[Bug fortran/69368] [6 Regression] spec2006 test case 416.gamess fails with the g++ 6.0 compiler starting with r232508

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69368

--- Comment #28 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 5 Feb 2016, alalaw01 at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69368
> 
> alalaw01 at gcc dot gnu.org changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>          Resolution|INVALID                     |FIXED
> 
> --- Comment #27 from alalaw01 at gcc dot gnu.org ---
> (In reply to Richard Biener from comment #25)
> > (In reply to alalaw01 from comment #23)
> > > Well, this one is not fixed by -fno-aggressive-loop-optimizations.
> > 
> > No, that just disabled one symptom of the issue at that point in time. 
> > Fixing the issue also fixes this occurance (well, I hope so ;))
> 
> So by "fixing the issue" - we mean, making --std=legacy prevent this (as
> although against the SPEC, colleagues with more FORTRAN knowledge than I
> suggest this is common)? SPEC seem to be saying they will not change the
> source: https://www.spec.org/cpu2006/Docs/faq.html#Run.05
> 
> 
> As Jakub suggested in comment #13:
> 
> > So, perhaps we want some flag on the Fortran COMMON decls that would be set on > COMMON that ends with an array and would tell get_ref_base_and_extent (and
> > other spots?) that accesses can be beyond end of the decl?
> 
> but only if --std=legacy ? ? ?
> 
> Should I raise a new bug for this, as both this and 53068 are CLOSED?

I think this has been discussed in some other dup already and
the Fortran FE folks disagreed (it was never "legal", not even in F77).

I also don't see how it can be a FE only fix.  Possibly we can
implemnet a middle-end switch that tells us that the size of commons
is not to be trusted.  The FE could then set that flag with -std=legacy.

You can, after all, "simulate" the very same failure with C.