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# LLVM Makefile Guide

- Introduction
- General Concepts
  - Projects
  - Variable Values
  - Including Makefiles
    - `Makefile`
    - `Makefile.common`
    - `Makefile.config`
    - `Makefile.rules`
    - Comments
- Tutorial
  - Libraries
    - Bitcode Modules
    - Loadable Modules
  - Tools
    - JIT Tools
- Targets Supported
  - `all` (default)
  - `all-local`
  - `check`
  - `check-local`
  - `clean`
  - `clean-local`
  - `dist`
  - `dist-check`
  - `dist-clean`
  - `install`
  - `preconditions`
  - `printvars`
  - `reconfigure`
  - `spotless`
  - `tags`
  - `uninstall`
- Variables
  - Control Variables
  - Override Variables
  - Readable Variables
  - Internal Variables

## Introduction

This document provides usage information about the LLVM makefile system. While loosely patterned after the BSD makefile system, LLVM has taken a departure from BSD in order to implement additional features needed by LLVM. Although makefile systems, such as `automake`, were attempted at one point, it has become clear that the features needed by LLVM and the `Makefile` norm are too great to use a more limited tool. Consequently, LLVM requires simply GNU Make 3.79, a widely portable makefile processor. LLVM unabashedly makes heavy use of the features of GNU Make so the dependency on GNU Make is firm. If you’re not familiar with `make`, it is recommended that you read the GNU Makefile Manual.

While this document is rightly part of the LLVM Programmer’s Manual, it is treated separately here because of the volume of content and because it is often an early source of bewilderment for new developers.

## General Concepts

The LLVM Makefile System is the component of LLVM that is responsible for building the software, testing it, generating distributions, checking those distributions, installing and uninstalling, etc. It consists of a several files throughout the source tree. These files and other general concepts are described in this section.

### Projects

The LLVM Makefile System is quite generous. It not only builds its own software, but it can build yours too. Built into the system is knowledge of the `llvm/projects` directory. Any directory under `projects` that has both a `configure` script and a `Makefile` is assumed to be a project that uses the LLVM Makefile system. Building software that uses LLVM does not require the LLVM Makefile System nor even placement in the `llvm/projects` directory. However, doing so will allow your project to get up and running quickly by utilizing the built-in features that are used to compile LLVM. LLVM compiles itself using the same features of the makefile system as used for projects.

For complete details on setting up your projects configuration, simply mimic the `llvm/projects/sample` project. Or for further details, consult the Projects page.

### Variable Values

To use the makefile system, you simply create a file named `Makefile` in your directory and declare values for certain variables. The variables and values that you select determine what the makefile system will do. These variables enable rules and processing in the makefile system that automatically Do The Right Thing (C).

### Including Makefiles

Setting variables alone is not enough. You must include into your Makefile additional files that provide the rules of the LLVM Makefile system. The various files involved are described in the sections that follow.

#### `Makefile`

Each directory to participate in the build needs to have a file named `Makefile`. This is the file first read by `make`. It has three sections:

1. Settable Variables — Required that must be set first.
2. `include $(LEVEL)/Makefile.common` — include the LLVM Makefile system.
3. Override Variables — Override variables set by the LLVM Makefile system.

#### `Makefile.common`

Every project must have a `Makefile.common` file at its top source directory. This file serves three purposes:

1. It includes the project’s configuration makefile to obtain values determined by the `configure` script. This is done by including the $(LEVEL)/Makefile.config file.
2. It specifies any other (static) values that are needed throughout the project. Only values that are used in all or a large proportion of the project’s directories should be placed here.
3. It includes the standard rules for the LLVM Makefile system, $(LLVM_SRC_ROOT)/Makefile.rules. This file is the guts of the LLVM `Makefile` system.

#### `Makefile.config`

Every project must have a `Makefile.config` at the top of its build directory. This file is generated by the `configure` script from the pattern provided by the `Makefile.config.in` file located at the top of the project’s source directory. The contents of this file depend largely on what configuration items the project uses, however most projects can get what they need by just relying on LLVM’s configuration found in `$(LLVM_OBJ_ROOT)/Makefile.config`.

#### `Makefile.rules`

This file, located at `$(LLVM_SRC_ROOT)/Makefile.rules` is the heart of the LLVM Makefile System. It provides all the logic, dependencies, and rules for building the targets supported by the system. What it does largely depends on the values of `make` variables that have been set before `Makefile.rules` is included.

#### Comments

User `Makefile`s need not have comments in them unless the construction is unusual or it does not strictly follow the rules and patterns of the LLVM makefile system. Makefile comments are invoked with the pound (`#`) character. The `#` character and any text following it, to the end of the line, are ignored by `make`.

## Tutorial

This section provides some examples of the different kinds of modules you can build with the LLVM makefile system. In general, each directory you provide will build a single object although that object may be composed of additionally compiled components.

### Libraries

Only a few variable definitions are needed to build a regular library. Normally, the makefile system will build all the software into a single `libname.o` (pre-linked) object. This means the library is not searchable and that the distinction between compilation units has been dissolved. Optionally, you can ask for a shared library (.so) or archive library (.a) built. Archive libraries are the default. For example:

    LIBRARYNAME = mylib
    SHARED_LIBRARY = 1
    ARCHIVE_LIBRARY = 1

says to build a library named `mylib` with both a shared library (`mylib.so`) and an archive library (`mylib.a`) version. The contents of all the libraries produced will be the same, they are just constructed differently. Note that you normally do not need to specify the sources involved. The LLVM Makefile system will infer the source files from the contents of the source directory.

The `LOADABLE_MODULE=1` directive can be used in conjunction with `SHARED_LIBRARY=1` to indicate that the resulting shared library should be openable with the `dlopen` function and searchable with the `dlsym` function (or your operating system’s equivalents). While this isn’t strictly necessary on Linux and a few other platforms, it is required on systems like HP-UX and Darwin. You should use `LOADABLE_MODULE` for any shared library that you intend to be loaded into an tool via the `-load` option. Pass documentation has an example of why you might want to do this.

#### Bitcode Modules

In some situations, it is desirable to build a single bitcode module from a variety of sources, instead of an archive, shared library, or bitcode library. Bitcode modules can be specified in addition to any of the other types of libraries by defining the MODULE_NAME variable. For example:

    LIBRARYNAME = mylib
    BYTECODE_LIBRARY = 1
    MODULE_NAME = mymod

will build a module named `mymod.bc` from the sources in the directory. This module will be an aggregation of all the bitcode modules derived from the sources. The example will also build a bitcode archive containing a bitcode module for each compiled source file. The difference is subtle, but important depending on how the module or library is to be linked.

#### Loadable Modules

In some situations, you need to create a loadable module. Loadable modules can be loaded into programs like `opt` or `llc` to specify additional passes to run or targets to support. Loadable modules are also useful for debugging a pass or providing a pass with another package if that pass can’t be included in LLVM.

LLVM provides complete support for building such a module. All you need to do is use the `LOADABLE_MODULE` variable in your `Makefile`. For example, to build a loadable module named `MyMod` that uses the LLVM libraries `LLVMSupport.a` and `LLVMSystem.a`, you would specify:

    LIBRARYNAME := MyMod
    LOADABLE_MODULE := 1
    LINK_COMPONENTS := support system

Use of the `LOADABLE_MODULE` facility implies several things:

1. There will be no “`lib`” prefix on the module. This differentiates it from

     a standard shared library of the same name.

2. The SHARED_LIBRARY variable is turned on.

3. The LINK_LIBS_IN_SHARED variable is turned on.

A loadable module is loaded by LLVM via the facilities of libtool’s libltdl library which is part of `lib/System` implementation.

### Tools

For building executable programs (tools), you must provide the name of the tool and the names of the libraries you wish to link with the tool. For example:

    TOOLNAME = mytool
    USEDLIBS = mylib
    LINK_COMPONENTS = support system

says that we are to build a tool name `mytool` and that it requires three libraries: `mylib`, `LLVMSupport.a` and `LLVMSystem.a`.

Note that two different variables are used to indicate which libraries are linked: `USEDLIBS` and `LLVMLIBS`. This distinction is necessary to support projects. `LLVMLIBS` refers to the LLVM libraries found in the LLVM object directory. `USEDLIBS` refers to the libraries built by your project. In the case of building LLVM tools, `USEDLIBS` and `LLVMLIBS` can be used interchangeably since the “project” is LLVM itself and `USEDLIBS` refers to the same place as `LLVMLIBS`.

Also note that there are two different ways of specifying a library: with a `.a` suffix and without. Without the suffix, the entry refers to the re-linked (.o) file which will include all symbols of the library. This is useful, for example, to include all passes from a library of passes. If the `.a` suffix is used then the library is linked as a searchable library (with the `-l` option). In this case, only the symbols that are unresolved at that point will be resolved from the library, if they exist. Other (unreferenced) symbols will not be included when the `.a` syntax is used. Note that in order to use the `.a` suffix, the library in question must have been built with the `ARCHIVE_LIBRARY` option set.

#### JIT Tools

Many tools will want to use the JIT features of LLVM. To do this, you simply specify that you want an execution ‘engine’, and the makefiles will automatically link in the appropriate JIT for the host or an interpreter if none is available:

    TOOLNAME = my_jit_tool
    USEDLIBS = mylib
    LINK_COMPONENTS = engine

Of course, any additional libraries may be listed as other components. To get a full understanding of how this changes the linker command, it is recommended that you:

    % cd examples/Fibonacci
    % make VERBOSE=1

## Targets Supported

This section describes each of the targets that can be built using the LLVM Makefile system. Any target can be invoked from any directory but not all are applicable to a given directory (e.g. “check”, “dist” and “install” will always operate as if invoked from the top level directory).

Target Name | Implied Targets | Target Description
--- | --- | ---
`all` |  | Compile the software recursively. Default target.
`all-local` |  | Compile the software in the local directory only.
`check` |  | Change to the `test` directory in a project and run the test suite there.
`check-local` |  | Run a local test suite. Generally this is only defined in the `Makefile` of the project’s `test` directory.
`clean` |  | Remove built objects recursively.
`clean-local` |  | Remove built objects from the local directory only.
`dist` | `all` | Prepare a source distribution tarball.
`dist-check` | `all` | Prepare a source distribution tarball and check that it builds.
`dist-clean` | `clean` | Clean source distribution tarball temporary files.
`install` | `all` | Copy built objects to installation directory.
`preconditions` | `all` | Check to make sure configuration and makefiles are up to date.
`printvars` | `all` | Prints variables defined by the makefile system (for debugging).
`tags` |  | Make C and C++ tags files for emacs and vi.
`uninstall` |  | Remove built objects from installation directory.

### `all` (default)

When you invoke `make` with no arguments, you are implicitly instructing it to seek the `all` target (goal). This target is used for building the software recursively and will do different things in different directories. For example, in a `lib` directory, the `all` target will compile source files and generate libraries. But, in a `tools` directory, it will link libraries and generate executables.

### `all-local`

This target is the same as all but it operates only on the current directory instead of recursively.

### `check`

This target can be invoked from anywhere within a project’s directories but always invokes the check-local target in the project’s `test` directory, if it exists and has a `Makefile`. A warning is produced otherwise. If TESTSUITE is defined on the `make` command line, it will be passed down to the invocation of `make check-local` in the `test` directory. The intended usage for this is to assist in running specific suites of tests. If `TESTSUITE` is not set, the implementation of `check-local` should run all normal tests. It is up to the project to define what different values for `TESTSUTE` will do. See the Testing Guide for further details.

### `check-local`

This target should be implemented by the `Makefile` in the project’s `test` directory. It is invoked by the `check` target elsewhere. Each project is free to define the actions of `check-local` as appropriate for that project. The LLVM project itself uses the Lit testing tool to run a suite of feature and regression tests. Other projects may choose to use lit or any other testing mechanism.

### `clean`

This target cleans the build directory, recursively removing all things that the Makefile builds. The cleaning rules have been made guarded so they shouldn’t go awry (via `rm -f $(UNSET_VARIABLE)/*` which will attempt to erase the entire directory structure).

### `clean-local`

This target does the same thing as `clean` but only for the current (local) directory.

### `dist`

This target builds a distribution tarball. It first builds the entire project using the `all` target and then tars up the necessary files and compresses it. The generated tarball is sufficient for a casual source distribution, but probably not for a release (see `dist-check`).

### `dist-check`

This target does the same thing as the `dist` target but also checks the distribution tarball. The check is made by unpacking the tarball to a new directory, configuring it, building it, installing it, and then verifying that the installation results are correct (by comparing to the original build). This target can take a long time to run but should be done before a release goes out to make sure that the distributed tarball can actually be built into a working release.

### `dist-clean`

This is a special form of the `clean` clean target. It performs a normal `clean` but also removes things pertaining to building the distribution.

### `install`

This target finalizes shared objects and executables and copies all libraries, headers, executables and documentation to the directory given with the `--prefix` option to `configure`. When completed, the prefix directory will have everything needed to use LLVM.

The LLVM makefiles can generate complete internal documentation for all the classes by using `doxygen`. By default, this feature is not enabled because it takes a long time and generates a massive amount of data (>100MB). If you want this feature, you must configure LLVM with the –enable-doxygen switch and ensure that a modern version of doxygen (1.3.7 or later) is available in your `PATH`. You can download doxygen from here.

### `preconditions`

This utility target checks to see if the `Makefile` in the object directory is older than the `Makefile` in the source directory and copies it if so. It also reruns the `configure` script if that needs to be done and rebuilds the `Makefile.config` file similarly. Users may overload this target to ensure that sanity checks are run before any building of targets as all the targets depend on `preconditions`.

### `printvars`

This utility target just causes the LLVM makefiles to print out some of the makefile variables so that you can double check how things are set.

### `reconfigure`

This utility target will force a reconfigure of LLVM or your project. It simply runs `$(PROJ_OBJ_ROOT)/config.status --recheck` to rerun the configuration tests and rebuild the configured files. This isn’t generally useful as the makefiles will reconfigure themselves whenever its necessary.

### `spotless`

Warning

Use with caution!

This utility target, only available when `$(PROJ_OBJ_ROOT)` is not the same as `$(PROJ_SRC_ROOT)`, will completely clean the `$(PROJ_OBJ_ROOT)` directory by removing its content entirely and reconfiguring the directory. This returns the `$(PROJ_OBJ_ROOT)` directory to a completely fresh state. All content in the directory except configured files and top-level makefiles will be lost.

### `tags`

This target will generate a `TAGS` file in the top-level source directory. It is meant for use with emacs, XEmacs, or ViM. The TAGS file provides an index of symbol definitions so that the editor can jump you to the definition quickly.

### `uninstall`

This target is the opposite of the `install` target. It removes the header, library and executable files from the installation directories. Note that the directories themselves are not removed because it is not guaranteed that LLVM is the only thing installing there (e.g. `--prefix=/usr`).

## Variables

Variables are used to tell the LLVM Makefile System what to do and to obtain information from it. Variables are also used internally by the LLVM Makefile System. Variable names that contain only the upper case alphabetic letters and underscore are intended for use by the end user. All other variables are internal to the LLVM Makefile System and should not be relied upon nor modified. The sections below describe how to use the LLVM Makefile variables.

### Control Variables

Variables listed in the table below should be set before the inclusion of $(LEVEL)/Makefile.common. These variables provide input to the LLVM make system that tell it what to do for the current directory.

`BUILD_ARCHIVE`
  If set to any value, causes an archive (.a) library to be built.
`BUILT_SOURCES`
  Specifies a set of source files that are generated from other source files. These sources will be built before any other target processing to ensure they are present.
`BYTECODE_LIBRARY`
  If set to any value, causes a bitcode library (.bc) to be built.
`CONFIG_FILES`
  Specifies a set of configuration files to be installed.
`DEBUG_SYMBOLS`
  If set to any value, causes the build to include debugging symbols even in optimized objects, libraries and executables. This alters the flags specified to the compilers and linkers. Debugging isn’t fun in an optimized build, but it is possible.
`DIRS`
  Specifies a set of directories, usually children of the current directory, that should also be made using the same goal. These directories will be built serially.
`DISABLE_AUTO_DEPENDENCIES`
  If set to any value, causes the makefiles to not automatically generate dependencies when running the compiler. Use of this feature is discouraged and it may be removed at a later date.
`ENABLE_OPTIMIZED`
  If set to 1, causes the build to generate optimized objects, libraries and executables. This alters the flags specified to the compilers and linkers. Generally debugging won’t be a fun experience with an optimized build.
`ENABLE_PROFILING`
  If set to 1, causes the build to generate both optimized and profiled objects, libraries and executables. This alters the flags specified to the compilers and linkers to ensure that profile data can be collected from the tools built. Use the `gprof` tool to analyze the output from the profiled tools (`gmon.out`).
`DISABLE_ASSERTIONS`
  If set to 1, causes the build to disable assertions, even if building a debug or profile build. This will exclude all assertion check code from the build. LLVM will execute faster, but with little help when things go wrong.
`EXPERIMENTAL_DIRS`
  Specify a set of directories that should be built, but if they fail, it should not cause the build to fail. Note that this should only be used temporarily while code is being written.
`EXPORTED_SYMBOL_FILE`
  Specifies the name of a single file that contains a list of the symbols to be exported by the linker. One symbol per line.
`EXPORTED_SYMBOL_LIST`
  Specifies a set of symbols to be exported by the linker.
`EXTRA_DIST`
  Specifies additional files that should be distributed with LLVM. All source files, all built sources, all Makefiles, and most documentation files will be automatically distributed. Use this variable to distribute any files that are not automatically distributed.
`KEEP_SYMBOLS`
  If set to any value, specifies that when linking executables the makefiles should retain debug symbols in the executable. Normally, symbols are stripped from the executable.
`LEVEL` (required)
  Specify the level of nesting from the top level. This variable must be set in each makefile as it is used to find the top level and thus the other makefiles.
`LIBRARYNAME`
  Specify the name of the library to be built. (Required For Libraries)
`LINK_COMPONENTS`
  When specified for building a tool, the value of this variable will be passed to the `llvm-config` tool to generate a link line for the tool. Unlike `USEDLIBS` and `LLVMLIBS`, not all libraries need to be specified. The `llvm-config` tool will figure out the library dependencies and add any libraries that are needed. The `USEDLIBS` variable can still be used in conjunction with `LINK_COMPONENTS` so that additional project-specific libraries can be linked with the LLVM libraries specified by `LINK_COMPONENTS`.

`LINK_LIBS_IN_SHARED`
  By default, shared library linking will ignore any libraries specified with the LLVMLIBS or USEDLIBS. This prevents shared libs from including things that will be in the LLVM tool the shared library will be loaded into. However, sometimes it is useful to link certain libraries into your shared library and this option enables that feature.

`LLVMLIBS`
  Specifies the set of libraries from the LLVM `$(ObjDir)` that will be linked into the tool or library.
`LOADABLE_MODULE`
  If set to any value, causes the shared library being built to also be a loadable module. Loadable modules can be opened with the dlopen() function and searched with dlsym (or the operating system’s equivalent). Note that setting this variable without also setting `SHARED_LIBRARY` will have no effect.

`MODULE_NAME`
  Specifies the name of a bitcode module to be created. A bitcode module can be specified in conjunction with other kinds of library builds or by itself. It constructs from the sources a single linked bitcode file.
`NO_INSTALL`
  Specifies that the build products of the directory should not be installed but should be built even if the `install` target is given. This is handy for directories that build libraries or tools that are only used as part of the build process, such as code generators (e.g. `tblgen`).
`OPTIONAL_DIRS`
  Specify a set of directories that may be built, if they exist, but it is not an error for them not to exist.
`PARALLEL_DIRS`
  Specify a set of directories to build recursively and in parallel if the `-j` option was used with `make`.

`SHARED_LIBRARY`
  If set to any value, causes a shared library (`.so`) to be built in addition to any other kinds of libraries. Note that this option will cause all source files to be built twice: once with options for position independent code and once without. Use it only where you really need a shared library.
`SOURCES` (optional)
  Specifies the list of source files in the current directory to be built. Source files of any type may be specified (programs, documentation, config files, etc.). If not specified, the makefile system will infer the set of source files from the files present in the current directory.
`SUFFIXES`
  Specifies a set of filename suffixes that occur in suffix match rules. Only set this if your local `Makefile` specifies additional suffix match rules.
`TARGET`
  Specifies the name of the LLVM code generation target that the current directory builds. Setting this variable enables additional rules to build `.inc` files from `.td` files.

`TESTSUITE`
  Specifies the directory of tests to run in `llvm/test`.
`TOOLNAME`
  Specifies the name of the tool that the current directory should build.
`TOOL_VERBOSE`
  Implies `VERBOSE` and also tells each tool invoked to be verbose. This is handy when you’re trying to see the sub-tools invoked by each tool invoked by the makefile. For example, this will pass `-v` to the GCC compilers which causes it to print out the command lines it uses to invoke sub-tools (compiler, assembler, linker).

`USEDLIBS`
  Specifies the list of project libraries that will be linked into the tool or library.
`VERBOSE`
  Tells the Makefile system to produce detailed output of what it is doing instead of just summary comments. This will generate a LOT of output.

### Override Variables

Override variables can be used to override the default values provided by the LLVM makefile system. These variables can be set in several ways:

- In the environment (e.g. setenv, export) — not recommended.
- On the `make` command line — recommended.
- On the `configure` command line.
- In the Makefile (only after the inclusion of $(LEVEL)/Makefile.common).

The override variables are given below:

`AR` (defaulted)
  Specifies the path to the `ar` tool.
`PROJ_OBJ_DIR`
  The directory into which the products of build rules will be placed. This might be the same as PROJ_SRC_DIR but typically is not.

`PROJ_SRC_DIR`
  The directory which contains the source files to be built.
`BUILD_EXAMPLES`
  If set to 1, build examples in `examples` and (if building Clang) `tools/clang/examples` directories.
`BZIP2` (configured)
  The path to the `bzip2` tool.
`CC` (configured)
  The path to the ‘C’ compiler.
`CFLAGS`
  Additional flags to be passed to the ‘C’ compiler.
`CPPFLAGS`
  Additional flags passed to the C/C++ preprocessor.
`CXX`
  Specifies the path to the C++ compiler.
`CXXFLAGS`
  Additional flags to be passed to the C++ compiler.
`DATE` (configured)
  Specifies the path to the `date` program or any program that can generate the current date and time on its standard output.
`DOT` (configured)
  Specifies the path to the `dot` tool or `false` if there isn’t one.
`ECHO` (configured)
  Specifies the path to the `echo` tool for printing output.
`EXEEXT` (configured)
  Provides the extension to be used on executables built by the makefiles. The value may be empty on platforms that do not use file extensions for executables (e.g. Unix).
`INSTALL` (configured)
  Specifies the path to the `install` tool.
`LDFLAGS` (configured)
  Allows users to specify additional flags to pass to the linker.
`LIBS` (configured)
  The list of libraries that should be linked with each tool.
`LIBTOOL` (configured)
  Specifies the path to the `libtool` tool. This tool is renamed `mklib` by the `configure` script.
`LLVMAS` (defaulted)
  Specifies the path to the `llvm-as` tool.
`LLVMCC`
  Specifies the path to the LLVM capable compiler.
`LLVMCXX`
  Specifies the path to the LLVM C++ capable compiler.
`LLVMGCC` (defaulted)
  Specifies the path to the LLVM version of the GCC ‘C’ Compiler.
`LLVMGXX` (defaulted)
  Specifies the path to the LLVM version of the GCC C++ Compiler.
`LLVMLD` (defaulted)
  Specifies the path to the LLVM bitcode linker tool
`LLVM_OBJ_ROOT` (configured)
  Specifies the top directory into which the output of the build is placed.
`LLVM_SRC_ROOT` (configured)
  Specifies the top directory in which the sources are found.
`LLVM_TARBALL_NAME` (configured)
  Specifies the name of the distribution tarball to create. This is configured from the name of the project and its version number.
`MKDIR` (defaulted)
  Specifies the path to the `mkdir` tool that creates directories.
`ONLY_TOOLS`
  If set, specifies the list of tools to build.
`PLATFORMSTRIPOPTS`
  The options to provide to the linker to specify that a stripped (no symbols) executable should be built.
`RANLIB` (defaulted)
  Specifies the path to the `ranlib` tool.
`RM` (defaulted)
  Specifies the path to the `rm` tool.
`SED` (defaulted)
  Specifies the path to the `sed` tool.
`SHLIBEXT` (configured)
  Provides the filename extension to use for shared libraries.
`TBLGEN` (defaulted)
  Specifies the path to the `tblgen` tool.
`TAR` (defaulted)
  Specifies the path to the `tar` tool.
`ZIP` (defaulted)
  Specifies the path to the `zip` tool.

### Readable Variables

Variables listed in the table below can be used by the user’s Makefile but should not be changed. Changing the value will generally cause the build to go wrong, so don’t do it.

`bindir`
  The directory into which executables will ultimately be installed. This value is derived from the `--prefix` option given to `configure`.
`BuildMode`
  The name of the type of build being performed: Debug, Release, or Profile.
`bytecode_libdir`
  The directory into which bitcode libraries will ultimately be installed. This value is derived from the `--prefix` option given to `configure`.
`ConfigureScriptFLAGS`
  Additional flags given to the `configure` script when reconfiguring.
`DistDir`
  The current directory for which a distribution copy is being made.

`Echo`
  The LLVM Makefile System output command. This provides the `llvm[n]` prefix and starts with `@` so the command itself is not printed by `make`.
`EchoCmd`
  Same as Echo but without the leading `@`.
`includedir`
  The directory into which include files will ultimately be installed. This value is derived from the `--prefix` option given to `configure`.
`libdir`
  The directory into which native libraries will ultimately be installed. This value is derived from the `--prefix` option given to `configure`.
`LibDir`
  The configuration specific directory into which libraries are placed before installation.
`MakefileConfig`
  Full path of the `Makefile.config` file.
`MakefileConfigIn`
  Full path of the `Makefile.config.in` file.
`ObjDir`
  The configuration and directory specific directory where build objects (compilation results) are placed.
`SubDirs`
  The complete list of sub-directories of the current directory as specified by other variables.
`Sources`
  The complete list of source files.
`sysconfdir`
  The directory into which configuration files will ultimately be installed. This value is derived from the `--prefix` option given to `configure`.
`ToolDir`
  The configuration specific directory into which executables are placed before they are installed.
`TopDistDir`
  The top most directory into which the distribution files are copied.
`Verb`
  Use this as the first thing on your build script lines to enable or disable verbose mode. It expands to either an `@` (quiet mode) or nothing (verbose mode).

### Internal Variables

Variables listed below are used by the LLVM Makefile System and considered internal. You should not use these variables under any circumstances.

    Archive
    AR.Flags
    BaseNameSources
    BCCompile.C
    BCCompile.CXX
    BCLinkLib
    C.Flags
    Compile.C
    CompileCommonOpts
    Compile.CXX
    ConfigStatusScript
    ConfigureScript
    CPP.Flags
    CPP.Flags
    CXX.Flags
    DependFiles
    DestArchiveLib
    DestBitcodeLib
    DestModule
    DestSharedLib
    DestTool
    DistAlways
    DistCheckDir
    DistCheckTop
    DistFiles
    DistName
    DistOther
    DistSources
    DistSubDirs
    DistTarBZ2
    DistTarGZip
    DistZip
    ExtraLibs
    FakeSources
    INCFiles
    InternalTargets
    LD.Flags
    LibName.A
    LibName.BC
    LibName.LA
    LibName.O
    LibTool.Flags
    Link
    LinkModule
    LLVMLibDir
    LLVMLibsOptions
    LLVMLibsPaths
    LLVMToolDir
    LLVMUsedLibs
    LocalTargets
    Module
    ObjectsBC
    ObjectsLO
    ObjectsO
    ObjMakefiles
    ParallelTargets
    PreConditions
    ProjLibsOptions
    ProjLibsPaths
    ProjUsedLibs
    Ranlib
    RecursiveTargets
    SrcMakefiles
    Strip
    StripWarnMsg
    TableGen
    TDFiles
    ToolBuildPath
    TopLevelTargets
    UserTargets

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