1 | /* |
2 | * Copyright (c) 2015-2017, Intel Corporation |
3 | * |
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27 | */ |
28 | |
29 | /** \file |
30 | * \brief Cyclic Path Redundancy pass. Removes redundant vertices on paths |
31 | * leading to a cyclic repeat. |
32 | * |
33 | * This is a graph reduction pass intended to remove vertices that are |
34 | * redundant because they lead solely to a cyclic vertex with a superset of |
35 | * their character reachability. For example, in this pattern: |
36 | * |
37 | * /(abc|def|abcghi).*0123/s |
38 | * |
39 | * The vertices for 'ghi' can be removed due to the presence of the dot-star |
40 | * repeat. |
41 | * |
42 | * Algorithm: |
43 | * |
44 | * for each cyclic vertex V: |
45 | * for each proper predecessor U of V: |
46 | * let S be the set of successors of U that are successors of V |
47 | * (including V itself) |
48 | * for each successor W of U not in S: |
49 | * perform a DFS forward from W, stopping exploration when a vertex |
50 | * in S is encountered; |
51 | * if a vertex with reach not in reach(V) or an accept is encountered: |
52 | * fail and continue to the next W. |
53 | * else: |
54 | * remove (U, W) |
55 | * |
56 | * NOTE: the following code is templated not just for fun, but so that we can |
57 | * run this analysis both forward and in reverse over the graph. |
58 | */ |
59 | #include "ng_cyclic_redundancy.h" |
60 | |
61 | #include "ng_holder.h" |
62 | #include "ng_prune.h" |
63 | #include "ng_util.h" |
64 | #include "util/container.h" |
65 | #include "util/flat_containers.h" |
66 | #include "util/graph_range.h" |
67 | #include "util/graph_small_color_map.h" |
68 | |
69 | #include <algorithm> |
70 | #include <boost/graph/depth_first_search.hpp> |
71 | #include <boost/graph/reverse_graph.hpp> |
72 | |
73 | using namespace std; |
74 | using boost::reverse_graph; |
75 | |
76 | namespace ue2 { |
77 | |
78 | namespace { |
79 | |
80 | // Terminator function for depth first traversal, tells us not to explore |
81 | // beyond vertices in set S. |
82 | template<class Vertex, class Graph> |
83 | class VertexInSet { |
84 | public: |
85 | explicit VertexInSet(const flat_set<Vertex> &s) : verts(s) {} |
86 | bool operator()(const Vertex &v, const Graph&) const { |
87 | return contains(verts, v); |
88 | } |
89 | |
90 | private: |
91 | const flat_set<Vertex> &verts; |
92 | }; |
93 | |
94 | struct SearchFailed {}; |
95 | |
96 | // Visitor for depth first traversal, throws an error if we encounter a vertex |
97 | // with bad reach or a report. |
98 | class SearchVisitor : public boost::default_dfs_visitor { |
99 | public: |
100 | explicit SearchVisitor(const CharReach &r) : cr(r) {} |
101 | |
102 | template<class Vertex, class Graph> |
103 | void discover_vertex(const Vertex &v, const Graph &g) const { |
104 | DEBUG_PRINTF("vertex %zu\n" , g[v].index); |
105 | if (is_special(v, g)) { |
106 | DEBUG_PRINTF("start or accept\n" ); |
107 | throw SearchFailed(); |
108 | } |
109 | |
110 | if (g[v].assert_flags) { |
111 | DEBUG_PRINTF("assert flags\n" ); |
112 | throw SearchFailed(); |
113 | } |
114 | |
115 | const CharReach &vcr = g[v].char_reach; |
116 | if (vcr != (vcr & cr)) { |
117 | DEBUG_PRINTF("bad reach\n" ); |
118 | throw SearchFailed(); |
119 | } |
120 | } |
121 | |
122 | private: |
123 | const CharReach &cr; |
124 | }; |
125 | |
126 | } // namespace |
127 | |
128 | template<class Graph, class ColorMap> |
129 | static |
130 | bool searchForward(const Graph &g, const CharReach &reach, |
131 | ColorMap &colours, |
132 | const flat_set<typename Graph::vertex_descriptor> &s, |
133 | typename Graph::vertex_descriptor w) { |
134 | colours.fill(small_color::white); |
135 | try { |
136 | depth_first_visit(g, w, SearchVisitor(reach), colours, |
137 | VertexInSet<typename Graph::vertex_descriptor, Graph>(s)); |
138 | } catch (SearchFailed &) { |
139 | return false; |
140 | } |
141 | |
142 | return true; |
143 | } |
144 | |
145 | static |
146 | NFAEdge to_raw(const NFAEdge &e, const NGHolder &) { |
147 | return e; |
148 | } |
149 | |
150 | static |
151 | NFAEdge to_raw(const reverse_graph<NGHolder, NGHolder &>::edge_descriptor &e, |
152 | const reverse_graph<NGHolder, NGHolder &> &g) { |
153 | return get(boost::edge_underlying, g, e); |
154 | } |
155 | |
156 | /* returns true if we did stuff */ |
157 | template<class Graph> |
158 | static |
159 | bool removeCyclicPathRedundancy(Graph &g, typename Graph::vertex_descriptor v, |
160 | NGHolder &raw) { |
161 | bool did_stuff = false; |
162 | |
163 | const CharReach &reach = g[v].char_reach; |
164 | |
165 | typedef typename Graph::vertex_descriptor vertex_descriptor; |
166 | |
167 | // Colour map used for depth_first_visit(). |
168 | auto colours = make_small_color_map(g); |
169 | |
170 | // precalc successors of v. |
171 | flat_set<vertex_descriptor> succ_v; |
172 | insert(&succ_v, adjacent_vertices(v, g)); |
173 | |
174 | flat_set<vertex_descriptor> s; |
175 | |
176 | for (const auto &e : in_edges_range(v, g)) { |
177 | vertex_descriptor u = source(e, g); |
178 | if (u == v) { |
179 | continue; |
180 | } |
181 | if (is_any_accept(u, g)) { |
182 | continue; |
183 | } |
184 | |
185 | DEBUG_PRINTF("- checking u %zu\n" , g[u].index); |
186 | |
187 | // let s be intersection(succ(u), succ(v)) |
188 | s.clear(); |
189 | for (auto b : adjacent_vertices_range(u, g)) { |
190 | if (contains(succ_v, b)) { |
191 | s.insert(b); |
192 | } |
193 | } |
194 | |
195 | for (const auto &e_u : make_vector_from(out_edges(u, g))) { |
196 | vertex_descriptor w = target(e_u, g); |
197 | if (is_special(w, g) || contains(s, w)) { |
198 | continue; |
199 | } |
200 | |
201 | const CharReach &w_reach = g[w].char_reach; |
202 | if (!w_reach.isSubsetOf(reach)) { |
203 | continue; |
204 | } |
205 | |
206 | DEBUG_PRINTF(" - checking w %zu\n" , g[w].index); |
207 | |
208 | if (!searchForward(g, reach, colours, s, w)) { |
209 | continue; |
210 | } |
211 | |
212 | DEBUG_PRINTF("removing edge (%zu,%zu)\n" , g[u].index, g[w].index); |
213 | /* we are currently iterating over the in-edges of v, so it |
214 | would be unwise to remove edges to v. However, */ |
215 | assert(w != v); /* as v is in s */ |
216 | remove_edge(to_raw(e_u, g), raw); |
217 | did_stuff = true; |
218 | } |
219 | } |
220 | |
221 | return did_stuff; |
222 | } |
223 | |
224 | template<class Graph> |
225 | static |
226 | bool cyclicPathRedundancyPass(Graph &g, NGHolder &raw) { |
227 | bool did_stuff = false; |
228 | |
229 | for (auto v : vertices_range(g)) { |
230 | if (is_special(v, g) || !edge(v, v, g).second) { |
231 | continue; |
232 | } |
233 | |
234 | DEBUG_PRINTF("examining cyclic vertex %zu\n" , g[v].index); |
235 | did_stuff |= removeCyclicPathRedundancy(g, v, raw); |
236 | } |
237 | |
238 | return did_stuff; |
239 | } |
240 | |
241 | bool removeCyclicPathRedundancy(NGHolder &g) { |
242 | assert(hasCorrectlyNumberedVertices(g)); |
243 | |
244 | // Forward pass. |
245 | bool f_changed = cyclicPathRedundancyPass(g, g); |
246 | if (f_changed) { |
247 | DEBUG_PRINTF("edges removed by forward pass\n" ); |
248 | pruneUseless(g); |
249 | } |
250 | |
251 | // Reverse pass. |
252 | DEBUG_PRINTF("REVERSE PASS\n" ); |
253 | typedef reverse_graph<NGHolder, NGHolder &> RevGraph; |
254 | RevGraph revg(g); |
255 | bool r_changed = cyclicPathRedundancyPass(revg, g); |
256 | if (r_changed) { |
257 | DEBUG_PRINTF("edges removed by reverse pass\n" ); |
258 | pruneUseless(g); |
259 | } |
260 | |
261 | return f_changed || r_changed; |
262 | } |
263 | |
264 | } // namespace ue2 |
265 | |