Spacer has a different defintion of is_clause() than ast_util.
It is currently only used in assertions.
Main difference:
x=y
where x and y are Bool atoms is considered to be an atom, so that
(or (= x y) (not (= z y)))
is a literal
Co-authored-by: Arie Gurfinkel <arie.gurfinkel@uwaterloo.ca>
Fixes a bug in computation of implicants inside spacer.
The instance now returns `unknown`. The root cause is the difference in what
proofs are in spacer and SMT. Spacer returns a proof of query, but horn_tactic
expects a proof of FALSE.
Exceptions caught by value incur needless cost in C++, most of them can
be caught by const-reference, especially as nearly none are actually
used. This could allow compiler generate a slightly more efficient code.
Controlled by fixedpoint.spacer.use_quanti_generalizer
measure cumulative time, number of invocations, and number of failed
SMT calls
Relaxing equality in a pattern: if a variable equals a numeral, relax with GE
pob::get_skolems() returns all skolems that might appear in the pob.
New skolems must be added above the largest index in that map,
even if they are not used in the pob itself.
pattern generalization should be done before the pattern is skolemized and
added into the new cube.
When asserting quantified lemmas are disabled, ground a lemma
explicitly during propagate to make sure that it is ground using our
local set of skolem constants.
The algorithms implemented in the engine are described in the following papers
Anvesh Komuravelli, Nikolaj Bjørner, Arie Gurfinkel, Kenneth L. McMillan:
Compositional Verification of Procedural Programs using Horn Clauses over Integers and Arrays. FMCAD 2015: 89-96
Nikolaj Bjørner, Arie Gurfinkel:
Property Directed Polyhedral Abstraction. VMCAI 2015: 263-281
Anvesh Komuravelli, Arie Gurfinkel, Sagar Chaki:
SMT-Based Model Checking for Recursive Programs. CAV 2014: 17-34
