[saynsedit]

It's not convoluted. It's actually clear and well-defined making it easier to reason about.

I'd call compiler specific alignment attributes more arcane, convoluted, and susceptible to future bugs.

Vectorization isn't a panacea. You need to benchmark to be sure, lacking that I expect GCC to be better at optimizing code than you. If you disagree, please manually write a vectorized one that handles non-aligned addition and post your results :)