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

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

[stephan.kramer at imperial dot ac.uk]

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: ‘a’ 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: ‘mpi_argv_null’ defined but not used
  test.f90:2:0: warning: ‘mpi_in_place’ defined but not used
  test.f90:2:0: warning: ‘mpi_status_ignore’ defined but not used
  test.f90:2:0: warning: ‘mpi_statuses_ignore’ defined but not used
  test.f90:3:0: warning: ‘petsc_comm_self’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_integer’ defined but not used
  test.f90:3:0: warning: ‘petsc_null’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_scalar’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_double’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_real’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_truth’ defined but not used
  test.f90:2:0: warning: ‘mpi_argvs_null’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_object’ defined but not used
  test.f90:3:0: warning: ‘petsc_comm_world’ defined but not used
  test.f90:2:0: warning: ‘mpi_argv_null’ defined but not used
  test.f90:2:0: warning: ‘mpi_argvs_null’ defined but not used
  test.f90:2:0: warning: ‘mpi_bottom’ defined but not used
  test.f90:2:0: warning: ‘mpi_errcodes_ignore’ defined but not used
  test.f90:2:0: warning: ‘mpi_in_place’ defined but not used
  test.f90:2:0: warning: ‘mpi_status_ignore’ defined but not used
  test.f90:2:0: warning: ‘mpi_statuses_ignore’ defined but not used
  test.f90:3:0: warning: ‘petsc_null_character’ defined but not used
  test.f90:2:0: warning: ‘mpi_bottom’ defined but not used
  test.f90:2:0: warning: ‘mpi_errcodes_ignore’ defined but not used

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

[longb at cray dot com]

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

Bill Long <longb at cray dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |longb at cray dot com

--- Comment #1 from Bill Long <longb at cray dot com> 2011-08-12 19:22:50 UTC ---
Had a user support with similar issues when using the MPI module.  Test case:

module dmi_mpi_global
   use mpi
   implicit none
   private

   logical,            save, public :: debug_print
   integer(4),         save, public :: iu06
   integer(4),         save, public :: mpi_io_rank = 0
   character(LEN=256), save, public :: mpi_decomp_file = 'mpi_decompo.txt'
   public :: dmpi_close

contains

  subroutine dmpi_close ( flag )
     implicit none
     logical, intent(in) :: flag
     integer(4) :: ierr

     if (flag) then
       write(*,'(a19)') 'Time to die for MPI'
     else
       write(iu06,'(a19)') 'Time to die for MPI'
     endif

     if (.not.flag) close (iu06)

     call mpi_finalize(ierr)

   end subroutine dmpi_close
end module dmi_mpi_global


> ftn -c -Wall test.f90
test.f90:2:0: warning: 'mpi_bottom' defined but not used [-Wunused-variable]
test.f90:2:0: warning: 'mpi_in_place' defined but not used [-Wunused-variable]
test.f90:2:0: warning: 'mpi_status_ignore' defined but not used
[-Wunused-variable]
test.f90:2:0: warning: 'mpi_statuses_ignore' defined but not used
[-Wunused-variable]
test.f90:2:0: warning: 'mpi_errcodes_ignore' defined but not used
[-Wunused-variable]
test.f90:2:0: warning: 'mpi_unweighted' defined but not used
[-Wunused-variable]
test.f90:2:0: warning: 'mpi_argvs_null' defined but not used
[-Wunused-variable]
test.f90:2:0: warning: 'mpi_argv_null' defined but not used [-Wunused-variable]

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

[harald at klimachs dot de]

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

Harald Klimach <harald at klimachs dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at klimachs dot de

--- Comment #2 from Harald Klimach <harald at klimachs dot de> 2011-12-30 00:12:07 UTC ---
Just also want to confirm this, I get the same messages with the mpi module of
openmpi. And I wanted to add, that these messages even persist, if I use an
only clause in the use mpi statement.

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

[tkoenig at gcc dot gnu.org]

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

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tkoenig at gcc dot gnu.org

--- Comment #3 from Thomas Koenig <tkoenig at gcc dot gnu.org> 2012-01-01 16:37:27 UTC ---
Testing this patch:

Index: toplev.c
===================================================================
--- toplev.c    (Revision 182754)
+++ toplev.c    (Arbeitskopie)
@@ -501,6 +501,9 @@
         to handle multiple external decls in different scopes.  */
       && ! (DECL_NAME (decl) && TREE_USED (DECL_NAME (decl)))
       && ! DECL_EXTERNAL (decl)
+      /* Don't warn about variables in Fortran common blocks because
+        they may be used elsewhere.  */
+      && ! DECL_COMMON(decl)
       && ! TREE_PUBLIC (decl)
       /* A volatile variable might be used in some non-obvious way.  */
       && ! TREE_THIS_VOLATILE (decl)

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

[tkoenig at gcc dot gnu.org]

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

--- Comment #4 from Thomas Koenig <tkoenig at gcc dot gnu.org> 2012-01-03 12:36:28 UTC ---
(In reply to comment #3)
> Testing this patch:

which doesn't work.

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

[tkoenig at gcc dot gnu.org]

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

--- Comment #5 from Thomas Koenig <tkoenig at gcc dot gnu.org> 2012-01-04 11:51:40 UTC ---
Author: tkoenig
Date: Wed Jan  4 11:51:37 2012
New Revision: 182869

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=182869
Log:
2012-01-04  Thomas Koenig  <tkoenig@gcc.gnu.org>

    PR fortran/49693
    * trans-common.c (create_common): Update copyright years.  Mark
    variables as used to avoid warnings about unused variables in
    common blocks.

2012-01-04  Thomas Koenig  <tkoenig@gcc.gnu.org>

    PR fortran/49693
    * gfortran.dg/common_17.f90:  New test.


Added:
    trunk/gcc/testsuite/gfortran.dg/common_17.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/trans-common.c
    trunk/gcc/testsuite/ChangeLog

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

[tkoenig at gcc dot gnu.org]

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

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED

--- Comment #6 from Thomas Koenig <tkoenig at gcc dot gnu.org> 2012-01-04 11:55:15 UTC ---
Fixed on trunk, closing.

If somebody really, really wants a backport to 4.6, please speak up.

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

[harald at klimachs dot de]

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

--- Comment #7 from Harald Klimach <harald at klimachs dot de> 2012-01-04 18:41:08 UTC ---
Thanks a lot!
Just ran the gcc trunk over my code, and the annoying warnings are gone.