1 | /* Template class for Dijkstra's algorithm on directed graphs. |
2 | Copyright (C) 2019-2023 Free Software Foundation, Inc. |
3 | Contributed by David Malcolm <dmalcolm@redhat.com>. |
4 | |
5 | This file is part of GCC. |
6 | |
7 | GCC is free software; you can redistribute it and/or modify it |
8 | under the terms of the GNU General Public License as published by |
9 | the Free Software Foundation; either version 3, or (at your option) |
10 | any later version. |
11 | |
12 | GCC is distributed in the hope that it will be useful, but |
13 | WITHOUT ANY WARRANTY; without even the implied warranty of |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
15 | General Public License for more details. |
16 | |
17 | You should have received a copy of the GNU General Public License |
18 | along with GCC; see the file COPYING3. If not see |
19 | <http://www.gnu.org/licenses/>. */ |
20 | |
21 | #ifndef GCC_SHORTEST_PATHS_H |
22 | #define GCC_SHORTEST_PATHS_H |
23 | |
24 | #include "timevar.h" |
25 | |
26 | enum shortest_path_sense |
27 | { |
28 | /* Find the shortest path from the given origin node to each |
29 | node in the graph. */ |
30 | SPS_FROM_GIVEN_ORIGIN, |
31 | |
32 | /* Find the shortest path from each node in the graph to the |
33 | given target node. */ |
34 | SPS_TO_GIVEN_TARGET |
35 | }; |
36 | |
37 | /* A record of the shortest path for each node relative to a special |
38 | "given node", either: |
39 | SPS_FROM_GIVEN_ORIGIN: |
40 | from the given origin node to each node in a graph, or |
41 | SPS_TO_GIVEN_TARGET: |
42 | from each node in a graph to the given target node. |
43 | |
44 | The constructor runs Dijkstra's algorithm, and the results are |
45 | stored in this class. */ |
46 | |
47 | template <typename GraphTraits, typename Path_t> |
48 | class shortest_paths |
49 | { |
50 | public: |
51 | typedef typename GraphTraits::graph_t graph_t; |
52 | typedef typename GraphTraits::node_t node_t; |
53 | typedef typename GraphTraits::edge_t edge_t; |
54 | typedef Path_t path_t; |
55 | |
56 | shortest_paths (const graph_t &graph, const node_t *given_node, |
57 | enum shortest_path_sense sense); |
58 | |
59 | path_t get_shortest_path (const node_t *other_node) const; |
60 | int get_shortest_distance (const node_t *other_node) const; |
61 | |
62 | private: |
63 | const graph_t &m_graph; |
64 | |
65 | enum shortest_path_sense m_sense; |
66 | |
67 | /* For each node (by index), the minimal distance between that node |
68 | and the given node (with direction depending on m_sense). */ |
69 | auto_vec<int> m_dist; |
70 | |
71 | /* For each node (by index): |
72 | SPS_FROM_GIVEN_ORIGIN: |
73 | the previous edge in the shortest path from the origin, |
74 | SPS_TO_GIVEN_TARGET: |
75 | the next edge in the shortest path to the target. */ |
76 | auto_vec<const edge_t *> m_best_edge; |
77 | }; |
78 | |
79 | /* shortest_paths's constructor. |
80 | |
81 | Use Dijkstra's algorithm relative to GIVEN_NODE to populate m_dist and |
82 | m_best_edge with enough information to be able to generate Path_t instances |
83 | to give the shortest path... |
84 | SPS_FROM_GIVEN_ORIGIN: to each node in a graph from the origin node, or |
85 | SPS_TO_GIVEN_TARGET: from each node in a graph to the target node. */ |
86 | |
87 | template <typename GraphTraits, typename Path_t> |
88 | inline |
89 | shortest_paths<GraphTraits, Path_t>:: |
90 | shortest_paths (const graph_t &graph, |
91 | const node_t *given_node, |
92 | enum shortest_path_sense sense) |
93 | : m_graph (graph), |
94 | m_sense (sense), |
95 | m_dist (graph.m_nodes.length ()), |
96 | m_best_edge (graph.m_nodes.length ()) |
97 | { |
98 | auto_timevar tv (TV_ANALYZER_SHORTEST_PATHS); |
99 | |
100 | auto_vec<int> queue (graph.m_nodes.length ()); |
101 | |
102 | for (unsigned i = 0; i < graph.m_nodes.length (); i++) |
103 | { |
104 | m_dist.quick_push (INT_MAX); |
105 | m_best_edge.quick_push (NULL); |
106 | queue.quick_push (i); |
107 | } |
108 | m_dist[given_node->m_index] = 0; |
109 | |
110 | while (queue.length () > 0) |
111 | { |
112 | /* Get minimal distance in queue. |
113 | FIXME: this is O(N^2); replace with a priority queue. */ |
114 | int idx_with_min_dist = -1; |
115 | int idx_in_queue_with_min_dist = -1; |
116 | int min_dist = INT_MAX; |
117 | for (unsigned i = 0; i < queue.length (); i++) |
118 | { |
119 | int idx = queue[i]; |
120 | if (m_dist[queue[i]] < min_dist) |
121 | { |
122 | min_dist = m_dist[idx]; |
123 | idx_with_min_dist = idx; |
124 | idx_in_queue_with_min_dist = i; |
125 | } |
126 | } |
127 | if (idx_with_min_dist == -1) |
128 | break; |
129 | gcc_assert (idx_in_queue_with_min_dist != -1); |
130 | |
131 | // FIXME: this is confusing: there are two indices here |
132 | |
133 | queue.unordered_remove (idx_in_queue_with_min_dist); |
134 | |
135 | node_t *n |
136 | = static_cast <node_t *> (m_graph.m_nodes[idx_with_min_dist]); |
137 | |
138 | if (m_sense == SPS_FROM_GIVEN_ORIGIN) |
139 | { |
140 | int i; |
141 | edge_t *succ; |
142 | FOR_EACH_VEC_ELT (n->m_succs, i, succ) |
143 | { |
144 | // TODO: only for dest still in queue |
145 | node_t *dest = succ->m_dest; |
146 | int alt = m_dist[n->m_index] + 1; |
147 | if (alt < m_dist[dest->m_index]) |
148 | { |
149 | m_dist[dest->m_index] = alt; |
150 | m_best_edge[dest->m_index] = succ; |
151 | } |
152 | } |
153 | } |
154 | else |
155 | { |
156 | int i; |
157 | edge_t *pred; |
158 | FOR_EACH_VEC_ELT (n->m_preds, i, pred) |
159 | { |
160 | // TODO: only for dest still in queue |
161 | node_t *src = pred->m_src; |
162 | int alt = m_dist[n->m_index] + 1; |
163 | if (alt < m_dist[src->m_index]) |
164 | { |
165 | m_dist[src->m_index] = alt; |
166 | m_best_edge[src->m_index] = pred; |
167 | } |
168 | } |
169 | } |
170 | } |
171 | } |
172 | |
173 | /* Generate an Path_t instance giving the shortest path between OTHER_NODE |
174 | and the given node. |
175 | |
176 | SPS_FROM_GIVEN_ORIGIN: shortest path from given origin node to OTHER_NODE |
177 | SPS_TO_GIVEN_TARGET: shortest path from OTHER_NODE to given target node. |
178 | |
179 | If no such path exists, return an empty path. */ |
180 | |
181 | template <typename GraphTraits, typename Path_t> |
182 | inline Path_t |
183 | shortest_paths<GraphTraits, Path_t>:: |
184 | get_shortest_path (const node_t *other_node) const |
185 | { |
186 | Path_t result; |
187 | |
188 | while (m_best_edge[other_node->m_index]) |
189 | { |
190 | result.m_edges.safe_push (m_best_edge[other_node->m_index]); |
191 | if (m_sense == SPS_FROM_GIVEN_ORIGIN) |
192 | other_node = m_best_edge[other_node->m_index]->m_src; |
193 | else |
194 | other_node = m_best_edge[other_node->m_index]->m_dest; |
195 | } |
196 | |
197 | if (m_sense == SPS_FROM_GIVEN_ORIGIN) |
198 | result.m_edges.reverse (); |
199 | |
200 | return result; |
201 | } |
202 | |
203 | /* Get the shortest distance... |
204 | SPS_FROM_GIVEN_ORIGIN: ...from given origin node to OTHER_NODE |
205 | SPS_TO_GIVEN_TARGET: ...from OTHER_NODE to given target node. */ |
206 | |
207 | template <typename GraphTraits, typename Path_t> |
208 | inline int |
209 | shortest_paths<GraphTraits, Path_t>:: |
210 | get_shortest_distance (const node_t *other_node) const |
211 | { |
212 | return m_dist[other_node->m_index]; |
213 | } |
214 | |
215 | #endif /* GCC_SHORTEST_PATHS_H */ |
216 | |