z3-z3-4.13.0.src.muz.spacer.spacer_notes.txt Maven / Gradle / Ivy
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a queue contains a model_node
let n = leaves.pop_top ()
if (!n.has_derivation ())
if n.pt ().must_reach (n.post ())
add parent of n to the leaves
return
check abstract reachability of n
if must reachable then
create new reachability fact for n.pt ()
add parent of n to the leaves
else if may reachable then
create derivation d for n
create model_node kid for the top of d
add kid to the leaves
else /* unreachable */
create a lemma for n.pt ()
p = parent of n
p.reset_derivation()
add p to the leaves
else if (n.has_derivation ())
create next model_node kid for n.get_derivation ()
if (kid != NULL)
add kid to leaves
else /* done with the derivation, no more kids */
// the derivation is reachable, otherwise it was reset in another branch
p = parent of n
p.reset_derivation ()
add p to the leaves
=================================================================================
create derivation for the top of d
input:
model M,
transition relation formula trans with auxiliary variables quantified out
sequence of pedicates P_i,
may and must summaries of P_i
=================================================================================
create first derivation child:
input: model
create next derivation child:
create new model
update trans by computing pre-image over new reachability facts
call create next derivation child
private:
create next derivation child using a given model, and starting index
=========================================================
create a next model for a derivation
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// an obligation
model_node
// NULL means root
model_node_ref parent
model_node_ref_vector kids
pred_transformer &predicate
expr* condition
unsigned level
unsigned depth
// monotonically increasing
unsigned id
bool open;
model_node::close ()
open = false
for k : kids do k.close ()
model_search
model_node_ref root;
// proof obligations
priority_queue m_obligations;
model_node_ref m_last_reachable;
bool model_node::operator< (model_node& other)
lexicographic order based on
level<, depth<, id>
assert (!m_last_reachable);
while (!m_obligations.empty ())
{
// propagate reachability as much as possible
while (m_last_reachable)
{
obl = m_last_reachable
m_last_reachable.reset ();
if (is_root (obl)) return true;
if (discharge_obligation (obl.get_parent ()) == l_true)
m_last_reachable = obl.get_parent ();
}
// at least one obligation is not closed, ow root was reachable
while (m_obligations.top ().is_closed ()) m_obligations.pop ();
assert (!m_obligations.empty ());
// process an obligation
assert (!m_last_reachable)
obl = m_obligations.top ();
switch (discharge_obligation (obl))
{
case l_true:
// if reachable, schedule a reachability round
m_last_reachable = m_obligations.top ();
m_obligations.pop ();
break;
case l_false:
// if unreachable removed from the queue
m_obligations.pop ();
/// bump level
obl.inc_level ();
/// optionally insert back into the queue
if (is_active (obl)) m_obligations.push (obl);
break;
default:
assert (m_obligations.top () != obl);
}
}
return false
/// with priority queue
bool is_active (model_node obl) { return level <= m_search.max_level (); }
/// with out priority queue. Discharged obligations are dropped
bool is_active (model_node obl) { return false; }
discharge_obligation (model_node obl)
{
assert (!obl.is_closed ());
switch (check_reachability (obl))
{
case l_true:
obl.close ()
update reachability facts
return l_true;
case l_false:
update lemmas
return l_false
case l_unknown:
create children
populate m_obligations queue
return l_unknown
}
}
=============================================================
a node keeps a derivation object
if a node is sat, a new node is constructed and inherits the derivation object
if a node is sat and the derivation is done, this is reported to the parent
expand_node(n):
process node ignoring derivation
if sat:
if concrete:
if has derivation and has next child
close current node and push new node
return l_undef
else
return l_true
else
create_child (creates a new node and optionally sets derivation)
else if unsat
generate lemmas
derivation remains unchanged to be used at a higher level
return
======================================================================
1. open disjunction for transition relation
- a fresh literal to open the disjunction of the transition relation
- expr* expand_init (expr *e) -- add e to initial state and return
new disj var
- close the disjunction by passing the negation of the literal
during various calls
- store the literal negated to have access to both positive and
negative versions
- with this, can do an optional check whether the lemmas alone are
strong enough to discharge the counterexample. Easiest is to
implement it as a separate pre-check.
2. auxiliary variables in lemmas and reach-facts.
- store and expect auxiliary variables
- quantify them out when necessary
3. initial rules as reach-facts
- add initial rules of a predicate to its reach-facts. Propagate them to uses.
- this way, the checks at level 0 will include initial rules of
immediate predecessors
======================================================================
reach_fact_ref_vector m_reach_facts
app_ref_vector m_reach_case_vars
bool is_must_reachable (expr *state, model_ref *model)
reach_fact* get_used_reach_fact (model_evaluator &mev)
app* mk_fresh_reach_case_var ()
expr* get_reach ()
expr* get_last_reach_case_var ()
app* get_reach_case_var (unsigned idx)
get_used_origin_reach_fact():
======================================================================
4. track relationship between an obligation and lemmas. Attempt to
generalize an obligation into the exact lemma that worked
before. Perhaps pick one lemma with highest level? Implement as
core-generalizer. Will require reworking how legacy_frames is implemented.