Rust does not generate machine code itself. It uses LLVM to do that and there is no proof that the transformations done by that continue to keep the borrow checker guarantees. One just assumes with sufficient testing all bugs will be discovered.

Then the machine code generated by LLVM is not run directly by modern CPUs and is translated into internal representation first. And the future CPUs will behave like JIT-compilers with even more complex transformations.

The intermediate C code generated by this project just adds yet another transformation not fundamentally different from any of the above.