List scheduling in the presence of branches: A theoretical evaluation

The extraction of operation level parallelism from sequential code has become an important problem in compiler research due to the proliferation of superscalar and VLIW architectures. This problem becomes especially hard for code containing a large number of conditional branches. In this paper we extend previous work on straight line code scheduling by looking at branching task systems whose control flow graph is acyclic. First, we define an optimality measure based on the probability of the various execution paths. Then, we apply a list scheduling algorithm to these systems and derive a worst case performance guarantee for this method. Finally, we show that there are branching task systems for which this bound is almost tight.