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.
43 #include "irgraph_t.h"
44 #include "irphase_t.h"
45 #include "iredges_t.h"
53 #include "irlivechk.h"
55 typedef struct _bl_info_t {
56 ir_node *block; /**< The block. */
58 int id; /**< a tight number for the block.
59 we're just reusing the pre num from
62 bitset_t *red_reachable; /**< Holds all id's if blocks reachable
63 in the CFG modulo back edges. */
65 bitset_t *be_tgt_reach; /**< target blocks of back edges whose
66 sources are reachable from this block
67 in the reduced graph. */
69 bitset_t *be_tgt_dom; /**< target blocks of back edges which
70 are dominated by this block. */
73 #define get_block_info(lv, bl) ((bl_info_t *) phase_get_irn_data(&(lv)->ph, bl))
78 DEBUG_ONLY(firm_dbg_module_t *dbg;)
80 bitset_t *back_edge_src;
81 bitset_t *back_edge_tgt;
85 static void *init_block_data(ir_phase *ph, ir_node *irn, void *old)
87 lv_chk_t *lv = container_of(ph, lv_chk_t, ph);
88 bl_info_t *bi = phase_alloc(ph, sizeof(bi[0]));
90 bi->id = dfs_get_pre_num(lv->dfs, irn);
92 bi->red_reachable = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
93 bi->be_tgt_reach = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
94 bi->be_tgt_dom = bitset_obstack_alloc(phase_obst(ph), lv->n_blocks);
99 * Filter function to select all nodes for which liveness is computed.
101 * @return 1 if the node shall be considered in liveness, 0 if not.
103 static INLINE int is_liveness_node(const ir_node *irn)
105 switch(get_irn_opcode(irn)) {
117 * Compute the transitive closure on the reduced graph.
118 * The reduced graph is the original graph without back edges.
119 * Since that is a DAG, a reverse post order of the graph gives a toposort
120 * which is ideally suited to compute the transitive closure.
121 * Note also, that the DFS tree of the reduced graph is the same than the one
122 * of the original graph. This saves us computing a new reverse post order.
123 * We also can re-use the DFS tree of the original graph.
125 static void red_trans_closure(lv_chk_t *lv)
129 for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
130 ir_node *bl = dfs_get_post_num_node(lv->dfs, i);
131 bl_info_t *bi = get_block_info(lv, bl);
133 const ir_edge_t *edge;
135 foreach_block_succ (bl, edge) {
136 ir_node *succ = get_edge_src_irn(edge);
137 bl_info_t *si = get_block_info(lv, succ);
138 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
141 * if the successor is no back edge, include all reachable
142 * blocks from there into the reachable set of the current node
144 if (kind != DFS_EDGE_BACK) {
145 assert(dfs_get_post_num(lv->dfs, bl)
146 > dfs_get_post_num(lv->dfs, succ));
147 bitset_or(bi->red_reachable, si->red_reachable);
148 bitset_set(bi->red_reachable, si->id);
151 /* mark the block as a back edge src and succ as back edge tgt. */
153 bitset_set(lv->back_edge_src, bi->id);
154 bitset_set(lv->back_edge_tgt, si->id);
163 * Compute the two back edge sets for each block.
164 * <code>be_tgt_reach</code> contains all target blocks of a back edges reachable from a node.
165 * <code>be_tgt_dom</code> contains all target blocks of back edges strictly dominated
168 static void compute_back_edge_sets(lv_chk_t *lv, ir_node *bl)
170 bl_info_t *bi = phase_get_or_set_irn_data(&(lv)->ph, bl);
171 bitset_t *tmp = bitset_alloca(lv->n_blocks);
176 dominates_for_each (bl, n) {
177 bl_info_t *ni = phase_get_or_set_irn_data(&(lv)->ph, n);
179 /* compute information for dominance sub tree */
180 compute_back_edge_sets(lv, n);
183 * of course all blocks dominated by blocks in the
184 * subtree are also dominated by bl.
186 bitset_or(bi->be_tgt_dom, ni->be_tgt_dom);
189 * add the immeditate dominee to the back edge tgt dominance
190 * bitset if it is the target node of a back edge.
192 if (bitset_is_set(lv->back_edge_tgt, ni->id))
193 bitset_set(bi->be_tgt_dom, ni->id);
197 * iterate over all back edge src nodes which are reachable from
198 * this nodes and put the targets of the back edges in the be_tgt_reach
199 * bitset of the node.
201 bitset_copy(tmp, bi->red_reachable);
202 bitset_set(tmp, bi->id);
203 bitset_and(tmp, lv->back_edge_src);
204 bitset_foreach (tmp, elm) {
205 ir_node *src = lv->map[elm]->block;
206 const ir_edge_t *edge;
208 foreach_block_succ (src, edge) {
209 ir_node *succ = get_edge_src_irn(edge);
210 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, src, succ);
212 if (kind == DFS_EDGE_BACK) {
213 bl_info_t *si = get_block_info(lv, succ);
214 bitset_set(bi->be_tgt_reach, si->id);
220 lv_chk_t *lv_chk_new(ir_graph *irg)
222 lv_chk_t *res = xmalloc(sizeof(res[0]));
223 struct obstack *obst;
226 phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
227 obst = phase_obst(&res->ph);
229 FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
231 res->dfs = dfs_new(&absgraph_irg_cfg_succ, irg);
232 res->n_blocks = dfs_get_n_nodes(res->dfs);
233 res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
234 res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
235 res->map = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
241 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
242 if ((f = fopen(name, "wt")) != NULL) {
243 dfs_dump(res->dfs, f);
246 dump_ir_block_graph(irg, "-lvchk");
250 /* fill the map which maps pre_num to block infos */
251 for (i = res->n_blocks - 1; i >= 0; --i) {
252 ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
253 res->map[i] = phase_get_or_set_irn_data(&res->ph, irn);
256 /* first of all, compute the transitive closure of the CFG *without* back edges */
257 red_trans_closure(res);
259 /* now fill the two remaining bitsets concerning back edges */
260 compute_back_edge_sets(res, get_irg_start_block(irg));
263 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
264 for (i = res->n_blocks - 1; i >= 0; --i) {
265 ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
266 bl_info_t *bi = get_block_info(res, irn);
267 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
268 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
269 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
270 DBG((res->dbg, LEVEL_1, "\ttgt dom: %B\n", bi->be_tgt_dom));
274 DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
275 DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
280 void lv_chk_free(lv_chk_t *lv)
282 obstack_free(phase_obst(&lv->ph), NULL);
288 * Check if a node is live at the end of a block.
289 * This function is for internal use as its code is shared between
290 * the in/end routines below. It is almost the "live_end" routine
291 * but passing in the bitset for recording the blocks where the variable
292 * is used saves some effort in the "live_in" routine. See below for
295 * @param lv The liveness check environment.
296 * @param what The node to check for.
297 * @param bl The block under investigation.
298 * @param uses A bitset where this routine records all ids of blocks
299 * where this variable is used. Note that the bitset
300 * is only guaranteed to be filled if the node was not
301 * live at the end of the block.
302 * @return 1, if @p what is live at the end at @p bl.
304 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *what)
308 assert(is_Block(bl) && "can only check for liveness in a block");
310 if (!is_liveness_node(what))
313 what_bl = get_nodes_block(what);
314 if (!block_dominates(what_bl, bl))
318 * If the block in question is the same as the definition block,
319 * the algorithm is simple. Just check for uses not inside this block.
323 const ir_edge_t *edge;
325 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", what, bl));
326 foreach_out_edge (what, edge) {
327 ir_node *use = get_edge_src_irn(edge);
330 if (!is_liveness_node(use))
333 use_bl = get_nodes_block(use);
335 int pos = get_edge_src_pos(edge);
336 use_bl = get_Block_cfgpred_block(use_bl, pos);
339 DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
340 res |= lv_chk_state_end;
344 if (use_bl != what_bl)
345 return lv_chk_state_end | lv_chk_state_out;
351 /* this is the complicated case */
353 bitset_t *visited = bitset_alloca(lv->n_blocks);
354 bitset_t *to_visit = bitset_alloca(lv->n_blocks);
355 bitset_t *next = bitset_alloca(lv->n_blocks);
356 bitset_t *uses = bitset_alloca(lv->n_blocks);
357 bl_info_t *def = get_block_info(lv, what_bl);
358 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);
368 if (!is_liveness_node(user))
371 use_bl = get_nodes_block(user);
373 int pos = get_edge_src_pos(edge);
375 use_bl = get_Block_cfgpred_block(use_bl, pos);
376 bi = get_block_info(lv, use_bl);
379 res |= lv_chk_state_end | lv_chk_state_in;
381 bitset_set(uses, bi->id);
385 bi = get_block_info(lv, use_bl);
386 bitset_set(uses, bi->id);
388 res |= lv_chk_state_in;
392 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
394 bitset_clear(uses, def->id);
395 bitset_set(to_visit, bli->id);
397 int id = bitset_next_set(to_visit, 0);
398 bl_info_t *bi = lv->map[id];
400 DBG((lv->dbg, LEVEL_2, "\tto visit: %B\n", to_visit));
401 DBG((lv->dbg, LEVEL_2, "\tvisited: %B\n", visited));
404 * if one of the blocks is reachable, the node must be live there.
405 * Note that this is not sufficient, since the nodes reachable
406 * via back edges are not contained in the red_reachable set.
408 if (bitset_intersect(bi->red_reachable, uses))
409 return lv_chk_state_end | lv_chk_state_out | lv_chk_state_in;
412 * if not, we have to check the back edges in question, if
413 * they lead to places which are reachable.
416 bitset_set(visited, id);
417 bitset_or(visited, bi->red_reachable);
419 bitset_copy(next, bi->be_tgt_reach);
420 bitset_and(next, def->be_tgt_dom);
421 DBG((lv->dbg, LEVEL_2, "\tnext: %B\n----\n", next));
423 if (bitset_intersect(uses, next))
424 return lv_chk_state_end | lv_chk_state_out | lv_chk_state_in;
426 bitset_or(to_visit, next);
427 bitset_andnot(to_visit, visited);
430 } while (!bitset_is_empty(to_visit));