Optimal weighted loop fusion for parallel programs
Nimrod Megiddo, Vivek Sarkar · 1997
Much of the computation involved in parallel programs occurs within loops, either nested loops as in parallel scientific applications or collections of loops as in stream-based applications. Loop fusion is a well-known program transformation that has shown to be effective in improving data locality in parallel programs by reducing inter-processor communication and improving register and cache locality. Weighted loop fusion is the problem of finding a legal partition of loop nests into fusible clusters so as to minimize the total inter-cluster weights. The loop nests may contain parallel or sequential loops; care is taken to ensure that a parallel loop does not get serialized after fusion. It has been shown in past work that the weighted loop fusion problem is NP-hard. Despite the NP-hardness property, we show how optimal solutions can be found efficiently (i.e., within the compile-time constraints of a product-quality optimizing compiler) for weighted loop fusion problem sizes that occ...