WIP libgccjit codegen backend for rust

Despite its name, libgccjit can be used for ahead-of-time compilation, as is used here.

Motivation

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 compilation speed improvement.

Building

This requires a patched libgccjit in order to work. The following two patches need to be applied:

• https://gcc.gnu.org/pipermail/jit/2020q3/001228.html
• https://gcc.gnu.org/pipermail/jit/2020q3/001247.html

Put the path to your custom build of libgccjit in the file gcc_path.

$ git clone https://github.com/antoyo/rustc_codegen_gcc.git
$ cd rustc_codegen_gcc
$ ./prepare.sh # download and patch sysroot src and install hyperfine for benchmarking
$ ./test.sh --release

Usage

$cg_gccjit_dir is the directory you cloned this repo into in the following instructions.

Cargo

$ CHANNEL="release" $cg_gccjit_dir/cargo.sh run

If you compiled cg_gccjit in debug mode (aka you didn't pass --release to ./test.sh) you should use CHANNEL="debug" instead or omit CHANNEL="release" completely.

Rustc

You should prefer using the Cargo method.

$ rustc +$(cat $cg_gccjit_dir/rust-toolchain) -Cpanic=abort -Zcodegen-backend=$cg_gccjit_dir/target/release/librustc_codegen_gcc.so --sysroot $cg_gccjit_dir/build_sysroot/sysroot my_crate.rs

Env vars

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