isl_map_union: special case universal input

In particular, there is no need to construct a new isl_map
as we can simply return the universal input map.

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

diff --git a/isl_map.c b/isl_map.c
index c83a446..3ef86f4 100644 (file)
--- a/isl_map.c
+++ b/isl_map.c
@@ -6446,12 +6446,23 @@ error:
        return NULL;
 }
 
+/* Return the union of "map1" and "map2", where we assume for now that
+ * "map1" and "map2" are disjoint.  Note that the basic maps inside
+ * "map1" or "map2" may not be disjoint from each other.
+ * Also note that this function is also called from isl_map_union,
+ * which takes care of handling the situation where "map1" and "map2"
+ * may not be disjoint.
+ *
+ * If one of the inputs is empty, we can simply return the other input.
+ * Similarly, if one of the inputs is universal, then it is equal to the union.
+ */
 static __isl_give isl_map *map_union_disjoint(__isl_take isl_map *map1,
        __isl_take isl_map *map2)
 {
        int i;
        unsigned flags = 0;
        struct isl_map *map = NULL;
+       int is_universe;
 
        if (!map1 || !map2)
                goto error;
@@ -6465,6 +6476,22 @@ static __isl_give isl_map *map_union_disjoint(__isl_take isl_map *map1,
                return map1;
        }
 
+       is_universe = isl_map_plain_is_universe(map1);
+       if (is_universe < 0)
+               goto error;
+       if (is_universe) {
+               isl_map_free(map2);
+               return map1;
+       }
+
+       is_universe = isl_map_plain_is_universe(map2);
+       if (is_universe < 0)
+               goto error;
+       if (is_universe) {
+               isl_map_free(map1);
+               return map2;
+       }
+
        isl_assert(map1->ctx, isl_space_is_equal(map1->dim, map2->dim), goto error);
 
        if (ISL_F_ISSET(map1, ISL_MAP_DISJOINT) &&