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   <!--*********************************************************************-->
   <h1>Hacking on Clang</h1>
   <!--*********************************************************************-->

   <p>This document provides some hints for how to get started hacking
   on Clang for developers who are new to the Clang and/or LLVM
   codebases.</p>
     <ul>
       <li><a href="#style">Coding Standards</a></li>
       <li><a href="#docs">Developer Documentation</a></li>
       <li><a href="#debugging">Debugging</a></li>
       <li><a href="#testing">Testing</a></li>
       <ul>
 	    <li><a href="#testingNonWindows">Testing on Unix-like Systems</a></li>
 	    <li><a href="#testingWindows">Testing using Visual Studio on Windows</a></li>
 	  </ul>
       <li><a href="#patches">Creating Patch Files</a></li>
       <li><a href="#irgen">LLVM IR Generation</a></li>
     </ul>

   <!--=====================================================================-->
   <h2 id="docs">Coding Standards</h2>
   <!--=====================================================================-->

   <p>Clang follows the
   LLVM <a href="http://llvm.org/docs/CodingStandards.html">Coding
   Standards</a>. When submitting patches, please take care to follow these standards
   and to match the style of the code to that present in Clang (for example, in
   terms of indentation, bracing, and statement spacing).</p>

   <p>Clang has a few additional coding standards:</p>
   <ul>
     <li><i>cstdio is forbidden</i>: library code should not output diagnostics
       or other information using <tt>cstdio</tt>; debugging routines should
       use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior
       upon clients and block integrating Clang as a library. Libraries should
       support <tt>raw_ostream</tt> based interfaces for textual
       output. See <a href="http://llvm.org/docs/CodingStandards.html#ll_raw_ostream">Coding
       Standards</a>.</li>
   </ul>

   <!--=====================================================================-->
   <h2 id="docs">Developer Documentation</h2>
   <!--=====================================================================-->

   <p>Both Clang and LLVM use doxygen to provide API documentation. Their
   respective web pages (generated nightly) are here:</p>
     <ul>
       <li><a href="http://clang.llvm.org/doxygen">Clang</a></li>
       <li><a href="http://llvm.org/doxygen">LLVM</a></li>
     </ul>

   <p>For work on the LLVM IR generation, the LLVM assembly language
   <a href="http://llvm.org/docs/LangRef.html">reference manual</a> is
   also useful.</p>

   <!--=====================================================================-->
   <h2 id="debugging">Debugging</h2>
   <!--=====================================================================-->

   <p>Inspecting data structures in a debugger:</p>
     <ul>
       <li>Many LLVM and Clang data structures provide
         a <tt>dump()</tt> method which will print a description of the
         data structure to <tt>stderr</tt>.</li>
       <li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
       structure is used pervasively. This is a simple value class for
       wrapping types with qualifiers; you can use
       the <tt>isConstQualified()</tt>, for example, to get one of the
       qualifiers, and the <tt>getTypePtr()</tt> method to get the
       wrapped <tt>Type*</tt> which you can then dump.</li>
     </ul>

   <!--=====================================================================-->
   <h2 id="testing">Testing</h2>
   <!--=====================================================================-->

   <p><i>[Note: The test running mechanism is currently under revision, so the
   following might change shortly.]</i></p>

   <!--=====================================================================-->
   <h3 id="testingNonWindows">Testing on Unix-like Systems</h3>
   <!--=====================================================================-->

   <p>Clang includes a basic regression suite in the tree which can be
   run with <tt>make test</tt> from the top-level clang directory, or
   just <tt>make</tt> in the <em>test</em> sub-directory.
   <tt>make VERBOSE=1</tt> can be used to show more detail
   about what is being run.</p>

   <p>If you built LLVM and Clang using CMake, the test suite can be run
   with <tt>make clang-test</tt> from the top-level LLVM directory.</p>

   <p>The tests primarily consist of a test runner script running the compiler
   under test on individual test files grouped in the directories under the
   test directory.  The individual test files include comments at the
   beginning indicating the Clang compile options to use, to be read
   by the test runner. Embedded comments also can do things like telling
   the test runner that an error is expected at the current line.
   Any output files produced by the test will be placed under
   a created Output directory.</p>

   <p>During the run of <tt>make test</tt>, the terminal output will
   display a line similar to the following:</p>

   <ul><tt>--- Running clang tests for i686-pc-linux-gnu ---</tt></ul>

   <p>followed by a line continually overwritten with the current test
   file being compiled, and an overall completion percentage.</p>

   <p>After the <tt>make test</tt> run completes, the absence of any
   <tt>Failing Tests (count):</tt> message indicates that no tests
   failed unexpectedly.  If any tests did fail, the
   <tt>Failing Tests (count):</tt> message will be followed by a list
   of the test source file paths that failed.  For example:</p>

   <tt><pre>
   Failing Tests (3):
       /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp
       /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp
       /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp
   </pre></tt>

   <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal
   output will reflect the error messages from the compiler and
   test runner.</p>

   <p>The regression suite can also be run with Valgrind by running
   <tt>make test VG=1</tt> in the top-level clang directory.</p>

   <p>For more intensive changes, running
   the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM
   Test Suite</a> with clang is recommended. Currently the best way to
   override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89"
   TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the
   full path).</p>

   <!--=====================================================================-->
   <h3 id="testingWindows">Testing using Visual Studio on Windows</h3>
   <!--=====================================================================-->

   <p>The Clang test suite can be run from either Visual Studio or
   the command line.</p>

   <p>Note that the test runner is based on
   Python, which must be installed.  Find Python at:
   <a href="http://www.python.org/download">http://www.python.org/download</a>.
   Download the latest stable version (2.6.2 at the time of this writing).</p>

   <p>The GnuWin32 tools are also necessary for running the tests.
   (Note that the grep from MSYS or Cygwin doesn't work with the tests
   because of embedded double-quotes in the search strings.  The GNU
   grep does work in this case.)
   Get them from <a href="http://getgnuwin32.sourceforge.net">
   http://getgnuwin32.sourceforge.net</a>.</p>

   <p>The cmake build tool is set up to create Visual Studio project files
   for running the tests, "clang-test" being the root.  Therefore, to
   run the test from Visual Studio, right-click the clang-test project
   and select "Build".</p>

   <p>To run all the tests from the command line, execute a command like
   the following:</p>

   <tt>
   python (path to llvm)/llvm/utils/lit/lit.py -sv --no-progress-bar
  (path to llvm)/llvm/tools/clang/test
   </tt>

   <p>To run a single test:</p>

   <tt>
   python (path to llvm)/llvm/utils/lit/lit.py -sv --no-progress-bar
  (path to llvm)/llvm/tools/clang/test/(dir)/(test)
   </tt>

   <p>For example:</p>

   <tt>
   python C:/Tools/llvm/utils/lit/lit.py -sv --no-progress-bar
   C:/Tools/llvm/tools/clang/test/Sema/wchar.c
   </tt>

   <p>The -sv option above tells the runner to show the test output if
   any tests failed, to help you determine the cause of failure.</p>

   <p>Note that a few tests currently fail on Windows.  We are working to
   correct this. Therefore your output might look something like this:</p>

 <tt><pre>lit.py: lit.cfg:152: note: using clang: 'C:/Tools/llvm/bin/Debug\\clang.EXE'
 -- Testing: 1723 tests, 2 threads --
 FAIL: Clang::(test path) (659 of 1723)
 ******************** TEST 'Clang::(test path)' FAILED ********************
 Script:
   (commands run)
 Command Output (stdout):
   (output here)
 Command Output (stderr):
   (output here)
 ********************
 Testing Time: 83.66s
 ********************
 Failing Tests (1):
     Clang::(test path)
   Expected Passes    : 1704
   Expected Failures  : 18
   Unexpected Failures: 1
 </pre></tt>

   <p>The last statistic, "Unexpected Failures", is the important one.</p>

   <!--=====================================================================-->
   <h2 id="patches">Creating Patch Files</h2>
   <!--=====================================================================-->

   <p>To return changes to the Clang team, unless you have checkin
   privileges, the prefered way is to send patch files to the
   cfe-commits mailing list, with an explanation of what the patch is for.
   Or, if you have questions, or want to have a wider discussion of what
   you are doing, such as if you are new to Clang development, you can use
   the cfe-dev mailing list also.
   </p>

   <p>To create these patch files, change directory
   to the llvm/tools/clang root and run:</p>

   <ul><tt>svn diff (relative path) >(patch file name)</tt></ul>

   <p>For example, for getting the diffs of all of clang:</p>

   <ul><tt>svn diff . >~/mypatchfile.patch</tt></ul>

   <p>For example, for getting the diffs of a single file:</p>

   <ul><tt>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</tt></ul>

   <p>Note that the paths embedded in the patch depend on where you run it,
   so changing directory to the llvm/tools/clang directory is recommended.</p>

   <!--=====================================================================-->
   <h2 id="irgen">LLVM IR Generation</h2>
   <!--=====================================================================-->

   <p>The LLVM IR generation part of clang handles conversion of the
     AST nodes output by the Sema module to the LLVM Intermediate
     Representation (IR). Historically, this was referred to as
     "codegen", and the Clang code for this lives
     in <tt>lib/CodeGen</tt>.</p>

   <p>The output is most easily inspected using the <tt>-emit-llvm</tt>
     option to clang (possibly in conjunction with <tt>-o -</tt>). You
     can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
     which can be processed by the suite of LLVM tools
     like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
     <a href="http://llvm.org/docs/CommandGuide/">Command Guide</a>
     for more information.</p>

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	<div id="content">
	<!--*********************************************************************-->
	<h1>Hacking on Clang</h1>
	<!--*********************************************************************-->

	<p>This document provides some hints for how to get started hacking
	on Clang for developers who are new to the Clang and/or LLVM
	codebases.</p>
	<ul>
	<li><a href="#style">Coding Standards</a></li>
	<li><a href="#docs">Developer Documentation</a></li>
	<li><a href="#debugging">Debugging</a></li>
	<li><a href="#testing">Testing</a></li>
	<ul>
	<li><a href="#testingNonWindows">Testing on Unix-like Systems</a></li>
	<li><a href="#testingWindows">Testing using Visual Studio on Windows</a></li>
	</ul>
	<li><a href="#patches">Creating Patch Files</a></li>
	<li><a href="#irgen">LLVM IR Generation</a></li>
	</ul>

	<!--=====================================================================-->
	<h2 id="docs">Coding Standards</h2>
	<!--=====================================================================-->

	<p>Clang follows the
	LLVM <a href="http://llvm.org/docs/CodingStandards.html">Coding
	Standards</a>. When submitting patches, please take care to follow these standards
	and to match the style of the code to that present in Clang (for example, in
	terms of indentation, bracing, and statement spacing).</p>

	<p>Clang has a few additional coding standards:</p>
	<ul>
	<li><i>cstdio is forbidden</i>: library code should not output diagnostics
	or other information using <tt>cstdio</tt>; debugging routines should
	use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior
	upon clients and block integrating Clang as a library. Libraries should
	support <tt>raw_ostream</tt> based interfaces for textual
	output. See <a href="http://llvm.org/docs/CodingStandards.html#ll_raw_ostream">Coding
	Standards</a>.</li>
	</ul>

	<!--=====================================================================-->
	<h2 id="docs">Developer Documentation</h2>
	<!--=====================================================================-->

	<p>Both Clang and LLVM use doxygen to provide API documentation. Their
	respective web pages (generated nightly) are here:</p>
	<ul>
	<li><a href="http://clang.llvm.org/doxygen">Clang</a></li>
	<li><a href="http://llvm.org/doxygen">LLVM</a></li>
	</ul>

	<p>For work on the LLVM IR generation, the LLVM assembly language
	<a href="http://llvm.org/docs/LangRef.html">reference manual</a> is
	also useful.</p>

	<!--=====================================================================-->
	<h2 id="debugging">Debugging</h2>
	<!--=====================================================================-->

	<p>Inspecting data structures in a debugger:</p>
	<ul>
	<li>Many LLVM and Clang data structures provide
	a <tt>dump()</tt> method which will print a description of the
	data structure to <tt>stderr</tt>.</li>
	<li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
	structure is used pervasively. This is a simple value class for
	wrapping types with qualifiers; you can use
	the <tt>isConstQualified()</tt>, for example, to get one of the
	qualifiers, and the <tt>getTypePtr()</tt> method to get the
	wrapped <tt>Type*</tt> which you can then dump.</li>
	</ul>

	<!--=====================================================================-->
	<h2 id="testing">Testing</h2>
	<!--=====================================================================-->

	<p><i>[Note: The test running mechanism is currently under revision, so the
	following might change shortly.]</i></p>

	<!--=====================================================================-->
	<h3 id="testingNonWindows">Testing on Unix-like Systems</h3>
	<!--=====================================================================-->

	<p>Clang includes a basic regression suite in the tree which can be
	run with <tt>make test</tt> from the top-level clang directory, or
	just <tt>make</tt> in the <em>test</em> sub-directory.
	<tt>make VERBOSE=1</tt> can be used to show more detail
	about what is being run.</p>

	<p>If you built LLVM and Clang using CMake, the test suite can be run
	with <tt>make clang-test</tt> from the top-level LLVM directory.</p>

	<p>The tests primarily consist of a test runner script running the compiler
	under test on individual test files grouped in the directories under the
	test directory. The individual test files include comments at the
	beginning indicating the Clang compile options to use, to be read
	by the test runner. Embedded comments also can do things like telling
	the test runner that an error is expected at the current line.
	Any output files produced by the test will be placed under
	a created Output directory.</p>

	<p>During the run of <tt>make test</tt>, the terminal output will
	display a line similar to the following:</p>

	<ul><tt>--- Running clang tests for i686-pc-linux-gnu ---</tt></ul>

	<p>followed by a line continually overwritten with the current test
	file being compiled, and an overall completion percentage.</p>

	<p>After the <tt>make test</tt> run completes, the absence of any
	<tt>Failing Tests (count):</tt> message indicates that no tests
	failed unexpectedly. If any tests did fail, the
	<tt>Failing Tests (count):</tt> message will be followed by a list
	of the test source file paths that failed. For example:</p>

	<tt><pre>
	Failing Tests (3):
	/home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp
	/home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp
	/home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp
	</pre></tt>

	<p>If you used the <tt>make VERBOSE=1</tt> option, the terminal
	output will reflect the error messages from the compiler and
	test runner.</p>

	<p>The regression suite can also be run with Valgrind by running
	<tt>make test VG=1</tt> in the top-level clang directory.</p>

	<p>For more intensive changes, running
	the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM
	Test Suite</a> with clang is recommended. Currently the best way to
	override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89"
	TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the
	full path).</p>

	<!--=====================================================================-->
	<h3 id="testingWindows">Testing using Visual Studio on Windows</h3>
	<!--=====================================================================-->

	<p>The Clang test suite can be run from either Visual Studio or
	the command line.</p>

	<p>Note that the test runner is based on
	Python, which must be installed. Find Python at:
	<a href="http://www.python.org/download">http://www.python.org/download</a>.
	Download the latest stable version (2.6.2 at the time of this writing).</p>

	<p>The GnuWin32 tools are also necessary for running the tests.
	(Note that the grep from MSYS or Cygwin doesn't work with the tests
	because of embedded double-quotes in the search strings. The GNU
	grep does work in this case.)
	Get them from <a href="http://getgnuwin32.sourceforge.net">
	http://getgnuwin32.sourceforge.net</a>.</p>

	<p>The cmake build tool is set up to create Visual Studio project files
	for running the tests, "clang-test" being the root. Therefore, to
	run the test from Visual Studio, right-click the clang-test project
	and select "Build".</p>

	<p>To run all the tests from the command line, execute a command like
	the following:</p>

	<tt>
	python (path to llvm)/llvm/utils/lit/lit.py -sv --no-progress-bar
	(path to llvm)/llvm/tools/clang/test
	</tt>

	<p>To run a single test:</p>

	<tt>
	python (path to llvm)/llvm/utils/lit/lit.py -sv --no-progress-bar
	(path to llvm)/llvm/tools/clang/test/(dir)/(test)
	</tt>

	<p>For example:</p>

	<tt>
	python C:/Tools/llvm/utils/lit/lit.py -sv --no-progress-bar
	C:/Tools/llvm/tools/clang/test/Sema/wchar.c
	</tt>

	<p>The -sv option above tells the runner to show the test output if
	any tests failed, to help you determine the cause of failure.</p>

	<p>Note that a few tests currently fail on Windows. We are working to
	correct this. Therefore your output might look something like this:</p>

	<tt><pre>lit.py: lit.cfg:152: note: using clang: 'C:/Tools/llvm/bin/Debug\\clang.EXE'
	-- Testing: 1723 tests, 2 threads --
	FAIL: Clang::(test path) (659 of 1723)
	****************** TEST 'Clang::(test path)' FAILED ******************
	Script:
	(commands run)
	Command Output (stdout):
	(output here)
	Command Output (stderr):
	(output here)
	********************
	Testing Time: 83.66s
	********************
	Failing Tests (1):
	Clang::(test path)
	Expected Passes : 1704
	Expected Failures : 18
	Unexpected Failures: 1
	</pre></tt>

	<p>The last statistic, "Unexpected Failures", is the important one.</p>

	<!--=====================================================================-->
	<h2 id="patches">Creating Patch Files</h2>
	<!--=====================================================================-->

	<p>To return changes to the Clang team, unless you have checkin
	privileges, the prefered way is to send patch files to the
	cfe-commits mailing list, with an explanation of what the patch is for.
	Or, if you have questions, or want to have a wider discussion of what
	you are doing, such as if you are new to Clang development, you can use
	the cfe-dev mailing list also.
	</p>

	<p>To create these patch files, change directory
	to the llvm/tools/clang root and run:</p>

	<ul><tt>svn diff (relative path) >(patch file name)</tt></ul>

	<p>For example, for getting the diffs of all of clang:</p>

	<ul><tt>svn diff . >~/mypatchfile.patch</tt></ul>

	<p>For example, for getting the diffs of a single file:</p>

	<ul><tt>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</tt></ul>

	<p>Note that the paths embedded in the patch depend on where you run it,
	so changing directory to the llvm/tools/clang directory is recommended.</p>

	<!--=====================================================================-->
	<h2 id="irgen">LLVM IR Generation</h2>
	<!--=====================================================================-->

	<p>The LLVM IR generation part of clang handles conversion of the
	AST nodes output by the Sema module to the LLVM Intermediate
	Representation (IR). Historically, this was referred to as
	"codegen", and the Clang code for this lives
	in <tt>lib/CodeGen</tt>.</p>

	<p>The output is most easily inspected using the <tt>-emit-llvm</tt>
	option to clang (possibly in conjunction with <tt>-o -</tt>). You
	can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
	which can be processed by the suite of LLVM tools
	like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
	<a href="http://llvm.org/docs/CommandGuide/">Command Guide</a>
	for more information.</p>

	</div>
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