Update isl to 93b8e43d

This update brings mostly interface cleanups, but also fixes two bugs in
imath (a memory leak, some undefined behavior).

llvm-svn: 238422
diff --git a/polly/lib/Transform/ScheduleOptimizer.cpp b/polly/lib/Transform/ScheduleOptimizer.cpp
index bef2354..97b701c 100644
--- a/polly/lib/Transform/ScheduleOptimizer.cpp
+++ b/polly/lib/Transform/ScheduleOptimizer.cpp
@@ -315,7 +315,7 @@
 __isl_give isl_union_map *
 IslScheduleOptimizer::getScheduleMap(__isl_keep isl_schedule *Schedule) {
   isl_schedule_node *Root = isl_schedule_get_root(Schedule);
-  Root = isl_schedule_node_map_descendant(
+  Root = isl_schedule_node_map_descendant_bottom_up(
       Root, IslScheduleOptimizer::optimizeBand, NULL);
   auto ScheduleMap = isl_schedule_node_get_subtree_schedule_union_map(Root);
   ScheduleMap = isl_union_map_detect_equalities(ScheduleMap);