Nice. It seems gcc/clang don't know that trick. They still divide and then check that x/3 * 3 == x. https://godbolt.org/g/V4kfuu https://godbolt.org/g/V4kfuu

Nice. It seems gcc/clang don't know that trick. They still divide and then check that x/3 * 3 == x. https://godbolt.org/g/V4kfuu https://godbolt.org/g/V4kfuu. (So do ICC17 and MSVC CL19).