Semantics-directed generation of compilers and abstract machines

In traditional compiler design the work of a compiler is divided into several phases: lexical, syntactical and semantical analysis, optimizations and code generation. For several of these phases generators exist -- most prominently LEX and YACC for generating lexical and syntactical analyzers. A common feature of all generators is that the phase in the compiler is described using a meta-language (e.g. regular expressions or context-free grammars) and that the generator produces the related compiler module. There exist several good textbooks on compiler design. However, all of these books present ready made mappings from source language constructs to target language constructs, the so called translation schemes, instead of deriving them. Hence, the reader is expected to learn how to design code generators by analysing translation schemes as opposed to from first principles. The same is true for abstract machines. Abstract machines are virtual target architectures which support the concepts of the source language. Typically abstract machines are presented together with translation schemes from the source language to the abstract machine language. There is only little work on how translation schemes and abstract machines are designed. The aim of our work is to detect underlying principles that relate abstract machines to programming language semantics, and to automate part of the design process for abstract machines. Thus, we need to ensure that the behaviour of a source program will be maintained by translating it into the abstract machine language, and then applying the abstract machine. The behaviour of a program will depend on it's semantics. Often this aspect of a programming language is only described in natural language which is both ambiguous and vague. We shall use formal techniques to describe the meaning of programs in a particular language and to prove that our transformations are correct. In this thesis we concentrate on natural semantics, but we also address action semantics

Semantics-directed generation of compilers and abstract machines

In traditional compiler design the work of a compiler is divided into several phases: lexical, syntactical and semantical analysis, optimizations and code generation. For several of these phases generators exist -- most prominently LEX and YACC for generating lexical and syntactical analyzers. A common feature of all generators is that the phase in the compiler is described using a meta-language (e.g. regular expressions or context-free grammars) and that the generator produces the related compiler module. There exist several good textbooks on compiler design. However, all of these books present ready made mappings from source language constructs to target language constructs, the so called translation schemes, instead of deriving them. Hence, the reader is expected to learn how to design code generators by analysing translation schemes as opposed to from first principles. The same is true for abstract machines. Abstract machines are virtual target architectures which support the concepts of the source language. Typically abstract machines are presented together with translation schemes from the source language to the abstract machine language. There is only little work on how translation schemes and abstract machines are designed. The aim of our work is to detect underlying principles that relate abstract machines to programming language semantics, and to automate part of the design process for abstract machines. Thus, we need to ensure that the behaviour of a source program will be maintained by translating it into the abstract machine language, and then applying the abstract machine. The behaviour of a program will depend on it\u27s semantics. Often this aspect of a programming language is only described in natural language which is both ambiguous and vague. We shall use formal techniques to describe the meaning of programs in a particular language and to prove that our transformations are correct. In this thesis we concentrate on natural semantics, but we also address action semantics

Galois : a system for parallel execution of irregular algorithms

textA programming model which allows users to program with high productivity and which produces high performance executions has been a goal for decades. This dissertation makes progress towards this elusive goal by describing the design and implementation of the Galois system, a parallel programming model for shared-memory, multicore machines. Central to the design is the idea that scheduling of a program can be decoupled from the core computational operator and data structures. However, efficient programs often require application-specific scheduling to achieve best performance. To bridge this gap, an extensible and abstract scheduling policy language is proposed, which allows programmers to focus on selecting high-level scheduling policies while delegating the tedious task of implementing the policy to a scheduler synthesizer and runtime system. Implementations of deterministic and prioritized scheduling also are described. An evaluation of a well-studied benchmark suite reveals that factoring programs into operators, schedulers and data structures can produce significant performance improvements over unfactored approaches. Comparison of the Galois system with existing programming models for graph analytics shows significant performance improvements, often orders of magnitude more, due to (1) better support for the restrictive programming models of existing systems and (2) better support for more sophisticated algorithms and scheduling, which cannot be expressed in other systems.Computer Science

Social machines for education driven by feedback agents

The aim of this paper is to explain some of the ways in which multi agent system (MAS) theory can be used to describe, design and enhance social machines (also referred to as Socio-Cognitive Systems). We believe there is a really opportunity for the MAS community to engage with emerging theory and practice of designing such systems. Social machines - also referred to as Socio-Cognitive Systems from the MAS community - are terms used to refer to the recent breed of technological systems which allow human and computational agents to socially interact, typically on a large scale and sometimes towards achieving shared goals. Examples include social networking platforms and crowd sourced encyclopaedias. The discussion of social machines and MAS is taken from three perspectives. Firstly, the theoretical notion of an abstract social machine as a socio-cognitive system containing humans and agents is introduced. Secondly, a speci#12;c instance of a social machine which has been designed to enable social music learning supported by agents is described. Thirdly, an agent architecture which is designed for operation within educational social machines is discussed, with particular focus on what we believe is the core currency of these machines: feedback.Much of of this work was undertaken as part of the FP7 project in the Technology Enhanced Learning Program called Practice and Performance Analysis Inspiring Social Education (PRAISE) involving the 1st and 2nd authors. We acknowledge Harry Brenton, Marco Gillies Andreu Grimalt-Reynes, Jonathan James, Edgar Jones, Julian Padget and Harko Harko Verhagen who have helped in discussions. The second author received support from the European Network for Social Intelligence, SINTELNET (FET Open Coordinated Action FP7-ICT-2009-C Project No. 286370) for short term visits to the IIIA to work with the 3rd author.Peer Reviewe

An open extensible tool environment for Event-B

Abstract. We consider modelling indispensable for the development of complex systems. Modelling must be carried out in a formal notation to reason and make meaningful conjectures about a model. But formal modelling of complex systems is a difficult task. Even when theorem provers improve further and get more powerful, modelling will remain difficult. The reason for this that modelling is an exploratory activity that requires ingenuity in order to arrive at a meaningful model. We are aware that automated theorem provers can discharge most of the onerous trivial proof obligations that appear when modelling systems. In this article we present a modelling tool that seamlessly integrates modelling and proving similar to what is offered today in modern integrated development environments for programming. The tool is extensible and configurable so that it can be adapted more easily to different application domains and development methods.

A compiler approach to scalable concurrent program design

The programmer's most powerful tool for controlling complexity in program design is abstraction. We seek to use abstraction in the design of concurrent programs, so as to separate design decisions concerned with decomposition, communication, synchronization, mapping, granularity, and load balancing. This paper describes programming and compiler techniques intended to facilitate this design strategy. The programming techniques are based on a core programming notation with two important properties: the ability to separate concurrent programming concerns, and extensibility with reusable programmer-defined abstractions. The compiler techniques are based on a simple transformation system together with a set of compilation transformations and portable run-time support. The transformation system allows programmer-defined abstractions to be defined as source-to-source transformations that convert abstractions into the core notation. The same transformation system is used to apply compilation transformations that incrementally transform the core notation toward an abstract concurrent machine. This machine can be implemented on a variety of concurrent architectures using simple run-time support. The transformation, compilation, and run-time system techniques have been implemented and are incorporated in a public-domain program development toolkit. This toolkit operates on a wide variety of networked workstations, multicomputers, and shared-memory multiprocessors. It includes a program transformer, concurrent compiler, syntax checker, debugger, performance analyzer, and execution animator. A variety of substantial applications have been developed using the toolkit, in areas such as climate modeling and fluid dynamics

Modelling and Refinement in CODA

This paper provides an overview of the CODA framework for modelling and refinement of component-based embedded systems. CODA is an extension of Event-B and UML-B and is supported by a plug-in for the Rodin toolset. CODA augments Event-B with constructs for component-based modelling including components, communications ports, port connectors, timed communications and timing triggers. Component behaviour is specified through a combination of UML-B state machines and Event-B. CODA communications and timing are given an Event-B semantics through translation rules. Refinement is based on Event-B refinement and allows layered construction of CODA models in a consistent way.Comment: In Proceedings Refine 2013, arXiv:1305.563

A Verified Information-Flow Architecture

SAFE is a clean-slate design for a highly secure computer system, with pervasive mechanisms for tracking and limiting information flows. At the lowest level, the SAFE hardware supports fine-grained programmable tags, with efficient and flexible propagation and combination of tags as instructions are executed. The operating system virtualizes these generic facilities to present an information-flow abstract machine that allows user programs to label sensitive data with rich confidentiality policies. We present a formal, machine-checked model of the key hardware and software mechanisms used to dynamically control information flow in SAFE and an end-to-end proof of noninterference for this model. We use a refinement proof methodology to propagate the noninterference property of the abstract machine down to the concrete machine level. We use an intermediate layer in the refinement chain that factors out the details of the information-flow control policy and devise a code generator for compiling such information-flow policies into low-level monitor code. Finally, we verify the correctness of this generator using a dedicated Hoare logic that abstracts from low-level machine instructions into a reusable set of verified structured code generators