llvm-gcc-4.2/libgomp/testsuite/libgomp.c/appendix-a/a.19.1.c

/* { dg-do run } */

int x, *p = &x;
extern void abort (void);
void
f1 (int *q)
{
  *q = 1;
#pragma omp flush
  /* x, p, and *q are flushed */
  /* because they are shared and accessible */
  /* q is not flushed because it is not shared. */
}

void
f2 (int *q)
{
#pragma omp barrier
  *q = 2;
#pragma omp barrier
  /*  a barrier implies a flush */
  /*  x, p, and *q are flushed */
  /*  because they are shared and accessible */
  /*  q is not flushed because it is not shared. */
}

int
g (int n)
{
  int i = 1, j, sum = 0;
  *p = 1;
#pragma omp parallel reduction(+: sum) num_threads(2)
  {
    f1 (&j);
    /* i, n and sum were not flushed */
    /* because they were not accessible in f1 */
    /* j was flushed because it was accessible */
    sum += j;
    f2 (&j);
    /* i, n, and sum were not flushed */
    /* because they were not accessible in f2 */
    /* j was flushed because it was accessible */
    sum += i + j + *p + n;
  }
  return sum;
}

int
main ()
{
  int result = g (10);
  if (result != 30)
    abort ();
  return 0;
}