Clang and GCC can do some amazing optimizations. However, these types of tricks often come into play as a result of clever data representation, i.e., instead of representing data as a bunch of objects in an array, you’ve figured out how to represent it, or a subset, in some cleverly packed bits and/or ints (and then can reap the benefit of these tricks).

It’s trivial for a compiler to see (x / 2) and substitute (x >> 1) but it is much harder for a compiler to go from seeing that you have a bunch of Foo objects and realizing that they could be better represented as clever bit vectors.