Understanding op-amp common mode voltage range when Vin+ is not equal Vin-
If the op-amp is working as an amplifier Vin(+) = Vin(-), of course. 

It cannot work as an amplifier when the input voltages are +3/0V since the output would have to be 6V to balance the amplifier and it will die at less than 3V. 

\$V_{OUT} = \frac{2K}{1K} (V_{TOP} - V_{BOTTOM})\$  (when balanced)

Input common mode range is maybe 0-1.6V taking temperature into account. You will exceed the common mode input range of the amplifier when the top input exceeds about 2.4V (2.55V at >=25°C), period.