Management of control-flow in a SIMD device

A single instruction multiple data SIMD processing device includes a plurality of processing elements (12). Each processing element includes an execute mask count register (20) storing a plurality of bits. The writing of data to registers in each processing element is enabled and disabled or masked in dependence on the multi bit data stored in the execute mask count register. By including a small set of control-flow instructions, a means of efficiently managing control-flow on a SIMD processor can be achieved.