[xaduha]

I'm in a camp that thinks compilers should also take care of the original

    unsigned average(unsigned a, unsigned b) {
        return (a + b) / 2;
    }

At the end of the day it's all just text. There are plenty of steps before any of it does anything at all.

[jws]

For C at least, the spec says that unsigned addition is modulo 2^64 (or 32 or 16 or whatever) so, imagine you had an 8 bit unsigned, 128+128 gives you 0. Divided by 2 is 0. That’s the right answer by the language specification. The trick is to get 128.

[Dylan16807]

What should happen if you store "a+b" in an intermediate value?

[xaduha]

If it is used and there's no way around it, then show a compilation warning that there might be overflow. If it can be resolved without being directly used, then it should be optimized away.