8bfe65ceb4
The LLVM Integrated Tester now generates an "easy to use" script to run clang tests. It is no longer needed to pass all of the commandline arguments to it. This PR simplifies the documentation a little by removing the unneeded commandline arguments and adding a link to the lit man page.
329 lines
15 KiB
HTML
Executable file
329 lines
15 KiB
HTML
Executable file
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
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<html>
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<head>
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<META http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Hacking on clang</title>
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<link type="text/css" rel="stylesheet" href="menu.css">
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<link type="text/css" rel="stylesheet" href="content.css">
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<style type="text/css">
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pre { margin-left: 1.5em; }
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</style>
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</head>
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<body>
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<!--#include virtual="menu.html.incl"-->
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<div id="content">
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<!--*********************************************************************-->
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<h1>Hacking on Clang</h1>
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<!--*********************************************************************-->
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<p>This document provides some hints for how to get started hacking
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on Clang for developers who are new to the Clang and/or LLVM
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codebases.</p>
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<ul>
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<li><a href="#style">Coding Standards</a></li>
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<li><a href="#docs">Developer Documentation</a></li>
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<li><a href="#debugging">Debugging</a></li>
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<li><a href="#testing">Testing</a>
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<ul>
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<li><a href="#testingNonWindows">Testing on Unix-like Systems</a></li>
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<li><a href="#testingWindows">Testing using Visual Studio on Windows</a></li>
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<li><a href="#testingCommands">Testing on the Command Line</a></li>
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<li><a href="#testingLibc++">Testing changes affecting libc++</a></li>
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</ul>
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</li>
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<li><a href="#patches">Creating Patch Files</a></li>
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<li><a href="#irgen">LLVM IR Generation</a></li>
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</ul>
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<!--=====================================================================-->
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<h2 id="style">Coding Standards</h2>
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<!--=====================================================================-->
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<p>Clang follows the
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LLVM <a href="https://llvm.org/docs/CodingStandards.html">Coding
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Standards</a>. When submitting patches, please take care to follow these standards
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and to match the style of the code to that present in Clang (for example, in
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terms of indentation, bracing, and statement spacing).</p>
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<p>Clang has a few additional coding standards:</p>
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<ul>
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<li><i>cstdio is forbidden</i>: library code should not output diagnostics
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or other information using <tt>cstdio</tt>; debugging routines should
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use <tt>llvm::errs()</tt>. Other uses of <tt>cstdio</tt> impose behavior
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upon clients and block integrating Clang as a library. Libraries should
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support <tt>raw_ostream</tt> based interfaces for textual
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output. See <a href="https://llvm.org/docs/CodingStandards.html#use-raw-ostream">Coding
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Standards</a>.</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="docs">Developer Documentation</h2>
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<!--=====================================================================-->
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<p>Both Clang and LLVM use doxygen to provide API documentation. Their
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respective web pages (generated nightly) are here:</p>
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<ul>
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<li><a href="https://clang.llvm.org/doxygen">Clang</a></li>
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<li><a href="https://llvm.org/doxygen">LLVM</a></li>
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</ul>
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<p>For work on the LLVM IR generation, the LLVM assembly language
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<a href="https://llvm.org/docs/LangRef.html">reference manual</a> is
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also useful.</p>
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<!--=====================================================================-->
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<h2 id="debugging">Debugging</h2>
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<!--=====================================================================-->
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<p>Inspecting data structures in a debugger:</p>
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<ul>
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<li>Many LLVM and Clang data structures provide
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a <tt>dump()</tt> method which will print a description of the
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data structure to <tt>stderr</tt>.</li>
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<li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
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structure is used pervasively. This is a simple value class for
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wrapping types with qualifiers; you can use
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the <tt>isConstQualified()</tt>, for example, to get one of the
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qualifiers, and the <tt>getTypePtr()</tt> method to get the
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wrapped <tt>Type*</tt> which you can then dump.</li>
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<li>For <a href="https://lldb.llvm.org"> <tt>LLDB</tt></a> users there are
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data formatters for LLVM data structures in
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<a href="https://github.com/llvm/llvm-project/blob/main/llvm/utils/lldbDataFormatters.py">
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<tt>llvm/utils/lldbDataFormatters.py</tt></a>.</li>
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</ul>
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<!--=====================================================================-->
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<h3 id="debuggingVisualStudio">Debugging using Visual Studio</h3>
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<!--=====================================================================-->
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<p>The files
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<a href="https://github.com/llvm/llvm-project/blob/main/llvm/utils/LLVMVisualizers/llvm.natvis">
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<tt>llvm/utils/LLVMVisualizers/llvm.natvis</tt></a> and
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<a href="https://github.com/llvm/llvm-project/blob/main/clang/utils/ClangVisualizers/clang.natvis">
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<tt>clang/utils/ClangVisualizers/clang.natvis</tt></a> provide debugger visualizers
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that make debugging of more complex data types much easier.</p>
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<p>Depending on how you configure the project, Visual Studio may automatically
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use these visualizers when debugging or you may be required to put the files
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into <tt>%USERPROFILE%\Documents\Visual Studio <version>\Visualizers</tt>
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or create a symbolic link so they update automatically. See
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<a href="https://learn.microsoft.com/en-us/visualstudio/debugger/create-custom-views-of-native-objects">
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Microsoft's documentation</a> for more details on use of NATVIS.</p>
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<!--=====================================================================-->
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<h2 id="testing">Testing</h2>
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<!--=====================================================================-->
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<!--=====================================================================-->
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<h3 id="testingNonWindows">Testing on Unix-like Systems</h3>
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<!--=====================================================================-->
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<p>Clang includes a basic regression suite in the tree which can be
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run with <tt>make test</tt> from the top-level clang directory, or
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just <tt>make</tt> in the <em>test</em> sub-directory.
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<tt>make VERBOSE=1</tt> can be used to show more detail
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about what is being run.</p>
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<p>If you built LLVM and Clang using CMake, the test suite can be run
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with <tt>make check-clang</tt> from the top-level LLVM directory.</p>
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<p>The tests primarily consist of a test runner script running the compiler
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under test on individual test files grouped in the directories under the
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test directory. The individual test files include comments at the
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beginning indicating the Clang compile options to use, to be read
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by the test runner. Embedded comments also can do things like telling
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the test runner that an error is expected at the current line.
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Any output files produced by the test will be placed under
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a created Output directory.</p>
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<p>During the run of <tt>make test</tt>, the terminal output will
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display a line similar to the following:</p>
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<pre>--- Running clang tests for i686-pc-linux-gnu ---</pre>
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<p>followed by a line continually overwritten with the current test
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file being compiled, and an overall completion percentage.</p>
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<p>After the <tt>make test</tt> run completes, the absence of any
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<tt>Failing Tests (count):</tt> message indicates that no tests
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failed unexpectedly. If any tests did fail, the
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<tt>Failing Tests (count):</tt> message will be followed by a list
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of the test source file paths that failed. For example:</p>
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<pre>
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Failing Tests (3):
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/home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp
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/home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp
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/home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp
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</pre>
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<p>If you used the <tt>make VERBOSE=1</tt> option, the terminal
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output will reflect the error messages from the compiler and
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test runner.</p>
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<p>The regression suite can also be run with Valgrind by running
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<tt>make test VG=1</tt> in the top-level clang directory.</p>
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<p>For more intensive changes, running
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the <a href="https://llvm.org/docs/TestingGuide.html#quick-start">LLVM
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Test Suite</a> with clang is recommended. Currently the best way to
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override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89"
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TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the
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full path).</p>
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<!--=====================================================================-->
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<h3 id="testingWindows">Testing using Visual Studio on Windows</h3>
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<!--=====================================================================-->
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<p>The Clang test suite can be run from either Visual Studio or
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the command line.</p>
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<p>Note that the test runner is based on
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Python, which must be installed. Find Python at:
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<a href="https://www.python.org/downloads/">https://www.python.org/downloads/</a>.
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Download the latest stable version.</p>
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<p>The GNU core utilities included in <b>Git For Windows</b>
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are also required to run the tests. This is available from
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<a href="https://git-scm.com/download"> https://git-scm.com/download</a>.
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You can specify the <tt>LLVM_LIT_TOOLS_DIR</tt> to CMake explicitly
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to override the location of the GNU core utilities used for testing.</p>
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<p>The cmake build tool is set up to create Visual Studio project files
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for running the tests, "check-clang" being the root. Therefore, to
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run the test from Visual Studio, right-click the check-clang project
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and select "Build".</p>
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<p>
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Please see also
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<a href="https://llvm.org/docs/GettingStartedVS.html">Getting Started
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with the LLVM System using Microsoft Visual Studio</a> and
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<a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a>.
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</p>
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<!--=====================================================================-->
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<h3 id="testingCommands">Testing on the Command Line</h3>
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<!--=====================================================================-->
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<p>If you want more control over how the tests are run, it may
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be convenient to run the test harness on the command-line directly. Running
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the <tt>check-clang</tt> build target will generate a script to start the
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<a href="https://llvm.org/docs/CommandGuide/lit.html">LLVM Integrated
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Tester</a> (<tt>lit</tt>) that can be used to run tests for your
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current configuration. Once the tests have started running, you can stop
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them with <tt>control+C</tt>, as the files are generated before running any
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tests.</p>
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<p>Once that is done, all the tests can be executed from the command line
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by running the generated <tt>llvm-lit</tt> script as follows:</p>
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<pre>
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(build dir)\bin\llvm-lit (path to llvm)\clang\test
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</pre>
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For example; if you have a Ninja build in the
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<tt>llvm-project\build_ninja</tt> directory, the command to execute from the
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<tt>llvm-project</tt> directory would be:
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<pre>
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build_ninja\bin\llvm-lit clang\test
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</pre>
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Or, for a Visual Studio Debug build in the <tt>llvm-project\build</tt>
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directory, the lit start command to execute from the <tt>llvm-project</tt>
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directory would be:
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<pre>
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build\Debug\bin\llvm-lit clang\test
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</pre>
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<p>You can run a single test or all tests in a specific folder by providing
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the target test or folder to <tt>lit</tt>. For example, we can run the
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<tt>wchar.c</tt> test:</p>
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<pre>
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build_ninja\bin\llvm-lit clang\test\Sema\wchar.c
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</pre>
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<p>or all tests in the <tt>Sema</tt> folder:</p>
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<pre>
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build_ninja\bin\llvm-lit clang\test\Sema
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</pre>
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<p>Pass in the <tt>--no-progress-bar</tt> option if you wish to disable
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progress indications while the tests are running.</p>
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<p>Your output might look something like this:</p>
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<pre>lit.py: lit.cfg:152: note: using clang: 'C:\Tools\llvm\bin\Release\clang.EXE'
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-- Testing: Testing: 2534 tests, 4 threads --
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Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
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Testing Time: 81.52s
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Passed : 2503
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Expectedly Failed: 28
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Unsupported : 3
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</pre>
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<p>The statistic, "Failed" (not shown if all tests pass), is the important one.</p>
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<!--=====================================================================-->
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<h3 id="testingLibc++">Testing changes affecting libc++</h3>
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<!--=====================================================================-->
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<p>Some changes in Clang affect <a href="https://libcxx.llvm.org">libc++</a>,
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for example:</p>
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<ul>
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<li>Changing the output of Clang's diagnostics.</li>
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<li>Changing compiler builtins, especially the builtins used for type traits
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or replacements of library functions like <tt>std::move</tt> or
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<tt>std::forward</tt>.</li>
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</ul>
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<p>After adjusting libc++ to work with the changes, the next revision will be
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tested by libc++'s
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<a href="https://buildkite.com/llvm-project/libcxx-ci">pre-commit CI</a>.
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<p>For most configurations, the pre-commit CI uses a recent
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<a href="https://apt.llvm.org/">nightly build</a> of Clang from LLVM's main
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branch. These configurations do <em>not</em> use the Clang changes in the
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patch. They only use the libc++ changes.</p>
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<p>The "Bootstrapping build" builds Clang and uses it to build and
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test libc++. This build <em>does</em> use the Clang changes in the patch.</p>
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<p>Libc++ supports multiple versions of Clang. Therefore when a patch changes
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the diagnostics it might be required to use a regex in the
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"expected" tests to make it pass the CI.</p>
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<p>Libc++ has more
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<a href="https://libcxx.llvm.org/Contributing.html#pre-commit-ci">
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documentation</a> about the pre-commit CI. For questions regarding
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libc++, the best place to ask is the <tt>#libcxx</tt> channel on
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<a href="https://discord.gg/jzUbyP26tQ">LLVM's Discord server</a>.</p>
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<!--=====================================================================-->
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<h2 id="patches">Creating Patch Files</h2>
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<!--=====================================================================-->
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<p>To contribute changes to Clang see
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<a href="https://llvm.org/docs/GettingStarted.html#sending-patches">LLVM's Getting Started page</a></p>
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<!--=====================================================================-->
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<h2 id="irgen">LLVM IR Generation</h2>
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<!--=====================================================================-->
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<p>The LLVM IR generation part of clang handles conversion of the
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AST nodes output by the Sema module to the LLVM Intermediate
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Representation (IR). Historically, this was referred to as
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"codegen", and the Clang code for this lives
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in <tt>lib/CodeGen</tt>.</p>
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<p>The output is most easily inspected using the <tt>-emit-llvm</tt>
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option to clang (possibly in conjunction with <tt>-o -</tt>). You
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can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
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which can be processed by the suite of LLVM tools
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like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
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<a href="https://llvm.org/docs/CommandGuide/">Command Guide</a>
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for more information.</p>
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</div>
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</body>
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</html>
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