Consider the following code

bool test_naive0(bool b, short i) {
    return (b ? i % 4 : i % 16)==0;
}

It could be optimized into

bool test_optim0(bool b, short i) {
    return (i & (b ? 15 : 3))==0;
}


Godbolt playground: https://godbolt.org/z/8vj999M3c

P.S.: Inspired by the manual optimizations in libstdc++ https://github.com/gcc-mirror/gcc/commit/b92d12d3fe3f1aa56d190d960e40c62869a6cfbb