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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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3<head>
4<title>jit.* Library</title>
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6<meta name="Author" content="Mike Pall">
7<meta name="Copyright" content="Copyright (C) 2005-2011, Mike Pall">
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13<div id="site">
14<a href="http://luajit.org"><span>Lua<span id="logo">JIT</span></span></a>
15</div>
16<div id="head">
17<h1><tt>jit.*</tt> Library</h1>
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57<p>
58The functions in this built-in module control the behavior of the JIT
59compiler engine. Note that JIT-compilation is fully automatic &mdash;
60you probably won't need to use any of the following functions unless
61you have special needs.
62</p>
63
64<h3 id="jit_onoff"><tt>jit.on()<br>
65jit.off()</tt></h3>
66<p>
67Turns the whole JIT compiler on (default) or off.
68</p>
69<p>
70These functions are typically used with the command line options
71<tt>-j on</tt> or <tt>-j off</tt>.
72</p>
73
74<h3 id="jit_flush"><tt>jit.flush()</tt></h3>
75<p>
76Flushes the whole cache of compiled code.
77</p>
78
79<h3 id="jit_onoff_func"><tt>jit.on(func|true [,true|false])<br>
80jit.off(func|true [,true|false])<br>
81jit.flush(func|true [,true|false])</tt></h3>
82<p>
83<tt>jit.on</tt> enables JIT compilation for a Lua function (this is
84the default).
85</p>
86<p>
87<tt>jit.off</tt> disables JIT compilation for a Lua function and
88flushes any already compiled code from the code cache.
89</p>
90<p>
91<tt>jit.flush</tt> flushes the code, but doesn't affect the
92enable/disable status.
93</p>
94<p>
95The current function, i.e. the Lua function calling this library
96function, can also be specified by passing <tt>true</tt> as the first
97argument.
98</p>
99<p>
100If the second argument is <tt>true</tt>, JIT compilation is also
101enabled, disabled or flushed recursively for all sub-functions of a
102function. With <tt>false</tt> only the sub-functions are affected.
103</p>
104<p>
105The <tt>jit.on</tt> and <tt>jit.off</tt> functions only set a flag
106which is checked when the function is about to be compiled. They do
107not trigger immediate compilation.
108</p>
109<p>
110Typical usage is <tt>jit.off(true, true)</tt> in the main chunk
111of a module to turn off JIT compilation for the whole module for
112debugging purposes.
113</p>
114
115<h3 id="jit_flush_tr"><tt>jit.flush(tr)</tt></h3>
116<p>
117Flushes the root trace, specified by its number, and all of its side
118traces from the cache. The code for the trace will be retained as long
119as there are any other traces which link to it.
120</p>
121
122<h3 id="jit_status"><tt>status, ... = jit.status()</tt></h3>
123<p>
124Returns the current status of the JIT compiler. The first result is
125either <tt>true</tt> or <tt>false</tt> if the JIT compiler is turned
126on or off. The remaining results are strings for CPU-specific features
127and enabled optimizations.
128</p>
129
130<h3 id="jit_version"><tt>jit.version</tt></h3>
131<p>
132Contains the LuaJIT version string.
133</p>
134
135<h3 id="jit_version_num"><tt>jit.version_num</tt></h3>
136<p>
137Contains the version number of the LuaJIT core. Version xx.yy.zz
138is represented by the decimal number xxyyzz.
139</p>
140
141<h3 id="jit_os"><tt>jit.os</tt></h3>
142<p>
143Contains the target OS name:
144"Windows", "Linux", "OSX", "BSD", "POSIX" or "Other".
145</p>
146
147<h3 id="jit_arch"><tt>jit.arch</tt></h3>
148<p>
149Contains the target architecture name:
150"x86", "x64" or "ppcspe".
151</p>
152
153<h2 id="jit_opt"><tt>jit.opt.*</tt> &mdash; JIT compiler optimization control</h2>
154<p>
155This sub-module provides the backend for the <tt>-O</tt> command line
156option.
157</p>
158<p>
159You can also use it programmatically, e.g.:
160</p>
161<pre class="code">
162jit.opt.start(2) -- same as -O2
163jit.opt.start("-dce")
164jit.opt.start("hotloop=10", "hotexit=2")
165</pre>
166<p>
167Unlike in LuaJIT 1.x, the module is built-in and
168<b>optimization is turned on by default!</b>
169It's no longer necessary to run <tt>require("jit.opt").start()</tt>,
170which was one of the ways to enable optimization.
171</p>
172
173<h2 id="jit_util"><tt>jit.util.*</tt> &mdash; JIT compiler introspection</h2>
174<p>
175This sub-module holds functions to introspect the bytecode, generated
176traces, the IR and the generated machine code. The functionality
177provided by this module is still in flux and therefore undocumented.
178</p>
179<p>
180The debug modules <tt>-jbc</tt>, <tt>-jv</tt> and <tt>-jdump</tt> make
181extensive use of these functions. Please check out their source code,
182if you want to know more.
183</p>
184<br class="flush">
185</div>
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188Copyright &copy; 2005-2011 Mike Pall
189<span class="noprint">
190&middot;
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