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Add new string repair heuristic (#7496)
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* Fixed spurious counterexamples in seq-sls. Updates might not be identity mapping

* Removed debug code

* One check was missing

* Trying different update generation function

* Renamed function

* Added parameter to select string update function
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@CEisenhofer
CEisenhofer authored Dec 30, 2024
1 parent e002c57 commit 19c95f8
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Showing 3 changed files with 64 additions and 14 deletions.
63 changes: 52 additions & 11 deletions src/ast/sls/sls_seq_plugin.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -95,9 +95,17 @@ Equality solving using stochastic Nelson.
#include "ast/sls/sls_seq_plugin.h"
#include "ast/sls/sls_context.h"
#include "ast/ast_pp.h"
#include "params/sls_params.hpp"


namespace sls {

struct zstring_hash_proc {
unsigned operator()(zstring const & s) const {
auto str = s.encode();
return string_hash(str.c_str(), static_cast<unsigned>(s.length()), 17);
}
};

seq_plugin::seq_plugin(context& c):
plugin(c),
Expand All @@ -107,6 +115,8 @@ namespace sls {
thrw(c.get_manager())
{
m_fid = seq.get_family_id();
sls_params p(c.get_params());
m_str_update_strategy = p.str_update_strategy() == 0 ? EDIT_CHAR : EDIT_SUBSTR;
}

void seq_plugin::propagate_literal(sat::literal lit) {
Expand Down Expand Up @@ -531,12 +541,12 @@ namespace sls {
return true;
if (len_u < val_x.length()) {
for (unsigned i = 0; i + len_u < val_x.length(); ++i)
m_str_updates.push_back({ x, val_x.extract(i, len_u), 1 });
m_str_updates.push_back({ x, val_x.extract(i, len_u), 1 });
}
if (!m_chars.empty()) {
zstring ch(m_chars[ctx.rand(m_chars.size())]);
m_str_updates.push_back({ x, val_x + ch, 1 });
m_str_updates.push_back({ x, ch + val_x, 1 });
m_str_updates.push_back({ x, ch + val_x, 1 });
}
return apply_update();
}
Expand Down Expand Up @@ -619,7 +629,7 @@ namespace sls {
if (!is_value(x))
m_str_updates.push_back({ x, strval1(y), 1 });
if (!is_value(y))
m_str_updates.push_back({ y, strval1(x), 1 });
m_str_updates.push_back({ y, strval1(x), 1 });
}
else {
// disequality
Expand Down Expand Up @@ -665,8 +675,39 @@ namespace sls {
return d[n][m];
}


void seq_plugin::add_edit_updates(ptr_vector<expr> const& w, zstring const& val, zstring const& val_other, uint_set const& chars) {
if (m_str_update_strategy == EDIT_CHAR)
add_char_edit_updates(w, val, val_other, chars);
else
add_substr_edit_updates(w, val, val_other, chars);
}

void seq_plugin::add_substr_edit_updates(ptr_vector<expr> const& w, zstring const& val, zstring const& val_other, uint_set const& chars) {
// all consecutive subsequences of val_other
hashtable<zstring, zstring_hash_proc, default_eq<zstring>> set;
set.insert(zstring(""));
for (unsigned i = 0; i < val_other.length(); ++i) {
for (unsigned j = val_other.length(); j > 0; ++j) {
zstring sub = val_other.extract(i, j);
if (set.contains(sub))
break;
set.insert(sub);
}
}

for (auto x : w) {
if (is_value(x))
continue;
zstring const& a = strval0(x);
for (auto& seq : set) {
if (seq == a)
continue;
m_str_updates.push_back({ x, seq, 1 });
}
}
}

void seq_plugin::add_char_edit_updates(ptr_vector<expr> const& w, zstring const& val, zstring const& val_other, uint_set const& chars) {
for (auto x : w) {
if (is_value(x))
continue;
Expand Down Expand Up @@ -1057,7 +1098,7 @@ namespace sls {
}
if (!is_value(xi)) {
m_str_updates.push_back({ xi, vi.extract(0, i), score });
m_str_updates.push_back({ xi, vi.extract(0, i) + zstring(vj[j]), score});
m_str_updates.push_back({ xi, vi.extract(0, i) + zstring(vj[j]), score});
}
if (!is_value(yj)) {
m_str_updates.push_back({ yj, vj.extract(0, j), score });
Expand Down Expand Up @@ -1236,7 +1277,7 @@ namespace sls {
if (!is_value(x)) {
m_str_updates.push_back({ x, zstring(), 1 });
if (lenx > r && r >= 0)
m_str_updates.push_back({ x, sx.extract(0, r.get_unsigned()), 1 });
m_str_updates.push_back({ x, sx.extract(0, r.get_unsigned()), 1 });
}
if (!m.is_value(y)) {
m_int_updates.push_back({ y, rational(lenx), 1 });
Expand Down Expand Up @@ -1287,7 +1328,7 @@ namespace sls {
if (value == -1) {
m_str_updates.push_back({ y, zstring(m_chars[ctx.rand(m_chars.size())]), 1 });
if (lenx > 0)
m_str_updates.push_back({ x, zstring(), 1 });
m_str_updates.push_back({ x, zstring(), 1 });
}
// change x:
// insert y into x at offset
Expand All @@ -1305,7 +1346,7 @@ namespace sls {
if (offset_r.is_unsigned() && 0 <= value && offset_u + value < lenx) {
unsigned offs = offset_u + value.get_unsigned();
for (unsigned i = offs; i < lenx; ++i)
m_str_updates.push_back({ y, sx.extract(offs, i - offs + 1), 1 });
m_str_updates.push_back({ y, sx.extract(offs, i - offs + 1), 1 });
}

// change offset:
Expand Down Expand Up @@ -1436,13 +1477,13 @@ namespace sls {
if (idx > 0)
su = sa.extract(0, idx);
su = su + sa.extract(idx + sb.length(), sa.length() - idx - sb.length());
m_str_updates.push_back({a, su, 1});
m_str_updates.push_back({ a, su, 1});
}
if (!m_chars.empty() && !is_value(b)) {
zstring sb1 = sb + zstring(m_chars[ctx.rand(m_chars.size())]);
zstring sb2 = zstring(m_chars[ctx.rand(m_chars.size())]) + sb;
m_str_updates.push_back({b, sb1, 1});
m_str_updates.push_back({b, sb2, 1});
m_str_updates.push_back({ b, sb1, 1});
m_str_updates.push_back({ b, sb2, 1});
}
}
return apply_update();
Expand Down
10 changes: 9 additions & 1 deletion src/ast/sls/sls_seq_plugin.h
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Original file line number Diff line number Diff line change
Expand Up @@ -42,13 +42,19 @@ namespace sls {
ptr_vector<expr> lhs, rhs;
};

enum edit_distance_strategy {
EDIT_CHAR,
EDIT_SUBSTR,
};

seq_util seq;
arith_util a;
seq_rewriter rw;
th_rewriter thrw;
scoped_ptr_vector<eval> m_values;
indexed_uint_set m_chars; // set of characters in the problem
bool m_initialized = false;
bool m_initialized = false;
edit_distance_strategy m_str_update_strategy;

struct str_update {
expr* e;
Expand Down Expand Up @@ -122,6 +128,8 @@ namespace sls {
unsigned edit_distance_with_updates(string_instance const& a, string_instance const& b);
unsigned edit_distance(zstring const& a, zstring const& b);
void add_edit_updates(ptr_vector<expr> const& w, zstring const& val, zstring const& val_other, uint_set const& chars);
void add_char_edit_updates(ptr_vector<expr> const& w, zstring const& val, zstring const& val_other, uint_set const& chars);
void add_substr_edit_updates(ptr_vector<expr> const& w, zstring const& val, zstring const& val_other, uint_set const& chars);

// regex functionality

Expand Down
5 changes: 3 additions & 2 deletions src/params/sls_params.pyg
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ def_module_params('sls',
description='Experimental Stochastic Local Search Solver (for QFBV only).',
params=(max_memory_param(),
('max_restarts', UINT, UINT_MAX, 'maximum number of restarts'),
('max_repairs', UINT, 1000, 'maximum number of repairs before restart'),
('max_repairs', UINT, 1000, 'maximum number of repairs before restart'),
('walksat', BOOL, 1, 'use walksat assertion selection (instead of gsat)'),
('walksat_ucb', BOOL, 1, 'use bandit heuristic for walksat assertion selection (instead of random)'),
('walksat_ucb_constant', DOUBLE, 20.0, 'the ucb constant c in the term score + c * f(touched)'),
Expand All @@ -24,5 +24,6 @@ def_module_params('sls',
('rescore', BOOL, 1, 'rescore/normalize top-level score every base restart interval'),
('dt_axiomatic', BOOL, True, 'use axiomatic mode or model reduction for datatype solver'),
('track_unsat', BOOL, 0, 'keep a list of unsat assertions as done in SAT - currently disabled internally'),
('random_seed', UINT, 0, 'random seed')
('random_seed', UINT, 0, 'random seed'),
('str_update_strategy', UINT, 1, 'string update candidate selection: 0 - single character based update, 1 - subsequence based update')
))

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