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Move seq axioms to theory independent module

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This commit is contained in:
Nikolaj Bjorner 2021-02-16 05:13:52 -08:00
parent 823830181b
commit 4f9117a921
5 changed files with 1112 additions and 81 deletions
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1
src/ast/rewriter/CMakeLists.txt
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@ -32,6 +32,7 @@ z3_add_component(rewriter
quant_hoist.cpp
recfun_rewriter.cpp
rewriter.cpp
seq_axioms.cpp
seq_rewriter.cpp
seq_skolem.cpp
th_rewriter.cpp

951
src/ast/rewriter/seq_axioms.cpp Normal file
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@ -0,0 +1,951 @@
/*++
Copyright (c) 2011 Microsoft Corporation
Module Name:
seq_axioms.cpp
Abstract:
Axiomatize string operations that can be reduced to
more basic operations. These axioms are kept outside
of a particular solver: they are mainly solver independent.
Author:
Nikolaj Bjorner (nbjorner) 2020-4-16
Revision History:
--*/
#include "ast/ast_pp.h"
#include "ast/ast_ll_pp.h"
#include "ast/rewriter/seq_axioms.h"
namespace seq {
axioms::axioms(th_rewriter& r):
m_rewrite(r),
m(r.m()),
a(m),
seq(m),
m_sk(m, r),
m_clause(m)
{}
expr_ref axioms::mk_sub(expr* x, expr* y) {
expr_ref result(a.mk_sub(x, y), m);
m_rewrite(result);
return result;
}
expr_ref axioms::purify(expr* e) {
if (!e)
return expr_ref(m);
if (get_depth(e) == 1)
return expr_ref(e, m);
expr_ref p = expr_ref(m.mk_fresh_const("seq.purify", e->get_sort()), m);
add_clause(mk_eq(p, e));
return expr_ref(p, m);
}
expr_ref axioms::mk_len(expr* s) {
expr_ref result(seq.str.mk_length(s), m);
m_rewrite(result);
return result;
}
void axioms::add_clause(expr_ref const& a) {
m_clause.reset();
m_clause.push_back(a);
m_add_clause(m_clause);
}
void axioms::add_clause(expr_ref const& a, expr_ref const& b) {
m_clause.reset();
m_clause.push_back(a);
m_clause.push_back(b);
m_add_clause(m_clause);
}
void axioms::add_clause(expr_ref const& a, expr_ref const& b, expr_ref const& c) {
m_clause.reset();
m_clause.push_back(a);
m_clause.push_back(b);
m_clause.push_back(c);
m_add_clause(m_clause);
}
void axioms::add_clause(expr_ref const& a, expr_ref const& b, expr_ref const& c, expr_ref const & d) {
m_clause.reset();
m_clause.push_back(a);
m_clause.push_back(b);
m_clause.push_back(c);
m_clause.push_back(d);
m_add_clause(m_clause);
}
void axioms::add_clause(expr_ref const& a, expr_ref const& b, expr_ref const& c, expr_ref const & d, expr_ref const& e) {
m_clause.reset();
m_clause.push_back(a);
m_clause.push_back(b);
m_clause.push_back(c);
m_clause.push_back(d);
m_clause.push_back(e);
m_add_clause(m_clause);
}
/***
let e = extract(s, i, l)
i is start index, l is length of substring starting at index.
i < 0 => e = ""
i >= |s| => e = ""
l <= 0 => e = ""
0 <= i < |s| & l > 0 => s = xey, |x| = i, |e| = min(l, |s|-i)
l <= 0 => e = ""
this translates to:
0 <= i <= |s| -> s = xey
0 <= i <= |s| -> len(x) = i
0 <= i <= |s| & 0 <= l <= |s| - i -> |e| = l
0 <= i <= |s| & |s| < l + i -> |e| = |s| - i
|e| = 0 <=> i < 0 | |s| <= i | l <= 0 | |s| <= 0
It follows that:
|e| = min(l, |s| - i) for 0 <= i < |s| and 0 < |l|
*/
void axioms::extract_axiom(expr* e) {
TRACE("seq", tout << mk_pp(e, m) << "\n";);
expr* _s = nullptr, *_i = nullptr, *_l = nullptr;
VERIFY(seq.str.is_extract(e, _s, _i, _l));
auto s = purify(_s);
auto i = purify(_i);
auto l = purify(_l);
if (is_tail(s, i, l)) {
tail_axiom(e, s);
return;
}
if (is_drop_last(s, i, l)) {
drop_last_axiom(e, s);
return;
}
if (is_extract_prefix0(s, i, l)) {
extract_prefix_axiom(e, s, l);
return;
}
expr_ref x = m_sk.mk_pre(s, i);
expr_ref ls = mk_len(s);
expr_ref lx = mk_len(x);
expr_ref le = mk_len(e);
expr_ref ls_minus_i_l(mk_sub(mk_sub(ls, i), l), m);
expr_ref y = m_sk.mk_post(s, a.mk_add(i, l));
expr_ref xe = mk_concat(x, e);
expr_ref xey = mk_concat(x, e, y);
expr_ref zero(a.mk_int(0), m);
expr_ref i_ge_0 = mk_ge(i, 0);
expr_ref i_le_ls = mk_le(mk_sub(i, ls), 0);
expr_ref ls_le_i = mk_le(mk_sub(ls, i), 0);
expr_ref ls_ge_li = mk_ge(ls_minus_i_l, 0);
expr_ref l_ge_0 = mk_ge(l, 0);
expr_ref l_le_0 = mk_le(l, 0);
expr_ref ls_le_0 = mk_le(ls, 0);
expr_ref le_is_0 = mk_eq(le, zero);
// 0 <= i & i <= |s| & 0 <= l => xey = s
// 0 <= i & i <= |s| => |x| = i
// 0 <= i & i <= |s| & l >= 0 & |s| >= l + i => |e| = l
// 0 <= i & i <= |s| & |s| < l + i => |e| = |s| - i
// i < 0 => |e| = 0
// |s| <= i => |e| = 0
// |s| <= 0 => |e| = 0
// l <= 0 => |e| = 0
// |e| = 0 & i >= 0 & |s| > i & |s| > 0 => l <= 0
add_clause(~i_ge_0, ~i_le_ls, ~l_ge_0, mk_seq_eq(xey, s));
add_clause(~i_ge_0, ~i_le_ls, mk_eq(lx, i));
add_clause(~i_ge_0, ~i_le_ls, ~l_ge_0, ~ls_ge_li, mk_eq(le, l));
add_clause(~i_ge_0, ~i_le_ls, ~l_ge_0, ls_ge_li, mk_eq(le, mk_sub(ls, i)));
add_clause(i_ge_0, le_is_0);
add_clause(~ls_le_i, le_is_0);
add_clause(~ls_le_0, le_is_0);
add_clause(~l_le_0, le_is_0);
add_clause(~le_is_0, ~i_ge_0, ls_le_i, ls_le_0, l_le_0);
}
void axioms::tail_axiom(expr* e, expr* s) {
expr_ref head(m), tail(m);
m_sk.decompose(s, head, tail);
TRACE("seq", tout << "tail " << mk_bounded_pp(e, m, 2) << " " << mk_bounded_pp(s, m, 2) << "\n";);
expr_ref emp = mk_eq_empty(s);
add_clause(emp, mk_seq_eq(s, mk_concat(head, e)));
add_clause(~emp, mk_eq_empty(e));
}
void axioms::drop_last_axiom(expr* e, expr* s) {
TRACE("seq", tout << "drop last " << mk_bounded_pp(e, m, 2) << " " << mk_bounded_pp(s, m, 2) << "\n";);
expr_ref emp = mk_eq_empty(s);
add_clause(emp, mk_seq_eq(s, mk_concat(e, seq.str.mk_unit(m_sk.mk_last(s)))));
add_clause(~emp, mk_eq_empty(e));
}
bool axioms::is_drop_last(expr* s, expr* i, expr* l) {
rational i1;
if (!a.is_numeral(i, i1) || !i1.is_zero()) {
return false;
}
expr_ref l2(m), l1(l, m);
l2 = mk_sub(mk_len(s), a.mk_int(1));
m_rewrite(l1);
m_rewrite(l2);
return l1 == l2;
}
bool axioms::is_tail(expr* s, expr* i, expr* l) {
rational i1;
if (!a.is_numeral(i, i1) || !i1.is_one()) {
return false;
}
expr_ref l2(m), l1(l, m);
l2 = mk_sub(mk_len(s), a.mk_int(1));
m_rewrite(l1);
m_rewrite(l2);
return l1 == l2;
}
bool axioms::is_extract_prefix0(expr* s, expr* i, expr* l) {
rational i1;
return a.is_numeral(i, i1) && i1.is_zero();
}
/*
s = ey
l <= 0 => e = empty
0 <= l <= len(s) => len(e) = l
len(s) < l => e = s
*/
void axioms::extract_prefix_axiom(expr* e, expr* s, expr* l) {
TRACE("seq", tout << "prefix " << mk_bounded_pp(e, m, 2) << " " << mk_bounded_pp(s, m, 2) << " " << mk_bounded_pp(l, m, 2) << "\n";);
expr_ref le = mk_len(e);
expr_ref ls = mk_len(s);
expr_ref ls_minus_l(mk_sub(ls, l), m);
expr_ref y = m_sk.mk_post(s, l);
expr_ref ey = mk_concat(e, y);
expr_ref l_le_s = mk_le(mk_sub(l, ls), 0);
add_clause(mk_seq_eq(s, ey));
add_clause(~mk_le(l, 0), mk_eq_empty(e));
add_clause(~mk_ge(l, 0), ~l_le_s, mk_eq(le, l));
add_clause(l_le_s, mk_eq(e, s));
}
/*
encode that s is not contained in of xs1
where s1 is all of s, except the last element.
s = "" or s = s1*(unit c)
s = "" or !contains(x*s1, s)
*/
void axioms::tightest_prefix(expr* s, expr* x) {
expr_ref s_eq_emp = mk_eq_empty(s);
if (seq.str.max_length(s) <= 1) {
add_clause(s_eq_emp, ~expr_ref(seq.str.mk_contains(x, s), m));
return;
}
expr_ref s1 = m_sk.mk_first(s);
expr_ref c = m_sk.mk_last(s);
expr_ref s1c = mk_concat(s1, seq.str.mk_unit(c));
add_clause(s_eq_emp, mk_seq_eq(s, s1c));
add_clause(s_eq_emp, ~expr_ref(seq.str.mk_contains(mk_concat(x, s1), s), m));
}
/*
[[str.indexof]](w, w2, i) is the smallest n such that for some some w1, w3
- w = w1w2w3
- i <= n = |w1|
if [[str.contains]](w, w2) = true, |w2| > 0 and i >= 0.
[[str.indexof]](w,w2,i) = -1 otherwise.
let i = Index(t, s, offset):
// index of s in t starting at offset.
|t| = 0 => |s| = 0 or indexof(t,s,offset) = -1
|t| = 0 & |s| = 0 => indexof(t,s,offset) = 0
offset >= len(t) => |s| = 0 or i = -1
len(t) != 0 & !contains(t, s) => i = -1
offset = 0 & len(t) != 0 & contains(t, s) => t = xsy & i = len(x)
tightest_prefix(x, s)
0 <= offset < len(t) => xy = t &
len(x) = offset &
(-1 = indexof(y, s, 0) => -1 = i) &
(indexof(y, s, 0) >= 0 => indexof(t, s, 0) + offset = i)
offset < 0 => i = -1
optional lemmas:
(len(s) > len(t) -> i = -1)
(len(s) <= len(t) -> i <= len(t)-len(s))
*/
void axioms::indexof_axiom(expr* i) {
expr* _s = nullptr, *_t = nullptr, *_offset = nullptr;
rational r;
VERIFY(seq.str.is_index(i, _t, _s) ||
seq.str.is_index(i, _t, _s, _offset));
expr_ref minus_one(a.mk_int(-1), m);
expr_ref zero(a.mk_int(0), m);
auto offset = purify(_offset);
auto s = purify(_s);
auto t = purify(_t);
expr_ref xsy(m);
expr_ref cnt(seq.str.mk_contains(t, s), m);
expr_ref i_eq_m1 = mk_eq(i, minus_one);
expr_ref i_eq_0 = mk_eq(i, zero);
expr_ref s_eq_empty = mk_eq_empty(s);
expr_ref t_eq_empty = mk_eq_empty(t);
// |t| = 0 => |s| = 0 or indexof(t,s,offset) = -1
// ~contains(t,s) <=> indexof(t,s,offset) = -1
add_clause(cnt, i_eq_m1);
add_clause(~t_eq_empty, s_eq_empty, i_eq_m1);
if (!offset || (a.is_numeral(offset, r) && r.is_zero())) {
// |s| = 0 => indexof(t,s,0) = 0
add_clause(~s_eq_empty, i_eq_0);
#if 1
expr_ref x = m_sk.mk_indexof_left(t, s);
expr_ref y = m_sk.mk_indexof_right(t, s);
xsy = mk_concat(x, s, y);
expr_ref lenx = mk_len(x);
// contains(t,s) & |s| != 0 => t = xsy & indexof(t,s,0) = |x|
add_clause(~cnt, s_eq_empty, mk_seq_eq(t, xsy));
add_clause(~cnt, s_eq_empty, mk_eq(i, lenx));
add_clause(~cnt, mk_ge(i, 0));
tightest_prefix(s, x);
#else
// let i := indexof(t,s,0)
// contains(t, s) & |s| != 0 => ~contains(substr(t,0,i+len(s)-1), s)
// => substr(t,0,i+len(s)) = substr(t,0,i) ++ s
//
expr_ref len_s = mk_len(s);
expr_ref mone(a.mk_int(-1), m);
add_clause(~cnt, s_eq_empty, ~mk_literal(seq.str.mk_contains(seq.str.mk_substr(t,zero,a.mk_add(i,len_s,mone)),s)));
add_clause(~cnt, s_eq_empty, mk_seq_eq(seq.str.mk_substr(t,zero,a.mk_add(i,len_s)),
seq.str.mk_concat(seq.str.mk_substr(t,zero,i), s)));
#endif
}
else {
// offset >= len(t) => |s| = 0 or indexof(t, s, offset) = -1
// offset > len(t) => indexof(t, s, offset) = -1
// offset = len(t) & |s| = 0 => indexof(t, s, offset) = offset
expr_ref len_t = mk_len(t);
expr_ref offset_ge_len = mk_ge(mk_sub(offset, len_t), 0);
expr_ref offset_le_len = mk_le(mk_sub(offset, len_t), 0);
expr_ref i_eq_offset = mk_eq(i, offset);
add_clause(~offset_ge_len, s_eq_empty, i_eq_m1);
add_clause(offset_le_len, i_eq_m1);
add_clause(~offset_ge_len, ~offset_le_len, ~s_eq_empty, i_eq_offset);
expr_ref x = m_sk.mk_indexof_left(t, s, offset);
expr_ref y = m_sk.mk_indexof_right(t, s, offset);
expr_ref indexof0(seq.str.mk_index(y, s, zero), m);
expr_ref offset_p_indexof0(a.mk_add(offset, indexof0), m);
expr_ref offset_ge_0 = mk_ge(offset, 0);
// 0 <= offset & offset < len(t) => t = xy
// 0 <= offset & offset < len(t) => len(x) = offset
// 0 <= offset & offset < len(t) & indexof(y,s,0) = -1 => -1 = i
// 0 <= offset & offset < len(t) & indexof(y,s,0) >= 0 =>
// -1 = indexof(y,s,0) + offset = indexof(t, s, offset)
add_clause(~offset_ge_0, offset_ge_len, mk_seq_eq(t, mk_concat(x, y)));
add_clause(~offset_ge_0, offset_ge_len, mk_eq(mk_len(x), offset));
add_clause(~offset_ge_0, offset_ge_len,
~mk_eq(indexof0, minus_one), i_eq_m1);
add_clause(~offset_ge_0, offset_ge_len,
~mk_ge(indexof0, 0),
mk_eq(offset_p_indexof0, i));
// offset < 0 => -1 = i
add_clause(offset_ge_0, i_eq_m1);
}
}
/**
!contains(t, s) => i = -1
|t| = 0 => |s| = 0 or i = -1
|t| = 0 & |s| = 0 => i = 0
|t| != 0 & contains(t, s) => t = xsy & i = len(x)
|s| = 0 or s = s_head*s_tail
|s| = 0 or !contains(s_tail*y, s)
*/
void axioms::last_indexof_axiom(expr* i) {
expr* _s = nullptr, *_t = nullptr;
VERIFY(seq.str.is_last_index(i, _t, _s));
auto t = purify(_t);
auto s = purify(_s);
expr_ref minus_one(a.mk_int(-1), m);
expr_ref zero(a.mk_int(0), m);
expr_ref x = m_sk.mk_last_indexof_left(t, s);
expr_ref y = m_sk.mk_last_indexof_right(t, s);
expr_ref s_head(m), s_tail(m);
m_sk.decompose(s, s_head, s_tail);
expr_ref cnt = expr_ref(seq.str.mk_contains(t, s), m);
expr_ref cnt2 = expr_ref(seq.str.mk_contains(mk_concat(s_tail, y), s), m);
expr_ref i_eq_m1 = mk_eq(i, minus_one);
expr_ref i_eq_0 = mk_eq(i, zero);
expr_ref s_eq_empty = mk_eq_empty(s);
expr_ref t_eq_empty = mk_eq_empty(t);
expr_ref xsy = mk_concat(x, s, y);
add_clause(cnt, i_eq_m1);
add_clause(~t_eq_empty, s_eq_empty, i_eq_m1);
add_clause(~t_eq_empty, ~s_eq_empty, i_eq_0);
add_clause(t_eq_empty, ~cnt, mk_seq_eq(t, xsy));
add_clause(t_eq_empty, ~cnt, mk_eq(i, mk_len(x)));
add_clause(s_eq_empty, mk_eq(s, mk_concat(s_head, s_tail)));
add_clause(s_eq_empty, ~cnt2);
}
/*
let r = replace(u, s, t)
- if s is empty, the result is to prepend t to u;
- if s does not occur in u then the result is u.
s = "" => r = t+u
u = "" => s = "" or r = u
~contains(u,s) => r = u
tightest_prefix(s, x)
contains(u, s) => r = xty & u = xsy
~contains(u, s) => r = u
*/
void axioms::replace_axiom(expr* r) {
expr* _u = nullptr, *_s = nullptr, *_t = nullptr;
VERIFY(seq.str.is_replace(r, _u, _s, _t));
auto u = purify(_u);
auto s = purify(_s);
auto t = purify(_t);
expr_ref x = m_sk.mk_indexof_left(u, s);
expr_ref y = m_sk.mk_indexof_right(u, s);
expr_ref xty = mk_concat(x, t, y);
expr_ref xsy = mk_concat(x, s, y);
expr_ref u_emp = mk_eq_empty(u);
expr_ref s_emp = mk_eq_empty(s);
expr_ref cnt = expr_ref(seq.str.mk_contains(u, s), m);
add_clause(~s_emp, mk_seq_eq(r, mk_concat(t, u)));
add_clause(~u_emp, s_emp, mk_seq_eq(r, u));
add_clause(cnt, mk_seq_eq(r, u));
add_clause(~cnt, u_emp, s_emp, mk_seq_eq(u, xsy));
add_clause(~cnt, u_emp, s_emp, mk_seq_eq(r, xty));
tightest_prefix(s, x);
}
/*
let e = at(s, i)
0 <= i < len(s) -> s = xey & len(x) = i & len(e) = 1
i < 0 \/ i >= len(s) -> e = empty
*/
void axioms::at_axiom(expr* e) {
TRACE("seq", tout << "at-axiom: " << mk_bounded_pp(e, m) << "\n";);
expr* _s = nullptr, *_i = nullptr;
VERIFY(seq.str.is_at(e, _s, _i));
auto s = purify(_s);
auto i = purify(_i);
expr_ref zero(a.mk_int(0), m);
expr_ref one(a.mk_int(1), m);
expr_ref emp(seq.str.mk_empty(e->get_sort()), m);
expr_ref len_s = mk_len(s);
expr_ref i_ge_0 = mk_ge(i, 0);
expr_ref i_ge_len_s = mk_ge(mk_sub(i, mk_len(s)), 0);
expr_ref len_e = mk_len(e);
rational iv;
if (a.is_numeral(i, iv) && iv.is_unsigned()) {
expr_ref_vector es(m);
expr_ref nth(m);
unsigned k = iv.get_unsigned();
for (unsigned j = 0; j <= k; ++j) {
es.push_back(seq.str.mk_unit(mk_nth(s, j)));
}
nth = es.back();
es.push_back(m_sk.mk_tail(s, i));
add_clause(~i_ge_0, i_ge_len_s, mk_seq_eq(s, seq.str.mk_concat(es, e->get_sort())));
add_clause(~i_ge_0, i_ge_len_s, mk_seq_eq(nth, e));
}
else {
expr_ref x = m_sk.mk_pre(s, i);
expr_ref y = m_sk.mk_tail(s, i);
expr_ref xey = mk_concat(x, e, y);
expr_ref len_x = mk_len(x);
add_clause(~i_ge_0, i_ge_len_s, mk_seq_eq(s, xey));
add_clause(~i_ge_0, i_ge_len_s, mk_eq(i, len_x));
}
add_clause(i_ge_0, mk_eq(e, emp));
add_clause(~i_ge_len_s, mk_eq(e, emp));
add_clause(~i_ge_0, i_ge_len_s, mk_eq(one, len_e));
add_clause(mk_le(len_e, 1));
}
/**
i >= 0 i < len(s) => unit(nth_i(s, i)) = at(s, i)
nth_i(unit(nth_i(s, i)), 0) = nth_i(s, i)
*/
void axioms::nth_axiom(expr* e) {
expr* s = nullptr, *i = nullptr;
rational n;
zstring str;
VERIFY(seq.str.is_nth_i(e, s, i));
if (seq.str.is_string(s, str) && a.is_numeral(i, n) &&
n.is_unsigned() && n.get_unsigned() < str.length()) {
app_ref ch(seq.str.mk_char(str[n.get_unsigned()]), m);
add_clause(mk_eq(ch, e));
}
else {
expr_ref zero(a.mk_int(0), m);
expr_ref i_ge_0 = mk_ge(i, 0);
expr_ref i_ge_len_s = mk_ge(mk_sub(i, mk_len(s)), 0);
// at(s,i) = [nth(s,i)]
expr_ref rhs(s, m);
expr_ref lhs(seq.str.mk_unit(e), m);
if (!seq.str.is_at(s) || zero != i) rhs = seq.str.mk_at(s, i);
m_rewrite(rhs);
add_clause(~i_ge_0, i_ge_len_s, mk_eq(lhs, rhs));
}
}
void axioms::itos_axiom(expr* e) {
expr* n = nullptr;
TRACE("seq", tout << mk_pp(e, m) << "\n";);
VERIFY(seq.str.is_itos(e, n));
// itos(n) = "" <=> n < 0
expr_ref zero(a.mk_int(0), m);
expr_ref eq1 = expr_ref(seq.str.mk_is_empty(e), m);
expr_ref ge0 = mk_ge(n, 0);
// n >= 0 => itos(n) != ""
// itos(n) = "" or n >= 0
add_clause(~eq1, ~ge0);
add_clause(eq1, ge0);
add_clause(mk_ge(mk_len(e), 0));
// n >= 0 => stoi(itos(n)) = n
app_ref stoi(seq.str.mk_stoi(e), m);
add_clause(~ge0, mk_eq(stoi, n));
// itos(n) does not start with "0" when n > 0
// n = 0 or at(itos(n),0) != "0"
// alternative: n >= 0 => itos(stoi(itos(n))) = itos(n)
expr_ref zs(seq.str.mk_string(symbol("0")), m);
m_rewrite(zs);
expr_ref eq0 = mk_eq(n, zero);
expr_ref at0 = mk_eq(seq.str.mk_at(e, zero), zs);
add_clause(eq0, ~at0);
add_clause(~eq0, mk_eq(e, zs));
}
/**
stoi(s) >= -1
stoi("") = -1
stoi(s) >= 0 => is_digit(nth(s,0))
*/
void axioms::stoi_axiom(expr* e) {
TRACE("seq", tout << mk_pp(e, m) << "\n";);
expr_ref ge0 = mk_ge(e, 0);
expr* s = nullptr;
VERIFY (seq.str.is_stoi(e, s));
add_clause(mk_ge(e, -1)); // stoi(s) >= -1
add_clause(~mk_eq_empty(s), mk_eq(e, a.mk_int(-1))); // s = "" => stoi(s) = -1
add_clause(~ge0, is_digit(mk_nth(s, 0))); // stoi(s) >= 0 => is_digit(nth(s,0))
}
/**
len(s) <= k => stoi(s) = stoi(s, k)
len(s) > 0, is_digit(nth(s,0)) => stoi(s, 0) = digit(nth_i(s, 0))
len(s) > 0, ~is_digit(nth(s,0)) => stoi(s, 0) = -1
0 < i, len(s) <= i => stoi(s, i) = stoi(s, i - 1)
0 < i, len(s) > i, stoi(s, i - 1) >= 0, is_digit(nth(s, i - 1)) => stoi(s, i) = 10*stoi(s, i - 1) + digit(nth_i(s, i - 1))
0 < i, len(s) > i, stoi(s, i - 1) < 0 => stoi(s, i) = -1
0 < i, len(s) > i, ~is_digit(nth(s, i - 1)) => stoi(s, i) = -1
Define auxiliary function with the property:
for 0 <= i < k
stoi(s, i) := stoi(extract(s, 0, i+1))
for 0 < i < k:
len(s) > i => stoi(s, i) := stoi(extract(s, 0, i))*10 + stoi(extract(s, i, 1))
len(s) <= i => stoi(s, i) := stoi(extract(s, 0, i-1), i-1)
for i <= i < k:
stoi(s) > = 0, len(s) > i => is_digit(nth(s, i))
*/
void axioms::stoi_axiom(expr* e, unsigned k) {
SASSERT(k > 0);
expr* _s = nullptr;
VERIFY (seq.str.is_stoi(e, _s));
expr_ref s(_s, m);
m_rewrite(s);
auto stoi2 = [&](unsigned j) { return m_sk.mk("seq.stoi", s, a.mk_int(j), a.mk_int()); };
auto digit = [&](unsigned j) { return mk_digit2int(mk_nth(s, j)); };
auto is_digit_ = [&](unsigned j) { return is_digit(mk_nth(s, j)); };
expr_ref len = mk_len(s);
expr_ref ge0 = mk_ge(e, 0);
expr_ref lek = mk_le(len, k);
add_clause(~lek, mk_eq(e, stoi2(k-1))); // len(s) <= k => stoi(s) = stoi(s, k-1)
add_clause(mk_le(len, 0), ~is_digit_(0), mk_eq(stoi2(0), digit(0))); // len(s) > 0, is_digit(nth(s, 0)) => stoi(s,0) = digit(s,0)
add_clause(mk_le(len, 0), is_digit_(0), mk_eq(stoi2(0), a.mk_int(-1))); // len(s) > 0, ~is_digit(nth(s, 0)) => stoi(s,0) = -1
for (unsigned i = 1; i < k; ++i) {
// len(s) <= i => stoi(s, i) = stoi(s, i - 1)
add_clause(~mk_le(len, i), mk_eq(stoi2(i), stoi2(i-1)));
// len(s) > i, stoi(s, i - 1) >= 0, is_digit(nth(s, i)) => stoi(s, i) = 10*stoi(s, i - 1) + digit(i)
// len(s) > i, stoi(s, i - 1) < 0 => stoi(s, i) = -1
// len(s) > i, ~is_digit(nth(s, i)) => stoi(s, i) = -1
add_clause(mk_le(len, i), ~mk_ge(stoi2(i-1), 0), ~is_digit_(i), mk_eq(stoi2(i), a.mk_add(a.mk_mul(a.mk_int(10), stoi2(i-1)), digit(i))));
add_clause(mk_le(len, i), is_digit_(i), mk_eq(stoi2(i), a.mk_int(-1)));
add_clause(mk_le(len, i), mk_ge(stoi2(i-1), 0), mk_eq(stoi2(i), a.mk_int(-1)));
// stoi(s) >= 0, i < len(s) => is_digit(nth(s, i))
add_clause(~ge0, mk_le(len, i), is_digit_(i));
}
}
/**
Let s := itos(e)
Relate values of e with len(s) where len(s) is bounded by k.
|s| = 0 => e < 0
|s| <= 1 => e < 10
|s| <= 2 => e < 100
|s| <= 3 => e < 1000
|s| >= 1 => e >= 0
|s| >= 2 => e >= 10
|s| >= 3 => e >= 100
There are no constraints to ensure that the string itos(e)
contains the valid digits corresponding to e >= 0.
The validity of itos(e) is ensured by the following property:
e is either of the form stoi(s) for some s, or there is a term
stoi(itos(e)) and axiom e >= 0 => stoi(itos(e)) = e.
Then the axioms for stoi(itos(e)) ensure that the characters of
itos(e) are valid digits and the axiom stoi(itos(e)) = e ensures
these digits encode e.
The option of constraining itos(e) digits directly does not
seem appealing becaues it requires an order of quadratic number
of constraints for all possible lengths of itos(e) (e.g, log_10(e)).
*/
void axioms::itos_axiom(expr* s, unsigned k) {
expr* e = nullptr;
VERIFY(seq.str.is_itos(s, e));
expr_ref len = mk_len(s);
add_clause(mk_ge(e, 10), mk_le(len, 1));
add_clause(mk_le(e, -1), mk_ge(len, 1));
rational lo(1);
for (unsigned i = 1; i <= k; ++i) {
lo *= rational(10);
add_clause(mk_ge(e, lo), mk_le(len, i));
add_clause(mk_le(e, lo - 1), mk_ge(len, i + 1));
}
}
expr_ref axioms::is_digit(expr* ch) {
expr_ref isd = expr_ref(m_sk.mk_is_digit(ch), m);
expr_ref lo(seq.mk_le(seq.mk_char('0'), ch), m);
expr_ref hi(seq.mk_le(ch, seq.mk_char('9')), m);
add_clause(~lo, ~hi, isd);
add_clause(~isd, lo);
add_clause(~isd, hi);
return isd;
}
expr_ref axioms::mk_digit2int(expr* ch) {
return expr_ref(a.mk_add(seq.mk_char2int(ch), a.mk_int(-((int)'0'))), m);;
}
/**
e1 < e2 => prefix(e1, e2) or e1 = xcy
e1 < e2 => prefix(e1, e2) or c < d
e1 < e2 => prefix(e1, e2) or e2 = xdz
e1 < e2 => e1 != e2
!(e1 < e2) => prefix(e2, e1) or e2 = xdz
!(e1 < e2) => prefix(e2, e1) or d < c
!(e1 < e2) => prefix(e2, e1) or e1 = xcy
!(e1 = e2) or !(e1 < e2)
optional:
e1 < e2 or e1 = e2 or e2 < e1
!(e1 = e2) or !(e2 < e1)
!(e1 < e2) or !(e2 < e1)
*/
void axioms::lt_axiom(expr* n) {
expr* _e1 = nullptr, *_e2 = nullptr;
VERIFY(seq.str.is_lt(n, _e1, _e2));
auto e1 = purify(_e1);
auto e2 = purify(_e2);
sort* s = e1->get_sort();
sort* char_sort = nullptr;
VERIFY(seq.is_seq(s, char_sort));
expr_ref lt = expr_ref(n, m);
expr_ref x = m_sk.mk("str.<.x", e1, e2);
expr_ref y = m_sk.mk("str.<.y", e1, e2);
expr_ref z = m_sk.mk("str.<.z", e1, e2);
expr_ref c = m_sk.mk("str.<.c", e1, e2, char_sort);
expr_ref d = m_sk.mk("str.<.d", e1, e2, char_sort);
expr_ref xcy = mk_concat(x, seq.str.mk_unit(c), y);
expr_ref xdz = mk_concat(x, seq.str.mk_unit(d), z);
expr_ref eq = mk_eq(e1, e2);
expr_ref pref21 = expr_ref(seq.str.mk_prefix(e2, e1), m);
expr_ref pref12 = expr_ref(seq.str.mk_prefix(e1, e2), m);
expr_ref e1xcy = mk_eq(e1, xcy);
expr_ref e2xdz = mk_eq(e2, xdz);
expr_ref ltcd = expr_ref(seq.mk_lt(c, d), m);
expr_ref ltdc = expr_ref(seq.mk_lt(d, c), m);
add_clause(~lt, pref12, e2xdz);
add_clause(~lt, pref12, e1xcy);
add_clause(~lt, pref12, ltcd);
add_clause(lt, pref21, e1xcy);
add_clause(lt, pref21, ltdc);
add_clause(lt, pref21, e2xdz);
add_clause(~eq, ~lt);
}
/**
e1 <= e2 <=> e1 < e2 or e1 = e2
*/
void axioms::le_axiom(expr* n) {
expr* e1 = nullptr, *e2 = nullptr;
VERIFY(seq.str.is_le(n, e1, e2));
expr_ref lt = expr_ref(seq.str.mk_lex_lt(e1, e2), m);
expr_ref le = expr_ref(n, m);
expr_ref eq = mk_eq(e1, e2);
add_clause(~le, lt, eq);
add_clause(~eq, le);
add_clause(~lt, le);
}
/**
is_digit(e) <=> to_code('0') <= to_code(e) <= to_code('9')
*/
void axioms::is_digit_axiom(expr* n) {
expr* e = nullptr;
VERIFY(seq.str.is_is_digit(n, e));
expr_ref is_digit = expr_ref(n, m);
expr_ref to_code(seq.str.mk_to_code(e), m);
expr_ref ge0 = mk_ge(to_code, (unsigned)'0');
expr_ref le9 = mk_le(to_code, (unsigned)'9');
add_clause(~is_digit, ge0);
add_clause(~is_digit, le9);
add_clause(is_digit, ~ge0, ~le9);
}
/**
len(e) = 1 => 0 <= to_code(e) <= max_code
len(e) = 1 => from_code(to_code(e)) = e
len(e) != 1 => to_code(e) = -1
*/
void axioms::str_to_code_axiom(expr* n) {
expr* e = nullptr;
VERIFY(seq.str.is_to_code(n, e));
expr_ref len_is1 = mk_eq(mk_len(e), a.mk_int(1));
add_clause(~len_is1, mk_ge(n, 0));
add_clause(~len_is1, mk_le(n, seq.max_char()));
add_clause(~len_is1, mk_eq(n, seq.mk_char2int(mk_nth(e, 0))));
if (!seq.str.is_from_code(e))
add_clause(~len_is1, mk_eq(e, seq.str.mk_from_code(n)));
add_clause(len_is1, mk_eq(n, a.mk_int(-1)));
}
/**
0 <= e <= max_char => len(from_code(e)) = 1
0 <= e <= max_char => to_code(from_code(e)) = e
e < 0 or e > max_char => len(from_code(e)) = ""
*/
void axioms::str_from_code_axiom(expr* n) {
expr* e = nullptr;
VERIFY(seq.str.is_from_code(n, e));
expr_ref ge = mk_ge(e, 0);
expr_ref le = mk_le(e, seq.max_char());
expr_ref emp = expr_ref(seq.str.mk_is_empty(n), m);
add_clause(~ge, ~le, mk_eq(mk_len(n), a.mk_int(1)));
if (!seq.str.is_to_code(e))
add_clause(~ge, ~le, mk_eq(seq.str.mk_to_code(n), e));
add_clause(ge, emp);
add_clause(le, emp);
}
/**
Unit is injective:
u = inv-unit(unit(u))
*/
void axioms::unit_axiom(expr* n) {
expr* u = nullptr;
VERIFY(seq.str.is_unit(n, u));
add_clause(mk_eq(u, m_sk.mk_unit_inv(n)));
}
/**
suffix(s, t) => s = seq.suffix_inv(s, t) + t
~suffix(s, t) => len(s) > len(t) or s = y(s, t) + unit(c(s, t)) + x(s, t)
~suffix(s, t) => len(s) > len(t) or t = z(s, t) + unit(d(s, t)) + x(s, t)
~suffix(s, t) => len(s) > len(t) or c(s,t) != d(s,t)
*/
void axioms::suffix_axiom(expr* e) {
expr* _s = nullptr, *_t = nullptr;
VERIFY(seq.str.is_suffix(e, _s, _t));
auto s = purify(_s);
auto t = purify(_t);
expr_ref lit = expr_ref(e, m);
expr_ref s_gt_t = mk_ge(mk_sub(mk_len(s), mk_len(t)), 1);
#if 0
expr_ref x = m_sk.mk_pre(t, mk_sub(mk_len(t), mk_len(s)));
expr_ref y = m_sk.mk_tail(t, mk_sub(mk_len(s), a.mk_int(1)));
add_clause(lit, s_gt_t, mk_seq_eq(t, mk_concat(x, y)));
add_clause(lit, s_gt_t, mk_eq(mk_len(y), mk_len(s)));
add_clause(lit, s_gt_t, ~mk_eq(y, s));
#else
sort* char_sort = nullptr;
VERIFY(seq.is_seq(s->get_sort(), char_sort));
expr_ref x = m_sk.mk("seq.suffix.x", s, t);
expr_ref y = m_sk.mk("seq.suffix.y", s, t);
expr_ref z = m_sk.mk("seq.suffix.z", s, t);
expr_ref c = m_sk.mk("seq.suffix.c", s, t, char_sort);
expr_ref d = m_sk.mk("seq.suffix.d", s, t, char_sort);
add_clause(lit, s_gt_t, mk_seq_eq(s, mk_concat(y, seq.str.mk_unit(c), x)));
add_clause(lit, s_gt_t, mk_seq_eq(t, mk_concat(z, seq.str.mk_unit(d), x)));
add_clause(lit, s_gt_t, ~mk_eq(c, d));
#endif
}
void axioms::prefix_axiom(expr* e) {
expr* _s = nullptr, *_t = nullptr;
VERIFY(seq.str.is_prefix(e, _s, _t));
auto s = purify(_s);
auto t = purify(_t);
expr_ref lit = expr_ref(e, m);
expr_ref s_gt_t = mk_ge(mk_sub(mk_len(s), mk_len(t)), 1);
#if 0
expr_ref x = m_sk.mk_pre(t, mk_len(s));
expr_ref y = m_sk.mk_tail(t, mk_sub(mk_sub(mk_len(t), mk_len(s)), a.mk_int(1)));
add_clause(lit, s_gt_t, mk_seq_eq(t, mk_concat(x, y)));
add_clause(lit, s_gt_t, mk_eq(mk_len(x), mk_len(s)));
add_clause(lit, s_gt_t, ~mk_eq(x, s));
#else
sort* char_sort = nullptr;
VERIFY(seq.is_seq(s->get_sort(), char_sort));
expr_ref x = m_sk.mk("seq.prefix.x", s, t);
expr_ref y = m_sk.mk("seq.prefix.y", s, t);
expr_ref z = m_sk.mk("seq.prefix.z", s, t);
expr_ref c = m_sk.mk("seq.prefix.c", s, t, char_sort);
expr_ref d = m_sk.mk("seq.prefix.d", s, t, char_sort);
add_clause(lit, s_gt_t, mk_seq_eq(s, mk_concat(x, seq.str.mk_unit(c), y)));
add_clause(lit, s_gt_t, mk_seq_eq(t, mk_concat(x, seq.str.mk_unit(d), z)), mk_seq_eq(t, x));
add_clause(lit, s_gt_t, ~mk_eq(c, d));
#endif
}
/***
let n = len(x)
- len(a ++ b) = len(a) + len(b) if x = a ++ b
- len(unit(u)) = 1 if x = unit(u)
- len(str) = str.length() if x = str
- len(empty) = 0 if x = empty
- len(int.to.str(i)) >= 1 if x = int.to.str(i) and more generally if i = 0 then 1 else 1+floor(log(|i|))
- len(x) >= 0 otherwise
*/
void axioms::length_axiom(expr* n) {
expr* x = nullptr;
VERIFY(seq.str.is_length(n, x));
if (seq.str.is_concat(x) ||
seq.str.is_unit(x) ||
seq.str.is_empty(x) ||
seq.str.is_string(x)) {
expr_ref len(n, m);
m_rewrite(len);
SASSERT(n != len);
add_clause(mk_eq(len, n));
}
else {
add_clause(mk_ge(n, 0));
}
}
/**
~contains(a, b) => ~prefix(b, a)
~contains(a, b) => ~contains(tail(a), b) or a = empty
~contains(a, b) & a = empty => b != empty
~(a = empty) => a = head + tail
*/
void axioms::unroll_not_contains(expr* e) {
expr_ref head(m), tail(m);
expr* a = nullptr, *b = nullptr;
VERIFY(seq.str.is_contains(e, a, b));
m_sk.decompose(a, head, tail);
expr_ref pref(seq.str.mk_prefix(b, a), m);
expr_ref postf(seq.str.mk_contains(tail, b), m);
expr_ref emp = mk_eq_empty(a);
expr_ref cnt = expr_ref(e, m);
add_clause(cnt, ~pref);
add_clause(cnt, ~postf);
add_clause(~emp, mk_eq_empty(tail));
add_clause(emp, mk_eq(a, seq.str.mk_concat(head, tail)));
}
expr_ref axioms::length_limit(expr* s, unsigned k) {
expr_ref bound_tracker = m_sk.mk_length_limit(s, k);
expr* s0 = nullptr;
if (seq.str.is_stoi(s, s0))
s = s0;
add_clause(~bound_tracker, mk_le(mk_len(s), k));
return bound_tracker;
}
}

102
src/ast/rewriter/seq_axioms.h Normal file
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@ -0,0 +1,102 @@
/*++
Copyright (c) 2011 Microsoft Corporation
Module Name:
seq_axioms.h
Abstract:
Axiomatize string operations that can be reduced to
more basic operations.
Author:
Nikolaj Bjorner (nbjorner) 2020-4-16
Revision History:
--*/
#pragma once
#include "ast/seq_decl_plugin.h"
#include "ast/arith_decl_plugin.h"
#include "ast/rewriter/th_rewriter.h"
#include "ast/rewriter/seq_skolem.h"
namespace seq {
class axioms {
ast_manager& m;
th_rewriter& m_rewrite;
arith_util a;
seq_util seq;
skolem m_sk;
expr_ref_vector m_clause;
std::function<void(expr_ref_vector const&)> m_add_clause;
expr_ref mk_len(expr* s);
expr_ref mk_sub(expr* x, expr* y);
expr_ref mk_concat(expr* e1, expr* e2, expr* e3) { return expr_ref(seq.str.mk_concat(e1, e2, e3), m); }
expr_ref mk_concat(expr* e1, expr* e2) { return expr_ref(seq.str.mk_concat(e1, e2), m); }
expr_ref mk_nth(expr* e, unsigned i) { return expr_ref(seq.str.mk_nth_i(e, a.mk_int(i)), m); }
expr_ref mk_eq(expr* a, expr* b) { return expr_ref(m.mk_eq(a, b), m); }
expr_ref mk_seq_eq(expr* a, expr* b) { SASSERT(seq.is_seq(a) && seq.is_seq(b)); return expr_ref(m_sk.mk_eq(a, b), m); }
expr_ref mk_eq_empty(expr* e) { return expr_ref(m.mk_eq(seq.str.mk_empty(e->get_sort()), e), m); }
expr_ref mk_ge(expr* x, unsigned n) { return expr_ref(a.mk_ge(x, a.mk_int(n)), m); }
expr_ref mk_le(expr* x, unsigned n) { return expr_ref(a.mk_le(x, a.mk_int(n)), m); }
expr_ref mk_ge(expr* x, rational const& n) { return expr_ref(a.mk_ge(x, a.mk_int(n)), m); }
expr_ref mk_le(expr* x, rational const& n) { return expr_ref(a.mk_le(x, a.mk_int(n)), m); }
expr_ref is_digit(expr* ch);
expr_ref purify(expr* e);
expr_ref mk_digit2int(expr* ch);
void add_clause(expr_ref const& a);
void add_clause(expr_ref const& a, expr_ref const& b);
void add_clause(expr_ref const& a, expr_ref const& b, expr_ref const& c);
void add_clause(expr_ref const& a, expr_ref const& b, expr_ref const& c, expr_ref const & d);
void add_clause(expr_ref const& a, expr_ref const& b, expr_ref const& c, expr_ref const & d, expr_ref const& e);
bool is_drop_last(expr* s, expr* i, expr* l);
bool is_tail(expr* s, expr* i, expr* l);
bool is_extract_prefix0(expr* s, expr* i, expr* l);
void tail_axiom(expr* e, expr* s);
void drop_last_axiom(expr* e, expr* s);
void extract_prefix_axiom(expr* e, expr* s, expr* l);
void tightest_prefix(expr* s, expr* x);
public:
axioms(th_rewriter& rw);
void set_add_clause(std::function<void(expr_ref_vector const&)>& ac) { m_add_clause = ac; }
void suffix_axiom(expr* n);
void prefix_axiom(expr* n);
void extract_axiom(expr* n);
void indexof_axiom(expr* n);
void last_indexof_axiom(expr* n);
void replace_axiom(expr* n);
void at_axiom(expr* n);
void nth_axiom(expr* n);
void itos_axiom(expr* n);
void stoi_axiom(expr* n);
void stoi_axiom(expr* e, unsigned k);
void itos_axiom(expr* s, unsigned k);
void lt_axiom(expr* n);
void le_axiom(expr* n);
void is_digit_axiom(expr* n);
void str_to_code_axiom(expr* n);
void str_from_code_axiom(expr* n);
void unit_axiom(expr* n);
void length_axiom(expr* n);
void unroll_not_contains(expr* e);
expr_ref length_limit(expr* s, unsigned k);
};
};

127
src/smt/seq_axioms.cpp
View file

@ -33,8 +33,12 @@ seq_axioms::seq_axioms(theory& th, th_rewriter& r):
a(m),
seq(m),
m_sk(m, r),
m_ax(r),
m_digits_initialized(false)
{}
{
std::function<void(expr_ref_vector const&)> _add_clause = [&](expr_ref_vector const& c) { add_clause(c); };
m_ax.set_add_clause(_add_clause);
}
literal seq_axioms::mk_eq(expr* a, expr* b) {
return th.mk_eq(a, b, false);
@ -54,13 +58,27 @@ expr_ref seq_axioms::mk_len(expr* s) {
literal seq_axioms::mk_literal(expr* _e) {
expr_ref e(_e, m);
if (a.is_arith_expr(e)) {
if (m.is_not(_e, _e))
return ~mk_literal(_e);
if (m.is_eq(e))
return mk_eq(to_app(e)->get_arg(0), to_app(e)->get_arg(1));
if (a.is_arith_expr(e))
m_rewrite(e);
}
th.ensure_enode(e);
return ctx().get_literal(e);
}
void seq_axioms::add_clause(expr_ref_vector const& clause) {
literal lits[5] = { null_literal, null_literal, null_literal, null_literal, null_literal };
unsigned idx = 0;
for (expr* e : clause) {
lits[idx++] = mk_literal(e);
SASSERT(idx <= 5);
}
add_axiom(lits[0], lits[1], lits[2], lits[3], lits[4]);
}
/***
let e = extract(s, i, l)
@ -87,6 +105,10 @@ this translates to:
*/
void seq_axioms::add_extract_axiom(expr* e) {
if (m_use_new_axioms) {
m_ax.extract_axiom(e);
return;
}
TRACE("seq", tout << mk_pp(e, m) << "\n";);
expr* _s = nullptr, *_i = nullptr, *_l = nullptr;
VERIFY(seq.str.is_extract(e, _s, _i, _l));
@ -694,68 +716,6 @@ void seq_axioms::ensure_digit_axiom() {
}
/**
e1 < e2 => prefix(e1, e2) or e1 = xcy
e1 < e2 => prefix(e1, e2) or c < d
e1 < e2 => prefix(e1, e2) or e2 = xdz
e1 < e2 => e1 != e2
!(e1 < e2) => prefix(e2, e1) or e2 = xdz
!(e1 < e2) => prefix(e2, e1) or d < c
!(e1 < e2) => prefix(e2, e1) or e1 = xcy
!(e1 = e2) or !(e1 < e2)
optional:
e1 < e2 or e1 = e2 or e2 < e1
!(e1 = e2) or !(e2 < e1)
!(e1 < e2) or !(e2 < e1)
*/
void seq_axioms::add_lt_axiom(expr* n) {
expr* _e1 = nullptr, *_e2 = nullptr;
VERIFY(seq.str.is_lt(n, _e1, _e2));
expr_ref e1(_e1, m), e2(_e2, m);
m_rewrite(e1);
m_rewrite(e2);
sort* s = e1->get_sort();
sort* char_sort = nullptr;
VERIFY(seq.is_seq(s, char_sort));
literal lt = mk_literal(n);
expr_ref x = m_sk.mk("str.<.x", e1, e2);
expr_ref y = m_sk.mk("str.<.y", e1, e2);
expr_ref z = m_sk.mk("str.<.z", e1, e2);
expr_ref c = m_sk.mk("str.<.c", e1, e2, char_sort);
expr_ref d = m_sk.mk("str.<.d", e1, e2, char_sort);
expr_ref xcy = mk_concat(x, seq.str.mk_unit(c), y);
expr_ref xdz = mk_concat(x, seq.str.mk_unit(d), z);
literal eq = mk_eq(e1, e2);
literal pref21 = mk_literal(seq.str.mk_prefix(e2, e1));
literal pref12 = mk_literal(seq.str.mk_prefix(e1, e2));
literal e1xcy = mk_eq(e1, xcy);
literal e2xdz = mk_eq(e2, xdz);
literal ltcd = mk_literal(seq.mk_lt(c, d));
literal ltdc = mk_literal(seq.mk_lt(d, c));
add_axiom(~lt, pref12, e2xdz);
add_axiom(~lt, pref12, e1xcy);
add_axiom(~lt, pref12, ltcd);
add_axiom(lt, pref21, e1xcy);
add_axiom(lt, pref21, ltdc);
add_axiom(lt, pref21, e2xdz);
add_axiom(~eq, ~lt);
}
/**
e1 <= e2 <=> e1 < e2 or e1 = e2
*/
void seq_axioms::add_le_axiom(expr* n) {
expr* e1 = nullptr, *e2 = nullptr;
VERIFY(seq.str.is_le(n, e1, e2));
literal lt = mk_literal(seq.str.mk_lex_lt(e1, e2));
literal le = mk_literal(n);
literal eq = mk_eq(e1, e2);
add_axiom(~le, lt, eq);
add_axiom(~eq, le);
add_axiom(~lt, le);
}
/**
is_digit(e) <=> to_code('0') <= to_code(e) <= to_code('9')
*/
@ -777,6 +737,10 @@ void seq_axioms::add_is_digit_axiom(expr* n) {
len(e) != 1 => to_code(e) = -1
*/
void seq_axioms::add_str_to_code_axiom(expr* n) {
if (m_use_new_axioms) {
m_ax.str_to_code_axiom(n);
return;
}
expr* e = nullptr;
VERIFY(seq.str.is_to_code(n, e));
literal len_is1 = mk_eq(mk_len(e), a.mk_int(1));
@ -794,6 +758,10 @@ void seq_axioms::add_str_to_code_axiom(expr* n) {
e < 0 or e > max_char => len(from_code(e)) = ""
*/
void seq_axioms::add_str_from_code_axiom(expr* n) {
if (m_use_new_axioms) {
m_ax.str_from_code_axiom(n);
return;
}
expr* e = nullptr;
VERIFY(seq.str.is_from_code(n, e));
literal ge = mk_ge(e, 0);
@ -807,18 +775,6 @@ void seq_axioms::add_str_from_code_axiom(expr* n) {
}
/**
Unit is injective:
u = inv-unit(unit(u))
*/
void seq_axioms::add_unit_axiom(expr* n) {
expr* u = nullptr;
VERIFY(seq.str.is_unit(n, u));
add_axiom(mk_eq(u, m_sk.mk_unit_inv(n)));
}
/**
suffix(s, t) => s = seq.suffix_inv(s, t) + t
@ -829,6 +785,10 @@ void seq_axioms::add_unit_axiom(expr* n) {
*/
void seq_axioms::add_suffix_axiom(expr* e) {
if (m_use_new_axioms) {
m_ax.suffix_axiom(e);
return;
}
expr* _s = nullptr, *_t = nullptr;
VERIFY(seq.str.is_suffix(e, _s, _t));
expr_ref s(_s, m), t(_t, m);
@ -857,6 +817,10 @@ void seq_axioms::add_suffix_axiom(expr* e) {
}
void seq_axioms::add_prefix_axiom(expr* e) {
if (m_use_new_axioms) {
m_ax.prefix_axiom(e);
return;
}
expr* _s = nullptr, *_t = nullptr;
VERIFY(seq.str.is_prefix(e, _s, _t));
expr_ref s(_s, m), t(_t, m);
@ -895,6 +859,11 @@ void seq_axioms::add_prefix_axiom(expr* e) {
- len(x) >= 0 otherwise
*/
void seq_axioms::add_length_axiom(expr* n) {
if (m_use_new_axioms) {
m_ax.length_axiom(n);
return;
}
expr* x = nullptr;
VERIFY(seq.str.is_length(n, x));
if (seq.str.is_concat(x) ||
@ -918,6 +887,10 @@ void seq_axioms::add_length_axiom(expr* n) {
~(a = empty) => a = head + tail
*/
void seq_axioms::unroll_not_contains(expr* e) {
if (m_use_new_axioms) {
m_ax.unroll_not_contains(e);
return;
}
expr_ref head(m), tail(m);
expr* a = nullptr, *b = nullptr;
VERIFY(seq.str.is_contains(e, a, b));

12
src/smt/seq_axioms.h
View file

@ -23,6 +23,7 @@ Revision History:
#include "ast/arith_decl_plugin.h"
#include "ast/rewriter/th_rewriter.h"
#include "ast/rewriter/seq_skolem.h"
#include "ast/rewriter/seq_axioms.h"
#include "smt/smt_theory.h"
namespace smt {
@ -33,8 +34,10 @@ namespace smt {
ast_manager& m;
arith_util a;
seq_util seq;
seq::skolem m_sk;
seq::skolem m_sk;
seq::axioms m_ax;
bool m_digits_initialized;
bool m_use_new_axioms { false };
literal mk_eq_empty(expr* e, bool phase = true) { return mk_eq_empty2(e, phase); }
context& ctx() { return th.get_context(); }
@ -60,6 +63,7 @@ namespace smt {
void add_extract_prefix_axiom(expr* e, expr* s, expr* l);
void tightest_prefix(expr* s, expr* x);
void ensure_digit_axiom();
void add_clause(expr_ref_vector const& lits);
public:
seq_axioms(theory& th, th_rewriter& r);
@ -80,12 +84,12 @@ namespace smt {
void add_stoi_axiom(expr* n);
void add_stoi_axiom(expr* e, unsigned k);
void add_itos_axiom(expr* s, unsigned k);
void add_lt_axiom(expr* n);
void add_le_axiom(expr* n);
void add_lt_axiom(expr* n) { m_ax.lt_axiom(n); }
void add_le_axiom(expr* n) { m_ax.le_axiom(n); }
void add_is_digit_axiom(expr* n);
void add_str_to_code_axiom(expr* n);
void add_str_from_code_axiom(expr* n);
void add_unit_axiom(expr* n);
void add_unit_axiom(expr* n) { m_ax.unit_axiom(n); }
void add_length_axiom(expr* n);
void unroll_not_contains(expr* n);