[huhtenberg]

How is basic loop unrolling is "not even close" to the expected result when you explicitly ask for optimization with O3?

[umanwizard]

This isn’t basic loop unrolling; it’s replacing an entire loop with a closed form mathematical formula.

[huhtenberg]

It's a form of loop unrolling. Regardless of the term, this is still very much in the ballpark of what you'd expect when asking for optimization.