Alloyed path-pattern scheme for branch prediction

For more accurate branch prediction, global as well as local histories have been studied and a need for hybrid history has emerged. Not only do different parts of a program require different types of histories, but some branches dynamically vary the type of history. To solve this problem, schemes involving dynamic selectors as opposed to static have been proposed. Initially, history represented the directions of previous branches (pattern-based). Then came the idea of storing the target addresses of previous branches, thus predicting based on the path (path-based). The path- and pattern-based schemes do have their drawback. This paper studies a potential problem faced by the path-and pattern-based schemes and alleviates it by presenting a new scheme, in which the path and pattern histories are alloyed. This scheme is proposed as opposed to having two predictors, path-based and pattern-based, and a selector that dynamically predicts between them. Alloying path and pattern, eliminates the problem of selecting between the two schemes and instead merges the information. It also diminishes the shortcoming of the two schemes and thus acts as a double-edged sword.