gcc/sched-ebb.c

   1 /* Instruction scheduling pass.
   2    Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   3    1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
   4    Free Software Foundation, Inc.
   5    Contributed by Michael Tiemann (tiemann@cygnus.com) Enhanced by,
   6    and currently maintained by, Jim Wilson (wilson@cygnus.com)
   7
   8 This file is part of GCC.
   9
  10 GCC is free software; you can redistribute it and/or modify it under
  11 the terms of the GNU General Public License as published by the Free
  12 Software Foundation; either version 3, or (at your option) any later
  13 version.
  14
  15 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  16 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  17 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  18 for more details.
  19
  20 You should have received a copy of the GNU General Public License
  21 along with GCC; see the file COPYING3.  If not see
  22 <http://www.gnu.org/licenses/>.  */
  23 \f
  24 #include "config.h"
  25 #include "system.h"
  26 #include "coretypes.h"
  27 #include "tm.h"
  28 #include "toplev.h"
  29 #include "rtl.h"
  30 #include "tm_p.h"
  31 #include "hard-reg-set.h"
  32 #include "regs.h"
  33 #include "function.h"
  34 #include "flags.h"
  35 #include "insn-config.h"
  36 #include "insn-attr.h"
  37 #include "except.h"
  38 #include "toplev.h"
  39 #include "recog.h"
  40 #include "cfglayout.h"
  41 #include "params.h"
  42 #include "sched-int.h"
  43 #include "target.h"
  44 #include "output.h"
  45
  46 \f
  47 /* The number of insns scheduled so far.  */
  48 static int sched_n_insns;
  49
  50 /* The number of insns to be scheduled in total.  */
  51 static int n_insns;
  52
  53 /* Set of blocks, that already have their dependencies calculated.  */
  54 static bitmap_head dont_calc_deps;
  55
  56 /* Last basic block in current ebb.  */
  57 static basic_block last_bb;
  58
  59 /* Implementations of the sched_info functions for region scheduling.  */
  60 static void init_ready_list (void);
  61 static void begin_schedule_ready (rtx, rtx);
  62 static int schedule_more_p (void);
  63 static const char *ebb_print_insn (rtx, int);
  64 static int rank (rtx, rtx);
  65 static int contributes_to_priority (rtx, rtx);
  66 static void compute_jump_reg_dependencies (rtx, regset, regset, regset);
  67 static basic_block earliest_block_with_similiar_load (basic_block, rtx);
  68 static void add_deps_for_risky_insns (rtx, rtx);
  69 static basic_block schedule_ebb (rtx, rtx);
  70
  71 static void add_remove_insn (rtx, int);
  72 static void add_block1 (basic_block, basic_block);
  73 static basic_block advance_target_bb (basic_block, rtx);
  74 static void fix_recovery_cfg (int, int, int);
  75
  76 /* Return nonzero if there are more insns that should be scheduled.  */
  77
  78 static int
  79 schedule_more_p (void)
  80 {
  81   return sched_n_insns < n_insns;
  82 }
  83
  84 /* Print dependency information about ebb between HEAD and TAIL.  */
  85 static void
  86 debug_ebb_dependencies (rtx head, rtx tail)
  87 {
  88   fprintf (sched_dump,
  89            ";;   --------------- forward dependences: ------------ \n");
  90
  91   fprintf (sched_dump, "\n;;   --- EBB Dependences --- from bb%d to bb%d \n",
  92            BLOCK_NUM (head), BLOCK_NUM (tail));
  93
  94   debug_dependencies (head, tail);
  95 }
  96
  97 /* Add all insns that are initially ready to the ready list READY.  Called
  98    once before scheduling a set of insns.  */
  99
 100 static void
 101 init_ready_list (void)
 102 {
 103   int n = 0;
 104   rtx prev_head = current_sched_info->prev_head;
 105   rtx next_tail = current_sched_info->next_tail;
 106   rtx insn;
 107
 108   sched_n_insns = 0;
 109
 110   /* Print debugging information.  */
 111   if (sched_verbose >= 5)
 112     debug_ebb_dependencies (NEXT_INSN (prev_head), PREV_INSN (next_tail));
 113
 114   /* Initialize ready list with all 'ready' insns in target block.
 115      Count number of insns in the target block being scheduled.  */
 116   for (insn = NEXT_INSN (prev_head); insn != next_tail; insn = NEXT_INSN (insn))
 117     {
 118       try_ready (insn);
 119       n++;
 120     }
 121
 122   gcc_assert (n == n_insns);
 123 }
 124
 125 /* INSN is being scheduled after LAST.  Update counters.  */
 126 static void
 127 begin_schedule_ready (rtx insn, rtx last)
 128 {
 129   sched_n_insns++;
 130
 131   if (BLOCK_FOR_INSN (insn) == last_bb
 132       /* INSN is a jump in the last block, ...  */
 133       && control_flow_insn_p (insn)
 134       /* that is going to be moved over some instructions.  */
 135       && last != PREV_INSN (insn))
 136     {
 137       edge e;
 138       edge_iterator ei;
 139       basic_block bb;
 140
 141       /* An obscure special case, where we do have partially dead
 142          instruction scheduled after last control flow instruction.
 143          In this case we can create new basic block.  It is
 144          always exactly one basic block last in the sequence.  */
 145
 146       FOR_EACH_EDGE (e, ei, last_bb->succs)
 147         if (e->flags & EDGE_FALLTHRU)
 148           break;
 149
 150 #ifdef ENABLE_CHECKING
 151       gcc_assert (!e || !(e->flags & EDGE_COMPLEX));
 152
 153       gcc_assert (BLOCK_FOR_INSN (insn) == last_bb
 154                   && !IS_SPECULATION_CHECK_P (insn)
 155                   && BB_HEAD (last_bb) != insn
 156                   && BB_END (last_bb) == insn);
 157
 158       {
 159         rtx x;
 160
 161         x = NEXT_INSN (insn);
 162         if (e)
 163           gcc_assert (NOTE_P (x) || LABEL_P (x));
 164         else
 165           gcc_assert (BARRIER_P (x));
 166       }
 167 #endif
 168
 169       if (e)
 170         {
 171           bb = split_edge (e);
 172           gcc_assert (NOTE_INSN_BASIC_BLOCK_P (BB_END (bb)));
 173         }
 174       else
 175         /* Create an empty unreachable block after the INSN.  */
 176         bb = create_basic_block (NEXT_INSN (insn), NULL_RTX, last_bb);
 177
 178       /* split_edge () creates BB before E->DEST.  Keep in mind, that
 179          this operation extends scheduling region till the end of BB.
 180          Hence, we need to shift NEXT_TAIL, so haifa-sched.c won't go out
 181          of the scheduling region.  */
 182       current_sched_info->next_tail = NEXT_INSN (BB_END (bb));
 183       gcc_assert (current_sched_info->next_tail);
 184
 185       add_block (bb, last_bb);
 186       gcc_assert (last_bb == bb);
 187     }
 188 }
 189
 190 /* Return a string that contains the insn uid and optionally anything else
 191    necessary to identify this insn in an output.  It's valid to use a
 192    static buffer for this.  The ALIGNED parameter should cause the string
 193    to be formatted so that multiple output lines will line up nicely.  */
 194
 195 static const char *
 196 ebb_print_insn (rtx insn, int aligned ATTRIBUTE_UNUSED)
 197 {
 198   static char tmp[80];
 199
 200   sprintf (tmp, "%4d", INSN_UID (insn));
 201   return tmp;
 202 }
 203
 204 /* Compare priority of two insns.  Return a positive number if the second
 205    insn is to be preferred for scheduling, and a negative one if the first
 206    is to be preferred.  Zero if they are equally good.  */
 207
 208 static int
 209 rank (rtx insn1, rtx insn2)
 210 {
 211   basic_block bb1 = BLOCK_FOR_INSN (insn1);
 212   basic_block bb2 = BLOCK_FOR_INSN (insn2);
 213
 214   if (bb1->count > bb2->count
 215       || bb1->frequency > bb2->frequency)
 216     return -1;
 217   if (bb1->count < bb2->count
 218       || bb1->frequency < bb2->frequency)
 219     return 1;
 220   return 0;
 221 }
 222
 223 /* NEXT is an instruction that depends on INSN (a backward dependence);
 224    return nonzero if we should include this dependence in priority
 225    calculations.  */
 226
 227 static int
 228 contributes_to_priority (rtx next ATTRIBUTE_UNUSED,
 229                          rtx insn ATTRIBUTE_UNUSED)
 230 {
 231   return 1;
 232 }
 233
 234  /* INSN is a JUMP_INSN, COND_SET is the set of registers that are
 235     conditionally set before INSN.  Store the set of registers that
 236     must be considered as used by this jump in USED and that of
 237     registers that must be considered as set in SET.  */
 238
 239 static void
 240 compute_jump_reg_dependencies (rtx insn, regset cond_set, regset used,
 241                                regset set)
 242 {
 243   basic_block b = BLOCK_FOR_INSN (insn);
 244   edge e;
 245   edge_iterator ei;
 246
 247   FOR_EACH_EDGE (e, ei, b->succs)
 248     if (e->flags & EDGE_FALLTHRU)
 249       /* The jump may be a by-product of a branch that has been merged
 250          in the main codepath after being conditionalized.  Therefore
 251          it may guard the fallthrough block from using a value that has
 252          conditionally overwritten that of the main codepath.  So we
 253          consider that it restores the value of the main codepath.  */
 254       bitmap_and (set, df_get_live_in (e->dest), cond_set);
 255     else
 256       bitmap_ior_into (used, df_get_live_in (e->dest));
 257 }
 258
 259 /* Used in schedule_insns to initialize current_sched_info for scheduling
 260    regions (or single basic blocks).  */
 261
 262 static struct sched_info ebb_sched_info =
 263 {
 264   init_ready_list,
 265   NULL,
 266   schedule_more_p,
 267   NULL,
 268   rank,
 269   ebb_print_insn,
 270   contributes_to_priority,
 271   compute_jump_reg_dependencies,
 272
 273   NULL, NULL,
 274   NULL, NULL,
 275   0, 1, 0,
 276
 277   add_remove_insn,
 278   begin_schedule_ready,
 279   add_block1,
 280   advance_target_bb,
 281   fix_recovery_cfg,
 282   SCHED_EBB
 283   /* We can create new blocks in begin_schedule_ready ().  */
 284   | NEW_BBS
 285 };
 286 \f
 287 /* Returns the earliest block in EBB currently being processed where a
 288    "similar load" 'insn2' is found, and hence LOAD_INSN can move
 289    speculatively into the found block.  All the following must hold:
 290
 291    (1) both loads have 1 base register (PFREE_CANDIDATEs).
 292    (2) load_insn and load2 have a def-use dependence upon
 293    the same insn 'insn1'.
 294
 295    From all these we can conclude that the two loads access memory
 296    addresses that differ at most by a constant, and hence if moving
 297    load_insn would cause an exception, it would have been caused by
 298    load2 anyhow.
 299
 300    The function uses list (given by LAST_BLOCK) of already processed
 301    blocks in EBB.  The list is formed in `add_deps_for_risky_insns'.  */
 302
 303 static basic_block
 304 earliest_block_with_similiar_load (basic_block last_block, rtx load_insn)
 305 {
 306   dep_link_t back_link;
 307   basic_block bb, earliest_block = NULL;
 308
 309   FOR_EACH_DEP_LINK (back_link, INSN_BACK_DEPS (load_insn))
 310     {
 311       rtx insn1 = DEP_LINK_PRO (back_link);
 312
 313       if (DEP_LINK_KIND (back_link) == REG_DEP_TRUE)
 314         {
 315           /* Found a DEF-USE dependence (insn1, load_insn).  */
 316           dep_link_t fore_link;
 317
 318           FOR_EACH_DEP_LINK (fore_link, INSN_FORW_DEPS (insn1))
 319             {
 320               rtx insn2 = DEP_LINK_CON (fore_link);
 321               basic_block insn2_block = BLOCK_FOR_INSN (insn2);
 322
 323               if (DEP_LINK_KIND (fore_link) == REG_DEP_TRUE)
 324                 {
 325                   if (earliest_block != NULL
 326                       && earliest_block->index < insn2_block->index)
 327                     continue;
 328
 329                   /* Found a DEF-USE dependence (insn1, insn2).  */
 330                   if (haifa_classify_insn (insn2) != PFREE_CANDIDATE)
 331                     /* insn2 not guaranteed to be a 1 base reg load.  */
 332                     continue;
 333
 334                   for (bb = last_block; bb; bb = bb->aux)
 335                     if (insn2_block == bb)
 336                       break;
 337
 338                   if (!bb)
 339                     /* insn2 is the similar load.  */
 340                     earliest_block = insn2_block;
 341                 }
 342             }
 343         }
 344     }
 345
 346   return earliest_block;
 347 }
 348
 349 /* The following function adds dependencies between jumps and risky
 350    insns in given ebb.  */
 351
 352 static void
 353 add_deps_for_risky_insns (rtx head, rtx tail)
 354 {
 355   rtx insn, prev;
 356   int class;
 357   rtx last_jump = NULL_RTX;
 358   rtx next_tail = NEXT_INSN (tail);
 359   basic_block last_block = NULL, bb;
 360
 361   for (insn = head; insn != next_tail; insn = NEXT_INSN (insn))
 362     if (control_flow_insn_p (insn))
 363       {
 364         bb = BLOCK_FOR_INSN (insn);
 365         bb->aux = last_block;
 366         last_block = bb;
 367         last_jump = insn;
 368       }
 369     else if (INSN_P (insn) && last_jump != NULL_RTX)
 370       {
 371         class = haifa_classify_insn (insn);
 372         prev = last_jump;
 373         switch (class)
 374           {
 375           case PFREE_CANDIDATE:
 376             if (flag_schedule_speculative_load)
 377               {
 378                 bb = earliest_block_with_similiar_load (last_block, insn);
 379                 if (bb)
 380                   {
 381                     bb = bb->aux;
 382                     if (!bb)
 383                       break;
 384                     prev = BB_END (bb);
 385                   }
 386               }
 387             /* Fall through.  */
 388           case TRAP_RISKY:
 389           case IRISKY:
 390           case PRISKY_CANDIDATE:
 391             /* ??? We could implement better checking PRISKY_CANDIDATEs
 392                analogous to sched-rgn.c.  */
 393             /* We can not change the mode of the backward
 394                dependency because REG_DEP_ANTI has the lowest
 395                rank.  */
 396             if (! sched_insns_conditions_mutex_p (insn, prev))
 397               {
 398                 if (!(current_sched_info->flags & DO_SPECULATION))
 399                   {
 400                     enum DEPS_ADJUST_RESULT res;
 401
 402                     res = add_or_update_back_dep (insn, prev,
 403                                                   REG_DEP_ANTI, DEP_ANTI);
 404
 405                     if (res == DEP_CREATED)
 406                       add_forw_dep (DEPS_LIST_FIRST (INSN_BACK_DEPS (insn)));
 407                     else
 408                       gcc_assert (res != DEP_CHANGED);
 409                   }
 410                 else
 411                   add_or_update_back_forw_dep (insn, prev, REG_DEP_ANTI,
 412                                                set_dep_weak (DEP_ANTI,
 413                                                              BEGIN_CONTROL,
 414                                                              MAX_DEP_WEAK));
 415               }
 416
 417             break;
 418
 419           default:
 420             break;
 421           }
 422       }
 423   /* Maintain the invariant that bb->aux is clear after use.  */
 424   while (last_block)
 425     {
 426       bb = last_block->aux;
 427       last_block->aux = NULL;
 428       last_block = bb;
 429     }
 430 }
 431
 432 /* Schedule a single extended basic block, defined by the boundaries HEAD
 433    and TAIL.  */
 434
 435 static basic_block
 436 schedule_ebb (rtx head, rtx tail)
 437 {
 438   basic_block first_bb, target_bb;
 439   struct deps tmp_deps;
 440
 441   first_bb = BLOCK_FOR_INSN (head);
 442   last_bb = BLOCK_FOR_INSN (tail);
 443
 444   if (no_real_insns_p (head, tail))
 445     return BLOCK_FOR_INSN (tail);
 446
 447   gcc_assert (INSN_P (head) && INSN_P (tail));
 448
 449   if (!bitmap_bit_p (&dont_calc_deps, first_bb->index))
 450     {
 451       init_deps_global ();
 452
 453       /* Compute backward dependencies.  */
 454       init_deps (&tmp_deps);
 455       sched_analyze (&tmp_deps, head, tail);
 456       free_deps (&tmp_deps);
 457
 458       /* Compute forward dependencies.  */
 459       compute_forward_dependences (head, tail);
 460
 461       add_deps_for_risky_insns (head, tail);
 462
 463       if (targetm.sched.dependencies_evaluation_hook)
 464         targetm.sched.dependencies_evaluation_hook (head, tail);
 465
 466       finish_deps_global ();
 467     }
 468   else
 469     /* Only recovery blocks can have their dependencies already calculated,
 470        and they always are single block ebbs.  */
 471     gcc_assert (first_bb == last_bb);
 472
 473   /* Set priorities.  */
 474   current_sched_info->sched_max_insns_priority = 0;
 475   n_insns = set_priorities (head, tail);
 476   current_sched_info->sched_max_insns_priority++;
 477
 478   current_sched_info->prev_head = PREV_INSN (head);
 479   current_sched_info->next_tail = NEXT_INSN (tail);
 480
 481   /* rm_other_notes only removes notes which are _inside_ the
 482      block---that is, it won't remove notes before the first real insn
 483      or after the last real insn of the block.  So if the first insn
 484      has a REG_SAVE_NOTE which would otherwise be emitted before the
 485      insn, it is redundant with the note before the start of the
 486      block, and so we have to take it out.  */
 487   if (INSN_P (head))
 488     {
 489       rtx note;
 490
 491       for (note = REG_NOTES (head); note; note = XEXP (note, 1))
 492         if (REG_NOTE_KIND (note) == REG_SAVE_NOTE)
 493           remove_note (head, note);
 494     }
 495
 496   /* Remove remaining note insns from the block, save them in
 497      note_list.  These notes are restored at the end of
 498      schedule_block ().  */
 499   rm_other_notes (head, tail);
 500
 501   unlink_bb_notes (first_bb, last_bb);
 502
 503   current_sched_info->queue_must_finish_empty = 1;
 504
 505   target_bb = first_bb;
 506   schedule_block (&target_bb, n_insns);
 507
 508   /* We might pack all instructions into fewer blocks,
 509      so we may made some of them empty.  Can't assert (b == last_bb).  */
 510
 511   /* Sanity check: verify that all region insns were scheduled.  */
 512   gcc_assert (sched_n_insns == n_insns);
 513   head = current_sched_info->head;
 514   tail = current_sched_info->tail;
 515
 516   if (EDGE_COUNT (last_bb->preds) == 0)
 517     /* LAST_BB is unreachable.  */
 518     {
 519       gcc_assert (first_bb != last_bb
 520                   && EDGE_COUNT (last_bb->succs) == 0);
 521       last_bb = last_bb->prev_bb;
 522       delete_basic_block (last_bb->next_bb);
 523     }
 524
 525   return last_bb;
 526 }
 527
 528 /* The one entry point in this file.  */
 529
 530 void
 531 schedule_ebbs (void)
 532 {
 533   basic_block bb;
 534   int probability_cutoff;
 535   rtx tail;
 536
 537   if (profile_info && flag_branch_probabilities)
 538     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
 539   else
 540     probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
 541   probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
 542
 543   /* Taking care of this degenerate case makes the rest of
 544      this code simpler.  */
 545   if (n_basic_blocks == NUM_FIXED_BLOCKS)
 546     return;
 547
 548   /* We need current_sched_info in init_dependency_caches, which is
 549      invoked via sched_init.  */
 550   current_sched_info = &ebb_sched_info;
 551
 552   df_set_flags (DF_LR_RUN_DCE);
 553   df_note_add_problem ();
 554   df_analyze ();
 555   df_clear_flags (DF_LR_RUN_DCE);
 556   regstat_compute_calls_crossed ();
 557   sched_init ();
 558
 559   compute_bb_for_insn ();
 560
 561   /* Initialize DONT_CALC_DEPS and ebb-{start, end} markers.  */
 562   bitmap_initialize (&dont_calc_deps, 0);
 563   bitmap_clear (&dont_calc_deps);
 564
 565   /* Schedule every region in the subroutine.  */
 566   FOR_EACH_BB (bb)
 567     {
 568       rtx head = BB_HEAD (bb);
 569
 570       for (;;)
 571         {
 572           edge e;
 573           edge_iterator ei;
 574           tail = BB_END (bb);
 575           if (bb->next_bb == EXIT_BLOCK_PTR
 576               || LABEL_P (BB_HEAD (bb->next_bb)))
 577             break;
 578           FOR_EACH_EDGE (e, ei, bb->succs)
 579             if ((e->flags & EDGE_FALLTHRU) != 0)
 580               break;
 581           if (! e)
 582             break;
 583           if (e->probability <= probability_cutoff)
 584             break;
 585           bb = bb->next_bb;
 586         }
 587
 588       /* Blah.  We should fix the rest of the code not to get confused by
 589          a note or two.  */
 590       while (head != tail)
 591         {
 592           if (NOTE_P (head))
 593             head = NEXT_INSN (head);
 594           else if (NOTE_P (tail))
 595             tail = PREV_INSN (tail);
 596           else if (LABEL_P (head))
 597             head = NEXT_INSN (head);
 598           else
 599             break;
 600         }
 601
 602       bb = schedule_ebb (head, tail);
 603     }
 604   bitmap_clear (&dont_calc_deps);
 605
 606   /* Reposition the prologue and epilogue notes in case we moved the
 607      prologue/epilogue insns.  */
 608   if (reload_completed)
 609     reposition_prologue_and_epilogue_notes ();
 610
 611   sched_finish ();
 612   regstat_free_calls_crossed ();
 613 }
 614
 615 /* INSN has been added to/removed from current ebb.  */
 616 static void
 617 add_remove_insn (rtx insn ATTRIBUTE_UNUSED, int remove_p)
 618 {
 619   if (!remove_p)
 620     n_insns++;
 621   else
 622     n_insns--;
 623 }
 624
 625 /* BB was added to ebb after AFTER.  */
 626 static void
 627 add_block1 (basic_block bb, basic_block after)
 628 {
 629   /* Recovery blocks are always bounded by BARRIERS,
 630      therefore, they always form single block EBB,
 631      therefore, we can use rec->index to identify such EBBs.  */
 632   if (after == EXIT_BLOCK_PTR)
 633     bitmap_set_bit (&dont_calc_deps, bb->index);
 634   else if (after == last_bb)
 635     last_bb = bb;
 636 }
 637
 638 /* Return next block in ebb chain.  For parameter meaning please refer to
 639    sched-int.h: struct sched_info: advance_target_bb.  */
 640 static basic_block
 641 advance_target_bb (basic_block bb, rtx insn)
 642 {
 643   if (insn)
 644     {
 645       if (BLOCK_FOR_INSN (insn) != bb
 646           && control_flow_insn_p (insn)
 647           /* We handle interblock movement of the speculation check
 648              or over a speculation check in
 649              haifa-sched.c: move_block_after_check ().  */
 650           && !IS_SPECULATION_BRANCHY_CHECK_P (insn)
 651           && !IS_SPECULATION_BRANCHY_CHECK_P (BB_END (bb)))
 652         {
 653           /* Assert that we don't move jumps across blocks.  */
 654           gcc_assert (!control_flow_insn_p (BB_END (bb))
 655                       && NOTE_INSN_BASIC_BLOCK_P (BB_HEAD (bb->next_bb)));
 656           return bb;
 657         }
 658       else
 659         return 0;
 660     }
 661   else
 662     /* Return next non empty block.  */
 663     {
 664       do
 665         {
 666           gcc_assert (bb != last_bb);
 667
 668           bb = bb->next_bb;
 669         }
 670       while (bb_note (bb) == BB_END (bb));
 671
 672       return bb;
 673     }
 674 }
 675
 676 /* Fix internal data after interblock movement of jump instruction.
 677    For parameter meaning please refer to
 678    sched-int.h: struct sched_info: fix_recovery_cfg.  */
 679 static void
 680 fix_recovery_cfg (int bbi ATTRIBUTE_UNUSED, int jump_bbi, int jump_bb_nexti)
 681 {
 682   gcc_assert (last_bb->index != bbi);
 683
 684   if (jump_bb_nexti == last_bb->index)
 685     last_bb = BASIC_BLOCK (jump_bbi);
 686 }