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.
46 #include "irgraph_t.h"
48 #include "irphase_t.h"
49 #include "iredges_t.h"
59 #include "irlivechk.h"
63 typedef struct _bl_info_t {
64 ir_node *block; /**< The block. */
67 int id : 31; /**< a tight number for the block.
68 we're just reusing the pre num from
70 bitset_t *red_reachable; /**< Holds all id's if blocks reachable
71 in the CFG modulo back edges. */
73 bitset_t *be_tgt_reach; /**< target blocks of back edges whose
74 sources are reachable from this block
75 in the reduced graph. */
78 #define get_block_info(lv, bl) ((bl_info_t *) phase_get_irn_data(&(lv)->ph, bl))
83 DEBUG_ONLY(firm_dbg_module_t *dbg;)
85 bitset_t *back_edge_src;
86 bitset_t *back_edge_tgt;
90 static void *init_block_data(ir_phase *ph, ir_node *irn, void *old)
92 lv_chk_t *lv = container_of(ph, lv_chk_t, ph);
93 bl_info_t *bi = phase_alloc(ph, sizeof(bi[0]));
95 bi->id = get_Block_dom_tree_pre_num(irn);
97 bi->red_reachable = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
98 bi->be_tgt_reach = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
105 * Filter function to select all nodes for which liveness is computed.
107 * @return 1 if the node shall be considered in liveness, 0 if not.
109 static INLINE int is_liveness_node(const ir_node *irn)
111 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 = 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, 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 = 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 = 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(sizeof(res[0]));
247 struct obstack *obst;
251 phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
252 obst = phase_obst(&res->ph);
254 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
257 res->n_blocks = dfs_get_n_nodes(res->dfs);
258 res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
259 res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
260 res->map = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
266 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
267 if ((f = fopen(name, "wt")) != NULL) {
268 dfs_dump(res->dfs, f);
271 dump_ir_block_graph(irg, "-lvchk");
275 /* fill the map which maps pre_num to block infos */
276 for (i = res->n_blocks - 1; i >= 0; --i) {
277 ir_node *irn = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
278 bl_info_t *bi = phase_get_or_set_irn_data(&res->ph, irn);
279 res->map[bi->id] = bi;
282 /* first of all, compute the transitive closure of the CFG *without* back edges */
283 red_trans_closure(res);
285 /* compute back edge chains */
286 compute_back_edge_chains(res);
289 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
290 for (i = res->n_blocks - 1; i >= 0; --i) {
291 const ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
292 bl_info_t *bi = get_block_info(res, irn);
293 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
294 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
295 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
299 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
300 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
302 stat_ev_tim_pop("lv_chk_cons_time");
306 void lv_chk_free(lv_chk_t *lv)
308 obstack_free(phase_obst(&lv->ph), NULL);
313 * Check if a node is live at the end of a block.
314 * This function is for internal use as its code is shared between
315 * the in/end routines below. It is almost the "live_end" routine
316 * but passing in the bitset for recording the blocks where the variable
317 * is used saves some effort in the "live_in" routine. See below for
320 * @param lv The liveness check environment.
321 * @param what The node to check for.
322 * @param bl The block under investigation.
323 * @param uses A bitset where this routine records all ids of blocks
324 * where this variable is used. Note that the bitset
325 * is only guaranteed to be filled if the node was not
326 * live at the end of the block.
327 * @return 1, if @p what is live at the end at @p bl.
329 unsigned lv_chk_bl_in_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
331 stat_ev_cnt_decl(uses);
334 const ir_edge_t *edge;
338 assert(is_Block(bl) && "can only check for liveness in a block");
340 if (!is_liveness_node(var))
343 def_bl = get_nodes_block(var);
344 if (def_bl == bl || !block_dominates(def_bl, bl)) {
349 bitset_t *uses = bitset_alloca(lv->n_blocks);
350 bitset_t *tmp = bitset_alloca(lv->n_blocks);
351 int min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
352 int max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
353 bl_info_t *bli = get_block_info(lv, bl);
356 DBG((lv->dbg, LEVEL_2, "lv check of %+F, def=%+F,%d != q=%+F,%d\n",
357 var, def_bl, min_dom - 1, bl, bli->id));
359 foreach_out_edge (var, edge) {
360 ir_node *user = get_edge_src_irn(edge);
364 if (!is_liveness_node(user))
367 stat_ev_cnt_inc(uses);
368 use_bl = get_nodes_block(user);
370 int pos = get_edge_src_pos(edge);
371 use_bl = get_Block_cfgpred_block(use_bl, pos);
375 res = lv_chk_state_in;
376 DBG((lv->dbg, LEVEL_2, "\tuse directly in block %+F by %+F\n", use_bl, user));
380 bi = get_block_info(lv, use_bl);
381 bitset_set(uses, bi->id);
384 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
388 bitset_copy(tmp, bli->be_tgt_reach);
389 bitset_set(tmp, bli->id);
391 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
392 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
393 bl_info_t *ti = lv->map[i];
394 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
395 if (bitset_intersect(ti->red_reachable, uses)) {
396 res = lv_chk_state_in;
400 bitset_andnot(tmp, ti->red_reachable);
409 unsigned lv_chk_bl_end_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
411 stat_ev_cnt_decl(uses);
414 const ir_edge_t *edge;
418 assert(is_Block(bl) && "can only check for liveness in a block");
420 if (!is_liveness_node(var))
423 def_bl = get_nodes_block(var);
424 if (!block_dominates(def_bl, bl)) {
429 bitset_t *uses = bitset_alloca(lv->n_blocks);
430 bitset_t *tmp = bitset_alloca(lv->n_blocks);
431 int min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
432 int max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
433 bl_info_t *bli = get_block_info(lv, bl);
436 DBG((lv->dbg, LEVEL_2, "lv end check of %+F, def=%+F,%d != q=%+F,%d\n",
437 var, def_bl, min_dom - 1, bl, bli->id));
439 foreach_out_edge (var, edge) {
440 ir_node *user = get_edge_src_irn(edge);
444 if (!is_liveness_node(user))
447 stat_ev_cnt_inc(uses);
448 use_bl = get_nodes_block(user);
450 int pos = get_edge_src_pos(edge);
451 use_bl = get_Block_cfgpred_block(use_bl, pos);
454 res |= lv_chk_state_end;
457 bi = get_block_info(lv, use_bl);
458 if (use_bl != bl || bitset_is_set(lv->back_edge_tgt, bi->id))
459 bitset_set(uses, bi->id);
462 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
464 bitset_copy(tmp, bli->be_tgt_reach);
465 bitset_set(tmp, bli->id);
467 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach + current: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
468 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
469 bl_info_t *ti = lv->map[i];
470 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
471 if (bitset_intersect(ti->red_reachable, uses)) {
472 res = lv_chk_state_out | lv_chk_state_end;
476 bitset_andnot(tmp, ti->red_reachable);
485 * Check a nodes liveness situation of a block.
486 * This routine considers both cases, the live in and end/out case.
488 * @param lv The liveness check environment.
489 * @param bl The block under investigation.
490 * @param var The node to check for.
491 * @return A bitmask of lv_chk_state_XXX fields.
493 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
495 stat_ev_cnt_decl(uses);
496 stat_ev_cnt_decl(iter);
501 assert(is_Block(bl) && "can only check for liveness in a block");
503 /* If the variable ist no liveness related var, bail out. */
504 if (!is_liveness_node(var))
507 stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
510 /* If there is no dominance relation, go out, too */
511 def_bl = get_nodes_block(var);
512 if (!block_dominates(def_bl, bl)) {
513 stat_ev("lv_chk_no_dom");
518 * If the block in question is the same as the definition block,
519 * the algorithm is simple. Just check for uses not inside this block.
522 const ir_edge_t *edge;
524 stat_ev("lv_chk_def_block");
525 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
526 foreach_out_edge (var, edge) {
527 ir_node *use = get_edge_src_irn(edge);
530 if (!is_liveness_node(use))
533 stat_ev_cnt_inc(uses);
534 use_bl = get_nodes_block(use);
536 int pos = get_edge_src_pos(edge);
537 use_bl = get_Block_cfgpred_block(use_bl, pos);
540 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
541 res |= lv_chk_state_end;
545 if (use_bl != def_bl) {
546 res = lv_chk_state_end | lv_chk_state_out;
555 * this is the more complicated case.
556 * We try to gather as much information as possible during looking
559 * Note that we know for shure that bl != def_bl. That is sometimes
560 * silently exploited below.
563 bl_info_t *def = get_block_info(lv, def_bl);
564 bl_info_t *bli = get_block_info(lv, bl);
565 bitset_t *uses = bitset_alloca(lv->n_blocks);
568 unsigned i, min_dom, max_dom;
569 const ir_edge_t *edge;
571 /* if the block has no DFS info, it cannot be reached.
572 * This can happen in functions with endless loops.
573 * we then go out, since nothing is live there.
575 * TODO: Is that right?
581 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
582 var, def_bl, def->id, bl, bli->id));
584 foreach_out_edge (var, edge) {
585 ir_node *user = get_edge_src_irn(edge);
586 int mask = lv_chk_state_in;
591 /* if the user is no liveness node, the use does not count */
592 if (!is_liveness_node(user))
595 stat_ev_cnt_inc(uses);
597 /* if the user is a phi, the use is in the predecessor
598 * furthermore, prepare a mask so that in the case where
599 * bl (the block in question) coincides with a use, it
600 * can be marked live_end there. */
601 use_bl = get_nodes_block(user);
603 int pos = get_edge_src_pos(edge);
604 use_bl = get_Block_cfgpred_block(use_bl, pos);
605 mask |= lv_chk_state_end;
609 /* if the use block coincides with the query block, we
610 * already gather a little liveness information.
611 * The variable is surely live there, since bl != def_bl
612 * (that case is treated above). */
616 bi = get_block_info(lv, use_bl);
619 bitset_set(uses, bi->id);
622 /* get the dominance range which really matters. all uses outside
623 * the definition's dominance range are not to consider. note,
624 * that the definition itself is also not considered. The case
625 * where bl == def_bl is considered above. */
626 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
627 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
629 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
631 /* prepare a set with all reachable back edge targets.
632 * this will determine our "looking points" from where
633 * we will search/find the calculated uses. */
634 Tq = bli->be_tgt_reach;
636 /* now, visit all viewing points in the temporary bitset lying
637 * in the dominance range of the variable. Note that for reducible
638 * flow-graphs the first iteration is sufficient and the loop
640 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
641 i = bitset_next_set(Tq, min_dom);
642 while(i <= max_dom) {
643 bl_info_t *ti = lv->map[i];
644 int use_in_current_block = bitset_is_set(uses, ti->id);
646 stat_ev_cnt_inc(iter);
649 * This is somehat tricky. Since this routine handles both, live in
650 * and end/out we have to handle all the border cases correctly.
651 * Each node is in its own red_reachable set (see calculation
652 * function above). That means, that in the case where bl == t, the
653 * intersection check of uses and rechability below will always
654 * find an intersection, namely t.
656 * However, if a block contains a use and the variable is dead
657 * afterwards, it is not live end/out at that block. Besides
658 * back-edge target. If a var is live-in at a back-edge target it
659 * is also live out/end there since the variable is live in the
660 * underlying loop. So in the case where t == bl and that is not
661 * a back-edge target, we have to remove that use from consideration
662 * to determine if the var is live out/end there.
664 * Note that the live in information has been calculated by the
665 * uses iteration above.
667 if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
668 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
669 bitset_clear(uses, ti->id);
672 /* If we can reach a use, the variable is live there and we say goodbye */
673 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
674 if (bitset_intersect(ti->red_reachable, uses)) {
675 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
680 * if we deleted a use do to the commentary above, we have to
681 * re-add it since it might be visible from further view points
682 * (we only need that in the non-reducible case).
684 if (use_in_current_block)
685 bitset_set(uses, ti->id);
687 i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
693 stat_ev_tim_pop("lv_chk_query_time");
694 stat_ev_cnt_done(uses, "lv_chk_uses");
695 stat_ev_cnt_done(iter, "lv_chk_iter");
696 stat_ev_ctx_pop("lv_chk");