[OpenMP] Stride in distribute parallel for loops with no chunk size

[grokos]

Summary

When we have a distribute parallel for the compiler calls __kmpc_for_static_init_* which in turn calls __kmp_for_static_init. In the latter function, when no chunk size is specified in the dist_schedule clause, the code does not set pstride correctly; *pstride is left to be equal to 1. Whereas this is OK for plain parallel for-loops with no chunk size, it is obviously wrong for distribute parallel for-loops and causes chunks of the distributed loop to be distributed multiple times to multiple teams. The fix is to set *pstride to some value at least as large as the loop trip count.

[jcownie]

Code looks fine to me, but it'd be really useful also to add a regression test...

[AndreyChurbanov]

LGTM

openmp/trunk/runtime/src/kmp_sched.cpp

case kmp_sch_static:
                         if( *pupper > *plower )
                             *pupper = traits_t<T>::min_value;
                         if( plastiter != NULL )
                             *plastiter = *plower >= old_upper && *pupper < old_upper - incr;
                         if ( *pupper < old_upper ) *pupper = old_upper; // tracker C73258
                     }
                 }
             }
+            *pstride = trip_count;
             break;
         }
     case kmp_sch_static_chunked:
         {
             register ST span;
             if ( chunk < 1 ) {
                 chunk = 1;
             }