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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
$ cd rustc_codegen_cranelift
$ ./ prepare # download and patch sysroot src and install hyperfine for benchmarking
$ ./ build

To run the test suite replace the last command with:

$ ./

This will implicitly build cg_clif too. Both build and accept a --debug argument to build in debug mode.

Alternatively you can download a pre built version from GHA. It is listed in the artifacts section of workflow runs. Unfortunately due to GHA restrictions you need to be logged in to access it.


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 ( prepare and build or

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

$ $cg_clif_dir/build/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


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

Not yet supported

  • Inline assembly (no cranelift support)
    • On Linux there is support for invoking an external assembler for global_asm! and asm!. llvm_asm! will remain unimplemented forever. asm! doesn't yet support reg classes. You have to specify specific registers instead.
  • SIMD (tracked here, some basic things work)


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.