'omp scan' struct block seq update for OpenMP 5.x

While OpenMP 5.0 required a single structured block before and after the
'omp scan' directive, OpenMP 5.1 changed this to a 'structured block sequence,
denoting 2 or more executable statements in OpenMP 5.1 (whoops!) and zero or
more in OpenMP 5.2. This commit updates C/C++ to accept zero statements (but
till requires the '{' ... '}' for the final-loop-body) and updates Fortran
to accept zero or more than one statements.

If there is no preceeding or succeeding executable statement, a warning is
shown.

gcc/c/ChangeLog:

	* c-parser.cc (c_parser_omp_scan_loop_body): Handle
	zero exec statements before/after 'omp scan'.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_omp_scan_loop_body): Handle
	zero exec statements before/after 'omp scan'.

gcc/fortran/ChangeLog:

	* openmp.cc (gfc_resolve_omp_do_blocks): Handle zero
	or more than one exec statements before/after 'omp scan'.
	* trans-openmp.cc (gfc_trans_omp_do): Likewise.

libgomp/ChangeLog:

	* testsuite/libgomp.c-c++-common/scan-1.c: New test.
	* testsuite/libgomp.c/scan-23.c: New test.
	* testsuite/libgomp.fortran/scan-2.f90: New test.

gcc/testsuite/ChangeLog:

	* g++.dg/gomp/attrs-7.C: Update dg-error/dg-warning.
	* gfortran.dg/gomp/loop-2.f90: Likewise.
	* gfortran.dg/gomp/reduction5.f90: Likewise.
	* gfortran.dg/gomp/reduction6.f90: Likewise.
	* gfortran.dg/gomp/scan-1.f90: Likewise.
	* gfortran.dg/gomp/taskloop-2.f90: Likewise.
	* c-c++-common/gomp/scan-6.c: New test.
	* gfortran.dg/gomp/scan-8.f90: New test.

1 files changed, 20 insertions, 2 deletions

diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index 21bc316..9398c7a 100644
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -20112,6 +20112,7 @@ c_parser_omp_scan_loop_body (c_parser *parser, bool open_brace_parsed)
   tree substmt;
   location_t loc;
   tree clauses = NULL_TREE;
+  bool found_scan = false;
 
   loc = c_parser_peek_token (parser)->location;
   if (!open_brace_parsed
@@ -20122,7 +20123,15 @@ c_parser_omp_scan_loop_body (c_parser *parser, bool open_brace_parsed)
       return;
     }
 
-  substmt = c_parser_omp_structured_block_sequence (parser, PRAGMA_OMP_SCAN);
+  if (c_parser_peek_token (parser)->pragma_kind != PRAGMA_OMP_SCAN)
+    substmt = c_parser_omp_structured_block_sequence (parser, PRAGMA_OMP_SCAN);
+  else
+    {
+      warning_at (c_parser_peek_token (parser)->location, 0,
+		  "%<#pragma omp scan%> with zero preceding executable "
+		  "statements");
+      substmt = build_empty_stmt (loc);
+    }
   substmt = build2 (OMP_SCAN, void_type_node, substmt, NULL_TREE);
   SET_EXPR_LOCATION (substmt, loc);
   add_stmt (substmt);
@@ -20131,6 +20140,7 @@ c_parser_omp_scan_loop_body (c_parser *parser, bool open_brace_parsed)
   if (c_parser_peek_token (parser)->pragma_kind == PRAGMA_OMP_SCAN)
     {
       enum omp_clause_code clause = OMP_CLAUSE_ERROR;
+      found_scan = true;
 
       c_parser_consume_pragma (parser);
 
@@ -20160,7 +20170,15 @@ c_parser_omp_scan_loop_body (c_parser *parser, bool open_brace_parsed)
     error ("expected %<#pragma omp scan%>");
 
   clauses = c_finish_omp_clauses (clauses, C_ORT_OMP);
-  substmt = c_parser_omp_structured_block_sequence (parser, PRAGMA_NONE);
+  if (!c_parser_next_token_is (parser, CPP_CLOSE_BRACE))
+    substmt = c_parser_omp_structured_block_sequence (parser, PRAGMA_NONE);
+  else
+    {
+      if (found_scan)
+	warning_at (loc, 0, "%<#pragma omp scan%> with zero succeeding "
+			    "executable statements");
+      substmt = build_empty_stmt (loc);
+    }
   substmt = build2 (OMP_SCAN, void_type_node, substmt, clauses);
   SET_EXPR_LOCATION (substmt, loc);
   add_stmt (substmt);