Instead of asserting theory axioms lazily we create them on the fly and allow propagation eagerly.
The approach uses a waterfall model as follows:
- terms are created: they are inserted into an index for (set.in x S) axiom creation.
- two terms are merged by an equality.
Loop over all new opportunities for axiom instantiation
New axioms are added to a queue of recently created axioms.
- an atomic formula was asserted by the SAT solver.
Update the watch list to find new propagations.
During propagation recently created axioms are either inserted into a propagation queue, or inserted into a watch list.
They are inserted into a propagation queue all or all but one literal is assigned to false.
They are inserted into a watch list if at least two literals are unassigned
They are dropped if the axiom contains a literal that is assigned to true
The propagation queue is processed by by asserting the theory axiom to the core.
Also add some elementary statistics.
A breaking change is to change the datatype for undo-trail in smt_context to not use a custom data-structure.
This can likely cause regressions. For example, the region allocator now comes from the stack_trail instead of being
owned within smt_context with a different declaration order. smt_context could crash during destruction or maybe even pop.
We take the risk as the change is overdue.
Add swap method to ref_vector.
other updates:
- change signature of advance_qhead to simplify call sites
- have model reconstruction replay work on a tail of dependent_expr state, while adding formulas to the tail.
