An apparatus comprising a processor comprising one or more block-based processor cores, each of the cores being configurable to execute one or more instruction blocks, each of the cores comprising: an execution unit configured to execute register read and write instructions contained in an instruction block to read from and/or write to, respectively, a register file comprising a plurality of registers; a hardware structure (167, 207, 730) comprising: a register write mask storing data that indicates which registers of the register file a current group of instructions will write to; and a register read mask storing data that indicates which registers of the register file a next group of instructions will read; and a control unit (160, 205, 720) configured to control issuing of individual register read and write instructions of the next group of instructions to the execution unit by comparing the register write mask data to the register read mask data and allowing execution of a respective one of the individual register read and write instructions when the register write mask indicates any register the respective individual instruction is dependent on has been written by the current group of instructions for selecting a register access instruction; and to execute the selected register access instruction. an execution unit configured to execute register read and write instructions contained in an instruction block to read from and/or write to, respectively, a register file comprising a plurality of registers; a hardware structure (167, 207, 730) comprising: a register write mask storing data that indicates which registers of the register file a current group of instructions will write to; and a register read mask storing data that indicates which registers of the register file a next group of instructions will read; and a control unit (160, 205, 720) configured to control issuing of individual register read and write instructions of the next group of instructions to the execution unit by comparing the register write mask data to the register read mask data and allowing execution of a respective one of the individual register read and write instructions when the register write mask indicates any register the respective individual instruction is dependent on has been written by the current group of instructions for selecting a register access instruction; and a register write mask storing data that indicates which registers of the register file a current group of instructions will write to; and a register read mask storing data that indicates which registers of the register file a next group of instructions will read; and a control unit (160, 205, 720) configured to control issuing of individual register read and write instructions of the next group of instructions to the execution unit by comparing the register write mask data to the register read mask data and allowing execution of a respective one of the individual register read and write instructions when the register write mask indicates any register the respective individual instruction is dependent on has been written by the current group of instructions for selecting a register access instruction; and