Power reduction in processor pipeline by detecting zeros

Techniques are described for power reduction in a computer processor based on detection of whether data destined for input to an arithmetic logic unit (ALU) has a particular value. The data is written to a register prior to performing an arithmetic or logical operation using the data as an operand. Depending on a timing of when the data is supplied to the register, the determination is made before or after the data is written to the register, and a memory associated with the register is updated with a result of the determination. Contents of the memory are used to make a decision whether to allow the ALU to perform the arithmetic or logical operation. The memory can be implemented as a non-architectural register.