An apparatus includes instruction fetching circuitry to read a set of instructions, including a speculative execution instruction and a speculative condition determination instruction; cache the instructions; and read the speculative execution instruction corresponding to the speculative condition of the speculative condition determination instruction. If an execution result of the speculative condition determination instruction indicates the speculative condition is incorrect, clear the instructions cached in the instruction fetching circuitry. Instruction decoding circuitry decodes instructions. Executing circuitry executes instructions, including executing the speculative condition determination instruction to obtain the execution result. Instruction retiring circuitry caches instructions executed by the executing circuitry, and in response to an instruction older than the speculative condition determination instruction being retired, instructs the executing circuitry to clear instructions in the executing circuitry and clear the instructions cached in the instruction retiring circuitry.