[Bug libgomp/59983] New: By using -fopenmp local-variable contains wrong value

[Bug libgomp/59983] New: By using -fopenmp local-variable contains wrong value

[ktietz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59983

            Bug ID: 59983
           Summary: By using -fopenmp local-variable contains wrong value
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktietz at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org

Following sample shows that amount of lions is calculate wrong by using
-fopenmp.

#include "stdio.h"
#include <omp.h>
#include <pthread.h>

void *do_thread(void *pa)
{
    int niterations = 4;
    int i = 0;
    pthread_self();

    #pragma omp parallel for
    for (i = 0; i < niterations; i++)
    {
        printf ("%s %d\n","ducks",i);
        fflush(0);
    }

    printf ("%s %d\n","lions",i);
    fflush(0);
    return NULL;
}

[Bug libgomp/59983] By using -fopenmp local-variable contains wrong value

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59983

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This is just wrong testcase.  Without lastprivate(i) clause the original value
of i after the parallel is undefined.
See e.g. OpenMP 3.1, in 2.5.1, page 40:
"Unless the variable is specified lastprivate on the loop construct, its value
after the loop is unspecified."
Same wording in OpenMP 4.0, in 2.6, page 51.