/*
* Learn a constraint for the exists variable based on the
* existing forall witness for constraint i:
* - the witness is defined by the uvars of constraint i
* and the values stored in uvalue_aux.
*
* This function adds a constraint to the exists_context that will remove the
* current exists model:
* - if solver->option is EF_NOGEN_OPTION, the new constraint is
* of the form (or (/= var[0] eval[k0]) ... (/= var[k-1] eval[k-1]))
* where var[0 ... k-1] are the exist variables of constraint i
* - if solver->option is EF_GEN_BY_SUBST_OPTION, we build a new
* constraint by substitution (option 2)
*
* If something goes wrong, then solver->status is updated to EF_STATUS_ERROR.
* If the new learned assertion makes the exist context trivially unsat
* then context->status is set to EF_STATUS_UNSAT.
* Otherwise context->status is kept as is.
*/
static void ef_solver_learn(ef_solver_t *solver, uint32_t i) {
ef_cnstr_t *cnstr;
term_t *val;
term_t new_constraint;
uint32_t n;
int32_t code;
assert(i < ef_prob_num_constraints(solver->prob));
cnstr = solver->prob->cnstr + i;
switch (solver->option) {
case EF_NOGEN_OPTION:
/*
* project solver->evalues on the existential
* variables that occur in constraint i.
* then build (or (/= evar[0] val[0]) ... (/= evar[n-1] val[n-1]))
*/
n = ef_constraint_num_evars(cnstr);
resize_ivector(&solver->evalue_aux, n);
solver->evalue_aux.size = n;
val = solver->evalue_aux.data;
ef_project_exists_model(solver->prob, solver->evalue, cnstr->evars, val, n);
new_constraint = ef_generalize1(solver->prob, cnstr->evars, val, n);
break;
case EF_GEN_BY_SUBST_OPTION:
val = solver->uvalue_aux.data;
new_constraint = ef_generalize2(solver->prob, i, val);
if (new_constraint < 0) {
// error in substitution
solver->status = EF_STATUS_SUBST_ERROR;
solver->error_code = new_constraint;
return;
}
break;
case EF_GEN_BY_PROJ_OPTION:
default: // added this to prevent bogus GCC warning
new_constraint = ef_generalize3(solver, i);
if (new_constraint < 0) {
return;
}
break;
}
// add the new constraint to the exists context
code = update_exists_context(solver, new_constraint);
if (code == TRIVIALLY_UNSAT) {
solver->status = EF_STATUS_UNSAT;
} else if (code < 0) {
solver->status = EF_STATUS_ASSERT_ERROR;
solver->error_code = code;
}
}
/*
* Sampling for the i-th constraint in solver->prob
* - search for at most max_samples y's that satisfy the assumption of constraint i in prob
* - for each such y, add a new constraint to the exist context ctx
* - max_samples = bound on the number of samples to take (must be positive)
*
* Constraint i is of the form
* (FORALL Y_i: B_i(Y_i) => C(X_i, Y_i))
* - every sample is a model y_i that satisfies B_i.
* - for each sample, we learn that any good candidate X_i must satisfy C(X_i, y_i).
* So we add the constraint C(X_i, y_i) to ctx.
*
* Update the solver->status to
* - EF_STATUS_UNSAT if the exits context is trivially unsat
* - EF_STATUS_..._ERRORif something goes wrong
* - EF_STATUS_INTERRUPTED if a call to check/recheck context is interrupted
* keep it unchanged otherwise (should be EF_STATUS_SEARCHING).
*/
static void ef_sample_constraint(ef_solver_t *solver, uint32_t i) {
context_t *sampling_ctx;
ef_cnstr_t *cnstr;
term_t *value;
uint32_t nvars, samples;
int32_t ucode, ecode;
smt_status_t status;
term_t cnd;
assert(i < ef_prob_num_constraints(solver->prob) && solver->max_samples > 0);
cnstr = solver->prob->cnstr + i;
/*
* make uvalue_aux large enough
* its size = number of universal variables in constraint i
*/
nvars = ef_constraint_num_uvars(cnstr);
resize_ivector(&solver->uvalue_aux, nvars);
solver->uvalue_aux.size = nvars;
value = solver->uvalue_aux.data;
samples = solver->max_samples;
/*
* assert the assumption in the forall context
*/
sampling_ctx = get_forall_context(solver);
ucode = assert_formula(sampling_ctx, cnstr->assumption);
while (ucode == CTX_NO_ERROR) {
status = satisfy_context(sampling_ctx, solver->parameters, cnstr->uvars, nvars, value, NULL);
switch (status) {
case STATUS_SAT:
case STATUS_UNKNOWN:
// learned condition on X:
cnd = ef_substitution(solver->prob, cnstr->uvars, value, nvars, cnstr->guarantee);
if (cnd < 0) {
solver->status = EF_STATUS_SUBST_ERROR;
solver->error_code = cnd;
goto done;
}
ecode = update_exists_context(solver, cnd);
if (ecode < 0) {
solver->status = EF_STATUS_ASSERT_ERROR;
solver->error_code = ecode;
goto done;
}
if (ecode == TRIVIALLY_UNSAT) {
solver->status = EF_STATUS_UNSAT;
goto done;
}
break;
case STATUS_UNSAT:
// no more samples for this constraints
goto done;
case STATUS_INTERRUPTED:
solver->status = EF_STATUS_INTERRUPTED;
goto done;
default:
solver->status = EF_STATUS_CHECK_ERROR;
solver->error_code = status;
goto done;
}
samples --;
if (samples == 0) goto done;
ucode = assert_blocking_clause(sampling_ctx);
}
/*
* if ucode < 0, something went wrong in assert_formula
* or in assert_blocking_clause
*/
if (ucode < 0) {
solver->status = EF_STATUS_ASSERT_ERROR;
solver->error_code = ucode;
}
done:
clear_forall_context(solver, true);
}