[LLVMdev] Selectively Jitting using MCJIT

[Jonatan Waern]

> Then a simple dlopen (with RTLD_LAZY) /dlsym/dlclose is not sufficient?
That actually seems to be an easier way to do it. I had no idea this  
existed. I'll try it out and see how it goes.

Thanks a lot!

Quoting Willy WOLFF <willy.wolff at etu.unistra.fr>:

>
> On 24 May 2014, at 00:46, Jonatan Waern wrote:
>
>>> As far as I know, ObjectFile is either COFF, ELF or MachO format,  
>>> statically compiled. But the pass manager for applying  
>>> optimisation passes works only on llvm-ir.
>> I would not need to apply optimisations on the parts of the program  
>> in the object file. These are meant to be optimised beforehand. The  
>> only parts I want to run passes on are specific function that I  
>> know beforehand.
>>
>
> Then a simple dlopen (with RTLD_LAZY) /dlsym/dlclose is not sufficient?
>
>>> What you can do is to isolate the function you want to jit by  
>>> extracting it to a new module. Load this module during runtime,  
>>> apply your pass and jitting it.
>> Yes this is exactly what I want to do. The interesting part is to  
>> load it during runtime. It is not sufficient for me to load it  
>> during JIT initialisation, but rather I want to load and JIT it  
>> during program execution. Hence my idea of declaring the function  
>> in the module as extern and load it through the lazy function  
>> creator.
>>
>> Quoting Willy WOLFF <willy.wolff at etu.unistra.fr>:
>>
>>>
>>> On 23 May 2014, at 14:55, Jonatan Waern wrote:
>>>
>>>> Hello, I am a novice at using the llvm api to do much of anything.
>>>>
>>>> I am trying to lazily apply certain optimisation passes on select  
>>>> functions when jitting a large program. It is undesirable to me  
>>>> to load the entire program as IR code and then generate code in  
>>>> memory for it (time concerns). It seems that there is a function  
>>>> in MCJIT "loadObjectFile" that would suit my purposes, allowing  
>>>> me to statically compile the program and then load it into the jit.
>>>>
>>>
>>> As far as I know, ObjectFile is either COFF, ELF or MachO format,  
>>> statically compiled. But the pass manager for applying  
>>> optimisation passes works only on llvm-ir.
>>>
>>>> My question is then what would be a good way to callback into the  
>>>> jit for applying the optimisation passes before calling one of  
>>>> the function? My current idea is to make the function extern in  
>>>> the llvm IR prior to static compile, and then use  
>>>> "installLazyFunctionCreator" to generate this function by loading  
>>>> ircode from an isolated module. Is this a feasible approach?
>>>>
>>>
>>> What you can do is to isolate the function you want to jit by  
>>> extracting it to a new module. Load this module during runtime,  
>>> apply your pass and jitting it.
>>> --
>>> Willy WOLFF
>
> --
> Willy WOLFF