mirror of
https://github.com/VectorCamp/vectorscan.git
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258 lines
8.0 KiB
C++
258 lines
8.0 KiB
C++
/*
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* Copyright (c) 2015-2016, Intel Corporation
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of Intel Corporation nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/** \file
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* \brief Cyclic Path Redundancy pass. Removes redundant vertices on paths
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* leading to a cyclic repeat.
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*
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* This is a graph reduction pass intended to remove vertices that are
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* redundant because they lead solely to a cyclic vertex with a superset of
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* their character reachability. For example, in this pattern:
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*
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* /(abc|def|abcghi).*0123/s
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*
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* The vertices for 'ghi' can be removed due to the presence of the dot-star
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* repeat.
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*
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* Algorithm:
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*
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* for each cyclic vertex V:
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* for each proper predecessor U of V:
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* let S be the set of successors of U that are successors of V
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* (including V itself)
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* for each successor W of U not in S:
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* perform a DFS forward from W, stopping exploration when a vertex
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* in S is encountered;
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* if a vertex with reach not in reach(V) or an accept is encountered:
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* fail and continue to the next W.
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* else:
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* remove (U, W)
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*
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* NOTE: the following code is templated not just for fun, but so that we can
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* run this analysis both forward and in reverse over the graph.
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*/
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#include "ng_cyclic_redundancy.h"
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#include "ng_holder.h"
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#include "ng_prune.h"
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#include "ng_util.h"
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#include "util/container.h"
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#include "util/graph_range.h"
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#include "util/ue2_containers.h"
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#include <boost/graph/depth_first_search.hpp>
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#include <boost/graph/reverse_graph.hpp>
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using namespace std;
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using boost::reverse_graph;
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namespace ue2 {
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namespace {
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// Terminator function for depth first traversal, tells us not to explore
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// beyond vertices in set S.
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template<class Vertex, class Graph>
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class VertexInSet {
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public:
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explicit VertexInSet(const flat_set<Vertex> &s) : verts(s) {}
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bool operator()(const Vertex &v, const Graph&) const {
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return contains(verts, v);
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}
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private:
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const flat_set<Vertex> &verts;
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};
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struct SearchFailed {};
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// Visitor for depth first traversal, throws an error if we encounter a vertex
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// with bad reach or a report.
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class SearchVisitor : public boost::default_dfs_visitor {
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public:
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explicit SearchVisitor(const CharReach &r) : cr(r) {}
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template<class Vertex, class Graph>
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void discover_vertex(const Vertex &v, const Graph &g) const {
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DEBUG_PRINTF("vertex %zu\n", g[v].index);
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if (is_special(v, g)) {
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DEBUG_PRINTF("start or accept\n");
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throw SearchFailed();
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}
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if (g[v].assert_flags) {
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DEBUG_PRINTF("assert flags\n");
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throw SearchFailed();
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}
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const CharReach &vcr = g[v].char_reach;
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if (vcr != (vcr & cr)) {
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DEBUG_PRINTF("bad reach\n");
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throw SearchFailed();
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}
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}
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private:
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const CharReach &cr;
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};
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} // namespace
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template<class Graph>
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static
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bool searchForward(const Graph &g, const CharReach &reach,
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const flat_set<typename Graph::vertex_descriptor> &s,
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typename Graph::vertex_descriptor w) {
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map<NFAVertex, boost::default_color_type> colours;
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try {
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depth_first_visit(g, w, SearchVisitor(reach),
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make_assoc_property_map(colours),
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VertexInSet<typename Graph::vertex_descriptor, Graph>(s));
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} catch (SearchFailed&) {
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return false;
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}
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return true;
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}
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static
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NFAEdge to_raw(const NFAEdge &e, const NGHolder &) {
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return e;
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}
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static
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NFAEdge to_raw(const reverse_graph<NGHolder, NGHolder &>::edge_descriptor &e,
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const reverse_graph<NGHolder, NGHolder &> &g) {
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return get(boost::edge_underlying, g, e);
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}
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/* returns true if we did stuff */
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template<class Graph>
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static
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bool removeCyclicPathRedundancy(Graph &g, typename Graph::vertex_descriptor v,
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NGHolder &raw) {
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bool did_stuff = false;
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const CharReach &reach = g[v].char_reach;
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typedef typename Graph::vertex_descriptor vertex_descriptor;
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// precalc successors of v.
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flat_set<vertex_descriptor> succ_v;
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insert(&succ_v, adjacent_vertices(v, g));
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flat_set<vertex_descriptor> s;
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for (const auto &e : in_edges_range(v, g)) {
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vertex_descriptor u = source(e, g);
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if (u == v) {
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continue;
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}
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if (is_any_accept(u, g)) {
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continue;
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}
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DEBUG_PRINTF("- checking u %zu\n", g[u].index);
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// let s be intersection(succ(u), succ(v))
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s.clear();
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for (auto b : adjacent_vertices_range(u, g)) {
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if (contains(succ_v, b)) {
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s.insert(b);
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}
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}
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for (const auto &e_u : make_vector_from(out_edges(u, g))) {
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vertex_descriptor w = target(e_u, g);
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if (is_special(w, g) || contains(s, w)) {
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continue;
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}
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const CharReach &w_reach = g[w].char_reach;
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if (!w_reach.isSubsetOf(reach)) {
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continue;
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}
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DEBUG_PRINTF(" - checking w %zu\n", g[w].index);
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if (!searchForward(g, reach, s, w)) {
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continue;
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}
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DEBUG_PRINTF("removing edge (%zu,%zu)\n", g[u].index, g[w].index);
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/* we are currently iterating over the in-edges of v, so it
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would be unwise to remove edges to v. However, */
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assert(w != v); /* as v is in s */
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remove_edge(to_raw(e_u, g), raw);
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did_stuff = true;
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}
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}
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return did_stuff;
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}
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template<class Graph>
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static
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bool cyclicPathRedundancyPass(Graph &g, NGHolder &raw) {
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bool did_stuff = false;
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for (auto v : vertices_range(g)) {
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if (is_special(v, g) || !edge(v, v, g).second) {
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continue;
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}
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DEBUG_PRINTF("examining cyclic vertex %zu\n", g[v].index);
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did_stuff |= removeCyclicPathRedundancy(g, v, raw);
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}
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return did_stuff;
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}
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bool removeCyclicPathRedundancy(NGHolder &g) {
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// Forward pass.
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bool f_changed = cyclicPathRedundancyPass(g, g);
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if (f_changed) {
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DEBUG_PRINTF("edges removed by forward pass\n");
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pruneUseless(g);
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}
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// Reverse pass.
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DEBUG_PRINTF("REVERSE PASS\n");
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typedef reverse_graph<NGHolder, NGHolder &> RevGraph;
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RevGraph revg(g);
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bool r_changed = cyclicPathRedundancyPass(revg, g);
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if (r_changed) {
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DEBUG_PRINTF("edges removed by reverse pass\n");
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pruneUseless(g);
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}
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return f_changed || r_changed;
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}
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} // namespace ue2
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