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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 myfork 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 shouldbe all you need. You can update therustc_codegen_gcc without worrying about GCC.

If you wrote a patch for GCC and want to test it without this backend, you will needto do a few more things.

To build it (most of these instructions come fromhere, 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 theconfigure:

--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 fileconfig.toml.

You now need to set thegcc-path value inconfig.toml with the result of this command:

$ dirname$(readlink -f`find. -name libgccjit.so`)

and to comment thedownload-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.shtest --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 useCHANNEL="debug" instead or omitCHANNEL="release" completely.

To use LTO, you need to set the variableFAT_LTO=1 andEMBED_LTO_BITCODE=1 in addition to settinglto = "fat" in theCargo.toml.Don't setFAT_LTO when compiling the sysroot, though: only setEMBED_LTO_BITCODE=1.

Failing to setEMBED_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

CG_GCCJIT_INCR_CACHE_DISABLED

Don't cache object files in the incremental cache. Useful during development of cg_gccjit to make it possible to use incremental mode for all analyses performed by rustc without caching object files when their content should have been changed by a change to cg_gccjit.

CG_GCCJIT_DISPLAY_CG_TIME

Display the time it took to perform codegen for a crate

CG_RUSTFLAGS

Send additional flags to rustc. Can be used to build the sysroot without unwinding by setting `CG_RUSTFLAGS=-Cpanic=abort`.

CG_GCCJIT_DUMP_TO_FILE

Dump a C-like representation to /tmp/gccjit_dumps and enable debug info in order to debug this C-like representation.

More specific documentation is available in thedoc folder:

• Common errors
• Debugging GCC LTO
• Debugging libgccjit
• Git subtree sync
• List of useful commands
• Send a patch to GCC

While this crate is licensed under a dual Apache/MIT license, it links tolibgccjit 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 withrustc_codegen_gcc do not need to be released under a GPL license.