OpenMP/OpenACC: mapping group list-handling improvements

This patch adjusts OpenMP/OpenACC clause list handling in a couple of
places, in preparation for the following mapping-clause expansion rework
patch. Firstly mapping groups are removed as a whole in the C and C++
front-ends when an error is detected, which avoids leaving "badly-formed"
mapping clause groups in the list.

Secondly, reindexing of the omp_mapping_group hashmap (during
omp_build_struct_sibling_lists) has been reimplemented, fixing some
tricky corner-cases where mapping groups are removed from a list at the
same time as it is being reordered.

Thirdly, code to check if a different clause on the same directive maps
the whole of a struct that we have a component mapping for (for example)
has been outlined, removing a bit of code duplication.

2022-09-13  Julian Brown  <julian@codesourcery.com>

gcc/
	* gimplify.cc (omp_group_last): Allow GOMP_MAP_ATTACH_DETACH after
	GOMP_MAP_STRUCT (for reindexing).
	(omp_gather_mapping_groups): Reimplement using...
	(omp_gather_mapping_groups_1): This new function.  Stop processing at
	GATHER_SENTINEL.
	(omp_group_base): Allow GOMP_MAP_TO_PSET without any following node.
	(omp_index_mapping_groups): Reimplement using...
	(omp_index_mapping_groups_1): This new function.  Handle
	REINDEX_SENTINEL.
	(omp_reindex_mapping_groups, omp_mapped_by_containing_struct): New
	functions.
	(omp_tsort_mapping_groups_1): Adjust handling of base group being the
	same as current group.  Use omp_mapped_by_containing_struct.
	(omp_build_struct_sibling_lists): Use omp_mapped_by_containing_struct
	and omp_reindex_mapping_groups.  Robustify group deletion for reordered
	lists.
	(gimplify_scan_omp_clauses): Update calls to
	omp_build_struct_sibling_lists.

gcc/c/
	* c-typeck.cc (c_finish_omp_clauses): Remove whole mapping node group
	on error.

gcc/cp/
	* semantics.cc (finish_omp_clauses): Likewise.

1 files changed, 23 insertions, 1 deletions

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 9ada5d2..43a910d 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -14238,12 +14238,19 @@ c_finish_omp_clauses (tree clauses, enum c_omp_region_type ort)
 	  break;
 	}
 
+  tree *grp_start_p = NULL, grp_sentinel = NULL_TREE;
+
   for (pc = &clauses, c = clauses; c ; c = *pc)
     {
       bool remove = false;
       bool need_complete = false;
       bool need_implicitly_determined = false;
 
+      /* We've reached the end of a list of expanded nodes.  Reset the group
+	 start pointer.  */
+      if (c == grp_sentinel)
+	grp_start_p = NULL;
+
       switch (OMP_CLAUSE_CODE (c))
 	{
 	case OMP_CLAUSE_SHARED:
@@ -15001,6 +15008,9 @@ c_finish_omp_clauses (tree clauses, enum c_omp_region_type ort)
 	  t = OMP_CLAUSE_DECL (c);
 	  if (TREE_CODE (t) == TREE_LIST)
 	    {
+	      grp_start_p = pc;
+	      grp_sentinel = OMP_CLAUSE_CHAIN (c);
+
 	      if (handle_omp_array_sections (c, ort))
 		remove = true;
 	      else
@@ -15644,7 +15654,19 @@ c_finish_omp_clauses (tree clauses, enum c_omp_region_type ort)
 	}
 
       if (remove)
-	*pc = OMP_CLAUSE_CHAIN (c);
+	{
+	  if (grp_start_p)
+	    {
+	      /* If we found a clause to remove, we want to remove the whole
+		 expanded group, otherwise gimplify
+		 (omp_resolve_clause_dependencies) can get confused.  */
+	      *grp_start_p = grp_sentinel;
+	      pc = grp_start_p;
+	      grp_start_p = NULL;
+	    }
+	  else
+	    *pc = OMP_CLAUSE_CHAIN (c);
+	}
       else
 	pc = &OMP_CLAUSE_CHAIN (c);
     }