[RFC] use templated isl types Scop::context()

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

@@ -32,6 +32,7 @@
 #include "tc/core/polyhedral/cuda/mapping_types.h"
 #include "tc/core/polyhedral/cuda/memory_promotion_heuristic.h"
 #include "tc/core/polyhedral/cuda/tighten_launch_bounds.h"
+#include "tc/core/polyhedral/domain_types.h"
 #include "tc/core/polyhedral/exceptions.h"
 #include "tc/core/polyhedral/schedule_transforms.h"
 #include "tc/core/polyhedral/schedule_tree_matcher.h"
@@ -895,7 +896,7 @@ std::unique_ptr<MappedScop> makeSpecializedMappedScop(
   // outer schedule dimensions, so the space of a parameter context code is that
   // of a zero-dimensional space.
   auto root = scop->scheduleRoot();
-  updateTopLevelContext(root, scop->context().from_params());
+  updateTopLevelContext(root, scop->context().from_params<Prefix>());
 
   tc::Grid grid = mappedScop.numBlocks;
   tc::Block block = mappedScop.numThreads;

tc/core/polyhedral/scop.h

@@ -92,10 +92,10 @@ struct Scop {
   // The schedule tree of the scop does not necessarily have
   // a context node.  Call updateTopLevelContext on the schedule tree
   // to introduce or refine such a context node.
-  isl::set context() const {
+  isl::Set<> context() const {
     auto ctx = domain().get_ctx();
     auto context = halide2isl::makeParamContext(ctx, halide.params);
-    return context.intersect(makeContext(parameterValues));
+    return isl::Set<>(context.intersect(makeContext(parameterValues)));
   }
 
   // Specialize a Scop by fixing the given parameters to the given sizes.