Self-Supervised Learning to Prove Equivalence Between Straight-Line Programs via Rewrite Rules

We target the problem of automatically synthesizing proofs of semantic equivalence between two programs made of sequences of statements. We represent programs using abstract syntax trees (AST), where a given set of semantics-preserving rewrite rules can be applied on a specific AST pattern to generate a transformed and semantically equivalent program. In our system, two programs are equivalent if there exists a sequence of application of these rewrite rules that leads to rewriting one program into the other. We propose a neural network architecture based on a transformer model to generate proofs of equivalence between program pairs. The system outputs a sequence of rewrites, and the validity of the sequence is simply checked by verifying it can be applied. If no valid sequence is produced by the neural network, the system reports the programs as non-equivalent, ensuring by design no programs may be incorrectly reported as equivalent. Our system is fully implemented for a given grammar which can represent straight-line programs with function calls and multiple types. To efficiently train the system to generate such sequences, we develop an original incremental training technique, named self-supervised sample selection. We extensively study the effectiveness of this novel training approach on proofs of increasing complexity and length. Our system, S4Eq, achieves 97% proof success on a curated dataset of 10,000 pairs of equivalent programsComment: 30 pages including appendi

Optimizing Coherence Traffic in Manycore Processors Using Closed-Form Caching/Home Agent Mappings

[Abstract] Manycore processors feature a high number of general-purpose cores designed to work in a multithreaded fashion. Recent manycore processors are kept coherent using scalable distributed directories. A paramount example is the Intel Mesh interconnect, which consists of a network-on-chip interconnecting “tiles”, each of which contains computation cores, local caches, and coherence masters. The distributed coherence subsystem must be queried for every out-of-tile access, imposing an overhead on memory latency. This paper studies the physical layout of an Intel Knights Landing processor, with a particular focus on the coherence subsystem, and uncovers the pseudo-random mapping function of physical memory blocks across the pieces of the distributed directory. Leveraging this knowledge, candidate optimizations to improve memory latency through the minimization of coherence traffic are studied. Although these optimizations do improve memory throughput, ultimately this does not translate into performance gains due to inherent overheads stemming from the computational complexity of the mapping functions.Ministerio de Educación; FPU16/00816U.S. National Science Foundation; CCF-1750399Xunta de Galicia and FEDER; ED431G 2019/01Ministerio de Ciencia e Innovación; PID2019-104184RB-I0

Cognitive Information Processing

Contains reports on three research projects.Center for Advanced Television StudiesAmerican Broadcasting CompanyAmpex CorporationColumbia Broadcasting Systems (until 5/86)Harris Corporation (until 5/86)Home Box OfficeKodak (from 1/87)Public Broadcasting ServiceNational Broadcasting CompanyRCA CorporationTektronixZenith (from 5/86)3M Company (until 5/86)International Business Machines, Inc.Defense Advanced Research Agency (Contract N00014-85-K-0213

Machine learning for computer aided programming: from stochastic program repair to verifiable program equivalence

2022 Spring.Includes bibliographical references.Computer programming has benefited from a virtuous cycle of innovation as improvements in computer hardware and software make higher levels of program abstraction and complexity possible. Recent advances in the field of machine learning, including neural network models for translating and answering questions about human language, can also be applied to computer programming itself. This thesis aims to make progress on the problem of using machine learning to improve the quality and robustness of computer programs by contributing new techniques for representation of programming problems, applying neural network models to code, and training procedures to create systems useful for computer aided programming. We first present background and preliminary studies of machine learning concepts. We then present a system that directly produces source code for automatic program repair which advances the state of the art by using a learned copy mechanism during generation. We extend a similar system to tune its learning for security vulnerability repair. We then develop a system for program equivalence which generates deterministically checkable output for equivalent programs. For this work we detail our contribution to the popular OpenNMT-py GitHub project used broadly for neural machine translation. Finally, we show how the deterministically checkable output can provide self-supervised sample selection which improves the performance and generalizability of the system. We develop breadth metrics to demonstrate that the range of problems addressed is representative of the problem space, while demonstrating that our deep neural networks generate proposed solutions which can be verified in linear time. Ultimately, our work provides promising results in multiple areas of computer aided programming which allow human developers to produce quality software more effectively