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This includes several improvements for cegqi with arithmetic:
- Randomly choose either lower or upper bounds instead of always using lower bounds (this is similar to cegqi+BV),
- Equalities are handled by processAssertions,
- Resort to *only* model values at full effort instead of trying to mix model values/bounds (this is also similar to cegqi+BV),
- cegqi+arithmetic does not try multiple instantiations unless the flag cbqiMultiInst is set. This makes it so that ceg_instantiator does not have exponential behavior when the strategy is non-monotonic.
It also includes a core fix to computing what bound is optimal based on an ordering that incorporates virtual terms. Previously, we would consider, e.g.:
`a+b*delta > c+d*delta if a>=c and b>=d`
Whereas the correct check is lexicographic:
`a+b*delta > c+d*delta if a>c or a=c and b>d`
This means e.g. 2+(-1)*delta > 3 was previously wrongly inferred.
This is part of merging https://github.com/ajreynol/CVC4/tree/cegqiSingleInst, which is +3-0 on SMTLIB BV and +12-9 on SMTLIB LIA+LRA+NRA+NIA.
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This includes:
- A missing case in the smt2 printer,
- A bug in an inference of int2bv applied to bv2nat where the types are different.
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- Introduces a system that validating that, when not using THEORY_SEP, that it is not possible to
obtain the separation logic heap/nil (validate_exception())
- Introduces a system test demonstrating how to use the separation logic theory, and then how
to use the "getters" to obtain and interrogate the heap/nil expressions (validate_getters())
- Refactors the original getters to avoid duplicate code
- Add a check as part of the getters to ensure that THEORY_SEP is in use
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Eager incremental solving is achieved via solving under assumptions. As soon as incremental and eager bit-blasting is enabled, assertions are passed to the SAT solver as assumptions rather than assertions. This requires the eager SAT solver to support incremental solving, which is currently only supported by CryptoMiniSat.
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The rewriter for lambda is currently too aggressive, there are cases like:
lambda xy. x = y
that are converted into an array representation that when indexing based on x gives (store y true false), which is subsequently converted to:
lambda fv_1 fv_2. fv_1 = y
where fv_1 and fv_2 are canonical free variables. Here, y is used as index but was not substituted hence is incorrectly made free.
To make things simpler, this PR disables any rewriting for lambda unless the array representation of the lambda is a constant, which hardcodes/simplifies a previous argument (reqConst=true). This fixes a sygus issue I ran into yesterday (regression added in this PR).
Some parts of the code were formatted as a result.
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(#2184)
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Fixes issue #2137. CnfProof has a stack of assertions that are being
converted to clauses. Previously, it could happen that while an
assertion was being added, TheoryProxy::explainPropagation() would be
called from Solver::reason() and push an assertion to the stack that was
then not removed. This lead to a clause id of the assertion being
associated with the explanation instead, which in turn could lead to a
wrong unsat core. This commit identifies two cases where
TheoryProxy::explainPropagation() is called without cleaning up the
assertion stack afterwards. It also adds an assertion that the assertion
stack must be empty when we are getting the unsat core.
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The issue is not triggered anymore after PR #2059 but the test case is
good to have for changes in MiniSat code.
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In MiniSat's analyze(), we were taking a reference of a clause that
could be invalidated by a call to resolveOutUnit(). resolveOutUnit() can
lead to allocation of clauses which in turn can lead to clauses being
reallocated, making the reference stale. The commit encloses the
reference in a code block that makes the lifetime of the reference more
obvious and removes uses of the potentially stale reference.
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This commit adds the Evaluator class that can be used to quickly
evaluate terms under a given substitution without going through the
rewriter. This has been shown to lead to significant performance
improvements on SyGuS PBE problems with a large number of inputs because
candidate solutions are evaluated on those inputs. With this commit, the
evaluator only gets called from the SyGuS solver but there are
potentially other places in the code that could profit from it.
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When moving the LFSC checker out of the CVC4 repository in commit
dfa69ff98a14fcc0f2387e59a0c9994ef440e7d0, we disabled checking unsat
cores when CVC4 was compiled without LFSC due to the complexity of the
regression script. This commit changes the new(-ish) Python regression
script to check unsat cores even when CVC4 was compiled without LFSC.
This is done by having two separate flags, --with-lfsc and
--enable-proof, for the regression script that mirror the configuration
flags. The regression script performs unsat cores and proofs checks
based on those flags.
Additionally, this commit changes the regression script to check proofs
and unsat cores in two independent runs. Testing them in a single run
masked issues #1953 and #1954.
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Commit 106e764a04e4099cc36d13de9cec47cbf717b6cc missed one test case.
This commit disables that test case for the competition build.
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This commit adds the option of skipping regressions when a specified
feature is enabled. It also changes some of the regression tests to be
skipped when it is a competition build because regressions fail
otherwise. In the tests changed in this commit, we do not care about
reproducing error messages in a competition build, so we can skip them.
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Some quick background: CVC4 has two primary contexts: the assertion
context (which corresponds to the push/pops issued by the user) and the
decision/SAT context (which corresponds to the push/pops done by the
user and each decision made by MiniSat.
Before 2cc0e2c6a691fb6d30ed8879832b49bc1f277d77, we had an additonal
push/pop when doing the actual solving. With these removed, it could
happen that we get a wrong result when doing incremental solving:
```
...
; check-sat call returns sat, the decision level in the SAT solver is
; non-zero at this point
(check-sat)
; Solver::addClause_() determines that we cannot add the clause to the
; SAT solver directly because the decision level is non-zero (i.e. the
; clause is treated like a theory lemma), thus it is added to the lemmas
; list.
(assert false)
; The solver stores some information about the current state, including
; the value of the "ok" flag in Solver, which indicates whether the
; current constraints are unsatisfiable. Note that "ok" is true at this
; point.
(push)
; Now, in Solver::updateLemmas(), we add clauses from the lemmas list.
; The problem is that empty clauses (which "false" is after removing "false"
; literals) and unit clauses are not added like normal clauses. Instead,
; the empty clause, essentially just results in the "ok" flag being set to
; false (unit clauses are added to the decision trail).
(check-sat)
; Here, the solver restores the information stored during
; (push), including the "ok" flag, which is now true again.
(pop)
; At this point, the solver has "forgotten" about (assert false) since
; the "ok" flag is back to true and it answers sat.
(check-sat)
```
There are multiple ways to look at the problem and to fix it:
- One could argue that an input assertion should always be added
directly to the clauses in the SAT solver, i.e. the solver should
always be at decision level 0 when we are adding input clauses. The
advantage of this is that it is relatively easy to implement,
corresponds to what the original MiniSat code does (it calls
Solver::cancelUntil(0) after solving), and is no worse than what we had
before commit 2cc0e2c6a691fb6d30ed8879832b49bc1f277d77 (push/pop do a
strict superset of what resetting the decision at the current assertion
level does). The disadvantage is that we might throw away some useful work.
- One could argue that is fine that (assert false) is treated like a
theory lemma. The advantage being that it might result in more efficient
solving and the disadvantage being that it is much trickier to
implement.
Unfortunately, it is not quite clear from the code what the original
intention was but we decided to implement the first solution. This
commit exposes a method in MiniSat to reset the decisions at the current
assertion level. We call this method from SmtEngine after solving.
Resetting the decisions directly after solving while we are still in
MiniSat does not work because it causes issues with datastructures in
the SMT solver that use the decision context (e.g.
TheoryEngine::d_incomplete seems to be reset too early, resulting in us
answering sat instead of unknown).
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This commit adds supprt for the `REQUIRES` directive in our regression
benchmarks. This directive can be used to enable certain benchmarks only
if CVC4 has been configured with certain features enabled.
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Further, fix a bug in the AIG bitblaster that was also uncovered with the
minimized file.
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