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diff --git a/README.md b/README.md index de0891a7044a..c8013e0426bd 100644 --- a/README.md +++ b/README.md @@ -3,3 +3,102 @@ This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. + +## Getting Started with the LLVM System + +Taken from 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 converts it 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/) front end. 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 + +### Getting the Source Code and Building LLVM + +The LLVM Getting Started documentation may be out of date.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 workflow and configuration to get and build the LLVM source: + +1. Checkout LLVM (including related subprojects 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`` + + * ``mkdir build`` + + * ``cd build`` + + * ``cmake -G <generator> [options] ../llvm`` + + Some common 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='...'`` --- semicolon-separated list of the LLVM + subprojects you'd like to additionally build. Can include any of: clang, + clang-tools-extra, libcxx, libcxxabi, libunwind, lldb, compiler-rt, lld, + polly, or debuginfo-tests. + + For example, to build LLVM, Clang, libcxx, and libcxxabi, use + ``-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"``. + + * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full + pathname of where you want the LLVM tools and libraries to be installed + (default ``/usr/local``). + + * ``-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). + + * Run your build tool of choice! + + * 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 build 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 + ``make -j NNN`` (NNN is the number of parallel jobs, use e.g. number of + CPUs you have.) + + * 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. |