When all hardware built for decades uses two's complement arithmetic and even the standards bodies have noticed this (e.g. https://www.open-std.org/jtc1/sc22/wg

When all hardware built for decades uses two's complement arithmetic and even the standards bodies have noticed this (e.g. https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2218.htm https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2218.htm) it's not remotely necessary to assume that overflowing a signed integer is undefined behaviour. It's totally defined exactly what that instruction is going to do on any hardware any electrical engineer is willing to build. However, some benchmarks use iteration on a signed integer, and assuming that loop terminates makes it slightly faster, so in order to retain that marginal advantage over other languages, signed iteration shall be assumed to never overflow. This is very typical of the C++ experience.