LuaJIT

LuaJIT

The logo featured on the LuaJIT website.
Original author(s)	Mike Pall
Stable release	2.0.5 (later v2.1.ROLLING is also updated, e.g. in 2023) / May 1, 2017(2017-05-01)
Repository	github/LuaJIT/LuaJIT
Written in	C,Lua
Operating system	Unix-like,MacOS,Windows,iOS,Android,PlayStation
Platform	x86,X86-64,PowerPC,ARM,MIPS
Type	Just-in-time compiler
License	MIT License
Website	luajit.org

LuaJITis atracing just-in-time compilerfor theLuaprogramming language. Mike Pall, a primary maintainer of the project had resigned in 2015, resorting only to occasional patching to the future 2.1 version.

History

The LuaJIT project was started in 2005 by developer Mike Pall, released under the MIT open source license.

The second major release of the compiler, 2.0.0, featured major performance increases.

The latest release, 2.0.5 is released in 2017. However, Mike Pall, the creator and maintainer recommends using the tip of the v2.1 branch, and does not believe in releases.

Notable users

• CERN,for their Methodical Accelerator Design 'next-generation' software for describing and simulating particle accelerators
• OpenResty,a fork ofnginxwith Lua scripting
• Neovim, a text editor based on vim that allows the use of Lua for plugins and configuration
• Kong, a web API gateway
• Cloudflare,who use LuaJIT in theirweb application firewallservice

Performance

LuaJIT is often the fastest Lua runtime.LuaJIT has also been named the fastest implementation of a dynamic programming language.

LuaJIT includes aForeign Function Interfacecompatible withCdata structures. Its use is encouraged for numerical computation.

Tracing

LuaJIT is atracing just-in-time compiler.LuaJIT chooses loops and function calls as trace anchors to begin recording possiblehot paths.Function calls will require twice as many invocations to begin recording as a loop. Once LuaJIT begins recording, all control flow, including jumps and calls, are inlined to form a linear trace. All executed bytecode instructions are stored and incrementally converted into LuaJIT'sstatic single-assignmentintermediate representation.LuaJIT's trace compiler is often capable ofinliningand removingdispatchesfrom object orientation,operators,andtype modifications.

Internal representation

LuaJIT uses two types of internal representation. Astack-based bytecodeis used for theinterpreter,and astatic single-assignmentform is used for the just-in-time compiler. The interpreter bytecode is frequently patched by the JIT compiler, often to begin executing a compiled trace or to mark a segment of bytecode for causing too many trace aborts.

-- Loop with if-statement

localx=0

fori=1,1e4do
x=x+11
ifi%10==0then-- if-statement
x=x+22
end
x=x+33
end

---- TRACE 1 start Ex.lua:5
---- TRACE 1 IR
0001 int SLOAD #2 CI
0002 > num SLOAD #1 T
0003 num ADD 0002 +11
0004 int MOD 0001 +10
0005 > int NE 0004 +0
0006 + num ADD 0003 +33
0007 + int ADD 0001 +1
0008 > int LE 0007 +10000
0009 ------ LOOP ------------
0010 num ADD 0006 +11
0011 int MOD 0007 +10
0012 > int NE 0011 +0
0013 + num ADD 0010 +33
0014 + int ADD 0007 +1
0015 > int LE 0014 +10000
0016 int PHI 0007 0014
0017 num PHI 0006 0013
---- TRACE 1 stop -> loop
---- TRACE 2 start 1/4 Ex.lua:8
---- TRACE 2 IR
0001 num SLOAD #1 PI
0002 int SLOAD #2 PI
0003 num ADD 0001 +22
0004 num ADD 0003 +33
0005 int ADD 0002 +1
0006 > int LE 0005 +10000
0007 num CONV 0005 num.int
---- TRACE 2 stop -> 1

Extensions

LuaJIT adds several extensions to its base implementation, Lua 5.1, most of which do not break compatibility.

• "BitOp" for binary operations on unsigned 32-bit integers (these operations are also compiled by the just-in-time compiler)
• "CoCo", which allows the VM to be fully resumable across all contexts
• Aforeign function interface
• Portable bytecode (regardless of architecture, word size, or endianness, not version)

DynASM

DynASM

Developer(s)	Mike Pall
Repository	luajit.org/git/luajit-2.0.git
Written in	Lua,C
Platform	x86,X86-64,PowerPC,ARM,MIPS
Type	Preprocessor,Linker
License	MIT License
Website	luajit.org/dynasm.html

DynASM is a lightweightpreprocessorfor C that provides its own flavor ofinline assembler,independent of the C compiler. DynASM replaces assembly code in C files with runtime writes to a 'code buffer', such that a developer may generate and then evoke code at runtime from a C program. It was created for LuaJIT 1.0.0 to make developing the just-in-time compiler easier.

DynASM includes a bare-bones Cheader filewhich is used at compile time for logic the preprocessor generates. The actual preprocessor is written in Lua.