[LLVMdev] MCJIT or ORC JIT for new project?

[Lang Hames]

Hi Kevin,

My recommendation for people starting new projects is to use ORC rather
than MCJIT where possible, as ORC has a strict superset of MCJIT's
functionality. There are no guarantees on ORC API stability however, so if
that's truly critical then MCJIT's C API would be a better fit for you.

If you're living on ToT (which we also generally recommend), then the
minimal day-to-day churn on Orc should be manageable. If you're planning to
live on stable releases you'll have the usual (and difficult-to-predict)
inter-release headaches.

Either way, let me know how your choice works out for you: I'm keen to keep
improving LLVM's JIT support.

Cheers,
Lang.


On Wed, Jul 1, 2015 at 10:50 PM, Kevin Atkinson <k at kevina.org> wrote:

>
> Hi,
>
> For a new language I am developing (in the very early stages, nothing
> public posted yet) I would like to able to use a JIT for several purposes:
>
> 1) Create a functional REPL as is done is done with in the Kaleidoscope
> tutorial.
>
> 2) Be able to interpret my language in addition to compiling.
>
> 3) While compiling, be able to execute arbitrary code at compile time.
> The simple case will be to get a value, similar to C++ constexpr but
> without any restrictions.  The complicated case will be to support a full
> macro system similar to syntax-rules in Racket or defmacro in Lisp.
>
> For (1) I would require being able to execute a function at a time. I
> would also like to be able to discard temporary functions used just to get
> a value.
>
> For (2) and (3) lazy compilation is required, catching the results would
> also be great.
>
> For right now I plan to use a direct AST based interpreter, but I would
> also like have JIT available when it is needed.
>
> It looks like the new ORC JIT will be better suited for my needs.  Would
> it be better to use the devel version of LLVM and the new JIT?  Or is the
> new ORC JIT too much of a moving target and would it be better to stick
> with MCJIT?
>
> If it is best to stick with MCJIT can someone point me to a working
> Kaleidoscope that will work with MCJIT and the latest released version of
> LLVM.  There are several versions floating around and I am confused on what
> version to use.  The examples in Kaleidoscope/MCJIT/lazy don't compile with
> 3.6.1 and I was hoping there was a version that would compile.
>
> Let me know if anything is unclear.
>
> Thanks in Advance,
> Kevin
>
>
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