openmp: Honor OpenMP 5.1 num_teams lower bound

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.

1 files changed, 26 insertions, 0 deletions

diff --git a/libgomp/target.c b/libgomp/target.c
index 196dba4..ecf09f9 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -3088,6 +3088,32 @@ GOMP_teams (unsigned int num_teams, unsigned int thread_limit)
   (void) num_teams;
 }
 
+bool
+GOMP_teams4 (unsigned int num_teams_low, unsigned int num_teams_high,
+	     unsigned int thread_limit, bool first)
+{
+  struct gomp_thread *thr = gomp_thread ();
+  if (first)
+    {
+      if (thread_limit)
+	{
+	  struct gomp_task_icv *icv = gomp_icv (true);
+	  icv->thread_limit_var
+	    = thread_limit > INT_MAX ? UINT_MAX : thread_limit;
+	}
+      (void) num_teams_high;
+      if (num_teams_low == 0)
+	num_teams_low = 1;
+      thr->num_teams = num_teams_low - 1;
+      thr->team_num = 0;
+    }
+  else if (thr->team_num == thr->num_teams)
+    return false;
+  else
+    ++thr->team_num;
+  return true;
+}
+
 void *
 omp_target_alloc (size_t size, int device_num)
 {