2 * Copyright (C) 1995-2007 Inria Rhone-Alpes. All right reserved.
4 * This file is part of libFirm.
6 * This file may be distributed and/or modified under the terms of the
7 * GNU General Public License version 2 as published by the Free Software
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
23 * @author Sebastian Hack
27 * Liveness checks as developed by Benoit Boissinot, Fabrice Rastello and myself.
29 * The speciality here is, that nothing has to be recomputed if new nodes are created
30 * or old ones deleted.
32 * This algo has one core routine check_live_end_internal() which performs the liveness check.
33 * It only relies on the precomputation done in the constructor, which in turn needs:
35 * - the dominance tree
36 * - data obtained from a depth-first-search
38 * The precomputation remains valid as long as the CFG is not altered.
44 #include "irgraph_t.h"
46 #include "irnodemap.h"
47 #include "iredges_t.h"
57 #include "irlivechk.h"
61 typedef struct bl_info_t {
62 const ir_node *block; /**< The block. */
65 int id : 31; /**< a tight number for the block.
66 we're just reusing the pre num from
68 bitset_t *red_reachable; /**< Holds all id's if blocks reachable
69 in the CFG modulo back edges. */
71 bitset_t *be_tgt_reach; /**< target blocks of back edges whose
72 sources are reachable from this block
73 in the reduced graph. */
77 ir_nodemap block_infos;
81 bitset_t *back_edge_src;
82 bitset_t *back_edge_tgt;
84 DEBUG_ONLY(firm_dbg_module_t *dbg;)
87 static bl_info_t *get_block_info(lv_chk_t *lv, const ir_node *block)
89 bl_info_t *info = ir_nodemap_get(&lv->block_infos, block);
91 info = obstack_alloc(&lv->obst, sizeof(*info));
92 info->id = get_Block_dom_tree_pre_num(block);
94 info->red_reachable = bitset_obstack_alloc(&lv->obst, lv->n_blocks);
95 info->be_tgt_reach = bitset_obstack_alloc(&lv->obst, lv->n_blocks);
96 info->be_tgt_calc = 0;
97 ir_nodemap_insert(&lv->block_infos, block, info);
103 * Filter function to select all nodes for which liveness is computed.
105 * @return 1 if the node shall be considered in liveness, 0 if not.
107 static inline int is_liveness_node(const ir_node *irn)
109 switch (get_irn_opcode(irn)) {
123 * Compute the transitive closure on the reduced graph.
124 * The reduced graph is the original graph without back edges.
125 * Since that is a DAG, a reverse post order of the graph gives a toposort
126 * which is ideally suited to compute the transitive closure.
127 * Note also, that the DFS tree of the reduced graph is the same than the one
128 * of the original graph. This saves us computing a new reverse post order.
129 * We also can re-use the DFS tree of the original graph.
131 static void red_trans_closure(lv_chk_t *lv)
135 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
136 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
137 bl_info_t *bi = get_block_info(lv, bl);
139 const ir_edge_t *edge;
141 bitset_set(bi->red_reachable, bi->id);
142 foreach_block_succ (bl, edge) {
143 ir_node *succ = get_edge_src_irn(edge);
144 bl_info_t *si = get_block_info(lv, succ);
145 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
148 * if the successor is no back edge, include all reachable
149 * blocks from there into the reachable set of the current node
151 if (kind != DFS_EDGE_BACK) {
152 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
153 bitset_or(bi->red_reachable, si->red_reachable);
156 /* mark the block as a back edge src and succ as back edge tgt. */
158 bitset_set(lv->back_edge_src, bi->id);
159 bitset_set(lv->back_edge_tgt, si->id);
167 static void compute_back_edge_chain(lv_chk_t *lv, const ir_node *bl)
169 bitset_t *tmp = bitset_alloca(lv->n_blocks);
170 bl_info_t *bi = get_block_info(lv, bl);
174 DBG((lv->dbg, LEVEL_2, "computing T_%d\n", bi->id));
176 /* put all back edge sources reachable (reduced) from here in tmp */
177 bitset_copy(tmp, bi->red_reachable);
178 bitset_set(tmp, bi->id);
179 bitset_and(tmp, lv->back_edge_src);
182 DBG((lv->dbg, LEVEL_2, "\treachable be src: %B\n", tmp));
184 /* iterate over them ... */
185 bitset_foreach(tmp, elm) {
186 bl_info_t *si = lv->map[elm];
187 const ir_edge_t *edge;
189 /* and find back edge targets which are not reduced reachable from bl */
190 foreach_block_succ (si->block, edge) {
191 ir_node *tgt = get_edge_src_irn(edge);
192 bl_info_t *ti = get_block_info(lv, tgt);
193 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, si->block, tgt);
195 if (kind == DFS_EDGE_BACK && !bitset_is_set(bi->red_reachable, ti->id)) {
196 if (!ti->be_tgt_calc)
197 compute_back_edge_chain(lv, tgt);
198 bitset_set(bi->be_tgt_reach, ti->id);
199 bitset_or(bi->be_tgt_reach, ti->be_tgt_reach);
202 bitset_clear(bi->be_tgt_reach, bi->id);
207 static inline void compute_back_edge_chains(lv_chk_t *lv)
212 DBG((lv->dbg, LEVEL_2, "back edge sources: %B\n", lv->back_edge_src));
213 bitset_foreach(lv->back_edge_src, elm) {
214 compute_back_edge_chain(lv, lv->map[elm]->block);
217 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
218 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
219 bl_info_t *bi = get_block_info(lv, bl);
221 const ir_edge_t *edge;
223 if (!bitset_is_set(lv->back_edge_tgt, bi->id)) {
224 foreach_block_succ (bl, edge) {
225 ir_node *succ = get_edge_src_irn(edge);
226 bl_info_t *si = get_block_info(lv, succ);
227 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
229 if (kind != DFS_EDGE_BACK) {
230 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
231 bitset_or(bi->be_tgt_reach, si->be_tgt_reach);
237 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
238 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
239 bl_info_t *bi = get_block_info(lv, bl);
240 bitset_set(bi->be_tgt_reach, bi->id);
244 lv_chk_t *lv_chk_new(ir_graph *irg, const dfs_t *dfs)
246 lv_chk_t *res = XMALLOC(lv_chk_t);
252 ir_nodemap_init(&res->block_infos, irg);
253 obstack_init(&res->obst);
255 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
258 res->n_blocks = dfs_get_n_nodes(res->dfs);
259 res->back_edge_src = bitset_obstack_alloc(&res->obst, res->n_blocks);
260 res->back_edge_tgt = bitset_obstack_alloc(&res->obst, res->n_blocks);
261 res->map = OALLOCNZ(&res->obst, bl_info_t*, res->n_blocks);
263 /* fill the map which maps pre_num to block infos */
264 for (i = res->n_blocks - 1; i >= 0; --i) {
265 ir_node *irn = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
266 bl_info_t *bi = get_block_info(res, irn);
267 assert(bi->id < res->n_blocks);
268 assert(res->map[bi->id] == NULL);
269 res->map[bi->id] = bi;
272 /* first of all, compute the transitive closure of the CFG *without* back edges */
273 red_trans_closure(res);
275 /* compute back edge chains */
276 compute_back_edge_chains(res);
279 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
280 for (i = res->n_blocks - 1; i >= 0; --i) {
281 const ir_node *irn = (const ir_node*) dfs_get_pre_num_node(res->dfs, i);
282 bl_info_t *bi = get_block_info(res, irn);
283 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
284 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
285 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
289 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
290 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
292 stat_ev_tim_pop("lv_chk_cons_time");
296 void lv_chk_free(lv_chk_t *lv)
298 obstack_free(&lv->obst, NULL);
299 ir_nodemap_destroy(&lv->block_infos);
304 * Check a nodes liveness situation of a block.
305 * This routine considers both cases, the live in and end/out case.
307 * @param lv The liveness check environment.
308 * @param bl The block under investigation.
309 * @param var The node to check for.
310 * @return A bitmask of lv_chk_state_XXX fields.
312 unsigned lv_chk_bl_xxx(lv_chk_t *lv, const ir_node *bl, const ir_node *var)
316 stat_ev_cnt_decl(uses);
317 stat_ev_cnt_decl(iter);
319 assert(is_Block(bl) && "can only check for liveness in a block");
321 /* If the variable ist no liveness related var, bail out. */
322 if (!is_liveness_node(var))
325 stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
328 /* If there is no dominance relation, go out, too */
329 def_bl = get_nodes_block(var);
330 if (!block_dominates(def_bl, bl)) {
331 stat_ev("lv_chk_no_dom");
336 * If the block in question is the same as the definition block,
337 * the algorithm is simple. Just check for uses not inside this block.
340 const ir_edge_t *edge;
342 stat_ev("lv_chk_def_block");
343 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
344 foreach_out_edge (var, edge) {
345 ir_node *use = get_edge_src_irn(edge);
348 if (!is_liveness_node(use))
351 stat_ev_cnt_inc(uses);
352 use_bl = get_nodes_block(use);
354 int pos = get_edge_src_pos(edge);
355 use_bl = get_Block_cfgpred_block(use_bl, pos);
358 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
359 res |= lv_chk_state_end;
363 if (use_bl != def_bl) {
364 res = lv_chk_state_end | lv_chk_state_out;
373 * this is the more complicated case.
374 * We try to gather as much information as possible during looking
377 * Note that we know for sure that bl != def_bl. That is sometimes
378 * silently exploited below.
381 bl_info_t *def = get_block_info(lv, def_bl);
382 bl_info_t *bli = get_block_info(lv, bl);
383 bitset_t *uses = bitset_alloca(lv->n_blocks);
387 unsigned min_dom, max_dom;
388 const ir_edge_t *edge;
390 /* if the block has no DFS info, it cannot be reached.
391 * This can happen in functions with endless loops.
392 * we then go out, since nothing is live there.
394 * TODO: Is that right?
400 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
401 var, def_bl, def->id, bl, bli->id));
403 foreach_out_edge (var, edge) {
404 ir_node *user = get_edge_src_irn(edge);
405 int mask = lv_chk_state_in;
410 /* if the user is no liveness node, the use does not count */
411 if (!is_liveness_node(user))
414 stat_ev_cnt_inc(uses);
416 /* if the user is a phi, the use is in the predecessor
417 * furthermore, prepare a mask so that in the case where
418 * bl (the block in question) coincides with a use, it
419 * can be marked live_end there. */
420 use_bl = get_nodes_block(user);
422 int pos = get_edge_src_pos(edge);
423 use_bl = get_Block_cfgpred_block(use_bl, pos);
424 mask |= lv_chk_state_end;
428 /* if the use block coincides with the query block, we
429 * already gather a little liveness information.
430 * The variable is surely live there, since bl != def_bl
431 * (that case is treated above). */
435 bi = get_block_info(lv, use_bl);
438 bitset_set(uses, bi->id);
441 /* get the dominance range which really matters. all uses outside
442 * the definition's dominance range are not to consider. note,
443 * that the definition itself is also not considered. The case
444 * where bl == def_bl is considered above. */
445 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
446 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
448 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
450 /* prepare a set with all reachable back edge targets.
451 * this will determine our "looking points" from where
452 * we will search/find the calculated uses. */
453 Tq = bli->be_tgt_reach;
455 /* now, visit all viewing points in the temporary bitset lying
456 * in the dominance range of the variable. Note that for reducible
457 * flow-graphs the first iteration is sufficient and the loop
459 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
460 i = bitset_next_set(Tq, min_dom);
461 while (i <= max_dom) {
462 bl_info_t *ti = lv->map[i];
463 int use_in_current_block = bitset_is_set(uses, ti->id);
465 stat_ev_cnt_inc(iter);
468 * This is somewhat tricky. Since this routine handles both, live in
469 * and end/out we have to handle all the border cases correctly.
470 * Each node is in its own red_reachable set (see calculation
471 * function above). That means, that in the case where bl == t, the
472 * intersection check of uses and reachability below will always
473 * find an intersection, namely t.
475 * However, if a block contains a use and the variable is dead
476 * afterwards, it is not live end/out at that block. Besides
477 * back-edge target. If a var is live-in at a back-edge target it
478 * is also live out/end there since the variable is live in the
479 * underlying loop. So in the case where t == bl and that is not
480 * a back-edge target, we have to remove that use from consideration
481 * to determine if the var is live out/end there.
483 * Note that the live in information has been calculated by the
484 * uses iteration above.
486 if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
487 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
488 bitset_clear(uses, ti->id);
491 /* If we can reach a use, the variable is live there and we say goodbye */
492 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
493 if (bitset_intersect(ti->red_reachable, uses)) {
494 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
499 * if we deleted a use do to the commentary above, we have to
500 * re-add it since it might be visible from further view points
501 * (we only need that in the non-reducible case).
503 if (use_in_current_block)
504 bitset_set(uses, ti->id);
506 i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
512 stat_ev_tim_pop("lv_chk_query_time");
513 stat_ev_cnt_done(uses, "lv_chk_uses");
514 stat_ev_cnt_done(iter, "lv_chk_iter");
515 stat_ev_ctx_pop("lv_chk");