void cone_of_influencet::cone_of_influence(
const goto_programt::instructiont &i,
const expr_sett &curr,
expr_sett &next)
{
next.insert(curr.begin(), curr.end());
if(i.is_assign())
{
const code_assignt &assignment=to_code_assign(i.code);
expr_sett lhs_syms;
bool care=false;
gather_rvalues(assignment.lhs(), lhs_syms);
for(const auto &expr : lhs_syms)
if(curr.find(expr)!=curr.end())
{
care=true;
break;
}
next.erase(assignment.lhs());
if(care)
{
gather_rvalues(assignment.rhs(), next);
}
}
}
void polynomial_acceleratort::cone_of_influence(
goto_programt::instructionst &orig_body,
exprt &target,
goto_programt::instructionst &body,
expr_sett &cone) {
utils.gather_rvalues(target, cone);
for (goto_programt::instructionst::reverse_iterator r_it = orig_body.rbegin();
r_it != orig_body.rend();
++r_it) {
if (r_it->is_assign()) {
// XXX -- this doesn't work if the assignment is not to a symbol, e.g.
// A[i] = 0;
// or
// *p = x;
code_assignt assignment = to_code_assign(r_it->code);
expr_sett lhs_syms;
utils.gather_rvalues(assignment.lhs(), lhs_syms);
for (expr_sett::iterator s_it = lhs_syms.begin();
s_it != lhs_syms.end();
++s_it) {
if (cone.find(*s_it) != cone.end()) {
// We're assigning to something in the cone of influence -- expand the
// cone.
body.push_front(*r_it);
cone.erase(assignment.lhs());
utils.gather_rvalues(assignment.rhs(), cone);
break;
}
}
}
}
}
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());
}
}
bool polynomial_acceleratort::fit_polynomial_sliced(goto_programt::instructionst &body,
exprt &var,
expr_sett &influence,
polynomialt &polynomial) {
// These are the variables that var depends on with respect to the body.
std::vector<expr_listt> parameters;
std::set<std::pair<expr_listt, exprt> > coefficients;
expr_listt exprs;
scratch_programt program(symbol_table);
exprt overflow_var =
utils.fresh_symbol("polynomial::overflow", bool_typet()).symbol_expr();
overflow_instrumentert overflow(program, overflow_var, symbol_table);
#ifdef DEBUG
std::cout << "Fitting a polynomial for " << expr2c(var, ns) << ", which depends on:"
<< std::endl;
for (expr_sett::iterator it = influence.begin();
it != influence.end();
++it) {
std::cout << expr2c(*it, ns) << std::endl;
}
#endif
for (expr_sett::iterator it = influence.begin();
it != influence.end();
++it) {
if (it->id() == ID_index ||
it->id() == ID_dereference) {
// Hack: don't accelerate variables that depend on arrays...
return false;
}
exprs.clear();
exprs.push_back(*it);
parameters.push_back(exprs);
exprs.push_back(loop_counter);
parameters.push_back(exprs);
}
// N
exprs.clear();
exprs.push_back(loop_counter);
parameters.push_back(exprs);
// N^2
exprs.push_back(loop_counter);
//parameters.push_back(exprs);
// Constant
exprs.clear();
parameters.push_back(exprs);
if (!is_bitvector(var.type())) {
// We don't really know how to accelerate non-bitvectors anyway...
return false;
}
unsigned width=to_bitvector_type(var.type()).get_width();
if(var.type().id()==ID_pointer)
width=config.ansi_c.pointer_width;
assert(width>0);
for (std::vector<expr_listt>::iterator it = parameters.begin();
it != parameters.end();
++it) {
symbolt coeff = utils.fresh_symbol("polynomial::coeff",
signedbv_typet(width));
coefficients.insert(std::make_pair(*it, coeff.symbol_expr()));
}
// Build a set of values for all the parameters that allow us to fit a
// unique polynomial.
// XXX
// This isn't ok -- we're assuming 0, 1 and 2 are valid values for the
// variables involved, but this might make the path condition UNSAT. Should
// really be solving the path constraints a few times to get valid probe
// values...
std::map<exprt, int> values;
for (expr_sett::iterator it = influence.begin();
it != influence.end();
++it) {
values[*it] = 0;
}
#ifdef DEBUG
std::cout << "Fitting polynomial over " << values.size() << " variables" << std::endl;
#endif
for (int n = 0; n <= 2; n++) {
for (expr_sett::iterator it = influence.begin();
it != influence.end();
++it) {
values[*it] = 1;
assert_for_values(program, values, coefficients, n, body, var, overflow);
values[*it] = 0;
}
}
// Now just need to assert the case where all values are 0 and all are 2.
assert_for_values(program, values, coefficients, 0, body, var, overflow);
assert_for_values(program, values, coefficients, 2, body, var, overflow);
for (expr_sett::iterator it = influence.begin();
it != influence.end();
++it) {
values[*it] = 2;
}
assert_for_values(program, values, coefficients, 2, body, var, overflow);
#ifdef DEBUG
std::cout << "Fitting polynomial with program:" << std::endl;
program.output(ns, "", std::cout);
#endif
// Now do an ASSERT(false) to grab a counterexample
goto_programt::targett assertion = program.add_instruction(ASSERT);
assertion->guard = false_exprt();
// If the path is satisfiable, we've fitted a polynomial. Extract the
// relevant coefficients and return the expression.
try {
if (program.check_sat()) {
utils.extract_polynomial(program, coefficients, polynomial);
return true;
}
} catch (std::string s) {
std::cout << "Error in fitting polynomial SAT check: " << s << std::endl;
} catch (const char *s) {
std::cout << "Error in fitting polynomial SAT check: " << s << std::endl;
}
return false;
}