perf fix for propagation behavior for equalities in the new core.
The old behavior was not to allow congruence closure on equalities.
The new behavior is to just not allow merging tf with equalities unless they appear somewhere in a foreign context (not under a Boolean operator)
The change re-surfaces merge_tf and enable_cgc distinction from the old core.
They can both be turned on or off.
merge_enabled renamed to cgc_enabled
The change is highly likely to introduce regressions in the new core.
Change propagation of literals from congruence:
- track antecedent enode. There are four ways to propagate
literals from the egraph.
- the literal is an equality and the two arguments are congruent
- the antecedent is merged with node n and the antecedent has a Boolean variable assignment.
- the antecedent is true or false, they are merged.
- the merge_tf flag is toggled to true but the node n has not been merged with true/false
- remove reduce_invertible. It is subsumed by reduce_uncstr(2)
- introduce a simplifier for reduce_unconstrained. It uses reference counting to deal with inefficiency bug of legacy reduce_uncstr. It decomposes theory plugins into expr_inverter.
reduce_invertible is a tactic used in most built-in scenarios. It is useful for removing subterms that can be eliminated using "cheap" quantifier elimination. Specifically variables that occur only once can be removed in many cases by computing an expression that represents the effect computing a value for the eliminated occurrence.
The theory plugins for variable elimination are very partial and should be augmented by extensions, esp. for the case of bit-vectors where the invertibility conditions are thoroughly documented by Niemetz and Preiner.
the solve_eqs_tactic is to be replaced by a re-implementation that uses solve_eqs in the simplifiers directory.
The re-implementation should address efficiency issues with the previous code.
At this point it punts on low level proofs. The plan is to use coarser
dependency tracking instead of low level proofs for pre-processing. Dependencies can be converted into a proof hint representation that can be checked using a stronger checker.
simplifiers layer is a common substrate for global non-incremental and incremental processing.
The first two layers are new, but others are to be ported form tactics.
- bv::slice - rewrites equations to cut-dice-slice bit-vector extractions until they align. It creates opportunities for rewriting portions of bit-vectors to common sub-expressions, including values.
- euf::completion - generalizes the KB simplifcation from asserted formulas to use the E-graph to establish a global and order-independent canonization.
The interface dependent_expr_simplifier is amenable to forming tactics. Plugins for asserted-formulas is also possible but not yet realized.
