I don’t think you have to reach for something as invasive as a borrow checker to handle most of these conditions. Bounds checks, for example, are rarely skipped intentionally in the vast majority of C programs; rather, they’re just skipped accidentally or performed incorrectly. Combine that with the extremely common and well-known compiler optimizations for BCE present in many compiled languages, and I don’t think C programmers get to trot out performance as an excuse for the language not supporting bounds checking by default, and providing escape hatches for people who really need to avoid it.

The same is true for overflow and unsafe math (tons of languages increase math and overflow safety on many paths without performance penalty, and baking that behavior into the type system with nondefault unsafe options is demonstrably tractable).

Hell, the prevalence of C static analyzers that warn about the vast majority of errors in these categories is proof that more safety is possible in C.

It’s not really about performance. It’s more the stubborn obsession with ABI compatibility at all costs and a pervasive lack of type system support and conventions relating to code reuse that hold C back.