A Two-Phase Infinite/Finite Low-Level Memory Model: Reconciling Integer–Pointer Casts, Finite Space, and undef at the LLVM IR Level of Abstraction

This paper provides a novel approach to reconciling complex low-level memory model features, such as pointer--integer casts, with desired refinements that are needed to justify the correctness of program transformations. The idea is to use a "two-phase" memory model, one with an unbounded...

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Bibliographic Details
Published in:Proceedings of ACM on programming languages Vol. 8; no. ICFP; pp. 789 - 817
Main Authors: Beck, Calvin, Yoon, Irene, Chen, Hanxi, Zakowski, Yannick, Zdancewic, Steve
Format: Journal Article
Language:English
Published: New York, NY, USA ACM 15.08.2024
Subjects:
Compilers
Computer Science
Denotational semantics
Program specifications
Program verification
Programming Languages
Semantics
Software and its engineering
Theory of computation
integer > pointer casts
semantics
coq
low-level memory model
Integer–pointer casts
Coq
Semantics
Low-level memory model
ISSN:2475-1421, 2475-1421
Online Access:Get full text
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Summary:This paper provides a novel approach to reconciling complex low-level memory model features, such as pointer--integer casts, with desired refinements that are needed to justify the correctness of program transformations. The idea is to use a "two-phase" memory model, one with an unbounded memory and corresponding unbounded integer type, and one with a finite memory; the connection between the two levels is made explicit by a notion of refinement that handles out-of-memory behaviors. This approach allows for more optimizations to be performed and establishes a clear boundary between the idealized semantics of a program and the implementation of that program on finite hardware. The two-phase memory model has been incorporated into an LLVM IR semantics, demonstrating its utility in practice in the context of a low-level language with features like undef and bitcast. This yields infinite and finite memory versions of the language semantics that are proven to be in refinement with respect to out-of-memory behaviors. Each semantics is accompanied by a verified executable reference interpreter. The semantics justify optimizations, such as dead-alloca-elimination, that were previously impossible or difficult to prove correct.
ISSN:2475-1421
2475-1421
DOI:10.1145/3674652