et-forest.c

/* ET-trees data structure implementation.
   Contributed by Pavel Nejedly
   Copyright (C) 2002, 2003, 2004, 2005, 2007, 2008, 2010 Free Software
   Foundation, Inc.

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

Libiberty 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
Library General Public License for more details.

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

  The ET-forest structure is described in:
    D. D. Sleator and R. E. Tarjan. A data structure for dynamic trees.
    J.  G'omput. System Sci., 26(3):362 381, 1983.
*/

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "et-forest.h"
#include "alloc-pool.h"

/* We do not enable this with ENABLE_CHECKING, since it is awfully slow.  */
#undef DEBUG_ET

#ifdef DEBUG_ET
#include "basic-block.h"
#endif

/* The occurrence of a node in the et tree.  */
struct et_occ
{
  struct et_node *of;		/* The node.  */

  struct et_occ *parent;	/* Parent in the splay-tree.  */
  struct et_occ *prev;		/* Left son in the splay-tree.  */
  struct et_occ *next;		/* Right son in the splay-tree.  */

  int depth;			/* The depth of the node is the sum of depth
				   fields on the path to the root.  */
  int min;			/* The minimum value of the depth in the subtree
				   is obtained by adding sum of depth fields
				   on the path to the root.  */
  struct et_occ *min_occ;	/* The occurrence in the subtree with the minimal
				   depth.  */
};

static alloc_pool et_nodes;
static alloc_pool et_occurrences;

/* Changes depth of OCC to D.  */

static inline void
set_depth (struct et_occ *occ, int d)
{
  if (!occ)
    return;

  occ->min += d - occ->depth;
  occ->depth = d;
}

/* Adds D to the depth of OCC.  */

static inline void
set_depth_add (struct et_occ *occ, int d)
{
  if (!occ)
    return;

  occ->min += d;
  occ->depth += d;
}

/* Sets prev field of OCC to P.  */

static inline void
set_prev (struct et_occ *occ, struct et_occ *t)
{
#ifdef DEBUG_ET
  gcc_assert (occ != t);
#endif

  occ->prev = t;
  if (t)
    t->parent = occ;
}

/* Sets next field of OCC to P.  */

static inline void
set_next (struct et_occ *occ, struct et_occ *t)
{
#ifdef DEBUG_ET
  gcc_assert (occ != t);
#endif

  occ->next = t;
  if (t)
    t->parent = occ;
}

/* Recompute minimum for occurrence OCC.  */

static inline void
et_recomp_min (struct et_occ *occ)
{
  struct et_occ *mson = occ->prev;

  if (!mson
      || (occ->next
	  && mson->min > occ->next->min))
      mson = occ->next;

  if (mson && mson->min < 0)
    {
      occ->min = mson->min + occ->depth;
      occ->min_occ = mson->min_occ;
    }
  else
    {
      occ->min = occ->depth;
      occ->min_occ = occ;
    }
}

#ifdef DEBUG_ET
/* Checks whether neighborhood of OCC seems sane.  */

static void
et_check_occ_sanity (struct et_occ *occ)
{
  if (!occ)
    return;

  gcc_assert (occ->parent != occ);
  gcc_assert (occ->prev != occ);
  gcc_assert (occ->next != occ);
  gcc_assert (!occ->next || occ->next != occ->prev);

  if (occ->next)
    {
      gcc_assert (occ->next != occ->parent);
      gcc_assert (occ->next->parent == occ);
    }

  if (occ->prev)
    {
      gcc_assert (occ->prev != occ->parent);
      gcc_assert (occ->prev->parent == occ);
    }

  gcc_assert (!occ->parent
	      || occ->parent->prev == occ
	      || occ->parent->next == occ);
}

/* Checks whether tree rooted at OCC is sane.  */

static void
et_check_sanity (struct et_occ *occ)
{
  et_check_occ_sanity (occ);
  if (occ->prev)
    et_check_sanity (occ->prev);
  if (occ->next)
    et_check_sanity (occ->next);
}

/* Checks whether tree containing OCC is sane.  */

static void
et_check_tree_sanity (struct et_occ *occ)
{
  while (occ->parent)
    occ = occ->parent;

  et_check_sanity (occ);
}

/* For recording the paths.  */

/* An ad-hoc constant; if the function has more blocks, this won't work,
   but since it is used for debugging only, it does not matter.  */
#define MAX_NODES 100000

static int len;
static void *datas[MAX_NODES];
static int depths[MAX_NODES];

/* Records the path represented by OCC, with depth incremented by DEPTH.  */

static int
record_path_before_1 (struct et_occ *occ, int depth)
{
  int mn, m;

  depth += occ->depth;
  mn = depth;

  if (occ->prev)
    {
      m = record_path_before_1 (occ->prev, depth);
      if (m < mn)
	mn = m;
    }

  fprintf (stderr, "%d (%d); ", ((basic_block) occ->of->data)->index, depth);

  gcc_assert (len < MAX_NODES);

  depths[len] = depth;
  datas[len] = occ->of;
  len++;

  if (occ->next)
    {
      m = record_path_before_1 (occ->next, depth);
      if (m < mn)
	mn = m;
    }

  gcc_assert (mn == occ->min + depth - occ->depth);

  return mn;
}

/* Records the path represented by a tree containing OCC.  */

static void
record_path_before (struct et_occ *occ)
{
  while (occ->parent)
    occ = occ->parent;

  len = 0;
  record_path_before_1 (occ, 0);
  fprintf (stderr, "\n");
}

/* Checks whether the path represented by OCC, with depth incremented by DEPTH,
   was not changed since the last recording.  */

static int
check_path_after_1 (struct et_occ *occ, int depth)
{
  int mn, m;

  depth += occ->depth;
  mn = depth;

  if (occ->next)
    {
      m = check_path_after_1 (occ->next, depth);
      if (m < mn)
	mn =  m;
    }

  len--;
  gcc_assert (depths[len] == depth && datas[len] == occ->of);

  if (occ->prev)
    {
      m = check_path_after_1 (occ->prev, depth);
      if (m < mn)
	mn =  m;
    }

  gcc_assert (mn == occ->min + depth - occ->depth);

  return mn;
}

/* Checks whether the path represented by a tree containing OCC was
   not changed since the last recording.  */

static void
check_path_after (struct et_occ *occ)
{
  while (occ->parent)
    occ = occ->parent;

  check_path_after_1 (occ, 0);
  gcc_assert (!len);
}

#endif

/* Splay the occurrence OCC to the root of the tree.  */

static void
et_splay (struct et_occ *occ)
{
  struct et_occ *f, *gf, *ggf;
  int occ_depth, f_depth, gf_depth;

#ifdef DEBUG_ET
  record_path_before (occ);
  et_check_tree_sanity (occ);
#endif

  while (occ->parent)
    {
      occ_depth = occ->depth;

      f = occ->parent;
      f_depth = f->depth;

      gf = f->parent;

      if (!gf)
	{
	  set_depth_add (occ, f_depth);
	  occ->min_occ = f->min_occ;
	  occ->min = f->min;

	  if (f->prev == occ)
	    {
	      /* zig */
	      set_prev (f, occ->next);
	      set_next (occ, f);
	      set_depth_add (f->prev, occ_depth);
	    }
	  else
	    {
	      /* zag */
	      set_next (f, occ->prev);
	      set_prev (occ, f);
	      set_depth_add (f->next, occ_depth);
	    }
	  set_depth (f, -occ_depth);
	  occ->parent = NULL;

	  et_recomp_min (f);
#ifdef DEBUG_ET
	  et_check_tree_sanity (occ);
	  check_path_after (occ);
#endif
	  return;
	}

      gf_depth = gf->depth;

      set_depth_add (occ, f_depth + gf_depth);
      occ->min_occ = gf->min_occ;
      occ->min = gf->min;

      ggf = gf->parent;

      if (gf->prev == f)
	{
	  if (f->prev == occ)
	    {
	      /* zig zig */
	      set_prev (gf, f->next);
	      set_prev (f, occ->next);
	      set_next (occ, f);
	      set_next (f, gf);

	      set_depth (f, -occ_depth);
	      set_depth_add (f->prev, occ_depth);
	      set_depth (gf, -f_depth);
	      set_depth_add (gf->prev, f_depth);
	    }
	  else
	    {
	      /* zag zig */
	      set_prev (gf, occ->next);
	      set_next (f, occ->prev);
	      set_prev (occ, f);
	      set_next (occ, gf);

	      set_depth (f, -occ_depth);
	      set_depth_add (f->next, occ_depth);
	      set_depth (gf, -occ_depth - f_depth);
	      set_depth_add (gf->prev, occ_depth + f_depth);
	    }
	}
      else
	{
	  if (f->prev == occ)
	    {
	      /* zig zag */
	      set_next (gf, occ->prev);
	      set_prev (f, occ->next);
	      set_prev (occ, gf);
	      set_next (occ, f);

	      set_depth (f, -occ_depth);
	      set_depth_add (f->prev, occ_depth);
	      set_depth (gf, -occ_depth - f_depth);
	      set_depth_add (gf->next, occ_depth + f_depth);
	    }
	  else
	    {
	      /* zag zag */
	      set_next (gf, f->prev);
	      set_next (f, occ->prev);
	      set_prev (occ, f);
	      set_prev (f, gf);

	      set_depth (f, -occ_depth);
	      set_depth_add (f->next, occ_depth);
	      set_depth (gf, -f_depth);
	      set_depth_add (gf->next, f_depth);
	    }
	}

      occ->parent = ggf;
      if (ggf)
	{
	  if (ggf->prev == gf)
	    ggf->prev = occ;
	  else
	    ggf->next = occ;
	}

      et_recomp_min (gf);
      et_recomp_min (f);
#ifdef DEBUG_ET
      et_check_tree_sanity (occ);
#endif
    }

#ifdef DEBUG_ET
  et_check_sanity (occ);
  check_path_after (occ);
#endif
}

/* Create a new et tree occurrence of NODE.  */

static struct et_occ *
et_new_occ (struct et_node *node)
{
  struct et_occ *nw;

  if (!et_occurrences)
    et_occurrences = create_alloc_pool ("et_occ pool", sizeof (struct et_occ), 300);
  nw = (struct et_occ *) pool_alloc (et_occurrences);

  nw->of = node;
  nw->parent = NULL;
  nw->prev = NULL;
  nw->next = NULL;

  nw->depth = 0;
  nw->min_occ = nw;
  nw->min = 0;

  return nw;
}

/* Create a new et tree containing DATA.  */

struct et_node *
et_new_tree (void *data)
{
  struct et_node *nw;

  if (!et_nodes)
    et_nodes = create_alloc_pool ("et_node pool", sizeof (struct et_node), 300);
  nw = (struct et_node *) pool_alloc (et_nodes);

  nw->data = data;
  nw->father = NULL;
  nw->left = NULL;
  nw->right = NULL;
  nw->son = NULL;

  nw->rightmost_occ = et_new_occ (nw);
  nw->parent_occ = NULL;

  return nw;
}

/* Releases et tree T.  */

void
et_free_tree (struct et_node *t)
{
  while (t->son)
    et_split (t->son);

  if (t->father)
    et_split (t);

  pool_free (et_occurrences, t->rightmost_occ);
  pool_free (et_nodes, t);
}

/* Releases et tree T without maintaining other nodes.  */

void
et_free_tree_force (struct et_node *t)
{
  pool_free (et_occurrences, t->rightmost_occ);
  if (t->parent_occ)
    pool_free (et_occurrences, t->parent_occ);
  pool_free (et_nodes, t);
}

/* Release the alloc pools, if they are empty.  */

void
et_free_pools (void)
{
  free_alloc_pool_if_empty (&et_occurrences);
  free_alloc_pool_if_empty (&et_nodes);
}

/* Sets father of et tree T to FATHER.  */

void
et_set_father (struct et_node *t, struct et_node *father)
{
  struct et_node *left, *right;
  struct et_occ *rmost, *left_part, *new_f_occ, *p;

  /* Update the path represented in the splay tree.  */
  new_f_occ = et_new_occ (father);

  rmost = father->rightmost_occ;
  et_splay (rmost);

  left_part = rmost->prev;

  p = t->rightmost_occ;
  et_splay (p);

  set_prev (new_f_occ, left_part);
  set_next (new_f_occ, p);

  p->depth++;
  p->min++;
  et_recomp_min (new_f_occ);

  set_prev (rmost, new_f_occ);

  if (new_f_occ->min + rmost->depth < rmost->min)
    {
      rmost->min = new_f_occ->min + rmost->depth;
      rmost->min_occ = new_f_occ->min_occ;
    }

  t->parent_occ = new_f_occ;

  /* Update the tree.  */
  t->father = father;
  right = father->son;
  if (right)
    left = right->left;
  else
    left = right = t;

  left->right = t;
  right->left = t;
  t->left = left;
  t->right = right;

  father->son = t;

#ifdef DEBUG_ET
  et_check_tree_sanity (rmost);
  record_path_before (rmost);
#endif
}

/* Splits the edge from T to its father.  */

void
et_split (struct et_node *t)
{
  struct et_node *father = t->father;
  struct et_occ *r, *l, *rmost, *p_occ;

  /* Update the path represented by the splay tree.  */
  rmost = t->rightmost_occ;
  et_splay (rmost);

  for (r = rmost->next; r->prev; r = r->prev)
    continue;
  et_splay (r);

  r->prev->parent = NULL;
  p_occ = t->parent_occ;
  et_splay (p_occ);
  t->parent_occ = NULL;

  l = p_occ->prev;
  p_occ->next->parent = NULL;

  set_prev (r, l);

  et_recomp_min (r);

  et_splay (rmost);
  rmost->depth = 0;
  rmost->min = 0;

  pool_free (et_occurrences, p_occ);

  /* Update the tree.  */
  if (father->son == t)
    father->son = t->right;
  if (father->son == t)
    father->son = NULL;
  else
    {
      t->left->right = t->right;
      t->right->left = t->left;
    }
  t->left = t->right = NULL;
  t->father = NULL;

#ifdef DEBUG_ET
  et_check_tree_sanity (rmost);
  record_path_before (rmost);

  et_check_tree_sanity (r);
  record_path_before (r);
#endif
}

/* Finds the nearest common ancestor of the nodes N1 and N2.  */

struct et_node *
et_nca (struct et_node *n1, struct et_node *n2)
{
  struct et_occ *o1 = n1->rightmost_occ, *o2 = n2->rightmost_occ, *om;
  struct et_occ *l, *r, *ret;
  int mn;

  if (n1 == n2)
    return n1;

  et_splay (o1);
  l = o1->prev;
  r = o1->next;
  if (l)
    l->parent = NULL;
  if (r)
    r->parent = NULL;
  et_splay (o2);

  if (l == o2 || (l && l->parent != NULL))
    {
      ret = o2->next;

      set_prev (o1, o2);
      if (r)
	r->parent = o1;
    }
  else if (r == o2 || (r && r->parent != NULL))
    {
      ret = o2->prev;

      set_next (o1, o2);
      if (l)
	l->parent = o1;
    }
  else
    {
      /* O1 and O2 are in different components of the forest.  */
      if (l)
	l->parent = o1;
      if (r)
	r->parent = o1;
      return NULL;
    }

  if (0 < o2->depth)
    {
      om = o1;
      mn = o1->depth;
    }
  else
    {
      om = o2;
      mn = o2->depth + o1->depth;
    }

#ifdef DEBUG_ET
  et_check_tree_sanity (o2);
#endif

  if (ret && ret->min + o1->depth + o2->depth < mn)
    return ret->min_occ->of;
  else
    return om->of;
}

/* Checks whether the node UP is an ancestor of the node DOWN.  */

bool
et_below (struct et_node *down, struct et_node *up)
{
  struct et_occ *u = up->rightmost_occ, *d = down->rightmost_occ;
  struct et_occ *l, *r;

  if (up == down)
    return true;

  et_splay (u);
  l = u->prev;
  r = u->next;

  if (!l)
    return false;

  l->parent = NULL;

  if (r)
    r->parent = NULL;

  et_splay (d);

  if (l == d || l->parent != NULL)
    {
      if (r)
	r->parent = u;
      set_prev (u, d);
#ifdef DEBUG_ET
      et_check_tree_sanity (u);
#endif
    }
  else
    {
      l->parent = u;

      /* In case O1 and O2 are in two different trees, we must just restore the
	 original state.  */
      if (r && r->parent != NULL)
	set_next (u, d);
      else
	set_next (u, r);

#ifdef DEBUG_ET
      et_check_tree_sanity (u);
#endif
      return false;
    }

  if (0 >= d->depth)
    return false;

  return !d->next || d->next->min + d->depth >= 0;
}

/* Returns the root of the tree that contains NODE.  */

struct et_node *
et_root (struct et_node *node)
{
  struct et_occ *occ = node->rightmost_occ, *r;

  /* The root of the tree corresponds to the rightmost occurrence in the
     represented path.  */
  et_splay (occ);
  for (r = occ; r->next; r = r->next)
    continue;
  et_splay (r);

  return r->of;
}