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8.7 KiB
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239 lines
8.7 KiB
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==================================================================
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Getting Started with the LLVM System using Microsoft Visual Studio
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==================================================================
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.. contents::
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:local:
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Overview
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========
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Welcome to LLVM on Windows! This document only covers LLVM on Windows using
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Visual Studio, not mingw or cygwin. In order to get started, you first need to
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know some basic information.
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There are many different projects that compose LLVM. The first piece is the
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LLVM suite. This contains all of the tools, libraries, and header files needed
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to use LLVM. It contains an assembler, disassembler, bitcode analyzer and
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bitcode optimizer. It also contains basic regression tests that can be used to
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test the LLVM tools and the Clang front end.
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The second piece is the `Clang <https://clang.llvm.org/>`_ front end. This
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component compiles C, C++, Objective C, and Objective C++ code into LLVM
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bitcode. Clang typically uses LLVM libraries to optimize the bitcode and emit
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machine code. LLVM fully supports the COFF object file format, which is
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compatible with all other existing Windows toolchains.
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The last major part of LLVM, the execution Test Suite, does not run on Windows,
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and this document does not discuss it.
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Additional information about the LLVM directory structure and tool chain
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can be found on the main :doc:`GettingStarted` page.
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Requirements
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============
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Before you begin to use the LLVM system, review the requirements given
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below. This may save you some trouble by knowing ahead of time what hardware
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and software you will need.
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Hardware
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--------
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Any system that can adequately run Visual Studio 2017 is fine. The LLVM
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source tree and object files, libraries and executables will consume
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approximately 3GB.
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Software
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--------
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You will need Visual Studio 2017 or higher, with the latest Update installed.
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You will also need the `CMake <http://www.cmake.org/>`_ build system since it
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generates the project files you will use to build with.
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If you would like to run the LLVM tests you will need `Python
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<http://www.python.org/>`_. Version 3.6 and newer are known to work. You will
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need `GnuWin32 <http://gnuwin32.sourceforge.net/>`_ tools, too.
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Do not install the LLVM directory tree into a path containing spaces (e.g.
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``C:\Documents and Settings\...``) as the configure step will fail.
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Getting Started
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===============
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Here's the short story for getting up and running quickly with LLVM:
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1. Read the documentation.
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2. Seriously, read the documentation.
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3. Remember that you were warned twice about reading the documentation.
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4. Get the Source Code
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* With the distributed files:
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1. ``cd <where-you-want-llvm-to-live>``
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2. ``gunzip --stdout llvm-VERSION.tar.gz | tar -xvf -``
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(*or use WinZip*)
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3. ``cd llvm``
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* With git access:
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*Note:* some regression tests require Unix-style line ending (``\n``).
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1. ``cd <where-you-want-llvm-to-live>``
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2. ``git clone https://github.com/llvm/llvm-project.git llvm``
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3. ``cd llvm``
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5. Use `CMake <http://www.cmake.org/>`_ to generate up-to-date project files:
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* Once CMake is installed then the simplest way is to just start the
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CMake GUI, select the directory where you have LLVM extracted to, and
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the default options should all be fine. One option you may really
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want to change, regardless of anything else, might be the
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``CMAKE_INSTALL_PREFIX`` setting to select a directory to INSTALL to
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once compiling is complete, although installation is not mandatory for
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using LLVM. Another important option is ``LLVM_TARGETS_TO_BUILD``,
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which controls the LLVM target architectures that are included on the
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build.
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* If CMake complains that it cannot find the compiler, make sure that
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you have the Visual Studio C++ Tools installed, not just Visual Studio
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itself (trying to create a C++ project in Visual Studio will generally
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download the C++ tools if they haven't already been).
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* See the :doc:`LLVM CMake guide <CMake>` for detailed information about
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how to configure the LLVM build.
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* CMake generates project files for all build types. To select a specific
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build type, use the Configuration manager from the VS IDE or the
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``/property:Configuration`` command line option when using MSBuild.
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* By default, the Visual Studio project files generated by CMake use the
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32-bit toolset. If you are developing on a 64-bit version of Windows and
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want to use the 64-bit toolset, pass the ``-Thost=x64`` flag when
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generating the Visual Studio solution. This requires CMake 3.8.0 or later.
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6. Start Visual Studio
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* In the directory you created the project files will have an ``llvm.sln``
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file, just double-click on that to open Visual Studio.
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7. Build the LLVM Suite:
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* The projects may still be built individually, but to build them all do
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not just select all of them in batch build (as some are meant as
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configuration projects), but rather select and build just the
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``ALL_BUILD`` project to build everything, or the ``INSTALL`` project,
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which first builds the ``ALL_BUILD`` project, then installs the LLVM
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headers, libs, and other useful things to the directory set by the
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``CMAKE_INSTALL_PREFIX`` setting when you first configured CMake.
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* The Fibonacci project is a sample program that uses the JIT. Modify the
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project's debugging properties to provide a numeric command line argument
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or run it from the command line. The program will print the
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corresponding fibonacci value.
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8. Test LLVM in Visual Studio:
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* If ``%PATH%`` does not contain GnuWin32, you may specify
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``LLVM_LIT_TOOLS_DIR`` on CMake for the path to GnuWin32.
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* You can run LLVM tests by merely building the project "check". The test
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results will be shown in the VS output window.
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9. Test LLVM on the command line:
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* The LLVM tests can be run by changing directory to the llvm source
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directory and running:
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.. code-block:: bat
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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
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This example assumes that Python is in your PATH variable, you
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have built a Win32 Debug version of llvm with a standard out of
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line build. You should not see any unexpected failures, but will
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see many unsupported tests and expected failures.
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A specific test or test directory can be run with:
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.. code-block:: bat
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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
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An Example Using the LLVM Tool Chain
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====================================
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1. First, create a simple C file, name it '``hello.c``':
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.. code-block:: c
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#include <stdio.h>
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int main() {
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printf("hello world\n");
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return 0;
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}
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2. Next, compile the C file into an LLVM bitcode file:
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.. code-block:: bat
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C:\..> clang -c hello.c -emit-llvm -o hello.bc
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This will create the result file ``hello.bc`` which is the LLVM bitcode
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that corresponds the compiled program and the library facilities that
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it required. You can execute this file directly using ``lli`` tool,
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compile it to native assembly with the ``llc``, optimize or analyze it
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further with the ``opt`` tool, etc.
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Alternatively you can directly output an executable with clang with:
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.. code-block:: bat
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C:\..> clang hello.c -o hello.exe
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The ``-o hello.exe`` is required because clang currently outputs ``a.out``
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when neither ``-o`` nor ``-c`` are given.
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3. Run the program using the just-in-time compiler:
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.. code-block:: bat
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C:\..> lli hello.bc
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4. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
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.. code-block:: bat
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C:\..> llvm-dis < hello.bc | more
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5. Compile the program to object code using the LLC code generator:
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.. code-block:: bat
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C:\..> llc -filetype=obj hello.bc
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6. Link to binary using Microsoft link:
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.. code-block:: bat
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C:\..> link hello.obj -defaultlib:libcmt
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7. Execute the native code program:
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.. code-block:: bat
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C:\..> hello.exe
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Common Problems
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===============
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If you are having problems building or using LLVM, or if you have any other
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general questions about LLVM, please consult the :doc:`Frequently Asked Questions
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<FAQ>` page.
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Links
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=====
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This document is just an **introduction** to how to use LLVM to do some simple
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things... there are many more interesting and complicated things that you can
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do that aren't documented here (but we'll gladly accept a patch if you want to
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write something up!). For more information about LLVM, check out:
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* `LLVM homepage <https://llvm.org/>`_
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* `LLVM doxygen tree <https://llvm.org/doxygen/>`_
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