openmp: Add nothing directive support

As has been clarified, it is intentional that nothing directive is accepted
in substatements of selection and looping statements and after labels and
is handled as if the directive just isn't there, so that
void
foo (int x)
{
  if (x)
    #pragma omp metadirective when (...:nothing) when (...:parallel)
    bar ();
}
behaves consistently; declarative and stand-alone directives aren't allowed
at that point, but constructs are parsed with the following statement as
the construct body and nothing or missing default on metadirective therefore
should handle the following statement as part of the if substatement instead
of having nothing as the substatement and bar done unconditionally after the
if.

2021-08-18  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c-pragma.h (enum pragma_kind): Add PRAGMA_OMP_NOTHING.
	* c-pragma.c (omp_pragmas): Add nothing directive.
	* c-omp.c (omp_directives): Uncomment nothing directive entry.
gcc/c/
	* c-parser.c (c_parser_omp_nothing): New function.
	(c_parser_pragma): Handle PRAGMA_OMP_NOTHING.
gcc/cp/
	* parser.c (cp_parser_omp_nothing): New function.
	(cp_parser_pragma): Handle PRAGMA_OMP_NOTHING.
gcc/testsuite/
	* c-c++-common/gomp/nothing-1.c: New test.
	* g++.dg/gomp/attrs-1.C (bar): Add nothing directive test.
	* g++.dg/gomp/attrs-2.C (bar): Likewise.
	* g++.dg/gomp/attrs-9.C: Likewise.
libgomp/
	* testsuite/libgomp.c-c++-common/nothing-1.c: New test.

1 files changed, 15 insertions, 0 deletions

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 565efc4..d5f51b1 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -1578,6 +1578,7 @@ static tree c_parser_omp_for_loop (location_t, c_parser *, enum tree_code,
 static void c_parser_omp_taskwait (c_parser *);
 static void c_parser_omp_taskyield (c_parser *);
 static void c_parser_omp_cancel (c_parser *);
+static void c_parser_omp_nothing (c_parser *);
 
 enum pragma_context { pragma_external, pragma_struct, pragma_param,
 		      pragma_stmt, pragma_compound };
@@ -12480,6 +12481,10 @@ c_parser_pragma (c_parser *parser, enum pragma_context context, bool *if_p)
       c_parser_omp_requires (parser);
       return false;
 
+    case PRAGMA_OMP_NOTHING:
+      c_parser_omp_nothing (parser);
+      return false;
+
     case PRAGMA_OMP_ORDERED:
       return c_parser_omp_ordered (parser, context, if_p);
 
@@ -21908,6 +21913,16 @@ c_parser_omp_taskloop (location_t loc, c_parser *parser,
   return ret;
 }
 
+/* OpenMP 5.1
+   #pragma omp nothing new-line  */
+
+static void
+c_parser_omp_nothing (c_parser *parser)
+{
+  c_parser_consume_pragma (parser);
+  c_parser_skip_to_pragma_eol (parser);
+}
+
 /* Main entry point to parsing most OpenMP pragmas.  */
 
 static void