CUDA __umul24 function, useful or not?

Question

Is worth replacing all multiplications with the __umul24 function in a CUDA kernel? I read different and opposite opinions and I can't still make a bechmark to figure it out

Answer 1

Only in devices with architecture prior to fermi, that is with cuda capabilities prior to 2.0 where the integer arithmetic unit is 24 bit.

On Cuda Device with capabilities >= 2.0 the architecture is 32 bit the _umul24 will be slower instead of faster. The reason is because it has to emulate the 24 bit operation with 32 bit architecture.

The question is now: Is it worth the effort for the speed gain ? Probably not.