I suspect that information about memory aliasing from the borrow checker (that things are not aliased) allows the compiler to add in many optimizations that C/C

I suspect that information about memory aliasing from the borrow checker (that things are not aliased) allows the compiler to add in many optimizations that C/C++ can't perform, and the benefit from that is similar to the cost of bounds checking. The memcpy vs. memmove thing comes to mind. So does stuff like iterating over the indices of a pointer to one std::vector while modifying another pointer to a std::vector. If you know you have exclusive access to the vector you are reading, then you know the size isn't changing, so you can just iterate from 0 to size and elide any bounds checking. With C++, if the pointers to the vectors could alias, then it will have to bounds check at runtime. Templates and Link time optimization helps with this sort of thing, but I'm guessing Rust still has an advantage.