I came across this question on Stack Overflow today. I think it's a good question for dsp.SE, but it's also on-topic on Stack Overflow. Is there a means to cross-list it on both sites, or should it just stay where it is? I don't want to flag it as off-topic there, because it really isn't, although it is also directly signal-processing-related.
I've deleted my previous answer, since I think it could've given the impression that this issue is settled, but I think a discussion on these type of questions is much needed.
I agreed with you yesterday that it is a good question for us, because if you remove the ARM NEON fluff, it's basically a theoretical question on vectorization, which could stand alone independent of the specific language details. However, I know nothing about ARM NEON, and just skipped that part when reading the question, and flagged it for migration here. phonon felt that it was primarily a programming question that should've never been migrated and I respect his judgement and he's probably right about that.
I have a suggestion though. For questions like these that have a good underlying theoretical answer, that's not immediately apparent from the way it's phrased (or a conceptual question hidden under 'gimme-the-codez' text), we can migrate it here to create a copy, and clear the migration history on both sites (clearing migration history means that it reverses it and is as if it never happened – like the Stack Overflow question that you linked above). Then edit the question here to make it more theoretical and fit our site better and flag answers that don't address the modified question.
Needless to say, this can't be done for every question and the flagger should be interested in leading the editing of the question to fit our site (without the editing part, it's bad to have two identical questions with identical answers on two sites). Perhaps you could also notify the other answerers that the scope has been changed and that they should either modify their answer or delete it (they don't lose anything, because whatever rep they gained on SO is intact). I've done this at times with a few questions, and it has worked out well for the OP who gets both his code answer and his conceptual question answered. So as far as this one goes, if you'll edit the current question to remove the programming aspect and make it theoretical, we can reopen it.