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