llvm-cbe

This LLVM C backend has been resurrected by Julia Computing with various improvements.

Installation instructions

This version of the LLVM C backend works with LLVM 16, for older versions please check the tags.

Step 1: Installing LLVM

Either install the LLVM packages on your system:

On macOS, use pkgsrc and run the following commands:

    ~$ pkgin in llvm clang

On CentOS, install the llvm-devel package:

    ~# dnf install llvm-devel clang

On Debian and derivatives, install the llvm-dev package via:

    ~# apt install llvm-dev clang

Or compile LLVM yourself:

Note: to convert C to LLVM IR to run the tests, you will also need a C compiler using the LLVM infrastructure, such as clang.

The first step is to compile LLVM on your machine (this assumes an in-tree build, but out-of-tree will also work):

     ~$ git clone https://github.com/llvm/llvm-project.git
     ~$ cd llvm-project
     llvm-project$ git checkout release/8.x
     llvm-project$ mkdir llvm/build
     llvm-project$ cd llvm/build
     build$ cmake ..
     build$ make

To run tests, you need to build lli.

Step 2: Compiling LLVM-CBE

Now you can download and compile llvm-cbe.

If you built LLVM yourself, put it in the same folder you built LLVM in:

    ~$ cd llvm-project/llvm/projects
    projects$ git clone https://github.com/JuliaComputing/llvm-cbe
    projects$ cd ../build
    build$ cmake -S ..
    build$ make llvm-cbe

If you used your distribution's package, put it wherever you feel like:

    ~$ git clone https://github.com/JuliaComputing/llvm-cbe
    ~$ cd llvm-cbe && mkdir build && cd build
    build$ cmake -S ..
    build$ make llvm-cbe

Step 3: Usage Examples

If llvm-cbe compiles, you should be able to run it with the following commands.

    llvm-cbe$ cd test/selectionsort
    selectionsort$ ls
    main.c
    selectionsort$ clang -S -emit-llvm -g main.c
    selectionsort$ ls
    main.c main.ll
    selectionsort$ ../../build/tools/llvm-cbe/llvm-cbe main.ll

You can find options to configure the C backend's output with llvm-cbe --help. Look for options beginning with --cbe-.

Compile Generated C Code and Run

    selectionsort$ gcc -o main.cbe main.cbe.c
    selectionsort$ ls
    main.c  main.cbe  main.cbe.c  main.ll
    selectionsort$ ./main.cbe

Running tests

Unit tests:

    llvm-project$ cd llvm/build
    build$ make CBEUnitTests && projects/llvm-cbe/unittests/CWriterTest

Note that you need to have passed -DLLVM_INCLUDE_TESTS=1 to cmake if you used your distribution's LLVM package. You also will need to install gtest (on Debian derivatives: apt install libgtest-dev).

Other tests:

First, compile llvm-cbe, and install pytest (e.g. pip install pytest). Then:

    llvm-cbe$ pytest

You might have to adjust the llvm-cbe and lli paths in that configuration.

If you want the tests to run faster, installing pytest-xdist will allow you to run the test suite in parallel, e.g. pytest -n 4 if you want to use 4 cores.