At the same time I have seen autovectorization to fail on things that would look like obvious candidates or to generate still sub-optimal code. I would prefer a

At the same time I have seen autovectorization to fail on things that would look like obvious candidates or to generate still sub-optimal code. I would prefer autovectorization over hand-written SIMD code everyday but that key here is reliability. If I cannot guarantee that the performance is going to stay the same across different compiler releases (which is often that case with autovectorization) it is much more convenient to just write the optimization myself and be sure that it is going to happen regardless of the environment.