And this is why type based alias analysis (TBAA) is insane and why projects like linux complies with fno-strict-aliasing.
C should issue a defect report and get rid of that nonsense from the standard.
C should issue a defect report and get rid of that nonsense from the standard.
This enables security analysis like valgrind/ASan and secure hardware like MTE/CHERI so it's very important and you can't get rid of it.
However, it's not possible to implement malloc() in C because malloc() is defined as returning new "memory objects" and there is no C operation which creates "memory objects" except malloc() itself. So it only works as long as you can't see into the implementation, or if the compiler gives you special forgiveness somehow.
C++ has such an operation called "placement new", so you want something like that.
It gets complicated when you have virtual memory and an OS involved but even then you can override the system malloc with a simple implementation that allocates from a large static array.
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.