This paper addresses the issue of the practicality of global flow analysis in logic program compilation, in terms of speed of the analysis, precision, and usefulness of the information obtained. To this end, design and implementation aspects are discussed for two practical abstract interpretation-based flow analysis systems: MA 3 , the MCC And-parallel Analyzer and Annotator; and Ms, an experimental mode inference system developed for SB-Prolog. The paper also provides performance data obtained from these implementations and, as an example of an application, a study of the usefulness of the mode information obtained in reducing run-time checks in independent and-parallelism. Based on the results obtained, it is concluded that the overhead of global flow analysis is not prohibitive, while the results of analysis can be quite precise and useful. 1 Introduction The extensive use of advanced compilation techniques [8, 22, 30, 32, 33, 34], coupled with parallel execution [5, 10,...

Machine (WAM) [33]. &- Prolog, the source language in this model, is basically Prolog, with the addition of the parallel conjunction operator "&" and a set of parallelism-related builtins, which includes several types of groundness and independence checks, and synchronization primitives. Parallel conditional execution graphs (which cause the execution of goals in parallel if certain conditions are met) can be constructed by combining these elements with the normal Prolog constructs, such as "-?" (if-then-else). For syntactic convenience (and historical reasons) an additional construct, the CGE, is also provided. We now study the correctness of CGEs. Definition 8. (CGE) A CGE (Conditional Graph Expression) is a structure of the form ( i cond =? goal 1 & goal 2 & ... & goal n ) where i cond is an independence condition as defined previously, and each goal i , i = 1; : : : ; n, is either a literal or (recursively) a CGE. CGEs appear as literals in the bodies of clauses. From an operat...

Since the early days of logic programming, researchers in the field realized the potential for exploitation of parallelism present in the execution of logic programs. Their high-level nature, the presence of non-determinism, and their referential transparency, among other characteristics, make logic programs interesting candidates for obtaining speedups through parallel execution. At the same time, the fact that the typical applications of logic programming frequently involve irregular computations, make heavy use of dynamic data structures with logical variables, and involve search and speculation, makes the techniques used in the corresponding parallelizing compilers and run-time systems potentially interesting even outside the field. The objective of this paper is to provide a comprehensive survey of the issues arising in parallel execution of logic programming languages along with the most relevant approaches explored to date in the field. Focus is mostly given to the challenges emerging from the parallel execution of Prolog programs. The paper describes the major techniques used for shared memory implementation of Or-parallelism, And-parallelism, and combinations of the two. We also explore some related issues, such as memory

. Irregular computations pose some of the most interesting and challenging problems in automatic parallelization. Irregularity appears in certain kinds of numerical problems and is pervasive in symbolic applications. Such computations often use dynamic data structures which make heavy use of pointers. This complicates all the steps of a parallelizing compiler, from independence detection to task partitioning and placement. In the past decade there has been significant progress in the development of parallelizing compilers for logic programming and, more recently, constraint programming. The typical applications of these paradigms frequently involve irregular computations, which arguably makes the techniques used in these compilers potentially interesting. In this paper we introduce in a tutorial way some of the problems faced by parallelizing compilers for logic and constraint programs. These include the need for inter-procedural pointer aliasing analysis for independence detection and...

Parallelism and logic programming are two fields that have been successfully combined, as is shown by recent implementations of parallel logic programming systems. There are two main sources of parallelism in logic programming, namely or-parallelism and and-parallelism. Or-parallelism is exploited when several alternative clauses to a goal are executed in parallel. And-parallelism is exploited when we execute two or more goals of the same clause simultaneously. Exploitation of full or-parallelism and and-parallelism is limited by the number of physical processors available in a system. And-parallelism is also limited by the interdependence among goals in a clause. In parallel logic programming systems which exploit both and-parallelism and or-parallelism, a problem that arises is how to distribute processors between the dynamically varying amounts of and-work and or-work that are available. Solutions have been reported for distributing only or-work, or distributing only and-work, but the issue of distributing processors between both kinds of work has not yet been addressed. In this thesis we discuss the problem of distributing and-work and or-work in the context of Andorra-I, a parallel logic programming system that exploits determinate and-parallelism and or-parallelism, and propose scheduling strategies that aim at effi ciently distributing processors between and-work and or-work. We study general criteria that every scheduling strategy should meet to reconfi gure processors without incurring too high overheads in the Andorra-I system. We propose two different strategies to reconfi gure processors between and-work and or-work based on these criteria. One strategy, work-guided, guides its decisions by looking at the amount of current and-work and or-work available in ...

] Logic programs provide many opportunities for parallel execution. Among different forms of parallelism found in logic programs, AND-parallelism and OR-parallelism have shown to be most effective in speeding up the execution of logic programs. Research in the exploitation of AND-parallelism, OR-parallelism alone and combined AND/OR-parallelism has led to the proposals and implementations of various execution models and working systems. This paper offers a review of major activities in exploiting AND-parallelism and combined AND/ORparallelism. Keywords: Logic programming, Prolog, AND-parallelism, Combined AND/OR-parallelism 1. INTRODUCTION There has been a flurry of research activities in parallel processing of logic programs in the last decade due to the growing demand for fast reasoning capabilities on the current parallel computers. Among different forms of parallelism inherent in logic programs, AND-parallelism and ORparallelism have shown to be most effective in speeding up the ...

This text summarises the main research work being carried out on the implementation of parallel logic programming systems. It concentrates on describing techniques for exploiting and-parallelism and or-parallelism while showing important aspects of some systems on shared-memory, distributed-memory and distributed-shared memory architectures. It also presents some important pointers to journals, conferences and sites with related information. 1 Introduction Parallel processing is a very important alternative to obtain good performance from programs, be them applications or basic software. Parallelism can be exploited implicitly or explicitly. Most well-known parallel systems are based on the imperative programming model and parallelism is exploited explicitly, making the programming task hard. Contrasting with imperative programming, declarative programming presents a higher-level programming model where the programmer needs to worry on what to solve and not on how to solve a problem....

Sharing among program variables is vital information when analyzing logic programs. This information is often expressed either as sets or as pairs of program variables that (may) share. That is, either as set-sharing or as pair-sharing. It has been recently argued that (a) set-sharing is interesting not as an observable property in itself, but as an encoding for accurate pair-sharing, and that (b) such an encoding is in fact redundant and can be significantly simplified without loss of pairsharing accuracy. We show that this is not the case when set-sharing is combined with other kinds of information, such as the popular freeness.

Facultad de Inform'atica Universidad Polit'ecnica de Madrid (UPM) 28660-Boadilla del Monte, Madrid- Spain Abstract: This paper presents a study of the effectiveness of three different algorithms for the parallelization of logic programs based on compile-time detection of independence among goals. The algorithms are embedded in a complete parallelizing compiler, which incorporates different abstract interpretation-based program analyses. The complete system shows the task of automatic program parallelization to be practical. The trade-offs involved in using each of the algorithms in this task are studied experimentally, weaknesses of these identified, and possible improvements discussed.