openmp: Handle OpenMP directives in attribute syntax in attribute-declaration

Now that we parse attribute-declaration (outside of functions), the following
patch handles OpenMP directives in its attribute(s).
What needs handling incrementally is diagnose mismatching begin/end pair
like
 [[omp::directive (declare target)]];
 int a;
 #pragma omp end declare target
or
 #pragma omp declare target
 int b;
 [[omp::directive (end declare target)]];
and handling declare simd/declare variant on declarations (function
definitions and declarations), for those in two different spots.

2021-07-31  Jakub Jelinek  <jakub@redhat.com>

	* parser.c (cp_parser_declaration): Handle OpenMP directives
	in attribute-declaration.

	* g++.dg/gomp/attrs-9.C: New test.

2 files changed, 34 insertions, 0 deletions

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index ab74e9d..47bf7d9 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -14431,6 +14431,25 @@ cp_parser_declaration (cp_parser* parser, tree prefix_attrs)
     {
       location_t attrs_loc = token1->location;
       tree std_attrs = cp_parser_std_attribute_spec_seq (parser);
+
+      if (std_attrs && (flag_openmp || flag_openmp_simd))
+	{
+	  gcc_assert (!parser->lexer->in_omp_attribute_pragma);
+	  std_attrs = cp_parser_handle_statement_omp_attributes (parser,
+								 std_attrs);
+	  if (parser->lexer->in_omp_attribute_pragma)
+	    {
+	      cp_lexer *lexer = parser->lexer;
+	      while (parser->lexer->in_omp_attribute_pragma)
+		{
+		  gcc_assert (cp_lexer_next_token_is (parser->lexer,
+						      CPP_PRAGMA));
+		  cp_parser_pragma (parser, pragma_external, NULL);
+		}
+	      cp_lexer_destroy (lexer);
+	    }
+	}
+
       if (std_attrs != NULL_TREE)
 	warning_at (make_location (attrs_loc, attrs_loc, parser->lexer),
 		    OPT_Wattributes, "attribute ignored");
diff --git a/gcc/testsuite/g++.dg/gomp/attrs-9.C b/gcc/testsuite/g++.dg/gomp/attrs-9.C
new file mode 100644
index 0000000..0af556c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/gomp/attrs-9.C
@@ -0,0 +1,15 @@
+// { dg-do compile { target c++11 } }
+
+[[omp::sequence (directive (requires, atomic_default_mem_order (seq_cst)))]];
+[[omp::directive (declare reduction (plus: int: omp_out += omp_in) initializer (omp_priv = 0))]];
+int a;
+[[omp::directive (declare target (a))]];
+int t;
+[[omp::sequence (omp::directive (threadprivate (t)))]];
+int b, c;
+[[omp::directive (declare target, to (b), link (c))]];
+[[omp::directive (declare target)]];
+[[omp::directive (declare target)]];
+int d;
+[[omp::directive (end declare target)]];
+[[omp::directive (end declare target)]];