Predicting an outcome of an instruction following a flush

Abstract

An apparatus is described, comprising processing circuitry to speculatively execute an earlier instruction and a later instruction by generating a prediction of an outcome of the earlier instruction and a prediction of an outcome of the later instruction, wherein the prediction of the outcome of the earlier instruction causes a first control flow path to be executed. The apparatus also comprises storage circuitry to store the outcome of the later instruction in response to the later instruction completing, and flush circuitry to generate a flush in response to the prediction of the outcome of the earlier instruction being incorrect. Permission circuitry permits the generating of the prediction by the processing circuitry. When re-executing the later instruction in a second control flow path following the flush, the processing circuitry is adapted to perform the generating the prediction of the outcome of the later instruction as the outcome stored in the storage circuitry during execution of the first control flow path. The permission circuitry is adapted to permit or inhibit generating the prediction of the outcome of the later instruction as the outcome stored in the storage circuitry in dependence on a condition.