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The following patch implements what I've been talking about earlier,
honor that for explicit num_teams clause we create at least the
lower-bound (if not specified, upper-bound) teams in the league.
For host fallback, it still means we only have one thread doing all the
teams, sequentially one after another.
For PTX and GCN, I think the new teams-2.c test and maybe teams-4.c too
will or might fail.
For these offloads, I think it is ok to remove symbols no longer used
from libgomp.a.
If num_teams_lower is bigger than the provided num_blocks or num_workgroups,
we should arrange for gomp_num_teams_var to be num_teams_lower - 1,
stop using the %ctaid.x or __builtin_gcn_dim_pos (0) for omp_get_team_num ()
and instead use for it some .shared var that GOMP_teams4 initializes to
%ctaid.x or __builtin_gcn_dim_pos (0) when first and for !first
increment that by num_blocks or num_workgroups each time and only
return false when we are above num_teams_lower.
Any help with actually implementing this for the 2 architectures highly
appreciated.
2021-11-12 Jakub Jelinek <jakub@redhat.com>
gcc/
* omp-builtins.def (BUILT_IN_GOMP_TEAMS): Remove.
(BUILT_IN_GOMP_TEAMS4): New.
* builtin-types.def (BT_FN_VOID_UINT_UINT): Remove.
(BT_FN_BOOL_UINT_UINT_UINT_BOOL): New.
* omp-low.c (lower_omp_teams): Use GOMP_teams4 instead of
GOMP_teams, pass to it also num_teams lower-bound expression
or a dup of upper-bound if it is missing and a flag whether
it is the first call or not.
gcc/fortran/
* types.def (BT_FN_VOID_UINT_UINT): Remove.
(BT_FN_BOOL_UINT_UINT_UINT_BOOL): New.
libgomp/
* libgomp_g.h (GOMP_teams4): Declare.
* libgomp.map (GOMP_5.1): Export GOMP_teams4.
* target.c (GOMP_teams4): New function.
* config/nvptx/target.c (GOMP_teams): Remove.
(GOMP_teams4): New function.
* config/gcn/target.c (GOMP_teams): Remove.
(GOMP_teams4): New function.
* testsuite/libgomp.c/teams-4.c (main): Expect exactly 2
teams instead of <= 2.
* testsuite/libgomp.c-c++-common/teams-2.c: New test.
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When thinking about GOMP_teams3, I've realized that using global variables
for the values returned by omp_get_num_teams()/omp_get_team_num() calls
is incorrect even with our right now dumb way of implementing host teams.
The problems are two, one is if host teams is used from multiple pthread_create
created threads - the spec says that host teams can't be nested inside of
explicit parallel or other teams constructs, but with pthread_create the
standard says obviously nothing about it. Another more important thing
is host fallback, right now we don't do anything for omp_get_num_teams()
or omp_get_team_num() which was fine before host teams was introduced and
the 5.1 requirement that num_teams clause specifies minimum of teams, but
with the global vars it means inside of target teams num_teams (2) we happily
return omp_get_num_teams() == 4 if the target teams is inside of host teams
with num_teams(4). With target fallback being invoked from parallel
regions global vars simply can't work right on the host.
So, this patch moves them to struct gomp_thread and propagates those for
parallel to child threads. For host fallback, the implicit zeroing of
*thr results in us returning omp_get_num_teams () == 1 and
omp_get_team_num () == 0 which is fine for target teams without num_teams
clause, for target teams with num_teams clause something to work on and
for target without teams nested in it I've asked on omp-lang what should
be done.
2021-11-11 Jakub Jelinek <jakub@redhat.com>
* libgomp.h (struct gomp_thread): Add num_teams and team_num members.
* team.c (struct gomp_thread_start_data): Likewise.
(gomp_thread_start): Initialize thr->num_teams and thr->team_num.
(gomp_team_start): Initialize start_data->num_teams and
start_data->team_num. Update nthr->num_teams and nthr->team_num.
* teams.c (gomp_num_teams, gomp_team_num): Remove.
(GOMP_teams_reg): Set and restore thr->num_teams and thr->team_num
instead of gomp_num_teams and gomp_team_num.
(omp_get_num_teams): Use thr->num_teams + 1 instead of gomp_num_teams.
(omp_get_team_num): Use thr->team_num instead of gomp_team_num.
* testsuite/libgomp.c/teams-4.c: New test.
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