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/* Template class for Dijkstra's algorithm on directed graphs.
Copyright (C) 2019-2021 Free Software Foundation, Inc.
Contributed by David Malcolm <dmalcolm@redhat.com>.
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/>. */
#ifndef GCC_SHORTEST_PATHS_H
#define GCC_SHORTEST_PATHS_H
#include "timevar.h"
/* A record of the shortest path to each node in an graph
from the origin node.
The constructor runs Dijkstra's algorithm, and the results are
stored in this class. */
template <typename GraphTraits, typename Path_t>
class shortest_paths
{
public:
typedef typename GraphTraits::graph_t graph_t;
typedef typename GraphTraits::node_t node_t;
typedef typename GraphTraits::edge_t edge_t;
typedef Path_t path_t;
shortest_paths (const graph_t &graph, const node_t *origin);
path_t get_shortest_path (const node_t *to) const;
private:
const graph_t &m_graph;
/* For each node (by index), the minimal distance to that node from the
origin. */
auto_vec<int> m_dist;
/* For each exploded_node (by index), the previous edge in the shortest
path from the origin. */
auto_vec<const edge_t *> m_prev;
};
/* shortest_paths's constructor.
Use Dijkstra's algorithm relative to ORIGIN to populate m_dist and
m_prev with enough information to be able to generate Path_t instances
to give the shortest path to any node in GRAPH from ORIGIN. */
template <typename GraphTraits, typename Path_t>
inline
shortest_paths<GraphTraits, Path_t>::shortest_paths (const graph_t &graph,
const node_t *origin)
: m_graph (graph),
m_dist (graph.m_nodes.length ()),
m_prev (graph.m_nodes.length ())
{
auto_timevar tv (TV_ANALYZER_SHORTEST_PATHS);
auto_vec<int> queue (graph.m_nodes.length ());
for (unsigned i = 0; i < graph.m_nodes.length (); i++)
{
m_dist.quick_push (INT_MAX);
m_prev.quick_push (NULL);
queue.quick_push (i);
}
m_dist[origin->m_index] = 0;
while (queue.length () > 0)
{
/* Get minimal distance in queue.
FIXME: this is O(N^2); replace with a priority queue. */
int idx_with_min_dist = -1;
int idx_in_queue_with_min_dist = -1;
int min_dist = INT_MAX;
for (unsigned i = 0; i < queue.length (); i++)
{
int idx = queue[i];
if (m_dist[queue[i]] < min_dist)
{
min_dist = m_dist[idx];
idx_with_min_dist = idx;
idx_in_queue_with_min_dist = i;
}
}
gcc_assert (idx_with_min_dist != -1);
gcc_assert (idx_in_queue_with_min_dist != -1);
// FIXME: this is confusing: there are two indices here
queue.unordered_remove (idx_in_queue_with_min_dist);
node_t *n
= static_cast <node_t *> (m_graph.m_nodes[idx_with_min_dist]);
int i;
edge_t *succ;
FOR_EACH_VEC_ELT (n->m_succs, i, succ)
{
// TODO: only for dest still in queue
node_t *dest = succ->m_dest;
int alt = m_dist[n->m_index] + 1;
if (alt < m_dist[dest->m_index])
{
m_dist[dest->m_index] = alt;
m_prev[dest->m_index] = succ;
}
}
}
}
/* Generate an Path_t instance giving the shortest path to the node
TO from the origin node. */
template <typename GraphTraits, typename Path_t>
inline Path_t
shortest_paths<GraphTraits, Path_t>::get_shortest_path (const node_t *to) const
{
Path_t result;
while (m_prev[to->m_index])
{
result.m_edges.safe_push (m_prev[to->m_index]);
to = m_prev[to->m_index]->m_src;
}
result.m_edges.reverse ();
return result;
}
#endif /* GCC_SHORTEST_PATHS_H */
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