">
	<p>
	Next: <a href="Xtensa-Immediate-Relaxation.html#Xtensa-Immediate-Relaxation" accesskey="n" rel="next">Xtensa Immediate Relaxation</a>, Previous: <a href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" accesskey="p" rel="prev">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>
	</div>
	<hr>
	<a name="Jump-Relaxation"></a>
	<h4 class="subsubsection">9.52.4.3 Jump Relaxation</h4>
	<a name="index-relaxation-of-jump-instructions"></a>
	<a name="index-jump-instructions_002c-relaxation"></a>

	<p>Jump instruction may require relaxation because the Xtensa jump instruction
	(<code>J</code>) provide a PC-relative offset of only 128 Kbytes in either
	direction. One option is to use jump long (<code>J.L</code>) instruction, which
	depending on jump distance may be assembled as jump (<code>J</code>) or indirect
	jump (<code>JX</code>). However it needs a free register. When there’s no spare
	register it is possible to plant intermediate jump sites (trampolines)
	between the jump instruction and its target. These sites may be located in
	areas unreachable by normal code execution flow, in that case they only
	contain intermediate jumps, or they may be inserted in the middle of code
	block, in which case there’s an additional jump from the beginning of the
	trampoline to the instruction past its end. So, for example:
	</p>
	<div class="smallexample">
	<pre class="smallexample"> j 1f
	...
	retw
	...
	mov a10, a2
	call8 func
	...
	1:
	...
	</pre></div>

	<p>might be relaxed to:
	</p>
	<div class="smallexample">
	<pre class="smallexample"> j .L0_TR_1
	...
	retw
	.L0_TR_1:
	j 1f
	...
	mov a10, a2
	call8 func
	...
	1:
	...
	</pre></div>

	<p>or to:
	</p>
	<div class="smallexample">
	<pre class="smallexample"> j .L0_TR_1
	...
	retw
	...
	mov a10, a2
	j .L0_TR_0
	.L0_TR_1:
	j 1f
	.L0_TR_0:
	call8 func
	...
	1:
	...
	</pre></div>

	<p>The Xtensa assempler uses trampolines with jump around only when it cannot
	find suitable unreachable trampoline. There may be multiple trampolines
	between the jump instruction and its target.
	</p>
	<p>This relaxation does not apply to jumps to undefined symbols, assuming they
	will reach their targets once resolved.
	</p>
	<p>Jump relaxation is enabled by default because it does not affect code size
	or performance while the code itself is small. This relaxation may be
	disabled completely with ‘<samp>--no-trampolines</samp>’ or ‘<samp>--no-transform</samp>’
	command-line options (see <a href="Xtensa-Options.html#Xtensa-Options">Command Line Options</a>).
	</p>
	<hr>
	<div class="header">
	<p>
	Next: <a href="Xtensa-Immediate-Relaxation.html#Xtensa-Immediate-Relaxation" accesskey="n" rel="next">Xtensa Immediate Relaxation</a>, Previous: <a href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" accesskey="p" rel="prev">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>
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