* testsuite/26_numerics/headers/cmath/hypot.cc: XFAIL on AIX.

[official-gcc.git] / gcc / cfgcleanup.c

/* Control flow optimization code for GNU compiler.
   Copyright (C) 1987-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

/* This file contains optimizer of the control flow.  The main entry point is
   cleanup_cfg.  Following optimizations are performed:

   - Unreachable blocks removal
   - Edge forwarding (edge to the forwarder block is forwarded to its
     successor.  Simplification of the branch instruction is performed by
     underlying infrastructure so branch can be converted to simplejump or
     eliminated).
   - Cross jumping (tail merging)
   - Conditional jump-around-simplejump simplification
   - Basic block merging.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "target.h"
#include "rtl.h"
#include "tree.h"
#include "cfghooks.h"
#include "df.h"
#include "memmodel.h"
#include "tm_p.h"
#include "insn-config.h"
#include "emit-rtl.h"
#include "cselib.h"
#include "params.h"
#include "tree-pass.h"
#include "cfgloop.h"
#include "cfgrtl.h"
#include "cfganal.h"
#include "cfgbuild.h"
#include "cfgcleanup.h"
#include "dce.h"
#include "dbgcnt.h"
#include "rtl-iter.h"

#define FORWARDER_BLOCK_P(BB) ((BB)->flags & BB_FORWARDER_BLOCK)

/* Set to true when we are running first pass of try_optimize_cfg loop.  */
static bool first_pass;

/* Set to true if crossjumps occurred in the latest run of try_optimize_cfg.  */
static bool crossjumps_occured;

/* Set to true if we couldn't run an optimization due to stale liveness
   information; we should run df_analyze to enable more opportunities.  */
static bool block_was_dirty;

static bool try_crossjump_to_edge (int, edge, edge, enum replace_direction);
static bool try_crossjump_bb (int, basic_block);
static bool outgoing_edges_match (int, basic_block, basic_block);
static enum replace_direction old_insns_match_p (int, rtx_insn *, rtx_insn *);

static void merge_blocks_move_predecessor_nojumps (basic_block, basic_block);
static void merge_blocks_move_successor_nojumps (basic_block, basic_block);
static bool try_optimize_cfg (int);
static bool try_simplify_condjump (basic_block);
static bool try_forward_edges (int, basic_block);
static edge thread_jump (edge, basic_block);
static bool mark_effect (rtx, bitmap);
static void notice_new_block (basic_block);
static void update_forwarder_flag (basic_block);
static void merge_memattrs (rtx, rtx);
\f
/* Set flags for newly created block.  */

static void
notice_new_block (basic_block bb)
{
  if (!bb)
    return;

  if (forwarder_block_p (bb))
    bb->flags |= BB_FORWARDER_BLOCK;
}

/* Recompute forwarder flag after block has been modified.  */

static void
update_forwarder_flag (basic_block bb)
{
  if (forwarder_block_p (bb))
    bb->flags |= BB_FORWARDER_BLOCK;
  else
    bb->flags &= ~BB_FORWARDER_BLOCK;
}
\f
/* Simplify a conditional jump around an unconditional jump.
   Return true if something changed.  */

static bool
try_simplify_condjump (basic_block cbranch_block)
{
  basic_block jump_block, jump_dest_block, cbranch_dest_block;
  edge cbranch_jump_edge, cbranch_fallthru_edge;
  rtx_insn *cbranch_insn;

  /* Verify that there are exactly two successors.  */
  if (EDGE_COUNT (cbranch_block->succs) != 2)
    return false;

  /* Verify that we've got a normal conditional branch at the end
     of the block.  */
  cbranch_insn = BB_END (cbranch_block);
  if (!any_condjump_p (cbranch_insn))
    return false;

  cbranch_fallthru_edge = FALLTHRU_EDGE (cbranch_block);
  cbranch_jump_edge = BRANCH_EDGE (cbranch_block);

  /* The next block must not have multiple predecessors, must not
     be the last block in the function, and must contain just the
     unconditional jump.  */
  jump_block = cbranch_fallthru_edge->dest;
  if (!single_pred_p (jump_block)
      || jump_block->next_bb == EXIT_BLOCK_PTR_FOR_FN (cfun)
      || !FORWARDER_BLOCK_P (jump_block))
    return false;
  jump_dest_block = single_succ (jump_block);

  /* If we are partitioning hot/cold basic blocks, we don't want to
     mess up unconditional or indirect jumps that cross between hot
     and cold sections.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (BB_PARTITION (jump_block) != BB_PARTITION (jump_dest_block)
      || (cbranch_jump_edge->flags & EDGE_CROSSING))
    return false;

  /* The conditional branch must target the block after the
     unconditional branch.  */
  cbranch_dest_block = cbranch_jump_edge->dest;

  if (cbranch_dest_block == EXIT_BLOCK_PTR_FOR_FN (cfun)
      || jump_dest_block == EXIT_BLOCK_PTR_FOR_FN (cfun)
      || !can_fallthru (jump_block, cbranch_dest_block))
    return false;

  /* Invert the conditional branch.  */
  if (!invert_jump (as_a <rtx_jump_insn *> (cbranch_insn),
                    block_label (jump_dest_block), 0))
    return false;

  if (dump_file)
    fprintf (dump_file, "Simplifying condjump %i around jump %i\n",
             INSN_UID (cbranch_insn), INSN_UID (BB_END (jump_block)));

  /* Success.  Update the CFG to match.  Note that after this point
     the edge variable names appear backwards; the redirection is done
     this way to preserve edge profile data.  */
  cbranch_jump_edge = redirect_edge_succ_nodup (cbranch_jump_edge,
                                                cbranch_dest_block);
  cbranch_fallthru_edge = redirect_edge_succ_nodup (cbranch_fallthru_edge,
                                                    jump_dest_block);
  cbranch_jump_edge->flags |= EDGE_FALLTHRU;
  cbranch_fallthru_edge->flags &= ~EDGE_FALLTHRU;
  update_br_prob_note (cbranch_block);

  /* Delete the block with the unconditional jump, and clean up the mess.  */
  delete_basic_block (jump_block);
  tidy_fallthru_edge (cbranch_jump_edge);
  update_forwarder_flag (cbranch_block);

  return true;
}
\f
/* Attempt to prove that operation is NOOP using CSElib or mark the effect
   on register.  Used by jump threading.  */

static bool
mark_effect (rtx exp, regset nonequal)
{
  rtx dest;
  switch (GET_CODE (exp))
    {
      /* In case we do clobber the register, mark it as equal, as we know the
         value is dead so it don't have to match.  */
    case CLOBBER:
      dest = XEXP (exp, 0);
      if (REG_P (dest))
        bitmap_clear_range (nonequal, REGNO (dest), REG_NREGS (dest));
      return false;

    case SET:
      if (rtx_equal_for_cselib_p (SET_DEST (exp), SET_SRC (exp)))
        return false;
      dest = SET_DEST (exp);
      if (dest == pc_rtx)
        return false;
      if (!REG_P (dest))
        return true;
      bitmap_set_range (nonequal, REGNO (dest), REG_NREGS (dest));
      return false;

    default:
      return false;
    }
}

/* Return true if X contains a register in NONEQUAL.  */
static bool
mentions_nonequal_regs (const_rtx x, regset nonequal)
{
  subrtx_iterator::array_type array;
  FOR_EACH_SUBRTX (iter, array, x, NONCONST)
    {
      const_rtx x = *iter;
      if (REG_P (x))
        {
          unsigned int end_regno = END_REGNO (x);
          for (unsigned int regno = REGNO (x); regno < end_regno; ++regno)
            if (REGNO_REG_SET_P (nonequal, regno))
              return true;
        }
    }
  return false;
}

/* Attempt to prove that the basic block B will have no side effects and
   always continues in the same edge if reached via E.  Return the edge
   if exist, NULL otherwise.  */

static edge
thread_jump (edge e, basic_block b)
{
  rtx set1, set2, cond1, cond2;
  rtx_insn *insn;
  enum rtx_code code1, code2, reversed_code2;
  bool reverse1 = false;
  unsigned i;
  regset nonequal;
  bool failed = false;
  reg_set_iterator rsi;

  if (b->flags & BB_NONTHREADABLE_BLOCK)
    return NULL;

  /* At the moment, we do handle only conditional jumps, but later we may
     want to extend this code to tablejumps and others.  */
  if (EDGE_COUNT (e->src->succs) != 2)
    return NULL;
  if (EDGE_COUNT (b->succs) != 2)
    {
      b->flags |= BB_NONTHREADABLE_BLOCK;
      return NULL;
    }

  /* Second branch must end with onlyjump, as we will eliminate the jump.  */
  if (!any_condjump_p (BB_END (e->src)))
    return NULL;

  if (!any_condjump_p (BB_END (b)) || !onlyjump_p (BB_END (b)))
    {
      b->flags |= BB_NONTHREADABLE_BLOCK;
      return NULL;
    }

  set1 = pc_set (BB_END (e->src));
  set2 = pc_set (BB_END (b));
  if (((e->flags & EDGE_FALLTHRU) != 0)
      != (XEXP (SET_SRC (set1), 1) == pc_rtx))
    reverse1 = true;

  cond1 = XEXP (SET_SRC (set1), 0);
  cond2 = XEXP (SET_SRC (set2), 0);
  if (reverse1)
    code1 = reversed_comparison_code (cond1, BB_END (e->src));
  else
    code1 = GET_CODE (cond1);

  code2 = GET_CODE (cond2);
  reversed_code2 = reversed_comparison_code (cond2, BB_END (b));

  if (!comparison_dominates_p (code1, code2)
      && !comparison_dominates_p (code1, reversed_code2))
    return NULL;

  /* Ensure that the comparison operators are equivalent.
     ??? This is far too pessimistic.  We should allow swapped operands,
     different CCmodes, or for example comparisons for interval, that
     dominate even when operands are not equivalent.  */
  if (!rtx_equal_p (XEXP (cond1, 0), XEXP (cond2, 0))
      || !rtx_equal_p (XEXP (cond1, 1), XEXP (cond2, 1)))
    return NULL;

  /* Short circuit cases where block B contains some side effects, as we can't
     safely bypass it.  */
  for (insn = NEXT_INSN (BB_HEAD (b)); insn != NEXT_INSN (BB_END (b));
       insn = NEXT_INSN (insn))
    if (INSN_P (insn) && side_effects_p (PATTERN (insn)))
      {
        b->flags |= BB_NONTHREADABLE_BLOCK;
        return NULL;
      }

  cselib_init (0);

  /* First process all values computed in the source basic block.  */
  for (insn = NEXT_INSN (BB_HEAD (e->src));
       insn != NEXT_INSN (BB_END (e->src));
       insn = NEXT_INSN (insn))
    if (INSN_P (insn))
      cselib_process_insn (insn);

  nonequal = BITMAP_ALLOC (NULL);
  CLEAR_REG_SET (nonequal);

  /* Now assume that we've continued by the edge E to B and continue
     processing as if it were same basic block.
     Our goal is to prove that whole block is an NOOP.  */

  for (insn = NEXT_INSN (BB_HEAD (b));
       insn != NEXT_INSN (BB_END (b)) && !failed;
       insn = NEXT_INSN (insn))
    {
      if (INSN_P (insn))
        {
          rtx pat = PATTERN (insn);

          if (GET_CODE (pat) == PARALLEL)
            {
              for (i = 0; i < (unsigned)XVECLEN (pat, 0); i++)
                failed |= mark_effect (XVECEXP (pat, 0, i), nonequal);
            }
          else
            failed |= mark_effect (pat, nonequal);
        }

      cselib_process_insn (insn);
    }

  /* Later we should clear nonequal of dead registers.  So far we don't
     have life information in cfg_cleanup.  */
  if (failed)
    {
      b->flags |= BB_NONTHREADABLE_BLOCK;
      goto failed_exit;
    }

  /* cond2 must not mention any register that is not equal to the
     former block.  */
  if (mentions_nonequal_regs (cond2, nonequal))
    goto failed_exit;

  EXECUTE_IF_SET_IN_REG_SET (nonequal, 0, i, rsi)
    goto failed_exit;

  BITMAP_FREE (nonequal);
  cselib_finish ();
  if ((comparison_dominates_p (code1, code2) != 0)
      != (XEXP (SET_SRC (set2), 1) == pc_rtx))
    return BRANCH_EDGE (b);
  else
    return FALLTHRU_EDGE (b);

failed_exit:
  BITMAP_FREE (nonequal);
  cselib_finish ();
  return NULL;
}
\f
/* Attempt to forward edges leaving basic block B.
   Return true if successful.  */

static bool
try_forward_edges (int mode, basic_block b)
{
  bool changed = false;
  edge_iterator ei;
  edge e, *threaded_edges = NULL;

  /* If we are partitioning hot/cold basic blocks, we don't want to
     mess up unconditional or indirect jumps that cross between hot
     and cold sections.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (JUMP_P (BB_END (b)) && CROSSING_JUMP_P (BB_END (b)))
    return false;

  for (ei = ei_start (b->succs); (e = ei_safe_edge (ei)); )
    {
      basic_block target, first;
      location_t goto_locus;
      int counter;
      bool threaded = false;
      int nthreaded_edges = 0;
      bool may_thread = first_pass || (b->flags & BB_MODIFIED) != 0;

      /* Skip complex edges because we don't know how to update them.

         Still handle fallthru edges, as we can succeed to forward fallthru
         edge to the same place as the branch edge of conditional branch
         and turn conditional branch to an unconditional branch.  */
      if (e->flags & EDGE_COMPLEX)
        {
          ei_next (&ei);
          continue;
        }

      target = first = e->dest;
      counter = NUM_FIXED_BLOCKS;
      goto_locus = e->goto_locus;

      /* If we are partitioning hot/cold basic_blocks, we don't want to mess
         up jumps that cross between hot/cold sections.

         Basic block partitioning may result in some jumps that appear
         to be optimizable (or blocks that appear to be mergeable), but which
         really must be left untouched (they are required to make it safely
         across partition boundaries).  See the comments at the top of
         bb-reorder.c:partition_hot_cold_basic_blocks for complete
         details.  */

      if (first != EXIT_BLOCK_PTR_FOR_FN (cfun)
          && JUMP_P (BB_END (first))
          && CROSSING_JUMP_P (BB_END (first)))
        return changed;

      while (counter < n_basic_blocks_for_fn (cfun))
        {
          basic_block new_target = NULL;
          bool new_target_threaded = false;
          may_thread |= (target->flags & BB_MODIFIED) != 0;

          if (FORWARDER_BLOCK_P (target)
              && !(single_succ_edge (target)->flags & EDGE_CROSSING)
              && single_succ (target) != EXIT_BLOCK_PTR_FOR_FN (cfun))
            {
              /* Bypass trivial infinite loops.  */
              new_target = single_succ (target);
              if (target == new_target)
                counter = n_basic_blocks_for_fn (cfun);
              else if (!optimize)
                {
                  /* When not optimizing, ensure that edges or forwarder
                     blocks with different locus are not optimized out.  */
                  location_t new_locus = single_succ_edge (target)->goto_locus;
                  location_t locus = goto_locus;

                  if (LOCATION_LOCUS (new_locus) != UNKNOWN_LOCATION
                      && LOCATION_LOCUS (locus) != UNKNOWN_LOCATION
                      && new_locus != locus)
                    new_target = NULL;
                  else
                    {
                      if (LOCATION_LOCUS (new_locus) != UNKNOWN_LOCATION)
                        locus = new_locus;

                      rtx_insn *last = BB_END (target);
                      if (DEBUG_INSN_P (last))
                        last = prev_nondebug_insn (last);
                      if (last && INSN_P (last))
                        new_locus = INSN_LOCATION (last);
                      else
                        new_locus = UNKNOWN_LOCATION;

                      if (LOCATION_LOCUS (new_locus) != UNKNOWN_LOCATION
                          && LOCATION_LOCUS (locus) != UNKNOWN_LOCATION
                          && new_locus != locus)
                        new_target = NULL;
                      else
                        {
                          if (LOCATION_LOCUS (new_locus) != UNKNOWN_LOCATION)
                            locus = new_locus;

                          goto_locus = locus;
                        }
                    }
                }
            }

          /* Allow to thread only over one edge at time to simplify updating
             of probabilities.  */
          else if ((mode & CLEANUP_THREADING) && may_thread)
            {
              edge t = thread_jump (e, target);
              if (t)
                {
                  if (!threaded_edges)
                    threaded_edges = XNEWVEC (edge,
                                              n_basic_blocks_for_fn (cfun));
                  else
                    {
                      int i;

                      /* Detect an infinite loop across blocks not
                         including the start block.  */
                      for (i = 0; i < nthreaded_edges; ++i)
                        if (threaded_edges[i] == t)
                          break;
                      if (i < nthreaded_edges)
                        {
                          counter = n_basic_blocks_for_fn (cfun);
                          break;
                        }
                    }

                  /* Detect an infinite loop across the start block.  */
                  if (t->dest == b)
                    break;

                  gcc_assert (nthreaded_edges
                              < (n_basic_blocks_for_fn (cfun)
                                 - NUM_FIXED_BLOCKS));
                  threaded_edges[nthreaded_edges++] = t;

                  new_target = t->dest;
                  new_target_threaded = true;
                }
            }

          if (!new_target)
            break;

          counter++;
          target = new_target;
          threaded |= new_target_threaded;
        }

      if (counter >= n_basic_blocks_for_fn (cfun))
        {
          if (dump_file)
            fprintf (dump_file, "Infinite loop in BB %i.\n",
                     target->index);
        }
      else if (target == first)
        ; /* We didn't do anything.  */
      else
        {
          /* Save the values now, as the edge may get removed.  */
          gcov_type edge_count = e->count;
          int edge_probability = e->probability;
          int edge_frequency;
          int n = 0;

          e->goto_locus = goto_locus;

          /* Don't force if target is exit block.  */
          if (threaded && target != EXIT_BLOCK_PTR_FOR_FN (cfun))
            {
              notice_new_block (redirect_edge_and_branch_force (e, target));
              if (dump_file)
                fprintf (dump_file, "Conditionals threaded.\n");
            }
          else if (!redirect_edge_and_branch (e, target))
            {
              if (dump_file)
                fprintf (dump_file,
                         "Forwarding edge %i->%i to %i failed.\n",
                         b->index, e->dest->index, target->index);
              ei_next (&ei);
              continue;
            }

          /* We successfully forwarded the edge.  Now update profile
             data: for each edge we traversed in the chain, remove
             the original edge's execution count.  */
          edge_frequency = apply_probability (b->frequency, edge_probability);

          do
            {
              edge t;

              if (!single_succ_p (first))
                {
                  gcc_assert (n < nthreaded_edges);
                  t = threaded_edges [n++];
                  gcc_assert (t->src == first);
                  update_bb_profile_for_threading (first, edge_frequency,
                                                   edge_count, t);
                  update_br_prob_note (first);
                }
              else
                {
                  first->count -= edge_count;
                  if (first->count < 0)
                    first->count = 0;
                  first->frequency -= edge_frequency;
                  if (first->frequency < 0)
                    first->frequency = 0;
                  /* It is possible that as the result of
                     threading we've removed edge as it is
                     threaded to the fallthru edge.  Avoid
                     getting out of sync.  */
                  if (n < nthreaded_edges
                      && first == threaded_edges [n]->src)
                    n++;
                  t = single_succ_edge (first);
                }

              t->count -= edge_count;
              if (t->count < 0)
                t->count = 0;
              first = t->dest;
            }
          while (first != target);

          changed = true;
          continue;
        }
      ei_next (&ei);
    }

  free (threaded_edges);
  return changed;
}
\f

/* Blocks A and B are to be merged into a single block.  A has no incoming
   fallthru edge, so it can be moved before B without adding or modifying
   any jumps (aside from the jump from A to B).  */

static void
merge_blocks_move_predecessor_nojumps (basic_block a, basic_block b)
{
  rtx_insn *barrier;

  /* If we are partitioning hot/cold basic blocks, we don't want to
     mess up unconditional or indirect jumps that cross between hot
     and cold sections.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (BB_PARTITION (a) != BB_PARTITION (b))
    return;

  barrier = next_nonnote_insn (BB_END (a));
  gcc_assert (BARRIER_P (barrier));
  delete_insn (barrier);

  /* Scramble the insn chain.  */
  if (BB_END (a) != PREV_INSN (BB_HEAD (b)))
    reorder_insns_nobb (BB_HEAD (a), BB_END (a), PREV_INSN (BB_HEAD (b)));
  df_set_bb_dirty (a);

  if (dump_file)
    fprintf (dump_file, "Moved block %d before %d and merged.\n",
             a->index, b->index);

  /* Swap the records for the two blocks around.  */

  unlink_block (a);
  link_block (a, b->prev_bb);

  /* Now blocks A and B are contiguous.  Merge them.  */
  merge_blocks (a, b);
}

/* Blocks A and B are to be merged into a single block.  B has no outgoing
   fallthru edge, so it can be moved after A without adding or modifying
   any jumps (aside from the jump from A to B).  */

static void
merge_blocks_move_successor_nojumps (basic_block a, basic_block b)
{
  rtx_insn *barrier, *real_b_end;
  rtx_insn *label;
  rtx_jump_table_data *table;

  /* If we are partitioning hot/cold basic blocks, we don't want to
     mess up unconditional or indirect jumps that cross between hot
     and cold sections.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (BB_PARTITION (a) != BB_PARTITION (b))
    return;

  real_b_end = BB_END (b);

  /* If there is a jump table following block B temporarily add the jump table
     to block B so that it will also be moved to the correct location.  */
  if (tablejump_p (BB_END (b), &label, &table)
      && prev_active_insn (label) == BB_END (b))
    {
      BB_END (b) = table;
    }

  /* There had better have been a barrier there.  Delete it.  */
  barrier = NEXT_INSN (BB_END (b));
  if (barrier && BARRIER_P (barrier))
    delete_insn (barrier);


  /* Scramble the insn chain.  */
  reorder_insns_nobb (BB_HEAD (b), BB_END (b), BB_END (a));

  /* Restore the real end of b.  */
  BB_END (b) = real_b_end;

  if (dump_file)
    fprintf (dump_file, "Moved block %d after %d and merged.\n",
             b->index, a->index);

  /* Now blocks A and B are contiguous.  Merge them.  */
  merge_blocks (a, b);
}

/* Attempt to merge basic blocks that are potentially non-adjacent.
   Return NULL iff the attempt failed, otherwise return basic block
   where cleanup_cfg should continue.  Because the merging commonly
   moves basic block away or introduces another optimization
   possibility, return basic block just before B so cleanup_cfg don't
   need to iterate.

   It may be good idea to return basic block before C in the case
   C has been moved after B and originally appeared earlier in the
   insn sequence, but we have no information available about the
   relative ordering of these two.  Hopefully it is not too common.  */

static basic_block
merge_blocks_move (edge e, basic_block b, basic_block c, int mode)
{
  basic_block next;

  /* If we are partitioning hot/cold basic blocks, we don't want to
     mess up unconditional or indirect jumps that cross between hot
     and cold sections.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (BB_PARTITION (b) != BB_PARTITION (c))
    return NULL;

  /* If B has a fallthru edge to C, no need to move anything.  */
  if (e->flags & EDGE_FALLTHRU)
    {
      int b_index = b->index, c_index = c->index;

      /* Protect the loop latches.  */
      if (current_loops && c->loop_father->latch == c)
        return NULL;

      merge_blocks (b, c);
      update_forwarder_flag (b);

      if (dump_file)
        fprintf (dump_file, "Merged %d and %d without moving.\n",
                 b_index, c_index);

      return b->prev_bb == ENTRY_BLOCK_PTR_FOR_FN (cfun) ? b : b->prev_bb;
    }

  /* Otherwise we will need to move code around.  Do that only if expensive
     transformations are allowed.  */
  else if (mode & CLEANUP_EXPENSIVE)
    {
      edge tmp_edge, b_fallthru_edge;
      bool c_has_outgoing_fallthru;
      bool b_has_incoming_fallthru;

      /* Avoid overactive code motion, as the forwarder blocks should be
         eliminated by edge redirection instead.  One exception might have
         been if B is a forwarder block and C has no fallthru edge, but
         that should be cleaned up by bb-reorder instead.  */
      if (FORWARDER_BLOCK_P (b) || FORWARDER_BLOCK_P (c))
        return NULL;

      /* We must make sure to not munge nesting of lexical blocks,
         and loop notes.  This is done by squeezing out all the notes
         and leaving them there to lie.  Not ideal, but functional.  */

      tmp_edge = find_fallthru_edge (c->succs);
      c_has_outgoing_fallthru = (tmp_edge != NULL);

      tmp_edge = find_fallthru_edge (b->preds);
      b_has_incoming_fallthru = (tmp_edge != NULL);
      b_fallthru_edge = tmp_edge;
      next = b->prev_bb;
      if (next == c)
        next = next->prev_bb;

      /* Otherwise, we're going to try to move C after B.  If C does
         not have an outgoing fallthru, then it can be moved
         immediately after B without introducing or modifying jumps.  */
      if (! c_has_outgoing_fallthru)
        {
          merge_blocks_move_successor_nojumps (b, c);
          return next == ENTRY_BLOCK_PTR_FOR_FN (cfun) ? next->next_bb : next;
        }

      /* If B does not have an incoming fallthru, then it can be moved
         immediately before C without introducing or modifying jumps.
         C cannot be the first block, so we do not have to worry about
         accessing a non-existent block.  */

      if (b_has_incoming_fallthru)
        {
          basic_block bb;

          if (b_fallthru_edge->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
            return NULL;
          bb = force_nonfallthru (b_fallthru_edge);
          if (bb)
            notice_new_block (bb);
        }

      merge_blocks_move_predecessor_nojumps (b, c);
      return next == ENTRY_BLOCK_PTR_FOR_FN (cfun) ? next->next_bb : next;
    }

  return NULL;
}
\f

/* Removes the memory attributes of MEM expression
   if they are not equal.  */

static void
merge_memattrs (rtx x, rtx y)
{
  int i;
  int j;
  enum rtx_code code;
  const char *fmt;

  if (x == y)
    return;
  if (x == 0 || y == 0)
    return;

  code = GET_CODE (x);

  if (code != GET_CODE (y))
    return;

  if (GET_MODE (x) != GET_MODE (y))
    return;

  if (code == MEM && !mem_attrs_eq_p (MEM_ATTRS (x), MEM_ATTRS (y)))
    {
      if (! MEM_ATTRS (x))
        MEM_ATTRS (y) = 0;
      else if (! MEM_ATTRS (y))
        MEM_ATTRS (x) = 0;
      else
        {
          HOST_WIDE_INT mem_size;

          if (MEM_ALIAS_SET (x) != MEM_ALIAS_SET (y))
            {
              set_mem_alias_set (x, 0);
              set_mem_alias_set (y, 0);
            }

          if (! mem_expr_equal_p (MEM_EXPR (x), MEM_EXPR (y)))
            {
              set_mem_expr (x, 0);
              set_mem_expr (y, 0);
              clear_mem_offset (x);
              clear_mem_offset (y);
            }
          else if (MEM_OFFSET_KNOWN_P (x) != MEM_OFFSET_KNOWN_P (y)
                   || (MEM_OFFSET_KNOWN_P (x)
                       && MEM_OFFSET (x) != MEM_OFFSET (y)))
            {
              clear_mem_offset (x);
              clear_mem_offset (y);
            }

          if (MEM_SIZE_KNOWN_P (x) && MEM_SIZE_KNOWN_P (y))
            {
              mem_size = MAX (MEM_SIZE (x), MEM_SIZE (y));
              set_mem_size (x, mem_size);
              set_mem_size (y, mem_size);
            }
          else
            {
              clear_mem_size (x);
              clear_mem_size (y);
            }

          set_mem_align (x, MIN (MEM_ALIGN (x), MEM_ALIGN (y)));
          set_mem_align (y, MEM_ALIGN (x));
        }
    }
  if (code == MEM)
    {
      if (MEM_READONLY_P (x) != MEM_READONLY_P (y))
        {
          MEM_READONLY_P (x) = 0;
          MEM_READONLY_P (y) = 0;
        }
      if (MEM_NOTRAP_P (x) != MEM_NOTRAP_P (y))
        {
          MEM_NOTRAP_P (x) = 0;
          MEM_NOTRAP_P (y) = 0;
        }
      if (MEM_VOLATILE_P (x) != MEM_VOLATILE_P (y))
        {
          MEM_VOLATILE_P (x) = 1;
          MEM_VOLATILE_P (y) = 1;
        }
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      switch (fmt[i])
        {
        case 'E':
          /* Two vectors must have the same length.  */
          if (XVECLEN (x, i) != XVECLEN (y, i))
            return;

          for (j = 0; j < XVECLEN (x, i); j++)
            merge_memattrs (XVECEXP (x, i, j), XVECEXP (y, i, j));

          break;

        case 'e':
          merge_memattrs (XEXP (x, i), XEXP (y, i));
        }
    }
  return;
}


 /* Checks if patterns P1 and P2 are equivalent, apart from the possibly
    different single sets S1 and S2.  */

static bool
equal_different_set_p (rtx p1, rtx s1, rtx p2, rtx s2)
{
  int i;
  rtx e1, e2;

  if (p1 == s1 && p2 == s2)
    return true;

  if (GET_CODE (p1) != PARALLEL || GET_CODE (p2) != PARALLEL)
    return false;

  if (XVECLEN (p1, 0) != XVECLEN (p2, 0))
    return false;

  for (i = 0; i < XVECLEN (p1, 0); i++)
    {
      e1 = XVECEXP (p1, 0, i);
      e2 = XVECEXP (p2, 0, i);
      if (e1 == s1 && e2 == s2)
        continue;
      if (reload_completed
          ? rtx_renumbered_equal_p (e1, e2) : rtx_equal_p (e1, e2))
        continue;

      return false;
    }

  return true;
}


/* NOTE1 is the REG_EQUAL note, if any, attached to an insn
   that is a single_set with a SET_SRC of SRC1.  Similarly
   for NOTE2/SRC2.

   So effectively NOTE1/NOTE2 are an alternate form of 
   SRC1/SRC2 respectively.

   Return nonzero if SRC1 or NOTE1 has the same constant
   integer value as SRC2 or NOTE2.   Else return zero.  */
static int
values_equal_p (rtx note1, rtx note2, rtx src1, rtx src2)
{
  if (note1
      && note2
      && CONST_INT_P (XEXP (note1, 0))
      && rtx_equal_p (XEXP (note1, 0), XEXP (note2, 0)))
    return 1;

  if (!note1
      && !note2
      && CONST_INT_P (src1)
      && CONST_INT_P (src2)
      && rtx_equal_p (src1, src2))
    return 1;

  if (note1
      && CONST_INT_P (src2)
      && rtx_equal_p (XEXP (note1, 0), src2))
    return 1;

  if (note2
      && CONST_INT_P (src1)
      && rtx_equal_p (XEXP (note2, 0), src1))
    return 1;

  return 0;
}

/* Examine register notes on I1 and I2 and return:
   - dir_forward if I1 can be replaced by I2, or
   - dir_backward if I2 can be replaced by I1, or
   - dir_both if both are the case.  */

static enum replace_direction
can_replace_by (rtx_insn *i1, rtx_insn *i2)
{
  rtx s1, s2, d1, d2, src1, src2, note1, note2;
  bool c1, c2;

  /* Check for 2 sets.  */
  s1 = single_set (i1);
  s2 = single_set (i2);
  if (s1 == NULL_RTX || s2 == NULL_RTX)
    return dir_none;

  /* Check that the 2 sets set the same dest.  */
  d1 = SET_DEST (s1);
  d2 = SET_DEST (s2);
  if (!(reload_completed
        ? rtx_renumbered_equal_p (d1, d2) : rtx_equal_p (d1, d2)))
    return dir_none;

  /* Find identical req_equiv or reg_equal note, which implies that the 2 sets
     set dest to the same value.  */
  note1 = find_reg_equal_equiv_note (i1);
  note2 = find_reg_equal_equiv_note (i2);

  src1 = SET_SRC (s1);
  src2 = SET_SRC (s2);

  if (!values_equal_p (note1, note2, src1, src2))
    return dir_none;

  if (!equal_different_set_p (PATTERN (i1), s1, PATTERN (i2), s2))
    return dir_none;

  /* Although the 2 sets set dest to the same value, we cannot replace
       (set (dest) (const_int))
     by
       (set (dest) (reg))
     because we don't know if the reg is live and has the same value at the
     location of replacement.  */
  c1 = CONST_INT_P (src1);
  c2 = CONST_INT_P (src2);
  if (c1 && c2)
    return dir_both;
  else if (c2)
    return dir_forward;
  else if (c1)
    return dir_backward;

  return dir_none;
}

/* Merges directions A and B.  */

static enum replace_direction
merge_dir (enum replace_direction a, enum replace_direction b)
{
  /* Implements the following table:
        |bo fw bw no
     ---+-----------
     bo |bo fw bw no
     fw |-- fw no no
     bw |-- -- bw no
     no |-- -- -- no.  */

  if (a == b)
    return a;

  if (a == dir_both)
    return b;
  if (b == dir_both)
    return a;

  return dir_none;
}

/* Examine I1 and I2 and return:
   - dir_forward if I1 can be replaced by I2, or
   - dir_backward if I2 can be replaced by I1, or
   - dir_both if both are the case.  */

static enum replace_direction
old_insns_match_p (int mode ATTRIBUTE_UNUSED, rtx_insn *i1, rtx_insn *i2)
{
  rtx p1, p2;

  /* Verify that I1 and I2 are equivalent.  */
  if (GET_CODE (i1) != GET_CODE (i2))
    return dir_none;

  /* __builtin_unreachable() may lead to empty blocks (ending with
     NOTE_INSN_BASIC_BLOCK).  They may be crossjumped. */
  if (NOTE_INSN_BASIC_BLOCK_P (i1) && NOTE_INSN_BASIC_BLOCK_P (i2))
    return dir_both;

  /* ??? Do not allow cross-jumping between different stack levels.  */
  p1 = find_reg_note (i1, REG_ARGS_SIZE, NULL);
  p2 = find_reg_note (i2, REG_ARGS_SIZE, NULL);
  if (p1 && p2)
    {
      p1 = XEXP (p1, 0);
      p2 = XEXP (p2, 0);
      if (!rtx_equal_p (p1, p2))
        return dir_none;

      /* ??? Worse, this adjustment had better be constant lest we
         have differing incoming stack levels.  */
      if (!frame_pointer_needed
          && find_args_size_adjust (i1) == HOST_WIDE_INT_MIN)
        return dir_none;
    }
  else if (p1 || p2)
    return dir_none;

  p1 = PATTERN (i1);
  p2 = PATTERN (i2);

  if (GET_CODE (p1) != GET_CODE (p2))
    return dir_none;

  /* If this is a CALL_INSN, compare register usage information.
     If we don't check this on stack register machines, the two
     CALL_INSNs might be merged leaving reg-stack.c with mismatching
     numbers of stack registers in the same basic block.
     If we don't check this on machines with delay slots, a delay slot may
     be filled that clobbers a parameter expected by the subroutine.

     ??? We take the simple route for now and assume that if they're
     equal, they were constructed identically.

     Also check for identical exception regions.  */

  if (CALL_P (i1))
    {
      /* Ensure the same EH region.  */
      rtx n1 = find_reg_note (i1, REG_EH_REGION, 0);
      rtx n2 = find_reg_note (i2, REG_EH_REGION, 0);

      if (!n1 && n2)
        return dir_none;

      if (n1 && (!n2 || XEXP (n1, 0) != XEXP (n2, 0)))
        return dir_none;

      if (!rtx_equal_p (CALL_INSN_FUNCTION_USAGE (i1),
                        CALL_INSN_FUNCTION_USAGE (i2))
          || SIBLING_CALL_P (i1) != SIBLING_CALL_P (i2))
        return dir_none;

      /* For address sanitizer, never crossjump __asan_report_* builtins,
         otherwise errors might be reported on incorrect lines.  */
      if (flag_sanitize & SANITIZE_ADDRESS)
        {
          rtx call = get_call_rtx_from (i1);
          if (call && GET_CODE (XEXP (XEXP (call, 0), 0)) == SYMBOL_REF)
            {
              rtx symbol = XEXP (XEXP (call, 0), 0);
              if (SYMBOL_REF_DECL (symbol)
                  && TREE_CODE (SYMBOL_REF_DECL (symbol)) == FUNCTION_DECL)
                {
                  if ((DECL_BUILT_IN_CLASS (SYMBOL_REF_DECL (symbol))
                       == BUILT_IN_NORMAL)
                      && DECL_FUNCTION_CODE (SYMBOL_REF_DECL (symbol))
                         >= BUILT_IN_ASAN_REPORT_LOAD1
                      && DECL_FUNCTION_CODE (SYMBOL_REF_DECL (symbol))
                         <= BUILT_IN_ASAN_STOREN)
                    return dir_none;
                }
            }
        }
    }

#ifdef STACK_REGS
  /* If cross_jump_death_matters is not 0, the insn's mode
     indicates whether or not the insn contains any stack-like
     regs.  */

  if ((mode & CLEANUP_POST_REGSTACK) && stack_regs_mentioned (i1))
    {
      /* If register stack conversion has already been done, then
         death notes must also be compared before it is certain that
         the two instruction streams match.  */

      rtx note;
      HARD_REG_SET i1_regset, i2_regset;

      CLEAR_HARD_REG_SET (i1_regset);
      CLEAR_HARD_REG_SET (i2_regset);

      for (note = REG_NOTES (i1); note; note = XEXP (note, 1))
        if (REG_NOTE_KIND (note) == REG_DEAD && STACK_REG_P (XEXP (note, 0)))
          SET_HARD_REG_BIT (i1_regset, REGNO (XEXP (note, 0)));

      for (note = REG_NOTES (i2); note; note = XEXP (note, 1))
        if (REG_NOTE_KIND (note) == REG_DEAD && STACK_REG_P (XEXP (note, 0)))
          SET_HARD_REG_BIT (i2_regset, REGNO (XEXP (note, 0)));

      if (!hard_reg_set_equal_p (i1_regset, i2_regset))
        return dir_none;
    }
#endif

  if (reload_completed
      ? rtx_renumbered_equal_p (p1, p2) : rtx_equal_p (p1, p2))
    return dir_both;

  return can_replace_by (i1, i2);
}
\f
/* When comparing insns I1 and I2 in flow_find_cross_jump or
   flow_find_head_matching_sequence, ensure the notes match.  */

static void
merge_notes (rtx_insn *i1, rtx_insn *i2)
{
  /* If the merged insns have different REG_EQUAL notes, then
     remove them.  */
  rtx equiv1 = find_reg_equal_equiv_note (i1);
  rtx equiv2 = find_reg_equal_equiv_note (i2);

  if (equiv1 && !equiv2)
    remove_note (i1, equiv1);
  else if (!equiv1 && equiv2)
    remove_note (i2, equiv2);
  else if (equiv1 && equiv2
           && !rtx_equal_p (XEXP (equiv1, 0), XEXP (equiv2, 0)))
    {
      remove_note (i1, equiv1);
      remove_note (i2, equiv2);
    }
}

 /* Walks from I1 in BB1 backward till the next non-debug insn, and returns the
    resulting insn in I1, and the corresponding bb in BB1.  At the head of a
    bb, if there is a predecessor bb that reaches this bb via fallthru, and
    FOLLOW_FALLTHRU, walks further in the predecessor bb and registers this in
    DID_FALLTHRU.  Otherwise, stops at the head of the bb.  */

static void
walk_to_nondebug_insn (rtx_insn **i1, basic_block *bb1, bool follow_fallthru,
                       bool *did_fallthru)
{
  edge fallthru;

  *did_fallthru = false;

  /* Ignore notes.  */
  while (!NONDEBUG_INSN_P (*i1))
    {
      if (*i1 != BB_HEAD (*bb1))
        {
          *i1 = PREV_INSN (*i1);
          continue;
        }

      if (!follow_fallthru)
        return;

      fallthru = find_fallthru_edge ((*bb1)->preds);
      if (!fallthru || fallthru->src == ENTRY_BLOCK_PTR_FOR_FN (cfun)
          || !single_succ_p (fallthru->src))
        return;

      *bb1 = fallthru->src;
      *i1 = BB_END (*bb1);
      *did_fallthru = true;
     }
}

/* Look through the insns at the end of BB1 and BB2 and find the longest
   sequence that are either equivalent, or allow forward or backward
   replacement.  Store the first insns for that sequence in *F1 and *F2 and
   return the sequence length.

   DIR_P indicates the allowed replacement direction on function entry, and
   the actual replacement direction on function exit.  If NULL, only equivalent
   sequences are allowed.

   To simplify callers of this function, if the blocks match exactly,
   store the head of the blocks in *F1 and *F2.  */

int
flow_find_cross_jump (basic_block bb1, basic_block bb2, rtx_insn **f1,
                      rtx_insn **f2, enum replace_direction *dir_p)
{
  rtx_insn *i1, *i2, *last1, *last2, *afterlast1, *afterlast2;
  int ninsns = 0;
  enum replace_direction dir, last_dir, afterlast_dir;
  bool follow_fallthru, did_fallthru;

  if (dir_p)
    dir = *dir_p;
  else
    dir = dir_both;
  afterlast_dir = dir;
  last_dir = afterlast_dir;

  /* Skip simple jumps at the end of the blocks.  Complex jumps still
     need to be compared for equivalence, which we'll do below.  */

  i1 = BB_END (bb1);
  last1 = afterlast1 = last2 = afterlast2 = NULL;
  if (onlyjump_p (i1)
      || (returnjump_p (i1) && !side_effects_p (PATTERN (i1))))
    {
      last1 = i1;
      i1 = PREV_INSN (i1);
    }

  i2 = BB_END (bb2);
  if (onlyjump_p (i2)
      || (returnjump_p (i2) && !side_effects_p (PATTERN (i2))))
    {
      last2 = i2;
      /* Count everything except for unconditional jump as insn.
         Don't count any jumps if dir_p is NULL.  */
      if (!simplejump_p (i2) && !returnjump_p (i2) && last1 && dir_p)
        ninsns++;
      i2 = PREV_INSN (i2);
    }

  while (true)
    {
      /* In the following example, we can replace all jumps to C by jumps to A.

         This removes 4 duplicate insns.
         [bb A] insn1            [bb C] insn1
                insn2                   insn2
         [bb B] insn3                   insn3
                insn4                   insn4
                jump_insn               jump_insn

         We could also replace all jumps to A by jumps to C, but that leaves B
         alive, and removes only 2 duplicate insns.  In a subsequent crossjump
         step, all jumps to B would be replaced with jumps to the middle of C,
         achieving the same result with more effort.
         So we allow only the first possibility, which means that we don't allow
         fallthru in the block that's being replaced.  */

      follow_fallthru = dir_p && dir != dir_forward;
      walk_to_nondebug_insn (&i1, &bb1, follow_fallthru, &did_fallthru);
      if (did_fallthru)
        dir = dir_backward;

      follow_fallthru = dir_p && dir != dir_backward;
      walk_to_nondebug_insn (&i2, &bb2, follow_fallthru, &did_fallthru);
      if (did_fallthru)
        dir = dir_forward;

      if (i1 == BB_HEAD (bb1) || i2 == BB_HEAD (bb2))
        break;

      dir = merge_dir (dir, old_insns_match_p (0, i1, i2));
      if (dir == dir_none || (!dir_p && dir != dir_both))
        break;

      merge_memattrs (i1, i2);

      /* Don't begin a cross-jump with a NOTE insn.  */
      if (INSN_P (i1))
        {
          merge_notes (i1, i2);

          afterlast1 = last1, afterlast2 = last2;
          last1 = i1, last2 = i2;
          afterlast_dir = last_dir;
          last_dir = dir;
          if (active_insn_p (i1))
            ninsns++;
        }

      i1 = PREV_INSN (i1);
      i2 = PREV_INSN (i2);
    }

  /* Don't allow the insn after a compare to be shared by
     cross-jumping unless the compare is also shared.  */
  if (HAVE_cc0 && ninsns && reg_mentioned_p (cc0_rtx, last1)
      && ! sets_cc0_p (last1))
    last1 = afterlast1, last2 = afterlast2, last_dir = afterlast_dir, ninsns--;

  /* Include preceding notes and labels in the cross-jump.  One,
     this may bring us to the head of the blocks as requested above.
     Two, it keeps line number notes as matched as may be.  */
  if (ninsns)
    {
      bb1 = BLOCK_FOR_INSN (last1);
      while (last1 != BB_HEAD (bb1) && !NONDEBUG_INSN_P (PREV_INSN (last1)))
        last1 = PREV_INSN (last1);

      if (last1 != BB_HEAD (bb1) && LABEL_P (PREV_INSN (last1)))
        last1 = PREV_INSN (last1);

      bb2 = BLOCK_FOR_INSN (last2);
      while (last2 != BB_HEAD (bb2) && !NONDEBUG_INSN_P (PREV_INSN (last2)))
        last2 = PREV_INSN (last2);

      if (last2 != BB_HEAD (bb2) && LABEL_P (PREV_INSN (last2)))
        last2 = PREV_INSN (last2);

      *f1 = last1;
      *f2 = last2;
    }

  if (dir_p)
    *dir_p = last_dir;
  return ninsns;
}

/* Like flow_find_cross_jump, except start looking for a matching sequence from
   the head of the two blocks.  Do not include jumps at the end.
   If STOP_AFTER is nonzero, stop after finding that many matching
   instructions.  If STOP_AFTER is zero, count all INSN_P insns, if it is
   non-zero, only count active insns.  */

int
flow_find_head_matching_sequence (basic_block bb1, basic_block bb2, rtx_insn **f1,
                                  rtx_insn **f2, int stop_after)
{
  rtx_insn *i1, *i2, *last1, *last2, *beforelast1, *beforelast2;
  int ninsns = 0;
  edge e;
  edge_iterator ei;
  int nehedges1 = 0, nehedges2 = 0;

  FOR_EACH_EDGE (e, ei, bb1->succs)
    if (e->flags & EDGE_EH)
      nehedges1++;
  FOR_EACH_EDGE (e, ei, bb2->succs)
    if (e->flags & EDGE_EH)
      nehedges2++;

  i1 = BB_HEAD (bb1);
  i2 = BB_HEAD (bb2);
  last1 = beforelast1 = last2 = beforelast2 = NULL;

  while (true)
    {
      /* Ignore notes, except NOTE_INSN_EPILOGUE_BEG.  */
      while (!NONDEBUG_INSN_P (i1) && i1 != BB_END (bb1))
        {
          if (NOTE_P (i1) && NOTE_KIND (i1) == NOTE_INSN_EPILOGUE_BEG)
            break;
          i1 = NEXT_INSN (i1);
        }

      while (!NONDEBUG_INSN_P (i2) && i2 != BB_END (bb2))
        {
          if (NOTE_P (i2) && NOTE_KIND (i2) == NOTE_INSN_EPILOGUE_BEG)
            break;
          i2 = NEXT_INSN (i2);
        }

      if ((i1 == BB_END (bb1) && !NONDEBUG_INSN_P (i1))
          || (i2 == BB_END (bb2) && !NONDEBUG_INSN_P (i2)))
        break;

      if (NOTE_P (i1) || NOTE_P (i2)
          || JUMP_P (i1) || JUMP_P (i2))
        break;

      /* A sanity check to make sure we're not merging insns with different
         effects on EH.  If only one of them ends a basic block, it shouldn't
         have an EH edge; if both end a basic block, there should be the same
         number of EH edges.  */
      if ((i1 == BB_END (bb1) && i2 != BB_END (bb2)
           && nehedges1 > 0)
          || (i2 == BB_END (bb2) && i1 != BB_END (bb1)
              && nehedges2 > 0)
          || (i1 == BB_END (bb1) && i2 == BB_END (bb2)
              && nehedges1 != nehedges2))
        break;

      if (old_insns_match_p (0, i1, i2) != dir_both)
        break;

      merge_memattrs (i1, i2);

      /* Don't begin a cross-jump with a NOTE insn.  */
      if (INSN_P (i1))
        {
          merge_notes (i1, i2);

          beforelast1 = last1, beforelast2 = last2;
          last1 = i1, last2 = i2;
          if (!stop_after || active_insn_p (i1))
            ninsns++;
        }

      if (i1 == BB_END (bb1) || i2 == BB_END (bb2)
          || (stop_after > 0 && ninsns == stop_after))
        break;

      i1 = NEXT_INSN (i1);
      i2 = NEXT_INSN (i2);
    }

  /* Don't allow a compare to be shared by cross-jumping unless the insn
     after the compare is also shared.  */
  if (HAVE_cc0 && ninsns && reg_mentioned_p (cc0_rtx, last1)
      && sets_cc0_p (last1))
    last1 = beforelast1, last2 = beforelast2, ninsns--;

  if (ninsns)
    {
      *f1 = last1;
      *f2 = last2;
    }

  return ninsns;
}

/* Return true iff outgoing edges of BB1 and BB2 match, together with
   the branch instruction.  This means that if we commonize the control
   flow before end of the basic block, the semantic remains unchanged.

   We may assume that there exists one edge with a common destination.  */

static bool
outgoing_edges_match (int mode, basic_block bb1, basic_block bb2)
{
  int nehedges1 = 0, nehedges2 = 0;
  edge fallthru1 = 0, fallthru2 = 0;
  edge e1, e2;
  edge_iterator ei;

  /* If we performed shrink-wrapping, edges to the exit block can
     only be distinguished for JUMP_INSNs.  The two paths may differ in
     whether they went through the prologue.  Sibcalls are fine, we know
     that we either didn't need or inserted an epilogue before them.  */
  if (crtl->shrink_wrapped
      && single_succ_p (bb1)
      && single_succ (bb1) == EXIT_BLOCK_PTR_FOR_FN (cfun)
      && !JUMP_P (BB_END (bb1))
      && !(CALL_P (BB_END (bb1)) && SIBLING_CALL_P (BB_END (bb1))))
    return false;
  
  /* If BB1 has only one successor, we may be looking at either an
     unconditional jump, or a fake edge to exit.  */
  if (single_succ_p (bb1)
      && (single_succ_edge (bb1)->flags & (EDGE_COMPLEX | EDGE_FAKE)) == 0
      && (!JUMP_P (BB_END (bb1)) || simplejump_p (BB_END (bb1))))
    return (single_succ_p (bb2)
            && (single_succ_edge (bb2)->flags
                & (EDGE_COMPLEX | EDGE_FAKE)) == 0
            && (!JUMP_P (BB_END (bb2)) || simplejump_p (BB_END (bb2))));

  /* Match conditional jumps - this may get tricky when fallthru and branch
     edges are crossed.  */
  if (EDGE_COUNT (bb1->succs) == 2
      && any_condjump_p (BB_END (bb1))
      && onlyjump_p (BB_END (bb1)))
    {
      edge b1, f1, b2, f2;
      bool reverse, match;
      rtx set1, set2, cond1, cond2;
      enum rtx_code code1, code2;

      if (EDGE_COUNT (bb2->succs) != 2
          || !any_condjump_p (BB_END (bb2))
          || !onlyjump_p (BB_END (bb2)))
        return false;

      b1 = BRANCH_EDGE (bb1);
      b2 = BRANCH_EDGE (bb2);
      f1 = FALLTHRU_EDGE (bb1);
      f2 = FALLTHRU_EDGE (bb2);

      /* Get around possible forwarders on fallthru edges.  Other cases
         should be optimized out already.  */
      if (FORWARDER_BLOCK_P (f1->dest))
        f1 = single_succ_edge (f1->dest);

      if (FORWARDER_BLOCK_P (f2->dest))
        f2 = single_succ_edge (f2->dest);

      /* To simplify use of this function, return false if there are
         unneeded forwarder blocks.  These will get eliminated later
         during cleanup_cfg.  */
      if (FORWARDER_BLOCK_P (f1->dest)
          || FORWARDER_BLOCK_P (f2->dest)
          || FORWARDER_BLOCK_P (b1->dest)
          || FORWARDER_BLOCK_P (b2->dest))
        return false;

      if (f1->dest == f2->dest && b1->dest == b2->dest)
        reverse = false;
      else if (f1->dest == b2->dest && b1->dest == f2->dest)
        reverse = true;
      else
        return false;

      set1 = pc_set (BB_END (bb1));
      set2 = pc_set (BB_END (bb2));
      if ((XEXP (SET_SRC (set1), 1) == pc_rtx)
          != (XEXP (SET_SRC (set2), 1) == pc_rtx))
        reverse = !reverse;

      cond1 = XEXP (SET_SRC (set1), 0);
      cond2 = XEXP (SET_SRC (set2), 0);
      code1 = GET_CODE (cond1);
      if (reverse)
        code2 = reversed_comparison_code (cond2, BB_END (bb2));
      else
        code2 = GET_CODE (cond2);

      if (code2 == UNKNOWN)
        return false;

      /* Verify codes and operands match.  */
      match = ((code1 == code2
                && rtx_renumbered_equal_p (XEXP (cond1, 0), XEXP (cond2, 0))
                && rtx_renumbered_equal_p (XEXP (cond1, 1), XEXP (cond2, 1)))
               || (code1 == swap_condition (code2)
                   && rtx_renumbered_equal_p (XEXP (cond1, 1),
                                              XEXP (cond2, 0))
                   && rtx_renumbered_equal_p (XEXP (cond1, 0),
                                              XEXP (cond2, 1))));

      /* If we return true, we will join the blocks.  Which means that
         we will only have one branch prediction bit to work with.  Thus
         we require the existing branches to have probabilities that are
         roughly similar.  */
      if (match
          && optimize_bb_for_speed_p (bb1)
          && optimize_bb_for_speed_p (bb2))
        {
          int prob2;

          if (b1->dest == b2->dest)
            prob2 = b2->probability;
          else
            /* Do not use f2 probability as f2 may be forwarded.  */
            prob2 = REG_BR_PROB_BASE - b2->probability;

          /* Fail if the difference in probabilities is greater than 50%.
             This rules out two well-predicted branches with opposite
             outcomes.  */
          if (abs (b1->probability - prob2) > REG_BR_PROB_BASE / 2)
            {
              if (dump_file)
                fprintf (dump_file,
                         "Outcomes of branch in bb %i and %i differ too much (%i %i)\n",
                         bb1->index, bb2->index, b1->probability, prob2);

              return false;
            }
        }

      if (dump_file && match)
        fprintf (dump_file, "Conditionals in bb %i and %i match.\n",
                 bb1->index, bb2->index);

      return match;
    }

  /* Generic case - we are seeing a computed jump, table jump or trapping
     instruction.  */

  /* Check whether there are tablejumps in the end of BB1 and BB2.
     Return true if they are identical.  */
    {
      rtx_insn *label1, *label2;
      rtx_jump_table_data *table1, *table2;

      if (tablejump_p (BB_END (bb1), &label1, &table1)
          && tablejump_p (BB_END (bb2), &label2, &table2)
          && GET_CODE (PATTERN (table1)) == GET_CODE (PATTERN (table2)))
        {
          /* The labels should never be the same rtx.  If they really are same
             the jump tables are same too. So disable crossjumping of blocks BB1
             and BB2 because when deleting the common insns in the end of BB1
             by delete_basic_block () the jump table would be deleted too.  */
          /* If LABEL2 is referenced in BB1->END do not do anything
             because we would loose information when replacing
             LABEL1 by LABEL2 and then LABEL2 by LABEL1 in BB1->END.  */
          if (label1 != label2 && !rtx_referenced_p (label2, BB_END (bb1)))
            {
              /* Set IDENTICAL to true when the tables are identical.  */
              bool identical = false;
              rtx p1, p2;

              p1 = PATTERN (table1);
              p2 = PATTERN (table2);
              if (GET_CODE (p1) == ADDR_VEC && rtx_equal_p (p1, p2))
                {
                  identical = true;
                }
              else if (GET_CODE (p1) == ADDR_DIFF_VEC
                       && (XVECLEN (p1, 1) == XVECLEN (p2, 1))
                       && rtx_equal_p (XEXP (p1, 2), XEXP (p2, 2))
                       && rtx_equal_p (XEXP (p1, 3), XEXP (p2, 3)))
                {
                  int i;

                  identical = true;
                  for (i = XVECLEN (p1, 1) - 1; i >= 0 && identical; i--)
                    if (!rtx_equal_p (XVECEXP (p1, 1, i), XVECEXP (p2, 1, i)))
                      identical = false;
                }

              if (identical)
                {
                  bool match;

                  /* Temporarily replace references to LABEL1 with LABEL2
                     in BB1->END so that we could compare the instructions.  */
                  replace_label_in_insn (BB_END (bb1), label1, label2, false);

                  match = (old_insns_match_p (mode, BB_END (bb1), BB_END (bb2))
                           == dir_both);
                  if (dump_file && match)
                    fprintf (dump_file,
                             "Tablejumps in bb %i and %i match.\n",
                             bb1->index, bb2->index);

                  /* Set the original label in BB1->END because when deleting
                     a block whose end is a tablejump, the tablejump referenced
                     from the instruction is deleted too.  */
                  replace_label_in_insn (BB_END (bb1), label2, label1, false);

                  return match;
                }
            }
          return false;
        }
    }

  /* Find the last non-debug non-note instruction in each bb, except
     stop when we see the NOTE_INSN_BASIC_BLOCK, as old_insns_match_p
     handles that case specially. old_insns_match_p does not handle
     other types of instruction notes.  */
  rtx_insn *last1 = BB_END (bb1);
  rtx_insn *last2 = BB_END (bb2);
  while (!NOTE_INSN_BASIC_BLOCK_P (last1) &&
         (DEBUG_INSN_P (last1) || NOTE_P (last1)))
    last1 = PREV_INSN (last1);
  while (!NOTE_INSN_BASIC_BLOCK_P (last2) &&
         (DEBUG_INSN_P (last2) || NOTE_P (last2)))
    last2 = PREV_INSN (last2);
  gcc_assert (last1 && last2);

  /* First ensure that the instructions match.  There may be many outgoing
     edges so this test is generally cheaper.  */
  if (old_insns_match_p (mode, last1, last2) != dir_both)
    return false;

  /* Search the outgoing edges, ensure that the counts do match, find possible
     fallthru and exception handling edges since these needs more
     validation.  */
  if (EDGE_COUNT (bb1->succs) != EDGE_COUNT (bb2->succs))
    return false;

  bool nonfakeedges = false;
  FOR_EACH_EDGE (e1, ei, bb1->succs)
    {
      e2 = EDGE_SUCC (bb2, ei.index);

      if ((e1->flags & EDGE_FAKE) == 0)
        nonfakeedges = true;

      if (e1->flags & EDGE_EH)
        nehedges1++;

      if (e2->flags & EDGE_EH)
        nehedges2++;

      if (e1->flags & EDGE_FALLTHRU)
        fallthru1 = e1;
      if (e2->flags & EDGE_FALLTHRU)
        fallthru2 = e2;
    }

  /* If number of edges of various types does not match, fail.  */
  if (nehedges1 != nehedges2
      || (fallthru1 != 0) != (fallthru2 != 0))
    return false;

  /* If !ACCUMULATE_OUTGOING_ARGS, bb1 (and bb2) have no successors
     and the last real insn doesn't have REG_ARGS_SIZE note, don't
     attempt to optimize, as the two basic blocks might have different
     REG_ARGS_SIZE depths.  For noreturn calls and unconditional
     traps there should be REG_ARG_SIZE notes, they could be missing
     for __builtin_unreachable () uses though.  */
  if (!nonfakeedges
      && !ACCUMULATE_OUTGOING_ARGS
      && (!INSN_P (last1)
          || !find_reg_note (last1, REG_ARGS_SIZE, NULL)))
    return false;

  /* fallthru edges must be forwarded to the same destination.  */
  if (fallthru1)
    {
      basic_block d1 = (forwarder_block_p (fallthru1->dest)
                        ? single_succ (fallthru1->dest): fallthru1->dest);
      basic_block d2 = (forwarder_block_p (fallthru2->dest)
                        ? single_succ (fallthru2->dest): fallthru2->dest);

      if (d1 != d2)
        return false;
    }

  /* Ensure the same EH region.  */
  {
    rtx n1 = find_reg_note (BB_END (bb1), REG_EH_REGION, 0);
    rtx n2 = find_reg_note (BB_END (bb2), REG_EH_REGION, 0);

    if (!n1 && n2)
      return false;

    if (n1 && (!n2 || XEXP (n1, 0) != XEXP (n2, 0)))
      return false;
  }

  /* The same checks as in try_crossjump_to_edge. It is required for RTL
     version of sequence abstraction.  */
  FOR_EACH_EDGE (e1, ei, bb2->succs)
    {
      edge e2;
      edge_iterator ei;
      basic_block d1 = e1->dest;

      if (FORWARDER_BLOCK_P (d1))
        d1 = EDGE_SUCC (d1, 0)->dest;

      FOR_EACH_EDGE (e2, ei, bb1->succs)
        {
          basic_block d2 = e2->dest;
          if (FORWARDER_BLOCK_P (d2))
            d2 = EDGE_SUCC (d2, 0)->dest;
          if (d1 == d2)
            break;
        }

      if (!e2)
        return false;
    }

  return true;
}

/* Returns true if BB basic block has a preserve label.  */

static bool
block_has_preserve_label (basic_block bb)
{
  return (bb
          && block_label (bb)
          && LABEL_PRESERVE_P (block_label (bb)));
}

/* E1 and E2 are edges with the same destination block.  Search their
   predecessors for common code.  If found, redirect control flow from
   (maybe the middle of) E1->SRC to (maybe the middle of) E2->SRC (dir_forward),
   or the other way around (dir_backward).  DIR specifies the allowed
   replacement direction.  */

static bool
try_crossjump_to_edge (int mode, edge e1, edge e2,
                       enum replace_direction dir)
{
  int nmatch;
  basic_block src1 = e1->src, src2 = e2->src;
  basic_block redirect_to, redirect_from, to_remove;
  basic_block osrc1, osrc2, redirect_edges_to, tmp;
  rtx_insn *newpos1, *newpos2;
  edge s;
  edge_iterator ei;

  newpos1 = newpos2 = NULL;

  /* If we have partitioned hot/cold basic blocks, it is a bad idea
     to try this optimization.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (crtl->has_bb_partition && reload_completed)
    return false;

  /* Search backward through forwarder blocks.  We don't need to worry
     about multiple entry or chained forwarders, as they will be optimized
     away.  We do this to look past the unconditional jump following a
     conditional jump that is required due to the current CFG shape.  */
  if (single_pred_p (src1)
      && FORWARDER_BLOCK_P (src1))
    e1 = single_pred_edge (src1), src1 = e1->src;

  if (single_pred_p (src2)
      && FORWARDER_BLOCK_P (src2))
    e2 = single_pred_edge (src2), src2 = e2->src;

  /* Nothing to do if we reach ENTRY, or a common source block.  */
  if (src1 == ENTRY_BLOCK_PTR_FOR_FN (cfun) || src2
      == ENTRY_BLOCK_PTR_FOR_FN (cfun))
    return false;
  if (src1 == src2)
    return false;

  /* Seeing more than 1 forwarder blocks would confuse us later...  */
  if (FORWARDER_BLOCK_P (e1->dest)
      && FORWARDER_BLOCK_P (single_succ (e1->dest)))
    return false;

  if (FORWARDER_BLOCK_P (e2->dest)
      && FORWARDER_BLOCK_P (single_succ (e2->dest)))
    return false;

  /* Likewise with dead code (possibly newly created by the other optimizations
     of cfg_cleanup).  */
  if (EDGE_COUNT (src1->preds) == 0 || EDGE_COUNT (src2->preds) == 0)
    return false;

  /* Look for the common insn sequence, part the first ...  */
  if (!outgoing_edges_match (mode, src1, src2))
    return false;

  /* ... and part the second.  */
  nmatch = flow_find_cross_jump (src1, src2, &newpos1, &newpos2, &dir);

  osrc1 = src1;
  osrc2 = src2;
  if (newpos1 != NULL_RTX)
    src1 = BLOCK_FOR_INSN (newpos1);
  if (newpos2 != NULL_RTX)
    src2 = BLOCK_FOR_INSN (newpos2);

  if (dir == dir_backward)
    {
#define SWAP(T, X, Y) do { T tmp = (X); (X) = (Y); (Y) = tmp; } while (0)
      SWAP (basic_block, osrc1, osrc2);
      SWAP (basic_block, src1, src2);
      SWAP (edge, e1, e2);
      SWAP (rtx_insn *, newpos1, newpos2);
#undef SWAP
    }

  /* Don't proceed with the crossjump unless we found a sufficient number
     of matching instructions or the 'from' block was totally matched
     (such that its predecessors will hopefully be redirected and the
     block removed).  */
  if ((nmatch < PARAM_VALUE (PARAM_MIN_CROSSJUMP_INSNS))
      && (newpos1 != BB_HEAD (src1)))
    return false;

  /* Avoid deleting preserve label when redirecting ABNORMAL edges.  */
  if (block_has_preserve_label (e1->dest)
      && (e1->flags & EDGE_ABNORMAL))
    return false;

  /* Here we know that the insns in the end of SRC1 which are common with SRC2
     will be deleted.
     If we have tablejumps in the end of SRC1 and SRC2
     they have been already compared for equivalence in outgoing_edges_match ()
     so replace the references to TABLE1 by references to TABLE2.  */
  {
      rtx_insn *label1, *label2;
      rtx_jump_table_data *table1, *table2;

      if (tablejump_p (BB_END (osrc1), &label1, &table1)
          && tablejump_p (BB_END (osrc2), &label2, &table2)
          && label1 != label2)
        {
          rtx_insn *insn;

          /* Replace references to LABEL1 with LABEL2.  */
          for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
            {
              /* Do not replace the label in SRC1->END because when deleting
                 a block whose end is a tablejump, the tablejump referenced
                 from the instruction is deleted too.  */
              if (insn != BB_END (osrc1))
                replace_label_in_insn (insn, label1, label2, true);
            }
        }
  }

  /* Avoid splitting if possible.  We must always split when SRC2 has
     EH predecessor edges, or we may end up with basic blocks with both
     normal and EH predecessor edges.  */
  if (newpos2 == BB_HEAD (src2)
      && !(EDGE_PRED (src2, 0)->flags & EDGE_EH))
    redirect_to = src2;
  else
    {
      if (newpos2 == BB_HEAD (src2))
        {
          /* Skip possible basic block header.  */
          if (LABEL_P (newpos2))
            newpos2 = NEXT_INSN (newpos2);
          while (DEBUG_INSN_P (newpos2))
            newpos2 = NEXT_INSN (newpos2);
          if (NOTE_P (newpos2))
            newpos2 = NEXT_INSN (newpos2);
          while (DEBUG_INSN_P (newpos2))
            newpos2 = NEXT_INSN (newpos2);
        }

      if (dump_file)
        fprintf (dump_file, "Splitting bb %i before %i insns\n",
                 src2->index, nmatch);
      redirect_to = split_block (src2, PREV_INSN (newpos2))->dest;
    }

  if (dump_file)
    fprintf (dump_file,
             "Cross jumping from bb %i to bb %i; %i common insns\n",
             src1->index, src2->index, nmatch);

  /* We may have some registers visible through the block.  */
  df_set_bb_dirty (redirect_to);

  if (osrc2 == src2)
    redirect_edges_to = redirect_to;
  else
    redirect_edges_to = osrc2;

  /* Recompute the frequencies and counts of outgoing edges.  */
  FOR_EACH_EDGE (s, ei, redirect_edges_to->succs)
    {
      edge s2;
      edge_iterator ei;
      basic_block d = s->dest;

      if (FORWARDER_BLOCK_P (d))
        d = single_succ (d);

      FOR_EACH_EDGE (s2, ei, src1->succs)
        {
          basic_block d2 = s2->dest;
          if (FORWARDER_BLOCK_P (d2))
            d2 = single_succ (d2);
          if (d == d2)
            break;
        }

      s->count += s2->count;

      /* Take care to update possible forwarder blocks.  We verified
         that there is no more than one in the chain, so we can't run
         into infinite loop.  */
      if (FORWARDER_BLOCK_P (s->dest))
        {
          single_succ_edge (s->dest)->count += s2->count;
          s->dest->count += s2->count;
          s->dest->frequency += EDGE_FREQUENCY (s);
        }

      if (FORWARDER_BLOCK_P (s2->dest))
        {
          single_succ_edge (s2->dest)->count -= s2->count;
          if (single_succ_edge (s2->dest)->count < 0)
            single_succ_edge (s2->dest)->count = 0;
          s2->dest->count -= s2->count;
          s2->dest->frequency -= EDGE_FREQUENCY (s);
          if (s2->dest->frequency < 0)
            s2->dest->frequency = 0;
          if (s2->dest->count < 0)
            s2->dest->count = 0;
        }

      if (!redirect_edges_to->frequency && !src1->frequency)
        s->probability = (s->probability + s2->probability) / 2;
      else
        s->probability
          = ((s->probability * redirect_edges_to->frequency +
              s2->probability * src1->frequency)
             / (redirect_edges_to->frequency + src1->frequency));
    }

  /* Adjust count and frequency for the block.  An earlier jump
     threading pass may have left the profile in an inconsistent
     state (see update_bb_profile_for_threading) so we must be
     prepared for overflows.  */
  tmp = redirect_to;
  do
    {
      tmp->count += src1->count;
      tmp->frequency += src1->frequency;
      if (tmp->frequency > BB_FREQ_MAX)
        tmp->frequency = BB_FREQ_MAX;
      if (tmp == redirect_edges_to)
        break;
      tmp = find_fallthru_edge (tmp->succs)->dest;
    }
  while (true);
  update_br_prob_note (redirect_edges_to);

  /* Edit SRC1 to go to REDIRECT_TO at NEWPOS1.  */

  /* Skip possible basic block header.  */
  if (LABEL_P (newpos1))
    newpos1 = NEXT_INSN (newpos1);

  while (DEBUG_INSN_P (newpos1))
    newpos1 = NEXT_INSN (newpos1);

  if (NOTE_INSN_BASIC_BLOCK_P (newpos1))
    newpos1 = NEXT_INSN (newpos1);

  while (DEBUG_INSN_P (newpos1))
    newpos1 = NEXT_INSN (newpos1);

  redirect_from = split_block (src1, PREV_INSN (newpos1))->src;
  to_remove = single_succ (redirect_from);

  redirect_edge_and_branch_force (single_succ_edge (redirect_from), redirect_to);
  delete_basic_block (to_remove);

  update_forwarder_flag (redirect_from);
  if (redirect_to != src2)
    update_forwarder_flag (src2);

  return true;
}

/* Search the predecessors of BB for common insn sequences.  When found,
   share code between them by redirecting control flow.  Return true if
   any changes made.  */

static bool
try_crossjump_bb (int mode, basic_block bb)
{
  edge e, e2, fallthru;
  bool changed;
  unsigned max, ix, ix2;

  /* Nothing to do if there is not at least two incoming edges.  */
  if (EDGE_COUNT (bb->preds) < 2)
    return false;

  /* Don't crossjump if this block ends in a computed jump,
     unless we are optimizing for size.  */
  if (optimize_bb_for_size_p (bb)
      && bb != EXIT_BLOCK_PTR_FOR_FN (cfun)
      && computed_jump_p (BB_END (bb)))
    return false;

  /* If we are partitioning hot/cold basic blocks, we don't want to
     mess up unconditional or indirect jumps that cross between hot
     and cold sections.

     Basic block partitioning may result in some jumps that appear to
     be optimizable (or blocks that appear to be mergeable), but which really
     must be left untouched (they are required to make it safely across
     partition boundaries).  See the comments at the top of
     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */

  if (BB_PARTITION (EDGE_PRED (bb, 0)->src) !=
                                        BB_PARTITION (EDGE_PRED (bb, 1)->src)
      || (EDGE_PRED (bb, 0)->flags & EDGE_CROSSING))
    return false;

  /* It is always cheapest to redirect a block that ends in a branch to
     a block that falls through into BB, as that adds no branches to the
     program.  We'll try that combination first.  */
  fallthru = NULL;
  max = PARAM_VALUE (PARAM_MAX_CROSSJUMP_EDGES);

  if (EDGE_COUNT (bb->preds) > max)
    return false;

  fallthru = find_fallthru_edge (bb->preds);

  changed = false;
  for (ix = 0; ix < EDGE_COUNT (bb->preds);)
    {
      e = EDGE_PRED (bb, ix);
      ix++;

      /* As noted above, first try with the fallthru predecessor (or, a
         fallthru predecessor if we are in cfglayout mode).  */
      if (fallthru)
        {
          /* Don't combine the fallthru edge into anything else.
             If there is a match, we'll do it the other way around.  */
          if (e == fallthru)
            continue;
          /* If nothing changed since the last attempt, there is nothing
             we can do.  */
          if (!first_pass
              && !((e->src->flags & BB_MODIFIED)
                   || (fallthru->src->flags & BB_MODIFIED)))
            continue;

          if (try_crossjump_to_edge (mode, e, fallthru, dir_forward))
            {
              changed = true;
              ix = 0;
              continue;
            }
        }

      /* Non-obvious work limiting check: Recognize that we're going
         to call try_crossjump_bb on every basic block.  So if we have
         two blocks with lots of outgoing edges (a switch) and they
         share lots of common destinations, then we would do the
         cross-jump check once for each common destination.

         Now, if the blocks actually are cross-jump candidates, then
         all of their destinations will be shared.  Which means that
         we only need check them for cross-jump candidacy once.  We
         can eliminate redundant checks of crossjump(A,B) by arbitrarily
         choosing to do the check from the block for which the edge
         in question is the first successor of A.  */
      if (EDGE_SUCC (e->src, 0) != e)
        continue;

      for (ix2 = 0; ix2 < EDGE_COUNT (bb->preds); ix2++)
        {
          e2 = EDGE_PRED (bb, ix2);

          if (e2 == e)
            continue;

          /* We've already checked the fallthru edge above.  */
          if (e2 == fallthru)
            continue;

          /* The "first successor" check above only prevents multiple
             checks of crossjump(A,B).  In order to prevent redundant
             checks of crossjump(B,A), require that A be the block
             with the lowest index.  */
          if (e->src->index > e2->src->index)
            continue;

          /* If nothing changed since the last attempt, there is nothing
             we can do.  */
          if (!first_pass
              && !((e->src->flags & BB_MODIFIED)
                   || (e2->src->flags & BB_MODIFIED)))
            continue;

          /* Both e and e2 are not fallthru edges, so we can crossjump in either
             direction.  */
          if (try_crossjump_to_edge (mode, e, e2, dir_both))
            {
              changed = true;
              ix = 0;
              break;
            }
        }
    }

  if (changed)
    crossjumps_occured = true;

  return changed;
}

/* Search the successors of BB for common insn sequences.  When found,
   share code between them by moving it across the basic block
   boundary.  Return true if any changes made.  */

static bool
try_head_merge_bb (basic_block bb)
{
  basic_block final_dest_bb = NULL;
  int max_match = INT_MAX;
  edge e0;
  rtx_insn **headptr, **currptr, **nextptr;
  bool changed, moveall;
  unsigned ix;
  rtx_insn *e0_last_head;
  rtx cond;
  rtx_insn *move_before;
  unsigned nedges = EDGE_COUNT (bb->succs);
  rtx_insn *jump = BB_END (bb);
  regset live, live_union;

  /* Nothing to do if there is not at least two outgoing edges.  */
  if (nedges < 2)
    return false;

  /* Don't crossjump if this block ends in a computed jump,
     unless we are optimizing for size.  */
  if (optimize_bb_for_size_p (bb)
      && bb != EXIT_BLOCK_PTR_FOR_FN (cfun)
      && computed_jump_p (BB_END (bb)))
    return false;

  cond = get_condition (jump, &move_before, true, false);
  if (cond == NULL_RTX)
    {
      if (HAVE_cc0 && reg_mentioned_p (cc0_rtx, jump))
        move_before = prev_nonnote_nondebug_insn (jump);
      else
        move_before = jump;
    }

  for (ix = 0; ix < nedges; ix++)
    if (EDGE_SUCC (bb, ix)->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
      return false;

  for (ix = 0; ix < nedges; ix++)
    {
      edge e = EDGE_SUCC (bb, ix);
      basic_block other_bb = e->dest;

      if (df_get_bb_dirty (other_bb))
        {
          block_was_dirty = true;
          return false;
        }

      if (e->flags & EDGE_ABNORMAL)
        return false;

      /* Normally, all destination blocks must only be reachable from this
         block, i.e. they must have one incoming edge.

         There is one special case we can handle, that of multiple consecutive
         jumps where the first jumps to one of the targets of the second jump.
         This happens frequently in switch statements for default labels.
         The structure is as follows:
         FINAL_DEST_BB
         ....
         if (cond) jump A;
         fall through
         BB
         jump with targets A, B, C, D...
         A
         has two incoming edges, from FINAL_DEST_BB and BB

         In this case, we can try to move the insns through BB and into
         FINAL_DEST_BB.  */
      if (EDGE_COUNT (other_bb->preds) != 1)
        {
          edge incoming_edge, incoming_bb_other_edge;
          edge_iterator ei;

          if (final_dest_bb != NULL
              || EDGE_COUNT (other_bb->preds) != 2)
            return false;

          /* We must be able to move the insns across the whole block.  */
          move_before = BB_HEAD (bb);
          while (!NONDEBUG_INSN_P (move_before))
            move_before = NEXT_INSN (move_before);

          if (EDGE_COUNT (bb->preds) != 1)
            return false;
          incoming_edge = EDGE_PRED (bb, 0);
          final_dest_bb = incoming_edge->src;
          if (EDGE_COUNT (final_dest_bb->succs) != 2)
            return false;
          FOR_EACH_EDGE (incoming_bb_other_edge, ei, final_dest_bb->succs)
            if (incoming_bb_other_edge != incoming_edge)
              break;
          if (incoming_bb_other_edge->dest != other_bb)
            return false;
        }
    }

  e0 = EDGE_SUCC (bb, 0);
  e0_last_head = NULL;
  changed = false;

  for (ix = 1; ix < nedges; ix++)
    {
      edge e = EDGE_SUCC (bb, ix);
      rtx_insn *e0_last, *e_last;
      int nmatch;

      nmatch = flow_find_head_matching_sequence (e0->dest, e->dest,
                                                 &e0_last, &e_last, 0);
      if (nmatch == 0)
        return false;

      if (nmatch < max_match)
        {
          max_match = nmatch;
          e0_last_head = e0_last;
        }
    }

  /* If we matched an entire block, we probably have to avoid moving the
     last insn.  */
  if (max_match > 0
      && e0_last_head == BB_END (e0->dest)
      && (find_reg_note (e0_last_head, REG_EH_REGION, 0)
          || control_flow_insn_p (e0_last_head)))
    {
      max_match--;
      if (max_match == 0)
        return false;
      do
        e0_last_head = prev_real_insn (e0_last_head);
      while (DEBUG_INSN_P (e0_last_head));
    }

  if (max_match == 0)
    return false;

  /* We must find a union of the live registers at each of the end points.  */
  live = BITMAP_ALLOC (NULL);
  live_union = BITMAP_ALLOC (NULL);

  currptr = XNEWVEC (rtx_insn *, nedges);
  headptr = XNEWVEC (rtx_insn *, nedges);
  nextptr = XNEWVEC (rtx_insn *, nedges);

  for (ix = 0; ix < nedges; ix++)
    {
      int j;
      basic_block merge_bb = EDGE_SUCC (bb, ix)->dest;
      rtx_insn *head = BB_HEAD (merge_bb);

      while (!NONDEBUG_INSN_P (head))
        head = NEXT_INSN (head);
      headptr[ix] = head;
      currptr[ix] = head;

      /* Compute the end point and live information  */
      for (j = 1; j < max_match; j++)
        do
          head = NEXT_INSN (head);
        while (!NONDEBUG_INSN_P (head));
      simulate_backwards_to_point (merge_bb, live, head);
      IOR_REG_SET (live_union, live);
    }

  /* If we're moving across two blocks, verify the validity of the
     first move, then adjust the target and let the loop below deal
     with the final move.  */
  if (final_dest_bb != NULL)
    {
      rtx_insn *move_upto;

      moveall = can_move_insns_across (currptr[0], e0_last_head, move_before,
                                       jump, e0->dest, live_union,
                                       NULL, &move_upto);
      if (!moveall)
        {
          if (move_upto == NULL_RTX)
            goto out;

          while (e0_last_head != move_upto)
            {
              df_simulate_one_insn_backwards (e0->dest, e0_last_head,
                                              live_union);
              e0_last_head = PREV_INSN (e0_last_head);
            }
        }
      if (e0_last_head == NULL_RTX)
        goto out;

      jump = BB_END (final_dest_bb);
      cond = get_condition (jump, &move_before, true, false);
      if (cond == NULL_RTX)
        {
          if (HAVE_cc0 && reg_mentioned_p (cc0_rtx, jump))
            move_before = prev_nonnote_nondebug_insn (jump);
          else
            move_before = jump;
        }
    }

  do
    {
      rtx_insn *move_upto;
      moveall = can_move_insns_across (currptr[0], e0_last_head,
                                       move_before, jump, e0->dest, live_union,
                                       NULL, &move_upto);
      if (!moveall && move_upto == NULL_RTX)
        {
          if (jump == move_before)
            break;

          /* Try again, using a different insertion point.  */
          move_before = jump;

          /* Don't try moving before a cc0 user, as that may invalidate
             the cc0.  */
          if (HAVE_cc0 && reg_mentioned_p (cc0_rtx, jump))
            break;

          continue;
        }

      if (final_dest_bb && !moveall)
        /* We haven't checked whether a partial move would be OK for the first
           move, so we have to fail this case.  */
        break;

      changed = true;
      for (;;)
        {
          if (currptr[0] == move_upto)
            break;
          for (ix = 0; ix < nedges; ix++)
            {
              rtx_insn *curr = currptr[ix];
              do
                curr = NEXT_INSN (curr);
              while (!NONDEBUG_INSN_P (curr));
              currptr[ix] = curr;
            }
        }

      /* If we can't currently move all of the identical insns, remember
         each insn after the range that we'll merge.  */
      if (!moveall)
        for (ix = 0; ix < nedges; ix++)
          {
            rtx_insn *curr = currptr[ix];
            do
              curr = NEXT_INSN (curr);
            while (!NONDEBUG_INSN_P (curr));
            nextptr[ix] = curr;
          }

      reorder_insns (headptr[0], currptr[0], PREV_INSN (move_before));
      df_set_bb_dirty (EDGE_SUCC (bb, 0)->dest);
      if (final_dest_bb != NULL)
        df_set_bb_dirty (final_dest_bb);
      df_set_bb_dirty (bb);
      for (ix = 1; ix < nedges; ix++)
        {
          df_set_bb_dirty (EDGE_SUCC (bb, ix)->dest);
          delete_insn_chain (headptr[ix], currptr[ix], false);
        }
      if (!moveall)
        {
          if (jump == move_before)
            break;

          /* For the unmerged insns, try a different insertion point.  */
          move_before = jump;

          /* Don't try moving before a cc0 user, as that may invalidate
             the cc0.  */
          if (HAVE_cc0 && reg_mentioned_p (cc0_rtx, jump))
            break;

          for (ix = 0; ix < nedges; ix++)
            currptr[ix] = headptr[ix] = nextptr[ix];
        }
    }
  while (!moveall);

 out:
  free (currptr);
  free (headptr);
  free (nextptr);

  crossjumps_occured |= changed;

  return changed;
}

/* Return true if BB contains just bb note, or bb note followed
   by only DEBUG_INSNs.  */

static bool
trivially_empty_bb_p (basic_block bb)
{
  rtx_insn *insn = BB_END (bb);

  while (1)
    {
      if (insn == BB_HEAD (bb))
        return true;
      if (!DEBUG_INSN_P (insn))
        return false;
      insn = PREV_INSN (insn);
    }
}

/* Return true if BB contains just a return and possibly a USE of the
   return value.  Fill in *RET and *USE with the return and use insns
   if any found, otherwise NULL.  */

static bool
bb_is_just_return (basic_block bb, rtx_insn **ret, rtx_insn **use)
{
  *ret = *use = NULL;
  rtx_insn *insn;

  if (bb == EXIT_BLOCK_PTR_FOR_FN (cfun))
    return false;

  FOR_BB_INSNS (bb, insn)
    if (NONDEBUG_INSN_P (insn))
      {
        if (!*ret && ANY_RETURN_P (PATTERN (insn)))
          *ret = insn;
        else if (!*ret && !*use && GET_CODE (PATTERN (insn)) == USE
            && REG_P (XEXP (PATTERN (insn), 0))
            && REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0)))
          *use = insn;
        else
          return false;
      }

  return !!*ret;
}

/* Do simple CFG optimizations - basic block merging, simplifying of jump
   instructions etc.  Return nonzero if changes were made.  */

static bool
try_optimize_cfg (int mode)
{
  bool changed_overall = false;
  bool changed;
  int iterations = 0;
  basic_block bb, b, next;

  if (mode & (CLEANUP_CROSSJUMP | CLEANUP_THREADING))
    clear_bb_flags ();

  crossjumps_occured = false;

  FOR_EACH_BB_FN (bb, cfun)
    update_forwarder_flag (bb);

  if (! targetm.cannot_modify_jumps_p ())
    {
      first_pass = true;
      /* Attempt to merge blocks as made possible by edge removal.  If
         a block has only one successor, and the successor has only
         one predecessor, they may be combined.  */
      do
        {
          block_was_dirty = false;
          changed = false;
          iterations++;

          if (dump_file)
            fprintf (dump_file,
                     "\n\ntry_optimize_cfg iteration %i\n\n",
                     iterations);

          for (b = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb; b
               != EXIT_BLOCK_PTR_FOR_FN (cfun);)
            {
              basic_block c;
              edge s;
              bool changed_here = false;

              /* Delete trivially dead basic blocks.  This is either
                 blocks with no predecessors, or empty blocks with no
                 successors.  However if the empty block with no
                 successors is the successor of the ENTRY_BLOCK, it is
                 kept.  This ensures that the ENTRY_BLOCK will have a
                 successor which is a precondition for many RTL
                 passes.  Empty blocks may result from expanding
                 __builtin_unreachable ().  */
              if (EDGE_COUNT (b->preds) == 0
                  || (EDGE_COUNT (b->succs) == 0
                      && trivially_empty_bb_p (b)
                      && single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun))->dest
                      != b))
                {
                  c = b->prev_bb;
                  if (EDGE_COUNT (b->preds) > 0)
                    {
                      edge e;
                      edge_iterator ei;

                      if (current_ir_type () == IR_RTL_CFGLAYOUT)
                        {
                          if (BB_FOOTER (b)
                              && BARRIER_P (BB_FOOTER (b)))
                            FOR_EACH_EDGE (e, ei, b->preds)
                              if ((e->flags & EDGE_FALLTHRU)
                                  && BB_FOOTER (e->src) == NULL)
                                {
                                  if (BB_FOOTER (b))
                                    {
                                      BB_FOOTER (e->src) = BB_FOOTER (b);
                                      BB_FOOTER (b) = NULL;
                                    }
                                  else
                                    {
                                      start_sequence ();
                                      BB_FOOTER (e->src) = emit_barrier ();
                                      end_sequence ();
                                    }
                                }
                        }
                      else
                        {
                          rtx_insn *last = get_last_bb_insn (b);
                          if (last && BARRIER_P (last))
                            FOR_EACH_EDGE (e, ei, b->preds)
                              if ((e->flags & EDGE_FALLTHRU))
                                emit_barrier_after (BB_END (e->src));
                        }
                    }
                  delete_basic_block (b);
                  changed = true;
                  /* Avoid trying to remove the exit block.  */
                  b = (c == ENTRY_BLOCK_PTR_FOR_FN (cfun) ? c->next_bb : c);
                  continue;
                }

              /* Remove code labels no longer used.  */
              if (single_pred_p (b)
                  && (single_pred_edge (b)->flags & EDGE_FALLTHRU)
                  && !(single_pred_edge (b)->flags & EDGE_COMPLEX)
                  && LABEL_P (BB_HEAD (b))
                  && !LABEL_PRESERVE_P (BB_HEAD (b))
                  /* If the previous block ends with a branch to this
                     block, we can't delete the label.  Normally this
                     is a condjump that is yet to be simplified, but
                     if CASE_DROPS_THRU, this can be a tablejump with
                     some element going to the same place as the
                     default (fallthru).  */
                  && (single_pred (b) == ENTRY_BLOCK_PTR_FOR_FN (cfun)
                      || !JUMP_P (BB_END (single_pred (b)))
                      || ! label_is_jump_target_p (BB_HEAD (b),
                                                   BB_END (single_pred (b)))))
                {
                  delete_insn (BB_HEAD (b));
                  if (dump_file)
                    fprintf (dump_file, "Deleted label in block %i.\n",
                             b->index);
                }

              /* If we fall through an empty block, we can remove it.  */
              if (!(mode & (CLEANUP_CFGLAYOUT | CLEANUP_NO_INSN_DEL))
                  && single_pred_p (b)
                  && (single_pred_edge (b)->flags & EDGE_FALLTHRU)
                  && !LABEL_P (BB_HEAD (b))
                  && FORWARDER_BLOCK_P (b)
                  /* Note that forwarder_block_p true ensures that
                     there is a successor for this block.  */
                  && (single_succ_edge (b)->flags & EDGE_FALLTHRU)
                  && n_basic_blocks_for_fn (cfun) > NUM_FIXED_BLOCKS + 1)
                {
                  if (dump_file)
                    fprintf (dump_file,
                             "Deleting fallthru block %i.\n",
                             b->index);

                  c = ((b->prev_bb == ENTRY_BLOCK_PTR_FOR_FN (cfun))
                       ? b->next_bb : b->prev_bb);
                  redirect_edge_succ_nodup (single_pred_edge (b),
                                            single_succ (b));
                  delete_basic_block (b);
                  changed = true;
                  b = c;
                  continue;
                }

              /* Merge B with its single successor, if any.  */
              if (single_succ_p (b)
                  && (s = single_succ_edge (b))
                  && !(s->flags & EDGE_COMPLEX)
                  && (c = s->dest) != EXIT_BLOCK_PTR_FOR_FN (cfun)
                  && single_pred_p (c)
                  && b != c)
                {
                  /* When not in cfg_layout mode use code aware of reordering
                     INSN.  This code possibly creates new basic blocks so it
                     does not fit merge_blocks interface and is kept here in
                     hope that it will become useless once more of compiler
                     is transformed to use cfg_layout mode.  */

                  if ((mode & CLEANUP_CFGLAYOUT)
                      && can_merge_blocks_p (b, c))
                    {
                      merge_blocks (b, c);
                      update_forwarder_flag (b);
                      changed_here = true;
                    }
                  else if (!(mode & CLEANUP_CFGLAYOUT)
                           /* If the jump insn has side effects,
                              we can't kill the edge.  */
                           && (!JUMP_P (BB_END (b))
                               || (reload_completed
                                   ? simplejump_p (BB_END (b))
                                   : (onlyjump_p (BB_END (b))
                                      && !tablejump_p (BB_END (b),
                                                       NULL, NULL))))
                           && (next = merge_blocks_move (s, b, c, mode)))
                      {
                        b = next;
                        changed_here = true;
                      }
                }

              /* Try to change a branch to a return to just that return.  */
              rtx_insn *ret, *use;
              if (single_succ_p (b)
                  && onlyjump_p (BB_END (b))
                  && bb_is_just_return (single_succ (b), &ret, &use))
                {
                  if (redirect_jump (as_a <rtx_jump_insn *> (BB_END (b)),
                                     PATTERN (ret), 0))
                    {
                      if (use)
                        emit_insn_before (copy_insn (PATTERN (use)),
                                          BB_END (b));
                      if (dump_file)
                        fprintf (dump_file, "Changed jump %d->%d to return.\n",
                                 b->index, single_succ (b)->index);
                      redirect_edge_succ (single_succ_edge (b),
                                          EXIT_BLOCK_PTR_FOR_FN (cfun));
                      single_succ_edge (b)->flags &= ~EDGE_CROSSING;
                      changed_here = true;
                    }
                }

              /* Try to change a conditional branch to a return to the
                 respective conditional return.  */
              if (EDGE_COUNT (b->succs) == 2
                  && any_condjump_p (BB_END (b))
                  && bb_is_just_return (BRANCH_EDGE (b)->dest, &ret, &use))
                {
                  if (redirect_jump (as_a <rtx_jump_insn *> (BB_END (b)),
                                     PATTERN (ret), 0))
                    {
                      if (use)
                        emit_insn_before (copy_insn (PATTERN (use)),
                                          BB_END (b));
                      if (dump_file)
                        fprintf (dump_file, "Changed conditional jump %d->%d "
                                 "to conditional return.\n",
                                 b->index, BRANCH_EDGE (b)->dest->index);
                      redirect_edge_succ (BRANCH_EDGE (b),
                                          EXIT_BLOCK_PTR_FOR_FN (cfun));
                      BRANCH_EDGE (b)->flags &= ~EDGE_CROSSING;
                      changed_here = true;
                    }
                }

              /* Try to flip a conditional branch that falls through to
                 a return so that it becomes a conditional return and a
                 new jump to the original branch target.  */
              if (EDGE_COUNT (b->succs) == 2
                  && BRANCH_EDGE (b)->dest != EXIT_BLOCK_PTR_FOR_FN (cfun)
                  && any_condjump_p (BB_END (b))
                  && bb_is_just_return (FALLTHRU_EDGE (b)->dest, &ret, &use))
                {
                  if (invert_jump (as_a <rtx_jump_insn *> (BB_END (b)),
                                   JUMP_LABEL (BB_END (b)), 0))
                    {
                      basic_block new_ft = BRANCH_EDGE (b)->dest;
                      if (redirect_jump (as_a <rtx_jump_insn *> (BB_END (b)),
                                         PATTERN (ret), 0))
                        {
                          if (use)
                            emit_insn_before (copy_insn (PATTERN (use)),
                                              BB_END (b));
                          if (dump_file)
                            fprintf (dump_file, "Changed conditional jump "
                                     "%d->%d to conditional return, adding "
                                     "fall-through jump.\n",
                                     b->index, BRANCH_EDGE (b)->dest->index);
                          redirect_edge_succ (BRANCH_EDGE (b),
                                              EXIT_BLOCK_PTR_FOR_FN (cfun));
                          BRANCH_EDGE (b)->flags &= ~EDGE_CROSSING;
                          std::swap (BRANCH_EDGE (b)->probability,
                                     FALLTHRU_EDGE (b)->probability);
                          update_br_prob_note (b);
                          basic_block jb = force_nonfallthru (FALLTHRU_EDGE (b));
                          notice_new_block (jb);
                          if (!redirect_jump (as_a <rtx_jump_insn *> (BB_END (jb)),
                                              block_label (new_ft), 0))
                            gcc_unreachable ();
                          redirect_edge_succ (single_succ_edge (jb), new_ft);
                          changed_here = true;
                        }
                      else
                        {
                          /* Invert the jump back to what it was.  This should
                             never fail.  */
                          if (!invert_jump (as_a <rtx_jump_insn *> (BB_END (b)),
                                            JUMP_LABEL (BB_END (b)), 0))
                            gcc_unreachable ();
                        }
                    }
                }

              /* Simplify branch over branch.  */
              if ((mode & CLEANUP_EXPENSIVE)
                   && !(mode & CLEANUP_CFGLAYOUT)
                   && try_simplify_condjump (b))
                changed_here = true;

              /* If B has a single outgoing edge, but uses a
                 non-trivial jump instruction without side-effects, we
                 can either delete the jump entirely, or replace it
                 with a simple unconditional jump.  */
              if (single_succ_p (b)
                  && single_succ (b) != EXIT_BLOCK_PTR_FOR_FN (cfun)
                  && onlyjump_p (BB_END (b))
                  && !CROSSING_JUMP_P (BB_END (b))
                  && try_redirect_by_replacing_jump (single_succ_edge (b),
                                                     single_succ (b),
                                                     (mode & CLEANUP_CFGLAYOUT) != 0))
                {
                  update_forwarder_flag (b);
                  changed_here = true;
                }

              /* Simplify branch to branch.  */
              if (try_forward_edges (mode, b))
                {
                  update_forwarder_flag (b);
                  changed_here = true;
                }

              /* Look for shared code between blocks.  */
              if ((mode & CLEANUP_CROSSJUMP)
                  && try_crossjump_bb (mode, b))
                changed_here = true;

              if ((mode & CLEANUP_CROSSJUMP)
                  /* This can lengthen register lifetimes.  Do it only after
                     reload.  */
                  && reload_completed
                  && try_head_merge_bb (b))
                changed_here = true;

              /* Don't get confused by the index shift caused by
                 deleting blocks.  */
              if (!changed_here)
                b = b->next_bb;
              else
                changed = true;
            }

          if ((mode & CLEANUP_CROSSJUMP)
              && try_crossjump_bb (mode, EXIT_BLOCK_PTR_FOR_FN (cfun)))
            changed = true;

          if (block_was_dirty)
            {
              /* This should only be set by head-merging.  */
              gcc_assert (mode & CLEANUP_CROSSJUMP);
              df_analyze ();
            }

          if (changed)
            {
              /* Edge forwarding in particular can cause hot blocks previously
                 reached by both hot and cold blocks to become dominated only
                 by cold blocks. This will cause the verification below to fail,
                 and lead to now cold code in the hot section. This is not easy
                 to detect and fix during edge forwarding, and in some cases
                 is only visible after newly unreachable blocks are deleted,
                 which will be done in fixup_partitions.  */
              fixup_partitions ();
              checking_verify_flow_info ();
            }

          changed_overall |= changed;
          first_pass = false;
        }
      while (changed);
    }

  FOR_ALL_BB_FN (b, cfun)
    b->flags &= ~(BB_FORWARDER_BLOCK | BB_NONTHREADABLE_BLOCK);

  return changed_overall;
}
\f
/* Delete all unreachable basic blocks.  */

bool
delete_unreachable_blocks (void)
{
  bool changed = false;
  basic_block b, prev_bb;

  find_unreachable_blocks ();

  /* When we're in GIMPLE mode and there may be debug insns, we should
     delete blocks in reverse dominator order, so as to get a chance
     to substitute all released DEFs into debug stmts.  If we don't
     have dominators information, walking blocks backward gets us a
     better chance of retaining most debug information than
     otherwise.  */
  if (MAY_HAVE_DEBUG_INSNS && current_ir_type () == IR_GIMPLE
      && dom_info_available_p (CDI_DOMINATORS))
    {
      for (b = EXIT_BLOCK_PTR_FOR_FN (cfun)->prev_bb;
           b != ENTRY_BLOCK_PTR_FOR_FN (cfun); b = prev_bb)
        {
          prev_bb = b->prev_bb;

          if (!(b->flags & BB_REACHABLE))
            {
              /* Speed up the removal of blocks that don't dominate
                 others.  Walking backwards, this should be the common
                 case.  */
              if (!first_dom_son (CDI_DOMINATORS, b))
                delete_basic_block (b);
              else
                {
                  vec<basic_block> h
                    = get_all_dominated_blocks (CDI_DOMINATORS, b);

                  while (h.length ())
                    {
                      b = h.pop ();

                      prev_bb = b->prev_bb;

                      gcc_assert (!(b->flags & BB_REACHABLE));

                      delete_basic_block (b);
                    }

                  h.release ();
                }

              changed = true;
            }
        }
    }
  else
    {
      for (b = EXIT_BLOCK_PTR_FOR_FN (cfun)->prev_bb;
           b != ENTRY_BLOCK_PTR_FOR_FN (cfun); b = prev_bb)
        {
          prev_bb = b->prev_bb;

          if (!(b->flags & BB_REACHABLE))
            {
              delete_basic_block (b);
              changed = true;
            }
        }
    }

  if (changed)
    tidy_fallthru_edges ();
  return changed;
}

/* Delete any jump tables never referenced.  We can't delete them at the
   time of removing tablejump insn as they are referenced by the preceding
   insns computing the destination, so we delay deleting and garbagecollect
   them once life information is computed.  */
void
delete_dead_jumptables (void)
{
  basic_block bb;

  /* A dead jump table does not belong to any basic block.  Scan insns
     between two adjacent basic blocks.  */
  FOR_EACH_BB_FN (bb, cfun)
    {
      rtx_insn *insn, *next;

      for (insn = NEXT_INSN (BB_END (bb));
           insn && !NOTE_INSN_BASIC_BLOCK_P (insn);
           insn = next)
        {
          next = NEXT_INSN (insn);
          if (LABEL_P (insn)
              && LABEL_NUSES (insn) == LABEL_PRESERVE_P (insn)
              && JUMP_TABLE_DATA_P (next))
            {
              rtx_insn *label = insn, *jump = next;

              if (dump_file)
                fprintf (dump_file, "Dead jumptable %i removed\n",
                         INSN_UID (insn));

              next = NEXT_INSN (next);
              delete_insn (jump);
              delete_insn (label);
            }
        }
    }
}

\f
/* Tidy the CFG by deleting unreachable code and whatnot.  */

bool
cleanup_cfg (int mode)
{
  bool changed = false;

  /* Set the cfglayout mode flag here.  We could update all the callers
     but that is just inconvenient, especially given that we eventually
     want to have cfglayout mode as the default.  */
  if (current_ir_type () == IR_RTL_CFGLAYOUT)
    mode |= CLEANUP_CFGLAYOUT;

  timevar_push (TV_CLEANUP_CFG);
  if (delete_unreachable_blocks ())
    {
      changed = true;
      /* We've possibly created trivially dead code.  Cleanup it right
         now to introduce more opportunities for try_optimize_cfg.  */
      if (!(mode & (CLEANUP_NO_INSN_DEL))
          && !reload_completed)
        delete_trivially_dead_insns (get_insns (), max_reg_num ());
    }

  compact_blocks ();

  /* To tail-merge blocks ending in the same noreturn function (e.g.
     a call to abort) we have to insert fake edges to exit.  Do this
     here once.  The fake edges do not interfere with any other CFG
     cleanups.  */
  if (mode & CLEANUP_CROSSJUMP)
    add_noreturn_fake_exit_edges ();

  if (!dbg_cnt (cfg_cleanup))
    return changed;

  while (try_optimize_cfg (mode))
    {
      delete_unreachable_blocks (), changed = true;
      if (!(mode & CLEANUP_NO_INSN_DEL))
        {
          /* Try to remove some trivially dead insns when doing an expensive
             cleanup.  But delete_trivially_dead_insns doesn't work after
             reload (it only handles pseudos) and run_fast_dce is too costly
             to run in every iteration.

             For effective cross jumping, we really want to run a fast DCE to
             clean up any dead conditions, or they get in the way of performing
             useful tail merges.

             Other transformations in cleanup_cfg are not so sensitive to dead
             code, so delete_trivially_dead_insns or even doing nothing at all
             is good enough.  */
          if ((mode & CLEANUP_EXPENSIVE) && !reload_completed
              && !delete_trivially_dead_insns (get_insns (), max_reg_num ()))
            break;
          if ((mode & CLEANUP_CROSSJUMP) && crossjumps_occured)
            run_fast_dce ();
        }
      else
        break;
    }

  if (mode & CLEANUP_CROSSJUMP)
    remove_fake_exit_edges ();

  /* Don't call delete_dead_jumptables in cfglayout mode, because
     that function assumes that jump tables are in the insns stream.
     But we also don't _have_ to delete dead jumptables in cfglayout
     mode because we shouldn't even be looking at things that are
     not in a basic block.  Dead jumptables are cleaned up when
     going out of cfglayout mode.  */
  if (!(mode & CLEANUP_CFGLAYOUT))
    delete_dead_jumptables ();

  /* ???  We probably do this way too often.  */
  if (current_loops
      && (changed
          || (mode & CLEANUP_CFG_CHANGED)))
    {
      timevar_push (TV_REPAIR_LOOPS);
      /* The above doesn't preserve dominance info if available.  */
      gcc_assert (!dom_info_available_p (CDI_DOMINATORS));
      calculate_dominance_info (CDI_DOMINATORS);
      fix_loop_structure (NULL);
      free_dominance_info (CDI_DOMINATORS);
      timevar_pop (TV_REPAIR_LOOPS);
    }

  timevar_pop (TV_CLEANUP_CFG);

  return changed;
}
\f
namespace {

const pass_data pass_data_jump =
{
  RTL_PASS, /* type */
  "jump", /* name */
  OPTGROUP_NONE, /* optinfo_flags */
  TV_JUMP, /* tv_id */
  0, /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  0, /* todo_flags_finish */
};

class pass_jump : public rtl_opt_pass
{
public:
  pass_jump (gcc::context *ctxt)
    : rtl_opt_pass (pass_data_jump, ctxt)
  {}

  /* opt_pass methods: */
  virtual unsigned int execute (function *);

}; // class pass_jump

unsigned int
pass_jump::execute (function *)
{
  delete_trivially_dead_insns (get_insns (), max_reg_num ());
  if (dump_file)
    dump_flow_info (dump_file, dump_flags);
  cleanup_cfg ((optimize ? CLEANUP_EXPENSIVE : 0)
               | (flag_thread_jumps ? CLEANUP_THREADING : 0));
  return 0;
}

} // anon namespace

rtl_opt_pass *
make_pass_jump (gcc::context *ctxt)
{
  return new pass_jump (ctxt);
}
\f
namespace {

const pass_data pass_data_jump2 =
{
  RTL_PASS, /* type */
  "jump2", /* name */
  OPTGROUP_NONE, /* optinfo_flags */
  TV_JUMP, /* tv_id */
  0, /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  0, /* todo_flags_finish */
};

class pass_jump2 : public rtl_opt_pass
{
public:
  pass_jump2 (gcc::context *ctxt)
    : rtl_opt_pass (pass_data_jump2, ctxt)
  {}

  /* opt_pass methods: */
  virtual unsigned int execute (function *)
    {
      cleanup_cfg (flag_crossjumping ? CLEANUP_CROSSJUMP : 0);
      return 0;
    }

}; // class pass_jump2

} // anon namespace

rtl_opt_pass *
make_pass_jump2 (gcc::context *ctxt)
{
  return new pass_jump2 (ctxt);
}