Comment by AlotOfReading

    Modern C++ conveniently allows you to replace many of the bits that have UB, per standard, with your own bits with defined behavior with zero overhead.

Okay, let's continue the example. Please demonstrate how to replace the addition operator on a primitive type. You can't within the confines of the language and that's a good thing in most cases. What you can do is pass -fwrapv, except that MSVC doesn't officially define a comparable flag.

    Developers don’t even have to be hardware experts, they just have to not use std for most things.

Signed overflow isn't a problem with std, the solution to it is in std. Null pointers aren't a problem with std, but the recommended fixes are again in std. Etc.

    If you have a foundational library that makes different and/or explicit guarantees than std, it is pretty easy to police that in a code base with automation.

As far as I'm aware, neither folly, absl, nor boost define custom integral types with defined overflow behavior. Please provide examples of anyone doing that.

    UB is a feature of the standard, not the implementation. 

If you're writing "high assurance code", surely you're writing to the standard and not the implementation? The implementation's guarantees change with every upgrade, every new flag, and each time you build for different targets. I certainly try to avoid compiler assumptions as someone who writes safety critical code.