[PATCH] libgomp, nvptx, v2: Honor OpenMP 5.1 num_teams lower bound

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Nov 12, 2021 at 02:20:23PM +0100, Jakub Jelinek via Gcc-patches wrote:
> This patch assumes that .shared variables are initialized to 0,
> https://docs.nvidia.com/cuda/parallel-thread-execution/index.html lists
> in Table 7. .shared as non-initializable.  If that isn't the case,
> we need to initialize it somewhere for the case of #pragma omp target
> without #pragma omp teams in it, maybe in libgcc/config/nvptx/crt0.c ?

A quick look at libgcc/config/nvptx/crt0.c shows the target supports
__attribute__((shared)), so perhaps either following instead, or, if
.shared isn't preinitialized to zero, defining the variable in
libgcc/config/nvptx/crt0.c , adding there __gomp_team_num = 0;
and adding extern keyword before int __gomp_team_num __attribute__((shared));
in libgomp/config/nvptx/target.c.

2021-11-12  Jakub Jelinek  <jakub@redhat.com>

	* config/nvptx/target.c (__gomp_team_num): Define as
	__attribute__((shared)) var.
	(GOMP_teams4): Use __gomp_team_num as the team number instead of
	%ctaid.x.  If first, initialize it to %ctaid.x.  If num_teams_lower
	is bigger than num_blocks, use num_teams_lower teams and arrange for
	bumping of __gomp_team_num if !first and returning false once we run
	out of teams.
	* config/nvptx/teams.c (__gomp_team_num): Declare as
	extern __attribute__((shared)) var.
	(omp_get_team_num): Return __gomp_team_num value instead of %ctaid.x.

--- libgomp/config/nvptx/target.c.jj	2021-11-12 12:41:11.433501988 +0100
+++ libgomp/config/nvptx/target.c	2021-11-12 14:21:39.451426717 +0100
@@ -26,28 +26,41 @@
 #include "libgomp.h"
 #include <limits.h>
 
+int __gomp_team_num __attribute__((shared));
+
 bool
 GOMP_teams4 (unsigned int num_teams_lower, unsigned int num_teams_upper,
 	     unsigned int thread_limit, bool first)
 {
+  unsigned int num_blocks, block_id;
+  asm ("mov.u32 %0, %%nctaid.x;" : "=r" (num_blocks));
   if (!first)
-    return false;
+    {
+      unsigned in team_num;
+      if (num_blocks > gomp_num_teams_var)
+	return false;
+      team_num = __gomp_team_num;
+      if (team_num > gomp_num_teams_var - num_blocks)
+	return false;
+      __gomp_team_num = team_num + num_blocks;
+      return true;
+    }
   if (thread_limit)
     {
       struct gomp_task_icv *icv = gomp_icv (true);
       icv->thread_limit_var
 	= thread_limit > INT_MAX ? UINT_MAX : thread_limit;
     }
-  unsigned int num_blocks, block_id;
-  asm ("mov.u32 %0, %%nctaid.x;" : "=r" (num_blocks));
-  asm ("mov.u32 %0, %%ctaid.x;" : "=r" (block_id));
-  /* FIXME: If num_teams_lower > num_blocks, we want to loop multiple
-     times for some CTAs.  */
-  (void) num_teams_lower;
-  if (!num_teams_upper || num_teams_upper >= num_blocks)
+  if (!num_teams_upper)
     num_teams_upper = num_blocks;
-  else if (block_id >= num_teams_upper)
+  else if (num_blocks < num_teams_lower)
+    num_teams_upper = num_teams_lower;
+  else if (num_blocks < num_teams_upper)
+    num_teams_upper = num_blocks;
+  asm ("mov.u32 %0, %%ctaid.x;" : "=r" (block_id));
+  if (block_id >= num_teams_upper)
     return false;
+  __gomp_team_num = block_id;
   gomp_num_teams_var = num_teams_upper - 1;
   return true;
 }
--- libgomp/config/nvptx/teams.c.jj	2021-01-05 00:13:58.255297642 +0100
+++ libgomp/config/nvptx/teams.c	2021-11-12 14:22:06.443039863 +0100
@@ -28,6 +28,8 @@
 
 #include "libgomp.h"
 
+extern int __gomp_team_num __attribute__((shared));
+
 void
 GOMP_teams_reg (void (*fn) (void *), void *data, unsigned int num_teams,
 		unsigned int thread_limit, unsigned int flags)
@@ -48,9 +50,7 @@ omp_get_num_teams (void)
 int
 omp_get_team_num (void)
 {
-  int ctaid;
-  asm ("mov.u32 %0, %%ctaid.x;" : "=r" (ctaid));
-  return ctaid;
+  return __gomp_team_num;
 }
 
 ialias (omp_get_num_teams)


	Jakub