Why wouldn't it?
For example, signed overflow is UB in C, but defined in Rust. Generated code can't simply use the + operator.
C has type-based alias analysis that makes some type casts illegal. Rust handles alias analysis through borrowing, so it's more forgiving about type casts.
Rust has an UnsafeCell wrapper type for hacks that break the safe memory model and would be UB otherwise. C doesn't have such thing, so only uses of UnsafeCell that are already allowed by C are safe.
There are also escape hatches for strict aliasing in the C standard - mainly using memcpy for all memory operations.
For example, a C compiler is allowed to optimize the expression a+1<a to false (if a is signed), but a Rust compiler isn't allowed to do this.
> For example, signed overflow is UB in C, but defined in Rust. Generated code can't simply use the + operator.
Obviously, yes, but it could generate overflow checks.