[Bug libgomp/59546] New: wrong behavior with reduction

[Bug libgomp/59546] New: wrong behavior with reduction

[valeryweber at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59546

            Bug ID: 59546
           Summary: wrong behavior with reduction
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: valeryweber at hotmail dot com
                CC: jakub at gcc dot gnu.org

hi all

the following code is producing strange result (removing the writes works
fine). is it a bug?

v


gfortran-trunk --version
GNU Fortran (GCC) 4.9.0 20131119 (experimental)
Copyright (C) 2013 Free Software Foundation, Inc.

GNU Fortran comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Fortran
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING

[vwe@triest semd]$ cat gcc_reduction.f90 
program test
  use omp_lib
  implicit none
  integer :: i

  !$omp parallel reduction(+:i)
  i=1

  !$omp master
  write(*,*) 'first write'
  write(*,*) 'second write'
  !$omp end master

  !$omp end parallel

  if(i.ne.omp_get_max_threads()) then
     write(*,*) i
     stop 'err1'
  endif

end program test
[vwe@triest semd]$ export OMP_NUM_THREADS=1; gfortran-trunk -fopenmp
gcc_reduction.f90   ;  ./a.out 
 first write
 second write
          49
STOP err1

[Bug libgomp/59546] wrong behavior with reduction

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59546

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
i is uninitialized before the reduction, so if you add some number of threads
to an uninitialized value, you can get pretty much anything.

Also, there is no guarantee !$omp parallel will create exactly
omp_get_max_threads () threads, that is just maximum for the number of threads,
it can depend on env vars etc.

[Bug libgomp/59546] wrong behavior with reduction

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59546

Richard Biener <rguenth at gcc dot gnu.org> changed:

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

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Invalid then.