So, I used to do this for a living. The main reasons assembler worked better were: - The compiler had to make conservative assumptions. Less true now you have

So, I used to do this for a living. The main reasons assembler worked better were: - The compiler had to make conservative assumptions. Less true now you have things like restrict pointers - The compiler didn't know how to do SIMD. Now it can with intrinsics. - The compiler didn't know how to do the necessary transforms to make use of in-order cores. out-of-order makes the cpu do this itself, and is making its way down to smaller processors.