Fixed problem introduced by part of https://reviews.llvm.org/D21196.

[AndreyChurbanov]

Summary

One of changes made by https://reviews.llvm.org/D21196 caused error because of broken Task Scheduling Constraint (TSC) when stolen non-descendant untied task produced tied tasks those cannot be scheduled by the thread according to TSC. This change fixes the problem by restoring TSC check for untied tasks during stealing.

[jlpeyton]

LGTM

openmp/trunk/runtime/src/kmp_tasking.c

if ( !is_constrained ) {
         // only child of current task can be scheduled
         kmp_taskdata_t * current = __kmp_threads[ gtid ]->th.th_current_task;
         kmp_int32        level = current->td_level;
         kmp_taskdata_t * parent = taskdata->td_parent;
         while ( parent != current && parent->td_level > level ) {
             parent = parent->td_parent;  // check generation up to the level of the current task
             KMP_DEBUG_ASSERT(parent != NULL);
         }
-        if ( parent != current && (taskdata->td_flags.tiedness == TASK_TIED) ) { // untied is always allowed to be stolen
-            // If the tail task is not a child, then no other childs can appear in the deque (?).
+        if ( parent != current ) {
+            // If the tail task is not a descendant of the current task then do not steal it.
             __kmp_release_bootstrap_lock( & victim_td -> td.td_deque_lock );
             KA_TRACE(10, ("__kmp_steal_task(exit #2): T#%d could not steal from T#%d: task_team=%p "
                           "ntasks=%d head=%u tail=%u\n",
                           gtid, __kmp_gtid_from_thread( threads_data[victim_tid].td.td_thr ),
                           task_team, victim_td->td.td_deque_ntasks,
                           victim_td->td.td_deque_head, victim_td->td.td_deque_tail) );
             return NULL;
         }