Where does the C standard describe overflow of signed integers?

[Matthew Woodcraft]

Paul Schlie wrote:
>As optimization seems to be a non-argument, as by analogy all
>optimizations which are available for unsigned arithmetic are
>correspondingly available for signed integer operations; as any signed
>value may then be thought of as being unsigned for the purposes of
>computation and/or comparison.

What about optimising x*2/2 to x?

-M-