addSingletonReferenceGroups: use get_map_list

This will make it easier to switch to templated types.

Author: Sven Verdoolaege

tc/core/polyhedral/memory_promotion.cc

@@ -302,7 +302,7 @@ void addSingletonReferenceGroups(
   // use currying to isolate the D part before intersecting with the domain
   // Compute initial groups with single reference per group.
   std::unordered_set<isl::id, isl::IslIdIslHash> unapproximatable;
-  for (auto a : isl::UnionAsVector<isl::union_map>(accesses)) {
+  for (auto a : accesses.get_map_list()) {
     if (isl::union_map(a.curry()).intersect_domain(domain).is_empty()) {
       continue;
     }