[LLVMdev] JVM Backend

[David Roberts]

>> > So it will stack overflow on tail calls
>>
>> At the moment, yes. But then again, so does java.
>
> Sure but a lot of people like me are using LLVM precisely because it offers
> these wonderful features. As long as your JVM backend does not handle these
> features correctly its utility is greatly diminished.
The issue is that current JVMs don't provide good support for tail
calls. Self recursive functions could probably be optimised into
loops, but apart from that I'm not sure what I can do. You're
obviously much more familiar with TCO than I am, so perhaps you can
suggest a solution.

>> No, structs are supported. The only unsupported types at the moment
>> (as far as I am aware) are things like i31 and f80.
>
> How do you support structs when the JVM is incapable of expressing value
> types? Do you box every aggregate in an object? Does insertvalue construct an
> entirely new object? If so, the performance degradation will be orders of
> magnitude. Optimizing structs for the JVM is not easy and you will never get
> decent performance out of the JVM in the general case.
Oh, sorry, I see what you mean. No, first-class structs aren't supported.

>> I haven't been working on this project for too long - you can't expect
>> it to be perfect on the first release.
>
> Nobody is asking for perfection, just completeness.
I'd just like to point out that I don't have a great deal of
experience in compiler development - I just thought that this would be
an interesting project to try. I realise that it isn't complete in
it's current state.

--
David Roberts
http://da.vidr.cc/



On Mon, Nov 30, 2009 at 04:46, Jon Harrop <jon at ffconsultancy.com> wrote:
> On Sunday 29 November 2009 02:06:04 you wrote:
>> > So it will stack overflow on tail calls
>>
>> At the moment, yes. But then again, so does java.
>
> Sure but a lot of people like me are using LLVM precisely because it offers
> these wonderful features. As long as your JVM backend does not handle these
> features correctly its utility is greatly diminished.
>
>> Also, it looks like they're working on support for tail calls in the Da
>> Vinci Machine[1].
>
> I believe that work was actually finished some time ago by my hero, Arnold
> Schwaighofer, who was also responsible for the excellent TCO implementation
> in LLVM.
>
>> > and break with run-time errors
>>
>> When I said it raises an assertion, I meant at compile-time.
>>
>> > on structs?
>>
>> No, structs are supported. The only unsupported types at the moment
>> (as far as I am aware) are things like i31 and f80.
>
> How do you support structs when the JVM is incapable of expressing value
> types? Do you box every aggregate in an object? Does insertvalue construct an
> entirely new object? If so, the performance degradation will be orders of
> magnitude. Optimizing structs for the JVM is not easy and you will never get
> decent performance out of the JVM in the general case.
>
>> > As Chris said, the LLVM world really needs any fully working solution
>> > rather than a selection of incomplete solutions.
>>
>> I haven't been working on this project for too long - you can't expect
>> it to be perfect on the first release.
>
> Nobody is asking for perfection, just completeness.
>
> --
> Dr Jon Harrop, Flying Frog Consultancy Ltd.
> http://www.ffconsultancy.com/?e
>