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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libgomp/97212] [OpenMP] 'depend' clause with 'target nowait'
 (!) + 'task' does not work
Date: Thu, 08 Oct 2020 17:47:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97212

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I believe the testcase is invalid.
As the explicit task doesn't have if(false) clause, the task isn't undeferr=
ed,
so it is up to the implementation whether it waits for its completion or ju=
st
continues (defers it).  And there is no task synchronization point before t=
he
if (sum !=3D N) __builtin_abort (); statement, so if the implementation dec=
ides
to defer it, then there is no guarantee it completes before that statement.
Without the target nowait task gcc wouldn't defer it because there is just =
an
implicit parallel region rather than explicit (e.g. if you add parallel
num_threads(1) around most of main and change target nowait to task, you'd =
get
the same behavior), but in order to support async target tasks we do create
intentionally a team and thus defer the task.
So, the testcase needs something like
#pragma omp taskwait
or taskwait with depend or add if(false) to the task.=