Re: Gnat, tasking, Vista

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Alex R. Mosteo writes:
> Ludovic Brenta wrote:
>
>> 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.
>
> This is very interesting. In regard to Ada 2005 features, the improvement is
> also noticeable. GPL 2006 bombed quite frequently, 2007 *much* less to the
> point of being a rarity. The only big thing I'm waiting to be useable is
> interfaces. I wonder about the amount of differences between the 2007 and
> 4.x branches.

AdaCore normally merge from GNAT Pro into GCC during Stage 1, and then
do almost nothing during Stages 2 and 3 (only a few bug fixes in the
middle-end and the back-end). That, however, changed for GCC 4.3 where
many Ada bug fixes happened during Stage 3 and I think the two
branches are now quite close.  By looking at the timeline of GCC's
development[1], one can establish a rough correspondence between GCC
and GNAT GPL releases:

GCC release | end of stage 1 | GNAT GPL release | release date
--------------------------------------------------------------
4.1         | 2005-04-25     | 2005             | 2005-09-15
4.2         | 2006-01-18     | 2006             | 2006-05-22
4.3         | 2007-01-20     | 2007             | 2007-05-11

The time between the end of Stage 1 and the final release of GCC is
approximately one year:

GCC release | release date | time since end of Stage 1
--------------------------------------------------------
4.1.0        | 2006-02-28  | 10 mo
4.2.0        | 2007-05-13  | 14 mo
4.3.0        | ????-??-??  | 10 mo and counting

This explains why GCC lags behind GNAT Pro and GNAT GPL in terms of
Ada support.

[1] http://gcc.gnu.org/develop.html#timeline

-- 
Ludovic Brenta.