1. Apparatus for processing data under control of a program having program instructions including sequences of individual program instructions corresponding to computational subgraphs identified within said program, each computational subgraph having a number of input operands and producing one or more output operands, said apparatus comprising: an operand store operable to store the input and output operands; processing logic operable to execute individual program instructions from said program; configurable accelerator logic operable, in response to reaching an execution point within said program corresponding to a sequence of individual program instructions corresponding to a computational subgraph, to evaluate one or more output functions associated with said computational subgraph, the evaluation of each output function generating an output operand for storing in the operand store, and each output operand corresponding to an output that would have been generated had the sequence of individual program instructions corresponding to the computational subgraph have been executed by the processing logic; configuration storage operable to store a single look-up table (LUT) configuration for each output function; for each output function to be evaluated, the accelerator logic being configured dependent on the associated single LUT configuration from the configuration storage such that on receipt of the input operands of the computational subgraph, the accelerator logic will generate the output operand.