Apparatus and method for performing branch prediction

Abstract

An apparatus and method are provided for performing branch prediction. The apparatus has processing circuitry for executing instructions, and branch prediction circuitry for making branch outcome predictions in respect of branch instructions. The branch prediction circuitry includes loop prediction circuitry having a plurality of entries, where each entry is used to maintain branch outcome prediction information for a loop controlling branch instruction that controls repeated execution of a loop comprising a number of instructions. The branch prediction circuitry is arranged to analyse blocks of instructions and to produce a prediction result for each block that is dependent on branch outcome predictions made for any branch instructions appearing in the associated block. A prediction queue then stores the prediction results produced by the branch prediction circuitry in order to determine the instructions to be executed by the processing circuitry. When the block of instructions being analysed comprises a loop controlling branch instruction that has an active entry in the loop prediction circuitry, and a determined condition is detected in respect of the associated loop, the loop prediction circuitry is arranged to produce a prediction result that identifies multiple iterations of the loop. This can significantly boost prediction bandwidth for certain types of loop.