[Bug testsuite/68705] New: libgomp.c/sort-1.c/sort missing synchronization

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68705

            Bug ID: 68705
           Summary: libgomp.c/sort-1.c/sort missing synchronization
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: testsuite
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Created attachment 36927
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36927&action=edit
libgomp.c/sort-1.c:sort1

Consider libgomp.c/sort-1.c:sort1 (attached).

There's a bit of code only performed by thread 0:
...
    if (omp_get_thread_num () == 0)
      {
        num_threads = omp_get_num_threads ();
        hi = count - 1;
        idle = false;
      }
...

It initializes shared variable num_threads. This num_threads variable is used
by all threads subsequently, but there doesn't seem to be a mechanism present
that guarantees that the initialization by thread 0 is done before any other
thread reads the value ().

Looking at similar testcases, it seems omp barrier is used.

Adding an omp barrier at the end of the snippet would add the missing
synchronization.