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This paper presents and illustrates with an example a practical approach to the dataflow analysis of programs written in constraint logic programming (CLP) languages using abstract interpretation. It is first argued that, from the framework point of view, it suffices to propose relatively simple extensions of traditional analysis methods which have already been proved useful and practical and for which efficient fixpoint algorithms have been developed. This is shown by proposing a simple but quite general extension of Bruynooghe's traditional framework to the analysis of CLP programs. In this extension constraints are viewed not as "suspended goals" but rather as new information in the store, following the traditional view of CLP. Using this approach, and as an example of its use, a complete, constraint system independent, abstract analysis is presented for approximating definiteness information. The analysis is in fact of quite general applicability. It has been implemented and used i...

A full mode analysis system for CLP(H,N) could result from a straightforward combination of the definiteness analysis (developed at U.P.M.) and the freeness analysis (developed at K.U.Leuven). However, the computational complexity of the freeness abstraction, which is due to an exhaustive enumeration of possible dependencies between variables, impedes this. This paper proposes two orthogonal approaches to reduce the size of the freeness abstraction. Using the definiteness information the first approach splits off the definite variables and their dependencies without any loss of precision. The second approach retains only basic freeness information -- the minimal information -- from which a safe approximation of the rest can be reconstructed. The combination of both approaches results in a practical full mode analysis system; to our knowledge this is the first full mode analysis system for CLP. The optimisations are implemented and timings of the resulting systems show their effectivene...

ing Numerical Values in CLP(H,N) Gerda Janssens 1 , Maurice Bruynooghe 1 , Vincent Englebert 2 1 Department of Computer Science, K.U. Leuven Celestijnenlaan 200A, B-3001 Heverlee, Belgium 2 Institut d'Informatique, Facult'es Universitaires Notre Dame de la Paix rue GrandGagnage 21, B-5000 Namur, Belgium Abstract. The paper defines approximations for the numerical leaves of variables in CLP(H,N) constraint systems. The abstractions are based on intervals which are computed by narrowing rules. The novelty of this approach lays in the fact that intervals are used as abstraction and that narrowing rules do not only correspond to numerical constraints but also to unification constraints. In the first abstraction the impact of the narrowing rules is limited. A prototype implementation has been developed and the obtained results are sufficiently precise to recognise (future) redundant constraints. The abstraction can be extended (1) by incorporating the narrowing rules more globally (...

We address the problem of compile-time detection of implicit and redundant numeric constraints in CLP programs. We discuss how this kind of constraints have several important applications in the general field of semantics based program manipulation and, specifically, optimized compilation. We attack the problem in an original and e#ective way. The basic ideas underlying our approach are: (1) the use of approximate and e#cient constraint inference techniques originally developed in the field of artificial intelligence. These techniques allow great flexibility in dealing with the complexity/precision tradeo# of the analysis. And (2) the integration of these techniques within an appropriate framework for the definition of non-standard semantics of CLP. We show that one notable advantage of this combined approach is that it allows to close the often existing gap between the formalization of data-flow analysis in terms of abstract interpretation and the possibility of e#cient im...

The main difficulty in the definition of a static analysis framework for CC programs is probably related to the correct approximation of the entailment relation between constraints. This approximation is needed for the abstract evaluation of the ask guards and directly influences the overall precision of the analysis. In this paper we provide a and the concrete domains of computation. The solution is domain independent in the sense that it can be applied to the class of downward closed observations. Properties falling in this class (e.g. freeness) have already been studied in the context of the analysis of sequential logic programs. We believe that the same abstract domains can be usefully applied to the CC context to provide meaningful ask approximations. 1

Program analysis based on abstract interpretation has proven very useful in compilation of constraint and logic programming languages. Unfortunately, the traditional goal-dependent framework is inherently imprecise. This is because they handle call and return in such a way that dataflow information may be re-asserted unnecessarily, leading to a loss of precision for many description domains. For a few specific domains, the literature contains proposals to overcome the problem, and some implementations use various unpublished tricks that sometimes avoid the precision loss. The purpose of this paper is to map the landscape of goal-dependent, goal-independent, and combined approaches to generic analysis of logic programs. This includes formalising existing methods and tricks in a way that is independent of specific description domains. Moreover, we suggest new methods for overcoming the loss of precision---altogether eight different semantics are considered and compared. We provide theore...

In this paper, we present a brief overview of most recent and ongoing research in logic programming at the K.U.Leuven Department of Computer Science. We specifically include some indications of its practical, current and/or prospective industrial relevance. For the benefit of the interested reader, we also provide a rich selection of references to papers published by the K.U.Leuven group in the scientific literature. 1 Introduction The research group on Logic Programming and Artificial Intelligence at the Department of Computer Science of the Katholieke Universiteit Leuven in Belgium can boast a long standing tradition of excellence in research on, development of and investigations with logic programming. Following an initial effort by Maurice Bruynooghe in the seventies and early eighties, the group has strongly expanded throughout the later eighties and early nineties. It currently ranks among Europe's leading groups in logic programming, frequently hosting foreign visiting scientis...