gcc/cfgbuild.c

   1 /* Control flow graph building code for GNU compiler.
   2    Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   3    1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 2, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING.  If not, write to the Free
  19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  20 02110-1301, USA.  */
  21
  22 /* find_basic_blocks divides the current function's rtl into basic
  23    blocks and constructs the CFG.  The blocks are recorded in the
  24    basic_block_info array; the CFG exists in the edge structures
  25    referenced by the blocks.
  26
  27    find_basic_blocks also finds any unreachable loops and deletes them.
  28
  29    Available functionality:
  30      - CFG construction
  31          find_basic_blocks  */
  32 \f
  33 #include "config.h"
  34 #include "system.h"
  35 #include "coretypes.h"
  36 #include "tm.h"
  37 #include "tree.h"
  38 #include "rtl.h"
  39 #include "hard-reg-set.h"
  40 #include "basic-block.h"
  41 #include "regs.h"
  42 #include "flags.h"
  43 #include "output.h"
  44 #include "function.h"
  45 #include "except.h"
  46 #include "toplev.h"
  47 #include "timevar.h"
  48
  49 static int count_basic_blocks (rtx);
  50 static void find_basic_blocks_1 (rtx);
  51 static void make_edges (basic_block, basic_block, int);
  52 static void make_label_edge (sbitmap, basic_block, rtx, int);
  53 static void find_bb_boundaries (basic_block);
  54 static void compute_outgoing_frequencies (basic_block);
  55 \f
  56 /* Return true if insn is something that should be contained inside basic
  57    block.  */
  58
  59 bool
  60 inside_basic_block_p (rtx insn)
  61 {
  62   switch (GET_CODE (insn))
  63     {
  64     case CODE_LABEL:
  65       /* Avoid creating of basic block for jumptables.  */
  66       return (NEXT_INSN (insn) == 0
  67               || !JUMP_P (NEXT_INSN (insn))
  68               || (GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_VEC
  69                   && GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_DIFF_VEC));
  70
  71     case JUMP_INSN:
  72       return (GET_CODE (PATTERN (insn)) != ADDR_VEC
  73               && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);
  74
  75     case CALL_INSN:
  76     case INSN:
  77       return true;
  78
  79     case BARRIER:
  80     case NOTE:
  81       return false;
  82
  83     default:
  84       gcc_unreachable ();
  85     }
  86 }
  87
  88 /* Return true if INSN may cause control flow transfer, so it should be last in
  89    the basic block.  */
  90
  91 bool
  92 control_flow_insn_p (rtx insn)
  93 {
  94   rtx note;
  95
  96   switch (GET_CODE (insn))
  97     {
  98     case NOTE:
  99     case CODE_LABEL:
 100       return false;
 101
 102     case JUMP_INSN:
 103       /* Jump insn always causes control transfer except for tablejumps.  */
 104       return (GET_CODE (PATTERN (insn)) != ADDR_VEC
 105               && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);
 106
 107     case CALL_INSN:
 108       /* Noreturn and sibling call instructions terminate the basic blocks
 109          (but only if they happen unconditionally).  */
 110       if ((SIBLING_CALL_P (insn)
 111            || find_reg_note (insn, REG_NORETURN, 0))
 112           && GET_CODE (PATTERN (insn)) != COND_EXEC)
 113         return true;
 114       /* Call insn may return to the nonlocal goto handler.  */
 115       return ((nonlocal_goto_handler_labels
 116                && (0 == (note = find_reg_note (insn, REG_EH_REGION,
 117                                                NULL_RTX))
 118                    || INTVAL (XEXP (note, 0)) >= 0))
 119               /* Or may trap.  */
 120               || can_throw_internal (insn));
 121
 122     case INSN:
 123       /* Treat trap instructions like noreturn calls (same provision).  */
 124       if (GET_CODE (PATTERN (insn)) == TRAP_IF
 125           && XEXP (PATTERN (insn), 0) == const1_rtx)
 126         return true;
 127
 128       return (flag_non_call_exceptions && can_throw_internal (insn));
 129
 130     case BARRIER:
 131       /* It is nonsense to reach barrier when looking for the
 132          end of basic block, but before dead code is eliminated
 133          this may happen.  */
 134       return false;
 135
 136     default:
 137       gcc_unreachable ();
 138     }
 139 }
 140
 141 /* Count the basic blocks of the function.  */
 142
 143 static int
 144 count_basic_blocks (rtx f)
 145 {
 146   int count = NUM_FIXED_BLOCKS;
 147   bool saw_insn = false;
 148   rtx insn;
 149
 150   for (insn = f; insn; insn = NEXT_INSN (insn))
 151     {
 152       /* Code labels and barriers causes current basic block to be
 153          terminated at previous real insn.  */
 154       if ((LABEL_P (insn) || BARRIER_P (insn))
 155           && saw_insn)
 156         count++, saw_insn = false;
 157
 158       /* Start basic block if needed.  */
 159       if (!saw_insn && inside_basic_block_p (insn))
 160         saw_insn = true;
 161
 162       /* Control flow insn causes current basic block to be terminated.  */
 163       if (saw_insn && control_flow_insn_p (insn))
 164         count++, saw_insn = false;
 165     }
 166
 167   if (saw_insn)
 168     count++;
 169
 170   /* The rest of the compiler works a bit smoother when we don't have to
 171      check for the edge case of do-nothing functions with no basic blocks.  */
 172   if (count == NUM_FIXED_BLOCKS)
 173     {
 174       emit_insn (gen_rtx_USE (VOIDmode, const0_rtx));
 175       count = NUM_FIXED_BLOCKS + 1;
 176     }
 177
 178   return count;
 179 }
 180 \f
 181 /* Create an edge between two basic blocks.  FLAGS are auxiliary information
 182    about the edge that is accumulated between calls.  */
 183
 184 /* Create an edge from a basic block to a label.  */
 185
 186 static void
 187 make_label_edge (sbitmap edge_cache, basic_block src, rtx label, int flags)
 188 {
 189   gcc_assert (LABEL_P (label));
 190
 191   /* If the label was never emitted, this insn is junk, but avoid a
 192      crash trying to refer to BLOCK_FOR_INSN (label).  This can happen
 193      as a result of a syntax error and a diagnostic has already been
 194      printed.  */
 195
 196   if (INSN_UID (label) == 0)
 197     return;
 198
 199   cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
 200 }
 201
 202 /* Create the edges generated by INSN in REGION.  */
 203
 204 void
 205 rtl_make_eh_edge (sbitmap edge_cache, basic_block src, rtx insn)
 206 {
 207   int is_call = CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0;
 208   rtx handlers, i;
 209
 210   handlers = reachable_handlers (insn);
 211
 212   for (i = handlers; i; i = XEXP (i, 1))
 213     make_label_edge (edge_cache, src, XEXP (i, 0),
 214                      EDGE_ABNORMAL | EDGE_EH | is_call);
 215
 216   free_INSN_LIST_list (&handlers);
 217 }
 218
 219 /* States of basic block as seen by find_many_sub_basic_blocks.  */
 220 enum state {
 221   /* Basic blocks created via split_block belong to this state.
 222      make_edges will examine these basic blocks to see if we need to
 223      create edges going out of them.  */
 224   BLOCK_NEW = 0,
 225
 226   /* Basic blocks that do not need examining belong to this state.
 227      These blocks will be left intact.  In particular, make_edges will
 228      not create edges going out of these basic blocks.  */
 229   BLOCK_ORIGINAL,
 230
 231   /* Basic blocks that may need splitting (due to a label appearing in
 232      the middle, etc) belong to this state.  After splitting them,
 233      make_edges will create edges going out of them as needed.  */
 234   BLOCK_TO_SPLIT
 235 };
 236
 237 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
 238 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
 239
 240 /* Used internally by purge_dead_tablejump_edges, ORed into state.  */
 241 #define BLOCK_USED_BY_TABLEJUMP         32
 242 #define FULL_STATE(BB) ((size_t) (BB)->aux)
 243
 244 /* Identify the edges going out of basic blocks between MIN and MAX,
 245    inclusive, that have their states set to BLOCK_NEW or
 246    BLOCK_TO_SPLIT.
 247
 248    UPDATE_P should be nonzero if we are updating CFG and zero if we
 249    are building CFG from scratch.  */
 250
 251 static void
 252 make_edges (basic_block min, basic_block max, int update_p)
 253 {
 254   basic_block bb;
 255   sbitmap edge_cache = NULL;
 256
 257   /* Heavy use of computed goto in machine-generated code can lead to
 258      nearly fully-connected CFGs.  In that case we spend a significant
 259      amount of time searching the edge lists for duplicates.  */
 260   if (forced_labels || cfun->max_jumptable_ents > 100)
 261     edge_cache = sbitmap_alloc (last_basic_block);
 262
 263   /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
 264      is always the entry.  */
 265   if (min == ENTRY_BLOCK_PTR->next_bb)
 266     make_edge (ENTRY_BLOCK_PTR, min, EDGE_FALLTHRU);
 267
 268   FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
 269     {
 270       rtx insn, x;
 271       enum rtx_code code;
 272       edge e;
 273       edge_iterator ei;
 274
 275       if (STATE (bb) == BLOCK_ORIGINAL)
 276         continue;
 277
 278       /* If we have an edge cache, cache edges going out of BB.  */
 279       if (edge_cache)
 280         {
 281           sbitmap_zero (edge_cache);
 282           if (update_p)
 283             {
 284               FOR_EACH_EDGE (e, ei, bb->succs)
 285                 if (e->dest != EXIT_BLOCK_PTR)
 286                   SET_BIT (edge_cache, e->dest->index);
 287             }
 288         }
 289
 290       if (LABEL_P (BB_HEAD (bb))
 291           && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))
 292         cached_make_edge (NULL, ENTRY_BLOCK_PTR, bb, 0);
 293
 294       /* Examine the last instruction of the block, and discover the
 295          ways we can leave the block.  */
 296
 297       insn = BB_END (bb);
 298       code = GET_CODE (insn);
 299
 300       /* A branch.  */
 301       if (code == JUMP_INSN)
 302         {
 303           rtx tmp;
 304
 305           /* Recognize exception handling placeholders.  */
 306           if (GET_CODE (PATTERN (insn)) == RESX)
 307             rtl_make_eh_edge (edge_cache, bb, insn);
 308
 309           /* Recognize a non-local goto as a branch outside the
 310              current function.  */
 311           else if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
 312             ;
 313
 314           /* Recognize a tablejump and do the right thing.  */
 315           else if (tablejump_p (insn, NULL, &tmp))
 316             {
 317               rtvec vec;
 318               int j;
 319
 320               if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)
 321                 vec = XVEC (PATTERN (tmp), 0);
 322               else
 323                 vec = XVEC (PATTERN (tmp), 1);
 324
 325               for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
 326                 make_label_edge (edge_cache, bb,
 327                                  XEXP (RTVEC_ELT (vec, j), 0), 0);
 328
 329               /* Some targets (eg, ARM) emit a conditional jump that also
 330                  contains the out-of-range target.  Scan for these and
 331                  add an edge if necessary.  */
 332               if ((tmp = single_set (insn)) != NULL
 333                   && SET_DEST (tmp) == pc_rtx
 334                   && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
 335                   && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
 336                 make_label_edge (edge_cache, bb,
 337                                  XEXP (XEXP (SET_SRC (tmp), 2), 0), 0);
 338             }
 339
 340           /* If this is a computed jump, then mark it as reaching
 341              everything on the forced_labels list.  */
 342           else if (computed_jump_p (insn))
 343             {
 344               for (x = forced_labels; x; x = XEXP (x, 1))
 345                 make_label_edge (edge_cache, bb, XEXP (x, 0), EDGE_ABNORMAL);
 346             }
 347
 348           /* Returns create an exit out.  */
 349           else if (returnjump_p (insn))
 350             cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, 0);
 351
 352           /* Otherwise, we have a plain conditional or unconditional jump.  */
 353           else
 354             {
 355               gcc_assert (JUMP_LABEL (insn));
 356               make_label_edge (edge_cache, bb, JUMP_LABEL (insn), 0);
 357             }
 358         }
 359
 360       /* If this is a sibling call insn, then this is in effect a combined call
 361          and return, and so we need an edge to the exit block.  No need to
 362          worry about EH edges, since we wouldn't have created the sibling call
 363          in the first place.  */
 364       if (code == CALL_INSN && SIBLING_CALL_P (insn))
 365         cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR,
 366                           EDGE_SIBCALL | EDGE_ABNORMAL);
 367
 368       /* If this is a CALL_INSN, then mark it as reaching the active EH
 369          handler for this CALL_INSN.  If we're handling non-call
 370          exceptions then any insn can reach any of the active handlers.
 371          Also mark the CALL_INSN as reaching any nonlocal goto handler.  */
 372       else if (code == CALL_INSN || flag_non_call_exceptions)
 373         {
 374           /* Add any appropriate EH edges.  */
 375           rtl_make_eh_edge (edge_cache, bb, insn);
 376
 377           if (code == CALL_INSN && nonlocal_goto_handler_labels)
 378             {
 379               /* ??? This could be made smarter: in some cases it's possible
 380                  to tell that certain calls will not do a nonlocal goto.
 381                  For example, if the nested functions that do the nonlocal
 382                  gotos do not have their addresses taken, then only calls to
 383                  those functions or to other nested functions that use them
 384                  could possibly do nonlocal gotos.  */
 385
 386               /* We do know that a REG_EH_REGION note with a value less
 387                  than 0 is guaranteed not to perform a non-local goto.  */
 388               rtx note = find_reg_note (insn, REG_EH_REGION, NULL_RTX);
 389
 390               if (!note || INTVAL (XEXP (note, 0)) >=  0)
 391                 for (x = nonlocal_goto_handler_labels; x; x = XEXP (x, 1))
 392                   make_label_edge (edge_cache, bb, XEXP (x, 0),
 393                                    EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
 394             }
 395         }
 396
 397       /* Find out if we can drop through to the next block.  */
 398       insn = NEXT_INSN (insn);
 399       e = find_edge (bb, EXIT_BLOCK_PTR);
 400       if (e && e->flags & EDGE_FALLTHRU)
 401         insn = NULL;
 402
 403       while (insn
 404              && NOTE_P (insn)
 405              && NOTE_LINE_NUMBER (insn) != NOTE_INSN_BASIC_BLOCK)
 406         insn = NEXT_INSN (insn);
 407
 408       if (!insn)
 409         cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU);
 410       else if (bb->next_bb != EXIT_BLOCK_PTR)
 411         {
 412           if (insn == BB_HEAD (bb->next_bb))
 413             cached_make_edge (edge_cache, bb, bb->next_bb, EDGE_FALLTHRU);
 414         }
 415     }
 416
 417   if (edge_cache)
 418     sbitmap_vector_free (edge_cache);
 419 }
 420 \f
 421 /* Find all basic blocks of the function whose first insn is F.
 422
 423    Collect and return a list of labels whose addresses are taken.  This
 424    will be used in make_edges for use with computed gotos.  */
 425
 426 static void
 427 find_basic_blocks_1 (rtx f)
 428 {
 429   rtx insn, next;
 430   rtx bb_note = NULL_RTX;
 431   rtx head = NULL_RTX;
 432   rtx end = NULL_RTX;
 433   basic_block prev = ENTRY_BLOCK_PTR;
 434
 435   /* We process the instructions in a slightly different way than we did
 436      previously.  This is so that we see a NOTE_BASIC_BLOCK after we have
 437      closed out the previous block, so that it gets attached at the proper
 438      place.  Since this form should be equivalent to the previous,
 439      count_basic_blocks continues to use the old form as a check.  */
 440
 441   for (insn = f; insn; insn = next)
 442     {
 443       enum rtx_code code = GET_CODE (insn);
 444
 445       next = NEXT_INSN (insn);
 446
 447       if ((LABEL_P (insn) || BARRIER_P (insn))
 448           && head)
 449         {
 450           prev = create_basic_block_structure (head, end, bb_note, prev);
 451           head = end = NULL_RTX;
 452           bb_note = NULL_RTX;
 453         }
 454
 455       if (inside_basic_block_p (insn))
 456         {
 457           if (head == NULL_RTX)
 458             head = insn;
 459           end = insn;
 460         }
 461
 462       if (head && control_flow_insn_p (insn))
 463         {
 464           prev = create_basic_block_structure (head, end, bb_note, prev);
 465           head = end = NULL_RTX;
 466           bb_note = NULL_RTX;
 467         }
 468
 469       switch (code)
 470         {
 471         case NOTE:
 472           {
 473             int kind = NOTE_LINE_NUMBER (insn);
 474
 475             /* Look for basic block notes with which to keep the
 476                basic_block_info pointers stable.  Unthread the note now;
 477                we'll put it back at the right place in create_basic_block.
 478                Or not at all if we've already found a note in this block.  */
 479             if (kind == NOTE_INSN_BASIC_BLOCK)
 480               {
 481                 if (bb_note == NULL_RTX)
 482                   bb_note = insn;
 483                 else
 484                   next = delete_insn (insn);
 485               }
 486             break;
 487           }
 488
 489         case CODE_LABEL:
 490         case JUMP_INSN:
 491         case CALL_INSN:
 492         case INSN:
 493         case BARRIER:
 494           break;
 495
 496         default:
 497           gcc_unreachable ();
 498         }
 499     }
 500
 501   if (head != NULL_RTX)
 502     create_basic_block_structure (head, end, bb_note, prev);
 503   else if (bb_note)
 504     delete_insn (bb_note);
 505
 506   gcc_assert (last_basic_block == n_basic_blocks);
 507
 508   clear_aux_for_blocks ();
 509 }
 510
 511
 512 /* Find basic blocks of the current function.
 513    F is the first insn of the function.  */
 514
 515 void
 516 find_basic_blocks (rtx f)
 517 {
 518   basic_block bb;
 519
 520   timevar_push (TV_CFG);
 521
 522   /* Flush out existing data.  */
 523   if (basic_block_info != NULL)
 524     {
 525       clear_edges ();
 526
 527       /* Clear bb->aux on all extant basic blocks.  We'll use this as a
 528          tag for reuse during create_basic_block, just in case some pass
 529          copies around basic block notes improperly.  */
 530       FOR_EACH_BB (bb)
 531         bb->aux = NULL;
 532
 533       basic_block_info = NULL;
 534     }
 535
 536   n_basic_blocks = count_basic_blocks (f);
 537   last_basic_block = NUM_FIXED_BLOCKS;
 538   ENTRY_BLOCK_PTR->next_bb = EXIT_BLOCK_PTR;
 539   EXIT_BLOCK_PTR->prev_bb = ENTRY_BLOCK_PTR;
 540
 541
 542   /* Size the basic block table.  The actual structures will be allocated
 543      by find_basic_blocks_1, since we want to keep the structure pointers
 544      stable across calls to find_basic_blocks.  */
 545   /* ??? This whole issue would be much simpler if we called find_basic_blocks
 546      exactly once, and thereafter we don't have a single long chain of
 547      instructions at all until close to the end of compilation when we
 548      actually lay them out.  */
 549
 550   basic_block_info = VEC_alloc (basic_block, gc, n_basic_blocks);
 551   VEC_safe_grow_cleared (basic_block, gc, basic_block_info, n_basic_blocks);
 552   SET_BASIC_BLOCK (ENTRY_BLOCK, ENTRY_BLOCK_PTR);
 553   SET_BASIC_BLOCK (EXIT_BLOCK, EXIT_BLOCK_PTR);
 554
 555   find_basic_blocks_1 (f);
 556
 557   profile_status = PROFILE_ABSENT;
 558
 559   /* Tell make_edges to examine every block for out-going edges.  */
 560   FOR_EACH_BB (bb)
 561     SET_STATE (bb, BLOCK_NEW);
 562
 563   /* Discover the edges of our cfg.  */
 564   make_edges (ENTRY_BLOCK_PTR->next_bb, EXIT_BLOCK_PTR->prev_bb, 0);
 565
 566   /* Do very simple cleanup now, for the benefit of code that runs between
 567      here and cleanup_cfg, e.g. thread_prologue_and_epilogue_insns.  */
 568   tidy_fallthru_edges ();
 569
 570 #ifdef ENABLE_CHECKING
 571   verify_flow_info ();
 572 #endif
 573   timevar_pop (TV_CFG);
 574 }
 575 \f
 576 static void
 577 mark_tablejump_edge (rtx label)
 578 {
 579   basic_block bb;
 580
 581   gcc_assert (LABEL_P (label));
 582   /* See comment in make_label_edge.  */
 583   if (INSN_UID (label) == 0)
 584     return;
 585   bb = BLOCK_FOR_INSN (label);
 586   SET_STATE (bb, FULL_STATE (bb) | BLOCK_USED_BY_TABLEJUMP);
 587 }
 588
 589 static void
 590 purge_dead_tablejump_edges (basic_block bb, rtx table)
 591 {
 592   rtx insn = BB_END (bb), tmp;
 593   rtvec vec;
 594   int j;
 595   edge_iterator ei;
 596   edge e;
 597
 598   if (GET_CODE (PATTERN (table)) == ADDR_VEC)
 599     vec = XVEC (PATTERN (table), 0);
 600   else
 601     vec = XVEC (PATTERN (table), 1);
 602
 603   for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
 604     mark_tablejump_edge (XEXP (RTVEC_ELT (vec, j), 0));
 605
 606   /* Some targets (eg, ARM) emit a conditional jump that also
 607      contains the out-of-range target.  Scan for these and
 608      add an edge if necessary.  */
 609   if ((tmp = single_set (insn)) != NULL
 610        && SET_DEST (tmp) == pc_rtx
 611        && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
 612        && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
 613     mark_tablejump_edge (XEXP (XEXP (SET_SRC (tmp), 2), 0));
 614
 615   for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
 616     {
 617       if (FULL_STATE (e->dest) & BLOCK_USED_BY_TABLEJUMP)
 618         SET_STATE (e->dest, FULL_STATE (e->dest)
 619                             & ~(size_t) BLOCK_USED_BY_TABLEJUMP);
 620       else if (!(e->flags & (EDGE_ABNORMAL | EDGE_EH)))
 621         {
 622           remove_edge (e);
 623           continue;
 624         }
 625       ei_next (&ei);
 626     }
 627 }
 628
 629 /* Scan basic block BB for possible BB boundaries inside the block
 630    and create new basic blocks in the progress.  */
 631
 632 static void
 633 find_bb_boundaries (basic_block bb)
 634 {
 635   basic_block orig_bb = bb;
 636   rtx insn = BB_HEAD (bb);
 637   rtx end = BB_END (bb);
 638   rtx table;
 639   rtx flow_transfer_insn = NULL_RTX;
 640   edge fallthru = NULL;
 641
 642   if (insn == BB_END (bb))
 643     return;
 644
 645   if (LABEL_P (insn))
 646     insn = NEXT_INSN (insn);
 647
 648   /* Scan insn chain and try to find new basic block boundaries.  */
 649   while (1)
 650     {
 651       enum rtx_code code = GET_CODE (insn);
 652
 653       /* On code label, split current basic block.  */
 654       if (code == CODE_LABEL)
 655         {
 656           fallthru = split_block (bb, PREV_INSN (insn));
 657           if (flow_transfer_insn)
 658             BB_END (bb) = flow_transfer_insn;
 659
 660           bb = fallthru->dest;
 661           remove_edge (fallthru);
 662           flow_transfer_insn = NULL_RTX;
 663           if (LABEL_ALT_ENTRY_P (insn))
 664             make_edge (ENTRY_BLOCK_PTR, bb, 0);
 665         }
 666
 667       /* In case we've previously seen an insn that effects a control
 668          flow transfer, split the block.  */
 669       if (flow_transfer_insn && inside_basic_block_p (insn))
 670         {
 671           fallthru = split_block (bb, PREV_INSN (insn));
 672           BB_END (bb) = flow_transfer_insn;
 673           bb = fallthru->dest;
 674           remove_edge (fallthru);
 675           flow_transfer_insn = NULL_RTX;
 676         }
 677
 678       if (control_flow_insn_p (insn))
 679         flow_transfer_insn = insn;
 680       if (insn == end)
 681         break;
 682       insn = NEXT_INSN (insn);
 683     }
 684
 685   /* In case expander replaced normal insn by sequence terminating by
 686      return and barrier, or possibly other sequence not behaving like
 687      ordinary jump, we need to take care and move basic block boundary.  */
 688   if (flow_transfer_insn)
 689     BB_END (bb) = flow_transfer_insn;
 690
 691   /* We've possibly replaced the conditional jump by conditional jump
 692      followed by cleanup at fallthru edge, so the outgoing edges may
 693      be dead.  */
 694   purge_dead_edges (bb);
 695
 696   /* purge_dead_edges doesn't handle tablejump's, but if we have split the
 697      basic block, we might need to kill some edges.  */
 698   if (bb != orig_bb && tablejump_p (BB_END (bb), NULL, &table))
 699     purge_dead_tablejump_edges (bb, table);
 700 }
 701
 702 /*  Assume that frequency of basic block B is known.  Compute frequencies
 703     and probabilities of outgoing edges.  */
 704
 705 static void
 706 compute_outgoing_frequencies (basic_block b)
 707 {
 708   edge e, f;
 709   edge_iterator ei;
 710
 711   if (EDGE_COUNT (b->succs) == 2)
 712     {
 713       rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);
 714       int probability;
 715
 716       if (note)
 717         {
 718           probability = INTVAL (XEXP (note, 0));
 719           e = BRANCH_EDGE (b);
 720           e->probability = probability;
 721           e->count = ((b->count * probability + REG_BR_PROB_BASE / 2)
 722                       / REG_BR_PROB_BASE);
 723           f = FALLTHRU_EDGE (b);
 724           f->probability = REG_BR_PROB_BASE - probability;
 725           f->count = b->count - e->count;
 726           return;
 727         }
 728     }
 729
 730   if (single_succ_p (b))
 731     {
 732       e = single_succ_edge (b);
 733       e->probability = REG_BR_PROB_BASE;
 734       e->count = b->count;
 735       return;
 736     }
 737   guess_outgoing_edge_probabilities (b);
 738   if (b->count)
 739     FOR_EACH_EDGE (e, ei, b->succs)
 740       e->count = ((b->count * e->probability + REG_BR_PROB_BASE / 2)
 741                   / REG_BR_PROB_BASE);
 742 }
 743
 744 /* Assume that some pass has inserted labels or control flow
 745    instructions within a basic block.  Split basic blocks as needed
 746    and create edges.  */
 747
 748 void
 749 find_many_sub_basic_blocks (sbitmap blocks)
 750 {
 751   basic_block bb, min, max;
 752
 753   FOR_EACH_BB (bb)
 754     SET_STATE (bb,
 755                TEST_BIT (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);
 756
 757   FOR_EACH_BB (bb)
 758     if (STATE (bb) == BLOCK_TO_SPLIT)
 759       find_bb_boundaries (bb);
 760
 761   FOR_EACH_BB (bb)
 762     if (STATE (bb) != BLOCK_ORIGINAL)
 763       break;
 764
 765   min = max = bb;
 766   for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)
 767     if (STATE (bb) != BLOCK_ORIGINAL)
 768       max = bb;
 769
 770   /* Now re-scan and wire in all edges.  This expect simple (conditional)
 771      jumps at the end of each new basic blocks.  */
 772   make_edges (min, max, 1);
 773
 774   /* Update branch probabilities.  Expect only (un)conditional jumps
 775      to be created with only the forward edges.  */
 776   if (profile_status != PROFILE_ABSENT)
 777     FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
 778       {
 779         edge e;
 780         edge_iterator ei;
 781
 782         if (STATE (bb) == BLOCK_ORIGINAL)
 783           continue;
 784         if (STATE (bb) == BLOCK_NEW)
 785           {
 786             bb->count = 0;
 787             bb->frequency = 0;
 788             FOR_EACH_EDGE (e, ei, bb->preds)
 789               {
 790                 bb->count += e->count;
 791                 bb->frequency += EDGE_FREQUENCY (e);
 792               }
 793           }
 794
 795         compute_outgoing_frequencies (bb);
 796       }
 797
 798   FOR_EACH_BB (bb)
 799     SET_STATE (bb, 0);
 800 }