ScheduleTreeElemSet: require isl::ctx in constructor

Since ScheduleTreeElemSet is now a subclass of ScheduleTree, it needs an
isl::ctx to construct the ScheduleTree.  It is available in all
callsites of the ScheduleTreeElemSet constructor.  Pass it as an
argument.

Author: ftynse

tc/core/polyhedral/schedule_isl_conversion.cc

@@ -284,7 +284,7 @@ std::unique_ptr<ScheduleTree> elemFromIslScheduleNode(isl::schedule_node node) {
     return std::unique_ptr<ScheduleTreeElemSequence>(
         new ScheduleTreeElemSequence(ctx));
   } else if (node.isa<isl::schedule_node_set>()) {
-    return std::unique_ptr<ScheduleTreeElemSet>(new ScheduleTreeElemSet());
+    return std::unique_ptr<ScheduleTreeElemSet>(new ScheduleTreeElemSet(ctx));
   }
   LOG(FATAL) << "NYI: ScheduleTree from type: "
              << isl_schedule_node_get_type(node.get());

tc/core/polyhedral/schedule_tree_elem.h

@@ -177,9 +177,8 @@ struct ScheduleTreeElemSequence : public ScheduleTree {
 struct ScheduleTreeElemSet : public ScheduleTree {
   static constexpr detail::ScheduleTreeType NodeType =
       detail::ScheduleTreeType::Set;
-  explicit ScheduleTreeElemSet()
-      : ScheduleTree(isl::with_exceptions::globalIslCtx(), {}, NodeType) {
-  } // FIXME: accept a ctx instead of using the global ctx
+  explicit ScheduleTreeElemSet(isl::ctx ctx)
+      : ScheduleTree(ctx, {}, NodeType) {}
   ScheduleTreeElemSet(const ScheduleTreeElemSet& eb) : ScheduleTree(eb) {}
   virtual ~ScheduleTreeElemSet() override {}
   bool operator==(const ScheduleTreeElemSet& other) const;