openmp: Diagnose invalid teams nested in target construct [PR99226]

The OpenMP standard says:
"A teams region can only be strictly nested within the implicit parallel region
or a target region. If a teams construct is nested within a target construct,
that target construct must contain no statements, declarations or directives
outside of the teams construct."
We weren't diagnosing that restriction, because we need to allow e.g.
 #pragma omp target
 {{{{{{
   #pragma omp teams
   ;
 }}}}}}
and as target doesn't need to have teams nested in it, using some special
parser of the target body didn't feel right.  And after the parsing,
the question is if e.g. already parsing of the clauses doesn't add some
statements before the teams statement (gimplification certainly will).

As we now have a bugreport where we ICE on the invalid code, this just
diagnoses a subset of the invalid programs, in particular those where
nest to the teams strictly nested in targets the target region contains
some other OpenMP construct.

2021-02-24  Jakub Jelinek  <jakub@redhat.com>

	PR fortran/99226
	* omp-low.c (struct omp_context): Add teams_nested_p and
	nonteams_nested_p members.
	(scan_omp_target): Diagnose teams nested inside of target with other
	directives strictly nested inside of the same target.
	(check_omp_nesting_restrictions): Set ctx->teams_nested_p or
	ctx->nonteams_nested_p as needed.

	* c-c++-common/gomp/pr99226.c: New test.
	* gfortran.dg/gomp/pr99226.f90: New test.

gcc/omp-low.c

@@ -171,6 +171,14 @@ struct omp_context
 
   /* True if there is bind clause on the construct (i.e. a loop construct).  */
   bool loop_p;
+
+  /* Only used for omp target contexts.  True if a teams construct is
+     strictly nested in it.  */
+  bool teams_nested_p;
+
+  /* Only used for omp target contexts.  True if an OpenMP construct other
+     than teams is strictly nested in it.  */
+  bool nonteams_nested_p;
 };
 
 static splay_tree all_contexts;
@@ -2956,6 +2964,14 @@ scan_omp_target (gomp_target *stmt, omp_context *outer_ctx)
       if (offloaded)
 	fixup_child_record_type (ctx);
     }
+
+  if (ctx->teams_nested_p && ctx->nonteams_nested_p)
+    {
+      error_at (gimple_location (stmt),
+		"%<target%> construct with nested %<teams%> construct "
+		"contains directives outside of the %<teams%> construct");
+      gimple_omp_set_body (stmt, gimple_build_bind (NULL, NULL, NULL));
+    }
 }
 
 /* Scan an OpenMP teams directive.  */
@@ -3025,6 +3041,14 @@ check_omp_nesting_restrictions (gimple *stmt, omp_context *ctx)
 
   if (ctx != NULL)
     {
+      if (gimple_code (ctx->stmt) == GIMPLE_OMP_TARGET
+	  && gimple_omp_target_kind (ctx->stmt) == GF_OMP_TARGET_KIND_REGION)
+	{
+	  if (gimple_code (stmt) == GIMPLE_OMP_TEAMS && !ctx->teams_nested_p)
+	    ctx->teams_nested_p = true;
+	  else
+	    ctx->nonteams_nested_p = true;
+	}
       if (gimple_code (ctx->stmt) == GIMPLE_OMP_SCAN
 	  && ctx->outer
 	  && gimple_code (ctx->outer->stmt) == GIMPLE_OMP_FOR)

gcc/testsuite/c-c++-common/gomp/pr99226.c

@@ -0,0 +1,17 @@
+/* PR fortran/99226 */
+/* { dg-do compile } */
+
+void
+foo (int n)
+{
+  int i;
+  #pragma omp target	/* { dg-error "construct with nested 'teams' construct contains directives outside of the 'teams' construct" } */
+  {
+    #pragma omp teams distribute dist_schedule (static, n + 4)
+    for (i = 0; i < 8; i++)
+      ;
+    #pragma omp teams distribute dist_schedule (static, n + 4)
+    for (i = 0; i < 8; i++)
+      ;
+  }
+}

gcc/testsuite/gfortran.dg/gomp/pr99226.f90

@@ -0,0 +1,13 @@
+! PR fortran/99226
+
+subroutine sub (n)
+   integer :: n, i
+   !$omp target	! { dg-error "construct with nested 'teams' construct contains directives outside of the 'teams' construct" }
+   !$omp teams distribute dist_schedule (static,n+4)
+   do i = 1, 8
+   end do
+   !$omp teams distribute dist_schedule (static,n+4)
+   do i = 1, 8
+   end do
+   !$omp end target
+end