Predicting detected branches as taken when cumulative weight values in a weight table selected by history register bits exceed a threshold value

Abstract

Program flow prediction circuitry comprises a history register to store history data for at least one or more most recently executed branch instructions; a memory to store a plurality of sets of weight values, one set for each of a group of portions of one or more bits of the history data; access circuitry to access, for a current branch instruction to be predicted, a weight value for each of the portions of one or more bits of the history data by selecting from the set of weight values in dependence upon a current value of the portions of the history data; a combiner to generate a combined weight value by combining the weight values accessed by the access circuitry; a comparator to compare the combined weight value with a prediction threshold value to detect whether or not a branch represented by the current branch instruction is predicted to be taken; and weight modifier circuitry to modify the accessed weight values in dependence upon a resolution of whether the branch represented by the current branch instruction is taken or not.