1==================================================================
2Getting Started with the LLVM System using Microsoft Visual Studio
3==================================================================
4
5.. contents::
6   :local:
7
8
9Overview
10========
11Welcome to LLVM on Windows! This document only covers LLVM on Windows using
12Visual Studio, not mingw or cygwin. In order to get started, you first need to
13know some basic information.
14
15There are many different projects that compose LLVM. The first piece is the
16LLVM suite. This contains all of the tools, libraries, and header files needed
17to use LLVM. It contains an assembler, disassembler, bitcode analyzer and
18bitcode optimizer. It also contains basic regression tests that can be used to
19test the LLVM tools and the Clang front end.
20
21The second piece is the `Clang <https://clang.llvm.org/>`_ front end.  This
22component compiles C, C++, Objective C, and Objective C++ code into LLVM
23bitcode. Clang typically uses LLVM libraries to optimize the bitcode and emit
24machine code. LLVM fully supports the COFF object file format, which is
25compatible with all other existing Windows toolchains.
26
27The last major part of LLVM, the execution Test Suite, does not run on Windows,
28and this document does not discuss it.
29
30Additional information about the LLVM directory structure and tool chain
31can be found on the main :doc:`GettingStarted` page.
32
33
34Requirements
35============
36Before you begin to use the LLVM system, review the requirements given
37below.  This may save you some trouble by knowing ahead of time what hardware
38and software you will need.
39
40Hardware
41--------
42Any system that can adequately run Visual Studio 2017 is fine. The LLVM
43source tree and object files, libraries and executables will consume
44approximately 3GB.
45
46Software
47--------
48You will need Visual Studio 2017 or higher, with the latest Update installed.
49
50You will also need the `CMake <http://www.cmake.org/>`_ build system since it
51generates the project files you will use to build with.
52
53If you would like to run the LLVM tests you will need `Python
54<http://www.python.org/>`_. Version 2.7 and newer are known to work. You will
55need `GnuWin32 <http://gnuwin32.sourceforge.net/>`_ tools, too.
56
57Do not install the LLVM directory tree into a path containing spaces (e.g.
58``C:\Documents and Settings\...``) as the configure step will fail.
59
60
61Getting Started
62===============
63Here's the short story for getting up and running quickly with LLVM:
64
651. Read the documentation.
662. Seriously, read the documentation.
673. Remember that you were warned twice about reading the documentation.
684. Get the Source Code
69
70   * With the distributed files:
71
72      1. ``cd <where-you-want-llvm-to-live>``
73      2. ``gunzip --stdout llvm-VERSION.tar.gz | tar -xvf -``
74         (*or use WinZip*)
75      3. ``cd llvm``
76
77   * With git access:
78
79     *Note:* some regression tests require Unix-style line ending (``\n``).
80
81      1. ``cd <where-you-want-llvm-to-live>``
82      2. ``git clone https://github.com/llvm/llvm-project.git llvm``
83      3. ``cd llvm``
84
855. Use `CMake <http://www.cmake.org/>`_ to generate up-to-date project files:
86
87   * Once CMake is installed then the simplest way is to just start the
88     CMake GUI, select the directory where you have LLVM extracted to, and
89     the default options should all be fine.  One option you may really
90     want to change, regardless of anything else, might be the
91     ``CMAKE_INSTALL_PREFIX`` setting to select a directory to INSTALL to
92     once compiling is complete, although installation is not mandatory for
93     using LLVM.  Another important option is ``LLVM_TARGETS_TO_BUILD``,
94     which controls the LLVM target architectures that are included on the
95     build.
96   * If CMake complains that it cannot find the compiler, make sure that
97     you have the Visual Studio C++ Tools installed, not just Visual Studio
98     itself (trying to create a C++ project in Visual Studio will generally
99     download the C++ tools if they haven't already been).
100   * See the :doc:`LLVM CMake guide <CMake>` for detailed information about
101     how to configure the LLVM build.
102   * CMake generates project files for all build types. To select a specific
103     build type, use the Configuration manager from the VS IDE or the
104     ``/property:Configuration`` command line option when using MSBuild.
105   * By default, the Visual Studio project files generated by CMake use the
106     32-bit toolset. If you are developing on a 64-bit version of Windows and
107     want to use the 64-bit toolset, pass the ``-Thost=x64`` flag when
108     generating the Visual Studio solution. This requires CMake 3.8.0 or later.
109
1106. Start Visual Studio
111
112   * In the directory you created the project files will have an ``llvm.sln``
113     file, just double-click on that to open Visual Studio.
114
1157. Build the LLVM Suite:
116
117   * The projects may still be built individually, but to build them all do
118     not just select all of them in batch build (as some are meant as
119     configuration projects), but rather select and build just the
120     ``ALL_BUILD`` project to build everything, or the ``INSTALL`` project,
121     which first builds the ``ALL_BUILD`` project, then installs the LLVM
122     headers, libs, and other useful things to the directory set by the
123     ``CMAKE_INSTALL_PREFIX`` setting when you first configured CMake.
124   * The Fibonacci project is a sample program that uses the JIT. Modify the
125     project's debugging properties to provide a numeric command line argument
126     or run it from the command line.  The program will print the
127     corresponding fibonacci value.
128
1298. Test LLVM in Visual Studio:
130
131   * If ``%PATH%`` does not contain GnuWin32, you may specify
132     ``LLVM_LIT_TOOLS_DIR`` on CMake for the path to GnuWin32.
133   * You can run LLVM tests by merely building the project "check". The test
134     results will be shown in the VS output window.
135
1369. Test LLVM on the command line:
137
138   * The LLVM tests can be run by changing directory to the llvm source
139     directory and running:
140
141     .. code-block:: bat
142
143        C:\..\llvm> python ..\build\bin\llvm-lit --param build_config=Win32 --param build_mode=Debug --param llvm_site_config=../build/test/lit.site.cfg test
144
145     This example assumes that Python is in your PATH variable, you
146     have built a Win32 Debug version of llvm with a standard out of
147     line build. You should not see any unexpected failures, but will
148     see many unsupported tests and expected failures.
149
150     A specific test or test directory can be run with:
151
152     .. code-block:: bat
153
154        C:\..\llvm> python ..\build\bin\llvm-lit --param build_config=Win32 --param build_mode=Debug --param llvm_site_config=../build/test/lit.site.cfg test/path/to/test
155
156
157An Example Using the LLVM Tool Chain
158====================================
159
1601. First, create a simple C file, name it '``hello.c``':
161
162   .. code-block:: c
163
164      #include <stdio.h>
165      int main() {
166        printf("hello world\n");
167        return 0;
168      }
169
1702. Next, compile the C file into an LLVM bitcode file:
171
172   .. code-block:: bat
173
174      C:\..> clang -c hello.c -emit-llvm -o hello.bc
175
176   This will create the result file ``hello.bc`` which is the LLVM bitcode
177   that corresponds the compiled program and the library facilities that
178   it required.  You can execute this file directly using ``lli`` tool,
179   compile it to native assembly with the ``llc``, optimize or analyze it
180   further with the ``opt`` tool, etc.
181
182   Alternatively you can directly output an executable with clang with:
183
184   .. code-block:: bat
185
186      C:\..> clang hello.c -o hello.exe
187
188   The ``-o hello.exe`` is required because clang currently outputs ``a.out``
189   when neither ``-o`` nor ``-c`` are given.
190
1913. Run the program using the just-in-time compiler:
192
193   .. code-block:: bat
194
195      C:\..> lli hello.bc
196
1974. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
198
199   .. code-block:: bat
200
201      C:\..> llvm-dis < hello.bc | more
202
2035. Compile the program to object code using the LLC code generator:
204
205   .. code-block:: bat
206
207      C:\..> llc -filetype=obj hello.bc
208
2096. Link to binary using Microsoft link:
210
211   .. code-block:: bat
212
213      C:\..> link hello.obj -defaultlib:libcmt
214
2157. Execute the native code program:
216
217   .. code-block:: bat
218
219      C:\..> hello.exe
220
221
222Common Problems
223===============
224If you are having problems building or using LLVM, or if you have any other
225general questions about LLVM, please consult the :doc:`Frequently Asked Questions
226<FAQ>` page.
227
228
229Links
230=====
231This document is just an **introduction** to how to use LLVM to do some simple
232things... there are many more interesting and complicated things that you can
233do that aren't documented here (but we'll gladly accept a patch if you want to
234write something up!).  For more information about LLVM, check out:
235
236* `LLVM homepage <https://llvm.org/>`_
237* `LLVM doxygen tree <https://llvm.org/doxygen/>`_
238
239