B Constant Propagation : Simple Constants 25

Since decades, basic-block (BB) graphs are the state-of-the-art means for representing programs in advanced industrial compiler environments. The usual justi cation for introducing the intermediate BB-structures in the program representation is performance: analyses on BB-graphs are generally assumed to outperform their counterparts on single-instruction (SI ) graphs, which, undoubtedly, are conceptually much simpler, easier to implement, and more straightforward to verify. In this article, we discuss the di erence between the two program representations and show by means of runtime measurements that, according to the new computer generations, performance is no longer on the side of the more complex BB-graphs. In fact, it turns out that no sensible reason for the BB-structure remains. Rather, we will demonstrate that edge-labeled SI-graphs, which in contrast to the classical ow graphs model statements in their edges instead of in their nodes, are most adequate, both for the theoretical reasoning about and for the implementation of analysis and optimization algorithms. We are convinced that this perception has far-reaching consequences for the design of compiler systems.