Program concept recognition and transformation

The automated recognition of abstract high-level conceptual information or concepts, which can greatly aid the understanding of programs and therefore support many software maintenance and reengineering activities, is considered. An approach to automated concept recognition and its application to maintenance-related program transformations are described. A unique characteristic of this approach is that transformations of code can be expressed as transformations of abstract concepts. This significantly elevates the level of transformation specifications     

Strongly Typed Rewriting For Coupled Software Transformation

Coupled transformations occur in software evolution when multiple artifacts must be modified in such a way that they remain consistent with each other. An important example involves the coupled transformation of a data type, its instances, and the programs that consume or produce it. Previously, we have provided a formal treatment of transformation of the first two: data types and instances. The treatment involved the construction of type-safe, type-changing strategic rewrite systems. In this paper, we extend our treatment to the transformation of corresponding data processing programs.The key insight underlying the extension is that both data migration functions and data processors can be represented type-safely by a generalized abstract data type (GADT). These representations are then subjected to program calculation rules, harnessed in type-safe, type-preserving strategic rewrite systems. For ease of calculation, we use point-free representations and corresponding calculation rules.Thus, coupled transformations are carried out in two steps. First, a type-changing rewrite system is applied to a source type to obtain a target type together with (representations of) migration functions between source and target. Then, a type-preserving rewrite system is applied to the composition of a migration function and a data processor on the source (or target) type to obtain a data processor on the target (or source) type. All rewrites are type-safe.     

Program Development as a Formal Activity

A methodology of program development by transformations is outlined. In particular, ways of representing the transformation rules are discussed, and the relationship between notions of their correctness and the semantic definition of programming languages is studied. How transformation techniques are complemented by the use of abstract data types and assertions is described. In the resulting calculus of transformations, the single rules not only represent design or optimization techniques, but they also incorporate verification principles. To illustrate this approach, the Warshall algorithm is developed by successive applications of transformations.     

Symbolic Semantics and Program Reduction

A class of transformations of functional programs based on symbolic execution and simplification of conditionals is presented. The operational symbolic semantics of a family of functional languages is defined exploiting a set-theoretic notion of symbolic constants. An effective transformation able to simplify a functional program via removal of conditionals is discussed. Finally, it is shown that a structural approach, based on abstract data type specifications, provides a suitable representation for symbolic constants.     

A portable lisp compiler

The programming language LISP is usually implemented via an interpreter, and a compiler is added later as a LISP program. However, all such production compilers known to the authors produce explicit instructions for the given computer being used. This paper describes the development of a portable LISP compiler in the sense that only Standard LISP functions are used in its definition and the output is a sequence of abstract machine codes, easily mapped to instruction sequences on current computers. The resulting code is quite efficient, demonstrating once again the maxim that most compiler optimization is largely machine independent.     

控制膨胀的程序结构化

目前人们通常单纯用增加临时变量和相关判断的方法，或者使用共享代码拷贝的方法来消除goto语句，但前一种方法会造成判定增加，语义分析困难，而后一种虽然使转变后的程序结构清晰，却造成了benchmark中的某些程序急剧膨胀，针对上述问题，本文提出了能控制膨胀的代码拷贝算法，且该算法还能有效地处理不可规约的程序。     

Program Behavior at the Symbolic Level

No application programmer writes machine-language programs–i.e., strings of ones and zeroes. That primitive pursuit has long been reserved for those few who create the very first modules of a software system for new hardware. Instead, programmers make use of a wide spectrum of symbolic programming languages, ranging from assembly code to high-level languages such as Fortran, Cobol, and the Algol family. Every programming language has semantics which define some abstract machine. For the assembly-language programmer this machine bears a great resemblance to the actual hardware on which the program will be interpreted, but even here the programmer will frequently use system-defined subroutines or macros which represent extensions of the base hardware facilities. The high-level language programmer's abstract machine reflects the control mechanisms and data structures characteristic of the language. The Fortran programmer, for example, can think in terms of multidimensional array structures, DO loops, subprogram facilities, and so on. In principle he need never be concerned with the manner in which his abstract Fortran machine is to be realized by a particular hardware and software system. The user of a modern electronic hand calculator needs no knowledge of the works inside the box, and a modern high-level language system should present to its users an equally consistent environment, completely defined in terms of the syntax and semantics of the source language.     

一种从Z规约到并行程序的精化方法

提出了一种通过对设计模式进行精化,从Z规约开发并行程序的方法.该方法对Z语言进行了并行扩充,从Z功能规约出发,通过使用扩展的设计模式逐步精化得到并行的设计规约,再通过保持语义的转换,得到可最后转换为并行代码的抽象并行程序.通过实例对这一方法进行了详细的描述.     

Experience with software conversion

Experience with a program to convert from LISP 1.6 to INTERLISP is described. The conversion program was designed with two goals in mind. First, it had to be capable of being executed in either of the languages's environments and it had to yield identical results. Second, the speed of the converted program was to be approximately the same as the original program. This meant that the conversion process must be completed prior to execution of the converted program. The various constraints and considerations imposed by these goals are examined. In addition, aside from problems in finding INTERLISP analogs for various LISP 1.6 constructs, careful consideration must also be paid to input/output functions, escape characters, global variables, representation of numbers and different string implementations.     

Program transformations for information personalization

Personalization constitutes the mechanisms necessary to automatically customize information content, structure, and presentation to the end-user to reduce information overload. Unlike traditional approaches to personalization, the central theme of our approach is to model a website as a program and conduct website transformation for personalization by program transformation (e.g., partial evaluation, program slicing). The goal of this paper is study personalization through a program transformation lens, and develop a formal model, based on program transformations, for personalized interaction with hierarchical hypermedia. The specific research issues addressed involve identifying and developing program representations and transformations suitable for classes of hierarchical hypermedia, and providing supplemental interactions for improving the personalized experience. The primary form of personalization discussed is out-of-turn interaction—a technique which empowers a user navigating a hierarchical website to postpone clicking on any of the hyperlinks presented on the current page and, instead, communicate the label of a hyperlink nested deeper in the hierarchy. When the user supplies out-of-turn input we personalize the hierarchy to reflect the user's informational need. While viewing a website as a program and site transformation as program transformation is non-traditional, it offers a new way of thinking about personalized interaction, especially with hierarchical hypermedia. Our use of program transformations casts personalization in a formal setting and provides a systematic and implementation-neutral approach to designing systems. Moreover, this approach helped connect our work to human-computer dialog management and, in particular, mixed-initiative interaction. Putting personalized web interaction on a fundamentally different landscape gave birth to this new line of research. Relating concepts in the web domain (e.g., sites, interactions) to notions in the program-theoretic domain (e.g., programs, transformations) constitutes the creativity in this work.     

Equivalent Transformations of Program Schemes for “Entangling” Programs

By entangling program, we mean its equivalent transformation that complicates understanding the program's logic. Conventionally, equivalent transformations of programs are designed on the basis of their schemes. The problem of constructing schemes that can be used for designing equivalent transformations is discussed. A general approach to solving this problem is presented. An example of its application to ALGOL-like programs without procedures is described in the case when program schemes are constructed from the program's algebraic models.     

Iteration of transformation passes over attributed program trees

Summary Transformations of attributed program trees form an essential part of compiler optimizations. A strategy of repeatedly applying alternate attribute evaluation and tree transformation phases is discussed. An attribute evaluation phase consists of a sequence of passes over the tree. A tree transformation phase consists of a single pass, which is never interrupted to carry out a re-evaluation. Both phases can be performed in parallel. This strategy requires a distinction between consistent (i.e., correct) and approximate attribute values. Tree transformations can be considered safe if they guarantee that the attribute values everywhere in the program tree will remain consistent or will become at least approximations of the consistent values, so that subsequent transformations can be applied correctly.This attribute evaluation and tree transformation strategy shows similarities with the evaluation methods for circular attribute grammars.     

一个面向C和Fortran数值程序的静态分析工具

程序的正确性验证一直以来都是计算机科学中的一个挑战性问题,抽象解释理论为程序静态分析提供了一个通用框架,可以在编译时自动地推导程序的动态性质。基于抽象解释的数值程序分析可以自动推导程序中数值变量间的不变式关系,这对于编译优化、程序错误检查至关重要。本文建立并实现了一个面向C和Fortran程序并支持过程间分析的数值程序分析框架和工具,C或Fortran源程序经过预处理后转化为具有统一格式的中间表示形式,然后基于该中间表示抽取与源程序语义等价的语义等式,最后在该语义等式上进行不动点迭代计算从而得到程序不变式。在此基础上,本文还对数组等复杂语法结构进行了建模和抽象。实验结果表明,该工具具有较高的可扩展性、精度,并能够处理大部分因数组的使用而带来的程序分析上的问题。     

Parallelization support for coupled grid applications with small meshes

Composite grid problems arise in important application areas, e.g. reactor simulation. Related physical phenomena are inherently parallel and their simulations are computationally intensive. Unfortunately, parallel languages, such as High Performance Fortran, provide little support for these problems. We illustrate topological connections via a coupling statement, develop a programming style and transformation system to support composite grid code development, and develop an algorithm that automatically determines distributions for composite grid problems with small meshes. A mesh is classified as small if the amount of computational work associated with the mesh is less than the amount of work to be assigned to a single processor. Precompiler transformations, such as cloning for alignment specification, are described. Excerpts from a High Performance Fortran program before and after transformation illustrate user programming style and transformation issues. Our distribution algorithm's alignment and distribution specifications are input to the transformed High Performance Fortran programs which applies the mapping for execution of the simulation code. Some advantages of this approach are: transformations are applied before compilation and allow communication optimization; data distribution may be determined for any number of problems without recompilation; user determined distribution for parallelization is unnecessary; portability is improved. We validate the topology-based data distribution algorithm using a number of reactor configurations. Two random distribution algorithms provide a basis of comparison with measures of load balance and communication cost. Experiments show that the topology-based distribution algorithm almost always obtains load balance at least as good as, and often significantly better than, random algorithms while reducing the total communication per iteration from 50% to as much as a factor of ten.     

A practical algorithm for static analysis of parallel programs

One approach to analyzing the behavior of a concurrent program requires determining the reachable program states. A program state consists of a set of task states, the values of shared variables used for synchronization, and local variables that derive the values directly from synchronization operations. However, the number of reachable states rises exponentially with the number of tasks and becomes intractable for many concurrent programs. A variation of this approach merges a set of related states into a single virtual state. Using this approach, the analysis of concurrent programs becomes feasible as the number of virtual states is often orders of magnitude less than the number of reachable states. This paper presents a method for determining the virtual states that describe the reachable program states, and the reduction in the number of states is analyzed. The algorithms given have been implemented in a static program analyzer for multitasking Fortran, and the results obtained are discussed.     

A Comparison of Co-Array Fortran and OpenMP Fortran for SPMD Programming

Co-Array Fortran, formally called F^––, is a small set of extensions to Fortran 90/95 for Single-Program-Multiple-Data (SPMD) parallel processing. OpenMP Fortran is a set of compiler directives that provide a high level interface to threads in Fortran, with both thread-local and thread-shared memory. OpenMP is primarily designed for loop-level directive-based parallelization, but it can also be used for SPMD programs by spawning multiple threads as soon as the program starts and having each thread then execute the same code independently for the duration of the run. The similarities and differences between these two SPMD programming models are described.Co-Array Fortran can be implemented using either threads or processes, and is therefore applicable to a wider range of machine types than OpenMP Fortran. It has also been designed from the ground up to support the SPMD programming style. To simplify the implementation of Co-Array Fortran, a formal Subset is introduced that allows the mapping of co-arrays onto standard Fortran arrays of higher rank. An OpenMP Fortran compiler can be extended to support Subset Co-Array Fortran with relatively little effort.     

Reusability Through Program Transformations

We describe a methodology and supporting programming environment that provide for reuse of abstract programs. Abstract programs are written using notations and constructs natural to the problem domain in a language realized by syntactic extension of a base language. Program transformations are employed to refine an abstract program into its concrete counterpart. We discuss the use of the methodology in the setting of rapid prototyping and custom tailoring.     

Generating Communication for Array Statements: Design,Implementation, and Evaluation

Array statements as included in Fortran 90 or High Performance Fortran (HPF) are a well-accepted way to specify data parallelism in programs. When generating code for such a data parallel program for a private memory parallel system, the compiler must determine when array elements must be moved from one processor to another. This paper describes a practical method to compute the set of array elements that are to be moved; it covers all the distributions that are included in HPF: block, cyclic, and block-cyclic. This method is the foundation for an efficient protocol for modern private memory parallel systems: for each block of data to be sent, the sender processor computes the local address in the receiver′s address space, and the address is then transmitted together with the data. This strategy increases the communication load but reduces the overhead on the receiving processor. We implemented this optimization in an experimental Fortran compiler, and this paper reports an empirical evaluation on a 64-node private memory iWarp system, using a number of different distributions.