Cabaret: A Fortran Case Base Reasoning System for Porting Code to High Performance Systems

1 Introduction High performance architectures are now widely available. They are characterized by the use of fast microprocessors and they are moderately parallel with a shared memory (for instance the SGI Power Challenge). Reaching good performance on these machines requires to make good usage of the parallelism and of cache memories. Porting Fortran codes to these machines requires generally three phases : code cleaning 4], performance measurements and nally code transformations. The last two phases are iteratively repeated to achieve the desired performance. The code cleaning phase must not be seen as a simple phase. In many cases, this may consist in converting a program written in old style Fortran 77 to Fortran 90. Part of porting the code can be done automatically, but there still remains a large amount to be done by an expert \hand". The Cabaret project aims at providing a set of integrated tools for speeding up the process of porting applications to high performance architecture using a novel approach based on case base reasoning techniques 2]. The main idea is to be able to recover easily an existing solution to a current problem (or close to). In other words we want to capitalize experience. One advantage of the case base reasoning techniques is that it does not depend on a formalization of the problem. This is essential since porting code to high performance architectures can hardly be reduced to a set of rules. Some works 5, 1, 3] have been proposed to detect patterns in code that can be replaced by calls to library functions. Our approach radically diiers because our system allows the user to update, automatically, the database with its own solutions and patterns. Because program transformations and performance measurements are very time consuming we complement the case base reasoning techniques with a set of pre-deened program transformations and a set of automatic instrumentation capabilities. Because we want to validate the idea on large programs the implementation is based on, a professional Fortran parser, the Foresys system 6]. The organization of the system is shown in Figure 1. In the following we present an overview of the system. 2 Case-Base Reasoning for Code Porting The main assumption the system is built on it that software engineers tend to repeat themselves. When one has a solution to port a program to a given machine, it can be reused and shared by many others. This …