[stephencanon]

Non-trivial vectorization is an entirely different sort of optimization than re-association to extract ILP (especially in the integer domain where the vector instructions often have no exact non-vector analogue).

Yes, there are people who have the knowledge and experience to regularly beat the compiler. I do it professionally. My point is not "don't bother optimizing, let the compiler do it". My point is "this particular micro-optimization is less valuable in the real world than focused benchmarks suggest, and good compilers often do it (this one specific optimization) for you, anyway."