CNode* VariableEliminator::remove_eq_var_with_no_parents(Clause& cl,
VariableTerm* evar)
{
set<EqLeaf*> to_delete;
set<EqLeaf*>::iterator it = cl.neg_eq.begin();
for(; it!= cl.neg_eq.end(); it++)
{
EqLeaf* eq = *it;
Term* lhs = eq->get_lhs();
Term* rhs = eq->get_rhs();
if(lhs->contains_term(evar) || rhs->contains_term(evar))
to_delete.insert(eq);
}
for(it=to_delete.begin(); it!= to_delete.end(); it++)
{
cl.neg_eq.erase(*it);
}
CNode* new_node = cl.to_cnode();
return new_node;
}
CNode* VariableEliminator::eliminate_var_conjunct(CNode* node, VariableTerm* evar)
{
if(DEBUG) {
cout << "IN ELIMINATE VAR FROM CONJUNCT " << node->to_string()<< endl;
cout << "Trying to eliminate: " << evar->to_string() <<endl;
}
int initial_count = fresh_var_counter;
assert(node->is_conjunct());
Clause cl(node);
map<Term*, Term*> denestings;
cl.denest( &denestings);
if(DEBUG) {
cout << "DENESTINGS: " << endl;
map<Term*, Term*>::iterator it = denestings.begin();
for(; it!= denestings.end(); it++)
{
cout << "\t " << it->first->to_string() <<
"-> " << it->second->to_string() << endl;
}
}
ClauseSolve cs(&cl, NULL);
bool res = cs.is_sat();
/*
* If the clause is UNSAT, the SNC is false.
* We call sat to ensure that all relevant interactions
* are propagated between the ILP and EQ domains. After calling
* sat, eq_members, var_to_cols etc are properly initialized.
*/
if(!res){
return False::make();
}
Term* rep = cs.find_representative(evar);
Term* valid_rep = NULL;
if(rep!=NULL && !rep->contains_term(evar) && denestings.count(rep)==0) {
valid_rep = rep;
}
else {
set<Term*>& eq_class = cs.eq_members[rep];
set<Term*>::iterator it = eq_class.begin();
for(; it!= eq_class.end(); it++) {
Term* cur_t = *it;
if(!cur_t->contains_term(evar)&&denestings.count(cur_t)==0){
valid_rep = cur_t;
break;
}
}
}
/*
* We found one member in the equivalence class of this variable
* that does not contain that variable.
*/
if(valid_rep != NULL) {
map<Term*, Term*> subs;
subs[evar] = valid_rep;
CNode* res = node->substitute(subs);
node = node->substitute(denestings);
return res;
}
set<FunctionTerm*> direct_parents;
get_direct_parents(evar, direct_parents, cs.eq_members);
if(!over_approximate) {
if(direct_parents.size() > 0) return False::make();
}
/*
* Base case: If this term does not contain any parent terms,
* eliminate it from the ILP domain
*/
if(direct_parents.size() == 0 && cs.ilp_vars.count(evar->get_var_id()) > 0 ){
set<CNode*> mod_constraints;
if(DEBUG) {
cout << "ELIMINATING FROM ILP: " << cl.to_string("&") << endl;
}
CNode* res= eliminate_var_from_ilp_domain(cl, evar, mod_constraints);
if(DEBUG) {
cout << "AFTER ELIMINATING FROM ILP: " << res->to_string() << endl;
}
res = eliminate_denestings(res, denestings, evar, initial_count, false);
return res;
}
else if(direct_parents.size() == 0)
{
CNode* res = remove_eq_var_with_no_parents(cl, evar);
return eliminate_denestings(res, denestings, evar, initial_count,
false);
}
/*
* We want to replace each function term in which the variable appears with
* a fresh term u, u' etc. and then introduce conditional equality
* constraints.
* For example, if we have f(x, a) = f(x, b), introduce a=b->u1=u2
* where u1 and u2 are the replacements for f(x,a) and f(x,b) respectively.
*/
map<VariableTerm*, FunctionTerm*> fresh_vars_to_functions;
map<FunctionTerm*, VariableTerm*> functions_to_fresh_vars;
/*
* A map from function id's (e.g. f) to all the function terms containing x
* as an argument to this function id.
*/
map<int, set<FunctionTerm*> > function_id_to_functions;
{
introduce_fresh_vars_for_function_terms(cl, evar, direct_parents,
fresh_vars_to_functions, functions_to_fresh_vars,
function_id_to_functions);
if(DEBUG) {
cout << "FUNCTION ID TO FUNCTIONS: " << endl;
map<int, set<FunctionTerm*> >::iterator it2 = function_id_to_functions.begin();
for(; it2 != function_id_to_functions.end(); it2++){
cout << "Function: " << CNode::get_varmap().get_name(it2->first);
set<FunctionTerm*>::iterator it3 = it2->second.begin();
for(; it3!= it2->second.end(); it3++) {
cout << "\t " << (*it3)->to_string() << endl;
}
}
}
}
/*
* Introduce conditional equalities
* First, introduce conditional equalities between u terms
*/
map<CNode*, CNode*> conditional_equalities;
map<int, set<FunctionTerm*> >::iterator it = function_id_to_functions.begin();
for(; it!= function_id_to_functions.end(); it++) {
set<FunctionTerm*>& s1 = it->second;
set<FunctionTerm*>::iterator it2 = s1.begin();
for(; it2!= s1.end(); it2++) {
FunctionTerm* ft1 = *it2;
set<FunctionTerm*>::iterator it3 = it2;
it3++;
for(; it3 != s1.end(); it3++) {
set<CNode*> ops;
FunctionTerm* ft2 = *it3;
assert(ft1->get_args().size() == ft2->get_args().size());
for(unsigned int i=0; i< ft1->get_args().size(); i++)
{
Term* cur_arg1 = ft1->get_args()[i];
Term* cur_arg2 = ft2->get_args()[i];
if(cur_arg1 == evar && cur_arg2 == evar) continue;
if(cur_arg1 == evar || cur_arg2 == evar) {
if(cs.ilp_vars.count(evar->get_var_id()) == 0) continue;
}
CNode* eq = EqLeaf::make(cur_arg1, cur_arg2);
ops.insert(eq);
}
if(ops.size() == 0) continue;
CNode* precedent = Connective::make_and(ops);
assert(functions_to_fresh_vars.count(ft1) > 0);
assert(functions_to_fresh_vars.count(ft2) > 0);
VariableTerm* fresh1 = functions_to_fresh_vars[ft1];
VariableTerm* fresh2 = functions_to_fresh_vars[ft2];
CNode* antecedent = EqLeaf::make(fresh1, fresh2);
conditional_equalities[precedent] = antecedent;
}
}
}
/*
* If the variable to be eliminated is a shared variable, also need to
* add conditional equalities with non-u terms.
*/
if(cs.ilp_vars.count(evar->get_var_id()) > 0) {
map<int, set<FunctionTerm*> > functions_in_clause;
get_function_terms_in_clause(cl, functions_in_clause);
it = function_id_to_functions.begin();
for(; it!= function_id_to_functions.end(); it++) {
set<FunctionTerm*>& evar_terms = it->second;
if(functions_in_clause.count(it->first)==0) continue;
set<FunctionTerm*>& clause_terms = functions_in_clause[it->first];
set<FunctionTerm*>::iterator it2 = evar_terms.begin();
for(; it2 != evar_terms.end(); it2++) {
FunctionTerm* ft1 = *it2;
set<FunctionTerm*>::iterator it3 = clause_terms.begin();
for(; it3 != clause_terms.end(); it3++) {
set<CNode*> ops;
FunctionTerm* ft2 = *it3;
assert(ft1->get_args().size() == ft2->get_args().size());
for(unsigned int i=0; i< ft1->get_args().size(); i++)
{
Term* cur_arg1 = ft1->get_args()[i];
Term* cur_arg2 = ft2->get_args()[i];
CNode* eq = EqLeaf::make(cur_arg1, cur_arg2);
ops.insert(eq);
}
if(ops.size() == 0) continue;
CNode* precedent = Connective::make_and(ops);
assert(functions_to_fresh_vars.count(ft1) > 0);
VariableTerm* fresh1 = functions_to_fresh_vars[ft1];
CNode* antecedent = EqLeaf::make(fresh1, ft2);
conditional_equalities[precedent] = antecedent;
}
}
}
}
if(DEBUG)
{
cout << "CONDITIONAL EQUALITIES: " << endl;
map<CNode*, CNode*>::iterator it = conditional_equalities.begin();
for(; it!= conditional_equalities.end(); it++) {
CNode* precedent = it->first;
CNode* antecedent = it->second;
cout << precedent->to_string() << " => " << antecedent->to_string()
<< endl;
}
}
/*
* Make the new formula anded with the conditional constraints
*/
set<CNode*> new_ops;
CNode* original = cl.to_cnode();
new_ops.insert(original);
map<CNode*, CNode*>::iterator cond_it = conditional_equalities.begin();
for(; cond_it != conditional_equalities.end(); cond_it++)
{
CNode* cur_cond = Connective::make_implies(cond_it->first,
cond_it->second);
new_ops.insert(cur_cond);
}
CNode* new_node = Connective::make_and(new_ops);
new_node = eliminate_denestings(new_node, denestings, evar, initial_count,
true);
return new_node;
}
