+ * 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(heights, n1);
+ h2 = get_irn_height(heights, n2);
+ if (h1 < h2) return 1;
+ if (h1 > h2) return -1;
+ /* Same height, so use a random (but stable) order */