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Fixes #4620.
The extended rewrite (and A B) ---> (and A (B * { A -> true } ) triggers an unsoundness when B contains witness terms. More generally, contextual substitution into witness terms is unsound since the skolemization of witness terms is added globally whereas the substitution corresponds to a fact that holds locally. This means that A -> true above may be added as a global constraint indirectly through witness skolemization.
A general example of this unsoundness:
(or (and (>= x 0) (P (witness ((z Int)) (=> (>= x 0) (= (* z z) x))))) F)
rewrites to
(or (and (>= x 0) (P (witness ((z Int)) (= (* z z) x)))) F)
preprocesses to
(and (or (and (>= x 0) (P k)) F) (= (* k k) x))
which now implies that (>= x 0) by the last conjunct, whereas this was not implied in the original formula
This PR limits the kinds that can be traversed when applying substitutions in the extended rewriter, including from the rewrite above. In particular, the fix ensures that the partialSubstitute method is used in the extended rewriter when applicable, which now explicitly disallows recursion on WITNESS.
Notice that this fixes contextual substitutions in the extended rewriter, but does not fix the more general issue. In particular, we still should be careful to check if contextual substitutions are applied by any other preprocessing passes.
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Fixes #4476.
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Fixes #4273 and fixes #4274 .
This also removes a spurious assertion from the Node::substitute method that the result node is not equal to the domain. This is violated for f(f(x)) { f(x) -> x }.
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This commit adds statistics for string rewrites. This is work towards proof
support in the string solver. At a high level, this commit adds a pointer to a
`SequenceStatistics` in the rewriters and modifies
`SequencesRewriter::returnRewrite()` to count the rewrites done. In practice,
to make this work requires a couple of changes, some of them temporary:
- We can't have a single `Rewriter` instance shared between different
`SmtEngine` instances anymore. Thus the `Rewriter` is now owned by the
`SmtEngine` and calling the rewriter retrieves the rewriter associated with
the current `SmtEngine`. This is a temporary workaround before we get rid of
singletons.
- Methods in the `SequencesRewriter` and the `StringsRewriter` are made
non-`static` because they need access to the statistics instance.
- `StringsEntail` now has non-`static` methods because it needs a reference to
the sequences rewriter that it can call.
- The interaction between the `StringsRewriter` and the `SequencesRewriter`
changed: the `StringsRewriter` is now a proper `TheoryRewriter` that inherits
from `SequencesRewriter` and calls its `postRewrite()` before applying its
own rewrites (this is essentially a reversal of roles from before: the
`SequencesRewriter` used to call `static` methods in the `StringsRewriter`).
- The theory rewriters are now owned by the individual theories. This design
mirrors the `EqualityEngine`s owned by the individual theories.
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Organization towards theory of sequences.
The motivation of this PR is to ensure that string-specific operators in the rewriter are in their own file; thus the use of mkConst<String> / getConst<String> is allowable in rewriter_str.cpp.
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Fixes all -Wshadow warnings and enables the -Wshadow compile flag globally.
Co-authored-by: Clark Barrett <barrett@cs.stanford.edu>
Co-authored-by: Andres Noetzli <andres.noetzli@gmail.com>
Co-authored-by: Aina Niemetz <aina.niemetz@gmail.com>
Co-authored-by: Alex Ozdemir <aozdemir@hmc.edu>
Co-authored-by: makaimann <makaim@stanford.edu>
Co-authored-by: yoni206 <yoni206@users.noreply.github.com>
Co-authored-by: Andrew Reynolds <andrew.j.reynolds@gmail.com>
Co-authored-by: AleksandarZeljic <zeljic@stanford.edu>
Co-authored-by: Caleb Donovick <cdonovick@users.noreply.github.com>
Co-authored-by: Amalee <amaleewilson@gmail.com>
Co-authored-by: Scott Kovach <dskovach@gmail.com>
Co-authored-by: ntsis <nekuna@gmail.com>
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arities (#3681)
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This was causing assertion failures when using Sets + Sygus.
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We found that the `ss-combine` rewrite hurts solving performance, so
this commit is moving it to the extended rewriter.
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This moves the extended rewrites for string equality to the main strings rewriter as a function rewriteEqualityExt, and makes this function called on every equality that is generated (from non-equalities) by our rewriter.
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This is work towards #2305.
With this PR, CVC4's performance is fairly reasonable on the Kind2 BMC benchmarks with --decision=internal --ext-rew-prep --ext-rew-prep-agg.
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* Add arithmetic monomial sum utility.
* Clang format
* Fix
* Address review.
* Fix missed comment.
* Format
* Fix
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* Split explain utility, invariance tests.
* Split extended rewriter.
* Remove unused function.
* Minor
* Move generic term utilities to term_util.
* Documentation, minor.
* Make arguments private in eval invariance.
* Document
* More documentation.
* Clang format.
* Fix, improve.
* Format
* Address review.
* Address missed comment.
* Add line breaks
* Format
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