+/**
+ * Push nodes that do not need to be permed through the Perm.
+ * This is commonly a reload cascade at block ends.
+ * @note This routine needs interference.
+ * @note Probably, we can implement it a little more efficient.
+ * Especially searching the frontier lazily might be better.
+ * @param perm The perm.
+ * @param data The walker data (lower_env_t).
+ * @return 1, if there is something left to perm over.
+ * 0, if removed the complete perm.
+ */
+static int push_through_perm(ir_node *perm, void *data)
+{
+ lower_env_t *env = data;
+ const arch_env_t *aenv = env->arch_env;
+
+ ir_graph *irg = get_irn_irg(perm);
+ ir_node *bl = get_nodes_block(perm);
+ ir_node *node;
+ int arity = get_irn_arity(perm);
+ int *map;
+ int *proj_map;
+ bitset_t *moved = bitset_alloca(arity);
+ int n_moved;
+ int new_size;
+ ir_node *frontier = sched_first(bl);
+ FIRM_DBG_REGISTER(firm_dbg_module_t *mod, "firm.be.lower.permmove");
+
+ int i, n;
+ const ir_edge_t *edge;
+ ir_node *last_proj, *irn;
+ const arch_register_class_t *cls;
+
+ DBG((mod, LEVEL_1, "perm move %+F irg %+F\n", perm, irg));
+
+ /* get some proj and find out the register class of the proj. */
+ foreach_out_edge (perm, edge) {
+ last_proj = get_edge_src_irn(edge);
+ cls = arch_get_irn_reg_class(aenv, last_proj, -1);
+ assert(is_Proj(last_proj));
+ break;
+ }
+
+ /* find the point in the schedule after which the
+ * potentially movable nodes must be defined.
+ * A perm will only be pushed up to first instruction
+ * which lets an operand of itself die. */
+
+ sched_foreach_reverse_from (sched_prev(perm), irn) {
+ for(i = get_irn_arity(irn) - 1; i >= 0; --i) {
+ ir_node *op = get_irn_n(irn, i);
+ if(arch_irn_consider_in_reg_alloc(aenv, cls, op)
+ && !values_interfere(env->birg, op, last_proj)) {
+ frontier = sched_next(irn);
+ goto found_front;
+ }
+ }
+ }
+found_front:
+
+ DBG((mod, LEVEL_2, "\tfrontier: %+F\n", frontier));
+
+ node = sched_prev(perm);
+ n_moved = 0;
+ while(!sched_is_begin(node)) {
+ const arch_register_req_t *req;
+ int input = -1;
+ ir_node *proj;
+
+ foreach_out_edge(perm, edge) {
+ ir_node *out = get_edge_src_irn(edge);
+ int pn = get_Proj_proj(out);
+ ir_node *in = get_irn_n(perm, pn);
+ if(node == in) {
+ proj = out;
+ input = pn;
+ break;
+ }
+ }
+ /* it wasn't an input to the perm, we can't do anything more */
+ if(input < 0)
+ break;
+ if(!sched_comes_after(frontier, node))
+ break;
+ if(arch_irn_is(aenv, node, modify_flags))
+ break;
+ if(is_Proj(node)) {
+ req = arch_get_register_req(aenv, get_Proj_pred(node),
+ -1 - get_Proj_proj(node));
+ } else {
+ req = arch_get_register_req(aenv, node, -1);
+ }
+ if(req->type != arch_register_req_type_normal)
+ break;
+ for(i = get_irn_arity(node) - 1; i >= 0; --i) {
+ ir_node *opop = get_irn_n(node, i);
+ if (arch_irn_consider_in_reg_alloc(aenv, cls, opop)) {
+ break;
+ }
+ }
+ if(i >= 0)
+ break;
+
+ DBG((mod, LEVEL_2, "\tmoving %+F after %+F, killing %+F\n", node, perm, proj));
+
+ /* move the movable node in front of the Perm */
+ sched_remove(node);
+ sched_add_after(perm, node);
+
+ /* give it the proj's register */
+ arch_set_irn_register(aenv, node, arch_get_irn_register(aenv, proj));
+
+ /* reroute all users of the proj to the moved node. */
+ edges_reroute(proj, node, irg);
+
+ /* and kill it */
+ set_Proj_pred(proj, new_Bad());
+ be_kill_node(proj);
+
+ bitset_set(moved, input);
+ n_moved++;
+
+ node = sched_prev(node);
+ }
+
+ /* well, we could not push anything through the perm */
+ if(n_moved == 0)
+ return 1;
+
+ new_size = arity - n_moved;
+ if(new_size == 0) {
+ return 0;
+ }
+
+ map = alloca(new_size * sizeof(map[0]));
+ proj_map = alloca(arity * sizeof(proj_map[0]));
+ memset(proj_map, -1, sizeof(proj_map[0]));
+ n = 0;
+ for(i = 0; i < arity; ++i) {
+ if(bitset_is_set(moved, i))
+ continue;
+ map[n] = i;
+ proj_map[i] = n;
+ n++;
+ }
+ assert(n == new_size);
+ foreach_out_edge(perm, edge) {
+ ir_node *proj = get_edge_src_irn(edge);
+ int pn = get_Proj_proj(proj);
+ pn = proj_map[pn];
+ assert(pn >= 0);
+ set_Proj_proj(proj, pn);
+ }
+
+ be_Perm_reduce(perm, new_size, map);
+ return 1;
+}