Re: [Caml-list] Why is some code compiled with 4.04.0 or 4.05.0 running 2.3 times slower than the same code compiled with 4.03.0?

[Berke Durak <berke.durak@gmail.com>]

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Thanks Mark & David.

Issue opened here: https://caml.inria.fr/mantis/view.php?id=7396


On Mon, Oct 31, 2016 at 12:37 AM, Mark Shinwell <mshinwell@janestreet.com>
wrote:

> Thanks for the report and bisection.  We're looking at this.  Please
> file a Mantis report in any case.
>
> Mark
>
> On 30 October 2016 at 16:49, David Allsopp <dra-news@metastack.com> wrote:
> > Berke Durak wrote:
> >> I compiled and ran a simple matrix-multiplication-style benchmark
> >> program written in imperative style with Bigarrays (see below)
> >> using versions 4.01.0, 4.03.0, 4.03.0+flambda, 4.04.0+trunk+flambda
> >> (with -version 4.04.0+dev9-2015-09-05), 4.04.0+beta2+flambda
> >> (4.04.0+beta2) and 4.05+trunk+flambda (4.05.0+dev0-2016-08-01).
> >>
> >> Execution time increased by a factor of 2.3 from 4.03+flambda to
> >> 4.04+trunk+flambda.  I tried a few of the newer optimization
> >> switches (-rounds X, -unboxed-types, -unbox-closures, etc.) but
> >> that didn't make a significant difference.
> >>
> >> Execution times, repeatable within ~5%:
> >>
> >> 4.01.0                5.45s
> >> 4.03.0                4.28s
> >> 4.03.0+flambda        4.44s
> >> 4.04.0+trunk+flambda  10.45s
> >> 4.04.0+beta2+flambda 10.72s
> >> 4.05.0+trunk+flambda  10.36s
> >
> > Note that this is specifically an flambda problem - neither 4.04 nor
> trunk exhibit the slowdown with flambda disabled.
> >
> > I've bisected and identified commit f7dcb as the problem (it was added
> to trunk after 4.03 was branched). The specific issue is the change in
> https://github.com/ocaml/ocaml/blob/trunk/bytecomp/simplif.ml#L473
> disabling conversion of refs to mutable variables when flambda is enabled.
> If you remove the `&& Config.flambda = false` and rebuild ocamlopt, you
> should find your benchmark speed restored. flambda is supposed to be
> performing that optimisation itself, so something is clearly (very) wrong!
> >
> > Could you open a Mantis PR for this, please?
> >
> >
> > David
> >
> > --
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>



-- 
Berke Durak, VA7OBD (CN88)

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