Index: modulo-sched.c
===================================================================
--- modulo-sched.c	(revision 129721)
+++ modulo-sched.c	(working copy)
@@ -1518,6 +1518,52 @@
     return 0;
 }
 
+
+/* Calculate MUST_PRECEDE and MUST_FOLLOW bitmaps of U_NODE; which is
+   the node currently been scheduled; using START, END and STEP which are
+   the boundaries of U_NODE's scheduling window, II and SCHED_NODES which
+   is the list of already scheduled nodes.  At the end of the calculation
+   MUST_PRECEDE (MUST_FOLLOW) should contain all already scheduled
+   predecessors (successors) of U_NODE that MUST_PRECEDE (MUST_FOLLOW) it
+   if they are all scheduled in the START or END row in order to preserve
+   the dependence between them.  */
+
+static void
+calculate_must_precede_and_must_follow (ddg_node_ptr u_node, int start,
+					int end, int step, int ii,
+					sbitmap sched_nodes,
+					sbitmap must_precede,
+					sbitmap must_follow)
+{
+  ddg_edge_ptr e;
+  int start_row = SMODULO (start, ii);
+  int end_row = SMODULO ((end - step), ii);
+
+  for (e = u_node->in; e != 0; e = e->next_in)
+    if (TEST_BIT (sched_nodes, e->src->cuid)
+	&& ((SMODULO (SCHED_TIME (e->src), ii) == start_row)
+	    || (SMODULO (SCHED_TIME (e->src), ii) == end_row)))
+      SET_BIT (must_precede, e->src->cuid);
+
+  for (e = u_node->out; e != 0; e = e->next_out)
+    if (TEST_BIT (sched_nodes, e->dest->cuid)
+	&& ((SMODULO (SCHED_TIME (e->dest), ii) == end_row)
+	    || (SMODULO (SCHED_TIME (e->dest), ii) == start_row)))
+      {
+	SET_BIT (must_follow, e->dest->cuid);
+
+	if (TEST_BIT (must_precede, e->dest->cuid))
+	  {
+            /* Avoid inserting the same node to both must_precede and
+               must_follow by considering edges with distance zero.  */
+	    if (e->distance == 0)
+	      RESET_BIT (must_precede, e->dest->cuid);
+	    else
+	      RESET_BIT (must_follow, e->dest->cuid);
+	  }
+      }
+}
+
 /* This function implements the scheduling algorithm for SMS according to the
    above algorithm.  */
 static partial_schedule_ptr
@@ -1527,7 +1573,6 @@
   int i, c, success, num_splits = 0;
   int flush_and_start_over = true;
   int num_nodes = g->num_nodes;
-  ddg_edge_ptr e;
   ps_insn_ptr psi;
   int start, end, step; /* Place together into one struct?  */
   sbitmap sched_nodes = sbitmap_alloc (num_nodes);
@@ -1590,18 +1635,11 @@
                  both scheduled in the same row.  The current check is less
                  conservative and content with the fact that both U and the
                  insn are scheduled in the same row.  */
-              for (e = u_node->in; e != 0; e = e->next_in)
-                if (TEST_BIT (sched_nodes, e->src->cuid)
-                    && (SMODULO (SCHED_TIME (e->src), ii) ==
-                        SMODULO (start, ii)))
-                  SET_BIT (must_precede, e->src->cuid);
+              calculate_must_precede_and_must_follow (u_node, start, end,
+                                                      step, ii, sched_nodes,
+                                                      must_precede,
+                                                      must_follow);
 
-              for (e = u_node->out; e != 0; e = e->next_out)
-                if (TEST_BIT (sched_nodes, e->dest->cuid)
-                    && (SMODULO (SCHED_TIME (e->dest), ii) ==
-                        SMODULO ((end - step), ii)))
-                  SET_BIT (must_follow, e->dest->cuid);
-
               gcc_assert ((step > 0 && start < end)
                           || (step < 0 && start > end));