isl_union_map_is_subset: properly handle non-obviously empty subsets

If the first argument of isl_union_map_is_subset contains an empty
set in some space that is not present in the second argument,
then isl_union_map_is_subset would incorrectly draw the conclusion
that the first is not a subset of the second.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>

diff --git a/isl_union_map.c b/isl_union_map.c
index f62a302..d47df15 100644 (file)
--- a/isl_union_map.c
+++ b/isl_union_map.c
@@ -1672,6 +1672,11 @@ static int is_subset_entry(void **entry, void *user)
        entry2 = isl_hash_table_find(data->umap2->dim->ctx, &data->umap2->table,
                                     hash, &has_dim, map->dim, 0);
        if (!entry2) {
+               int empty = isl_map_is_empty(map);
+               if (empty < 0)
+                       return -1;
+               if (empty)
+                       return 0;
                data->is_subset = 0;
                return -1;
        }