An apparatus comprising: processing circuitry to perform data processing in response to instructions; and instruction fusing circuitry to fuse a move prefix instruction and an immediately following instruction fetched from a data store to generate a fused data processing instruction to be issued to an execute unit (20, 22, 24) of the processing circuitry for executing the fused data processing instruction instead of said move prefix instruction and said immediately following instruction; wherein the move prefix instruction identifies a move destination register and a move source register specifying a data value to be at least partially copied to the move destination register; and in response to detecting said move prefix instruction, the instruction fusing circuitry is configured to determine whether to fuse said move prefix instruction and said immediately following instruction independently of whether the move destination register of the move prefix instruction is the same register as any register specified by said immediately following instruction; wherein the fused data processing instruction comprises a constructive data processing instruction separately identifying at least two operand registers and a result register to be set to a result value corresponding to a result of applying a processing operation to values specified by said at least two operand registers; and the instruction fusing circuitry is configured to generate said constructive data processing instruction with: said result register corresponding to one of said move destination register of the move prefix instruction and a destination register of the immediately following instruction; and said at least two operand registers corresponding to said move source register of said move prefix instruction and at least one source register of the immediately following instruction. processing circuitry to perform data processing in response to instructions; and instruction fusing circuitry to fuse a move prefix instruction and an immediately following instruction fetched from a data store to generate a fused data processing instruction to be issued to an execute unit (20, 22, 24) of the processing circuitry for executing the fused data processing instruction instead of said move prefix instruction and said immediately following instruction; wherein the move prefix instruction identifies a move destination register and a move source register specifying a data value to be at least partially copied to the move destination register; and in response to detecting said move prefix instruction, the instruction fusing circuitry is configured to determine whether to fuse said move prefix instruction and said immediately following instruction independently of whether the move destination register of the move prefix instruction is the same register as any register specified by said immediately following instruction; wherein the fused data processing instruction comprises a constructive data processing instruction separately identifying at least two operand registers and a result register to be set to a result value corresponding to a result of applying a processing operation to values specified by said at least two operand registers; and the instruction fusing circuitry is configured to generate said constructive data processing instruction with: said result register corresponding to one of said move destination register of the move prefix instruction and a destination register of the immediately following instruction; and said at least two operand registers corresponding to said move source register of said move prefix instruction and at least one source register of the immediately following instruction. said result register corresponding to one of said move destination register of the move prefix instruction and a destination register of the immediately following instruction; and said at least two operand registers corresponding to said move source register of said move prefix instruction and at least one source register of the immediately following instruction.