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 "irphase_t.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. */
76 #define get_block_info(lv, bl) ((bl_info_t *) phase_get_irn_data(&(lv)->ph, bl))
82 bitset_t *back_edge_src;
83 bitset_t *back_edge_tgt;
85 DEBUG_ONLY(firm_dbg_module_t *dbg;)
88 static void *init_block_data(ir_phase *ph, const ir_node *irn, void *old)
90 lv_chk_t *lv = container_of(ph, lv_chk_t, ph);
91 bl_info_t *bi = phase_alloc(ph, sizeof(bi[0]));
93 bi->id = get_Block_dom_tree_pre_num(irn);
95 bi->red_reachable = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
96 bi->be_tgt_reach = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
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)) {
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 = 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 = 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 = 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, const dfs_t *dfs)
245 lv_chk_t *res = XMALLOC(lv_chk_t);
246 struct obstack *obst;
249 edges_deactivate(irg);
254 phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
255 obst = phase_obst(&res->ph);
257 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
260 res->n_blocks = dfs_get_n_nodes(res->dfs);
261 res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
262 res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
263 res->map = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
264 memset(res->map, 0, res->n_blocks * sizeof(res->map[0]));
270 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
271 if ((f = fopen(name, "wt")) != NULL) {
272 dfs_dump(res->dfs, f);
275 dump_ir_block_graph(irg, "-lvchk");
279 /* fill the map which maps pre_num to block infos */
280 for (i = res->n_blocks - 1; i >= 0; --i) {
281 ir_node *irn = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
282 bl_info_t *bi = phase_get_or_set_irn_data(&res->ph, irn);
283 assert(bi->id < res->n_blocks);
284 assert(res->map[bi->id] == NULL);
285 res->map[bi->id] = bi;
288 /* first of all, compute the transitive closure of the CFG *without* back edges */
289 red_trans_closure(res);
291 /* compute back edge chains */
292 compute_back_edge_chains(res);
295 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
296 for (i = res->n_blocks - 1; i >= 0; --i) {
297 const ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
298 bl_info_t *bi = get_block_info(res, irn);
299 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
300 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
301 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
305 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
306 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
308 stat_ev_tim_pop("lv_chk_cons_time");
312 void lv_chk_free(lv_chk_t *lv)
319 * Check if a node is live at the end of a block.
320 * This function is for internal use as its code is shared between
321 * the in/end routines below. It is almost the "live_end" routine
322 * but passing in the bitset for recording the blocks where the variable
323 * is used saves some effort in the "live_in" routine. See below for
326 * @param lv The liveness check environment.
327 * @param what The node to check for.
328 * @param bl The block under investigation.
329 * @param uses A bitset where this routine records all ids of blocks
330 * where this variable is used. Note that the bitset
331 * is only guaranteed to be filled if the node was not
332 * live at the end of the block.
333 * @return 1, if @p what is live at the end at @p bl.
335 unsigned lv_chk_bl_in_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
338 const ir_edge_t *edge;
340 stat_ev_cnt_decl(uses);
344 assert(is_Block(bl) && "can only check for liveness in a block");
346 if (!is_liveness_node(var))
349 def_bl = get_nodes_block(var);
350 if (def_bl == bl || !block_dominates(def_bl, bl)) {
355 bitset_t *uses = bitset_alloca(lv->n_blocks);
356 bitset_t *tmp = bitset_alloca(lv->n_blocks);
357 int min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
358 int max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
359 bl_info_t *bli = get_block_info(lv, bl);
362 DBG((lv->dbg, LEVEL_2, "lv check of %+F, def=%+F,%d != q=%+F,%d\n",
363 var, def_bl, min_dom - 1, bl, bli->id));
365 foreach_out_edge (var, edge) {
366 ir_node *user = get_edge_src_irn(edge);
370 if (!is_liveness_node(user))
373 stat_ev_cnt_inc(uses);
374 use_bl = get_nodes_block(user);
376 int pos = get_edge_src_pos(edge);
377 use_bl = get_Block_cfgpred_block(use_bl, pos);
381 res = lv_chk_state_in;
382 DBG((lv->dbg, LEVEL_2, "\tuse directly in block %+F by %+F\n", use_bl, user));
386 bi = get_block_info(lv, use_bl);
387 bitset_set(uses, bi->id);
390 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
394 bitset_copy(tmp, bli->be_tgt_reach);
395 bitset_set(tmp, bli->id);
397 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
398 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
399 bl_info_t *ti = lv->map[i];
400 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
401 if (bitset_intersect(ti->red_reachable, uses)) {
402 res = lv_chk_state_in;
406 bitset_andnot(tmp, ti->red_reachable);
415 unsigned lv_chk_bl_end_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
418 const ir_edge_t *edge;
420 stat_ev_cnt_decl(uses);
424 assert(is_Block(bl) && "can only check for liveness in a block");
426 if (!is_liveness_node(var))
429 def_bl = get_nodes_block(var);
430 if (!block_dominates(def_bl, bl)) {
433 bitset_t *uses = bitset_alloca(lv->n_blocks);
434 bitset_t *tmp = bitset_alloca(lv->n_blocks);
435 int min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
436 int max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
437 bl_info_t *bli = get_block_info(lv, bl);
440 DBG((lv->dbg, LEVEL_2, "lv end check of %+F, def=%+F,%d != q=%+F,%d\n",
441 var, def_bl, min_dom - 1, bl, bli->id));
443 foreach_out_edge (var, edge) {
444 ir_node *user = get_edge_src_irn(edge);
448 if (!is_liveness_node(user))
451 stat_ev_cnt_inc(uses);
452 use_bl = get_nodes_block(user);
454 int pos = get_edge_src_pos(edge);
455 use_bl = get_Block_cfgpred_block(use_bl, pos);
458 res |= lv_chk_state_end;
461 bi = get_block_info(lv, use_bl);
462 if (use_bl != bl || bitset_is_set(lv->back_edge_tgt, bi->id))
463 bitset_set(uses, bi->id);
466 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
468 bitset_copy(tmp, bli->be_tgt_reach);
469 bitset_set(tmp, bli->id);
471 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach + current: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
472 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
473 bl_info_t *ti = lv->map[i];
474 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
475 if (bitset_intersect(ti->red_reachable, uses)) {
476 res = lv_chk_state_out | lv_chk_state_end;
480 bitset_andnot(tmp, ti->red_reachable);
489 * Check a nodes liveness situation of a block.
490 * This routine considers both cases, the live in and end/out case.
492 * @param lv The liveness check environment.
493 * @param bl The block under investigation.
494 * @param var The node to check for.
495 * @return A bitmask of lv_chk_state_XXX fields.
497 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
501 stat_ev_cnt_decl(uses);
502 stat_ev_cnt_decl(iter);
504 assert(is_Block(bl) && "can only check for liveness in a block");
506 /* If the variable ist no liveness related var, bail out. */
507 if (!is_liveness_node(var))
510 stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
513 /* If there is no dominance relation, go out, too */
514 def_bl = get_nodes_block(var);
515 if (!block_dominates(def_bl, bl)) {
516 stat_ev("lv_chk_no_dom");
521 * If the block in question is the same as the definition block,
522 * the algorithm is simple. Just check for uses not inside this block.
525 const ir_edge_t *edge;
527 stat_ev("lv_chk_def_block");
528 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
529 foreach_out_edge (var, edge) {
530 ir_node *use = get_edge_src_irn(edge);
533 if (!is_liveness_node(use))
536 stat_ev_cnt_inc(uses);
537 use_bl = get_nodes_block(use);
539 int pos = get_edge_src_pos(edge);
540 use_bl = get_Block_cfgpred_block(use_bl, pos);
543 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
544 res |= lv_chk_state_end;
548 if (use_bl != def_bl) {
549 res = lv_chk_state_end | lv_chk_state_out;
558 * this is the more complicated case.
559 * We try to gather as much information as possible during looking
562 * Note that we know for sure that bl != def_bl. That is sometimes
563 * silently exploited below.
566 bl_info_t *def = get_block_info(lv, def_bl);
567 bl_info_t *bli = get_block_info(lv, bl);
568 bitset_t *uses = bitset_alloca(lv->n_blocks);
571 unsigned i, min_dom, max_dom;
572 const ir_edge_t *edge;
574 /* if the block has no DFS info, it cannot be reached.
575 * This can happen in functions with endless loops.
576 * we then go out, since nothing is live there.
578 * TODO: Is that right?
584 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
585 var, def_bl, def->id, bl, bli->id));
587 foreach_out_edge (var, edge) {
588 ir_node *user = get_edge_src_irn(edge);
589 int mask = lv_chk_state_in;
594 /* if the user is no liveness node, the use does not count */
595 if (!is_liveness_node(user))
598 stat_ev_cnt_inc(uses);
600 /* if the user is a phi, the use is in the predecessor
601 * furthermore, prepare a mask so that in the case where
602 * bl (the block in question) coincides with a use, it
603 * can be marked live_end there. */
604 use_bl = get_nodes_block(user);
606 int pos = get_edge_src_pos(edge);
607 use_bl = get_Block_cfgpred_block(use_bl, pos);
608 mask |= lv_chk_state_end;
612 /* if the use block coincides with the query block, we
613 * already gather a little liveness information.
614 * The variable is surely live there, since bl != def_bl
615 * (that case is treated above). */
619 bi = get_block_info(lv, use_bl);
622 bitset_set(uses, bi->id);
625 /* get the dominance range which really matters. all uses outside
626 * the definition's dominance range are not to consider. note,
627 * that the definition itself is also not considered. The case
628 * where bl == def_bl is considered above. */
629 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
630 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
632 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
634 /* prepare a set with all reachable back edge targets.
635 * this will determine our "looking points" from where
636 * we will search/find the calculated uses. */
637 Tq = bli->be_tgt_reach;
639 /* now, visit all viewing points in the temporary bitset lying
640 * in the dominance range of the variable. Note that for reducible
641 * flow-graphs the first iteration is sufficient and the loop
643 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
644 i = bitset_next_set(Tq, min_dom);
645 while(i <= max_dom) {
646 bl_info_t *ti = lv->map[i];
647 int use_in_current_block = bitset_is_set(uses, ti->id);
649 stat_ev_cnt_inc(iter);
652 * This is somewhat tricky. Since this routine handles both, live in
653 * and end/out we have to handle all the border cases correctly.
654 * Each node is in its own red_reachable set (see calculation
655 * function above). That means, that in the case where bl == t, the
656 * intersection check of uses and reachability below will always
657 * find an intersection, namely t.
659 * However, if a block contains a use and the variable is dead
660 * afterwards, it is not live end/out at that block. Besides
661 * back-edge target. If a var is live-in at a back-edge target it
662 * is also live out/end there since the variable is live in the
663 * underlying loop. So in the case where t == bl and that is not
664 * a back-edge target, we have to remove that use from consideration
665 * to determine if the var is live out/end there.
667 * Note that the live in information has been calculated by the
668 * uses iteration above.
670 if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
671 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
672 bitset_clear(uses, ti->id);
675 /* If we can reach a use, the variable is live there and we say goodbye */
676 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
677 if (bitset_intersect(ti->red_reachable, uses)) {
678 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
683 * if we deleted a use do to the commentary above, we have to
684 * re-add it since it might be visible from further view points
685 * (we only need that in the non-reducible case).
687 if (use_in_current_block)
688 bitset_set(uses, ti->id);
690 i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
696 stat_ev_tim_pop("lv_chk_query_time");
697 stat_ev_cnt_done(uses, "lv_chk_uses");
698 stat_ev_cnt_done(iter, "lv_chk_iter");
699 stat_ev_ctx_pop("lv_chk");