| # The LLVM Compiler Infrastructure |
| |
| This directory and its sub-directories contain the source code for LLVM, |
| a toolkit for the construction of highly optimized compilers, |
| optimizers, and run-time environments. |
| |
| The README briefly describes how to get started with building LLVM. |
| For more information on how to contribute to the LLVM project, please |
| take a look at the |
| [Contributing to LLVM](https://llvm.org/docs/Contributing.html) guide. |
| |
| ## Getting Started with the LLVM System |
| |
| Taken from [here](https://llvm.org/docs/GettingStarted.html). |
| |
| ### Overview |
| |
| Welcome to the LLVM project! |
| |
| The LLVM project has multiple components. The core of the project is |
| itself called "LLVM". This contains all of the tools, libraries, and header |
| files needed to process intermediate representations and convert them into |
| object files. Tools include an assembler, disassembler, bitcode analyzer, and |
| bitcode optimizer. It also contains basic regression tests. |
| |
| C-like languages use the [Clang](http://clang.llvm.org/) frontend. This |
| component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode |
| -- and from there into object files, using LLVM. |
| |
| Other components include: |
| the [libc++ C++ standard library](https://libcxx.llvm.org), |
| the [LLD linker](https://lld.llvm.org), and more. |
| |
| ### Getting the Source Code and Building LLVM |
| |
| The LLVM Getting Started documentation may be out of date. The [Clang |
| Getting Started](http://clang.llvm.org/get_started.html) page might have more |
| accurate information. |
| |
| This is an example work-flow and configuration to get and build the LLVM source: |
| |
| 1. Checkout LLVM (including related sub-projects like Clang): |
| |
| * ``git clone https://github.com/llvm/llvm-project.git`` |
| |
| * Or, on windows, ``git clone --config core.autocrlf=false |
| https://github.com/llvm/llvm-project.git`` |
| |
| 2. Configure and build LLVM and Clang: |
| |
| * ``cd llvm-project`` |
| |
| * ``cmake -S llvm -B build -G <generator> [options]`` |
| |
| Some common build system generators are: |
| |
| * ``Ninja`` --- for generating [Ninja](https://ninja-build.org) |
| build files. Most llvm developers use Ninja. |
| * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles. |
| * ``Visual Studio`` --- for generating Visual Studio projects and |
| solutions. |
| * ``Xcode`` --- for generating Xcode projects. |
| |
| Some common options: |
| |
| * ``-DLLVM_ENABLE_PROJECTS='...'`` and ``-DLLVM_ENABLE_RUNTIMES='...'`` --- |
| semicolon-separated list of the LLVM sub-projects and runtimes you'd like to |
| additionally build. ``LLVM_ENABLE_PROJECTS`` can include any of: clang, |
| clang-tools-extra, cross-project-tests, flang, libc, libclc, lld, lldb, |
| mlir, openmp, polly, or pstl. ``LLVM_ENABLE_RUNTIMES`` can include any of |
| libcxx, libcxxabi, libunwind, compiler-rt, libc or openmp. Some runtime |
| projects can be specified either in ``LLVM_ENABLE_PROJECTS`` or in |
| ``LLVM_ENABLE_RUNTIMES``. |
| |
| For example, to build LLVM, Clang, libcxx, and libcxxabi, use |
| ``-DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"``. |
| |
| * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full |
| path name of where you want the LLVM tools and libraries to be installed |
| (default ``/usr/local``). Be careful if you install runtime libraries: if |
| your system uses those provided by LLVM (like libc++ or libc++abi), you |
| must not overwrite your system's copy of those libraries, since that |
| could render your system unusable. In general, using something like |
| ``/usr`` is not advised, but ``/usr/local`` is fine. |
| |
| * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug, |
| Release, RelWithDebInfo, and MinSizeRel. Default is Debug. |
| |
| * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled |
| (default is Yes for Debug builds, No for all other build types). |
| |
| * ``cmake --build build [-- [options] <target>]`` or your build system specified above |
| directly. |
| |
| * The default target (i.e. ``ninja`` or ``make``) will build all of LLVM. |
| |
| * The ``check-all`` target (i.e. ``ninja check-all``) will run the |
| regression tests to ensure everything is in working order. |
| |
| * CMake will generate targets for each tool and library, and most |
| LLVM sub-projects generate their own ``check-<project>`` target. |
| |
| * Running a serial build will be **slow**. To improve speed, try running a |
| parallel build. That's done by default in Ninja; for ``make``, use the option |
| ``-j NNN``, where ``NNN`` is the number of parallel jobs to run. |
| In most cases, you get the best performance if you specify the number of CPU threads you have. |
| On some Unix systems, you can specify this with ``-j$(nproc)``. |
| |
| * For more information see [CMake](https://llvm.org/docs/CMake.html). |
| |
| Consult the |
| [Getting Started with LLVM](https://llvm.org/docs/GettingStarted.html#getting-started-with-llvm) |
| page for detailed information on configuring and compiling LLVM. You can visit |
| [Directory Layout](https://llvm.org/docs/GettingStarted.html#directory-layout) |
| to learn about the layout of the source code tree. |
| |
| ## Getting in touch |
| |
| Join [LLVM Discourse forums](https://discourse.llvm.org/), [discord chat](https://discord.gg/xS7Z362) or #llvm IRC channel on [OFTC](https://oftc.net/). |
| |
| The LLVM project has adopted a [code of conduct](https://llvm.org/docs/CodeOfConduct.html) for |
| participants to all modes of communication within the project. |