[Bug libfortran/58020] Code for handling IEEE exceptions

["burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58020

--- Comment #5 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Cross-ref: See also PR29383.

(In reply to Fred Krogh from comment #0)
> Dr. Richard Hanson has written code to provide IEEE exception handling to
> gfortran.

Cool! I think it should be linked from the Wiki and somewhat made known. Even
prior (or without) inclusion in GCC/gfortran, the code is very useful for
users!


(In reply to kargl from comment #1)
> 1) Hanson needs to have a copyright assignment on file with FSF
>    before the code can be used.

Or rather: Before it can be included in GCC/shipped with gfortran.

(In reply to Fred Krogh from comment #2)
> 1. Hanson is willing to assign the copyright if you expect to be using this
> work.  There were thoughts to include this work on a SIAM website where we
> think SIAM would want the copyright

The Free Software Foundation (FSF) only requires a nonexclusive copyright
transfer (for inclusion in GCC). Thus, it could be additionally posted to the
SIAM webpage - assuming SIAM also is fine with a nonexclusive copyright
transfer. See http://gcc.gnu.org/wiki/GettingStarted (Basics, Item 1) for
details.


(In reply to kargl from comment #1)
> 2) More importantly, the code appears to only support the i386
>    and amd64 architectures.  gfortran runs are far more processors
>    than these.

My personal long-term plan is to add the necessary bits for IEEE to
libgfortran/config/ - and then to use them from there. Currently supported are
setting/getting the rounding mode, obtaining the set exceptions flags and
setting the exception trapping. That's supported for i386/x86-64, GLIBC, SysV
(at least: FreeBSD and Solaris) and AIX; see
http://gcc.gnu.org/viewcvs/gcc/trunk/libgfortran/config/

[Note: Those are currently only internally exported. Before making them
externally callable, one should ensure that the ABI won't change.]

Additionally, I'd like to generate the IEEE modules "on the fly" - like
ISO_C_Binding and Fortran_Dev. That gives some more optimization possibilities
and also could be used to honor SH's/Alpha's -mieee compiler flag.


One way forward would be to check whether libgfortran/config/'s function are
sufficient - and if not, add more or modify the ABI. Those could then be
exported (public ABI).

In principle, one could then also ship the modules - However, the biggest
question is how to handle the functions in the module. Those then become part
of the public ABI of gfortran and has to continued to be supported, even if we
could move some function to the compiler itself (generated code).


> 3) messy_m.f90 includes the statement:
>    I haven't looked at the code to determine if messy_m.f90 is actually
>    needed.

It seems to be only used for testing. (In any case, it would be useful to have
some test cases in the testsuite.)