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fix co-factoring
Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner
parent
f40becf099
commit
5348af3c4c
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@ -19,6 +19,9 @@ Author:
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#include "smt/seq_regex.h"
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#include "smt/theory_seq.h"
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#include "ast/expr_abstract.h"
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#include "ast/ast_util.h"
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#include "ast/for_each_expr.h"
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#include <ast/rewriter/expr_safe_replace.h>
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namespace smt {
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@ -533,7 +536,62 @@ namespace smt {
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return true;
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}
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return r == u;
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}
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}
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/**
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* is_non_empty(r, u) => nullable or \/_i (c_i and is_non_empty(r_i, u union r))
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*
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* for each (c_i, r_i) in cofactors (min-terms)
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*
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* is_non_empty(r_i, u union r) := false if r_i in u
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*
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*/
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void seq_regex::propagate_is_non_empty(literal lit) {
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expr* e = ctx.bool_var2expr(lit.var()), *r = nullptr, *u = nullptr, *n = nullptr;
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VERIFY(sk().is_is_non_empty(e, r, u, n));
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if (block_if_empty(r, lit))
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return;
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TRACE("seq_regex", tout << "propagate nonempty: " << mk_pp(e, m) << std::endl;);
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STRACE("seq_regex_brief", tout
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<< std::endl << "PNE(" << expr_id_str(e) << "," << state_str(r)
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<< "," << expr_id_str(u) << "," << expr_id_str(n) << ") ";);
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expr_ref is_nullable = is_nullable_wrapper(r);
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if (m.is_true(is_nullable))
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return;
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literal null_lit = th.mk_literal(is_nullable);
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expr_ref hd = mk_first(r, n);
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expr_ref d(m);
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d = mk_derivative_wrapper(hd, r);
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literal_vector lits;
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lits.push_back(~lit);
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if (null_lit != false_literal)
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lits.push_back(null_lit);
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expr_ref_pair_vector cofactors(m);
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get_cofactors(d, cofactors);
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for (auto const& p : cofactors) {
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if (is_member(p.second, u))
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continue;
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expr_ref cond(p.first, m);
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seq_rw().elim_condition(hd, cond);
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rewrite(cond);
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if (m.is_false(cond))
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continue;
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expr_ref next_non_empty = sk().mk_is_non_empty(p.second, re().mk_union(u, p.second), n);
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if (!m.is_true(cond))
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next_non_empty = m.mk_and(cond, next_non_empty);
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lits.push_back(th.mk_literal(next_non_empty));
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}
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th.add_axiom(lits);
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}
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/*
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Given a string s, index i, and a derivative r, return an
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@ -681,39 +739,47 @@ namespace smt {
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Return a list of all (cond, leaf) pairs in a given derivative
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expression r.
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Note: this recursive implementation is inefficient, since if nodes
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are repeated often in the expression DAG, they may be visited
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many times. For this reason, prefer mk_deriv_accept and
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get_all_derivatives when possible.
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Note: this implementation is inefficient: it simply collects all expressions under an if and
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iterates over all combinations.
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This method is still used by:
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propagate_is_empty
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propagate_is_non_empty
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*/
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void seq_regex::get_cofactors(expr* r, expr_ref_pair_vector& result) {
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expr_ref_vector conds(m);
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get_cofactors_rec(r, conds, result);
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STRACE("seq_regex", tout << "Number of derivatives: "
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<< result.size() << std::endl;);
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STRACE("seq_regex_brief", tout << "#derivs=" << result.size() << " ";);
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}
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void seq_regex::get_cofactors_rec(expr* r, expr_ref_vector& conds,
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expr_ref_pair_vector& result) {
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expr* cond = nullptr, *r1 = nullptr, *r2 = nullptr;
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if (m.is_ite(r, cond, r1, r2)) {
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conds.push_back(cond);
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get_cofactors_rec(r1, conds, result);
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conds.pop_back();
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conds.push_back(mk_not(m, cond));
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get_cofactors_rec(r2, conds, result);
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conds.pop_back();
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obj_hashtable<expr> ifs;
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expr* cond = nullptr, * r1 = nullptr, * r2 = nullptr;
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for (expr* e : subterms::ground(expr_ref(r, m)))
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if (m.is_ite(e, cond, r1, r2))
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ifs.insert(cond);
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expr_ref_vector rs(m);
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vector<expr_ref_vector> conds;
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conds.push_back(expr_ref_vector(m));
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rs.push_back(r);
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for (expr* c : ifs) {
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unsigned sz = conds.size();
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expr_safe_replace rep1(m);
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expr_safe_replace rep2(m);
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rep1.insert(c, m.mk_true());
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rep2.insert(c, m.mk_false());
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expr_ref r2(m);
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for (unsigned i = 0; i < sz; ++i) {
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expr_ref_vector cs = conds[i];
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cs.push_back(mk_not(m, c));
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conds.push_back(cs);
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conds[i].push_back(c);
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expr_ref r1(rs.get(i), m);
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rep1(r1, r2);
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rs[i] = r2;
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rep2(r1, r2);
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rs.push_back(r2);
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}
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}
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else if (re().is_union(r, r1, r2)) {
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get_cofactors_rec(r1, conds, result);
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get_cofactors_rec(r2, conds, result);
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}
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else {
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expr_ref conj = mk_and(conds);
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for (unsigned i = 0; i < conds.size(); ++i) {
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expr_ref conj = mk_and(conds[i]);
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expr_ref r(rs.get(i), m);
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ctx.get_rewriter()(r);
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if (!m.is_false(conj) && !re().is_empty(r))
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result.push_back(conj, r);
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}
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@ -165,8 +165,6 @@ namespace smt {
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expr_ref mk_deriv_accept(expr* s, unsigned i, expr* r);
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void get_derivative_targets(expr* r, expr_ref_vector& targets);
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void get_cofactors(expr* r, expr_ref_pair_vector& result);
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void get_cofactors_rec(expr* r, expr_ref_vector& conds,
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expr_ref_pair_vector& result);
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/*
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Pretty print the regex of the state id to the out stream,
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@ -186,6 +184,8 @@ namespace smt {
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bool block_if_empty(expr* r, literal lit);
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void propagate_is_non_empty(literal lit);
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public:
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seq_regex(theory_seq& th);
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