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4 * This file is part of libFirm.
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15 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
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22 * @brief Dead node elimination
23 * @author Michael Beck, Goetz Lindenmaier
24 * @version $Id: opt_inline.c 27265 2010-03-07 15:13:00Z matze $
26 * Strictly speaking dead node elimination is unnecessary in firm - everthying
27 * which is not used can't be found by any walker.
28 * The only drawback is that the nodes still take up memory. This phase fixes
29 * this by copying all (reachable) nodes to a new obstack and throwing away
34 #include "iroptimize.h"
36 #include "irgraph_t.h"
37 #include "irphase_t.h"
38 #include "iredges_t.h"
49 /** a pointer to the new phases */
50 static ir_phase *new_phases[PHASE_LAST + 1];
53 * Reroute the inputs of a node from nodes in the old graph to copied nodes in
56 static void rewire_inputs(ir_node *node, void *env)
59 irn_rewire_inputs(node);
62 static void copy_node_dce(ir_node *node, void *env)
65 ir_node *new_node = exact_copy(node);
66 ir_graph *irg = get_irn_irg(new_node);
69 /* preserve the node numbers for easier debugging */
70 new_node->node_nr = node->node_nr;
72 /* copy phase information for this node */
73 for (i = 0; i <= PHASE_LAST; i++) {
74 ir_phase *phase = irg_get_phase(irg, i);
77 if (!phase_get_irn_data(phase, node))
79 phase_set_irn_data(new_phases[i], new_node,
80 phase_get_irn_data(phase, node));
83 set_irn_link(node, new_node);
84 hook_dead_node_elim_subst(irg, node, new_node);
88 * Copies the graph reachable from current_ir_graph->end to the obstack
89 * in current_ir_graph and fixes the environment.
90 * Then fixes the fields in current_ir_graph containing nodes of the
93 * @param copy_node_nr If non-zero, the node number will be copied
95 static void copy_graph_env(ir_graph *irg)
100 /* init the new_phases array */
101 /* TODO: this is wrong, it should only allocate a new data_ptr inside
103 for (i = 0; i <= PHASE_LAST; i++) {
104 ir_phase *old_ph = irg_get_phase(irg, i);
105 if (old_ph == NULL) {
106 new_phases[i] = NULL;
108 new_phases[i] = new_phase(irg, old_ph->data_init);
109 new_phases[i]->priv = old_ph->priv;
114 irg_walk_anchors(irg, copy_node_dce, rewire_inputs, NULL);
117 new_anchor = get_irn_link(irg->anchor);
118 assert(new_anchor != NULL);
119 irg->anchor = new_anchor;
121 /* copy the new phases into the irg */
122 for (i = 0; i <= PHASE_LAST; i++) {
123 ir_phase *old_ph = irg_get_phase(irg, i);
127 /* Matze: commented out for now: This is a memory leak, but for a real
128 * fix we must not create new phases here, but reuse the old phases
129 * and just create a new data array */
130 /* phase_free(old_ph); */
131 irg->phases[i] = new_phases[i];
136 * Copies all reachable nodes to a new obstack. Removes bad inputs
137 * from block nodes and the corresponding inputs from Phi nodes.
138 * Merges single exit blocks with single entry blocks and removes
140 * Adds all new nodes to a new hash table for CSE. Does not
141 * perform CSE, so the hash table might contain common subexpressions.
143 void dead_node_elimination(ir_graph *irg)
146 struct obstack *graveyard_obst = NULL;
147 struct obstack *rebirth_obst = NULL;
149 edges_deactivate(irg);
151 /* inform statistics that we started a dead-node elimination run */
152 hook_dead_node_elim(irg, 1);
154 /* Remember external state of current_ir_graph. */
155 rem = current_ir_graph;
156 current_ir_graph = irg;
158 assert(get_irg_phase_state(irg) != phase_building);
160 /* Handle graph state */
161 free_callee_info(irg);
164 free_loop_information(irg);
165 set_irg_doms_inconsistent(irg);
167 /* A quiet place, where the old obstack can rest in peace,
168 until it will be cremated. */
169 graveyard_obst = irg->obst;
171 /* A new obstack, where the reachable nodes will be copied to. */
172 rebirth_obst = XMALLOC(struct obstack);
173 irg->obst = rebirth_obst;
174 obstack_init(irg->obst);
175 irg->last_node_idx = 0;
177 /* We also need a new value table for CSE */
180 /* Copy the graph from the old to the new obstack */
183 /* Free memory from old unoptimized obstack */
184 obstack_free(graveyard_obst, 0); /* First empty the obstack ... */
185 xfree(graveyard_obst); /* ... then free it. */
187 /* inform statistics that the run is over */
188 hook_dead_node_elim(irg, 0);
190 current_ir_graph = rem;
193 ir_graph_pass_t *dead_node_elimination_pass(const char *name)
195 return def_graph_pass(name ? name : "dce", dead_node_elimination);
202 __)|_| | \_/ | \_/(/_ |_/\__|__
204 The following stuff implements a facility that automatically patches
205 registered ir_node pointers to the new node when a dead node elimination
208 Warning: This is considered a hack - try hard to avoid this!
211 struct survive_dce_t {
215 hook_entry_t dead_node_elim;
216 hook_entry_t dead_node_elim_subst;
219 typedef struct survive_dce_list_t {
220 struct survive_dce_list_t *next;
222 } survive_dce_list_t;
224 static void dead_node_hook(void *context, ir_graph *irg, int start)
226 survive_dce_t *sd = context;
229 /* Create a new map before the dead node elimination is performed. */
231 sd->new_places = pmap_create_ex(pmap_count(sd->places));
233 /* Patch back all nodes if dead node elimination is over and something is to be done. */
234 pmap_destroy(sd->places);
235 sd->places = sd->new_places;
236 sd->new_places = NULL;
241 * Hook called when dead node elimination replaces old by nw.
243 static void dead_node_subst_hook(void *context, ir_graph *irg, ir_node *old, ir_node *nw)
245 survive_dce_t *sd = context;
246 survive_dce_list_t *list = pmap_get(sd->places, old);
249 /* If the node is to be patched back, write the new address to all registered locations. */
251 survive_dce_list_t *p;
253 for (p = list; p; p = p->next)
256 pmap_insert(sd->new_places, nw, list);
261 * Make a new Survive DCE environment.
263 survive_dce_t *new_survive_dce(void)
265 survive_dce_t *res = XMALLOC(survive_dce_t);
266 obstack_init(&res->obst);
267 res->places = pmap_create();
268 res->new_places = NULL;
270 res->dead_node_elim.hook._hook_dead_node_elim = dead_node_hook;
271 res->dead_node_elim.context = res;
272 res->dead_node_elim.next = NULL;
274 res->dead_node_elim_subst.hook._hook_dead_node_elim_subst = dead_node_subst_hook;
275 res->dead_node_elim_subst.context = res;
276 res->dead_node_elim_subst.next = NULL;
278 register_hook(hook_dead_node_elim, &res->dead_node_elim);
279 register_hook(hook_dead_node_elim_subst, &res->dead_node_elim_subst);
284 * Free a Survive DCE environment.
286 void free_survive_dce(survive_dce_t *sd)
288 obstack_free(&sd->obst, NULL);
289 pmap_destroy(sd->places);
290 unregister_hook(hook_dead_node_elim, &sd->dead_node_elim);
291 unregister_hook(hook_dead_node_elim_subst, &sd->dead_node_elim_subst);
296 * Register a node pointer to be patched upon DCE.
297 * When DCE occurs, the node pointer specified by @p place will be
298 * patched to the new address of the node it is pointing to.
300 * @param sd The Survive DCE environment.
301 * @param place The address of the node pointer.
303 void survive_dce_register_irn(survive_dce_t *sd, ir_node **place)
305 if (*place != NULL) {
306 ir_node *irn = *place;
307 survive_dce_list_t *curr = pmap_get(sd->places, irn);
308 survive_dce_list_t *nw = OALLOC(&sd->obst, survive_dce_list_t);
313 pmap_insert(sd->places, irn, nw);