libgomp: Don't access gomp_sem_t as int using atomics unconditionally

This patch introduces gomp_sem_getcount wrapper, which uses sem_getvalue
for POSIX and atomic loads for linux futex and accel.  rtems for now
remains broken.

2021-01-18  Jakub Jelinek  <jakub@redhat.com>

	* config/linux/sem.h (gomp_sem_getcount): New function.
	* config/posix/sem.h (gomp_sem_getcount): New function.
	* config/posix/sem.c (gomp_sem_getcount): New function.
	* config/accel/sem.h (gomp_sem_getcount): New function.
	* task.c (task_fulfilled_p): Use gomp_sem_getcount.
	(omp_fulfill_event): Likewise.

libgomp/config/accel/sem.h

@@ -62,4 +62,13 @@ gomp_sem_post (gomp_sem_t *sem)
 {
   (void) __atomic_add_fetch (sem, 1, MEMMODEL_RELEASE);
 }
+
+static inline int
+gomp_sem_getcount (gomp_sem_t *sem)
+{
+  int count = __atomic_load_n (sem, MEMMODEL_RELAXED);
+  if (count < 0)
+    return -1;
+  return count;
+}
 #endif /* GOMP_SEM_H */

libgomp/config/linux/sem.h

@@ -85,4 +85,13 @@ gomp_sem_post (gomp_sem_t *sem)
   if (__builtin_expect (count & SEM_WAIT, 0))
     gomp_sem_post_slow (sem);
 }
+
+static inline int
+gomp_sem_getcount (gomp_sem_t *sem)
+{
+  int count = __atomic_load_n (sem, MEMMODEL_RELAXED);
+  if ((count & SEM_WAIT) != 0)
+    return -1;
+  return count / SEM_INC;
+}
 #endif /* GOMP_SEM_H */

libgomp/config/posix/sem.c

@@ -112,6 +112,26 @@ void gomp_sem_destroy (gomp_sem_t *sem)
 
   return;
 }
+
+int gomp_sem_getcount (gomp_sem_t *sem)
+{
+  int ret, count;
+
+  ret = pthread_mutex_lock (&sem->mutex);
+  if (ret)
+    return -1;
+
+  count = sem->value;
+
+  ret = pthread_mutex_unlock (&sem->mutex);
+  if (ret)
+    return -1;
+
+  if (count < 0)
+    return -1;
+
+  return count;
+}
 #else /* HAVE_BROKEN_POSIX_SEMAPHORES  */
 void
 gomp_sem_wait (gomp_sem_t *sem)

libgomp/config/posix/sem.h

@@ -64,6 +64,8 @@ extern void gomp_sem_post (gomp_sem_t *sem);
 
 extern void gomp_sem_destroy (gomp_sem_t *sem);
 
+extern int gomp_sem_getcount (gomp_sem_t *sem);
+
 #else /* HAVE_BROKEN_POSIX_SEMAPHORES  */
 
 typedef sem_t gomp_sem_t;
@@ -84,5 +86,13 @@ static inline void gomp_sem_destroy (gomp_sem_t *sem)
 {
   sem_destroy (sem);
 }
+
+static inline int gomp_sem_getcount (gomp_sem_t *sem)
+{
+  int val;
+  if (sem_getvalue (sem, &val) < 0)
+    return -1;
+  return val;  
+}
 #endif /* doesn't HAVE_BROKEN_POSIX_SEMAPHORES  */
 #endif /* GOMP_SEM_H  */

libgomp/task.c

@@ -330,7 +330,7 @@ gomp_task_handle_depend (struct gomp_task *task, struct gomp_task *parent,
 static bool
 task_fulfilled_p (struct gomp_task *task)
 {
-  return __atomic_load_n (&task->completion_sem, __ATOMIC_RELAXED);
+  return gomp_sem_getcount (&task->completion_sem) > 0;
 }
 
 /* Called when encountering an explicit task directive.  If IF_CLAUSE is
@@ -2406,7 +2406,7 @@ omp_fulfill_event (omp_event_handle_t event)
   struct gomp_thread *thr = gomp_thread ();
   struct gomp_team *team = thr ? thr->ts.team : NULL;
 
-  if (__atomic_load_n (sem, __ATOMIC_RELAXED))
+  if (gomp_sem_getcount (sem) > 0)
     gomp_fatal ("omp_fulfill_event: %p event already fulfilled!\n", sem);
 
   gomp_debug (0, "omp_fulfill_event: %p\n", sem);