The language could make those guarantees if it wanted to. This might add overhead on some architectures, but would be possible. An example is integer overflow. If we limit to machines using two's complement (thus any machine architecture used during last thirty years) this could be fully defined easily. And if C is ever used on a other architecture they could build a workaround using some form of oberflow trap. (Since CPU design would take C into consideration)

Or evaluation order - `i = ++i;` could easily be defined in some way. But might prevent some niche optimisations by the compiler.

Of course by C's nature there are limits (C won't be able to detect use after free or similar without changing language notably) but there is room where UB could be reduced, if it was seen as neccisary.