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1 # The LLVM Compiler Infrastructure
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2
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3 This directory and its sub-directories contain the source code for LLVM,
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4 a toolkit for the construction of highly optimized compilers,
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5 optimizers, and run-time environments.
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6
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7 The README briefly describes how to get started with building LLVM.
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8 For more information on how to contribute to the LLVM project, please
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9 take a look at the
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10 [Contributing to LLVM](https://llvm.org/docs/Contributing.html) guide.
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11
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12 ## Getting Started with the LLVM System
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13
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14 Taken from [here](https://llvm.org/docs/GettingStarted.html).
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15
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16 ### Overview
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17
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18 Welcome to the LLVM project!
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19
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20 The LLVM project has multiple components. The core of the project is
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21 itself called "LLVM". This contains all of the tools, libraries, and header
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22 files needed to process intermediate representations and convert them into
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23 object files. Tools include an assembler, disassembler, bitcode analyzer, and
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24 bitcode optimizer. It also contains basic regression tests.
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25
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26 C-like languages use the [Clang](http://clang.llvm.org/) frontend. This
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27 component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode
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28 -- and from there into object files, using LLVM.
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29
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30 Other components include:
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31 the [libc++ C++ standard library](https://libcxx.llvm.org),
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32 the [LLD linker](https://lld.llvm.org), and more.
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33
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34 ### Getting the Source Code and Building LLVM
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35
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36 The LLVM Getting Started documentation may be out of date. The [Clang
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37 Getting Started](http://clang.llvm.org/get_started.html) page might have more
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38 accurate information.
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39
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40 This is an example work-flow and configuration to get and build the LLVM source:
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41
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42 1. Checkout LLVM (including related sub-projects like Clang):
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43
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44 * ``git clone https://github.com/llvm/llvm-project.git``
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45
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46 * Or, on windows, ``git clone --config core.autocrlf=false
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47 https://github.com/llvm/llvm-project.git``
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48
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49 2. Configure and build LLVM and Clang:
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50
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51 * ``cd llvm-project``
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52
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53 * ``cmake -S llvm -B build -G <generator> [options]``
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54
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55 Some common build system generators are:
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56
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57 * ``Ninja`` --- for generating [Ninja](https://ninja-build.org)
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58 build files. Most llvm developers use Ninja.
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59 * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
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60 * ``Visual Studio`` --- for generating Visual Studio projects and
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61 solutions.
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62 * ``Xcode`` --- for generating Xcode projects.
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63
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64 Some common options:
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65
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66 * ``-DLLVM_ENABLE_PROJECTS='...'`` and ``-DLLVM_ENABLE_RUNTIMES='...'`` ---
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67 semicolon-separated list of the LLVM sub-projects and runtimes you'd like to
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68 additionally build. ``LLVM_ENABLE_PROJECTS`` can include any of: clang,
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69 clang-tools-extra, cross-project-tests, flang, libc, libclc, lld, lldb,
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70 mlir, openmp, polly, or pstl. ``LLVM_ENABLE_RUNTIMES`` can include any of
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71 libcxx, libcxxabi, libunwind, compiler-rt, libc or openmp. Some runtime
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72 projects can be specified either in ``LLVM_ENABLE_PROJECTS`` or in
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73 ``LLVM_ENABLE_RUNTIMES``.
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74
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75 For example, to build LLVM, Clang, libcxx, and libcxxabi, use
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76 ``-DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"``.
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77
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78 * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
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79 path name of where you want the LLVM tools and libraries to be installed
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80 (default ``/usr/local``). Be careful if you install runtime libraries: if
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81 your system uses those provided by LLVM (like libc++ or libc++abi), you
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82 must not overwrite your system's copy of those libraries, since that
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83 could render your system unusable. In general, using something like
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84 ``/usr`` is not advised, but ``/usr/local`` is fine.
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85
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86 * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
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87 Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
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88
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89 * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
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90 (default is Yes for Debug builds, No for all other build types).
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91
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92 * ``cmake --build build [-- [options] <target>]`` or your build system specified above
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93 directly.
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94
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95 * The default target (i.e. ``ninja`` or ``make``) will build all of LLVM.
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96
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97 * The ``check-all`` target (i.e. ``ninja check-all``) will run the
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98 regression tests to ensure everything is in working order.
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99
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100 * CMake will generate targets for each tool and library, and most
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101 LLVM sub-projects generate their own ``check-<project>`` target.
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102
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103 * Running a serial build will be **slow**. To improve speed, try running a
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104 parallel build. That's done by default in Ninja; for ``make``, use the option
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105 ``-j NNN``, where ``NNN`` is the number of parallel jobs to run.
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106 In most cases, you get the best performance if you specify the number of CPU threads you have.
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107 On some Unix systems, you can specify this with ``-j$(nproc)``.
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108
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109 * For more information see [CMake](https://llvm.org/docs/CMake.html).
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110
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111 Consult the
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112 [Getting Started with LLVM](https://llvm.org/docs/GettingStarted.html#getting-started-with-llvm)
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113 page for detailed information on configuring and compiling LLVM. You can visit
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114 [Directory Layout](https://llvm.org/docs/GettingStarted.html#directory-layout)
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115 to learn about the layout of the source code tree.
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117 ## Getting in touch
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119 Join [LLVM Discourse forums](https://discourse.llvm.org/), [discord chat](https://discord.gg/xS7Z362) or #llvm IRC channel on [OFTC](https://oftc.net/).
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121 The LLVM project has adopted a [code of conduct](https://llvm.org/docs/CodeOfConduct.html) for
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122 participants to all modes of communication within the project.
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