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  * @brief
  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                 break;
 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                 const 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, const 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         unsigned 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         unsigned 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                 const 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         for (i = 0, n = dfs_get_n_nodes(lv->dfs); i < n; ++i) {
 238                 const ir_node *bl = dfs_get_post_num_node(lv->dfs, i);
 239                 bl_info_t *bi     = get_block_info(lv, bl);
 240                 bitset_set(bi->be_tgt_reach, bi->id);
 241         }
 242 }
 243
 244 lv_chk_t *lv_chk_new(ir_graph *irg, const dfs_t *dfs)
 245 {
 246         lv_chk_t *res = XMALLOC(lv_chk_t);
 247         struct obstack *obst;
 248         int i;
 249
 250         edges_deactivate(irg);
 251         edges_activate(irg);
 252         compute_doms(irg);
 253
 254         stat_ev_tim_push();
 255         phase_init(&res->ph, irg, init_block_data);
 256         obst = phase_obst(&res->ph);
 257
 258         FIRM_DBG_REGISTER(res->dbg, "ir.ana.lvchk");
 259
 260         res->dfs           = dfs;
 261         res->n_blocks      = dfs_get_n_nodes(res->dfs);
 262         res->back_edge_src = bitset_obstack_alloc(obst, res->n_blocks);
 263         res->back_edge_tgt = bitset_obstack_alloc(obst, res->n_blocks);
 264         res->map           = OALLOCNZ(obst, bl_info_t*, res->n_blocks);
 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_deinit(&lv->ph);
 315         xfree(lv);
 316 }
 317
 318 #if 0
 319 /**
 320  * Check if a node is live at the end of a block.
 321  * This function is for internal use as its code is shared between
 322  * the in/end routines below. It is almost the "live_end" routine
 323  * but passing in the bitset for recording the blocks where the variable
 324  * is used saves some effort in the "live_in" routine. See below for
 325  * details.
 326  *
 327  * @param lv    The liveness check environment.
 328  * @param what  The node to check for.
 329  * @param bl    The block under investigation.
 330  * @param uses  A bitset where this routine records all ids of blocks
 331  *              where this variable is used. Note that the bitset
 332  *              is only guaranteed to be filled if the node was not
 333  *              live at the end of the block.
 334  * @return      1, if @p what is live at the end at @p bl.
 335  */
 336 unsigned lv_chk_bl_in_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 337 {
 338         ir_node *def_bl;
 339         const ir_edge_t *edge;
 340
 341         stat_ev_cnt_decl(uses);
 342
 343         int res = 0;
 344
 345         assert(is_Block(bl) && "can only check for liveness in a block");
 346
 347         if (!is_liveness_node(var))
 348                 return 0;
 349
 350         def_bl = get_nodes_block(var);
 351         if (def_bl == bl || !block_dominates(def_bl, bl)) {
 352                 goto end;
 353         }
 354
 355         else {
 356                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 357                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 358                 int min_dom    = get_Block_dom_tree_pre_num(def_bl) + 1;
 359                 int max_dom    = get_Block_dom_max_subtree_pre_num(def_bl);
 360                 bl_info_t *bli = get_block_info(lv, bl);
 361                 int i;
 362
 363                 DBG((lv->dbg, LEVEL_2, "lv check of %+F, def=%+F,%d != q=%+F,%d\n",
 364                                         var, def_bl, min_dom - 1, bl, bli->id));
 365
 366                 foreach_out_edge (var, edge) {
 367                         ir_node *user = get_edge_src_irn(edge);
 368                         ir_node *use_bl;
 369                         bl_info_t *bi;
 370
 371                         if (!is_liveness_node(user))
 372                                 continue;
 373
 374                         stat_ev_cnt_inc(uses);
 375                         use_bl = get_nodes_block(user);
 376                         if (is_Phi(user)) {
 377                                 int pos = get_edge_src_pos(edge);
 378                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 379                         }
 380
 381                         if (use_bl == bl) {
 382                                 res = lv_chk_state_in;
 383                                 DBG((lv->dbg, LEVEL_2, "\tuse directly in block %+F by %+F\n", use_bl, user));
 384                                 goto end;
 385                         }
 386
 387                         bi = get_block_info(lv, use_bl);
 388                         bitset_set(uses, bi->id);
 389                 }
 390
 391                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 392
 393                 {
 394
 395                         bitset_copy(tmp, bli->be_tgt_reach);
 396                         bitset_set(tmp, bli->id);
 397
 398                         DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 399                         for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 400                                 bl_info_t *ti = lv->map[i];
 401                                 DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 402                                 if (bitset_intersect(ti->red_reachable, uses)) {
 403                                         res = lv_chk_state_in;
 404                                         goto end;
 405                                 }
 406
 407                                 bitset_andnot(tmp, ti->red_reachable);
 408                         }
 409                 }
 410         }
 411
 412 end:
 413         return res;
 414 }
 415
 416 unsigned lv_chk_bl_end_mask(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 417 {
 418         ir_node *def_bl;
 419         const ir_edge_t *edge;
 420
 421         stat_ev_cnt_decl(uses);
 422
 423         int res = 0;
 424
 425         assert(is_Block(bl) && "can only check for liveness in a block");
 426
 427         if (!is_liveness_node(var))
 428                 return 0;
 429
 430         def_bl = get_nodes_block(var);
 431         if (!block_dominates(def_bl, bl)) {
 432                 goto end;
 433         } else {
 434                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 435                 bitset_t *tmp  = bitset_alloca(lv->n_blocks);
 436                 int min_dom    = get_Block_dom_tree_pre_num(def_bl) + 1;
 437                 int max_dom    = get_Block_dom_max_subtree_pre_num(def_bl);
 438                 bl_info_t *bli = get_block_info(lv, bl);
 439                 int i;
 440
 441                 DBG((lv->dbg, LEVEL_2, "lv end check of %+F, def=%+F,%d != q=%+F,%d\n",
 442                                         var, def_bl, min_dom - 1, bl, bli->id));
 443
 444                 foreach_out_edge (var, edge) {
 445                         ir_node *user = get_edge_src_irn(edge);
 446                         ir_node *use_bl;
 447                         bl_info_t *bi;
 448
 449                         if (!is_liveness_node(user))
 450                                 continue;
 451
 452                         stat_ev_cnt_inc(uses);
 453                         use_bl = get_nodes_block(user);
 454                         if (is_Phi(user)) {
 455                                 int pos = get_edge_src_pos(edge);
 456                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 457
 458                                 if (bl == use_bl)
 459                                         res |= lv_chk_state_end;
 460                         }
 461
 462                         bi = get_block_info(lv, use_bl);
 463                         if (use_bl != bl || bitset_is_set(lv->back_edge_tgt, bi->id))
 464                                 bitset_set(uses, bi->id);
 465                 }
 466
 467                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 468
 469                 bitset_copy(tmp, bli->be_tgt_reach);
 470                 bitset_set(tmp, bli->id);
 471
 472                 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach + current: %B, dom span: [%d, %d]\n", tmp, min_dom, max_dom));
 473                 for (i = bitset_next_set(tmp, min_dom); i >= 0 && i <= max_dom; i = bitset_next_set(tmp, i + 1)) {
 474                         bl_info_t *ti = lv->map[i];
 475                         DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 476                         if (bitset_intersect(ti->red_reachable, uses)) {
 477                                 res = lv_chk_state_out | lv_chk_state_end;
 478                                 goto end;
 479                         }
 480
 481                         bitset_andnot(tmp, ti->red_reachable);
 482                 }
 483         }
 484
 485 end:
 486         return res;
 487 }
 488 #endif
 489
 490 /**
 491  * Check a nodes liveness situation of a block.
 492  * This routine considers both cases, the live in and end/out case.
 493  *
 494  * @param lv   The liveness check environment.
 495  * @param bl   The block under investigation.
 496  * @param var  The node to check for.
 497  * @return     A bitmask of lv_chk_state_XXX fields.
 498  */
 499 unsigned lv_chk_bl_xxx(const lv_chk_t *lv, const ir_node *bl, const ir_node *var)
 500 {
 501         int res  = 0;
 502         ir_node *def_bl;
 503         stat_ev_cnt_decl(uses);
 504         stat_ev_cnt_decl(iter);
 505
 506         assert(is_Block(bl) && "can only check for liveness in a block");
 507
 508         /* If the variable ist no liveness related var, bail out. */
 509         if (!is_liveness_node(var))
 510                 return 0;
 511
 512         stat_ev_ctx_push_fmt("lv_chk", "%u", get_irn_idx(var));
 513         stat_ev_tim_push();
 514
 515         /* If there is no dominance relation, go out, too */
 516         def_bl = get_nodes_block(var);
 517         if (!block_dominates(def_bl, bl)) {
 518                 stat_ev("lv_chk_no_dom");
 519                 goto end;
 520         }
 521
 522         /*
 523          * If the block in question is the same as the definition block,
 524          * the algorithm is simple. Just check for uses not inside this block.
 525          */
 526         if (def_bl == bl) {
 527                 const ir_edge_t *edge;
 528
 529                 stat_ev("lv_chk_def_block");
 530                 DBG((lv->dbg, LEVEL_2, "lv check same block %+F in %+F\n", var, bl));
 531                 foreach_out_edge (var, edge) {
 532                         ir_node *use    = get_edge_src_irn(edge);
 533                         ir_node *use_bl;
 534
 535                         if (!is_liveness_node(use))
 536                                 continue;
 537
 538                         stat_ev_cnt_inc(uses);
 539                         use_bl = get_nodes_block(use);
 540                         if (is_Phi(use)) {
 541                                 int pos = get_edge_src_pos(edge);
 542                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 543
 544                                 if (use_bl == bl) {
 545                                         DBG((lv->dbg, LEVEL_2, "\tphi %+F in succ %+F,%d -> live end\n", use, use_bl, pos));
 546                                         res |= lv_chk_state_end;
 547                                 }
 548                         }
 549
 550                         if (use_bl != def_bl) {
 551                                 res = lv_chk_state_end | lv_chk_state_out;
 552                                 goto end;
 553                         }
 554                 }
 555
 556                 goto end;
 557         }
 558
 559         /*
 560          * this is the more complicated case.
 561          * We try to gather as much information as possible during looking
 562          * at the uses.
 563          *
 564          * Note that we know for sure that bl != def_bl. That is sometimes
 565          * silently exploited below.
 566          */
 567         else {
 568                 bl_info_t *def = get_block_info(lv, def_bl);
 569                 bl_info_t *bli = get_block_info(lv, bl);
 570                 bitset_t *uses = bitset_alloca(lv->n_blocks);
 571                 bitset_t *Tq;
 572
 573                 unsigned i, min_dom, max_dom;
 574                 const ir_edge_t *edge;
 575
 576                 /* if the block has no DFS info, it cannot be reached.
 577                  * This can happen in functions with endless loops.
 578                  * we then go out, since nothing is live there.
 579                  *
 580                  * TODO: Is that right?
 581                  */
 582                 if (!bli)
 583                         goto end;
 584
 585                 (void) def;
 586                 DBG((lv->dbg, LEVEL_2, "lv check %+F (def in %+F #%d) in different block %+F #%d\n",
 587                                         var, def_bl, def->id, bl, bli->id));
 588
 589                 foreach_out_edge (var, edge) {
 590                         ir_node *user = get_edge_src_irn(edge);
 591                         int mask      = lv_chk_state_in;
 592
 593                         ir_node *use_bl;
 594                         bl_info_t *bi;
 595
 596                         /* if the user is no liveness node, the use does not count */
 597                         if (!is_liveness_node(user))
 598                                 continue;
 599
 600                         stat_ev_cnt_inc(uses);
 601
 602                         /* if the user is a phi, the use is in the predecessor
 603                          * furthermore, prepare a mask so that in the case where
 604                          * bl (the block in question) coincides with a use, it
 605                          * can be marked live_end there. */
 606                         use_bl = get_nodes_block(user);
 607                         if (is_Phi(user)) {
 608                                 int pos = get_edge_src_pos(edge);
 609                                 use_bl  = get_Block_cfgpred_block(use_bl, pos);
 610                                 mask   |= lv_chk_state_end;
 611                         }
 612
 613
 614                         /* if the use block coincides with the query block, we
 615                          * already gather a little liveness information.
 616                          * The variable is surely live there, since bl != def_bl
 617                          * (that case is treated above). */
 618                         if (use_bl == bl)
 619                                 res |= mask;
 620
 621                         bi = get_block_info(lv, use_bl);
 622
 623                         if (bi)
 624                                 bitset_set(uses, bi->id);
 625                 }
 626
 627                 /* get the dominance range which really matters. all uses outside
 628                  * the definition's dominance range are not to consider. note,
 629                  * that the definition itself is also not considered. The case
 630                  * where bl == def_bl is considered above. */
 631                 min_dom = get_Block_dom_tree_pre_num(def_bl) + 1;
 632                 max_dom = get_Block_dom_max_subtree_pre_num(def_bl);
 633
 634                 DBG((lv->dbg, LEVEL_2, "\tuses: %B\n", uses));
 635
 636                 /* prepare a set with all reachable back edge targets.
 637                  * this will determine our "looking points" from where
 638                  * we will search/find the calculated uses. */
 639                 Tq = bli->be_tgt_reach;
 640
 641                 /* now, visit all viewing points in the temporary bitset lying
 642                  * in the dominance range of the variable. Note that for reducible
 643                  * flow-graphs the first iteration is sufficient and the loop
 644                  * will be left. */
 645                 DBG((lv->dbg, LEVEL_2, "\tbe tgt reach: %B, dom span: [%d, %d]\n", Tq, min_dom, max_dom));
 646                 i = bitset_next_set(Tq, min_dom);
 647                 while (i <= max_dom) {
 648                         bl_info_t *ti = lv->map[i];
 649                         int use_in_current_block = bitset_is_set(uses, ti->id);
 650
 651                         stat_ev_cnt_inc(iter);
 652
 653                         /*
 654                          * This is somewhat tricky. Since this routine handles both, live in
 655                          * and end/out we have to handle all the border cases correctly.
 656                          * Each node is in its own red_reachable set (see calculation
 657                          * function above). That means, that in the case where bl == t, the
 658                          * intersection check of uses and reachability below will always
 659                          * find an intersection, namely t.
 660                          *
 661                          * However, if a block contains a use and the variable is dead
 662                          * afterwards, it is not live end/out at that block. Besides
 663                          * back-edge target. If a var is live-in at a back-edge target it
 664                          * is also live out/end there since the variable is live in the
 665                          * underlying loop. So in the case where t == bl and that is not
 666                          * a back-edge target, we have to remove that use from consideration
 667                          * to determine if the var is live out/end there.
 668                          *
 669                          * Note that the live in information has been calculated by the
 670                          * uses iteration above.
 671                          */
 672                         if (ti == bli && !bitset_is_set(lv->back_edge_tgt, ti->id)) {
 673                                 DBG((lv->dbg, LEVEL_2, "\tlooking not from a back edge target and q == t. removing use: %d\n", ti->id));
 674                                 bitset_clear(uses, ti->id);
 675                         }
 676
 677                         /* If we can reach a use, the variable is live there and we say goodbye */
 678                         DBG((lv->dbg, LEVEL_2, "\tlooking from %d: seeing %B\n", ti->id, ti->red_reachable));
 679                         if (bitset_intersect(ti->red_reachable, uses)) {
 680                                 res |= lv_chk_state_in | lv_chk_state_out | lv_chk_state_end;
 681                                 goto end;
 682                         }
 683
 684                         /*
 685                          * if we deleted a use do to the commentary above, we have to
 686                          * re-add it since it might be visible from further view points
 687                          * (we only need that in the non-reducible case).
 688                          */
 689                         if (use_in_current_block)
 690                                 bitset_set(uses, ti->id);
 691
 692                         i = bitset_next_set(Tq, get_Block_dom_max_subtree_pre_num(ti->block) + 1);
 693                 }
 694
 695         }
 696
 697 end:
 698         stat_ev_tim_pop("lv_chk_query_time");
 699         stat_ev_cnt_done(uses, "lv_chk_uses");
 700         stat_ev_cnt_done(iter, "lv_chk_iter");
 701         stat_ev_ctx_pop("lv_chk");
 702
 703         return res;
 704 }