> where a and b are int values, the compiler would emit an ADD instruction in assembly. This isn't necessarily true anymore, because compilers are allowed to a

> where a and b are int values, the compiler would emit an ADD instruction in assembly. This isn't necessarily true anymore, because compilers are allowed to assume that signed overflow doesn't happen, which makes writing correct overflow-detection so difficult and non-intuitive. it's the exact opposite - if you want your compiler to just emit an ADD no matter which platform you are on, then it cannot be the language that defines the semantics of "+" in the corner cases (thus UB). If you define it as overflow on 2's complement, then on a DSP with saturating arithmetic your compiler will have to emit additional instructions to detect if you are saturating and wrap instead.