Parallélisme des nids de boucles pour l'optimisation du temps d'exécution et de la taille du code. (Nested loop parallelism to optimize execution time and code size)

The real time implementation algorithms always include nested loops which require important execution times. Thus, several nested loop parallelism techniques have been proposed with the aim of decreasing their execution times. These techniques can be classified in terms of granularity, which are the iteration level parallelism and the instruction level parallelism. In the case of the instruction level parallelism, the techniques aim to achieve a full parallelism. However, the loop carried dependencies implies shifting instructions in both side of nested loops. Consequently, these techniques provide implementations with nonoptimal execution times and important code sizes, which represent limiting factors when implemented on embedded real-time systems. In this work, we are interested on enhancing the parallelism strategies of nested loops. The first contribution consists of purposing a novel instruction level parallelism technique, called “delayed multidimensional retiming”. It aims to scheduling the nested loops with the minimal cycle period, without achieving a full parallelism. The second contribution consists of employing the “delayed multidimensional retiming” when providing nested loop implementations on real time embedded systems. The aim is to respect an execution time constraint while using minimal code size. In this context, we proposed a first approach that selects the minimal instruction parallelism level allowing the execution time constraint respect. The second approach employs both instruction level parallelism and iteration level parallelism, by using the “delayed multidimensional retiming” and the “loop striping”.