[LLVMdev] MCJIT and Lazy Function Creators

[Kaylor, Andrew]

Yes, I agree that it's better to have it done correctly in the library.

-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Óscar Fuentes
Sent: Tuesday, November 27, 2012 11:45 AM
To: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] MCJIT and Lazy Function Creators

"Kaylor, Andrew" <andrew.kaylor at intel.com> writes:

> I guess we'll have to add that to the list of things that needs to be 
> done to replace the old JIT.
>
> In the projects I've worked on that use MCJIT, we've been using 
> getPointerToFunction and then calling it from outside the MCJIT 
> engine, but I suppose that the generic handling in runFunction would 
> be useful in some cases.

FWIW, in my language `main' and other externally-callable function does not have a fixed signature: it can take and return any type(s) from a set of well-known types. Most test cases here are failing because, for returning a string, `main' is called with a pointer parameter of type
[i8 x 8]* pointing to the space reserved for the returned value. Even that simple case is not supported by MCJIT::runFunction. Looking at how JIT::runFunction implements the generic case I can see why MCJIT can't do the same: JIT::runFunction creates and calls a stub function on the fly, which is then used for calling the real function. This is not doable with MCJIT, at least not easily.

I could do what you describe: get the pointer to the function and implement all the handling for my language's supported types and a reasonably large number of parameters. That sort of exercise on combinatorics could work for me, but others would be forced to replicate the work for they own projects and that's precisely what a library should avoid. And, possibly, on some cases a user might need a truly generic method: think on a paremeter or return value with user-defined type (`user' here means the guy who wrote the code being compiled, not the compiler's writer.)

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