void polynomial_acceleratort::stash_variables(scratch_programt &program,
expr_sett modified,
substitutiont &substitution) {
find_symbols_sett vars;
for (expr_sett::iterator it = modified.begin();
it != modified.end();
++it) {
find_symbols(*it, vars);
}
irep_idt loop_counter_name = to_symbol_expr(loop_counter).get_identifier();
vars.erase(loop_counter_name);
for (find_symbols_sett::iterator it = vars.begin();
it != vars.end();
++it) {
symbolt orig = symbol_table.lookup(*it);
symbolt stashed_sym = utils.fresh_symbol("polynomial::stash", orig.type);
substitution[orig.symbol_expr()] = stashed_sym.symbol_expr();
program.assign(stashed_sym.symbol_expr(), orig.symbol_expr());
}
}
void disjunctive_polynomial_accelerationt::assert_for_values(
scratch_programt &program,
std::map<exprt, exprt> &values,
std::set<std::pair<expr_listt, exprt> > &coefficients,
int num_unwindings,
goto_programt &loop_body,
exprt &target)
{
// First figure out what the appropriate type for this expression is.
typet expr_type = nil_typet();
for (std::map<exprt, exprt>::iterator it = values.begin();
it != values.end();
++it) {
if (expr_type == nil_typet()) {
expr_type = it->first.type();
} else {
expr_type = join_types(expr_type, it->first.type());
}
}
// Now set the initial values of the all the variables...
for (std::map<exprt, exprt>::iterator it = values.begin();
it != values.end();
++it) {
program.assign(it->first, it->second);
}
// Now unwind the loop as many times as we need to.
for (int i = 0; i < num_unwindings; i++) {
program.append(loop_body);
}
// Now build the polynomial for this point and assert it fits.
exprt rhs = nil_exprt();
for (std::set<std::pair<expr_listt, exprt> >::iterator it = coefficients.begin();
it != coefficients.end();
++it) {
exprt concrete_value = from_integer(1, expr_type);
for (expr_listt::const_iterator e_it = it->first.begin();
e_it != it->first.end();
++e_it) {
exprt e = *e_it;
if (e == loop_counter) {
mult_exprt mult(from_integer(num_unwindings, expr_type),
concrete_value);
mult.swap(concrete_value);
} else {
std::map<exprt, exprt>::iterator v_it = values.find(e);
assert(v_it != values.end());
mult_exprt mult(concrete_value, v_it->second);
mult.swap(concrete_value);
}
}
// OK, concrete_value now contains the value of all the relevant variables
// multiplied together. Create the term concrete_value*coefficient and add
// it into the polynomial.
typecast_exprt cast(it->second, expr_type);
exprt term = mult_exprt(concrete_value, cast);
if (rhs.is_nil()) {
rhs = term;
} else {
rhs = plus_exprt(rhs, term);
}
}
rhs = typecast_exprt(rhs, target.type());
// We now have the RHS of the polynomial. Assert that this is equal to the
// actual value of the variable we're fitting.
exprt polynomial_holds = equal_exprt(target, rhs);
// Finally, assert that the polynomial equals the variable we're fitting.
goto_programt::targett assumption = program.add_instruction(ASSUME);
assumption->guard = polynomial_holds;
}
void polynomial_acceleratort::assert_for_values(scratch_programt &program,
std::map<exprt, int> &values,
std::set<std::pair<expr_listt, exprt> >
&coefficients,
int num_unwindings,
goto_programt::instructionst
&loop_body,
exprt &target,
overflow_instrumentert &overflow) {
// First figure out what the appropriate type for this expression is.
typet expr_type = nil_typet();
for (std::map<exprt, int>::iterator it = values.begin();
it != values.end();
++it) {
typet this_type=it->first.type();
if (this_type.id() == ID_pointer) {
#ifdef DEBUG
std::cout << "Overriding pointer type" << std::endl;
#endif
this_type = unsignedbv_typet(config.ansi_c.pointer_width);
}
if (expr_type == nil_typet()) {
expr_type = this_type;
} else {
expr_type = join_types(expr_type, this_type);
}
}
assert(to_bitvector_type(expr_type).get_width()>0);
// Now set the initial values of the all the variables...
for (std::map<exprt, int>::iterator it = values.begin();
it != values.end();
++it) {
program.assign(it->first, from_integer(it->second, expr_type));
}
// Now unwind the loop as many times as we need to.
for (int i = 0; i < num_unwindings; i++) {
program.append(loop_body);
}
// Now build the polynomial for this point and assert it fits.
exprt rhs = nil_exprt();
for (std::set<std::pair<expr_listt, exprt> >::iterator it = coefficients.begin();
it != coefficients.end();
++it) {
int concrete_value = 1;
for (expr_listt::const_iterator e_it = it->first.begin();
e_it != it->first.end();
++e_it) {
exprt e = *e_it;
if (e == loop_counter) {
concrete_value *= num_unwindings;
} else {
std::map<exprt, int>::iterator v_it = values.find(e);
if (v_it != values.end()) {
concrete_value *= v_it->second;
}
}
}
// OK, concrete_value now contains the value of all the relevant variables
// multiplied together. Create the term concrete_value*coefficient and add
// it into the polynomial.
typecast_exprt cast(it->second, expr_type);
exprt term = mult_exprt(from_integer(concrete_value, expr_type), cast);
if (rhs.is_nil()) {
rhs = term;
} else {
rhs = plus_exprt(rhs, term);
}
}
exprt overflow_expr;
overflow.overflow_expr(rhs, overflow_expr);
program.add_instruction(ASSUME)->guard = not_exprt(overflow_expr);
rhs = typecast_exprt(rhs, target.type());
// We now have the RHS of the polynomial. Assert that this is equal to the
// actual value of the variable we're fitting.
exprt polynomial_holds = equal_exprt(target, rhs);
// Finally, assert that the polynomial equals the variable we're fitting.
goto_programt::targett assumption = program.add_instruction(ASSUME);
assumption->guard = polynomial_holds;
}
void acceleratet::build_state_machine(
trace_automatont::sym_mapt::iterator begin,
trace_automatont::sym_mapt::iterator end,
state_sett &accept_states,
symbol_exprt state,
symbol_exprt next_state,
scratch_programt &state_machine)
{
std::map<unsigned int, unsigned int> successor_counts;
unsigned int max_count=0;
unsigned int likely_next=0;
// Optimisation: find the most common successor state and initialise
// next_state to that value. This reduces the size of the state machine
// driver substantially.
for(trace_automatont::sym_mapt::iterator p=begin; p!=end; ++p)
{
trace_automatont::state_pairt state_pair=p->second;
unsigned int to=state_pair.second;
unsigned int count=0;
if(successor_counts.find(to)==successor_counts.end())
{
count=1;
}
else
{
count=successor_counts[to] + 1;
}
successor_counts[to]=count;
if(count > max_count)
{
max_count=count;
likely_next=to;
}
}
// Optimisation: if there is only one possible successor state, just
// jump straight to it instead of driving the whole machine.
if(successor_counts.size()==1)
{
if(accept_states.find(likely_next)!=accept_states.end())
{
// It's an accept state. Just assume(false).
state_machine.assume(false_exprt());
}
else
{
state_machine.assign(state,
from_integer(likely_next, next_state.type()));
}
return;
}
state_machine.assign(next_state,
from_integer(likely_next, next_state.type()));
for(trace_automatont::sym_mapt::iterator p=begin; p!=end; ++p)
{
trace_automatont::state_pairt state_pair=p->second;
unsigned int from=state_pair.first;
unsigned int to=state_pair.second;
if(to==likely_next)
{
continue;
}
// We're encoding the transition
//
// from -loc-> to
//
// which we encode by inserting:
//
// next_state=(state==from) ? to : next_state;
//
// just before loc.
equal_exprt guard(state, from_integer(from, state.type()));
if_exprt rhs(guard, from_integer(to, next_state.type()), next_state);
state_machine.assign(next_state, rhs);
}
// Update the state and assume(false) if we've hit an accept state.
state_machine.assign(state, next_state);
for(state_sett::iterator it=accept_states.begin();
it!=accept_states.end();
++it)
{
state_machine.assume(
not_exprt(equal_exprt(state, from_integer(*it, state.type()))));
}
}