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
26 * Liveness checks as developed by Benoit Boissinot, Fabrice Rastello and myself.
28 * The speciality here is, that nothing has to be recomputed if new nodes are created
29 * or old ones deleted.
31 * This algo has one core routine check_live_end_internal() which performs the liveness check.
32 * It only relies on the precomputation done in the constructor, which in turn needs:
34 * - the dominance tree
35 * - data obtained from a depth-first-search
37 * The precomputation remains valid as long as the CFG is not altered.
43 #include "irgraph_t.h"
45 #include "irnodemap.h"
46 #include "iredges_t.h"
56 #include "irlivechk.h"
60 typedef struct bl_info_t {
61 const ir_node *block; /**< The block. */
64 int id : 31; /**< a tight number for the block.
65 we're just reusing the pre num from
67 bitset_t *red_reachable; /**< Holds all id's if blocks reachable
68 in the CFG modulo back edges. */
70 bitset_t *be_tgt_reach; /**< target blocks of back edges whose
71 sources are reachable from this block
72 in the reduced graph. */
76 ir_nodemap block_infos;
80 bitset_t *back_edge_src;
81 bitset_t *back_edge_tgt;
83 DEBUG_ONLY(firm_dbg_module_t *dbg;)
86 static bl_info_t *get_block_info(lv_chk_t *lv, const ir_node *block)
88 bl_info_t *info = (bl_info_t*)ir_nodemap_get(&lv->block_infos, block);
90 info = OALLOC(&lv->obst, bl_info_t);
91 info->id = get_Block_dom_tree_pre_num(block);
93 info->red_reachable = bitset_obstack_alloc(&lv->obst, lv->n_blocks);
94 info->be_tgt_reach = bitset_obstack_alloc(&lv->obst, lv->n_blocks);
95 info->be_tgt_calc = 0;
96 ir_nodemap_insert(&lv->block_infos, block, info);
102 * Filter function to select all nodes for which liveness is computed.
104 * @return 1 if the node shall be considered in liveness, 0 if not.
106 static inline int is_liveness_node(const ir_node *irn)
108 switch (get_irn_opcode(irn)) {
122 * Compute the transitive closure on the reduced graph.
123 * The reduced graph is the original graph without back edges.
124 * Since that is a DAG, a reverse post order of the graph gives a toposort
125 * which is ideally suited to compute the transitive closure.
126 * Note also, that the DFS tree of the reduced graph is the same than the one
127 * of the original graph. This saves us computing a new reverse post order.
128 * We also can re-use the DFS tree of the original graph.
130 static void red_trans_closure(lv_chk_t *lv)
134 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
135 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
136 bl_info_t *bi = get_block_info(lv, bl);
138 const ir_edge_t *edge;
140 bitset_set(bi->red_reachable, bi->id);
141 foreach_block_succ (bl, edge) {
142 ir_node *succ = get_edge_src_irn(edge);
143 bl_info_t *si = get_block_info(lv, succ);
144 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
147 * if the successor is no back edge, include all reachable
148 * blocks from there into the reachable set of the current node
150 if (kind != DFS_EDGE_BACK) {
151 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
152 bitset_or(bi->red_reachable, si->red_reachable);
155 /* mark the block as a back edge src and succ as back edge tgt. */
157 bitset_set(lv->back_edge_src, bi->id);
158 bitset_set(lv->back_edge_tgt, si->id);
166 static void compute_back_edge_chain(lv_chk_t *lv, const ir_node *bl)
168 bitset_t *tmp = bitset_alloca(lv->n_blocks);
169 bl_info_t *bi = get_block_info(lv, bl);
173 DBG((lv->dbg, LEVEL_2, "computing T_%d\n", bi->id));
175 /* put all back edge sources reachable (reduced) from here in tmp */
176 bitset_copy(tmp, bi->red_reachable);
177 bitset_set(tmp, bi->id);
178 bitset_and(tmp, lv->back_edge_src);
181 DBG((lv->dbg, LEVEL_2, "\treachable be src: %B\n", tmp));
183 /* iterate over them ... */
184 bitset_foreach(tmp, elm) {
185 bl_info_t *si = lv->map[elm];
186 const ir_edge_t *edge;
188 /* and find back edge targets which are not reduced reachable from bl */
189 foreach_block_succ (si->block, edge) {
190 ir_node *tgt = get_edge_src_irn(edge);
191 bl_info_t *ti = get_block_info(lv, tgt);
192 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, si->block, tgt);
194 if (kind == DFS_EDGE_BACK && !bitset_is_set(bi->red_reachable, ti->id)) {
195 if (!ti->be_tgt_calc)
196 compute_back_edge_chain(lv, tgt);
197 bitset_set(bi->be_tgt_reach, ti->id);
198 bitset_or(bi->be_tgt_reach, ti->be_tgt_reach);
201 bitset_clear(bi->be_tgt_reach, bi->id);
206 static inline void compute_back_edge_chains(lv_chk_t *lv)
211 DBG((lv->dbg, LEVEL_2, "back edge sources: %B\n", lv->back_edge_src));
212 bitset_foreach(lv->back_edge_src, elm) {
213 compute_back_edge_chain(lv, lv->map[elm]->block);
216 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
217 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
218 bl_info_t *bi = get_block_info(lv, bl);
220 const ir_edge_t *edge;
222 if (!bitset_is_set(lv->back_edge_tgt, bi->id)) {
223 foreach_block_succ (bl, edge) {
224 ir_node *succ = get_edge_src_irn(edge);
225 bl_info_t *si = get_block_info(lv, succ);
226 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
228 if (kind != DFS_EDGE_BACK) {
229 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
230 bitset_or(bi->be_tgt_reach, si->be_tgt_reach);
236 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
237 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
238 bl_info_t *bi = get_block_info(lv, bl);
239 bitset_set(bi->be_tgt_reach, bi->id);
243 lv_chk_t *lv_chk_new(ir_graph *irg)
245 lv_chk_t *res = XMALLOC(lv_chk_t);
251 ir_nodemap_init(&res->block_infos, irg);
252 obstack_init(&res->obst);
254 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
256 res->dfs = dfs_new(&absgraph_irg_cfg_succ, irg);
257 res->n_blocks = dfs_get_n_nodes(res->dfs);
258 res->back_edge_src = bitset_obstack_alloc(&res->obst, res->n_blocks);
259 res->back_edge_tgt = bitset_obstack_alloc(&res->obst, res->n_blocks);
260 res->map = OALLOCNZ(&res->obst, bl_info_t*, res->n_blocks);
262 /* fill the map which maps pre_num to block infos */
263 for (i = res->n_blocks - 1; i >= 0; --i) {
264 ir_node *irn = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
265 bl_info_t *bi = get_block_info(res, irn);
266 assert(bi->id < res->n_blocks);
267 assert(res->map[bi->id] == NULL);
268 res->map[bi->id] = bi;
271 /* first of all, compute the transitive closure of the CFG *without* back edges */
272 red_trans_closure(res);
274 /* compute back edge chains */
275 compute_back_edge_chains(res);
278 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
279 for (i = res->n_blocks - 1; i >= 0; --i) {
280 const ir_node *irn = (const ir_node*) dfs_get_pre_num_node(res->dfs, i);
281 bl_info_t *bi = get_block_info(res, irn);
282 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
283 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
284 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
288 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
289 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
291 stat_ev_tim_pop("lv_chk_cons_time");
295 void lv_chk_free(lv_chk_t *lv)
298 obstack_free(&lv->obst, NULL);
299 ir_nodemap_destroy(&lv->block_infos);
303 unsigned lv_chk_bl_xxx(lv_chk_t *lv, const ir_node *bl, const ir_node *var)
307 stat_ev_cnt_decl(uses);
308 stat_ev_cnt_decl(iter);
310 assert(is_Block(bl) && "can only check for liveness in a block");
312 /* If the variable ist no liveness related var, bail out. */
313 if (!is_liveness_node(var))
316 stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
319 /* If there is no dominance relation, go out, too */
320 def_bl = get_nodes_block(var);
321 if (!block_dominates(def_bl, bl)) {
322 stat_ev("lv_chk_no_dom");
327 * If the block in question is the same as the definition block,
328 * the algorithm is simple. Just check for uses not inside this block.
331 const ir_edge_t *edge;
333 stat_ev("lv_chk_def_block");
334 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
335 foreach_out_edge (var, edge) {
336 ir_node *use = get_edge_src_irn(edge);
339 if (!is_liveness_node(use))
342 stat_ev_cnt_inc(uses);
343 use_bl = get_nodes_block(use);
345 int pos = get_edge_src_pos(edge);
346 use_bl = get_Block_cfgpred_block(use_bl, pos);
349 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
350 res |= lv_chk_state_end;
354 if (use_bl != def_bl) {
355 res = lv_chk_state_end | lv_chk_state_out;
364 * this is the more complicated case.
365 * We try to gather as much information as possible during looking
368 * Note that we know for sure that bl != def_bl. That is sometimes
369 * silently exploited below.
372 bl_info_t *def = get_block_info(lv, def_bl);
373 bl_info_t *bli = get_block_info(lv, bl);
374 bitset_t *uses = bitset_alloca(lv->n_blocks);
378 unsigned min_dom, max_dom;
379 const ir_edge_t *edge;
381 /* if the block has no DFS info, it cannot be reached.
382 * This can happen in functions with endless loops.
383 * we then go out, since nothing is live there.
385 * TODO: Is that right?
391 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
392 var, def_bl, def->id, bl, bli->id));
394 foreach_out_edge (var, edge) {
395 ir_node *user = get_edge_src_irn(edge);
396 int mask = lv_chk_state_in;
401 /* if the user is no liveness node, the use does not count */
402 if (!is_liveness_node(user))
405 stat_ev_cnt_inc(uses);
407 /* if the user is a phi, the use is in the predecessor
408 * furthermore, prepare a mask so that in the case where
409 * bl (the block in question) coincides with a use, it
410 * can be marked live_end there. */
411 use_bl = get_nodes_block(user);
413 int pos = get_edge_src_pos(edge);
414 use_bl = get_Block_cfgpred_block(use_bl, pos);
415 mask |= lv_chk_state_end;
419 /* if the use block coincides with the query block, we
420 * already gather a little liveness information.
421 * The variable is surely live there, since bl != def_bl
422 * (that case is treated above). */
426 bi = get_block_info(lv, use_bl);
429 bitset_set(uses, bi->id);
432 /* get the dominance range which really matters. all uses outside
433 * the definition's dominance range are not to consider. note,
434 * that the definition itself is also not considered. The case
435 * where bl == def_bl is considered above. */
436 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
437 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
439 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
441 /* prepare a set with all reachable back edge targets.
442 * this will determine our "looking points" from where
443 * we will search/find the calculated uses. */
444 Tq = bli->be_tgt_reach;
446 /* now, visit all viewing points in the temporary bitset lying
447 * in the dominance range of the variable. Note that for reducible
448 * flow-graphs the first iteration is sufficient and the loop
450 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
451 i = bitset_next_set(Tq, min_dom);
452 while (i <= max_dom) {
453 bl_info_t *ti = lv->map[i];
454 int use_in_current_block = bitset_is_set(uses, ti->id);
456 stat_ev_cnt_inc(iter);
459 * This is somewhat tricky. Since this routine handles both, live in
460 * and end/out we have to handle all the border cases correctly.
461 * Each node is in its own red_reachable set (see calculation
462 * function above). That means, that in the case where bl == t, the
463 * intersection check of uses and reachability below will always
464 * find an intersection, namely t.
466 * However, if a block contains a use and the variable is dead
467 * afterwards, it is not live end/out at that block. Besides
468 * back-edge target. If a var is live-in at a back-edge target it
469 * is also live out/end there since the variable is live in the
470 * underlying loop. So in the case where t == bl and that is not
471 * a back-edge target, we have to remove that use from consideration
472 * to determine if the var is live out/end there.
474 * Note that the live in information has been calculated by the
475 * uses iteration above.
477 if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
478 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
479 bitset_clear(uses, ti->id);
482 /* If we can reach a use, the variable is live there and we say goodbye */
483 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
484 if (bitset_intersect(ti->red_reachable, uses)) {
485 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
490 * if we deleted a use do to the commentary above, we have to
491 * re-add it since it might be visible from further view points
492 * (we only need that in the non-reducible case).
494 if (use_in_current_block)
495 bitset_set(uses, ti->id);
497 i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
503 stat_ev_tim_pop("lv_chk_query_time");
504 stat_ev_cnt_done(uses, "lv_chk_uses");
505 stat_ev_cnt_done(iter, "lv_chk_iter");
506 stat_ev_ctx_pop("lv_chk");