It won't be. They plan to use the exact same code!
Rust is designed to compile fine without any borrow checking (it reduces it to the C level of safety, but valid programs generate valid code).
GCC will compile itself without a borrow checker. Then it will compile the existing borrow checker written in Rust, and then recompile itself with borrow checking.
Rust is designed to compile fine without any borrow checking (it reduces it to the C level of safety, but valid programs generate valid code).
GCC will compile itself without a borrow checker. Then it will compile the existing borrow checker written in Rust, and then recompile itself with borrow checking.