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);
238 lv_chk_t *lv_chk_new(ir_graph *irg, const dfs_t *dfs)
240 lv_chk_t *res = xmalloc(sizeof(res[0]));
241 struct obstack *obst;
244 phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
245 obst = phase_obst(&res->ph);
247 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
249 // res->dfs = dfs_new(&absgraph_irg_cfg_succ, irg);
251 res->n_blocks = dfs_get_n_nodes(res->dfs);
252 res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
253 res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
254 res->map = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
260 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
261 if ((f = fopen(name, "wt")) != NULL) {
262 dfs_dump(res->dfs, f);
265 dump_ir_block_graph(irg, "-lvchk");
269 /* fill the map which maps pre_num to block infos */
270 for (i = res->n_blocks - 1; i >= 0; --i) {
271 ir_node *irn = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
272 bl_info_t *bi = phase_get_or_set_irn_data(&res->ph, irn);
273 res->map[bi->id] = bi;
276 /* first of all, compute the transitive closure of the CFG *without* back edges */
277 red_trans_closure(res);
279 /* compute back edge chains */
280 compute_back_edge_chains(res);
283 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
284 for (i = res->n_blocks - 1; i >= 0; --i) {
285 const ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
286 bl_info_t *bi = get_block_info(res, irn);
287 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
288 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
289 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
293 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
294 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
299 void lv_chk_free(lv_chk_t *lv)
301 obstack_free(phase_obst(&lv->ph), NULL);
306 * Check if a node is live at the end of a block.
307 * This function is for internal use as its code is shared between
308 * the in/end routines below. It is almost the "live_end" routine
309 * but passing in the bitset for recording the blocks where the variable
310 * is used saves some effort in the "live_in" routine. See below for
313 * @param lv The liveness check environment.
314 * @param what The node to check for.
315 * @param bl The block under investigation.
316 * @param uses A bitset where this routine records all ids of blocks
317 * where this variable is used. Note that the bitset
318 * is only guaranteed to be filled if the node was not
319 * live at the end of the block.
320 * @return 1, if @p what is live at the end at @p bl.
322 unsigned lv_chk_bl_in_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
324 stat_ev_cnt_decl(uses);
327 const ir_edge_t *edge;
331 assert(is_Block(bl) && "can only check for liveness in a block");
333 if (!is_liveness_node(var))
336 def_bl = get_nodes_block(var);
337 if (def_bl == bl || !block_dominates(def_bl, bl)) {
342 bitset_t *uses = bitset_alloca(lv->n_blocks);
343 bitset_t *tmp = bitset_alloca(lv->n_blocks);
344 int min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
345 int max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
346 bl_info_t *bli = get_block_info(lv, bl);
349 DBG((lv->dbg, LEVEL_2, "lv check of %+F, def=%+F,%d != q=%+F,%d\n",
350 var, def_bl, min_dom - 1, bl, bli->id));
352 foreach_out_edge (var, edge) {
353 ir_node *user = get_edge_src_irn(edge);
357 if (!is_liveness_node(user))
360 stat_ev_cnt_inc(uses);
361 use_bl = get_nodes_block(user);
363 int pos = get_edge_src_pos(edge);
364 use_bl = get_Block_cfgpred_block(use_bl, pos);
368 res = lv_chk_state_in;
369 DBG((lv->dbg, LEVEL_2, "\tuse directly in block %+F by %+F\n", use_bl, user));
373 bi = get_block_info(lv, use_bl);
374 bitset_set(uses, bi->id);
377 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
381 bitset_copy(tmp, bli->be_tgt_reach);
382 bitset_set(tmp, bli->id);
384 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
385 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
386 bl_info_t *ti = lv->map[i];
387 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
388 if (bitset_intersect(ti->red_reachable, uses)) {
389 res = lv_chk_state_in;
393 bitset_andnot(tmp, ti->red_reachable);
402 unsigned lv_chk_bl_end_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
404 stat_ev_cnt_decl(uses);
407 const ir_edge_t *edge;
411 assert(is_Block(bl) && "can only check for liveness in a block");
413 if (!is_liveness_node(var))
416 def_bl = get_nodes_block(var);
417 if (!block_dominates(def_bl, bl)) {
422 bitset_t *uses = bitset_alloca(lv->n_blocks);
423 bitset_t *tmp = bitset_alloca(lv->n_blocks);
424 int min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
425 int max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
426 bl_info_t *bli = get_block_info(lv, bl);
429 DBG((lv->dbg, LEVEL_2, "lv end check of %+F, def=%+F,%d != q=%+F,%d\n",
430 var, def_bl, min_dom - 1, bl, bli->id));
432 foreach_out_edge (var, edge) {
433 ir_node *user = get_edge_src_irn(edge);
437 if (!is_liveness_node(user))
440 stat_ev_cnt_inc(uses);
441 use_bl = get_nodes_block(user);
443 int pos = get_edge_src_pos(edge);
444 use_bl = get_Block_cfgpred_block(use_bl, pos);
447 res |= lv_chk_state_end;
450 bi = get_block_info(lv, use_bl);
451 if (use_bl != bl || bitset_is_set(lv->back_edge_tgt, bi->id))
452 bitset_set(uses, bi->id);
455 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
457 bitset_copy(tmp, bli->be_tgt_reach);
458 bitset_set(tmp, bli->id);
460 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach + current: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
461 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
462 bl_info_t *ti = lv->map[i];
463 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
464 if (bitset_intersect(ti->red_reachable, uses)) {
465 res = lv_chk_state_out | lv_chk_state_end;
469 bitset_andnot(tmp, ti->red_reachable);
478 * Check a nodes liveness situation of a block.
479 * This routine considers both cases, the live in and end/out case.
481 * @param lv The liveness check environment.
482 * @param bl The block under investigation.
483 * @param var The node to check for.
484 * @return A bitmask of lv_chk_state_XXX fields.
486 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
488 stat_ev_cnt_decl(uses);
489 stat_ev_cnt_decl(iter);
494 assert(is_Block(bl) && "can only check for liveness in a block");
496 /* If the variable ist no liveness related var, bail out. */
497 if (!is_liveness_node(var))
502 /* If there is no dominance relation, go out, too */
503 def_bl = get_nodes_block(var);
504 if (!block_dominates(def_bl, bl)) {
505 stat_ev("lv_chk_no_dom");
510 * If the block in question is the same as the definition block,
511 * the algorithm is simple. Just check for uses not inside this block.
514 const ir_edge_t *edge;
516 stat_ev("lv_chk_def_block");
517 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
518 foreach_out_edge (var, edge) {
519 ir_node *use = get_edge_src_irn(edge);
522 if (!is_liveness_node(use))
525 stat_ev_cnt_inc(uses);
526 use_bl = get_nodes_block(use);
528 int pos = get_edge_src_pos(edge);
529 use_bl = get_Block_cfgpred_block(use_bl, pos);
532 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
533 res |= lv_chk_state_end;
537 if (use_bl != def_bl) {
538 res = lv_chk_state_end | lv_chk_state_out;
547 * this is the more complicated case.
548 * We try to gather as much information as possible during looking
551 * Note that we know for shure that bl != def_bl. That is sometimes
552 * silently exploited below.
555 bitset_t *tmp = bitset_alloca(lv->n_blocks);
556 bitset_t *uses = bitset_alloca(lv->n_blocks);
557 bl_info_t *def = get_block_info(lv, def_bl);
558 bl_info_t *bli = get_block_info(lv, bl);
560 int i, min_dom, max_dom;
561 const ir_edge_t *edge;
563 /* if the block has no DFS info, it cannot be reached.
564 * This can happen in functions with endless loops.
565 * we then go out, since nothing is live there.
567 * TODO: Is that right?
572 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
573 var, def_bl, def->id, bl, bli->id));
575 foreach_out_edge (var, edge) {
576 ir_node *user = get_edge_src_irn(edge);
577 int mask = lv_chk_state_in;
582 /* if the user is no liveness node, the use does not count */
583 if (!is_liveness_node(user))
586 stat_ev_cnt_inc(uses);
588 /* if the user is a phi, the use is in the predecessor
589 * furthermore, prepare a mask so that in the case where
590 * bl (the block in question) coincides with a use, it
591 * can be marked live_end there. */
592 use_bl = get_nodes_block(user);
594 int pos = get_edge_src_pos(edge);
595 use_bl = get_Block_cfgpred_block(use_bl, pos);
596 mask |= lv_chk_state_end;
600 /* if the use block coincides with the query block, we
601 * already gather a little liveness information.
602 * The variable is surely live there, since bl != def_bl
603 * (that case is treated above). */
607 bi = get_block_info(lv, use_bl);
610 bitset_set(uses, bi->id);
613 /* get the dominance range which really matters. all uses outside
614 * the definition's dominance range are not to consider. note,
615 * that the definition itself is also not considered. The case
616 * where bl == def_bl is considered above. */
617 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
618 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
620 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
622 /* prepare a set with all reachable back edge targets.
623 * this will determine our "looking points" from where
624 * we will search/find the calculated uses.
626 * Since there might be no reachable back edge targets
627 * we add the current block also since reachability of
628 * uses are then checked from there. */
629 bitset_copy(tmp, bli->be_tgt_reach);
630 bitset_set (tmp, bli->id);
632 /* now, visit all viewing points in the temporary bitset lying
633 * in the dominance range of the variable. Note that for reducible
634 * flow-graphs the first iteration is sufficient and the loop
636 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
637 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
638 bl_info_t *ti = lv->map[i];
639 int use_in_current_block = bitset_is_set(uses, ti->id);
641 stat_ev_cnt_inc(iter);
644 * This is somehat tricky. Since this routine handles both, live in
645 * and end/out we have to handle all the border cases correctly.
646 * Each node is in its own red_reachable set (see calculation
647 * function above). That means, that in the case where bl == t, the
648 * intersection check of uses and rechability below will always
649 * find an intersection, namely t.
651 * However, if a block contains a use and the variable is dead
652 * afterwards, it is not live end/out at that block. Besides
653 * back-edge target. If a var is live-in at a back-edge target it
654 * is also live out/end there since the variable is live in the
655 * underlying loop. So in the case where t == bl and that is not
656 * a back-edge target, we have to remove that use from consideration
657 * to determine if the var is live out/end there.
659 * Note that the live in information has been calculated by the
660 * uses iteration above.
662 if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
663 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
664 bitset_clear(uses, ti->id);
667 /* If we can reach a use, the variable is live there and we say goodbye */
668 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
669 if (bitset_intersect(ti->red_reachable, uses)) {
670 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
674 bitset_andnot(tmp, ti->red_reachable);
677 * if we deleted a use do to the commentary above, we have to
678 * re-add it since it might be visible from further view points
679 * (we only need that in the non-reducible case).
681 if (use_in_current_block)
682 bitset_set(uses, ti->id);
688 stat_ev_cnt_done(uses, "lv_chk_uses");
689 stat_ev_cnt_done(iter, "lv_chk_iter");