dataflow analysis: allow absence of "textual" order during sorting of sources

When sorting the potential sources, we would implicitly assume
that for any given pair of sources, one always appears before the other
at a certain level.  However, for more generic schedules, this may
not necessarily be the case.

To avoid that the results would depend on the order that the accesses
are given in case accesses overlap, we extend the partial order to
a (nearly) total order by taking into account the description of the
sources.

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

diff --git a/isl_flow.c b/isl_flow.c
index e8b9c58..fd9754e 100644 (file)
--- a/isl_flow.c
+++ b/isl_flow.c
@@ -156,11 +156,19 @@ struct isl_access_sort_info {
  * sorted first.
  * If they both share no levels, then the order is irrelevant.
  * Otherwise, if p1 appears before p2, then it should be sorted first.
+ * For more generic initial schedules, it is possible that neither
+ * p1 nor p2 appears before the other, or at least not in any obvious way.
+ * We therefore also check if p2 appears before p1, in which case p2
+ * should be sorted first.
+ * If not, we try to order the two statements based on the description
+ * of the iteration domains.  This results in an arbitrary, but fairly
+ * stable ordering.
  */
 static int access_sort_cmp(const void *p1, const void *p2)
 {
        const struct isl_access_sort_info *i1, *i2;
        int level1, level2;
+       uint32_t h1, h2;
        i1 = (const struct isl_access_sort_info *) p1;
        i2 = (const struct isl_access_sort_info *) p2;
 
@@ -171,8 +179,16 @@ static int access_sort_cmp(const void *p1, const void *p2)
                return level1 - level2;
 
        level1 = i1->acc->level_before(i1->source_data, i2->source_data);
+       if (level1 % 2)
+               return -1;
+
+       level2 = i1->acc->level_before(i2->source_data, i1->source_data);
+       if (level2 % 2)
+               return 1;
 
-       return (level1 % 2) ? -1 : 1;
+       h1 = isl_map_get_hash(i1->source_map);
+       h2 = isl_map_get_hash(i2->source_map);
+       return h1 - h2;
 }
 
 /* Sort the must source accesses in order of increasing number of shared