I don’t mean this in a rude way but you should really read the posts I linked, it’s interesting and part 3 especially answers these questions

Direct link to part 3 (but read the others first for context if you can): https://blog.llvm.org/2011/05/what-every-c-programmer-should...

You don’t want warnings for every piece of code in a library you’re not using or sanity check you added that isn’t supposed to be hit

And you can’t warn when you’re optimising based on undefined behaviour because you can’t know when it will happen, that is equivalent to the halting problem

If you warned whenever undefined behaviour could be happening then e.g. every single pointer deference would say “warning: compiling assuming pointer is not null or unaligned”