Extensions to Cycle Shrinking

Abstract

An important part of a parallelizing compiler is the restructuring phase, which extracts parallelism from a sequential program. We consider an important restructuring transformation called cycle shrinking [5], which partitions the iteration space of a loop so that the iterations within each group of the partition can be executed in parallel. The method in [5] mainly deals with dependences with constant distances. In this paper, we propose certain extensions to the cycle shrinking transformation. For dependences with constant distances, we present an algorithm which, under certain fairly general conditions, partitions the iteration space in a minimal number of groups. Under such conditions, our method is optimal while the previous methods are not. We have also proposed an algorithm to handle a large class of loops which have dependences with variable distances. This problem is considerably harder and has not been considered before in full generality.