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/* Graph representation and manipulation functions.

   Copyright (C) 2007

   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/>.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "obstack.h"

#include "bitmap.h"

#include "vec.h"

#include "vecprim.h"

#include "graphds.h"

/* Dumps graph G into F.  */

void

dump_graph (FILE *f, struct graph *g)

{

  int i;

  struct graph_edge *e;

  for (i = 0; i < g->n_vertices; i++)

    {

      if (!g->vertices[i].pred

          && !g->vertices[i].succ)

        continue;

      fprintf (f, "%d (%d)\t<-", i, g->vertices[i].component);

      for (e = g->vertices[i].pred; e; e = e->pred_next)

        fprintf (f, " %d", e->src);

      fprintf (f, "\n");

      fprintf (f, "\t->");

      for (e = g->vertices[i].succ; e; e = e->succ_next)

        fprintf (f, " %d", e->dest);

      fprintf (f, "\n");

    }

}

/* Creates a new graph with N_VERTICES vertices.  */

struct graph *

new_graph (int n_vertices)

{

  struct graph *g = XNEW (struct graph);

  g->n_vertices = n_vertices;

  g->vertices = XCNEWVEC (struct vertex, n_vertices);

  return g;

}

/* Adds an edge from F to T to graph G.  The new edge is returned.  */

struct graph_edge *

add_edge (struct graph *g, int f, int t)

{

  struct graph_edge *e = XNEW (struct graph_edge);

  struct vertex *vf = &g->vertices[f], *vt = &g->vertices[t];

  e->src = f;

  e->dest = t;

  e->pred_next = vt->pred;

  vt->pred = e;

  e->succ_next = vf->succ;

  vf->succ = e;

  return e;

}

/* Moves all the edges incident with U to V.  */

void

identify_vertices (struct graph *g, int v, int u)

{

  struct vertex *vv = &g->vertices[v];

  struct vertex *uu = &g->vertices[u];

  struct graph_edge *e, *next;

  for (e = uu->succ; e; e = next)

    {

      next = e->succ_next;

      e->src = v;

      e->succ_next = vv->succ;

      vv->succ = e;

    }

  uu->succ = NULL;

  for (e = uu->pred; e; e = next)

    {

      next = e->pred_next;

      e->dest = v;

      e->pred_next = vv->pred;

      vv->pred = e;

    }

  uu->pred = NULL;

}

/* Helper function for graphds_dfs.  Returns the source vertex of E, in the

   direction given by FORWARD.  */

static inline int

dfs_edge_src (struct graph_edge *e, bool forward)

{

  return forward ? e->src : e->dest;

}

/* Helper function for graphds_dfs.  Returns the destination vertex of E, in

   the direction given by FORWARD.  */

static inline int

dfs_edge_dest (struct graph_edge *e, bool forward)

{

  return forward ? e->dest : e->src;

}

/* Helper function for graphds_dfs.  Returns the first edge after E (including

   E), in the graph direction given by FORWARD, that belongs to SUBGRAPH.  */

static inline struct graph_edge *

foll_in_subgraph (struct graph_edge *e, bool forward, bitmap subgraph)

{

  int d;

  if (!subgraph)

    return e;

  while (e)

    {

      d = dfs_edge_dest (e, forward);

      if (bitmap_bit_p (subgraph, d))

        return e;

      e = forward ? e->succ_next : e->pred_next;

    }

  return e;

}

/* Helper function for graphds_dfs.  Select the first edge from V in G, in the

   direction given by FORWARD, that belongs to SUBGRAPH.  */

static inline struct graph_edge *

dfs_fst_edge (struct graph *g, int v, bool forward, bitmap subgraph)

{

  struct graph_edge *e;

  e = (forward ? g->vertices[v].succ : g->vertices[v].pred);

  return foll_in_subgraph (e, forward, subgraph);

}

/* Helper function for graphds_dfs.  Returns the next edge after E, in the

   graph direction given by FORWARD, that belongs to SUBGRAPH.  */

static inline struct graph_edge *

dfs_next_edge (struct graph_edge *e, bool forward, bitmap subgraph)

{

  return foll_in_subgraph (forward ? e->succ_next : e->pred_next,

                           forward, subgraph);

}

/* Runs dfs search over vertices of G, from NQ vertices in queue QS.

   The vertices in postorder are stored into QT.  If FORWARD is false,

   backward dfs is run.  If SUBGRAPH is not NULL, it specifies the

   subgraph of G to run DFS on.  Returns the number of the components

   of the graph (number of the restarts of DFS).  */

int

graphds_dfs (struct graph *g, int *qs, int nq, VEC (int, heap) **qt,

             bool forward, bitmap subgraph)

{

  int i, tick = 0, v, comp = 0, top;

  struct graph_edge *e;

  struct graph_edge **stack = XNEWVEC (struct graph_edge *, g->n_vertices);

  bitmap_iterator bi;

  unsigned av;

  if (subgraph)

    {

      EXECUTE_IF_SET_IN_BITMAP (subgraph, 0, av, bi)

        {

          g->vertices[av].component = -1;

          g->vertices[av].post = -1;

        }

    }

  else

    {

      for (i = 0; i < g->n_vertices; i++)

        {

          g->vertices[i].component = -1;

          g->vertices[i].post = -1;

        }

    }

  for (i = 0; i < nq; i++)

    {

      v = qs[i];

      if (g->vertices[v].post != -1)

        continue;

      g->vertices[v].component = comp++;

      e = dfs_fst_edge (g, v, forward, subgraph);

      top = 0;

      while (1)

        {

          while (e)

            {

              if (g->vertices[dfs_edge_dest (e, forward)].component

                  == -1)

                break;

              e = dfs_next_edge (e, forward, subgraph);

            }

          if (!e)

            {

              if (qt)

                VEC_safe_push (int, heap, *qt, v);

              g->vertices[v].post = tick++;

              if (!top)

                break;

              e = stack[--top];

              v = dfs_edge_src (e, forward);

              e = dfs_next_edge (e, forward, subgraph);

              continue;

            }

          stack[top++] = e;

          v = dfs_edge_dest (e, forward);

          e = dfs_fst_edge (g, v, forward, subgraph);

          g->vertices[v].component = comp - 1;

        }

    }

  free (stack);

  return comp;

}

/* Determines the strongly connected components of G, using the algorithm of

   Tarjan -- first determine the postorder dfs numbering in reversed graph,

   then run the dfs on the original graph in the order given by decreasing

   numbers assigned by the previous pass.  If SUBGRAPH is not NULL, it

   specifies the subgraph of G whose strongly connected components we want

   to determine.

   After running this function, v->component is the number of the strongly

   connected component for each vertex of G.  Returns the number of the

   sccs of G.  */

int

graphds_scc (struct graph *g, bitmap subgraph)

{

  int *queue = XNEWVEC (int, g->n_vertices);

  VEC (int, heap) *postorder = NULL;

  int nq, i, comp;

  unsigned v;

  bitmap_iterator bi;

  if (subgraph)

    {

      nq = 0;

      EXECUTE_IF_SET_IN_BITMAP (subgraph, 0, v, bi)

        {

          queue[nq++] = v;

        }

    }

  else

    {

      for (i = 0; i < g->n_vertices; i++)

        queue[i] = i;

      nq = g->n_vertices;

    }

  graphds_dfs (g, queue, nq, &postorder, false, subgraph);

  gcc_assert (VEC_length (int, postorder) == (unsigned) nq);

  for (i = 0; i < nq; i++)

    queue[i] = VEC_index (int, postorder, nq - i - 1);

  comp = graphds_dfs (g, queue, nq, NULL, true, subgraph);

  free (queue);

  VEC_free (int, heap, postorder);

  return comp;

}

/* Runs CALLBACK for all edges in G.  */

void

for_each_edge (struct graph *g, graphds_edge_callback callback)

{

  struct graph_edge *e;

  int i;

  for (i = 0; i < g->n_vertices; i++)

    for (e = g->vertices[i].succ; e; e = e->succ_next)

      callback (g, e);

}

/* Releases the memory occupied by G.  */

void

free_graph (struct graph *g)

{

  struct graph_edge *e, *n;

  struct vertex *v;

  int i;

  for (i = 0; i < g->n_vertices; i++)

    {

      v = &g->vertices[i];

      for (e = v->succ; e; e = n)

        {

          n = e->succ_next;

          free (e);

        }

    }

  free (g->vertices);

  free (g);

}

/* Returns the nearest common ancestor of X and Y in tree whose parent

   links are given by PARENT.  MARKS is the array used to mark the

   vertices of the tree, and MARK is the number currently used as a mark.  */

static int

tree_nca (int x, int y, int *parent, int *marks, int mark)

{

  if (x == -1 || x == y)

    return y;

  /* We climb with X and Y up the tree, marking the visited nodes.  When

     we first arrive to a marked node, it is the common ancestor.  */

  marks[x] = mark;

  marks[y] = mark;

  while (1)

    {

      x = parent[x];

      if (x == -1)

        break;

      if (marks[x] == mark)

        return x;

      marks[x] = mark;

      y = parent[y];

      if (y == -1)

        break;

      if (marks[y] == mark)

        return y;

      marks[y] = mark;

    }

  /* If we reached the root with one of the vertices, continue

     with the other one till we reach the marked part of the

     tree.  */

  if (x == -1)

    {

      for (y = parent[y]; marks[y] != mark; y = parent[y])

        continue;

      return y;

    }

  else

    {

      for (x = parent[x]; marks[x] != mark; x = parent[x])

        continue;

      return x;

    }

}

/* Determines the dominance tree of G (stored in the PARENT, SON and BROTHER

   arrays), where the entry node is ENTRY.  */

void

graphds_domtree (struct graph *g, int entry,

                 int *parent, int *son, int *brother)

{

  VEC (int, heap) *postorder = NULL;

  int *marks = XCNEWVEC (int, g->n_vertices);

  int mark = 1, i, v, idom;

  bool changed = true;

  struct graph_edge *e;

  /* We use a slight modification of the standard iterative algorithm, as

     described in

     K. D. Cooper, T. J. Harvey and K. Kennedy: A Simple, Fast Dominance

        Algorithm

     sort vertices in reverse postorder

     foreach v

       dom(v) = everything

     dom(entry) = entry;

     while (anything changes)

       foreach v

         dom(v) = {v} union (intersection of dom(p) over all predecessors of v)

     The sets dom(v) are represented by the parent links in the current version

     of the dominance tree.  */

  for (i = 0; i < g->n_vertices; i++)

    {

      parent[i] = -1;

      son[i] = -1;

      brother[i] = -1;

    }

  graphds_dfs (g, &entry, 1, &postorder, true, NULL);

  gcc_assert (VEC_length (int, postorder) == (unsigned) g->n_vertices);

  gcc_assert (VEC_index (int, postorder, g->n_vertices - 1) == entry);

  while (changed)

    {

      changed = false;

      for (i = g->n_vertices - 2; i >= 0; i--)

        {

          v = VEC_index (int, postorder, i);

          idom = -1;

          for (e = g->vertices[v].pred; e; e = e->pred_next)

            {

              if (e->src != entry

                  && parent[e->src] == -1)

                continue;

              idom = tree_nca (idom, e->src, parent, marks, mark++);

            }

          if (idom != parent[v])

            {

              parent[v] = idom;

              changed = true;

            }

        }

    }

  free (marks);

  VEC_free (int, heap, postorder);

  for (i = 0; i < g->n_vertices; i++)

    if (parent[i] != -1)

      {

        brother[i] = son[parent[i]];

        son[parent[i]] = i;

      }

}