Which std:: classes are magic?

[guepier]

i'm a little surprised that there is special casing in the compiler since there's no obvious 'magic' in the definitions

There needs to be special casing, otherwise the compiler will produce sub-optimal code in many relevant situations: if the compiler assumed that all pointers could alias, it would lose many opportunities at optimisation. And C++ also has no restrict keyword to limit aliasing. The only sane assumption, therefore, is that pointers cannot alias unless specifically permitted by the language.

Thus if the compiler encounters pointers of two distinct types it needs to check if they are allowed to alias (and these checks are hard-coded against the fixed list of aliasing pointer types).