An apparatus and method of optimising divergent processing in thread groups

A data processor is disclosed in which groups of execution threads comprising a thread group can execute a set of instructions in lockstep, and in which a plurality of execution lanes can perform processing operations for the execution threads. In response to an execution thread issuing circuit determining whether a portion of active threads of a first thread group and a portion of active threads of a second thread group use different execution lanes of the plurality of execution lanes, the execution thread issuing circuit issuing both the portion of active threads of a first thread group and a portion of active threads of a second thread group for execution. This can have the effect of increasing data processor efficiency, thereby increasing throughput and reducing latency.