tightenLaunchBounds: check that at least some paths in the tree are mapped

This is just a basic sanity check.
Checking that all paths are mapped would require special cases
for nodes such as synchronizations that should not be (explicitly)
mapped to threads.

Author: Sven Verdoolaege

tc/core/polyhedral/cuda/tighten_launch_bounds.cc

@@ -89,6 +89,7 @@ size_t maxValue(const Scop& scop, const MappingIdType& id) {
       << "Opportunity for tightening launch bounds with shifting -> min:"
       << min;
   TC_CHECK(max < sizetMax) << "missing mapping to " << id << "\n" << *root;
+  TC_CHECK(min < sizetMax) << "missing mapping to " << id << " type\n" << *root;
   // Inclusive range needs + 1 to translate to sizes
   return max + 1;
 }