I was thinking about eliminating this shift-into-left bit UB. There was a previous attempt though that failed to get consensus. (but long enough ago that one could try again).

But all this signed overflow UB can be turned into traps using sanitizers. In practice, generally mandating a trap is difficult though in ISO C. My plan is to mandate this as part of a special mode, in which case I would just leave this UB in the main standard.

(One problem we also have that some special interests groups in WG14 are rather hostile to our work and the rest of the C community - so I encourage everybody who is actually using C and caring about it to join).

> I was thinking about eliminating this shift-into-left bit UB.

At least make it "change of the sign bit is UB" — if 0 shifts into the sign-bit of a positive number, or 1 shifts into the sign-bit of a negative number, that shouldn't be UB. This would make left-shifts of negative numbers well-defined, their behaviour being that of two's complement numbers. And C23 already demands two's complement from the implementations, doesn't?

> signed overflow UB can be turned into traps using sanitizers.

Well, yeah, sure, but shifting -1 one place to the left doesn't overflow, it produces -2; only shifting INT_MIN or something up to and including INT_MIN + (INT_MAX/2) would overflow.