[LLVMdev] Thoughts about ExecutionEngine/MCJIT interface

[Lang Hames]

Hi Pawel,

I agree. ExecutionEngine, in its current form, is unhelpful. I'd be in
favor of cutting the common interface back to something like:

class ExecutionEngine {
public:
  virtual void addModule(std::unique_ptr<Module> M) = 0;
  virtual void* getGlobalValueAddress(const GlobalValue *GV) = 0;
  virtual GenericValue runFunction(const Function *F,
                                   const std::vector<GenericValue> &Args) =
0;
};

That's the obvious common functionality that both the interpreter and MCJIT
provide. Beyond that I think things get pretty implementation specific.

For what it's worth, this is an issue that I'm trying to address with the
new Orc JIT APIs. Those expose the internals directly to give you more
control. If you don't want to be able to switch the underlying
execution-engine, they may be a good fit for your use-case.

Cheers,
Lang.


On Sat, Mar 14, 2015 at 4:57 AM, Paweł Bylica <chfast at gmail.com> wrote:

> Hi,
>
> I think ExecutionEngine as a common interface for both Interpreter and
> MCJIT is almost useless in the current form. There are separated methods in
> ExecutionEngine for similar or the same features provided by Interpreter
> and MCJIT, i.e. to get a pointer to function you should call
> getPointerToFunction() for Interpreter or getFunctionAddress() for MCJIT.
>
> Personally, I'm using MCJIT and wish to have access to some methods not
> available from ExecutionEngine. E.g. I would like to use getSymbolAddress()
> instead of getFunctionAddress() sometimes as getFunctionAddress() do some
> additional work what I'm sure has be done already.
>
> Maybe it's time face the truth that Interpreter and MCJIT based solutions
> are not so similar and different interfaces are needed. Or maybe some
> unification is possible?
>
> My propositions / discussion starting points:
>
>    1. Expose MCJIT header in public API. It will allow users to cast
>    ExecutionEngine instance to MCJIT instance.
>    2. Separate Interpreter and MCJIT interfaces and add them to API.
>    ExecutionEngine can still be a base class for real common part (like module
>    list).
>    3. Try to alter ExecutionEngine interface to unify common Interpreter
>    and MCJIT features. Is it possible to have one getFunction() method?
>
> - Paweł
>
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