[OpenMP][Clang] Force use of num_teams and thread_limit for bare kernel (#68373)

This patch makes `num_teams` and `thread_limit` mandatory for bare
kernels,
similar to a reguar kernel language that when launching a kernel, the
grid size
has to be set explicitly.

Author: shiltian

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11368,6 +11368,8 @@ def err_openmp_vla_in_task_untied : Error<
 def warn_omp_unterminated_declare_target : Warning<
   "expected '#pragma omp end declare target' at end of file to match '#pragma omp %0'">,
   InGroup<SourceUsesOpenMP>;
+def err_ompx_bare_no_grid : Error<
+  "'ompx_bare' clauses requires explicit grid size via 'num_teams' and 'thread_limit' clauses">;
 } // end of OpenMP category
 
 let CategoryName = "Related Result Type Issue" in {

clang/lib/Sema/SemaOpenMP.cpp

@@ -14658,6 +14658,19 @@ StmtResult Sema::ActOnOpenMPTargetTeamsDirective(ArrayRef<OMPClause *> Clauses,
   }
   setFunctionHasBranchProtectedScope();
 
+  const OMPClause *BareClause = nullptr;
+  bool HasThreadLimitAndNumTeamsClause = hasClauses(Clauses, OMPC_num_teams) &&
+                                         hasClauses(Clauses, OMPC_thread_limit);
+  bool HasBareClause = llvm::any_of(Clauses, [&](const OMPClause *C) {
+    BareClause = C;
+    return C->getClauseKind() == OMPC_ompx_bare;
+  });
+
+  if (HasBareClause && !HasThreadLimitAndNumTeamsClause) {
+    Diag(BareClause->getBeginLoc(), diag::err_ompx_bare_no_grid);
+    return StmtError();
+  }
+
   return OMPTargetTeamsDirective::Create(Context, StartLoc, EndLoc, Clauses,
                                          AStmt);
 }

clang/test/OpenMP/nvptx_target_teams_ompx_bare_codegen.cpp

@@ -10,7 +10,7 @@ template<typename tx>
 tx ftemplate(int n) {
   tx a = 0;
 
-  #pragma omp target teams ompx_bare
+  #pragma omp target teams ompx_bare num_teams(1) thread_limit(32)
   {
     a = 2;
   }

clang/test/OpenMP/ompx_bare_messages.c

@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -verify -fopenmp -triple x86_64-unknown-unknown %s
- // RUN: %clang_cc1 -verify -fopenmp-simd -triple x86_64-unknown-unknown %s
- // RUN: %clang_cc1 -verify -fopenmp -triple x86_64-unknown-unknown -fopenmp-targets=nvptx64 %s
+// RUN: %clang_cc1 -verify -fopenmp-simd -triple x86_64-unknown-unknown %s
+// RUN: %clang_cc1 -verify -fopenmp -triple x86_64-unknown-unknown -fopenmp-targets=nvptx64 %s
 
 void foo() {
 }
@@ -18,4 +18,7 @@ void bar() {
 #pragma omp target
 #pragma omp teams ompx_bare // expected-error {{unexpected OpenMP clause 'ompx_bare' in directive '#pragma omp teams'}} expected-note {{OpenMP extension clause 'ompx_bare' only allowed with '#pragma omp target teams'}}
   foo();
+
+#pragma omp target teams ompx_bare // expected-error {{'ompx_bare' clauses requires explicit grid size via 'num_teams' and 'thread_limit' clauses}}
+  foo();
 }

clang/test/OpenMP/target_teams_ast_print.cpp

@@ -111,8 +111,8 @@ int main (int argc, char **argv) {
 // CHECK-NEXT: #pragma omp target teams
   a=2;
 // CHECK-NEXT: a = 2;
-#pragma omp target teams ompx_bare
-// CHECK-NEXT: #pragma omp target teams ompx_bare
+#pragma omp target teams ompx_bare num_teams(1) thread_limit(32)
+// CHECK-NEXT: #pragma omp target teams ompx_bare num_teams(1) thread_limit(32)
   a=3;
 // CHECK-NEXT: a = 3;
 #pragma omp target teams default(none), private(argc,b) num_teams(f) firstprivate(argv) reduction(| : c, d) reduction(* : e) thread_limit(f+g)