You Can Have It All:

ion and Good Cache Performance Juliana Franco Imperial College London United Kingdom [email protected] Martin Hagelin∗ Dirac Sweden Tobias Wrigstad Uppsala University Sweden [email protected] Sophia Drossopoulou Imperial College London United Kingdom [email protected] Susan Eisenbach Imperial College London United Kingdom [email protected] Abstract On current architectures, the optimisation of an application’s performance often involves data being stored according to access affinity — what is accessed together should be stored together, rather than logical affinity — what belongs together logically stays together. Such low level techniques lead to faster, but more error prone code, and end up tangling the program’s logic with low-level data layout details. Our vision, which we call SHAPES— Safe, High-level, Abstractions for oPtimisation of mEmory cacheS — is that the layout of a data structure should be defined only once, upon instantiation, and the remainder of the code should be layout agnostic. This enables performance improvements while also guaranteeing memory safety, and supports the separation of program logic from low level concerns. In this paper we investigate how this vision can be supported by extending a programming language. We describe the core language features supporting this vision: classes can be customized to support different layouts, and layout information is carried around in types; the remaining source code is layout-unaware and the compiler emits layout-aware code. We then discuss our SHAPES implementation through a prototype library, which we also used for preliminary evaluations. Finally, we discuss how the core could be expanded so as to deliver SHAPES’s full potential: the incorporation of compacting garbage collection,On current architectures, the optimisation of an application’s performance often involves data being stored according to access affinity — what is accessed together should be stored together, rather than logical affinity — what belongs together logically stays together. Such low level techniques lead to faster, but more error prone code, and end up tangling the program’s logic with low-level data layout details. Our vision, which we call SHAPES— Safe, High-level, Abstractions for oPtimisation of mEmory cacheS — is that the layout of a data structure should be defined only once, upon instantiation, and the remainder of the code should be layout agnostic. This enables performance improvements while also guaranteeing memory safety, and supports the separation of program logic from low level concerns. In this paper we investigate how this vision can be supported by extending a programming language. We describe the core language features supporting this vision: classes can be customized to support different layouts, and layout information is carried around in types; the remaining source code is layout-unaware and the compiler emits layout-aware code. We then discuss our SHAPES implementation through a prototype library, which we also used for preliminary evaluations. Finally, we discuss how the core could be expanded so as to deliver SHAPES’s full potential: the incorporation of compacting garbage collection, ∗Work done while at Uppsala University. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]. Onward!’17, October 25–27, 2017, Vancouver, Canada © 2017 Copyright held by the owner/author(s). Publication rights licensed to the Association for Computing Machinery. ACM ISBN 978-1-4503-5530-8/17/10. . . $15.00 https://doi.org/10.1145/3133850.3133861 ad hoc polymorphism and late binding, synchronization of representations of different collections, support for dynamic change of representation, etc. CCS Concepts • Software and its engineering → Secondary storage; Object oriented languages; Data types and structures; Extra-functional properties;