[Bug libgomp/33894] New: [libgomp/parallel mode] pragma omp atomic broken

["singler at ira dot uka dot de" <gcc-bugzilla at gcc dot gnu dot org>]

In code like this from include/parallel/workstealing.h (libstdc++ parallel
mode)

          // After reaching this point, a thread's job list is empty.
          if (iam_working)
            {
              //This thread no longer has work.
              #pragma omp atomic
              busy--;

              iam_working = false;
            }


the instruction belonging to the omp atomic pragma is skipped by the compiler,
i. e. busy is _not_ decremented. 

Adding pragma omp flush before and after does not help either. Replacing the
two lines by "__sync_fetch_and_add(&busy, -1);" makes the program work
correctly.

Unfortunately, I have not yet succeeded in constructing a test case simpler
than calling e. g. parallel for_each, and checking the result. The problem
could maybe be caused by incorrect inlining.


-- 
           Summary: [libgomp/parallel mode] pragma omp atomic broken
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: singler at ira dot uka dot de
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33894