An implementation of retargetable code generators in prolog

Abstract

A major problem in deriving a compiler from a formal definition is the production of correct and efficient object code. In this context, we propose a solution to the problem of code generator generation.

Our approach is based on a target machine description where the basic concepts used (storage classes, access modes, access classes and instructions) are hierarchically described by tree-patterns. These tree-patterns are written in an abstract tree language which is also used to write the program intermediate representation (input to the code generator). The code generation process is based on access mode template-driven rewritings in which the program intermediate representation is progressively transformed. The result is that each program instruction is reduced to a sequence of elementary machine instructions, each of them representing an instance of an instruction template. A data base of clauses is derived automatically from the target machine description. It is used by the kernel of the rewriting system implemented in Prolog.

First, this paper presents a way of structuring formal specifications of target machines in order to decrease the size of the description. We propose to get complete specification components by instances of parameterized specifications. As a consequence, legibility which is an important requirement of large specifications is improved.

Second a theoretical support of the intermediate rewritings based on abstract data types is given.

Third the code generation algorithm is presented and illustrated.

Finally an implementation in Prolog of a code generator based on our appoach is developped.