nsz Git - libfirm/blob - ir/ana/irlivechk.c

   1 /*
   2  * Copyright (C) 1995-2007 Inria Rhone-Alpes.  All right reserved.
   3  *
   4  * This file is part of libFirm.
   5  *
   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.
  10  *
  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.
  14  *
  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
  17  * PURPOSE.
  18  */
  19
  20 /**
  21  * @file    livechk.c
  22  * @date    21.04.2007
  23  * @author  Sebastian Hack
  24  * @version $Id$
  25  * @summary
  26  *
  27  * Liveness checks as developed by Benoit Boissinot, Fabrice Rastello and myself.
  28  *
  29  * The speciality here is, that nothing has to be recomputed if new nodes are created
  30  * or old ones deleted.
  31  *
  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:
  34  * - out edges
  35  * - the dominance tree
  36  * - data obtained from a depth-first-search
  37  *
  38  * The precomputation remains valid as long as the CFG is not altered.
  39  */
  40 #ifdef HAVE_CONFIG_H
  41 #include <config.h>
  42 #endif
  43
  44 #include <stdio.h>
  45
  46 #include "irgraph_t.h"
  47 #include "irnode_t.h"
  48 #include "irphase_t.h"
  49 #include "iredges_t.h"
  50
  51 #include "irprintf.h"
  52 #include "irdom.h"
  53 #include "irdump.h"
  54
  55 #include "dfs_t.h"
  56 #include "bitset.h"
  57 #include "util.h"
  58
  59 #include "irlivechk.h"
  60
  61 #include "statev.h"
  62
  63 typedef struct _bl_info_t {
  64         const ir_node *block;      /**< The block. */
  65
  66         int be_tgt_calc : 1;
  67         int id : 31;               /**< a tight number for the block.
  68                                                                  we're just reusing the pre num from
  69                                                                  the DFS. */
  70         bitset_t *red_reachable;   /**< Holds all id's if blocks reachable
  71                                                                  in the CFG modulo back edges. */
  72
  73         bitset_t *be_tgt_reach;    /**< target blocks of back edges whose
  74                                                                  sources are reachable from this block
  75                                                                  in the reduced graph. */
  76 } bl_info_t;
  77
  78 #define get_block_info(lv, bl) ((bl_info_t *) phase_get_irn_data(&(lv)->ph, bl))
  79
  80 struct _lv_chk_t {
  81         ir_phase ph;
  82         const dfs_t *dfs;
  83         DEBUG_ONLY(firm_dbg_module_t *dbg;)
  84         int n_blocks;
  85         bitset_t *back_edge_src;
  86         bitset_t *back_edge_tgt;
  87         bl_info_t **map;
  88 };
  89
  90 static void *init_block_data(ir_phase *ph, const ir_node *irn, void *old)
  91 {
  92         lv_chk_t *lv      = container_of(ph, lv_chk_t, ph);
  93         bl_info_t *bi     = phase_alloc(ph, sizeof(bi[0]));
  94
  95         bi->id            = get_Block_dom_tree_pre_num(irn);
  96         bi->block         = 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);
  99         bi->be_tgt_calc   = 0;
 100         (void) old;
 101         return bi;
 102 }
 103
 104 /**
 105  * Filter function to select all nodes for which liveness is computed.
 106  * @param irn A node.
 107  * @return    1 if the node shall be considered in liveness, 0 if not.
 108  */
 109 static INLINE int is_liveness_node(const ir_node *irn)
 110 {
 111         switch(get_irn_opcode(irn)) {
 112         case iro_Block:
 113         case iro_Bad:
 114         case iro_End:
 115         case iro_Anchor:
 116                 return 0;
 117         default:;
 118         }
 119
 120         return 1;
 121 }
 122
 123 /**
 124  * Compute the transitive closure on the reduced graph.
 125  * The reduced graph is the original graph without back edges.
 126  * Since that is a DAG, a reverse post order of the graph gives a toposort
 127  * which is ideally suited to compute the transitive closure.
 128  * Note also, that the DFS tree of the reduced graph is the same than the one
 129  * of the original graph. This saves us computing a new reverse post order.
 130  * We also can re-use the DFS tree of the original graph.
 131  */
 132 static void red_trans_closure(lv_chk_t *lv)
 133 {
 134         int i, n;
 135
 136         for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
 137                 const ir_node *bl   = dfs_get_post_num_node(lv->dfs, i);
 138                 bl_info_t *bi = get_block_info(lv, bl);
 139
 140                 const ir_edge_t *edge;
 141
 142                 bitset_set(bi->red_reachable, bi->id);
 143                 foreach_block_succ (bl, edge) {
 144                         ir_node *succ = get_edge_src_irn(edge);
 145                         bl_info_t *si = get_block_info(lv, succ);
 146                         dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
 147
 148                         /*
 149                          * if the successor is no back edge, include all reachable
 150                          * blocks from there into the reachable set of the current node
 151                          */
 152                         if (kind != DFS_EDGE_BACK) {
 153                                 assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
 154                                 bitset_or(bi->red_reachable, si->red_reachable);
 155                         }
 156
 157                         /* mark the block as a back edge src and succ as back edge tgt. */
 158                         else {
 159                                 bitset_set(lv->back_edge_src, bi->id);
 160                                 bitset_set(lv->back_edge_tgt, si->id);
 161                         }
 162                 }
 163
 164         }
 165
 166 }
 167
 168 static void compute_back_edge_chain(lv_chk_t *lv, const ir_node *bl)
 169 {
 170         bitset_t *tmp = bitset_alloca(lv->n_blocks);
 171         bl_info_t *bi = get_block_info(lv, bl);
 172
 173         bitset_pos_t elm;
 174
 175         DBG((lv->dbg, LEVEL_2, "computing T_%d\n", bi->id));
 176
 177         /* put all back edge sources reachable (reduced) from here in tmp */
 178         bitset_copy(tmp, bi->red_reachable);
 179         bitset_set(tmp, bi->id);
 180         bitset_and(tmp, lv->back_edge_src);
 181         bi->be_tgt_calc = 1;
 182
 183         DBG((lv->dbg, LEVEL_2, "\treachable be src: %B\n", tmp));
 184
 185         /* iterate over them ... */
 186         bitset_foreach(tmp, elm) {
 187                 bl_info_t *si = lv->map[elm];
 188                 const ir_edge_t *edge;
 189
 190                 /* and find back edge targets which are not reduced reachable from bl */
 191                 foreach_block_succ (si->block, edge) {
 192                         ir_node *tgt         = get_edge_src_irn(edge);
 193                         bl_info_t *ti        = get_block_info(lv, tgt);
 194                         dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, si->block, tgt);
 195
 196                         if (kind == DFS_EDGE_BACK && !bitset_is_set(bi->red_reachable, ti->id)) {
 197                                 if (!ti->be_tgt_calc)
 198                                         compute_back_edge_chain(lv, tgt);
 199                                 bitset_set(bi->be_tgt_reach, ti->id);
 200                                 bitset_or(bi->be_tgt_reach, ti->be_tgt_reach);
 201                         }
 202                 }
 203                 bitset_clear(bi->be_tgt_reach, bi->id);
 204         }
 205 }
 206
 207
 208 static INLINE void compute_back_edge_chains(lv_chk_t *lv)
 209 {
 210         bitset_pos_t elm;
 211         int i, n;
 212
 213         DBG((lv->dbg, LEVEL_2, "back edge sources: %B\n", lv->back_edge_src));
 214         bitset_foreach(lv->back_edge_src, elm) {
 215                 compute_back_edge_chain(lv, lv->map[elm]->block);
 216         }
 217
 218         for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
 219                 const ir_node *bl = dfs_get_post_num_node(lv->dfs, i);
 220                 bl_info_t *bi     = get_block_info(lv, bl);
 221
 222                 const ir_edge_t *edge;
 223
 224                 if (!bitset_is_set(lv->back_edge_tgt, bi->id)) {
 225                         foreach_block_succ (bl, edge) {
 226                                 ir_node *succ = get_edge_src_irn(edge);
 227                                 bl_info_t *si = get_block_info(lv, succ);
 228                                 dfs_edge_kind_t kind = dfs_get_edge_kind(lv->dfs, bl, succ);
 229
 230                                 if (kind != DFS_EDGE_BACK) {
 231                                         assert(dfs_get_post_num(lv->dfs, bl) > dfs_get_post_num(lv->dfs, succ));
 232                                         bitset_or(bi->be_tgt_reach, si->be_tgt_reach);
 233                                 }
 234                         }
 235                 }
 236         }
 237
 238         for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
 239                 const ir_node *bl = dfs_get_post_num_node(lv->dfs, i);
 240                 bl_info_t *bi     = get_block_info(lv, bl);
 241                 bitset_set(bi->be_tgt_reach, bi->id);
 242         }
 243 }
 244
 245 lv_chk_t *lv_chk_new(ir_graph *irg, const dfs_t *dfs)
 246 {
 247         lv_chk_t *res = XMALLOC(lv_chk_t);
 248         struct obstack *obst;
 249         int i;
 250
 251         edges_deactivate(irg);
 252         edges_activate(irg);
 253         compute_doms(irg);
 254
 255         stat_ev_tim_push();
 256         phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
 257         obst = phase_obst(&res->ph);
 258
 259         FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
 260
 261         res->dfs           = dfs;
 262         res->n_blocks      = dfs_get_n_nodes(res->dfs);
 263         res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
 264         res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
 265         res->map           = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
 266         memset(res->map, 0, res->n_blocks * sizeof(res->map[0]));
 267
 268 #if 0
 269         {
 270                 char name[256];
 271                 FILE *f;
 272                 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
 273                 if ((f = fopen(name, "wt")) != NULL) {
 274                         dfs_dump(res->dfs, f);
 275                         fclose(f);
 276                 }
 277                 dump_ir_block_graph(irg, "-lvchk");
 278         }
 279 #endif
 280
 281         /* fill the map which maps pre_num to block infos */
 282         for (i = res->n_blocks - 1; i >= 0; --i) {
 283                 ir_node *irn  = (ir_node *) dfs_get_pre_num_node(res->dfs, i);
 284                 bl_info_t *bi = phase_get_or_set_irn_data(&res->ph, irn);
 285                 assert(bi->id < res->n_blocks);
 286                 assert(res->map[bi->id] == NULL);
 287                 res->map[bi->id] = bi;
 288         }
 289
 290         /* first of all, compute the transitive closure of the CFG *without* back edges */
 291         red_trans_closure(res);
 292
 293         /* compute back edge chains */
 294         compute_back_edge_chains(res);
 295
 296 #ifndef NDEBUG
 297         DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
 298         for (i = res->n_blocks - 1; i >= 0; --i) {
 299                 const ir_node *irn = dfs_get_pre_num_node(res->dfs, i);
 300                 bl_info_t *bi      = get_block_info(res, irn);
 301                 DBG((res->dbg, LEVEL_1, "lv_chk for %d -> %+F\n", i, irn));
 302                 DBG((res->dbg, LEVEL_1, "\tred reach: %B\n", bi->red_reachable));
 303                 DBG((res->dbg, LEVEL_1, "\ttgt reach: %B\n", bi->be_tgt_reach));
 304         }
 305 #endif
 306
 307         DBG((res->dbg, LEVEL_1, "back edge src: %B\n", res->back_edge_src));
 308         DBG((res->dbg, LEVEL_1, "back edge tgt: %B\n", res->back_edge_tgt));
 309
 310         stat_ev_tim_pop("lv_chk_cons_time");
 311         return res;
 312 }
 313
 314 void lv_chk_free(lv_chk_t *lv)
 315 {
 316         phase_free(&lv->ph);
 317         xfree(lv);
 318 }
 319
 320 /**
 321  * Check if a node is live at the end of a block.
 322  * This function is for internal use as its code is shared between
 323  * the in/end routines below. It is almost the "live_end" routine
 324  * but passing in the bitset for recording the blocks where the variable
 325  * is used saves some effort in the "live_in" routine. See below for
 326  * details.
 327  *
 328  * @param lv    The liveness check environment.
 329  * @param what  The node to check for.
 330  * @param bl    The block under investigation.
 331  * @param uses  A bitset where this routine records all ids of blocks
 332  *              where this variable is used. Note that the bitset
 333  *              is only guaranteed to be filled if the node was not
 334  *              live at the end of the block.
 335  * @return      1, if @p what is live at the end at @p bl.
 336  */
 337 unsigned lv_chk_bl_in_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 338 {
 339         stat_ev_cnt_decl(uses);
 340
 341         ir_node *def_bl;
 342         const ir_edge_t *edge;
 343
 344         int res = 0;
 345
 346         assert(is_Block(bl) && "can only check for liveness in a block");
 347
 348         if (!is_liveness_node(var))
 349                 return 0;
 350
 351         def_bl = get_nodes_block(var);
 352         if (def_bl == bl || !block_dominates(def_bl, bl)) {
 353                 goto end;
 354         }
 355
 356         else {
 357                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 358                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 359                 int min_dom    = get_Block_dom_tree_pre_num(def_bl) + 1;
 360                 int max_dom    = get_Block_dom_max_subtree_pre_num(def_bl);
 361                 bl_info_t *bli = get_block_info(lv, bl);
 362                 int i;
 363
 364                 DBG((lv->dbg, LEVEL_2, "lv check of %+F, def=%+F,%d != q=%+F,%d\n",
 365                                         var, def_bl, min_dom - 1, bl, bli->id));
 366
 367                 foreach_out_edge (var, edge) {
 368                         ir_node *user = get_edge_src_irn(edge);
 369                         ir_node *use_bl;
 370                         bl_info_t *bi;
 371
 372                         if (!is_liveness_node(user))
 373                                 continue;
 374
 375                         stat_ev_cnt_inc(uses);
 376                         use_bl = get_nodes_block(user);
 377                         if (is_Phi(user)) {
 378                                 int pos = get_edge_src_pos(edge);
 379                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 380                         }
 381
 382                         if (use_bl == bl) {
 383                                 res = lv_chk_state_in;
 384                                 DBG((lv->dbg, LEVEL_2, "\tuse directly in block %+F by %+F\n", use_bl, user));
 385                                 goto end;
 386                         }
 387
 388                         bi = get_block_info(lv, use_bl);
 389                         bitset_set(uses, bi->id);
 390                 }
 391
 392                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 393
 394                 {
 395
 396                         bitset_copy(tmp, bli->be_tgt_reach);
 397                         bitset_set(tmp, bli->id);
 398
 399                         DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 400                         for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 401                                 bl_info_t *ti = lv->map[i];
 402                                 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 403                                 if (bitset_intersect(ti->red_reachable, uses)) {
 404                                         res = lv_chk_state_in;
 405                                         goto end;
 406                                 }
 407
 408                                 bitset_andnot(tmp, ti->red_reachable);
 409                         }
 410                 }
 411         }
 412
 413 end:
 414         return res;
 415 }
 416
 417 unsigned lv_chk_bl_end_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 418 {
 419         stat_ev_cnt_decl(uses);
 420
 421         ir_node *def_bl;
 422         const ir_edge_t *edge;
 423
 424         int res = 0;
 425
 426         assert(is_Block(bl) && "can only check for liveness in a block");
 427
 428         if (!is_liveness_node(var))
 429                 return 0;
 430
 431         def_bl = get_nodes_block(var);
 432         if (!block_dominates(def_bl, bl)) {
 433                 goto end;
 434         }
 435
 436         else {
 437                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 438                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 439                 int min_dom    = get_Block_dom_tree_pre_num(def_bl) + 1;
 440                 int max_dom    = get_Block_dom_max_subtree_pre_num(def_bl);
 441                 bl_info_t *bli = get_block_info(lv, bl);
 442                 int i;
 443
 444                 DBG((lv->dbg, LEVEL_2, "lv end check of %+F, def=%+F,%d != q=%+F,%d\n",
 445                                         var, def_bl, min_dom - 1, bl, bli->id));
 446
 447                 foreach_out_edge (var, edge) {
 448                         ir_node *user = get_edge_src_irn(edge);
 449                         ir_node *use_bl;
 450                         bl_info_t *bi;
 451
 452                         if (!is_liveness_node(user))
 453                                 continue;
 454
 455                         stat_ev_cnt_inc(uses);
 456                         use_bl = get_nodes_block(user);
 457                         if (is_Phi(user)) {
 458                                 int pos = get_edge_src_pos(edge);
 459                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 460
 461                                 if (bl == use_bl)
 462                                         res |= lv_chk_state_end;
 463                         }
 464
 465                         bi = get_block_info(lv, use_bl);
 466                         if (use_bl != bl || bitset_is_set(lv->back_edge_tgt, bi->id))
 467                                 bitset_set(uses, bi->id);
 468                 }
 469
 470                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 471
 472                 bitset_copy(tmp, bli->be_tgt_reach);
 473                 bitset_set(tmp, bli->id);
 474
 475                 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach + current: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 476                 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 477                         bl_info_t *ti = lv->map[i];
 478                         DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 479                         if (bitset_intersect(ti->red_reachable, uses)) {
 480                                 res = lv_chk_state_out | lv_chk_state_end;
 481                                 goto end;
 482                         }
 483
 484                         bitset_andnot(tmp, ti->red_reachable);
 485                 }
 486         }
 487
 488 end:
 489         return res;
 490 }
 491
 492 /**
 493  * Check a nodes liveness situation of a block.
 494  * This routine considers both cases, the live in and end/out case.
 495  *
 496  * @param lv   The liveness check environment.
 497  * @param bl   The block under investigation.
 498  * @param var  The node to check for.
 499  * @return     A bitmask of lv_chk_state_XXX fields.
 500  */
 501 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 502 {
 503         stat_ev_cnt_decl(uses);
 504         stat_ev_cnt_decl(iter);
 505
 506         int res  = 0;
 507         ir_node *def_bl;
 508
 509         assert(is_Block(bl) && "can only check for liveness in a block");
 510
 511         /* If the variable ist no liveness related var, bail out. */
 512         if (!is_liveness_node(var))
 513                 return 0;
 514
 515         stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
 516         stat_ev_tim_push();
 517
 518         /* If there is no dominance relation, go out, too */
 519         def_bl = get_nodes_block(var);
 520         if (!block_dominates(def_bl, bl)) {
 521                 stat_ev("lv_chk_no_dom");
 522                 goto end;
 523         }
 524
 525         /*
 526          * If the block in question is the same as the definition block,
 527          * the algorithm is simple. Just check for uses not inside this block.
 528          */
 529         if (def_bl == bl) {
 530                 const ir_edge_t *edge;
 531
 532                 stat_ev("lv_chk_def_block");
 533                 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
 534                 foreach_out_edge (var, edge) {
 535                         ir_node *use    = get_edge_src_irn(edge);
 536                         ir_node *use_bl;
 537
 538                         if (!is_liveness_node(use))
 539                                 continue;
 540
 541                         stat_ev_cnt_inc(uses);
 542                         use_bl = get_nodes_block(use);
 543                         if (is_Phi(use)) {
 544                                 int pos = get_edge_src_pos(edge);
 545                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 546
 547                                 if (use_bl == bl) {
 548                                         DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
 549                                         res |= lv_chk_state_end;
 550                                 }
 551                         }
 552
 553                         if (use_bl != def_bl) {
 554                                 res = lv_chk_state_end | lv_chk_state_out;
 555                                 goto end;
 556                         }
 557                 }
 558
 559                 goto end;
 560         }
 561
 562         /*
 563          * this is the more complicated case.
 564          * We try to gather as much information as possible during looking
 565          * at the uses.
 566          *
 567          * Note that we know for shure that bl != def_bl. That is sometimes
 568          * silently exploited below.
 569          */
 570         else {
 571                 bl_info_t *def = get_block_info(lv, def_bl);
 572                 bl_info_t *bli = get_block_info(lv, bl);
 573                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 574                 bitset_t *Tq;
 575
 576                 unsigned i, min_dom, max_dom;
 577                 const ir_edge_t *edge;
 578
 579                 /* if the block has no DFS info, it cannot be reached.
 580                  * This can happen in functions with endless loops.
 581                  * we then go out, since nothing is live there.
 582                  *
 583                  * TODO: Is that right?
 584                  */
 585                 if (!bli)
 586                         goto end;
 587
 588                 (void) def;
 589                 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
 590                                         var, def_bl, def->id, bl, bli->id));
 591
 592                 foreach_out_edge (var, edge) {
 593                         ir_node *user = get_edge_src_irn(edge);
 594                         int mask      = lv_chk_state_in;
 595
 596                         ir_node *use_bl;
 597                         bl_info_t *bi;
 598
 599                         /* if the user is no liveness node, the use does not count */
 600                         if (!is_liveness_node(user))
 601                                 continue;
 602
 603                         stat_ev_cnt_inc(uses);
 604
 605                         /* if the user is a phi, the use is in the predecessor
 606                          * furthermore, prepare a mask so that in the case where
 607                          * bl (the block in question) coincides with a use, it
 608                          * can be marked live_end there. */
 609                         use_bl = get_nodes_block(user);
 610                         if (is_Phi(user)) {
 611                                 int pos = get_edge_src_pos(edge);
 612                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 613                                 mask   |= lv_chk_state_end;
 614                         }
 615
 616
 617                         /* if the use block coincides with the query block, we
 618                          * already gather a little liveness information.
 619                          * The variable is surely live there, since bl != def_bl
 620                          * (that case is treated above). */
 621                         if (use_bl == bl)
 622                                 res |= mask;
 623
 624                         bi = get_block_info(lv, use_bl);
 625
 626                         if (bi)
 627                                 bitset_set(uses, bi->id);
 628                 }
 629
 630                 /* get the dominance range which really matters. all uses outside
 631                  * the definition's dominance range are not to consider. note,
 632                  * that the definition itself is also not considered. The case
 633                  * where bl == def_bl is considered above. */
 634                 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
 635                 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
 636
 637                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 638
 639                 /* prepare a set with all reachable back edge targets.
 640                  * this will determine our "looking points" from where
 641                  * we will search/find the calculated uses. */
 642                 Tq = bli->be_tgt_reach;
 643
 644                 /* now, visit all viewing points in the temporary bitset lying
 645                  * in the dominance range of the variable. Note that for reducible
 646                  * flow-graphs the first iteration is sufficient and the loop
 647                  * will be left. */
 648                 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
 649                 i = bitset_next_set(Tq, min_dom);
 650                 while(i <= max_dom) {
 651                         bl_info_t *ti = lv->map[i];
 652                         int use_in_current_block = bitset_is_set(uses, ti->id);
 653
 654                         stat_ev_cnt_inc(iter);
 655
 656                         /*
 657                          * This is somehat tricky. Since this routine handles both, live in
 658                          * and end/out we have to handle all the border cases correctly.
 659                          * Each node is in its own red_reachable set (see calculation
 660                          * function above). That means, that in the case where bl == t, the
 661                          * intersection check of uses and rechability below will always
 662                          * find an intersection, namely t.
 663                          *
 664                          * However, if a block contains a use and the variable is dead
 665                          * afterwards, it is not live end/out at that block. Besides
 666                          * back-edge target. If a var is live-in at a back-edge target it
 667                          * is also live out/end there since the variable is live in the
 668                          * underlying loop. So in the case where t == bl and that is not
 669                          * a back-edge target, we have to remove that use from consideration
 670                          * to determine if the var is live out/end there.
 671                          *
 672                          * Note that the live in information has been calculated by the
 673                          * uses iteration above.
 674                          */
 675                         if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
 676                                 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
 677                                 bitset_clear(uses, ti->id);
 678                         }
 679
 680                         /* If we can reach a use, the variable is live there and we say goodbye */
 681                         DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 682                         if (bitset_intersect(ti->red_reachable, uses)) {
 683                                 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
 684                                 goto end;
 685                         }
 686
 687                         /*
 688                          * if we deleted a use do to the commentary above, we have to
 689                          * re-add it since it might be visible from further view points
 690                          * (we only need that in the non-reducible case).
 691                          */
 692                         if (use_in_current_block)
 693                                 bitset_set(uses, ti->id);
 694
 695                         i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
 696                 }
 697
 698         }
 699
 700 end:
 701         stat_ev_tim_pop("lv_chk_query_time");
 702         stat_ev_cnt_done(uses, "lv_chk_uses");
 703         stat_ev_cnt_done(iter, "lv_chk_iter");
 704         stat_ev_ctx_pop("lv_chk");
 705
 706         return res;
 707 }