Enable building libgomp with Intel CET
[gcc.git] / libgomp / task.c
index 7d3233c6e1b3506dee10d5bfa4b2d23cd883eeaf..fa35a1a1eda7c4d597c99c9ab2949ba9e9b99bb6 100644 (file)
@@ -1,7 +1,8 @@
-/* Copyright (C) 2007-2014 Free Software Foundation, Inc.
+/* Copyright (C) 2007-2017 Free Software Foundation, Inc.
    Contributed by Richard Henderson <rth@redhat.com>.
 
-   This file is part of the GNU OpenMP Library (libgomp).
+   This file is part of the GNU Offloading and Multi Processing Library
+   (libgomp).
 
    Libgomp is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
@@ -28,6 +29,7 @@
 #include "libgomp.h"
 #include <stdlib.h>
 #include <string.h>
+#include "gomp-constants.h"
 
 typedef struct gomp_task_depend_entry *hash_entry_type;
 
@@ -63,6 +65,14 @@ void
 gomp_init_task (struct gomp_task *task, struct gomp_task *parent_task,
                struct gomp_task_icv *prev_icv)
 {
+  /* It would seem that using memset here would be a win, but it turns
+     out that partially filling gomp_task allows us to keep the
+     overhead of task creation low.  In the nqueens-1.c test, for a
+     sufficiently large N, we drop the overhead from 5-6% to 1%.
+
+     Note, the nqueens-1.c test in serial mode is a good test to
+     benchmark the overhead of creating tasks as there are millions of
+     tiny tasks created that all run undeferred.  */
   task->parent = parent_task;
   task->icv = *prev_icv;
   task->kind = GOMP_TASK_IMPLICIT;
@@ -71,7 +81,7 @@ gomp_init_task (struct gomp_task *task, struct gomp_task *parent_task,
   task->final_task = false;
   task->copy_ctors_done = false;
   task->parent_depends_on = false;
-  task->children = NULL;
+  priority_queue_init (&task->children_queue);
   task->taskgroup = NULL;
   task->dependers = NULL;
   task->depend_hash = NULL;
@@ -90,30 +100,194 @@ gomp_end_task (void)
   thr->task = task->parent;
 }
 
+/* Clear the parent field of every task in LIST.  */
+
 static inline void
-gomp_clear_parent (struct gomp_task *children)
+gomp_clear_parent_in_list (struct priority_list *list)
 {
-  struct gomp_task *task = children;
-
-  if (task)
+  struct priority_node *p = list->tasks;
+  if (p)
     do
       {
-       task->parent = NULL;
-       task = task->next_child;
+       priority_node_to_task (PQ_CHILDREN, p)->parent = NULL;
+       p = p->next;
       }
-    while (task != children);
+    while (p != list->tasks);
+}
+
+/* Splay tree version of gomp_clear_parent_in_list.
+
+   Clear the parent field of every task in NODE within SP, and free
+   the node when done.  */
+
+static void
+gomp_clear_parent_in_tree (prio_splay_tree sp, prio_splay_tree_node node)
+{
+  if (!node)
+    return;
+  prio_splay_tree_node left = node->left, right = node->right;
+  gomp_clear_parent_in_list (&node->key.l);
+#if _LIBGOMP_CHECKING_
+  memset (node, 0xaf, sizeof (*node));
+#endif
+  /* No need to remove the node from the tree.  We're nuking
+     everything, so just free the nodes and our caller can clear the
+     entire splay tree.  */
+  free (node);
+  gomp_clear_parent_in_tree (sp, left);
+  gomp_clear_parent_in_tree (sp, right);
 }
 
-static void gomp_task_maybe_wait_for_dependencies (void **depend);
+/* Clear the parent field of every task in Q and remove every task
+   from Q.  */
+
+static inline void
+gomp_clear_parent (struct priority_queue *q)
+{
+  if (priority_queue_multi_p (q))
+    {
+      gomp_clear_parent_in_tree (&q->t, q->t.root);
+      /* All the nodes have been cleared in gomp_clear_parent_in_tree.
+        No need to remove anything.  We can just nuke everything.  */
+      q->t.root = NULL;
+    }
+  else
+    gomp_clear_parent_in_list (&q->l);
+}
+
+/* Helper function for GOMP_task and gomp_create_target_task.
+
+   For a TASK with in/out dependencies, fill in the various dependency
+   queues.  PARENT is the parent of said task.  DEPEND is as in
+   GOMP_task.  */
+
+static void
+gomp_task_handle_depend (struct gomp_task *task, struct gomp_task *parent,
+                        void **depend)
+{
+  size_t ndepend = (uintptr_t) depend[0];
+  size_t nout = (uintptr_t) depend[1];
+  size_t i;
+  hash_entry_type ent;
+
+  task->depend_count = ndepend;
+  task->num_dependees = 0;
+  if (parent->depend_hash == NULL)
+    parent->depend_hash = htab_create (2 * ndepend > 12 ? 2 * ndepend : 12);
+  for (i = 0; i < ndepend; i++)
+    {
+      task->depend[i].addr = depend[2 + i];
+      task->depend[i].next = NULL;
+      task->depend[i].prev = NULL;
+      task->depend[i].task = task;
+      task->depend[i].is_in = i >= nout;
+      task->depend[i].redundant = false;
+      task->depend[i].redundant_out = false;
+
+      hash_entry_type *slot = htab_find_slot (&parent->depend_hash,
+                                             &task->depend[i], INSERT);
+      hash_entry_type out = NULL, last = NULL;
+      if (*slot)
+       {
+         /* If multiple depends on the same task are the same, all but the
+            first one are redundant.  As inout/out come first, if any of them
+            is inout/out, it will win, which is the right semantics.  */
+         if ((*slot)->task == task)
+           {
+             task->depend[i].redundant = true;
+             continue;
+           }
+         for (ent = *slot; ent; ent = ent->next)
+           {
+             if (ent->redundant_out)
+               break;
+
+             last = ent;
+
+             /* depend(in:...) doesn't depend on earlier depend(in:...).  */
+             if (i >= nout && ent->is_in)
+               continue;
+
+             if (!ent->is_in)
+               out = ent;
+
+             struct gomp_task *tsk = ent->task;
+             if (tsk->dependers == NULL)
+               {
+                 tsk->dependers
+                   = gomp_malloc (sizeof (struct gomp_dependers_vec)
+                                  + 6 * sizeof (struct gomp_task *));
+                 tsk->dependers->n_elem = 1;
+                 tsk->dependers->allocated = 6;
+                 tsk->dependers->elem[0] = task;
+                 task->num_dependees++;
+                 continue;
+               }
+             /* We already have some other dependency on tsk from earlier
+                depend clause.  */
+             else if (tsk->dependers->n_elem
+                      && (tsk->dependers->elem[tsk->dependers->n_elem - 1]
+                          == task))
+               continue;
+             else if (tsk->dependers->n_elem == tsk->dependers->allocated)
+               {
+                 tsk->dependers->allocated
+                   = tsk->dependers->allocated * 2 + 2;
+                 tsk->dependers
+                   = gomp_realloc (tsk->dependers,
+                                   sizeof (struct gomp_dependers_vec)
+                                   + (tsk->dependers->allocated
+                                      * sizeof (struct gomp_task *)));
+               }
+             tsk->dependers->elem[tsk->dependers->n_elem++] = task;
+             task->num_dependees++;
+           }
+         task->depend[i].next = *slot;
+         (*slot)->prev = &task->depend[i];
+       }
+      *slot = &task->depend[i];
+
+      /* There is no need to store more than one depend({,in}out:) task per
+        address in the hash table chain for the purpose of creation of
+        deferred tasks, because each out depends on all earlier outs, thus it
+        is enough to record just the last depend({,in}out:).  For depend(in:),
+        we need to keep all of the previous ones not terminated yet, because
+        a later depend({,in}out:) might need to depend on all of them.  So, if
+        the new task's clause is depend({,in}out:), we know there is at most
+        one other depend({,in}out:) clause in the list (out).  For
+        non-deferred tasks we want to see all outs, so they are moved to the
+        end of the chain, after first redundant_out entry all following
+        entries should be redundant_out.  */
+      if (!task->depend[i].is_in && out)
+       {
+         if (out != last)
+           {
+             out->next->prev = out->prev;
+             out->prev->next = out->next;
+             out->next = last->next;
+             out->prev = last;
+             last->next = out;
+             if (out->next)
+               out->next->prev = out;
+           }
+         out->redundant_out = true;
+       }
+    }
+}
 
 /* Called when encountering an explicit task directive.  If IF_CLAUSE is
    false, then we must not delay in executing the task.  If UNTIED is true,
-   then the task may be executed by any member of the team.  */
+   then the task may be executed by any member of the team.
+
+   DEPEND is an array containing:
+       depend[0]: number of depend elements.
+       depend[1]: number of depend elements of type "out".
+       depend[2..N+1]: address of [1..N]th depend element.  */
 
 void
 GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
           long arg_size, long arg_align, bool if_clause, unsigned flags,
-          void **depend)
+          void **depend, int priority)
 {
   struct gomp_thread *thr = gomp_thread ();
   struct gomp_team *team = thr->ts.team;
@@ -125,8 +299,7 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
      might be running on different thread than FN.  */
   if (cpyfn)
     if_clause = false;
-  if (flags & 1)
-    flags &= ~1;
+  flags &= ~GOMP_TASK_FLAG_UNTIED;
 #endif
 
   /* If parallel or taskgroup has been cancelled, don't start new tasks.  */
@@ -135,6 +308,11 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
          || (thr->task->taskgroup && thr->task->taskgroup->cancelled)))
     return;
 
+  if ((flags & GOMP_TASK_FLAG_PRIORITY) == 0)
+    priority = 0;
+  else if (priority > gomp_max_task_priority_var)
+    priority = gomp_max_task_priority_var;
+
   if (!if_clause || team == NULL
       || (thr->task && thr->task->final_task)
       || team->task_count > 64 * team->nthreads)
@@ -147,12 +325,15 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
         depend clauses for non-deferred tasks other than this, because
         the parent task is suspended until the child task finishes and thus
         it can't start further child tasks.  */
-      if ((flags & 8) && thr->task && thr->task->depend_hash)
+      if ((flags & GOMP_TASK_FLAG_DEPEND)
+         && thr->task && thr->task->depend_hash)
        gomp_task_maybe_wait_for_dependencies (depend);
 
       gomp_init_task (&task, thr->task, gomp_icv (false));
-      task.kind = GOMP_TASK_IFFALSE;
-      task.final_task = (thr->task && thr->task->final_task) || (flags & 2);
+      task.kind = GOMP_TASK_UNDEFERRED;
+      task.final_task = (thr->task && thr->task->final_task)
+                       || (flags & GOMP_TASK_FLAG_FINAL);
+      task.priority = priority;
       if (thr->task)
        {
          task.in_tied_task = thr->task->in_tied_task;
@@ -178,10 +359,10 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
         child thread, but seeing a stale non-NULL value is not a
         problem.  Once past the task_lock acquisition, this thread
         will see the real value of task.children.  */
-      if (task.children != NULL)
+      if (!priority_queue_empty_p (&task.children_queue, MEMMODEL_RELAXED))
        {
          gomp_mutex_lock (&team->task_lock);
-         gomp_clear_parent (task.children);
+         gomp_clear_parent (&task.children_queue);
          gomp_mutex_unlock (&team->task_lock);
        }
       gomp_end_task ();
@@ -195,7 +376,7 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
       bool do_wake;
       size_t depend_size = 0;
 
-      if (flags & 8)
+      if (flags & GOMP_TASK_FLAG_DEPEND)
        depend_size = ((uintptr_t) depend[0]
                       * sizeof (struct gomp_task_depend_entry));
       task = gomp_malloc (sizeof (*task) + depend_size
@@ -203,7 +384,8 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
       arg = (char *) (((uintptr_t) (task + 1) + depend_size + arg_align - 1)
                      & ~(uintptr_t) (arg_align - 1));
       gomp_init_task (task, parent, gomp_icv (false));
-      task->kind = GOMP_TASK_IFFALSE;
+      task->priority = priority;
+      task->kind = GOMP_TASK_UNDEFERRED;
       task->in_tied_task = parent->in_tied_task;
       task->taskgroup = taskgroup;
       thr->task = task;
@@ -218,7 +400,7 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
       task->kind = GOMP_TASK_WAITING;
       task->fn = fn;
       task->fn_data = arg;
-      task->final_task = (flags & 2) >> 1;
+      task->final_task = (flags & GOMP_TASK_FLAG_FINAL) >> 1;
       gomp_mutex_lock (&team->task_lock);
       /* If parallel or taskgroup has been cancelled, don't start new
         tasks.  */
@@ -235,171 +417,39 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
        taskgroup->num_children++;
       if (depend_size)
        {
-         size_t ndepend = (uintptr_t) depend[0];
-         size_t nout = (uintptr_t) depend[1];
-         size_t i;
-         hash_entry_type ent;
-
-         task->depend_count = ndepend;
-         task->num_dependees = 0;
-         if (parent->depend_hash == NULL)
-           parent->depend_hash
-             = htab_create (2 * ndepend > 12 ? 2 * ndepend : 12);
-         for (i = 0; i < ndepend; i++)
-           {
-             task->depend[i].addr = depend[2 + i];
-             task->depend[i].next = NULL;
-             task->depend[i].prev = NULL;
-             task->depend[i].task = task;
-             task->depend[i].is_in = i >= nout;
-             task->depend[i].redundant = false;
-             task->depend[i].redundant_out = false;
-
-             hash_entry_type *slot
-               = htab_find_slot (&parent->depend_hash, &task->depend[i],
-                                 INSERT);
-             hash_entry_type out = NULL, last = NULL;
-             if (*slot)
-               {
-                 /* If multiple depends on the same task are the
-                    same, all but the first one are redundant.
-                    As inout/out come first, if any of them is
-                    inout/out, it will win, which is the right
-                    semantics.  */
-                 if ((*slot)->task == task)
-                   {
-                     task->depend[i].redundant = true;
-                     continue;
-                   }
-                 for (ent = *slot; ent; ent = ent->next)
-                   {
-                     if (ent->redundant_out)
-                       break;
-
-                     last = ent;
-
-                     /* depend(in:...) doesn't depend on earlier
-                        depend(in:...).  */
-                     if (i >= nout && ent->is_in)
-                       continue;
-
-                     if (!ent->is_in)
-                       out = ent;
-
-                     struct gomp_task *tsk = ent->task;
-                     if (tsk->dependers == NULL)
-                       {
-                         tsk->dependers
-                           = gomp_malloc (sizeof (struct gomp_dependers_vec)
-                                          + 6 * sizeof (struct gomp_task *));
-                         tsk->dependers->n_elem = 1;
-                         tsk->dependers->allocated = 6;
-                         tsk->dependers->elem[0] = task;
-                         task->num_dependees++;
-                         continue;
-                       }
-                     /* We already have some other dependency on tsk
-                        from earlier depend clause.  */
-                     else if (tsk->dependers->n_elem
-                              && (tsk->dependers->elem[tsk->dependers->n_elem
-                                                       - 1]
-                                  == task))
-                       continue;
-                     else if (tsk->dependers->n_elem
-                              == tsk->dependers->allocated)
-                       {
-                         tsk->dependers->allocated
-                           = tsk->dependers->allocated * 2 + 2;
-                         tsk->dependers
-                           = gomp_realloc (tsk->dependers,
-                                           sizeof (struct gomp_dependers_vec)
-                                           + (tsk->dependers->allocated
-                                              * sizeof (struct gomp_task *)));
-                       }
-                     tsk->dependers->elem[tsk->dependers->n_elem++] = task;
-                     task->num_dependees++;
-                   }
-                 task->depend[i].next = *slot;
-                 (*slot)->prev = &task->depend[i];
-               }
-             *slot = &task->depend[i];
-
-             /* There is no need to store more than one depend({,in}out:)
-                task per address in the hash table chain for the purpose
-                of creation of deferred tasks, because each out
-                depends on all earlier outs, thus it is enough to record
-                just the last depend({,in}out:).  For depend(in:), we need
-                to keep all of the previous ones not terminated yet, because
-                a later depend({,in}out:) might need to depend on all of
-                them.  So, if the new task's clause is depend({,in}out:),
-                we know there is at most one other depend({,in}out:) clause
-                in the list (out).  For non-deferred tasks we want to see
-                all outs, so they are moved to the end of the chain,
-                after first redundant_out entry all following entries
-                should be redundant_out.  */
-             if (!task->depend[i].is_in && out)
-               {
-                 if (out != last)
-                   {
-                     out->next->prev = out->prev;
-                     out->prev->next = out->next;
-                     out->next = last->next;
-                     out->prev = last;
-                     last->next = out;
-                     if (out->next)
-                       out->next->prev = out;
-                   }
-                 out->redundant_out = true;
-               }
-           }
+         gomp_task_handle_depend (task, parent, depend);
          if (task->num_dependees)
            {
+             /* Tasks that depend on other tasks are not put into the
+                various waiting queues, so we are done for now.  Said
+                tasks are instead put into the queues via
+                gomp_task_run_post_handle_dependers() after their
+                dependencies have been satisfied.  After which, they
+                can be picked up by the various scheduling
+                points.  */
              gomp_mutex_unlock (&team->task_lock);
              return;
            }
        }
-      if (parent->children)
-       {
-         task->next_child = parent->children;
-         task->prev_child = parent->children->prev_child;
-         task->next_child->prev_child = task;
-         task->prev_child->next_child = task;
-       }
-      else
-       {
-         task->next_child = task;
-         task->prev_child = task;
-       }
-      parent->children = task;
+
+      priority_queue_insert (PQ_CHILDREN, &parent->children_queue,
+                            task, priority,
+                            PRIORITY_INSERT_BEGIN,
+                            /*adjust_parent_depends_on=*/false,
+                            task->parent_depends_on);
       if (taskgroup)
-       {
-         if (taskgroup->children)
-           {
-             task->next_taskgroup = taskgroup->children;
-             task->prev_taskgroup = taskgroup->children->prev_taskgroup;
-             task->next_taskgroup->prev_taskgroup = task;
-             task->prev_taskgroup->next_taskgroup = task;
-           }
-         else
-           {
-             task->next_taskgroup = task;
-             task->prev_taskgroup = task;
-           }
-         taskgroup->children = task;
-       }
-      if (team->task_queue)
-       {
-         task->next_queue = team->task_queue;
-         task->prev_queue = team->task_queue->prev_queue;
-         task->next_queue->prev_queue = task;
-         task->prev_queue->next_queue = task;
-       }
-      else
-       {
-         task->next_queue = task;
-         task->prev_queue = task;
-         team->task_queue = task;
-       }
+       priority_queue_insert (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
+                              task, priority,
+                              PRIORITY_INSERT_BEGIN,
+                              /*adjust_parent_depends_on=*/false,
+                              task->parent_depends_on);
+
+      priority_queue_insert (PQ_TEAM, &team->task_queue,
+                            task, priority,
+                            PRIORITY_INSERT_END,
+                            /*adjust_parent_depends_on=*/false,
+                            task->parent_depends_on);
+
       ++team->task_count;
       ++team->task_queued_count;
       gomp_team_barrier_set_task_pending (&team->barrier);
@@ -411,36 +461,529 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
     }
 }
 
-static inline bool
-gomp_task_run_pre (struct gomp_task *child_task, struct gomp_task *parent,
-                  struct gomp_taskgroup *taskgroup, struct gomp_team *team)
+ialias (GOMP_taskgroup_start)
+ialias (GOMP_taskgroup_end)
+
+#define TYPE long
+#define UTYPE unsigned long
+#define TYPE_is_long 1
+#include "taskloop.c"
+#undef TYPE
+#undef UTYPE
+#undef TYPE_is_long
+
+#define TYPE unsigned long long
+#define UTYPE TYPE
+#define GOMP_taskloop GOMP_taskloop_ull
+#include "taskloop.c"
+#undef TYPE
+#undef UTYPE
+#undef GOMP_taskloop
+
+static void inline
+priority_queue_move_task_first (enum priority_queue_type type,
+                               struct priority_queue *head,
+                               struct gomp_task *task)
 {
+#if _LIBGOMP_CHECKING_
+  if (!priority_queue_task_in_queue_p (type, head, task))
+    gomp_fatal ("Attempt to move first missing task %p", task);
+#endif
+  struct priority_list *list;
+  if (priority_queue_multi_p (head))
+    {
+      list = priority_queue_lookup_priority (head, task->priority);
+#if _LIBGOMP_CHECKING_
+      if (!list)
+       gomp_fatal ("Unable to find priority %d", task->priority);
+#endif
+    }
+  else
+    list = &head->l;
+  priority_list_remove (list, task_to_priority_node (type, task), 0);
+  priority_list_insert (type, list, task, task->priority,
+                       PRIORITY_INSERT_BEGIN, type == PQ_CHILDREN,
+                       task->parent_depends_on);
+}
+
+/* Actual body of GOMP_PLUGIN_target_task_completion that is executed
+   with team->task_lock held, or is executed in the thread that called
+   gomp_target_task_fn if GOMP_PLUGIN_target_task_completion has been
+   run before it acquires team->task_lock.  */
+
+static void
+gomp_target_task_completion (struct gomp_team *team, struct gomp_task *task)
+{
+  struct gomp_task *parent = task->parent;
   if (parent)
+    priority_queue_move_task_first (PQ_CHILDREN, &parent->children_queue,
+                                   task);
+
+  struct gomp_taskgroup *taskgroup = task->taskgroup;
+  if (taskgroup)
+    priority_queue_move_task_first (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
+                                   task);
+
+  priority_queue_insert (PQ_TEAM, &team->task_queue, task, task->priority,
+                        PRIORITY_INSERT_BEGIN, false,
+                        task->parent_depends_on);
+  task->kind = GOMP_TASK_WAITING;
+  if (parent && parent->taskwait)
     {
-      if (parent->children == child_task)
-       parent->children = child_task->next_child;
-      if (__builtin_expect (child_task->parent_depends_on, 0)
-         && parent->taskwait->last_parent_depends_on == child_task)
+      if (parent->taskwait->in_taskwait)
        {
-         if (child_task->prev_child->kind == GOMP_TASK_WAITING
-             && child_task->prev_child->parent_depends_on)
-           parent->taskwait->last_parent_depends_on = child_task->prev_child;
-         else
-           parent->taskwait->last_parent_depends_on = NULL;
+         /* One more task has had its dependencies met.
+            Inform any waiters.  */
+         parent->taskwait->in_taskwait = false;
+         gomp_sem_post (&parent->taskwait->taskwait_sem);
        }
+      else if (parent->taskwait->in_depend_wait)
+       {
+         /* One more task has had its dependencies met.
+            Inform any waiters.  */
+         parent->taskwait->in_depend_wait = false;
+         gomp_sem_post (&parent->taskwait->taskwait_sem);
+       }
+    }
+  if (taskgroup && taskgroup->in_taskgroup_wait)
+    {
+      /* One more task has had its dependencies met.
+        Inform any waiters.  */
+      taskgroup->in_taskgroup_wait = false;
+      gomp_sem_post (&taskgroup->taskgroup_sem);
     }
-  if (taskgroup && taskgroup->children == child_task)
-    taskgroup->children = child_task->next_taskgroup;
-  child_task->prev_queue->next_queue = child_task->next_queue;
-  child_task->next_queue->prev_queue = child_task->prev_queue;
-  if (team->task_queue == child_task)
+
+  ++team->task_queued_count;
+  gomp_team_barrier_set_task_pending (&team->barrier);
+  /* I'm afraid this can't be done after releasing team->task_lock,
+     as gomp_target_task_completion is run from unrelated thread and
+     therefore in between gomp_mutex_unlock and gomp_team_barrier_wake
+     the team could be gone already.  */
+  if (team->nthreads > team->task_running_count)
+    gomp_team_barrier_wake (&team->barrier, 1);
+}
+
+/* Signal that a target task TTASK has completed the asynchronously
+   running phase and should be requeued as a task to handle the
+   variable unmapping.  */
+
+void
+GOMP_PLUGIN_target_task_completion (void *data)
+{
+  struct gomp_target_task *ttask = (struct gomp_target_task *) data;
+  struct gomp_task *task = ttask->task;
+  struct gomp_team *team = ttask->team;
+
+  gomp_mutex_lock (&team->task_lock);
+  if (ttask->state == GOMP_TARGET_TASK_READY_TO_RUN)
     {
-      if (child_task->next_queue != child_task)
-       team->task_queue = child_task->next_queue;
+      ttask->state = GOMP_TARGET_TASK_FINISHED;
+      gomp_mutex_unlock (&team->task_lock);
+      return;
+    }
+  ttask->state = GOMP_TARGET_TASK_FINISHED;
+  gomp_target_task_completion (team, task);
+  gomp_mutex_unlock (&team->task_lock);
+}
+
+static void gomp_task_run_post_handle_depend_hash (struct gomp_task *);
+
+/* Called for nowait target tasks.  */
+
+bool
+gomp_create_target_task (struct gomp_device_descr *devicep,
+                        void (*fn) (void *), size_t mapnum, void **hostaddrs,
+                        size_t *sizes, unsigned short *kinds,
+                        unsigned int flags, void **depend, void **args,
+                        enum gomp_target_task_state state)
+{
+  struct gomp_thread *thr = gomp_thread ();
+  struct gomp_team *team = thr->ts.team;
+
+  /* If parallel or taskgroup has been cancelled, don't start new tasks.  */
+  if (team
+      && (gomp_team_barrier_cancelled (&team->barrier)
+         || (thr->task->taskgroup && thr->task->taskgroup->cancelled)))
+    return true;
+
+  struct gomp_target_task *ttask;
+  struct gomp_task *task;
+  struct gomp_task *parent = thr->task;
+  struct gomp_taskgroup *taskgroup = parent->taskgroup;
+  bool do_wake;
+  size_t depend_size = 0;
+  uintptr_t depend_cnt = 0;
+  size_t tgt_align = 0, tgt_size = 0;
+
+  if (depend != NULL)
+    {
+      depend_cnt = (uintptr_t) depend[0];
+      depend_size = depend_cnt * sizeof (struct gomp_task_depend_entry);
+    }
+  if (fn)
+    {
+      /* GOMP_MAP_FIRSTPRIVATE need to be copied first, as they are
+        firstprivate on the target task.  */
+      size_t i;
+      for (i = 0; i < mapnum; i++)
+       if ((kinds[i] & 0xff) == GOMP_MAP_FIRSTPRIVATE)
+         {
+           size_t align = (size_t) 1 << (kinds[i] >> 8);
+           if (tgt_align < align)
+             tgt_align = align;
+           tgt_size = (tgt_size + align - 1) & ~(align - 1);
+           tgt_size += sizes[i];
+         }
+      if (tgt_align)
+       tgt_size += tgt_align - 1;
       else
-       team->task_queue = NULL;
+       tgt_size = 0;
+    }
+
+  task = gomp_malloc (sizeof (*task) + depend_size
+                     + sizeof (*ttask)
+                     + mapnum * (sizeof (void *) + sizeof (size_t)
+                                 + sizeof (unsigned short))
+                     + tgt_size);
+  gomp_init_task (task, parent, gomp_icv (false));
+  task->priority = 0;
+  task->kind = GOMP_TASK_WAITING;
+  task->in_tied_task = parent->in_tied_task;
+  task->taskgroup = taskgroup;
+  ttask = (struct gomp_target_task *) &task->depend[depend_cnt];
+  ttask->devicep = devicep;
+  ttask->fn = fn;
+  ttask->mapnum = mapnum;
+  ttask->args = args;
+  memcpy (ttask->hostaddrs, hostaddrs, mapnum * sizeof (void *));
+  ttask->sizes = (size_t *) &ttask->hostaddrs[mapnum];
+  memcpy (ttask->sizes, sizes, mapnum * sizeof (size_t));
+  ttask->kinds = (unsigned short *) &ttask->sizes[mapnum];
+  memcpy (ttask->kinds, kinds, mapnum * sizeof (unsigned short));
+  if (tgt_align)
+    {
+      char *tgt = (char *) &ttask->kinds[mapnum];
+      size_t i;
+      uintptr_t al = (uintptr_t) tgt & (tgt_align - 1);
+      if (al)
+       tgt += tgt_align - al;
+      tgt_size = 0;
+      for (i = 0; i < mapnum; i++)
+       if ((kinds[i] & 0xff) == GOMP_MAP_FIRSTPRIVATE)
+         {
+           size_t align = (size_t) 1 << (kinds[i] >> 8);
+           tgt_size = (tgt_size + align - 1) & ~(align - 1);
+           memcpy (tgt + tgt_size, hostaddrs[i], sizes[i]);
+           ttask->hostaddrs[i] = tgt + tgt_size;
+           tgt_size = tgt_size + sizes[i];
+         }
     }
+  ttask->flags = flags;
+  ttask->state = state;
+  ttask->task = task;
+  ttask->team = team;
+  task->fn = NULL;
+  task->fn_data = ttask;
+  task->final_task = 0;
+  gomp_mutex_lock (&team->task_lock);
+  /* If parallel or taskgroup has been cancelled, don't start new tasks.  */
+  if (__builtin_expect (gomp_team_barrier_cancelled (&team->barrier)
+                       || (taskgroup && taskgroup->cancelled), 0))
+    {
+      gomp_mutex_unlock (&team->task_lock);
+      gomp_finish_task (task);
+      free (task);
+      return true;
+    }
+  if (depend_size)
+    {
+      gomp_task_handle_depend (task, parent, depend);
+      if (task->num_dependees)
+       {
+         if (taskgroup)
+           taskgroup->num_children++;
+         gomp_mutex_unlock (&team->task_lock);
+         return true;
+       }
+    }
+  if (state == GOMP_TARGET_TASK_DATA)
+    {
+      gomp_task_run_post_handle_depend_hash (task);
+      gomp_mutex_unlock (&team->task_lock);
+      gomp_finish_task (task);
+      free (task);
+      return false;
+    }
+  if (taskgroup)
+    taskgroup->num_children++;
+  /* For async offloading, if we don't need to wait for dependencies,
+     run the gomp_target_task_fn right away, essentially schedule the
+     mapping part of the task in the current thread.  */
+  if (devicep != NULL
+      && (devicep->capabilities & GOMP_OFFLOAD_CAP_OPENMP_400))
+    {
+      priority_queue_insert (PQ_CHILDREN, &parent->children_queue, task, 0,
+                            PRIORITY_INSERT_END,
+                            /*adjust_parent_depends_on=*/false,
+                            task->parent_depends_on);
+      if (taskgroup)
+       priority_queue_insert (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
+                              task, 0, PRIORITY_INSERT_END,
+                              /*adjust_parent_depends_on=*/false,
+                              task->parent_depends_on);
+      task->pnode[PQ_TEAM].next = NULL;
+      task->pnode[PQ_TEAM].prev = NULL;
+      task->kind = GOMP_TASK_TIED;
+      ++team->task_count;
+      gomp_mutex_unlock (&team->task_lock);
+
+      thr->task = task;
+      gomp_target_task_fn (task->fn_data);
+      thr->task = parent;
+
+      gomp_mutex_lock (&team->task_lock);
+      task->kind = GOMP_TASK_ASYNC_RUNNING;
+      /* If GOMP_PLUGIN_target_task_completion has run already
+        in between gomp_target_task_fn and the mutex lock,
+        perform the requeuing here.  */
+      if (ttask->state == GOMP_TARGET_TASK_FINISHED)
+       gomp_target_task_completion (team, task);
+      else
+       ttask->state = GOMP_TARGET_TASK_RUNNING;
+      gomp_mutex_unlock (&team->task_lock);
+      return true;
+    }
+  priority_queue_insert (PQ_CHILDREN, &parent->children_queue, task, 0,
+                        PRIORITY_INSERT_BEGIN,
+                        /*adjust_parent_depends_on=*/false,
+                        task->parent_depends_on);
+  if (taskgroup)
+    priority_queue_insert (PQ_TASKGROUP, &taskgroup->taskgroup_queue, task, 0,
+                          PRIORITY_INSERT_BEGIN,
+                          /*adjust_parent_depends_on=*/false,
+                          task->parent_depends_on);
+  priority_queue_insert (PQ_TEAM, &team->task_queue, task, 0,
+                        PRIORITY_INSERT_END,
+                        /*adjust_parent_depends_on=*/false,
+                        task->parent_depends_on);
+  ++team->task_count;
+  ++team->task_queued_count;
+  gomp_team_barrier_set_task_pending (&team->barrier);
+  do_wake = team->task_running_count + !parent->in_tied_task
+           < team->nthreads;
+  gomp_mutex_unlock (&team->task_lock);
+  if (do_wake)
+    gomp_team_barrier_wake (&team->barrier, 1);
+  return true;
+}
+
+/* Given a parent_depends_on task in LIST, move it to the front of its
+   priority so it is run as soon as possible.
+
+   Care is taken to update the list's LAST_PARENT_DEPENDS_ON field.
+
+   We rearrange the queue such that all parent_depends_on tasks are
+   first, and last_parent_depends_on points to the last such task we
+   rearranged.  For example, given the following tasks in a queue
+   where PD[123] are the parent_depends_on tasks:
+
+       task->children
+       |
+       V
+       C1 -> C2 -> C3 -> PD1 -> PD2 -> PD3 -> C4
+
+       We rearrange such that:
+
+       task->children
+       |              +--- last_parent_depends_on
+       |              |
+       V              V
+       PD1 -> PD2 -> PD3 -> C1 -> C2 -> C3 -> C4.  */
+
+static void inline
+priority_list_upgrade_task (struct priority_list *list,
+                           struct priority_node *node)
+{
+  struct priority_node *last_parent_depends_on
+    = list->last_parent_depends_on;
+  if (last_parent_depends_on)
+    {
+      node->prev->next = node->next;
+      node->next->prev = node->prev;
+      node->prev = last_parent_depends_on;
+      node->next = last_parent_depends_on->next;
+      node->prev->next = node;
+      node->next->prev = node;
+    }
+  else if (node != list->tasks)
+    {
+      node->prev->next = node->next;
+      node->next->prev = node->prev;
+      node->prev = list->tasks->prev;
+      node->next = list->tasks;
+      list->tasks = node;
+      node->prev->next = node;
+      node->next->prev = node;
+    }
+  list->last_parent_depends_on = node;
+}
+
+/* Given a parent_depends_on TASK in its parent's children_queue, move
+   it to the front of its priority so it is run as soon as possible.
+
+   PARENT is passed as an optimization.
+
+   (This function could be defined in priority_queue.c, but we want it
+   inlined, and putting it in priority_queue.h is not an option, given
+   that gomp_task has not been properly defined at that point).  */
+
+static void inline
+priority_queue_upgrade_task (struct gomp_task *task,
+                            struct gomp_task *parent)
+{
+  struct priority_queue *head = &parent->children_queue;
+  struct priority_node *node = &task->pnode[PQ_CHILDREN];
+#if _LIBGOMP_CHECKING_
+  if (!task->parent_depends_on)
+    gomp_fatal ("priority_queue_upgrade_task: task must be a "
+               "parent_depends_on task");
+  if (!priority_queue_task_in_queue_p (PQ_CHILDREN, head, task))
+    gomp_fatal ("priority_queue_upgrade_task: cannot find task=%p", task);
+#endif
+  if (priority_queue_multi_p (head))
+    {
+      struct priority_list *list
+       = priority_queue_lookup_priority (head, task->priority);
+      priority_list_upgrade_task (list, node);
+    }
+  else
+    priority_list_upgrade_task (&head->l, node);
+}
+
+/* Given a CHILD_TASK in LIST that is about to be executed, move it out of
+   the way in LIST so that other tasks can be considered for
+   execution.  LIST contains tasks of type TYPE.
+
+   Care is taken to update the queue's LAST_PARENT_DEPENDS_ON field
+   if applicable.  */
+
+static void inline
+priority_list_downgrade_task (enum priority_queue_type type,
+                             struct priority_list *list,
+                             struct gomp_task *child_task)
+{
+  struct priority_node *node = task_to_priority_node (type, child_task);
+  if (list->tasks == node)
+    list->tasks = node->next;
+  else if (node->next != list->tasks)
+    {
+      /* The task in NODE is about to become TIED and TIED tasks
+        cannot come before WAITING tasks.  If we're about to
+        leave the queue in such an indeterminate state, rewire
+        things appropriately.  However, a TIED task at the end is
+        perfectly fine.  */
+      struct gomp_task *next_task = priority_node_to_task (type, node->next);
+      if (next_task->kind == GOMP_TASK_WAITING)
+       {
+         /* Remove from list.  */
+         node->prev->next = node->next;
+         node->next->prev = node->prev;
+         /* Rewire at the end.  */
+         node->next = list->tasks;
+         node->prev = list->tasks->prev;
+         list->tasks->prev->next = node;
+         list->tasks->prev = node;
+       }
+    }
+
+  /* If the current task is the last_parent_depends_on for its
+     priority, adjust last_parent_depends_on appropriately.  */
+  if (__builtin_expect (child_task->parent_depends_on, 0)
+      && list->last_parent_depends_on == node)
+    {
+      struct gomp_task *prev_child = priority_node_to_task (type, node->prev);
+      if (node->prev != node
+         && prev_child->kind == GOMP_TASK_WAITING
+         && prev_child->parent_depends_on)
+       list->last_parent_depends_on = node->prev;
+      else
+       {
+         /* There are no more parent_depends_on entries waiting
+            to run, clear the list.  */
+         list->last_parent_depends_on = NULL;
+       }
+    }
+}
+
+/* Given a TASK in HEAD that is about to be executed, move it out of
+   the way so that other tasks can be considered for execution.  HEAD
+   contains tasks of type TYPE.
+
+   Care is taken to update the queue's LAST_PARENT_DEPENDS_ON field
+   if applicable.
+
+   (This function could be defined in priority_queue.c, but we want it
+   inlined, and putting it in priority_queue.h is not an option, given
+   that gomp_task has not been properly defined at that point).  */
+
+static void inline
+priority_queue_downgrade_task (enum priority_queue_type type,
+                              struct priority_queue *head,
+                              struct gomp_task *task)
+{
+#if _LIBGOMP_CHECKING_
+  if (!priority_queue_task_in_queue_p (type, head, task))
+    gomp_fatal ("Attempt to downgrade missing task %p", task);
+#endif
+  if (priority_queue_multi_p (head))
+    {
+      struct priority_list *list
+       = priority_queue_lookup_priority (head, task->priority);
+      priority_list_downgrade_task (type, list, task);
+    }
+  else
+    priority_list_downgrade_task (type, &head->l, task);
+}
+
+/* Setup CHILD_TASK to execute.  This is done by setting the task to
+   TIED, and updating all relevant queues so that CHILD_TASK is no
+   longer chosen for scheduling.  Also, remove CHILD_TASK from the
+   overall team task queue entirely.
+
+   Return TRUE if task or its containing taskgroup has been
+   cancelled.  */
+
+static inline bool
+gomp_task_run_pre (struct gomp_task *child_task, struct gomp_task *parent,
+                  struct gomp_team *team)
+{
+#if _LIBGOMP_CHECKING_
+  if (child_task->parent)
+    priority_queue_verify (PQ_CHILDREN,
+                          &child_task->parent->children_queue, true);
+  if (child_task->taskgroup)
+    priority_queue_verify (PQ_TASKGROUP,
+                          &child_task->taskgroup->taskgroup_queue, false);
+  priority_queue_verify (PQ_TEAM, &team->task_queue, false);
+#endif
+
+  /* Task is about to go tied, move it out of the way.  */
+  if (parent)
+    priority_queue_downgrade_task (PQ_CHILDREN, &parent->children_queue,
+                                  child_task);
+
+  /* Task is about to go tied, move it out of the way.  */
+  struct gomp_taskgroup *taskgroup = child_task->taskgroup;
+  if (taskgroup)
+    priority_queue_downgrade_task (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
+                                  child_task);
+
+  priority_queue_remove (PQ_TEAM, &team->task_queue, child_task,
+                        MEMMODEL_RELAXED);
+  child_task->pnode[PQ_TEAM].next = NULL;
+  child_task->pnode[PQ_TEAM].prev = NULL;
   child_task->kind = GOMP_TASK_TIED;
+
   if (--team->task_queued_count == 0)
     gomp_team_barrier_clear_task_pending (&team->barrier);
   if ((gomp_team_barrier_cancelled (&team->barrier)
@@ -478,6 +1021,14 @@ gomp_task_run_post_handle_depend_hash (struct gomp_task *child_task)
       }
 }
 
+/* After a CHILD_TASK has been run, adjust the dependency queue for
+   each task that depends on CHILD_TASK, to record the fact that there
+   is one less dependency to worry about.  If a task that depended on
+   CHILD_TASK now has no dependencies, place it in the various queues
+   so it gets scheduled to run.
+
+   TEAM is the team to which CHILD_TASK belongs to.  */
+
 static size_t
 gomp_task_run_post_handle_dependers (struct gomp_task *child_task,
                                     struct gomp_team *team)
@@ -487,91 +1038,60 @@ gomp_task_run_post_handle_dependers (struct gomp_task *child_task,
   for (i = 0; i < count; i++)
     {
       struct gomp_task *task = child_task->dependers->elem[i];
+
+      /* CHILD_TASK satisfies a dependency for TASK.  Keep track of
+        TASK's remaining dependencies.  Once TASK has no other
+        depenencies, put it into the various queues so it will get
+        scheduled for execution.  */
       if (--task->num_dependees != 0)
        continue;
 
       struct gomp_taskgroup *taskgroup = task->taskgroup;
       if (parent)
        {
-         if (parent->children)
-           {
-             /* If parent is in gomp_task_maybe_wait_for_dependencies
-                and it doesn't need to wait for this task, put it after
-                all ready to run tasks it needs to wait for.  */
-             if (parent->taskwait && parent->taskwait->last_parent_depends_on
-                 && !task->parent_depends_on)
-               {
-                 struct gomp_task *last_parent_depends_on
-                   = parent->taskwait->last_parent_depends_on;
-                 task->next_child = last_parent_depends_on->next_child;
-                 task->prev_child = last_parent_depends_on;
-               }
-             else
-               {
-                 task->next_child = parent->children;
-                 task->prev_child = parent->children->prev_child;
-                 parent->children = task;
-               }
-             task->next_child->prev_child = task;
-             task->prev_child->next_child = task;
-           }
-         else
-           {
-             task->next_child = task;
-             task->prev_child = task;
-             parent->children = task;
-           }
+         priority_queue_insert (PQ_CHILDREN, &parent->children_queue,
+                                task, task->priority,
+                                PRIORITY_INSERT_BEGIN,
+                                /*adjust_parent_depends_on=*/true,
+                                task->parent_depends_on);
          if (parent->taskwait)
            {
              if (parent->taskwait->in_taskwait)
                {
+                 /* One more task has had its dependencies met.
+                    Inform any waiters.  */
                  parent->taskwait->in_taskwait = false;
                  gomp_sem_post (&parent->taskwait->taskwait_sem);
                }
              else if (parent->taskwait->in_depend_wait)
                {
+                 /* One more task has had its dependencies met.
+                    Inform any waiters.  */
                  parent->taskwait->in_depend_wait = false;
                  gomp_sem_post (&parent->taskwait->taskwait_sem);
                }
-             if (parent->taskwait->last_parent_depends_on == NULL
-                 && task->parent_depends_on)
-               parent->taskwait->last_parent_depends_on = task;
            }
        }
       if (taskgroup)
        {
-         if (taskgroup->children)
-           {
-             task->next_taskgroup = taskgroup->children;
-             task->prev_taskgroup = taskgroup->children->prev_taskgroup;
-             task->next_taskgroup->prev_taskgroup = task;
-             task->prev_taskgroup->next_taskgroup = task;
-           }
-         else
-           {
-             task->next_taskgroup = task;
-             task->prev_taskgroup = task;
-           }
-         taskgroup->children = task;
+         priority_queue_insert (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
+                                task, task->priority,
+                                PRIORITY_INSERT_BEGIN,
+                                /*adjust_parent_depends_on=*/false,
+                                task->parent_depends_on);
          if (taskgroup->in_taskgroup_wait)
            {
+             /* One more task has had its dependencies met.
+                Inform any waiters.  */
              taskgroup->in_taskgroup_wait = false;
              gomp_sem_post (&taskgroup->taskgroup_sem);
            }
        }
-      if (team->task_queue)
-       {
-         task->next_queue = team->task_queue;
-         task->prev_queue = team->task_queue->prev_queue;
-         task->next_queue->prev_queue = task;
-         task->prev_queue->next_queue = task;
-       }
-      else
-       {
-         task->next_queue = task;
-         task->prev_queue = task;
-         team->task_queue = task;
-       }
+      priority_queue_insert (PQ_TEAM, &team->task_queue,
+                            task, task->priority,
+                            PRIORITY_INSERT_END,
+                            /*adjust_parent_depends_on=*/false,
+                            task->parent_depends_on);
       ++team->task_count;
       ++team->task_queued_count;
       ++ret;
@@ -601,12 +1121,18 @@ gomp_task_run_post_handle_depend (struct gomp_task *child_task,
   return gomp_task_run_post_handle_dependers (child_task, team);
 }
 
+/* Remove CHILD_TASK from its parent.  */
+
 static inline void
 gomp_task_run_post_remove_parent (struct gomp_task *child_task)
 {
   struct gomp_task *parent = child_task->parent;
   if (parent == NULL)
     return;
+
+  /* If this was the last task the parent was depending on,
+     synchronize with gomp_task_maybe_wait_for_dependencies so it can
+     clean up and return.  */
   if (__builtin_expect (child_task->parent_depends_on, 0)
       && --parent->taskwait->n_depend == 0
       && parent->taskwait->in_depend_wait)
@@ -614,36 +1140,31 @@ gomp_task_run_post_remove_parent (struct gomp_task *child_task)
       parent->taskwait->in_depend_wait = false;
       gomp_sem_post (&parent->taskwait->taskwait_sem);
     }
-  child_task->prev_child->next_child = child_task->next_child;
-  child_task->next_child->prev_child = child_task->prev_child;
-  if (parent->children != child_task)
-    return;
-  if (child_task->next_child != child_task)
-    parent->children = child_task->next_child;
-  else
+
+  if (priority_queue_remove (PQ_CHILDREN, &parent->children_queue,
+                            child_task, MEMMODEL_RELEASE)
+      && parent->taskwait && parent->taskwait->in_taskwait)
     {
-      /* We access task->children in GOMP_taskwait
-        outside of the task lock mutex region, so
-        need a release barrier here to ensure memory
-        written by child_task->fn above is flushed
-        before the NULL is written.  */
-      __atomic_store_n (&parent->children, NULL, MEMMODEL_RELEASE);
-      if (parent->taskwait && parent->taskwait->in_taskwait)
-       {
-         parent->taskwait->in_taskwait = false;
-         gomp_sem_post (&parent->taskwait->taskwait_sem);
-       }
+      parent->taskwait->in_taskwait = false;
+      gomp_sem_post (&parent->taskwait->taskwait_sem);
     }
+  child_task->pnode[PQ_CHILDREN].next = NULL;
+  child_task->pnode[PQ_CHILDREN].prev = NULL;
 }
 
+/* Remove CHILD_TASK from its taskgroup.  */
+
 static inline void
 gomp_task_run_post_remove_taskgroup (struct gomp_task *child_task)
 {
   struct gomp_taskgroup *taskgroup = child_task->taskgroup;
   if (taskgroup == NULL)
     return;
-  child_task->prev_taskgroup->next_taskgroup = child_task->next_taskgroup;
-  child_task->next_taskgroup->prev_taskgroup = child_task->prev_taskgroup;
+  bool empty = priority_queue_remove (PQ_TASKGROUP,
+                                     &taskgroup->taskgroup_queue,
+                                     child_task, MEMMODEL_RELAXED);
+  child_task->pnode[PQ_TASKGROUP].next = NULL;
+  child_task->pnode[PQ_TASKGROUP].prev = NULL;
   if (taskgroup->num_children > 1)
     --taskgroup->num_children;
   else
@@ -655,18 +1176,10 @@ gomp_task_run_post_remove_taskgroup (struct gomp_task *child_task)
         before the NULL is written.  */
       __atomic_store_n (&taskgroup->num_children, 0, MEMMODEL_RELEASE);
     }
-  if (taskgroup->children != child_task)
-    return;
-  if (child_task->next_taskgroup != child_task)
-    taskgroup->children = child_task->next_taskgroup;
-  else
+  if (empty && taskgroup->in_taskgroup_wait)
     {
-      taskgroup->children = NULL;
-      if (taskgroup->in_taskgroup_wait)
-       {
-         taskgroup->in_taskgroup_wait = false;
-         gomp_sem_post (&taskgroup->taskgroup_sem);
-       }
+      taskgroup->in_taskgroup_wait = false;
+      gomp_sem_post (&taskgroup->taskgroup_sem);
     }
 }
 
@@ -696,11 +1209,15 @@ gomp_barrier_handle_tasks (gomp_barrier_state_t state)
   while (1)
     {
       bool cancelled = false;
-      if (team->task_queue != NULL)
+      if (!priority_queue_empty_p (&team->task_queue, MEMMODEL_RELAXED))
        {
-         child_task = team->task_queue;
+         bool ignored;
+         child_task
+           = priority_queue_next_task (PQ_TEAM, &team->task_queue,
+                                       PQ_IGNORED, NULL,
+                                       &ignored);
          cancelled = gomp_task_run_pre (child_task, child_task->parent,
-                                        child_task->taskgroup, team);
+                                        team);
          if (__builtin_expect (cancelled, 0))
            {
              if (to_free)
@@ -729,7 +1246,29 @@ gomp_barrier_handle_tasks (gomp_barrier_state_t state)
       if (child_task)
        {
          thr->task = child_task;
-         child_task->fn (child_task->fn_data);
+         if (__builtin_expect (child_task->fn == NULL, 0))
+           {
+             if (gomp_target_task_fn (child_task->fn_data))
+               {
+                 thr->task = task;
+                 gomp_mutex_lock (&team->task_lock);
+                 child_task->kind = GOMP_TASK_ASYNC_RUNNING;
+                 team->task_running_count--;
+                 struct gomp_target_task *ttask
+                   = (struct gomp_target_task *) child_task->fn_data;
+                 /* If GOMP_PLUGIN_target_task_completion has run already
+                    in between gomp_target_task_fn and the mutex lock,
+                    perform the requeuing here.  */
+                 if (ttask->state == GOMP_TARGET_TASK_FINISHED)
+                   gomp_target_task_completion (team, child_task);
+                 else
+                   ttask->state = GOMP_TARGET_TASK_RUNNING;
+                 child_task = NULL;
+                 continue;
+               }
+           }
+         else
+           child_task->fn (child_task->fn_data);
          thr->task = task;
        }
       else
@@ -741,7 +1280,7 @@ gomp_barrier_handle_tasks (gomp_barrier_state_t state)
          size_t new_tasks
            = gomp_task_run_post_handle_depend (child_task, team);
          gomp_task_run_post_remove_parent (child_task);
-         gomp_clear_parent (child_task->children);
+         gomp_clear_parent (&child_task->children_queue);
          gomp_task_run_post_remove_taskgroup (child_task);
          to_free = child_task;
          child_task = NULL;
@@ -765,7 +1304,9 @@ gomp_barrier_handle_tasks (gomp_barrier_state_t state)
     }
 }
 
-/* Called when encountering a taskwait directive.  */
+/* Called when encountering a taskwait directive.
+
+   Wait for all children of the current task.  */
 
 void
 GOMP_taskwait (void)
@@ -785,15 +1326,16 @@ GOMP_taskwait (void)
      child thread task work function are seen before we exit from
      GOMP_taskwait.  */
   if (task == NULL
-      || __atomic_load_n (&task->children, MEMMODEL_ACQUIRE) == NULL)
+      || priority_queue_empty_p (&task->children_queue, MEMMODEL_ACQUIRE))
     return;
 
   memset (&taskwait, 0, sizeof (taskwait));
+  bool child_q = false;
   gomp_mutex_lock (&team->task_lock);
   while (1)
     {
       bool cancelled = false;
-      if (task->children == NULL)
+      if (priority_queue_empty_p (&task->children_queue, MEMMODEL_RELAXED))
        {
          bool destroy_taskwait = task->taskwait != NULL;
          task->taskwait = NULL;
@@ -807,12 +1349,14 @@ GOMP_taskwait (void)
            gomp_sem_destroy (&taskwait.taskwait_sem);
          return;
        }
-      if (task->children->kind == GOMP_TASK_WAITING)
+      struct gomp_task *next_task
+       = priority_queue_next_task (PQ_CHILDREN, &task->children_queue,
+                                   PQ_TEAM, &team->task_queue, &child_q);
+      if (next_task->kind == GOMP_TASK_WAITING)
        {
-         child_task = task->children;
+         child_task = next_task;
          cancelled
-           = gomp_task_run_pre (child_task, task, child_task->taskgroup,
-                                team);
+           = gomp_task_run_pre (child_task, task, team);
          if (__builtin_expect (cancelled, 0))
            {
              if (to_free)
@@ -826,8 +1370,10 @@ GOMP_taskwait (void)
        }
       else
        {
-         /* All tasks we are waiting for are already running
-            in other threads.  Wait for them.  */
+       /* All tasks we are waiting for are either running in other
+          threads, or they are tasks that have not had their
+          dependencies met (so they're not even in the queue).  Wait
+          for them.  */
          if (task->taskwait == NULL)
            {
              taskwait.in_depend_wait = false;
@@ -851,7 +1397,28 @@ GOMP_taskwait (void)
       if (child_task)
        {
          thr->task = child_task;
-         child_task->fn (child_task->fn_data);
+         if (__builtin_expect (child_task->fn == NULL, 0))
+           {
+             if (gomp_target_task_fn (child_task->fn_data))
+               {
+                 thr->task = task;
+                 gomp_mutex_lock (&team->task_lock);
+                 child_task->kind = GOMP_TASK_ASYNC_RUNNING;
+                 struct gomp_target_task *ttask
+                   = (struct gomp_target_task *) child_task->fn_data;
+                 /* If GOMP_PLUGIN_target_task_completion has run already
+                    in between gomp_target_task_fn and the mutex lock,
+                    perform the requeuing here.  */
+                 if (ttask->state == GOMP_TARGET_TASK_FINISHED)
+                   gomp_target_task_completion (team, child_task);
+                 else
+                   ttask->state = GOMP_TARGET_TASK_RUNNING;
+                 child_task = NULL;
+                 continue;
+               }
+           }
+         else
+           child_task->fn (child_task->fn_data);
          thr->task = task;
        }
       else
@@ -862,17 +1429,19 @@ GOMP_taskwait (void)
         finish_cancelled:;
          size_t new_tasks
            = gomp_task_run_post_handle_depend (child_task, team);
-         child_task->prev_child->next_child = child_task->next_child;
-         child_task->next_child->prev_child = child_task->prev_child;
-         if (task->children == child_task)
+
+         if (child_q)
            {
-             if (child_task->next_child != child_task)
-               task->children = child_task->next_child;
-             else
-               task->children = NULL;
+             priority_queue_remove (PQ_CHILDREN, &task->children_queue,
+                                    child_task, MEMMODEL_RELAXED);
+             child_task->pnode[PQ_CHILDREN].next = NULL;
+             child_task->pnode[PQ_CHILDREN].prev = NULL;
            }
-         gomp_clear_parent (child_task->children);
+
+         gomp_clear_parent (&child_task->children_queue);
+
          gomp_task_run_post_remove_taskgroup (child_task);
+
          to_free = child_task;
          child_task = NULL;
          team->task_count--;
@@ -887,10 +1456,20 @@ GOMP_taskwait (void)
     }
 }
 
-/* This is like GOMP_taskwait, but we only wait for tasks that the
-   upcoming task depends on.  */
+/* An undeferred task is about to run.  Wait for all tasks that this
+   undeferred task depends on.
 
-static void
+   This is done by first putting all known ready dependencies
+   (dependencies that have their own dependencies met) at the top of
+   the scheduling queues.  Then we iterate through these imminently
+   ready tasks (and possibly other high priority tasks), and run them.
+   If we run out of ready dependencies to execute, we either wait for
+   the reamining dependencies to finish, or wait for them to get
+   scheduled so we can run them.
+
+   DEPEND is as in GOMP_task.  */
+
+void
 gomp_task_maybe_wait_for_dependencies (void **depend)
 {
   struct gomp_thread *thr = gomp_thread ();
@@ -898,7 +1477,6 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
   struct gomp_team *team = thr->ts.team;
   struct gomp_task_depend_entry elem, *ent = NULL;
   struct gomp_taskwait taskwait;
-  struct gomp_task *last_parent_depends_on = NULL;
   size_t ndepend = (uintptr_t) depend[0];
   size_t nout = (uintptr_t) depend[1];
   size_t i;
@@ -922,32 +1500,11 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
              {
                tsk->parent_depends_on = true;
                ++num_awaited;
+               /* If depenency TSK itself has no dependencies and is
+                  ready to run, move it up front so that we run it as
+                  soon as possible.  */
                if (tsk->num_dependees == 0 && tsk->kind == GOMP_TASK_WAITING)
-                 {
-                   /* If a task we need to wait for is not already
-                      running and is ready to be scheduled, move it
-                      to front, so that we run it as soon as possible.  */
-                   if (last_parent_depends_on)
-                     {
-                       tsk->prev_child->next_child = tsk->next_child;
-                       tsk->next_child->prev_child = tsk->prev_child;
-                       tsk->prev_child = last_parent_depends_on;
-                       tsk->next_child = last_parent_depends_on->next_child;
-                       tsk->prev_child->next_child = tsk;
-                       tsk->next_child->prev_child = tsk;
-                     }
-                   else if (tsk != task->children)
-                     {
-                       tsk->prev_child->next_child = tsk->next_child;
-                       tsk->next_child->prev_child = tsk->prev_child;
-                       tsk->prev_child = task->children;
-                       tsk->next_child = task->children->next_child;
-                       task->children = tsk;
-                       tsk->prev_child->next_child = tsk;
-                       tsk->next_child->prev_child = tsk;
-                     }
-                   last_parent_depends_on = tsk;
-                 }
+                 priority_queue_upgrade_task (tsk, task);
              }
          }
     }
@@ -959,7 +1516,6 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
 
   memset (&taskwait, 0, sizeof (taskwait));
   taskwait.n_depend = num_awaited;
-  taskwait.last_parent_depends_on = last_parent_depends_on;
   gomp_sem_init (&taskwait.taskwait_sem, 0);
   task->taskwait = &taskwait;
 
@@ -978,12 +1534,30 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
          gomp_sem_destroy (&taskwait.taskwait_sem);
          return;
        }
-      if (task->children->kind == GOMP_TASK_WAITING)
+
+      /* Theoretically when we have multiple priorities, we should
+        chose between the highest priority item in
+        task->children_queue and team->task_queue here, so we should
+        use priority_queue_next_task().  However, since we are
+        running an undeferred task, perhaps that makes all tasks it
+        depends on undeferred, thus a priority of INF?  This would
+        make it unnecessary to take anything into account here,
+        but the dependencies.
+
+        On the other hand, if we want to use priority_queue_next_task(),
+        care should be taken to only use priority_queue_remove()
+        below if the task was actually removed from the children
+        queue.  */
+      bool ignored;
+      struct gomp_task *next_task
+       = priority_queue_next_task (PQ_CHILDREN, &task->children_queue,
+                                   PQ_IGNORED, NULL, &ignored);
+
+      if (next_task->kind == GOMP_TASK_WAITING)
        {
-         child_task = task->children;
+         child_task = next_task;
          cancelled
-           = gomp_task_run_pre (child_task, task, child_task->taskgroup,
-                                team);
+           = gomp_task_run_pre (child_task, task, team);
          if (__builtin_expect (cancelled, 0))
            {
              if (to_free)
@@ -996,8 +1570,10 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
            }
        }
       else
-       /* All tasks we are waiting for are already running
-          in other threads.  Wait for them.  */
+       /* All tasks we are waiting for are either running in other
+          threads, or they are tasks that have not had their
+          dependencies met (so they're not even in the queue).  Wait
+          for them.  */
        taskwait.in_depend_wait = true;
       gomp_mutex_unlock (&team->task_lock);
       if (do_wake)
@@ -1014,7 +1590,28 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
       if (child_task)
        {
          thr->task = child_task;
-         child_task->fn (child_task->fn_data);
+         if (__builtin_expect (child_task->fn == NULL, 0))
+           {
+             if (gomp_target_task_fn (child_task->fn_data))
+               {
+                 thr->task = task;
+                 gomp_mutex_lock (&team->task_lock);
+                 child_task->kind = GOMP_TASK_ASYNC_RUNNING;
+                 struct gomp_target_task *ttask
+                   = (struct gomp_target_task *) child_task->fn_data;
+                 /* If GOMP_PLUGIN_target_task_completion has run already
+                    in between gomp_target_task_fn and the mutex lock,
+                    perform the requeuing here.  */
+                 if (ttask->state == GOMP_TARGET_TASK_FINISHED)
+                   gomp_target_task_completion (team, child_task);
+                 else
+                   ttask->state = GOMP_TARGET_TASK_RUNNING;
+                 child_task = NULL;
+                 continue;
+               }
+           }
+         else
+           child_task->fn (child_task->fn_data);
          thr->task = task;
        }
       else
@@ -1027,16 +1624,13 @@ gomp_task_maybe_wait_for_dependencies (void **depend)
            = gomp_task_run_post_handle_depend (child_task, team);
          if (child_task->parent_depends_on)
            --taskwait.n_depend;
-         child_task->prev_child->next_child = child_task->next_child;
-         child_task->next_child->prev_child = child_task->prev_child;
-         if (task->children == child_task)
-           {
-             if (child_task->next_child != child_task)
-               task->children = child_task->next_child;
-             else
-               task->children = NULL;
-           }
-         gomp_clear_parent (child_task->children);
+
+         priority_queue_remove (PQ_CHILDREN, &task->children_queue,
+                                child_task, MEMMODEL_RELAXED);
+         child_task->pnode[PQ_CHILDREN].next = NULL;
+         child_task->pnode[PQ_CHILDREN].prev = NULL;
+
+         gomp_clear_parent (&child_task->children_queue);
          gomp_task_run_post_remove_taskgroup (child_task);
          to_free = child_task;
          child_task = NULL;
@@ -1069,14 +1663,14 @@ GOMP_taskgroup_start (void)
   struct gomp_taskgroup *taskgroup;
 
   /* If team is NULL, all tasks are executed as
-     GOMP_TASK_IFFALSE tasks and thus all children tasks of
+     GOMP_TASK_UNDEFERRED tasks and thus all children tasks of
      taskgroup and their descendant tasks will be finished
      by the time GOMP_taskgroup_end is called.  */
   if (team == NULL)
     return;
   taskgroup = gomp_malloc (sizeof (struct gomp_taskgroup));
   taskgroup->prev = task->taskgroup;
-  taskgroup->children = NULL;
+  priority_queue_init (&taskgroup->taskgroup_queue);
   taskgroup->in_taskgroup_wait = false;
   taskgroup->cancelled = false;
   taskgroup->num_children = 0;
@@ -1098,6 +1692,17 @@ GOMP_taskgroup_end (void)
   if (team == NULL)
     return;
   taskgroup = task->taskgroup;
+  if (__builtin_expect (taskgroup == NULL, 0)
+      && thr->ts.level == 0)
+    {
+      /* This can happen if GOMP_taskgroup_start is called when
+        thr->ts.team == NULL, but inside of the taskgroup there
+        is #pragma omp target nowait that creates an implicit
+        team with a single thread.  In this case, we want to wait
+        for all outstanding tasks in this team.  */
+      gomp_team_barrier_wait (&team->barrier);
+      return;
+    }
 
   /* The acquire barrier on load of taskgroup->num_children here
      synchronizes with the write of 0 in gomp_task_run_post_remove_taskgroup.
@@ -1108,19 +1713,25 @@ GOMP_taskgroup_end (void)
   if (__atomic_load_n (&taskgroup->num_children, MEMMODEL_ACQUIRE) == 0)
     goto finish;
 
+  bool unused;
   gomp_mutex_lock (&team->task_lock);
   while (1)
     {
       bool cancelled = false;
-      if (taskgroup->children == NULL)
+      if (priority_queue_empty_p (&taskgroup->taskgroup_queue,
+                                 MEMMODEL_RELAXED))
        {
          if (taskgroup->num_children)
            {
-             if (task->children == NULL)
+             if (priority_queue_empty_p (&task->children_queue,
+                                         MEMMODEL_RELAXED))
                goto do_wait;
-             child_task = task->children;
-            }
-          else
+             child_task
+               = priority_queue_next_task (PQ_CHILDREN, &task->children_queue,
+                                           PQ_TEAM, &team->task_queue,
+                                           &unused);
+           }
+         else
            {
              gomp_mutex_unlock (&team->task_lock);
              if (to_free)
@@ -1132,12 +1743,13 @@ GOMP_taskgroup_end (void)
            }
        }
       else
-       child_task = taskgroup->children;
+       child_task
+         = priority_queue_next_task (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
+                                     PQ_TEAM, &team->task_queue, &unused);
       if (child_task->kind == GOMP_TASK_WAITING)
        {
          cancelled
-           = gomp_task_run_pre (child_task, child_task->parent, taskgroup,
-                                team);
+           = gomp_task_run_pre (child_task, child_task->parent, team);
          if (__builtin_expect (cancelled, 0))
            {
              if (to_free)
@@ -1153,8 +1765,10 @@ GOMP_taskgroup_end (void)
        {
          child_task = NULL;
         do_wait:
-         /* All tasks we are waiting for are already running
-            in other threads.  Wait for them.  */
+       /* All tasks we are waiting for are either running in other
+          threads, or they are tasks that have not had their
+          dependencies met (so they're not even in the queue).  Wait
+          for them.  */
          taskgroup->in_taskgroup_wait = true;
        }
       gomp_mutex_unlock (&team->task_lock);
@@ -1172,7 +1786,28 @@ GOMP_taskgroup_end (void)
       if (child_task)
        {
          thr->task = child_task;
-         child_task->fn (child_task->fn_data);
+         if (__builtin_expect (child_task->fn == NULL, 0))
+           {
+             if (gomp_target_task_fn (child_task->fn_data))
+               {
+                 thr->task = task;
+                 gomp_mutex_lock (&team->task_lock);
+                 child_task->kind = GOMP_TASK_ASYNC_RUNNING;
+                 struct gomp_target_task *ttask
+                   = (struct gomp_target_task *) child_task->fn_data;
+                 /* If GOMP_PLUGIN_target_task_completion has run already
+                    in between gomp_target_task_fn and the mutex lock,
+                    perform the requeuing here.  */
+                 if (ttask->state == GOMP_TARGET_TASK_FINISHED)
+                   gomp_target_task_completion (team, child_task);
+                 else
+                   ttask->state = GOMP_TARGET_TASK_RUNNING;
+                 child_task = NULL;
+                 continue;
+               }
+           }
+         else
+           child_task->fn (child_task->fn_data);
          thr->task = task;
        }
       else
@@ -1184,7 +1819,7 @@ GOMP_taskgroup_end (void)
          size_t new_tasks
            = gomp_task_run_post_handle_depend (child_task, team);
          gomp_task_run_post_remove_parent (child_task);
-         gomp_clear_parent (child_task->children);
+         gomp_clear_parent (&child_task->children_queue);
          gomp_task_run_post_remove_taskgroup (child_task);
          to_free = child_task;
          child_task = NULL;