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Cranelift codegen backend for rust

The goal of this project is to create an alternative codegen backend for the rust compiler based on Cranelift. This has the potential to improve compilation times in debug mode. If your project doesn’t use any of the things listed under “Not yet supported”, it should work fine. If not please open an issue.

Building and testing

$ git clone https://github.com/bjorn3/rustc_codegen_cranelift
$ cd rustc_codegen_cranelift
$ ./y.sh prepare
$ ./y.sh build

To run the test suite replace the last command with:

$ ./test.sh

For more docs on how to build and test see build_system/usage.txt or the help message of ./y.sh.

Precompiled builds

Alternatively you can download a pre built version from the releases page. Extract the dist directory in the archive anywhere you want. If you want to use cargo clif build instead of having to specify the full path to the cargo-clif executable, you can add the bin subdirectory of the extracted dist directory to your PATH. (tutorial for Windows, and for Linux/MacOS).


rustc_codegen_cranelift can be used as a near-drop-in replacement for cargo build or cargo run for existing projects.

Assuming $cg_clif_dir is the directory you cloned this repo into and you followed the instructions (y.sh prepare and y.sh build or test.sh).

In the directory with your project (where you can do the usual cargo build), run:

$ $cg_clif_dir/dist/cargo-clif build

This will build your project with rustc_codegen_cranelift instead of the usual LLVM backend.

For additional ways to use rustc_codegen_cranelift like the JIT mode see usage.md.

Building and testing with changes in rustc code

This is useful when changing code in rustc_codegen_cranelift as part of changing main Rust repository. This can happen, for example, when you are implementing a new compiler intrinsic.

Instruction below uses $RustCheckoutDir as substitute for any folder where you cloned Rust repository.

You need to do this steps to successfully compile and use the cranelift backend with your changes in rustc code:

  1. cd $RustCheckoutDir
  2. Run python x.py setup and choose option for compiler (b).
  3. Build compiler and necessary tools: python x.py build --stage=2 compiler library/std src/tools/rustdoc src/tools/rustfmt
  4. Copy exectutable files from ./build/host/stage2-tools/<your hostname triple>/release to ./build/host/stage2/bin/. Note that you would need to do this every time you rebuilt rust repository.
  5. Copy cargo from another toolchain: cp $(rustup which cargo) .build/<your hostname triple>/stage2/bin/cargo
  6. Link your new rustc to toolchain: rustup toolchain link stage2 ./build/host/stage2/.
  7. (Windows only) compile y.rs: rustc +stage2 -O y.rs.
  8. You need to prefix every ./y.rs (or y if you built y.rs) command by rustup run stage2 to make cg_clif use your local changes in rustc.
  1. Now you can use your cg_clif build to compile other Rust programs, e.g. you can open any Rust crate and run commands like $RustCheckoutDir/compiler/rustc_codegen_cranelift/dist/cargo-clif build --release.


See the documentation on the BackendConfig struct in config.rs for all configuration options.

Not yet supported


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be dual licensed as above, without any additional terms or conditions.