[flohofwoe]

The thing is that the actual compiler behaviour matters more for real-world projects than what the C standard says. E.g. the C standard was always retroactive, it merely tried to reign in wildly different compiler behaviour at the time when the standard was new. It mostly succeeded, but still the most useful C and C++ compiler features are living in non-standard extensions.

[leni536]

Unaligned access being fine in one architecture, but not in others would create separate dialects, regardless of being blessed by ISO C.

Just don't do unaligned access, it's a dialect that doesn't exist currently, and should never exist.

[eru]

> Unaligned access being fine in one architecture, but not in others would create separate dialects, regardless of being blessed by ISO C.

That doesn't mean unaligned access would need to be UB. It could be implementation defined. Or could just be defined to result in an error on all machines.

[leni536]

Implementation-defined without further constraining the behavior is not much better than undefined.

Defining it to always error would add overhead even for proper aligned access on x86, as the generated code would need to explicitly check in many cases.

[eru]

> Implementation-defined without further constraining the behavior is not much better than undefined.

No, it's a lot better. Because implementations have to define it.