It's called loop unrolling. Most optimizing compilers do it to increase performance. The most obvious gain is that you minimize your branch penalty. The Wiki

It's called loop unrolling. Most optimizing compilers do it to increase performance. The most obvious gain is that you minimize your branch penalty. The Wikipedia article on it is quite good with examples: https://en.wikipedia.org/wiki/Loop_unrolling https://en.wikipedia.org/wiki/Loop_unrolling