'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, 17 insertions, 14 deletions

diff --git a/gcc/fortran/trans-openmp.cc b/gcc/fortran/trans-openmp.cc
index 84c0184..4ff9c59 100644
--- a/gcc/fortran/trans-openmp.cc
+++ b/gcc/fortran/trans-openmp.cc
@@ -5603,26 +5603,29 @@ gfc_trans_omp_do (gfc_code *code, gfc_exec_op op, stmtblock_t *pblock,
   /* Main loop body.  */
   if (clauses->lists[OMP_LIST_REDUCTION_INSCAN])
     {
-      gcc_assert (code->block->next->next->op == EXEC_OMP_SCAN);
-      gcc_assert (code->block->next->next->next->next == NULL);
-      locus *cloc = &code->block->next->next->loc;
-      location_t loc = gfc_get_location (cloc);
-
-      gfc_code code2 = *code->block->next;
-      code2.next = NULL;
-      tmp = gfc_trans_code (&code2);
+      gfc_code *code1, *scan, *code2, *tmpcode;
+      code1 = tmpcode = code->block->next;
+      if (tmpcode && tmpcode->op != EXEC_OMP_SCAN)
+	while (tmpcode && tmpcode->next && tmpcode->next->op != EXEC_OMP_SCAN)
+	  tmpcode = tmpcode->next;
+      scan = tmpcode->op == EXEC_OMP_SCAN ? tmpcode : tmpcode->next;
+      if (code1 != scan)
+	tmpcode->next = NULL;
+      code2 = scan->next;
+      gcc_assert (scan->op == EXEC_OMP_SCAN);
+      location_t loc = gfc_get_location (&scan->loc);
+
+      tmp = code1 != scan ? gfc_trans_code (code1) : build_empty_stmt (loc);
       tmp = build2 (OMP_SCAN, void_type_node, tmp, NULL_TREE);
       SET_EXPR_LOCATION (tmp, loc);
       gfc_add_expr_to_block (&body, tmp);
       input_location = loc;
-      tree c = gfc_trans_omp_clauses (&body,
-				      code->block->next->next->ext.omp_clauses,
-				      *cloc);
-      code2 = *code->block->next->next->next;
-      code2.next = NULL;
-      tmp = gfc_trans_code (&code2);
+      tree c = gfc_trans_omp_clauses (&body, scan->ext.omp_clauses, scan->loc);
+      tmp = code2 ? gfc_trans_code (code2) : build_empty_stmt (loc);
       tmp = build2 (OMP_SCAN, void_type_node, tmp, c);
       SET_EXPR_LOCATION (tmp, loc);
+      if (code1 != scan)
+	tmpcode->next = scan;
     }
   else
     tmp = gfc_trans_omp_code (code->block->next, true);