2 * This file is part of libFirm.
3 * Copyright (C) 2012 Inria Rhone-Alpes.
9 * @author Sebastian Hack
12 * Liveness checks as developed by Benoit Boissinot, Fabrice Rastello and myself.
14 * The speciality here is, that nothing has to be recomputed if new nodes are created
15 * or old ones deleted.
17 * This algo has one core routine check_live_end_internal() which performs the liveness check.
18 * It only relies on the precomputation done in the constructor, which in turn needs:
20 * - the dominance tree
21 * - data obtained from a depth-first-search
23 * The precomputation remains valid as long as the CFG is not altered.
29 /* statev is expensive here, only enable when needed */
30 #define DISABLE_STATEV
32 #include "irgraph_t.h"
34 #include "irnodemap.h"
35 #include "iredges_t.h"
45 #include "irlivechk.h"
49 typedef struct bl_info_t {
50 const ir_node *block; /**< The block. */
53 int id : 31; /**< a tight number for the block.
54 we're just reusing the pre num from
56 bitset_t *red_reachable; /**< Holds all id's if blocks reachable
57 in the CFG modulo back edges. */
59 bitset_t *be_tgt_reach; /**< target blocks of back edges whose
60 sources are reachable from this block
61 in the reduced graph. */
65 ir_nodemap block_infos;
69 bitset_t *back_edge_src;
70 bitset_t *back_edge_tgt;
72 DEBUG_ONLY(firm_dbg_module_t *dbg;)
75 static bl_info_t *get_block_info(lv_chk_t *lv, const ir_node *block)
77 bl_info_t *info = ir_nodemap_get(bl_info_t, &lv->block_infos, block);
79 info = OALLOC(&lv->obst, bl_info_t);
80 info->id = get_Block_dom_tree_pre_num(block);
82 info->red_reachable = bitset_obstack_alloc(&lv->obst, lv->n_blocks);
83 info->be_tgt_reach = bitset_obstack_alloc(&lv->obst, lv->n_blocks);
84 info->be_tgt_calc = 0;
85 ir_nodemap_insert(&lv->block_infos, block, info);
91 * Compute the transitive closure on the reduced graph.
92 * The reduced graph is the original graph without back edges.
93 * Since that is a DAG, a reverse post order of the graph gives a toposort
94 * which is ideally suited to compute the transitive closure.
95 * Note also, that the DFS tree of the reduced graph is the same than the one
96 * of the original graph. This saves us computing a new reverse post order.
97 * We also can re-use the DFS tree of the original graph.
99 static void red_trans_closure(lv_chk_t *lv)
103 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
104 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
105 bl_info_t *bi = get_block_info(lv, bl);
107 bitset_set(bi->red_reachable, bi->id);
108 foreach_block_succ (bl, edge) {
109 ir_node *succ = get_edge_src_irn(edge);
110 bl_info_t *si = get_block_info(lv, succ);
111 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
114 * if the successor is no back edge, include all reachable
115 * blocks from there into the reachable set of the current node
117 if (kind != DFS_EDGE_BACK) {
118 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
119 bitset_or(bi->red_reachable, si->red_reachable);
122 /* mark the block as a back edge src and succ as back edge tgt. */
124 bitset_set(lv->back_edge_src, bi->id);
125 bitset_set(lv->back_edge_tgt, si->id);
133 static void compute_back_edge_chain(lv_chk_t *lv, const ir_node *bl)
135 bitset_t *tmp = bitset_alloca(lv->n_blocks);
136 bl_info_t *bi = get_block_info(lv, bl);
138 DBG((lv->dbg, LEVEL_2, "computing T_%d\n", bi->id));
140 /* put all back edge sources reachable (reduced) from here in tmp */
141 bitset_copy(tmp, bi->red_reachable);
142 bitset_set(tmp, bi->id);
143 bitset_and(tmp, lv->back_edge_src);
146 DBG((lv->dbg, LEVEL_2, "\treachable be src: %B\n", tmp));
148 /* iterate over them ... */
149 bitset_foreach(tmp, elm) {
150 bl_info_t *si = lv->map[elm];
152 /* and find back edge targets which are not reduced reachable from bl */
153 foreach_block_succ (si->block, edge) {
154 ir_node *tgt = get_edge_src_irn(edge);
155 bl_info_t *ti = get_block_info(lv, tgt);
156 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, si->block, tgt);
158 if (kind == DFS_EDGE_BACK && !bitset_is_set(bi->red_reachable, ti->id)) {
159 if (!ti->be_tgt_calc)
160 compute_back_edge_chain(lv, tgt);
161 bitset_set(bi->be_tgt_reach, ti->id);
162 bitset_or(bi->be_tgt_reach, ti->be_tgt_reach);
165 bitset_clear(bi->be_tgt_reach, bi->id);
170 static inline void compute_back_edge_chains(lv_chk_t *lv)
174 DBG((lv->dbg, LEVEL_2, "back edge sources: %B\n", lv->back_edge_src));
175 bitset_foreach(lv->back_edge_src, elm) {
176 compute_back_edge_chain(lv, lv->map[elm]->block);
179 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
180 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
181 bl_info_t *bi = get_block_info(lv, bl);
183 if (!bitset_is_set(lv->back_edge_tgt, bi->id)) {
184 foreach_block_succ (bl, edge) {
185 ir_node *succ = get_edge_src_irn(edge);
186 bl_info_t *si = get_block_info(lv, succ);
187 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
189 if (kind != DFS_EDGE_BACK) {
190 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
191 bitset_or(bi->be_tgt_reach, si->be_tgt_reach);
197 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
198 const ir_node *bl = (const ir_node*) dfs_get_post_num_node(lv->dfs, i);
199 bl_info_t *bi = get_block_info(lv, bl);
200 bitset_set(bi->be_tgt_reach, bi->id);
204 lv_chk_t *lv_chk_new(ir_graph *irg)
206 lv_chk_t *res = XMALLOC(lv_chk_t);
212 ir_nodemap_init(&res->block_infos, irg);
213 obstack_init(&res->obst);
215 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
217 res->dfs = dfs_new(&absgraph_irg_cfg_succ, irg);
218 res->n_blocks = dfs_get_n_nodes(res->dfs);
219 res->back_edge_src = bitset_obstack_alloc(&res->obst, res->n_blocks);
220 res->back_edge_tgt = bitset_obstack_alloc(&res->obst, res->n_blocks);
221 res->map = OALLOCNZ(&res->obst, bl_info_t*, res->n_blocks);
223 /* fill the map which maps pre_num to block infos */
224 for (i = res->n_blocks - 1; i >= 0; --i) {
225 ir_node *irn = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
226 bl_info_t *bi = get_block_info(res, irn);
227 assert(bi->id < res->n_blocks);
228 assert(res->map[bi->id] == NULL);
229 res->map[bi->id] = bi;
232 /* first of all, compute the transitive closure of the CFG *without* back edges */
233 red_trans_closure(res);
235 /* compute back edge chains */
236 compute_back_edge_chains(res);
239 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
240 for (i = res->n_blocks - 1; i >= 0; --i) {
241 const ir_node *irn = (const ir_node*) dfs_get_pre_num_node(res->dfs, i);
242 bl_info_t *bi = get_block_info(res, irn);
243 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
244 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
245 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
249 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
250 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
252 stat_ev_tim_pop("lv_chk_cons_time");
256 void lv_chk_free(lv_chk_t *lv)
259 obstack_free(&lv->obst, NULL);
260 ir_nodemap_destroy(&lv->block_infos);
264 unsigned lv_chk_bl_xxx(lv_chk_t *lv, const ir_node *bl, const ir_node *var)
268 stat_ev_cnt_decl(uses);
269 stat_ev_cnt_decl(iter);
271 assert(is_Block(bl) && "can only check for liveness in a block");
273 /* If the variable ist no liveness related var, bail out. */
274 if (!is_liveness_node(var))
277 stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
280 /* If there is no dominance relation, go out, too */
281 def_bl = get_nodes_block(var);
282 if (!block_dominates(def_bl, bl)) {
283 stat_ev("lv_chk_no_dom");
288 * If the block in question is the same as the definition block,
289 * the algorithm is simple. Just check for uses not inside this block.
292 stat_ev("lv_chk_def_block");
293 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
294 foreach_out_edge (var, edge) {
295 ir_node *use = get_edge_src_irn(edge);
298 if (!is_liveness_node(use))
301 stat_ev_cnt_inc(uses);
302 use_bl = get_nodes_block(use);
304 int pos = get_edge_src_pos(edge);
305 use_bl = get_Block_cfgpred_block(use_bl, pos);
308 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
309 res |= lv_chk_state_end;
313 if (use_bl != def_bl) {
314 res = lv_chk_state_end | lv_chk_state_out;
323 * this is the more complicated case.
324 * We try to gather as much information as possible during looking
327 * Note that we know for sure that bl != def_bl. That is sometimes
328 * silently exploited below.
331 bl_info_t *def = get_block_info(lv, def_bl);
332 bl_info_t *bli = get_block_info(lv, bl);
333 bitset_t *uses = bitset_alloca(lv->n_blocks);
337 unsigned min_dom, max_dom;
339 /* if the block has no DFS info, it cannot be reached.
340 * This can happen in functions with endless loops.
341 * we then go out, since nothing is live there.
343 * TODO: Is that right?
349 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
350 var, def_bl, def->id, bl, bli->id));
352 foreach_out_edge (var, edge) {
353 ir_node *user = get_edge_src_irn(edge);
354 int mask = lv_chk_state_in;
359 /* if the user is no liveness node, the use does not count */
360 if (!is_liveness_node(user))
363 stat_ev_cnt_inc(uses);
365 /* if the user is a phi, the use is in the predecessor
366 * furthermore, prepare a mask so that in the case where
367 * bl (the block in question) coincides with a use, it
368 * can be marked live_end there. */
369 use_bl = get_nodes_block(user);
371 int pos = get_edge_src_pos(edge);
372 use_bl = get_Block_cfgpred_block(use_bl, pos);
373 mask |= lv_chk_state_end;
377 /* if the use block coincides with the query block, we
378 * already gather a little liveness information.
379 * The variable is surely live there, since bl != def_bl
380 * (that case is treated above). */
384 bi = get_block_info(lv, use_bl);
387 bitset_set(uses, bi->id);
390 /* get the dominance range which really matters. all uses outside
391 * the definition's dominance range are not to consider. note,
392 * that the definition itself is also not considered. The case
393 * where bl == def_bl is considered above. */
394 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
395 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
397 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
399 /* prepare a set with all reachable back edge targets.
400 * this will determine our "looking points" from where
401 * we will search/find the calculated uses. */
402 Tq = bli->be_tgt_reach;
404 /* now, visit all viewing points in the temporary bitset lying
405 * in the dominance range of the variable. Note that for reducible
406 * flow-graphs the first iteration is sufficient and the loop
408 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
409 i = bitset_next_set(Tq, min_dom);
410 while (i <= max_dom) {
411 bl_info_t *ti = lv->map[i];
412 int use_in_current_block = bitset_is_set(uses, ti->id);
414 stat_ev_cnt_inc(iter);
417 * This is somewhat tricky. Since this routine handles both, live in
418 * and end/out we have to handle all the border cases correctly.
419 * Each node is in its own red_reachable set (see calculation
420 * function above). That means, that in the case where bl == t, the
421 * intersection check of uses and reachability below will always
422 * find an intersection, namely t.
424 * However, if a block contains a use and the variable is dead
425 * afterwards, it is not live end/out at that block. Besides
426 * back-edge target. If a var is live-in at a back-edge target it
427 * is also live out/end there since the variable is live in the
428 * underlying loop. So in the case where t == bl and that is not
429 * a back-edge target, we have to remove that use from consideration
430 * to determine if the var is live out/end there.
432 * Note that the live in information has been calculated by the
433 * uses iteration above.
435 if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
436 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
437 bitset_clear(uses, ti->id);
440 /* If we can reach a use, the variable is live there and we say goodbye */
441 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
442 if (bitset_intersect(ti->red_reachable, uses)) {
443 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
448 * if we deleted a use do to the commentary above, we have to
449 * re-add it since it might be visible from further view points
450 * (we only need that in the non-reducible case).
452 if (use_in_current_block)
453 bitset_set(uses, ti->id);
455 i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
461 stat_ev_tim_pop("lv_chk_query_time");
462 stat_ev_cnt_done(uses, "lv_chk_uses");
463 stat_ev_cnt_done(iter, "lv_chk_iter");
464 stat_ev_ctx_pop("lv_chk");