[Bug fortran/49693] New: Spurious "unused-variable" warnings for COMMON block module variables.

["stephan.kramer at imperial dot ac.uk" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49693

           Summary: Spurious "unused-variable" warnings for COMMON block
                    module variables.
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: stephan.kramer@imperial.ac.uk


As of gfortran 4.6, module variables that are also part of a common block cause
spurious "unused variable" warnings. The following example

  module foo
  implicit none
  integer:: a, b
  common a
  end module foo

produces:

  $ gfortran -c -Wall test.f90 
  test.f90:3:0: warning: âaâ defined but not used [-Wunused-variable]

Although common variables are deprecated they're still commonly used in
libraries such as mpi and petsc to define some global paramaters. I therefore
get quite a few warning messages in every module that uses these (and also
everywhere module that subsequently uses such modules). Example here with
openmpi:

  $ cat test.f90 
  module foo
  use mpi
  use petsc
  end module

  $ mpif90 -I/usr/lib/petscdir/3.1/linux-gnu-c-opt/include/ -Wall -c test.f90
  test.f90:2:0: warning: âmpi_argv_nullâ defined but not used
  test.f90:2:0: warning: âmpi_in_placeâ defined but not used
  test.f90:2:0: warning: âmpi_status_ignoreâ defined but not used
  test.f90:2:0: warning: âmpi_statuses_ignoreâ defined but not used
  test.f90:3:0: warning: âpetsc_comm_selfâ defined but not used
  test.f90:3:0: warning: âpetsc_null_integerâ defined but not used
  test.f90:3:0: warning: âpetsc_nullâ defined but not used
  test.f90:3:0: warning: âpetsc_null_scalarâ defined but not used
  test.f90:3:0: warning: âpetsc_null_doubleâ defined but not used
  test.f90:3:0: warning: âpetsc_null_realâ defined but not used
  test.f90:3:0: warning: âpetsc_null_truthâ defined but not used
  test.f90:2:0: warning: âmpi_argvs_nullâ defined but not used
  test.f90:3:0: warning: âpetsc_null_objectâ defined but not used
  test.f90:3:0: warning: âpetsc_comm_worldâ defined but not used
  test.f90:2:0: warning: âmpi_argv_nullâ defined but not used
  test.f90:2:0: warning: âmpi_argvs_nullâ defined but not used
  test.f90:2:0: warning: âmpi_bottomâ defined but not used
  test.f90:2:0: warning: âmpi_errcodes_ignoreâ defined but not used
  test.f90:2:0: warning: âmpi_in_placeâ defined but not used
  test.f90:2:0: warning: âmpi_status_ignoreâ defined but not used
  test.f90:2:0: warning: âmpi_statuses_ignoreâ defined but not used
  test.f90:3:0: warning: âpetsc_null_characterâ defined but not used
  test.f90:2:0: warning: âmpi_bottomâ defined but not used
  test.f90:2:0: warning: âmpi_errcodes_ignoreâ defined but not used