Efficient optimization of memory accesses in parallel programs

The power, frequency, and memory wall problems have caused a major shift in mainstream computing by introducing processors that contain multiple low power cores. As multi-core processors are becoming ubiquitous, software trends in both parallel programming languages and dynamic compilation have added new challenges to program compilation for multi-core processors. This thesis proposes a combination of high-level and low-level compiler optimizations to address these challenges. The high-level optimizations introduced in this thesis include new approaches to May-Happen-in-Parallel analysis and Side-Effect analysis for parallel programs and a novel parallelism-aware Scalar Replacement for Load Elimination transformation. A new Isolation Consistency (IC) memory model is described that permits several scalar replacement transformation opportunities compared to many existing memory models. The low-level optimizations include a novel approach to register allocation that retains the compile time and space efficiency of Linear Scan, while delivering runtime performance superior to both Linear Scan and Graph Coloring. The allocation phase is modeled as an optimization problem on a Bipartite Liveness Graph (BLG) data structure. The assignment phase focuses on reducing the number of spill instructions by using register-to-register move and exchange instructions wherever possible. Experimental evaluations of our scalar replacement for load elimination transformation in the Jikes RVM dynamic compiler show decreases in dynamic counts for getfield operations of up to 99.99%, and performance improvements of up to 1.76x on 1 core, and 1.39x on 16 cores, when compared with the load elimination algorithm available in Jikes RVM. A prototype implementation of our BLG register allocator in Jikes RVM demonstrates runtime performance improvements of up to 3.52x relative to Linear Scan on an x86 processor. When compared to Graph Coloring register allocator in the GCC compiler framework, our allocator resulted in an execution time improvement of up to 5.8%, with an average improvement of 2.3% on a POWER5 processor. With the experimental evaluations combined with the foundations presented in this thesis, we believe that the proposed high-level and low-level optimizations are useful in addressing some of the new challenges emerging in the optimization of parallel programs for multi-core architectures

Formal foundations for hybrid effect analysis

Type-and-effect systems are a powerful tool for program construction and verification. Type-and-effect systems are useful because it can help reduce bugs in computer programs, enable compiler optimizations and also provide sort of program documentation. As software systems increasingly embrace dynamic features and complex modes of compilation, static effect systems have to reconcile over competing goals such as precision, soundness, modularity, and programmer productivity. In this thesis, we propose the idea of combining static and dynamic analysis for effect systems to improve precision and flexibility. We describe intensional effect polymorphism, a new foundation for effect systems that integrates static and dynamic effect checking. Our system allows the effect of polymorphic code to be intensionally inspected. It supports a highly precise notion of effect polymorphism through a lightweight notion of dynamic typing. When coupled with parametric polymorphism, the powerful system utilizes runtime information to enable precise effect reasoning, while at the same time retains strong type safety guarantees. The technical innovations of our design include a relational notion of effect checking, the use of bounded existential types to capture the subtle interactions between static typing and dynamic typing, and a differential alignment strategy to achieve efficiency in dynamic typing. We introduce the idea of first-class effects, where the computational effect of an expression can be programmatically reflected, passed around as values, and analyzed at run time. A broad range of designs “hard-coded in existing effect-guided analyses can be supported through intuitive programming abstractions. The core technical development is a type system with a couple of features. Our type system provides static guarantees to application-specific effect management properties through refinement types, promoting “correct-by-design effect-guided programming. Also, our type system computes not only the over-approximation of effects, but also their under-approximation. The duality unifies the common theme of permission vs. obligation in effect reasoning. Finally, we show the potential benefit of intensional effects by applying it to an event-driven system to obtain safe concurrency. The technical innovations of our system include a novel effect system to soundly approximate the dynamism introduced by runtime handlers registration, a static analysis to precompute the effects and a dynamic analysis that uses the precomputed effects to improve concurrency. Our design simplifies modular concurrency reasoning and avoids concurrency hazards

Reductie van het geheugengebruik van besturingssysteemkernen Memory Footprint Reduction for Operating System Kernels

In ingebedde systemen is er vaak maar een beperkte hoeveelheid geheugen beschikbaar. Daarom wordt er veel aandacht besteed aan het produceren van compacte programma's voor deze systemen, en zijn er allerhande technieken ontwikkeld die automatisch het geheugengebruik van programma's kunnen verkleinen. Tot nu toe richtten die technieken zich voornamelijk op de toepassingssoftware die op het systeem draait, en werd het besturingssysteem over het hoofd gezien. In dit proefschrift worden een aantal technieken beschreven die het mogelijk maken om op een geautomatiseerde manier het geheugengebruik van een besturingssysteemkern gevoelig te verkleinen. Daarbij wordt in eerste instantie gebruik gemaakt van compactietransformaties tijdens het linken. Als we de hardware en software waaruit het systeem samengesteld is kennen, is het mogelijk om nog verdere reducties te bekomen. Daartoe wordt de kern gespecialiseerd voor een bepaalde hardware-software combinatie. Overbodige functionaliteit wordt opgespoord en uit de kern verwijderd, terwijl de resterende functionaliteit wordt aangepast aan de specifieke gebruikspatronen die uit de hardware en software kunnen afgeleid worden. Als laatste worden technieken voorgesteld die het mogelijk maken om weinig of niet uitgevoerde code (bijvoorbeeld code voor het afhandelen van slechts zeldzaam optredende foutcondities) uit het geheugen te verwijderen. Deze code wordt dan enkel ingeladen op het moment dat ze effectief nodig is. Voor ons testsysteem kunnen we met de gecombineerde technieken het geheugengebruik van een Linux 2.4 kern met meer dan 48% verminderen

C의 저수준 기능과 컴파일러 최적화 조화시키기

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 컴퓨터공학부, 2019. 2. 허충길.주류 C 컴파일러들은 프로그램의 성능을 높이기 위해 공격적인 최적화를 수행하는데, 그런 최적화는 저수준 기능을 사용하는 프로그램의 행동을 바꾸기도 한다. 불행히도 C 언어를 디자인할 때 저수준 기능과 컴파일러 최적화를 적절하게 조화시키가 굉장히 어렵다는 것이 학계와 업계의 중론이다. 저수준 기능을 위해서는, 그러한 기능이 시스템 프로그래밍에 사용되는 패턴을 잘 지원해야 한다. 컴파일러 최적화를 위해서는, 주류 컴파일러가 수행하는 복잡하고도 효과적인 최적화를 잘 지원해야 한다. 그러나 저수준 기능과 컴파일러 최적화를 동시에 잘 지원하는 실행의미는 오늘날까지 제안된 바가 없다. 본 박사학위 논문은 시스템 프로그래밍에서 요긴하게 사용되는 저수준 기능과 주요한 컴파일러 최적화를 조화시킨다. 구체적으로, 우린 다음 성질을 만족하는 느슨한 동시성, 분할 컴파일, 정수-포인터 변환의 실행의미를 처음으로 제안한다. 첫째, 기능이 시스템 프로그래밍에서 사용되는 패턴과, 그러한 패턴을 논증할 수 있는 기법을 지원한다. 둘째, 주요한 컴파일러 최적화들을 지원한다. 우리가 제안한 실행의미에 자신감을 얻기 위해 우리는 논문의 주요 결과를 대부분 Coq 증명기 위에서 증명하고, 그 증명을 기계적이고 엄밀하게 확인했다.To improve the performance of C programs, mainstream compilers perform aggressive optimizations that may change the behaviors of programs that use low-level features in unidiomatic ways. Unfortunately, despite many years of research and industrial efforts, it has proven very difficult to adequately balance the conflicting criteria for low-level features and compiler optimizations in the design of the C programming language. On the one hand, C should support the common usage patterns of the low-level features in systems programming. On the other hand, C should also support the sophisticated and yet effective optimizations performed by mainstream compilers. None of the existing proposals for C semantics, however, sufficiently support low-level features and compiler optimizations at the same time. In this dissertation, we resolve the conflict between some of the low-level features crucially used in systems programming and major compiler optimizations. Specifically, we develop the first formal semantics of relaxed-memory concurrency, separate compilation, and cast between integers and pointers that (1) supports their common usage patterns and reasoning principles for programmers, and (2) provably validates major compiler optimizations at the same time. To establish confidence in our formal semantics, we have formalized most of our key results in the Coq theorem prover, which automatically and rigorously checks the validity of the results.Abstract Acknowledgements Chapter I Prologue Chapter II Relaxed-Memory Concurrency Chapter III Separate Compilation and Linking Chapter IV Cast between Integers and Pointers Chapter V Epilogue 초록Docto

Intensional Effect Polymorphism

Type-and-effect systems are a powerful tool for program construction and verification. We describe intensional effect polymorphism, a new foundation for effect systems that integrates static and dynamic effect checking. Our system allows the effect of polymorphic code to be intensionally inspected through a lightweight notion of dynamic typing. When coupled with parametric polymorphism, the powerful system utilizes runtime information to enable precise effect reasoning, while at the same time retains strong type safety guarantees. We build our ideas on top of an imperative core calculus with regions. The technical innovations of our design include a relational notion of effect checking, the use of bounded existential types to capture the subtle interactions between static typing and dynamic typing, and a differential alignment strategy to achieve efficiency in dynamic typing. We demonstrate the applications of intensional effect polymorphism in concurrent programming, security, graphical user interface access, and memoization

Micro Virtual Machines: A Solid Foundation for Managed Language Implementation

Today new programming languages proliferate, but many of them suffer from poor performance and inscrutable semantics. We assert that the root of many of the performance and semantic problems of today's languages is that language implementation is extremely difficult. This thesis addresses the fundamental challenges of efficiently developing high-level managed languages. Modern high-level languages provide abstractions over execution, memory management and concurrency. It requires enormous intellectual capability and engineering effort to properly manage these concerns. Lacking such resources, developers usually choose naive implementation approaches in the early stages of language design, a strategy which too often has long-term consequences, hindering the future development of the language. Existing language development platforms have failed to provide the right level of abstraction, and forced implementers to reinvent low-level mechanisms in order to obtain performance. My thesis is that the introduction of micro virtual machines will allow the development of higher-quality, high-performance managed languages. The first contribution of this thesis is the design of Mu, with the specification of Mu as the main outcome. Mu is the first micro virtual machine, a robust, performant, and light-weight abstraction over just three concerns: execution, concurrency and garbage collection. Such a foundation attacks three of the most fundamental and challenging issues that face existing language designs and implementations, leaving the language implementers free to focus on the higher levels of their language design. The second contribution is an in-depth analysis of on-stack replacement and its efficient implementation. This low-level mechanism underpins run-time feedback-directed optimisation, which is key to the efficient implementation of dynamic languages. The third contribution is demonstrating the viability of Mu through RPython, a real-world non-trivial language implementation. We also did some preliminary research of GHC as a Mu client. We have created the Mu specification and its reference implementation, both of which are open-source. We show that that Mu's on-stack replacement API can gracefully support dynamic languages such as JavaScript, and it is implementable on concrete hardware. Our RPython client has been able to translate and execute non-trivial RPython programs, and can run the RPySOM interpreter and the core of the PyPy interpreter. With micro virtual machines providing a low-level substrate, language developers now have the option to build their next language on a micro virtual machine. We believe that the quality of programming languages will be improved as a result

An Ada-like language to facilitate reliable coding of low cost embedded systems

Due to a lack of operating system (0/S) support, it is more difficult to develop programs for embedded systems than for workstations. For those developing on a low budget, the problem is often further compounded by the necessity of using inappropriate, 0/S dependent, compilers. This study attempts to ascertain those elements of a High Level Language (HLL) which are absolutely necessary and implementable to produce reliable, efficient, embedded programs without the benefit of a large budget. The study is based upon the Ada philosophy as the Ada language incorporates many desirable features for modelling real-world problems in terms of embedded solutions. By implication, the research provides a small step towards an increased availability of low cost tools to assist in the development of reliable and efficient code for use in medium performance embedded systems

Programming Languages and Systems

This open access book constitutes the proceedings of the 29th European Symposium on Programming, ESOP 2020, which was planned to take place in Dublin, Ireland, in April 2020, as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2020. The actual ETAPS 2020 meeting was postponed due to the Corona pandemic. The papers deal with fundamental issues in the specification, design, analysis, and implementation of programming languages and systems