memory promotion heuristic: introduce collectMappingsTo

This function returns the union of all mapping filters that map to the
given type of mapping ids.  It is similar in functionality to
extractDomainToIds except for the return type.  In particular, it
ignores elements introduced by extension nodes. It will be used to
collect block and thread mappings in the following commits.

Author: ftynse

tc/core/polyhedral/cuda/memory_promotion_heuristic.cc

@@ -323,6 +323,29 @@ bool promotionImprovesCoalescing(
   return false;
 }
 
+/*
+ * Returns the union of all mapping filters to "MappingType" in "scop".
+ *
+ * Note: similarly to MappedScop::[thread|block]MappingSchedule, this function
+ * does not take into account elements introduced by extension nodes.
+ */
+template <typename MappingType>
+isl::union_set collectMappingsTo(const Scop& scop) {
+  auto root = scop.scheduleRoot();
+  auto domain = scop.domain();
+  auto mappingFilters = detail::ScheduleTree::collect(
+      root, detail::ScheduleTreeType::MappingFilter);
+  mappingFilters = functional::Filter(isMappingTo<MappingType>, mappingFilters);
+  auto mapping = isl::union_set::empty(domain.get_space());
+  for (auto mf : mappingFilters) {
+    auto filterNode = mf->elemAs<detail::ScheduleTreeElemMappingFilter>();
+    auto filter = filterNode->filter_.intersect(
+        activeDomainPointsNoMappingNoExtension(root, mf));
+    mapping = mapping.unite(filterNode->filter_);
+  }
+  return mapping;
+}
+
 /*
  * Check if the given "group" can be promoted to registers for the given
  * mapping to thread identifiers and within the given outer schedule.