Return address restoration

Abstract

An apparatus comprises speculative return address tracking circuitry to maintain a speculative call return stack structure to track speculative return addresses predicted based on speculative program flow; branch prediction circuitry to predict a target address of a return branch instruction based on the speculative call return stack structure; committed return address tracking circuitry to maintain a committed call return stack structure to track committed return addresses detected based on committed program flow for instructions executed by processing circuitry; and return address restoration circuitry responsive to a pipeline flush event to perform return address restoration based on one or more committed return addresses from the committed call return stack structure to prevent the branch prediction circuitry using one or more cancelled speculative return addresses of the speculative call return stack structure for predicting the target address of the return branch instruction. The committed call return stack structure has a smaller capacity for storing return addresses than the speculative call return stack structure.