It's interesting to see which things Rust has defined where C refused to, such as fixing a strict evaluation order (mostly post-order on the AST), requiring signed integers to be 2's complement or masking shift amounts (`x << n` being `x << (n % bitwidth)`).

Where does C actually gain anything nowadays? Signed integer UB is mostly useful for optimizing misuses of `int` for unsigned values (https://news.ycombinator.com/item?id=17191295), and is evaluation order even relevant anymore? (I don't think clang can pass that information down to LLVM, at all)

The only example I gave which has known drawbacks is the shift one, where modern platforms differ in the behavior, and LLVM will only optimize out the masking of the shift amount on the platforms that have that same behavior in their shift instructions (I think x86, but not ARM).

However, even if you make all of these changes to C, there's still a lot of UB left, in the form of memory accesses, which is much harder to get rid of (see the other comments, some of which mention Rust as well).