Apparatus and method for performing branch prediction using loop minimum iteration prediction

Abstract

An apparatus and method are provided for performing branch prediction. The apparatus has processing circuitry to execute instructions, and branch prediction circuitry for making branch outcome predictions in respect of branch instructions. The branch prediction circuitry includes loop minimum iteration prediction circuitry having one or more entries, where each entry is associated with a loop controlling branch instruction that controls repeated execution of a loop comprising a number of instructions. During a training phase for an entry, the loop minimum iteration prediction circuitry seeks to identify a minimum number of iterations of the loop. The loop minimum iteration prediction circuitry is then arranged, when the training phase has successfully identified a minimum number of iterations, to subsequently identify a branch outcome prediction for the associated loop controlling branch instruction for use during the minimum number of iterations. It has been found that such an approach can significantly improve prediction accuracy for loop controlling branch instructions associated with loops that do not have a stable total number of iterations.