A data processing apparatus has permutation circuitry for performing a permutation operation for changing a data element size or data element positioning of at least one source operand to generate first and second SIMD operands, and SIMD processing circuitry for performing a SIMD operation on the first and second SIMD operands. In response to a first SIMD instruction requiring a permutation operation, the instruction decoder controls the permutation circuitry to perform the permutation operation to generate the first and second SIMD operands and then controls the SIMD processing circuitry to perform the SIMD operation using these operands. In response to a second SIMD instruction not requiring a permutation operation, the instruction decoder controls the SIMD processing circuitry to perform the SIMD operation using the first and second SIMD operands identified by the instruction, without passing them via the permutation circuitry.