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		<title>Creating an LLVM Project</title>
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	<center><h1>Creating an LLVM Project<br></h1></center>

	<!--===============================================================-->
	<h2><a name="a">Overview</a><hr></h2>
	<!--===============================================================-->

	The LLVM build system is designed to facilitate the building of third party
	projects that use LLVM header files, libraries, and tools.  In order to use
	these facilities, a Makefile from a project must do the following things:

	<ol>
		<li>Set environment variables.
		<p>
		There are several environment variables that a Makefile needs to set to
		use the LLVM build system:
		<dl compact>
			<dt>LLVM_SRC_ROOT
			<dd>
			The root of the LLVM source tree.
			<p>

			<dt>LLVM_OBJ_ROOT
			<dd>
			The root of the LLVM object tree.
			<p>

			<dt>BUILD_SRC_ROOT
			<dd>
			The root of the project's source tree.
			<p>

			<dt>BUILD_OBJ_ROOT
			<dd>
			The root of the project's object tree.
			<p>

			<dt>BUILD_SRC_DIR
			<dd>
			The directory containing the current source to be compiled.
			<p>

			<dt>BUILD_OBJ_DIR
			<dd>
			The directory where the current source will place the new object
			files.  This should always be the current directory.
			<p>

			<dt>LEVEL
			<dd>
			The relative path from the current directory to the root of the
			object tree.
			<p>
		</dl>

		<li>Include the LLVM Makefile.config from $(LLVM_OBJ_ROOT).
		<p>

		<li>Include the LLVM Makefile.rules from $(LLVM_SRC_ROOT).
	</ol>

	There are two ways that you can set all of these variables:
	<ol>
		<li>
		You can write your own Makefiles which hard-code these values.

		<li>
		You can use the pre-made LLVM sample project.  This sample project
		includes Makefiles, a configure script that can be used to configure
		the location of LLVM, and the ability to support multiple object
		directories from a single source directory.
	</ol>

	This document assumes that you will base your project off of the LLVM
	sample project found in <tt>llvm/projects/sample</tt>.  If you want to
	devise your own build system, studying the sample project and LLVM
	Makefiles will probably provide enough information on how to write your own
	Makefiles.
	<p>

	<!--===============================================================-->
	<h2><a name="a">Create a Project from the Sample Project</a><hr></h2>
	<!--===============================================================-->

	Follow these simple steps to start your project:

	<ol>
		<li>
		Copy the <tt>llvm/projects/sample</tt> directory to any place
		of your choosing.  You can place it anywhere you like.  Rename the
		directory to match the name of your project.
		<p>

		<li>
		Add your source code and Makefiles to your source tree.
		<p>

		<li>
		If you want your Makefiles to be configured by the
		<tt>configure</tt> script, or if you want to support multiple
		object directories, add your Makefiles to the <tt>configure</tt>
		script by adding them into the <tt>autoconf/configure.ac</tt> file.
		The macro <tt>AC_CONFIG_MAKEFILE</tt> will copy a file, unmodified,
		from the source directory to the object directory.

		<p>
		After updating <tt>autoconf/configure.ac</tt>, regenerate the
		configure script with these commands:
		<p>
		<tt>
		cd autoconf<br>
		autoconf -o ../configure
		</tt>

		<p>

		You must be using Autoconf version 2.57 or higher.
		<p>

		<li>
		Run <tt>configure</tt> in the directory in which you want to place
		object code.  Use the following options to tell your project where it
		can find LLVM:

		<dl compact>
			<dt><tt>--with-llvmsrc=&lt;directory&gt;</tt>
			<dd>
			Tell your project where the LLVM source tree is located.
			<p>
			<dt><tt>--with-llvmobj=&lt;directory&gt;</tt>
			<dd>
			Tell your project where the LLVM object tree is located.
		</dl>
	</ol>

	That's it!  Now all you have to do is type <tt>gmake</tt> in the root of
	your object directory, and your project should build.

	<!--===============================================================-->
	<h2><a name="Source Tree Layout">Source Tree Layout</a><hr></h2>
	<!--===============================================================-->

	In order to use the LLVM build system, you will want to organize your
	source code so that it can benefit from the build system's features.
	Mainly, you want your source tree layout to look similar to the LLVM
	source tree layout.  The best way to do this is to just copy the
	project tree from <tt>llvm/projects/sample</tt> and modify it to meet
	your needs, but you can certainly add to it if you want.

	Underneath your top level directory, you should have the following
	directories:

	<dl compact>
		<dt><b>lib</b>
		<dd>
		This subdirectory should contain all of your library source
		code.  For each library that you build, you will have one
		directory in <b>lib</b> that will contain that library's source
		code.

		<p>
		Libraries can be object files, archives, or dynamic libraries.
		The <b>lib</b> directory is just a convenient place for libraries
		as it places them all in a directory from which they can be linked
		later.

		<dt><b>include</b>
		<dd>
		This subdirectory should contain any header files that are
		global to your project.  By global, we mean that they are used
		by more than one library or executable of your project.
		<p>
		By placing your header files in <b>include</b>, they will be
		found automatically by the LLVM build system.  For example, if
		you have a file <b>include/jazz/note.h</b>, then your source
		files can include it simply with <b>#include "jazz/note.h"</b>.

		<dt><b>tools</b>
		<dd>
		This subdirectory should contain all of your source
		code for executables.  For each program that you build, you
		will have one directory in <b>tools</b> that will contain that
		program's source code.
		<p>

		<dt><b>test</b>
		<dd>
		This subdirectory should contain tests that verify that your code
		works correctly.  Automated tests are especially useful.
		<p>
		Currently, the LLVM build system provides little support for tests,
		although some exists.  Expanded support for tests will hopefully
		occur in the future.  In the meantime, the LLVM system does provide the
		following:
		<ul>
			<li>
			LLVM provides several QMTest test classes that can be used to
			create tests.  They can be found in
			<tt>llvm/test/QMTest/llvm.py</tt>.  These test classes perform a
			variety of functions, including code optimization tests, assembly
			tests,  and code analysis tests.  The Makefile in
			<tt>llvm/test</tt> provides the QMTest context needed by LLVM test
			classes.
			<p>

			<li>
			The LLVM source tree provides benchmarks and programs which are
			known to compile with the LLVM GCC front ends.  You can use these
			programs to test your code, gather statistics information, and
			compare it to the current LLVM performance statistics.  These
			programs are found in the <tt>llvm/test/Programs</tt> directory.
			<p>
			Currently, there is no way to hook your tests directly into the
			<tt>llvm/test/Programs</tt> testing harness.  You will simply
			need to find a way to use the source provided within that directory
			on your own.
		</ul>
	</dl>

	Typically, you will want to build your <b>lib</b> directory first
	followed by your <b>tools</b> directory.

	<!--===============================================================-->
	<h2><a name="Makefile Variables">Writing LLVM Style Makefiles</a><hr></h2>
	<!--===============================================================-->
	The LLVM build system provides a convenient way to build libraries and
	executables.  Most of your project Makefiles will only need to define a few
	variables.  Below is a list of the variables one can set and what they can
	do:

	<h3> Required Variables </h3>
	<dl compact>
		<dt>LEVEL
		<dd>
		This variable is the relative path from this Makefile to the
		top directory of your project's source code.  For example, if
		your source code is in /tmp/src, then the Makefile in
		/tmp/src/jump/high would set LEVEL to "../..".
	</dl>

	<h3> Variables for Building Subdirectories</h3>
	<dl compact>
		<dt>DIRS
		<dd>
		This is a space separated list of subdirectories that should be
		built.  They will be built, one at a time, in the order
		specified.
		<p>

		<dt>PARALLEL_DIRS
		<dd>
		This is a list of directories that can be built in parallel.
		These will be built after the directories in DIRS have been
		built.
		<p>

		<dt>OPTIONAL_DIRS
		<dd>
		This is a list of directories that can be built if they exist,
		but will not cause an error if they do not exist.  They are
		built serially in the order in which they are listed.
	</dl>

	<h3> Variables for Building Libraries</h3>
	<dl compact>
		<dt>LIBRARYNAME
		<dd>
		This variable contains the base name of the library that will
		be built.  For example, to build a library named
		<tt>libsample.a</tt>, LIBRARYNAME should be set to
		<tt>sample</tt>.
		<p>

		<dt>BUILD_ARCHIVE
		<dd>
		By default, a library is a <tt>.o</tt> file that is linked
		directly into a program.  To build an archive (also known as
		a static library), set the BUILD_ARCHIVE variable.
		<p>

		<dt>SHARED_LIBRARY
		<dd>
		If SHARED_LIBRARY is defined in your Makefile, a shared
		(or dynamic) library will be built.
	</dl>

	<h3> Variables for Building Programs</h3>
	<dl compact>
		<dt>TOOLNAME
		<dd>
		This variable contains the name of the program that will
		be built.  For example, to build an executable named
		<tt>sample</tt>, TOOLNAME should be set to <tt>sample</tt>.
		<p>

		<dt>USEDLIBS
		<dd>
		This variable holds a space separated list of libraries that
		should be linked into the program.  These libraries must either
		be LLVM libraries or libraries that come from your <b>lib</b>
		directory.  The libraries must be specified by their base name.
		For example, to link libsample.a, you would set USEDLIBS to
		<tt>sample</tt>.
		<p>
		Note that this works only for statically linked libraries.
		<p>

		<dt>LIBS
		<dd>
		To link dynamic libraries, add <tt>-l&lt;library base name&gt;</tt> to
		the LIBS variable.  The LLVM build system will look in the same places
		for dynamic libraries as it does for static libraries.
		<p>
		For example, to link <tt>libsample.so</tt>, you would have the
		following line in your <tt>Makefile</tt>:
		<p>
		<tt>
		LIBS+=-lsample
		</tt>
	</dl>

	<h3> Miscellaneous Variables</h3>
	<dl compact>
		<dt>ExtraSource
		<dd>
		This variable contains a space separated list of extra source
		files that need to be built.  It is useful for including the
		output of Lex and Yacc programs.
		<p>

		<dt>CFLAGS
		<dt>CPPFLAGS
		<dd>
		This variable can be used to add options to the C and C++
		compiler, respectively.  It is typically used to add options
		that tell the compiler the location of additional directories
		to search for header files.
		<p>
		It is highly suggested that you append to CFLAGS and CPPFLAGS as
		opposed to overwriting them.  The master Makefiles may already
		have useful options in them that you may not want to overwrite.
		<p>
	</dl>

	<!--===============================================================-->
	<h2><a name="objcode">Placement of Object Code</a><hr></h2>
	<!--===============================================================-->

	The final location of built libraries and executables will depend upon
	whether you do a Debug, Release, or Profile build.

	<dl compact>
		<dt>Libraries
		<dd>
		All libraries (static and dynamic) will be stored in
		BUILD_OBJ_ROOT/lib/&lt;type&gt;, where type is <tt>Debug</tt>,
		<tt>Release</tt>, or <tt>Profile</tt> for a debug, optimized, or
		profiled build, respectively.
		<p>

		<dt>Executables
		<dd>
		All executables will be stored in BUILD_OBJ_ROOT/lib/&lt;type&gt;,
		where type is <tt>Debug</tt>, <tt>Release</tt>, or <tt>Profile</tt> for
		a debug, optimized, or profiled build, respectively.
	</dl>

	<!--===============================================================-->
	<h2><a name="help">Further Help</a><hr></h2>
	<!--===============================================================-->

	If you have any questions or need any help creating an LLVM project,
	the LLVM team would be more than happy to help.  You can always post your
	questions to the LLVM Developers Mailing List (<a
	href="mailto:llvmdev.cs.uiuc.edu">llvmdev@cs.uiuc.edu</a>).
	
<hr>
Written by <a href="mailto:criswell@uiuc.edu">John Criswell</a>.
<br>
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
<br>
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