A Uniform Internal Representation for High-Level and Instruction-Level Transformations Eduard Ayguadé, Cristina Barrado, Jesús Labarta, David López, Susana Moreno, David Padua, and Mateo Valero

this paper we describe a strategy that will make it possible, after applying a small number of changes, to represent low-level operations as part of the internal representation of a conventional source-to-source Fortran translator. Briefly, our strategy is to represent the low-level operations as Fortran statements. In this way, all the transformation and analysis routines available in the source-to-source restructurer can be applied to the lowlevel representation of the program. The source-to-source parallelizer could then be extended to include many traditional analysis and transformation steps, such as strength reduction and register allocation, not usually performed by this translator. The generation of machine instructions is done as a last step by a direct mapping from each Fortran statement onto one or more machine instructions. The source-to-source restructurer is therefore extended into a complete compiler as shown in Figure 1. All transformations, including high-level parallelization and the traditional scalar optimizations, can now be performed in a unified framework based on a single internal representation. One additional advantage of representing the low-level operations as Fortran statements is that the outcome of each transformation, both high and low level, can be trivially transformed into a Fortran program that could be executed to test the correctness of the transformation. Another approach that also uses a uniform representation for both high-level parallelization and scalar optimizations was the one followed in the IBM Fortran compiler [ScKo86]. The main difference with our approach is that this compiler evolved from a traditional back-end compiler which was extended to do some of the high-level transformations usually performed in other systems by..