openacc: Fix up C++ #pragma acc routine handling [PR101731]

The following testcase ICEs because two function declarations are nested in
each other and the acc routine handling code isn't prepared to put the
pragma on both.

The fix is similar to what #pragma omp declare {simd,variant} does,
in particular set the fndecl_seen flag already in cp_parser_late_parsing*
when we encounter it rather than only after we finalize it.

In cp_finalize_oacc_routine I had to move the fndecl_seen diagnostics to
non-FUNCTION_DECL block, because for FUNCTION_DECLs the flag is already
known to be set from cp_parser_late_parsing_oacc_routine, but can't be
removed altogether, because that regresses quality of 2 goacc/routine-5.c
diagnostics - we drop "a single " from the
'#pragma acc routine' not immediately followed by a single function declaration or definition
diagnostic say on
 #pragma acc routine
 int foo (), b;
if we drop it altogether.

2021-11-22  Jakub Jelinek  <jakub@redhat.com>

	PR c++/101731
	* parser.c (cp_parser_late_parsing_oacc_routine): Set
	parser->oacc_routine->fndecl_seen here, rather than ...
	(cp_finalize_oacc_routine): ... here.  Don't error if
	parser->oacc_routine->fndecl_seen is set for FUNCTION_DECLs.

	* c-c++-common/goacc/routine-6.c: New test.

1 files changed, 11 insertions, 15 deletions

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index aa7f0e4..e2b5d68 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -46852,8 +46852,8 @@ cp_parser_late_parsing_oacc_routine (cp_parser *parser, tree attrs)
      emission easier.  */
   parser->oacc_routine->clauses = nreverse (parser->oacc_routine->clauses);
   cp_parser_pop_lexer (parser);
-  /* Later, cp_finalize_oacc_routine will process the clauses, and then set
-     fndecl_seen.  */
+  /* Later, cp_finalize_oacc_routine will process the clauses.  */
+  parser->oacc_routine->fndecl_seen = true;
 
   return attrs;
 }
@@ -46871,16 +46871,17 @@ cp_finalize_oacc_routine (cp_parser *parser, tree fndecl, bool is_defn)
 	  || fndecl == error_mark_node)
 	return;
 
-      if (parser->oacc_routine->fndecl_seen)
-	{
-	  error_at (parser->oacc_routine->loc,
-		    "%<#pragma acc routine%> not immediately followed by"
-		    " a single function declaration or definition");
-	  parser->oacc_routine = NULL;
-	  return;
-	}
       if (TREE_CODE (fndecl) != FUNCTION_DECL)
 	{
+	  if (parser->oacc_routine->fndecl_seen)
+	    {
+	      error_at (parser->oacc_routine->loc,
+			"%<#pragma acc routine%> not immediately followed by"
+			" a single function declaration or definition");
+	      parser->oacc_routine = NULL;
+	      return;
+	    }
+
 	  cp_ensure_no_oacc_routine (parser);
 	  return;
 	}
@@ -46921,11 +46922,6 @@ cp_finalize_oacc_routine (cp_parser *parser, tree fndecl, bool is_defn)
 			 parser->oacc_routine->clauses,
 			 DECL_ATTRIBUTES (fndecl));
 	}
-
-      /* Don't unset parser->oacc_routine here: we may still need it to
-	 diagnose wrong usage.  But, remember that we've used this "#pragma acc
-	 routine".  */
-      parser->oacc_routine->fndecl_seen = true;
     }
 }