1. Apparatus for processing data under control of program instructions, said apparatus comprising: first execution circuitry configured to execute program instructions; second execution circuitry configured to execute said program instructions, said second execution circuitry having a lower energy consumption when executing said program instruction than said first execution circuitry, and said second execution circuitry requiring a longer time to execute said program instructions than said first execution circuitry; and control circuitry configured to control whether said program instructions are executed by said first execution circuitry or said second execution circuitry, wherein said control circuitry comprises prediction circuitry configured: (i) to predict a predicted identity of a next sequence of program instructions to be executed in dependence upon a most recently executed sequence of program instructions; and (ii) in dependence upon said predicted identity, to predict a predicted execution target corresponding to whether said next sequence of program instructions should be executed with said first execution circuitry or said second execution circuitry; and said control circuitry is configured to select either said first execution circuitry or said second execution circuitry to execute said next sequence of program instructions in dependence upon said predicted execution target.