[LLVMdev] Reminder: Please switch to MCJIT, as the old JIT will be removed soon.

[Yaron Keren]

Thanks!



2014-08-08 2:33 GMT+03:00 Keno Fischer <kfischer at college.harvard.edu>:

> I feel really bad for answering this sooner. I had a draft email but
> for some reason never sent it out (though I had). My apologies.
>
> > * Compiled IR functions are emitted to a shadow module.
> Julia has two different modes of compilation. In one we do the shadow
> module thing and whenever we need to call something that's not been
> pulled out yet, we compile it and the closure of it's callgraph and
> pull it out into a separate module, because we later dump the shadow
> module as a whole and compile it as a shared library for caching
> generated code. In the other we create a module per function and just
> emit it into the module directly (because we don't want to keep around
> the bitcode if we're not going to use it, so we delete it right
> aftre). Eventually I'm going to have to reevaluate this, because one
> module per function is slightly expensive (though not as bad now as it
> used to be because of some changes in MCJIT).
>
> > * Any used function is cloned into its own new module and the module is
> added to MCJIT.
> Basically correct
> Correct, when the shadow module exists, yes.
>
> > * Called functions or globalvars are only declared in that module.
> I'm not sure what you mean by that. When generating the code (or
> copying it), we declare all used global in the module.
>
> > * Modules are never removed meaning "old" functions are abandoned rather
> then replaced.
> > * All function calls go through a trampoline function doing the multiple
> dispatch, also enabling old function replacement to new version.
>
> Correct, though this is actually a long standing issue we have where
> we are not correctly replacing functions if they are sufficiently
> optimized (so that we don't go through the trampoline). I'm hoping to
> address this soon using patchpoints, but haven't gotten to that yet.
>
> For now what people who want to replace functions basically do is
> replace the bindings in the repl which will force the old code to be
> abandoned.
>
> Hope that helps and sorry for forgetting to send this out, please do
> send further questions and I'll promise I'll respond more swiftly.
>
>
> Keno
>
> On Tue, Jul 29, 2014 at 2:07 PM, Yaron Keren <yaron.keren at gmail.com>
> wrote:
> > Hi Keno,
> >
> > Could you give a short high-level overview of the way Julia works now
> with
> > MCJIT instead the JIT:
> >
> > What I gather so far...
> >
> > * Compiled IR functions are emitted to a shadow module.
> > * Any used function is cloned into its own new module and the module is
> > added to MCJIT.
> > * Called functions or globalvars are only declared in that module.
> > * Modules are never removed meaning "old" functions are abandoned rather
> > then replaced.
> > * All function calls go through a trampoline function doing the multiple
> > dispatch, also enabling old function replacement to new version.
> >
> > Thanks,
> >
> > Yaron
> >
> >
> >
> >
> > 2014-07-25 22:23 GMT+03:00 Keno Fischer <kfischer at college.harvard.edu>:
> >>
> >> If you have specific questions about this transition, I might be able
> >> to help out here, as I've gone through this process with Julia (the
> >> process should be a lot smoother now that it's working for a good set
> >> of people, so most bugs should have been found)
> >>
> >> Keno
> >>
> >> On Fri, Jul 25, 2014 at 3:13 PM, Lang Hames <lhames at gmail.com> wrote:
> >> > Hi Everyone,
> >> >
> >> > If you're JITing with LLVM and haven't made the switch to MCJIT
> already,
> >> > now
> >> > is the time. As per discussions on the mailing list and at the last
> dev
> >> > meeting, LLVM 3.5 will be the last release to support the old JIT
> >> > infrastructure. Now that LLVM 3.5 has branched, we plan to start
> >> > removing
> >> > the old JIT from the mainline.
> >> >
> >> > If you're looking for help in making the switch, Andy Kaylor wrote a
> >> > great
> >> > LLVM blog post about porting Kaleidoscope to MCJIT, which you can find
> >> > at
> >> >
> >> >
> http://blog.llvm.org/2013/07/using-mcjit-with-kaleidoscope-tutorial.html.
> >> > I'll also be working to update the LLVM docs and the Kaleidoscope
> >> > tutorial,
> >> > and as always you can ask for help in the mailing lists and on IRC.
> >> >
> >> > Good luck with the switch over!
> >> >
> >> > Cheers,
> >> > Lang.
> >> >
> >> >
> >> > _______________________________________________
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> >> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >> >
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> >
> >
>
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