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Discussion thread: https://lists.llvm.org/pipermail/llvm-dev/2021-January/148048.html Move debuginfo-test into a subdirectory of a new top-level directory, called cross-project-tests. The new name replaces "debuginfo-test" as an LLVM project enabled via LLVM_ENABLE_PROJECTS. Differential Revision: https://reviews.llvm.org/D95339 Reviewed by: aprantl
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ReStructuredText
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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 the LLVM project!
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The LLVM project has multiple components. The core of the project is
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itself called "LLVM". This contains all of the tools, libraries, and header
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files needed to process intermediate representations and converts it into
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object files. Tools include an assembler, disassembler, bitcode analyzer, and
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bitcode optimizer. It also contains basic regression tests.
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C-like languages use 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 bitcode
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-- and from there into object files, using LLVM.
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Other components include:
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the `libc++ C++ standard library <https://libcxx.llvm.org>`_,
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the `LLD linker <https://lld.llvm.org>`_, and more.
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Getting the Source Code and Building LLVM
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=========================================
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The LLVM Getting Started documentation may be out of date. The `Clang
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Getting Started <https://clang.llvm.org/get_started.html>`_ page might have more
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accurate information.
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This is an example workflow and configuration to get and build the LLVM source:
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#. Checkout LLVM (including related subprojects like Clang):
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* ``git clone https://github.com/llvm/llvm-project.git``
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* Or, on windows, ``git clone --config core.autocrlf=false
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https://github.com/llvm/llvm-project.git``
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* To save storage and speed-up the checkout time, you may want to do a
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`shallow clone <https://git-scm.com/docs/git-clone#Documentation/git-clone.txt---depthltdepthgt>`_.
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For example, to get the latest revision of the LLVM project, use
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``git clone --depth 1 https://github.com/llvm/llvm-project.git``
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#. Configure and build LLVM and Clang:
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* ``cd llvm-project``
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* ``mkdir build``
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* ``cd build``
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* ``cmake -G <generator> [options] ../llvm``
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Some common build system generators are:
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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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* ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
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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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* ``-DLLVM_ENABLE_PROJECTS='...'`` --- semicolon-separated list of the LLVM
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subprojects you'd like to additionally build. Can include any of: clang,
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clang-tools-extra, libcxx, libcxxabi, libunwind, lldb, compiler-rt, lld,
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polly, or cross-project-tests.
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For example, to build LLVM, Clang, libcxx, and libcxxabi, use
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``-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"``.
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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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* ``cmake --build . [--target <target>]`` or the build system specified
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above directly.
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* The default target (i.e. ``cmake --build .`` or ``make``) will build all of
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LLVM.
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* The ``check-all`` target (i.e. ``ninja 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**. To improve speed, try running a
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parallel build. That's done by default in Ninja; for ``make``, use the
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option ``-j NN``, where ``NN`` is the number of parallel jobs, e.g. the
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number of available CPUs.
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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 GCC, Clang
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Linux Mips GCC, Clang
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Linux PowerPC GCC, Clang
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Linux SystemZ 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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NetBSD x86\ :sup:`1` GCC, Clang
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NetBSD amd64 GCC, Clang
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macOS\ :sup:`2` PowerPC GCC
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macOS 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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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 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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`CMake <http://cmake.org/>`__ >=3.13.4 Makefile/workspace generator
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`GCC <http://gcc.gnu.org/>`_ >=5.1.0 C/C++ compiler\ :sup:`1`
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`python <http://www.python.org/>`_ >=3.6 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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`GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor\ :sup:`4`
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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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#. Optional, you can use any other build tool supported by CMake.
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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 also attempt to follow improvements and developments in
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the C++ language and library reasonably closely. As such, we require a modern
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host C++ toolchain, both compiler and standard library, in order to build LLVM.
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LLVM is written using the subset of C++ documented in :doc:`coding
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standards<CodingStandards>`. To enforce this language version, we check the most
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popular host toolchains for specific minimum versions in our build systems:
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* Clang 3.5
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* Apple Clang 6.0
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* GCC 5.1
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* Visual Studio 2017
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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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**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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Getting a Modern Host C++ Toolchain
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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This section mostly applies to Linux and older BSDs. On macOS, 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. Windows does not have a "system compiler", so you must install either Visual
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Studio 2017 or a recent version of mingw64. 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 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`_ and a
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`github gist`_ with updated commands. However, not all users can use PPAs and
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there are many other distributions, so it may be necessary (or just useful, if
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you're here you *are* doing compiler development after all) to build and install
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GCC from source. It is also quite easy to do 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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https://askubuntu.com/questions/466651/how-do-i-use-the-latest-gcc-on-ubuntu/581497#58149
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.. _github gist:
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https://gist.github.com/application2000/73fd6f4bf1be6600a2cf9f56315a2d91
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Easy steps for installing GCC 5.1.0:
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.. code-block:: console
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% gcc_version=5.1.0
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% wget https://ftp.gnu.org/gnu/gcc/gcc-${gcc_version}/gcc-${gcc_version}.tar.bz2
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% wget https://ftp.gnu.org/gnu/gcc/gcc-${gcc_version}/gcc-${gcc_version}.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-${gcc_version}.tar.bz2.sig`
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% if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
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% tar -xvjf gcc-${gcc_version}.tar.bz2
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% cd gcc-${gcc_version}
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% ./contrib/download_prerequisites
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% cd ..
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% mkdir gcc-${gcc_version}-build
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% cd gcc-${gcc_version}-build
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% $PWD/../gcc-${gcc_version}/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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https://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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This method will add an absolute path to the rpath of all executables. That's
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fine for local development. If you want to distribute the binaries you build
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so that they can run on older systems, copy ``libstdc++.so.6`` into the
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``lib/`` directory. All of LLVM's shipping binaries have an rpath pointing at
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``$ORIGIN/../lib``, so they will find ``libstdc++.so.6`` there. Non-distributed
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binaries don't have an rpath set and won't find ``libstdc++.so.6``. Pass
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``-DLLVM_LOCAL_RPATH="$HOME/toolchains/lib64"`` to cmake to add an absolute
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path to ``libstdc++.so.6`` as above. Since these binaries are not distributed,
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having an absolute local path is fine for them.
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When you build Clang, you will need to give *it* access to modern C++
|
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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
|
||
give you some basic information about the LLVM environment.
|
||
|
||
The later sections of this guide describe the `general layout`_ of the LLVM
|
||
source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
|
||
more information about LLVM or to get help via e-mail.
|
||
|
||
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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|
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This is the top level directory of the LLVM source tree.
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|
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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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|
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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
|
||
begin to compile it. LLVM is distributed as a number of different
|
||
subprojects. Each one has its own download which is a TAR archive that is
|
||
compressed with the gzip program.
|
||
|
||
The files are as follows, with *x.y* marking the version number:
|
||
|
||
``llvm-x.y.tar.gz``
|
||
|
||
Source release for the LLVM libraries and tools.
|
||
|
||
``cfe-x.y.tar.gz``
|
||
|
||
Source release for the Clang frontend.
|
||
|
||
.. _checkout:
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Checkout LLVM from Git
|
||
----------------------
|
||
|
||
You can also checkout the source code for LLVM from Git.
|
||
|
||
.. note::
|
||
|
||
Passing ``--config core.autocrlf=false`` should not be required in
|
||
the future after we adjust the .gitattribute settings correctly, but
|
||
is required for Windows users at the time of this writing.
|
||
|
||
Simply run:
|
||
|
||
.. code-block:: console
|
||
|
||
% git clone https://github.com/llvm/llvm-project.git
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|
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or on Windows,
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||
|
||
.. code-block:: console
|
||
|
||
% git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git
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||
|
||
This will create an '``llvm-project``' directory in the current directory and
|
||
fully populate it with all of the source code, test directories, and local
|
||
copies of documentation files for LLVM and all the related subprojects. Note
|
||
that unlike the tarballs, which contain each subproject in a separate file, the
|
||
git repository contains all of the projects together.
|
||
|
||
If you want to get a specific release (as opposed to the most recent revision),
|
||
you can check out a tag after cloning the repository. E.g., `git checkout
|
||
llvmorg-6.0.1` inside the ``llvm-project`` directory created by the above
|
||
command. Use `git tag -l` to list all of them.
|
||
|
||
Sending patches
|
||
^^^^^^^^^^^^^^^
|
||
|
||
Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
|
||
|
||
We don't currently accept github pull requests, so you'll need to send patches
|
||
either via emailing to llvm-commits, or, preferably, via :ref:`Phabricator
|
||
<phabricator-reviews>`.
|
||
|
||
You'll generally want to make sure your branch has a single commit,
|
||
corresponding to the review you wish to send, up-to-date with the upstream
|
||
``origin/main`` branch, and doesn't contain merges. Once you have that, you
|
||
can start `a Phabricator review <Phabricator.html>`_ (or use ``git show`` or
|
||
``git format-patch`` to output the diff, and attach it to an email message).
|
||
|
||
However, using the "Arcanist" tool is often easier. After `installing
|
||
arcanist`_, you can upload the latest commit using:
|
||
|
||
.. code-block:: console
|
||
|
||
% arc diff HEAD~1
|
||
|
||
Additionally, before sending a patch for review, please also try to ensure it's
|
||
formatted properly. We use ``clang-format`` for this, which has git integration
|
||
through the ``git-clang-format`` script. On some systems, it may already be
|
||
installed (or be installable via your package manager). If so, you can simply
|
||
run it -- the following command will format only the code changed in the most
|
||
recent commit:
|
||
|
||
.. code-block:: console
|
||
|
||
% git clang-format HEAD~1
|
||
|
||
Note that this modifies the files, but doesn't commit them -- you'll likely want
|
||
to run
|
||
|
||
.. code-block:: console
|
||
|
||
% git commit --amend -a
|
||
|
||
in order to update the last commit with all pending changes.
|
||
|
||
.. note::
|
||
If you don't already have ``clang-format`` or ``git clang-format`` installed
|
||
on your system, the ``clang-format`` binary will be built alongside clang, and
|
||
the git integration can be run from
|
||
``clang/tools/clang-format/git-clang-format``.
|
||
|
||
|
||
.. _commit_from_git:
|
||
|
||
For developers to commit changes from Git
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
Once a patch is reviewed, you should rebase it, re-test locally, and commit the
|
||
changes to LLVM's main branch. This is done using `git push` if you have the
|
||
required access rights. See `committing a change
|
||
<Phabricator.html#committing-a-change>`_ for Phabricator based commits or
|
||
`obtaining commit access <DeveloperPolicy.html#obtaining-commit-access>`_
|
||
for commit access.
|
||
|
||
Here is an example workflow using git. This workflow assumes you have an
|
||
accepted commit on the branch named `branch-with-change`.
|
||
|
||
.. code-block:: console
|
||
|
||
# Go to the branch with your accepted commit.
|
||
% git checkout branch-with-change
|
||
# Rebase your change onto the latest commits on Github.
|
||
% git pull --rebase origin main
|
||
# Rerun the appropriate tests if needed.
|
||
% ninja check-$whatever
|
||
# Check that the list of commits about to be pushed is correct.
|
||
% git log origin/main...HEAD --oneline
|
||
# Push to Github.
|
||
% git push origin HEAD:main
|
||
|
||
LLVM currently has a linear-history policy, which means that merge commits are
|
||
not allowed. The `llvm-project` repo on github is configured to reject pushes
|
||
that include merges, so the `git rebase` step above is required.
|
||
|
||
Please ask for help if you're having trouble with your particular git workflow.
|
||
|
||
|
||
.. _git_pre_push_hook:
|
||
|
||
Git pre-push hook
|
||
^^^^^^^^^^^^^^^^^
|
||
|
||
We include an optional pre-push hook that run some sanity checks on the revisions
|
||
you are about to push and ask confirmation if you push multiple commits at once.
|
||
You can set it up (on Unix systems) by running from the repository root:
|
||
|
||
.. code-block:: console
|
||
|
||
% ln -sf ../../llvm/utils/git/pre-push.py .git/hooks/pre-push
|
||
|
||
Bisecting commits
|
||
^^^^^^^^^^^^^^^^^
|
||
|
||
See `Bisecting LLVM code <GitBisecting.html>`_ for how to use ``git bisect``
|
||
on LLVM.
|
||
|
||
Reverting a change
|
||
^^^^^^^^^^^^^^^^^^
|
||
|
||
When reverting changes using git, the default message will say "This reverts
|
||
commit XYZ". Leave this at the end of the commit message, but add some details
|
||
before it as to why the commit is being reverted. A brief explanation and/or
|
||
links to bots that demonstrate the problem are sufficient.
|
||
|
||
Local LLVM Configuration
|
||
------------------------
|
||
|
||
Once checked out 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. |
|
||
+-------------------------+----------------------------------------------------+
|
||
| PYTHON_EXECUTABLE | Forces CMake to use a specific Python version by |
|
||
| | passing a path to a Python interpreter. By default |
|
||
| | the Python version of the interpreter in your PATH |
|
||
| | is used. |
|
||
+-------------------------+----------------------------------------------------+
|
||
| LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
|
||
| | targets will be built and linked into llvm. |
|
||
| | 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, AVR, BPF, Hexagon, Lanai, |
|
||
| | Mips, MSP430, NVPTX, PowerPC, RISCV, Sparc, |
|
||
| | SystemZ, WebAssembly, 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_PROJECTS | A semicolon-delimited list selecting which of the |
|
||
| | other LLVM subprojects to additionally build. (Only|
|
||
| | effective when using a side-by-side project layout |
|
||
| | e.g. via git). The default list is empty. Can |
|
||
| | include: clang, libcxx, libcxxabi, libunwind, lldb,|
|
||
| | compiler-rt, lld, polly, or debuginfo-tests. |
|
||
+-------------------------+----------------------------------------------------+
|
||
| 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. Sphinx version |
|
||
| | 1.5 or later recommended. |
|
||
+-------------------------+----------------------------------------------------+
|
||
| 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``. This option is|
|
||
| | not available on Windows. |
|
||
+-------------------------+----------------------------------------------------+
|
||
| 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=/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 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 macOS
|
||
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
|
||
<https://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
|
||
`<https://llvm.org/doxygen/>`_. The following is a brief introduction to code
|
||
layout:
|
||
|
||
``llvm/cmake``
|
||
--------------
|
||
Genereates system build files.
|
||
|
||
``llvm/cmake/modules``
|
||
Build configuration for llvm user defined options. Checks compiler version and
|
||
linker flags.
|
||
|
||
``llvm/cmake/platforms``
|
||
Toolchain configuration for Android NDK, iOS systems and non-Windows hosts to
|
||
target MSVC.
|
||
|
||
``llvm/examples``
|
||
-----------------
|
||
|
||
- Some simple examples showing how to use LLVM as a compiler for a custom
|
||
language - including lowering, optimization, and code generation.
|
||
|
||
- Kaleidoscope Tutorial: Kaleidoscope language tutorial run through the
|
||
implementation of a nice little compiler for a non-trivial language
|
||
including a hand-written lexer, parser, AST, as well as code generation
|
||
support using LLVM- both static (ahead of time) and various approaches to
|
||
Just In Time (JIT) compilation.
|
||
`Kaleidoscope Tutorial for complete beginner
|
||
<https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/index.html>`_.
|
||
|
||
- BuildingAJIT: Examples of the `BuildingAJIT tutorial
|
||
<https://llvm.org/docs/tutorial/BuildingAJIT1.html>`_ that shows how LLVM’s
|
||
ORC JIT APIs interact with other parts of LLVM. It also, teaches how to
|
||
recombine them to build a custom JIT that is suited to your use-case.
|
||
|
||
``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 ``cmake``. They wrap "standard" UNIX and
|
||
C header files. Source code can include these header files which
|
||
automatically take care of the conditional #includes that ``cmake``
|
||
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/``
|
||
|
||
The libraries represent and process code at machine code level. Handles
|
||
assembly and object-file emission.
|
||
|
||
``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/bindings``
|
||
----------------------
|
||
|
||
Contains bindings for the LLVM compiler infrastructure to allow
|
||
programs written in languages other than C or C++ to take advantage of the LLVM
|
||
infrastructure.
|
||
LLVM project provides language bindings for Go, OCaml and Python.
|
||
|
||
``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. This comes in a ``separate git repository
|
||
<https://github.com/llvm/llvm-test-suite>``, because it contains a
|
||
large amount of third-party code under a variety of licenses. 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.
|
||
|
||
``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.
|
||
|
||
``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.
|
||
|
||
If you are having problems with limited memory and build time, please try
|
||
building with ninja instead of make. Please consider configuring the
|
||
following options with cmake:
|
||
|
||
* -G Ninja
|
||
Setting this option will allow you to build with ninja instead of make.
|
||
Building with ninja significantly improves your build time, especially with
|
||
incremental builds, and improves your memory usage.
|
||
|
||
* -DLLVM_USE_LINKER
|
||
Setting this option to lld will significantly reduce linking time for LLVM
|
||
executables on ELF-based platforms, such as Linux. If you are building LLVM
|
||
for the first time and lld is not available to you as a binary package, then
|
||
you may want to use the gold linker as a faster alternative to GNU ld.
|
||
|
||
* -DCMAKE_BUILD_TYPE
|
||
|
||
- Debug --- This is the default build type. This disables optimizations while
|
||
compiling LLVM and enables debug info. On ELF-based platforms (e.g. Linux)
|
||
linking with debug info may consume a large amount of memory.
|
||
|
||
- Release --- Turns on optimizations and disables debug info. Combining the
|
||
Release build type with -DLLVM_ENABLE_ASSERTIONS=ON may be a good trade-off
|
||
between speed and debugability during development, particularly for running
|
||
the test suite.
|
||
|
||
* -DLLVM_ENABLE_ASSERTIONS
|
||
This option defaults to ON for Debug builds and defaults to OFF for Release
|
||
builds. As mentioned in the previous option, using the Release build type and
|
||
enabling assertions may be a good alternative to using the Debug build type.
|
||
|
||
* -DLLVM_PARALLEL_LINK_JOBS
|
||
Set this equal to number of jobs you wish to run simultaneously. This is
|
||
similar to the -j option used with make, but only for link jobs. This option
|
||
can only be used with ninja. You may wish to use a very low number of jobs,
|
||
as this will greatly reduce the amount of memory used during the build
|
||
process. If you have limited memory, you may wish to set this to 1.
|
||
|
||
* -DLLVM_TARGETS_TO_BUILD
|
||
Set this equal to the target you wish to build. You may wish to set this to
|
||
X86; however, you will find a full list of targets within the
|
||
llvm-project/llvm/lib/Target directory.
|
||
|
||
* -DLLVM_OPTIMIZED_TABLEGEN
|
||
Set this to ON to generate a fully optimized tablegen during your build. This
|
||
will significantly improve your build time. This is only useful if you are
|
||
using the Debug build type.
|
||
|
||
* -DLLVM_ENABLE_PROJECTS
|
||
Set this equal to the projects you wish to compile (e.g. clang, lld, etc.) If
|
||
compiling more than one project, separate the items with a semicolon. Should
|
||
you run into issues with the semicolon, try surrounding it with single quotes.
|
||
|
||
* -DCLANG_ENABLE_STATIC_ANALYZER
|
||
Set this option to OFF if you do not require the clang static analyzer. This
|
||
should improve your build time slightly.
|
||
|
||
* -DLLVM_USE_SPLIT_DWARF
|
||
Consider setting this to ON if you require a debug build, as this will ease
|
||
memory pressure on the linker. This will make linking much faster, as the
|
||
binaries will not contain any of the debug information; however, this will
|
||
generate the debug information in the form of a DWARF object file (with the
|
||
extension .dwo). This only applies to host platforms using ELF, such as Linux.
|
||
|
||
.. _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 <https://llvm.org/>`_
|
||
* `LLVM Doxygen Tree <https://llvm.org/doxygen/>`_
|
||
* `Starting a Project that Uses LLVM <https://llvm.org/docs/Projects.html>`_
|
||
|
||
.. _installing arcanist: https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/
|