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         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         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, 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                 return 0;
 116         default:;
 117         }
 118
 119         return 1;
 120 }
 121
 122 /**
 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.
 130  */
 131 static void red_trans_closure(lv_chk_t *lv)
 132 {
 133         int i, n;
 134
 135         for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
 136                 ir_node *bl   = dfs_get_post_num_node(lv->dfs, i);
 137                 bl_info_t *bi = get_block_info(lv, bl);
 138
 139                 const ir_edge_t *edge;
 140
 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);
 146
 147                         /*
 148                          * if the successor is no back edge, include all reachable
 149                          * blocks from there into the reachable set of the current node
 150                          */
 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);
 154                         }
 155
 156                         /* mark the block as a back edge src and succ as back edge tgt. */
 157                         else {
 158                                 bitset_set(lv->back_edge_src, bi->id);
 159                                 bitset_set(lv->back_edge_tgt, si->id);
 160                         }
 161                 }
 162
 163         }
 164
 165 }
 166
 167 static void compute_back_edge_chain(lv_chk_t *lv, ir_node *bl)
 168 {
 169         bitset_t *tmp = bitset_alloca(lv->n_blocks);
 170         bl_info_t *bi = get_block_info(lv, bl);
 171
 172         bitset_pos_t elm;
 173
 174         DBG((lv->dbg, LEVEL_2, "computing T_%d\n", bi->id));
 175
 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);
 180         bi->be_tgt_calc = 1;
 181
 182         DBG((lv->dbg, LEVEL_2, "\treachable be src: %B\n", tmp));
 183
 184         /* iterate over them ... */
 185         bitset_foreach(tmp, elm) {
 186                 bl_info_t *si = lv->map[elm];
 187                 const ir_edge_t *edge;
 188
 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);
 194
 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);
 200                         }
 201                 }
 202                 bitset_clear(bi->be_tgt_reach, bi->id);
 203         }
 204 }
 205
 206
 207 static INLINE void compute_back_edge_chains(lv_chk_t *lv)
 208 {
 209         bitset_pos_t elm;
 210         int i, n;
 211
 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);
 215         }
 216
 217         for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
 218                 ir_node *bl   = dfs_get_post_num_node(lv->dfs, i);
 219                 bl_info_t *bi = get_block_info(lv, bl);
 220
 221                 const ir_edge_t *edge;
 222
 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);
 228
 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);
 232                                 }
 233                         }
 234                 }
 235         }
 236 }
 237
 238 lv_chk_t *lv_chk_new(ir_graph *irg)
 239 {
 240         lv_chk_t *res = xmalloc(sizeof(res[0]));
 241         struct obstack *obst;
 242         int i;
 243
 244         phase_init(&res->ph, "liveness check", irg, PHASE_DEFAULT_GROWTH, init_block_data, NULL);
 245         obst = phase_obst(&res->ph);
 246
 247         FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
 248
 249         res->dfs           = dfs_new(&absgraph_irg_cfg_succ, irg);
 250         res->n_blocks      = dfs_get_n_nodes(res->dfs);
 251         res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
 252         res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
 253         res->map           = obstack_alloc(obst, res->n_blocks * sizeof(res->map[0]));
 254
 255 #if 0
 256         {
 257                 char name[256];
 258                 FILE *f;
 259                 ir_snprintf(name, sizeof(name), "dfs_%F.dot", irg);
 260                 if ((f = fopen(name, "wt")) != NULL) {
 261                         dfs_dump(res->dfs, f);
 262                         fclose(f);
 263                 }
 264                 dump_ir_block_graph(irg, "-lvchk");
 265         }
 266 #endif
 267
 268         /* fill the map which maps pre_num to block infos */
 269         for (i = res->n_blocks - 1; i >= 0; --i) {
 270                 ir_node *irn     = dfs_get_pre_num_node(res->dfs, i);
 271                 bl_info_t *bi    = phase_get_or_set_irn_data(&res->ph, irn);
 272                 res->map[bi->id] = bi;
 273         }
 274
 275         /* first of all, compute the transitive closure of the CFG *without* back edges */
 276         red_trans_closure(res);
 277
 278         /* compute back edge chains */
 279         compute_back_edge_chains(res);
 280
 281
 282 DEBUG_ONLY({
 283                 DBG((res->dbg, LEVEL_1, "liveness chk in %+F\n", irg));
 284                 for (i = res->n_blocks - 1; i >= 0; --i) {
 285                         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));
 290                 }
 291         })
 292
 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));
 295
 296         return res;
 297 }
 298
 299 void lv_chk_free(lv_chk_t *lv)
 300 {
 301         obstack_free(phase_obst(&lv->ph), NULL);
 302         dfs_free(lv->dfs);
 303         xfree(lv);
 304 }
 305
 306 /**
 307  * Check if a node is live at the end of a block.
 308  * This function is for internal use as its code is shared between
 309  * the in/end routines below. It is almost the "live_end" routine
 310  * but passing in the bitset for recording the blocks where the variable
 311  * is used saves some effort in the "live_in" routine. See below for
 312  * details.
 313  *
 314  * @param lv    The liveness check environment.
 315  * @param what  The node to check for.
 316  * @param bl    The block under investigation.
 317  * @param uses  A bitset where this routine records all ids of blocks
 318  *              where this variable is used. Note that the bitset
 319  *              is only guaranteed to be filled if the node was not
 320  *              live at the end of the block.
 321  * @return      1, if @p what is live at the end at @p bl.
 322  */
 323 unsigned lv_chk_bl_in_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 324 {
 325         stat_ev_cnt_decl(uses);
 326         stat_ev_cnt_decl(iter);
 327
 328         ir_node *def_bl;
 329         const ir_edge_t *edge;
 330
 331         int res = 0;
 332
 333         assert(is_Block(bl) && "can only check for liveness in a block");
 334
 335         if (!is_liveness_node(var))
 336                 return 0;
 337
 338         def_bl = get_nodes_block(var);
 339         if (def_bl == bl || !block_dominates(def_bl, bl)) {
 340                 goto end;
 341         }
 342
 343         else {
 344                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 345                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 346                 int min_dom    = get_Block_dom_tree_pre_num(def_bl) + 1;
 347                 int max_dom    = get_Block_dom_max_subtree_pre_num(def_bl);
 348                 bl_info_t *bli = get_block_info(lv, bl);
 349                 int i;
 350
 351                 DBG((lv->dbg, LEVEL_2, "lv check of %+F, def=%+F,%d != q=%+F,%d\n",
 352                                         var, def_bl, min_dom - 1, bl, bli->id));
 353
 354                 foreach_out_edge (var, edge) {
 355                         ir_node *user = get_edge_src_irn(edge);
 356                         ir_node *use_bl;
 357                         bl_info_t *bi;
 358
 359                         if (!is_liveness_node(user))
 360                                 continue;
 361
 362                         stat_ev_cnt_inc(uses);
 363                         use_bl = get_nodes_block(user);
 364                         if (is_Phi(user)) {
 365                                 int pos = get_edge_src_pos(edge);
 366                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 367                         }
 368
 369                         if (use_bl == bl) {
 370                                 res = lv_chk_state_in;
 371                                 DBG((lv->dbg, LEVEL_2, "\tuse directly in block %+F by %+F\n", use_bl, user));
 372                                 goto end;
 373                         }
 374
 375                         bi = get_block_info(lv, use_bl);
 376                         bitset_set(uses, bi->id);
 377                 }
 378
 379                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 380
 381                 {
 382
 383                         bitset_copy(tmp, bli->be_tgt_reach);
 384                         bitset_set(tmp, bli->id);
 385
 386                         DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 387                         for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 388                                 bl_info_t *ti = lv->map[i];
 389                                 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 390                                 if (bitset_intersect(ti->red_reachable, uses)) {
 391                                         res = lv_chk_state_in;
 392                                         goto end;
 393                                 }
 394
 395                                 bitset_andnot(tmp, ti->red_reachable);
 396                         }
 397                 }
 398         }
 399
 400 end:
 401         return res;
 402 }
 403
 404 unsigned lv_chk_bl_end_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 405 {
 406         stat_ev_cnt_decl(uses);
 407         stat_ev_cnt_decl(iter);
 408
 409         ir_node *def_bl;
 410         const ir_edge_t *edge;
 411
 412         int res = 0;
 413
 414         assert(is_Block(bl) && "can only check for liveness in a block");
 415
 416         if (!is_liveness_node(var))
 417                 return 0;
 418
 419         def_bl = get_nodes_block(var);
 420         if (!block_dominates(def_bl, bl)) {
 421                 goto end;
 422         }
 423
 424         else {
 425                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 426                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 427                 int min_dom    = get_Block_dom_tree_pre_num(def_bl) + 1;
 428                 int max_dom    = get_Block_dom_max_subtree_pre_num(def_bl);
 429                 bl_info_t *bli = get_block_info(lv, bl);
 430                 int i;
 431
 432                 DBG((lv->dbg, LEVEL_2, "lv end check of %+F, def=%+F,%d != q=%+F,%d\n",
 433                                         var, def_bl, min_dom - 1, bl, bli->id));
 434
 435                 foreach_out_edge (var, edge) {
 436                         ir_node *user = get_edge_src_irn(edge);
 437                         ir_node *use_bl;
 438                         bl_info_t *bi;
 439
 440                         if (!is_liveness_node(user))
 441                                 continue;
 442
 443                         stat_ev_cnt_inc(uses);
 444                         use_bl = get_nodes_block(user);
 445                         if (is_Phi(user)) {
 446                                 int pos = get_edge_src_pos(edge);
 447                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 448
 449                                 if (bl == use_bl)
 450                                         res |= lv_chk_state_end;
 451                         }
 452
 453                         bi = get_block_info(lv, use_bl);
 454                         if (use_bl != bl || bitset_is_set(lv->back_edge_tgt, bi->id))
 455                                 bitset_set(uses, bi->id);
 456                 }
 457
 458                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 459
 460                 bitset_copy(tmp, bli->be_tgt_reach);
 461                 bitset_set(tmp, bli->id);
 462
 463                 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach + current: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 464                 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 465                         bl_info_t *ti = lv->map[i];
 466                         DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 467                         if (bitset_intersect(ti->red_reachable, uses)) {
 468                                 res = lv_chk_state_out | lv_chk_state_end;
 469                                 goto end;
 470                         }
 471
 472                         bitset_andnot(tmp, ti->red_reachable);
 473                 }
 474         }
 475
 476 end:
 477         return res;
 478 }
 479
 480 /**
 481  * Check a nodes liveness situation of a block.
 482  * This routine considers both cases, the live in and end/out case.
 483  *
 484  * @param lv   The liveness check environment.
 485  * @param bl   The block under investigation.
 486  * @param var  The node to check for.
 487  * @return     A bitmask of lv_chk_state_XXX fields.
 488  */
 489 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 490 {
 491         stat_ev_cnt_decl(uses);
 492         stat_ev_cnt_decl(iter);
 493
 494         int res  = 0;
 495         ir_node *def_bl;
 496
 497         assert(is_Block(bl) && "can only check for liveness in a block");
 498
 499         /* If the variable ist no liveness related var, bail out. */
 500         if (!is_liveness_node(var))
 501                 return 0;
 502
 503         stat_ev_ctx_push_fobj("node", var);
 504         stat_ev("lv_chk");
 505
 506         /* If there is no dominance relation, go out, too */
 507         def_bl = get_nodes_block(var);
 508         if (!block_dominates(def_bl, bl)) {
 509                 stat_ev("lv_chk_no_dom");
 510                 goto end;
 511         }
 512
 513         /*
 514          * If the block in question is the same as the definition block,
 515          * the algorithm is simple. Just check for uses not inside this block.
 516          */
 517         if (def_bl == bl) {
 518                 const ir_edge_t *edge;
 519
 520                 stat_ev("lv_chk_def_block");
 521                 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
 522                 foreach_out_edge (var, edge) {
 523                         ir_node *use    = get_edge_src_irn(edge);
 524                         ir_node *use_bl;
 525
 526                         if (!is_liveness_node(use))
 527                                 continue;
 528
 529                         stat_ev_cnt_inc(uses);
 530                         use_bl = get_nodes_block(use);
 531                         if (is_Phi(use)) {
 532                                 int pos = get_edge_src_pos(edge);
 533                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 534
 535                                 if (use_bl == bl) {
 536                                         DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
 537                                         res |= lv_chk_state_end;
 538                                 }
 539                         }
 540
 541                         if (use_bl != def_bl) {
 542                                 res = lv_chk_state_end | lv_chk_state_out;
 543                                 goto end;
 544                         }
 545                 }
 546
 547                 goto end;
 548         }
 549
 550         /*
 551          * this is the more complicated case.
 552          * We try to gather as much information as possible during looking
 553          * at the uses.
 554          *
 555          * Note that we know for shure that bl != def_bl. That is sometimes
 556          * silently exploited below.
 557          */
 558         else {
 559                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 560                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 561                 bl_info_t *def = get_block_info(lv, def_bl);
 562                 bl_info_t *bli = get_block_info(lv, bl);
 563
 564                 int i, min_dom, max_dom;
 565                 const ir_edge_t *edge;
 566
 567                 /* if the block has no DFS info, it cannot be reached.
 568                  * This can happen in functions with endless loops.
 569                  * we then go out, since nothing is live there.
 570                  *
 571                  * TODO: Is that right?
 572                  */
 573                 if (!bli)
 574                         goto end;
 575
 576                 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
 577                                         var, def_bl, def->id, bl, bli->id));
 578
 579                 foreach_out_edge (var, edge) {
 580                         ir_node *user = get_edge_src_irn(edge);
 581                         int mask      = lv_chk_state_in;
 582
 583                         ir_node *use_bl;
 584                         bl_info_t *bi;
 585
 586                         /* if the user is no liveness node, the use does not count */
 587                         if (!is_liveness_node(user))
 588                                 continue;
 589
 590                         stat_ev_cnt_inc(uses);
 591
 592                         /* if the user is a phi, the use is in the predecessor
 593                          * furthermore, prepare a mask so that in the case where
 594                          * bl (the block in question) coincides with a use, it
 595                          * can be marked live_end there. */
 596                         use_bl = get_nodes_block(user);
 597                         if (is_Phi(user)) {
 598                                 int pos = get_edge_src_pos(edge);
 599                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 600                                 mask   |= lv_chk_state_end;
 601                         }
 602
 603
 604                         /* if the use block coincides with the query block, we
 605                          * already gather a little liveness information.
 606                          * The variable is surely live there, since bl != def_bl
 607                          * (that case is treated above). */
 608                         if (use_bl == bl)
 609                                 res |= mask;
 610
 611                         bi = get_block_info(lv, use_bl);
 612                         bitset_set(uses, bi->id);
 613
 614                 }
 615
 616                 /* get the dominance range which really matters. all uses outside
 617                  * the definition's dominance range are not to consider. note,
 618                  * that the definition itself is also not considered. The case
 619                  * where bl == def_bl is considered above. */
 620                 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
 621                 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
 622
 623                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 624
 625                 /* prepare a set with all reachable back edge targets.
 626                  * this will determine our "looking points" from where
 627                  * we will search/find the calculated uses.
 628                  *
 629                  * Since there might be no reachable back edge targets
 630                  * we add the current block also since reachability of
 631                  * uses are then checked from there. */
 632                 bitset_copy(tmp, bli->be_tgt_reach);
 633                 bitset_set (tmp, bli->id);
 634
 635                 /* now, visit all viewing points in the temporary bitset lying
 636                  * in the dominance range of the variable. Note that for reducible
 637                  * flow-graphs the first iteration is sufficient and the loop
 638                  * will be left. */
 639                 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 640                 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 641                         bl_info_t *ti = lv->map[i];
 642                         int use_in_current_block = bitset_is_set(uses, ti->id);
 643
 644                         /*
 645                          * This is somehat tricky. Since this routine handles both, live in
 646                          * and end/out we have to handle all the border cases correctly.
 647                          * Each node is in its own red_reachable set (see calculation
 648                          * function above). That means, that in the case where bl == t, the
 649                          * intersection check of uses and rechability below will always
 650                          * find an intersection, namely t.
 651                          *
 652                          * However, if a block contains a use and the variable is dead
 653                          * afterwards, it is not live end/out at that block. Besides
 654                          * back-edge target. If a var is live-in at a back-edge target it
 655                          * is also live out/end there since the variable is live in the
 656                          * underlying loop. So in the case where t == bl and that is not
 657                          * a back-edge target, we have to remove that use from consideration
 658                          * to determine if the var is live out/end there.
 659                          *
 660                          * Note that the live in information has been calculated by the
 661                          * uses iteration above.
 662                          */
 663                         if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
 664                                 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
 665                                 bitset_clear(uses, ti->id);
 666                         }
 667
 668                         /* If we can reach a use, the variable is live there and we say goodbye */
 669                         DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 670                         if (bitset_intersect(ti->red_reachable, uses)) {
 671                                 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
 672                                 goto end;
 673                         }
 674
 675                         bitset_andnot(tmp, ti->red_reachable);
 676
 677                         /*
 678                          * if we deleted a use do to the commentary above, we have to
 679                          * re-add it since it might be visible from further view points
 680                          * (we only need that in the non-reducible case).
 681                          */
 682                         if (use_in_current_block)
 683                                 bitset_set(uses, ti->id);
 684                 }
 685
 686         }
 687
 688 end:
 689         stat_ev_cnt_done(uses, "lv_chk_uses");
 690         stat_ev_cnt_done(iter, "lv_chk_iter");
 691         stat_ev_ctx_pop();
 692
 693         return res;
 694 }