New C++ papers available
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/2018-02-pre-Jacksonville.htm …
What'll make it to C+20? 
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Looking forward for the updated paper... can't think on one reason to keep UB and not assume two's complement everywhere. If someone really needs a different behavior, why not create a different type for *that*? (like a `weird_int`)
There are three main reasons imo: optimization, optimization, and optimization. ;) Overflow UB allows compilers to use larger integer registers with simpler code. Quite common for eg 32 bit arithmetic on x86_64.
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Does the optimization really pay for the error-proneness in this case? Unsigned overflow is already well-defined, so it's inconsistent to have UB for signed. There are a lot of intentional overflow out there, waiting to be broken because of these UB-dependent optimizations.
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That's why you should use unsigned integers when you need wrap around overflow behavior. Is the better performance worth the complications? Idk.. depends on what you are doing. But I have seen 10-20% improvements in performance critical code just from changing uint to int.
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Differentiate pointer overflow (which I don’t touch) from missing optimizations on integers (which I touch).
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