LuaJIT

Notable users

• CERN, for their Methodical Accelerator Design 'next-generation' software for describing and simulating particle accelerators
• OpenResty, a fork of nginx with 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 their web application firewall service

Performance

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

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

Tracing

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.

Internal representation

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.

<span id="mwfA"></span><span class="c1" id="mwfQ">-- Loop with if-statement</span> <span class="kd" id="mwfg">local</span><span class="w" id="mwfw"> </span><span class="nv" id="mwgA">x</span><span class="w" id="mwgQ"> </span><span class="o" id="mwgg">=</span><span class="w" id="mwgw"> </span><span class="mi" id="mwhA">0</span> <span class="kr" id="mwhQ">for</span><span class="w" id="mwhg"> </span><span class="nv" id="mwhw">i</span><span class="o" id="mwiA">=</span><span class="mi" id="mwiQ">1</span><span class="p" id="mwig">,</span><span class="mf" id="mwiw">1e4</span><span class="w" id="mwjA"> </span><span class="kr" id="mwjQ">do</span> <span class="w" id="mwjg"> </span><span class="nv" id="mwjw">x</span><span class="w" id="mwkA"> </span><span class="o" id="mwkQ">=</span><span class="w" id="mwkg"> </span><span class="nv" id="mwkw">x</span><span class="w" id="mwlA"> </span><span class="o" id="mwlQ">+</span><span class="w" id="mwlg"> </span><span class="mi" id="mwlw">11</span> <span class="w" id="mwmA"> </span><span class="kr" id="mwmQ">if</span><span class="w" id="mwmg"> </span><span class="nv" id="mwmw">i</span><span class="o" id="mwnA">%</span><span class="mi" id="mwnQ">10</span><span class="w" id="mwng"> </span><span class="o" id="mwnw">==</span><span class="w" id="mwoA"> </span><span class="mi" id="mwoQ">0</span><span class="w" id="mwog"> </span><span class="kr" id="mwow">then</span><span class="w" id="mwpA"> </span><span class="c1" id="mwpQ">-- if-statement</span> <span class="w" id="mwpg"> </span><span class="nv" id="mwpw">x</span><span class="w" id="mwqA"> </span><span class="o" id="mwqQ">=</span><span class="w" id="mwqg"> </span><span class="nv" id="mwqw">x</span><span class="w" id="mwrA"> </span><span class="o" id="mwrQ">+</span><span class="w" id="mwrg"> </span><span class="mi" id="mwrw">22</span> <span class="w" id="mwsA"> </span><span class="kr" id="mwsQ">end</span> <span class="w" id="mwsg"> </span><span class="nv" id="mwsw">x</span><span class="w" id="mwtA"> </span><span class="o" id="mwtQ">=</span><span class="w" id="mwtg"> </span><span class="nv" id="mwtw">x</span><span class="w" id="mwuA"> </span><span class="o" id="mwuQ">+</span><span class="w" id="mwug"> </span><span class="mi" id="mwuw">33</span> <span class="kr" id="mwvA">end</span>

<span id="mwvw"></span><span class="go" id="mwwA">---- TRACE 1 start Ex.lua:5</span> <span class="go" id="mwwQ">---- TRACE 1 IR</span> <span class="go" id="mwwg">0001 int SLOAD #2 CI</span> <span class="go" id="mwww">0002 > num SLOAD #1 T</span> <span class="go" id="mwxA">0003 num ADD 0002 +11</span> <span class="go" id="mwxQ">0004 int MOD 0001 +10</span> <span class="go" id="mwxg">0005 > int NE 0004 +0</span> <span class="go" id="mwxw">0006 + num ADD 0003 +33</span> <span class="go" id="mwyA">0007 + int ADD 0001 +1</span> <span class="go" id="mwyQ">0008 > int LE 0007 +10000</span> <span class="go" id="mwyg">0009 ------ LOOP ------------</span> <span class="go" id="mwyw">0010 num ADD 0006 +11</span> <span class="go" id="mwzA">0011 int MOD 0007 +10</span> <span class="go" id="mwzQ">0012 > int NE 0011 +0</span> <span class="go" id="mwzg">0013 + num ADD 0010 +33</span> <span class="go" id="mwzw">0014 + int ADD 0007 +1</span> <span class="go" id="mw0A">0015 > int LE 0014 +10000</span> <span class="go" id="mw0Q">0016 int PHI 0007 0014</span> <span class="go" id="mw0g">0017 num PHI 0006 0013</span> <span class="go" id="mw0w">---- TRACE 1 stop -> loop</span> <span class="go" id="mw1A">---- TRACE 2 start 1/4 Ex.lua:8</span> <span class="go" id="mw1Q">---- TRACE 2 IR</span> <span class="go" id="mw1g">0001 num SLOAD #1 PI</span> <span class="go" id="mw1w">0002 int SLOAD #2 PI</span> <span class="go" id="mw2A">0003 num ADD 0001 +22</span> <span class="go" id="mw2Q">0004 num ADD 0003 +33</span> <span class="go" id="mw2g">0005 int ADD 0002 +1</span> <span class="go" id="mw2w">0006 > int LE 0005 +10000</span> <span class="go" id="mw3A">0007 num CONV 0005 num.int</span> <span class="go" id="mw3Q">---- TRACE 2 stop -> 1</span>

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
• A foreign function interface
• Portable bytecode (regardless of architecture, word size, or endianness, not version)