Re: [Patch, Fortran] PR 50163 - ICE with nonconst expr in init expr

[Tobias Burnus <burnus@net-b.de>]

On 08/24/2011 12:12 PM, Mikael Morin wrote:
> On Tuesday 23 August 2011 14:26:59 Tobias Burnus wrote:
>> OK for the trunk?
> OK.

Thanks for the review! Committed to the 4.7 trunk (Rev. 178038); I will 
backport the patch later. (For cross-readers: That's a patch for a 4.3+ 
ice-on-invalid-code regression.)


> Isn't there some rules about backporting? The way we do it now, it 
> looks completely arbitrary.

I think it *is* arbitrary - and unavoidable so.

The main idea behind regression fixing is to make sure that what once 
worked should continue to work. But what always had been broken can 
remain broken and will be only fixed on the trunk.  Reason: If you fix 
more, the behaviour on the branch changes and you may introduce 
regressions. If thinks are known to be broken, you can simply work 
around them.

Additional ingredients are: How serious is the problem? A wrong-code 
issue occurring in a potentially often used part has a different 
priority than an accepts-invalid or ice-on-invalid-code issue. Also, a 
patch which is huge is less suited than a small "trivial" patch. 
Regressions, which existed for a long time are typically also less 
important - otherwise they would have been fixed or found before.

But there are also other items such as: Which is the last maintained 
version in GCC, which versions are still being used (such that it makes 
sense to backport), and which patches (Linux) distributions want to see. 
Additionally, as backporting takes time (bootstrap, regtesting, and 
maybe even adapting the patch slightly): How much time wants the 
developer spend on backporting.

My impression is that gfortran is currently doing too much 
non-regression backporting, which should be left to serious ICE-on-valid 
code and wrong-code issues. Especially as older versions do not see as 
much testing as the trunk.

On the other hand, backporting simple fixes to regressions or really bad 
wrong-code issues (which we hadn't for a while) down to 4.4 should be 
also fine.

I think every modern (= F2003) developer can relatively simply update to 
4.6 or the trunk. The older versions are mostly for those using the 
default compiler of the system; those typically only need some Fortran 
77/90 compiler, for which the older versions (4.4 or 4.5) should be fine.

But at the end it is question of style. That's similar to Linux 
distributions. I think Jakub/Red Hat ports many patches (bug fixes but 
also features) back to their old versions, while for instance 
Richard/SUSE's package has only few patches and essentially grabs the 
current branch. Both approaches makes sense and either one has 
advantages and disadvantages.

I think we should try extra hard to avoid regressions on the branches 
and mostly concentrate on the trunk, but we can still backport one patch 
or the other to the branches.

I didn't really answer your question, did I?

Tobias