bechordal: Process Phis before live-in nodes again.

Add a comment, why this is an important property.

ir/be/bechordal_common.c

@@ -87,9 +87,6 @@ void create_borders(ir_node *block, void *env_ptr)
 	 * relevant for the interval borders.
 	 */
 	sched_foreach_reverse(block, irn) {
-		if (is_Phi(irn))
-			break;
-
 		DB((dbg, LEVEL_1, "\tinsn: %+F\n", irn));
 
 		be_foreach_definition(irn, env->cls, def, req,
@@ -101,23 +98,27 @@ void create_borders(ir_node *block, void *env_ptr)
 			border_def(def, step, 1);
 		);
 
-		/* Examine the uses. */
-		be_foreach_use(irn, env->cls, in_req_, op, op_req_,
-			const char *msg = "-";
+		/* If the node is no phi node we can examine the uses. */
+		if (!is_Phi(irn)) {
+			be_foreach_use(irn, env->cls, in_req_, op, op_req_,
+				const char *msg = "-";
 
-			if (ir_nodeset_insert(&live, op)) {
-				border_use(op, step, 1);
-				msg = "X";
-			}
+				if (ir_nodeset_insert(&live, op)) {
+					border_use(op, step, 1);
+					msg = "X";
+				}
 
-			DB((dbg, LEVEL_4, "\t\t%s pos: %d, use: %+F\n", msg, i_, op));
-		);
+				DB((dbg, LEVEL_4, "\t\t%s pos: %d, use: %+F\n", msg, i_, op));
+			);
+		}
 		++step;
 	}
 
+	/* Process live-ins last. In particular all Phis are handled before, so when
+	 * iterating the borders the live-ins come before all Phis ("live-start"). */
 	foreach_ir_nodeset(&live, irn, iter) {
-		assert(be_is_live_in(lv, block, irn) ^ (is_Phi(irn) && get_nodes_block(irn) == block));
-		border_def(irn, step, get_nodes_block(irn) == block);
+		assert(be_is_live_in(lv, block, irn));
+		border_def(irn, step, 0);
 	}
 
 	ir_nodeset_destroy(&live);