Work in progress cranelift codegen backend for rust

⚠⚠⚠ This doesn't do much useful yet ⚠⚠⚠

Building

$ git clone https://github.com/bjorn3/rustc_codegen_cranelift.git
$ cd rustc_codegen_cranelift
$ rustup override set nightly # This uses unstable api's which will never be stabilized
$ cargo install xargo         # Used for building the sysroot
$ cargo install hyperfine     # Used for benchmarking in build.sh
$ cargo build

Usage

$ rustc -Zcodegen-backend=$(pwd)/target/debug/librustc_codegen_cranelift.so my_crate.rs

Build sysroot and test

$ rustup component add rust-src # Make sure the sysroot source is availablr
$ ./prepare_libcore.sh          # Patch the sysroot source for some not yet supported things
$ ./build.sh

Not yet supported

• Good non-rust abi support (non scalars are not yet supported for the "C" abi)
• Checked binops (some missing instructions in cranelift)
• Inline assembly (no cranelift support)
• Varargs (no cranelift support)
• libstd (needs varargs and some other stuff) (tracked here)
• u128 and i128 (no cranelift support)
• SIMD (huge amount of work to get all intrinsics implemented, so may never be supported)