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LuaJIT
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<title>Running LuaJIT</title>
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<div id="site">
<a href="http://luajit.org"><span>Lua<span id="logo">JIT</span></span></a>
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<div id="head">
<h1>Running LuaJIT</h1>
</div>
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<ul><li>
<a href="luajit.html">LuaJIT</a>
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<a href="install.html">Installation</a>
</li><li>
<a class="current" href="running.html">Running</a>
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<p>
LuaJIT has only a single stand-alone executable, called <tt>luajit</tt> on
POSIX systems or <tt>luajit.exe</tt> on Windows. It can be used to run simple
Lua statements or whole Lua applications from the command line. It has an
interactive mode, too.
</p>
<p class="indent" style="color: #c00000;">
Note: the beta test releases only install under the versioned name on
POSIX systems (to avoid overwriting a previous version). You either need
to type <tt>luajit-2.0.0-beta3</tt> to start it or create a symlink
with a command like this:
</p>
<pre class="code" style="color: #c00000;">
sudo ln -sf luajit-2.0.0-beta3&nbsp;/usr/local/bin/luajit
</pre>
<p>
Unlike previous versions <b>optimization is turned on by default</b> in
LuaJIT 2.0!<br>It's no longer necessary to use <tt>luajit&nbsp;-O</tt>.
</p>

<h2 id="options">Command Line Options</h2>
<p>
The <tt>luajit</tt> stand-alone executable is just a slightly modified
version of the regular <tt>lua</tt> stand-alone executable.
It supports the same basic options, too. <tt>luajit&nbsp;-h</tt>
prints a short list of the available options. Please have a look at the
<a href="http://www.lua.org/manual/5.1/manual.html#6"><span class="ext">&raquo;</span>&nbsp;Lua manual</a>
for details.
</p>
<p>
Two additional options control the behavior of LuaJIT:
</p>

<h3 id="opt_j"><tt>-j cmd[=arg[,arg...]]</tt></h3>
<p>
This option performs a LuaJIT control command or activates one of the
loadable extension modules. The command is first looked up in the
<tt>jit.*</tt> library. If no matching function is found, a module
named <tt>jit.&lt;cmd&gt;</tt> is loaded and the <tt>start()</tt>
function of the module is called with the specified arguments (if
any). The space between <tt>-j</tt> and <tt>cmd</tt> is optional.
</p>
<p>
Here are the available LuaJIT control commands:
</p>
<ul>
<li id="j_on"><tt>-jon</tt> &mdash; Turns the JIT compiler on (default).</li>
<li id="j_off"><tt>-joff</tt> &mdash; Turns the JIT compiler off (only use the interpreter).</li>
<li id="j_flush"><tt>-jflush</tt> &mdash; Flushes the whole cache of compiled code.</li>
<li id="j_v"><tt>-jv</tt> &mdash; Shows verbose information about the progress of the JIT compiler.</li>
<li id="j_dump"><tt>-jdump</tt> &mdash; Dumps the code and structures used in various compiler stages.</li>
</ul>
<p>
The <tt>-jv</tt> and <tt>-jdump</tt> commands are extension modules
written in Lua. They are mainly used for debugging the JIT compiler
itself. For a description of their options and output format, please
read the comment block at the start of their source.
They can be found in the <tt>lib</tt> directory of the source
distribution or installed under the <tt>jit</tt> directory. By default
this is <tt>/usr/local/share/luajit-2.0.0-beta3/jit</tt> on POSIX
systems.
</p>

<h3 id="opt_O"><tt>-O[level]</tt><br>
<tt>-O[+]flag</tt> <tt>-O-flag</tt><br>
<tt>-Oparam=value</tt></h3>
<p>
This options allows fine-tuned control of the optimizations used by
the JIT compiler. This is mainly intended for debugging LuaJIT itself.
Please note that the JIT compiler is extremely fast (we are talking
about the microsecond to millisecond range). Disabling optimizations
doesn't have any visible impact on its overhead, but usually generates
code that runs slower.
</p>
<p>
The first form sets an optimization level &mdash; this enables a
specific mix of optimization flags. <tt>-O0</tt> turns off all
optimizations and higher numbers enable more optimizations. Omitting
the level (i.e. just <tt>-O</tt>) sets the default optimization level,
which is <tt>-O3</tt> in the current version.
</p>
<p>
The second form adds or removes individual optimization flags.
The third form sets a parameter for the VM or the JIT compiler
to a specific value.
</p>
<p>
You can either use this option multiple times (like <tt>-Ocse
-O-dce -Ohotloop=10</tt>) or separate several settings with a comma
(like <tt>-O+cse,-dce,hotloop=10</tt>). The settings are applied from
left to right and later settings override earlier ones. You can freely
mix the three forms, but note that setting an optimization level
overrides all earlier flags.
</p>
<p>
Here are the available flags and at what optimization levels they
are enabled:
</p>
<table class="opt">
<tr class="opthead">
<td class="flag_name">Flag</td>
<td class="flag_level">-O1</td>
<td class="flag_level">-O2</td>
<td class="flag_level">-O3</td>
<td class="flag_desc">&nbsp;</td>
</tr>
<tr class="odd separate">
<td class="flag_name">fold</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_desc">Constant Folding, Simplifications and Reassociation</td></tr>
<tr class="even">
<td class="flag_name">cse</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_desc">Common-Subexpression Elimination</td></tr>
<tr class="odd">
<td class="flag_name">dce</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_desc">Dead-Code Elimination</td></tr>
<tr class="even">
<td class="flag_name">narrow</td><td class="flag_level">&nbsp;</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_desc">Narrowing of numbers to integers</td></tr>
<tr class="odd">
<td class="flag_name">loop</td><td class="flag_level">&nbsp;</td><td class="flag_level">&bull;</td><td class="flag_level">&bull;</td><td class="flag_desc">Loop Optimizations (code hoisting)</td></tr>
<tr class="even">
<td class="flag_name">fwd</td><td class="flag_level">&nbsp;</td><td class="flag_level">&nbsp;</td><td class="flag_level">&bull;</td><td class="flag_desc">Load Forwarding (L2L) and Store Forwarding (S2L)</td></tr>
<tr class="odd">
<td class="flag_name">dse</td><td class="flag_level">&nbsp;</td><td class="flag_level">&nbsp;</td><td class="flag_level">&bull;</td><td class="flag_desc">Dead-Store Elimination</td></tr>
<tr class="even">
<td class="flag_name">fuse</td><td class="flag_level">&nbsp;</td><td class="flag_level">&nbsp;</td><td class="flag_level">&bull;</td><td class="flag_desc">Fusion of operands into instructions</td></tr>
</table>
<p>
Here are the parameters and their default settings:
</p>
<table class="opt">
<tr class="opthead">
<td class="param_name">Parameter</td>
<td class="param_default">Default</td>
<td class="param_desc">&nbsp;</td>
</tr>
<tr class="odd separate">
<td class="param_name">maxtrace</td><td class="param_default">1000</td><td class="param_desc">Max. number of traces in the cache</td></tr>
<tr class="even">
<td class="param_name">maxrecord</td><td class="param_default">2000</td><td class="param_desc">Max. number of recorded IR instructions</td></tr>
<tr class="odd">
<td class="param_name">maxirconst</td><td class="param_default">500</td><td class="param_desc">Max. number of IR constants of a trace</td></tr>
<tr class="even">
<td class="param_name">maxside</td><td class="param_default">100</td><td class="param_desc">Max. number of side traces of a root trace</td></tr>
<tr class="odd">
<td class="param_name">maxsnap</td><td class="param_default">100</td><td class="param_desc">Max. number of snapshots for a trace</td></tr>
<tr class="even separate">
<td class="param_name">hotloop</td><td class="param_default">56</td><td class="param_desc">Number of iterations to detect a hot loop or hot call</td></tr>
<tr class="odd">
<td class="param_name">hotexit</td><td class="param_default">10</td><td class="param_desc">Number of taken exits to start a side trace</td></tr>
<tr class="even">
<td class="param_name">tryside</td><td class="param_default">4</td><td class="param_desc">Number of attempts to compile a side trace</td></tr>
<tr class="odd separate">
<td class="param_name">instunroll</td><td class="param_default">4</td><td class="param_desc">Max. unroll factor for instable loops</td></tr>
<tr class="even">
<td class="param_name">loopunroll</td><td class="param_default">7</td><td class="param_desc">Max. unroll factor for loop ops in side traces</td></tr>
<tr class="odd">
<td class="param_name">callunroll</td><td class="param_default">3</td><td class="param_desc">Max. unroll factor for pseudo-recursive calls</td></tr>
<tr class="even">
<td class="param_name">recunroll</td><td class="param_default">2</td><td class="param_desc">Min. unroll factor for true recursion</td></tr>
<tr class="odd separate">
<td class="param_name">sizemcode</td><td class="param_default">32</td><td class="param_desc">Size of each machine code area in KBytes (Windows: 64K)</td></tr>
<tr class="even">
<td class="param_name">maxmcode</td><td class="param_default">512</td><td class="param_desc">Max. total size of all machine code areas in KBytes</td></tr>
</table>
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