flow.c

   1 /*
   2  * Flow - walk the linearized flowgraph, simplifying it as we
   3  * go along.
   4  *
   5  * Copyright (C) 2004 Linus Torvalds
   6  */
   7
   8 #include <string.h>
   9 #include <stdarg.h>
  10 #include <stdlib.h>
  11 #include <stdio.h>
  12 #include <stddef.h>
  13 #include <assert.h>
  14
  15 #include "parse.h"
  16 #include "expression.h"
  17 #include "linearize.h"
  18 #include "flow.h"
  19 #include "target.h"
  20
  21 unsigned long bb_generation;
  22
  23 /*
  24  * Dammit, if we have a phi-node followed by a conditional
  25  * branch on that phi-node, we should damn well be able to
  26  * do something about the source. Maybe.
  27  */
  28 static int rewrite_branch(struct basic_block *bb,
  29         struct basic_block **ptr,
  30         struct basic_block *old,
  31         struct basic_block *new)
  32 {
  33         if (*ptr != old || new == old)
  34                 return 0;
  35
  36         /* We might find new if-conversions or non-dominating CSEs */
  37         repeat_phase |= REPEAT_CSE;
  38         *ptr = new;
  39         replace_bb_in_list(&bb->children, old, new, 1);
  40         remove_bb_from_list(&old->parents, bb, 1);
  41         add_bb(&new->parents, bb);
  42         return 1;
  43 }
  44
  45 /*
  46  * Return the known truth value of a pseudo, or -1 if
  47  * it's not known.
  48  */
  49 static int pseudo_truth_value(pseudo_t pseudo)
  50 {
  51         switch (pseudo->type) {
  52         case PSEUDO_VAL:
  53                 return !!pseudo->value;
  54
  55         case PSEUDO_REG: {
  56                 struct instruction *insn = pseudo->def;
  57
  58                 /* A symbol address is always considered true.. */
  59                 if (insn->opcode == OP_SYMADDR && insn->target == pseudo)
  60                         return 1;
  61         }
  62                 /* Fall through */
  63         default:
  64                 return -1;
  65         }
  66 }
  67
  68 /*
  69  * Does a basic block depend on the pseudos that "src" defines?
  70  */
  71 static int bb_depends_on(struct basic_block *target, struct basic_block *src)
  72 {
  73         pseudo_t pseudo;
  74
  75         FOR_EACH_PTR(src->defines, pseudo) {
  76                 if (pseudo_in_list(target->needs, pseudo))
  77                         return 1;
  78         } END_FOR_EACH_PTR(pseudo);
  79         return 0;
  80 }
  81
  82 /*
  83  * When we reach here, we have:
  84  *  - a basic block that ends in a conditional branch and
  85  *    that has no side effects apart from the pseudos it
  86  *    may change.
  87  *  - the phi-node that the conditional branch depends on
  88  *  - full pseudo liveness information
  89  *
  90  * We need to check if any of the _sources_ of the phi-node
  91  * may be constant, and not actually need this block at all.
  92  */
  93 static int try_to_simplify_bb(struct basic_block *bb, struct instruction *first, struct instruction *second)
  94 {
  95         int changed = 0;
  96         pseudo_t phi;
  97
  98         FOR_EACH_PTR(first->phi_list, phi) {
  99                 struct instruction *def = phi->def;
 100                 struct basic_block *source, *target;
 101                 pseudo_t pseudo;
 102                 struct instruction *br;
 103                 int true;
 104
 105                 if (!def)
 106                         continue;
 107                 source = def->bb;
 108                 pseudo = def->src1;
 109                 if (!pseudo || !source)
 110                         continue;
 111                 br = last_instruction(source->insns);
 112                 if (!br)
 113                         continue;
 114                 if (br->opcode != OP_BR)
 115                         continue;
 116                 true = pseudo_truth_value(pseudo);
 117                 if (true < 0)
 118                         continue;
 119                 target = true ? second->bb_true : second->bb_false;
 120                 if (bb_depends_on(target, bb))
 121                         continue;
 122                 changed |= rewrite_branch(source, &br->bb_true, bb, target);
 123                 changed |= rewrite_branch(source, &br->bb_false, bb, target);
 124         } END_FOR_EACH_PTR(phi);
 125         return changed;
 126 }
 127
 128 static int bb_has_side_effects(struct basic_block *bb)
 129 {
 130         struct instruction *insn;
 131         FOR_EACH_PTR(bb->insns, insn) {
 132                 switch (insn->opcode) {
 133                 case OP_CALL:
 134                         /* FIXME! This should take "const" etc into account */
 135                         return 1;
 136
 137                 case OP_STORE:
 138                 case OP_CONTEXT:
 139                         return 1;
 140
 141                 case OP_ASM:
 142                         /* FIXME! This should take "volatile" etc into account */
 143                         return 1;
 144
 145                 default:
 146                         continue;
 147                 }
 148         } END_FOR_EACH_PTR(insn);
 149         return 0;
 150 }
 151
 152 static int simplify_phi_branch(struct basic_block *bb, struct instruction *br)
 153 {
 154         pseudo_t cond = br->cond;
 155         struct instruction *def;
 156
 157         if (cond->type != PSEUDO_REG)
 158                 return 0;
 159         def = cond->def;
 160         if (def->bb != bb || def->opcode != OP_PHI)
 161                 return 0;
 162         if (bb_has_side_effects(bb))
 163                 return 0;
 164         return try_to_simplify_bb(bb, def, br);
 165 }
 166
 167 static int simplify_branch_branch(struct basic_block *bb, struct instruction *br,
 168         struct basic_block **target_p, int true)
 169 {
 170         struct basic_block *target = *target_p, *final;
 171         struct instruction *insn;
 172         int retval;
 173
 174         if (target == bb)
 175                 return 0;
 176         insn = last_instruction(target->insns);
 177         if (!insn || insn->opcode != OP_BR || insn->cond != br->cond)
 178                 return 0;
 179         /*
 180          * Ahhah! We've found a branch to a branch on the same conditional!
 181          * Now we just need to see if we can rewrite the branch..
 182          */
 183         retval = 0;
 184         final = true ? insn->bb_true : insn->bb_false;
 185         if (bb_has_side_effects(target))
 186                 goto try_to_rewrite_target;
 187         if (bb_depends_on(final, target))
 188                 goto try_to_rewrite_target;
 189         return rewrite_branch(bb, target_p, target, final);
 190
 191 try_to_rewrite_target:
 192         /*
 193          * If we're the only parent, at least we can rewrite the
 194          * now-known second branch.
 195          */
 196         if (bb_list_size(target->parents) != 1)
 197                 return retval;
 198         insert_branch(target, insn, final);
 199         kill_instruction(insn);
 200         return 1;
 201 }
 202
 203 static int simplify_one_branch(struct basic_block *bb, struct instruction *br)
 204 {
 205         if (simplify_phi_branch(bb, br))
 206                 return 1;
 207         return simplify_branch_branch(bb, br, &br->bb_true, 1) |
 208                simplify_branch_branch(bb, br, &br->bb_false, 0);
 209 }
 210
 211 static int simplify_branch_nodes(struct entrypoint *ep)
 212 {
 213         int changed = 0;
 214         struct basic_block *bb;
 215
 216         FOR_EACH_PTR(ep->bbs, bb) {
 217                 struct instruction *br = last_instruction(bb->insns);
 218
 219                 if (!br || br->opcode != OP_BR || !br->bb_false)
 220                         continue;
 221                 changed |= simplify_one_branch(bb, br);
 222         } END_FOR_EACH_PTR(bb);
 223         return changed;
 224 }
 225
 226 /*
 227  * This is called late - when we have intra-bb liveness information..
 228  */
 229 int simplify_flow(struct entrypoint *ep)
 230 {
 231         return simplify_branch_nodes(ep);
 232 }
 233
 234 static inline void concat_user_list(struct pseudo_user_list *src, struct pseudo_user_list **dst)
 235 {
 236         concat_ptr_list((struct ptr_list *)src, (struct ptr_list **)dst);
 237 }
 238
 239 void convert_instruction_target(struct instruction *insn, pseudo_t src)
 240 {
 241         pseudo_t target;
 242         struct pseudo_user *pu;
 243         /*
 244          * Go through the "insn->users" list and replace them all..
 245          */
 246         target = insn->target;
 247         if (target == src)
 248                 return;
 249         FOR_EACH_PTR(target->users, pu) {
 250                 if (*pu->userp != VOID) {
 251                         assert(*pu->userp == target);
 252                         *pu->userp = src;
 253                 }
 254         } END_FOR_EACH_PTR(pu);
 255         concat_user_list(target->users, &src->users);
 256         target->users = NULL;
 257 }
 258
 259 void convert_load_instruction(struct instruction *insn, pseudo_t src)
 260 {
 261         convert_instruction_target(insn, src);
 262         /* Turn the load into a no-op */
 263         insn->opcode = OP_LNOP;
 264         insn->bb = NULL;
 265 }
 266
 267 static int overlapping_memop(struct instruction *a, struct instruction *b)
 268 {
 269         unsigned int a_start = bytes_to_bits(a->offset);
 270         unsigned int b_start = bytes_to_bits(b->offset);
 271         unsigned int a_size = a->size;
 272         unsigned int b_size = b->size;
 273
 274         if (a_size + a_start <= b_start)
 275                 return 0;
 276         if (b_size + b_start <= a_start)
 277                 return 0;
 278         return 1;
 279 }
 280
 281 static inline int same_memop(struct instruction *a, struct instruction *b)
 282 {
 283         return  a->offset == b->offset && a->size == b->size;
 284 }
 285
 286 /*
 287  * Return 1 if "dom" dominates the access to "pseudo"
 288  * in "insn".
 289  *
 290  * Return 0 if it doesn't, and -1 if you don't know.
 291  */
 292 int dominates(pseudo_t pseudo, struct instruction *insn, struct instruction *dom, int local)
 293 {
 294         int opcode = dom->opcode;
 295
 296         if (opcode == OP_CALL || opcode == OP_ENTRY)
 297                 return local ? 0 : -1;
 298         if (opcode != OP_LOAD && opcode != OP_STORE)
 299                 return 0;
 300         if (dom->src != pseudo) {
 301                 if (local)
 302                         return 0;
 303                 /* We don't think two explicitly different symbols ever alias */
 304                 if (dom->src->type == PSEUDO_SYM)
 305                         return 0;
 306                 /* We could try to do some alias analysis here */
 307                 return -1;
 308         }
 309         if (!same_memop(insn, dom)) {
 310                 if (dom->opcode == OP_LOAD)
 311                         return 0;
 312                 if (!overlapping_memop(insn, dom))
 313                         return 0;
 314                 return -1;
 315         }
 316         return 1;
 317 }
 318
 319 static int phisrc_in_bb(struct pseudo_list *list, struct basic_block *bb)
 320 {
 321         pseudo_t p;
 322         FOR_EACH_PTR(list, p) {
 323                 if (p->def->bb == bb)
 324                         return 1;
 325         } END_FOR_EACH_PTR(p);
 326
 327         return 0;
 328 }
 329
 330 static int find_dominating_parents(pseudo_t pseudo, struct instruction *insn,
 331         struct basic_block *bb, unsigned long generation, struct pseudo_list **dominators,
 332         int local)
 333 {
 334         struct basic_block *parent;
 335
 336         if (!bb->parents)
 337                 return !!local;
 338
 339         FOR_EACH_PTR(bb->parents, parent) {
 340                 struct instruction *one;
 341                 struct instruction *br;
 342                 pseudo_t phi;
 343
 344                 FOR_EACH_PTR_REVERSE(parent->insns, one) {
 345                         int dominance;
 346                         if (one == insn)
 347                                 goto no_dominance;
 348                         dominance = dominates(pseudo, insn, one, local);
 349                         if (dominance < 0) {
 350                                 if (one->opcode == OP_LOAD)
 351                                         continue;
 352                                 return 0;
 353                         }
 354                         if (!dominance)
 355                                 continue;
 356                         goto found_dominator;
 357                 } END_FOR_EACH_PTR_REVERSE(one);
 358 no_dominance:
 359                 if (parent->generation == generation)
 360                         continue;
 361                 parent->generation = generation;
 362
 363                 if (!find_dominating_parents(pseudo, insn, parent, generation, dominators, local))
 364                         return 0;
 365                 continue;
 366
 367 found_dominator:
 368                 if (dominators && phisrc_in_bb(*dominators, parent))
 369                         continue;
 370                 br = delete_last_instruction(&parent->insns);
 371                 phi = alloc_phi(parent, one->target, one->size);
 372                 phi->ident = phi->ident ? : pseudo->ident;
 373                 add_instruction(&parent->insns, br);
 374                 use_pseudo(insn, phi, add_pseudo(dominators, phi));
 375         } END_FOR_EACH_PTR(parent);
 376         return 1;
 377 }
 378
 379 /*
 380  * We should probably sort the phi list just to make it easier to compare
 381  * later for equality.
 382  */
 383 void rewrite_load_instruction(struct instruction *insn, struct pseudo_list *dominators)
 384 {
 385         pseudo_t new, phi;
 386
 387         /*
 388          * Check for somewhat common case of duplicate
 389          * phi nodes.
 390          */
 391         new = first_pseudo(dominators)->def->src1;
 392         FOR_EACH_PTR(dominators, phi) {
 393                 if (new != phi->def->src1)
 394                         goto complex_phi;
 395                 new->ident = new->ident ? : phi->ident;
 396         } END_FOR_EACH_PTR(phi);
 397
 398         /*
 399          * All the same pseudo - mark the phi-nodes unused
 400          * and convert the load into a LNOP and replace the
 401          * pseudo.
 402          */
 403         FOR_EACH_PTR(dominators, phi) {
 404                 phi->def->bb = NULL;
 405         } END_FOR_EACH_PTR(phi);
 406         convert_load_instruction(insn, new);
 407         return;
 408
 409 complex_phi:
 410         /* We leave symbol pseudos with a bogus usage list here */
 411         if (insn->src->type != PSEUDO_SYM)
 412                 kill_use(&insn->src);
 413         insn->opcode = OP_PHI;
 414         insn->phi_list = dominators;
 415 }
 416
 417 static int find_dominating_stores(pseudo_t pseudo, struct instruction *insn,
 418         unsigned long generation, int local)
 419 {
 420         struct basic_block *bb = insn->bb;
 421         struct instruction *one, *dom = NULL;
 422         struct pseudo_list *dominators;
 423         int partial;
 424
 425         /* Unreachable load? Undo it */
 426         if (!bb) {
 427                 insn->opcode = OP_LNOP;
 428                 return 1;
 429         }
 430
 431         partial = 0;
 432         FOR_EACH_PTR(bb->insns, one) {
 433                 int dominance;
 434                 if (one == insn)
 435                         goto found;
 436                 dominance = dominates(pseudo, insn, one, local);
 437                 if (dominance < 0) {
 438                         /* Ignore partial load dominators */
 439                         if (one->opcode == OP_LOAD)
 440                                 continue;
 441                         dom = NULL;
 442                         partial = 1;
 443                         continue;
 444                 }
 445                 if (!dominance)
 446                         continue;
 447                 dom = one;
 448                 partial = 0;
 449         } END_FOR_EACH_PTR(one);
 450         /* Whaa? */
 451         warning(pseudo->sym->pos, "unable to find symbol read");
 452         return 0;
 453 found:
 454         if (partial)
 455                 return 0;
 456
 457         if (dom) {
 458                 convert_load_instruction(insn, dom->target);
 459                 return 1;
 460         }
 461
 462         /* OK, go find the parents */
 463         bb->generation = generation;
 464
 465         dominators = NULL;
 466         if (!find_dominating_parents(pseudo, insn, bb, generation, &dominators, local))
 467                 return 0;
 468
 469         /* This happens with initial assignments to structures etc.. */
 470         if (!dominators) {
 471                 if (!local)
 472                         return 0;
 473                 check_access(insn);
 474                 convert_load_instruction(insn, value_pseudo(0));
 475                 return 1;
 476         }
 477
 478         /*
 479          * If we find just one dominating instruction, we
 480          * can turn it into a direct thing. Otherwise we'll
 481          * have to turn the load into a phi-node of the
 482          * dominators.
 483          */
 484         rewrite_load_instruction(insn, dominators);
 485         return 1;
 486 }
 487
 488 static void kill_store(struct instruction *insn)
 489 {
 490         if (insn) {
 491                 insn->bb = NULL;
 492                 insn->opcode = OP_SNOP;
 493                 kill_use(&insn->target);
 494         }
 495 }
 496
 497 /* Kill a pseudo that is dead on exit from the bb */
 498 static void kill_dead_stores(pseudo_t pseudo, unsigned long generation, struct basic_block *bb, int local)
 499 {
 500         struct instruction *insn;
 501         struct basic_block *parent;
 502
 503         if (bb->generation == generation)
 504                 return;
 505         bb->generation = generation;
 506         FOR_EACH_PTR_REVERSE(bb->insns, insn) {
 507                 int opcode = insn->opcode;
 508
 509                 if (opcode != OP_LOAD && opcode != OP_STORE) {
 510                         if (local)
 511                                 continue;
 512                         if (opcode == OP_CALL)
 513                                 return;
 514                         continue;
 515                 }
 516                 if (insn->src == pseudo) {
 517                         if (opcode == OP_LOAD)
 518                                 return;
 519                         kill_store(insn);
 520                         continue;
 521                 }
 522                 if (local)
 523                         continue;
 524                 if (insn->src->type != PSEUDO_SYM)
 525                         return;
 526         } END_FOR_EACH_PTR_REVERSE(insn);
 527
 528         FOR_EACH_PTR(bb->parents, parent) {
 529                 struct basic_block *child;
 530                 FOR_EACH_PTR(parent->children, child) {
 531                         if (child && child != bb)
 532                                 return;
 533                 } END_FOR_EACH_PTR(child);
 534                 kill_dead_stores(pseudo, generation, parent, local);
 535         } END_FOR_EACH_PTR(parent);
 536 }
 537
 538 /*
 539  * This should see if the "insn" trivially dominates some previous store, and kill the
 540  * store if unnecessary.
 541  */
 542 static void kill_dominated_stores(pseudo_t pseudo, struct instruction *insn,
 543         unsigned long generation, struct basic_block *bb, int local, int found)
 544 {
 545         struct instruction *one;
 546         struct basic_block *parent;
 547
 548         /* Unreachable store? Undo it */
 549         if (!bb) {
 550                 kill_store(insn);
 551                 return;
 552         }
 553         if (bb->generation == generation)
 554                 return;
 555         bb->generation = generation;
 556         FOR_EACH_PTR_REVERSE(bb->insns, one) {
 557                 int dominance;
 558                 if (!found) {
 559                         if (one != insn)
 560                                 continue;
 561                         found = 1;
 562                         continue;
 563                 }
 564                 dominance = dominates(pseudo, insn, one, local);
 565                 if (!dominance)
 566                         continue;
 567                 if (dominance < 0)
 568                         return;
 569                 if (one->opcode == OP_LOAD)
 570                         return;
 571                 kill_store(one);
 572         } END_FOR_EACH_PTR_REVERSE(one);
 573
 574         if (!found) {
 575                 warning(bb->pos, "Unable to find instruction");
 576                 return;
 577         }
 578
 579         FOR_EACH_PTR(bb->parents, parent) {
 580                 struct basic_block *child;
 581                 FOR_EACH_PTR(parent->children, child) {
 582                         if (child && child != bb)
 583                                 return;
 584                 } END_FOR_EACH_PTR(child);
 585                 kill_dominated_stores(pseudo, insn, generation, parent, local, found);
 586         } END_FOR_EACH_PTR(parent);
 587 }
 588
 589 void check_access(struct instruction *insn)
 590 {
 591         pseudo_t pseudo = insn->src;
 592
 593         if (insn->bb && pseudo->type == PSEUDO_SYM) {
 594                 int offset = insn->offset, bit = bytes_to_bits(offset) + insn->size;
 595                 struct symbol *sym = pseudo->sym;
 596
 597                 if (sym->bit_size > 0 && (offset < 0 || bit > sym->bit_size))
 598                         warning(insn->pos, "invalid access %s '%s' (%d %d)",
 599                                 offset < 0 ? "below" : "past the end of",
 600                                 show_ident(sym->ident), offset,
 601                                 bits_to_bytes(sym->bit_size));
 602         }
 603 }
 604
 605 static void simplify_one_symbol(struct entrypoint *ep, struct symbol *sym)
 606 {
 607         pseudo_t pseudo, src;
 608         struct pseudo_user *pu;
 609         struct instruction *def;
 610         unsigned long mod;
 611         int all, stores, complex;
 612
 613         /* Never used as a symbol? */
 614         pseudo = sym->pseudo;
 615         if (!pseudo)
 616                 return;
 617
 618         /* We don't do coverage analysis of volatiles.. */
 619         if (sym->ctype.modifiers & MOD_VOLATILE)
 620                 return;
 621
 622         /* ..and symbols with external visibility need more care */
 623         mod = sym->ctype.modifiers & (MOD_NONLOCAL | MOD_STATIC | MOD_ADDRESSABLE);
 624         if (mod)
 625                 goto external_visibility;
 626
 627         def = NULL;
 628         stores = 0;
 629         complex = 0;
 630         FOR_EACH_PTR(pseudo->users, pu) {
 631                 /* We know that the symbol-pseudo use is the "src" in the instruction */
 632                 struct instruction *insn = pu->insn;
 633
 634                 switch (insn->opcode) {
 635                 case OP_STORE:
 636                         stores++;
 637                         def = insn;
 638                         break;
 639                 case OP_LOAD:
 640                         break;
 641                 case OP_SYMADDR:
 642                         if (!insn->bb)
 643                                 continue;
 644                         mod |= MOD_ADDRESSABLE;
 645                         goto external_visibility;
 646                 case OP_NOP:
 647                 case OP_SNOP:
 648                 case OP_LNOP:
 649                 case OP_PHI:
 650                         continue;
 651                 default:
 652                         warning(sym->pos, "symbol '%s' pseudo used in unexpected way", show_ident(sym->ident));
 653                 }
 654                 complex |= insn->offset;
 655         } END_FOR_EACH_PTR(pu);
 656
 657         if (complex)
 658                 goto complex_def;
 659         if (stores > 1)
 660                 goto multi_def;
 661
 662         /*
 663          * Goodie, we have a single store (if even that) in the whole
 664          * thing. Replace all loads with moves from the pseudo,
 665          * replace the store with a def.
 666          */
 667         src = VOID;
 668         if (def)
 669                 src = def->target;
 670
 671         FOR_EACH_PTR(pseudo->users, pu) {
 672                 struct instruction *insn = pu->insn;
 673                 if (insn->opcode == OP_LOAD) {
 674                         check_access(insn);
 675                         convert_load_instruction(insn, src);
 676                 }
 677         } END_FOR_EACH_PTR(pu);
 678
 679         /* Turn the store into a no-op */
 680         kill_store(def);
 681         return;
 682
 683 multi_def:
 684 complex_def:
 685 external_visibility:
 686         all = 1;
 687         FOR_EACH_PTR_REVERSE(pseudo->users, pu) {
 688                 struct instruction *insn = pu->insn;
 689                 if (insn->opcode == OP_LOAD)
 690                         all &= find_dominating_stores(pseudo, insn, ++bb_generation, !mod);
 691         } END_FOR_EACH_PTR_REVERSE(pu);
 692
 693         /* If we converted all the loads, remove the stores. They are dead */
 694         if (all && !mod) {
 695                 FOR_EACH_PTR(pseudo->users, pu) {
 696                         struct instruction *insn = pu->insn;
 697                         if (insn->opcode == OP_STORE)
 698                                 kill_store(insn);
 699                 } END_FOR_EACH_PTR(pu);
 700         } else {
 701                 /*
 702                  * If we couldn't take the shortcut, see if we can at least kill some
 703                  * of them..
 704                  */
 705                 FOR_EACH_PTR(pseudo->users, pu) {
 706                         struct instruction *insn = pu->insn;
 707                         if (insn->opcode == OP_STORE)
 708                                 kill_dominated_stores(pseudo, insn, ++bb_generation, insn->bb, !mod, 0);
 709                 } END_FOR_EACH_PTR(pu);
 710
 711                 if (!(mod & (MOD_NONLOCAL | MOD_STATIC))) {
 712                         struct basic_block *bb;
 713                         FOR_EACH_PTR(ep->bbs, bb) {
 714                                 if (!bb->children)
 715                                         kill_dead_stores(pseudo, ++bb_generation, bb, !mod);
 716                         } END_FOR_EACH_PTR(bb);
 717                 }
 718         }
 719
 720         return;
 721 }
 722
 723 void simplify_symbol_usage(struct entrypoint *ep)
 724 {
 725         pseudo_t pseudo;
 726
 727         FOR_EACH_PTR(ep->accesses, pseudo) {
 728                 simplify_one_symbol(ep, pseudo->sym);
 729         } END_FOR_EACH_PTR(pseudo);
 730 }
 731
 732 static void mark_bb_reachable(struct basic_block *bb, unsigned long generation)
 733 {
 734         struct basic_block *child;
 735
 736         if (bb->generation == generation)
 737                 return;
 738         bb->generation = generation;
 739         FOR_EACH_PTR(bb->children, child) {
 740                 mark_bb_reachable(child, generation);
 741         } END_FOR_EACH_PTR(child);
 742 }
 743
 744 static void kill_defs(struct instruction *insn)
 745 {
 746         pseudo_t target = insn->target;
 747
 748         if (!has_use_list(target))
 749                 return;
 750         if (target->def != insn)
 751                 return;
 752
 753         convert_instruction_target(insn, VOID);
 754 }
 755
 756 void kill_bb(struct basic_block *bb)
 757 {
 758         struct instruction *insn;
 759         struct basic_block *child, *parent;
 760
 761         FOR_EACH_PTR(bb->insns, insn) {
 762                 kill_instruction(insn);
 763                 kill_defs(insn);
 764                 /*
 765                  * We kill unreachable instructions even if they
 766                  * otherwise aren't "killable" (e.g. volatile loads)
 767                  */
 768                 insn->bb = NULL;
 769         } END_FOR_EACH_PTR(insn);
 770         bb->insns = NULL;
 771
 772         FOR_EACH_PTR(bb->children, child) {
 773                 remove_bb_from_list(&child->parents, bb, 0);
 774         } END_FOR_EACH_PTR(child);
 775         bb->children = NULL;
 776
 777         FOR_EACH_PTR(bb->parents, parent) {
 778                 remove_bb_from_list(&parent->children, bb, 0);
 779         } END_FOR_EACH_PTR(parent);
 780         bb->parents = NULL;
 781 }
 782
 783 void kill_unreachable_bbs(struct entrypoint *ep)
 784 {
 785         struct basic_block *bb;
 786         unsigned long generation = ++bb_generation;
 787
 788         mark_bb_reachable(ep->entry->bb, generation);
 789         FOR_EACH_PTR(ep->bbs, bb) {
 790                 if (bb->generation == generation)
 791                         continue;
 792                 /* Mark it as being dead */
 793                 kill_bb(bb);
 794                 bb->ep = NULL;
 795                 DELETE_CURRENT_PTR(bb);
 796         } END_FOR_EACH_PTR(bb);
 797         PACK_PTR_LIST(&ep->bbs);
 798 }
 799
 800 static int rewrite_parent_branch(struct basic_block *bb, struct basic_block *old, struct basic_block *new)
 801 {
 802         int changed = 0;
 803         struct instruction *insn = last_instruction(bb->insns);
 804
 805         if (!insn)
 806                 return 0;
 807
 808         /* Infinite loops: let's not "optimize" them.. */
 809         if (old == new)
 810                 return 0;
 811
 812         switch (insn->opcode) {
 813         case OP_BR:
 814                 changed |= rewrite_branch(bb, &insn->bb_true, old, new);
 815                 changed |= rewrite_branch(bb, &insn->bb_false, old, new);
 816                 assert(changed);
 817                 return changed;
 818         case OP_SWITCH: {
 819                 struct multijmp *jmp;
 820                 FOR_EACH_PTR(insn->multijmp_list, jmp) {
 821                         changed |= rewrite_branch(bb, &jmp->target, old, new);
 822                 } END_FOR_EACH_PTR(jmp);
 823                 assert(changed);
 824                 return changed;
 825         }
 826         default:
 827                 return 0;
 828         }
 829 }
 830
 831 static struct basic_block * rewrite_branch_bb(struct basic_block *bb, struct instruction *br)
 832 {
 833         struct basic_block *parent;
 834         struct basic_block *target = br->bb_true;
 835         struct basic_block *false = br->bb_false;
 836
 837         if (target && false) {
 838                 pseudo_t cond = br->cond;
 839                 if (cond->type != PSEUDO_VAL)
 840                         return NULL;
 841                 target = cond->value ? target : false;
 842         }
 843
 844         /*
 845          * We can't do FOR_EACH_PTR() here, because the parent list
 846          * may change when we rewrite the parent.
 847          */
 848         while ((parent = first_basic_block(bb->parents)) != NULL) {
 849                 if (!rewrite_parent_branch(parent, bb, target))
 850                         return NULL;
 851         }
 852         return target;
 853 }
 854
 855 static void vrfy_bb_in_list(struct basic_block *bb, struct basic_block_list *list)
 856 {
 857         if (bb) {
 858                 struct basic_block *tmp;
 859                 int no_bb_in_list = 0;
 860
 861                 FOR_EACH_PTR(list, tmp) {
 862                         if (bb == tmp)
 863                                 return;
 864                 } END_FOR_EACH_PTR(tmp);
 865                 assert(no_bb_in_list);
 866         }
 867 }
 868
 869 static void vrfy_parents(struct basic_block *bb)
 870 {
 871         struct basic_block *tmp;
 872         FOR_EACH_PTR(bb->parents, tmp) {
 873                 vrfy_bb_in_list(bb, tmp->children);
 874         } END_FOR_EACH_PTR(tmp);
 875 }
 876
 877 static void vrfy_children(struct basic_block *bb)
 878 {
 879         struct basic_block *tmp;
 880         struct instruction *br = last_instruction(bb->insns);
 881
 882         if (!br) {
 883                 assert(!bb->children);
 884                 return;
 885         }
 886         switch (br->opcode) {
 887                 struct multijmp *jmp;
 888         case OP_BR:
 889                 vrfy_bb_in_list(br->bb_true, bb->children);
 890                 vrfy_bb_in_list(br->bb_false, bb->children);
 891                 break;
 892         case OP_SWITCH:
 893         case OP_COMPUTEDGOTO:
 894                 FOR_EACH_PTR(br->multijmp_list, jmp) {
 895                         vrfy_bb_in_list(jmp->target, bb->children);
 896                 } END_FOR_EACH_PTR(jmp);
 897                 break;
 898         default:
 899                 break;
 900         }
 901
 902         FOR_EACH_PTR(bb->children, tmp) {
 903                 vrfy_bb_in_list(bb, tmp->parents);
 904         } END_FOR_EACH_PTR(tmp);
 905 }
 906
 907 static void vrfy_bb_flow(struct basic_block *bb)
 908 {
 909         vrfy_children(bb);
 910         vrfy_parents(bb);
 911 }
 912
 913 void vrfy_flow(struct entrypoint *ep)
 914 {
 915         struct basic_block *bb;
 916         struct basic_block *entry = ep->entry->bb;
 917
 918         FOR_EACH_PTR(ep->bbs, bb) {
 919                 if (bb == entry)
 920                         entry = NULL;
 921                 vrfy_bb_flow(bb);
 922         } END_FOR_EACH_PTR(bb);
 923         assert(!entry);
 924 }
 925
 926 void pack_basic_blocks(struct entrypoint *ep)
 927 {
 928         struct basic_block *bb;
 929
 930         /* See if we can merge a bb into another one.. */
 931         FOR_EACH_PTR(ep->bbs, bb) {
 932                 struct instruction *first, *insn;
 933                 struct basic_block *parent, *child, *last;
 934
 935                 if (!bb_reachable(bb))
 936                         continue;
 937
 938                 /*
 939                  * Just a branch?
 940                  */
 941                 FOR_EACH_PTR(bb->insns, first) {
 942                         if (!first->bb)
 943                                 continue;
 944                         switch (first->opcode) {
 945                         case OP_NOP: case OP_LNOP: case OP_SNOP:
 946                                 continue;
 947                         case OP_BR: {
 948                                 struct basic_block *replace;
 949                                 replace = rewrite_branch_bb(bb, first);
 950                                 if (replace) {
 951                                         kill_bb(bb);
 952                                         goto no_merge;
 953                                 }
 954                         }
 955                         /* fallthrough */
 956                         default:
 957                                 goto out;
 958                         }
 959                 } END_FOR_EACH_PTR(first);
 960
 961 out:
 962                 /*
 963                  * See if we only have one parent..
 964                  */
 965                 last = NULL;
 966                 FOR_EACH_PTR(bb->parents, parent) {
 967                         if (last) {
 968                                 if (last != parent)
 969                                         goto no_merge;
 970                                 continue;
 971                         }
 972                         last = parent;
 973                 } END_FOR_EACH_PTR(parent);
 974
 975                 parent = last;
 976                 if (!parent || parent == bb)
 977                         continue;
 978
 979                 /*
 980                  * Goodie. See if the parent can merge..
 981                  */
 982                 FOR_EACH_PTR(parent->children, child) {
 983                         if (child != bb)
 984                                 goto no_merge;
 985                 } END_FOR_EACH_PTR(child);
 986
 987                 /*
 988                  * Merge the two.
 989                  */
 990                 repeat_phase |= REPEAT_CSE;
 991
 992                 parent->children = bb->children;
 993                 bb->children = NULL;
 994                 bb->parents = NULL;
 995
 996                 FOR_EACH_PTR(parent->children, child) {
 997                         replace_bb_in_list(&child->parents, bb, parent, 0);
 998                 } END_FOR_EACH_PTR(child);
 999
1000                 kill_instruction(delete_last_instruction(&parent->insns));
1001                 FOR_EACH_PTR(bb->insns, insn) {
1002                         if (insn->bb) {
1003                                 assert(insn->bb == bb);
1004                                 insn->bb = parent;
1005                         }
1006                         add_instruction(&parent->insns, insn);
1007                 } END_FOR_EACH_PTR(insn);
1008                 bb->insns = NULL;
1009
1010         no_merge:
1011                 /* nothing to do */;
1012         } END_FOR_EACH_PTR(bb);
1013 }
1014
1015