ScheduleTreeElemMappingFilter: only check identifiers once

The original code would loop over all sets in a filter and
then over all possible mapping identifiers, performing some
check on the identifiers that only need to be performed once.
Perform loop interchange to avoid the confusing duplicate checks.

Author: Sven Verdoolaege

tc/core/polyhedral/schedule_tree_elem.h

@@ -152,24 +152,24 @@ struct ScheduleTreeElemMappingFilter : public ScheduleTreeElemFilter {
           typename mapping::MappingId::Hash>& ids)
       : ScheduleTreeElemFilter(us), mappingIds(ids) {
     USING_MAPPING_SHORT_NAMES(BX, BY, BZ, TX, TY, TZ);
-    for (auto s : us.get_set_list()) {
-      for (auto id : std::vector<mapping::MappingId>{BX, BY, BZ, TX, TY, TZ}) {
-        if (mappingIds.count(id) > 0) {
-          CHECK_EQ(1u, ids.count(id)) << "id: " << id << " mapped >1 times";
+    for (auto id : std::vector<mapping::MappingId>{BX, BY, BZ, TX, TY, TZ}) {
+      if (mappingIds.count(id) > 0) {
+        CHECK_EQ(1u, ids.count(id)) << "id: " << id << " mapped >1 times";
+        for (auto s : us.get_set_list()) {
           CHECK(s.involves_param(id))
               << "unexpected missing id: " << id << " in filter: " << s;
-        } else {
-          if (s.involves_param(id)) {
-            std::stringstream ss;
-            for (auto id : ids) {
-              ss << id.to_str() << " ";
-            }
-            // TODO: will need to relax this if we map the same loop
-            // iteratively without stripmining it beforehand
-            CHECK(false) << "unexpected involved id: " << id
-                         << " in filter: " << s
-                         << " but not present in filter id list: " << ss.str();
+        }
+      } else {
+        if (us.involves_param(id)) {
+          std::stringstream ss;
+          for (auto id : ids) {
+            ss << id.to_str() << " ";
           }
+          // TODO: will need to relax this if we map the same loop
+          // iteratively without stripmining it beforehand
+          CHECK(false) << "unexpected involved id: " << id
+                       << " in filter: " << us
+                       << " but not present in filter id list: " << ss.str();
         }
       }
     }