[RFC] use templated isl types prefixScheduleMupa

Templated isl types require the user to specify the domain and range
universes of isl objects, allowing the compiler to check whether
it makes sense to combine pairs of objects.
This RFC only converts isPromotableToRegistersBelow and some related
functions to illustrate the effect.
The isPromotableToRegistersBelow was already applying operations
correctly, so the code itself did not require any changes.
However, one variable was reused to store different types
of intermediate result and this one had to be split up into
several variables because they now have different types.

Author: Sven Verdoolaege

tc/core/polyhedral/schedule_utils.cc

@@ -251,11 +251,13 @@ isl::multi_union_pw_aff infixScheduleMupa(
   return prefix;
 }
 
+namespace detail {
 isl::multi_union_pw_aff prefixScheduleMupa(
     const ScheduleTree* root,
     const ScheduleTree* tree) {
   return infixScheduleMupa(root, root, tree);
 }
+} // namespace detail
 
 isl::multi_union_pw_aff partialScheduleMupa(
     const detail::ScheduleTree* root,

tc/core/polyhedral/schedule_utils.h

@@ -19,6 +19,7 @@
 
 #include "tc/core/check.h"
 #include "tc/core/constants.h"
+#include "tc/core/polyhedral/domain_types.h"
 #include "tc/core/polyhedral/schedule_tree.h"
 #include "tc/core/polyhedral/schedule_tree_elem.h"
 
@@ -78,9 +79,18 @@ isl::multi_union_pw_aff infixScheduleMupa(
 // function on the universe domain of the schedule tree.
 // Note that unlike isl_schedule_node_get_prefix_schedule_multi_union_pw_aff,
 // this function does not take into account any intermediate filter nodes.
+namespace detail {
 isl::multi_union_pw_aff prefixScheduleMupa(
     const detail::ScheduleTree* root,
     const detail::ScheduleTree* tree);
+}
+template <typename Schedule>
+isl::MultiUnionPwAff<Statement, Schedule> prefixScheduleMupa(
+    const detail::ScheduleTree* root,
+    const detail::ScheduleTree* tree) {
+  auto prefix = detail::prefixScheduleMupa(root, tree);
+  return isl::MultiUnionPwAff<Statement, Schedule>(prefix);
+}
 
 // Return the concatenation of all outer band node partial schedules,
 // including that of the node itself.