Code generation = A* + BURS

Abstract

Abstract.A system called BURS that is based on term rewrite systems and a search algorithm A are combined to produce a code generator that generates optimal code. The theory underlying BURS is re-developed, formalised and explained in this work. The search algorithm uses a cost heuristic that is derived from the term rewrite system to direct the search. The advantage of using a search algorithm is that we need to compute only those costs that may be part of an optimal rewrite sequence.Key words: compiler generators, code generation, term rewrite systems, search algorithms, formal techniquesCompiler building is a time-consuming and error-prone activity. Building the frontend (i.e. scanner, parser and intermediate-code generator) is straightforward-the theory is well established, and there is ample tool support. The main problem lies with the back-end, namely the code generator and optimiser-there is little theory and even less tool support. Generating a code generator from an abstract specification, also called automatic code generation, remains a very difficult problem.Pattern matching and selection is a general class of code-generation technique that has been studied in many forms. The most successful form uses a code generator that works predominantly bottom-up; a so-called bottom-up pattern matcher (BUPM). A variation of this technique is based on term rewrite systems. This technique, popularised under the name BURS, and developed by Pelegrí-Llopart and Graham [31], has arguably been considered the state of the art in automatic code generation. BURS, which stands for bottom-up rewrite system, has an underlying theory that is poorly understood. The theory has received virtually no attention in the literature since its initial publication [30]. The only research that has been carried out in this technique has been on improved tablecompression methods. Many researchers who claim to use BURS theory (e.g. [32,14]) generally use 'weaker' tree grammars instead of term rewrite systems, or equate BURS with a system that does a static cost analysis (e.g. [13]). We argue that a static cost analysis is neither necessary nor sufficient to warrant a BURS label, and that a system that is based on tree grammars cannot be a BURS.In this work we present an outline of formal BURS theory. Due to space restrictions, we present the full theory in [29]. This formalisation of BURS contrasts with the semiformal work of Pelegrí-Llopart and Graham. But there are other important differences in our work. We do not, for example, use instruction costs to do static pattern selection, and we do not use dynamic programming. Instead we use a heuristic search algorithm that only needs to dynamically compute costs for those patterns that may contribute to ?

Combinatorial Interaction Testing for Test Selection in Grammar-Based Testing

“…From this specification the compiler module is generated that translates the internal program representation of the compiler into the assembly language. A good introduction into this technique is given in [4]. The Itanium compiler is build with the CoSy [5].…”

Instruction Selection

“…To the best of my knowledge, the only recent technique (less than 20 years old) to use this kind of recursive top-down methodology for tree covering is that of Nymeyer et al [270,271]. In two papers from 1996 and 1997, Nymeyer et al introduce a method where A * search-another strategy for exploring the search space (see [297])-is combined with BURS theory.…”

Pattern-matching algorithms based on term rewrite systems

“…In earlier work[20,21] we referred to the innermost normal form as simply the normal form 3. In earlier work referred to as strong normal rewrite sequences.…”