[pclmulqdq]

Great, those checks can stay in "serious" code, and those of us who don't want them can take the UB. C++ 20 actually ended up specifying that all ints are twos complement, removing this from the category of "UB," but a lot more weird stuff is programmed in C.

[gpderetta]

Note that signed overflow is still UB in c++ even with 2-complement being guaranteed for signed types.