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Constraints solvers play a significant role in the analysis, synthesis, and formal verification of complex cyber-physical systems. In this article, we study the problem of designing a scalable constraints solver for an important class of constraints named polynomial constraint inequalities (also known as nonlinear real arithmetic theory). In this article, we introduce a solver named PolyARBerNN that uses convex polynomials as abstractions for highly nonlinears polynomials. Such abstractions were previously shown to be powerful to prune the search space and restrict the usage of sound and complete solvers to small search spaces. Compared with the previous efforts on using convex abstractions, PolyARBerNN provides three main contributions namely (i) a neural network guided abstraction refinement procedure that helps selecting the right abstraction out of a set of pre-defined abstractions, (ii) a Bernstein polynomial-based search space pruning mechanism that can be used to compute tight estimates of the polynomial maximum and minimum values which can be used as an additional abstraction of the polynomials, and (iii) an optimizer that transforms polynomial objective functions into polynomial constraints (on the gradient of the objective function) whose solutions are guaranteed to be close to the global optima. These enhancements together allowed the PolyARBerNN solver to solve complex instances and scales more favorably compared to the state-of-the-art nonlinear real arithmetic solvers while maintaining the soundness and completeness of the resulting solver. In particular, our test benches show that PolyARBerNN achieved 100X speedup compared with Z3 8.9, Yices 2.6, and PVS (a solver that uses Bernstein expansion to solve multivariate polynomial constraints) on a variety of standard test benches. Finally, we implemented an optimizer called PolyAROpt that uses PolyARBerNN to solve constrained polynomial optimization problems. Numerical results show that PolyAROpt is able to solve high-dimensional and high order polynomial optimization problems with higher speed compared to the built-in optimizer in the Z3 8.9 solver.
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SMT Theory Arbitrage: Approximating Unbounded Constraints using Bounded Theories
SMT solvers are foundational tools for reasoning about constraints in practical problems both within and outside program analysis. Faster SMT solving improves the performance of practical tools and expands the set of tractable problems. Existing approaches to improving solver performance either focus on general algorithms applied below the level of individual theories, or focus on optimizations within a single theory. Unbounded constraints in which the number of possible variable values is infinite, such as real numbers and integers, pose a particularly difficult challenge for solvers. Bounded constraints in which the set of possible values is finite, such as bitvectors and floating-point numbers, on the other hand, are decidable and have been the subject of extensive performance improvement efforts. This paper introduces a theory arbitrage: we transform unbounded constraints, which are often expensive to solve, into bounded constraints, which are typically cheaper to solve. By converting unbounded problems into bounded ones, theory arbitrage takes advantage of better performance on bounded constraints and unlocks optimization techniques that only apply to bounded theories. The transformation is achieved by harnessing a novel abstract interpretation strategy to infer bounds. The bounded transformed constraint is then an underapproximation of the semantics of the unbounded original. We realize our method for the theories of integers and real numbers with a practical tool (STAUB). Our evaluation demonstrates that theory arbitrage alone can speed up individual constraints by orders of magnitude and achieve up to a 1.4× speedup on average across nonlinear integer benchmarks. Furthermore, it enables the use of the recent compiler optimization-based technique SLOT for unbounded SMT theories, unlocking a further speedup of up to 3×. Finally, we incorporate STAUB into a practical termination proving tool and observe an overall 9% improvement in performance.
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- PAR ID:
- 10541919
- Publisher / Repository:
- ACM
- Date Published:
- Journal Name:
- Proceedings of the ACM on Programming Languages
- Volume:
- 8
- Issue:
- PLDI
- ISSN:
- 2475-1421
- Page Range / eLocation ID:
- 246 to 271
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1145/3656387
