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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.The patches inthis repository need to be applied.(Those patches should work when applied on master, but in case it doesn't work, they are known to work when applied on 079c23cfe079f203d5df83fea8e92a60c7d7e878.)You can also use myfork of gcc which already includes these patches.

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 filegcc_path.

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

You also need to set RUST_COMPILER_RT_ROOT:

$ git clone https://github.com/llvm/llvm-project llvm --depth 1 --single-branch$export RUST_COMPILER_RT_ROOT="$PWD/llvm/compiler-rt"

Then you can run commands like this:

$ ./prepare.sh# download and patch sysroot src and install hyperfine for benchmarking$ LIBRARY_PATH=$(cat gcc_path) LD_LIBRARY_PATH=$(cat gcc_path) ./build.sh --release

To run the tests:

$ ./test.sh --release

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

$ 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 useCHANNEL="debug" instead or omitCHANNEL="release" completely.

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

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

Sometimes, libgccjit will crash and output an error like this:

during RTL pass: expandlibgccjit.so: error: in expmed_mode_index, at expmed.h:2490x7f0da2e61a35 expmed_mode_index../../../gcc/gcc/expmed.h:2490x7f0da2e61aa4 expmed_op_cost_ptr../../../gcc/gcc/expmed.h:2710x7f0da2e620dc sdiv_cost_ptr../../../gcc/gcc/expmed.h:5400x7f0da2e62129 sdiv_cost../../../gcc/gcc/expmed.h:5580x7f0da2e73c12 expand_divmod(int, tree_code, machine_mode, rtx_def*, rtx_def*, rtx_def*, int)../../../gcc/gcc/expmed.c:43350x7f0da2ea1423 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode, expand_modifier)../../../gcc/gcc/expr.c:92400x7f0da2cd1a1e expand_gimple_stmt_1../../../gcc/gcc/cfgexpand.c:37960x7f0da2cd1c30 expand_gimple_stmt../../../gcc/gcc/cfgexpand.c:38570x7f0da2cd90a9 expand_gimple_basic_block../../../gcc/gcc/cfgexpand.c:58980x7f0da2cdade8 execute../../../gcc/gcc/cfgexpand.c:6582

To see the code which causes this error, call the following function:

gcc_jit_context_dump_to_file(ctxt,"/tmp/output.c",1/* update_locations */)

This will create a C-like file and add the locations into the IR pointing to this C file.Then, rerun the program and it will output the location in the second line:

libgccjit.so: /tmp/something.c:61322:0: error: in expmed_mode_index, at expmed.h:249

Or add a breakpoint toadd_error in gdb and print the line number using:

p loc->m_linep loc->m_filename->m_buffer

To print a debug representation of a tree:

debug_tree(expr);

(defined in print-tree.h)

To print a debug reprensentation of a gimple struct:

debug_gimple_stmt(gimple_struct)

To get therustc command to run ingdb, add the--verbose flag tocargo build.

To have the correct file paths ingdb instead of/usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_personality.cc:

Maybe by calling the following at the beginning of gdb:

set substitute-path /usr/src/debug/gcc /path/to/gcc-repo/gcc

TODO(antoyo): but that's not what I remember I was doing.

• Build the stage2 compiler (rustup toolchain link debug-current build/x86_64-unknown-linux-gnu/stage2).
• Clean and rebuild the codegen withdebug-current in the filerust-toolchain.

Using git-subtree withrustc requires a patched git to make it work.The PR that is needed ishere.Use the following instructions to install it:

git clone git@github.com:tqc/git.gitcd gitgit checkout tqc/subtreemakemake installcd contrib/subtreemakecp git-subtree ~/bin

rustc needs to be built withoutjemalloc so thatmem-trace can overloadmalloc sincejemalloc is linked statically, so aLD_PRELOAD-ed library won't a chance to intercept the calls tomalloc.

• Follow these instructions:https://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/ with the following changes:
• Configure gcc with../gcc/configure --enable-host-shared --disable-multilib --enable-languages=c,jit,c++ --disable-bootstrap --enable-checking=release --prefix=/opt/m68k-gcc/ --target=m68k-linux --without-headers.
• Some shells, like fish, don't define the environment variable$MACHTYPE.
• AddCFLAGS="-Wno-error=attributes -g -O2" at the end of the configure command for building glibc (CFLAGS="-Wno-error=attributes -Wno-error=array-parameter -Wno-error=stringop-overflow -Wno-error=array-bounds -g -O2" for glibc 2.31, which is useful for Debian).

• SetTARGET_TRIPLE="m68k-unknown-linux-gnu" in config.sh.
• Since rustc doesn't support this architecture yet, set it back toTARGET_TRIPLE="mips-unknown-linux-gnu" (or another target having the same attributes). Alternatively, create atarget specification file (note that thearch specified in this file must be supported by the rust compiler).
• Setlinker='-Clinker=m68k-linux-gcc'.
• Set the path to the cross-compiling libgccjit ingcc_path.
• Comment the line:context.add_command_line_option("-masm=intel"); in src/base.rs.
• (might not be necessary) Disable the compilation of libstd.so (and possibly libcore.so?).