forked from qingkaishi/z3
-
Notifications
You must be signed in to change notification settings - Fork 0
/
sat_scc.cpp
278 lines (246 loc) · 10.1 KB
/
sat_scc.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
/*++
Copyright (c) 2011 Microsoft Corporation
Module Name:
sat_scc.cpp
Abstract:
Use binary clauses to compute strongly connected components.
Author:
Leonardo de Moura (leonardo) 2011-05-26.
Revision History:
--*/
#include "sat/sat_scc.h"
#include "sat/sat_solver.h"
#include "sat/sat_elim_eqs.h"
#include "util/stopwatch.h"
#include "util/trace.h"
#include "sat/sat_scc_params.hpp"
namespace sat {
scc::scc(solver & s, params_ref const & p):
m_solver(s),
m_big(s.m_rand) {
reset_statistics();
updt_params(p);
}
struct frame {
unsigned m_lidx;
unsigned m_succ_idx;
bool m_first;
watched * m_it;
watched * m_end;
frame(unsigned lidx, watched * it, watched * end, unsigned sidx = 0):m_lidx(lidx), m_succ_idx(sidx), m_first(true), m_it(it), m_end(end) {}
};
typedef svector<frame> frames;
struct scc::report {
scc & m_scc;
stopwatch m_watch;
unsigned m_num_elim;
unsigned m_num_elim_bin;
unsigned m_trail_size;
report(scc & c):
m_scc(c),
m_num_elim(c.m_num_elim),
m_num_elim_bin(c.m_num_elim_bin),
m_trail_size(c.m_solver.init_trail_size()) {
m_watch.start();
}
~report() {
m_watch.stop();
unsigned elim_bin = m_scc.m_num_elim_bin - m_num_elim_bin;
unsigned num_units = m_scc.m_solver.init_trail_size() - m_trail_size;
IF_VERBOSE(2,
verbose_stream() << " (sat-scc :elim-vars " << (m_scc.m_num_elim - m_num_elim);
if (elim_bin > 0) verbose_stream() << " :elim-bin " << elim_bin;
if (num_units > 0) verbose_stream() << " :units " << num_units;
verbose_stream() << m_watch << ")\n";);
}
};
unsigned scc::operator()() {
if (m_solver.m_inconsistent)
return 0;
if (!m_scc)
return 0;
CASSERT("scc_bug", m_solver.check_invariant());
report rpt(*this);
TRACE("scc", m_solver.display(tout););
TRACE("scc_details", m_solver.display_watches(tout););
unsigned_vector index;
unsigned_vector lowlink;
unsigned_vector s;
svector<char> in_s;
unsigned num_lits = m_solver.num_vars() * 2;
index.resize(num_lits, UINT_MAX);
lowlink.resize(num_lits, UINT_MAX);
in_s.resize(num_lits, false);
literal_vector roots, lits;
roots.resize(m_solver.num_vars(), null_literal);
unsigned next_index = 0;
svector<frame> frames;
bool_var_vector to_elim;
for (unsigned l_idx = 0; l_idx < num_lits; l_idx++) {
if (index[l_idx] != UINT_MAX)
continue;
if (m_solver.was_eliminated(to_literal(l_idx).var()))
continue;
m_solver.checkpoint();
#define NEW_NODE(LIDX) { \
index[LIDX] = next_index; \
lowlink[LIDX] = next_index; \
next_index++; \
s.push_back(LIDX); \
in_s[LIDX] = true; \
watch_list & wlist = m_solver.get_wlist(LIDX); \
frames.push_back(frame(LIDX, wlist.begin(), wlist.end())); \
}
NEW_NODE(l_idx);
while (!frames.empty()) {
loop:
frame & fr = frames.back();
unsigned l_idx = fr.m_lidx;
if (!fr.m_first) {
SASSERT(fr.m_it->is_binary_clause());
// after visiting child
literal l2 = fr.m_it->get_literal();
unsigned l2_idx = l2.index();
SASSERT(index[l2_idx] != UINT_MAX);
if (lowlink[l2_idx] < lowlink[l_idx])
lowlink[l_idx] = lowlink[l2_idx];
fr.m_it++;
}
fr.m_first = false;
while (fr.m_it != fr.m_end) {
if (!fr.m_it->is_binary_clause()) {
fr.m_it++;
continue;
}
literal l2 = fr.m_it->get_literal();
unsigned l2_idx = l2.index();
if (index[l2_idx] == UINT_MAX) {
NEW_NODE(l2_idx);
goto loop;
}
else if (in_s[l2_idx]) {
if (index[l2_idx] < lowlink[l_idx])
lowlink[l_idx] = index[l2_idx];
}
fr.m_it++;
}
// visited all successors
if (lowlink[l_idx] == index[l_idx]) {
// found new SCC
CTRACE("scc_cycle", s.back() != l_idx, {
tout << "cycle: ";
unsigned j = s.size() - 1;
unsigned l2_idx;
do {
l2_idx = s[j];
j--;
tout << to_literal(l2_idx) << " ";
} while (l2_idx != l_idx);
tout << "\n";
});
SASSERT(!s.empty());
literal l = to_literal(l_idx);
bool_var v = l.var();
if (roots[v] != null_literal) {
// variable was already assigned... just consume stack
TRACE("scc_detail", tout << "consuming stack...\n";);
unsigned l2_idx;
do {
l2_idx = s.back();
s.pop_back();
in_s[l2_idx] = false;
SASSERT(roots[to_literal(l2_idx).var()].var() == roots[v].var());
} while (l2_idx != l_idx);
}
else {
// check if the SCC has an external variable, and check for conflicts
TRACE("scc_detail", tout << "assigning roots...\n";);
literal r = null_literal;
unsigned j = s.size() - 1;
unsigned l2_idx;
do {
l2_idx = s[j];
j--;
if (to_literal(l2_idx) == ~l) {
m_solver.set_conflict();
return 0;
}
if (m_solver.is_external(to_literal(l2_idx).var())) {
r = to_literal(l2_idx);
break;
}
} while (l2_idx != l_idx);
if (r == null_literal) {
// SCC does not contain external variable
r = to_literal(l_idx);
}
TRACE("scc_detail", tout << "r: " << r << "\n";);
do {
l2_idx = s.back();
s.pop_back();
in_s[l2_idx] = false;
literal l2 = to_literal(l2_idx);
bool_var v2 = l2.var();
if (roots[v2] == null_literal) {
if (l2.sign()) {
roots[v2] = ~r;
}
else {
roots[v2] = r;
}
if (v2 != r.var())
to_elim.push_back(v2);
}
} while (l2_idx != l_idx);
}
}
frames.pop_back();
}
}
for (unsigned i = 0; i < m_solver.num_vars(); ++i) {
if (roots[i] == null_literal) {
roots[i] = literal(i, false);
}
}
TRACE("scc", for (unsigned i = 0; i < roots.size(); i++) { tout << i << " -> " << roots[i] << "\n"; }
tout << "to_elim: "; for (unsigned v : to_elim) tout << v << " "; tout << "\n";);
m_num_elim += to_elim.size();
elim_eqs eliminator(m_solver);
eliminator(roots, to_elim);
TRACE("scc_detail", m_solver.display(tout););
CASSERT("scc_bug", m_solver.check_invariant());
if (m_scc_tr) {
reduce_tr();
}
TRACE("scc_detail", m_solver.display(tout););
return to_elim.size();
}
unsigned scc::reduce_tr(bool learned) {
init_big(learned);
unsigned num_elim = m_big.reduce_tr(m_solver);
m_num_elim_bin += num_elim;
return num_elim;
}
void scc::reduce_tr() {
unsigned quota = 0, num_reduced = 0, count = 0;
while ((num_reduced = reduce_tr(false)) > quota && count++ < 10) { quota = std::max(100u, num_reduced / 2); }
quota = 0; count = 0;
while ((num_reduced = reduce_tr(true)) > quota && count++ < 10) { quota = std::max(100u, num_reduced / 2); }
}
void scc::collect_statistics(statistics & st) const {
st.update("sat scc elim vars", m_num_elim);
st.update("sat scc elim binary", m_num_elim_bin);
}
void scc::reset_statistics() {
m_num_elim = 0;
m_num_elim_bin = 0;
}
void scc::updt_params(params_ref const & _p) {
sat_scc_params p(_p);
m_scc = p.scc();
m_scc_tr = p.scc_tr();
}
void scc::collect_param_descrs(param_descrs & d) {
sat_scc_params::collect_param_descrs(d);
}
};