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ReStructuredText
1261 lines
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ReStructuredText
====================================
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Getting Started with the LLVM System
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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! In order to get started, you first need to know some basic
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information.
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First, LLVM comes in three pieces. The first piece is the LLVM suite. This
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contains all of the tools, libraries, and header files needed to use LLVM. It
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contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It
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also contains basic regression tests that can be used to test the LLVM tools and
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the Clang front end.
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The second piece is the `Clang <http://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. Once compiled into LLVM bitcode, a program can be manipulated with the
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LLVM tools from the LLVM suite.
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There is a third, optional piece called Test Suite. It is a suite of programs
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with a testing harness that can be used to further test LLVM's functionality
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and performance.
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Getting Started Quickly (A Summary)
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===================================
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The LLVM Getting Started documentation may be out of date. So, the `Clang
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Getting Started <http://clang.llvm.org/get_started.html>`_ page might also be a
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good place to start.
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Here's the short story for getting up and running quickly with LLVM:
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#. Read the documentation.
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#. Read the documentation.
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#. Remember that you were warned twice about reading the documentation.
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* In particular, the *relative paths specified are important*.
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#. Checkout LLVM:
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* ``cd where-you-want-llvm-to-live``
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* ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
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#. Checkout Clang:
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* ``cd where-you-want-llvm-to-live``
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* ``cd llvm/tools``
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* ``svn co http://llvm.org/svn/llvm-project/cfe/trunk clang``
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#. Checkout Compiler-RT (required to build the sanitizers) **[Optional]**:
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* ``cd where-you-want-llvm-to-live``
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* ``cd llvm/projects``
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* ``svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt``
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#. Checkout Libomp (required for OpenMP support) **[Optional]**:
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* ``cd where-you-want-llvm-to-live``
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* ``cd llvm/projects``
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* ``svn co http://llvm.org/svn/llvm-project/openmp/trunk openmp``
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#. Checkout libcxx and libcxxabi **[Optional]**:
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* ``cd where-you-want-llvm-to-live``
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* ``cd llvm/projects``
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* ``svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx``
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* ``svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi``
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#. Get the Test Suite Source Code **[Optional]**
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* ``cd where-you-want-llvm-to-live``
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* ``cd llvm/projects``
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* ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
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#. Configure and build LLVM and Clang:
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*Warning:* Make sure you've checked out *all of* the source code
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before trying to configure with cmake. cmake does not pickup newly
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added source directories in incremental builds.
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The build uses `CMake <CMake.html>`_.
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Although the build is known to work with CMake >= 2.8.8, we recommend CMake
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>= v3.2, especially if you're generating Ninja build files.
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* ``cd where you want to build llvm``
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* ``mkdir build``
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* ``cd build``
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* ``cmake -G <generator> [options] <path to llvm sources>``
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Some common generators are:
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* ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
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* ``Ninja`` --- for generating `Ninja <https://ninja-build.org>`_
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build files. Most llvm developers use Ninja.
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* ``Visual Studio`` --- for generating Visual Studio projects and
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solutions.
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* ``Xcode`` --- for generating Xcode projects.
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Some Common options:
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* ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
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pathname of where you want the LLVM tools and libraries to be installed
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(default ``/usr/local``).
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* ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
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Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
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* ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
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(default is Yes for Debug builds, No for all other build types).
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* Run your build tool of choice!
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* The default target (i.e. ``make``) will build all of LLVM
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* The ``check-all`` target (i.e. ``make check-all``) will run the
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regression tests to ensure everything is in working order.
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* CMake will generate build targets for each tool and library, and most
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LLVM sub-projects generate their own ``check-<project>`` target.
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* Running a serial build will be *slow*. Make sure you run a
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parallel build; for ``make``, use ``make -j``.
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* For more information see `CMake <CMake.html>`_
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* If you get an "internal compiler error (ICE)" or test failures, see
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`below`_.
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Consult the `Getting Started with LLVM`_ section for detailed information on
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configuring and compiling LLVM. Go to `Directory Layout`_ to learn about the
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layout of the source code tree.
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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 below.
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This may save you some trouble by knowing ahead of time what hardware and
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software you will need.
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Hardware
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--------
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LLVM is known to work on the following host platforms:
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================== ===================== =============
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OS Arch Compilers
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================== ===================== =============
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Linux x86\ :sup:`1` GCC, Clang
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Linux amd64 GCC, Clang
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Linux ARM\ :sup:`4` GCC, Clang
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Linux PowerPC GCC, Clang
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Solaris V9 (Ultrasparc) GCC
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FreeBSD x86\ :sup:`1` GCC, Clang
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FreeBSD amd64 GCC, Clang
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MacOS X\ :sup:`2` PowerPC GCC
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MacOS X x86 GCC, Clang
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Cygwin/Win32 x86\ :sup:`1, 3` GCC
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Windows x86\ :sup:`1` Visual Studio
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Windows x64 x86-64 Visual Studio
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================== ===================== =============
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.. note::
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#. Code generation supported for Pentium processors and up
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#. Code generation supported for 32-bit ABI only
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#. To use LLVM modules on Win32-based system, you may configure LLVM
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with ``-DBUILD_SHARED_LIBS=On``.
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#. MCJIT not working well pre-v7, old JIT engine not supported any more.
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Note that Debug builds require a lot of time and disk space. An LLVM-only build
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will need about 1-3 GB of space. A full build of LLVM and Clang will need around
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15-20 GB of disk space. The exact space requirements will vary by system. (It
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is so large because of all the debugging information and the fact that the
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libraries are statically linked into multiple tools).
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If you you are space-constrained, you can build only selected tools or only
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selected targets. The Release build requires considerably less space.
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The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
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so. If compilation is successful, the LLVM utilities should be able to
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assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
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should work as well, although the generated native code may not work on your
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platform.
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Software
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--------
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Compiling LLVM requires that you have several software packages installed. The
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table below lists those required packages. The Package column is the usual name
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for the software package that LLVM depends on. The Version column provides
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"known to work" versions of the package. The Notes column describes how LLVM
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uses the package and provides other details.
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=========================================================== ============ ==========================================
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Package Version Notes
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=========================================================== ============ ==========================================
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`GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
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`GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
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`python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
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`zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`3`
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=========================================================== ============ ==========================================
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.. note::
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#. Only the C and C++ languages are needed so there's no need to build the
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other languages for LLVM's purposes. See `below` for specific version
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info.
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#. Only needed if you want to run the automated test suite in the
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``llvm/test`` directory.
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#. Optional, adds compression / uncompression capabilities to selected LLVM
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tools.
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Additionally, your compilation host is expected to have the usual plethora of
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Unix utilities. Specifically:
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* **ar** --- archive library builder
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* **bzip2** --- bzip2 command for distribution generation
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* **bunzip2** --- bunzip2 command for distribution checking
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* **chmod** --- change permissions on a file
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* **cat** --- output concatenation utility
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* **cp** --- copy files
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* **date** --- print the current date/time
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* **echo** --- print to standard output
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* **egrep** --- extended regular expression search utility
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* **find** --- find files/dirs in a file system
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* **grep** --- regular expression search utility
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* **gzip** --- gzip command for distribution generation
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* **gunzip** --- gunzip command for distribution checking
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* **install** --- install directories/files
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* **mkdir** --- create a directory
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* **mv** --- move (rename) files
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* **ranlib** --- symbol table builder for archive libraries
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* **rm** --- remove (delete) files and directories
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* **sed** --- stream editor for transforming output
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* **sh** --- Bourne shell for make build scripts
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* **tar** --- tape archive for distribution generation
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* **test** --- test things in file system
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* **unzip** --- unzip command for distribution checking
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* **zip** --- zip command for distribution generation
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.. _below:
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.. _check here:
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Host C++ Toolchain, both Compiler and Standard Library
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------------------------------------------------------
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LLVM is very demanding of the host C++ compiler, and as such tends to expose
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bugs in the compiler. We are also planning to follow improvements and
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developments in the C++ language and library reasonably closely. As such, we
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require a modern host C++ toolchain, both compiler and standard library, in
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order to build LLVM.
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For the most popular host toolchains we check for specific minimum versions in
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our build systems:
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* Clang 3.1
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* GCC 4.7
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* Visual Studio 2013
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Anything older than these toolchains *may* work, but will require forcing the
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build system with a special option and is not really a supported host platform.
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Also note that older versions of these compilers have often crashed or
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miscompiled LLVM.
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For less widely used host toolchains such as ICC or xlC, be aware that a very
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recent version may be required to support all of the C++ features used in LLVM.
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We track certain versions of software that are *known* to fail when used as
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part of the host toolchain. These even include linkers at times.
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**GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
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in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
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**GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
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warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
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defined in a discarded section. You can safely ignore these messages as they are
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erroneous and the linkage is correct. These messages disappear using ld 2.17.
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**GNU binutils 2.17**: Binutils 2.17 contains `a bug
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<http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
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times (minutes instead of seconds) when building LLVM. We recommend upgrading
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to a newer version (2.17.50.0.4 or later).
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**GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
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<http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
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intermittent failures when building LLVM with position independent code. The
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symptom is an error about cyclic dependencies. We recommend upgrading to a
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newer version of Gold.
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**Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
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Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
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3.0 does not implement a few builtins that are used in this library. We
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recommend using the system GCC to compile LLVM and Clang in this case.
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**Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
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least some (``cxxabi.h``) libstdc++ headers.
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**Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
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contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
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causes Clang to refuse to compile condition_variable header file. At the time
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of writing, this breaks LLD build.
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Getting a Modern Host C++ Toolchain
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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This section mostly applies to Linux and older BSDs. On Mac OS X, you should
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have a sufficiently modern Xcode, or you will likely need to upgrade until you
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do. On Windows, just use Visual Studio 2013 as the host compiler, it is
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explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
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Clang as the system compiler.
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However, some Linux distributions and some other or older BSDs sometimes have
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extremely old versions of GCC. These steps attempt to help you upgrade you
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compiler even on such a system. However, if at all possible, we encourage you
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to use a recent version of a distribution with a modern system compiler that
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meets these requirements. Note that it is tempting to to install a prior
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version of Clang and libc++ to be the host compiler, however libc++ was not
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well tested or set up to build on Linux until relatively recently. As
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a consequence, this guide suggests just using libstdc++ and a modern GCC as the
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initial host in a bootstrap, and then using Clang (and potentially libc++).
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The first step is to get a recent GCC toolchain installed. The most common
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distribution on which users have struggled with the version requirements is
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Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
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the `toolchain testing PPA`_ and use it to install a modern GCC. There is
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a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
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not all users can use PPAs and there are many other distributions, so it may be
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necessary (or just useful, if you're here you *are* doing compiler development
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after all) to build and install GCC from source. It is also quite easy to do
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these days.
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.. _toolchain testing PPA:
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https://launchpad.net/~ubuntu-toolchain-r/+archive/test
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.. _ask ubuntu stack exchange:
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http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
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Easy steps for installing GCC 4.8.2:
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.. code-block:: console
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% wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
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% wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
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% wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
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% signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
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% if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
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% tar -xvjf gcc-4.8.2.tar.bz2
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% cd gcc-4.8.2
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% ./contrib/download_prerequisites
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% cd ..
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% mkdir gcc-4.8.2-build
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% cd gcc-4.8.2-build
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% $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
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% make -j$(nproc)
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% make install
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For more details, check out the excellent `GCC wiki entry`_, where I got most
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of this information from.
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.. _GCC wiki entry:
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http://gcc.gnu.org/wiki/InstallingGCC
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Once you have a GCC toolchain, configure your build of LLVM to use the new
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toolchain for your host compiler and C++ standard library. Because the new
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version of libstdc++ is not on the system library search path, you need to pass
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extra linker flags so that it can be found at link time (``-L``) and at runtime
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(``-rpath``). If you are using CMake, this invocation should produce working
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binaries:
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.. code-block:: console
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% mkdir build
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% cd build
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% CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
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cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
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If you fail to set rpath, most LLVM binaries will fail on startup with a message
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from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
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found``. This means you need to tweak the -rpath linker flag.
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When you build Clang, you will need to give *it* access to modern C++11
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standard library in order to use it as your new host in part of a bootstrap.
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There are two easy ways to do this, either build (and install) libc++ along
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with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
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or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
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Clang will look within its own prefix for libstdc++ and use it if found. You
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can also add an explicit prefix for Clang to look in for a GCC toolchain with
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the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
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link commands when using your just-built-Clang to bootstrap.
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.. _Getting Started with LLVM:
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Getting Started with LLVM
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=========================
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The remainder of this guide is meant to get you up and running with LLVM and to
|
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give you some basic information about the LLVM environment.
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The later sections of this guide describe the `general layout`_ of the LLVM
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source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
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more information about LLVM or to get help via e-mail.
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|
Terminology and Notation
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------------------------
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Throughout this manual, the following names are used to denote paths specific to
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the local system and working environment. *These are not environment variables
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you need to set but just strings used in the rest of this document below*. In
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any of the examples below, simply replace each of these names with the
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appropriate pathname on your local system. All these paths are absolute:
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``SRC_ROOT``
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This is the top level directory of the LLVM source tree.
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``OBJ_ROOT``
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This is the top level directory of the LLVM object tree (i.e. the tree where
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object files and compiled programs will be placed. It can be the same as
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SRC_ROOT).
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Unpacking the LLVM Archives
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---------------------------
|
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If you have the LLVM distribution, you will need to unpack it before you can
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begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
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and the LLVM GCC front end compiled for your platform. There is an additional
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test suite that is optional. Each file is a TAR archive that is compressed with
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the gzip program.
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The files are as follows, with *x.y* marking the version number:
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``llvm-x.y.tar.gz``
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Source release for the LLVM libraries and tools.
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``llvm-test-x.y.tar.gz``
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Source release for the LLVM test-suite.
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.. _checkout:
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Checkout LLVM from Subversion
|
|
-----------------------------
|
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|
If you have access to our Subversion repository, you can get a fresh copy of the
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entire source code. All you need to do is check it out from Subversion as
|
|
follows:
|
|
|
|
* ``cd where-you-want-llvm-to-live``
|
|
* Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
|
|
* Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
|
|
|
|
This will create an '``llvm``' directory in the current directory and fully
|
|
populate it with the LLVM source code, Makefiles, test directories, and local
|
|
copies of documentation files.
|
|
|
|
If you want to get a specific release (as opposed to the most recent revision),
|
|
you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
|
|
following releases are located in the following subdirectories of the '``tags``'
|
|
directory:
|
|
|
|
* Release 3.4: **RELEASE_34/final**
|
|
* Release 3.3: **RELEASE_33/final**
|
|
* Release 3.2: **RELEASE_32/final**
|
|
* Release 3.1: **RELEASE_31/final**
|
|
* Release 3.0: **RELEASE_30/final**
|
|
* Release 2.9: **RELEASE_29/final**
|
|
* Release 2.8: **RELEASE_28**
|
|
* Release 2.7: **RELEASE_27**
|
|
* Release 2.6: **RELEASE_26**
|
|
* Release 2.5: **RELEASE_25**
|
|
* Release 2.4: **RELEASE_24**
|
|
* Release 2.3: **RELEASE_23**
|
|
* Release 2.2: **RELEASE_22**
|
|
* Release 2.1: **RELEASE_21**
|
|
* Release 2.0: **RELEASE_20**
|
|
* Release 1.9: **RELEASE_19**
|
|
* Release 1.8: **RELEASE_18**
|
|
* Release 1.7: **RELEASE_17**
|
|
* Release 1.6: **RELEASE_16**
|
|
* Release 1.5: **RELEASE_15**
|
|
* Release 1.4: **RELEASE_14**
|
|
* Release 1.3: **RELEASE_13**
|
|
* Release 1.2: **RELEASE_12**
|
|
* Release 1.1: **RELEASE_11**
|
|
* Release 1.0: **RELEASE_1**
|
|
|
|
If you would like to get the LLVM test suite (a separate package as of 1.4), you
|
|
get it from the Subversion repository:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm/projects
|
|
% svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
|
|
|
|
By placing it in the ``llvm/projects``, it will be automatically configured by
|
|
the LLVM cmake configuration.
|
|
|
|
Git Mirror
|
|
----------
|
|
|
|
Git mirrors are available for a number of LLVM subprojects. These mirrors sync
|
|
automatically with each Subversion commit and contain all necessary git-svn
|
|
marks (so, you can recreate git-svn metadata locally). Note that right now
|
|
mirrors reflect only ``trunk`` for each project. You can do the read-only Git
|
|
clone of LLVM via:
|
|
|
|
.. code-block:: console
|
|
|
|
% git clone http://llvm.org/git/llvm.git
|
|
|
|
If you want to check out clang too, run:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm/tools
|
|
% git clone http://llvm.org/git/clang.git
|
|
|
|
If you want to check out compiler-rt (required to build the sanitizers), run:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm/projects
|
|
% git clone http://llvm.org/git/compiler-rt.git
|
|
|
|
If you want to check out libomp (required for OpenMP support), run:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm/projects
|
|
% git clone http://llvm.org/git/openmp.git
|
|
|
|
If you want to check out libcxx and libcxxabi (optional), run:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm/projects
|
|
% git clone http://llvm.org/git/libcxx.git
|
|
% git clone http://llvm.org/git/libcxxabi.git
|
|
|
|
If you want to check out the Test Suite Source Code (optional), run:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm/projects
|
|
% git clone http://llvm.org/git/test-suite.git
|
|
|
|
Since the upstream repository is in Subversion, you should use ``git
|
|
pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
|
|
in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
|
|
master branch, run the following command:
|
|
|
|
.. code-block:: console
|
|
|
|
% git config branch.master.rebase true
|
|
|
|
Sending patches with Git
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
|
|
|
|
Assume ``master`` points the upstream and ``mybranch`` points your working
|
|
branch, and ``mybranch`` is rebased onto ``master``. At first you may check
|
|
sanity of whitespaces:
|
|
|
|
.. code-block:: console
|
|
|
|
% git diff --check master..mybranch
|
|
|
|
The easiest way to generate a patch is as below:
|
|
|
|
.. code-block:: console
|
|
|
|
% git diff master..mybranch > /path/to/mybranch.diff
|
|
|
|
It is a little different from svn-generated diff. git-diff-generated diff has
|
|
prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
|
|
could be accepted with ``patch -p1 -N``.
|
|
|
|
But you may generate patchset with git-format-patch. It generates by-each-commit
|
|
patchset. To generate patch files to attach to your article:
|
|
|
|
.. code-block:: console
|
|
|
|
% git format-patch --no-attach master..mybranch -o /path/to/your/patchset
|
|
|
|
If you would like to send patches directly, you may use git-send-email or
|
|
git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
|
|
|
|
.. code-block:: console
|
|
|
|
% git format-patch --attach master..mybranch --stdout | git imap-send
|
|
|
|
Then, your .git/config should have [imap] sections.
|
|
|
|
.. code-block:: ini
|
|
|
|
[imap]
|
|
host = imaps://imap.gmail.com
|
|
user = your.gmail.account@gmail.com
|
|
pass = himitsu!
|
|
port = 993
|
|
sslverify = false
|
|
; in English
|
|
folder = "[Gmail]/Drafts"
|
|
; example for Japanese, "Modified UTF-7" encoded.
|
|
folder = "[Gmail]/&Tgtm+DBN-"
|
|
; example for Traditional Chinese
|
|
folder = "[Gmail]/&g0l6Pw-"
|
|
|
|
.. _developers-work-with-git-svn:
|
|
|
|
For developers to work with git-svn
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
To set up clone from which you can submit code using ``git-svn``, run:
|
|
|
|
.. code-block:: console
|
|
|
|
% git clone http://llvm.org/git/llvm.git
|
|
% cd llvm
|
|
% git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
|
|
% git config svn-remote.svn.fetch :refs/remotes/origin/master
|
|
% git svn rebase -l # -l avoids fetching ahead of the git mirror.
|
|
|
|
# If you have clang too:
|
|
% cd tools
|
|
% git clone http://llvm.org/git/clang.git
|
|
% cd clang
|
|
% git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
|
|
% git config svn-remote.svn.fetch :refs/remotes/origin/master
|
|
% git svn rebase -l
|
|
|
|
Likewise for compiler-rt, libomp and test-suite.
|
|
|
|
To update this clone without generating git-svn tags that conflict with the
|
|
upstream Git repo, run:
|
|
|
|
.. code-block:: console
|
|
|
|
% git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
|
|
% git checkout master
|
|
% git svn rebase -l
|
|
% (cd tools/clang &&
|
|
git checkout master &&
|
|
git svn rebase -l)
|
|
|
|
Likewise for compiler-rt, libomp and test-suite.
|
|
|
|
This leaves your working directories on their master branches, so you'll need to
|
|
``checkout`` each working branch individually and ``rebase`` it on top of its
|
|
parent branch.
|
|
|
|
For those who wish to be able to update an llvm repo/revert patches easily using
|
|
git-svn, please look in the directory for the scripts ``git-svnup`` and
|
|
``git-svnrevert``.
|
|
|
|
To perform the aforementioned update steps go into your source directory and
|
|
just type ``git-svnup`` or ``git svnup`` and everything will just work.
|
|
|
|
If one wishes to revert a commit with git-svn, but do not want the git hash to
|
|
escape into the commit message, one can use the script ``git-svnrevert`` or
|
|
``git svnrevert`` which will take in the git hash for the commit you want to
|
|
revert, look up the appropriate svn revision, and output a message where all
|
|
references to the git hash have been replaced with the svn revision.
|
|
|
|
To commit back changes via git-svn, use ``git svn dcommit``:
|
|
|
|
.. code-block:: console
|
|
|
|
% git svn dcommit
|
|
|
|
Note that git-svn will create one SVN commit for each Git commit you have pending,
|
|
so squash and edit each commit before executing ``dcommit`` to make sure they all
|
|
conform to the coding standards and the developers' policy.
|
|
|
|
On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
|
|
please make sure your current branch is up-to-date (via fetch/rebase) before
|
|
proceeding.
|
|
|
|
The git-svn metadata can get out of sync after you mess around with branches and
|
|
``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
|
|
about files with uncommitted changes. The fix is to rebuild the metadata:
|
|
|
|
.. code-block:: console
|
|
|
|
% rm -rf .git/svn
|
|
% git svn rebase -l
|
|
|
|
Please, refer to the Git-SVN manual (``man git-svn``) for more information.
|
|
|
|
Local LLVM Configuration
|
|
------------------------
|
|
|
|
Once checked out from the Subversion repository, the LLVM suite source code must
|
|
be configured before being built. This process uses CMake.
|
|
Unlinke the normal ``configure`` script, CMake
|
|
generates the build files in whatever format you request as well as various
|
|
``*.inc`` files, and ``llvm/include/Config/config.h``.
|
|
|
|
Variables are passed to ``cmake`` on the command line using the format
|
|
``-D<variable name>=<value>``. The following variables are some common options
|
|
used by people developing LLVM.
|
|
|
|
+-------------------------+----------------------------------------------------+
|
|
| Variable | Purpose |
|
|
+=========================+====================================================+
|
|
| CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
|
|
| | default, this will be /usr/bin/cc. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
|
|
| | default, this will be /usr/bin/c++. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
|
|
| | to generate files for. Valid options are Debug, |
|
|
| | Release, RelWithDebInfo, and MinSizeRel. Default |
|
|
| | is Debug. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
|
|
| | running the install action of the build files. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
|
|
| | targets will be built and linked into llc. This is |
|
|
| | equivalent to the ``--enable-targets`` option in |
|
|
| | the configure script. The default list is defined |
|
|
| | as ``LLVM_ALL_TARGETS``, and can be set to include |
|
|
| | out-of-tree targets. The default value includes: |
|
|
| | ``AArch64, AMDGPU, ARM, BPF, CppBackend, Hexagon, |
|
|
| | Mips, MSP430, NVPTX, PowerPC, Sparc, SystemZ |
|
|
| | X86, XCore``. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
|
|
| | code This is disabled by default because it is |
|
|
| | slow and generates a lot of output. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
|
|
| | code. This is disabled by default because it is |
|
|
| | slow and generates a lot of output. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
|
|
| | default set of LLVM components that can be |
|
|
| | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
|
|
| | default contains most of LLVM and is defined in |
|
|
| | ``tools/llvm-shlib/CMakelists.txt``. |
|
|
+-------------------------+----------------------------------------------------+
|
|
| LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
|
|
| | the LLVM build. This can dramatically speed up |
|
|
| | debug builds. |
|
|
+-------------------------+----------------------------------------------------+
|
|
|
|
To configure LLVM, follow these steps:
|
|
|
|
#. Change directory into the object root directory:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd OBJ_ROOT
|
|
|
|
#. Run the ``cmake``:
|
|
|
|
.. code-block:: console
|
|
|
|
% cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
|
|
[other options] SRC_ROOT
|
|
|
|
Compiling the LLVM Suite Source Code
|
|
------------------------------------
|
|
|
|
Unlike with autotools, with CMake your build type is defined at configuration.
|
|
If you want to change your build type, you can re-run cmake with the following
|
|
invocation:
|
|
|
|
.. code-block:: console
|
|
|
|
% cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
|
|
|
|
Between runs, CMake preserves the values set for all options. CMake has the
|
|
following build types defined:
|
|
|
|
Debug
|
|
|
|
These builds are the default. The build system will compile the tools and
|
|
libraries unoptimized, with debugging information, and asserts enabled.
|
|
|
|
Release
|
|
|
|
For these builds, the build system will compile the tools and libraries
|
|
with optimizations enabled and not generate debug info. CMakes default
|
|
optimization level is -O3. This can be configured by setting the
|
|
``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
|
|
|
|
RelWithDebInfo
|
|
|
|
These builds are useful when debugging. They generate optimized binaries with
|
|
debug information. CMakes default optimization level is -O2. This can be
|
|
configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
|
|
CMake command line.
|
|
|
|
Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
|
|
directory and issuing the following command:
|
|
|
|
.. code-block:: console
|
|
|
|
% make
|
|
|
|
If the build fails, please `check here`_ to see if you are using a version of
|
|
GCC that is known not to compile LLVM.
|
|
|
|
If you have multiple processors in your machine, you may wish to use some of the
|
|
parallel build options provided by GNU Make. For example, you could use the
|
|
command:
|
|
|
|
.. code-block:: console
|
|
|
|
% make -j2
|
|
|
|
There are several special targets which are useful when working with the LLVM
|
|
source code:
|
|
|
|
``make clean``
|
|
|
|
Removes all files generated by the build. This includes object files,
|
|
generated C/C++ files, libraries, and executables.
|
|
|
|
``make install``
|
|
|
|
Installs LLVM header files, libraries, tools, and documentation in a hierarchy
|
|
under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
|
|
defaults to ``/usr/local``.
|
|
|
|
``make docs-llvm-html``
|
|
|
|
If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
|
|
at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
|
|
|
|
Cross-Compiling LLVM
|
|
--------------------
|
|
|
|
It is possible to cross-compile LLVM itself. That is, you can create LLVM
|
|
executables and libraries to be hosted on a platform different from the platform
|
|
where they are built (a Canadian Cross build). To generate build files for
|
|
cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
|
|
define compiler flags and variables used during the CMake test operations.
|
|
|
|
The result of such a build is executables that are not runnable on on the build
|
|
host but can be executed on the target. As an example the following CMake
|
|
invocation can generate build files targeting iOS. This will work on Mac OS X
|
|
with the latest Xcode:
|
|
|
|
.. code-block:: console
|
|
|
|
% cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES="armv7;armv7s;arm64"
|
|
-DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
|
|
-DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
|
|
-DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
|
|
<PATH_TO_LLVM>
|
|
|
|
Note: There are some additional flags that need to be passed when building for
|
|
iOS due to limitations in the iOS SDK.
|
|
|
|
Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
|
|
<http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
|
|
about cross-compiling.
|
|
|
|
The Location of LLVM Object Files
|
|
---------------------------------
|
|
|
|
The LLVM build system is capable of sharing a single LLVM source tree among
|
|
several LLVM builds. Hence, it is possible to build LLVM for several different
|
|
platforms or configurations using the same source tree.
|
|
|
|
* Change directory to where the LLVM object files should live:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd OBJ_ROOT
|
|
|
|
* Run ``cmake``:
|
|
|
|
.. code-block:: console
|
|
|
|
% cmake -G "Unix Makefiles" SRC_ROOT
|
|
|
|
The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
|
|
LLVM source tree. At each level where source files are present in the source
|
|
tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
|
|
Underneath that directory there is another directory with a name ending in
|
|
``.dir`` under which you'll find object files for each source.
|
|
|
|
For example:
|
|
|
|
.. code-block:: console
|
|
|
|
% cd llvm_build_dir
|
|
% find lib/Support/ -name APFloat*
|
|
lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
|
|
|
|
Optional Configuration Items
|
|
----------------------------
|
|
|
|
If you're running on a Linux system that supports the `binfmt_misc
|
|
<http://en.wikipedia.org/wiki/binfmt_misc>`_
|
|
module, and you have root access on the system, you can set your system up to
|
|
execute LLVM bitcode files directly. To do this, use commands like this (the
|
|
first command may not be required if you are already using the module):
|
|
|
|
.. code-block:: console
|
|
|
|
% mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
|
|
% echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
|
|
% chmod u+x hello.bc (if needed)
|
|
% ./hello.bc
|
|
|
|
This allows you to execute LLVM bitcode files directly. On Debian, you can also
|
|
use this command instead of the 'echo' command above:
|
|
|
|
.. code-block:: console
|
|
|
|
% sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
|
|
|
|
.. _Program Layout:
|
|
.. _general layout:
|
|
|
|
Directory Layout
|
|
================
|
|
|
|
One useful source of information about the LLVM source base is the LLVM `doxygen
|
|
<http://www.doxygen.org/>`_ documentation available at
|
|
`<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
|
|
layout:
|
|
|
|
``llvm/examples``
|
|
-----------------
|
|
|
|
Simple examples using the LLVM IR and JIT.
|
|
|
|
``llvm/include``
|
|
----------------
|
|
|
|
Public header files exported from the LLVM library. The three main subdirectories:
|
|
|
|
``llvm/include/llvm``
|
|
|
|
All LLVM-specific header files, and subdirectories for different portions of
|
|
LLVM: ``Analysis``, ``CodeGen``, ``Target``, ``Transforms``, etc...
|
|
|
|
``llvm/include/llvm/Support``
|
|
|
|
Generic support libraries provided with LLVM but not necessarily specific to
|
|
LLVM. For example, some C++ STL utilities and a Command Line option processing
|
|
library store header files here.
|
|
|
|
``llvm/include/llvm/Config``
|
|
|
|
Header files configured by the ``configure`` script.
|
|
They wrap "standard" UNIX and C header files. Source code can include these
|
|
header files which automatically take care of the conditional #includes that
|
|
the ``configure`` script generates.
|
|
|
|
``llvm/lib``
|
|
------------
|
|
|
|
Most source files are here. By putting code in libraries, LLVM makes it easy to
|
|
share code among the `tools`_.
|
|
|
|
``llvm/lib/IR/``
|
|
|
|
Core LLVM source files that implement core classes like Instruction and
|
|
BasicBlock.
|
|
|
|
``llvm/lib/AsmParser/``
|
|
|
|
Source code for the LLVM assembly language parser library.
|
|
|
|
``llvm/lib/Bitcode/``
|
|
|
|
Code for reading and writing bitcode.
|
|
|
|
``llvm/lib/Analysis/``
|
|
|
|
A variety of program analyses, such as Call Graphs, Induction Variables,
|
|
Natural Loop Identification, etc.
|
|
|
|
``llvm/lib/Transforms/``
|
|
|
|
IR-to-IR program transformations, such as Aggressive Dead Code Elimination,
|
|
Sparse Conditional Constant Propagation, Inlining, Loop Invariant Code Motion,
|
|
Dead Global Elimination, and many others.
|
|
|
|
``llvm/lib/Target/``
|
|
|
|
Files describing target architectures for code generation. For example,
|
|
``llvm/lib/Target/X86`` holds the X86 machine description.
|
|
|
|
``llvm/lib/CodeGen/``
|
|
|
|
The major parts of the code generator: Instruction Selector, Instruction
|
|
Scheduling, and Register Allocation.
|
|
|
|
``llvm/lib/MC/``
|
|
|
|
(FIXME: T.B.D.) ....?
|
|
|
|
``llvm/lib/ExecutionEngine/``
|
|
|
|
Libraries for directly executing bitcode at runtime in interpreted and
|
|
JIT-compiled scenarios.
|
|
|
|
``llvm/lib/Support/``
|
|
|
|
Source code that corresponding to the header files in ``llvm/include/ADT/``
|
|
and ``llvm/include/Support/``.
|
|
|
|
``llvm/projects``
|
|
-----------------
|
|
|
|
Projects not strictly part of LLVM but shipped with LLVM. This is also the
|
|
directory for creating your own LLVM-based projects which leverage the LLVM
|
|
build system.
|
|
|
|
``llvm/test``
|
|
-------------
|
|
|
|
Feature and regression tests and other sanity checks on LLVM infrastructure. These
|
|
are intended to run quickly and cover a lot of territory without being exhaustive.
|
|
|
|
``test-suite``
|
|
--------------
|
|
|
|
A comprehensive correctness, performance, and benchmarking test suite for LLVM.
|
|
Comes in a separate Subversion module because not every LLVM user is interested
|
|
in such a comprehensive suite. For details see the :doc:`Testing Guide
|
|
<TestingGuide>` document.
|
|
|
|
.. _tools:
|
|
|
|
``llvm/tools``
|
|
--------------
|
|
|
|
Executables built out of the libraries
|
|
above, which form the main part of the user interface. You can always get help
|
|
for a tool by typing ``tool_name -help``. The following is a brief introduction
|
|
to the most important tools. More detailed information is in
|
|
the `Command Guide <CommandGuide/index.html>`_.
|
|
|
|
``bugpoint``
|
|
|
|
``bugpoint`` is used to debug optimization passes or code generation backends
|
|
by narrowing down the given test case to the minimum number of passes and/or
|
|
instructions that still cause a problem, whether it is a crash or
|
|
miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
|
|
``bugpoint``.
|
|
|
|
``llvm-ar``
|
|
|
|
The archiver produces an archive containing the given LLVM bitcode files,
|
|
optionally with an index for faster lookup.
|
|
|
|
``llvm-as``
|
|
|
|
The assembler transforms the human readable LLVM assembly to LLVM bitcode.
|
|
|
|
``llvm-dis``
|
|
|
|
The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
|
|
|
|
``llvm-link``
|
|
|
|
``llvm-link``, not surprisingly, links multiple LLVM modules into a single
|
|
program.
|
|
|
|
``lli``
|
|
|
|
``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
|
|
(although very slowly...). For architectures that support it (currently x86,
|
|
Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
|
|
compiler (if the functionality was compiled in), and will execute the code
|
|
*much* faster than the interpreter.
|
|
|
|
``llc``
|
|
|
|
``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
|
|
native code assembly file or to C code (with the ``-march=c`` option).
|
|
|
|
``opt``
|
|
|
|
``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
|
|
(which are specified on the command line), and outputs the resultant
|
|
bitcode. '``opt -help``' is a good way to get a list of the
|
|
program transformations available in LLVM.
|
|
|
|
``opt`` can also run a specific analysis on an input LLVM bitcode
|
|
file and print the results. Primarily useful for debugging
|
|
analyses, or familiarizing yourself with what an analysis does.
|
|
|
|
``llvm/utils``
|
|
--------------
|
|
|
|
Utilities for working with LLVM source code; some are part of the build process
|
|
because they are code generators for parts of the infrastructure.
|
|
|
|
|
|
``codegen-diff``
|
|
|
|
``codegen-diff`` finds differences between code that LLC
|
|
generates and code that LLI generates. This is useful if you are
|
|
debugging one of them, assuming that the other generates correct output. For
|
|
the full user manual, run ```perldoc codegen-diff'``.
|
|
|
|
``emacs/``
|
|
|
|
Emacs and XEmacs syntax highlighting for LLVM assembly files and TableGen
|
|
description files. See the ``README`` for information on using them.
|
|
|
|
``getsrcs.sh``
|
|
|
|
Finds and outputs all non-generated source files,
|
|
useful if one wishes to do a lot of development across directories
|
|
and does not want to find each file. One way to use it is to run,
|
|
for example: ``xemacs `utils/getsources.sh``` from the top of the LLVM source
|
|
tree.
|
|
|
|
``llvmgrep``
|
|
|
|
Performs an ``egrep -H -n`` on each source file in LLVM and
|
|
passes to it a regular expression provided on ``llvmgrep``'s command
|
|
line. This is an efficient way of searching the source base for a
|
|
particular regular expression.
|
|
|
|
``makellvm``
|
|
|
|
Compiles all files in the current directory, then
|
|
compiles and links the tool that is the first argument. For example, assuming
|
|
you are in ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
|
|
path, running ``makellvm llc`` will make a build of the current
|
|
directory, switch to directory ``llvm/tools/llc`` and build it, causing a
|
|
re-linking of LLC.
|
|
|
|
``TableGen/``
|
|
|
|
Contains the tool used to generate register
|
|
descriptions, instruction set descriptions, and even assemblers from common
|
|
TableGen description files.
|
|
|
|
``vim/``
|
|
|
|
vim syntax-highlighting for LLVM assembly files
|
|
and TableGen description files. See the ``README`` for how to use them.
|
|
|
|
.. _simple example:
|
|
|
|
An Example Using the LLVM Tool Chain
|
|
====================================
|
|
|
|
This section gives an example of using LLVM with the Clang front end.
|
|
|
|
Example with clang
|
|
------------------
|
|
|
|
#. First, create a simple C file, name it 'hello.c':
|
|
|
|
.. code-block:: c
|
|
|
|
#include <stdio.h>
|
|
|
|
int main() {
|
|
printf("hello world\n");
|
|
return 0;
|
|
}
|
|
|
|
#. Next, compile the C file into a native executable:
|
|
|
|
.. code-block:: console
|
|
|
|
% clang hello.c -o hello
|
|
|
|
.. note::
|
|
|
|
Clang works just like GCC by default. The standard -S and -c arguments
|
|
work as usual (producing a native .s or .o file, respectively).
|
|
|
|
#. Next, compile the C file into an LLVM bitcode file:
|
|
|
|
.. code-block:: console
|
|
|
|
% clang -O3 -emit-llvm hello.c -c -o hello.bc
|
|
|
|
The -emit-llvm option can be used with the -S or -c options to emit an LLVM
|
|
``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
|
|
the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
|
|
|
|
#. Run the program in both forms. To run the program, use:
|
|
|
|
.. code-block:: console
|
|
|
|
% ./hello
|
|
|
|
and
|
|
|
|
.. code-block:: console
|
|
|
|
% lli hello.bc
|
|
|
|
The second examples shows how to invoke the LLVM JIT, :doc:`lli
|
|
<CommandGuide/lli>`.
|
|
|
|
#. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
|
|
|
|
.. code-block:: console
|
|
|
|
% llvm-dis < hello.bc | less
|
|
|
|
#. Compile the program to native assembly using the LLC code generator:
|
|
|
|
.. code-block:: console
|
|
|
|
% llc hello.bc -o hello.s
|
|
|
|
#. Assemble the native assembly language file into a program:
|
|
|
|
.. code-block:: console
|
|
|
|
% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
|
|
|
|
% gcc hello.s -o hello.native # On others
|
|
|
|
#. Execute the native code program:
|
|
|
|
.. code-block:: console
|
|
|
|
% ./hello.native
|
|
|
|
Note that using clang to compile directly to native code (i.e. when the
|
|
``-emit-llvm`` option is not present) does steps 6/7/8 for you.
|
|
|
|
Common Problems
|
|
===============
|
|
|
|
If you are having problems building or using LLVM, or if you have any other
|
|
general questions about LLVM, please consult the `Frequently Asked
|
|
Questions <FAQ.html>`_ page.
|
|
|
|
.. _links:
|
|
|
|
Links
|
|
=====
|
|
|
|
This document is just an **introduction** on how to use LLVM to do some simple
|
|
things... there are many more interesting and complicated things that you can do
|
|
that aren't documented here (but we'll gladly accept a patch if you want to
|
|
write something up!). For more information about LLVM, check out:
|
|
|
|
* `LLVM Homepage <http://llvm.org/>`_
|
|
* `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
|
|
* `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_
|