Benedikt Meurer JavaScript Engine Hacker and Programming Language Enthusiast.

OCamlJIT 2.0

OCamlJit 2.0 is a new Just-In-Time engine for Objective Caml 3.12.0 on desktop processors (x86/x86-64). It translates the OCaml byte-code used by the interpreter (ocamlrun and ocaml) to x86/x86-64 native code on-demand and runs the generated native code instead of interpreting the byte-code. It is designed to run with minimal compilation overhead (translating only what is being executed, avoiding costly code generation and optimization techniques), while being 100% compatible with the byte-code runtime (including serialization and hashing of closures, etc.).

OCamlJit 2.0 was specifically designed for desktop processors and is not really portable to anything else in its current shape, because the target audience are people using the interactive top-level and the byte-code interpreter for rapid prototyping/development (which is unlikely to happen on anything else but x86/x86-64). The implementation currently requires a system that adheres to the SysV ABI, which includes Linux, BSD, OS X, but excludes Win32/Win64 (patches/ideas are welcome). It was tested on Linux/x86 (Debian), Linux/amd64 (CentOS) and Mac OS X 10.6 (64bit). The x86 implementation requires SSE2 capable processors (otherwise it falls back to the byte-code interpreter), so it won't speedup your OCaml programs running on 486 CPUs. :-)

OCamlJit 2.0 runs most benchmarks at 2-6 times faster than the byte-code interpreter. The interactive top-level benefits twice when used with the JIT engine:

  1. the compiler stages are JIT compiled and
  2. the generated byte-code is JIT compiled.

A tech report describing a slightly earlier prototype and including performance measures of OCamlJit 2.0 on Mac OS X (64bit) is available at:

The source code is available from the Git repository (master branch) at:

Installation is similar to installation of Objective Caml, just run

./configure -prefix /path/to/ocamljit2 [options]

followed by

make world opt
make install

This will install a fully working Objective Caml 3.12.0 to /path/to/ocamljit2, where /path/to/ocamljit2/bin/ocamlrun and /path/to/ocamljit2/lib/ include the JIT engine in addition to the byte-code interpreter (fallback to the byte-code interpreter is necessary for debugging with ocamldebug). The configure script prints a line indicating whether the JIT engine is enabled or not (if not, it'll be just a regular OCaml 3.12 installation).


See the discussion on the Caml mailing list, and the more recent work on OCamlJIT2.