mono/mini/branch-opts.c

   1 /*
   2  * branch-opts.c: Branch optimizations support
   3  *
   4  * Authors:
   5  *   Patrik Torstensson (Patrik.Torstesson at gmail.com)
   6  *
   7  * (C) 2005 Ximian, Inc.  http://www.ximian.com
   8  * Copyright 2011 Xamarin Inc.  http://www.xamarin.com
   9  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  10  */
  11
  12 #include "config.h"
  13 #ifndef DISABLE_JIT
  14
  15 #include "mini.h"
  16
  17 /*
  18  * Returns true if @bb is a basic block which falls through the next block.
  19  * TODO verify if it helps to check if the bb last ins is a branch to its successor.
  20  */
  21 static gboolean
  22 mono_bb_is_fall_through (MonoCompile *cfg, MonoBasicBlock *bb)
  23 {
  24         return  bb->next_bb && bb->next_bb->region == bb->region && /*fall throught between regions is not really interesting or useful*/
  25                         (bb->last_ins == NULL || !MONO_IS_BRANCH_OP (bb->last_ins)); /*and the last op can't be a branch too*/
  26 }
  27
  28 /*
  29  * Used by the arch code to replace the exception handling
  30  * with a direct branch. This is safe to do if the
  31  * exception object isn't used, no rethrow statement and
  32  * no filter statement (verify).
  33  *
  34  */
  35 MonoInst *
  36 mono_branch_optimize_exception_target (MonoCompile *cfg, MonoBasicBlock *bb, const char * exname)
  37 {
  38         MonoMethodHeader *header = cfg->header;
  39         MonoExceptionClause *clause;
  40         MonoClass *exclass;
  41         int i;
  42
  43         if (!(cfg->opt & MONO_OPT_EXCEPTION))
  44                 return NULL;
  45
  46         if (bb->region == -1 || !MONO_BBLOCK_IS_IN_REGION (bb, MONO_REGION_TRY))
  47                 return NULL;
  48
  49         exclass = mono_class_load_from_name (mono_get_corlib (), "System", exname);
  50         /* search for the handler */
  51         for (i = 0; i < header->num_clauses; ++i) {
  52                 clause = &header->clauses [i];
  53                 if (MONO_OFFSET_IN_CLAUSE (clause, bb->real_offset)) {
  54                         if (clause->flags == MONO_EXCEPTION_CLAUSE_NONE && clause->data.catch_class && mono_class_is_assignable_from (clause->data.catch_class, exclass)) {
  55                                 MonoBasicBlock *tbb;
  56
  57                                 /* get the basic block for the handler and
  58                                  * check if the exception object is used.
  59                                  * Flag is set during method_to_ir due to
  60                                  * pop-op is optmized away in codegen (burg).
  61                                  */
  62                                 tbb = cfg->cil_offset_to_bb [clause->handler_offset];
  63                                 if (tbb && tbb->flags & BB_EXCEPTION_DEAD_OBJ && !(tbb->flags & BB_EXCEPTION_UNSAFE)) {
  64                                         MonoBasicBlock *targetbb = tbb;
  65                                         gboolean unsafe = FALSE;
  66
  67                                         /* Check if this catch clause is ok to optimize by
  68                                          * looking for the BB_EXCEPTION_UNSAFE in every BB that
  69                                          * belongs to the same region.
  70                                          *
  71                                          * UNSAFE flag is set during method_to_ir (OP_RETHROW)
  72                                          */
  73                                         while (!unsafe && tbb->next_bb && tbb->region == tbb->next_bb->region) {
  74                                                 if (tbb->next_bb->flags & BB_EXCEPTION_UNSAFE)  {
  75                                                         unsafe = TRUE;
  76                                                         break;
  77                                                 }
  78                                                 tbb = tbb->next_bb;
  79                                         }
  80
  81                                         if (!unsafe) {
  82                                                 MonoInst *jump;
  83
  84                                                 /* Create dummy inst to allow easier integration in
  85                                                  * arch dependent code (opcode ignored)
  86                                                  */
  87                                                 MONO_INST_NEW (cfg, jump, OP_BR);
  88
  89                                                 /* Allocate memory for our branch target */
  90                                                 jump->inst_i1 = (MonoInst *)mono_mempool_alloc0 (cfg->mempool, sizeof (MonoInst));
  91                                                 jump->inst_true_bb = targetbb;
  92
  93                                                 if (cfg->verbose_level > 2)
  94                                                         g_print ("found exception to optimize - returning branch to BB%d (%s) (instead of throw) for method %s:%s\n", targetbb->block_num, clause->data.catch_class->name, cfg->method->klass->name, cfg->method->name);
  95
  96                                                 return jump;
  97                                         }
  98
  99                                         return NULL;
 100                                 } else {
 101                                         /* Branching to an outer clause could skip inner clauses */
 102                                         return NULL;
 103                                 }
 104                         } else {
 105                                 /* Branching to an outer clause could skip inner clauses */
 106                                 return NULL;
 107                         }
 108                 }
 109         }
 110
 111         return NULL;
 112 }
 113
 114 static const int int_cmov_opcodes [] = {
 115         OP_CMOV_IEQ,
 116         OP_CMOV_INE_UN,
 117         OP_CMOV_ILE,
 118         OP_CMOV_IGE,
 119         OP_CMOV_ILT,
 120         OP_CMOV_IGT,
 121         OP_CMOV_ILE_UN,
 122         OP_CMOV_IGE_UN,
 123         OP_CMOV_ILT_UN,
 124         OP_CMOV_IGT_UN
 125 };
 126
 127 static const int long_cmov_opcodes [] = {
 128         OP_CMOV_LEQ,
 129         OP_CMOV_LNE_UN,
 130         OP_CMOV_LLE,
 131         OP_CMOV_LGE,
 132         OP_CMOV_LLT,
 133         OP_CMOV_LGT,
 134         OP_CMOV_LLE_UN,
 135         OP_CMOV_LGE_UN,
 136         OP_CMOV_LLT_UN,
 137         OP_CMOV_LGT_UN
 138 };
 139
 140 static G_GNUC_UNUSED int
 141 br_to_br_un (int opcode)
 142 {
 143         switch (opcode) {
 144         case OP_IBGT:
 145                 return OP_IBGT_UN;
 146                 break;
 147         case OP_IBLE:
 148                 return OP_IBLE_UN;
 149                 break;
 150         case OP_LBGT:
 151                 return OP_LBGT_UN;
 152                 break;
 153         case OP_LBLE:
 154                 return OP_LBLE_UN;
 155                 break;
 156         default:
 157                 g_assert_not_reached ();
 158                 return -1;
 159         }
 160 }
 161
 162 /**
 163  * mono_replace_ins:
 164  *
 165  *   Replace INS with its decomposition which is stored in a series of bblocks starting
 166  * at FIRST_BB and ending at LAST_BB. On enter, PREV points to the predecessor of INS.
 167  * On return, it will be set to the last ins of the decomposition.
 168  */
 169 void
 170 mono_replace_ins (MonoCompile *cfg, MonoBasicBlock *bb, MonoInst *ins, MonoInst **prev, MonoBasicBlock *first_bb, MonoBasicBlock *last_bb)
 171 {
 172         MonoInst *next = ins->next;
 173
 174         if (next && next->opcode == OP_NOP) {
 175                 /* Avoid NOPs following branches */
 176                 ins->next = next->next;
 177                 next = next->next;
 178         }
 179
 180         if (first_bb == last_bb) {
 181                 /*
 182                  * Only one replacement bb, merge the code into
 183                  * the current bb.
 184                  */
 185
 186                 /* Delete links between the first_bb and its successors */
 187                 while (first_bb->out_count)
 188                         mono_unlink_bblock (cfg, first_bb, first_bb->out_bb [0]);
 189
 190                 /* Head */
 191                 if (*prev) {
 192                         (*prev)->next = first_bb->code;
 193                         first_bb->code->prev = (*prev);
 194                 } else {
 195                         bb->code = first_bb->code;
 196                 }
 197
 198                 /* Tail */
 199                 last_bb->last_ins->next = next;
 200                 if (next)
 201                         next->prev = last_bb->last_ins;
 202                 else
 203                         bb->last_ins = last_bb->last_ins;
 204                 *prev = last_bb->last_ins;
 205                 bb->has_array_access |= first_bb->has_array_access;
 206         } else {
 207                 int i, count;
 208                 MonoBasicBlock **tmp_bblocks, *tmp;
 209                 MonoInst *last;
 210
 211                 /* Multiple BBs */
 212
 213                 /* Set region/real_offset */
 214                 for (tmp = first_bb; tmp; tmp = tmp->next_bb) {
 215                         tmp->region = bb->region;
 216                         tmp->real_offset = bb->real_offset;
 217                 }
 218
 219                 /* Split the original bb */
 220                 if (ins->next)
 221                         ins->next->prev = NULL;
 222                 ins->next = NULL;
 223                 bb->last_ins = ins;
 224
 225                 /* Merge the second part of the original bb into the last bb */
 226                 if (last_bb->last_ins) {
 227                         last_bb->last_ins->next = next;
 228                         if (next)
 229                                 next->prev = last_bb->last_ins;
 230                 } else {
 231                         last_bb->code = next;
 232                 }
 233                 last_bb->has_array_access |= bb->has_array_access;
 234
 235                 if (next) {
 236                         for (last = next; last->next != NULL; last = last->next)
 237                                 ;
 238                         last_bb->last_ins = last;
 239                 }
 240
 241                 for (i = 0; i < bb->out_count; ++i)
 242                         mono_link_bblock (cfg, last_bb, bb->out_bb [i]);
 243
 244                 /* Merge the first (dummy) bb to the original bb */
 245                 if (*prev) {
 246                         (*prev)->next = first_bb->code;
 247                         first_bb->code->prev = (*prev);
 248                 } else {
 249                         bb->code = first_bb->code;
 250                 }
 251                 bb->last_ins = first_bb->last_ins;
 252                 bb->has_array_access |= first_bb->has_array_access;
 253
 254                 /* Delete the links between the original bb and its successors */
 255                 tmp_bblocks = mono_mempool_alloc0 (cfg->mempool, sizeof (MonoBasicBlock*) * bb->out_count);
 256                 memcpy (tmp_bblocks, bb->out_bb, sizeof (MonoBasicBlock*) * bb->out_count);
 257                 count = bb->out_count;
 258                 for (i = 0; i < count; ++i)
 259                         mono_unlink_bblock (cfg, bb, tmp_bblocks [i]);
 260
 261                 /* Add links between the original bb and the first_bb's successors */
 262                 for (i = 0; i < first_bb->out_count; ++i) {
 263                         MonoBasicBlock *out_bb = first_bb->out_bb [i];
 264
 265                         mono_link_bblock (cfg, bb, out_bb);
 266                 }
 267                 /* Delete links between the first_bb and its successors */
 268                 for (i = 0; i < bb->out_count; ++i) {
 269                         MonoBasicBlock *out_bb = bb->out_bb [i];
 270
 271                         mono_unlink_bblock (cfg, first_bb, out_bb);
 272                 }
 273                 last_bb->next_bb = bb->next_bb;
 274                 bb->next_bb = first_bb->next_bb;
 275
 276                 *prev = NULL;
 277         }
 278 }
 279
 280 void
 281 mono_if_conversion (MonoCompile *cfg)
 282 {
 283 #ifdef MONO_ARCH_HAVE_CMOV_OPS
 284         MonoBasicBlock *bb;
 285         gboolean changed = FALSE;
 286         int filter = FILTER_NOP | FILTER_IL_SEQ_POINT;
 287
 288         if (!(cfg->opt & MONO_OPT_CMOV))
 289                 return;
 290
 291         // FIXME: Make this work with extended bblocks
 292
 293         /*
 294          * This pass requires somewhat optimized IR code so it should be run after
 295          * local cprop/deadce. Also, it should be run before dominator computation, since
 296          * it changes control flow.
 297          */
 298         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 299                 MonoBasicBlock *bb1, *bb2;
 300
 301         restart:
 302                 /* Look for the IR code generated from cond ? a : b
 303                  * which is:
 304                  * BB:
 305                  * b<cond> [BB1BB2]
 306                  * BB1:
 307                  * <var> <- <a>
 308                  * br BB3
 309                  * BB2:
 310                  * <var> <- <b>
 311                  * br BB3
 312                  */
 313                 if (!(bb->out_count == 2 && !bb->extended))
 314                         continue;
 315
 316                 bb1 = bb->out_bb [0];
 317                 bb2 = bb->out_bb [1];
 318
 319                 if (bb1->in_count == 1 && bb2->in_count == 1 && bb1->out_count == 1 && bb2->out_count == 1 && bb1->out_bb [0] == bb2->out_bb [0]) {
 320                         MonoInst *compare, *branch, *ins1, *ins2, *cmov, *move, *tmp;
 321                         MonoBasicBlock *true_bb, *false_bb;
 322                         gboolean simple, ret;
 323                         int dreg, tmp_reg;
 324                         CompType comp_type;
 325
 326                         branch = mono_bb_last_inst (bb, filter);
 327
 328                         if (!branch || branch->opcode == OP_BR_REG || branch->opcode == OP_BR)
 329                                 continue;
 330
 331                         /* Find the compare instruction */
 332                         compare = mono_inst_prev (branch, filter);
 333                         if (!compare)
 334                                 continue;
 335
 336                         if (!MONO_IS_COND_BRANCH_OP (branch))
 337                                 /* This can happen if a cond branch is optimized away */
 338                                 continue;
 339
 340                         true_bb = branch->inst_true_bb;
 341                         false_bb = branch->inst_false_bb;
 342
 343                         /*
 344                          * Check that bb1 and bb2 are 'simple' and both assign to the same
 345                          * variable.
 346                          */
 347                         /* FIXME: Get rid of the nops earlier */
 348                         ins1 = mono_bb_first_inst (true_bb, filter);
 349                         ins2 = mono_bb_first_inst (false_bb, filter);
 350
 351                         if (!(ins1 && ins2 && ins1->dreg == ins2->dreg && ins1->dreg != -1))
 352                                 continue;
 353
 354                         simple = TRUE;
 355                         for (tmp = ins1->next; tmp; tmp = tmp->next)
 356                                 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
 357                                         simple = FALSE;
 358
 359                         for (tmp = ins2->next; tmp; tmp = tmp->next)
 360                                 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
 361                                         simple = FALSE;
 362
 363                         if (!simple)
 364                                 continue;
 365
 366                         /* We move ins1/ins2 before the compare so they should have no side effect */
 367                         if (!(MONO_INS_HAS_NO_SIDE_EFFECT (ins1) && MONO_INS_HAS_NO_SIDE_EFFECT (ins2)))
 368                                 continue;
 369
 370                         /* Moving ins1/ins2 could change the comparison */
 371                         /* FIXME: */
 372                         if (!((compare->sreg1 != ins1->dreg) && (compare->sreg2 != ins1->dreg)))
 373                                 continue;
 374
 375                         /* FIXME: */
 376                         comp_type = mono_opcode_to_type (branch->opcode, compare->opcode);
 377                         if (!((comp_type == CMP_TYPE_I) || (comp_type == CMP_TYPE_L)))
 378                                 continue;
 379
 380                         /* FIXME: */
 381                         /* ins->type might not be set */
 382                         if (INS_INFO (ins1->opcode) [MONO_INST_DEST] != 'i')
 383                                 continue;
 384
 385                         if (cfg->verbose_level > 2) {
 386                                 printf ("\tBranch -> CMove optimization in BB%d on\n", bb->block_num);
 387                                 printf ("\t\t"); mono_print_ins (compare);
 388                                 printf ("\t\t"); mono_print_ins (mono_inst_next (compare, filter));
 389                                 printf ("\t\t"); mono_print_ins (ins1);
 390                                 printf ("\t\t"); mono_print_ins (ins2);
 391                         }
 392
 393                         changed = TRUE;
 394
 395                         //printf ("HIT!\n");
 396
 397                         /* Assignments to the return register must remain at the end of bbs */
 398                         if (cfg->ret)
 399                                 ret = ins1->dreg == cfg->ret->dreg;
 400                         else
 401                                 ret = FALSE;
 402
 403                         tmp_reg = mono_alloc_dreg (cfg, STACK_I4);
 404                         dreg = ins1->dreg;
 405
 406                         /* Rewrite ins1 to emit to tmp_reg */
 407                         ins1->dreg = tmp_reg;
 408
 409                         if (ret) {
 410                                 dreg = mono_alloc_dreg (cfg, STACK_I4);
 411                                 ins2->dreg = dreg;
 412                         }
 413
 414                         /* Remove ins1/ins2 from bb1/bb2 */
 415                         MONO_REMOVE_INS (true_bb, ins1);
 416                         MONO_REMOVE_INS (false_bb, ins2);
 417
 418                         /* Move ins1 and ins2 before the comparison */
 419                         /* ins1 comes first to avoid ins1 overwriting an argument of ins2 */
 420                         mono_bblock_insert_before_ins (bb, compare, ins2);
 421                         mono_bblock_insert_before_ins (bb, ins2, ins1);
 422
 423                         /* Add cmov instruction */
 424                         MONO_INST_NEW (cfg, cmov, OP_NOP);
 425                         cmov->dreg = dreg;
 426                         cmov->sreg1 = dreg;
 427                         cmov->sreg2 = tmp_reg;
 428                         switch (mono_opcode_to_type (branch->opcode, compare->opcode)) {
 429                         case CMP_TYPE_I:
 430                                 cmov->opcode = int_cmov_opcodes [mono_opcode_to_cond (branch->opcode)];
 431                                 break;
 432                         case CMP_TYPE_L:
 433                                 cmov->opcode = long_cmov_opcodes [mono_opcode_to_cond (branch->opcode)];
 434                                 break;
 435                         default:
 436                                 g_assert_not_reached ();
 437                         }
 438                         mono_bblock_insert_after_ins (bb, compare, cmov);
 439
 440                         if (ret) {
 441                                 /* Add an extra move */
 442                                 MONO_INST_NEW (cfg, move, OP_MOVE);
 443                                 move->dreg = cfg->ret->dreg;
 444                                 move->sreg1 = dreg;
 445                                 mono_bblock_insert_after_ins (bb, cmov, move);
 446                         }
 447
 448                         /* Rewrite the branch */
 449                         branch->opcode = OP_BR;
 450                         branch->inst_target_bb = true_bb->out_bb [0];
 451                         mono_link_bblock (cfg, bb, branch->inst_target_bb);
 452
 453                         /* Reorder bblocks */
 454                         mono_unlink_bblock (cfg, bb, true_bb);
 455                         mono_unlink_bblock (cfg, bb, false_bb);
 456                         mono_unlink_bblock (cfg, true_bb, true_bb->out_bb [0]);
 457                         mono_unlink_bblock (cfg, false_bb, false_bb->out_bb [0]);
 458                         mono_remove_bblock (cfg, true_bb);
 459                         mono_remove_bblock (cfg, false_bb);
 460
 461                         /* Merge bb and its successor if possible */
 462                         if ((bb->out_bb [0]->in_count == 1) && (bb->out_bb [0] != cfg->bb_exit) &&
 463                                 (bb->region == bb->out_bb [0]->region)) {
 464                                 mono_merge_basic_blocks (cfg, bb, bb->out_bb [0]);
 465                                 goto restart;
 466                         }
 467                 }
 468
 469                 /* Look for the IR code generated from if (cond) <var> <- <a>
 470                  * which is:
 471                  * BB:
 472                  * b<cond> [BB1BB2]
 473                  * BB1:
 474                  * <var> <- <a>
 475                  * br BB2
 476                  */
 477
 478                 if ((bb2->in_count == 1 && bb2->out_count == 1 && bb2->out_bb [0] == bb1) ||
 479                         (bb1->in_count == 1 && bb1->out_count == 1 && bb1->out_bb [0] == bb2)) {
 480                         MonoInst *compare, *branch, *ins1, *cmov, *tmp;
 481                         gboolean simple;
 482                         int dreg, tmp_reg;
 483                         CompType comp_type;
 484                         CompRelation cond;
 485                         MonoBasicBlock *next_bb, *code_bb;
 486
 487                         /* code_bb is the bblock containing code, next_bb is the successor bblock */
 488                         if (bb2->in_count == 1 && bb2->out_count == 1 && bb2->out_bb [0] == bb1) {
 489                                 code_bb = bb2;
 490                                 next_bb = bb1;
 491                         } else {
 492                                 code_bb = bb1;
 493                                 next_bb = bb2;
 494                         }
 495
 496                         ins1 = mono_bb_first_inst (code_bb, filter);
 497
 498                         if (!ins1)
 499                                 continue;
 500
 501                         /* Check that code_bb is simple */
 502                         simple = TRUE;
 503                         for (tmp = ins1; tmp; tmp = tmp->next)
 504                                 if (!((tmp->opcode == OP_NOP) || (tmp->opcode == OP_IL_SEQ_POINT) || (tmp->opcode == OP_BR)))
 505                                         simple = FALSE;
 506
 507                         if (!simple)
 508                                 continue;
 509
 510                         /* We move ins1 before the compare so it should have no side effect */
 511                         if (!MONO_INS_HAS_NO_SIDE_EFFECT (ins1))
 512                                 continue;
 513
 514                         branch = mono_bb_last_inst (bb, filter);
 515
 516                         if (!branch || branch->opcode == OP_BR_REG)
 517                                 continue;
 518
 519                         /* Find the compare instruction */
 520                         compare = mono_inst_prev (branch, filter);
 521                         if (!compare)
 522                                 continue;
 523
 524                         if (!MONO_IS_COND_BRANCH_OP (branch))
 525                                 /* This can happen if a cond branch is optimized away */
 526                                 continue;
 527
 528                         /* FIXME: */
 529                         comp_type = mono_opcode_to_type (branch->opcode, compare->opcode);
 530                         if (!((comp_type == CMP_TYPE_I) || (comp_type == CMP_TYPE_L)))
 531                                 continue;
 532
 533                         /* FIXME: */
 534                         /* ins->type might not be set */
 535                         if (INS_INFO (ins1->opcode) [MONO_INST_DEST] != 'i')
 536                                 continue;
 537
 538                         /* FIXME: */
 539                         if (cfg->ret && ins1->dreg == cfg->ret->dreg)
 540                                 continue;
 541
 542                         if (!(cfg->opt & MONO_OPT_DEADCE))
 543                                 /*
 544                                  * It is possible that dreg is never set before, so we can't use
 545                                  * it as an sreg of the cmov instruction (#582322).
 546                                  */
 547                                 continue;
 548
 549                         if (cfg->verbose_level > 2) {
 550                                 printf ("\tBranch -> CMove optimization (2) in BB%d on\n", bb->block_num);
 551                                 printf ("\t\t"); mono_print_ins (compare);
 552                                 printf ("\t\t"); mono_print_ins (mono_inst_next (compare, filter));
 553                                 printf ("\t\t"); mono_print_ins (ins1);
 554                         }
 555
 556                         changed = TRUE;
 557
 558                         //printf ("HIT!\n");
 559
 560                         tmp_reg = mono_alloc_dreg (cfg, STACK_I4);
 561                         dreg = ins1->dreg;
 562
 563                         /* Rewrite ins1 to emit to tmp_reg */
 564                         ins1->dreg = tmp_reg;
 565
 566                         /* Remove ins1 from code_bb */
 567                         MONO_REMOVE_INS (code_bb, ins1);
 568
 569                         /* Move ins1 before the comparison */
 570                         mono_bblock_insert_before_ins (bb, compare, ins1);
 571
 572                         /* Add cmov instruction */
 573                         MONO_INST_NEW (cfg, cmov, OP_NOP);
 574                         cmov->dreg = dreg;
 575                         cmov->sreg1 = dreg;
 576                         cmov->sreg2 = tmp_reg;
 577                         cond = mono_opcode_to_cond (branch->opcode);
 578                         if (branch->inst_false_bb == code_bb)
 579                                 cond = mono_negate_cond (cond);
 580                         switch (mono_opcode_to_type (branch->opcode, compare->opcode)) {
 581                         case CMP_TYPE_I:
 582                                 cmov->opcode = int_cmov_opcodes [cond];
 583                                 break;
 584                         case CMP_TYPE_L:
 585                                 cmov->opcode = long_cmov_opcodes [cond];
 586                                 break;
 587                         default:
 588                                 g_assert_not_reached ();
 589                         }
 590                         mono_bblock_insert_after_ins (bb, compare, cmov);
 591
 592                         /* Rewrite the branch */
 593                         branch->opcode = OP_BR;
 594                         branch->inst_target_bb = next_bb;
 595                         mono_link_bblock (cfg, bb, branch->inst_target_bb);
 596
 597                         /* Nullify the branch at the end of code_bb */
 598                         if (code_bb->code) {
 599                                 branch = code_bb->code;
 600                                 MONO_DELETE_INS (code_bb, branch);
 601                         }
 602
 603                         /* Reorder bblocks */
 604                         mono_unlink_bblock (cfg, bb, code_bb);
 605                         mono_unlink_bblock (cfg, code_bb, next_bb);
 606
 607                         /* Merge bb and its successor if possible */
 608                         if ((bb->out_bb [0]->in_count == 1) && (bb->out_bb [0] != cfg->bb_exit) &&
 609                                 (bb->region == bb->out_bb [0]->region)) {
 610                                 mono_merge_basic_blocks (cfg, bb, bb->out_bb [0]);
 611
 612                                 /*
 613                                  * bbn might have fallen through to the next bb without a branch,
 614                                  * have to add one now (#474718).
 615                                  * FIXME: Maybe need to do this more generally in
 616                                  * merge_basic_blocks () ?
 617                                  */
 618                                 if (!(bb->last_ins && MONO_IS_BRANCH_OP (bb->last_ins)) && bb->out_count) {
 619                                         MONO_INST_NEW (cfg, ins1, OP_BR);
 620                                         ins1->inst_target_bb = bb->out_bb [0];
 621                                         MONO_ADD_INS (bb, ins1);
 622                                 }
 623                                 goto restart;
 624                         }
 625                 }
 626         }
 627
 628         /*
 629          * Optimize checks like: if (v < 0 || v > limit) by changing then to unsigned
 630          * compares. This isn't really if conversion, but it easier to do here than in
 631          * optimize_branches () since the IR is already optimized.
 632          */
 633         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 634                 MonoBasicBlock *bb1, *bb2, *next_bb;
 635                 MonoInst *branch1, *branch2, *compare1, *ins, *next;
 636
 637                 /* Look for the IR code generated from if (<var> < 0 || v > <limit>)
 638                  * after branch opts which is:
 639                  * BB:
 640                  * icompare_imm R [0]
 641                  * int_blt [BB1BB2]
 642                  * BB2:
 643                  * icompare_imm R [<limit>]
 644                  * int_ble [BB3BB1]
 645                  */
 646                 if (!(bb->out_count == 2 && !bb->extended))
 647                         continue;
 648
 649                 bb1 = bb->out_bb [0];
 650                 bb2 = bb->out_bb [1];
 651
 652                 // FIXME: Add more cases
 653
 654                 /* Check structure */
 655                 if (!(bb1->in_count == 2 && bb1->in_bb [0] == bb && bb1->in_bb [1] == bb2 && bb2->in_count == 1 && bb2->out_count == 2))
 656                         continue;
 657
 658                 next_bb = bb2;
 659
 660                 /* Check first branch */
 661                 branch1 = mono_bb_last_inst (bb, filter);
 662                 if (!(branch1 && ((branch1->opcode == OP_IBLT) || (branch1->opcode == OP_LBLT)) && (branch1->inst_false_bb == next_bb)))
 663                         continue;
 664
 665                 /* Check second branch */
 666                 branch2 = mono_bb_last_inst (next_bb, filter);
 667                 if (!branch2)
 668                         continue;
 669
 670                 /* mcs sometimes generates inverted branches */
 671                 if (((branch2->opcode == OP_IBGT) || (branch2->opcode == OP_LBGT)) && branch2->inst_true_bb == branch1->inst_true_bb)
 672                         ;
 673                 else if (((branch2->opcode == OP_IBLE) || (branch2->opcode == OP_LBLE)) && branch2->inst_false_bb == branch1->inst_true_bb)
 674                         ;
 675                 else
 676                         continue;
 677
 678                 /* Check first compare */
 679                 compare1 = mono_inst_prev (mono_bb_last_inst (bb, filter), filter);
 680                 if (!(compare1 && ((compare1->opcode == OP_ICOMPARE_IMM) || (compare1->opcode == OP_LCOMPARE_IMM)) && compare1->inst_imm == 0))
 681                         continue;
 682
 683                 /* Check second bblock */
 684                 ins = mono_bb_first_inst (next_bb, filter);
 685                 if (!ins)
 686                         continue;
 687                 next = mono_inst_next (ins, filter);
 688                 if (((ins->opcode == OP_ICOMPARE_IMM) || (ins->opcode == OP_LCOMPARE_IMM)) && ins->sreg1 == compare1->sreg1 && next == branch2) {
 689                         /* The second arg must be positive */
 690                         if (ins->inst_imm < 0)
 691                                 continue;
 692                 } else if (((ins->opcode == OP_LDLEN) || (ins->opcode == OP_STRLEN)) && ins->dreg != compare1->sreg1 && next && next->opcode == OP_ICOMPARE && next->sreg1 == compare1->sreg1 && next->sreg2 == ins->dreg && mono_inst_next (next, filter) == branch2) {
 693                         /* Another common case: if (index < 0 || index > arr.Length) */
 694                 } else {
 695                         continue;
 696                 }
 697
 698                 if (cfg->verbose_level > 2) {
 699                         printf ("\tSigned->unsigned compare optimization in BB%d on\n", bb->block_num);
 700                         printf ("\t\t"); mono_print_ins (compare1);
 701                         printf ("\t\t"); mono_print_ins (mono_inst_next (compare1, filter));
 702                         printf ("\t\t"); mono_print_ins (ins);
 703                 }
 704
 705                 /* Rewrite the first compare+branch */
 706                 MONO_DELETE_INS (bb, compare1);
 707                 branch1->opcode = OP_BR;
 708                 mono_unlink_bblock (cfg, bb, branch1->inst_true_bb);
 709                 mono_unlink_bblock (cfg, bb, branch1->inst_false_bb);
 710                 branch1->inst_target_bb = next_bb;
 711                 mono_link_bblock (cfg, bb, next_bb);
 712
 713                 /* Rewrite the second branch */
 714                 branch2->opcode = br_to_br_un (branch2->opcode);
 715
 716                 mono_merge_basic_blocks (cfg, bb, next_bb);
 717         }
 718
 719 #if 0
 720         for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
 721                 MonoBasicBlock *bb1, *bb2;
 722                 MonoInst *prev, *compare, *branch, *ins1, *ins2, *cmov, *move, *tmp;
 723                 gboolean simple, ret;
 724                 int dreg, tmp_reg;
 725                 CompType comp_type;
 726
 727                 /* Look for the IR code generated from if (cond) <var> <- <a>
 728                  * after branch opts which is:
 729                  * BB:
 730                  * compare
 731                  * b<cond> [BB1]
 732                  * <var> <- <a>
 733                  * BB1:
 734                  */
 735                 if (!(bb->out_count == 1 && bb->extended && bb->code && bb->code->next && bb->code->next->next))
 736                         continue;
 737
 738                 mono_print_bb (bb, "");
 739
 740                 /* Find the compare instruction */
 741                 prev = NULL;
 742                 compare = bb->code;
 743                 g_assert (compare);
 744                 while (compare->next->next && compare->next->next != bb->last_ins) {
 745                         prev = compare;
 746                         compare = compare->next;
 747                 }
 748                 branch = compare->next;
 749                 if (!MONO_IS_COND_BRANCH_OP (branch))
 750                         continue;
 751         }
 752 #endif
 753
 754         if (changed) {
 755                 if (cfg->opt & MONO_OPT_BRANCH)
 756                         mono_optimize_branches (cfg);
 757                 /* Merging bblocks could make some variables local */
 758                 mono_handle_global_vregs (cfg);
 759                 if (cfg->opt & (MONO_OPT_CONSPROP | MONO_OPT_COPYPROP))
 760                         mono_local_cprop (cfg);
 761                 if (cfg->opt & MONO_OPT_DEADCE)
 762                         mono_local_deadce (cfg);
 763         }
 764 #endif
 765 }
 766
 767 void
 768 mono_nullify_basic_block (MonoBasicBlock *bb)
 769 {
 770         bb->in_count = 0;
 771         bb->out_count = 0;
 772         bb->in_bb = NULL;
 773         bb->out_bb = NULL;
 774         bb->next_bb = NULL;
 775         bb->code = bb->last_ins = NULL;
 776         bb->cil_code = NULL;
 777 }
 778
 779 static void
 780 replace_out_block (MonoBasicBlock *bb, MonoBasicBlock *orig,  MonoBasicBlock *repl)
 781 {
 782         int i;
 783
 784         for (i = 0; i < bb->out_count; i++) {
 785                 MonoBasicBlock *ob = bb->out_bb [i];
 786                 if (ob == orig) {
 787                         if (!repl) {
 788                                 if (bb->out_count > 1) {
 789                                         bb->out_bb [i] = bb->out_bb [bb->out_count - 1];
 790                                 }
 791                                 bb->out_count--;
 792                         } else {
 793                                 bb->out_bb [i] = repl;
 794                         }
 795                 }
 796         }
 797 }
 798
 799 static void
 800 replace_in_block (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl)
 801 {
 802         int i;
 803
 804         for (i = 0; i < bb->in_count; i++) {
 805                 MonoBasicBlock *ib = bb->in_bb [i];
 806                 if (ib == orig) {
 807                         if (!repl) {
 808                                 if (bb->in_count > 1) {
 809                                         bb->in_bb [i] = bb->in_bb [bb->in_count - 1];
 810                                 }
 811                                 bb->in_count--;
 812                         } else {
 813                                 bb->in_bb [i] = repl;
 814                         }
 815                 }
 816         }
 817 }
 818
 819 static void
 820 replace_out_block_in_code (MonoBasicBlock *bb, MonoBasicBlock *orig, MonoBasicBlock *repl) {
 821         MonoInst *ins;
 822
 823 #if defined(__native_client_codegen__)
 824         /* Need to maintain this flag for the new block because */
 825         /* we can't jump indirectly to a non-aligned block.     */
 826         if (orig->flags & BB_INDIRECT_JUMP_TARGET)
 827         {
 828                 repl->flags |= BB_INDIRECT_JUMP_TARGET;
 829         }
 830 #endif
 831
 832         for (ins = bb->code; ins != NULL; ins = ins->next) {
 833                 switch (ins->opcode) {
 834                 case OP_BR:
 835                         if (ins->inst_target_bb == orig)
 836                                 ins->inst_target_bb = repl;
 837                         break;
 838                 case OP_CALL_HANDLER:
 839                         if (ins->inst_target_bb == orig)
 840                                 ins->inst_target_bb = repl;
 841                         break;
 842                 case OP_SWITCH: {
 843                         int i;
 844                         int n = GPOINTER_TO_INT (ins->klass);
 845                         for (i = 0; i < n; i++ ) {
 846                                 if (ins->inst_many_bb [i] == orig)
 847                                         ins->inst_many_bb [i] = repl;
 848                         }
 849                         break;
 850                 }
 851                 default:
 852                         if (MONO_IS_COND_BRANCH_OP (ins)) {
 853                                 if (ins->inst_true_bb == orig)
 854                                         ins->inst_true_bb = repl;
 855                                 if (ins->inst_false_bb == orig)
 856                                         ins->inst_false_bb = repl;
 857                         } else if (MONO_IS_JUMP_TABLE (ins)) {
 858                                 int i;
 859                                 MonoJumpInfoBBTable *table = (MonoJumpInfoBBTable *)MONO_JUMP_TABLE_FROM_INS (ins);
 860                                 for (i = 0; i < table->table_size; i++ ) {
 861                                         if (table->table [i] == orig)
 862                                                 table->table [i] = repl;
 863                                 }
 864                         }
 865
 866                         break;
 867                 }
 868         }
 869 }
 870
 871 /**
 872   * Check if a bb is useless (is just made of NOPs and ends with an
 873   * unconditional branch, or nothing).
 874   * If it is so, unlink it from the CFG and nullify it, and return TRUE.
 875   * Otherwise, return FALSE;
 876   */
 877 static gboolean
 878 remove_block_if_useless (MonoCompile *cfg, MonoBasicBlock *bb, MonoBasicBlock *previous_bb) {
 879         MonoBasicBlock *target_bb = NULL;
 880         MonoInst *inst;
 881
 882         /* Do not touch handlers */
 883         if (bb->region != -1) {
 884                 bb->not_useless = TRUE;
 885                 return FALSE;
 886         }
 887
 888         MONO_BB_FOR_EACH_INS (bb, inst) {
 889                 switch (inst->opcode) {
 890                 case OP_NOP:
 891                 case OP_IL_SEQ_POINT:
 892                         break;
 893                 case OP_BR:
 894                         target_bb = inst->inst_target_bb;
 895                         break;
 896                 default:
 897                         bb->not_useless = TRUE;
 898                         return FALSE;
 899                 }
 900         }
 901
 902         if (target_bb == NULL) {
 903                 if ((bb->out_count == 1) && (bb->out_bb [0] == bb->next_bb)) {
 904                         target_bb = bb->next_bb;
 905                 } else {
 906                         /* Do not touch empty BBs that do not "fall through" to their next BB (like the exit BB) */
 907                         return FALSE;
 908                 }
 909         }
 910
 911         /* Do not touch BBs following a switch (they are the "default" branch) */
 912         if ((previous_bb->last_ins != NULL) && (previous_bb->last_ins->opcode == OP_SWITCH)) {
 913                 return FALSE;
 914         }
 915
 916         /* Do not touch BBs following the entry BB and jumping to something that is not */
 917         /* thiry "next" bb (the entry BB cannot contain the branch) */
 918         if ((previous_bb == cfg->bb_entry) && (bb->next_bb != target_bb)) {
 919                 return FALSE;
 920         }
 921
 922         /*
 923          * Do not touch BBs following a try block as the code in
 924          * mini_method_compile needs them to compute the length of the try block.
 925          */
 926         if (MONO_BBLOCK_IS_IN_REGION (previous_bb, MONO_REGION_TRY))
 927                 return FALSE;
 928
 929         /* Check that there is a target BB, and that bb is not an empty loop (Bug 75061) */
 930         if ((target_bb != NULL) && (target_bb != bb)) {
 931                 int i;
 932
 933                 if (cfg->verbose_level > 1) {
 934                         printf ("remove_block_if_useless, removed BB%d\n", bb->block_num);
 935                 }
 936
 937                 /* unlink_bblock () modifies the bb->in_bb array so can't use a for loop here */
 938                 while (bb->in_count) {
 939                         MonoBasicBlock *in_bb = bb->in_bb [0];
 940                         mono_unlink_bblock (cfg, in_bb, bb);
 941                         mono_link_bblock (cfg, in_bb, target_bb);
 942                         replace_out_block_in_code (in_bb, bb, target_bb);
 943                 }
 944
 945                 mono_unlink_bblock (cfg, bb, target_bb);
 946                 if (previous_bb != cfg->bb_entry && mono_bb_is_fall_through (cfg, previous_bb)) {
 947                         for (i = 0; i < previous_bb->out_count; i++) {
 948                                 if (previous_bb->out_bb [i] == target_bb) {
 949                                         MonoInst *jump;
 950                                         MONO_INST_NEW (cfg, jump, OP_BR);
 951                                         MONO_ADD_INS (previous_bb, jump);
 952                                         jump->cil_code = previous_bb->cil_code;
 953                                         jump->inst_target_bb = target_bb;
 954                                         break;
 955                                 }
 956                         }
 957                 }
 958
 959                 previous_bb->next_bb = bb->next_bb;
 960                 mono_nullify_basic_block (bb);
 961
 962                 return TRUE;
 963         } else {
 964                 return FALSE;
 965         }
 966 }
 967
 968 void
 969 mono_merge_basic_blocks (MonoCompile *cfg, MonoBasicBlock *bb, MonoBasicBlock *bbn)
 970 {
 971         MonoInst *inst;
 972         MonoBasicBlock *prev_bb;
 973         int i;
 974
 975         bb->has_array_access |= bbn->has_array_access;
 976         bb->extended |= bbn->extended;
 977
 978         /* Compute prev_bb if possible to avoid the linear search below */
 979         prev_bb = NULL;
 980         for (i = 0; i < bbn->in_count; ++i)
 981                 if (bbn->in_bb [0]->next_bb == bbn)
 982                         prev_bb = bbn->in_bb [0];
 983
 984         mono_unlink_bblock (cfg, bb, bbn);
 985         for (i = 0; i < bbn->out_count; ++i)
 986                 mono_link_bblock (cfg, bb, bbn->out_bb [i]);
 987         while (bbn->out_count)
 988                 mono_unlink_bblock (cfg, bbn, bbn->out_bb [0]);
 989
 990         /* Handle the branch at the end of the bb */
 991         if (bb->has_call_handler) {
 992                 for (inst = bb->code; inst != NULL; inst = inst->next) {
 993                         if (inst->opcode == OP_CALL_HANDLER) {
 994                                 g_assert (inst->inst_target_bb == bbn);
 995                                 NULLIFY_INS (inst);
 996                         }
 997                 }
 998         }
 999         if (bb->has_jump_table) {
1000                 for (inst = bb->code; inst != NULL; inst = inst->next) {
1001                         if (MONO_IS_JUMP_TABLE (inst)) {
1002                                 int i;
1003                                 MonoJumpInfoBBTable *table = (MonoJumpInfoBBTable *)MONO_JUMP_TABLE_FROM_INS (inst);
1004                                 for (i = 0; i < table->table_size; i++ ) {
1005                                         /* Might be already NULL from a previous merge */
1006                                         if (table->table [i])
1007                                                 g_assert (table->table [i] == bbn);
1008                                         table->table [i] = NULL;
1009                                 }
1010                                 /* Can't nullify this as later instructions depend on it */
1011                         }
1012                 }
1013         }
1014         if (bb->last_ins && MONO_IS_COND_BRANCH_OP (bb->last_ins)) {
1015                 g_assert (bb->last_ins->inst_false_bb == bbn);
1016                 bb->last_ins->inst_false_bb = NULL;
1017                 bb->extended = TRUE;
1018         } else if (bb->last_ins && MONO_IS_BRANCH_OP (bb->last_ins)) {
1019                 NULLIFY_INS (bb->last_ins);
1020         }
1021
1022         bb->has_call_handler |= bbn->has_call_handler;
1023         bb->has_jump_table |= bbn->has_jump_table;
1024
1025         if (bb->last_ins) {
1026                 if (bbn->code) {
1027                         bb->last_ins->next = bbn->code;
1028                         bbn->code->prev = bb->last_ins;
1029                         bb->last_ins = bbn->last_ins;
1030                 }
1031         } else {
1032                 bb->code = bbn->code;
1033                 bb->last_ins = bbn->last_ins;
1034         }
1035
1036         if (!prev_bb) {
1037                 for (prev_bb = cfg->bb_entry; prev_bb && prev_bb->next_bb != bbn; prev_bb = prev_bb->next_bb)
1038                         ;
1039         }
1040         if (prev_bb) {
1041                 prev_bb->next_bb = bbn->next_bb;
1042         } else {
1043                 /* bbn might not be in the bb list yet */
1044                 if (bb->next_bb == bbn)
1045                         bb->next_bb = bbn->next_bb;
1046         }
1047         mono_nullify_basic_block (bbn);
1048
1049         /*
1050          * If bbn fell through to its next bblock, have to add a branch, since bb
1051          * will not fall though to the same bblock (#513931).
1052          */
1053         if (bb->last_ins && bb->out_count == 1 && bb->out_bb [0] != bb->next_bb && !MONO_IS_BRANCH_OP (bb->last_ins)) {
1054                 MONO_INST_NEW (cfg, inst, OP_BR);
1055                 inst->inst_target_bb = bb->out_bb [0];
1056                 MONO_ADD_INS (bb, inst);
1057         }
1058 }
1059
1060 static void
1061 move_basic_block_to_end (MonoCompile *cfg, MonoBasicBlock *bb)
1062 {
1063         MonoBasicBlock *bbn, *next;
1064
1065         next = bb->next_bb;
1066
1067         /* Find the previous */
1068         for (bbn = cfg->bb_entry; bbn->next_bb && bbn->next_bb != bb; bbn = bbn->next_bb)
1069                 ;
1070         if (bbn->next_bb) {
1071                 bbn->next_bb = bb->next_bb;
1072         }
1073
1074         /* Find the last */
1075         for (bbn = cfg->bb_entry; bbn->next_bb; bbn = bbn->next_bb)
1076                 ;
1077         bbn->next_bb = bb;
1078         bb->next_bb = NULL;
1079
1080         /* Add a branch */
1081         if (next && (!bb->last_ins || ((bb->last_ins->opcode != OP_NOT_REACHED) && (bb->last_ins->opcode != OP_BR) && (bb->last_ins->opcode != OP_BR_REG) && (!MONO_IS_COND_BRANCH_OP (bb->last_ins))))) {
1082                 MonoInst *ins;
1083
1084                 MONO_INST_NEW (cfg, ins, OP_BR);
1085                 MONO_ADD_INS (bb, ins);
1086                 mono_link_bblock (cfg, bb, next);
1087                 ins->inst_target_bb = next;
1088         }
1089 }
1090
1091 /*
1092  * mono_remove_block:
1093  *
1094  *   Remove BB from the control flow graph
1095  */
1096 void
1097 mono_remove_bblock (MonoCompile *cfg, MonoBasicBlock *bb)
1098 {
1099         MonoBasicBlock *tmp_bb;
1100
1101         for (tmp_bb = cfg->bb_entry; tmp_bb && tmp_bb->next_bb != bb; tmp_bb = tmp_bb->next_bb)
1102                 ;
1103
1104         g_assert (tmp_bb);
1105         tmp_bb->next_bb = bb->next_bb;
1106 }
1107
1108 void
1109 mono_remove_critical_edges (MonoCompile *cfg)
1110 {
1111         MonoBasicBlock *bb;
1112         MonoBasicBlock *previous_bb;
1113
1114         if (cfg->verbose_level > 3) {
1115                 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
1116                         int i;
1117                         printf ("remove_critical_edges, BEFORE BB%d (in:", bb->block_num);
1118                         for (i = 0; i < bb->in_count; i++) {
1119                                 printf (" %d", bb->in_bb [i]->block_num);
1120                         }
1121                         printf (") (out:");
1122                         for (i = 0; i < bb->out_count; i++) {
1123                                 printf (" %d", bb->out_bb [i]->block_num);
1124                         }
1125                         printf (")");
1126                         if (bb->last_ins != NULL) {
1127                                 printf (" ");
1128                                 mono_print_ins (bb->last_ins);
1129                         }
1130                         printf ("\n");
1131                 }
1132         }
1133
1134         for (previous_bb = cfg->bb_entry, bb = previous_bb->next_bb; bb != NULL; previous_bb = previous_bb->next_bb, bb = bb->next_bb) {
1135                 if (bb->in_count > 1) {
1136                         int in_bb_index;
1137                         for (in_bb_index = 0; in_bb_index < bb->in_count; in_bb_index++) {
1138                                 MonoBasicBlock *in_bb = bb->in_bb [in_bb_index];
1139                                 /*
1140                                  * Have to remove non-critical edges whose source ends with a BR_REG
1141                                  * ins too, since inserting a computation before the BR_REG could
1142                                  * overwrite the sreg1 of the ins.
1143                                  */
1144                                 if ((in_bb->out_count > 1) || (in_bb->out_count == 1 && in_bb->last_ins && in_bb->last_ins->opcode == OP_BR_REG)) {
1145                                         MonoBasicBlock *new_bb = (MonoBasicBlock *)mono_mempool_alloc0 ((cfg)->mempool, sizeof (MonoBasicBlock));
1146                                         new_bb->block_num = cfg->num_bblocks++;
1147 //                                      new_bb->real_offset = bb->real_offset;
1148                                         new_bb->region = bb->region;
1149
1150                                         /* Do not alter the CFG while altering the BB list */
1151                                         if (mono_bb_is_fall_through (cfg, previous_bb)) {
1152                                                 if (previous_bb != cfg->bb_entry) {
1153                                                         int i;
1154                                                         /* Make sure previous_bb really falls through bb */
1155                                                         for (i = 0; i < previous_bb->out_count; i++) {
1156                                                                 if (previous_bb->out_bb [i] == bb) {
1157                                                                         MonoInst *jump;
1158                                                                         MONO_INST_NEW (cfg, jump, OP_BR);
1159                                                                         MONO_ADD_INS (previous_bb, jump);
1160                                                                         jump->cil_code = previous_bb->cil_code;
1161                                                                         jump->inst_target_bb = bb;
1162                                                                         break;
1163                                                                 }
1164                                                         }
1165                                                 } else {
1166                                                         /* We cannot add any inst to the entry BB, so we must */
1167                                                         /* put a new BB in the middle to hold the OP_BR */
1168                                                         MonoInst *jump;
1169                                                         MonoBasicBlock *new_bb_after_entry = (MonoBasicBlock *)mono_mempool_alloc0 ((cfg)->mempool, sizeof (MonoBasicBlock));
1170                                                         new_bb_after_entry->block_num = cfg->num_bblocks++;
1171 //                                                      new_bb_after_entry->real_offset = bb->real_offset;
1172                                                         new_bb_after_entry->region = bb->region;
1173
1174                                                         MONO_INST_NEW (cfg, jump, OP_BR);
1175                                                         MONO_ADD_INS (new_bb_after_entry, jump);
1176                                                         jump->cil_code = bb->cil_code;
1177                                                         jump->inst_target_bb = bb;
1178
1179                                                         mono_unlink_bblock (cfg, previous_bb, bb);
1180                                                         mono_link_bblock (cfg, new_bb_after_entry, bb);
1181                                                         mono_link_bblock (cfg, previous_bb, new_bb_after_entry);
1182
1183                                                         previous_bb->next_bb = new_bb_after_entry;
1184                                                         previous_bb = new_bb_after_entry;
1185
1186                                                         if (cfg->verbose_level > 2) {
1187                                                                 printf ("remove_critical_edges, added helper BB%d jumping to BB%d\n", new_bb_after_entry->block_num, bb->block_num);
1188                                                         }
1189                                                 }
1190                                         }
1191
1192                                         /* Insert new_bb in the BB list */
1193                                         previous_bb->next_bb = new_bb;
1194                                         new_bb->next_bb = bb;
1195                                         previous_bb = new_bb;
1196
1197                                         /* Setup in_bb and out_bb */
1198                                         new_bb->in_bb = (MonoBasicBlock **)mono_mempool_alloc ((cfg)->mempool, sizeof (MonoBasicBlock*));
1199                                         new_bb->in_bb [0] = in_bb;
1200                                         new_bb->in_count = 1;
1201                                         new_bb->out_bb = (MonoBasicBlock **)mono_mempool_alloc ((cfg)->mempool, sizeof (MonoBasicBlock*));
1202                                         new_bb->out_bb [0] = bb;
1203                                         new_bb->out_count = 1;
1204
1205                                         /* Relink in_bb and bb to (from) new_bb */
1206                                         replace_out_block (in_bb, bb, new_bb);
1207                                         replace_out_block_in_code (in_bb, bb, new_bb);
1208                                         replace_in_block (bb, in_bb, new_bb);
1209
1210                                         if (cfg->verbose_level > 2) {
1211                                                 printf ("remove_critical_edges, removed critical edge from BB%d to BB%d (added BB%d)\n", in_bb->block_num, bb->block_num, new_bb->block_num);
1212                                         }
1213                                 }
1214                         }
1215                 }
1216         }
1217
1218         if (cfg->verbose_level > 3) {
1219                 for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
1220                         int i;
1221                         printf ("remove_critical_edges, AFTER BB%d (in:", bb->block_num);
1222                         for (i = 0; i < bb->in_count; i++) {
1223                                 printf (" %d", bb->in_bb [i]->block_num);
1224                         }
1225                         printf (") (out:");
1226                         for (i = 0; i < bb->out_count; i++) {
1227                                 printf (" %d", bb->out_bb [i]->block_num);
1228                         }
1229                         printf (")");
1230                         if (bb->last_ins != NULL) {
1231                                 printf (" ");
1232                                 mono_print_ins (bb->last_ins);
1233                         }
1234                         printf ("\n");
1235                 }
1236         }
1237 }
1238
1239 /*
1240  * Optimizes the branches on the Control Flow Graph
1241  *
1242  */
1243 void
1244 mono_optimize_branches (MonoCompile *cfg)
1245 {
1246         int i, count = 0, changed = FALSE;
1247         MonoBasicBlock *bb, *bbn;
1248         guint32 niterations;
1249         MonoInst *bbn_first_inst;
1250         int filter = FILTER_IL_SEQ_POINT;
1251
1252         /*
1253          * Some crazy loops could cause the code below to go into an infinite
1254          * loop, see bug #53003 for an example. To prevent this, we put an upper
1255          * bound on the number of iterations.
1256          */
1257         if (cfg->num_bblocks > 1000)
1258                 niterations = cfg->num_bblocks * 2;
1259         else
1260                 niterations = 1000;
1261
1262         do {
1263                 MonoBasicBlock *previous_bb;
1264                 changed = FALSE;
1265                 niterations --;
1266
1267                 /* we skip the entry block (exit is handled specially instead ) */
1268                 for (previous_bb = cfg->bb_entry, bb = cfg->bb_entry->next_bb; bb; previous_bb = bb, bb = bb->next_bb) {
1269                         count ++;
1270                         if (count == 1000) {
1271                                 mono_threads_safepoint ();
1272                                 count = 0;
1273                         }
1274                         /* dont touch code inside exception clauses */
1275                         if (bb->region != -1)
1276                                 continue;
1277
1278                         if (!bb->not_useless && remove_block_if_useless (cfg, bb, previous_bb)) {
1279                                 changed = TRUE;
1280                                 continue;
1281                         }
1282
1283                         if ((bbn = bb->next_bb) && bbn->in_count == 0 && bbn != cfg->bb_exit && bb->region == bbn->region) {
1284                                 if (cfg->verbose_level > 2)
1285                                         g_print ("nullify block triggered %d\n", bbn->block_num);
1286
1287                                 bb->next_bb = bbn->next_bb;
1288
1289                                 for (i = 0; i < bbn->out_count; i++)
1290                                         replace_in_block (bbn->out_bb [i], bbn, NULL);
1291
1292                                 mono_nullify_basic_block (bbn);
1293                                 changed = TRUE;
1294                         }
1295
1296                         if (bb->out_count == 1) {
1297                                 bbn = bb->out_bb [0];
1298
1299                                 /* conditional branches where true and false targets are the same can be also replaced with OP_BR */
1300                                 if (bb->last_ins && (bb->last_ins->opcode != OP_BR) && MONO_IS_COND_BRANCH_OP (bb->last_ins)) {
1301                                         bb->last_ins->opcode = OP_BR;
1302                                         bb->last_ins->inst_target_bb = bb->last_ins->inst_true_bb;
1303                                         changed = TRUE;
1304                                         if (cfg->verbose_level > 2)
1305                                                 g_print ("cond branch removal triggered in %d %d\n", bb->block_num, bb->out_count);
1306                                 }
1307
1308                                 if (bb->region == bbn->region && bb->next_bb == bbn) {
1309                                         /* the block are in sequence anyway ... */
1310
1311                                         /* branches to the following block can be removed */
1312                                         if (bb->last_ins && bb->last_ins->opcode == OP_BR && !bbn->out_of_line) {
1313                                                 NULLIFY_INS (bb->last_ins);
1314                                                 changed = TRUE;
1315                                                 if (cfg->verbose_level > 2)
1316                                                         g_print ("br removal triggered %d -> %d\n", bb->block_num, bbn->block_num);
1317                                         }
1318
1319                                         if (bbn->in_count == 1 && !bb->extended) {
1320                                                 if (bbn != cfg->bb_exit) {
1321                                                         if (cfg->verbose_level > 2)
1322                                                                 g_print ("block merge triggered %d -> %d\n", bb->block_num, bbn->block_num);
1323                                                         mono_merge_basic_blocks (cfg, bb, bbn);
1324                                                         changed = TRUE;
1325                                                         continue;
1326                                                 }
1327
1328                                                 //mono_print_bb_code (bb);
1329                                         }
1330                                 }
1331                         }
1332
1333                         if ((bbn = bb->next_bb) && bbn->in_count == 0 && bbn != cfg->bb_exit && bb->region == bbn->region) {
1334                                 if (cfg->verbose_level > 2) {
1335                                         g_print ("nullify block triggered %d\n", bbn->block_num);
1336                                 }
1337                                 bb->next_bb = bbn->next_bb;
1338
1339                                 for (i = 0; i < bbn->out_count; i++)
1340                                         replace_in_block (bbn->out_bb [i], bbn, NULL);
1341
1342                                 mono_nullify_basic_block (bbn);
1343                                 changed = TRUE;
1344                                 continue;
1345                         }
1346
1347                         if (bb->out_count == 1) {
1348                                 bbn = bb->out_bb [0];
1349
1350                                 if (bb->last_ins && bb->last_ins->opcode == OP_BR) {
1351                                         bbn = bb->last_ins->inst_target_bb;
1352                                         bbn_first_inst = mono_bb_first_inst (bbn, filter);
1353                                         if (bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1354                                                 bbn_first_inst->inst_target_bb != bbn &&
1355                                                 bbn_first_inst->inst_target_bb->region == bb->region) {
1356
1357                                                 if (cfg->verbose_level > 2)
1358                                                         g_print ("branch to branch triggered %d -> %d -> %d\n", bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num);
1359
1360                                                 replace_in_block (bbn, bb, NULL);
1361                                                 replace_out_block (bb, bbn, bbn_first_inst->inst_target_bb);
1362                                                 mono_link_bblock (cfg, bb, bbn_first_inst->inst_target_bb);
1363                                                 bb->last_ins->inst_target_bb = bbn_first_inst->inst_target_bb;
1364                                                 changed = TRUE;
1365                                                 continue;
1366                                         }
1367                                 }
1368                         } else if (bb->out_count == 2) {
1369                                 if (bb->last_ins && MONO_IS_COND_BRANCH_NOFP (bb->last_ins)) {
1370                                         int branch_result;
1371                                         MonoBasicBlock *taken_branch_target = NULL, *untaken_branch_target = NULL;
1372
1373                                         if (bb->last_ins->flags & MONO_INST_CFOLD_TAKEN)
1374                                                 branch_result = BRANCH_TAKEN;
1375                                         else if (bb->last_ins->flags & MONO_INST_CFOLD_NOT_TAKEN)
1376                                                 branch_result = BRANCH_NOT_TAKEN;
1377                                         else
1378                                                 branch_result = BRANCH_UNDEF;
1379
1380                                         if (branch_result == BRANCH_TAKEN) {
1381                                                 taken_branch_target = bb->last_ins->inst_true_bb;
1382                                                 untaken_branch_target = bb->last_ins->inst_false_bb;
1383                                         } else if (branch_result == BRANCH_NOT_TAKEN) {
1384                                                 taken_branch_target = bb->last_ins->inst_false_bb;
1385                                                 untaken_branch_target = bb->last_ins->inst_true_bb;
1386                                         }
1387                                         if (taken_branch_target) {
1388                                                 /* if mono_eval_cond_branch () is ever taken to handle
1389                                                  * non-constant values to compare, issue a pop here.
1390                                                  */
1391                                                 bb->last_ins->opcode = OP_BR;
1392                                                 bb->last_ins->inst_target_bb = taken_branch_target;
1393                                                 if (!bb->extended)
1394                                                         mono_unlink_bblock (cfg, bb, untaken_branch_target);
1395                                                 changed = TRUE;
1396                                                 continue;
1397                                         }
1398                                         bbn = bb->last_ins->inst_true_bb;
1399                                         bbn_first_inst = mono_bb_first_inst (bbn, filter);
1400                                         if (bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1401                                             bbn_first_inst->inst_target_bb->region == bb->region) {
1402                                                 if (cfg->verbose_level > 2)
1403                                                         g_print ("cbranch1 to branch triggered %d -> (%d) %d (0x%02x)\n",
1404                                                                  bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num,
1405                                                                  bbn_first_inst->opcode);
1406
1407                                                 /*
1408                                                  * Unlink, then relink bblocks to avoid various
1409                                                  * tricky situations when the two targets of the branch
1410                                                  * are equal, or will become equal after the change.
1411                                                  */
1412                                                 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1413                                                 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1414
1415                                                 bb->last_ins->inst_true_bb = bbn_first_inst->inst_target_bb;
1416
1417                                                 mono_link_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1418                                                 mono_link_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1419
1420                                                 changed = TRUE;
1421                                                 continue;
1422                                         }
1423
1424                                         bbn = bb->last_ins->inst_false_bb;
1425                                         bbn_first_inst = mono_bb_first_inst (bbn, filter);
1426                                         if (bbn && bb->region == bbn->region && bbn_first_inst && bbn_first_inst->opcode == OP_BR &&
1427                                                 bbn_first_inst->inst_target_bb->region == bb->region) {
1428                                                 if (cfg->verbose_level > 2)
1429                                                         g_print ("cbranch2 to branch triggered %d -> (%d) %d (0x%02x)\n",
1430                                                                  bb->block_num, bbn->block_num, bbn_first_inst->inst_target_bb->block_num,
1431                                                                  bbn_first_inst->opcode);
1432
1433                                                 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1434                                                 mono_unlink_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1435
1436                                                 bb->last_ins->inst_false_bb = bbn_first_inst->inst_target_bb;
1437
1438                                                 mono_link_bblock (cfg, bb, bb->last_ins->inst_true_bb);
1439                                                 mono_link_bblock (cfg, bb, bb->last_ins->inst_false_bb);
1440
1441                                                 changed = TRUE;
1442                                                 continue;
1443                                         }
1444
1445                                         bbn = bb->last_ins->inst_false_bb;
1446                                         /*
1447                                          * If bb is an extended bb, it could contain an inside branch to bbn.
1448                                          * FIXME: Enable the optimization if that is not true.
1449                                          * If bblocks_linked () is true, then merging bb and bbn
1450                                          * would require addition of an extra branch at the end of bbn
1451                                          * slowing down loops.
1452                                          */
1453                                         if (bbn && bb->region == bbn->region && bbn->in_count == 1 && cfg->enable_extended_bblocks && bbn != cfg->bb_exit && !bb->extended && !bbn->out_of_line && !mono_bblocks_linked (bbn, bb)) {
1454                                                 g_assert (bbn->in_bb [0] == bb);
1455                                                 if (cfg->verbose_level > 2)
1456                                                         g_print ("merge false branch target triggered BB%d -> BB%d\n", bb->block_num, bbn->block_num);
1457                                                 mono_merge_basic_blocks (cfg, bb, bbn);
1458                                                 changed = TRUE;
1459                                                 continue;
1460                                         }
1461                                 }
1462
1463                                 if (bb->last_ins && MONO_IS_COND_BRANCH_NOFP (bb->last_ins)) {
1464                                         if (bb->last_ins->inst_false_bb && bb->last_ins->inst_false_bb->out_of_line && (bb->region == bb->last_ins->inst_false_bb->region) && !cfg->disable_out_of_line_bblocks) {
1465                                                 /* Reverse the branch */
1466                                                 bb->last_ins->opcode = mono_reverse_branch_op (bb->last_ins->opcode);
1467                                                 bbn = bb->last_ins->inst_false_bb;
1468                                                 bb->last_ins->inst_false_bb = bb->last_ins->inst_true_bb;
1469                                                 bb->last_ins->inst_true_bb = bbn;
1470
1471                                                 move_basic_block_to_end (cfg, bb->last_ins->inst_true_bb);
1472                                                 if (cfg->verbose_level > 2)
1473                                                         g_print ("cbranch to throw block triggered %d.\n",
1474                                                                          bb->block_num);
1475                                         }
1476                                 }
1477                         }
1478                 }
1479         } while (changed && (niterations > 0));
1480 }
1481
1482 #endif /* DISABLE_JIT */