2 * Copyright (C) 1995-2008 University of Karlsruhe. All right reserved.
4 * This file is part of libFirm.
6 * This file may be distributed and/or modified under the terms of the
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8 * Foundation and appearing in the file LICENSE.GPL included in the
9 * packaging of this file.
11 * Licensees holding valid libFirm Professional Edition licenses may use
12 * this file in accordance with the libFirm Commercial License.
13 * Agreement provided with the Software.
15 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
16 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * @brief Dead node elimination
23 * @author Michael Beck, Goetz Lindenmaier
25 * Strictly speaking dead node elimination is unnecessary in firm - everthying
26 * which is not used can't be found by any walker.
27 * The only drawback is that the nodes still take up memory. This phase fixes
28 * this by copying all (reachable) nodes to a new obstack and throwing away
33 #include "iroptimize.h"
35 #include "irgraph_t.h"
36 #include "iredges_t.h"
48 * Reroute the inputs of a node from nodes in the old graph to copied nodes in
51 static void rewire_inputs(ir_node *node, void *env)
54 irn_rewire_inputs(node);
57 static void copy_node_dce(ir_node *node, void *env)
59 ir_node *new_node = exact_copy(node);
62 /* preserve the node numbers for easier debugging */
63 new_node->node_nr = node->node_nr;
65 set_irn_link(node, new_node);
69 * Copies the graph reachable from the End node to the obstack
70 * in irg. Then fixes the fields containing nodes of the graph.
72 * @param copy_node_nr If non-zero, the node number will be copied
74 static void copy_graph_env(ir_graph *irg)
76 ir_node *anchor = irg->anchor;
80 irg_walk_in_or_dep(anchor, copy_node_dce, rewire_inputs, NULL);
83 new_anchor = (ir_node*)get_irn_link(anchor);
84 assert(new_anchor != NULL);
85 irg->anchor = new_anchor;
89 * Copies all reachable nodes to a new obstack. Removes bad inputs
90 * from block nodes and the corresponding inputs from Phi nodes.
91 * Merges single exit blocks with single entry blocks and removes
93 * Adds all new nodes to a new hash table for CSE. Does not
94 * perform CSE, so the hash table might contain common subexpressions.
96 void dead_node_elimination(ir_graph *irg)
98 struct obstack *graveyard_obst = NULL;
99 struct obstack *rebirth_obst = NULL;
101 edges_deactivate(irg);
103 /* inform statistics that we started a dead-node elimination run */
104 hook_dead_node_elim(irg, 1);
106 assert(get_irg_phase_state(irg) != phase_building);
108 /* Handle graph state */
109 free_callee_info(irg);
112 free_loop_information(irg);
114 clear_irg_properties(irg, IR_GRAPH_PROPERTY_CONSISTENT_DOMINANCE);
116 /* A quiet place, where the old obstack can rest in peace,
117 until it will be cremated. */
118 graveyard_obst = irg->obst;
120 /* A new obstack, where the reachable nodes will be copied to. */
121 rebirth_obst = XMALLOC(struct obstack);
122 irg->obst = rebirth_obst;
123 obstack_init(irg->obst);
124 irg->last_node_idx = 0;
126 /* We also need a new value table for CSE */
129 /* Copy the graph from the old to the new obstack */
132 /* Free memory from old unoptimized obstack */
133 obstack_free(graveyard_obst, 0); /* First empty the obstack ... */
134 xfree(graveyard_obst); /* ... then free it. */
136 /* inform statistics that the run is over */
137 hook_dead_node_elim(irg, 0);
140 ir_graph_pass_t *dead_node_elimination_pass(const char *name)
142 return def_graph_pass(name ? name : "dce", dead_node_elimination);