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throttel extract/ite rewriting to avoid perf-bug exposed in example from Lucas Cordeiro and Alessandro Trindade

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2018-12-07 17:54:49 +00:00
parent 9635ddd8fc
commit a20e68facc
3 changed files with 79 additions and 49 deletions
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114
src/ast/rewriter/seq_rewriter.cpp
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@ -387,8 +387,9 @@ eautomaton* re2automaton::seq2aut(expr* e) {
br_status seq_rewriter::mk_app_core(func_decl * f, unsigned num_args, expr * const * args, expr_ref & result) {
SASSERT(f->get_family_id() == get_fid());
br_status st = BR_FAILED;
switch(f->get_decl_kind()) {
case OP_SEQ_UNIT:
SASSERT(num_args == 1);
return mk_seq_unit(args[0], result);
@ -448,7 +449,8 @@ br_status seq_rewriter::mk_app_core(func_decl * f, unsigned num_args, expr * con
return mk_seq_length(args[0], result);
case OP_SEQ_EXTRACT:
SASSERT(num_args == 3);
return mk_seq_extract(args[0], args[1], args[2], result);
st = mk_seq_extract(args[0], args[1], args[2], result);
break;
case OP_SEQ_CONTAINS:
SASSERT(num_args == 2);
return mk_seq_contains(args[0], args[1], result);
@ -499,7 +501,8 @@ br_status seq_rewriter::mk_app_core(func_decl * f, unsigned num_args, expr * con
case _OP_STRING_STRIDOF:
UNREACHABLE();
}
return BR_FAILED;
TRACE("seq", tout << result << "\n";);
return st;
}
/*
@ -607,6 +610,7 @@ br_status seq_rewriter::mk_seq_extract(expr* a, expr* b, expr* c, expr_ref& resu
bool constantPos = m_autil.is_numeral(b, pos);
bool constantLen = m_autil.is_numeral(c, len);
// case 1: pos<0 or len<=0
// rewrite to ""
if ( (constantPos && pos.is_neg()) || (constantLen && !len.is_pos()) ) {
@ -615,7 +619,7 @@ br_status seq_rewriter::mk_seq_extract(expr* a, expr* b, expr* c, expr_ref& resu
}
// case 1.1: pos >= length(base)
// rewrite to ""
if (constantBase && constantPos && pos >= rational(s.length())) {
if (constantPos && constantBase && pos >= rational(s.length())) {
result = m_util.str.mk_empty(m().get_sort(a));
return BR_DONE;
}
@ -623,52 +627,74 @@ br_status seq_rewriter::mk_seq_extract(expr* a, expr* b, expr* c, expr_ref& resu
constantPos &= pos.is_unsigned();
constantLen &= len.is_unsigned();
if (constantBase && constantPos && constantLen) {
if (pos.get_unsigned() + len.get_unsigned() >= s.length()) {
// case 2: pos+len goes past the end of the string
unsigned _len = s.length() - pos.get_unsigned() + 1;
result = m_util.str.mk_string(s.extract(pos.get_unsigned(), _len));
} else {
// case 3: pos+len still within string
result = m_util.str.mk_string(s.extract(pos.get_unsigned(), len.get_unsigned()));
}
return BR_DONE;
}
if (constantPos && constantLen) {
if (constantPos && constantLen && constantBase) {
unsigned _pos = pos.get_unsigned();
unsigned _len = len.get_unsigned();
SASSERT(_len > 0);
expr_ref_vector as(m()), bs(m());
m_util.str.get_concat(a, as);
if (as.empty()) {
result = a;
return BR_DONE;
}
for (unsigned i = 0; i < as.size() && _len > 0; ++i) {
if (m_util.str.is_unit(as[i].get())) {
if (_pos == 0) {
bs.push_back(as[i].get());
--_len;
}
else {
--_pos;
}
}
else {
return BR_FAILED;
}
}
if (bs.empty()) {
result = m_util.str.mk_empty(m().get_sort(a));
}
else {
result = m_util.str.mk_concat(bs);
if (_pos + _len >= s.length()) {
// case 2: pos+len goes past the end of the string
unsigned _len = s.length() - _pos + 1;
result = m_util.str.mk_string(s.extract(_pos, _len));
} else {
// case 3: pos+len still within string
result = m_util.str.mk_string(s.extract(_pos, _len));
}
return BR_DONE;
}
return BR_FAILED;
expr_ref_vector as(m()), bs(m());
m_util.str.get_concat_units(a, as);
if (as.empty()) {
result = m_util.str.mk_empty(m().get_sort(a));
return BR_DONE;
}
if (!constantPos) {
return BR_FAILED;
}
unsigned _pos = pos.get_unsigned();
// (extract s 0 (len s)) = s
expr* a2 = nullptr;
if (_pos == 0 && m_util.str.is_length(c, a2) && a == a2) {
result = a;
return BR_DONE;
}
unsigned offset = 0;
for (; offset < as.size() && m_util.str.is_unit(as.get(offset)) && offset < _pos; ++offset) {};
if (offset == 0 && _pos > 0) {
return BR_FAILED;
}
if (_pos == 0 && !constantLen) {
return BR_FAILED;
}
// (extract (++ (unit x) (unit y)) 3 c) = empty
if (offset == as.size()) {
result = m_util.str.mk_empty(m().get_sort(a));
return BR_DONE;
}
SASSERT(offset != 0 || _pos == 0);
if (constantLen && _pos == offset) {
unsigned _len = len.get_unsigned();
// (extract (++ (unit a) (unit b) (unit c) x) 1 2) = (++ (unit b) (unit c))
unsigned i = offset;
for (; i < as.size() && m_util.str.is_unit(as.get(i)) && i - offset < _len; ++i);
if (i - offset == _len) {
result = m_util.str.mk_concat(_len, as.c_ptr() + offset);
return BR_DONE;
}
}
if (offset == 0) {
return BR_FAILED;
}
expr_ref len1(m()), pos1(m());
pos1 = m_autil.mk_sub(b, m_autil.mk_int(offset));
len1 = m_autil.mk_sub(c, m_autil.mk_int(offset));
result = m_util.str.mk_concat(as.size() - offset, as.c_ptr() + offset);
result = m_util.str.mk_substr(result, pos1, len1);
return BR_REWRITE3;
}
bool seq_rewriter::cannot_contain_suffix(expr* a, expr* b) {