[Bug fortran/90329] Incompatibility between gfortran and C lapack calls

[jb at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90329

--- Comment #18 from Janne Blomqvist <jb at gcc dot gnu.org> ---
(In reply to Thomas Koenig from comment #15)
> Since we applied the fix for PR 87689 to gcc 7, gcc 8 and gcc 9,
> I would suggest that we make -fno-optimize-sibling-calls
> the default on these branches.  Maintaining binary compatibility
> (even if it is bug compatibility) with existing packages is
> something we should strive for, especially with such
> important software packages as BLAS and LAPACK.

+1. Especially considering Steve's benchmark suggesting there's practically no
difference, although there may of course be other code where sibling call
optimization makes a difference.

> For current trunk, I would recommend keeping the current
> hehavior and contact the LAPACK maintainers to a) give them
> a heads-up for this problem, and b) a year to work out
> the problem.

Yes. Closer to GCC 10, we can revisit this. I suspect we'll have to make
-fno-optimize-sibling-calls the default for GCC 10 as well; while we might be
able to help LAPACK maintainers fix LAPACKE there's in this timeframe there's
certainly a lot of other code out there with custom C-Fortran interfaces which
might be affected.