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fix co-factoring

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-12-14 10:01:53 -08:00
parent f40becf099
commit 5348af3c4c
2 changed files with 95 additions and 29 deletions
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120
src/smt/seq_regex.cpp
View file

@ -19,6 +19,9 @@ Author:
#include "smt/seq_regex.h"
#include "smt/theory_seq.h"
#include "ast/expr_abstract.h"
#include "ast/ast_util.h"
#include "ast/for_each_expr.h"
#include <ast/rewriter/expr_safe_replace.h>
namespace smt {
@ -533,7 +536,62 @@ namespace smt {
return true;
}
return r == u;
}
}
/**
* is_non_empty(r, u) => nullable or \/_i (c_i and is_non_empty(r_i, u union r))
*
* for each (c_i, r_i) in cofactors (min-terms)
*
* is_non_empty(r_i, u union r) := false if r_i in u
*
*/
void seq_regex::propagate_is_non_empty(literal lit) {
expr* e = ctx.bool_var2expr(lit.var()), *r = nullptr, *u = nullptr, *n = nullptr;
VERIFY(sk().is_is_non_empty(e, r, u, n));
if (block_if_empty(r, lit))
return;
TRACE("seq_regex", tout << "propagate nonempty: " << mk_pp(e, m) << std::endl;);
STRACE("seq_regex_brief", tout
<< std::endl << "PNE(" << expr_id_str(e) << "," << state_str(r)
<< "," << expr_id_str(u) << "," << expr_id_str(n) << ") ";);
expr_ref is_nullable = is_nullable_wrapper(r);
if (m.is_true(is_nullable))
return;
literal null_lit = th.mk_literal(is_nullable);
expr_ref hd = mk_first(r, n);
expr_ref d(m);
d = mk_derivative_wrapper(hd, r);
literal_vector lits;
lits.push_back(~lit);
if (null_lit != false_literal)
lits.push_back(null_lit);
expr_ref_pair_vector cofactors(m);
get_cofactors(d, cofactors);
for (auto const& p : cofactors) {
if (is_member(p.second, u))
continue;
expr_ref cond(p.first, m);
seq_rw().elim_condition(hd, cond);
rewrite(cond);
if (m.is_false(cond))
continue;
expr_ref next_non_empty = sk().mk_is_non_empty(p.second, re().mk_union(u, p.second), n);
if (!m.is_true(cond))
next_non_empty = m.mk_and(cond, next_non_empty);
lits.push_back(th.mk_literal(next_non_empty));
}
th.add_axiom(lits);
}
/*
Given a string s, index i, and a derivative r, return an
@ -681,39 +739,47 @@ namespace smt {
Return a list of all (cond, leaf) pairs in a given derivative
expression r.
Note: this recursive implementation is inefficient, since if nodes
are repeated often in the expression DAG, they may be visited
many times. For this reason, prefer mk_deriv_accept and
get_all_derivatives when possible.
Note: this implementation is inefficient: it simply collects all expressions under an if and
iterates over all combinations.
This method is still used by:
propagate_is_empty
propagate_is_non_empty
*/
void seq_regex::get_cofactors(expr* r, expr_ref_pair_vector& result) {
expr_ref_vector conds(m);
get_cofactors_rec(r, conds, result);
STRACE("seq_regex", tout << "Number of derivatives: "
<< result.size() << std::endl;);
STRACE("seq_regex_brief", tout << "#derivs=" << result.size() << " ";);
}
void seq_regex::get_cofactors_rec(expr* r, expr_ref_vector& conds,
expr_ref_pair_vector& result) {
expr* cond = nullptr, *r1 = nullptr, *r2 = nullptr;
if (m.is_ite(r, cond, r1, r2)) {
conds.push_back(cond);
get_cofactors_rec(r1, conds, result);
conds.pop_back();
conds.push_back(mk_not(m, cond));
get_cofactors_rec(r2, conds, result);
conds.pop_back();
obj_hashtable<expr> ifs;
expr* cond = nullptr, * r1 = nullptr, * r2 = nullptr;
for (expr* e : subterms::ground(expr_ref(r, m)))
if (m.is_ite(e, cond, r1, r2))
ifs.insert(cond);
expr_ref_vector rs(m);
vector<expr_ref_vector> conds;
conds.push_back(expr_ref_vector(m));
rs.push_back(r);
for (expr* c : ifs) {
unsigned sz = conds.size();
expr_safe_replace rep1(m);
expr_safe_replace rep2(m);
rep1.insert(c, m.mk_true());
rep2.insert(c, m.mk_false());
expr_ref r2(m);
for (unsigned i = 0; i < sz; ++i) {
expr_ref_vector cs = conds[i];
cs.push_back(mk_not(m, c));
conds.push_back(cs);
conds[i].push_back(c);
expr_ref r1(rs.get(i), m);
rep1(r1, r2);
rs[i] = r2;
rep2(r1, r2);
rs.push_back(r2);
}
}
else if (re().is_union(r, r1, r2)) {
get_cofactors_rec(r1, conds, result);
get_cofactors_rec(r2, conds, result);
}
else {
expr_ref conj = mk_and(conds);
for (unsigned i = 0; i < conds.size(); ++i) {
expr_ref conj = mk_and(conds[i]);
expr_ref r(rs.get(i), m);
ctx.get_rewriter()(r);
if (!m.is_false(conj) && !re().is_empty(r))
result.push_back(conj, r);
}

4
src/smt/seq_regex.h
View file

@ -165,8 +165,6 @@ namespace smt {
expr_ref mk_deriv_accept(expr* s, unsigned i, expr* r);
void get_derivative_targets(expr* r, expr_ref_vector& targets);
void get_cofactors(expr* r, expr_ref_pair_vector& result);
void get_cofactors_rec(expr* r, expr_ref_vector& conds,
expr_ref_pair_vector& result);
/*
Pretty print the regex of the state id to the out stream,
@ -186,6 +184,8 @@ namespace smt {
bool block_if_empty(expr* r, literal lit);
void propagate_is_non_empty(literal lit);
public:
seq_regex(theory_seq& th);