On Sun, 24 Oct 2021 at 03:45, Matt Bentley via SG14 <sg14@lists.isocpp.org> wrote:
* "Opt-in UB on Unsigned Overflow" = more info on this and how it could
present performance gains would be good.

Technically, unsigned overflow is not a thing. I read "Opt-in UB on Unsigned Overflow" to mean "Opt-in overflow on unsigned integers".

Overflow is an unambiguous bug in C++ which affords signed integers some opportunities for optimisation that are lacking in unsigned integers. Some helpful examples can be found in this article and in the second half of this talk by Chandler Carruth.

Note that lack of UB also makes it harder to test for bugs in code that uses unsigned integers.