add note/error message about critical edge splitting and IJmps

[r26084]

ir/opt/critical_edges.c

@@ -72,6 +72,12 @@ static void walk_critical_cf_edges(ir_node *n, void *env) {
 					continue;
 				goto insert;
 			}
+			if (is_IJmp(pre)) {
+				/* we can't add blocks in between ijmp and its destinations
+				 * TODO: What now, we can't split all critical edges because of this... */
+				fprintf(stderr, "libfirm warning: Couldn't split all critical edges (compiler will probably fail now)\n");
+				continue;
+			}
 			/* we don't want place nodes in the start block, so handle it like forking */
 			if (is_op_forking(cfop) || cfop == op_Start) {
 				/* Predecessor has multiple successors. Insert new control flow edge edges. */