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LuaJIT

=head1 C<jit.*> Library

=over

=item * LuaJIT

=over

=item * Download E<rchevron>

=item * Installation

=item * Running

=back

=item * Extensions

=over

=item * FFI Library

=over

=item * FFI Tutorial

=item * ffi.* API

=item * FFI Semantics

=back

=item * jit.* Library

=item * Lua/C API

=item * Profiler

=back

=item * Status

=over

=item * Changes

=back

=item * FAQ

=item * Performance E<rchevron>

=item * Wiki E<rchevron>

=item * Mailing List E<rchevron>

=back

The functions in this built-in module control the behavior of the JIT
compiler engine. Note that JIT-compilation is fully automatic E<mdash>
you probably won't need to use any of the following functions unless
you have special needs.

=head2 jit.on()

jit.off()

Turns the whole JIT compiler on (default) or off.

These functions are typically used with the command line options C<-j
on> or C<-j off>.

=head2 C<jit.flush()>

Flushes the whole cache of compiled code.

=head2 jit.on(func|true [,true|false])

jit.off(func|true [,true|false])

jit.flush(func|true [,true|false])

C<jit.on> enables JIT compilation for a Lua function (this is the
default).

C<jit.off> disables JIT compilation for a Lua function and flushes any
already compiled code from the code cache.

C<jit.flush> flushes the code, but doesn't affect the enable/disable
status.

The current function, i.e. the Lua function calling this library
function, can also be specified by passing C<true> as the first
argument.

If the second argument is C<true>, JIT compilation is also enabled,
disabled or flushed recursively for all sub-functions of a function.
With C<false> only the sub-functions are affected.

The C<jit.on> and C<jit.off> functions only set a flag which is checked
when the function is about to be compiled. They do not trigger
immediate compilation.

Typical usage is C<jit.off(true, true)> in the main chunk of a module
to turn off JIT compilation for the whole module for debugging
purposes.

=head2 C<jit.flush(tr)>

Flushes the root trace, specified by its number, and all of its side
traces from the cache. The code for the trace will be retained as long
as there are any other traces which link to it.

=head2 C<status, ... = jit.status()>

Returns the current status of the JIT compiler. The first result is
either C<true> or C<false> if the JIT compiler is turned on or off. The
remaining results are strings for CPU-specific features and enabled
optimizations.

=head2 C<jit.version>

Contains the LuaJIT version string.

=head2 C<jit.version_num>

Contains the version number of the LuaJIT core. Version xx.yy.zz is
represented by the decimal number xxyyzz.

=head2 C<jit.os>

Contains the target OS name: "Windows", "Linux", "OSX", "BSD", "POSIX"
or "Other".

=head2 C<jit.arch>

Contains the target architecture name: "x86", "x64", "arm", "arm64",
"ppc", "mips" or "mips64".

=head2 C<jit.opt.*> E<mdash> JIT compiler optimization control

This sub-module provides the backend for the C<-O> command line option.

You can also use it programmatically, e.g.:

 jit.opt.start(2) -- same as -O2
 jit.opt.start("-dce")
 jit.opt.start("hotloop=10", "hotexit=2")

Unlike in LuaJIT 1.x, the module is built-in and B<optimization is
turned on by default!> It's no longer necessary to run
C<require("jit.opt").start()>, which was one of the ways to enable
optimization.

=head2 C<jit.util.*> E<mdash> JIT compiler introspection

This sub-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.

The debug modules C<-jbc>, C<-jv> and C<-jdump> make extensive use of
these functions. Please check out their source code, if you want to
know more.

----

Copyright E<copy> 2005-2017 Mike Pall E<middot> Contact

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