1. A method of processing data in a graphics processing system, the method comprising: the graphics processing system: when the processing of data to be processed by the graphics processing system requires further data, attempting to fetch that further data from memory; in response to the attempted fetch not returning the further data from the memory, then generating the required data and using the generated data for processing the data to be processed; and in response to the attempted fetch detecting that the further data is available in the memory, then fetching that further data from the memory and using the fetched further data for processing the data to be processed without generating that further data.