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From: Keean Schupke <keean.schupke@googlemail.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT (GCC) Profile Guided Compilation
Date: Fri, 29 Jun 2012 03:01:30 -0700 (PDT)
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Date: 2012-06-29T03:01:30-07:00
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On Friday, 29 June 2012 10:34:19 UTC+1, Dmitry A. Kazakov  wrote:
> On Fri, 29 Jun 2012 02:17:19 -0700 (PDT), Keean Schupke wrote:
>=20
> > Anyone have any ideas why profile guided compilation performs so poorly
> > with Ada compared to C++?
>=20
> Probably because you programmed it using low level C-ish stuff like
> addresses instead of accessing data directly. In general, if you write a =
C
> program in Ada (or any other language), you cannot expect it do better th=
an
> in C. To beat C, the precondition is to design it in Ada way.
>=20
> --=20
> Regards,
> Dmitry A. Kazakov
> http://www.dmitry-kazakov.de

I don't think you are right here, but I would be happy to be proved wrong.=
=20

In general I find the choice of algorithm dominates performance. In this ca=
se most of the performance is dominated by a disjoint-set (union-find) algo=
rithm operating on an array of data. The data nominally represents a 2D spa=
ce (although I am using a 1D array to avoid the cost of multiplication on e=
very access).

Most operations access the neighbouring cells, hence require a +/- one cell=
, or +/- one row operations.

Maintaining the address of the current cell is faster than using indexed ad=
dressing (mainly because of the extra parameter that needs to be passed aro=
und increasing the pressure on register allocation).

I would be interested to understand how an algorithm can be implemented in =
a more Ada way?


Cheers,
Keean.