This is a GCC codegen for rustc, which means it can be loaded by the existing rustc frontend, but benefits from GCC: more architectures are supported and GCC's optimizations are used.
Despite its name, libgccjit can be used for ahead-of-time compilation, as is used here.
The primary goal of this project is to be able to compile Rust code on platforms unsupported by LLVM. A secondary goal is to check if using the gcc backend will provide any run-time speed improvement for the programs compiled using rustc.
This requires a patched libgccjit in order to work. You need to use my fork of gcc which already includes these patches.
$ cp config.example.toml config.toml
If don't need to test GCC patches you wrote in our GCC fork, then the default configuration should be all you need. You can update the rustc_codegen_gcc without worrying about GCC.
If you wrote a patch for GCC and want to test it without this backend, you will need to do a few more things.
To build it (most of these instructions come from here, so don't hesitate to take a look there if you encounter an issue):
$ git clone https://github.com/antoyo/gcc $ sudo apt install flex libmpfr-dev libgmp-dev libmpc3 libmpc-dev $ mkdir gcc-build gcc-install $ cd gcc-build $ ../gcc/configure \ --enable-host-shared \ --enable-languages=jit \ --enable-checking=release \ # it enables extra checks which allow to find bugs --disable-bootstrap \ --disable-multilib \ --prefix=$(pwd)/../gcc-install $ make -j4 # You can replace `4` with another number depending on how many cores you have.
If you want to run libgccjit tests, you will need to also enable the C++ language in the configure:
--enable-languages=jit,c++
Then to run libgccjit tests:
$ cd gcc # from the `gcc-build` folder $ make check-jit # To run one specific test: $ make check-jit RUNTESTFLAGS="-v -v -v jit.exp=jit.dg/test-asm.cc"
Put the path to your custom build of libgccjit in the file config.toml.
You now need to set the gcc-path value in config.toml with the result of this command:
$ dirname $(readlink -f `find . -name libgccjit.so`)
and to comment the download-gccjit setting:
gcc-path = "[MY PATH]" # download-gccjit = true
Then you can run commands like this:
$ ./y.sh prepare # download and patch sysroot src and install hyperfine for benchmarking $ ./y.sh build --release
To run the tests:
$ ./y.sh test --release
$CG_GCCJIT_DIR is the directory you cloned this repo into in the following instructions:
export CG_GCCJIT_DIR=[the full path to rustc_codegen_gcc]
$ CHANNEL="release" $CG_GCCJIT_DIR/y.sh cargo run
If you compiled cg_gccjit in debug mode (aka you didn't pass --release to ./y.sh test) you should use CHANNEL="debug" instead or omit CHANNEL="release" completely.
To use LTO, you need to set the variable FAT_LTO=1 and EMBED_LTO_BITCODE=1 in addition to setting lto = "fat" in the Cargo.toml. Don't set FAT_LTO when compiling the sysroot, though: only set EMBED_LTO_BITCODE=1.
Failing to set EMBED_LTO_BITCODE will give you the following error:
error: failed to copy bitcode to object file: No such file or directory (os error 2)
You should prefer using the Cargo method.
$ LIBRARY_PATH="[gcc-path value]" LD_LIBRARY_PATH="[gcc-path value]" rustc +$(cat $CG_GCCJIT_DIR/rust-toolchain | grep 'channel' | cut -d '=' -f 2 | sed 's/"//g' | sed 's/ //g') -Cpanic=abort -Zcodegen-backend=$CG_GCCJIT_DIR/target/release/librustc_codegen_gcc.so --sysroot $CG_GCCJIT_DIR/build_sysroot/sysroot my_crate.rs
More specific documentation is available in the doc folder:
While this crate is licensed under a dual Apache/MIT license, it links to libgccjit which is under the GPLv3+ and thus, the resulting toolchain (rustc + GCC codegen) will need to be released under the GPL license.
However, programs compiled with rustc_codegen_gcc do not need to be released under a GPL license.