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258 lines
9.4 KiB
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========================
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Creating an LLVM Project
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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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The LLVM build system is designed to facilitate the building of third party
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projects that use LLVM header files, libraries, and tools. In order to use
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these facilities, a ``Makefile`` from a project must do the following things:
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* Set ``make`` variables. There are several variables that a ``Makefile`` needs
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to set to use the LLVM build system:
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* ``PROJECT_NAME`` - The name by which your project is known.
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* ``LLVM_SRC_ROOT`` - The root of the LLVM source tree.
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* ``LLVM_OBJ_ROOT`` - The root of the LLVM object tree.
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* ``PROJ_SRC_ROOT`` - The root of the project's source tree.
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* ``PROJ_OBJ_ROOT`` - The root of the project's object tree.
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* ``PROJ_INSTALL_ROOT`` - The root installation directory.
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* ``LEVEL`` - The relative path from the current directory to the
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project's root ``($PROJ_OBJ_ROOT)``.
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* Include ``Makefile.config`` from ``$(LLVM_OBJ_ROOT)``.
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* Include ``Makefile.rules`` from ``$(LLVM_SRC_ROOT)``.
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There are two ways that you can set all of these variables:
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* You can write your own ``Makefiles`` which hard-code these values.
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* You can use the pre-made LLVM sample project. This sample project includes
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``Makefiles``, a configure script that can be used to configure the location
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of LLVM, and the ability to support multiple object directories from a single
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source directory.
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If you want to devise your own build system, studying other projects and LLVM
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``Makefiles`` will probably provide enough information on how to write your own
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``Makefiles``.
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Source Tree Layout
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==================
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In order to use the LLVM build system, you will want to organize your source
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code so that it can benefit from the build system's features. Mainly, you want
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your source tree layout to look similar to the LLVM source tree layout.
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Underneath your top level directory, you should have the following directories:
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**lib**
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This subdirectory should contain all of your library source code. For each
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library that you build, you will have one directory in **lib** that will
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contain that library's source code.
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Libraries can be object files, archives, or dynamic libraries. The **lib**
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directory is just a convenient place for libraries as it places them all in
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a directory from which they can be linked later.
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**include**
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This subdirectory should contain any header files that are global to your
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project. By global, we mean that they are used by more than one library or
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executable of your project.
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By placing your header files in **include**, they will be found
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automatically by the LLVM build system. For example, if you have a file
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**include/jazz/note.h**, then your source files can include it simply with
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**#include "jazz/note.h"**.
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**tools**
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This subdirectory should contain all of your source code for executables.
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For each program that you build, you will have one directory in **tools**
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that will contain that program's source code.
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**test**
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This subdirectory should contain tests that verify that your code works
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correctly. Automated tests are especially useful.
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Currently, the LLVM build system provides basic support for tests. The LLVM
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system provides the following:
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* LLVM contains regression tests in ``llvm/test``. These tests are run by the
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:doc:`Lit <CommandGuide/lit>` testing tool. This test procedure uses ``RUN``
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lines in the actual test case to determine how to run the test. See the
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:doc:`TestingGuide` for more details.
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* LLVM contains an optional package called ``llvm-test``, which provides
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benchmarks and programs that are known to compile with the Clang front
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end. You can use these programs to test your code, gather statistical
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information, and compare it to the current LLVM performance statistics.
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Currently, there is no way to hook your tests directly into the ``llvm/test``
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testing harness. You will simply need to find a way to use the source
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provided within that directory on your own.
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Typically, you will want to build your **lib** directory first followed by your
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**tools** directory.
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Writing LLVM Style Makefiles
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============================
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The LLVM build system provides a convenient way to build libraries and
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executables. Most of your project Makefiles will only need to define a few
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variables. Below is a list of the variables one can set and what they can
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do:
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Required Variables
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------------------
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``LEVEL``
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This variable is the relative path from this ``Makefile`` to the top
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directory of your project's source code. For example, if your source code
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is in ``/tmp/src``, then the ``Makefile`` in ``/tmp/src/jump/high``
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would set ``LEVEL`` to ``"../.."``.
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Variables for Building Subdirectories
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-------------------------------------
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``DIRS``
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This is a space separated list of subdirectories that should be built. They
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will be built, one at a time, in the order specified.
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``PARALLEL_DIRS``
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This is a list of directories that can be built in parallel. These will be
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built after the directories in DIRS have been built.
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``OPTIONAL_DIRS``
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This is a list of directories that can be built if they exist, but will not
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cause an error if they do not exist. They are built serially in the order
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in which they are listed.
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Variables for Building Libraries
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--------------------------------
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``LIBRARYNAME``
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This variable contains the base name of the library that will be built. For
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example, to build a library named ``libsample.a``, ``LIBRARYNAME`` should
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be set to ``sample``.
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``BUILD_ARCHIVE``
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By default, a library is a ``.o`` file that is linked directly into a
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program. To build an archive (also known as a static library), set the
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``BUILD_ARCHIVE`` variable.
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``SHARED_LIBRARY``
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If ``SHARED_LIBRARY`` is defined in your Makefile, a shared (or dynamic)
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library will be built.
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Variables for Building Programs
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-------------------------------
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``TOOLNAME``
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This variable contains the name of the program that will be built. For
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example, to build an executable named ``sample``, ``TOOLNAME`` should be set
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to ``sample``.
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``USEDLIBS``
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This variable holds a space separated list of libraries that should be
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linked into the program. These libraries must be libraries that come from
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your **lib** directory. The libraries must be specified without their
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``lib`` prefix. For example, to link ``libsample.a``, you would set
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``USEDLIBS`` to ``sample.a``.
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Note that this works only for statically linked libraries.
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``LLVMLIBS``
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This variable holds a space separated list of libraries that should be
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linked into the program. These libraries must be LLVM libraries. The
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libraries must be specified without their ``lib`` prefix. For example, to
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link with a driver that performs an IR transformation you might set
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``LLVMLIBS`` to this minimal set of libraries ``LLVMSupport.a LLVMCore.a
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LLVMBitReader.a LLVMAsmParser.a LLVMAnalysis.a LLVMTransformUtils.a
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LLVMScalarOpts.a LLVMTarget.a``.
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Note that this works only for statically linked libraries. LLVM is split
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into a large number of static libraries, and the list of libraries you
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require may be much longer than the list above. To see a full list of
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libraries use: ``llvm-config --libs all``. Using ``LINK_COMPONENTS`` as
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described below, obviates the need to set ``LLVMLIBS``.
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``LINK_COMPONENTS``
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This variable holds a space separated list of components that the LLVM
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``Makefiles`` pass to the ``llvm-config`` tool to generate a link line for
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the program. For example, to link with all LLVM libraries use
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``LINK_COMPONENTS = all``.
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``LIBS``
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To link dynamic libraries, add ``-l<library base name>`` to the ``LIBS``
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variable. The LLVM build system will look in the same places for dynamic
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libraries as it does for static libraries.
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For example, to link ``libsample.so``, you would have the following line in
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your ``Makefile``:
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.. code-block:: makefile
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LIBS += -lsample
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Note that ``LIBS`` must occur in the Makefile after the inclusion of
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``Makefile.common``.
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Miscellaneous Variables
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-----------------------
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``CFLAGS`` & ``CPPFLAGS``
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This variable can be used to add options to the C and C++ compiler,
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respectively. It is typically used to add options that tell the compiler
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the location of additional directories to search for header files.
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It is highly suggested that you append to ``CFLAGS`` and ``CPPFLAGS`` as
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opposed to overwriting them. The master ``Makefiles`` may already have
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useful options in them that you may not want to overwrite.
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Placement of Object Code
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========================
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The final location of built libraries and executables will depend upon whether
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you do a ``Debug``, ``Release``, or ``Profile`` build.
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Libraries
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All libraries (static and dynamic) will be stored in
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``PROJ_OBJ_ROOT/<type>/lib``, where *type* is ``Debug``, ``Release``, or
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``Profile`` for a debug, optimized, or profiled build, respectively.
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Executables
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All executables will be stored in ``PROJ_OBJ_ROOT/<type>/bin``, where *type*
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is ``Debug``, ``Release``, or ``Profile`` for a debug, optimized, or
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profiled build, respectively.
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Further Help
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============
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If you have any questions or need any help creating an LLVM project, the LLVM
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team would be more than happy to help. You can always post your questions to
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the `LLVM Developers Mailing List
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<http://lists.llvm.org/pipermail/llvm-dev/>`_.
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