Merge trunk version 190524 into gupc branch.

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

/* Control flow graph manipulation code for GNU compiler.
   Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
   2011, 2012 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 low level functions to manipulate the CFG and analyze it
   that are aware of the RTL intermediate language.

   Available functionality:
     - Basic CFG/RTL manipulation API documented in cfghooks.h
     - CFG-aware instruction chain manipulation
         delete_insn, delete_insn_chain
     - Edge splitting and committing to edges
         insert_insn_on_edge, commit_edge_insertions
     - CFG updating after insn simplification
         purge_dead_edges, purge_all_dead_edges
     - CFG fixing after coarse manipulation
        fixup_abnormal_edges

   Functions not supposed for generic use:
     - Infrastructure to determine quickly basic block for insn
         compute_bb_for_insn, update_bb_for_insn, set_block_for_insn,
     - Edge redirection with updating and optimizing of insn chain
         block_label, tidy_fallthru_edge, force_nonfallthru  */
\f
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "regs.h"
#include "flags.h"
#include "function.h"
#include "except.h"
#include "rtl-error.h"
#include "tm_p.h"
#include "obstack.h"
#include "insn-attr.h"
#include "insn-config.h"
#include "expr.h"
#include "target.h"
#include "common/common-target.h"
#include "cfgloop.h"
#include "ggc.h"
#include "tree-pass.h"
#include "df.h"

/* Holds the interesting leading and trailing notes for the function.
   Only applicable if the CFG is in cfglayout mode.  */
static GTY(()) rtx cfg_layout_function_footer;
static GTY(()) rtx cfg_layout_function_header;

static rtx skip_insns_after_block (basic_block);
static void record_effective_endpoints (void);
static rtx label_for_bb (basic_block);
static void fixup_reorder_chain (void);

void verify_insn_chain (void);
static void fixup_fallthru_exit_predecessor (void);
static int can_delete_note_p (const_rtx);
static int can_delete_label_p (const_rtx);
static basic_block rtl_split_edge (edge);
static bool rtl_move_block_after (basic_block, basic_block);
static int rtl_verify_flow_info (void);
static basic_block cfg_layout_split_block (basic_block, void *);
static edge cfg_layout_redirect_edge_and_branch (edge, basic_block);
static basic_block cfg_layout_redirect_edge_and_branch_force (edge, basic_block);
static void cfg_layout_delete_block (basic_block);
static void rtl_delete_block (basic_block);
static basic_block rtl_redirect_edge_and_branch_force (edge, basic_block);
static edge rtl_redirect_edge_and_branch (edge, basic_block);
static basic_block rtl_split_block (basic_block, void *);
static void rtl_dump_bb (FILE *, basic_block, int, int);
static int rtl_verify_flow_info_1 (void);
static void rtl_make_forwarder_block (edge);
\f
/* Return true if NOTE is not one of the ones that must be kept paired,
   so that we may simply delete it.  */

static int
can_delete_note_p (const_rtx note)
{
  switch (NOTE_KIND (note))
    {
    case NOTE_INSN_DELETED:
    case NOTE_INSN_BASIC_BLOCK:
    case NOTE_INSN_EPILOGUE_BEG:
      return true;

    default:
      return false;
    }
}

/* True if a given label can be deleted.  */

static int
can_delete_label_p (const_rtx label)
{
  return (!LABEL_PRESERVE_P (label)
          /* User declared labels must be preserved.  */
          && LABEL_NAME (label) == 0
          && !in_expr_list_p (forced_labels, label));
}

/* Delete INSN by patching it out.  */

void
delete_insn (rtx insn)
{
  rtx note;
  bool really_delete = true;

  if (LABEL_P (insn))
    {
      /* Some labels can't be directly removed from the INSN chain, as they
         might be references via variables, constant pool etc.
         Convert them to the special NOTE_INSN_DELETED_LABEL note.  */
      if (! can_delete_label_p (insn))
        {
          const char *name = LABEL_NAME (insn);
          basic_block bb = BLOCK_FOR_INSN (insn);
          rtx bb_note = NEXT_INSN (insn);

          really_delete = false;
          PUT_CODE (insn, NOTE);
          NOTE_KIND (insn) = NOTE_INSN_DELETED_LABEL;
          NOTE_DELETED_LABEL_NAME (insn) = name;

          if (bb_note != NULL_RTX && NOTE_INSN_BASIC_BLOCK_P (bb_note)
              && BLOCK_FOR_INSN (bb_note) == bb)
            {
              reorder_insns_nobb (insn, insn, bb_note);
              BB_HEAD (bb) = bb_note;
              if (BB_END (bb) == bb_note)
                BB_END (bb) = insn;
            }
        }

      remove_node_from_expr_list (insn, &nonlocal_goto_handler_labels);
    }

  if (really_delete)
    {
      /* If this insn has already been deleted, something is very wrong.  */
      gcc_assert (!INSN_DELETED_P (insn));
      remove_insn (insn);
      INSN_DELETED_P (insn) = 1;
    }

  /* If deleting a jump, decrement the use count of the label.  Deleting
     the label itself should happen in the normal course of block merging.  */
  if (JUMP_P (insn))
    {
      if (JUMP_LABEL (insn)
          && LABEL_P (JUMP_LABEL (insn)))
        LABEL_NUSES (JUMP_LABEL (insn))--;

      /* If there are more targets, remove them too.  */
      while ((note
              = find_reg_note (insn, REG_LABEL_TARGET, NULL_RTX)) != NULL_RTX
             && LABEL_P (XEXP (note, 0)))
        {
          LABEL_NUSES (XEXP (note, 0))--;
          remove_note (insn, note);
        }
    }

  /* Also if deleting any insn that references a label as an operand.  */
  while ((note = find_reg_note (insn, REG_LABEL_OPERAND, NULL_RTX)) != NULL_RTX
         && LABEL_P (XEXP (note, 0)))
    {
      LABEL_NUSES (XEXP (note, 0))--;
      remove_note (insn, note);
    }

  if (JUMP_TABLE_DATA_P (insn))
    {
      rtx pat = PATTERN (insn);
      int diff_vec_p = GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC;
      int len = XVECLEN (pat, diff_vec_p);
      int i;

      for (i = 0; i < len; i++)
        {
          rtx label = XEXP (XVECEXP (pat, diff_vec_p, i), 0);

          /* When deleting code in bulk (e.g. removing many unreachable
             blocks) we can delete a label that's a target of the vector
             before deleting the vector itself.  */
          if (!NOTE_P (label))
            LABEL_NUSES (label)--;
        }
    }
}

/* Like delete_insn but also purge dead edges from BB.  */

void
delete_insn_and_edges (rtx insn)
{
  bool purge = false;

  if (INSN_P (insn)
      && BLOCK_FOR_INSN (insn)
      && BB_END (BLOCK_FOR_INSN (insn)) == insn)
    purge = true;
  delete_insn (insn);
  if (purge)
    purge_dead_edges (BLOCK_FOR_INSN (insn));
}

/* Unlink a chain of insns between START and FINISH, leaving notes
   that must be paired.  If CLEAR_BB is true, we set bb field for
   insns that cannot be removed to NULL.  */

void
delete_insn_chain (rtx start, rtx finish, bool clear_bb)
{
  rtx prev, current;

  /* Unchain the insns one by one.  It would be quicker to delete all of these
     with a single unchaining, rather than one at a time, but we need to keep
     the NOTE's.  */
  current = finish;
  while (1)
    {
      prev = PREV_INSN (current);
      if (NOTE_P (current) && !can_delete_note_p (current))
        ;
      else
        delete_insn (current);

      if (clear_bb && !INSN_DELETED_P (current))
        set_block_for_insn (current, NULL);

      if (current == start)
        break;
      current = prev;
    }
}
\f
/* Create a new basic block consisting of the instructions between HEAD and END
   inclusive.  This function is designed to allow fast BB construction - reuses
   the note and basic block struct in BB_NOTE, if any and do not grow
   BASIC_BLOCK chain and should be used directly only by CFG construction code.
   END can be NULL in to create new empty basic block before HEAD.  Both END
   and HEAD can be NULL to create basic block at the end of INSN chain.
   AFTER is the basic block we should be put after.  */

basic_block
create_basic_block_structure (rtx head, rtx end, rtx bb_note, basic_block after)
{
  basic_block bb;

  if (bb_note
      && (bb = NOTE_BASIC_BLOCK (bb_note)) != NULL
      && bb->aux == NULL)
    {
      /* If we found an existing note, thread it back onto the chain.  */

      rtx after;

      if (LABEL_P (head))
        after = head;
      else
        {
          after = PREV_INSN (head);
          head = bb_note;
        }

      if (after != bb_note && NEXT_INSN (after) != bb_note)
        reorder_insns_nobb (bb_note, bb_note, after);
    }
  else
    {
      /* Otherwise we must create a note and a basic block structure.  */

      bb = alloc_block ();

      init_rtl_bb_info (bb);
      if (!head && !end)
        head = end = bb_note
          = emit_note_after (NOTE_INSN_BASIC_BLOCK, get_last_insn ());
      else if (LABEL_P (head) && end)
        {
          bb_note = emit_note_after (NOTE_INSN_BASIC_BLOCK, head);
          if (head == end)
            end = bb_note;
        }
      else
        {
          bb_note = emit_note_before (NOTE_INSN_BASIC_BLOCK, head);
          head = bb_note;
          if (!end)
            end = head;
        }

      NOTE_BASIC_BLOCK (bb_note) = bb;
    }

  /* Always include the bb note in the block.  */
  if (NEXT_INSN (end) == bb_note)
    end = bb_note;

  BB_HEAD (bb) = head;
  BB_END (bb) = end;
  bb->index = last_basic_block++;
  bb->flags = BB_NEW | BB_RTL;
  link_block (bb, after);
  SET_BASIC_BLOCK (bb->index, bb);
  df_bb_refs_record (bb->index, false);
  update_bb_for_insn (bb);
  BB_SET_PARTITION (bb, BB_UNPARTITIONED);

  /* Tag the block so that we know it has been used when considering
     other basic block notes.  */
  bb->aux = bb;

  return bb;
}

/* Create new basic block consisting of instructions in between HEAD and END
   and place it to the BB chain after block AFTER.  END can be NULL to
   create a new empty basic block before HEAD.  Both END and HEAD can be
   NULL to create basic block at the end of INSN chain.  */

static basic_block
rtl_create_basic_block (void *headp, void *endp, basic_block after)
{
  rtx head = (rtx) headp, end = (rtx) endp;
  basic_block bb;

  /* Grow the basic block array if needed.  */
  if ((size_t) last_basic_block >= VEC_length (basic_block, basic_block_info))
    {
      size_t new_size = last_basic_block + (last_basic_block + 3) / 4;
      VEC_safe_grow_cleared (basic_block, gc, basic_block_info, new_size);
    }

  n_basic_blocks++;

  bb = create_basic_block_structure (head, end, NULL, after);
  bb->aux = NULL;
  return bb;
}

static basic_block
cfg_layout_create_basic_block (void *head, void *end, basic_block after)
{
  basic_block newbb = rtl_create_basic_block (head, end, after);

  return newbb;
}
\f
/* Delete the insns in a (non-live) block.  We physically delete every
   non-deleted-note insn, and update the flow graph appropriately.

   Return nonzero if we deleted an exception handler.  */

/* ??? Preserving all such notes strikes me as wrong.  It would be nice
   to post-process the stream to remove empty blocks, loops, ranges, etc.  */

static void
rtl_delete_block (basic_block b)
{
  rtx insn, end;

  /* If the head of this block is a CODE_LABEL, then it might be the
     label for an exception handler which can't be reached.  We need
     to remove the label from the exception_handler_label list.  */
  insn = BB_HEAD (b);

  end = get_last_bb_insn (b);

  /* Selectively delete the entire chain.  */
  BB_HEAD (b) = NULL;
  delete_insn_chain (insn, end, true);


  if (dump_file)
    fprintf (dump_file, "deleting block %d\n", b->index);
  df_bb_delete (b->index);
}
\f
/* Records the basic block struct in BLOCK_FOR_INSN for every insn.  */

void
compute_bb_for_insn (void)
{
  basic_block bb;

  FOR_EACH_BB (bb)
    {
      rtx end = BB_END (bb);
      rtx insn;

      for (insn = BB_HEAD (bb); ; insn = NEXT_INSN (insn))
        {
          BLOCK_FOR_INSN (insn) = bb;
          if (insn == end)
            break;
        }
    }
}

/* Release the basic_block_for_insn array.  */

unsigned int
free_bb_for_insn (void)
{
  rtx insn;
  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    if (!BARRIER_P (insn))
      BLOCK_FOR_INSN (insn) = NULL;
  return 0;
}

static unsigned int
rest_of_pass_free_cfg (void)
{
#ifdef DELAY_SLOTS
  /* The resource.c machinery uses DF but the CFG isn't guaranteed to be
     valid at that point so it would be too late to call df_analyze.  */
  if (optimize > 0 && flag_delayed_branch)
    {
      df_note_add_problem ();
      df_analyze ();
    }
#endif

  free_bb_for_insn ();
  return 0;
}

struct rtl_opt_pass pass_free_cfg =
{
 {
  RTL_PASS,
  "*free_cfg",                          /* name */
  NULL,                                 /* gate */
  rest_of_pass_free_cfg,                /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_NONE,                              /* tv_id */
  0,                                    /* properties_required */
  0,                                    /* properties_provided */
  PROP_cfg,                             /* properties_destroyed */
  0,                                    /* todo_flags_start */
  0,                                    /* todo_flags_finish */
 }
};

/* Return RTX to emit after when we want to emit code on the entry of function.  */
rtx
entry_of_function (void)
{
  return (n_basic_blocks > NUM_FIXED_BLOCKS ?
          BB_HEAD (ENTRY_BLOCK_PTR->next_bb) : get_insns ());
}

/* Emit INSN at the entry point of the function, ensuring that it is only
   executed once per function.  */
void
emit_insn_at_entry (rtx insn)
{
  edge_iterator ei = ei_start (ENTRY_BLOCK_PTR->succs);
  edge e = ei_safe_edge (ei);
  gcc_assert (e->flags & EDGE_FALLTHRU);

  insert_insn_on_edge (insn, e);
  commit_edge_insertions ();
}

/* Update BLOCK_FOR_INSN of insns between BEGIN and END
   (or BARRIER if found) and notify df of the bb change.
   The insn chain range is inclusive
   (i.e. both BEGIN and END will be updated. */

static void
update_bb_for_insn_chain (rtx begin, rtx end, basic_block bb)
{
  rtx insn;

  end = NEXT_INSN (end);
  for (insn = begin; insn != end; insn = NEXT_INSN (insn))
    if (!BARRIER_P (insn))
      df_insn_change_bb (insn, bb);
}

/* Update BLOCK_FOR_INSN of insns in BB to BB,
   and notify df of the change.  */

void
update_bb_for_insn (basic_block bb)
{
  update_bb_for_insn_chain (BB_HEAD (bb), BB_END (bb), bb);
}

\f
/* Like active_insn_p, except keep the return value clobber around
   even after reload.  */

static bool
flow_active_insn_p (const_rtx insn)
{
  if (active_insn_p (insn))
    return true;

  /* A clobber of the function return value exists for buggy
     programs that fail to return a value.  Its effect is to
     keep the return value from being live across the entire
     function.  If we allow it to be skipped, we introduce the
     possibility for register lifetime confusion.  */
  if (GET_CODE (PATTERN (insn)) == CLOBBER
      && REG_P (XEXP (PATTERN (insn), 0))
      && REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0)))
    return true;

  return false;
}

/* Return true if the block has no effect and only forwards control flow to
   its single destination.  */
/* FIXME: Make this a cfg hook.  */

bool
forwarder_block_p (const_basic_block bb)
{
  rtx insn;

  if (bb == EXIT_BLOCK_PTR || bb == ENTRY_BLOCK_PTR
      || !single_succ_p (bb))
    return false;

  /* Protect loop latches, headers and preheaders.  */
  if (current_loops)
    {
      basic_block dest;
      if (bb->loop_father->header == bb)
        return false;
      dest = EDGE_SUCC (bb, 0)->dest;
      if (dest->loop_father->header == dest)
        return false;
    }

  for (insn = BB_HEAD (bb); insn != BB_END (bb); insn = NEXT_INSN (insn))
    if (INSN_P (insn) && flow_active_insn_p (insn))
      return false;

  return (!INSN_P (insn)
          || (JUMP_P (insn) && simplejump_p (insn))
          || !flow_active_insn_p (insn));
}

/* Return nonzero if we can reach target from src by falling through.  */
/* FIXME: Make this a cfg hook.  */

bool
can_fallthru (basic_block src, basic_block target)
{
  rtx insn = BB_END (src);
  rtx insn2;
  edge e;
  edge_iterator ei;

  if (target == EXIT_BLOCK_PTR)
    return true;
  if (src->next_bb != target)
    return 0;
  FOR_EACH_EDGE (e, ei, src->succs)
    if (e->dest == EXIT_BLOCK_PTR
        && e->flags & EDGE_FALLTHRU)
      return 0;

  insn2 = BB_HEAD (target);
  if (insn2 && !active_insn_p (insn2))
    insn2 = next_active_insn (insn2);

  /* ??? Later we may add code to move jump tables offline.  */
  return next_active_insn (insn) == insn2;
}

/* Return nonzero if we could reach target from src by falling through,
   if the target was made adjacent.  If we already have a fall-through
   edge to the exit block, we can't do that.  */
static bool
could_fall_through (basic_block src, basic_block target)
{
  edge e;
  edge_iterator ei;

  if (target == EXIT_BLOCK_PTR)
    return true;
  FOR_EACH_EDGE (e, ei, src->succs)
    if (e->dest == EXIT_BLOCK_PTR
        && e->flags & EDGE_FALLTHRU)
      return 0;
  return true;
}
\f
/* Return the NOTE_INSN_BASIC_BLOCK of BB.  */
rtx
bb_note (basic_block bb)
{
  rtx note;

  note = BB_HEAD (bb);
  if (LABEL_P (note))
    note = NEXT_INSN (note);

  gcc_assert (NOTE_INSN_BASIC_BLOCK_P (note));
  return note;
}

/* Return the INSN immediately following the NOTE_INSN_BASIC_BLOCK
   note associated with the BLOCK.  */

static rtx
first_insn_after_basic_block_note (basic_block block)
{
  rtx insn;

  /* Get the first instruction in the block.  */
  insn = BB_HEAD (block);

  if (insn == NULL_RTX)
    return NULL_RTX;
  if (LABEL_P (insn))
    insn = NEXT_INSN (insn);
  gcc_assert (NOTE_INSN_BASIC_BLOCK_P (insn));

  return NEXT_INSN (insn);
}

/* Creates a new basic block just after basic block B by splitting
   everything after specified instruction I.  */

static basic_block
rtl_split_block (basic_block bb, void *insnp)
{
  basic_block new_bb;
  rtx insn = (rtx) insnp;
  edge e;
  edge_iterator ei;

  if (!insn)
    {
      insn = first_insn_after_basic_block_note (bb);

      if (insn)
        {
          rtx next = insn;

          insn = PREV_INSN (insn);

          /* If the block contains only debug insns, insn would have
             been NULL in a non-debug compilation, and then we'd end
             up emitting a DELETED note.  For -fcompare-debug
             stability, emit the note too.  */
          if (insn != BB_END (bb)
              && DEBUG_INSN_P (next)
              && DEBUG_INSN_P (BB_END (bb)))
            {
              while (next != BB_END (bb) && DEBUG_INSN_P (next))
                next = NEXT_INSN (next);

              if (next == BB_END (bb))
                emit_note_after (NOTE_INSN_DELETED, next);
            }
        }
      else
        insn = get_last_insn ();
    }

  /* We probably should check type of the insn so that we do not create
     inconsistent cfg.  It is checked in verify_flow_info anyway, so do not
     bother.  */
  if (insn == BB_END (bb))
    emit_note_after (NOTE_INSN_DELETED, insn);

  /* Create the new basic block.  */
  new_bb = create_basic_block (NEXT_INSN (insn), BB_END (bb), bb);
  BB_COPY_PARTITION (new_bb, bb);
  BB_END (bb) = insn;

  /* Redirect the outgoing edges.  */
  new_bb->succs = bb->succs;
  bb->succs = NULL;
  FOR_EACH_EDGE (e, ei, new_bb->succs)
    e->src = new_bb;

  /* The new block starts off being dirty.  */
  df_set_bb_dirty (bb);
  return new_bb;
}

/* Return true if the single edge between blocks A and B is the only place
   in RTL which holds some unique locus.  */

static bool
unique_locus_on_edge_between_p (basic_block a, basic_block b)
{
  const int goto_locus = EDGE_SUCC (a, 0)->goto_locus;
  rtx insn, end;

  if (!goto_locus)
    return false;

  /* First scan block A backward.  */
  insn = BB_END (a);
  end = PREV_INSN (BB_HEAD (a));
  while (insn != end && (!NONDEBUG_INSN_P (insn) || INSN_LOCATOR (insn) == 0))
    insn = PREV_INSN (insn);

  if (insn != end && locator_eq (INSN_LOCATOR (insn), goto_locus))
    return false;

  /* Then scan block B forward.  */
  insn = BB_HEAD (b);
  if (insn)
    {
      end = NEXT_INSN (BB_END (b));
      while (insn != end && !NONDEBUG_INSN_P (insn))
        insn = NEXT_INSN (insn);

      if (insn != end && INSN_LOCATOR (insn) != 0
          && locator_eq (INSN_LOCATOR (insn), goto_locus))
        return false;
    }

  return true;
}

/* If the single edge between blocks A and B is the only place in RTL which
   holds some unique locus, emit a nop with that locus between the blocks.  */

static void
emit_nop_for_unique_locus_between (basic_block a, basic_block b)
{
  if (!unique_locus_on_edge_between_p (a, b))
    return;

  BB_END (a) = emit_insn_after_noloc (gen_nop (), BB_END (a), a);
  INSN_LOCATOR (BB_END (a)) = EDGE_SUCC (a, 0)->goto_locus;
}

/* Blocks A and B are to be merged into a single block A.  The insns
   are already contiguous.  */

static void
rtl_merge_blocks (basic_block a, basic_block b)
{
  rtx b_head = BB_HEAD (b), b_end = BB_END (b), a_end = BB_END (a);
  rtx del_first = NULL_RTX, del_last = NULL_RTX;
  rtx b_debug_start = b_end, b_debug_end = b_end;
  bool forwarder_p = (b->flags & BB_FORWARDER_BLOCK) != 0;
  int b_empty = 0;

  if (dump_file)
    fprintf (dump_file, "Merging block %d into block %d...\n", b->index,
             a->index);

  while (DEBUG_INSN_P (b_end))
    b_end = PREV_INSN (b_debug_start = b_end);

  /* If there was a CODE_LABEL beginning B, delete it.  */
  if (LABEL_P (b_head))
    {
      /* Detect basic blocks with nothing but a label.  This can happen
         in particular at the end of a function.  */
      if (b_head == b_end)
        b_empty = 1;

      del_first = del_last = b_head;
      b_head = NEXT_INSN (b_head);
    }

  /* Delete the basic block note and handle blocks containing just that
     note.  */
  if (NOTE_INSN_BASIC_BLOCK_P (b_head))
    {
      if (b_head == b_end)
        b_empty = 1;
      if (! del_last)
        del_first = b_head;

      del_last = b_head;
      b_head = NEXT_INSN (b_head);
    }

  /* If there was a jump out of A, delete it.  */
  if (JUMP_P (a_end))
    {
      rtx prev;

      for (prev = PREV_INSN (a_end); ; prev = PREV_INSN (prev))
        if (!NOTE_P (prev)
            || NOTE_INSN_BASIC_BLOCK_P (prev)
            || prev == BB_HEAD (a))
          break;

      del_first = a_end;

#ifdef HAVE_cc0
      /* If this was a conditional jump, we need to also delete
         the insn that set cc0.  */
      if (only_sets_cc0_p (prev))
        {
          rtx tmp = prev;

          prev = prev_nonnote_insn (prev);
          if (!prev)
            prev = BB_HEAD (a);
          del_first = tmp;
        }
#endif

      a_end = PREV_INSN (del_first);
    }
  else if (BARRIER_P (NEXT_INSN (a_end)))
    del_first = NEXT_INSN (a_end);

  /* Delete everything marked above as well as crap that might be
     hanging out between the two blocks.  */
  BB_END (a) = a_end;
  BB_HEAD (b) = b_empty ? NULL_RTX : b_head;
  delete_insn_chain (del_first, del_last, true);

  /* When not optimizing CFG and the edge is the only place in RTL which holds
     some unique locus, emit a nop with that locus in between.  */
  if (!optimize)
    {
      emit_nop_for_unique_locus_between (a, b);
      a_end = BB_END (a);
    }

  /* Reassociate the insns of B with A.  */
  if (!b_empty)
    {
      update_bb_for_insn_chain (a_end, b_debug_end, a);

      BB_END (a) = b_debug_end;
      BB_HEAD (b) = NULL_RTX;
    }
  else if (b_end != b_debug_end)
    {
      /* Move any deleted labels and other notes between the end of A
         and the debug insns that make up B after the debug insns,
         bringing the debug insns into A while keeping the notes after
         the end of A.  */
      if (NEXT_INSN (a_end) != b_debug_start)
        reorder_insns_nobb (NEXT_INSN (a_end), PREV_INSN (b_debug_start),
                            b_debug_end);
      update_bb_for_insn_chain (b_debug_start, b_debug_end, a);
      BB_END (a) = b_debug_end;
    }

  df_bb_delete (b->index);

  /* If B was a forwarder block, propagate the locus on the edge.  */
  if (forwarder_p && !EDGE_SUCC (b, 0)->goto_locus)
    EDGE_SUCC (b, 0)->goto_locus = EDGE_SUCC (a, 0)->goto_locus;

  if (dump_file)
    fprintf (dump_file, "Merged blocks %d and %d.\n", a->index, b->index);
}


/* Return true when block A and B can be merged.  */

static bool
rtl_can_merge_blocks (basic_block a, basic_block b)
{
  /* 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 false;

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

  /* There must be exactly one edge in between the blocks.  */
  return (single_succ_p (a)
          && single_succ (a) == b
          && single_pred_p (b)
          && a != b
          /* Must be simple edge.  */
          && !(single_succ_edge (a)->flags & EDGE_COMPLEX)
          && a->next_bb == b
          && a != ENTRY_BLOCK_PTR && b != EXIT_BLOCK_PTR
          /* If the jump insn has side effects,
             we can't kill the edge.  */
          && (!JUMP_P (BB_END (a))
              || (reload_completed
                  ? simplejump_p (BB_END (a)) : onlyjump_p (BB_END (a)))));
}
\f
/* Return the label in the head of basic block BLOCK.  Create one if it doesn't
   exist.  */

rtx
block_label (basic_block block)
{
  if (block == EXIT_BLOCK_PTR)
    return NULL_RTX;

  if (!LABEL_P (BB_HEAD (block)))
    {
      BB_HEAD (block) = emit_label_before (gen_label_rtx (), BB_HEAD (block));
    }

  return BB_HEAD (block);
}

/* Attempt to perform edge redirection by replacing possibly complex jump
   instruction by unconditional jump or removing jump completely.  This can
   apply only if all edges now point to the same block.  The parameters and
   return values are equivalent to redirect_edge_and_branch.  */

edge
try_redirect_by_replacing_jump (edge e, basic_block target, bool in_cfglayout)
{
  basic_block src = e->src;
  rtx insn = BB_END (src), kill_from;
  rtx set;
  int fallthru = 0;

  /* 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 (find_reg_note (insn, REG_CROSSING_JUMP, NULL_RTX)
      || BB_PARTITION (src) != BB_PARTITION (target))
    return NULL;

  /* We can replace or remove a complex jump only when we have exactly
     two edges.  Also, if we have exactly one outgoing edge, we can
     redirect that.  */
  if (EDGE_COUNT (src->succs) >= 3
      /* Verify that all targets will be TARGET.  Specifically, the
         edge that is not E must also go to TARGET.  */
      || (EDGE_COUNT (src->succs) == 2
          && EDGE_SUCC (src, EDGE_SUCC (src, 0) == e)->dest != target))
    return NULL;

  if (!onlyjump_p (insn))
    return NULL;
  if ((!optimize || reload_completed) && tablejump_p (insn, NULL, NULL))
    return NULL;

  /* Avoid removing branch with side effects.  */
  set = single_set (insn);
  if (!set || side_effects_p (set))
    return NULL;

  /* In case we zap a conditional jump, we'll need to kill
     the cc0 setter too.  */
  kill_from = insn;
#ifdef HAVE_cc0
  if (reg_mentioned_p (cc0_rtx, PATTERN (insn))
      && only_sets_cc0_p (PREV_INSN (insn)))
    kill_from = PREV_INSN (insn);
#endif

  /* See if we can create the fallthru edge.  */
  if (in_cfglayout || can_fallthru (src, target))
    {
      if (dump_file)
        fprintf (dump_file, "Removing jump %i.\n", INSN_UID (insn));
      fallthru = 1;

      /* Selectively unlink whole insn chain.  */
      if (in_cfglayout)
        {
          rtx insn = BB_FOOTER (src);

          delete_insn_chain (kill_from, BB_END (src), false);

          /* Remove barriers but keep jumptables.  */
          while (insn)
            {
              if (BARRIER_P (insn))
                {
                  if (PREV_INSN (insn))
                    NEXT_INSN (PREV_INSN (insn)) = NEXT_INSN (insn);
                  else
                    BB_FOOTER (src) = NEXT_INSN (insn);
                  if (NEXT_INSN (insn))
                    PREV_INSN (NEXT_INSN (insn)) = PREV_INSN (insn);
                }
              if (LABEL_P (insn))
                break;
              insn = NEXT_INSN (insn);
            }
        }
      else
        delete_insn_chain (kill_from, PREV_INSN (BB_HEAD (target)),
                           false);
    }

  /* If this already is simplejump, redirect it.  */
  else if (simplejump_p (insn))
    {
      if (e->dest == target)
        return NULL;
      if (dump_file)
        fprintf (dump_file, "Redirecting jump %i from %i to %i.\n",
                 INSN_UID (insn), e->dest->index, target->index);
      if (!redirect_jump (insn, block_label (target), 0))
        {
          gcc_assert (target == EXIT_BLOCK_PTR);
          return NULL;
        }
    }

  /* Cannot do anything for target exit block.  */
  else if (target == EXIT_BLOCK_PTR)
    return NULL;

  /* Or replace possibly complicated jump insn by simple jump insn.  */
  else
    {
      rtx target_label = block_label (target);
      rtx barrier, label, table;

      emit_jump_insn_after_noloc (gen_jump (target_label), insn);
      JUMP_LABEL (BB_END (src)) = target_label;
      LABEL_NUSES (target_label)++;
      if (dump_file)
        fprintf (dump_file, "Replacing insn %i by jump %i\n",
                 INSN_UID (insn), INSN_UID (BB_END (src)));


      delete_insn_chain (kill_from, insn, false);

      /* Recognize a tablejump that we are converting to a
         simple jump and remove its associated CODE_LABEL
         and ADDR_VEC or ADDR_DIFF_VEC.  */
      if (tablejump_p (insn, &label, &table))
        delete_insn_chain (label, table, false);

      barrier = next_nonnote_insn (BB_END (src));
      if (!barrier || !BARRIER_P (barrier))
        emit_barrier_after (BB_END (src));
      else
        {
          if (barrier != NEXT_INSN (BB_END (src)))
            {
              /* Move the jump before barrier so that the notes
                 which originally were or were created before jump table are
                 inside the basic block.  */
              rtx new_insn = BB_END (src);

              update_bb_for_insn_chain (NEXT_INSN (BB_END (src)),
                                        PREV_INSN (barrier), src);

              NEXT_INSN (PREV_INSN (new_insn)) = NEXT_INSN (new_insn);
              PREV_INSN (NEXT_INSN (new_insn)) = PREV_INSN (new_insn);

              NEXT_INSN (new_insn) = barrier;
              NEXT_INSN (PREV_INSN (barrier)) = new_insn;

              PREV_INSN (new_insn) = PREV_INSN (barrier);
              PREV_INSN (barrier) = new_insn;
            }
        }
    }

  /* Keep only one edge out and set proper flags.  */
  if (!single_succ_p (src))
    remove_edge (e);
  gcc_assert (single_succ_p (src));

  e = single_succ_edge (src);
  if (fallthru)
    e->flags = EDGE_FALLTHRU;
  else
    e->flags = 0;

  e->probability = REG_BR_PROB_BASE;
  e->count = src->count;

  if (e->dest != target)
    redirect_edge_succ (e, target);
  return e;
}

/* Subroutine of redirect_branch_edge that tries to patch the jump
   instruction INSN so that it reaches block NEW.  Do this
   only when it originally reached block OLD.  Return true if this
   worked or the original target wasn't OLD, return false if redirection
   doesn't work.  */

static bool
patch_jump_insn (rtx insn, rtx old_label, basic_block new_bb)
{
  rtx tmp;
  /* Recognize a tablejump and adjust all matching cases.  */
  if (tablejump_p (insn, NULL, &tmp))
    {
      rtvec vec;
      int j;
      rtx new_label = block_label (new_bb);

      if (new_bb == EXIT_BLOCK_PTR)
        return false;
      if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)
        vec = XVEC (PATTERN (tmp), 0);
      else
        vec = XVEC (PATTERN (tmp), 1);

      for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
        if (XEXP (RTVEC_ELT (vec, j), 0) == old_label)
          {
            RTVEC_ELT (vec, j) = gen_rtx_LABEL_REF (Pmode, new_label);
            --LABEL_NUSES (old_label);
            ++LABEL_NUSES (new_label);
          }

      /* Handle casesi dispatch insns.  */
      if ((tmp = single_set (insn)) != NULL
          && SET_DEST (tmp) == pc_rtx
          && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
          && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF
          && XEXP (XEXP (SET_SRC (tmp), 2), 0) == old_label)
        {
          XEXP (SET_SRC (tmp), 2) = gen_rtx_LABEL_REF (Pmode,
                                                       new_label);
          --LABEL_NUSES (old_label);
          ++LABEL_NUSES (new_label);
        }
    }
  else if ((tmp = extract_asm_operands (PATTERN (insn))) != NULL)
    {
      int i, n = ASM_OPERANDS_LABEL_LENGTH (tmp);
      rtx new_label, note;

      if (new_bb == EXIT_BLOCK_PTR)
        return false;
      new_label = block_label (new_bb);

      for (i = 0; i < n; ++i)
        {
          rtx old_ref = ASM_OPERANDS_LABEL (tmp, i);
          gcc_assert (GET_CODE (old_ref) == LABEL_REF);
          if (XEXP (old_ref, 0) == old_label)
            {
              ASM_OPERANDS_LABEL (tmp, i)
                = gen_rtx_LABEL_REF (Pmode, new_label);
              --LABEL_NUSES (old_label);
              ++LABEL_NUSES (new_label);
            }
        }

      if (JUMP_LABEL (insn) == old_label)
        {
          JUMP_LABEL (insn) = new_label;
          note = find_reg_note (insn, REG_LABEL_TARGET, new_label);
          if (note)
            remove_note (insn, note);
        }
      else
        {
          note = find_reg_note (insn, REG_LABEL_TARGET, old_label);
          if (note)
            remove_note (insn, note);
          if (JUMP_LABEL (insn) != new_label
              && !find_reg_note (insn, REG_LABEL_TARGET, new_label))
            add_reg_note (insn, REG_LABEL_TARGET, new_label);
        }
      while ((note = find_reg_note (insn, REG_LABEL_OPERAND, old_label))
             != NULL_RTX)
        XEXP (note, 0) = new_label;
    }
  else
    {
      /* ?? We may play the games with moving the named labels from
         one basic block to the other in case only one computed_jump is
         available.  */
      if (computed_jump_p (insn)
          /* A return instruction can't be redirected.  */
          || returnjump_p (insn))
        return false;

      if (!currently_expanding_to_rtl || JUMP_LABEL (insn) == old_label)
        {
          /* If the insn doesn't go where we think, we're confused.  */
          gcc_assert (JUMP_LABEL (insn) == old_label);

          /* If the substitution doesn't succeed, die.  This can happen
             if the back end emitted unrecognizable instructions or if
             target is exit block on some arches.  */
          if (!redirect_jump (insn, block_label (new_bb), 0))
            {
              gcc_assert (new_bb == EXIT_BLOCK_PTR);
              return false;
            }
        }
    }
  return true;
}


/* Redirect edge representing branch of (un)conditional jump or tablejump,
   NULL on failure  */
static edge
redirect_branch_edge (edge e, basic_block target)
{
  rtx old_label = BB_HEAD (e->dest);
  basic_block src = e->src;
  rtx insn = BB_END (src);

  /* We can only redirect non-fallthru edges of jump insn.  */
  if (e->flags & EDGE_FALLTHRU)
    return NULL;
  else if (!JUMP_P (insn) && !currently_expanding_to_rtl)
    return NULL;

  if (!currently_expanding_to_rtl)
    {
      if (!patch_jump_insn (insn, old_label, target))
        return NULL;
    }
  else
    /* When expanding this BB might actually contain multiple
       jumps (i.e. not yet split by find_many_sub_basic_blocks).
       Redirect all of those that match our label.  */
    FOR_BB_INSNS (src, insn)
      if (JUMP_P (insn) && !patch_jump_insn (insn, old_label, target))
        return NULL;

  if (dump_file)
    fprintf (dump_file, "Edge %i->%i redirected to %i\n",
             e->src->index, e->dest->index, target->index);

  if (e->dest != target)
    e = redirect_edge_succ_nodup (e, target);

  return e;
}

/* Attempt to change code to redirect edge E to TARGET.  Don't do that on
   expense of adding new instructions or reordering basic blocks.

   Function can be also called with edge destination equivalent to the TARGET.
   Then it should try the simplifications and do nothing if none is possible.

   Return edge representing the branch if transformation succeeded.  Return NULL
   on failure.
   We still return NULL in case E already destinated TARGET and we didn't
   managed to simplify instruction stream.  */

static edge
rtl_redirect_edge_and_branch (edge e, basic_block target)
{
  edge ret;
  basic_block src = e->src;

  if (e->flags & (EDGE_ABNORMAL_CALL | EDGE_EH))
    return NULL;

  if (e->dest == target)
    return e;

  if ((ret = try_redirect_by_replacing_jump (e, target, false)) != NULL)
    {
      df_set_bb_dirty (src);
      return ret;
    }

  ret = redirect_branch_edge (e, target);
  if (!ret)
    return NULL;

  df_set_bb_dirty (src);
  return ret;
}

/* Like force_nonfallthru below, but additionally performs redirection
   Used by redirect_edge_and_branch_force.  JUMP_LABEL is used only
   when redirecting to the EXIT_BLOCK, it is either ret_rtx or
   simple_return_rtx, indicating which kind of returnjump to create.
   It should be NULL otherwise.  */

basic_block
force_nonfallthru_and_redirect (edge e, basic_block target, rtx jump_label)
{
  basic_block jump_block, new_bb = NULL, src = e->src;
  rtx note;
  edge new_edge;
  int abnormal_edge_flags = 0;
  bool asm_goto_edge = false;
  int loc;

  /* In the case the last instruction is conditional jump to the next
     instruction, first redirect the jump itself and then continue
     by creating a basic block afterwards to redirect fallthru edge.  */
  if (e->src != ENTRY_BLOCK_PTR && e->dest != EXIT_BLOCK_PTR
      && any_condjump_p (BB_END (e->src))
      && JUMP_LABEL (BB_END (e->src)) == BB_HEAD (e->dest))
    {
      rtx note;
      edge b = unchecked_make_edge (e->src, target, 0);
      bool redirected;

      redirected = redirect_jump (BB_END (e->src), block_label (target), 0);
      gcc_assert (redirected);

      note = find_reg_note (BB_END (e->src), REG_BR_PROB, NULL_RTX);
      if (note)
        {
          int prob = INTVAL (XEXP (note, 0));

          b->probability = prob;
          b->count = e->count * prob / REG_BR_PROB_BASE;
          e->probability -= e->probability;
          e->count -= b->count;
          if (e->probability < 0)
            e->probability = 0;
          if (e->count < 0)
            e->count = 0;
        }
    }

  if (e->flags & EDGE_ABNORMAL)
    {
      /* Irritating special case - fallthru edge to the same block as abnormal
         edge.
         We can't redirect abnormal edge, but we still can split the fallthru
         one and create separate abnormal edge to original destination.
         This allows bb-reorder to make such edge non-fallthru.  */
      gcc_assert (e->dest == target);
      abnormal_edge_flags = e->flags & ~EDGE_FALLTHRU;
      e->flags &= EDGE_FALLTHRU;
    }
  else
    {
      gcc_assert (e->flags & EDGE_FALLTHRU);
      if (e->src == ENTRY_BLOCK_PTR)
        {
          /* We can't redirect the entry block.  Create an empty block
             at the start of the function which we use to add the new
             jump.  */
          edge tmp;
          edge_iterator ei;
          bool found = false;

          basic_block bb = create_basic_block (BB_HEAD (e->dest), NULL, ENTRY_BLOCK_PTR);

          /* Change the existing edge's source to be the new block, and add
             a new edge from the entry block to the new block.  */
          e->src = bb;
          for (ei = ei_start (ENTRY_BLOCK_PTR->succs); (tmp = ei_safe_edge (ei)); )
            {
              if (tmp == e)
                {
                  VEC_unordered_remove (edge, ENTRY_BLOCK_PTR->succs, ei.index);
                  found = true;
                  break;
                }
              else
                ei_next (&ei);
            }

          gcc_assert (found);

          VEC_safe_push (edge, gc, bb->succs, e);
          make_single_succ_edge (ENTRY_BLOCK_PTR, bb, EDGE_FALLTHRU);
        }
    }

  /* If e->src ends with asm goto, see if any of the ASM_OPERANDS_LABELs
     don't point to the target or fallthru label.  */
  if (JUMP_P (BB_END (e->src))
      && target != EXIT_BLOCK_PTR
      && (e->flags & EDGE_FALLTHRU)
      && (note = extract_asm_operands (PATTERN (BB_END (e->src)))))
    {
      int i, n = ASM_OPERANDS_LABEL_LENGTH (note);

      for (i = 0; i < n; ++i)
        {
          if (XEXP (ASM_OPERANDS_LABEL (note, i), 0) == BB_HEAD (e->dest))
            XEXP (ASM_OPERANDS_LABEL (note, i), 0) = block_label (target);
          if (XEXP (ASM_OPERANDS_LABEL (note, i), 0) == BB_HEAD (target))
            asm_goto_edge = true;
        }
    }

  if (EDGE_COUNT (e->src->succs) >= 2 || abnormal_edge_flags || asm_goto_edge)
    {
      gcov_type count = e->count;
      int probability = e->probability;
      /* Create the new structures.  */

      /* If the old block ended with a tablejump, skip its table
         by searching forward from there.  Otherwise start searching
         forward from the last instruction of the old block.  */
      if (!tablejump_p (BB_END (e->src), NULL, &note))
        note = BB_END (e->src);
      note = NEXT_INSN (note);

      jump_block = create_basic_block (note, NULL, e->src);
      jump_block->count = count;
      jump_block->frequency = EDGE_FREQUENCY (e);

      /* Make sure new block ends up in correct hot/cold section.  */

      BB_COPY_PARTITION (jump_block, e->src);
      if (flag_reorder_blocks_and_partition
          && targetm_common.have_named_sections
          && JUMP_P (BB_END (jump_block))
          && !any_condjump_p (BB_END (jump_block))
          && (EDGE_SUCC (jump_block, 0)->flags & EDGE_CROSSING))
        add_reg_note (BB_END (jump_block), REG_CROSSING_JUMP, NULL_RTX);

      /* Wire edge in.  */
      new_edge = make_edge (e->src, jump_block, EDGE_FALLTHRU);
      new_edge->probability = probability;
      new_edge->count = count;

      /* Redirect old edge.  */
      redirect_edge_pred (e, jump_block);
      e->probability = REG_BR_PROB_BASE;

      /* If asm goto has any label refs to target's label,
         add also edge from asm goto bb to target.  */
      if (asm_goto_edge)
        {
          new_edge->probability /= 2;
          new_edge->count /= 2;
          jump_block->count /= 2;
          jump_block->frequency /= 2;
          new_edge = make_edge (new_edge->src, target,
                                e->flags & ~EDGE_FALLTHRU);
          new_edge->probability = probability - probability / 2;
          new_edge->count = count - count / 2;
        }

      new_bb = jump_block;
    }
  else
    jump_block = e->src;

  if (e->goto_locus && e->goto_block == NULL)
    loc = e->goto_locus;
  else
    loc = 0;
  e->flags &= ~EDGE_FALLTHRU;
  if (target == EXIT_BLOCK_PTR)
    {
      if (jump_label == ret_rtx)
        {
#ifdef HAVE_return
          emit_jump_insn_after_setloc (gen_return (), BB_END (jump_block), loc);
#else
          gcc_unreachable ();
#endif
        }
      else
        {
          gcc_assert (jump_label == simple_return_rtx);
#ifdef HAVE_simple_return
          emit_jump_insn_after_setloc (gen_simple_return (),
                                       BB_END (jump_block), loc);
#else
          gcc_unreachable ();
#endif
        }
      set_return_jump_label (BB_END (jump_block));
    }
  else
    {
      rtx label = block_label (target);
      emit_jump_insn_after_setloc (gen_jump (label), BB_END (jump_block), loc);
      JUMP_LABEL (BB_END (jump_block)) = label;
      LABEL_NUSES (label)++;
    }

  emit_barrier_after (BB_END (jump_block));
  redirect_edge_succ_nodup (e, target);

  if (abnormal_edge_flags)
    make_edge (src, target, abnormal_edge_flags);

  df_mark_solutions_dirty ();
  return new_bb;
}

/* Edge E is assumed to be fallthru edge.  Emit needed jump instruction
   (and possibly create new basic block) to make edge non-fallthru.
   Return newly created BB or NULL if none.  */

static basic_block
rtl_force_nonfallthru (edge e)
{
  return force_nonfallthru_and_redirect (e, e->dest, NULL_RTX);
}

/* Redirect edge even at the expense of creating new jump insn or
   basic block.  Return new basic block if created, NULL otherwise.
   Conversion must be possible.  */

static basic_block
rtl_redirect_edge_and_branch_force (edge e, basic_block target)
{
  if (redirect_edge_and_branch (e, target)
      || e->dest == target)
    return NULL;

  /* In case the edge redirection failed, try to force it to be non-fallthru
     and redirect newly created simplejump.  */
  df_set_bb_dirty (e->src);
  return force_nonfallthru_and_redirect (e, target, NULL_RTX);
}

/* The given edge should potentially be a fallthru edge.  If that is in
   fact true, delete the jump and barriers that are in the way.  */

static void
rtl_tidy_fallthru_edge (edge e)
{
  rtx q;
  basic_block b = e->src, c = b->next_bb;

  /* ??? In a late-running flow pass, other folks may have deleted basic
     blocks by nopping out blocks, leaving multiple BARRIERs between here
     and the target label. They ought to be chastised and fixed.

     We can also wind up with a sequence of undeletable labels between
     one block and the next.

     So search through a sequence of barriers, labels, and notes for
     the head of block C and assert that we really do fall through.  */

  for (q = NEXT_INSN (BB_END (b)); q != BB_HEAD (c); q = NEXT_INSN (q))
    if (INSN_P (q))
      return;

  /* Remove what will soon cease being the jump insn from the source block.
     If block B consisted only of this single jump, turn it into a deleted
     note.  */
  q = BB_END (b);
  if (JUMP_P (q)
      && onlyjump_p (q)
      && (any_uncondjump_p (q)
          || single_succ_p (b)))
    {
#ifdef HAVE_cc0
      /* If this was a conditional jump, we need to also delete
         the insn that set cc0.  */
      if (any_condjump_p (q) && only_sets_cc0_p (PREV_INSN (q)))
        q = PREV_INSN (q);
#endif

      q = PREV_INSN (q);
    }

  /* Selectively unlink the sequence.  */
  if (q != PREV_INSN (BB_HEAD (c)))
    delete_insn_chain (NEXT_INSN (q), PREV_INSN (BB_HEAD (c)), false);

  e->flags |= EDGE_FALLTHRU;
}
\f
/* Should move basic block BB after basic block AFTER.  NIY.  */

static bool
rtl_move_block_after (basic_block bb ATTRIBUTE_UNUSED,
                      basic_block after ATTRIBUTE_UNUSED)
{
  return false;
}

/* Split a (typically critical) edge.  Return the new block.
   The edge must not be abnormal.

   ??? The code generally expects to be called on critical edges.
   The case of a block ending in an unconditional jump to a
   block with multiple predecessors is not handled optimally.  */

static basic_block
rtl_split_edge (edge edge_in)
{
  basic_block bb;
  rtx before;

  /* Abnormal edges cannot be split.  */
  gcc_assert (!(edge_in->flags & EDGE_ABNORMAL));

  /* We are going to place the new block in front of edge destination.
     Avoid existence of fallthru predecessors.  */
  if ((edge_in->flags & EDGE_FALLTHRU) == 0)
    {
      edge e = find_fallthru_edge (edge_in->dest->preds);

      if (e)
        force_nonfallthru (e);
    }

  /* Create the basic block note.  */
  if (edge_in->dest != EXIT_BLOCK_PTR)
    before = BB_HEAD (edge_in->dest);
  else
    before = NULL_RTX;

  /* If this is a fall through edge to the exit block, the blocks might be
     not adjacent, and the right place is after the source.  */
  if ((edge_in->flags & EDGE_FALLTHRU) && edge_in->dest == EXIT_BLOCK_PTR)
    {
      before = NEXT_INSN (BB_END (edge_in->src));
      bb = create_basic_block (before, NULL, edge_in->src);
      BB_COPY_PARTITION (bb, edge_in->src);
    }
  else
    {
      bb = create_basic_block (before, NULL, edge_in->dest->prev_bb);
      /* ??? Why not edge_in->dest->prev_bb here?  */
      BB_COPY_PARTITION (bb, edge_in->dest);
    }

  make_single_succ_edge (bb, edge_in->dest, EDGE_FALLTHRU);

  /* For non-fallthru edges, we must adjust the predecessor's
     jump instruction to target our new block.  */
  if ((edge_in->flags & EDGE_FALLTHRU) == 0)
    {
      edge redirected = redirect_edge_and_branch (edge_in, bb);
      gcc_assert (redirected);
    }
  else
    {
      if (edge_in->src != ENTRY_BLOCK_PTR)
        {
          /* For asm goto even splitting of fallthru edge might
             need insn patching, as other labels might point to the
             old label.  */
          rtx last = BB_END (edge_in->src);
          if (last
              && JUMP_P (last)
              && edge_in->dest != EXIT_BLOCK_PTR
              && extract_asm_operands (PATTERN (last)) != NULL_RTX
              && patch_jump_insn (last, before, bb))
            df_set_bb_dirty (edge_in->src);
        }
      redirect_edge_succ (edge_in, bb);
    }

  return bb;
}

/* Queue instructions for insertion on an edge between two basic blocks.
   The new instructions and basic blocks (if any) will not appear in the
   CFG until commit_edge_insertions is called.  */

void
insert_insn_on_edge (rtx pattern, edge e)
{
  /* We cannot insert instructions on an abnormal critical edge.
     It will be easier to find the culprit if we die now.  */
  gcc_assert (!((e->flags & EDGE_ABNORMAL) && EDGE_CRITICAL_P (e)));

  if (e->insns.r == NULL_RTX)
    start_sequence ();
  else
    push_to_sequence (e->insns.r);

  emit_insn (pattern);

  e->insns.r = get_insns ();
  end_sequence ();
}

/* Update the CFG for the instructions queued on edge E.  */

void
commit_one_edge_insertion (edge e)
{
  rtx before = NULL_RTX, after = NULL_RTX, insns, tmp, last;
  basic_block bb;

  /* Pull the insns off the edge now since the edge might go away.  */
  insns = e->insns.r;
  e->insns.r = NULL_RTX;

  /* Figure out where to put these insns.  If the destination has
     one predecessor, insert there.  Except for the exit block.  */
  if (single_pred_p (e->dest) && e->dest != EXIT_BLOCK_PTR)
    {
      bb = e->dest;

      /* Get the location correct wrt a code label, and "nice" wrt
         a basic block note, and before everything else.  */
      tmp = BB_HEAD (bb);
      if (LABEL_P (tmp))
        tmp = NEXT_INSN (tmp);
      if (NOTE_INSN_BASIC_BLOCK_P (tmp))
        tmp = NEXT_INSN (tmp);
      if (tmp == BB_HEAD (bb))
        before = tmp;
      else if (tmp)
        after = PREV_INSN (tmp);
      else
        after = get_last_insn ();
    }

  /* If the source has one successor and the edge is not abnormal,
     insert there.  Except for the entry block.  */
  else if ((e->flags & EDGE_ABNORMAL) == 0
           && single_succ_p (e->src)
           && e->src != ENTRY_BLOCK_PTR)
    {
      bb = e->src;

      /* It is possible to have a non-simple jump here.  Consider a target
         where some forms of unconditional jumps clobber a register.  This
         happens on the fr30 for example.

         We know this block has a single successor, so we can just emit
         the queued insns before the jump.  */
      if (JUMP_P (BB_END (bb)))
        before = BB_END (bb);
      else
        {
          /* We'd better be fallthru, or we've lost track of what's what.  */
          gcc_assert (e->flags & EDGE_FALLTHRU);

          after = BB_END (bb);
        }
    }

  /* Otherwise we must split the edge.  */
  else
    {
      bb = split_edge (e);
      after = BB_END (bb);

      if (flag_reorder_blocks_and_partition
          && targetm_common.have_named_sections
          && e->src != ENTRY_BLOCK_PTR
          && BB_PARTITION (e->src) == BB_COLD_PARTITION
          && !(e->flags & EDGE_CROSSING)
          && JUMP_P (after)
          && !any_condjump_p (after)
          && (single_succ_edge (bb)->flags & EDGE_CROSSING))
        add_reg_note (after, REG_CROSSING_JUMP, NULL_RTX);
    }

  /* Now that we've found the spot, do the insertion.  */
  if (before)
    {
      emit_insn_before_noloc (insns, before, bb);
      last = prev_nonnote_insn (before);
    }
  else
    last = emit_insn_after_noloc (insns, after, bb);

  if (returnjump_p (last))
    {
      /* ??? Remove all outgoing edges from BB and add one for EXIT.
         This is not currently a problem because this only happens
         for the (single) epilogue, which already has a fallthru edge
         to EXIT.  */

      e = single_succ_edge (bb);
      gcc_assert (e->dest == EXIT_BLOCK_PTR
                  && single_succ_p (bb) && (e->flags & EDGE_FALLTHRU));

      e->flags &= ~EDGE_FALLTHRU;
      emit_barrier_after (last);

      if (before)
        delete_insn (before);
    }
  else
    gcc_assert (!JUMP_P (last));
}

/* Update the CFG for all queued instructions.  */

void
commit_edge_insertions (void)
{
  basic_block bb;

#ifdef ENABLE_CHECKING
  verify_flow_info ();
#endif

  FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb)
    {
      edge e;
      edge_iterator ei;

      FOR_EACH_EDGE (e, ei, bb->succs)
        if (e->insns.r)
          commit_one_edge_insertion (e);
    }
}
\f

/* Print out RTL-specific basic block information (live information
   at start and end with TDF_DETAILS).  FLAGS are the TDF_* masks
   documented in dumpfile.h.  */

static void
rtl_dump_bb (FILE *outf, basic_block bb, int indent, int flags)
{
  rtx insn;
  rtx last;
  char *s_indent;

  s_indent = (char *) alloca ((size_t) indent + 1);
  memset (s_indent, ' ', (size_t) indent);
  s_indent[indent] = '\0';

  if (df && (flags & TDF_DETAILS))
    {
      df_dump_top (bb, outf);
      putc ('\n', outf);
    }

  if (bb->index != ENTRY_BLOCK && bb->index != EXIT_BLOCK)
    for (insn = BB_HEAD (bb), last = NEXT_INSN (BB_END (bb)); insn != last;
         insn = NEXT_INSN (insn))
      {
        if (! (flags & TDF_SLIM))
          print_rtl_single (outf, insn);
        else
          dump_insn_slim (outf, insn);

      }

  if (df && (flags & TDF_DETAILS))
    {
      df_dump_bottom (bb, outf);
      putc ('\n', outf);
    }

}
\f
/* Like dump_function_to_file, but for RTL.  Print out dataflow information
   for the start of each basic block.  FLAGS are the TDF_* masks documented
   in dumpfile.h.  */

void
print_rtl_with_bb (FILE *outf, const_rtx rtx_first, int flags)
{
  const_rtx tmp_rtx;
  if (rtx_first == 0)
    fprintf (outf, "(nil)\n");
  else
    {
      enum bb_state { NOT_IN_BB, IN_ONE_BB, IN_MULTIPLE_BB };
      int max_uid = get_max_uid ();
      basic_block *start = XCNEWVEC (basic_block, max_uid);
      basic_block *end = XCNEWVEC (basic_block, max_uid);
      enum bb_state *in_bb_p = XCNEWVEC (enum bb_state, max_uid);
      basic_block bb;

      /* After freeing the CFG, we still have BLOCK_FOR_INSN set on most
         insns, but the CFG is not maintained so the basic block info
         is not reliable.  Therefore it's omitted from the dumps.  */
      if (! (cfun->curr_properties & PROP_cfg))
        flags &= ~TDF_BLOCKS;

      if (df)
        df_dump_start (outf);

      if (flags & TDF_BLOCKS)
        {
          FOR_EACH_BB_REVERSE (bb)
            {
              rtx x;

              start[INSN_UID (BB_HEAD (bb))] = bb;
              end[INSN_UID (BB_END (bb))] = bb;
              for (x = BB_HEAD (bb); x != NULL_RTX; x = NEXT_INSN (x))
                {
                  enum bb_state state = IN_MULTIPLE_BB;

                  if (in_bb_p[INSN_UID (x)] == NOT_IN_BB)
                    state = IN_ONE_BB;
                  in_bb_p[INSN_UID (x)] = state;

                  if (x == BB_END (bb))
                    break;
                }
            }
        }

      for (tmp_rtx = rtx_first; NULL != tmp_rtx; tmp_rtx = NEXT_INSN (tmp_rtx))
        {
          if (flags & TDF_BLOCKS)
            {
              bb = start[INSN_UID (tmp_rtx)];
              if (bb != NULL)
                {
                  dump_bb_info (outf, bb, 0, dump_flags | TDF_COMMENT, true, false);
                  if (df && (flags & TDF_DETAILS))
                    df_dump_top (bb, outf);
                }

              if (in_bb_p[INSN_UID (tmp_rtx)] == NOT_IN_BB
                  && !NOTE_P (tmp_rtx)
                  && !BARRIER_P (tmp_rtx))
                fprintf (outf, ";; Insn is not within a basic block\n");
              else if (in_bb_p[INSN_UID (tmp_rtx)] == IN_MULTIPLE_BB)
                fprintf (outf, ";; Insn is in multiple basic blocks\n");
            }

          if (! (flags & TDF_SLIM))
            print_rtl_single (outf, tmp_rtx);
          else
            dump_insn_slim (outf, tmp_rtx);

          if (flags & TDF_BLOCKS)
            {
              bb = end[INSN_UID (tmp_rtx)];
              if (bb != NULL)
                {
                  dump_bb_info (outf, bb, 0, dump_flags | TDF_COMMENT, false, true);
                  if (df && (flags & TDF_DETAILS))
                    df_dump_bottom (bb, outf);
                  putc ('\n', outf);
                }
            }
        }

      free (start);
      free (end);
      free (in_bb_p);
    }

  if (crtl->epilogue_delay_list != 0)
    {
      fprintf (outf, "\n;; Insns in epilogue delay list:\n\n");
      for (tmp_rtx = crtl->epilogue_delay_list; tmp_rtx != 0;
           tmp_rtx = XEXP (tmp_rtx, 1))
        print_rtl_single (outf, XEXP (tmp_rtx, 0));
    }
}
\f
/* Update the branch probability of BB if a REG_BR_PROB is present.  */

void
update_br_prob_note (basic_block bb)
{
  rtx note;
  if (!JUMP_P (BB_END (bb)))
    return;
  note = find_reg_note (BB_END (bb), REG_BR_PROB, NULL_RTX);
  if (!note || INTVAL (XEXP (note, 0)) == BRANCH_EDGE (bb)->probability)
    return;
  XEXP (note, 0) = GEN_INT (BRANCH_EDGE (bb)->probability);
}

/* Get the last insn associated with block BB (that includes barriers and
   tablejumps after BB).  */
rtx
get_last_bb_insn (basic_block bb)
{
  rtx tmp;
  rtx end = BB_END (bb);

  /* Include any jump table following the basic block.  */
  if (tablejump_p (end, NULL, &tmp))
    end = tmp;

  /* Include any barriers that may follow the basic block.  */
  tmp = next_nonnote_insn_bb (end);
  while (tmp && BARRIER_P (tmp))
    {
      end = tmp;
      tmp = next_nonnote_insn_bb (end);
    }

  return end;
}
\f
/* Verify the CFG and RTL consistency common for both underlying RTL and
   cfglayout RTL.

   Currently it does following checks:

   - overlapping of basic blocks
   - insns with wrong BLOCK_FOR_INSN pointers
   - headers of basic blocks (the NOTE_INSN_BASIC_BLOCK note)
   - tails of basic blocks (ensure that boundary is necessary)
   - scans body of the basic block for JUMP_INSN, CODE_LABEL
     and NOTE_INSN_BASIC_BLOCK
   - verify that no fall_thru edge crosses hot/cold partition boundaries
   - verify that there are no pending RTL branch predictions

   In future it can be extended check a lot of other stuff as well
   (reachability of basic blocks, life information, etc. etc.).  */

static int
rtl_verify_flow_info_1 (void)
{
  rtx x;
  int err = 0;
  basic_block bb;

  /* Check the general integrity of the basic blocks.  */
  FOR_EACH_BB_REVERSE (bb)
    {
      rtx insn;

      if (!(bb->flags & BB_RTL))
        {
          error ("BB_RTL flag not set for block %d", bb->index);
          err = 1;
        }

      FOR_BB_INSNS (bb, insn)
        if (BLOCK_FOR_INSN (insn) != bb)
          {
            error ("insn %d basic block pointer is %d, should be %d",
                   INSN_UID (insn),
                   BLOCK_FOR_INSN (insn) ? BLOCK_FOR_INSN (insn)->index : 0,
                   bb->index);
            err = 1;
          }

      for (insn = BB_HEADER (bb); insn; insn = NEXT_INSN (insn))
        if (!BARRIER_P (insn)
            && BLOCK_FOR_INSN (insn) != NULL)
          {
            error ("insn %d in header of bb %d has non-NULL basic block",
                   INSN_UID (insn), bb->index);
            err = 1;
          }
      for (insn = BB_FOOTER (bb); insn; insn = NEXT_INSN (insn))
        if (!BARRIER_P (insn)
            && BLOCK_FOR_INSN (insn) != NULL)
          {
            error ("insn %d in footer of bb %d has non-NULL basic block",
                   INSN_UID (insn), bb->index);
            err = 1;
          }
    }

  /* Now check the basic blocks (boundaries etc.) */
  FOR_EACH_BB_REVERSE (bb)
    {
      int n_fallthru = 0, n_eh = 0, n_call = 0, n_abnormal = 0, n_branch = 0;
      edge e, fallthru = NULL;
      rtx note;
      edge_iterator ei;

      if (JUMP_P (BB_END (bb))
          && (note = find_reg_note (BB_END (bb), REG_BR_PROB, NULL_RTX))
          && EDGE_COUNT (bb->succs) >= 2
          && any_condjump_p (BB_END (bb)))
        {
          if (INTVAL (XEXP (note, 0)) != BRANCH_EDGE (bb)->probability
              && profile_status != PROFILE_ABSENT)
            {
              error ("verify_flow_info: REG_BR_PROB does not match cfg %wi %i",
                     INTVAL (XEXP (note, 0)), BRANCH_EDGE (bb)->probability);
              err = 1;
            }
        }
      FOR_EACH_EDGE (e, ei, bb->succs)
        {
          bool is_crossing;

          if (e->flags & EDGE_FALLTHRU)
            n_fallthru++, fallthru = e;

          is_crossing = (BB_PARTITION (e->src) != BB_PARTITION (e->dest)
                         && e->src != ENTRY_BLOCK_PTR
                         && e->dest != EXIT_BLOCK_PTR);
          if (e->flags & EDGE_CROSSING)
            {
              if (!is_crossing)
                {
                  error ("EDGE_CROSSING incorrectly set across same section");
                  err = 1;
                }
              if (e->flags & EDGE_FALLTHRU)
                {
                  error ("fallthru edge crosses section boundary (bb %i)",
                         e->src->index);
                  err = 1;
                }
              if (e->flags & EDGE_EH)
                {
                  error ("EH edge crosses section boundary (bb %i)",
                         e->src->index);
                  err = 1;
                }
            }
          else if (is_crossing)
            {
              error ("EDGE_CROSSING missing across section boundary");
              err = 1;
            }

          if ((e->flags & ~(EDGE_DFS_BACK
                            | EDGE_CAN_FALLTHRU
                            | EDGE_IRREDUCIBLE_LOOP
                            | EDGE_LOOP_EXIT
                            | EDGE_CROSSING
                            | EDGE_PRESERVE)) == 0)
            n_branch++;

          if (e->flags & EDGE_ABNORMAL_CALL)
            n_call++;

          if (e->flags & EDGE_EH)
            n_eh++;
          else if (e->flags & EDGE_ABNORMAL)
            n_abnormal++;
        }

      if (n_eh && !find_reg_note (BB_END (bb), REG_EH_REGION, NULL_RTX))
        {
          error ("missing REG_EH_REGION note in the end of bb %i", bb->index);
          err = 1;
        }
      if (n_eh > 1)
        {
          error ("too many eh edges %i", bb->index);
          err = 1;
        }
      if (n_branch
          && (!JUMP_P (BB_END (bb))
              || (n_branch > 1 && (any_uncondjump_p (BB_END (bb))
                                   || any_condjump_p (BB_END (bb))))))
        {
          error ("too many outgoing branch edges from bb %i", bb->index);
          err = 1;
        }
      if (n_fallthru && any_uncondjump_p (BB_END (bb)))
        {
          error ("fallthru edge after unconditional jump %i", bb->index);
          err = 1;
        }
      if (n_branch != 1 && any_uncondjump_p (BB_END (bb)))
        {
          error ("wrong number of branch edges after unconditional jump %i",
                 bb->index);
          err = 1;
        }
      if (n_branch != 1 && any_condjump_p (BB_END (bb))
          && JUMP_LABEL (BB_END (bb)) != BB_HEAD (fallthru->dest))
        {
          error ("wrong amount of branch edges after conditional jump %i",
                 bb->index);
          err = 1;
        }
      if (n_call && !CALL_P (BB_END (bb)))
        {
          error ("call edges for non-call insn in bb %i", bb->index);
          err = 1;
        }
      if (n_abnormal
          && (!CALL_P (BB_END (bb)) && n_call != n_abnormal)
          && (!JUMP_P (BB_END (bb))
              || any_condjump_p (BB_END (bb))
              || any_uncondjump_p (BB_END (bb))))
        {
          error ("abnormal edges for no purpose in bb %i", bb->index);
          err = 1;
        }

      for (x = BB_HEAD (bb); x != NEXT_INSN (BB_END (bb)); x = NEXT_INSN (x))
        /* We may have a barrier inside a basic block before dead code
           elimination.  There is no BLOCK_FOR_INSN field in a barrier.  */
        if (!BARRIER_P (x) && BLOCK_FOR_INSN (x) != bb)
          {
            debug_rtx (x);
            if (! BLOCK_FOR_INSN (x))
              error
                ("insn %d inside basic block %d but block_for_insn is NULL",
                 INSN_UID (x), bb->index);
            else
              error
                ("insn %d inside basic block %d but block_for_insn is %i",
                 INSN_UID (x), bb->index, BLOCK_FOR_INSN (x)->index);

            err = 1;
          }

      /* OK pointers are correct.  Now check the header of basic
         block.  It ought to contain optional CODE_LABEL followed
         by NOTE_BASIC_BLOCK.  */
      x = BB_HEAD (bb);
      if (LABEL_P (x))
        {
          if (BB_END (bb) == x)
            {
              error ("NOTE_INSN_BASIC_BLOCK is missing for block %d",
                     bb->index);
              err = 1;
            }

          x = NEXT_INSN (x);
        }

      if (!NOTE_INSN_BASIC_BLOCK_P (x) || NOTE_BASIC_BLOCK (x) != bb)
        {
          error ("NOTE_INSN_BASIC_BLOCK is missing for block %d",
                 bb->index);
          err = 1;
        }

      if (BB_END (bb) == x)
        /* Do checks for empty blocks here.  */
        ;
      else
        for (x = NEXT_INSN (x); x; x = NEXT_INSN (x))
          {
            if (NOTE_INSN_BASIC_BLOCK_P (x))
              {
                error ("NOTE_INSN_BASIC_BLOCK %d in middle of basic block %d",
                       INSN_UID (x), bb->index);
                err = 1;
              }

            if (x == BB_END (bb))
              break;

            if (control_flow_insn_p (x))
              {
                error ("in basic block %d:", bb->index);
                fatal_insn ("flow control insn inside a basic block", x);
              }
          }
    }

  /* Clean up.  */
  return err;
}

/* Verify the CFG and RTL consistency common for both underlying RTL and
   cfglayout RTL.

   Currently it does following checks:
   - all checks of rtl_verify_flow_info_1
   - test head/end pointers
   - check that all insns are in the basic blocks
     (except the switch handling code, barriers and notes)
   - check that all returns are followed by barriers
   - check that all fallthru edge points to the adjacent blocks.  */

static int
rtl_verify_flow_info (void)
{
  basic_block bb;
  int err = rtl_verify_flow_info_1 ();
  rtx x;
  rtx last_head = get_last_insn ();
  basic_block *bb_info;
  int num_bb_notes;
  const rtx rtx_first = get_insns ();
  basic_block last_bb_seen = ENTRY_BLOCK_PTR, curr_bb = NULL;
  const int max_uid = get_max_uid ();

  bb_info = XCNEWVEC (basic_block, max_uid);

  FOR_EACH_BB_REVERSE (bb)
    {
      edge e;
      rtx head = BB_HEAD (bb);
      rtx end = BB_END (bb);

      for (x = last_head; x != NULL_RTX; x = PREV_INSN (x))
        {
          /* Verify the end of the basic block is in the INSN chain.  */
          if (x == end)
            break;

          /* And that the code outside of basic blocks has NULL bb field.  */
        if (!BARRIER_P (x)
            && BLOCK_FOR_INSN (x) != NULL)
          {
            error ("insn %d outside of basic blocks has non-NULL bb field",
                   INSN_UID (x));
            err = 1;
          }
        }

      if (!x)
        {
          error ("end insn %d for block %d not found in the insn stream",
                 INSN_UID (end), bb->index);
          err = 1;
        }

      /* Work backwards from the end to the head of the basic block
         to verify the head is in the RTL chain.  */
      for (; x != NULL_RTX; x = PREV_INSN (x))
        {
          /* While walking over the insn chain, verify insns appear
             in only one basic block.  */
          if (bb_info[INSN_UID (x)] != NULL)
            {
              error ("insn %d is in multiple basic blocks (%d and %d)",
                     INSN_UID (x), bb->index, bb_info[INSN_UID (x)]->index);
              err = 1;
            }

          bb_info[INSN_UID (x)] = bb;

          if (x == head)
            break;
        }
      if (!x)
        {
          error ("head insn %d for block %d not found in the insn stream",
                 INSN_UID (head), bb->index);
          err = 1;
        }

      last_head = PREV_INSN (x);

      e = find_fallthru_edge (bb->succs);
      if (!e)
        {
          rtx insn;

          /* Ensure existence of barrier in BB with no fallthru edges.  */
          for (insn = NEXT_INSN (BB_END (bb)); ; insn = NEXT_INSN (insn))
            {
              if (!insn || NOTE_INSN_BASIC_BLOCK_P (insn))
                {
                  error ("missing barrier after block %i", bb->index);
                  err = 1;
                  break;
                }
              if (BARRIER_P (insn))
                break;
            }
        }
      else if (e->src != ENTRY_BLOCK_PTR
               && e->dest != EXIT_BLOCK_PTR)
        {
          rtx insn;

          if (e->src->next_bb != e->dest)
            {
              error
                ("verify_flow_info: Incorrect blocks for fallthru %i->%i",
                 e->src->index, e->dest->index);
              err = 1;
            }
          else
            for (insn = NEXT_INSN (BB_END (e->src)); insn != BB_HEAD (e->dest);
                 insn = NEXT_INSN (insn))
              if (BARRIER_P (insn) || INSN_P (insn))
                {
                  error ("verify_flow_info: Incorrect fallthru %i->%i",
                         e->src->index, e->dest->index);
                  fatal_insn ("wrong insn in the fallthru edge", insn);
                  err = 1;
                }
        }
    }

  for (x = last_head; x != NULL_RTX; x = PREV_INSN (x))
    {
      /* Check that the code before the first basic block has NULL
         bb field.  */
      if (!BARRIER_P (x)
          && BLOCK_FOR_INSN (x) != NULL)
        {
          error ("insn %d outside of basic blocks has non-NULL bb field",
                 INSN_UID (x));
          err = 1;
        }
    }
  free (bb_info);

  num_bb_notes = 0;
  last_bb_seen = ENTRY_BLOCK_PTR;

  for (x = rtx_first; x; x = NEXT_INSN (x))
    {
      if (NOTE_INSN_BASIC_BLOCK_P (x))
        {
          bb = NOTE_BASIC_BLOCK (x);

          num_bb_notes++;
          if (bb != last_bb_seen->next_bb)
            internal_error ("basic blocks not laid down consecutively");

          curr_bb = last_bb_seen = bb;
        }

      if (!curr_bb)
        {
          switch (GET_CODE (x))
            {
            case BARRIER:
            case NOTE:
              break;

            case CODE_LABEL:
              /* An addr_vec is placed outside any basic block.  */
              if (NEXT_INSN (x)
                  && JUMP_TABLE_DATA_P (NEXT_INSN (x)))
                x = NEXT_INSN (x);

              /* But in any case, non-deletable labels can appear anywhere.  */
              break;

            default:
              fatal_insn ("insn outside basic block", x);
            }
        }

      if (JUMP_P (x)
          && returnjump_p (x) && ! condjump_p (x)
          && ! (next_nonnote_insn (x) && BARRIER_P (next_nonnote_insn (x))))
            fatal_insn ("return not followed by barrier", x);
      if (curr_bb && x == BB_END (curr_bb))
        curr_bb = NULL;
    }

  if (num_bb_notes != n_basic_blocks - NUM_FIXED_BLOCKS)
    internal_error
      ("number of bb notes in insn chain (%d) != n_basic_blocks (%d)",
       num_bb_notes, n_basic_blocks);

   return err;
}
\f
/* Assume that the preceding pass has possibly eliminated jump instructions
   or converted the unconditional jumps.  Eliminate the edges from CFG.
   Return true if any edges are eliminated.  */

bool
purge_dead_edges (basic_block bb)
{
  edge e;
  rtx insn = BB_END (bb), note;
  bool purged = false;
  bool found;
  edge_iterator ei;

  if (DEBUG_INSN_P (insn) && insn != BB_HEAD (bb))
    do
      insn = PREV_INSN (insn);
    while ((DEBUG_INSN_P (insn) || NOTE_P (insn)) && insn != BB_HEAD (bb));

  /* If this instruction cannot trap, remove REG_EH_REGION notes.  */
  if (NONJUMP_INSN_P (insn)
      && (note = find_reg_note (insn, REG_EH_REGION, NULL)))
    {
      rtx eqnote;

      if (! may_trap_p (PATTERN (insn))
          || ((eqnote = find_reg_equal_equiv_note (insn))
              && ! may_trap_p (XEXP (eqnote, 0))))
        remove_note (insn, note);
    }

  /* Cleanup abnormal edges caused by exceptions or non-local gotos.  */
  for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
    {
      bool remove = false;

      /* There are three types of edges we need to handle correctly here: EH
         edges, abnormal call EH edges, and abnormal call non-EH edges.  The
         latter can appear when nonlocal gotos are used.  */
      if (e->flags & EDGE_ABNORMAL_CALL)
        {
          if (!CALL_P (insn))
            remove = true;
          else if (can_nonlocal_goto (insn))
            ;
          else if ((e->flags & EDGE_EH) && can_throw_internal (insn))
            ;
          else if (flag_tm && find_reg_note (insn, REG_TM, NULL))
            ;
          else
            remove = true;
        }
      else if (e->flags & EDGE_EH)
        remove = !can_throw_internal (insn);

      if (remove)
        {
          remove_edge (e);
          df_set_bb_dirty (bb);
          purged = true;
        }
      else
        ei_next (&ei);
    }

  if (JUMP_P (insn))
    {
      rtx note;
      edge b,f;
      edge_iterator ei;

      /* We do care only about conditional jumps and simplejumps.  */
      if (!any_condjump_p (insn)
          && !returnjump_p (insn)
          && !simplejump_p (insn))
        return purged;

      /* Branch probability/prediction notes are defined only for
         condjumps.  We've possibly turned condjump into simplejump.  */
      if (simplejump_p (insn))
        {
          note = find_reg_note (insn, REG_BR_PROB, NULL);
          if (note)
            remove_note (insn, note);
          while ((note = find_reg_note (insn, REG_BR_PRED, NULL)))
            remove_note (insn, note);
        }

      for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
        {
          /* Avoid abnormal flags to leak from computed jumps turned
             into simplejumps.  */

          e->flags &= ~EDGE_ABNORMAL;

          /* See if this edge is one we should keep.  */
          if ((e->flags & EDGE_FALLTHRU) && any_condjump_p (insn))
            /* A conditional jump can fall through into the next
               block, so we should keep the edge.  */
            {
              ei_next (&ei);
              continue;
            }
          else if (e->dest != EXIT_BLOCK_PTR
                   && BB_HEAD (e->dest) == JUMP_LABEL (insn))
            /* If the destination block is the target of the jump,
               keep the edge.  */
            {
              ei_next (&ei);
              continue;
            }
          else if (e->dest == EXIT_BLOCK_PTR && returnjump_p (insn))
            /* If the destination block is the exit block, and this
               instruction is a return, then keep the edge.  */
            {
              ei_next (&ei);
              continue;
            }
          else if ((e->flags & EDGE_EH) && can_throw_internal (insn))
            /* Keep the edges that correspond to exceptions thrown by
               this instruction and rematerialize the EDGE_ABNORMAL
               flag we just cleared above.  */
            {
              e->flags |= EDGE_ABNORMAL;
              ei_next (&ei);
              continue;
            }

          /* We do not need this edge.  */
          df_set_bb_dirty (bb);
          purged = true;
          remove_edge (e);
        }

      if (EDGE_COUNT (bb->succs) == 0 || !purged)
        return purged;

      if (dump_file)
        fprintf (dump_file, "Purged edges from bb %i\n", bb->index);

      if (!optimize)
        return purged;

      /* Redistribute probabilities.  */
      if (single_succ_p (bb))
        {
          single_succ_edge (bb)->probability = REG_BR_PROB_BASE;
          single_succ_edge (bb)->count = bb->count;
        }
      else
        {
          note = find_reg_note (insn, REG_BR_PROB, NULL);
          if (!note)
            return purged;

          b = BRANCH_EDGE (bb);
          f = FALLTHRU_EDGE (bb);
          b->probability = INTVAL (XEXP (note, 0));
          f->probability = REG_BR_PROB_BASE - b->probability;
          b->count = bb->count * b->probability / REG_BR_PROB_BASE;
          f->count = bb->count * f->probability / REG_BR_PROB_BASE;
        }

      return purged;
    }
  else if (CALL_P (insn) && SIBLING_CALL_P (insn))
    {
      /* First, there should not be any EH or ABCALL edges resulting
         from non-local gotos and the like.  If there were, we shouldn't
         have created the sibcall in the first place.  Second, there
         should of course never have been a fallthru edge.  */
      gcc_assert (single_succ_p (bb));
      gcc_assert (single_succ_edge (bb)->flags
                  == (EDGE_SIBCALL | EDGE_ABNORMAL));

      return 0;
    }

  /* If we don't see a jump insn, we don't know exactly why the block would
     have been broken at this point.  Look for a simple, non-fallthru edge,
     as these are only created by conditional branches.  If we find such an
     edge we know that there used to be a jump here and can then safely
     remove all non-fallthru edges.  */
  found = false;
  FOR_EACH_EDGE (e, ei, bb->succs)
    if (! (e->flags & (EDGE_COMPLEX | EDGE_FALLTHRU)))
      {
        found = true;
        break;
      }

  if (!found)
    return purged;

  /* Remove all but the fake and fallthru edges.  The fake edge may be
     the only successor for this block in the case of noreturn
     calls.  */
  for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
    {
      if (!(e->flags & (EDGE_FALLTHRU | EDGE_FAKE)))
        {
          df_set_bb_dirty (bb);
          remove_edge (e);
          purged = true;
        }
      else
        ei_next (&ei);
    }

  gcc_assert (single_succ_p (bb));

  single_succ_edge (bb)->probability = REG_BR_PROB_BASE;
  single_succ_edge (bb)->count = bb->count;

  if (dump_file)
    fprintf (dump_file, "Purged non-fallthru edges from bb %i\n",
             bb->index);
  return purged;
}

/* Search all basic blocks for potentially dead edges and purge them.  Return
   true if some edge has been eliminated.  */

bool
purge_all_dead_edges (void)
{
  int purged = false;
  basic_block bb;

  FOR_EACH_BB (bb)
    {
      bool purged_here = purge_dead_edges (bb);

      purged |= purged_here;
    }

  return purged;
}

/* This is used by a few passes that emit some instructions after abnormal
   calls, moving the basic block's end, while they in fact do want to emit
   them on the fallthru edge.  Look for abnormal call edges, find backward
   the call in the block and insert the instructions on the edge instead.

   Similarly, handle instructions throwing exceptions internally.

   Return true when instructions have been found and inserted on edges.  */

bool
fixup_abnormal_edges (void)
{
  bool inserted = false;
  basic_block bb;

  FOR_EACH_BB (bb)
    {
      edge e;
      edge_iterator ei;

      /* Look for cases we are interested in - calls or instructions causing
         exceptions.  */
      FOR_EACH_EDGE (e, ei, bb->succs)
        if ((e->flags & EDGE_ABNORMAL_CALL)
            || ((e->flags & (EDGE_ABNORMAL | EDGE_EH))
                == (EDGE_ABNORMAL | EDGE_EH)))
          break;

      if (e && !CALL_P (BB_END (bb)) && !can_throw_internal (BB_END (bb)))
        {
          rtx insn;

          /* Get past the new insns generated.  Allow notes, as the insns
             may be already deleted.  */
          insn = BB_END (bb);
          while ((NONJUMP_INSN_P (insn) || NOTE_P (insn))
                 && !can_throw_internal (insn)
                 && insn != BB_HEAD (bb))
            insn = PREV_INSN (insn);

          if (CALL_P (insn) || can_throw_internal (insn))
            {
              rtx stop, next;

              e = find_fallthru_edge (bb->succs);

              stop = NEXT_INSN (BB_END (bb));
              BB_END (bb) = insn;

              for (insn = NEXT_INSN (insn); insn != stop; insn = next)
                {
                  next = NEXT_INSN (insn);
                  if (INSN_P (insn))
                    {
                      delete_insn (insn);

                      /* Sometimes there's still the return value USE.
                         If it's placed after a trapping call (i.e. that
                         call is the last insn anyway), we have no fallthru
                         edge.  Simply delete this use and don't try to insert
                         on the non-existent edge.  */
                      if (GET_CODE (PATTERN (insn)) != USE)
                        {
                          /* We're not deleting it, we're moving it.  */
                          INSN_DELETED_P (insn) = 0;
                          PREV_INSN (insn) = NULL_RTX;
                          NEXT_INSN (insn) = NULL_RTX;

                          insert_insn_on_edge (insn, e);
                          inserted = true;
                        }
                    }
                  else if (!BARRIER_P (insn))
                    set_block_for_insn (insn, NULL);
                }
            }

          /* It may be that we don't find any trapping insn.  In this
             case we discovered quite late that the insn that had been
             marked as can_throw_internal in fact couldn't trap at all.
             So we should in fact delete the EH edges out of the block.  */
          else
            purge_dead_edges (bb);
        }
    }

  return inserted;
}
\f
/* Cut the insns from FIRST to LAST out of the insns stream.  */

rtx
unlink_insn_chain (rtx first, rtx last)
{
  rtx prevfirst = PREV_INSN (first);
  rtx nextlast = NEXT_INSN (last);

  PREV_INSN (first) = NULL;
  NEXT_INSN (last) = NULL;
  if (prevfirst)
    NEXT_INSN (prevfirst) = nextlast;
  if (nextlast)
    PREV_INSN (nextlast) = prevfirst;
  else
    set_last_insn (prevfirst);
  if (!prevfirst)
    set_first_insn (nextlast);
  return first;
}
\f
/* Skip over inter-block insns occurring after BB which are typically
   associated with BB (e.g., barriers). If there are any such insns,
   we return the last one. Otherwise, we return the end of BB.  */

static rtx
skip_insns_after_block (basic_block bb)
{
  rtx insn, last_insn, next_head, prev;

  next_head = NULL_RTX;
  if (bb->next_bb != EXIT_BLOCK_PTR)
    next_head = BB_HEAD (bb->next_bb);

  for (last_insn = insn = BB_END (bb); (insn = NEXT_INSN (insn)) != 0; )
    {
      if (insn == next_head)
        break;

      switch (GET_CODE (insn))
        {
        case BARRIER:
          last_insn = insn;
          continue;

        case NOTE:
          switch (NOTE_KIND (insn))
            {
            case NOTE_INSN_BLOCK_END:
              gcc_unreachable ();
              continue;
            default:
              continue;
              break;
            }
          break;

        case CODE_LABEL:
          if (NEXT_INSN (insn)
              && JUMP_TABLE_DATA_P (NEXT_INSN (insn)))
            {
              insn = NEXT_INSN (insn);
              last_insn = insn;
              continue;
            }
          break;

        default:
          break;
        }

      break;
    }

  /* It is possible to hit contradictory sequence.  For instance:

     jump_insn
     NOTE_INSN_BLOCK_BEG
     barrier

     Where barrier belongs to jump_insn, but the note does not.  This can be
     created by removing the basic block originally following
     NOTE_INSN_BLOCK_BEG.  In such case reorder the notes.  */

  for (insn = last_insn; insn != BB_END (bb); insn = prev)
    {
      prev = PREV_INSN (insn);
      if (NOTE_P (insn))
        switch (NOTE_KIND (insn))
          {
          case NOTE_INSN_BLOCK_END:
            gcc_unreachable ();
            break;
          case NOTE_INSN_DELETED:
          case NOTE_INSN_DELETED_LABEL:
          case NOTE_INSN_DELETED_DEBUG_LABEL:
            continue;
          default:
            reorder_insns (insn, insn, last_insn);
          }
    }

  return last_insn;
}

/* Locate or create a label for a given basic block.  */

static rtx
label_for_bb (basic_block bb)
{
  rtx label = BB_HEAD (bb);

  if (!LABEL_P (label))
    {
      if (dump_file)
        fprintf (dump_file, "Emitting label for block %d\n", bb->index);

      label = block_label (bb);
    }

  return label;
}

/* Locate the effective beginning and end of the insn chain for each
   block, as defined by skip_insns_after_block above.  */

static void
record_effective_endpoints (void)
{
  rtx next_insn;
  basic_block bb;
  rtx insn;

  for (insn = get_insns ();
       insn
       && NOTE_P (insn)
       && NOTE_KIND (insn) != NOTE_INSN_BASIC_BLOCK;
       insn = NEXT_INSN (insn))
    continue;
  /* No basic blocks at all?  */
  gcc_assert (insn);

  if (PREV_INSN (insn))
    cfg_layout_function_header =
            unlink_insn_chain (get_insns (), PREV_INSN (insn));
  else
    cfg_layout_function_header = NULL_RTX;

  next_insn = get_insns ();
  FOR_EACH_BB (bb)
    {
      rtx end;

      if (PREV_INSN (BB_HEAD (bb)) && next_insn != BB_HEAD (bb))
        BB_HEADER (bb) = unlink_insn_chain (next_insn,
                                              PREV_INSN (BB_HEAD (bb)));
      end = skip_insns_after_block (bb);
      if (NEXT_INSN (BB_END (bb)) && BB_END (bb) != end)
        BB_FOOTER (bb) = unlink_insn_chain (NEXT_INSN (BB_END (bb)), end);
      next_insn = NEXT_INSN (BB_END (bb));
    }

  cfg_layout_function_footer = next_insn;
  if (cfg_layout_function_footer)
    cfg_layout_function_footer = unlink_insn_chain (cfg_layout_function_footer, get_last_insn ());
}
\f
static unsigned int
into_cfg_layout_mode (void)
{
  cfg_layout_initialize (0);
  return 0;
}

static unsigned int
outof_cfg_layout_mode (void)
{
  basic_block bb;

  FOR_EACH_BB (bb)
    if (bb->next_bb != EXIT_BLOCK_PTR)
      bb->aux = bb->next_bb;

  cfg_layout_finalize ();

  return 0;
}

struct rtl_opt_pass pass_into_cfg_layout_mode =
{
 {
  RTL_PASS,
  "into_cfglayout",                     /* name */
  NULL,                                 /* gate */
  into_cfg_layout_mode,                 /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_CFG,                               /* tv_id */
  0,                                    /* properties_required */
  PROP_cfglayout,                       /* properties_provided */
  0,                                    /* properties_destroyed */
  0,                                    /* todo_flags_start */
  0                                     /* todo_flags_finish */
 }
};

struct rtl_opt_pass pass_outof_cfg_layout_mode =
{
 {
  RTL_PASS,
  "outof_cfglayout",                    /* name */
  NULL,                                 /* gate */
  outof_cfg_layout_mode,                /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_CFG,                               /* tv_id */
  0,                                    /* properties_required */
  0,                                    /* properties_provided */
  PROP_cfglayout,                       /* properties_destroyed */
  0,                                    /* todo_flags_start */
  0                                     /* todo_flags_finish */
 }
};
\f

/* Link the basic blocks in the correct order, compacting the basic
   block queue while at it.  If STAY_IN_CFGLAYOUT_MODE is false, this
   function also clears the basic block header and footer fields.

   This function is usually called after a pass (e.g. tracer) finishes
   some transformations while in cfglayout mode.  The required sequence
   of the basic blocks is in a linked list along the bb->aux field.
   This functions re-links the basic block prev_bb and next_bb pointers
   accordingly, and it compacts and renumbers the blocks.

   FIXME: This currently works only for RTL, but the only RTL-specific
   bits are the STAY_IN_CFGLAYOUT_MODE bits.  The tracer pass was moved
   to GIMPLE a long time ago, but it doesn't relink the basic block
   chain.  It could do that (to give better initial RTL) if this function
   is made IR-agnostic (and moved to cfganal.c or cfg.c while at it).  */

void
relink_block_chain (bool stay_in_cfglayout_mode)
{
  basic_block bb, prev_bb;
  int index;

  /* Maybe dump the re-ordered sequence.  */
  if (dump_file)
    {
      fprintf (dump_file, "Reordered sequence:\n");
      for (bb = ENTRY_BLOCK_PTR->next_bb, index = NUM_FIXED_BLOCKS;
           bb;
           bb = (basic_block) bb->aux, index++)
        {
          fprintf (dump_file, " %i ", index);
          if (get_bb_original (bb))
            fprintf (dump_file, "duplicate of %i ",
                     get_bb_original (bb)->index);
          else if (forwarder_block_p (bb)
                   && !LABEL_P (BB_HEAD (bb)))
            fprintf (dump_file, "compensation ");
          else
            fprintf (dump_file, "bb %i ", bb->index);
          fprintf (dump_file, " [%i]\n", bb->frequency);
        }
    }

  /* Now reorder the blocks.  */
  prev_bb = ENTRY_BLOCK_PTR;
  bb = ENTRY_BLOCK_PTR->next_bb;
  for (; bb; prev_bb = bb, bb = (basic_block) bb->aux)
    {
      bb->prev_bb = prev_bb;
      prev_bb->next_bb = bb;
    }
  prev_bb->next_bb = EXIT_BLOCK_PTR;
  EXIT_BLOCK_PTR->prev_bb = prev_bb;

  /* Then, clean up the aux fields.  */
  FOR_ALL_BB (bb)
    {
      bb->aux = NULL;
      if (!stay_in_cfglayout_mode)
        BB_HEADER (bb) = BB_FOOTER (bb) = NULL;
    }

  /* Maybe reset the original copy tables, they are not valid anymore
     when we renumber the basic blocks in compact_blocks.  If we are
     are going out of cfglayout mode, don't re-allocate the tables.  */
  free_original_copy_tables ();
  if (stay_in_cfglayout_mode)
    initialize_original_copy_tables ();

  /* Finally, put basic_block_info in the new order.  */
  compact_blocks ();
}
\f

/* Given a reorder chain, rearrange the code to match.  */

static void
fixup_reorder_chain (void)
{
  basic_block bb;
  rtx insn = NULL;

  if (cfg_layout_function_header)
    {
      set_first_insn (cfg_layout_function_header);
      insn = cfg_layout_function_header;
      while (NEXT_INSN (insn))
        insn = NEXT_INSN (insn);
    }

  /* First do the bulk reordering -- rechain the blocks without regard to
     the needed changes to jumps and labels.  */

  for (bb = ENTRY_BLOCK_PTR->next_bb; bb; bb = (basic_block) bb->aux)
    {
      if (BB_HEADER (bb))
        {
          if (insn)
            NEXT_INSN (insn) = BB_HEADER (bb);
          else
            set_first_insn (BB_HEADER (bb));
          PREV_INSN (BB_HEADER (bb)) = insn;
          insn = BB_HEADER (bb);
          while (NEXT_INSN (insn))
            insn = NEXT_INSN (insn);
        }
      if (insn)
        NEXT_INSN (insn) = BB_HEAD (bb);
      else
        set_first_insn (BB_HEAD (bb));
      PREV_INSN (BB_HEAD (bb)) = insn;
      insn = BB_END (bb);
      if (BB_FOOTER (bb))
        {
          NEXT_INSN (insn) = BB_FOOTER (bb);
          PREV_INSN (BB_FOOTER (bb)) = insn;
          while (NEXT_INSN (insn))
            insn = NEXT_INSN (insn);
        }
    }

  NEXT_INSN (insn) = cfg_layout_function_footer;
  if (cfg_layout_function_footer)
    PREV_INSN (cfg_layout_function_footer) = insn;

  while (NEXT_INSN (insn))
    insn = NEXT_INSN (insn);

  set_last_insn (insn);
#ifdef ENABLE_CHECKING
  verify_insn_chain ();
#endif

  /* Now add jumps and labels as needed to match the blocks new
     outgoing edges.  */

  for (bb = ENTRY_BLOCK_PTR->next_bb; bb ; bb = (basic_block) bb->aux)
    {
      edge e_fall, e_taken, e;
      rtx bb_end_insn;
      rtx ret_label = NULL_RTX;
      basic_block nb, src_bb;
      edge_iterator ei;

      if (EDGE_COUNT (bb->succs) == 0)
        continue;

      /* Find the old fallthru edge, and another non-EH edge for
         a taken jump.  */
      e_taken = e_fall = NULL;

      FOR_EACH_EDGE (e, ei, bb->succs)
        if (e->flags & EDGE_FALLTHRU)
          e_fall = e;
        else if (! (e->flags & EDGE_EH))
          e_taken = e;

      bb_end_insn = BB_END (bb);
      if (JUMP_P (bb_end_insn))
        {
          ret_label = JUMP_LABEL (bb_end_insn);
          if (any_condjump_p (bb_end_insn))
            {
              /* This might happen if the conditional jump has side
                 effects and could therefore not be optimized away.
                 Make the basic block to end with a barrier in order
                 to prevent rtl_verify_flow_info from complaining.  */
              if (!e_fall)
                {
                  gcc_assert (!onlyjump_p (bb_end_insn)
                              || returnjump_p (bb_end_insn));
                  BB_FOOTER (bb) = emit_barrier_after (bb_end_insn);
                  continue;
                }

              /* If the old fallthru is still next, nothing to do.  */
              if (bb->aux == e_fall->dest
                  || e_fall->dest == EXIT_BLOCK_PTR)
                continue;

              /* The degenerated case of conditional jump jumping to the next
                 instruction can happen for jumps with side effects.  We need
                 to construct a forwarder block and this will be done just
                 fine by force_nonfallthru below.  */
              if (!e_taken)
                ;

              /* There is another special case: if *neither* block is next,
                 such as happens at the very end of a function, then we'll
                 need to add a new unconditional jump.  Choose the taken
                 edge based on known or assumed probability.  */
              else if (bb->aux != e_taken->dest)
                {
                  rtx note = find_reg_note (bb_end_insn, REG_BR_PROB, 0);

                  if (note
                      && INTVAL (XEXP (note, 0)) < REG_BR_PROB_BASE / 2
                      && invert_jump (bb_end_insn,
                                      (e_fall->dest == EXIT_BLOCK_PTR
                                       ? NULL_RTX
                                       : label_for_bb (e_fall->dest)), 0))
                    {
                      e_fall->flags &= ~EDGE_FALLTHRU;
                      gcc_checking_assert (could_fall_through
                                           (e_taken->src, e_taken->dest));
                      e_taken->flags |= EDGE_FALLTHRU;
                      update_br_prob_note (bb);
                      e = e_fall, e_fall = e_taken, e_taken = e;
                    }
                }

              /* If the "jumping" edge is a crossing edge, and the fall
                 through edge is non-crossing, leave things as they are.  */
              else if ((e_taken->flags & EDGE_CROSSING)
                       && !(e_fall->flags & EDGE_CROSSING))
                continue;

              /* Otherwise we can try to invert the jump.  This will
                 basically never fail, however, keep up the pretense.  */
              else if (invert_jump (bb_end_insn,
                                    (e_fall->dest == EXIT_BLOCK_PTR
                                     ? NULL_RTX
                                     : label_for_bb (e_fall->dest)), 0))
                {
                  e_fall->flags &= ~EDGE_FALLTHRU;
                  gcc_checking_assert (could_fall_through
                                       (e_taken->src, e_taken->dest));
                  e_taken->flags |= EDGE_FALLTHRU;
                  update_br_prob_note (bb);
                  if (LABEL_NUSES (ret_label) == 0
                      && single_pred_p (e_taken->dest))
                    delete_insn (ret_label);
                  continue;
                }
            }
          else if (extract_asm_operands (PATTERN (bb_end_insn)) != NULL)
            {
              /* If the old fallthru is still next or if
                 asm goto doesn't have a fallthru (e.g. when followed by
                 __builtin_unreachable ()), nothing to do.  */
              if (! e_fall
                  || bb->aux == e_fall->dest
                  || e_fall->dest == EXIT_BLOCK_PTR)
                continue;

              /* Otherwise we'll have to use the fallthru fixup below.  */
            }
          else
            {
              /* Otherwise we have some return, switch or computed
                 jump.  In the 99% case, there should not have been a
                 fallthru edge.  */
              gcc_assert (returnjump_p (bb_end_insn) || !e_fall);
              continue;
            }
        }
      else
        {
          /* No fallthru implies a noreturn function with EH edges, or
             something similarly bizarre.  In any case, we don't need to
             do anything.  */
          if (! e_fall)
            continue;

          /* If the fallthru block is still next, nothing to do.  */
          if (bb->aux == e_fall->dest)
            continue;

          /* A fallthru to exit block.  */
          if (e_fall->dest == EXIT_BLOCK_PTR)
            continue;
        }

      /* We got here if we need to add a new jump insn. 
         Note force_nonfallthru can delete E_FALL and thus we have to
         save E_FALL->src prior to the call to force_nonfallthru.  */
      src_bb = e_fall->src;
      nb = force_nonfallthru_and_redirect (e_fall, e_fall->dest, ret_label);
      if (nb)
        {
          nb->aux = bb->aux;
          bb->aux = nb;
          /* Don't process this new block.  */
          bb = nb;

          /* Make sure new bb is tagged for correct section (same as
             fall-thru source, since you cannot fall-thru across
             section boundaries).  */
          BB_COPY_PARTITION (src_bb, single_pred (bb));
          if (flag_reorder_blocks_and_partition
              && targetm_common.have_named_sections
              && JUMP_P (BB_END (bb))
              && !any_condjump_p (BB_END (bb))
              && (EDGE_SUCC (bb, 0)->flags & EDGE_CROSSING))
            add_reg_note (BB_END (bb), REG_CROSSING_JUMP, NULL_RTX);
        }
    }

  relink_block_chain (/*stay_in_cfglayout_mode=*/false);

  /* Annoying special case - jump around dead jumptables left in the code.  */
  FOR_EACH_BB (bb)
    {
      edge e = find_fallthru_edge (bb->succs);

      if (e && !can_fallthru (e->src, e->dest))
        force_nonfallthru (e);
    }

  /* Ensure goto_locus from edges has some instructions with that locus
     in RTL.  */
  if (!optimize)
    FOR_EACH_BB (bb)
      {
        edge e;
        edge_iterator ei;

        FOR_EACH_EDGE (e, ei, bb->succs)
          if (e->goto_locus && !(e->flags & EDGE_ABNORMAL))
            {
              edge e2;
              edge_iterator ei2;
              basic_block dest, nb;
              rtx end;

              insn = BB_END (e->src);
              end = PREV_INSN (BB_HEAD (e->src));
              while (insn != end
                     && (!NONDEBUG_INSN_P (insn) || INSN_LOCATOR (insn) == 0))
                insn = PREV_INSN (insn);
              if (insn != end
                  && locator_eq (INSN_LOCATOR (insn), (int) e->goto_locus))
                continue;
              if (simplejump_p (BB_END (e->src))
                  && INSN_LOCATOR (BB_END (e->src)) == 0)
                {
                  INSN_LOCATOR (BB_END (e->src)) = e->goto_locus;
                  continue;
                }
              dest = e->dest;
              if (dest == EXIT_BLOCK_PTR)
                {
                  /* Non-fallthru edges to the exit block cannot be split.  */
                  if (!(e->flags & EDGE_FALLTHRU))
                    continue;
                }
              else
                {
                  insn = BB_HEAD (dest);
                  end = NEXT_INSN (BB_END (dest));
                  while (insn != end && !NONDEBUG_INSN_P (insn))
                    insn = NEXT_INSN (insn);
                  if (insn != end && INSN_LOCATOR (insn)
                      && locator_eq (INSN_LOCATOR (insn), (int) e->goto_locus))
                    continue;
                }
              nb = split_edge (e);
              if (!INSN_P (BB_END (nb)))
                BB_END (nb) = emit_insn_after_noloc (gen_nop (), BB_END (nb),
                                                     nb);
              INSN_LOCATOR (BB_END (nb)) = e->goto_locus;

              /* If there are other incoming edges to the destination block
                 with the same goto locus, redirect them to the new block as
                 well, this can prevent other such blocks from being created
                 in subsequent iterations of the loop.  */
              for (ei2 = ei_start (dest->preds); (e2 = ei_safe_edge (ei2)); )
                if (e2->goto_locus
                    && !(e2->flags & (EDGE_ABNORMAL | EDGE_FALLTHRU))
                    && locator_eq (e->goto_locus, e2->goto_locus))
                  redirect_edge_and_branch (e2, nb);
                else
                  ei_next (&ei2);
            }
      }
}
\f
/* Perform sanity checks on the insn chain.
   1. Check that next/prev pointers are consistent in both the forward and
      reverse direction.
   2. Count insns in chain, going both directions, and check if equal.
   3. Check that get_last_insn () returns the actual end of chain.  */

DEBUG_FUNCTION void
verify_insn_chain (void)
{
  rtx x, prevx, nextx;
  int insn_cnt1, insn_cnt2;

  for (prevx = NULL, insn_cnt1 = 1, x = get_insns ();
       x != 0;
       prevx = x, insn_cnt1++, x = NEXT_INSN (x))
    gcc_assert (PREV_INSN (x) == prevx);

  gcc_assert (prevx == get_last_insn ());

  for (nextx = NULL, insn_cnt2 = 1, x = get_last_insn ();
       x != 0;
       nextx = x, insn_cnt2++, x = PREV_INSN (x))
    gcc_assert (NEXT_INSN (x) == nextx);

  gcc_assert (insn_cnt1 == insn_cnt2);
}
\f
/* If we have assembler epilogues, the block falling through to exit must
   be the last one in the reordered chain when we reach final.  Ensure
   that this condition is met.  */
static void
fixup_fallthru_exit_predecessor (void)
{
  edge e;
  basic_block bb = NULL;

  /* This transformation is not valid before reload, because we might
     separate a call from the instruction that copies the return
     value.  */
  gcc_assert (reload_completed);

  e = find_fallthru_edge (EXIT_BLOCK_PTR->preds);
  if (e)
    bb = e->src;

  if (bb && bb->aux)
    {
      basic_block c = ENTRY_BLOCK_PTR->next_bb;

      /* If the very first block is the one with the fall-through exit
         edge, we have to split that block.  */
      if (c == bb)
        {
          bb = split_block (bb, NULL)->dest;
          bb->aux = c->aux;
          c->aux = bb;
          BB_FOOTER (bb) = BB_FOOTER (c);
          BB_FOOTER (c) = NULL;
        }

      while (c->aux != bb)
        c = (basic_block) c->aux;

      c->aux = bb->aux;
      while (c->aux)
        c = (basic_block) c->aux;

      c->aux = bb;
      bb->aux = NULL;
    }
}

/* In case there are more than one fallthru predecessors of exit, force that
   there is only one.  */

static void
force_one_exit_fallthru (void)
{
  edge e, predecessor = NULL;
  bool more = false;
  edge_iterator ei;
  basic_block forwarder, bb;

  FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
    if (e->flags & EDGE_FALLTHRU)
      {
        if (predecessor == NULL)
          predecessor = e;
        else
          {
            more = true;
            break;
          }
      }

  if (!more)
    return;

  /* Exit has several fallthru predecessors.  Create a forwarder block for
     them.  */
  forwarder = split_edge (predecessor);
  for (ei = ei_start (EXIT_BLOCK_PTR->preds); (e = ei_safe_edge (ei)); )
    {
      if (e->src == forwarder
          || !(e->flags & EDGE_FALLTHRU))
        ei_next (&ei);
      else
        redirect_edge_and_branch_force (e, forwarder);
    }

  /* Fix up the chain of blocks -- make FORWARDER immediately precede the
     exit block.  */
  FOR_EACH_BB (bb)
    {
      if (bb->aux == NULL && bb != forwarder)
        {
          bb->aux = forwarder;
          break;
        }
    }
}
\f
/* Return true in case it is possible to duplicate the basic block BB.  */

static bool
cfg_layout_can_duplicate_bb_p (const_basic_block bb)
{
  /* Do not attempt to duplicate tablejumps, as we need to unshare
     the dispatch table.  This is difficult to do, as the instructions
     computing jump destination may be hoisted outside the basic block.  */
  if (tablejump_p (BB_END (bb), NULL, NULL))
    return false;

  /* Do not duplicate blocks containing insns that can't be copied.  */
  if (targetm.cannot_copy_insn_p)
    {
      rtx insn = BB_HEAD (bb);
      while (1)
        {
          if (INSN_P (insn) && targetm.cannot_copy_insn_p (insn))
            return false;
          if (insn == BB_END (bb))
            break;
          insn = NEXT_INSN (insn);
        }
    }

  return true;
}

rtx
duplicate_insn_chain (rtx from, rtx to)
{
  rtx insn, last, copy;

  /* Avoid updating of boundaries of previous basic block.  The
     note will get removed from insn stream in fixup.  */
  last = emit_note (NOTE_INSN_DELETED);

  /* Create copy at the end of INSN chain.  The chain will
     be reordered later.  */
  for (insn = from; insn != NEXT_INSN (to); insn = NEXT_INSN (insn))
    {
      switch (GET_CODE (insn))
        {
        case DEBUG_INSN:
          /* Don't duplicate label debug insns.  */
          if (TREE_CODE (INSN_VAR_LOCATION_DECL (insn)) == LABEL_DECL)
            break;
          /* FALLTHRU */
        case INSN:
        case CALL_INSN:
        case JUMP_INSN:
          /* Avoid copying of dispatch tables.  We never duplicate
             tablejumps, so this can hit only in case the table got
             moved far from original jump.  */
          if (GET_CODE (PATTERN (insn)) == ADDR_VEC
              || GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC)
            {
              /* Avoid copying following barrier as well if any
                 (and debug insns in between).  */
              rtx next;

              for (next = NEXT_INSN (insn);
                   next != NEXT_INSN (to);
                   next = NEXT_INSN (next))
                if (!DEBUG_INSN_P (next))
                  break;
              if (next != NEXT_INSN (to) && BARRIER_P (next))
                insn = next;
              break;
            }
          copy = emit_copy_of_insn_after (insn, get_last_insn ());
          if (JUMP_P (insn) && JUMP_LABEL (insn) != NULL_RTX
              && ANY_RETURN_P (JUMP_LABEL (insn)))
            JUMP_LABEL (copy) = JUMP_LABEL (insn);
          maybe_copy_prologue_epilogue_insn (insn, copy);
          break;

        case CODE_LABEL:
          break;

        case BARRIER:
          emit_barrier ();
          break;

        case NOTE:
          switch (NOTE_KIND (insn))
            {
              /* In case prologue is empty and function contain label
                 in first BB, we may want to copy the block.  */
            case NOTE_INSN_PROLOGUE_END:

            case NOTE_INSN_DELETED:
            case NOTE_INSN_DELETED_LABEL:
            case NOTE_INSN_DELETED_DEBUG_LABEL:
              /* No problem to strip these.  */
            case NOTE_INSN_FUNCTION_BEG:
              /* There is always just single entry to function.  */
            case NOTE_INSN_BASIC_BLOCK:
              break;

            case NOTE_INSN_EPILOGUE_BEG:
            case NOTE_INSN_SWITCH_TEXT_SECTIONS:
              emit_note_copy (insn);
              break;

            default:
              /* All other notes should have already been eliminated.  */
              gcc_unreachable ();
            }
          break;
        default:
          gcc_unreachable ();
        }
    }
  insn = NEXT_INSN (last);
  delete_insn (last);
  return insn;
}

/* Create a duplicate of the basic block BB.  */

static basic_block
cfg_layout_duplicate_bb (basic_block bb)
{
  rtx insn;
  basic_block new_bb;

  insn = duplicate_insn_chain (BB_HEAD (bb), BB_END (bb));
  new_bb = create_basic_block (insn,
                               insn ? get_last_insn () : NULL,
                               EXIT_BLOCK_PTR->prev_bb);

  BB_COPY_PARTITION (new_bb, bb);
  if (BB_HEADER (bb))
    {
      insn = BB_HEADER (bb);
      while (NEXT_INSN (insn))
        insn = NEXT_INSN (insn);
      insn = duplicate_insn_chain (BB_HEADER (bb), insn);
      if (insn)
        BB_HEADER (new_bb) = unlink_insn_chain (insn, get_last_insn ());
    }

  if (BB_FOOTER (bb))
    {
      insn = BB_FOOTER (bb);
      while (NEXT_INSN (insn))
        insn = NEXT_INSN (insn);
      insn = duplicate_insn_chain (BB_FOOTER (bb), insn);
      if (insn)
        BB_FOOTER (new_bb) = unlink_insn_chain (insn, get_last_insn ());
    }

  return new_bb;
}

\f
/* Main entry point to this module - initialize the datastructures for
   CFG layout changes.  It keeps LOOPS up-to-date if not null.

   FLAGS is a set of additional flags to pass to cleanup_cfg().  */

void
cfg_layout_initialize (unsigned int flags)
{
  rtx x;
  basic_block bb;

  initialize_original_copy_tables ();

  cfg_layout_rtl_register_cfg_hooks ();

  record_effective_endpoints ();

  /* Make sure that the targets of non local gotos are marked.  */
  for (x = nonlocal_goto_handler_labels; x; x = XEXP (x, 1))
    {
      bb = BLOCK_FOR_INSN (XEXP (x, 0));
      bb->flags |= BB_NON_LOCAL_GOTO_TARGET;
    }

  cleanup_cfg (CLEANUP_CFGLAYOUT | flags);
}

/* Splits superblocks.  */
void
break_superblocks (void)
{
  sbitmap superblocks;
  bool need = false;
  basic_block bb;

  superblocks = sbitmap_alloc (last_basic_block);
  sbitmap_zero (superblocks);

  FOR_EACH_BB (bb)
    if (bb->flags & BB_SUPERBLOCK)
      {
        bb->flags &= ~BB_SUPERBLOCK;
        SET_BIT (superblocks, bb->index);
        need = true;
      }

  if (need)
    {
      rebuild_jump_labels (get_insns ());
      find_many_sub_basic_blocks (superblocks);
    }

  free (superblocks);
}

/* Finalize the changes: reorder insn list according to the sequence specified
   by aux pointers, enter compensation code, rebuild scope forest.  */

void
cfg_layout_finalize (void)
{
#ifdef ENABLE_CHECKING
  verify_flow_info ();
#endif
  force_one_exit_fallthru ();
  rtl_register_cfg_hooks ();
  if (reload_completed
#ifdef HAVE_epilogue
      && !HAVE_epilogue
#endif
      )
    fixup_fallthru_exit_predecessor ();
  fixup_reorder_chain ();

  rebuild_jump_labels (get_insns ());
  delete_dead_jumptables ();

#ifdef ENABLE_CHECKING
  verify_insn_chain ();
  verify_flow_info ();
#endif
}


/* Same as split_block but update cfg_layout structures.  */

static basic_block
cfg_layout_split_block (basic_block bb, void *insnp)
{
  rtx insn = (rtx) insnp;
  basic_block new_bb = rtl_split_block (bb, insn);

  BB_FOOTER (new_bb) = BB_FOOTER (bb);
  BB_FOOTER (bb) = NULL;

  return new_bb;
}

/* Redirect Edge to DEST.  */
static edge
cfg_layout_redirect_edge_and_branch (edge e, basic_block dest)
{
  basic_block src = e->src;
  edge ret;

  if (e->flags & (EDGE_ABNORMAL_CALL | EDGE_EH))
    return NULL;

  if (e->dest == dest)
    return e;

  if (e->src != ENTRY_BLOCK_PTR
      && (ret = try_redirect_by_replacing_jump (e, dest, true)))
    {
      df_set_bb_dirty (src);
      return ret;
    }

  if (e->src == ENTRY_BLOCK_PTR
      && (e->flags & EDGE_FALLTHRU) && !(e->flags & EDGE_COMPLEX))
    {
      if (dump_file)
        fprintf (dump_file, "Redirecting entry edge from bb %i to %i\n",
                 e->src->index, dest->index);

      df_set_bb_dirty (e->src);
      redirect_edge_succ (e, dest);
      return e;
    }

  /* Redirect_edge_and_branch may decide to turn branch into fallthru edge
     in the case the basic block appears to be in sequence.  Avoid this
     transformation.  */

  if (e->flags & EDGE_FALLTHRU)
    {
      /* Redirect any branch edges unified with the fallthru one.  */
      if (JUMP_P (BB_END (src))
          && label_is_jump_target_p (BB_HEAD (e->dest),
                                     BB_END (src)))
        {
          edge redirected;

          if (dump_file)
            fprintf (dump_file, "Fallthru edge unified with branch "
                     "%i->%i redirected to %i\n",
                     e->src->index, e->dest->index, dest->index);
          e->flags &= ~EDGE_FALLTHRU;
          redirected = redirect_branch_edge (e, dest);
          gcc_assert (redirected);
          redirected->flags |= EDGE_FALLTHRU;
          df_set_bb_dirty (redirected->src);
          return redirected;
        }
      /* In case we are redirecting fallthru edge to the branch edge
         of conditional jump, remove it.  */
      if (EDGE_COUNT (src->succs) == 2)
        {
          /* Find the edge that is different from E.  */
          edge s = EDGE_SUCC (src, EDGE_SUCC (src, 0) == e);

          if (s->dest == dest
              && any_condjump_p (BB_END (src))
              && onlyjump_p (BB_END (src)))
            delete_insn (BB_END (src));
        }
      if (dump_file)
        fprintf (dump_file, "Redirecting fallthru edge %i->%i to %i\n",
                 e->src->index, e->dest->index, dest->index);
      ret = redirect_edge_succ_nodup (e, dest);
    }
  else
    ret = redirect_branch_edge (e, dest);

  /* We don't want simplejumps in the insn stream during cfglayout.  */
  gcc_assert (!simplejump_p (BB_END (src)));

  df_set_bb_dirty (src);
  return ret;
}

/* Simple wrapper as we always can redirect fallthru edges.  */
static basic_block
cfg_layout_redirect_edge_and_branch_force (edge e, basic_block dest)
{
  edge redirected = cfg_layout_redirect_edge_and_branch (e, dest);

  gcc_assert (redirected);
  return NULL;
}

/* Same as delete_basic_block but update cfg_layout structures.  */

static void
cfg_layout_delete_block (basic_block bb)
{
  rtx insn, next, prev = PREV_INSN (BB_HEAD (bb)), *to, remaints;

  if (BB_HEADER (bb))
    {
      next = BB_HEAD (bb);
      if (prev)
        NEXT_INSN (prev) = BB_HEADER (bb);
      else
        set_first_insn (BB_HEADER (bb));
      PREV_INSN (BB_HEADER (bb)) = prev;
      insn = BB_HEADER (bb);
      while (NEXT_INSN (insn))
        insn = NEXT_INSN (insn);
      NEXT_INSN (insn) = next;
      PREV_INSN (next) = insn;
    }
  next = NEXT_INSN (BB_END (bb));
  if (BB_FOOTER (bb))
    {
      insn = BB_FOOTER (bb);
      while (insn)
        {
          if (BARRIER_P (insn))
            {
              if (PREV_INSN (insn))
                NEXT_INSN (PREV_INSN (insn)) = NEXT_INSN (insn);
              else
                BB_FOOTER (bb) = NEXT_INSN (insn);
              if (NEXT_INSN (insn))
                PREV_INSN (NEXT_INSN (insn)) = PREV_INSN (insn);
            }
          if (LABEL_P (insn))
            break;
          insn = NEXT_INSN (insn);
        }
      if (BB_FOOTER (bb))
        {
          insn = BB_END (bb);
          NEXT_INSN (insn) = BB_FOOTER (bb);
          PREV_INSN (BB_FOOTER (bb)) = insn;
          while (NEXT_INSN (insn))
            insn = NEXT_INSN (insn);
          NEXT_INSN (insn) = next;
          if (next)
            PREV_INSN (next) = insn;
          else
            set_last_insn (insn);
        }
    }
  if (bb->next_bb != EXIT_BLOCK_PTR)
    to = &BB_HEADER (bb->next_bb);
  else
    to = &cfg_layout_function_footer;

  rtl_delete_block (bb);

  if (prev)
    prev = NEXT_INSN (prev);
  else
    prev = get_insns ();
  if (next)
    next = PREV_INSN (next);
  else
    next = get_last_insn ();

  if (next && NEXT_INSN (next) != prev)
    {
      remaints = unlink_insn_chain (prev, next);
      insn = remaints;
      while (NEXT_INSN (insn))
        insn = NEXT_INSN (insn);
      NEXT_INSN (insn) = *to;
      if (*to)
        PREV_INSN (*to) = insn;
      *to = remaints;
    }
}

/* Return true when blocks A and B can be safely merged.  */

static bool
cfg_layout_can_merge_blocks_p (basic_block a, basic_block b)
{
  /* 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 false;

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

  /* If we would end up moving B's instructions, make sure it doesn't fall
     through into the exit block, since we cannot recover from a fallthrough
     edge into the exit block occurring in the middle of a function.  */
  if (NEXT_INSN (BB_END (a)) != BB_HEAD (b))
    {
      edge e = find_fallthru_edge (b->succs);
      if (e && e->dest == EXIT_BLOCK_PTR)
        return false;
    }

  /* There must be exactly one edge in between the blocks.  */
  return (single_succ_p (a)
          && single_succ (a) == b
          && single_pred_p (b) == 1
          && a != b
          /* Must be simple edge.  */
          && !(single_succ_edge (a)->flags & EDGE_COMPLEX)
          && a != ENTRY_BLOCK_PTR && b != EXIT_BLOCK_PTR
          /* If the jump insn has side effects, we can't kill the edge.
             When not optimizing, try_redirect_by_replacing_jump will
             not allow us to redirect an edge by replacing a table jump.  */
          && (!JUMP_P (BB_END (a))
              || ((!optimize || reload_completed)
                  ? simplejump_p (BB_END (a)) : onlyjump_p (BB_END (a)))));
}

/* Merge block A and B.  The blocks must be mergeable.  */

static void
cfg_layout_merge_blocks (basic_block a, basic_block b)
{
  bool forwarder_p = (b->flags & BB_FORWARDER_BLOCK) != 0;
  rtx insn;

  gcc_checking_assert (cfg_layout_can_merge_blocks_p (a, b));

  if (dump_file)
    fprintf (dump_file, "Merging block %d into block %d...\n", b->index,
                         a->index);

  /* If there was a CODE_LABEL beginning B, delete it.  */
  if (LABEL_P (BB_HEAD (b)))
    {
      delete_insn (BB_HEAD (b));
    }

  /* We should have fallthru edge in a, or we can do dummy redirection to get
     it cleaned up.  */
  if (JUMP_P (BB_END (a)))
    try_redirect_by_replacing_jump (EDGE_SUCC (a, 0), b, true);
  gcc_assert (!JUMP_P (BB_END (a)));

  /* When not optimizing CFG and the edge is the only place in RTL which holds
     some unique locus, emit a nop with that locus in between.  */
  if (!optimize)
    emit_nop_for_unique_locus_between (a, b);

  /* Possible line number notes should appear in between.  */
  if (BB_HEADER (b))
    {
      rtx first = BB_END (a), last;

      last = emit_insn_after_noloc (BB_HEADER (b), BB_END (a), a);
      /* The above might add a BARRIER as BB_END, but as barriers
         aren't valid parts of a bb, remove_insn doesn't update
         BB_END if it is a barrier.  So adjust BB_END here.  */
      while (BB_END (a) != first && BARRIER_P (BB_END (a)))
        BB_END (a) = PREV_INSN (BB_END (a));
      delete_insn_chain (NEXT_INSN (first), last, false);
      BB_HEADER (b) = NULL;
    }

  /* In the case basic blocks are not adjacent, move them around.  */
  if (NEXT_INSN (BB_END (a)) != BB_HEAD (b))
    {
      insn = unlink_insn_chain (BB_HEAD (b), BB_END (b));

      emit_insn_after_noloc (insn, BB_END (a), a);
    }
  /* Otherwise just re-associate the instructions.  */
  else
    {
      insn = BB_HEAD (b);
      BB_END (a) = BB_END (b);
    }

  /* emit_insn_after_noloc doesn't call df_insn_change_bb.
     We need to explicitly call. */
  update_bb_for_insn_chain (insn, BB_END (b), a);

  /* Skip possible DELETED_LABEL insn.  */
  if (!NOTE_INSN_BASIC_BLOCK_P (insn))
    insn = NEXT_INSN (insn);
  gcc_assert (NOTE_INSN_BASIC_BLOCK_P (insn));
  BB_HEAD (b) = NULL;
  delete_insn (insn);

  df_bb_delete (b->index);

  /* Possible tablejumps and barriers should appear after the block.  */
  if (BB_FOOTER (b))
    {
      if (!BB_FOOTER (a))
        BB_FOOTER (a) = BB_FOOTER (b);
      else
        {
          rtx last = BB_FOOTER (a);

          while (NEXT_INSN (last))
            last = NEXT_INSN (last);
          NEXT_INSN (last) = BB_FOOTER (b);
          PREV_INSN (BB_FOOTER (b)) = last;
        }
      BB_FOOTER (b) = NULL;
    }

  /* If B was a forwarder block, propagate the locus on the edge.  */
  if (forwarder_p && !EDGE_SUCC (b, 0)->goto_locus)
    EDGE_SUCC (b, 0)->goto_locus = EDGE_SUCC (a, 0)->goto_locus;

  if (dump_file)
    fprintf (dump_file, "Merged blocks %d and %d.\n", a->index, b->index);
}

/* Split edge E.  */

static basic_block
cfg_layout_split_edge (edge e)
{
  basic_block new_bb =
    create_basic_block (e->src != ENTRY_BLOCK_PTR
                        ? NEXT_INSN (BB_END (e->src)) : get_insns (),
                        NULL_RTX, e->src);

  if (e->dest == EXIT_BLOCK_PTR)
    BB_COPY_PARTITION (new_bb, e->src);
  else
    BB_COPY_PARTITION (new_bb, e->dest);
  make_edge (new_bb, e->dest, EDGE_FALLTHRU);
  redirect_edge_and_branch_force (e, new_bb);

  return new_bb;
}

/* Do postprocessing after making a forwarder block joined by edge FALLTHRU.  */

static void
rtl_make_forwarder_block (edge fallthru ATTRIBUTE_UNUSED)
{
}

/* Return 1 if BB ends with a call, possibly followed by some
   instructions that must stay with the call, 0 otherwise.  */

static bool
rtl_block_ends_with_call_p (basic_block bb)
{
  rtx insn = BB_END (bb);

  while (!CALL_P (insn)
         && insn != BB_HEAD (bb)
         && (keep_with_call_p (insn)
             || NOTE_P (insn)
             || DEBUG_INSN_P (insn)))
    insn = PREV_INSN (insn);
  return (CALL_P (insn));
}

/* Return 1 if BB ends with a conditional branch, 0 otherwise.  */

static bool
rtl_block_ends_with_condjump_p (const_basic_block bb)
{
  return any_condjump_p (BB_END (bb));
}

/* Return true if we need to add fake edge to exit.
   Helper function for rtl_flow_call_edges_add.  */

static bool
need_fake_edge_p (const_rtx insn)
{
  if (!INSN_P (insn))
    return false;

  if ((CALL_P (insn)
       && !SIBLING_CALL_P (insn)
       && !find_reg_note (insn, REG_NORETURN, NULL)
       && !(RTL_CONST_OR_PURE_CALL_P (insn))))
    return true;

  return ((GET_CODE (PATTERN (insn)) == ASM_OPERANDS
           && MEM_VOLATILE_P (PATTERN (insn)))
          || (GET_CODE (PATTERN (insn)) == PARALLEL
              && asm_noperands (insn) != -1
              && MEM_VOLATILE_P (XVECEXP (PATTERN (insn), 0, 0)))
          || GET_CODE (PATTERN (insn)) == ASM_INPUT);
}

/* Add fake edges to the function exit for any non constant and non noreturn
   calls, volatile inline assembly in the bitmap of blocks specified by
   BLOCKS or to the whole CFG if BLOCKS is zero.  Return the number of blocks
   that were split.

   The goal is to expose cases in which entering a basic block does not imply
   that all subsequent instructions must be executed.  */

static int
rtl_flow_call_edges_add (sbitmap blocks)
{
  int i;
  int blocks_split = 0;
  int last_bb = last_basic_block;
  bool check_last_block = false;

  if (n_basic_blocks == NUM_FIXED_BLOCKS)
    return 0;

  if (! blocks)
    check_last_block = true;
  else
    check_last_block = TEST_BIT (blocks, EXIT_BLOCK_PTR->prev_bb->index);

  /* In the last basic block, before epilogue generation, there will be
     a fallthru edge to EXIT.  Special care is required if the last insn
     of the last basic block is a call because make_edge folds duplicate
     edges, which would result in the fallthru edge also being marked
     fake, which would result in the fallthru edge being removed by
     remove_fake_edges, which would result in an invalid CFG.

     Moreover, we can't elide the outgoing fake edge, since the block
     profiler needs to take this into account in order to solve the minimal
     spanning tree in the case that the call doesn't return.

     Handle this by adding a dummy instruction in a new last basic block.  */
  if (check_last_block)
    {
      basic_block bb = EXIT_BLOCK_PTR->prev_bb;
      rtx insn = BB_END (bb);

      /* Back up past insns that must be kept in the same block as a call.  */
      while (insn != BB_HEAD (bb)
             && keep_with_call_p (insn))
        insn = PREV_INSN (insn);

      if (need_fake_edge_p (insn))
        {
          edge e;

          e = find_edge (bb, EXIT_BLOCK_PTR);
          if (e)
            {
              insert_insn_on_edge (gen_use (const0_rtx), e);
              commit_edge_insertions ();
            }
        }
    }

  /* Now add fake edges to the function exit for any non constant
     calls since there is no way that we can determine if they will
     return or not...  */

  for (i = NUM_FIXED_BLOCKS; i < last_bb; i++)
    {
      basic_block bb = BASIC_BLOCK (i);
      rtx insn;
      rtx prev_insn;

      if (!bb)
        continue;

      if (blocks && !TEST_BIT (blocks, i))
        continue;

      for (insn = BB_END (bb); ; insn = prev_insn)
        {
          prev_insn = PREV_INSN (insn);
          if (need_fake_edge_p (insn))
            {
              edge e;
              rtx split_at_insn = insn;

              /* Don't split the block between a call and an insn that should
                 remain in the same block as the call.  */
              if (CALL_P (insn))
                while (split_at_insn != BB_END (bb)
                       && keep_with_call_p (NEXT_INSN (split_at_insn)))
                  split_at_insn = NEXT_INSN (split_at_insn);

              /* The handling above of the final block before the epilogue
                 should be enough to verify that there is no edge to the exit
                 block in CFG already.  Calling make_edge in such case would
                 cause us to mark that edge as fake and remove it later.  */

#ifdef ENABLE_CHECKING
              if (split_at_insn == BB_END (bb))
                {
                  e = find_edge (bb, EXIT_BLOCK_PTR);
                  gcc_assert (e == NULL);
                }
#endif

              /* Note that the following may create a new basic block
                 and renumber the existing basic blocks.  */
              if (split_at_insn != BB_END (bb))
                {
                  e = split_block (bb, split_at_insn);
                  if (e)
                    blocks_split++;
                }

              make_edge (bb, EXIT_BLOCK_PTR, EDGE_FAKE);
            }

          if (insn == BB_HEAD (bb))
            break;
        }
    }

  if (blocks_split)
    verify_flow_info ();

  return blocks_split;
}

/* Add COMP_RTX as a condition at end of COND_BB.  FIRST_HEAD is
   the conditional branch target, SECOND_HEAD should be the fall-thru
   there is no need to handle this here the loop versioning code handles
   this.  the reason for SECON_HEAD is that it is needed for condition
   in trees, and this should be of the same type since it is a hook.  */
static void
rtl_lv_add_condition_to_bb (basic_block first_head ,
                            basic_block second_head ATTRIBUTE_UNUSED,
                            basic_block cond_bb, void *comp_rtx)
{
  rtx label, seq, jump;
  rtx op0 = XEXP ((rtx)comp_rtx, 0);
  rtx op1 = XEXP ((rtx)comp_rtx, 1);
  enum rtx_code comp = GET_CODE ((rtx)comp_rtx);
  enum machine_mode mode;


  label = block_label (first_head);
  mode = GET_MODE (op0);
  if (mode == VOIDmode)
    mode = GET_MODE (op1);

  start_sequence ();
  op0 = force_operand (op0, NULL_RTX);
  op1 = force_operand (op1, NULL_RTX);
  do_compare_rtx_and_jump (op0, op1, comp, 0,
                           mode, NULL_RTX, NULL_RTX, label, -1);
  jump = get_last_insn ();
  JUMP_LABEL (jump) = label;
  LABEL_NUSES (label)++;
  seq = get_insns ();
  end_sequence ();

  /* Add the new cond , in the new head.  */
  emit_insn_after(seq, BB_END(cond_bb));
}


/* Given a block B with unconditional branch at its end, get the
   store the return the branch edge and the fall-thru edge in
   BRANCH_EDGE and FALLTHRU_EDGE respectively.  */
static void
rtl_extract_cond_bb_edges (basic_block b, edge *branch_edge,
                           edge *fallthru_edge)
{
  edge e = EDGE_SUCC (b, 0);

  if (e->flags & EDGE_FALLTHRU)
    {
      *fallthru_edge = e;
      *branch_edge = EDGE_SUCC (b, 1);
    }
  else
    {
      *branch_edge = e;
      *fallthru_edge = EDGE_SUCC (b, 1);
    }
}

void
init_rtl_bb_info (basic_block bb)
{
  gcc_assert (!bb->il.x.rtl);
  bb->il.x.head_ = NULL;
  bb->il.x.rtl = ggc_alloc_cleared_rtl_bb_info ();
}

/* Returns true if it is possible to remove edge E by redirecting
   it to the destination of the other edge from E->src.  */

static bool
rtl_can_remove_branch_p (const_edge e)
{
  const_basic_block src = e->src;
  const_basic_block target = EDGE_SUCC (src, EDGE_SUCC (src, 0) == e)->dest;
  const_rtx insn = BB_END (src), set;

  /* The conditions are taken from try_redirect_by_replacing_jump.  */
  if (target == EXIT_BLOCK_PTR)
    return false;

  if (e->flags & (EDGE_ABNORMAL_CALL | EDGE_EH))
    return false;

  if (find_reg_note (insn, REG_CROSSING_JUMP, NULL_RTX)
      || BB_PARTITION (src) != BB_PARTITION (target))
    return false;

  if (!onlyjump_p (insn)
      || tablejump_p (insn, NULL, NULL))
    return false;

  set = single_set (insn);
  if (!set || side_effects_p (set))
    return false;

  return true;
}

static basic_block
rtl_duplicate_bb (basic_block bb)
{
  bb = cfg_layout_duplicate_bb (bb);
  bb->aux = NULL;
  return bb;
}

/* Implementation of CFG manipulation for linearized RTL.  */
struct cfg_hooks rtl_cfg_hooks = {
  "rtl",
  rtl_verify_flow_info,
  rtl_dump_bb,
  rtl_create_basic_block,
  rtl_redirect_edge_and_branch,
  rtl_redirect_edge_and_branch_force,
  rtl_can_remove_branch_p,
  rtl_delete_block,
  rtl_split_block,
  rtl_move_block_after,
  rtl_can_merge_blocks,  /* can_merge_blocks_p */
  rtl_merge_blocks,
  rtl_predict_edge,
  rtl_predicted_by_p,
  cfg_layout_can_duplicate_bb_p,
  rtl_duplicate_bb,
  rtl_split_edge,
  rtl_make_forwarder_block,
  rtl_tidy_fallthru_edge,
  rtl_force_nonfallthru,
  rtl_block_ends_with_call_p,
  rtl_block_ends_with_condjump_p,
  rtl_flow_call_edges_add,
  NULL, /* execute_on_growing_pred */
  NULL, /* execute_on_shrinking_pred */
  NULL, /* duplicate loop for trees */
  NULL, /* lv_add_condition_to_bb */
  NULL, /* lv_adjust_loop_header_phi*/
  NULL, /* extract_cond_bb_edges */
  NULL          /* flush_pending_stmts */
};

/* Implementation of CFG manipulation for cfg layout RTL, where
   basic block connected via fallthru edges does not have to be adjacent.
   This representation will hopefully become the default one in future
   version of the compiler.  */

struct cfg_hooks cfg_layout_rtl_cfg_hooks = {
  "cfglayout mode",
  rtl_verify_flow_info_1,
  rtl_dump_bb,
  cfg_layout_create_basic_block,
  cfg_layout_redirect_edge_and_branch,
  cfg_layout_redirect_edge_and_branch_force,
  rtl_can_remove_branch_p,
  cfg_layout_delete_block,
  cfg_layout_split_block,
  rtl_move_block_after,
  cfg_layout_can_merge_blocks_p,
  cfg_layout_merge_blocks,
  rtl_predict_edge,
  rtl_predicted_by_p,
  cfg_layout_can_duplicate_bb_p,
  cfg_layout_duplicate_bb,
  cfg_layout_split_edge,
  rtl_make_forwarder_block,
  NULL, /* tidy_fallthru_edge */
  rtl_force_nonfallthru,
  rtl_block_ends_with_call_p,
  rtl_block_ends_with_condjump_p,
  rtl_flow_call_edges_add,
  NULL, /* execute_on_growing_pred */
  NULL, /* execute_on_shrinking_pred */
  duplicate_loop_to_header_edge, /* duplicate loop for trees */
  rtl_lv_add_condition_to_bb, /* lv_add_condition_to_bb */
  NULL, /* lv_adjust_loop_header_phi*/
  rtl_extract_cond_bb_edges, /* extract_cond_bb_edges */
  NULL          /* flush_pending_stmts */
};

#include "gt-cfgrtl.h"