Re: [Caml-list] Closing the performance gap to C

[Yotam Barnoy <yotambarnoy@gmail.com>]

On Wed, Dec 21, 2016 at 11:31 AM, Gerd Stolpmann <info@gerd-stolpmann.de> wrote:
> Dumb question because you are effectively suggesting an alternate
> calling convention in addition to the existing one: wouldn't it make
> more sense to switch to a completely different convention? Like: we
> pass fp values always in fp registers so far available?
>
>
> Gerd

As far as I understand, the current calling convention has to do with
generic functions. Having to be polymorphic over all types, including
primitive ones, such as floating point and ints of different widths,
is really difficult. This is why OOP languages don't do it -- only
classes are polymorphic.

And Alain, even if we create these alternate calling conventions, the
tricky part is still detecting when it's ok to call using direct
calling conventions. That's the hard part, and it's best done by
Flambda with its inlining.

-Yotam

>
> Am Mittwoch, den 21.12.2016, 17:06 +0100 schrieb Alain Frisch:
>> On 21/12/2016 15:45, Yotam Barnoy wrote:
>> >
>> > I think it's not worth the effort. You need to examine all the code
>> > dealing with a parameter (ie. its flow) to see if any generic
>> > function
>> > is called on that parameter.
>> This would be treated a bit like the stubs for optional arguments
>> with a
>> default value.  Any function taking float arguments or returning a
>> float
>> would be compiled to a specialized version with an unboxed calling
>> convention plus a stub which implements the generic calling
>> convention
>> and delegate the call to the specialized version (or copy its body if
>> it
>> is small enough).  On call site, when the called function is known,
>> one
>> calls the specialized version instead.  This is a systematic, local
>> compilation scheme, similar to other optimizations made in
>> closure/cmmgen; it does not require a more global analysis nor a
>> radically different representation of the code.
>>
>> About the "it's not worth the effort": the effort has largely been
>> done,
>> since the ticket came with a working patch (some more effort would
>> be
>> needed to bring it up to date, though).  In my opinion, this seems
>> like
>> a rather low-hanging fruit with very immediate and significant
>> gains.
>> I'd rather have this soon than wait for flambda to become stable and
>> usable on large projects.
>>
>>
>>
>> -- Alain
>>
> --
> ------------------------------------------------------------
> Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
> My OCaml site:          http://www.camlcity.org
> Contact details:        http://www.camlcity.org/contact.html
> Company homepage:       http://www.gerd-stolpmann.de
> ------------------------------------------------------------
>
>