isl_basic_map_gist: prefer contraints without existentially quantified variables

[platform/upstream/isl.git] / isl_map_simplify.c

diff --git a/isl_map_simplify.c b/isl_map_simplify.c
index 302c123..093d1ca 100644 (file)
--- a/isl_map_simplify.c
+++ b/isl_map_simplify.c
@@ -1702,6 +1702,13 @@ error:
  * We first compute the integer affine hull of the intersection,
  * compute the gist inside this affine hull and then add back
  * those equalities that are not implied by the context.
+ *
+ * If two constraints are mutually redundant, then uset_gist_full
+ * will remove the second of those constraints.  We therefore first
+ * sort the constraints so that constraints not involving existentially
+ * quantified variables are given precedence over those that do.
+ * We have to perform this sorting before the variable compression,
+ * because that may effect the order of the variables.
  */
 static __isl_give isl_basic_set *uset_gist(__isl_take isl_basic_set *bset,
        __isl_take isl_basic_set *context)
@@ -1720,6 +1727,7 @@ static __isl_give isl_basic_set *uset_gist(__isl_take isl_basic_set *bset,
                isl_basic_set_free(context);
                return bset;
        }
+       bset = isl_basic_set_sort_constraints(bset);
        aff = isl_basic_set_affine_hull(isl_basic_set_copy(bset));
        if (!aff)
                goto error;