[Bug fortran/41227] COMMON block, BIND(C) and LTO interoperability issues

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

------- Comment #6 from burnus at gcc dot gnu dot org  2010-02-23 09:08 -------
Regarding my question, Toon ask this question to Bill Long @ Cray and Jim Xia @
IBM at the Las Vegas meeting of J3/WG5 - they came to different conclusions ;-)

Bill Long stated what he also wrote at
  http://j3-fortran.org/pipermail/j3/2010-February/003358.html

Namely: The "OR" is to be read as exclusive "OR":
> > Does a common block containing a single variable (e.g. of type
> > "integer(c_int)") need to be interoperable with the C variable ("int")
>  > only [i.e. only (2)] 
>
>  Yes, this is my interpretation.

Toon agreed more with Bill and commented: "I think this is due to the fact that
- as every 'vendor' knows - the C compiler being the 'companion processor' (C
interoperability terminology) to its Fortran processor, it can allow additional
interoperability (for instance, allow COMMON /blah/ I interoperate with struct
{int i;} blah;)."

Thus, from the standard in a three-to-two-reading*, one only needs to
interoperate with the single variable and not with the struct. (* My reading,
Toon's, Bill's vs. Nick's (fortran@gcc) and Jim's.) -- Note: I have not
submitted an official interpretation request, for which all J3/WG5 members have
to vote.

I really wonder whether supporting both in LTO would be the better option
compared with changing it to a single variable in the frontend.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41227