Re: [Caml-list] Status of Flambda in OCaml 4.03

[Yotam Barnoy <yotambarnoy@gmail.com>]

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While we await the manual, can you explain what you mean by 'enabled at
configure time'? Will a -flambda -O-something argument passed to the normal
4.03 compiler enable flambda optimizations? Flambda is clearly the star of
the 4.03 release, so not enabling it using command line options seems
counter-intuitive (if this is the case).

-Yotam

On Wed, Mar 9, 2016 at 7:59 PM, Markus Mottl <markus.mottl@gmail.com> wrote:

> I've just tested Flambda, and it seems to already be doing a pretty
> decent job on some non-trivial examples (e.g. inlining combinations of
> functors and first class functions).  I hope there will be a stable
> 4.03 OPAM switch that enables it.  I'm looking forward to being able
> to write more elegant, abstract code that's still efficient.
>
> Regards,
> Markus
>
> On Wed, Mar 9, 2016 at 2:14 AM, Mark Shinwell <mshinwell@janestreet.com>
> wrote:
> > It will not be enabled by default in 4.03.  For the majority of
> > programs, in the current state, it should improve performance (mainly
> > by lowering allocation).  It should never generate wrong code.
> > However we know of examples that don't improve as much as we would
> > like, which we will try to address for 4.04.
> >
> > There will be a draft version of the new Flambda manual chapter
> > available shortly (hopefully this week).  Amongst other things this
> > documents what you found about the configure options and the flags'
> > operation.
> >
> > Mark
> >
> > On 9 March 2016 at 03:55, Markus Mottl <markus.mottl@gmail.com> wrote:
> >> Hi Alain,
> >>
> >> I see, thanks.  It was a little confusing, because the command line
> >> options for tuning flambda were still available even without Flambda
> >> being enabled.
> >>
> >> Will Flambda be enabled by default in OCaml 4.03 or is it still
> >> considered to be too experimental?  It could turn out to become one of
> >> the most impactful new features in terms of how I write code.
> >>
> >> Regards,
> >> Markus
> >>
> >> On Tue, Mar 8, 2016 at 5:53 PM, Alain Frisch <alain.frisch@lexifi.com>
> wrote:
> >>> Hi Markus,
> >>>
> >>> flambda needs to be enabled explicitly at configure time with the
> "-flambda"
> >>> flag.  The new optimizer will then be used unconditionally, and you can
> >>> tweak it using command-line parameters passed to ocamlopt (see
> "ocamlopt
> >>> -h").
> >>>
> >>>
> >>> Alain
> >>>
> >>>
> >>> On 08/03/2016 23:10, Markus Mottl wrote:
> >>>>
> >>>> Hi,
> >>>>
> >>>> I'm trying out OCaml 4.03.0+beta1 right now and wanted to test Flambda
> >>>> optimizations.  But looking at the generated assembly, it doesn't seem
> >>>> to be doing much if anything on the simple test examples that I
> >>>> thought would benefit.
> >>>>
> >>>> To give an example of what I expected to see, lets consider this code:
> >>>>
> >>>> -----
> >>>> let map_pair f (x, y) = f x, f y
> >>>>
> >>>> let succ x = x + 1
> >>>> let map_pair_succ1 pair = map_pair succ pair
> >>>> let map_pair_succ2 (x, y) = succ x, succ y
> >>>> -----
> >>>>
> >>>> I would have thought that the "succ" function would be inlined in
> >>>> "map_pair_succ1" as the compiler would do for "map_pair_succ2".
> >>>> But the generated code looks like this:
> >>>>
> >>>> -----
> >>>> L101:
> >>>>    movq  %rax, %rdi
> >>>>    movq  %rdi, 8(%rsp)
> >>>>    movq  %rbx, (%rsp)
> >>>>    movq  8(%rbx), %rax
> >>>>    movq  (%rdi), %rsi
> >>>>    movq  %rdi, %rbx
> >>>>    call  *%rsi
> >>>> L102:
> >>>>    movq  %rax, 16(%rsp)
> >>>>    movq  (%rsp), %rax
> >>>>    movq  (%rax), %rax
> >>>>    movq  8(%rsp), %rbx
> >>>>    movq  (%rbx), %rdi
> >>>>    call  *%rdi
> >>>> -----
> >>>>
> >>>> Is Flambda supposed to work out of the box with the current beta?
> >>>> What flags or annotations should I use for testing?  Any showcase
> >>>> examples I should try out that are expected to be improved?
> >>>>
> >>>> Regards,
> >>>> Markus
> >>>>
> >>>
> >>
> >>
> >>
> >> --
> >> Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com
> >>
> >> --
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>
>
>
> --
> Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com
>
> --
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