2 * Copyright (C) 1995-2007 University of Karlsruhe. 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.
40 * Copyright (C) 2007 Universitaet Karlsruhe
41 * Released under the GPL
46 #include "irgraph_t.h"
47 #include "irphase_t.h"
48 #include "iredges_t.h"
56 #include "irlivechk.h"
58 typedef struct _bl_info_t {
59 ir_node *block; /**< The block. */
61 int id; /**< a tight number for the block.
62 we're just reusing the pre num from
65 bitset_t *red_reachable; /**< Holds all id's if blocks reachable
66 in the CFG modulo back edges. */
68 bitset_t *be_tgt_reach; /**< target blocks of back edges whose
69 sources are reachable from this block
70 in the reduced graph. */
72 bitset_t *be_tgt_dom; /**< target blocks of back edges which
73 are dominated by this block. */
76 #define get_block_info(lv, bl) ((bl_info_t *) phase_get_irn_data(&(lv)->ph, bl))
81 firm_dbg_module_t *dbg;
83 bitset_t *back_edge_src;
84 bitset_t *back_edge_tgt;
88 static void *init_block_data(ir_phase *ph, 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 = dfs_get_pre_num(lv->dfs, 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);
97 bi->be_tgt_dom = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
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)) {
120 * Compute the transitive closure on the reduced graph.
121 * The reduced graph is the original graph without back edges.
122 * Since that is a DAG, a reverse post order of the graph gives a toposort
123 * which is ideally suited to compute the transitive closure.
124 * Note also, that the DFS tree of the reduced graph is the same than the one
125 * of the original graph. This saves us computing a new reverse post order.
126 * We also can re-use the DFS tree of the original graph.
128 static void red_trans_closure(lv_chk_t *lv)
132 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
133 ir_node *bl = dfs_get_post_num_node(lv->dfs, i);
134 bl_info_t *bi = get_block_info(lv, bl);
136 const ir_edge_t *edge;
138 foreach_block_succ (bl, edge) {
139 ir_node *succ = get_edge_src_irn(edge);
140 bl_info_t *si = get_block_info(lv, succ);
141 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
144 * if the successor is no back edge, include all reachable
145 * blocks from there into the reachable set of the current node
147 if (kind != DFS_EDGE_BACK) {
148 assert(dfs_get_post_num(lv->dfs, bl)
149 > dfs_get_post_num(lv->dfs, succ));
150 bitset_or(bi->red_reachable, si->red_reachable);
151 bitset_set(bi->red_reachable, si->id);
154 /* mark the block as a back edge src and succ as back edge tgt. */
156 bitset_set(lv->back_edge_src, bi->id);
157 bitset_set(lv->back_edge_tgt, si->id);
166 * Compute the two back edge sets for each block.
167 * <code>be_tgt_reach</code> contains all target blocks of a back edges reachable from a node.
168 * <code>be_tgt_dom</code> contains all target blocks of back edges strictly dominated
171 static void compute_back_edge_sets(lv_chk_t *lv, ir_node *bl)
173 bl_info_t *bi = get_block_info(lv, bl);
174 bitset_t *tmp = bitset_alloca(lv->n_blocks);
179 dominates_for_each (bl, n) {
180 bl_info_t *ni = get_block_info(lv, n);
182 /* compute information for dominance sub tree */
183 compute_back_edge_sets(lv, n);
186 * of course all blocks dominated by blocks in the
187 * subtree are also dominated by bl.
189 bitset_or(bi->be_tgt_dom, ni->be_tgt_dom);
192 * add the immeditate dominee to the back edge tgt dominance
193 * bitset if it is the target node of a back edge.
195 if (bitset_is_set(lv->back_edge_tgt, ni->id))
196 bitset_set(bi->be_tgt_dom, ni->id);
200 * iterate over all back edge src nodes which are reachable from
201 * this nodes and put the targets of the back edges in the be_tgt_reach
202 * bitset of the node.
204 bitset_copy(tmp, bi->red_reachable);
205 bitset_set(tmp, bi->id);
206 bitset_and(tmp, lv->back_edge_src);
207 bitset_foreach (tmp, elm) {
208 ir_node *src = lv->map[elm]->block;
209 const ir_edge_t *edge;
211 foreach_block_succ (src, edge) {
212 ir_node *succ = get_edge_src_irn(edge);
213 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, src, succ);
215 if (kind == DFS_EDGE_BACK) {
216 bl_info_t *si = get_block_info(lv, succ);
217 bitset_set(bi->be_tgt_reach, si->id);
223 lv_chk_t *lv_chk_new(ir_graph *irg)
225 lv_chk_t *res = xmalloc(sizeof(res[0]));
226 struct obstack *obst;
229 phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
230 obst = phase_obst(&res->ph);
232 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
234 res->dfs = dfs_new(&absgraph_irg_cfg_succ, irg);
235 res->n_blocks = dfs_get_n_nodes(res->dfs);
236 res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
237 res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
238 res->map = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
244 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
245 if ((f = fopen(name, "wt")) != NULL) {
246 dfs_dump(res->dfs, f);
249 dump_ir_block_graph(irg, "-lvchk");
253 /* fill the map which maps pre_num to block infos */
254 for (i = res->n_blocks - 1; i >= 0; --i) {
255 ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
256 res->map[i] = phase_get_or_set_irn_data(&res->ph, irn);
259 /* first of all, compute the transitive closure of the CFG *without* back edges */
260 red_trans_closure(res);
262 /* now fill the two remaining bitsets concerning back edges */
263 compute_back_edge_sets(res, get_irg_start_block(irg));
265 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
266 for (i = res->n_blocks - 1; i >= 0; --i) {
267 ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
268 bl_info_t *bi = get_block_info(res, irn);
269 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
270 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
271 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
272 DBG((res->dbg, LEVEL_1, "\ttgt dom: %B\n", bi->be_tgt_dom));
275 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
276 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
281 void lv_chk_free(lv_chk_t *lv)
283 obstack_free(phase_obst(&lv->ph), NULL);
289 * Check if a node is live at the end of a block.
290 * This function is for internal use as its code is shared between
291 * the in/end routines below. It is almost the "live_end" routine
292 * but passing in the bitset for recording the blocks where the variable
293 * is used saves some effort in the "live_in" routine. See below for
296 * @param lv The liveness check environment.
297 * @param what The node to check for.
298 * @param bl The block under investigation.
299 * @param end If 1, it is tested if the node is live at the end.
300 * If 0, it is only tested if the node is live out.
301 * @param uses A bitset where this routine records all ids of blocks
302 * where this variable is used. Note that the bitset
303 * is only guaranteed to be filled if the node was not
304 * live at the end of the block.
305 * @return 1, if @p what is live at the end at @p bl.
307 static int check_live_internal(const lv_chk_t *lv, const ir_node *what, const ir_node *bl, int end, bitset_t *uses)
311 assert(is_Block(bl) && "can only check for liveness in a block");
313 if (!is_liveness_node(what))
316 what_bl = get_nodes_block(what);
317 if (!block_dominates(what_bl, bl))
321 * If the block in question is the same as the definition block,
322 * the algorithm is simple. JUst check for uses not inside this block.
325 const ir_edge_t *edge;
327 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", what, bl));
328 foreach_out_edge (what, edge) {
329 ir_node *use = get_edge_src_irn(edge);
332 if (!is_liveness_node(use))
335 use_bl = get_nodes_block(use);
337 int pos = get_edge_src_pos(edge);
338 use_bl = get_Block_cfgpred_block(use_bl, pos);
340 if (end && use_bl == bl) {
341 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
346 if (use_bl != what_bl)
353 /* this is the complicated case */
355 bitset_t *visited = bitset_alloca(lv->n_blocks);
356 bitset_t *to_visit = bitset_alloca(lv->n_blocks);
357 bitset_t *next = bitset_alloca(lv->n_blocks);
358 bl_info_t *def = get_block_info(lv, what_bl);
359 bl_info_t *bli = get_block_info(lv, bl);
361 const ir_edge_t *edge;
363 foreach_out_edge (what, edge) {
364 ir_node *user = get_edge_src_irn(edge);
367 if (!is_liveness_node(user))
370 use_bl = get_nodes_block(user);
372 int pos = get_edge_src_pos(edge);
373 ir_node *pred_bl = get_Block_cfgpred_block(use_bl, pos);
374 bl_info_t *bi = get_block_info(lv, pred_bl);
376 if (end && pred_bl == bl)
379 bitset_set(uses, bi->id);
383 bl_info_t *bi = get_block_info(lv, use_bl);
384 bitset_set(uses, bi->id);
387 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
389 bitset_clear(uses, def->id);
390 bitset_set(to_visit, bli->id);
392 int id = bitset_next_set(to_visit, 0);
393 bl_info_t *bi = lv->map[id];
395 DBG((lv->dbg, LEVEL_2, "\tto visit: %B\n", to_visit));
396 DBG((lv->dbg, LEVEL_2, "\tvisited: %B\n", visited));
399 * if one of the blocks is reachable, the node must be live there.
400 * Not that this is not sufficient, since the nodes reachable
401 * via back edges are not contained in the red_reachable set.
403 if (bitset_intersect(bi->red_reachable, uses))
407 * if not, we have to check the back edges in question, if
408 * they lead to places which are reachable.
411 bitset_set(visited, id);
412 bitset_or(visited, bi->red_reachable);
414 bitset_copy(next, bi->be_tgt_reach);
415 bitset_and(next, def->be_tgt_dom);
416 DBG((lv->dbg, LEVEL_2, "\tnext: %B\n----\n", next));
418 if (bitset_intersect(uses, next))
421 bitset_or(to_visit, next);
422 bitset_andnot(to_visit, visited);
425 } while (!bitset_is_empty(to_visit));
431 int lv_chk_bl_end(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
433 bitset_t *uses = bitset_alloca(lv->n_blocks);
434 return check_live_internal(lv, what, bl, 1, uses);
437 int lv_chk_bl_out(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
439 bitset_t *uses = bitset_alloca(lv->n_blocks);
440 return check_live_internal(lv, what, bl, 0, uses);
443 int lv_chk_bl_in(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
446 * only check, if the node is not defined in this block.
447 * Under SSA, a node can never be live in at its definition block.
449 if (get_nodes_block(what) != bl) {
450 bl_info_t *bi = get_block_info(lv, bl);
452 bitset_t *uses = bitset_alloca(lv->n_blocks);
453 int live_at_end = check_live_internal(lv, what, bl, 1, uses);
455 /* to be live in, the value must be live at the end or have a use in this block */
456 return live_at_end || bitset_is_set(uses, id);