[Bug fortran/54301] New: Add optional warning if pointer assigning a local variable to a nonlocal pointer

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54301

             Bug #: 54301
           Summary: Add optional warning if pointer assigning a local
                    variable to a nonlocal pointer
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org
                CC: tkoenig@gcc.gnu.org


Suggested by ISO/IEC Project 22.24772 "Guidance for Avoiding Vulnerabilities
through Language Selection and Use"  (see links at
http://gcc.gnu.org/wiki/GFortranStandards)

From the Fortran appendix (draft at
ftp://ftp.nag.co.uk/sc22wg5/N1901-N1950/N1929.pdf)

At the end there is the suggestion:

"Fortran.58.1 Implications for Standardization"
"Future standardization eorts should consider:"
...
"* Requiring that processors have the ability to detect and report the
occurrence within a submitted program unit of pointer assignment of
a pointer whose lifetime is known to be longer than the lifetime of the
target."


I think can be diagnosed with some -W... warning in the following case: The LHS
of the pointer assignment is

a) A function result variable
b) A dummy argument
c) A host- or use-associated variable
d) A common-block variable

and the RHS is a local variable (local to the procedure or local to a BLOCK) -
but, crucially, RHS variable is not a pointer.

[At least the case (a) I have already seen in some bugreport.]