llvm dev - Feb 2015 - [LLVMdev] Some basic questions regarding MCJIT and Kaleidoscope sample

HI Dibyendu,

A single MCJIT instance can notionally manage multiple modules, but there
are caveats (which I'm afraid I don't remember off the top of my head)
that
make it unattractive in practice. I believe most clients opt for something
like the ExecutionEngine-per-Module model used in the Kaleidoscope
tutorials.

As Dave mentioned, I'm also working on some new JIT APIs (Orc) that are
intended to be more feature-rich and easier to use than MCJIT. If you would
like to try them out and have any questions about how they work please
don't hesitate to ask. You'll need to live on the bleeding edge for
those
though - they're not available on 3.5.

Cheers,
Lang.


On Tue, Feb 10, 2015 at 2:14 PM, David Blaikie <dblaikie at gmail.com>
wrote:
> We (and by 'we' I mean 'Lang' (cc'd)) have recently
been experimenting
> with improvements/replacements to the MCJIT in the form of Orc, a new
> layered, composable JIT API. There are examples of this in the Kaleidoscope
> code samples (llvm/examples/Kaleidoscope/Orc) though not comprehensive
> tutorials as yet.
>
> On Tue, Feb 10, 2015 at 1:57 PM, Dibyendu Majumdar <mobile at
majumdar.org.uk
> > wrote:
>
>> Hi,
>>
>> I am building a new JIT compiler for Lua (actually a derivative of
>> Lua), and am planning to use LLVM for this. I have trying out some
>> basic functions using LLVM 3.5.1. I have been puzzled by one aspect of
>> the MCJIT versions of the Kaleidoscope sample, and would hugely
>> appreciate some insight.
>>
>> Can a single MCJIT instance be used to manage several modules?
>> Why is a separate MCJIT instance created for each module?
>>
>> Unfortunately the tutorial text does not explain the rationale for
this.
>>
>> At the moment in my implementation I am putting each compiled function
>> in its own module and creating an engine for it. This is so that each
>> function can be managed independently and linked to garbage collection
>> in Lua. However I do not know if there is a better way - for example
>> creating a shared engine across all modules. I would also like to
>> understand the trade offs with this approach versus other approaches.
>>
>> Many thanks
>>
>> Regards
>> Dibyendu
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
>
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Hi James,

On 10 February 2015 at 22:28, Lang Hames wrote:
>
> A single MCJIT instance can notionally manage multiple modules, but there
> are caveats (which I'm afraid I don't remember off the top of my
head) that
> make it unattractive in practice. I believe most clients opt for something
> like the ExecutionEngine-per-Module model used in the Kaleidoscope
> tutorials.
I see. That's good to know.
> As Dave mentioned, I'm also working on some new JIT APIs (Orc) that are
> intended to be more feature-rich and easier to use than MCJIT. If you would
> like to try them out and have any questions about how they work please
don't
> hesitate to ask. You'll need to live on the bleeding edge for those
though -
> they're not available on 3.5.
>
I am at an early stage of development so I can use Orc provided there
is some assurance that this will be mainstream in future. Else I can
use the MCJIT replacement that uses Orc. If I wanted to do this should
I clone the latest code from github?

In any case I am abstracting the creation and management of engines,
modules etc in my code so that I can change this in future if
necessary.

Thanks and Regards

Dibyendu

Hi Lang,

Sincere apologies for the name typo below!

Regards

On 10 February 2015 at 22:46, Dibyendu Majumdar <mobile at
majumdar.org.uk> wrote:
> Hi James,
>
> On 10 February 2015 at 22:28, Lang Hames wrote:
>>
>> A single MCJIT instance can notionally manage multiple modules, but
there
>> are caveats (which I'm afraid I don't remember off the top of
my head) that
>> make it unattractive in practice. I believe most clients opt for
something
>> like the ExecutionEngine-per-Module model used in the Kaleidoscope
>> tutorials.
>
> I see. That's good to know.
>
>> As Dave mentioned, I'm also working on some new JIT APIs (Orc) that
are
>> intended to be more feature-rich and easier to use than MCJIT. If you
would
>> like to try them out and have any questions about how they work please
don't
>> hesitate to ask. You'll need to live on the bleeding edge for those
though -
>> they're not available on 3.5.
>>
>
> I am at an early stage of development so I can use Orc provided there
> is some assurance that this will be mainstream in future. Else I can
> use the MCJIT replacement that uses Orc. If I wanted to do this should
> I clone the latest code from github?
>
> In any case I am abstracting the creation and management of engines,
> modules etc in my code so that I can change this in future if
> necessary.
>
> Thanks and Regards
>
> Dibyendu