nsz Git - libfirm/blob - ir/opt/jumpthreading.c

   1 /*
   2  * Copyright (C) 1995-2008 University of Karlsruhe.  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
  22  * @brief   Path-Sensitive Jump Threading
  23  * @date    10. Sep. 2006
  24  * @author  Christoph Mallon, Matthias Braun
  25  * @version $Id$
  26  */
  27 #include "config.h"
  28
  29 #include "iroptimize.h"
  30
  31 #include <assert.h>
  32 #include "array_t.h"
  33 #include "debug.h"
  34 #include "ircons.h"
  35 #include "irgmod.h"
  36 #include "irgopt.h"
  37 #include "irgwalk.h"
  38 #include "irnode.h"
  39 #include "irnode_t.h"
  40 #include "iredges.h"
  41 #include "iredges_t.h"
  42 #include "irtools.h"
  43 #include "irgraph.h"
  44 #include "tv.h"
  45 #include "opt_confirms.h"
  46 #include "iropt_dbg.h"
  47 #include "irpass.h"
  48
  49 #undef AVOID_PHIB
  50
  51 DEBUG_ONLY(static firm_dbg_module_t *dbg);
  52
  53 /**
  54  * Add the new predecessor x to node node, which is either a Block or a Phi
  55  */
  56 static void add_pred(ir_node* node, ir_node* x)
  57 {
  58         ir_node** ins;
  59         int n;
  60         int i;
  61
  62         assert(is_Block(node) || is_Phi(node));
  63
  64         n = get_irn_arity(node);
  65         NEW_ARR_A(ir_node*, ins, n + 1);
  66         for (i = 0; i < n; i++)
  67                 ins[i] = get_irn_n(node, i);
  68         ins[n] = x;
  69         set_irn_in(node, n + 1, ins);
  70 }
  71
  72 static ir_node *ssa_second_def;
  73 static ir_node *ssa_second_def_block;
  74
  75 static ir_node *search_def_and_create_phis(ir_node *block, ir_mode *mode,
  76                                            int first)
  77 {
  78         int i;
  79         int n_cfgpreds;
  80         ir_graph *irg;
  81         ir_node *phi;
  82         ir_node **in;
  83
  84         /* This is needed because we create bads sometimes */
  85         if (is_Bad(block))
  86                 return new_Bad();
  87
  88         /* the other defs can't be marked for cases where a user of the original
  89          * value is in the same block as the alternative definition.
  90          * In this case we mustn't use the alternative definition.
  91          * So we keep a flag that indicated wether we walked at least 1 block
  92          * away and may use the alternative definition */
  93         if (block == ssa_second_def_block && !first) {
  94                 return ssa_second_def;
  95         }
  96
  97         /* already processed this block? */
  98         if (irn_visited(block)) {
  99                 ir_node *value = (ir_node*) get_irn_link(block);
 100                 return value;
 101         }
 102
 103         irg = get_irn_irg(block);
 104         assert(block != get_irg_start_block(irg));
 105
 106         /* a Block with only 1 predecessor needs no Phi */
 107         n_cfgpreds = get_Block_n_cfgpreds(block);
 108         if (n_cfgpreds == 1) {
 109                 ir_node *pred_block = get_Block_cfgpred_block(block, 0);
 110                 ir_node *value      = search_def_and_create_phis(pred_block, mode, 0);
 111
 112                 set_irn_link(block, value);
 113                 mark_irn_visited(block);
 114                 return value;
 115         }
 116
 117         /* create a new Phi */
 118         NEW_ARR_A(ir_node*, in, n_cfgpreds);
 119         for(i = 0; i < n_cfgpreds; ++i)
 120                 in[i] = new_Unknown(mode);
 121
 122         phi = new_r_Phi(block, n_cfgpreds, in, mode);
 123         set_irn_link(block, phi);
 124         mark_irn_visited(block);
 125
 126         /* set Phi predecessors */
 127         for(i = 0; i < n_cfgpreds; ++i) {
 128                 ir_node *pred_block = get_Block_cfgpred_block(block, i);
 129                 ir_node *pred_val   = search_def_and_create_phis(pred_block, mode, 0);
 130
 131                 set_irn_n(phi, i, pred_val);
 132         }
 133
 134         return phi;
 135 }
 136
 137 /**
 138  * Given a set of values this function constructs SSA-form for the users of the
 139  * first value (the users are determined through the out-edges of the value).
 140  * Uses the irn_visited flags. Works without using the dominance tree.
 141  */
 142 static void construct_ssa(ir_node *orig_block, ir_node *orig_val,
 143                           ir_node *second_block, ir_node *second_val)
 144 {
 145         ir_graph *irg;
 146         ir_mode *mode;
 147         const ir_edge_t *edge;
 148         const ir_edge_t *next;
 149
 150         /* no need to do anything */
 151         if (orig_val == second_val)
 152                 return;
 153
 154         irg = get_irn_irg(orig_val);
 155         inc_irg_visited(irg);
 156
 157         mode = get_irn_mode(orig_val);
 158         set_irn_link(orig_block, orig_val);
 159         mark_irn_visited(orig_block);
 160
 161         ssa_second_def_block = second_block;
 162         ssa_second_def       = second_val;
 163
 164         /* Only fix the users of the first, i.e. the original node */
 165         foreach_out_edge_safe(orig_val, edge, next) {
 166                 ir_node *user = get_edge_src_irn(edge);
 167                 int j = get_edge_src_pos(edge);
 168                 ir_node *user_block = get_nodes_block(user);
 169                 ir_node *newval;
 170
 171                 /* ignore keeps */
 172                 if (is_End(user))
 173                         continue;
 174
 175                 DB((dbg, LEVEL_3, ">>> Fixing user %+F (pred %d == %+F)\n", user, j, get_irn_n(user, j)));
 176
 177                 if (is_Phi(user)) {
 178                         ir_node *pred_block = get_Block_cfgpred_block(user_block, j);
 179                         newval = search_def_and_create_phis(pred_block, mode, 1);
 180                 } else {
 181                         newval = search_def_and_create_phis(user_block, mode, 1);
 182                 }
 183
 184                 /* don't fix newly created Phis from the SSA construction */
 185                 if (newval != user) {
 186                         DB((dbg, LEVEL_4, ">>>> Setting input %d of %+F to %+F\n", j, user, newval));
 187                         set_irn_n(user, j, newval);
 188                 }
 189         }
 190 }
 191
 192 static void split_critical_edge(ir_node *block, int pos) {
 193         ir_graph *irg = get_irn_irg(block);
 194         ir_node *in[1];
 195         ir_node *new_block;
 196         ir_node *new_jmp;
 197
 198         in[0] = get_Block_cfgpred(block, pos);
 199         new_block = new_r_Block(irg, 1, in);
 200         new_jmp = new_r_Jmp(new_block);
 201         set_Block_cfgpred(block, pos, new_jmp);
 202 }
 203
 204 typedef struct jumpthreading_env_t {
 205         ir_node       *true_block;
 206         ir_node       *cmp;        /**< The Compare node that might be partial evaluated */
 207         pn_Cmp         pnc;        /**< The Compare mode of the Compare node. */
 208         ir_node       *cnst;
 209         tarval        *tv;
 210         ir_visited_t   visited_nr;
 211
 212         ir_node       *cnst_pred;   /**< the block before the constant */
 213         int            cnst_pos;    /**< the pos to the constant block (needed to
 214                                           kill that edge later) */
 215 } jumpthreading_env_t;
 216
 217 static ir_node *copy_and_fix_node(const jumpthreading_env_t *env,
 218                                   ir_node *block, ir_node *copy_block, int j,
 219                                   ir_node *node)
 220 {
 221         int      i, arity;
 222         ir_node *copy;
 223
 224         /* we can evaluate Phis right now, all other nodes get copied */
 225         if (is_Phi(node)) {
 226                 copy = get_Phi_pred(node, j);
 227                 /* we might have to evaluate a Phi-cascade */
 228                 if (get_irn_visited(copy) >= env->visited_nr) {
 229                         copy = get_irn_link(copy);
 230                 }
 231         } else {
 232                 copy = exact_copy(node);
 233                 set_nodes_block(copy, copy_block);
 234
 235                 assert(get_irn_mode(copy) != mode_X);
 236
 237                 arity = get_irn_arity(copy);
 238                 for(i = 0; i < arity; ++i) {
 239                         ir_node *pred     = get_irn_n(copy, i);
 240                         ir_node *new_pred;
 241
 242                         if (get_nodes_block(pred) != block)
 243                                 continue;
 244
 245                         if (get_irn_visited(pred) >= env->visited_nr) {
 246                                 new_pred = get_irn_link(pred);
 247                         } else {
 248                                 new_pred = copy_and_fix_node(env, block, copy_block, j, pred);
 249                         }
 250                         DB((dbg, LEVEL_2, ">> Set Pred of %+F to %+F\n", copy, new_pred));
 251                         set_irn_n(copy, i, new_pred);
 252                 }
 253         }
 254
 255         set_irn_link(node, copy);
 256         set_irn_visited(node, env->visited_nr);
 257
 258         return copy;
 259 }
 260
 261 static void copy_and_fix(const jumpthreading_env_t *env, ir_node *block,
 262                          ir_node *copy_block, int j)
 263 {
 264         const ir_edge_t *edge;
 265
 266         /* Look at all nodes in the cond_block and copy them into pred */
 267         foreach_out_edge(block, edge) {
 268                 ir_node *node = get_edge_src_irn(edge);
 269                 ir_node *copy;
 270                 ir_mode *mode;
 271
 272                 if (is_Block(node)) {
 273                         /* Block->Block edge, should be the MacroBlock edge */
 274                         assert(get_Block_MacroBlock(node) == block && "Block->Block edge found");
 275                         continue;
 276                 }
 277
 278                 /* ignore control flow */
 279                 mode = get_irn_mode(node);
 280                 if (mode == mode_X || is_Cond(node))
 281                         continue;
 282 #ifdef AVOID_PHIB
 283                 /* we may not copy mode_b nodes, because this could produce Phi with
 284                  * mode_bs which can't be handled in all backends. Instead we duplicate
 285                  * the node and move it to its users */
 286                 if (mode == mode_b) {
 287                         const ir_edge_t *edge, *next;
 288                         ir_node *pred;
 289                         int      pn;
 290
 291                         assert(is_Proj(node));
 292
 293                         pred = get_Proj_pred(node);
 294                         pn   = get_Proj_proj(node);
 295
 296                         foreach_out_edge_safe(node, edge, next) {
 297                                 ir_node *cmp_copy;
 298                                 ir_node *user       = get_edge_src_irn(edge);
 299                                 int pos             = get_edge_src_pos(edge);
 300                                 ir_node *user_block = get_nodes_block(user);
 301
 302                                 if (user_block == block)
 303                                         continue;
 304
 305                                 cmp_copy = exact_copy(pred);
 306                                 set_nodes_block(cmp_copy, user_block);
 307                                 copy = new_r_Proj(current_ir_graph, user_block, cmp_copy, mode_b, pn);
 308                                 set_irn_n(user, pos, copy);
 309                         }
 310                         continue;
 311                 }
 312 #endif
 313
 314                 copy = copy_and_fix_node(env, block, copy_block, j, node);
 315
 316                 /* we might hit values in blocks that have already been processed by a
 317                  * recursive find_phi_with_const() call */
 318                 assert(get_irn_visited(copy) <= env->visited_nr);
 319                 if (get_irn_visited(copy) >= env->visited_nr) {
 320                         ir_node *prev_copy = get_irn_link(copy);
 321                         if (prev_copy != NULL)
 322                                 set_irn_link(node, prev_copy);
 323                 }
 324         }
 325
 326         /* fix data-flow (and reconstruct SSA if needed) */
 327         foreach_out_edge(block, edge) {
 328                 ir_node *node = get_edge_src_irn(edge);
 329                 ir_node *copy_node;
 330                 ir_mode *mode;
 331
 332                 if (is_Block(node)) {
 333                         /* Block->Block edge, should be the MacroBlock edge */
 334                         assert(get_Block_MacroBlock(node) == block && "Block->Block edge found");
 335                         continue;
 336                 }
 337
 338                 mode = get_irn_mode(node);
 339                 if (mode == mode_X || is_Cond(node))
 340                         continue;
 341 #ifdef AVOID_PHIB
 342                 if (mode == mode_b)
 343                         continue;
 344 #endif
 345
 346                 DB((dbg, LEVEL_2, ">> Fixing users of %+F\n", node));
 347
 348                 copy_node = get_irn_link(node);
 349                 construct_ssa(block, node, copy_block, copy_node);
 350         }
 351 }
 352
 353 /**
 354  * returns whether the cmp evaluates to true or false, or can't be evaluated!
 355  * 1: true, 0: false, -1: can't evaluate
 356  *
 357  * @param pnc       the compare mode of the Compare
 358  * @param tv_left   the left tarval
 359  * @param tv_right  the right tarval
 360  */
 361 static int eval_cmp_tv(pn_Cmp pnc, tarval *tv_left, tarval *tv_right)
 362 {
 363         pn_Cmp cmp_result = tarval_cmp(tv_left, tv_right);
 364
 365         /* does the compare evaluate to true? */
 366         if (cmp_result == pn_Cmp_False)
 367                 return -1;
 368         if ((cmp_result & pnc) != cmp_result)
 369                 return 0;
 370
 371         return 1;
 372 }
 373
 374 /**
 375  * returns whether the cmp evaluates to true or false, or can't be evaluated!
 376  * 1: true, 0: false, -1: can't evaluate
 377  *
 378  * @param env      the environment
 379  * @param cand     the candidate node, either a Const or a Confirm
 380  */
 381 static int eval_cmp(jumpthreading_env_t *env, ir_node *cand)
 382 {
 383         if (is_Const(cand)) {
 384                 tarval *tv_cand   = get_Const_tarval(cand);
 385                 tarval *tv_cmp    = get_Const_tarval(env->cnst);
 386
 387                 return eval_cmp_tv(env->pnc, tv_cand, tv_cmp);
 388         } else { /* a Confirm */
 389                 tarval *res = computed_value_Cmp_Confirm(env->cmp, cand, env->cnst, env->pnc);
 390
 391                 if (res == tarval_bad)
 392                         return -1;
 393                 return res == tarval_b_true;
 394         }
 395 }
 396
 397 /**
 398  * Check for Const or Confirm with Const.
 399  */
 400 static int is_Const_or_Confirm(const ir_node *node)
 401 {
 402         if (is_Confirm(node))
 403                 node = get_Confirm_bound(node);
 404         return is_Const(node);
 405 }
 406
 407 /**
 408  * get the tarval of a Const or Confirm with
 409  */
 410 static tarval *get_Const_or_Confirm_tarval(const ir_node *node)
 411 {
 412         if (is_Confirm(node)) {
 413                 if (get_Confirm_bound(node))
 414                         node = get_Confirm_bound(node);
 415         }
 416         return get_Const_tarval(node);
 417 }
 418
 419 static ir_node *find_const_or_confirm(jumpthreading_env_t *env, ir_node *jump,
 420                                       ir_node *value)
 421 {
 422         ir_node *block = get_nodes_block(jump);
 423
 424         if (irn_visited_else_mark(value))
 425                 return NULL;
 426
 427         if (is_Const_or_Confirm(value)) {
 428                 if (eval_cmp(env, value) <= 0) {
 429                         return NULL;
 430                 }
 431
 432                 DB((
 433                         dbg, LEVEL_1,
 434                         "> Found jump threading candidate %+F->%+F\n",
 435                         env->true_block, block
 436                 ));
 437
 438                 /* adjust true_block to point directly towards our jump */
 439                 add_pred(env->true_block, jump);
 440
 441                 split_critical_edge(env->true_block, 0);
 442
 443                 /* we need a bigger visited nr when going back */
 444                 env->visited_nr++;
 445
 446                 return block;
 447         }
 448
 449         if (is_Phi(value)) {
 450                 int i, arity;
 451
 452                 /* the Phi has to be in the same Block as the Jmp */
 453                 if (get_nodes_block(value) != block) {
 454                         return NULL;
 455                 }
 456
 457                 arity = get_irn_arity(value);
 458                 for(i = 0; i < arity; ++i) {
 459                         ir_node *copy_block;
 460                         ir_node *phi_pred = get_Phi_pred(value, i);
 461                         ir_node *cfgpred  = get_Block_cfgpred(block, i);
 462
 463                         copy_block = find_const_or_confirm(env, cfgpred, phi_pred);
 464                         if (copy_block == NULL)
 465                                 continue;
 466
 467                         /* copy duplicated nodes in copy_block and fix SSA */
 468                         copy_and_fix(env, block, copy_block, i);
 469
 470                         if (copy_block == get_nodes_block(cfgpred)) {
 471                                 env->cnst_pred = block;
 472                                 env->cnst_pos  = i;
 473                         }
 474
 475                         /* return now as we can't process more possibilities in 1 run */
 476                         return copy_block;
 477                 }
 478         }
 479
 480         return NULL;
 481 }
 482
 483 static ir_node *find_candidate(jumpthreading_env_t *env, ir_node *jump,
 484                                ir_node *value)
 485 {
 486         ir_node *block = get_nodes_block(jump);
 487
 488         if (irn_visited_else_mark(value)) {
 489                 return NULL;
 490         }
 491
 492         if (is_Const_or_Confirm(value)) {
 493                 tarval *tv = get_Const_or_Confirm_tarval(value);
 494
 495                 if (tv != env->tv)
 496                         return NULL;
 497
 498                 DB((
 499                         dbg, LEVEL_1,
 500                         "> Found jump threading candidate %+F->%+F\n",
 501                         env->true_block, block
 502                 ));
 503
 504                 /* adjust true_block to point directly towards our jump */
 505                 add_pred(env->true_block, jump);
 506
 507                 split_critical_edge(env->true_block, 0);
 508
 509                 /* we need a bigger visited nr when going back */
 510                 env->visited_nr++;
 511
 512                 return block;
 513         }
 514         if (is_Phi(value)) {
 515                 int i, arity;
 516
 517                 /* the Phi has to be in the same Block as the Jmp */
 518                 if (get_nodes_block(value) != block)
 519                         return NULL;
 520
 521                 arity = get_irn_arity(value);
 522                 for(i = 0; i < arity; ++i) {
 523                         ir_node *copy_block;
 524                         ir_node *phi_pred = get_Phi_pred(value, i);
 525                         ir_node *cfgpred  = get_Block_cfgpred(block, i);
 526
 527                         copy_block = find_candidate(env, cfgpred, phi_pred);
 528                         if (copy_block == NULL)
 529                                 continue;
 530
 531                         /* copy duplicated nodes in copy_block and fix SSA */
 532                         copy_and_fix(env, block, copy_block, i);
 533
 534                         if (copy_block == get_nodes_block(cfgpred)) {
 535                                 env->cnst_pred = block;
 536                                 env->cnst_pos  = i;
 537                         }
 538
 539                         /* return now as we can't process more possibilities in 1 run */
 540                         return copy_block;
 541                 }
 542         }
 543         if (is_Proj(value)) {
 544                 ir_node *left;
 545                 ir_node *right;
 546                 int      pnc;
 547                 ir_node *cmp = get_Proj_pred(value);
 548                 if (!is_Cmp(cmp))
 549                         return NULL;
 550
 551                 left  = get_Cmp_left(cmp);
 552                 right = get_Cmp_right(cmp);
 553                 pnc   = get_Proj_proj(value);
 554
 555                 /* we assume that the constant is on the right side, swap left/right
 556                  * if needed */
 557                 if (is_Const(left)) {
 558                         ir_node *t = left;
 559                         left       = right;
 560                         right      = t;
 561
 562                         pnc        = get_inversed_pnc(pnc);
 563                 }
 564
 565                 if (!is_Const(right))
 566                         return 0;
 567
 568                 if (get_nodes_block(left) != block) {
 569                         return 0;
 570                 }
 571
 572                 /* negate condition when we're looking for the false block */
 573                 if (env->tv == tarval_b_false) {
 574                         pnc = get_negated_pnc(pnc, get_irn_mode(right));
 575                 }
 576
 577                 /* (recursively) look if a pred of a Phi is a constant or a Confirm */
 578                 env->cmp  = cmp;
 579                 env->pnc  = pnc;
 580                 env->cnst = right;
 581
 582                 return find_const_or_confirm(env, jump, left);
 583         }
 584
 585         return NULL;
 586 }
 587
 588 /**
 589  * Block-walker: searches for the following construct
 590  *
 591  *  Const or Phi with constants
 592  *           |
 593  *          Cmp
 594  *           |
 595  *         Cond
 596  *          /
 597  *       ProjX
 598  *        /
 599  *     Block
 600  */
 601 static void thread_jumps(ir_node* block, void* data)
 602 {
 603         jumpthreading_env_t env;
 604         int *changed = data;
 605         ir_node *selector;
 606         ir_node *projx;
 607         ir_node *cond;
 608         ir_node *copy_block;
 609         int      selector_evaluated;
 610         const ir_edge_t *edge, *next;
 611         ir_node *bad;
 612         size_t   cnst_pos;
 613
 614         if (get_Block_n_cfgpreds(block) != 1)
 615                 return;
 616
 617         projx = get_Block_cfgpred(block, 0);
 618         if (!is_Proj(projx))
 619                 return;
 620         assert(get_irn_mode(projx) == mode_X);
 621
 622         cond = get_Proj_pred(projx);
 623         if (!is_Cond(cond))
 624                 return;
 625
 626         selector = get_Cond_selector(cond);
 627         /* TODO handle switch Conds */
 628         if (get_irn_mode(selector) != mode_b)
 629                 return;
 630
 631         /* handle cases that can be immediately evaluated */
 632         selector_evaluated = -1;
 633         if (is_Proj(selector)) {
 634                 ir_node *cmp = get_Proj_pred(selector);
 635                 if (is_Cmp(cmp)) {
 636                         ir_node *left  = get_Cmp_left(cmp);
 637                         ir_node *right = get_Cmp_right(cmp);
 638                         if (is_Const(left) && is_Const(right)) {
 639                                 int     pnc      = get_Proj_proj(selector);
 640                                 tarval *tv_left  = get_Const_tarval(left);
 641                                 tarval *tv_right = get_Const_tarval(right);
 642
 643                                 selector_evaluated = eval_cmp_tv(pnc, tv_left, tv_right);
 644                                 if (selector_evaluated < 0)
 645                                         return;
 646                         }
 647                 }
 648         } else if (is_Const_or_Confirm(selector)) {
 649                 tarval *tv = get_Const_or_Confirm_tarval(selector);
 650                 if (tv == tarval_b_true) {
 651                         selector_evaluated = 1;
 652                 } else {
 653                         assert(tv == tarval_b_false);
 654                         selector_evaluated = 0;
 655                 }
 656         }
 657
 658         env.cnst_pred = NULL;
 659         if (get_Proj_proj(projx) == pn_Cond_false) {
 660                 env.tv = tarval_b_false;
 661                 if (selector_evaluated >= 0)
 662                         selector_evaluated = !selector_evaluated;
 663         } else {
 664                 env.tv = tarval_b_true;
 665         }
 666
 667         if (selector_evaluated == 0) {
 668                 bad = new_Bad();
 669                 exchange(projx, bad);
 670                 *changed = 1;
 671                 return;
 672         } else if (selector_evaluated == 1) {
 673                 dbg_info *dbgi = get_irn_dbg_info(selector);
 674                 ir_node  *jmp  = new_rd_Jmp(dbgi, get_nodes_block(projx));
 675                 DBG_OPT_JUMPTHREADING(projx, jmp);
 676                 exchange(projx, jmp);
 677                 *changed = 1;
 678                 return;
 679         }
 680
 681         /* (recursively) look if a pred of a Phi is a constant or a Confirm */
 682         env.true_block = block;
 683         inc_irg_visited(current_ir_graph);
 684         env.visited_nr = get_irg_visited(current_ir_graph);
 685
 686         copy_block = find_candidate(&env, projx, selector);
 687         if (copy_block == NULL)
 688                 return;
 689
 690         /* we have to remove the edge towards the pred as the pred now
 691          * jumps into the true_block. We also have to shorten Phis
 692          * in our block because of this */
 693         bad      = new_Bad();
 694         cnst_pos = env.cnst_pos;
 695
 696         /* shorten Phis */
 697         foreach_out_edge_safe(env.cnst_pred, edge, next) {
 698                 ir_node *node = get_edge_src_irn(edge);
 699
 700                 if (is_Phi(node))
 701                         set_Phi_pred(node, cnst_pos, bad);
 702         }
 703
 704         set_Block_cfgpred(env.cnst_pred, cnst_pos, bad);
 705
 706         /* the graph is changed now */
 707         *changed = 1;
 708 }
 709
 710 void opt_jumpthreading(ir_graph* irg)
 711 {
 712         int changed, rerun;
 713
 714         FIRM_DBG_REGISTER(dbg, "firm.opt.jumpthreading");
 715
 716         DB((dbg, LEVEL_1, "===> Performing jumpthreading on %+F\n", irg));
 717
 718         remove_critical_cf_edges(irg);
 719
 720         edges_assure(irg);
 721         ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK | IR_RESOURCE_IRN_VISITED);
 722
 723         changed = 0;
 724         do {
 725                 rerun = 0;
 726                 irg_block_walk_graph(irg, thread_jumps, NULL, &rerun);
 727                 changed |= rerun;
 728         } while (rerun);
 729
 730         ir_free_resources(irg, IR_RESOURCE_IRN_LINK | IR_RESOURCE_IRN_VISITED);
 731
 732         if (changed) {
 733                 /* control flow changed, some blocks may become dead */
 734                 set_irg_outs_inconsistent(irg);
 735                 set_irg_doms_inconsistent(irg);
 736                 set_irg_extblk_inconsistent(irg);
 737                 set_irg_loopinfo_inconsistent(irg);
 738                 set_irg_entity_usage_state(irg, ir_entity_usage_not_computed);
 739
 740                 /* Dead code might be created. Optimize it away as it is dangerous
 741                  * to call optimize_df() an dead code. */
 742                 optimize_cf(irg);
 743         }
 744 }
 745
 746 /* Creates an ir_graph pass for opt_jumpthreading. */
 747 ir_graph_pass_t *opt_jumpthreading_pass(const char *name)
 748 {
 749         return def_graph_pass(name ? name : "jumpthreading", opt_jumpthreading);
 750 }  /* opt_jumpthreading_pass */