> Given that Apple has been making its own CPU cores for years now, I suspect overflowing checking on Apple CPUs is virtually free (aside from code size).

Never make guesses based on a particular programming language. In Apple's own C documentation (https://developer.apple.com/documentation/xcode/integer-over...) it is stated that "Overflows result in undefined behavior." and enabling wrapping behaviour "may adversely impact performance", indicating that overflow detection is in fact not "virtually free".

Code size (and branch table entries) are not free, of course. The other thing to note is that trapping operators often need to trap precisely which can lead to missed optimizations.