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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 in this 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 my fork of gcc which already includes these patches.
Put the path to your custom build of libgccjit in the file
gcc_path
.
$ git clone https://github.com/rust-lang/rustc_codegen_gcc.git
$ cd rustc_codegen_gcc
$ git clone https://github.com/llvm/llvm-project llvm --depth 1 --single-branch
$ export RUST_COMPILER_RT_ROOT="$PWD/llvm/compiler-rt"
$ ./prepare_build.sh # download and patch sysroot src
$ ./build.sh --release
To run the tests:
$ ./prepare.sh # download and patch sysroot src and install hyperfine for benchmarking
$ ./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 use
CHANNEL="debug"
instead or omit
CHANNEL="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 $cg_gccjit_dir/build_sysroot/sysroot my_crate.rs
Sometimes, libgccjit will crash and output an error like this:
during RTL pass: expand
libgccjit.so: error: in expmed_mode_index, at expmed.h:249
0x7f0da2e61a35 expmed_mode_index
../../../gcc/gcc/expmed.h:249
0x7f0da2e61aa4 expmed_op_cost_ptr
../../../gcc/gcc/expmed.h:271
0x7f0da2e620dc sdiv_cost_ptr
../../../gcc/gcc/expmed.h:540
0x7f0da2e62129 sdiv_cost
../../../gcc/gcc/expmed.h:558
0x7f0da2e73c12 expand_divmod(int, tree_code, machine_mode, rtx_def*, rtx_def*, rtx_def*, int)
../../../gcc/gcc/expmed.c:4335
0x7f0da2ea1423 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode, expand_modifier)
../../../gcc/gcc/expr.c:9240
0x7f0da2cd1a1e expand_gimple_stmt_1
../../../gcc/gcc/cfgexpand.c:3796
0x7f0da2cd1c30 expand_gimple_stmt
../../../gcc/gcc/cfgexpand.c:3857
0x7f0da2cd90a9 expand_gimple_basic_block
../../../gcc/gcc/cfgexpand.c:5898
0x7f0da2cdade8 execute
../../../gcc/gcc/cfgexpand.c:6582
To see the code which causes this error, call the following function:
(ctxt, "/tmp/output.c", 1 /* update_locations */) gcc_jit_context_dump_to_file
This will create a C-like file and add the locations into the IR pointing to this C file. Then, rerun the program and it will output the location in the second line:
libgccjit.so: /tmp/something.c:61322:0: error: in expmed_mode_index, at expmed.h:249
Or add a breakpoint to add_error
in gdb and print the
line number using:
p loc->m_line
p loc->m_filename->m_buffer
To print a debug representation of a tree:
(expr); debug_tree
To get the rustc
command to run in gdb
, add
the --verbose
flag to cargo build
.
rustup toolchain link debug-current build/x86_64-unknown-linux-gnu/stage2
).debug-current
in the
file rust-toolchain
.../gcc/configure --enable-host-shared --disable-multilib --enable-languages=c,jit,c++ --disable-bootstrap --enable-checking=release --prefix=/opt/m68k-gcc/ --target=m68k-linux --without-headers
.$MACHTYPE
.CFLAGS="-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).TARGET_TRIPLE="m68k-unknown-linux-gnu"
in
config.sh.TARGET_TRIPLE="mips-unknown-linux-gnu"
(or another target
having the same attributes). Alternatively, create a target
specification file (note that the arch
specified in
this file must be supported by the rust compiler).linker='-Clinker=m68k-linux-gcc'
.gcc_path
.let i128_type = context.new_type::<i64>();
in context.rs
(same for u128_type).context.add_command_line_option("-masm=intel");
in
src/base.rs.