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# The LLVM Compiler Infrastructure
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This directory and its sub-directories contain 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.
For more information on how to contribute to the LLVM project, please
take a look at the
[Contributing to LLVM](https://llvm.org/docs/Contributing.html) guide.

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## Getting Started with the LLVM System

Taken from https://llvm.org/docs/GettingStarted.html.

### Overview

Welcome to the LLVM project!

The LLVM project has multiple components. The core of the project is
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
bitcode optimizer.  It also contains basic regression tests.

C-like languages use 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 bitcode
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-- and from there into object files, using LLVM.

Other components include:
the [libc++ C++ standard library](https://libcxx.llvm.org),
the [LLD linker](https://lld.llvm.org), and more.

### Getting the Source Code and Building LLVM

The LLVM Getting Started documentation may be out of date.  The [Clang
Getting Started](http://clang.llvm.org/get_started.html) page might have more
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``

     * Or, on windows, ``git clone --config core.autocrlf=false
    https://github.com/llvm/llvm-project.git``

2. Configure and build LLVM and Clang:

     * ``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)
          build files. Most llvm developers use Ninja.
        * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
        * ``Visual Studio`` --- for generating Visual Studio projects and
          solutions.
        * ``Xcode`` --- for generating Xcode projects.

        Some Common options:

        * ``-DLLVM_ENABLE_PROJECTS='...'`` --- semicolon-separated list of the LLVM
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          sub-projects 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
          ``-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi"``.

        * ``-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``).

        * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
          Release, RelWithDebInfo, and MinSizeRel. Default is Debug.

        * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
          (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.

        * The ``check-all`` target (i.e. ``ninja check-all``) will run the
          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
          parallel build.  That's done by default in Ninja; for ``make``, use the option
          ``-j NNN``, where ``NNN`` is the number of parallel jobs, e.g. the number of
          CPUs you have.
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      * For more information see [CMake](https://llvm.org/docs/CMake.html)

Consult the
[Getting Started with LLVM](https://llvm.org/docs/GettingStarted.html#getting-started-with-llvm)
page for detailed information on configuring and compiling LLVM. You can visit
[Directory Layout](https://llvm.org/docs/GettingStarted.html#directory-layout)
to learn about the layout of the source code tree.