* doc/loop.texi: Document recording of loop exits.

[thirdparty/gcc.git] / gcc / cfgloop.c

/* Natural loop discovery code for GNU compiler.
   Copyright (C) 2000, 2001, 2003, 2004, 2005 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 2, 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 COPYING.  If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "hard-reg-set.h"
#include "obstack.h"
#include "function.h"
#include "basic-block.h"
#include "toplev.h"
#include "cfgloop.h"
#include "flags.h"
#include "tree.h"
#include "tree-flow.h"

/* Ratio of frequencies of edges so that one of more latch edges is
   considered to belong to inner loop with same header.  */
#define HEAVY_EDGE_RATIO 8

#define HEADER_BLOCK(B) (* (int *) (B)->aux)
#define LATCH_EDGE(E) (*(int *) (E)->aux)

static void flow_loops_cfg_dump (FILE *);
static void establish_preds (struct loop *);
static void canonicalize_loop_headers (void);
static bool glb_enum_p (basic_block, void *);
\f
/* Dump loop related CFG information.  */

static void
flow_loops_cfg_dump (FILE *file)
{
  basic_block bb;

  if (!file)
    return;

  FOR_EACH_BB (bb)
    {
      edge succ;
      edge_iterator ei;

      fprintf (file, ";; %d succs { ", bb->index);
      FOR_EACH_EDGE (succ, ei, bb->succs)
        fprintf (file, "%d ", succ->dest->index);
      fprintf (file, "}\n");
    }
}

/* Return nonzero if the nodes of LOOP are a subset of OUTER.  */

bool
flow_loop_nested_p (const struct loop *outer, const struct loop *loop)
{
  return (loop->depth > outer->depth
         && loop->pred[outer->depth] == outer);
}

/* Returns the loop such that LOOP is nested DEPTH (indexed from zero)
   loops within LOOP.  */

struct loop *
superloop_at_depth (struct loop *loop, unsigned depth)
{
  gcc_assert (depth <= (unsigned) loop->depth);

  if (depth == (unsigned) loop->depth)
    return loop;

  return loop->pred[depth];
}

/* Dump the loop information specified by LOOP to the stream FILE
   using auxiliary dump callback function LOOP_DUMP_AUX if non null.  */

void
flow_loop_dump (const struct loop *loop, FILE *file,
                void (*loop_dump_aux) (const struct loop *, FILE *, int),
                int verbose)
{
  basic_block *bbs;
  unsigned i;

  if (! loop || ! loop->header)
    return;

  fprintf (file, ";;\n;; Loop %d\n", loop->num);

  fprintf (file, ";;  header %d, latch %d\n",
           loop->header->index, loop->latch->index);
  fprintf (file, ";;  depth %d, outer %ld\n",
           loop->depth, (long) (loop->outer ? loop->outer->num : -1));

  fprintf (file, ";;  nodes:");
  bbs = get_loop_body (loop);
  for (i = 0; i < loop->num_nodes; i++)
    fprintf (file, " %d", bbs[i]->index);
  free (bbs);
  fprintf (file, "\n");

  if (loop_dump_aux)
    loop_dump_aux (loop, file, verbose);
}

/* Dump the loop information about loops to the stream FILE,
   using auxiliary dump callback function LOOP_DUMP_AUX if non null.  */

void
flow_loops_dump (FILE *file, void (*loop_dump_aux) (const struct loop *, FILE *, int), int verbose)
{
  loop_iterator li;
  struct loop *loop;

  if (!current_loops || ! file)
    return;

  fprintf (file, ";; %d loops found\n", number_of_loops ());

  FOR_EACH_LOOP (li, loop, LI_INCLUDE_ROOT)
    {
      flow_loop_dump (loop, file, loop_dump_aux, verbose);
    }

  if (verbose)
    flow_loops_cfg_dump (file);
}

/* Free data allocated for LOOP.  */
void
flow_loop_free (struct loop *loop)
{
  struct loop_exit *exit, *next;

  if (loop->pred)
    free (loop->pred);

  /* Break the list of the loop exit records.  They will be freed when the
     corresponding edge is rescanned or removed, and this avoids
     accessing the (already released) head of the list stored in the
     loop structure.  */
  for (exit = loop->exits.next; exit != &loop->exits; exit = next)
    {
      next = exit->next;
      exit->next = exit;
      exit->prev = exit;
    }
    
  free (loop);
}

/* Free all the memory allocated for LOOPS.  */

void
flow_loops_free (struct loops *loops)
{
  if (loops->larray)
    {
      unsigned i;
      loop_p loop;

      /* Free the loop descriptors.  */
      for (i = 0; VEC_iterate (loop_p, loops->larray, i, loop); i++)
        {
          if (!loop)
            continue;

          flow_loop_free (loop);
        }

      VEC_free (loop_p, heap, loops->larray);
      loops->larray = NULL;
    }
}

/* Find the nodes contained within the LOOP with header HEADER.
   Return the number of nodes within the loop.  */

int
flow_loop_nodes_find (basic_block header, struct loop *loop)
{
  basic_block *stack;
  int sp;
  int num_nodes = 1;

  header->loop_father = loop;
  header->loop_depth = loop->depth;

  if (loop->latch->loop_father != loop)
    {
      stack = XNEWVEC (basic_block, n_basic_blocks);
      sp = 0;
      num_nodes++;
      stack[sp++] = loop->latch;
      loop->latch->loop_father = loop;
      loop->latch->loop_depth = loop->depth;

      while (sp)
        {
          basic_block node;
          edge e;
          edge_iterator ei;

          node = stack[--sp];

          FOR_EACH_EDGE (e, ei, node->preds)
            {
              basic_block ancestor = e->src;

              if (ancestor != ENTRY_BLOCK_PTR
                  && ancestor->loop_father != loop)
                {
                  ancestor->loop_father = loop;
                  ancestor->loop_depth = loop->depth;
                  num_nodes++;
                  stack[sp++] = ancestor;
                }
            }
        }
      free (stack);
    }
  return num_nodes;
}

static void
establish_preds (struct loop *loop)
{
  struct loop *ploop, *father = loop->outer;

  loop->depth = father->depth + 1;

  /* Remember the current loop depth if it is the largest seen so far.  */
  cfun->max_loop_depth = MAX (cfun->max_loop_depth, loop->depth);

  if (loop->pred)
    free (loop->pred);
  loop->pred = XNEWVEC (struct loop *, loop->depth);
  memcpy (loop->pred, father->pred, sizeof (struct loop *) * father->depth);
  loop->pred[father->depth] = father;

  for (ploop = loop->inner; ploop; ploop = ploop->next)
    establish_preds (ploop);
}

/* Add LOOP to the loop hierarchy tree where FATHER is father of the
   added loop.  If LOOP has some children, take care of that their
   pred field will be initialized correctly.  */

void
flow_loop_tree_node_add (struct loop *father, struct loop *loop)
{
  loop->next = father->inner;
  father->inner = loop;
  loop->outer = father;

  establish_preds (loop);
}

/* Remove LOOP from the loop hierarchy tree.  */

void
flow_loop_tree_node_remove (struct loop *loop)
{
  struct loop *prev, *father;

  father = loop->outer;
  loop->outer = NULL;

  /* Remove loop from the list of sons.  */
  if (father->inner == loop)
    father->inner = loop->next;
  else
    {
      for (prev = father->inner; prev->next != loop; prev = prev->next);
      prev->next = loop->next;
    }

  loop->depth = -1;
  free (loop->pred);
  loop->pred = NULL;
}

/* A callback to update latch and header info for basic block JUMP created
   by redirecting an edge.  */

static void
update_latch_info (basic_block jump)
{
  alloc_aux_for_block (jump, sizeof (int));
  HEADER_BLOCK (jump) = 0;
  alloc_aux_for_edge (single_pred_edge (jump), sizeof (int));
  LATCH_EDGE (single_pred_edge (jump)) = 0;
  set_immediate_dominator (CDI_DOMINATORS, jump, single_pred (jump));
}

/* A callback for make_forwarder block, to redirect all edges except for
   MFB_KJ_EDGE to the entry part.  E is the edge for that we should decide
   whether to redirect it.  */

static edge mfb_kj_edge;
static bool
mfb_keep_just (edge e)
{
  return e != mfb_kj_edge;
}

/* A callback for make_forwarder block, to redirect the latch edges into an
   entry part.  E is the edge for that we should decide whether to redirect
   it.  */

static bool
mfb_keep_nonlatch (edge e)
{
  return LATCH_EDGE (e);
}

/* Takes care of merging natural loops with shared headers.  */

static void
canonicalize_loop_headers (void)
{
  basic_block header;
  edge e;

  alloc_aux_for_blocks (sizeof (int));
  alloc_aux_for_edges (sizeof (int));

  /* Split blocks so that each loop has only single latch.  */
  FOR_EACH_BB (header)
    {
      edge_iterator ei;
      int num_latches = 0;
      int have_abnormal_edge = 0;

      FOR_EACH_EDGE (e, ei, header->preds)
        {
          basic_block latch = e->src;

          if (e->flags & EDGE_ABNORMAL)
            have_abnormal_edge = 1;

          if (latch != ENTRY_BLOCK_PTR
              && dominated_by_p (CDI_DOMINATORS, latch, header))
            {
              num_latches++;
              LATCH_EDGE (e) = 1;
            }
        }
      if (have_abnormal_edge)
        HEADER_BLOCK (header) = 0;
      else
        HEADER_BLOCK (header) = num_latches;
    }

  if (HEADER_BLOCK (single_succ (ENTRY_BLOCK_PTR)))
    {
      basic_block bb;

      /* We could not redirect edges freely here. On the other hand,
         we can simply split the edge from entry block.  */
      bb = split_edge (single_succ_edge (ENTRY_BLOCK_PTR));

      alloc_aux_for_edge (single_succ_edge (bb), sizeof (int));
      LATCH_EDGE (single_succ_edge (bb)) = 0;
      alloc_aux_for_block (bb, sizeof (int));
      HEADER_BLOCK (bb) = 0;
    }

  FOR_EACH_BB (header)
    {
      int max_freq, is_heavy;
      edge heavy, tmp_edge;
      edge_iterator ei;

      if (HEADER_BLOCK (header) <= 1)
        continue;

      /* Find a heavy edge.  */
      is_heavy = 1;
      heavy = NULL;
      max_freq = 0;
      FOR_EACH_EDGE (e, ei, header->preds)
        if (LATCH_EDGE (e) &&
            EDGE_FREQUENCY (e) > max_freq)
          max_freq = EDGE_FREQUENCY (e);
      FOR_EACH_EDGE (e, ei, header->preds)
        if (LATCH_EDGE (e) &&
            EDGE_FREQUENCY (e) >= max_freq / HEAVY_EDGE_RATIO)
          {
            if (heavy)
              {
                is_heavy = 0;
                break;
              }
            else
              heavy = e;
          }

      if (is_heavy)
        {
          /* Split out the heavy edge, and create inner loop for it.  */
          mfb_kj_edge = heavy;
          tmp_edge = make_forwarder_block (header, mfb_keep_just,
                                           update_latch_info);
          alloc_aux_for_block (tmp_edge->dest, sizeof (int));
          HEADER_BLOCK (tmp_edge->dest) = 1;
          alloc_aux_for_edge (tmp_edge, sizeof (int));
          LATCH_EDGE (tmp_edge) = 0;
          HEADER_BLOCK (header)--;
        }

      if (HEADER_BLOCK (header) > 1)
        {
          /* Create a new latch block.  */
          tmp_edge = make_forwarder_block (header, mfb_keep_nonlatch,
                                           update_latch_info);
          alloc_aux_for_block (tmp_edge->dest, sizeof (int));
          HEADER_BLOCK (tmp_edge->src) = 0;
          HEADER_BLOCK (tmp_edge->dest) = 1;
          alloc_aux_for_edge (tmp_edge, sizeof (int));
          LATCH_EDGE (tmp_edge) = 1;
        }
    }

  free_aux_for_blocks ();
  free_aux_for_edges ();

#ifdef ENABLE_CHECKING
  verify_dominators (CDI_DOMINATORS);
#endif
}

/* Allocates and returns new loop structure.  */

struct loop *
alloc_loop (void)
{
  struct loop *loop = XCNEW (struct loop);

  loop->exits.next = loop->exits.prev = &loop->exits;
  return loop;
}

/* Find all the natural loops in the function and save in LOOPS structure and
   recalculate loop_depth information in basic block structures.
   Return the number of natural loops found.  */

int
flow_loops_find (struct loops *loops)
{
  int b;
  int num_loops;
  edge e;
  sbitmap headers;
  int *dfs_order;
  int *rc_order;
  basic_block header;
  basic_block bb;
  struct loop *root;

  memset (loops, 0, sizeof *loops);

  /* We are going to recount the maximum loop depth,
     so throw away the last count.  */
  cfun->max_loop_depth = 0;

  /* Taking care of this degenerate case makes the rest of
     this code simpler.  */
  if (n_basic_blocks == NUM_FIXED_BLOCKS)
    return 0;

  dfs_order = NULL;
  rc_order = NULL;

  /* Ensure that the dominators are computed.  */
  calculate_dominance_info (CDI_DOMINATORS);

  /* Join loops with shared headers.  */
  canonicalize_loop_headers ();

  /* Count the number of loop headers.  This should be the
     same as the number of natural loops.  */
  headers = sbitmap_alloc (last_basic_block);
  sbitmap_zero (headers);

  num_loops = 0;
  FOR_EACH_BB (header)
    {
      edge_iterator ei;
      int more_latches = 0;

      header->loop_depth = 0;

      /* If we have an abnormal predecessor, do not consider the
         loop (not worth the problems).  */
      FOR_EACH_EDGE (e, ei, header->preds)
        if (e->flags & EDGE_ABNORMAL)
          break;
      if (e)
        continue;

      FOR_EACH_EDGE (e, ei, header->preds)
        {
          basic_block latch = e->src;

          gcc_assert (!(e->flags & EDGE_ABNORMAL));

          /* Look for back edges where a predecessor is dominated
             by this block.  A natural loop has a single entry
             node (header) that dominates all the nodes in the
             loop.  It also has single back edge to the header
             from a latch node.  */
          if (latch != ENTRY_BLOCK_PTR
              && dominated_by_p (CDI_DOMINATORS, latch, header))
            {
              /* Shared headers should be eliminated by now.  */
              gcc_assert (!more_latches);
              more_latches = 1;
              SET_BIT (headers, header->index);
              num_loops++;
            }
        }
    }

  /* Allocate loop structures.  */
  loops->larray = VEC_alloc (loop_p, heap, num_loops + 1);

  /* Dummy loop containing whole function.  */
  root = alloc_loop ();
  root->num_nodes = n_basic_blocks;
  root->latch = EXIT_BLOCK_PTR;
  root->header = ENTRY_BLOCK_PTR;
  ENTRY_BLOCK_PTR->loop_father = root;
  EXIT_BLOCK_PTR->loop_father = root;

  VEC_quick_push (loop_p, loops->larray, root);
  loops->tree_root = root;

  /* Find and record information about all the natural loops
     in the CFG.  */
  FOR_EACH_BB (bb)
    bb->loop_father = loops->tree_root;

  if (num_loops)
    {
      /* Compute depth first search order of the CFG so that outer
         natural loops will be found before inner natural loops.  */
      dfs_order = XNEWVEC (int, n_basic_blocks);
      rc_order = XNEWVEC (int, n_basic_blocks);
      pre_and_rev_post_order_compute (dfs_order, rc_order, false);

      num_loops = 1;

      for (b = 0; b < n_basic_blocks - NUM_FIXED_BLOCKS; b++)
        {
          struct loop *loop;
          edge_iterator ei;

          /* Search the nodes of the CFG in reverse completion order
             so that we can find outer loops first.  */
          if (!TEST_BIT (headers, rc_order[b]))
            continue;

          header = BASIC_BLOCK (rc_order[b]);

          loop = alloc_loop ();
          VEC_quick_push (loop_p, loops->larray, loop);

          loop->header = header;
          loop->num = num_loops;
          num_loops++;

          /* Look for the latch for this header block.  */
          FOR_EACH_EDGE (e, ei, header->preds)
            {
              basic_block latch = e->src;

              if (latch != ENTRY_BLOCK_PTR
                  && dominated_by_p (CDI_DOMINATORS, latch, header))
                {
                  loop->latch = latch;
                  break;
                }
            }

          flow_loop_tree_node_add (header->loop_father, loop);
          loop->num_nodes = flow_loop_nodes_find (loop->header, loop);
        }

      free (dfs_order);
      free (rc_order);
    }

  sbitmap_free (headers);

  loops->exits = NULL;
  loops->state = 0;
  return VEC_length (loop_p, loops->larray);
}

/* Return nonzero if basic block BB belongs to LOOP.  */
bool
flow_bb_inside_loop_p (const struct loop *loop, const basic_block bb)
{
  struct loop *source_loop;

  if (bb == ENTRY_BLOCK_PTR || bb == EXIT_BLOCK_PTR)
    return 0;

  source_loop = bb->loop_father;
  return loop == source_loop || flow_loop_nested_p (loop, source_loop);
}

/* Enumeration predicate for get_loop_body.  */
static bool
glb_enum_p (basic_block bb, void *glb_header)
{
  return bb != (basic_block) glb_header;
}

/* Gets basic blocks of a LOOP.  Header is the 0-th block, rest is in dfs
   order against direction of edges from latch.  Specially, if
   header != latch, latch is the 1-st block.  */
basic_block *
get_loop_body (const struct loop *loop)
{
  basic_block *tovisit, bb;
  unsigned tv = 0;

  gcc_assert (loop->num_nodes);

  tovisit = XCNEWVEC (basic_block, loop->num_nodes);
  tovisit[tv++] = loop->header;

  if (loop->latch == EXIT_BLOCK_PTR)
    {
      /* There may be blocks unreachable from EXIT_BLOCK.  */
      gcc_assert (loop->num_nodes == (unsigned) n_basic_blocks);
      FOR_EACH_BB (bb)
        tovisit[tv++] = bb;
      tovisit[tv++] = EXIT_BLOCK_PTR;
    }
  else if (loop->latch != loop->header)
    {
      tv = dfs_enumerate_from (loop->latch, 1, glb_enum_p,
                               tovisit + 1, loop->num_nodes - 1,
                               loop->header) + 1;
    }

  gcc_assert (tv == loop->num_nodes);
  return tovisit;
}

/* Fills dominance descendants inside LOOP of the basic block BB into
   array TOVISIT from index *TV.  */

static void
fill_sons_in_loop (const struct loop *loop, basic_block bb,
                   basic_block *tovisit, int *tv)
{
  basic_block son, postpone = NULL;

  tovisit[(*tv)++] = bb;
  for (son = first_dom_son (CDI_DOMINATORS, bb);
       son;
       son = next_dom_son (CDI_DOMINATORS, son))
    {
      if (!flow_bb_inside_loop_p (loop, son))
        continue;

      if (dominated_by_p (CDI_DOMINATORS, loop->latch, son))
        {
          postpone = son;
          continue;
        }
      fill_sons_in_loop (loop, son, tovisit, tv);
    }

  if (postpone)
    fill_sons_in_loop (loop, postpone, tovisit, tv);
}

/* Gets body of a LOOP (that must be different from the outermost loop)
   sorted by dominance relation.  Additionally, if a basic block s dominates
   the latch, then only blocks dominated by s are be after it.  */

basic_block *
get_loop_body_in_dom_order (const struct loop *loop)
{
  basic_block *tovisit;
  int tv;

  gcc_assert (loop->num_nodes);

  tovisit = XCNEWVEC (basic_block, loop->num_nodes);

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  tv = 0;
  fill_sons_in_loop (loop, loop->header, tovisit, &tv);

  gcc_assert (tv == (int) loop->num_nodes);

  return tovisit;
}

/* Get body of a LOOP in breadth first sort order.  */

basic_block *
get_loop_body_in_bfs_order (const struct loop *loop)
{
  basic_block *blocks;
  basic_block bb;
  bitmap visited;
  unsigned int i = 0;
  unsigned int vc = 1;

  gcc_assert (loop->num_nodes);
  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  blocks = XCNEWVEC (basic_block, loop->num_nodes);
  visited = BITMAP_ALLOC (NULL);

  bb = loop->header;
  while (i < loop->num_nodes)
    {
      edge e;
      edge_iterator ei;

      if (!bitmap_bit_p (visited, bb->index))
        {
          /* This basic block is now visited */
          bitmap_set_bit (visited, bb->index);
          blocks[i++] = bb;
        }

      FOR_EACH_EDGE (e, ei, bb->succs)
        {
          if (flow_bb_inside_loop_p (loop, e->dest))
            {
              if (!bitmap_bit_p (visited, e->dest->index))
                {
                  bitmap_set_bit (visited, e->dest->index);
                  blocks[i++] = e->dest;
                }
            }
        }

      gcc_assert (i >= vc);

      bb = blocks[vc++];
    }

  BITMAP_FREE (visited);
  return blocks;
}

/* Hash function for struct loop_exit.  */

static hashval_t
loop_exit_hash (const void *ex)
{
  struct loop_exit *exit = (struct loop_exit *) ex;

  return htab_hash_pointer (exit->e);
}

/* Equality function for struct loop_exit.  Compares with edge.  */

static int
loop_exit_eq (const void *ex, const void *e)
{
  struct loop_exit *exit = (struct loop_exit *) ex;

  return exit->e == e;
}

/* Frees the list of loop exit descriptions EX.  */

static void
loop_exit_free (void *ex)
{
  struct loop_exit *exit = (struct loop_exit *) ex, *next;

  for (; exit; exit = next)
    {
      next = exit->next_e;
          
      exit->next->prev = exit->prev;
      exit->prev->next = exit->next;

      free (exit);
    }
}

/* Returns the list of records for E as an exit of a loop.  */

static struct loop_exit *
get_exit_descriptions (edge e)
{
  return htab_find_with_hash (current_loops->exits, e,
                              htab_hash_pointer (e));
}

/* Updates the lists of loop exits in that E appears.
   If REMOVED is true, E is being removed, and we
   just remove it from the lists of exits.
   If NEW_EDGE is true and E is not a loop exit, we
   do not try to remove it from loop exit lists.  */

void
rescan_loop_exit (edge e, bool new_edge, bool removed)
{
  void **slot;
  struct loop_exit *exits = NULL, *exit;
  struct loop *aloop, *cloop;

  if ((current_loops->state & LOOPS_HAVE_RECORDED_EXITS) == 0)
    return;

  if (!removed
      && e->src->loop_father != NULL
      && e->dest->loop_father != NULL
      && !flow_bb_inside_loop_p (e->src->loop_father, e->dest))
    {
      cloop = find_common_loop (e->src->loop_father, e->dest->loop_father);
      for (aloop = e->src->loop_father;
           aloop != cloop;
           aloop = aloop->outer)
        {
          exit = XNEW (struct loop_exit);
          exit->e = e;

          exit->next = aloop->exits.next;
          exit->prev = &aloop->exits;
          exit->next->prev = exit;
          exit->prev->next = exit;

          exit->next_e = exits;
          exits = exit;
        }
    } 

  if (!exits && new_edge)
    return;

  slot = htab_find_slot_with_hash (current_loops->exits, e,
                                   htab_hash_pointer (e),
                                   exits ? INSERT : NO_INSERT);
  if (!slot)
    return;

  if (exits)
    {
      if (*slot)
        loop_exit_free (*slot);
      *slot = exits;
    }
  else
    htab_clear_slot (current_loops->exits, slot);
}

/* For each loop, record list of exit edges, and start maintaining these
   lists.  */

void
record_loop_exits (void)
{
  basic_block bb;
  edge_iterator ei;
  edge e;

  if (current_loops->state & LOOPS_HAVE_RECORDED_EXITS)
    return;
  current_loops->state |= LOOPS_HAVE_RECORDED_EXITS;

  gcc_assert (current_loops->exits == NULL);
  current_loops->exits = htab_create (2 * number_of_loops (),
                                      loop_exit_hash,
                                      loop_exit_eq,
                                      loop_exit_free);

  FOR_EACH_BB (bb)
    {
      FOR_EACH_EDGE (e, ei, bb->succs)
        {
          rescan_loop_exit (e, true, false);
        }
    }
}

/* Dumps information about the exit in *SLOT to FILE.
   Callback for htab_traverse.  */

static int
dump_recorded_exit (void **slot, void *file)
{
  struct loop_exit *exit = *slot;
  unsigned n = 0;
  edge e = exit->e;

  for (; exit != NULL; exit = exit->next_e)
    n++;

  fprintf (file, "Edge %d->%d exits %u loops\n",
           e->src->index, e->dest->index, n);

  return 1;
}

/* Dumps the recorded exits of loops to FILE.  */

extern void dump_recorded_exits (FILE *);
void
dump_recorded_exits (FILE *file)
{
  if (!current_loops->exits)
    return;
  htab_traverse (current_loops->exits, dump_recorded_exit, file);
}

/* Releases lists of loop exits.  */

void
release_recorded_exits (void)
{
  gcc_assert (current_loops->state & LOOPS_HAVE_RECORDED_EXITS);
  htab_delete (current_loops->exits);
  current_loops->exits = NULL;
  current_loops->state &= ~LOOPS_HAVE_RECORDED_EXITS;
}

/* Returns the list of the exit edges of a LOOP.  */

VEC (edge, heap) *
get_loop_exit_edges (const struct loop *loop)
{
  VEC (edge, heap) *edges = NULL;
  edge e;
  unsigned i;
  basic_block *body;
  edge_iterator ei;
  struct loop_exit *exit;

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  /* If we maintain the lists of exits, use them.  Otherwise we must
     scan the body of the loop.  */
  if (current_loops->state & LOOPS_HAVE_RECORDED_EXITS)
    {
      for (exit = loop->exits.next; exit->e; exit = exit->next)
        VEC_safe_push (edge, heap, edges, exit->e);
    }
  else
    {
      body = get_loop_body (loop);
      for (i = 0; i < loop->num_nodes; i++)
        FOR_EACH_EDGE (e, ei, body[i]->succs)
          {
            if (!flow_bb_inside_loop_p (loop, e->dest))
              VEC_safe_push (edge, heap, edges, e);
          }
      free (body);
    }

  return edges;
}

/* Counts the number of conditional branches inside LOOP.  */

unsigned
num_loop_branches (const struct loop *loop)
{
  unsigned i, n;
  basic_block * body;

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  body = get_loop_body (loop);
  n = 0;
  for (i = 0; i < loop->num_nodes; i++)
    if (EDGE_COUNT (body[i]->succs) >= 2)
      n++;
  free (body);

  return n;
}

/* Adds basic block BB to LOOP.  */
void
add_bb_to_loop (basic_block bb, struct loop *loop)
{
  int i;
  edge_iterator ei;
  edge e;

  gcc_assert (bb->loop_father == NULL);
  bb->loop_father = loop;
  bb->loop_depth = loop->depth;
  loop->num_nodes++;
  for (i = 0; i < loop->depth; i++)
    loop->pred[i]->num_nodes++;

  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      rescan_loop_exit (e, true, false);
    }
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      rescan_loop_exit (e, true, false);
    }
}

/* Remove basic block BB from loops.  */
void
remove_bb_from_loops (basic_block bb)
{
  int i;
  struct loop *loop = bb->loop_father;
  edge_iterator ei;
  edge e;

  gcc_assert (loop != NULL);
  loop->num_nodes--;
  for (i = 0; i < loop->depth; i++)
    loop->pred[i]->num_nodes--;
  bb->loop_father = NULL;
  bb->loop_depth = 0;

  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      rescan_loop_exit (e, false, true);
    }
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      rescan_loop_exit (e, false, true);
    }
}

/* Finds nearest common ancestor in loop tree for given loops.  */
struct loop *
find_common_loop (struct loop *loop_s, struct loop *loop_d)
{
  if (!loop_s) return loop_d;
  if (!loop_d) return loop_s;

  if (loop_s->depth < loop_d->depth)
    loop_d = loop_d->pred[loop_s->depth];
  else if (loop_s->depth > loop_d->depth)
    loop_s = loop_s->pred[loop_d->depth];

  while (loop_s != loop_d)
    {
      loop_s = loop_s->outer;
      loop_d = loop_d->outer;
    }
  return loop_s;
}

/* Removes LOOP from structures and frees its data.  */

void
delete_loop (struct loop *loop)
{
  /* Remove the loop from structure.  */
  flow_loop_tree_node_remove (loop);

  /* Remove loop from loops array.  */
  VEC_replace (loop_p, current_loops->larray, loop->num, NULL);

  /* Free loop data.  */
  flow_loop_free (loop);
}

/* Cancels the LOOP; it must be innermost one.  */

static void
cancel_loop (struct loop *loop)
{
  basic_block *bbs;
  unsigned i;

  gcc_assert (!loop->inner);

  /* Move blocks up one level (they should be removed as soon as possible).  */
  bbs = get_loop_body (loop);
  for (i = 0; i < loop->num_nodes; i++)
    bbs[i]->loop_father = loop->outer;

  delete_loop (loop);
}

/* Cancels LOOP and all its subloops.  */
void
cancel_loop_tree (struct loop *loop)
{
  while (loop->inner)
    cancel_loop_tree (loop->inner);
  cancel_loop (loop);
}

/* Checks that information about loops is correct
     -- sizes of loops are all right
     -- results of get_loop_body really belong to the loop
     -- loop header have just single entry edge and single latch edge
     -- loop latches have only single successor that is header of their loop
     -- irreducible loops are correctly marked
  */
void
verify_loop_structure (void)
{
  unsigned *sizes, i, j;
  sbitmap irreds;
  basic_block *bbs, bb;
  struct loop *loop;
  int err = 0;
  edge e;
  unsigned num = number_of_loops ();
  loop_iterator li;
  struct loop_exit *exit, *mexit;

  /* Check sizes.  */
  sizes = XCNEWVEC (unsigned, num);
  sizes[0] = 2;

  FOR_EACH_BB (bb)
    for (loop = bb->loop_father; loop; loop = loop->outer)
      sizes[loop->num]++;

  FOR_EACH_LOOP (li, loop, LI_INCLUDE_ROOT)
    {
      i = loop->num;

      if (loop->num_nodes != sizes[i])
        {
          error ("size of loop %d should be %d, not %d",
                   i, sizes[i], loop->num_nodes);
          err = 1;
        }
    }

  /* Check get_loop_body.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      bbs = get_loop_body (loop);

      for (j = 0; j < loop->num_nodes; j++)
        if (!flow_bb_inside_loop_p (loop, bbs[j]))
          {
            error ("bb %d do not belong to loop %d",
                    bbs[j]->index, loop->num);
            err = 1;
          }
      free (bbs);
    }

  /* Check headers and latches.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      i = loop->num;

      if ((current_loops->state & LOOPS_HAVE_PREHEADERS)
          && EDGE_COUNT (loop->header->preds) != 2)
        {
          error ("loop %d's header does not have exactly 2 entries", i);
          err = 1;
        }
      if (current_loops->state & LOOPS_HAVE_SIMPLE_LATCHES)
        {
          if (!single_succ_p (loop->latch))
            {
              error ("loop %d's latch does not have exactly 1 successor", i);
              err = 1;
            }
          if (single_succ (loop->latch) != loop->header)
            {
              error ("loop %d's latch does not have header as successor", i);
              err = 1;
            }
          if (loop->latch->loop_father != loop)
            {
              error ("loop %d's latch does not belong directly to it", i);
              err = 1;
            }
        }
      if (loop->header->loop_father != loop)
        {
          error ("loop %d's header does not belong directly to it", i);
          err = 1;
        }
      if ((current_loops->state & LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS)
          && (loop_latch_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP))
        {
          error ("loop %d's latch is marked as part of irreducible region", i);
          err = 1;
        }
    }

  /* Check irreducible loops.  */
  if (current_loops->state & LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS)
    {
      /* Record old info.  */
      irreds = sbitmap_alloc (last_basic_block);
      FOR_EACH_BB (bb)
        {
          edge_iterator ei;
          if (bb->flags & BB_IRREDUCIBLE_LOOP)
            SET_BIT (irreds, bb->index);
          else
            RESET_BIT (irreds, bb->index);
          FOR_EACH_EDGE (e, ei, bb->succs)
            if (e->flags & EDGE_IRREDUCIBLE_LOOP)
              e->flags |= EDGE_ALL_FLAGS + 1;
        }

      /* Recount it.  */
      mark_irreducible_loops ();

      /* Compare.  */
      FOR_EACH_BB (bb)
        {
          edge_iterator ei;

          if ((bb->flags & BB_IRREDUCIBLE_LOOP)
              && !TEST_BIT (irreds, bb->index))
            {
              error ("basic block %d should be marked irreducible", bb->index);
              err = 1;
            }
          else if (!(bb->flags & BB_IRREDUCIBLE_LOOP)
              && TEST_BIT (irreds, bb->index))
            {
              error ("basic block %d should not be marked irreducible", bb->index);
              err = 1;
            }
          FOR_EACH_EDGE (e, ei, bb->succs)
            {
              if ((e->flags & EDGE_IRREDUCIBLE_LOOP)
                  && !(e->flags & (EDGE_ALL_FLAGS + 1)))
                {
                  error ("edge from %d to %d should be marked irreducible",
                         e->src->index, e->dest->index);
                  err = 1;
                }
              else if (!(e->flags & EDGE_IRREDUCIBLE_LOOP)
                       && (e->flags & (EDGE_ALL_FLAGS + 1)))
                {
                  error ("edge from %d to %d should not be marked irreducible",
                         e->src->index, e->dest->index);
                  err = 1;
                }
              e->flags &= ~(EDGE_ALL_FLAGS + 1);
            }
        }
      free (irreds);
    }

  /* Check the recorded loop exits.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      if (loop->exits.e != NULL)
        {
          error ("corrupted head of the exits list of loop %d",
                 loop->num);
          err = 1;
        }
      else
        {
          /* Check that the list forms a cycle, and all elements except
             for the head are nonnull.  */
          for (mexit = &loop->exits, exit = mexit->next, i = 0;
               exit->e && exit != mexit;
               exit = exit->next)
            {
              if (i++ & 1)
                mexit = mexit->next;
            }

          if (exit != &loop->exits)
            {
              error ("corrupted exits list of loop %d", loop->num);
              err = 1;
            }
        }

      if ((current_loops->state & LOOPS_HAVE_RECORDED_EXITS) == 0)
        {
          if (loop->exits.next != &loop->exits)
            {
              error ("nonempty exits list of loop %d, but exits are not recorded",
                     loop->num);
              err = 1;
            }
        }
    }

  if (current_loops->state & LOOPS_HAVE_RECORDED_EXITS)
    {
      unsigned n_exits = 0, eloops;

      memset (sizes, 0, sizeof (unsigned) * num);
      FOR_EACH_BB (bb)
        {
          edge_iterator ei;
          if (bb->loop_father == current_loops->tree_root)
            continue;
          FOR_EACH_EDGE (e, ei, bb->succs)
            {
              if (flow_bb_inside_loop_p (bb->loop_father, e->dest))
                continue;

              n_exits++;
              exit = get_exit_descriptions (e);
              if (!exit)
                {
                  error ("Exit %d->%d not recorded", 
                         e->src->index, e->dest->index);
                  err = 1;
                }
              eloops = 0;
              for (; exit; exit = exit->next_e)
                eloops++;

              for (loop = bb->loop_father;
                   loop != e->dest->loop_father;
                   loop = loop->outer)
                {
                  eloops--;
                  sizes[loop->num]++;
                }

              if (eloops != 0)
                {
                  error ("Wrong list of exited loops for edge  %d->%d", 
                         e->src->index, e->dest->index);
                  err = 1;
                }
            }
        }

      if (n_exits != htab_elements (current_loops->exits))
        {
          error ("Too many loop exits recorded");
          err = 1;
        }

      FOR_EACH_LOOP (li, loop, 0)
        {
          eloops = 0;
          for (exit = loop->exits.next; exit->e; exit = exit->next)
            eloops++;
          if (eloops != sizes[loop->num])
            {
              error ("%d exits recorded for loop %d (having %d exits)",
                     eloops, loop->num, sizes[loop->num]);
              err = 1;
            }
        }
    }

  gcc_assert (!err);

  free (sizes);
}

/* Returns latch edge of LOOP.  */
edge
loop_latch_edge (const struct loop *loop)
{
  return find_edge (loop->latch, loop->header);
}

/* Returns preheader edge of LOOP.  */
edge
loop_preheader_edge (const struct loop *loop)
{
  edge e;
  edge_iterator ei;

  FOR_EACH_EDGE (e, ei, loop->header->preds)
    if (e->src != loop->latch)
      break;

  return e;
}

/* Returns true if E is an exit of LOOP.  */

bool
loop_exit_edge_p (const struct loop *loop, edge e)
{
  return (flow_bb_inside_loop_p (loop, e->src)
          && !flow_bb_inside_loop_p (loop, e->dest));
}

/* Returns the single exit edge of LOOP, or NULL if LOOP has either no exit
   or more than one exit.  If loops do not have the exits recorded, NULL
   is returned always.  */

edge
single_exit (const struct loop *loop)
{
  struct loop_exit *exit = loop->exits.next;

  if ((current_loops->state & LOOPS_HAVE_RECORDED_EXITS) == 0)
    return NULL;

  if (exit->e && exit->next == &loop->exits)
    return exit->e;
  else
    return NULL;
}