The standard is written to accommodate obsolete tagged memory architectures that require special support. They aren't relevant today and data pointers are fungible regardless of where they originate.
But in practice it's not always true on Apple A12 or later because they support PAC (so pointers of different type to the same address can be not equal bit-wise) and is even less true on very latest Android because it supports the really big gun MTE. And MTE is great; you don't want to miss out on it. No explainer here because there's no Wikipedia article for it(!).
Also becomes not true on any system if you use -fbounds-safety or some of the sanitizers.
This was never true because of something called provenance: https://www.ralfj.de/blog/2020/12/14/provenance.html. Though it usually doesn't matter and I think it annoys anyone who finds out about it.
But in practice it's not always true on Apple A12 or later because they support PAC (so pointers of different type to the same address can be not equal bit-wise) and is even less true on very latest Android because it supports the really big gun MTE. And MTE is great; you don't want to miss out on it. No explainer here because there's no Wikipedia article for it(!).
Also becomes not true on any system if you use -fbounds-safety or some of the sanitizers.