Clang, and I believe gcc and many other compilers, can synthesize a memcpy from simple loops. I don't say this to vouch for its abilities, and in general I don'

Clang, and I believe gcc and many other compilers, can synthesize a memcpy from simple loops. I don't say this to vouch for its abilities, and in general I don't recommend relying on such transformations, but it will help probably for a non-trivial amount of such custom code -- but of course, nowhere near all.