The title is somewhat misleading as to the scope of this project, as this looks to be a project for adding GCC backend support to the existing Rust compiler (though this isn't a criticism, that's exactly the approach that I would take!).
The (simplified) way that rustc works is that it translates Rust source code into a custom intermediate language called MIR, does a bunch of analysis and a few optimizations, and at the very end translates MIR to LLVM IR and passes that into LLVM. This project looks to add support for translating MIR to GCC's own IR instead of LLVM IR, allowing it to reuse all the other work that has been done writing rustc.
For a from-scratch reimplementation of (most of) a Rust frontend, see mrustc ( https://github.com/thepowersgang/mrustc ), which is written in C++, and served to demonstrate that (a prior version of) rustc did not feature a reflections-on-trusting-trust attack (via diverse double compilation).
The (simplified) way that rustc works is that it translates Rust source code into a custom intermediate language called MIR, does a bunch of analysis and a few optimizations, and at the very end translates MIR to LLVM IR and passes that into LLVM. This project looks to add support for translating MIR to GCC's own IR instead of LLVM IR, allowing it to reuse all the other work that has been done writing rustc.
For a from-scratch reimplementation of (most of) a Rust frontend, see mrustc ( https://github.com/thepowersgang/mrustc ), which is written in C++, and served to demonstrate that (a prior version of) rustc did not feature a reflections-on-trusting-trust attack (via diverse double compilation).