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gcc/libgomp/taskloop.c
Jakub Jelinek 58ce047087 openmp: Fix up taskloop reduction ICE if taskloop has no iterations [PR100471] 
When a taskloop doesn't have any iterations, GOMP_taskloop* takes an early
return, doesn't create any tasks and more importantly, doesn't create
a taskgroup and doesn't register task reductions.  But, the code emitted
in the callers assumes task reductions have been registered and performs
the reduction handling and task reduction unregistration.  The pointer
to the task reduction private variables is reused, on input it is the alignment
and only on output it is the pointer, so in the case taskloop with no iterations
the caller attempts to dereference the alignment value as if it was a pointer
and crashes.  We could in the early returns register the task reductions
only to have them looped over and unregistered in the caller, but I think
it is better to tell the caller there is nothing to task reduce and bypass
all that.

2021-05-11  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/100471
	* omp-low.c (lower_omp_task_reductions): For OMP_TASKLOOP, if data
	is 0, bypass the reduction loop including
	GOMP_taskgroup_reduction_unregister call.

	* taskloop.c (GOMP_taskloop): If GOMP_TASK_FLAG_REDUCTION and not
	GOMP_TASK_FLAG_NOGROUP, when doing early return clear the task
	reduction pointer.
	* testsuite/libgomp.c/task-reduction-4.c: New test.

(cherry picked from commit 98acbb3111)
2021-05-12 15:19:29 +02:00

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/* Copyright (C) 2015-2021 Free Software Foundation, Inc.
Contributed by Jakub Jelinek <jakub@redhat.com>.
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
the Free Software Foundation; either version 3, or (at your option)
any later version.
Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
/* This file handles the taskloop construct. It is included twice, once
for the long and once for unsigned long long variant. */
/* 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. */
void
GOMP_taskloop (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
long arg_size, long arg_align, unsigned flags,
unsigned long num_tasks, int priority,
TYPE start, TYPE end, TYPE step)
{
struct gomp_thread *thr = gomp_thread ();
struct gomp_team *team = thr->ts.team;
#ifdef HAVE_BROKEN_POSIX_SEMAPHORES
/* If pthread_mutex_* is used for omp_*lock*, then each task must be
tied to one thread all the time. This means UNTIED tasks must be
tied and if CPYFN is non-NULL IF(0) must be forced, as CPYFN
might be running on different thread than FN. */
if (cpyfn)
flags &= ~GOMP_TASK_FLAG_IF;
flags &= ~GOMP_TASK_FLAG_UNTIED;
#endif
/* If parallel or taskgroup has been cancelled, don't start new tasks. */
if (team && gomp_team_barrier_cancelled (&team->barrier))
{
early_return:
if ((flags & (GOMP_TASK_FLAG_NOGROUP | GOMP_TASK_FLAG_REDUCTION))
== GOMP_TASK_FLAG_REDUCTION)
{
struct gomp_data_head { TYPE t1, t2; uintptr_t *ptr; };
uintptr_t *ptr = ((struct gomp_data_head *) data)->ptr;
/* Tell callers GOMP_taskgroup_reduction_register has not been
called. */
ptr[2] = 0;
}
return;
}
#ifdef TYPE_is_long
TYPE s = step;
if (step > 0)
{
if (start >= end)
goto early_return;
s--;
}
else
{
if (start <= end)
goto early_return;
s++;
}
UTYPE n = (end - start + s) / step;
#else
UTYPE n;
if (flags & GOMP_TASK_FLAG_UP)
{
if (start >= end)
goto early_return;
n = (end - start + step - 1) / step;
}
else
{
if (start <= end)
goto early_return;
n = (start - end - step - 1) / -step;
}
#endif
TYPE task_step = step;
unsigned long nfirst = n;
if (flags & GOMP_TASK_FLAG_GRAINSIZE)
{
unsigned long grainsize = num_tasks;
#ifdef TYPE_is_long
num_tasks = n / grainsize;
#else
UTYPE ndiv = n / grainsize;
num_tasks = ndiv;
if (num_tasks != ndiv)
num_tasks = ~0UL;
#endif
if (num_tasks <= 1)
{
num_tasks = 1;
task_step = end - start;
}
else if (num_tasks >= grainsize
#ifndef TYPE_is_long
&& num_tasks != ~0UL
#endif
)
{
UTYPE mul = num_tasks * grainsize;
task_step = (TYPE) grainsize * step;
if (mul != n)
{
task_step += step;
nfirst = n - mul - 1;
}
}
else
{
UTYPE div = n / num_tasks;
UTYPE mod = n % num_tasks;
task_step = (TYPE) div * step;
if (mod)
{
task_step += step;
nfirst = mod - 1;
}
}
}
else
{
if (num_tasks == 0)
num_tasks = team ? team->nthreads : 1;
if (num_tasks >= n)
num_tasks = n;
else
{
UTYPE div = n / num_tasks;
UTYPE mod = n % num_tasks;
task_step = (TYPE) div * step;
if (mod)
{
task_step += step;
nfirst = mod - 1;
}
}
}
if (flags & GOMP_TASK_FLAG_NOGROUP)
{
if (__builtin_expect (gomp_cancel_var, 0)
&& thr->task
&& thr->task->taskgroup)
{
if (thr->task->taskgroup->cancelled)
return;
if (thr->task->taskgroup->workshare
&& thr->task->taskgroup->prev
&& thr->task->taskgroup->prev->cancelled)
return;
}
}
else
{
ialias_call (GOMP_taskgroup_start) ();
if (flags & GOMP_TASK_FLAG_REDUCTION)
{
struct gomp_data_head { TYPE t1, t2; uintptr_t *ptr; };
uintptr_t *ptr = ((struct gomp_data_head *) data)->ptr;
ialias_call (GOMP_taskgroup_reduction_register) (ptr);
}
}
if (priority > gomp_max_task_priority_var)
priority = gomp_max_task_priority_var;
if ((flags & GOMP_TASK_FLAG_IF) == 0 || team == NULL
|| (thr->task && thr->task->final_task)
|| team->task_count + num_tasks > 64 * team->nthreads)
{
unsigned long i;
if (__builtin_expect (cpyfn != NULL, 0))
{
struct gomp_task task[num_tasks];
struct gomp_task *parent = thr->task;
arg_size = (arg_size + arg_align - 1) & ~(arg_align - 1);
char buf[num_tasks * arg_size + arg_align - 1];
char *arg = (char *) (((uintptr_t) buf + arg_align - 1)
& ~(uintptr_t) (arg_align - 1));
char *orig_arg = arg;
for (i = 0; i < num_tasks; i++)
{
gomp_init_task (&task[i], parent, gomp_icv (false));
task[i].priority = priority;
task[i].kind = GOMP_TASK_UNDEFERRED;
task[i].final_task = (thr->task && thr->task->final_task)
|| (flags & GOMP_TASK_FLAG_FINAL);
if (thr->task)
{
task[i].in_tied_task = thr->task->in_tied_task;
task[i].taskgroup = thr->task->taskgroup;
}
thr->task = &task[i];
cpyfn (arg, data);
arg += arg_size;
}
arg = orig_arg;
for (i = 0; i < num_tasks; i++)
{
thr->task = &task[i];
((TYPE *)arg)[0] = start;
start += task_step;
((TYPE *)arg)[1] = start;
if (i == nfirst)
task_step -= step;
fn (arg);
arg += arg_size;
if (!priority_queue_empty_p (&task[i].children_queue,
MEMMODEL_RELAXED))
{
gomp_mutex_lock (&team->task_lock);
gomp_clear_parent (&task[i].children_queue);
gomp_mutex_unlock (&team->task_lock);
}
gomp_end_task ();
}
}
else
for (i = 0; i < num_tasks; i++)
{
struct gomp_task task;
gomp_init_task (&task, thr->task, gomp_icv (false));
task.priority = priority;
task.kind = GOMP_TASK_UNDEFERRED;
task.final_task = (thr->task && thr->task->final_task)
|| (flags & GOMP_TASK_FLAG_FINAL);
if (thr->task)
{
task.in_tied_task = thr->task->in_tied_task;
task.taskgroup = thr->task->taskgroup;
}
thr->task = &task;
((TYPE *)data)[0] = start;
start += task_step;
((TYPE *)data)[1] = start;
if (i == nfirst)
task_step -= step;
fn (data);
if (!priority_queue_empty_p (&task.children_queue,
MEMMODEL_RELAXED))
{
gomp_mutex_lock (&team->task_lock);
gomp_clear_parent (&task.children_queue);
gomp_mutex_unlock (&team->task_lock);
}
gomp_end_task ();
}
}
else
{
struct gomp_task *tasks[num_tasks];
struct gomp_task *parent = thr->task;
struct gomp_taskgroup *taskgroup = parent->taskgroup;
char *arg;
int do_wake;
unsigned long i;
for (i = 0; i < num_tasks; i++)
{
struct gomp_task *task
= gomp_malloc (sizeof (*task) + arg_size + arg_align - 1);
tasks[i] = task;
arg = (char *) (((uintptr_t) (task + 1) + arg_align - 1)
& ~(uintptr_t) (arg_align - 1));
gomp_init_task (task, parent, gomp_icv (false));
task->priority = priority;
task->kind = GOMP_TASK_UNDEFERRED;
task->in_tied_task = parent->in_tied_task;
task->taskgroup = taskgroup;
thr->task = task;
if (cpyfn)
{
cpyfn (arg, data);
task->copy_ctors_done = true;
}
else
memcpy (arg, data, arg_size);
((TYPE *)arg)[0] = start;
start += task_step;
((TYPE *)arg)[1] = start;
if (i == nfirst)
task_step -= step;
thr->task = parent;
task->kind = GOMP_TASK_WAITING;
task->fn = fn;
task->fn_data = arg;
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. */
if (__builtin_expect (gomp_cancel_var, 0)
&& cpyfn == NULL)
{
if (gomp_team_barrier_cancelled (&team->barrier))
{
do_cancel:
gomp_mutex_unlock (&team->task_lock);
for (i = 0; i < num_tasks; i++)
{
gomp_finish_task (tasks[i]);
free (tasks[i]);
}
if ((flags & GOMP_TASK_FLAG_NOGROUP) == 0)
ialias_call (GOMP_taskgroup_end) ();
return;
}
if (taskgroup)
{
if (taskgroup->cancelled)
goto do_cancel;
if (taskgroup->workshare
&& taskgroup->prev
&& taskgroup->prev->cancelled)
goto do_cancel;
}
}
if (taskgroup)
taskgroup->num_children += num_tasks;
for (i = 0; i < num_tasks; i++)
{
struct gomp_task *task = tasks[i];
priority_queue_insert (PQ_CHILDREN, &parent->children_queue,
task, priority,
PRIORITY_INSERT_BEGIN,
/*last_parent_depends_on=*/false,
task->parent_depends_on);
if (taskgroup)
priority_queue_insert (PQ_TASKGROUP, &taskgroup->taskgroup_queue,
task, priority, PRIORITY_INSERT_BEGIN,
/*last_parent_depends_on=*/false,
task->parent_depends_on);
priority_queue_insert (PQ_TEAM, &team->task_queue, task, priority,
PRIORITY_INSERT_END,
/*last_parent_depends_on=*/false,
task->parent_depends_on);
++team->task_count;
++team->task_queued_count;
}
gomp_team_barrier_set_task_pending (&team->barrier);
if (team->task_running_count + !parent->in_tied_task
< team->nthreads)
{
do_wake = team->nthreads - team->task_running_count
- !parent->in_tied_task;
if ((unsigned long) do_wake > num_tasks)
do_wake = num_tasks;
}
else
do_wake = 0;
gomp_mutex_unlock (&team->task_lock);
if (do_wake)
gomp_team_barrier_wake (&team->barrier, do_wake);
}
if ((flags & GOMP_TASK_FLAG_NOGROUP) == 0)
ialias_call (GOMP_taskgroup_end) ();
}
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