[saynsedit]

I'm not sure I understand your deal breaker. For the platform he was targeting it produces optimal code, for other platforms it's merely slower (but not specifically slower, since the compiler is likely not a great optimizer across the board).

Vectorization is in general not applicable here since it usually requires aligned memory... not all implementations do, but most. In any case, benchmarking is more appropriate than armchair optimizing.

[qb45]

You are writing convoluted code and hoping that your compiler will figure it out and convert it internally to the form I posted. Sometimes it does, sometimes it doesn't. In this case it generates reasonable code but doesn't vectorize it for some reason. WTF.

I prefer to just add alignment specification and move on, assuming I don't care about portability. If portability matters, reread my original post ;)

[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 :)