c# - Is it possible to write a JIT compiler (to native code) entirely in a managed .NET language

Question

I'm toying with the idea of writing a JIT compiler and am just wondering if it is even theoretically possible to write the whole thing in managed code. In particular, once you've generated assembler into a byte array how do you jump into it to begin execution?

Answer 1

Yes, you can. In fact, it's my job :)

I've written GPU.NET entirely in F# (modulo our unit tests) -- it actually disassembles and JITs IL at run-time, just like the .NET CLR does. We emit native code for whatever underlying acceleration device you want to use; currently we only support Nvidia GPU's, but I've designed our system to be retargetable with a minimum of work so it's likely we'll support other platforms in the future.

As for performance, I have F# to thank -- when compiled in optimized mode (with tailcalls), our JIT compiler itself is probably about as fast as the compiler within the CLR (which is written in C++, IIRC).

For execution, we have the benefit of being able to pass control to hardware drivers to run the jitted code; however, this wouldn't be any harder to do on the CPU since .NET supports function pointers to unmanaged/native code (though you'd lose any safety/security normally provided by .NET).