openmp: Reject #pragma omp atomic update, [PR101297]

I've noticed that we allow a trailing comma on OpenMP atomic construct
if there is at least one clause.  Commas should be only allowed to
separate the clauses (or in OpenMP 5.1 to separate directive name
from the clauses).

2021-07-02  Jakub Jelinek  <jakub@redhat.com>

	PR c/101297
	* c-parser.c (c_parser_omp_atomic): Consume comma only if it
	appears before a CPP_NAME.

	* parser.c (cp_parser_omp_atomic): Consume comma only if it
	appears before a CPP_NAME.

	* c-c++-common/gomp/atomic-24.c: New test.

3 files changed, 18 insertions, 2 deletions

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 3922b56..9a56e0c 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -17533,7 +17533,9 @@ c_parser_omp_atomic (location_t loc, c_parser *parser, bool openacc)
 
   while (c_parser_next_token_is_not (parser, CPP_PRAGMA_EOL))
     {
-      if (!first && c_parser_next_token_is (parser, CPP_COMMA))
+      if (!first
+	  && c_parser_next_token_is (parser, CPP_COMMA)
+	  && c_parser_peek_2nd_token (parser)->type == CPP_NAME)
 	c_parser_consume_token (parser);
 
       first = false;
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 02daa7a..3550cd0 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -39171,7 +39171,9 @@ cp_parser_omp_atomic (cp_parser *parser, cp_token *pragma_tok, bool openacc)
 
   while (cp_lexer_next_token_is_not (parser->lexer, CPP_PRAGMA_EOL))
     {
-      if (!first && cp_lexer_next_token_is (parser->lexer, CPP_COMMA))
+      if (!first
+	  && cp_lexer_next_token_is (parser->lexer, CPP_COMMA)
+	  && cp_lexer_nth_token_is (parser->lexer, 2, CPP_NAME))
 	cp_lexer_consume_token (parser->lexer);
 
       first = false;
diff --git a/gcc/testsuite/c-c++-common/gomp/atomic-24.c b/gcc/testsuite/c-c++-common/gomp/atomic-24.c
new file mode 100644
index 0000000..f70c805
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/gomp/atomic-24.c
@@ -0,0 +1,12 @@
+/* PR c/101297 */
+
+int i;
+
+void
+foo (void)
+{
+  #pragma omp atomic update,	/* { dg-error "expected end of line before ',' token" } */
+  i++;
+  #pragma omp atomic update,,	/* { dg-error "expected end of line before ',' token" } */
+  i++;
+}