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 <a name="Xtensa"></a>
 <div class="header">
 <p>
 Previous: <a href="WIN32.html#WIN32" accesskey="p" rel="prev">WIN32</a>, Up: <a href="Machine-Dependent.html#Machine-Dependent" accesskey="u" rel="up">Machine Dependent</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="ld-and-Xtensa-Processors"></a>
 <h3 class="section">4.17 <code>ld</code> and Xtensa Processors</h3>

 <a name="index-Xtensa-processors"></a>
 <p>The default <code>ld</code> behavior for Xtensa processors is to interpret
 <code>SECTIONS</code> commands so that lists of explicitly named sections in a
 specification with a wildcard file will be interleaved when necessary to
 keep literal pools within the range of PC-relative load offsets.  For
 example, with the command:
 </p>
 <div class="smallexample">
 <pre class="smallexample">SECTIONS
 {
   .text : {
     *(.literal .text)
   }
 }
 </pre></div>

 <p><code>ld</code> may interleave some of the <code>.literal</code>
 and <code>.text</code> sections from different object files to ensure that the
 literal pools are within the range of PC-relative load offsets.  A valid
 interleaving might place the <code>.literal</code> sections from an initial
 group of files followed by the <code>.text</code> sections of that group of
 files.  Then, the <code>.literal</code> sections from the rest of the files
 and the <code>.text</code> sections from the rest of the files would follow.
 </p>
 <a name="index-_002d_002drelax-on-Xtensa"></a>
 <a name="index-relaxing-on-Xtensa"></a>
 <p>Relaxation is enabled by default for the Xtensa version of <code>ld</code> and
 provides two important link-time optimizations.  The first optimization
 is to combine identical literal values to reduce code size.  A redundant
 literal will be removed and all the <code>L32R</code> instructions that use it
 will be changed to reference an identical literal, as long as the
 location of the replacement literal is within the offset range of all
 the <code>L32R</code> instructions.  The second optimization is to remove
 unnecessary overhead from assembler-generated &ldquo;longcall&rdquo; sequences of
 <code>L32R</code>/<code>CALLX<var>n</var></code> when the target functions are within
 range of direct <code>CALL<var>n</var></code> instructions.
 </p>
 <p>For each of these cases where an indirect call sequence can be optimized
 to a direct call, the linker will change the <code>CALLX<var>n</var></code>
 instruction to a <code>CALL<var>n</var></code> instruction, remove the <code>L32R</code>
 instruction, and remove the literal referenced by the <code>L32R</code>
 instruction if it is not used for anything else.  Removing the
 <code>L32R</code> instruction always reduces code size but can potentially
 hurt performance by changing the alignment of subsequent branch targets.
 By default, the linker will always preserve alignments, either by
 switching some instructions between 24-bit encodings and the equivalent
 density instructions or by inserting a no-op in place of the <code>L32R</code>
 instruction that was removed.  If code size is more important than
 performance, the <samp>--size-opt</samp> option can be used to prevent the
 linker from widening density instructions or inserting no-ops, except in
 a few cases where no-ops are required for correctness.
 </p>
 <p>The following Xtensa-specific command-line options can be used to
 control the linker:
 </p>
 <a name="index-Xtensa-options"></a>
 <dl compact="compact">
 <dt><samp>--size-opt</samp></dt>
 <dd><p>When optimizing indirect calls to direct calls, optimize for code size
 more than performance.  With this option, the linker will not insert
 no-ops or widen density instructions to preserve branch target
 alignment.  There may still be some cases where no-ops are required to
 preserve the correctness of the code.
 </p></dd>
 </dl>


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	<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
	<a name="Xtensa"></a>
	<div class="header">
	<p>
	Previous: <a href="WIN32.html#WIN32" accesskey="p" rel="prev">WIN32</a>, Up: <a href="Machine-Dependent.html#Machine-Dependent" accesskey="u" rel="up">Machine Dependent</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="ld-and-Xtensa-Processors"></a>
	<h3 class="section">4.17 <code>ld</code> and Xtensa Processors</h3>

	<a name="index-Xtensa-processors"></a>
	<p>The default <code>ld</code> behavior for Xtensa processors is to interpret
	<code>SECTIONS</code> commands so that lists of explicitly named sections in a
	specification with a wildcard file will be interleaved when necessary to
	keep literal pools within the range of PC-relative load offsets. For
	example, with the command:
	</p>
	<div class="smallexample">
	<pre class="smallexample">SECTIONS
	{
	.text : {
	*(.literal .text)
	}
	}
	</pre></div>

	<p><code>ld</code> may interleave some of the <code>.literal</code>
	and <code>.text</code> sections from different object files to ensure that the
	literal pools are within the range of PC-relative load offsets. A valid
	interleaving might place the <code>.literal</code> sections from an initial
	group of files followed by the <code>.text</code> sections of that group of
	files. Then, the <code>.literal</code> sections from the rest of the files
	and the <code>.text</code> sections from the rest of the files would follow.
	</p>
	<a name="index-_002d_002drelax-on-Xtensa"></a>
	<a name="index-relaxing-on-Xtensa"></a>
	<p>Relaxation is enabled by default for the Xtensa version of <code>ld</code> and
	provides two important link-time optimizations. The first optimization
	is to combine identical literal values to reduce code size. A redundant
	literal will be removed and all the <code>L32R</code> instructions that use it
	will be changed to reference an identical literal, as long as the
	location of the replacement literal is within the offset range of all
	the <code>L32R</code> instructions. The second optimization is to remove
	unnecessary overhead from assembler-generated “longcall” sequences of
	<code>L32R</code>/<code>CALLX<var>n</var></code> when the target functions are within
	range of direct <code>CALL<var>n</var></code> instructions.
	</p>
	<p>For each of these cases where an indirect call sequence can be optimized
	to a direct call, the linker will change the <code>CALLX<var>n</var></code>
	instruction to a <code>CALL<var>n</var></code> instruction, remove the <code>L32R</code>
	instruction, and remove the literal referenced by the <code>L32R</code>
	instruction if it is not used for anything else. Removing the
	<code>L32R</code> instruction always reduces code size but can potentially
	hurt performance by changing the alignment of subsequent branch targets.
	By default, the linker will always preserve alignments, either by
	switching some instructions between 24-bit encodings and the equivalent
	density instructions or by inserting a no-op in place of the <code>L32R</code>
	instruction that was removed. If code size is more important than
	performance, the <samp>--size-opt</samp> option can be used to prevent the
	linker from widening density instructions or inserting no-ops, except in
	a few cases where no-ops are required for correctness.
	</p>
	<p>The following Xtensa-specific command-line options can be used to
	control the linker:
	</p>
	<a name="index-Xtensa-options"></a>
	<dl compact="compact">
	<dt><samp>--size-opt</samp></dt>
	<dd><p>When optimizing indirect calls to direct calls, optimize for code size
	more than performance. With this option, the linker will not insert
	no-ops or widen density instructions to preserve branch target
	alignment. There may still be some cases where no-ops are required to
	preserve the correctness of the code.
	</p></dd>
	</dl>


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	<p>
	Previous: <a href="WIN32.html#WIN32" accesskey="p" rel="prev">WIN32</a>, Up: <a href="Machine-Dependent.html#Machine-Dependent" accesskey="u" rel="up">Machine Dependent</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
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