[LLVMdev] I want to do something moderately insane, please help!

[Sarah Thompson]

Hi,

As some of you may remember, I'm implementing an LLVM-based model 
checker. I'm doing something a little odd, in that mostly I'm using the 
interpreter (currently a hacked version of lli with threads) for most 
things because I need to hook into lots of stuff that would be difficult 
to manage otherwise, but I'm also using the jitter for some things that 
need to be fast and/or link with external code. I currently expose some 
functions from the code being checked that allow you to slot in your own 
thread management, but I need this to be as fast as possible because it 
gets called a *lot*. I have managed OK with simply exposing a function 
and jitting it, then calling it through the runFunction member of the 
Jitter class, which works fine but seems a little slow. How feasible 
would it be to get at the underlying function pointer directly, seeing 
as the type signature is well-known in advance, then just calling it 
with a normal C-style call to a function pointer, e.g. (*compfn)(a,b).

Yes, this is all a bit nuts, and yes, it's not really how either the 
interpreter or the jitter was meant to be used, but if I can make this 
particular trick work, it will significantly speed up the model checker, 
particularly since I'll be able to use it for a few other things too.

Thanks,
Sarah