Abstract
Weak memory models determine the behavior of concurrent programs. While they are often understood in terms of reorderings that the hardware or the compiler may perform, their formal definitions are typically given in a very different style—either axiomatic or operational. In this paper, we investigate to what extent weak behaviors of existing memory models can be fully explained in terms of reorderings and other program transformations. We prove that TSO is equivalent to a set of two local transformations over sequential consistency, but that non-multi-copy-atomic models (such as C11, Power and ARM) cannot be explained in terms of local transformations over sequential consistency. We then show that transformations over a basic non-multi-copy-atomic model account for the relaxed behaviors of (a large fragment of) Power, but that ARM’s relaxed behaviors cannot be explained in a similar way. Our positive results may be used to simplify correctness of compilation proofs from a high-level language to TSO or Power.
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Notes
- 1.
Different models may include some additional relations (e.g., a dependency relation between events is used for Power, see Sect. 5).
- 2.
Lahav et al. [13] treat fence instructions as syntactic sugar for atomic updates of a distinguished location. Here, we have fences as primitive instructions that induce fence events in the program executions.
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Acknowledgments
We would like to thank the FM’16 reviewers for their feedback. This research was supported by an ERC Consolidator Grant for the project “RustBelt”, funded under Horizon 2020 grant agreement no. 683289.
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Lahav, O., Vafeiadis, V. (2016). Explaining Relaxed Memory Models with Program Transformations. In: Fitzgerald, J., Heitmeyer, C., Gnesi, S., Philippou, A. (eds) FM 2016: Formal Methods. FM 2016. Lecture Notes in Computer Science(), vol 9995. Springer, Cham. https://doi.org/10.1007/978-3-319-48989-6_29
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