“However, violating either pre- or post-conditions is unspecified behaviour, and a compiler may optimize code as if they are always true – even if a potential bug may cause them to be violated”
This implies that a compiler would be permitted to remove precisely that actual code that checks the condition in non-safe mode.
This implies that a compiler would be permitted to remove precisely that actual code that checks the condition in non-safe mode.
Seems like a deliberately introduced footgun.