This paper is concerned with the problem of removing, from a given logic program, redundant arguments. These are arguments which can be removed without affecting correctness. Most program specialisation techniques, even though they perform argument filtering and redundant clause removal, fail to remove a substantial number of redundant arguments, yielding in some cases rather inefficient residual programs. We formalise the notion of a redundant argument and show that one cannot decide effectively whether a given argument is redundant. We then give a safe, effective approximation of the notion of a redundant argument and describe several simple and efficient algorithms calculating based on the approximative notion. We conduct extensive experiments with our algorithms on mechanically generated programs illustrating the practical benefits of our approach.

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This paper gives a gentle introduction to Turchin's supercompilation and its applications in metacomputation with an emphasis on recent developments. First, a complete supercompiler, including positive driving and generalization, is defined for a functional language and illustrated with examples. Then a taxonomy of related transformers is given and compared to the supercompiler. Finally, we put supercompilation into the larger perspective of metacomputation and consider three metacomputation tasks: specialization, composition, and inversion.

"Classical" partial deduction, within the framework by Lloyd and Shepherdson, computes partial deduction for separate atoms independently. As a consequence, a number of program optimisations, known from unfold/fold transformations and supercompilation, cannot be achieved. In this paper, we show that this restriction can be lifted through (polygenetic) specialisation of entire atom conjunctions. We present a generic algorithm for such partial deduction and discuss its correctness in an extended formal framework. We concentrate on novel control challenges specific to this "conjunctive" partial deduction. We refine the generic algorithm into a fully automatic concrete one that registers partially deduced conjunctions in a global tree, and prove its termination and correctness. We discuss some further control refinements and illustrate the operation of the concrete algorithm and/or some of its possible variants on interesting transformation examples.

. Recently, partial deduction of logic programs has been extended to conceptually embed folding. To this end, partial deductions are no longer computed of single atoms, but rather of entire conjunctions; Hence the term "conjunctive partial deduction". Conjunctive partial deduction aims at achieving unfold/fold-like program transformations such as tupling and deforestation within fully automated partial deduction. However, its merits greatly surpass that limited context: Also other major efficiency improvements are obtained through considerably improved side-ways information propagation. In this extended abstract, we investigate conjunctive partial deduction in practice. We describe the concrete options used in the implementation(s), look at abstraction in a practical Prolog context, include and discuss an extensive set of benchmark results. From these, we can conclude that conjunctive partial deduction indeed pays off in practice, thoroughly beating its conventional precursor on a wide...

This report is a revised version of my thesis of the same title, which was accepted for the Ph.D. degree in Computer Science at University of Aarhus, Denmark, in June 1993

Abstract. The unfold/fold framework constitutes the spine of many program transformation strategies. However, by unrestricted use of folding the target program may terminate less often than the source program. Several authors have investigated the problem of setting up conditions of syntactic nature, i.e. not based on some well-founded ordering of the arguments, which guarantee preservation of termination properties. These conditions are typically formulated in a way which makes it hard to grasp the basic intuition why they work, and in a way which makes it hard to give elegant proofs of correctness. The aim of this paper will be to give a more unified treatment by setting up a model which enables us to reason about termination preservation in a cleaner and more algebraic fashion. The model resembles a logic language and is parametrized with respect to evaluation order, but it should not be too difficult to transfer the ideas to other languages. 1

We consider the replacement transformation operation, a very general and powerful transformation, and study under which conditions it preserves universal termination besides computed answer substitutions. With this safe replacement we can significantly extend the safe unfold/fold transformation sequence presented in [11]. By exploiting typing information, more useful conditions can be defined and we may deal with some special cases of replacement very common in practice, namely switching two atoms in the body of a clause and the associativity of a predicate. This is a first step in the direction of exploiting a Pre/Post specification on the intended use of the program to be transformed. Such specification can restrict the instances of queries and clauses to be considered and then relax the applicability conditions on the transformation operations.

. Tupling transformation strategy can be used to merge loops together by combining recursive calls and also to eliminate redundant calls for a class of programs. In the latter case, this transformation can produce super-linear speedup. Existing works in deriving a safe and automatic tupling only apply to a very limited class of programs. In this paper, we present a novel parameter analysis, called synchronisation analysis, to solve the termination problem for tupling. With it, we can perform tupling on functions with multiple recursion and accumulative arguments without the risk of non-termination. This significantly widens the scope for tupling, and potentially enhances its usefulness. The analysis is shown to be of polynomial complexity; this makes tupling suitable as a compiler optimisation. 1 Introduction Source-to-source transformation can achieve global optimisation through specialisation for recursive functions. Two well-known techniques are partial evaluation [9] a...

. Partial deduction within Lloyd and Shepherdson's framework transforms different atoms of a goal independently and therefore fails to achieve a number of unfold/fold transformations. A recent framework for conjunctive partial deduction allows unfold/fold transformations by specialisation of entire conjunctions, but does not give an actual algorithm for conjunctive partial deduction, and in particular does not address control issues (e.g. how to select atoms for unfolding). Focusing on novel challenges specific to local and global control, we describe a generic algorithm for conjunctive partial deduction, refine it into a fully automatic concrete algorithm, and prove termination and correctness. 1 Introduction Partial deduction, introduced by Komorowski [17] and formalised by Lloyd and Shepherdson [24], takes a program and a query and returns a specialised program tuned towards answering any instance of the query. Partial deduction in Lloyd and Shepherdson's framework cannot achieve c...