1==================================================================
2Getting Started with the LLVM System using Microsoft Visual Studio
3==================================================================
4
5
6.. contents::
7   :local:
8
9
10Overview
11========
12Welcome to LLVM on Windows! This document only covers LLVM on Windows using
13Visual Studio, not WSL, mingw or cygwin. In order to get started, you first need
14to know some basic information.
15
16There are many different projects that compose LLVM. The first piece is the
17LLVM suite. This contains all of the tools, libraries, and header files needed
18to use LLVM. It contains an assembler, disassembler, bitcode analyzer and
19bitcode optimizer. It also contains basic regression tests that can be used to
20test the LLVM tools and the Clang front end.
21
22The second piece is the `Clang <https://clang.llvm.org/>`_ front end.  This
23component compiles C, C++, Objective C, and Objective C++ code into LLVM
24bitcode. Clang typically uses LLVM libraries to optimize the bitcode and emit
25machine code. LLVM fully supports the COFF object file format, which is
26compatible with all other existing Windows toolchains.
27
28There are more LLVM projects which this document does not discuss.
29
30
31Requirements
32============
33Before you begin to use the LLVM system, review the requirements given
34below.  This may save you some trouble by knowing ahead of time what hardware
35and software you will need.
36
37Hardware
38--------
39Any system that can adequately run Visual Studio 2017 is fine. The LLVM
40source tree including the git index consumes approximately 3GB.
41Object files, libraries and executables consume approximately 5GB in
42Release mode and much more in Debug mode. SSD drive and >16GB RAM are
43recommended.
44
45
46Software
47--------
48You will need `Visual Studio <https://visualstudio.microsoft.com/>`_ 2017 or
49higher, with the latest Update installed. Visual Studio Community Edition
50suffices.
51
52You will also need the `CMake <http://www.cmake.org/>`_ build system since it
53generates the project files you will use to build with. CMake is bundled with
54Visual Studio 2019 so separate installation is not required.
55
56If you would like to run the LLVM tests you will need `Python
57<http://www.python.org/>`_. Version 3.6 and newer are known to work. You can
58install Python with Visual Studio 2019, from the Microsoft store or from
59the `Python web site <http://www.python.org/>`_. We recommend the latter since it
60allows you to to adjust installation options.
61
62You will need `Git for Windows <https://git-scm.com/>`_ with bash tools, too.
63Git for Windows is also bundled with Visual Studio 2019.
64
65
66Getting Started
67===============
68Here's the short story for getting up and running quickly with LLVM.
69These instruction were tested with Visual Studio 2019 and Python 3.9.6:
70
711. Download and install `Visual Studio <https://visualstudio.microsoft.com/>`_.
722. In the Visual Studio installer, Workloads tab, select the
73   **Desktop development with C++** workload. Under Individual components tab,
74   select **Git for Windows**.
753. Complete the Visual Studio installation.
764. Download and install the latest `Python 3 release <http://www.python.org/>`_.
775. In the first install screen, select both **Install launcher for all users**
78   and **Add Python to the PATH**. This will allow installing psutil for all
79   users for the regression tests and make Python available from the command
80   line.
816. In the second install screen, select (again) **Install for all users** and
82   if you want to develop `lldb <https://lldb.llvm.org/>`_, selecting
83   **Download debug binaries** is useful.
847. Complete the Python installation.
858. Run a "Developer Command Prompt for VS 2019" **as administrator**. This command
86    prompt provides correct path and environment variables to Visual Studio and
87    the installed tools.
889. In the terminal window, type the commands:
89
90   .. code-block:: bat
91
92     c:
93     cd \
94
95  You may install the llvm sources in other location than ``c:\llvm`` but do not
96  install into a path containing spaces (e.g. ``c:\Documents and Settings\...``)
97  as it will fail.
98
9910. Register the Microsoft Debug Interface Access (DIA) DLLs
100
101    .. code-block:: bat
102
103     regsvr32 "%VSINSTALLDIR%\DIA SDK\bin\msdia140.dll"
104     regsvr32 "%VSINSTALLDIR%\DIA SDK\bin\amd64\msdia140.dll"
105
106 The DIA library is required for LLVM PDB tests and
107 `LLDB development <https://lldb.llvm.org/resources/build.html>`_.
108
10911. Install psutil and obtain LLVM source code:
110
111    .. code-block:: bat
112
113     pip install psutil
114     git clone https://github.com/llvm/llvm-project.git llvm
115
116 Instead of ``git clone`` you may download a compressed source distribution
117 from the `releases page <https://github.com/llvm/llvm-project/releases>`_.
118 Select the last link: ``Source code (zip)`` and unpack the downloaded file using
119 Windows Explorer built-in zip support or any other unzip tool.
120
12112. Finally, configure LLVM using CMake:
122
123    .. code-block:: bat
124
125       cmake -S llvm\llvm -B build -DLLVM_ENABLE_PROJECTS=clang -DLLVM_TARGETS_TO_BUILD=X86 -Thost=x64
126       exit
127
128   ``LLVM_ENABLE_PROJECTS`` specifies any additional LLVM projects you want to
129   build while ``LLVM_TARGETS_TO_BUILD`` selects the compiler targets. If
130   ``LLVM_TARGETS_TO_BUILD`` is omitted by default all targets are built
131   slowing compilation and using more disk space.
132   See the :doc:`LLVM CMake guide <CMake>` for detailed information about
133   how to configure the LLVM build.
134
135   The ``cmake`` command line tool is bundled with Visual Studio but its GUI is
136   not. You may install `CMake <http://www.cmake.org/>`_ to use its GUI to change
137   CMake variables or modify the above command line.
138
139   * Once CMake is installed then the simplest way is to just start the
140     CMake GUI, select the directory where you have LLVM extracted to, and
141     the default options should all be fine.  One option you may really
142     want to change, regardless of anything else, might be the
143     ``CMAKE_INSTALL_PREFIX`` setting to select a directory to INSTALL to
144     once compiling is complete, although installation is not mandatory for
145     using LLVM.  Another important option is ``LLVM_TARGETS_TO_BUILD``,
146     which controls the LLVM target architectures that are included on the
147     build.
148   * CMake generates project files for all build types. To select a specific
149     build type, use the Configuration manager from the VS IDE or the
150     ``/property:Configuration`` command line option when using MSBuild.
151   * By default, the Visual Studio project files generated by CMake use the
152     32-bit toolset. If you are developing on a 64-bit version of Windows and
153     want to use the 64-bit toolset, pass the ``-Thost=x64`` flag when
154     generating the Visual Studio solution. This requires CMake 3.8.0 or later.
155
15613. Start Visual Studio and select configuration:
157
158   In the directory you created the project files will have an ``llvm.sln``
159   file, just double-click on that to open Visual Studio. The default Visual
160   Studio configuration is **Debug** which is slow and generates a huge amount
161   of debug information on disk. For now, we recommend selecting **Release**
162   configuration for the LLVM project which will build the fastest or
163   **RelWithDebInfo** which is also several time larger than Release.
164   Another technique is to build all of LLVM in Release mode and change
165   compiler flags, disabling optimization and enabling debug information, only
166   for specific librares or source files you actually need to debug.
167
16814. Test LLVM in Visual Studio:
169
170   You can run LLVM tests by merely building the project "check-all". The test
171   results will be shown in the VS output window. Once the build succeeds, you
172   have verified a working LLVM development environment!
173
174   You should not see any unexpected failures, but will see many unsupported
175   tests and expected failures:
176
177   ::
178
179    114>Testing Time: 1124.66s
180    114>  Skipped          :    39
181    114>  Unsupported      : 21649
182    114>  Passed           : 51615
183    114>  Expectedly Failed:    93
184    ========== Build: 114 succeeded, 0 failed, 321 up-to-date, 0 skipped ==========``
185
186Alternatives to manual installation
187===================================
188Instead of the steps above, to simplify the installation procedure you can use
189`Chocolatey <https://chocolatey.org/>`_ as package manager.
190After the `installation <https://chocolatey.org/install>`_ of Chocolatey,
191run these commands in an admin shell to install the required tools:
192
193.. code-block:: bat
194
195   choco install -y git cmake python3
196   pip3 install psutil
197
198There is also a Windows
199`Dockerfile <https://github.com/llvm/llvm-zorg/blob/main/buildbot/google/docker/windows-base-vscode2019/Dockerfile>`_
200with the entire build tool chain. This can be used to test the build with a
201tool chain different from your host installation or to create build servers.
202
203Next steps
204==========
2051. Read the documentation.
2062. Seriously, read the documentation.
2073. Remember that you were warned twice about reading the documentation.
208
209Test LLVM on the command line:
210------------------------------
211The LLVM tests can be run by changing directory to the llvm source
212directory and running:
213
214.. code-block:: bat
215
216  c:\llvm> python ..\build\Release\bin\llvm-lit.py llvm\test
217
218This example assumes that Python is in your PATH variable, which would be
219after **Add Python to the PATH** was selected during Python installation.
220If you had opened a command window prior to Python installation, you would
221have to close and reopen it to get the updated PATH.
222
223A specific test or test directory can be run with:
224
225.. code-block:: bat
226
227  c:\llvm> python ..\build\Release\bin\llvm-lit.py llvm\test\Transforms\Util
228
229Build the LLVM Suite:
230---------------------
231* The projects may still be built individually, but to build them all do
232  not just select all of them in batch build (as some are meant as
233  configuration projects), but rather select and build just the
234  ``ALL_BUILD`` project to build everything, or the ``INSTALL`` project,
235  which first builds the ``ALL_BUILD`` project, then installs the LLVM
236  headers, libs, and other useful things to the directory set by the
237  ``CMAKE_INSTALL_PREFIX`` setting when you first configured CMake.
238* The Fibonacci project is a sample program that uses the JIT. Modify the
239  project's debugging properties to provide a numeric command line argument
240  or run it from the command line.  The program will print the
241  corresponding fibonacci value.
242
243
244Links
245=====
246This document is just an **introduction** to how to use LLVM to do some simple
247things... there are many more interesting and complicated things that you can
248do that aren't documented here (but we'll gladly accept a patch if you want to
249write something up!).  For more information about LLVM, check out:
250
251* `LLVM homepage <https://llvm.org/>`_
252* `LLVM doxygen tree <https://llvm.org/doxygen/>`_
253* Additional information about the LLVM directory structure and tool chain
254  can be found on the main :doc:`GettingStarted` page.
255* If you are having problems building or using LLVM, or if you have any other
256  general questions about LLVM, please consult the
257  :doc:`Frequently Asked Questions <FAQ>` page.
258