ocaml-gccjit is a OCaml library that provides bidings for libgccjit. libgccjit is an embeddable shared library included in GCC 5 for adding compilation to existing programs using GCC as the backend.

For example, consider this C function:

int square (int i)
{
  return i * i;
}

We can construct this function at runtime using libgccjit, as follows:

open Gccjit

let square =
  let ctx = Context.create () in

  (* Create parameter "i" *)
  let param_i = Param.create ctx Type.(get ctx Int) "i" in

  (* Create the function *)
  let fn = Function.create ctx Function.Exported Type.(get ctx Int) "square" [ param_i ] in

  (* Create a basic block within the function *)
  let block = Block.create ~name:"entry" fn in

  (* This basic block is relatively simple *)
  let expr = RValue.binary_op ctx Mult Type.(get ctx Int) (RValue.param param_i) (RValue.param param_i) in
  Block.return block expr;

  (* Having populated the context, compile it *)
  let jit_result = Context.compile ctx in

  (* Look up a specific machine code routine within the gccjit.Result, in this
     case, the function we created above: *)
  Result.code jit_result "square" Ctypes.(int @-> returning int)

We can now call the function by doing simply

(* Now try running the code *)
Printf.printf "square(5) = %d\n%!" (square 5)

Installation

# Soon: opam install gccjit
opam pin add gccjit git://github.com/nojb/ocaml-gccjit

In order for compilation to be successful the library libgccjit needs to be found by the C compiler using the -lgccjit flag. If the libgccjit library in your system is a non-standard location, please set the LIBGCCJIT_DIR environment variable before installing this package, like this:

LIBGCCJIT_DIR=<libgccjit dir> opam pin add gccjit git://github.com/nojb/ocaml-gccjit

Links

• API documentation
• Tutorial
• The C header file
• libgccjit wiki
• Experiments in JIT compilation

Contact

Nicolas Ojeda Bar: n.oje.bar@gmail.com