Fix beabi call sorting

Difference of idx for Calls with no order relation is stable,
but may lead to circular dependencies. Fixed by looking at
the heights first.

Fixes backend/transform_loop.c (with -O0)

[r28436]

diff --git a/ir/be/beabi.c b/ir/be/beabi.c
index e5eb80f..3348a69 100644 (file)
--- a/ir/be/beabi.c
+++ b/ir/be/beabi.c
@@ -979,6 +979,7 @@ static int cmp_call_dependency(const void *c1, const void *c2)
 {
        ir_node *n1 = *(ir_node **) c1;
        ir_node *n2 = *(ir_node **) c2;
+       unsigned h1, h2;
 
        /*
                Classical qsort() comparison function behavior:
@@ -993,7 +994,16 @@ static int cmp_call_dependency(const void *c1, const void *c2)
                return 1;
 
        /* The nodes have no depth order, but we need a total order because qsort()
-        * is not stable. */
+        * is not stable.
+        *
+        * Additionally, we need to respect transitive dependencies. Consider a
+        * Call a depending on Call b and an independent Call c.
+        * We MUST NOT order c > a and b > c. */
+       h1 = get_irn_height(ir_heights, n1);
+       h2 = get_irn_height(ir_heights, n2);
+       if (h1 < h2) return -1;
+       if (h1 > h2) return  1;
+       /* Same height, so use a random (but stable) order */
        return get_irn_idx(n1) - get_irn_idx(n2);
 }