Signed overflow optimization hazards in the kernel

One objection was that there really are still non-twos-complement machines in common use. As was noted by the comment to this article discussing saturating adders, where 32767+1==32767. But this would be addressed by "implementation defined" rather than "undefined".

Another objection was that there are systems still in common use that trap on signed integer overflow. If the C standard required wrapping, compilers for such systems would require special edge-case checks on pretty much any signed integer operation.

And there was of course also the objection that signed integer overflow always has been undefined. ;-)