[RFC] use templated isl types makeSpecializationSet

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/scop.h

@@ -134,7 +134,7 @@ struct Scop {
   isl::set makeContext(
       const std::unordered_map<std::string, T>& sizes =
           std::unordered_map<std::string, T>()) const {
-    auto s = domain().get_space();
+    auto s = isl::Space<>(domain().get_space());
     return makeSpecializationSet(s, sizes);
   }
 

tc/external/detail/islpp.h

@@ -322,18 +322,18 @@ inline isl::set makeParameterContext(
 // that ties the space parameter to the values.
 //
 template <typename T>
-inline isl::set makeSpecializationSet(
-    isl::space space,
+inline isl::Set<> makeSpecializationSet(
+    isl::Space<> space,
     const std::unordered_map<std::string, T>& paramValues) {
   auto ctx = space.get_ctx();
   for (auto kvp : paramValues) {
     space = space.add_param(isl::id(ctx, kvp.first));
   }
-  auto set = isl::set::universe(space);
+  auto set = isl::Set<>::universe(space);
   for (auto kvp : paramValues) {
     auto id = isl::id(ctx, kvp.first);
-    isl::aff affParam(isl::aff::param_on_domain_space(space, id));
-    set = set & (isl::aff_set(affParam) == kvp.second);
+    auto affParam(isl::AffOn<>::param_on_domain_space(space, id));
+    set = set & (isl::PwAffOn<>(affParam - kvp.second)).zero_set();
   }
   return set;
 }