c
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LuaJIT
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<a href="http://luajit.org"><span>Lua<span id="logo">JIT</span></span></a>
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<h1>API Extensions</h1>
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<p>
LuaJIT is fully upwards-compatible with Lua 5.1. It supports all
<a href="http://www.lua.org/manual/5.1/manual.html#5"><span class="ext">&raquo;</span>&nbsp;standard Lua
library functions</a> and the full set of
<a href="http://www.lua.org/manual/5.1/manual.html#3"><span class="ext">&raquo;</span>&nbsp;Lua/C API
functions</a>.
</p>
<p>
LuaJIT is also fully ABI-compatible to Lua 5.1 at the linker/dynamic
loader level. This means you can compile a C&nbsp;module against the
standard Lua headers and load the same shared library from either Lua
or LuaJIT.
</p>

<h2 id="bit"><tt>bit.*</tt> &mdash; Bitwise Operations</h2>
<p>
LuaJIT supports all bitwise operations as defined by
<a href="http://bitop.luajit.org"><span class="ext">&raquo;</span>&nbsp;Lua BitOp</a>:
</p>
<pre class="code">
bit.tobit  bit.tohex  bit.bnot    bit.band bit.bor  bit.bxor
bit.lshift bit.rshift bit.arshift bit.rol  bit.ror  bit.bswap
</pre>
<p>
This module is a LuaJIT built-in &mdash; you don't need to download or
install Lua BitOp. The Lua BitOp site has full documentation for all
<a href="http://bitop.luajit.org/api.html"><span class="ext">&raquo;</span>&nbsp;Lua BitOp API functions</a>.
</p>
<p>
Please make sure to <tt>require</tt> the module before using any of
its functions:
</p>
<pre class="code">
local bit = require("bit")
</pre>
<p>
An already installed Lua BitOp module is ignored by LuaJIT.
This way you can use bit operations from both Lua and LuaJIT on a
shared installation.
</p>

<h2 id="jit"><tt>jit.*</tt> &mdash; JIT compiler control</h2>
<p>
The functions in this built-in module control the behavior
of the JIT compiler engine.
</p>

<h3 id="jit_onoff"><tt>jit.on()<br>
jit.off()</tt></h3>
<p>
Turns the whole JIT compiler on (default) or off.
</p>
<p>
These functions are typically used with the command line options
<tt>-j on</tt> or <tt>-j off</tt>.
</p>

<h3 id="jit_flush"><tt>jit.flush()</tt></h3>
<p>
Flushes the whole cache of compiled code.
</p>

<h3 id="jit_flush_tr"><tt>jit.flush(tr)</tt></h3>
<p>
Flushes the code for the specified root trace and all of its
side traces from the cache.
</p>

<h3 id="jit_onoff_func"><tt>jit.on(func|true [,true|false])<br>
jit.off(func|true [,true|false])<br>
jit.flush(func|true [,true|false])</tt></h3>
<p>
<tt>jit.on</tt> enables JIT compilation for a Lua function (this is
the default).
</p>
<p>
<tt>jit.off</tt> disables JIT compilation for a Lua function and
flushes any already compiled code from the code cache.
</p>
<p>
<tt>jit.flush</tt> flushes the code, but doesn't affect the
enable/disable status.
</p>
<p>
The current function, i.e. the Lua function calling this library
function, can also be specified by passing <tt>true</tt> as the first
argument.
</p>
<p>
If the second argument is <tt>true</tt>, JIT compilation is also
enabled, disabled or flushed recursively for all subfunctions of a
function. With <tt>false</tt> only the subfunctions are affected.
</p>
<p>
The <tt>jit.on</tt> and <tt>jit.off</tt> functions only set a flag
which is checked when the function is about to be compiled. They do
not trigger immediate compilation.
</p>
<p>
Typical usage is <tt>jit.off(true, true)</tt> in the main chunk
of a module to turn off JIT compilation for the whole module for
debugging purposes.
</p>

<h3 id="jit_version"><tt>jit.version</tt></h3>
<p>
Contains the LuaJIT version string.
</p>

<h3 id="jit_version_num"><tt>jit.version_num</tt></h3>
<p>
Contains the version number of the LuaJIT core. Version xx.yy.zz
is represented by the decimal number xxyyzz.
</p>

<h3 id="jit_arch"><tt>jit.arch</tt></h3>
<p>
Contains the target architecture name (CPU and optional ABI).
</p>

<h2 id="jit_opt"><tt>jit.opt.*</tt> &mdash; JIT compiler optimization control</h2>
<p>
This module provides the backend for the <tt>-O</tt> command line
option.
</p>
<p>
You can also use it programmatically, e.g.:
</p>
<pre class="code">
jit.opt.start(2) -- same as -O2
jit.opt.start("-dce")
jit.opt.start("hotloop=10", "hotexit=2")
</pre>
<p>
Unlike in LuaJIT 1.x, the module is built-in and
<b>optimization is turned on by default!</b>
It's no longer necessary to run <tt>require("jit.opt").start()</tt>,
which was one of the ways to enable optimization.
</p>

<h2 id="jit_util"><tt>jit.util.*</tt> &mdash; JIT compiler introspection</h2>
<p>
This module holds functions to introspect the bytecode, generated
traces, the IR and the generated machine code. The functionality
provided by this module is still in flux and therefore undocumented.
</p>
<p>
The debug modules <tt>-jbc</tt>, <tt>-jv</tt> and <tt>-jdump</tt> make
extensive use of these functions. Please check out their source code,
if you want to know more.
</p>
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Copyright &copy; 2005-2009 Mike Pall
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