[RFC] use templated isl types isSingleReductionWithin

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/cuda/mapped_scop.cc

@@ -285,7 +285,7 @@ bool MappedScop::detectReductions(ScheduleTree* tree) {
   // a single reduction for now.
   // Support for multiple reductions would require a check
   // that these reductions do not interfere with each other.
-  auto domain = band->mupa_.domain();
+  auto domain = isl::UnionSet<Statement>(band->mupa_.domain());
   auto updates = reductionUpdates(domain, scop());
   if (updates.n_set() != 1) {
     return false;

tc/core/polyhedral/schedule_tree_matcher-inl.h

@@ -291,13 +291,14 @@ inline std::vector<const detail::ScheduleTree*> match(
   return matchDFSPreorder(matcher, tree);
 }
 
+template <typename Prefix>
 inline bool isSingleReductionWithin(
-    isl::union_set domain,
-    isl::multi_union_pw_aff prefix,
+    isl::UnionSet<Statement> domain,
+    isl::MultiUnionPwAff<Statement, Prefix> prefix,
     const Scop& scop) {
   auto reductions = scop.body.reductions;
   reductions = reductions.intersect_domain(domain);
-  auto prefixMap = isl::union_map::from(prefix);
+  auto prefixMap = prefix.toUnionMap();
   auto prefixToReduction = reductions.apply_domain(prefixMap);
   return prefixToReduction.is_single_valued();
 }

tc/core/polyhedral/schedule_tree_matcher.h

@@ -34,8 +34,8 @@ isl::UnionSet<Statement> reductionUpdates(isl::union_set domain, const Scop& sco
 // In particular, do the elements of "domain" access a single tensor
 // element within "prefix"?
 bool isSingleReductionWithin(
-    isl::union_set domain,
-    isl::multi_union_pw_aff prefix,
+    isl::UnionSet<Statement> domain,
+    isl::MultiUnionPwAff<Statement, Prefix> prefix,
     const Scop& scop);
 
 } // namespace polyhedral