The Ludicrous JIT Compiler

Ludicrous speed? Sir, we've never gone that fast before.

Ludicrous is a just-in-time compiler for Ruby 1.8 and 1.9. Though still in the experimental stage, its performance is roughly on par with YARV (better in some benchmarks, though that may change as more features are added). It's easy to use:

  class MyClass
    include Ludicrous::Speed
    # (or Ludicrous::JITCompiled)

How it works

When you include the Ludicrous::JITCompiled module, stub methods are installed for all the instance methods in that class. When a stub method is called, the method is compiled and the stub replaced with the compiled method.

To JIT-compile singleton methods, include the JITCompiled module in the singleton class.


To install it, you'll need libjit:

  $ wget
  $ tar xvfz libjit-0.1.2.tar.gz
  $ cd libjit-0.1.2
  $ ./configure
  $ make
  $ sudo make install
(on cygwin you'll need to build a little differently)
  $ CC=gcc CXX=g++ ac_cv_func__setjmp=no ./configure
  $ make
  $ sudo make install

You'll also need ruby-libjit and ruby-internal:

  $ gem install ruby-internal
  $ gem install ruby-libjit

now you can build and install ludicrous:

  $ git clone git://
  $ cd ludicrous
  $ ruby setup.rb config
  $ ruby setup.rb setup
  $ sudo ruby setup.rb install
  $ cd ..

and enjoy Ludicrous Speed:

  class Spaceball1

It's Spaceball 1. They've gone to plaid!


Ludicrous supports many features of Ruby, and passes all of the tests in bfts as well as many of the tests that come with Ruby 1.8.6. However, there are some features that are unsupported, and will prove to be difficult to support. These include, but are not limited to:

Ludicrous will attempt to detect these cases and will throw an exception at compile-time if it encounters any of them. The stub method will then be removed and replaced with the original method.

Ludicrous is also known to prevent thread switching in some cases.

It is impossible to trace functions that have been compiled with Ludicrous.

Method arity is likely to change when a method is compiled with Ludicrous, since arity is calculated differently for methods defined as C function pointers.

Ludicrous currently makes assumptions that certain builtin methods will not be redefined, such as arithmetic operators on Fixnum objects. In the future, Ludicrous will detect redefinition of these methods and fall back on slow method calls if they are redefined (like YARV does now).

Ludicrous does not currently handle bignums.


Ludicrous has been developed and tested on Ubuntu Linux on a Pentium 3 with Ruby 1.8.6. It will likely work on any 32-bit platform where libjit has been ported. It is known to not work on 64-bit architectures.


Ludicrous is licensed under the BSD license.

Older versions of Ludicrous were licensed under the GPL, because of the dependency on libjit. Libjit has been re-licensed to LGPL and the next release of libjit will be under this license.