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 #include "vrp.h"
  49
  50 #undef AVOID_PHIB
  51
  52 DEBUG_ONLY(static firm_dbg_module_t *dbg);
  53
  54 /**
  55  * Add the new predecessor x to node node, which is either a Block or a Phi
  56  */
  57 static void add_pred(ir_node* node, ir_node* x)
  58 {
  59         ir_node** ins;
  60         int n;
  61         int i;
  62
  63         assert(is_Block(node) || is_Phi(node));
  64
  65         n = get_irn_arity(node);
  66         NEW_ARR_A(ir_node*, ins, n + 1);
  67         for (i = 0; i < n; i++)
  68                 ins[i] = get_irn_n(node, i);
  69         ins[n] = x;
  70         set_irn_in(node, n + 1, ins);
  71 }
  72
  73 static ir_node *ssa_second_def;
  74 static ir_node *ssa_second_def_block;
  75
  76 static ir_node *search_def_and_create_phis(ir_node *block, ir_mode *mode,
  77                                            int first)
  78 {
  79         int i;
  80         int n_cfgpreds;
  81         ir_graph *irg;
  82         ir_node *phi;
  83         ir_node **in;
  84
  85         /* This is needed because we create bads sometimes */
  86         if (is_Bad(block))
  87                 return new_Bad();
  88
  89         /* the other defs can't be marked for cases where a user of the original
  90          * value is in the same block as the alternative definition.
  91          * In this case we mustn't use the alternative definition.
  92          * So we keep a flag that indicated wether we walked at least 1 block
  93          * away and may use the alternative definition */
  94         if (block == ssa_second_def_block && !first) {
  95                 return ssa_second_def;
  96         }
  97
  98         /* already processed this block? */
  99         if (irn_visited(block)) {
 100                 ir_node *value = (ir_node*) get_irn_link(block);
 101                 return value;
 102         }
 103
 104         irg = get_irn_irg(block);
 105         assert(block != get_irg_start_block(irg));
 106
 107         /* a Block with only 1 predecessor needs no Phi */
 108         n_cfgpreds = get_Block_n_cfgpreds(block);
 109         if (n_cfgpreds == 1) {
 110                 ir_node *pred_block = get_Block_cfgpred_block(block, 0);
 111                 ir_node *value      = search_def_and_create_phis(pred_block, mode, 0);
 112
 113                 set_irn_link(block, value);
 114                 mark_irn_visited(block);
 115                 return value;
 116         }
 117
 118         /* create a new Phi */
 119         NEW_ARR_A(ir_node*, in, n_cfgpreds);
 120         for(i = 0; i < n_cfgpreds; ++i)
 121                 in[i] = new_Unknown(mode);
 122
 123         phi = new_r_Phi(block, n_cfgpreds, in, mode);
 124         set_irn_link(block, phi);
 125         mark_irn_visited(block);
 126
 127         /* set Phi predecessors */
 128         for(i = 0; i < n_cfgpreds; ++i) {
 129                 ir_node *pred_block = get_Block_cfgpred_block(block, i);
 130                 ir_node *pred_val   = search_def_and_create_phis(pred_block, mode, 0);
 131
 132                 set_irn_n(phi, i, pred_val);
 133         }
 134
 135         return phi;
 136 }
 137
 138 /**
 139  * Given a set of values this function constructs SSA-form for the users of the
 140  * first value (the users are determined through the out-edges of the value).
 141  * Uses the irn_visited flags. Works without using the dominance tree.
 142  */
 143 static void construct_ssa(ir_node *orig_block, ir_node *orig_val,
 144                           ir_node *second_block, ir_node *second_val)
 145 {
 146         ir_graph *irg;
 147         ir_mode *mode;
 148         const ir_edge_t *edge;
 149         const ir_edge_t *next;
 150
 151         /* no need to do anything */
 152         if (orig_val == second_val)
 153                 return;
 154
 155         irg = get_irn_irg(orig_val);
 156         inc_irg_visited(irg);
 157
 158         mode = get_irn_mode(orig_val);
 159         set_irn_link(orig_block, orig_val);
 160         mark_irn_visited(orig_block);
 161
 162         ssa_second_def_block = second_block;
 163         ssa_second_def       = second_val;
 164
 165         /* Only fix the users of the first, i.e. the original node */
 166         foreach_out_edge_safe(orig_val, edge, next) {
 167                 ir_node *user = get_edge_src_irn(edge);
 168                 int j = get_edge_src_pos(edge);
 169                 ir_node *user_block = get_nodes_block(user);
 170                 ir_node *newval;
 171
 172                 /* ignore keeps */
 173                 if (is_End(user))
 174                         continue;
 175
 176                 DB((dbg, LEVEL_3, ">>> Fixing user %+F (pred %d == %+F)\n", user, j, get_irn_n(user, j)));
 177
 178                 if (is_Phi(user)) {
 179                         ir_node *pred_block = get_Block_cfgpred_block(user_block, j);
 180                         newval = search_def_and_create_phis(pred_block, mode, 1);
 181                 } else {
 182                         newval = search_def_and_create_phis(user_block, mode, 1);
 183                 }
 184
 185                 /* don't fix newly created Phis from the SSA construction */
 186                 if (newval != user) {
 187                         DB((dbg, LEVEL_4, ">>>> Setting input %d of %+F to %+F\n", j, user, newval));
 188                         set_irn_n(user, j, newval);
 189                 }
 190         }
 191 }
 192
 193 static void split_critical_edge(ir_node *block, int pos) {
 194         ir_graph *irg = get_irn_irg(block);
 195         ir_node *in[1];
 196         ir_node *new_block;
 197         ir_node *new_jmp;
 198
 199         in[0] = get_Block_cfgpred(block, pos);
 200         new_block = new_r_Block(irg, 1, in);
 201         new_jmp = new_r_Jmp(new_block);
 202         set_Block_cfgpred(block, pos, new_jmp);
 203 }
 204
 205 typedef struct jumpthreading_env_t {
 206         ir_node       *true_block;
 207         ir_node       *cmp;        /**< The Compare node that might be partial evaluated */
 208         pn_Cmp         pnc;        /**< The Compare mode of the Compare node. */
 209         ir_node       *cnst;
 210         tarval        *tv;
 211         ir_visited_t   visited_nr;
 212
 213         ir_node       *cnst_pred;   /**< the block before the constant */
 214         int            cnst_pos;    /**< the pos to the constant block (needed to
 215                                           kill that edge later) */
 216 } jumpthreading_env_t;
 217
 218 static ir_node *copy_and_fix_node(const jumpthreading_env_t *env,
 219                                   ir_node *block, ir_node *copy_block, int j,
 220                                   ir_node *node)
 221 {
 222         int      i, arity;
 223         ir_node *copy;
 224
 225         /* we can evaluate Phis right now, all other nodes get copied */
 226         if (is_Phi(node)) {
 227                 copy = get_Phi_pred(node, j);
 228                 /* we might have to evaluate a Phi-cascade */
 229                 if (get_irn_visited(copy) >= env->visited_nr) {
 230                         copy = get_irn_link(copy);
 231                 }
 232         } else {
 233                 copy = exact_copy(node);
 234                 set_nodes_block(copy, copy_block);
 235
 236                 assert(get_irn_mode(copy) != mode_X);
 237
 238                 arity = get_irn_arity(copy);
 239                 for(i = 0; i < arity; ++i) {
 240                         ir_node *pred     = get_irn_n(copy, i);
 241                         ir_node *new_pred;
 242
 243                         if (get_nodes_block(pred) != block)
 244                                 continue;
 245
 246                         if (get_irn_visited(pred) >= env->visited_nr) {
 247                                 new_pred = get_irn_link(pred);
 248                         } else {
 249                                 new_pred = copy_and_fix_node(env, block, copy_block, j, pred);
 250                         }
 251                         DB((dbg, LEVEL_2, ">> Set Pred of %+F to %+F\n", copy, new_pred));
 252                         set_irn_n(copy, i, new_pred);
 253                 }
 254         }
 255
 256         set_irn_link(node, copy);
 257         set_irn_visited(node, env->visited_nr);
 258
 259         return copy;
 260 }
 261
 262 static void copy_and_fix(const jumpthreading_env_t *env, ir_node *block,
 263                          ir_node *copy_block, int j)
 264 {
 265         const ir_edge_t *edge;
 266
 267         /* Look at all nodes in the cond_block and copy them into pred */
 268         foreach_out_edge(block, edge) {
 269                 ir_node *node = get_edge_src_irn(edge);
 270                 ir_node *copy;
 271                 ir_mode *mode;
 272
 273                 if (is_Block(node)) {
 274                         /* Block->Block edge, should be the MacroBlock edge */
 275                         assert(get_Block_MacroBlock(node) == block && "Block->Block edge found");
 276                         continue;
 277                 }
 278
 279                 /* ignore control flow */
 280                 mode = get_irn_mode(node);
 281                 if (mode == mode_X || is_Cond(node))
 282                         continue;
 283 #ifdef AVOID_PHIB
 284                 /* we may not copy mode_b nodes, because this could produce Phi with
 285                  * mode_bs which can't be handled in all backends. Instead we duplicate
 286                  * the node and move it to its users */
 287                 if (mode == mode_b) {
 288                         const ir_edge_t *edge, *next;
 289                         ir_node *pred;
 290                         int      pn;
 291
 292                         assert(is_Proj(node));
 293
 294                         pred = get_Proj_pred(node);
 295                         pn   = get_Proj_proj(node);
 296
 297                         foreach_out_edge_safe(node, edge, next) {
 298                                 ir_node *cmp_copy;
 299                                 ir_node *user       = get_edge_src_irn(edge);
 300                                 int pos             = get_edge_src_pos(edge);
 301                                 ir_node *user_block = get_nodes_block(user);
 302
 303                                 if (user_block == block)
 304                                         continue;
 305
 306                                 cmp_copy = exact_copy(pred);
 307                                 set_nodes_block(cmp_copy, user_block);
 308                                 copy = new_r_Proj(current_ir_graph, user_block, cmp_copy, mode_b, pn);
 309                                 set_irn_n(user, pos, copy);
 310                         }
 311                         continue;
 312                 }
 313 #endif
 314
 315                 copy = copy_and_fix_node(env, block, copy_block, j, node);
 316
 317                 /* we might hit values in blocks that have already been processed by a
 318                  * recursive find_phi_with_const() call */
 319                 assert(get_irn_visited(copy) <= env->visited_nr);
 320                 if (get_irn_visited(copy) >= env->visited_nr) {
 321                         ir_node *prev_copy = get_irn_link(copy);
 322                         if (prev_copy != NULL)
 323                                 set_irn_link(node, prev_copy);
 324                 }
 325         }
 326
 327         /* fix data-flow (and reconstruct SSA if needed) */
 328         foreach_out_edge(block, edge) {
 329                 ir_node *node = get_edge_src_irn(edge);
 330                 ir_node *copy_node;
 331                 ir_mode *mode;
 332
 333                 if (is_Block(node)) {
 334                         /* Block->Block edge, should be the MacroBlock edge */
 335                         assert(get_Block_MacroBlock(node) == block && "Block->Block edge found");
 336                         continue;
 337                 }
 338
 339                 mode = get_irn_mode(node);
 340                 if (mode == mode_X || is_Cond(node))
 341                         continue;
 342 #ifdef AVOID_PHIB
 343                 if (mode == mode_b)
 344                         continue;
 345 #endif
 346
 347                 DB((dbg, LEVEL_2, ">> Fixing users of %+F\n", node));
 348
 349                 copy_node = get_irn_link(node);
 350                 construct_ssa(block, node, copy_block, copy_node);
 351         }
 352 }
 353
 354 /**
 355  * returns whether the cmp evaluates to true or false, or can't be evaluated!
 356  * 1: true, 0: false, -1: can't evaluate
 357  *
 358  * @param pnc       the compare mode of the Compare
 359  * @param tv_left   the left tarval
 360  * @param tv_right  the right tarval
 361  */
 362 static int eval_cmp_tv(pn_Cmp pnc, tarval *tv_left, tarval *tv_right)
 363 {
 364         pn_Cmp cmp_result = tarval_cmp(tv_left, tv_right);
 365
 366         /* does the compare evaluate to true? */
 367         if (cmp_result == pn_Cmp_False)
 368                 return -1;
 369         if ((cmp_result & pnc) != cmp_result)
 370                 return 0;
 371
 372         return 1;
 373 }
 374
 375 /**
 376  * returns whether the cmp evaluates to true or false according to vrp
 377  * information , or can't be evaluated!
 378  * 1: true, 0: false, -1: can't evaluate
 379  *
 380  * @param pnc       the compare mode of the Compare
 381  * @param left   the left node
 382  * @param right  the right node
 383  */
 384 static int eval_cmp_vrp(pn_Cmp pnc, ir_node *left, ir_node *right)
 385 {
 386         pn_Cmp cmp_result = vrp_cmp(left, right);
 387
 388         /* does the compare evaluate to true? */
 389         if (cmp_result == pn_Cmp_False)
 390                 return -1;
 391         if ((cmp_result & pnc) != cmp_result)
 392                 return 0;
 393
 394         return 1;
 395 }
 396 /**
 397  * returns whether the cmp evaluates to true or false, or can't be evaluated!
 398  * 1: true, 0: false, -1: can't evaluate
 399  *
 400  * @param env      the environment
 401  * @param cand     the candidate node, either a Const or a Confirm
 402  */
 403 static int eval_cmp(jumpthreading_env_t *env, ir_node *cand)
 404 {
 405         if (is_Const(cand)) {
 406                 tarval *tv_cand   = get_Const_tarval(cand);
 407                 tarval *tv_cmp    = get_Const_tarval(env->cnst);
 408
 409                 return eval_cmp_tv(env->pnc, tv_cand, tv_cmp);
 410         } else { /* a Confirm */
 411                 tarval *res = computed_value_Cmp_Confirm(env->cmp, cand, env->cnst, env->pnc);
 412
 413                 if (res == tarval_bad)
 414                         return -1;
 415                 return res == tarval_b_true;
 416         }
 417 }
 418
 419 /**
 420  * Check for Const or Confirm with Const.
 421  */
 422 static int is_Const_or_Confirm(const ir_node *node)
 423 {
 424         if (is_Confirm(node))
 425                 node = get_Confirm_bound(node);
 426         return is_Const(node);
 427 }
 428
 429 /**
 430  * get the tarval of a Const or Confirm with
 431  */
 432 static tarval *get_Const_or_Confirm_tarval(const ir_node *node)
 433 {
 434         if (is_Confirm(node)) {
 435                 if (get_Confirm_bound(node))
 436                         node = get_Confirm_bound(node);
 437         }
 438         return get_Const_tarval(node);
 439 }
 440
 441 static ir_node *find_const_or_confirm(jumpthreading_env_t *env, ir_node *jump,
 442                                       ir_node *value)
 443 {
 444         ir_node *block = get_nodes_block(jump);
 445
 446         if (irn_visited_else_mark(value))
 447                 return NULL;
 448
 449         if (is_Const_or_Confirm(value)) {
 450                 if (eval_cmp(env, value) <= 0) {
 451                         return NULL;
 452                 }
 453
 454                 DB((
 455                         dbg, LEVEL_1,
 456                         "> Found jump threading candidate %+F->%+F\n",
 457                         env->true_block, block
 458                 ));
 459
 460                 /* adjust true_block to point directly towards our jump */
 461                 add_pred(env->true_block, jump);
 462
 463                 split_critical_edge(env->true_block, 0);
 464
 465                 /* we need a bigger visited nr when going back */
 466                 env->visited_nr++;
 467
 468                 return block;
 469         }
 470
 471         if (is_Phi(value)) {
 472                 int i, arity;
 473
 474                 /* the Phi has to be in the same Block as the Jmp */
 475                 if (get_nodes_block(value) != block) {
 476                         return NULL;
 477                 }
 478
 479                 arity = get_irn_arity(value);
 480                 for(i = 0; i < arity; ++i) {
 481                         ir_node *copy_block;
 482                         ir_node *phi_pred = get_Phi_pred(value, i);
 483                         ir_node *cfgpred  = get_Block_cfgpred(block, i);
 484
 485                         copy_block = find_const_or_confirm(env, cfgpred, phi_pred);
 486                         if (copy_block == NULL)
 487                                 continue;
 488
 489                         /* copy duplicated nodes in copy_block and fix SSA */
 490                         copy_and_fix(env, block, copy_block, i);
 491
 492                         if (copy_block == get_nodes_block(cfgpred)) {
 493                                 env->cnst_pred = block;
 494                                 env->cnst_pos  = i;
 495                         }
 496
 497                         /* return now as we can't process more possibilities in 1 run */
 498                         return copy_block;
 499                 }
 500         }
 501
 502         return NULL;
 503 }
 504
 505 static ir_node *find_candidate(jumpthreading_env_t *env, ir_node *jump,
 506                                ir_node *value)
 507 {
 508         ir_node *block = get_nodes_block(jump);
 509
 510         if (irn_visited_else_mark(value)) {
 511                 return NULL;
 512         }
 513
 514         if (is_Const_or_Confirm(value)) {
 515                 tarval *tv = get_Const_or_Confirm_tarval(value);
 516
 517                 if (tv != env->tv)
 518                         return NULL;
 519
 520                 DB((
 521                         dbg, LEVEL_1,
 522                         "> Found jump threading candidate %+F->%+F\n",
 523                         env->true_block, block
 524                 ));
 525
 526                 /* adjust true_block to point directly towards our jump */
 527                 add_pred(env->true_block, jump);
 528
 529                 split_critical_edge(env->true_block, 0);
 530
 531                 /* we need a bigger visited nr when going back */
 532                 env->visited_nr++;
 533
 534                 return block;
 535         }
 536         if (is_Phi(value)) {
 537                 int i, arity;
 538
 539                 /* the Phi has to be in the same Block as the Jmp */
 540                 if (get_nodes_block(value) != block)
 541                         return NULL;
 542
 543                 arity = get_irn_arity(value);
 544                 for(i = 0; i < arity; ++i) {
 545                         ir_node *copy_block;
 546                         ir_node *phi_pred = get_Phi_pred(value, i);
 547                         ir_node *cfgpred  = get_Block_cfgpred(block, i);
 548
 549                         copy_block = find_candidate(env, cfgpred, phi_pred);
 550                         if (copy_block == NULL)
 551                                 continue;
 552
 553                         /* copy duplicated nodes in copy_block and fix SSA */
 554                         copy_and_fix(env, block, copy_block, i);
 555
 556                         if (copy_block == get_nodes_block(cfgpred)) {
 557                                 env->cnst_pred = block;
 558                                 env->cnst_pos  = i;
 559                         }
 560
 561                         /* return now as we can't process more possibilities in 1 run */
 562                         return copy_block;
 563                 }
 564         }
 565         if (is_Proj(value)) {
 566                 ir_node *left;
 567                 ir_node *right;
 568                 int      pnc;
 569                 ir_node *cmp = get_Proj_pred(value);
 570                 if (!is_Cmp(cmp))
 571                         return NULL;
 572
 573                 left  = get_Cmp_left(cmp);
 574                 right = get_Cmp_right(cmp);
 575                 pnc   = get_Proj_proj(value);
 576
 577                 /* we assume that the constant is on the right side, swap left/right
 578                  * if needed */
 579                 if (is_Const(left)) {
 580                         ir_node *t = left;
 581                         left       = right;
 582                         right      = t;
 583
 584                         pnc        = get_inversed_pnc(pnc);
 585                 }
 586
 587                 if (!is_Const(right))
 588                         return 0;
 589
 590                 if (get_nodes_block(left) != block) {
 591                         return 0;
 592                 }
 593
 594                 /* negate condition when we're looking for the false block */
 595                 if (env->tv == tarval_b_false) {
 596                         pnc = get_negated_pnc(pnc, get_irn_mode(right));
 597                 }
 598
 599                 /* (recursively) look if a pred of a Phi is a constant or a Confirm */
 600                 env->cmp  = cmp;
 601                 env->pnc  = pnc;
 602                 env->cnst = right;
 603
 604                 return find_const_or_confirm(env, jump, left);
 605         }
 606
 607         return NULL;
 608 }
 609
 610 /**
 611  * Block-walker: searches for the following construct
 612  *
 613  *  Const or Phi with constants
 614  *           |
 615  *          Cmp
 616  *           |
 617  *         Cond
 618  *          /
 619  *       ProjX
 620  *        /
 621  *     Block
 622  */
 623 static void thread_jumps(ir_node* block, void* data)
 624 {
 625         jumpthreading_env_t env;
 626         int *changed = data;
 627         ir_node *selector;
 628         ir_node *projx;
 629         ir_node *cond;
 630         ir_node *copy_block;
 631         int      selector_evaluated;
 632         const ir_edge_t *edge, *next;
 633         ir_node *bad;
 634         size_t   cnst_pos;
 635
 636         if (get_Block_n_cfgpreds(block) != 1)
 637                 return;
 638
 639         projx = get_Block_cfgpred(block, 0);
 640         if (!is_Proj(projx))
 641                 return;
 642         assert(get_irn_mode(projx) == mode_X);
 643
 644         cond = get_Proj_pred(projx);
 645         if (!is_Cond(cond))
 646                 return;
 647
 648         selector = get_Cond_selector(cond);
 649         /* TODO handle switch Conds */
 650         if (get_irn_mode(selector) != mode_b)
 651                 return;
 652
 653         /* handle cases that can be immediately evaluated */
 654         selector_evaluated = -1;
 655         if (is_Proj(selector)) {
 656                 ir_node *cmp = get_Proj_pred(selector);
 657                 if (is_Cmp(cmp)) {
 658                         ir_node *left  = get_Cmp_left(cmp);
 659                         ir_node *right = get_Cmp_right(cmp);
 660                         if (is_Const(left) && is_Const(right)) {
 661                                 int     pnc      = get_Proj_proj(selector);
 662                                 tarval *tv_left  = get_Const_tarval(left);
 663                                 tarval *tv_right = get_Const_tarval(right);
 664
 665                                 selector_evaluated = eval_cmp_tv(pnc, tv_left, tv_right);
 666                         }
 667                         if (selector_evaluated < 0) {
 668                                 /* This is only the case if the predecessor nodes are not
 669                                  * constant or the comparison could not be evaluated.
 670                                  * Try with VRP information now.
 671                                  */
 672                                 int pnc = get_Proj_proj(selector);
 673
 674                                 selector_evaluated = eval_cmp_vrp(pnc, left, right);
 675                         }
 676                 }
 677         } else if (is_Const_or_Confirm(selector)) {
 678                 tarval *tv = get_Const_or_Confirm_tarval(selector);
 679                 if (tv == tarval_b_true) {
 680                         selector_evaluated = 1;
 681                 } else {
 682                         assert(tv == tarval_b_false);
 683                         selector_evaluated = 0;
 684                 }
 685         }
 686
 687         env.cnst_pred = NULL;
 688         if (get_Proj_proj(projx) == pn_Cond_false) {
 689                 env.tv = tarval_b_false;
 690                 if (selector_evaluated >= 0)
 691                         selector_evaluated = !selector_evaluated;
 692         } else {
 693                 env.tv = tarval_b_true;
 694         }
 695
 696         if (selector_evaluated == 0) {
 697                 bad = new_Bad();
 698                 exchange(projx, bad);
 699                 *changed = 1;
 700                 return;
 701         } else if (selector_evaluated == 1) {
 702                 dbg_info *dbgi = get_irn_dbg_info(selector);
 703                 ir_node  *jmp  = new_rd_Jmp(dbgi, get_nodes_block(projx));
 704                 DBG_OPT_JUMPTHREADING(projx, jmp);
 705                 exchange(projx, jmp);
 706                 *changed = 1;
 707                 return;
 708         }
 709
 710         /* (recursively) look if a pred of a Phi is a constant or a Confirm */
 711         env.true_block = block;
 712         inc_irg_visited(current_ir_graph);
 713         env.visited_nr = get_irg_visited(current_ir_graph);
 714
 715         copy_block = find_candidate(&env, projx, selector);
 716         if (copy_block == NULL)
 717                 return;
 718
 719         /* we have to remove the edge towards the pred as the pred now
 720          * jumps into the true_block. We also have to shorten Phis
 721          * in our block because of this */
 722         bad      = new_Bad();
 723         cnst_pos = env.cnst_pos;
 724
 725         /* shorten Phis */
 726         foreach_out_edge_safe(env.cnst_pred, edge, next) {
 727                 ir_node *node = get_edge_src_irn(edge);
 728
 729                 if (is_Phi(node))
 730                         set_Phi_pred(node, cnst_pos, bad);
 731         }
 732
 733         set_Block_cfgpred(env.cnst_pred, cnst_pos, bad);
 734
 735         /* the graph is changed now */
 736         *changed = 1;
 737 }
 738
 739 void opt_jumpthreading(ir_graph* irg)
 740 {
 741         int changed, rerun;
 742
 743         FIRM_DBG_REGISTER(dbg, "firm.opt.jumpthreading");
 744
 745         DB((dbg, LEVEL_1, "===> Performing jumpthreading on %+F\n", irg));
 746
 747         remove_critical_cf_edges(irg);
 748
 749         edges_assure(irg);
 750         ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK | IR_RESOURCE_IRN_VISITED);
 751
 752         changed = 0;
 753         do {
 754                 rerun = 0;
 755                 irg_block_walk_graph(irg, thread_jumps, NULL, &rerun);
 756                 changed |= rerun;
 757         } while (rerun);
 758
 759         ir_free_resources(irg, IR_RESOURCE_IRN_LINK | IR_RESOURCE_IRN_VISITED);
 760
 761         if (changed) {
 762                 /* control flow changed, some blocks may become dead */
 763                 set_irg_outs_inconsistent(irg);
 764                 set_irg_doms_inconsistent(irg);
 765                 set_irg_extblk_inconsistent(irg);
 766                 set_irg_loopinfo_inconsistent(irg);
 767                 set_irg_entity_usage_state(irg, ir_entity_usage_not_computed);
 768
 769                 /* Dead code might be created. Optimize it away as it is dangerous
 770                  * to call optimize_df() an dead code. */
 771                 optimize_cf(irg);
 772         }
 773 }
 774
 775 /* Creates an ir_graph pass for opt_jumpthreading. */
 776 ir_graph_pass_t *opt_jumpthreading_pass(const char *name)
 777 {
 778         return def_graph_pass(name ? name : "jumpthreading", opt_jumpthreading);
 779 }  /* opt_jumpthreading_pass */