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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Gnat, tasking, Vista
Date: Wed, 23 Jan 2008 00:32:54 -0800 (PST)
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tmo...@acm.org wrote:
>   My understanding is that the current Gnat is not a 3.15p with
> improvements, but is rather a substantially new thing, with new,
> unknown, bugs.  Is that a mis-understanding?

IMHO your understanding is correct up to a point, but not for the
current version of GCC (4.2.2) or the next version.

When AdaCore merged GNAT into the GCC sources, a long period of
instability ensued for the reasons you outline. I never considered
versions 3.1, 3.2 or 3.3 production-worthy and this is where I agree
with your understanding. However, 3.4 was OK. With version 4.0, a
major change to the back-end ("tree-SSA") introduced some new bugs in
the interface with the Ada front-end, but 4.1 was OK again and the Ada
part of GCC has steadily improved since (i.e. no or very few
regressions). I have a very good feeling about the upcoming GCC 4.3
because AdaCore and Sam Tardieu have recently fixed several dozen old
bugs, most of which have been present since GNAT 3.15p or before. I
anticipate that GCC 4.3 will be the best version of GCC ever as
regards Ada.

Debian reflects this opinion of mine: in 3.1 "Sarge" the Ada compiler
was GNAT 3.15p, in 4.0 "Etch" it is GCC 4.1, and in the upcoming
"Lenny" it will probably be 4.3.

Of course, none of the above applies to GNAT Pro or GNAT GPL Edition
because AdaCore are careful not to introduce regressions when
switching to a new GCC back-end, and do so only infrequently:

GNAT Pro 3.x: GCC 2.8.1
GNAT Pro 5.x and GNAT GPL 2005 Edition: GCC 3.4
GNAT Pro 6.x and GNAT GPL 2006 and 2007 Edition: GCC 4.1

--
Ludovic Brenta.