isl_map_compute_divs: handle non-obviously empty input

In particular, properly handle the case where variable compression
detects that the input map is actually empty.

diff --git a/isl_map.c b/isl_map.c
index 49a7281..6512f03 100644 (file)
--- a/isl_map.c
+++ b/isl_map.c
@@ -4322,6 +4322,13 @@ static struct isl_set *parameter_compute_divs(struct isl_basic_set *bset)
                0, 1 + nparam);
        eq = isl_mat_cow(eq);
        T = isl_mat_variable_compression(isl_mat_copy(eq), &T2);
+       if (T && T->n_col == 0) {
+               isl_mat_free(T);
+               isl_mat_free(T2);
+               isl_mat_free(eq);
+               bset = isl_basic_set_set_to_empty(bset);
+               return isl_set_from_basic_set(bset);
+       }
        bset = basic_set_parameter_preimage(bset, T);
 
        set = isl_basic_set_lexmin(bset);