[llvm-dev] MCJIT -- Poor run-time performance for Fibonacci example in LLVM 3.8.1

Lang Hames via llvm-dev llvm-dev at lists.llvm.org
Fri Jun 10 22:59:48 PDT 2016

Hi Riyaz, Renato,

I've updated MCJIT and the Fibonacci example in r272455. The example
performance should now be comparable to llvm-3.4. I'll update it again in
the near future to use ORC rather than MCJIT.

Riyaz - You may want to consider moving straight to ORC, rather than MCJIT.
ORC provides a superset of MCJIT's functionality (including support for
lazy JITing on some platforms), and is better at managing memory. The new
tutorial series that I'm working on might be helpful:
http://llvm.org/docs/tutorial/BuildingAJIT1.html .

- Lang.

On Fri, Jun 10, 2016 at 5:06 PM, Lang Hames <lhames at gmail.com> wrote:

> Hi Riyaz, Renato,
> Attempting to run Fibonacci from LLVM 3.8.1 on Darwin I get:
> ./fib381: Failed to construct ExecutionEngine: Interpreter has not been
> linked in.
> This suggests that the reason for the slowdown isn't in the JIT itself.
> Instead, when we removed the old JIT we probably didn't update the
> Fibonacci example to request a JIT at all, so now it's falling back to the
> interpreter. I'm just digging in to confirm this now, and will update the
> example code as needed to fix this.
> Cheers,
> Lang.
> On Fri, Jun 10, 2016 at 5:38 AM, Renato Golin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>> On 10 June 2016 at 05:31, Riyaz Puthiyapurayil via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > We have been using LLVM 3.4 and are currently migrating to LLVM 3.8.1.
>> We
>> > have been using the Old JIT and since it has been removed since 3.6, we
>> have
>> > to use MCJIT.
>> Hi Riyaz,
>> I don't know much about it, but MCJIT was also replaced, by a new JIT
>> called "ORC".
>> The Kaleidoscope example has been updated, you can look there:
>> http://llvm.org/docs/tutorial/LangImpl4.html
>> cheers,
>> --renato
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
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