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LuaJIT

=head1 Running LuaJIT

=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

LuaJIT has only a single stand-alone executable, called C<luajit> on
POSIX systems or C<luajit.exe> 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.

=head2 Command Line Options

The C<luajit> stand-alone executable is just a slightly modified
version of the regular C<lua> stand-alone executable. It supports the
same basic options, too. C<luajit -h> prints a short list of the
available options. Please have a look at the E<rchevron> Lua manual for
details.

LuaJIT has some additional options:

=head2 C<-b[options] input output>

This option saves or lists bytecode. The following additional options
are accepted:

=over

=item * C<-l> E<mdash> Only list bytecode.

=item * C<-s> E<mdash> Strip debug info (this is the default).

=item * C<-g> E<mdash> Keep debug info.

=item * C<-n name> E<mdash> Set module name (default: auto-detect from
input name)

=item * C<-t type> E<mdash> Set output file type (default: auto-detect
from output name).

=item * C<-a arch> E<mdash> Override architecture for object files
(default: native).

=item * C<-o os> E<mdash> Override OS for object files (default:
native).

=item * C<-e chunk> E<mdash> Use chunk string as input.

=item * C<-> (a single minus sign) E<mdash> Use stdin as input and/or
stdout as output.

=back

The output file type is auto-detected from the extension of the output
file name:

=over

=item * C<c> E<mdash> C source file, exported bytecode data.

=item * C<h> E<mdash> C header file, static bytecode data.

=item * C<obj> or C<o> E<mdash> Object file, exported bytecode data
(OS- and architecture-specific).

=item * C<raw> or any other extension E<mdash> Raw bytecode file
(portable).

=back

Notes:

=over

=item * See also string.dump() for information on bytecode portability
and compatibility.

=item * A file in raw bytecode format is auto-detected and can be
loaded like any Lua source file. E.g. directly from the command line or
with C<loadfile()>, C<dofile()> etc.

=item * To statically embed the bytecode of a module in your
application, generate an object file and just link it with your
application.

=item * On most ELF-based systems (e.g. Linux) you need to explicitly
export the global symbols when linking your application, e.g. with:
C<-Wl,-E>

=item * C<require()> tries to load embedded bytecode data from exported
symbols (in C<*.exe> or C<lua51.dll> on Windows) and from shared
libraries in C<package.cpath>.

=back

Typical usage examples:

 luajit -b test.lua test.out                 # Save bytecode to test.out
 luajit -bg test.lua test.out                # Keep debug info
 luajit -be "print('hello world')" test.out  # Save cmdline script
 
 luajit -bl test.lua                         # List to stdout
 luajit -bl test.lua test.txt                # List to test.txt
 luajit -ble "print('hello world')"          # List cmdline script
 
 luajit -b test.lua test.obj                 # Generate object file
 # Link test.obj with your application and load it with require("test")

=head2 C<-j cmd[=arg[,arg...]]>

This option performs a LuaJIT control command or activates one of the
loadable extension modules. The command is first looked up in the
C<jit.*> library. If no matching function is found, a module named
C<jit.E<lt>cmdE<gt>> is loaded and the C<start()> function of the
module is called with the specified arguments (if any). The space
between C<-j> and C<cmd> is optional.

Here are the available LuaJIT control commands:

=over

=item * C<-jon> E<mdash> Turns the JIT compiler on (default).

=item * C<-joff> E<mdash> Turns the JIT compiler off (only use the
interpreter).

=item * C<-jflush> E<mdash> Flushes the whole cache of compiled code.

=item * C<-jv> E<mdash> Shows verbose information about the progress of
the JIT compiler.

=item * C<-jdump> E<mdash> Dumps the code and structures used in
various compiler stages.

=item * C<-jp> E<mdash> Start the integrated profiler.

=back

The C<-jv> and C<-jdump> 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 C<lib>
directory of the source distribution or installed under the C<jit>
directory. By default this is C</usr/local/share/luajit-2.0.5/jit> on
POSIX systems.

=head2 C<-O[level]>

C<-O[+]flag> C<-O-flag>

C<-Oparam=value>

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.

The first form sets an optimization level E<mdash> this enables a
specific mix of optimization flags. C<-O0> turns off all optimizations
and higher numbers enable more optimizations. Omitting the level (i.e.
just C<-O>) sets the default optimization level, which is C<-O3> in the
current version.

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.

You can either use this option multiple times (like C<-Ocse -O-dce
-Ohotloop=10>) or separate several settings with a comma (like
C<-O+cse,-dce,hotloop=10>). 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.

Here are the available flags and at what optimization levels they are
enabled:

Flag

-O1

-O2

-O3

fold

E<bull>

E<bull>

E<bull>

Constant Folding, Simplifications and Reassociation

cse

E<bull>

E<bull>

E<bull>

Common-Subexpression Elimination

dce

E<bull>

E<bull>

E<bull>

Dead-Code Elimination

narrow

E<bull>

E<bull>

Narrowing of numbers to integers

loop

E<bull>

E<bull>

Loop Optimizations (code hoisting)

fwd

E<bull>

Load Forwarding (L2L) and Store Forwarding (S2L)

dse

E<bull>

Dead-Store Elimination

abc

E<bull>

Array Bounds Check Elimination

sink

E<bull>

Allocation/Store Sinking

fuse

E<bull>

Fusion of operands into instructions

Here are the parameters and their default settings:

Parameter

Default

maxtrace

1000

Max. number of traces in the cache

maxrecord

4000

Max. number of recorded IR instructions

maxirconst

500

Max. number of IR constants of a trace

maxside

100

Max. number of side traces of a root trace

maxsnap

500

Max. number of snapshots for a trace

hotloop

56

Number of iterations to detect a hot loop or hot call

hotexit

10

Number of taken exits to start a side trace

tryside

4

Number of attempts to compile a side trace

instunroll

4

Max. unroll factor for instable loops

loopunroll

15

Max. unroll factor for loop ops in side traces

callunroll

3

Max. unroll factor for pseudo-recursive calls

recunroll

2

Min. unroll factor for true recursion

sizemcode

32

Size of each machine code area in KBytes (Windows: 64K)

maxmcode

512

Max. total size of all machine code areas in KBytes

----

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

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