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LuaJIT

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LuaJIT
Original author(s)Mike Pall
Stable release
v2.1.ROLLING[1] / August 21, 2023; 14 months ago (2023-08-21)
Repositorygithub.com/LuaJIT/LuaJIT
Written inC, Lua
Operating systemUnix-like, MacOS, Windows, iOS, Android, PlayStation
Platformx86, X86-64, PowerPC, ARM, MIPS[2]
TypeJust-in-time compiler
LicenseMIT License[3]
Websiteluajit.org

LuaJIT is a tracing just-in-time compiler for the Lua programming language. Mike Pall, a primary maintainer of the project had resigned in 2015, resorting only to occasional patching to the future 2.1 version.[4]

History

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The LuaJIT project was started in 2005 by developer Mike Pall, released under the MIT open source license.[5]

The second major release of the compiler, 2.0.0, featured major performance increases.[6]

LuaJIT uses rolling releases. Mike Pall, the creator and maintainer recommends using the tip of the v2.1 branch, and does not believe in releases.[7]

Notable users

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  • CERN, for their Methodical Accelerator Design 'next-generation' software for describing and simulating particle accelerators[8]
  • OpenResty, a fork of nginx with Lua scripting[9]
  • Neovim, a text editor based on vim that allows the use of Lua for plugins and configuration[10]
  • Kong, a web API gateway[11]
  • Cloudflare, who use LuaJIT in their web application firewall service[12]

Performance

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LuaJIT is often the fastest Lua runtime.[13] LuaJIT has also been named the fastest implementation of a dynamic programming language.[14][15]

LuaJIT includes a Foreign Function Interface compatible with C data structures. Its use is encouraged for numerical computation.[16]

Tracing

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LuaJIT is a tracing just-in-time compiler. LuaJIT chooses loops and function calls as trace anchors to begin recording possible hot 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's static single-assignment intermediate representation. LuaJIT's trace compiler is often capable of inlining and removing dispatches from object orientation, operators, and type modifications.[17]

Internal representation

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LuaJIT uses two types of internal representation. A stack-based bytecode is used for the interpreter, and a static single-assignment form 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.[15]

-- Loop with if-statement

local x = 0

for i=1,1e4 do
    x = x + 11
    if i%10 == 0 then -- 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

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LuaJIT adds several extensions to its base implementation, Lua 5.1, most of which do not break compatibility.[18]

  • "BitOp" for binary operations on unsigned 32-bit integers (these operations are also compiled by the just-in-time compiler)[19]
  • "CoCo", which allows the VM to be fully resumable across all contexts[20]
  • A foreign function interface[21]
  • Portable bytecode (regardless of architecture, word size, or endianness, not version)[22]

DynASM

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DynASM
Developer(s)Mike Pall
Repository
Written inLua, C[23]
Platformx86, X86-64, PowerPC, ARM, MIPS
TypePreprocessor, Linker
LicenseMIT License[3]
Websiteluajit.org/dynasm.html

DynASM is a lightweight preprocessor for C that provides its own flavor of inline 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.[citation needed]

DynASM includes a bare-bones C header file which is used at compile time for logic the preprocessor generates. The actual preprocessor is written in Lua.

References

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  1. ^ LuaJIT tags
  2. ^ "LuaJIT". LuaJIT. Retrieved 25 February 2022.
  3. ^ a b "LuaJIT/COPYRIGHT at v2.1 · LuaJIT/LuaJIT". GitHub. 7 January 2022.
  4. ^ "[ANN] Looking for new LuaJIT maintainers - luajit - FreeLists". www.freelists.org. Retrieved 2023-03-29.
  5. ^ "The LuaJIT Project". luajit.org. Retrieved 2023-06-17.
  6. ^ Pall, Mike. "Re: [ANN] llvm-lua 1.0". lua-users.org. Retrieved 25 February 2022.
  7. ^ "Project status - Issue #665 - LuaJIT/LuaJIT". GitHub. Retrieved 3 February 2023.
  8. ^ Deniau, Laurent. "Lua(Jit) for computing accelerator beam physics". CERN Document Server. CERN. Retrieved 25 February 2022.
  9. ^ "OpenResty® - Official Site". openresty.org.
  10. ^ "Lua - Neovim docs". neovim.io. Retrieved 2024-05-07.
  11. ^ "Kong/kong". GitHub. Kong. 25 February 2022. Retrieved 25 February 2022.
  12. ^ "Helping to make Luajit faster". blog.cloudflare.com. 19 October 2017. Retrieved 25 February 2022.
  13. ^ "LuaJIT Performance".
  14. ^ "Laurence Tratt: The Impact of Meta-Tracing on VM Design and Implementation". tratt.net. Retrieved 2 March 2022.
  15. ^ a b d'Andrea, Laurent (2019). Behavioural Analysis of Tracing JIT Compiler Embedded in the Methodical Accelerator Design Software (Thesis). CERN. Retrieved 31 July 2022.
  16. ^ Pall, Mike. "Tuning numerical computations for LuaJIT (was Re: [ANN] Sci-1.0-beta1) - luajit - FreeLists". www.freelists.org.
  17. ^ Rottenkolber, Max. "Later Binding: Just-in-Time Compilation of a Younger Dynamic Programming Language." ELS. 2020
  18. ^ "Extensions". LuaJIT. Retrieved 25 February 2022.
  19. ^ "BitOp Semantics". LuaJIT. Retrieved 25 February 2022.
  20. ^ "Coco - True C Coroutines". LuaJIT. Retrieved 25 February 2022.
  21. ^ "FFI Library". LuaJIT. Retrieved 25 February 2022.
  22. ^ "Extensions". luajit.org. Retrieved 2022-08-25.
  23. ^ "DynASM Features". DynASM. Retrieved 25 February 2022.