[RFC] use templated isl types reductionUpdates

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/reduction_matcher.cc

@@ -54,7 +54,7 @@ bool isSupportedReductionUpdateId(isl::id id, const Scop& scop) {
 
 } // namespace
 
-isl::union_set reductionUpdates(isl::union_set domain, const Scop& scop) {
+isl::UnionSet<Statement> reductionUpdates(isl::union_set domain, const Scop& scop) {
   domain = scop.body.reductions.intersect_domain(domain).domain();
   auto update = isl::union_set::empty(domain.get_space());
   domain.foreach_set([&update, &scop](isl::set set) {
@@ -63,7 +63,7 @@ isl::union_set reductionUpdates(isl::union_set domain, const Scop& scop) {
       update = update.unite(set);
     }
   });
-  return update;
+  return isl::UnionSet<Statement>(update);
 }
 
 } // namespace polyhedral

tc/core/polyhedral/schedule_tree_matcher.h

@@ -19,6 +19,7 @@
 #include <utility>
 #include <vector>
 
+#include "tc/core/polyhedral/domain_types.h"
 #include "tc/core/polyhedral/schedule_tree.h"
 #include "tc/core/polyhedral/scop.h"
 
@@ -27,7 +28,7 @@ namespace polyhedral {
 
 // Return the union of the reduction update statements
 // that appear in "domain".
-isl::union_set reductionUpdates(isl::union_set domain, const Scop& scop);
+isl::UnionSet<Statement> reductionUpdates(isl::union_set domain, const Scop& scop);
 
 // Does "prefix" partition "domain" into individual reductions?
 // In particular, do the elements of "domain" access a single tensor