[docs] Update README and GettingStarted
Funnel fetching and building LLVM instructions into GettingStarted. Modernize the build steps a little. Remove comments saying CMAKE_BUILD_TYPE defaults to Debug as that's not true anymore (must explicitly pass it). Reviewed By: MaskRay, hans Differential Revision: https://reviews.llvm.org/D145413
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Arthur Eubanks
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README.md
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README.md
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@ -1,27 +1,16 @@
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# The LLVM Compiler Infrastructure
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This directory and its sub-directories contain the source code for LLVM,
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a toolkit for the construction of highly optimized compilers,
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optimizers, and run-time environments.
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The README briefly describes how to get started with building LLVM.
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For more information on how to contribute to the LLVM project, please
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take a look at the
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[Contributing to LLVM](https://llvm.org/docs/Contributing.html) guide.
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## Getting Started with the LLVM System
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Taken from [here](https://llvm.org/docs/GettingStarted.html).
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### Overview
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Welcome to the LLVM project!
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This repository contains the source code for LLVM, a toolkit for the
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construction of highly optimized compilers, optimizers, and run-time
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environments.
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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 convert them 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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bitcode optimizer.
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C-like languages use the [Clang](http://clang.llvm.org/) frontend. This
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component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode
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@ -31,92 +20,20 @@ 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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The LLVM Getting Started documentation may be out of date. The [Clang
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Getting Started](http://clang.llvm.org/get_started.html) page might have more
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accurate information.
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This is an example work-flow and configuration to get and build the LLVM source:
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1. Checkout LLVM (including related sub-projects 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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2. Configure and build LLVM and Clang:
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* ``cd llvm-project``
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* ``cmake -S llvm -B build -G <generator> [options]``
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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='...'`` and ``-DLLVM_ENABLE_RUNTIMES='...'`` ---
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semicolon-separated list of the LLVM sub-projects and runtimes you'd like to
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additionally build. ``LLVM_ENABLE_PROJECTS`` can include any of: clang,
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clang-tools-extra, cross-project-tests, flang, libc, libclc, lld, lldb,
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mlir, openmp, polly, or pstl. ``LLVM_ENABLE_RUNTIMES`` can include any of
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libcxx, libcxxabi, libunwind, compiler-rt, libc or openmp. Some runtime
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projects can be specified either in ``LLVM_ENABLE_PROJECTS`` or in
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``LLVM_ENABLE_RUNTIMES``.
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For example, to build LLVM, Clang, libcxx, and libcxxabi, use
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``-DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"``.
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* ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
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path name of where you want the LLVM tools and libraries to be installed
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(default ``/usr/local``). Be careful if you install runtime libraries: if
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your system uses those provided by LLVM (like libc++ or libc++abi), you
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must not overwrite your system's copy of those libraries, since that
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could render your system unusable. In general, using something like
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``/usr`` is not advised, but ``/usr/local`` is fine.
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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 build [-- [options] <target>]`` or your build system specified above
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directly.
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* The default target (i.e. ``ninja`` or ``make``) will build all of 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 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 option
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``-j NNN``, where ``NNN`` is the number of parallel jobs to run.
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In most cases, you get the best performance if you specify the number of CPU threads you have.
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On some Unix systems, you can specify this with ``-j$(nproc)``.
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* For more information see [CMake](https://llvm.org/docs/CMake.html).
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## Getting the Source Code and Building LLVM
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Consult the
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[Getting Started with LLVM](https://llvm.org/docs/GettingStarted.html#getting-started-with-llvm)
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page for detailed information on configuring and compiling LLVM. You can visit
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[Directory Layout](https://llvm.org/docs/GettingStarted.html#directory-layout)
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to learn about the layout of the source code tree.
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[Getting Started with LLVM](https://llvm.org/docs/GettingStarted.html#getting-the-source-code-and-building-llvm)
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page for information on building and running LLVM.
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For information on how to contribute to the LLVM project, please take a look at
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the [Contributing to LLVM](https://llvm.org/docs/Contributing.html) guide.
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## Getting in touch
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Join [LLVM Discourse forums](https://discourse.llvm.org/), [discord chat](https://discord.gg/xS7Z362) or #llvm IRC channel on [OFTC](https://oftc.net/).
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Join the [LLVM Discourse forums](https://discourse.llvm.org/), [Discord
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chat](https://discord.gg/xS7Z362), or #llvm IRC channel on
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[OFTC](https://oftc.net/).
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The LLVM project has adopted a [code of conduct](https://llvm.org/docs/CodeOfConduct.html) for
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participants to all modes of communication within the project.
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@ -191,9 +191,6 @@ used variables that control features of LLVM and enabled subprojects.
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**CMAKE_BUILD_TYPE**:STRING
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This configures the optimization level for ``make`` or ``ninja`` builds.
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The default ``CMAKE_BUILD_TYPE`` is set to ``Debug`` but you should
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carefully read the list below to figure out what configuration matches
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your use case the best.
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Possible values:
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@ -27,28 +27,23 @@ 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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#. Check out LLVM (including 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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* Or, on windows:
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``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> -DCMAKE_BUILD_TYPE=<type> [options] ../llvm``
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* ``cmake -S llvm -B build -G <generator> [options]``
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Some common build system generators are:
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@ -59,27 +54,30 @@ This is an example workflow and configuration to get and build the LLVM source:
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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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* See the `CMake docs
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<https://cmake.org/cmake/help/latest/manual/cmake-generators.7.html>`_
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for a more comprehensive list.
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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, lldb, compiler-rt, lld, polly, or cross-project-tests.
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clang-tools-extra, lldb, lld, 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" -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"``.
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For example, to build LLVM, Clang, and LLD, use
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``-DLLVM_ENABLE_PROJECTS="clang;lld"``.
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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`` --- Controls optimization level and debug information
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of the build. The default value is ``Debug`` which fits people who want
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to work on LLVM or its libraries. ``Release`` is a better fit for most
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users of LLVM and Clang. For more detailed information see
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:ref:`CMAKE_BUILD_TYPE <cmake_build_type>`.
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* ``-DCMAKE_BUILD_TYPE=type`` --- Controls optimization level and debug
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information of the build. Valid options for *type* are ``Debug``,
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``Release``, ``RelWithDebInfo``, and ``MinSizeRel``. For more detailed
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information see :ref:`CMAKE_BUILD_TYPE <cmake_build_type>`.
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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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* ``-DLLVM_ENABLE_ASSERTIONS=ON`` --- Compile with assertion checks enabled
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(default is ON for Debug builds, OFF 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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@ -98,10 +96,19 @@ This is an example workflow and configuration to get and build the LLVM source:
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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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* A basic CMake and build/test invocation which only builds LLVM and no other
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subprojects:
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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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``cmake -S llvm -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug``
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``ninja -C build check-llvm``
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This will setup an LLVM build with debugging info, then compile LLVM and
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run LLVM tests.
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* For more detailed information on CMake options, see `CMake <CMake.html>`__
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* If you get build or test failures, see `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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@ -601,8 +608,11 @@ used by people developing LLVM.
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| | out-of-tree targets. The default value includes: |
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| | ``AArch64, AMDGPU, ARM, AVR, BPF, Hexagon, Lanai, |
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| | Mips, MSP430, NVPTX, PowerPC, RISCV, Sparc, |
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| | SystemZ, WebAssembly, X86, XCore``. |
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| | |
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| | SystemZ, WebAssembly, X86, XCore``. Setting this |
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| | to ``"host"`` will only compile the host |
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| | architecture (e.g. equivalent to specifying ``X86``|
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| | on an x86 host machine) can |
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| | significantly speed up compile and test times. |
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+-------------------------+----------------------------------------------------+
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| LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
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| | code This is disabled by default because it is |
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