[DeLICM] Use polly::singleton to allow empty result.

isl_map_from_union_map cannot determine the map's space if the union_map
is empty. polly::singleton was designed for this case. We pass the
expected map space to avoid crashing in isl_map_from_union_map.

This fixes an issue found by the aosp buildbot. Thanks to Eli Friedman
for the reproducer.

llvm-svn: 361290

1 files changed, 3 insertions, 2 deletions

diff --git a/polly/lib/Transform/DeLICM.cpp b/polly/lib/Transform/DeLICM.cpp
index b229d6008e2..7191993e845 100644
--- a/polly/lib/Transform/DeLICM.cpp
+++ b/polly/lib/Transform/DeLICM.cpp
@@ -900,8 +900,9 @@ private:
     }
 
     //  { DomainRead[] -> Scatter[] }
-    auto PerPHIWriteScatter =
-        isl::map::from_union_map(PerPHIWrites.apply_range(Schedule));
+    isl::union_map PerPHIWriteScatterUmap = PerPHIWrites.apply_range(Schedule);
+    isl::map PerPHIWriteScatter =
+        singleton(PerPHIWriteScatterUmap, PHISched.get_space());
 
     // { DomainRead[] -> Zone[] }
     auto Lifetime = betweenScatter(PerPHIWriteScatter, PHISched, false, true);