[www-releases] r238136 - Add clang docs for 3.6.1
Tom Stellard
thomas.stellard at amd.com
Mon May 25 06:58:02 PDT 2015
Author: tstellar
Date: Mon May 25 08:58:01 2015
New Revision: 238136
URL: http://llvm.org/viewvc/llvm-project?rev=238136&view=rev
Log:
Add clang docs for 3.6.1
Added:
www-releases/trunk/3.6.1/tools/
www-releases/trunk/3.6.1/tools/clang/
www-releases/trunk/3.6.1/tools/clang/docs/
www-releases/trunk/3.6.1/tools/clang/docs/AddressSanitizer.html
www-releases/trunk/3.6.1/tools/clang/docs/AttributeReference.html
www-releases/trunk/3.6.1/tools/clang/docs/AutomaticReferenceCounting.html
www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.html
www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.txt
www-releases/trunk/3.6.1/tools/clang/docs/BlockLanguageSpec.html
www-releases/trunk/3.6.1/tools/clang/docs/ClangCheck.html
www-releases/trunk/3.6.1/tools/clang/docs/ClangFormat.html
www-releases/trunk/3.6.1/tools/clang/docs/ClangFormatStyleOptions.html
www-releases/trunk/3.6.1/tools/clang/docs/ClangPlugins.html
www-releases/trunk/3.6.1/tools/clang/docs/ClangTools.html
www-releases/trunk/3.6.1/tools/clang/docs/CrossCompilation.html
www-releases/trunk/3.6.1/tools/clang/docs/DataFlowSanitizer.html
www-releases/trunk/3.6.1/tools/clang/docs/DataFlowSanitizerDesign.html
www-releases/trunk/3.6.1/tools/clang/docs/DriverInternals.html
www-releases/trunk/3.6.1/tools/clang/docs/ExternalClangExamples.html
www-releases/trunk/3.6.1/tools/clang/docs/FAQ.html
www-releases/trunk/3.6.1/tools/clang/docs/HowToSetupToolingForLLVM.html
www-releases/trunk/3.6.1/tools/clang/docs/InternalsManual.html
www-releases/trunk/3.6.1/tools/clang/docs/IntroductionToTheClangAST.html
www-releases/trunk/3.6.1/tools/clang/docs/JSONCompilationDatabase.html
www-releases/trunk/3.6.1/tools/clang/docs/LanguageExtensions.html
www-releases/trunk/3.6.1/tools/clang/docs/LeakSanitizer.html
www-releases/trunk/3.6.1/tools/clang/docs/LibASTMatchers.html
www-releases/trunk/3.6.1/tools/clang/docs/LibASTMatchersReference.html
www-releases/trunk/3.6.1/tools/clang/docs/LibASTMatchersTutorial.html
www-releases/trunk/3.6.1/tools/clang/docs/LibFormat.html
www-releases/trunk/3.6.1/tools/clang/docs/LibTooling.html
www-releases/trunk/3.6.1/tools/clang/docs/MSVCCompatibility.html
www-releases/trunk/3.6.1/tools/clang/docs/MemorySanitizer.html
www-releases/trunk/3.6.1/tools/clang/docs/Modules.html
www-releases/trunk/3.6.1/tools/clang/docs/ObjectiveCLiterals.html
www-releases/trunk/3.6.1/tools/clang/docs/PCHInternals.html
www-releases/trunk/3.6.1/tools/clang/docs/PTHInternals.html
www-releases/trunk/3.6.1/tools/clang/docs/RAVFrontendAction.html
www-releases/trunk/3.6.1/tools/clang/docs/ReleaseNotes.html
www-releases/trunk/3.6.1/tools/clang/docs/SanitizerSpecialCaseList.html
www-releases/trunk/3.6.1/tools/clang/docs/ThreadSafetyAnalysis.html
www-releases/trunk/3.6.1/tools/clang/docs/ThreadSanitizer.html
www-releases/trunk/3.6.1/tools/clang/docs/Tooling.html
www-releases/trunk/3.6.1/tools/clang/docs/UsersManual.html
www-releases/trunk/3.6.1/tools/clang/docs/_images/
www-releases/trunk/3.6.1/tools/clang/docs/_images/DriverArchitecture.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_images/PCHLayout.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_sources/
www-releases/trunk/3.6.1/tools/clang/docs/_sources/AddressSanitizer.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/AttributeReference.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/AutomaticReferenceCounting.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/Block-ABI-Apple.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/BlockLanguageSpec.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ClangCheck.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ClangFormat.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ClangFormatStyleOptions.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ClangPlugins.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ClangTools.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/CrossCompilation.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/DataFlowSanitizer.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/DataFlowSanitizerDesign.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/DriverInternals.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ExternalClangExamples.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/FAQ.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/HowToSetupToolingForLLVM.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/InternalsManual.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/IntroductionToTheClangAST.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/JSONCompilationDatabase.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/LanguageExtensions.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/LeakSanitizer.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/LibASTMatchers.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/LibASTMatchersTutorial.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/LibFormat.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/LibTooling.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/MSVCCompatibility.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/MemorySanitizer.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/Modules.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ObjectiveCLiterals.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/PCHInternals.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/PTHInternals.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/RAVFrontendAction.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ReleaseNotes.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/SanitizerSpecialCaseList.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ThreadSafetyAnalysis.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/ThreadSanitizer.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/Tooling.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/UsersManual.txt
www-releases/trunk/3.6.1/tools/clang/docs/_sources/index.txt
www-releases/trunk/3.6.1/tools/clang/docs/_static/
www-releases/trunk/3.6.1/tools/clang/docs/_static/ajax-loader.gif (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/alert_info_32.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/alert_warning_32.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/basic.css
www-releases/trunk/3.6.1/tools/clang/docs/_static/bg-page.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/bullet_orange.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/comment-bright.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/comment-close.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/comment.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/doctools.js
www-releases/trunk/3.6.1/tools/clang/docs/_static/down-pressed.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/down.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/file.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/haiku.css
www-releases/trunk/3.6.1/tools/clang/docs/_static/jquery.js
www-releases/trunk/3.6.1/tools/clang/docs/_static/minus.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/plus.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/pygments.css
www-releases/trunk/3.6.1/tools/clang/docs/_static/searchtools.js
www-releases/trunk/3.6.1/tools/clang/docs/_static/underscore.js
www-releases/trunk/3.6.1/tools/clang/docs/_static/up-pressed.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/up.png (with props)
www-releases/trunk/3.6.1/tools/clang/docs/_static/websupport.js
www-releases/trunk/3.6.1/tools/clang/docs/genindex.html
www-releases/trunk/3.6.1/tools/clang/docs/index.html
www-releases/trunk/3.6.1/tools/clang/docs/objects.inv (with props)
www-releases/trunk/3.6.1/tools/clang/docs/search.html
www-releases/trunk/3.6.1/tools/clang/docs/searchindex.js
Added: www-releases/trunk/3.6.1/tools/clang/docs/AddressSanitizer.html
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.6.1/tools/clang/docs/AddressSanitizer.html?rev=238136&view=auto
==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/AddressSanitizer.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/AddressSanitizer.html Mon May 25 08:58:01 2015
@@ -0,0 +1,283 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>AddressSanitizer — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
+ <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="ThreadSanitizer" href="ThreadSanitizer.html" />
+ <link rel="prev" title="Thread Safety Analysis" href="ThreadSafetyAnalysis.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>AddressSanitizer</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="ThreadSafetyAnalysis.html">Thread Safety Analysis</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ThreadSanitizer.html">ThreadSanitizer</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="addresssanitizer">
+<h1>AddressSanitizer<a class="headerlink" href="#addresssanitizer" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
+<li><a class="reference internal" href="#how-to-build" id="id2">How to build</a></li>
+<li><a class="reference internal" href="#usage" id="id3">Usage</a><ul>
+<li><a class="reference internal" href="#has-feature-address-sanitizer" id="id4"><tt class="docutils literal"><span class="pre">__has_feature(address_sanitizer)</span></tt></a></li>
+<li><a class="reference internal" href="#attribute-no-sanitize-address" id="id5"><tt class="docutils literal"><span class="pre">__attribute__((no_sanitize_address))</span></tt></a></li>
+<li><a class="reference internal" href="#initialization-order-checking" id="id6">Initialization order checking</a></li>
+<li><a class="reference internal" href="#blacklist" id="id7">Blacklist</a></li>
+<li><a class="reference internal" href="#memory-leak-detection" id="id8">Memory leak detection</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#supported-platforms" id="id9">Supported Platforms</a></li>
+<li><a class="reference internal" href="#limitations" id="id10">Limitations</a></li>
+<li><a class="reference internal" href="#current-status" id="id11">Current Status</a></li>
+<li><a class="reference internal" href="#more-information" id="id12">More Information</a></li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id1">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>AddressSanitizer is a fast memory error detector. It consists of a compiler
+instrumentation module and a run-time library. The tool can detect the
+following types of bugs:</p>
+<ul class="simple">
+<li>Out-of-bounds accesses to heap, stack and globals</li>
+<li>Use-after-free</li>
+<li>Use-after-return (to some extent)</li>
+<li>Double-free, invalid free</li>
+<li>Memory leaks (experimental)</li>
+</ul>
+<p>Typical slowdown introduced by AddressSanitizer is <strong>2x</strong>.</p>
+</div>
+<div class="section" id="how-to-build">
+<h2><a class="toc-backref" href="#id2">How to build</a><a class="headerlink" href="#how-to-build" title="Permalink to this headline">¶</a></h2>
+<p>Follow the <a class="reference external" href="../get_started.html">clang build instructions</a>. CMake build is
+supported.</p>
+</div>
+<div class="section" id="usage">
+<h2><a class="toc-backref" href="#id3">Usage</a><a class="headerlink" href="#usage" title="Permalink to this headline">¶</a></h2>
+<p>Simply compile and link your program with <tt class="docutils literal"><span class="pre">-fsanitize=address</span></tt> flag. The
+AddressSanitizer run-time library should be linked to the final executable, so
+make sure to use <tt class="docutils literal"><span class="pre">clang</span></tt> (not <tt class="docutils literal"><span class="pre">ld</span></tt>) for the final link step. When linking
+shared libraries, the AddressSanitizer run-time is not linked, so
+<tt class="docutils literal"><span class="pre">-Wl,-z,defs</span></tt> may cause link errors (don’t use it with AddressSanitizer). To
+get a reasonable performance add <tt class="docutils literal"><span class="pre">-O1</span></tt> or higher. To get nicer stack traces
+in error messages add <tt class="docutils literal"><span class="pre">-fno-omit-frame-pointer</span></tt>. To get perfect stack traces
+you may need to disable inlining (just use <tt class="docutils literal"><span class="pre">-O1</span></tt>) and tail call elimination
+(<tt class="docutils literal"><span class="pre">-fno-optimize-sibling-calls</span></tt>).</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">%</span> cat example_UseAfterFree.cc
+<span class="go">int main(int argc, char **argv) {</span>
+<span class="go"> int *array = new int[100];</span>
+<span class="go"> delete [] array;</span>
+<span class="go"> return array[argc]; // BOOM</span>
+<span class="go">}</span>
+
+<span class="gp">#</span> Compile and link
+<span class="gp">%</span> clang -O1 -g -fsanitize<span class="o">=</span>address -fno-omit-frame-pointer example_UseAfterFree.cc
+</pre></div>
+</div>
+<p>or:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">#</span> Compile
+<span class="gp">%</span> clang -O1 -g -fsanitize<span class="o">=</span>address -fno-omit-frame-pointer -c example_UseAfterFree.cc
+<span class="gp">#</span> Link
+<span class="gp">%</span> clang -g -fsanitize<span class="o">=</span>address example_UseAfterFree.o
+</pre></div>
+</div>
+<p>If a bug is detected, the program will print an error message to stderr and
+exit with a non-zero exit code. To make AddressSanitizer symbolize its output
+you need to set the <tt class="docutils literal"><span class="pre">ASAN_SYMBOLIZER_PATH</span></tt> environment variable to point to
+the <tt class="docutils literal"><span class="pre">llvm-symbolizer</span></tt> binary (or make sure <tt class="docutils literal"><span class="pre">llvm-symbolizer</span></tt> is in your
+<tt class="docutils literal"><span class="pre">$PATH</span></tt>):</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">%</span> <span class="nv">ASAN_SYMBOLIZER_PATH</span><span class="o">=</span>/usr/local/bin/llvm-symbolizer ./a.out
+<span class="go">==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8</span>
+<span class="go">READ of size 4 at 0x7f7ddab8c084 thread T0</span>
+<span class="go"> #0 0x403c8c in main example_UseAfterFree.cc:4</span>
+<span class="go"> #1 0x7f7ddabcac4d in __libc_start_main ??:0</span>
+<span class="go">0x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210)</span>
+<span class="go">freed by thread T0 here:</span>
+<span class="go"> #0 0x404704 in operator delete[](void*) ??:0</span>
+<span class="go"> #1 0x403c53 in main example_UseAfterFree.cc:4</span>
+<span class="go"> #2 0x7f7ddabcac4d in __libc_start_main ??:0</span>
+<span class="go">previously allocated by thread T0 here:</span>
+<span class="go"> #0 0x404544 in operator new[](unsigned long) ??:0</span>
+<span class="go"> #1 0x403c43 in main example_UseAfterFree.cc:2</span>
+<span class="go"> #2 0x7f7ddabcac4d in __libc_start_main ??:0</span>
+<span class="go">==9442== ABORTING</span>
+</pre></div>
+</div>
+<p>If that does not work for you (e.g. your process is sandboxed), you can use a
+separate script to symbolize the result offline (online symbolization can be
+force disabled by setting <tt class="docutils literal"><span class="pre">ASAN_OPTIONS=symbolize=0</span></tt>):</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">%</span> <span class="nv">ASAN_OPTIONS</span><span class="o">=</span><span class="nv">symbolize</span><span class="o">=</span>0 ./a.out 2> log
+<span class="gp">%</span> projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt
+<span class="go">==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8</span>
+<span class="go">READ of size 4 at 0x7f7ddab8c084 thread T0</span>
+<span class="go"> #0 0x403c8c in main example_UseAfterFree.cc:4</span>
+<span class="go"> #1 0x7f7ddabcac4d in __libc_start_main ??:0</span>
+<span class="go">...</span>
+</pre></div>
+</div>
+<p>Note that on OS X you may need to run <tt class="docutils literal"><span class="pre">dsymutil</span></tt> on your binary to have the
+file:line info in the AddressSanitizer reports.</p>
+<p>AddressSanitizer exits on the first detected error. This is by design.
+One reason: it makes the generated code smaller and faster (both by
+~5%). Another reason: this makes fixing bugs unavoidable. With Valgrind,
+it is often the case that users treat Valgrind warnings as false
+positives (which they are not) and don’t fix them.</p>
+<div class="section" id="has-feature-address-sanitizer">
+<h3><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">__has_feature(address_sanitizer)</span></tt></a><a class="headerlink" href="#has-feature-address-sanitizer" title="Permalink to this headline">¶</a></h3>
+<p>In some cases one may need to execute different code depending on whether
+AddressSanitizer is enabled.
+<a class="reference internal" href="LanguageExtensions.html#langext-has-feature-has-extension"><em>__has_feature</em></a> can be used for
+this purpose.</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="cp">#if defined(__has_feature)</span>
+<span class="cp"># if __has_feature(address_sanitizer)</span>
+<span class="c1">// code that builds only under AddressSanitizer</span>
+<span class="cp"># endif</span>
+<span class="cp">#endif</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="attribute-no-sanitize-address">
+<h3><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">__attribute__((no_sanitize_address))</span></tt></a><a class="headerlink" href="#attribute-no-sanitize-address" title="Permalink to this headline">¶</a></h3>
+<p>Some code should not be instrumented by AddressSanitizer. One may use the
+function attribute
+<a class="reference internal" href="AttributeReference.html#langext-address-sanitizer"><em>no_sanitize_address</em></a>
+(or a deprecated synonym <cite>no_address_safety_analysis</cite>)
+to disable instrumentation of a particular function. This attribute may not be
+supported by other compilers, so we suggest to use it together with
+<tt class="docutils literal"><span class="pre">__has_feature(address_sanitizer)</span></tt>.</p>
+</div>
+<div class="section" id="initialization-order-checking">
+<h3><a class="toc-backref" href="#id6">Initialization order checking</a><a class="headerlink" href="#initialization-order-checking" title="Permalink to this headline">¶</a></h3>
+<p>AddressSanitizer can optionally detect dynamic initialization order problems,
+when initialization of globals defined in one translation unit uses
+globals defined in another translation unit. To enable this check at runtime,
+you should set environment variable
+<tt class="docutils literal"><span class="pre">ASAN_OPTIONS=check_initialization_order=1</span></tt>.</p>
+</div>
+<div class="section" id="blacklist">
+<h3><a class="toc-backref" href="#id7">Blacklist</a><a class="headerlink" href="#blacklist" title="Permalink to this headline">¶</a></h3>
+<p>AddressSanitizer supports <tt class="docutils literal"><span class="pre">src</span></tt> and <tt class="docutils literal"><span class="pre">fun</span></tt> entity types in
+<a class="reference internal" href="SanitizerSpecialCaseList.html"><em>Sanitizer special case list</em></a>, that can be used to suppress error reports
+in the specified source files or functions. Additionally, AddressSanitizer
+introduces <tt class="docutils literal"><span class="pre">global</span></tt> and <tt class="docutils literal"><span class="pre">type</span></tt> entity types that can be used to
+suppress error reports for out-of-bound access to globals with certain
+names and types (you may only specify class or struct types).</p>
+<p>You may use an <tt class="docutils literal"><span class="pre">init</span></tt> category to suppress reports about initialization-order
+problems happening in certain source files or with certain global variables.</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Suppress error reports for code in a file or in a function:</span>
+src:bad_file.cpp
+<span class="c"># Ignore all functions with names containing MyFooBar:</span>
+fun:*MyFooBar*
+<span class="c"># Disable out-of-bound checks for global:</span>
+global:bad_array
+<span class="c"># Disable out-of-bound checks for global instances of a given class ...</span>
+<span class="nb">type</span>:Namespace::BadClassName
+<span class="c"># ... or a given struct. Use wildcard to deal with anonymous namespace.</span>
+<span class="nb">type</span>:Namespace2::*::BadStructName
+<span class="c"># Disable initialization-order checks for globals:</span>
+global:bad_init_global<span class="o">=</span>init
+<span class="nb">type</span>:*BadInitClassSubstring*<span class="o">=</span>init
+src:bad/init/files/*<span class="o">=</span>init
+</pre></div>
+</div>
+</div>
+<div class="section" id="memory-leak-detection">
+<h3><a class="toc-backref" href="#id8">Memory leak detection</a><a class="headerlink" href="#memory-leak-detection" title="Permalink to this headline">¶</a></h3>
+<p>For the experimental memory leak detector in AddressSanitizer, see
+<a class="reference internal" href="LeakSanitizer.html"><em>LeakSanitizer</em></a>.</p>
+</div>
+</div>
+<div class="section" id="supported-platforms">
+<h2><a class="toc-backref" href="#id9">Supported Platforms</a><a class="headerlink" href="#supported-platforms" title="Permalink to this headline">¶</a></h2>
+<p>AddressSanitizer is supported on</p>
+<ul class="simple">
+<li>Linux i386/x86_64 (tested on Ubuntu 12.04);</li>
+<li>MacOS 10.6 - 10.9 (i386/x86_64).</li>
+<li>Android ARM</li>
+<li>FreeBSD i386/x86_64 (tested on FreeBSD 11-current)</li>
+</ul>
+<p>Ports to various other platforms are in progress.</p>
+</div>
+<div class="section" id="limitations">
+<h2><a class="toc-backref" href="#id10">Limitations</a><a class="headerlink" href="#limitations" title="Permalink to this headline">¶</a></h2>
+<ul class="simple">
+<li>AddressSanitizer uses more real memory than a native run. Exact overhead
+depends on the allocations sizes. The smaller the allocations you make the
+bigger the overhead is.</li>
+<li>AddressSanitizer uses more stack memory. We have seen up to 3x increase.</li>
+<li>On 64-bit platforms AddressSanitizer maps (but not reserves) 16+ Terabytes of
+virtual address space. This means that tools like <tt class="docutils literal"><span class="pre">ulimit</span></tt> may not work as
+usually expected.</li>
+<li>Static linking is not supported.</li>
+</ul>
+</div>
+<div class="section" id="current-status">
+<h2><a class="toc-backref" href="#id11">Current Status</a><a class="headerlink" href="#current-status" title="Permalink to this headline">¶</a></h2>
+<p>AddressSanitizer is fully functional on supported platforms starting from LLVM
+3.1. The test suite is integrated into CMake build and can be run with <tt class="docutils literal"><span class="pre">make</span>
+<span class="pre">check-asan</span></tt> command.</p>
+</div>
+<div class="section" id="more-information">
+<h2><a class="toc-backref" href="#id12">More Information</a><a class="headerlink" href="#more-information" title="Permalink to this headline">¶</a></h2>
+<p><a class="reference external" href="http://code.google.com/p/address-sanitizer/">http://code.google.com/p/address-sanitizer</a></p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ThreadSafetyAnalysis.html">Thread Safety Analysis</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ThreadSanitizer.html">ThreadSanitizer</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
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+ </body>
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+++ www-releases/trunk/3.6.1/tools/clang/docs/AttributeReference.html Mon May 25 08:58:01 2015
@@ -0,0 +1,1759 @@
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+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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+ <title>Attributes in Clang — Clang 3.6 documentation</title>
+
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+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Attributes in Clang</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="AutomaticReferenceCounting.html">Objective-C Automatic Reference Counting (ARC)</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="CrossCompilation.html">Cross-compilation using Clang</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="attributes-in-clang">
+<h1>Attributes in Clang<a class="headerlink" href="#attributes-in-clang" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
+<li><a class="reference internal" href="#function-attributes" id="id3">Function Attributes</a><ul>
+<li><a class="reference internal" href="#interrupt" id="id4">interrupt</a></li>
+<li><a class="reference internal" href="#acquire-capability-acquire-shared-capability-clang-acquire-capability-clang-acquire-shared-capability" id="id5">acquire_capability (acquire_shared_capability, clang::acquire_capability, clang::acquire_shared_capability)</a></li>
+<li><a class="reference internal" href="#assert-capability-assert-shared-capability-clang-assert-capability-clang-assert-shared-capability" id="id6">assert_capability (assert_shared_capability, clang::assert_capability, clang::assert_shared_capability)</a></li>
+<li><a class="reference internal" href="#availability" id="id7">availability</a></li>
+<li><a class="reference internal" href="#noreturn" id="id8">_Noreturn</a></li>
+<li><a class="reference internal" href="#id1" id="id9">noreturn</a></li>
+<li><a class="reference internal" href="#carries-dependency" id="id10">carries_dependency</a></li>
+<li><a class="reference internal" href="#enable-if" id="id11">enable_if</a></li>
+<li><a class="reference internal" href="#flatten-gnu-flatten" id="id12">flatten (gnu::flatten)</a></li>
+<li><a class="reference internal" href="#format-gnu-format" id="id13">format (gnu::format)</a></li>
+<li><a class="reference internal" href="#noduplicate-clang-noduplicate" id="id14">noduplicate (clang::noduplicate)</a></li>
+<li><a class="reference internal" href="#no-sanitize-address-no-address-safety-analysis-gnu-no-address-safety-analysis-gnu-no-sanitize-address" id="id15">no_sanitize_address (no_address_safety_analysis, gnu::no_address_safety_analysis, gnu::no_sanitize_address)</a></li>
+<li><a class="reference internal" href="#no-sanitize-memory" id="id16">no_sanitize_memory</a></li>
+<li><a class="reference internal" href="#no-sanitize-thread" id="id17">no_sanitize_thread</a></li>
+<li><a class="reference internal" href="#no-split-stack-gnu-no-split-stack" id="id18">no_split_stack (gnu::no_split_stack)</a></li>
+<li><a class="reference internal" href="#objc-method-family" id="id19">objc_method_family</a></li>
+<li><a class="reference internal" href="#objc-requires-super" id="id20">objc_requires_super</a></li>
+<li><a class="reference internal" href="#optnone-clang-optnone" id="id21">optnone (clang::optnone)</a></li>
+<li><a class="reference internal" href="#overloadable" id="id22">overloadable</a></li>
+<li><a class="reference internal" href="#pcs-gnu-pcs" id="id23">pcs (gnu::pcs)</a></li>
+<li><a class="reference internal" href="#release-capability-release-shared-capability-clang-release-capability-clang-release-shared-capability" id="id24">release_capability (release_shared_capability, clang::release_capability, clang::release_shared_capability)</a></li>
+<li><a class="reference internal" href="#try-acquire-capability-try-acquire-shared-capability-clang-try-acquire-capability-clang-try-acquire-shared-capability" id="id25">try_acquire_capability (try_acquire_shared_capability, clang::try_acquire_capability, clang::try_acquire_shared_capability)</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#variable-attributes" id="id26">Variable Attributes</a><ul>
+<li><a class="reference internal" href="#section-gnu-section-declspec-allocate" id="id27">section (gnu::section, __declspec(allocate))</a></li>
+<li><a class="reference internal" href="#tls-model-gnu-tls-model" id="id28">tls_model (gnu::tls_model)</a></li>
+<li><a class="reference internal" href="#thread" id="id29">thread</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#type-attributes" id="id30">Type Attributes</a><ul>
+<li><a class="reference internal" href="#single-inhertiance-multiple-inheritance-virtual-inheritance" id="id31">__single_inhertiance, __multiple_inheritance, __virtual_inheritance</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#statement-attributes" id="id32">Statement Attributes</a><ul>
+<li><a class="reference internal" href="#fallthrough-clang-fallthrough" id="id33">fallthrough (clang::fallthrough)</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#consumed-annotation-checking" id="id34">Consumed Annotation Checking</a><ul>
+<li><a class="reference internal" href="#callable-when" id="id35">callable_when</a></li>
+<li><a class="reference internal" href="#consumable" id="id36">consumable</a></li>
+<li><a class="reference internal" href="#param-typestate" id="id37">param_typestate</a></li>
+<li><a class="reference internal" href="#return-typestate" id="id38">return_typestate</a></li>
+<li><a class="reference internal" href="#set-typestate" id="id39">set_typestate</a></li>
+<li><a class="reference internal" href="#test-typestate" id="id40">test_typestate</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#type-safety-checking" id="id41">Type Safety Checking</a><ul>
+<li><a class="reference internal" href="#argument-with-type-tag" id="id42">argument_with_type_tag</a></li>
+<li><a class="reference internal" href="#pointer-with-type-tag" id="id43">pointer_with_type_tag</a></li>
+<li><a class="reference internal" href="#type-tag-for-datatype" id="id44">type_tag_for_datatype</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id2">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>This page lists the attributes currently supported by Clang.</p>
+</div>
+<div class="section" id="function-attributes">
+<h2><a class="toc-backref" href="#id3">Function Attributes</a><a class="headerlink" href="#function-attributes" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="interrupt">
+<h3><a class="toc-backref" href="#id4">interrupt</a><a class="headerlink" href="#interrupt" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Clang supports the GNU style <tt class="docutils literal"><span class="pre">__attribute__((interrupt("TYPE")))</span></tt> attribute on
+ARM targets. This attribute may be attached to a function definition and
+instructs the backend to generate appropriate function entry/exit code so that
+it can be used directly as an interrupt service routine.</p>
+<p>The parameter passed to the interrupt attribute is optional, but if
+provided it must be a string literal with one of the following values: “IRQ”,
+“FIQ”, “SWI”, “ABORT”, “UNDEF”.</p>
+<p>The semantics are as follows:</p>
+<ul>
+<li><p class="first">If the function is AAPCS, Clang instructs the backend to realign the stack to
+8 bytes on entry. This is a general requirement of the AAPCS at public
+interfaces, but may not hold when an exception is taken. Doing this allows
+other AAPCS functions to be called.</p>
+</li>
+<li><p class="first">If the CPU is M-class this is all that needs to be done since the architecture
+itself is designed in such a way that functions obeying the normal AAPCS ABI
+constraints are valid exception handlers.</p>
+</li>
+<li><p class="first">If the CPU is not M-class, the prologue and epilogue are modified to save all
+non-banked registers that are used, so that upon return the user-mode state
+will not be corrupted. Note that to avoid unnecessary overhead, only
+general-purpose (integer) registers are saved in this way. If VFP operations
+are needed, that state must be saved manually.</p>
+<p>Specifically, interrupt kinds other than “FIQ” will save all core registers
+except “lr” and “sp”. “FIQ” interrupts will save r0-r7.</p>
+</li>
+<li><p class="first">If the CPU is not M-class, the return instruction is changed to one of the
+canonical sequences permitted by the architecture for exception return. Where
+possible the function itself will make the necessary “lr” adjustments so that
+the “preferred return address” is selected.</p>
+<p>Unfortunately the compiler is unable to make this guarantee for an “UNDEF”
+handler, where the offset from “lr” to the preferred return address depends on
+the execution state of the code which generated the exception. In this case
+a sequence equivalent to “movs pc, lr” will be used.</p>
+</li>
+</ul>
+</div>
+<div class="section" id="acquire-capability-acquire-shared-capability-clang-acquire-capability-clang-acquire-shared-capability">
+<h3><a class="toc-backref" href="#id5">acquire_capability (acquire_shared_capability, clang::acquire_capability, clang::acquire_shared_capability)</a><a class="headerlink" href="#acquire-capability-acquire-shared-capability-clang-acquire-capability-clang-acquire-shared-capability" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Marks a function as acquiring a capability.</p>
+</div>
+<div class="section" id="assert-capability-assert-shared-capability-clang-assert-capability-clang-assert-shared-capability">
+<h3><a class="toc-backref" href="#id6">assert_capability (assert_shared_capability, clang::assert_capability, clang::assert_shared_capability)</a><a class="headerlink" href="#assert-capability-assert-shared-capability-clang-assert-capability-clang-assert-shared-capability" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Marks a function that dynamically tests whether a capability is held, and halts
+the program if it is not held.</p>
+</div>
+<div class="section" id="availability">
+<h3><a class="toc-backref" href="#id7">availability</a><a class="headerlink" href="#availability" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">availability</span></tt> attribute can be placed on declarations to describe the
+lifecycle of that declaration relative to operating system versions. Consider
+the function declaration for a hypothetical function <tt class="docutils literal"><span class="pre">f</span></tt>:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">f</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.4</span><span class="p">,</span><span class="n">deprecated</span><span class="o">=</span><span class="mf">10.6</span><span class="p">,</span><span class="n">obsoleted</span><span class="o">=</span><span class="mf">10.7</span><span class="p">)));</span>
+</pre></div>
+</div>
+<p>The availability attribute states that <tt class="docutils literal"><span class="pre">f</span></tt> was introduced in Mac OS X 10.4,
+deprecated in Mac OS X 10.6, and obsoleted in Mac OS X 10.7. This information
+is used by Clang to determine when it is safe to use <tt class="docutils literal"><span class="pre">f</span></tt>: for example, if
+Clang is instructed to compile code for Mac OS X 10.5, a call to <tt class="docutils literal"><span class="pre">f()</span></tt>
+succeeds. If Clang is instructed to compile code for Mac OS X 10.6, the call
+succeeds but Clang emits a warning specifying that the function is deprecated.
+Finally, if Clang is instructed to compile code for Mac OS X 10.7, the call
+fails because <tt class="docutils literal"><span class="pre">f()</span></tt> is no longer available.</p>
+<p>The availability attribute is a comma-separated list starting with the
+platform name and then including clauses specifying important milestones in the
+declaration’s lifetime (in any order) along with additional information. Those
+clauses can be:</p>
+<dl class="docutils">
+<dt>introduced=<em>version</em></dt>
+<dd>The first version in which this declaration was introduced.</dd>
+<dt>deprecated=<em>version</em></dt>
+<dd>The first version in which this declaration was deprecated, meaning that
+users should migrate away from this API.</dd>
+<dt>obsoleted=<em>version</em></dt>
+<dd>The first version in which this declaration was obsoleted, meaning that it
+was removed completely and can no longer be used.</dd>
+<dt>unavailable</dt>
+<dd>This declaration is never available on this platform.</dd>
+<dt>message=<em>string-literal</em></dt>
+<dd>Additional message text that Clang will provide when emitting a warning or
+error about use of a deprecated or obsoleted declaration. Useful to direct
+users to replacement APIs.</dd>
+</dl>
+<p>Multiple availability attributes can be placed on a declaration, which may
+correspond to different platforms. Only the availability attribute with the
+platform corresponding to the target platform will be used; any others will be
+ignored. If no availability attribute specifies availability for the current
+target platform, the availability attributes are ignored. Supported platforms
+are:</p>
+<dl class="docutils">
+<dt><tt class="docutils literal"><span class="pre">ios</span></tt></dt>
+<dd>Apple’s iOS operating system. The minimum deployment target is specified by
+the <tt class="docutils literal"><span class="pre">-mios-version-min=*version*</span></tt> or <tt class="docutils literal"><span class="pre">-miphoneos-version-min=*version*</span></tt>
+command-line arguments.</dd>
+<dt><tt class="docutils literal"><span class="pre">macosx</span></tt></dt>
+<dd>Apple’s Mac OS X operating system. The minimum deployment target is
+specified by the <tt class="docutils literal"><span class="pre">-mmacosx-version-min=*version*</span></tt> command-line argument.</dd>
+</dl>
+<p>A declaration can be used even when deploying back to a platform version prior
+to when the declaration was introduced. When this happens, the declaration is
+<a class="reference external" href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly linked</a>,
+as if the <tt class="docutils literal"><span class="pre">weak_import</span></tt> attribute were added to the declaration. A
+weakly-linked declaration may or may not be present a run-time, and a program
+can determine whether the declaration is present by checking whether the
+address of that declaration is non-NULL.</p>
+<p>If there are multiple declarations of the same entity, the availability
+attributes must either match on a per-platform basis or later
+declarations must not have availability attributes for that
+platform. For example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.4</span><span class="p">)));</span>
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.4</span><span class="p">)));</span> <span class="c1">// okay, matches</span>
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">ios</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">4.0</span><span class="p">)));</span> <span class="c1">// okay, adds a new platform</span>
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span> <span class="c1">// okay, inherits both macosx and ios availability from above.</span>
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.5</span><span class="p">)));</span> <span class="c1">// error: mismatch</span>
+</pre></div>
+</div>
+<p>When one method overrides another, the overriding method can be more widely available than the overridden method, e.g.,:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="k">@interface</span> <span class="nc">A</span>
+<span class="k">-</span> <span class="p">(</span><span class="kt">id</span><span class="p">)</span><span class="nf">method</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.4</span><span class="p">)));</span>
+<span class="k">-</span> <span class="p">(</span><span class="kt">id</span><span class="p">)</span><span class="nf">method2</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.4</span><span class="p">)));</span>
+<span class="k">@end</span>
+
+<span class="k">@interface</span> <span class="nc">B</span> : <span class="nc">A</span>
+<span class="k">-</span> <span class="p">(</span><span class="kt">id</span><span class="p">)</span><span class="nf">method</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.3</span><span class="p">)));</span> <span class="c1">// okay: method moved into base class later</span>
+<span class="k">-</span> <span class="p">(</span><span class="kt">id</span><span class="p">)</span><span class="nf">method</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">availability</span><span class="p">(</span><span class="n">macosx</span><span class="p">,</span><span class="n">introduced</span><span class="o">=</span><span class="mf">10.5</span><span class="p">)));</span> <span class="c1">// error: this method was available via the base class in 10.4</span>
+<span class="k">@end</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="noreturn">
+<h3><a class="toc-backref" href="#id8">_Noreturn</a><a class="headerlink" href="#noreturn" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td> </td>
+<td> </td>
+<td> </td>
+<td>X</td>
+</tr>
+</tbody>
+</table>
+<p>A function declared as <tt class="docutils literal"><span class="pre">_Noreturn</span></tt> shall not return to its caller. The
+compiler will generate a diagnostic for a function declared as <tt class="docutils literal"><span class="pre">_Noreturn</span></tt>
+that appears to be capable of returning to its caller.</p>
+</div>
+<div class="section" id="id1">
+<h3><a class="toc-backref" href="#id9">noreturn</a><a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td> </td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>A function declared as <tt class="docutils literal"><span class="pre">[[noreturn]]</span></tt> shall not return to its caller. The
+compiler will generate a diagnostic for a function declared as <tt class="docutils literal"><span class="pre">[[noreturn]]</span></tt>
+that appears to be capable of returning to its caller.</p>
+</div>
+<div class="section" id="carries-dependency">
+<h3><a class="toc-backref" href="#id10">carries_dependency</a><a class="headerlink" href="#carries-dependency" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">carries_dependency</span></tt> attribute specifies dependency propagation into and
+out of functions.</p>
+<p>When specified on a function or Objective-C method, the <tt class="docutils literal"><span class="pre">carries_dependency</span></tt>
+attribute means that the return value carries a dependency out of the function,
+so that the implementation need not constrain ordering upon return from that
+function. Implementations of the function and its caller may choose to preserve
+dependencies instead of emitting memory ordering instructions such as fences.</p>
+<p>Note, this attribute does not change the meaning of the program, but may result
+in generation of more efficient code.</p>
+</div>
+<div class="section" id="enable-if">
+<h3><a class="toc-backref" href="#id11">enable_if</a><a class="headerlink" href="#enable-if" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<div class="admonition note">
+<p class="first admonition-title">Note</p>
+<p class="last">Some features of this attribute are experimental. The meaning of
+multiple enable_if attributes on a single declaration is subject to change in
+a future version of clang. Also, the ABI is not standardized and the name
+mangling may change in future versions. To avoid that, use asm labels.</p>
+</div>
+<p>The <tt class="docutils literal"><span class="pre">enable_if</span></tt> attribute can be placed on function declarations to control
+which overload is selected based on the values of the function’s arguments.
+When combined with the <tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute, this feature is also
+available in C.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">isdigit</span><span class="p">(</span><span class="kt">int</span> <span class="n">c</span><span class="p">);</span>
+<span class="kt">int</span> <span class="nf">isdigit</span><span class="p">(</span><span class="kt">int</span> <span class="n">c</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="n">c</span> <span class="o"><=</span> <span class="o">-</span><span class="mi">1</span> <span class="o">||</span> <span class="n">c</span> <span class="o">></span> <span class="mi">255</span><span class="p">,</span> <span class="s">"chosen when 'c' is out of range"</span><span class="p">)))</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">unavailable</span><span class="p">(</span><span class="s">"'c' must have the value of an unsigned char or EOF"</span><span class="p">)));</span>
+
+<span class="kt">void</span> <span class="nf">foo</span><span class="p">(</span><span class="kt">char</span> <span class="n">c</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">isdigit</span><span class="p">(</span><span class="n">c</span><span class="p">);</span>
+ <span class="n">isdigit</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>
+ <span class="n">isdigit</span><span class="p">(</span><span class="o">-</span><span class="mi">10</span><span class="p">);</span> <span class="c1">// results in a compile-time error.</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The enable_if attribute takes two arguments, the first is an expression written
+in terms of the function parameters, the second is a string explaining why this
+overload candidate could not be selected to be displayed in diagnostics. The
+expression is part of the function signature for the purposes of determining
+whether it is a redeclaration (following the rules used when determining
+whether a C++ template specialization is ODR-equivalent), but is not part of
+the type.</p>
+<p>The enable_if expression is evaluated as if it were the body of a
+bool-returning constexpr function declared with the arguments of the function
+it is being applied to, then called with the parameters at the callsite. If the
+result is false or could not be determined through constant expression
+evaluation, then this overload will not be chosen and the provided string may
+be used in a diagnostic if the compile fails as a result.</p>
+<p>Because the enable_if expression is an unevaluated context, there are no global
+state changes, nor the ability to pass information from the enable_if
+expression to the function body. For example, suppose we want calls to
+strnlen(strbuf, maxlen) to resolve to strnlen_chk(strbuf, maxlen, size of
+strbuf) only if the size of strbuf can be determined:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">__attribute__</span><span class="p">((</span><span class="n">always_inline</span><span class="p">))</span>
+<span class="k">static</span> <span class="kr">inline</span> <span class="kt">size_t</span> <span class="n">strnlen</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">s</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">maxlen</span><span class="p">)</span>
+ <span class="n">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">))</span>
+ <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="n">__builtin_object_size</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span> <span class="o">!=</span> <span class="o">-</span><span class="mi">1</span><span class="p">))),</span>
+ <span class="s">"chosen when the buffer size is known but 'maxlen' is not"</span><span class="p">)))</span>
+<span class="p">{</span>
+ <span class="k">return</span> <span class="n">strnlen_chk</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">maxlen</span><span class="p">,</span> <span class="n">__builtin_object_size</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="mi">0</span><span class="p">));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Multiple enable_if attributes may be applied to a single declaration. In this
+case, the enable_if expressions are evaluated from left to right in the
+following manner. First, the candidates whose enable_if expressions evaluate to
+false or cannot be evaluated are discarded. If the remaining candidates do not
+share ODR-equivalent enable_if expressions, the overload resolution is
+ambiguous. Otherwise, enable_if overload resolution continues with the next
+enable_if attribute on the candidates that have not been discarded and have
+remaining enable_if attributes. In this way, we pick the most specific
+overload out of a number of viable overloads using enable_if.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">f</span><span class="p">()</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="nb">true</span><span class="p">,</span> <span class="s">""</span><span class="p">)));</span> <span class="c1">// #1</span>
+<span class="kt">void</span> <span class="nf">f</span><span class="p">()</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="nb">true</span><span class="p">,</span> <span class="s">""</span><span class="p">)))</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="nb">true</span><span class="p">,</span> <span class="s">""</span><span class="p">)));</span> <span class="c1">// #2</span>
+
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span> <span class="n">i</span><span class="p">,</span> <span class="kt">int</span> <span class="n">j</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="s">""</span><span class="p">)));</span> <span class="c1">// #1</span>
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span> <span class="n">i</span><span class="p">,</span> <span class="kt">int</span> <span class="n">j</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="n">j</span><span class="p">,</span> <span class="s">""</span><span class="p">)))</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">enable_if</span><span class="p">(</span><span class="nb">true</span><span class="p">)));</span> <span class="c1">// #2</span>
+</pre></div>
+</div>
+<p>In this example, a call to f() is always resolved to #2, as the first enable_if
+expression is ODR-equivalent for both declarations, but #1 does not have another
+enable_if expression to continue evaluating, so the next round of evaluation has
+only a single candidate. In a call to g(1, 1), the call is ambiguous even though
+#2 has more enable_if attributes, because the first enable_if expressions are
+not ODR-equivalent.</p>
+<p>Query for this feature with <tt class="docutils literal"><span class="pre">__has_attribute(enable_if)</span></tt>.</p>
+</div>
+<div class="section" id="flatten-gnu-flatten">
+<h3><a class="toc-backref" href="#id12">flatten (gnu::flatten)</a><a class="headerlink" href="#flatten-gnu-flatten" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">flatten</span></tt> attribute causes calls within the attributed function to
+be inlined unless it is impossible to do so, for example if the body of the
+callee is unavailable or if the callee has the <tt class="docutils literal"><span class="pre">noinline</span></tt> attribute.</p>
+</div>
+<div class="section" id="format-gnu-format">
+<h3><a class="toc-backref" href="#id13">format (gnu::format)</a><a class="headerlink" href="#format-gnu-format" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Clang supports the <tt class="docutils literal"><span class="pre">format</span></tt> attribute, which indicates that the function
+accepts a <tt class="docutils literal"><span class="pre">printf</span></tt> or <tt class="docutils literal"><span class="pre">scanf</span></tt>-like format string and corresponding
+arguments or a <tt class="docutils literal"><span class="pre">va_list</span></tt> that contains these arguments.</p>
+<p>Please see <a class="reference external" href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html">GCC documentation about format attribute</a> to find details
+about attribute syntax.</p>
+<p>Clang implements two kinds of checks with this attribute.</p>
+<ol class="arabic">
+<li><p class="first">Clang checks that the function with the <tt class="docutils literal"><span class="pre">format</span></tt> attribute is called with
+a format string that uses format specifiers that are allowed, and that
+arguments match the format string. This is the <tt class="docutils literal"><span class="pre">-Wformat</span></tt> warning, it is
+on by default.</p>
+</li>
+<li><p class="first">Clang checks that the format string argument is a literal string. This is
+the <tt class="docutils literal"><span class="pre">-Wformat-nonliteral</span></tt> warning, it is off by default.</p>
+<p>Clang implements this mostly the same way as GCC, but there is a difference
+for functions that accept a <tt class="docutils literal"><span class="pre">va_list</span></tt> argument (for example, <tt class="docutils literal"><span class="pre">vprintf</span></tt>).
+GCC does not emit <tt class="docutils literal"><span class="pre">-Wformat-nonliteral</span></tt> warning for calls to such
+fuctions. Clang does not warn if the format string comes from a function
+parameter, where the function is annotated with a compatible attribute,
+otherwise it warns. For example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">__attribute__</span><span class="p">((</span><span class="n">__format__</span> <span class="p">(</span><span class="n">__scanf__</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">)))</span>
+<span class="kt">void</span> <span class="n">foo</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">s</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf</span><span class="p">,</span> <span class="p">...)</span> <span class="p">{</span>
+ <span class="kt">va_list</span> <span class="n">ap</span><span class="p">;</span>
+ <span class="n">va_start</span><span class="p">(</span><span class="n">ap</span><span class="p">,</span> <span class="n">buf</span><span class="p">);</span>
+
+ <span class="n">vprintf</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">ap</span><span class="p">);</span> <span class="c1">// warning: format string is not a string literal</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>In this case we warn because <tt class="docutils literal"><span class="pre">s</span></tt> contains a format string for a
+<tt class="docutils literal"><span class="pre">scanf</span></tt>-like function, but it is passed to a <tt class="docutils literal"><span class="pre">printf</span></tt>-like function.</p>
+<p>If the attribute is removed, clang still warns, because the format string is
+not a string literal.</p>
+<p>Another example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">__attribute__</span><span class="p">((</span><span class="n">__format__</span> <span class="p">(</span><span class="n">__printf__</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">)))</span>
+<span class="kt">void</span> <span class="n">foo</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">s</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span><span class="n">buf</span><span class="p">,</span> <span class="p">...)</span> <span class="p">{</span>
+ <span class="kt">va_list</span> <span class="n">ap</span><span class="p">;</span>
+ <span class="n">va_start</span><span class="p">(</span><span class="n">ap</span><span class="p">,</span> <span class="n">buf</span><span class="p">);</span>
+
+ <span class="n">vprintf</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">ap</span><span class="p">);</span> <span class="c1">// warning</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>In this case Clang does not warn because the format string <tt class="docutils literal"><span class="pre">s</span></tt> and
+the corresponding arguments are annotated. If the arguments are
+incorrect, the caller of <tt class="docutils literal"><span class="pre">foo</span></tt> will receive a warning.</p>
+</li>
+</ol>
+</div>
+<div class="section" id="noduplicate-clang-noduplicate">
+<h3><a class="toc-backref" href="#id14">noduplicate (clang::noduplicate)</a><a class="headerlink" href="#noduplicate-clang-noduplicate" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">noduplicate</span></tt> attribute can be placed on function declarations to control
+whether function calls to this function can be duplicated or not as a result of
+optimizations. This is required for the implementation of functions with
+certain special requirements, like the OpenCL “barrier” function, that might
+need to be run concurrently by all the threads that are executing in lockstep
+on the hardware. For example this attribute applied on the function
+“nodupfunc” in the code below avoids that:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">nodupfunc</span><span class="p">()</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">noduplicate</span><span class="p">));</span>
+<span class="c1">// Setting it as a C++11 attribute is also valid</span>
+<span class="c1">// void nodupfunc() [[clang::noduplicate]];</span>
+<span class="kt">void</span> <span class="nf">foo</span><span class="p">();</span>
+<span class="kt">void</span> <span class="nf">bar</span><span class="p">();</span>
+
+<span class="n">nodupfunc</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">a</span> <span class="o">></span> <span class="n">n</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">foo</span><span class="p">();</span>
+<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+ <span class="n">bar</span><span class="p">();</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>gets possibly modified by some optimizations into code similar to this:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="n">a</span> <span class="o">></span> <span class="n">n</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">nodupfunc</span><span class="p">();</span>
+ <span class="n">foo</span><span class="p">();</span>
+<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+ <span class="n">nodupfunc</span><span class="p">();</span>
+ <span class="n">bar</span><span class="p">();</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>where the call to “nodupfunc” is duplicated and sunk into the two branches
+of the condition.</p>
+</div>
+<div class="section" id="no-sanitize-address-no-address-safety-analysis-gnu-no-address-safety-analysis-gnu-no-sanitize-address">
+<h3><a class="toc-backref" href="#id15">no_sanitize_address (no_address_safety_analysis, gnu::no_address_safety_analysis, gnu::no_sanitize_address)</a><a class="headerlink" href="#no-sanitize-address-no-address-safety-analysis-gnu-no-address-safety-analysis-gnu-no-sanitize-address" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p id="langext-address-sanitizer">Use <tt class="docutils literal"><span class="pre">__attribute__((no_sanitize_address))</span></tt> on a function declaration to
+specify that address safety instrumentation (e.g. AddressSanitizer) should
+not be applied to that function.</p>
+</div>
+<div class="section" id="no-sanitize-memory">
+<h3><a class="toc-backref" href="#id16">no_sanitize_memory</a><a class="headerlink" href="#no-sanitize-memory" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p id="langext-memory-sanitizer">Use <tt class="docutils literal"><span class="pre">__attribute__((no_sanitize_memory))</span></tt> on a function declaration to
+specify that checks for uninitialized memory should not be inserted
+(e.g. by MemorySanitizer). The function may still be instrumented by the tool
+to avoid false positives in other places.</p>
+</div>
+<div class="section" id="no-sanitize-thread">
+<h3><a class="toc-backref" href="#id17">no_sanitize_thread</a><a class="headerlink" href="#no-sanitize-thread" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p id="langext-thread-sanitizer">Use <tt class="docutils literal"><span class="pre">__attribute__((no_sanitize_thread))</span></tt> on a function declaration to
+specify that checks for data races on plain (non-atomic) memory accesses should
+not be inserted by ThreadSanitizer. The function is still instrumented by the
+tool to avoid false positives and provide meaningful stack traces.</p>
+</div>
+<div class="section" id="no-split-stack-gnu-no-split-stack">
+<h3><a class="toc-backref" href="#id18">no_split_stack (gnu::no_split_stack)</a><a class="headerlink" href="#no-split-stack-gnu-no-split-stack" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">no_split_stack</span></tt> attribute disables the emission of the split stack
+preamble for a particular function. It has no effect if <tt class="docutils literal"><span class="pre">-fsplit-stack</span></tt>
+is not specified.</p>
+</div>
+<div class="section" id="objc-method-family">
+<h3><a class="toc-backref" href="#id19">objc_method_family</a><a class="headerlink" href="#objc-method-family" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Many methods in Objective-C have conventional meanings determined by their
+selectors. It is sometimes useful to be able to mark a method as having a
+particular conventional meaning despite not having the right selector, or as
+not having the conventional meaning that its selector would suggest. For these
+use cases, we provide an attribute to specifically describe the “method family”
+that a method belongs to.</p>
+<p><strong>Usage</strong>: <tt class="docutils literal"><span class="pre">__attribute__((objc_method_family(X)))</span></tt>, where <tt class="docutils literal"><span class="pre">X</span></tt> is one of
+<tt class="docutils literal"><span class="pre">none</span></tt>, <tt class="docutils literal"><span class="pre">alloc</span></tt>, <tt class="docutils literal"><span class="pre">copy</span></tt>, <tt class="docutils literal"><span class="pre">init</span></tt>, <tt class="docutils literal"><span class="pre">mutableCopy</span></tt>, or <tt class="docutils literal"><span class="pre">new</span></tt>. This
+attribute can only be placed at the end of a method declaration:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="k">-</span> <span class="p">(</span><span class="n">NSString</span> <span class="o">*</span><span class="p">)</span><span class="nf">initMyStringValue</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">objc_method_family</span><span class="p">(</span><span class="n">none</span><span class="p">)));</span>
+</pre></div>
+</div>
+<p>Users who do not wish to change the conventional meaning of a method, and who
+merely want to document its non-standard retain and release semantics, should
+use the retaining behavior attributes (<tt class="docutils literal"><span class="pre">ns_returns_retained</span></tt>,
+<tt class="docutils literal"><span class="pre">ns_returns_not_retained</span></tt>, etc).</p>
+<p>Query for this feature with <tt class="docutils literal"><span class="pre">__has_attribute(objc_method_family)</span></tt>.</p>
+</div>
+<div class="section" id="objc-requires-super">
+<h3><a class="toc-backref" href="#id20">objc_requires_super</a><a class="headerlink" href="#objc-requires-super" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Some Objective-C classes allow a subclass to override a particular method in a
+parent class but expect that the overriding method also calls the overridden
+method in the parent class. For these cases, we provide an attribute to
+designate that a method requires a “call to <tt class="docutils literal"><span class="pre">super</span></tt>” in the overriding
+method in the subclass.</p>
+<p><strong>Usage</strong>: <tt class="docutils literal"><span class="pre">__attribute__((objc_requires_super))</span></tt>. This attribute can only
+be placed at the end of a method declaration:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="k">-</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span><span class="nf">foo</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">objc_requires_super</span><span class="p">));</span>
+</pre></div>
+</div>
+<p>This attribute can only be applied the method declarations within a class, and
+not a protocol. Currently this attribute does not enforce any placement of
+where the call occurs in the overriding method (such as in the case of
+<tt class="docutils literal"><span class="pre">-dealloc</span></tt> where the call must appear at the end). It checks only that it
+exists.</p>
+<p>Note that on both OS X and iOS that the Foundation framework provides a
+convenience macro <tt class="docutils literal"><span class="pre">NS_REQUIRES_SUPER</span></tt> that provides syntactic sugar for this
+attribute:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="k">-</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span><span class="nf">foo</span> <span class="n">NS_REQUIRES_SUPER</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>This macro is conditionally defined depending on the compiler’s support for
+this attribute. If the compiler does not support the attribute the macro
+expands to nothing.</p>
+<p>Operationally, when a method has this annotation the compiler will warn if the
+implementation of an override in a subclass does not call super. For example:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="nl">warning:</span> <span class="n">method</span> <span class="n">possibly</span> <span class="n">missing</span> <span class="n">a</span> <span class="p">[</span><span class="n">super</span> <span class="n">AnnotMeth</span><span class="p">]</span> <span class="n">call</span>
+<span class="o">-</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">AnnotMeth</span><span class="p">{};</span>
+ <span class="o">^</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="optnone-clang-optnone">
+<h3><a class="toc-backref" href="#id21">optnone (clang::optnone)</a><a class="headerlink" href="#optnone-clang-optnone" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">optnone</span></tt> attribute suppresses essentially all optimizations
+on a function or method, regardless of the optimization level applied to
+the compilation unit as a whole. This is particularly useful when you
+need to debug a particular function, but it is infeasible to build the
+entire application without optimization. Avoiding optimization on the
+specified function can improve the quality of the debugging information
+for that function.</p>
+<p>This attribute is incompatible with the <tt class="docutils literal"><span class="pre">always_inline</span></tt> attribute.</p>
+</div>
+<div class="section" id="overloadable">
+<h3><a class="toc-backref" href="#id22">overloadable</a><a class="headerlink" href="#overloadable" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Clang provides support for C++ function overloading in C. Function overloading
+in C is introduced using the <tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute. For example, one
+might provide several overloaded versions of a <tt class="docutils literal"><span class="pre">tgsin</span></tt> function that invokes
+the appropriate standard function computing the sine of a value with <tt class="docutils literal"><span class="pre">float</span></tt>,
+<tt class="docutils literal"><span class="pre">double</span></tt>, or <tt class="docutils literal"><span class="pre">long</span> <span class="pre">double</span></tt> precision:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="cp">#include <math.h></span>
+<span class="kt">float</span> <span class="nf">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">))</span> <span class="n">tgsin</span><span class="p">(</span><span class="kt">float</span> <span class="n">x</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">sinf</span><span class="p">(</span><span class="n">x</span><span class="p">);</span> <span class="p">}</span>
+<span class="kt">double</span> <span class="nf">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">))</span> <span class="n">tgsin</span><span class="p">(</span><span class="kt">double</span> <span class="n">x</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">sin</span><span class="p">(</span><span class="n">x</span><span class="p">);</span> <span class="p">}</span>
+<span class="kt">long</span> <span class="kt">double</span> <span class="nf">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">))</span> <span class="n">tgsin</span><span class="p">(</span><span class="kt">long</span> <span class="kt">double</span> <span class="n">x</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">sinl</span><span class="p">(</span><span class="n">x</span><span class="p">);</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>Given these declarations, one can call <tt class="docutils literal"><span class="pre">tgsin</span></tt> with a <tt class="docutils literal"><span class="pre">float</span></tt> value to
+receive a <tt class="docutils literal"><span class="pre">float</span></tt> result, with a <tt class="docutils literal"><span class="pre">double</span></tt> to receive a <tt class="docutils literal"><span class="pre">double</span></tt> result,
+etc. Function overloading in C follows the rules of C++ function overloading
+to pick the best overload given the call arguments, with a few C-specific
+semantics:</p>
+<ul class="simple">
+<li>Conversion from <tt class="docutils literal"><span class="pre">float</span></tt> or <tt class="docutils literal"><span class="pre">double</span></tt> to <tt class="docutils literal"><span class="pre">long</span> <span class="pre">double</span></tt> is ranked as a
+floating-point promotion (per C99) rather than as a floating-point conversion
+(as in C++).</li>
+<li>A conversion from a pointer of type <tt class="docutils literal"><span class="pre">T*</span></tt> to a pointer of type <tt class="docutils literal"><span class="pre">U*</span></tt> is
+considered a pointer conversion (with conversion rank) if <tt class="docutils literal"><span class="pre">T</span></tt> and <tt class="docutils literal"><span class="pre">U</span></tt> are
+compatible types.</li>
+<li>A conversion from type <tt class="docutils literal"><span class="pre">T</span></tt> to a value of type <tt class="docutils literal"><span class="pre">U</span></tt> is permitted if <tt class="docutils literal"><span class="pre">T</span></tt>
+and <tt class="docutils literal"><span class="pre">U</span></tt> are compatible types. This conversion is given “conversion” rank.</li>
+</ul>
+<p>The declaration of <tt class="docutils literal"><span class="pre">overloadable</span></tt> functions is restricted to function
+declarations and definitions. Most importantly, if any function with a given
+name is given the <tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute, then all function declarations
+and definitions with that name (and in that scope) must have the
+<tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute. This rule even applies to redeclarations of
+functions whose original declaration had the <tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute, e.g.,</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">f</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">));</span>
+<span class="kt">float</span> <span class="nf">f</span><span class="p">(</span><span class="kt">float</span><span class="p">);</span> <span class="c1">// error: declaration of "f" must have the "overloadable" attribute</span>
+
+<span class="kt">int</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">));</span>
+<span class="kt">int</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span><span class="p">)</span> <span class="p">{</span> <span class="p">}</span> <span class="c1">// error: redeclaration of "g" must also have the "overloadable" attribute</span>
+</pre></div>
+</div>
+<p>Functions marked <tt class="docutils literal"><span class="pre">overloadable</span></tt> must have prototypes. Therefore, the
+following code is ill-formed:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">h</span><span class="p">()</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">));</span> <span class="c1">// error: h does not have a prototype</span>
+</pre></div>
+</div>
+<p>However, <tt class="docutils literal"><span class="pre">overloadable</span></tt> functions are allowed to use a ellipsis even if there
+are no named parameters (as is permitted in C++). This feature is particularly
+useful when combined with the <tt class="docutils literal"><span class="pre">unavailable</span></tt> attribute:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">honeypot</span><span class="p">(...)</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">overloadable</span><span class="p">,</span> <span class="n">unavailable</span><span class="p">));</span> <span class="c1">// calling me is an error</span>
+</pre></div>
+</div>
+<p>Functions declared with the <tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute have their names mangled
+according to the same rules as C++ function names. For example, the three
+<tt class="docutils literal"><span class="pre">tgsin</span></tt> functions in our motivating example get the mangled names
+<tt class="docutils literal"><span class="pre">_Z5tgsinf</span></tt>, <tt class="docutils literal"><span class="pre">_Z5tgsind</span></tt>, and <tt class="docutils literal"><span class="pre">_Z5tgsine</span></tt>, respectively. There are two
+caveats to this use of name mangling:</p>
+<ul class="simple">
+<li>Future versions of Clang may change the name mangling of functions overloaded
+in C, so you should not depend on an specific mangling. To be completely
+safe, we strongly urge the use of <tt class="docutils literal"><span class="pre">static</span> <span class="pre">inline</span></tt> with <tt class="docutils literal"><span class="pre">overloadable</span></tt>
+functions.</li>
+<li>The <tt class="docutils literal"><span class="pre">overloadable</span></tt> attribute has almost no meaning when used in C++,
+because names will already be mangled and functions are already overloadable.
+However, when an <tt class="docutils literal"><span class="pre">overloadable</span></tt> function occurs within an <tt class="docutils literal"><span class="pre">extern</span> <span class="pre">"C"</span></tt>
+linkage specification, it’s name <em>will</em> be mangled in the same way as it
+would in C.</li>
+</ul>
+<p>Query for this feature with <tt class="docutils literal"><span class="pre">__has_extension(attribute_overloadable)</span></tt>.</p>
+</div>
+<div class="section" id="pcs-gnu-pcs">
+<h3><a class="toc-backref" href="#id23">pcs (gnu::pcs)</a><a class="headerlink" href="#pcs-gnu-pcs" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>On ARM targets, this can attribute can be used to select calling conventions,
+similar to <tt class="docutils literal"><span class="pre">stdcall</span></tt> on x86. Valid parameter values are “aapcs” and
+“aapcs-vfp”.</p>
+</div>
+<div class="section" id="release-capability-release-shared-capability-clang-release-capability-clang-release-shared-capability">
+<h3><a class="toc-backref" href="#id24">release_capability (release_shared_capability, clang::release_capability, clang::release_shared_capability)</a><a class="headerlink" href="#release-capability-release-shared-capability-clang-release-capability-clang-release-shared-capability" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Marks a function as releasing a capability.</p>
+</div>
+<div class="section" id="try-acquire-capability-try-acquire-shared-capability-clang-try-acquire-capability-clang-try-acquire-shared-capability">
+<h3><a class="toc-backref" href="#id25">try_acquire_capability (try_acquire_shared_capability, clang::try_acquire_capability, clang::try_acquire_shared_capability)</a><a class="headerlink" href="#try-acquire-capability-try-acquire-shared-capability-clang-try-acquire-capability-clang-try-acquire-shared-capability" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Marks a function that attempts to acquire a capability. This function may fail to
+actually acquire the capability; they accept a Boolean value determining
+whether acquiring the capability means success (true), or failing to acquire
+the capability means success (false).</p>
+</div>
+</div>
+<div class="section" id="variable-attributes">
+<h2><a class="toc-backref" href="#id26">Variable Attributes</a><a class="headerlink" href="#variable-attributes" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="section-gnu-section-declspec-allocate">
+<h3><a class="toc-backref" href="#id27">section (gnu::section, __declspec(allocate))</a><a class="headerlink" href="#section-gnu-section-declspec-allocate" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td>X</td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">section</span></tt> attribute allows you to specify a specific section a
+global variable or function should be in after translation.</p>
+</div>
+<div class="section" id="tls-model-gnu-tls-model">
+<h3><a class="toc-backref" href="#id28">tls_model (gnu::tls_model)</a><a class="headerlink" href="#tls-model-gnu-tls-model" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">tls_model</span></tt> attribute allows you to specify which thread-local storage
+model to use. It accepts the following strings:</p>
+<ul class="simple">
+<li>global-dynamic</li>
+<li>local-dynamic</li>
+<li>initial-exec</li>
+<li>local-exec</li>
+</ul>
+<p>TLS models are mutually exclusive.</p>
+</div>
+<div class="section" id="thread">
+<h3><a class="toc-backref" href="#id29">thread</a><a class="headerlink" href="#thread" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td> </td>
+<td> </td>
+<td>X</td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">__declspec(thread)</span></tt> attribute declares a variable with thread local
+storage. It is available under the <tt class="docutils literal"><span class="pre">-fms-extensions</span></tt> flag for MSVC
+compatibility. Documentation for the Visual C++ attribute is available on <a class="reference external" href="http://msdn.microsoft.com/en-us/library/9w1sdazb.aspx">MSDN</a>.</p>
+<p>In Clang, <tt class="docutils literal"><span class="pre">__declspec(thread)</span></tt> is generally equivalent in functionality to the
+GNU <tt class="docutils literal"><span class="pre">__thread</span></tt> keyword. The variable must not have a destructor and must have
+a constant initializer, if any. The attribute only applies to variables
+declared with static storage duration, such as globals, class static data
+members, and static locals.</p>
+</div>
+</div>
+<div class="section" id="type-attributes">
+<h2><a class="toc-backref" href="#id30">Type Attributes</a><a class="headerlink" href="#type-attributes" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="single-inhertiance-multiple-inheritance-virtual-inheritance">
+<h3><a class="toc-backref" href="#id31">__single_inhertiance, __multiple_inheritance, __virtual_inheritance</a><a class="headerlink" href="#single-inhertiance-multiple-inheritance-virtual-inheritance" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td> </td>
+<td> </td>
+<td> </td>
+<td>X</td>
+</tr>
+</tbody>
+</table>
+<p>This collection of keywords is enabled under <tt class="docutils literal"><span class="pre">-fms-extensions</span></tt> and controls
+the pointer-to-member representation used on <tt class="docutils literal"><span class="pre">*-*-win32</span></tt> targets.</p>
+<p>The <tt class="docutils literal"><span class="pre">*-*-win32</span></tt> targets utilize a pointer-to-member representation which
+varies in size and alignment depending on the definition of the underlying
+class.</p>
+<p>However, this is problematic when a forward declaration is only available and
+no definition has been made yet. In such cases, Clang is forced to utilize the
+most general representation that is available to it.</p>
+<p>These keywords make it possible to use a pointer-to-member representation other
+than the most general one regardless of whether or not the definition will ever
+be present in the current translation unit.</p>
+<p>This family of keywords belong between the <tt class="docutils literal"><span class="pre">class-key</span></tt> and <tt class="docutils literal"><span class="pre">class-name</span></tt>:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__single_inheritance</span> <span class="n">S</span><span class="p">;</span>
+<span class="kt">int</span> <span class="n">S</span><span class="o">::*</span><span class="n">i</span><span class="p">;</span>
+<span class="k">struct</span> <span class="n">S</span> <span class="p">{};</span>
+</pre></div>
+</div>
+<p>This keyword can be applied to class templates but only has an effect when used
+on full specializations:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="p">,</span> <span class="k">typename</span> <span class="n">U</span><span class="o">></span> <span class="k">struct</span> <span class="n">__single_inheritance</span> <span class="n">A</span><span class="p">;</span> <span class="c1">// warning: inheritance model ignored on primary template</span>
+<span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="o">></span> <span class="k">struct</span> <span class="n">__multiple_inheritance</span> <span class="n">A</span><span class="o"><</span><span class="n">T</span><span class="p">,</span> <span class="n">T</span><span class="o">></span><span class="p">;</span> <span class="c1">// warning: inheritance model ignored on partial specialization</span>
+<span class="k">template</span> <span class="o"><></span> <span class="k">struct</span> <span class="n">__single_inheritance</span> <span class="n">A</span><span class="o"><</span><span class="kt">int</span><span class="p">,</span> <span class="kt">float</span><span class="o">></span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Note that choosing an inheritance model less general than strictly necessary is
+an error:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__multiple_inheritance</span> <span class="n">S</span><span class="p">;</span> <span class="c1">// error: inheritance model does not match definition</span>
+<span class="kt">int</span> <span class="n">S</span><span class="o">::*</span><span class="n">i</span><span class="p">;</span>
+<span class="k">struct</span> <span class="n">S</span> <span class="p">{};</span>
+</pre></div>
+</div>
+</div>
+</div>
+<div class="section" id="statement-attributes">
+<h2><a class="toc-backref" href="#id32">Statement Attributes</a><a class="headerlink" href="#statement-attributes" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="fallthrough-clang-fallthrough">
+<h3><a class="toc-backref" href="#id33">fallthrough (clang::fallthrough)</a><a class="headerlink" href="#fallthrough-clang-fallthrough" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td> </td>
+<td>X</td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">clang::fallthrough</span></tt> attribute is used along with the
+<tt class="docutils literal"><span class="pre">-Wimplicit-fallthrough</span></tt> argument to annotate intentional fall-through
+between switch labels. It can only be applied to a null statement placed at a
+point of execution between any statement and the next switch label. It is
+common to mark these places with a specific comment, but this attribute is
+meant to replace comments with a more strict annotation, which can be checked
+by the compiler. This attribute doesn’t change semantics of the code and can
+be used wherever an intended fall-through occurs. It is designed to mimic
+control-flow statements like <tt class="docutils literal"><span class="pre">break;</span></tt>, so it can be placed in most places
+where <tt class="docutils literal"><span class="pre">break;</span></tt> can, but only if there are no statements on the execution path
+between it and the next switch label.</p>
+<p>Here is an example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// compile with -Wimplicit-fallthrough</span>
+<span class="k">switch</span> <span class="p">(</span><span class="n">n</span><span class="p">)</span> <span class="p">{</span>
+<span class="k">case</span> <span class="mi">22</span>:
+<span class="k">case</span> <span class="mi">33</span>: <span class="c1">// no warning: no statements between case labels</span>
+ <span class="n">f</span><span class="p">();</span>
+<span class="k">case</span> <span class="mi">44</span>: <span class="c1">// warning: unannotated fall-through</span>
+ <span class="n">g</span><span class="p">();</span>
+ <span class="p">[[</span><span class="n">clang</span><span class="o">::</span><span class="n">fallthrough</span><span class="p">]];</span>
+<span class="k">case</span> <span class="mi">55</span>: <span class="c1">// no warning</span>
+ <span class="k">if</span> <span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">h</span><span class="p">();</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="p">}</span>
+ <span class="k">else</span> <span class="p">{</span>
+ <span class="n">i</span><span class="p">();</span>
+ <span class="p">[[</span><span class="n">clang</span><span class="o">::</span><span class="n">fallthrough</span><span class="p">]];</span>
+ <span class="p">}</span>
+<span class="k">case</span> <span class="mi">66</span>: <span class="c1">// no warning</span>
+ <span class="n">p</span><span class="p">();</span>
+ <span class="p">[[</span><span class="n">clang</span><span class="o">::</span><span class="n">fallthrough</span><span class="p">]];</span> <span class="c1">// warning: fallthrough annotation does not</span>
+ <span class="c1">// directly precede case label</span>
+ <span class="n">q</span><span class="p">();</span>
+<span class="k">case</span> <span class="mi">77</span>: <span class="c1">// warning: unannotated fall-through</span>
+ <span class="n">r</span><span class="p">();</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+</div>
+<div class="section" id="consumed-annotation-checking">
+<h2><a class="toc-backref" href="#id34">Consumed Annotation Checking</a><a class="headerlink" href="#consumed-annotation-checking" title="Permalink to this headline">¶</a></h2>
+<p>Clang supports additional attributes for checking basic resource management
+properties, specifically for unique objects that have a single owning reference.
+The following attributes are currently supported, although <strong>the implementation
+for these annotations is currently in development and are subject to change.</strong></p>
+<div class="section" id="callable-when">
+<h3><a class="toc-backref" href="#id35">callable_when</a><a class="headerlink" href="#callable-when" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Use <tt class="docutils literal"><span class="pre">__attribute__((callable_when(...)))</span></tt> to indicate what states a method
+may be called in. Valid states are unconsumed, consumed, or unknown. Each
+argument to this attribute must be a quoted string. E.g.:</p>
+<p><tt class="docutils literal"><span class="pre">__attribute__((callable_when("unconsumed",</span> <span class="pre">"unknown")))</span></tt></p>
+</div>
+<div class="section" id="consumable">
+<h3><a class="toc-backref" href="#id36">consumable</a><a class="headerlink" href="#consumable" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Each <tt class="docutils literal"><span class="pre">class</span></tt> that uses any of the typestate annotations must first be marked
+using the <tt class="docutils literal"><span class="pre">consumable</span></tt> attribute. Failure to do so will result in a warning.</p>
+<p>This attribute accepts a single parameter that must be one of the following:
+<tt class="docutils literal"><span class="pre">unknown</span></tt>, <tt class="docutils literal"><span class="pre">consumed</span></tt>, or <tt class="docutils literal"><span class="pre">unconsumed</span></tt>.</p>
+</div>
+<div class="section" id="param-typestate">
+<h3><a class="toc-backref" href="#id37">param_typestate</a><a class="headerlink" href="#param-typestate" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>This attribute specifies expectations about function parameters. Calls to an
+function with annotated parameters will issue a warning if the corresponding
+argument isn’t in the expected state. The attribute is also used to set the
+initial state of the parameter when analyzing the function’s body.</p>
+</div>
+<div class="section" id="return-typestate">
+<h3><a class="toc-backref" href="#id38">return_typestate</a><a class="headerlink" href="#return-typestate" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>The <tt class="docutils literal"><span class="pre">return_typestate</span></tt> attribute can be applied to functions or parameters.
+When applied to a function the attribute specifies the state of the returned
+value. The function’s body is checked to ensure that it always returns a value
+in the specified state. On the caller side, values returned by the annotated
+function are initialized to the given state.</p>
+<p>When applied to a function parameter it modifies the state of an argument after
+a call to the function returns. The function’s body is checked to ensure that
+the parameter is in the expected state before returning.</p>
+</div>
+<div class="section" id="set-typestate">
+<h3><a class="toc-backref" href="#id39">set_typestate</a><a class="headerlink" href="#set-typestate" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Annotate methods that transition an object into a new state with
+<tt class="docutils literal"><span class="pre">__attribute__((set_typestate(new_state)))</span></tt>. The new new state must be
+unconsumed, consumed, or unknown.</p>
+</div>
+<div class="section" id="test-typestate">
+<h3><a class="toc-backref" href="#id40">test_typestate</a><a class="headerlink" href="#test-typestate" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Use <tt class="docutils literal"><span class="pre">__attribute__((test_typestate(tested_state)))</span></tt> to indicate that a method
+returns true if the object is in the specified state..</p>
+</div>
+</div>
+<div class="section" id="type-safety-checking">
+<h2><a class="toc-backref" href="#id41">Type Safety Checking</a><a class="headerlink" href="#type-safety-checking" title="Permalink to this headline">¶</a></h2>
+<p>Clang supports additional attributes to enable checking type safety properties
+that can’t be enforced by the C type system. Use cases include:</p>
+<ul class="simple">
+<li>MPI library implementations, where these attributes enable checking that
+the buffer type matches the passed <tt class="docutils literal"><span class="pre">MPI_Datatype</span></tt>;</li>
+<li>for HDF5 library there is a similar use case to MPI;</li>
+<li>checking types of variadic functions’ arguments for functions like
+<tt class="docutils literal"><span class="pre">fcntl()</span></tt> and <tt class="docutils literal"><span class="pre">ioctl()</span></tt>.</li>
+</ul>
+<p>You can detect support for these attributes with <tt class="docutils literal"><span class="pre">__has_attribute()</span></tt>. For
+example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#if defined(__has_attribute)</span>
+<span class="cp"># if __has_attribute(argument_with_type_tag) && \</span>
+<span class="cp"> __has_attribute(pointer_with_type_tag) && \</span>
+<span class="cp"> __has_attribute(type_tag_for_datatype)</span>
+<span class="cp"># define ATTR_MPI_PWT(buffer_idx, type_idx) __attribute__((pointer_with_type_tag(mpi,buffer_idx,type_idx)))</span>
+<span class="cm">/* ... other macros ... */</span>
+<span class="cp"># endif</span>
+<span class="cp">#endif</span>
+
+<span class="cp">#if !defined(ATTR_MPI_PWT)</span>
+<span class="cp"># define ATTR_MPI_PWT(buffer_idx, type_idx)</span>
+<span class="cp">#endif</span>
+
+<span class="kt">int</span> <span class="nf">MPI_Send</span><span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="n">buf</span><span class="p">,</span> <span class="kt">int</span> <span class="n">count</span><span class="p">,</span> <span class="n">MPI_Datatype</span> <span class="n">datatype</span> <span class="cm">/*, other args omitted */</span><span class="p">)</span>
+ <span class="n">ATTR_MPI_PWT</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">);</span>
+</pre></div>
+</div>
+<div class="section" id="argument-with-type-tag">
+<h3><a class="toc-backref" href="#id42">argument_with_type_tag</a><a class="headerlink" href="#argument-with-type-tag" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Use <tt class="docutils literal"><span class="pre">__attribute__((argument_with_type_tag(arg_kind,</span> <span class="pre">arg_idx,</span>
+<span class="pre">type_tag_idx)))</span></tt> on a function declaration to specify that the function
+accepts a type tag that determines the type of some other argument.
+<tt class="docutils literal"><span class="pre">arg_kind</span></tt> is an identifier that should be used when annotating all
+applicable type tags.</p>
+<p>This attribute is primarily useful for checking arguments of variadic functions
+(<tt class="docutils literal"><span class="pre">pointer_with_type_tag</span></tt> can be used in most non-variadic cases).</p>
+<p>For example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">fcntl</span><span class="p">(</span><span class="kt">int</span> <span class="n">fd</span><span class="p">,</span> <span class="kt">int</span> <span class="n">cmd</span><span class="p">,</span> <span class="p">...)</span>
+ <span class="n">__attribute__</span><span class="p">((</span> <span class="n">argument_with_type_tag</span><span class="p">(</span><span class="n">fcntl</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">)</span> <span class="p">));</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="pointer-with-type-tag">
+<h3><a class="toc-backref" href="#id43">pointer_with_type_tag</a><a class="headerlink" href="#pointer-with-type-tag" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Use <tt class="docutils literal"><span class="pre">__attribute__((pointer_with_type_tag(ptr_kind,</span> <span class="pre">ptr_idx,</span> <span class="pre">type_tag_idx)))</span></tt>
+on a function declaration to specify that the function accepts a type tag that
+determines the pointee type of some other pointer argument.</p>
+<p>For example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">MPI_Send</span><span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="n">buf</span><span class="p">,</span> <span class="kt">int</span> <span class="n">count</span><span class="p">,</span> <span class="n">MPI_Datatype</span> <span class="n">datatype</span> <span class="cm">/*, other args omitted */</span><span class="p">)</span>
+ <span class="n">__attribute__</span><span class="p">((</span> <span class="n">pointer_with_type_tag</span><span class="p">(</span><span class="n">mpi</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">)</span> <span class="p">));</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="type-tag-for-datatype">
+<h3><a class="toc-backref" href="#id44">type_tag_for_datatype</a><a class="headerlink" href="#type-tag-for-datatype" title="Permalink to this headline">¶</a></h3>
+<table border="1" class="docutils">
+<caption>Supported Syntaxes</caption>
+<colgroup>
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+<col width="25%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">GNU</th>
+<th class="head">C++11</th>
+<th class="head">__declspec</th>
+<th class="head">Keyword</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>X</td>
+<td> </td>
+<td> </td>
+<td> </td>
+</tr>
+</tbody>
+</table>
+<p>Clang supports annotating type tags of two forms.</p>
+<ul>
+<li><p class="first"><strong>Type tag that is an expression containing a reference to some declared
+identifier.</strong> Use <tt class="docutils literal"><span class="pre">__attribute__((type_tag_for_datatype(kind,</span> <span class="pre">type)))</span></tt> on a
+declaration with that identifier:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">extern</span> <span class="k">struct</span> <span class="n">mpi_datatype</span> <span class="n">mpi_datatype_int</span>
+ <span class="nf">__attribute__</span><span class="p">((</span> <span class="n">type_tag_for_datatype</span><span class="p">(</span><span class="n">mpi</span><span class="p">,</span><span class="kt">int</span><span class="p">)</span> <span class="p">));</span>
+<span class="cp">#define MPI_INT ((MPI_Datatype) &mpi_datatype_int)</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first"><strong>Type tag that is an integral literal.</strong> Introduce a <tt class="docutils literal"><span class="pre">static</span> <span class="pre">const</span></tt>
+variable with a corresponding initializer value and attach
+<tt class="docutils literal"><span class="pre">__attribute__((type_tag_for_datatype(kind,</span> <span class="pre">type)))</span></tt> on that declaration,
+for example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#define MPI_INT ((MPI_Datatype) 42)</span>
+<span class="k">static</span> <span class="k">const</span> <span class="n">MPI_Datatype</span> <span class="n">mpi_datatype_int</span>
+ <span class="n">__attribute__</span><span class="p">((</span> <span class="n">type_tag_for_datatype</span><span class="p">(</span><span class="n">mpi</span><span class="p">,</span><span class="kt">int</span><span class="p">)</span> <span class="p">))</span> <span class="o">=</span> <span class="mi">42</span>
+</pre></div>
+</div>
+</li>
+</ul>
+<p>The attribute also accepts an optional third argument that determines how the
+expression is compared to the type tag. There are two supported flags:</p>
+<ul>
+<li><p class="first"><tt class="docutils literal"><span class="pre">layout_compatible</span></tt> will cause types to be compared according to
+layout-compatibility rules (C++11 [class.mem] p 17, 18). This is
+implemented to support annotating types like <tt class="docutils literal"><span class="pre">MPI_DOUBLE_INT</span></tt>.</p>
+<p>For example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cm">/* In mpi.h */</span>
+<span class="k">struct</span> <span class="n">internal_mpi_double_int</span> <span class="p">{</span> <span class="kt">double</span> <span class="n">d</span><span class="p">;</span> <span class="kt">int</span> <span class="n">i</span><span class="p">;</span> <span class="p">};</span>
+<span class="k">extern</span> <span class="k">struct</span> <span class="n">mpi_datatype</span> <span class="n">mpi_datatype_double_int</span>
+ <span class="nf">__attribute__</span><span class="p">((</span> <span class="n">type_tag_for_datatype</span><span class="p">(</span><span class="n">mpi</span><span class="p">,</span> <span class="k">struct</span> <span class="n">internal_mpi_double_int</span><span class="p">,</span> <span class="n">layout_compatible</span><span class="p">)</span> <span class="p">));</span>
+
+<span class="cp">#define MPI_DOUBLE_INT ((MPI_Datatype) &mpi_datatype_double_int)</span>
+
+<span class="cm">/* In user code */</span>
+<span class="k">struct</span> <span class="n">my_pair</span> <span class="p">{</span> <span class="kt">double</span> <span class="n">a</span><span class="p">;</span> <span class="kt">int</span> <span class="n">b</span><span class="p">;</span> <span class="p">};</span>
+<span class="k">struct</span> <span class="n">my_pair</span> <span class="o">*</span><span class="n">buffer</span><span class="p">;</span>
+<span class="n">MPI_Send</span><span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">MPI_DOUBLE_INT</span> <span class="cm">/*, ... */</span><span class="p">);</span> <span class="c1">// no warning</span>
+
+<span class="k">struct</span> <span class="n">my_int_pair</span> <span class="p">{</span> <span class="kt">int</span> <span class="n">a</span><span class="p">;</span> <span class="kt">int</span> <span class="n">b</span><span class="p">;</span> <span class="p">}</span>
+<span class="k">struct</span> <span class="n">my_int_pair</span> <span class="o">*</span><span class="n">buffer2</span><span class="p">;</span>
+<span class="n">MPI_Send</span><span class="p">(</span><span class="n">buffer2</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">MPI_DOUBLE_INT</span> <span class="cm">/*, ... */</span><span class="p">);</span> <span class="c1">// warning: actual buffer element</span>
+ <span class="c1">// type 'struct my_int_pair'</span>
+ <span class="c1">// doesn't match specified MPI_Datatype</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">must_be_null</span></tt> specifies that the expression should be a null pointer
+constant, for example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cm">/* In mpi.h */</span>
+<span class="k">extern</span> <span class="k">struct</span> <span class="n">mpi_datatype</span> <span class="n">mpi_datatype_null</span>
+ <span class="nf">__attribute__</span><span class="p">((</span> <span class="n">type_tag_for_datatype</span><span class="p">(</span><span class="n">mpi</span><span class="p">,</span> <span class="kt">void</span><span class="p">,</span> <span class="n">must_be_null</span><span class="p">)</span> <span class="p">));</span>
+
+<span class="cp">#define MPI_DATATYPE_NULL ((MPI_Datatype) &mpi_datatype_null)</span>
+
+<span class="cm">/* In user code */</span>
+<span class="n">MPI_Send</span><span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">MPI_DATATYPE_NULL</span> <span class="cm">/*, ... */</span><span class="p">);</span> <span class="c1">// warning: MPI_DATATYPE_NULL</span>
+ <span class="c1">// was specified but buffer</span>
+ <span class="c1">// is not a null pointer</span>
+</pre></div>
+</div>
+</li>
+</ul>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="AutomaticReferenceCounting.html">Objective-C Automatic Reference Counting (ARC)</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="CrossCompilation.html">Cross-compilation using Clang</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/AutomaticReferenceCounting.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/AutomaticReferenceCounting.html Mon May 25 08:58:01 2015
@@ -0,0 +1,2083 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>Objective-C Automatic Reference Counting (ARC) — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
+ <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="up" title="Clang Language Extensions" href="LanguageExtensions.html" />
+ <link rel="next" title="Attributes in Clang" href="AttributeReference.html" />
+ <link rel="prev" title="Block Implementation Specification" href="Block-ABI-Apple.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Objective-C Automatic Reference Counting (ARC)</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="Block-ABI-Apple.html">Block Implementation Specification</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="AttributeReference.html">Attributes in Clang</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <style>
+ .arc-term { font-style: italic; font-weight: bold; }
+ .revision { font-style: italic; }
+ .when-revised { font-weight: bold; font-style: normal; }
+
+ /*
+ * Automatic numbering is described in this article:
+ * http://dev.opera.com/articles/view/automatic-numbering-with-css-counters/
+ */
+ /*
+ * Automatic numbering for the TOC.
+ * This is wrong from the semantics point of view, since it is an ordered
+ * list, but uses "ul" tag.
+ */
+ div#contents.contents.local ul {
+ counter-reset: toc-section;
+ list-style-type: none;
+ }
+ div#contents.contents.local ul li {
+ counter-increment: toc-section;
+ background: none; // Remove bullets
+ }
+ div#contents.contents.local ul li a.reference:before {
+ content: counters(toc-section, ".") " ";
+ }
+
+ /* Automatic numbering for the body. */
+ body {
+ counter-reset: section subsection subsubsection;
+ }
+ .section h2 {
+ counter-reset: subsection subsubsection;
+ counter-increment: section;
+ }
+ .section h2 a.toc-backref:before {
+ content: counter(section) " ";
+ }
+ .section h3 {
+ counter-reset: subsubsection;
+ counter-increment: subsection;
+ }
+ .section h3 a.toc-backref:before {
+ content: counter(section) "." counter(subsection) " ";
+ }
+ .section h4 {
+ counter-increment: subsubsection;
+ }
+ .section h4 a.toc-backref:before {
+ content: counter(section) "." counter(subsection) "." counter(subsubsection) " ";
+ }
+</style><div class="section" id="objective-c-automatic-reference-counting-arc">
+<h1>Objective-C Automatic Reference Counting (ARC)<a class="headerlink" href="#objective-c-automatic-reference-counting-arc" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#about-this-document" id="id4">About this document</a><ul>
+<li><a class="reference internal" href="#purpose" id="id5">Purpose</a></li>
+<li><a class="reference internal" href="#background" id="id6">Background</a></li>
+<li><a class="reference internal" href="#evolution" id="id7">Evolution</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#general" id="id8">General</a></li>
+<li><a class="reference internal" href="#retainable-object-pointers" id="id9">Retainable object pointers</a><ul>
+<li><a class="reference internal" href="#retain-count-semantics" id="id10">Retain count semantics</a></li>
+<li><a class="reference internal" href="#retainable-object-pointers-as-operands-and-arguments" id="id11">Retainable object pointers as operands and arguments</a><ul>
+<li><a class="reference internal" href="#consumed-parameters" id="id12">Consumed parameters</a></li>
+<li><a class="reference internal" href="#retained-return-values" id="id13">Retained return values</a></li>
+<li><a class="reference internal" href="#unretained-return-values" id="id14">Unretained return values</a></li>
+<li><a class="reference internal" href="#bridged-casts" id="id15">Bridged casts</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#restrictions" id="id16">Restrictions</a><ul>
+<li><a class="reference internal" href="#conversion-of-retainable-object-pointers" id="id17">Conversion of retainable object pointers</a></li>
+<li><a class="reference internal" href="#conversion-to-retainable-object-pointer-type-of-expressions-with-known-semantics" id="id18">Conversion to retainable object pointer type of expressions with known semantics</a></li>
+<li><a class="reference internal" href="#conversion-from-retainable-object-pointer-type-in-certain-contexts" id="id19">Conversion from retainable object pointer type in certain contexts</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#ownership-qualification" id="id20">Ownership qualification</a><ul>
+<li><a class="reference internal" href="#spelling" id="id21">Spelling</a><ul>
+<li><a class="reference internal" href="#property-declarations" id="id22">Property declarations</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#semantics" id="id23">Semantics</a></li>
+<li><a class="reference internal" href="#arc-ownership-restrictions" id="id24">Restrictions</a><ul>
+<li><a class="reference internal" href="#weak-unavailable-types" id="id25">Weak-unavailable types</a></li>
+<li><a class="reference internal" href="#storage-duration-of-autoreleasing-objects" id="id26">Storage duration of <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> objects</a></li>
+<li><a class="reference internal" href="#conversion-of-pointers-to-ownership-qualified-types" id="id27">Conversion of pointers to ownership-qualified types</a></li>
+<li><a class="reference internal" href="#passing-to-an-out-parameter-by-writeback" id="id28">Passing to an out parameter by writeback</a></li>
+<li><a class="reference internal" href="#ownership-qualified-fields-of-structs-and-unions" id="id29">Ownership-qualified fields of structs and unions</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#ownership-inference" id="id30">Ownership inference</a><ul>
+<li><a class="reference internal" href="#objects" id="id31">Objects</a></li>
+<li><a class="reference internal" href="#indirect-parameters" id="id32">Indirect parameters</a></li>
+<li><a class="reference internal" href="#template-arguments" id="id33">Template arguments</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#method-families" id="id34">Method families</a><ul>
+<li><a class="reference internal" href="#explicit-method-family-control" id="id35">Explicit method family control</a></li>
+<li><a class="reference internal" href="#semantics-of-method-families" id="id36">Semantics of method families</a><ul>
+<li><a class="reference internal" href="#semantics-of-init" id="id37">Semantics of <tt class="docutils literal"><span class="pre">init</span></tt></a></li>
+<li><a class="reference internal" href="#related-result-types" id="id38">Related result types</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#optimization" id="id39">Optimization</a><ul>
+<li><a class="reference internal" href="#object-liveness" id="id40">Object liveness</a></li>
+<li><a class="reference internal" href="#no-object-lifetime-extension" id="id41">No object lifetime extension</a></li>
+<li><a class="reference internal" href="#precise-lifetime-semantics" id="id42">Precise lifetime semantics</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#miscellaneous" id="id43">Miscellaneous</a><ul>
+<li><a class="reference internal" href="#special-methods" id="id44">Special methods</a><ul>
+<li><a class="reference internal" href="#memory-management-methods" id="id45">Memory management methods</a></li>
+<li><a class="reference internal" href="#dealloc" id="id46"><tt class="docutils literal"><span class="pre">dealloc</span></tt></a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#autoreleasepool" id="id47"><tt class="docutils literal"><span class="pre">@autoreleasepool</span></tt></a></li>
+<li><a class="reference internal" href="#self" id="id48"><tt class="docutils literal"><span class="pre">self</span></tt></a></li>
+<li><a class="reference internal" href="#fast-enumeration-iteration-variables" id="id49">Fast enumeration iteration variables</a></li>
+<li><a class="reference internal" href="#blocks" id="id50">Blocks</a></li>
+<li><a class="reference internal" href="#exceptions" id="id51">Exceptions</a></li>
+<li><a class="reference internal" href="#interior-pointers" id="id52">Interior pointers</a></li>
+<li><a class="reference internal" href="#c-retainable-pointer-types" id="id53">C retainable pointer types</a><ul>
+<li><a class="reference internal" href="#auditing-of-c-retainable-pointer-interfaces" id="id54">Auditing of C retainable pointer interfaces</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#runtime-support" id="id55">Runtime support</a><ul>
+<li><a class="reference internal" href="#arc-runtime-objc-autorelease" id="id56"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_autorelease(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#void-objc-autoreleasepoolpop-void-pool" id="id57"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_autoreleasePoolPop(void</span> <span class="pre">*pool);</span></tt></a></li>
+<li><a class="reference internal" href="#void-objc-autoreleasepoolpush-void" id="id58"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">*objc_autoreleasePoolPush(void);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-autoreleasereturnvalue" id="id59"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_autoreleaseReturnValue(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#void-objc-copyweak-id-dest-id-src" id="id60"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_copyWeak(id</span> <span class="pre">*dest,</span> <span class="pre">id</span> <span class="pre">*src);</span></tt></a></li>
+<li><a class="reference internal" href="#void-objc-destroyweak-id-object" id="id61"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_destroyWeak(id</span> <span class="pre">*object);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-initweak" id="id62"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_initWeak(id</span> <span class="pre">*object,</span> <span class="pre">id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-loadweak" id="id63"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_loadWeak(id</span> <span class="pre">*object);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-loadweakretained" id="id64"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_loadWeakRetained(id</span> <span class="pre">*object);</span></tt></a></li>
+<li><a class="reference internal" href="#void-objc-moveweak-id-dest-id-src" id="id65"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_moveWeak(id</span> <span class="pre">*dest,</span> <span class="pre">id</span> <span class="pre">*src);</span></tt></a></li>
+<li><a class="reference internal" href="#void-objc-release-id-value" id="id66"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_release(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-retain" id="id67"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retain(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-retainautorelease" id="id68"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainAutorelease(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-retainautoreleasereturnvalue" id="id69"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainAutoreleaseReturnValue(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-retainautoreleasedreturnvalue" id="id70"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainAutoreleasedReturnValue(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-retainblock" id="id71"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainBlock(id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-storestrong" id="id72"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_storeStrong(id</span> <span class="pre">*object,</span> <span class="pre">id</span> <span class="pre">value);</span></tt></a></li>
+<li><a class="reference internal" href="#arc-runtime-objc-storeweak" id="id73"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_storeWeak(id</span> <span class="pre">*object,</span> <span class="pre">id</span> <span class="pre">value);</span></tt></a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="about-this-document">
+<span id="arc-meta"></span><h2><a class="toc-backref" href="#id4">About this document</a><a class="headerlink" href="#about-this-document" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="purpose">
+<span id="arc-meta-purpose"></span><h3><a class="toc-backref" href="#id5">Purpose</a><a class="headerlink" href="#purpose" title="Permalink to this headline">¶</a></h3>
+<p>The first and primary purpose of this document is to serve as a complete
+technical specification of Automatic Reference Counting. Given a core
+Objective-C compiler and runtime, it should be possible to write a compiler and
+runtime which implements these new semantics.</p>
+<p>The secondary purpose is to act as a rationale for why ARC was designed in this
+way. This should remain tightly focused on the technical design and should not
+stray into marketing speculation.</p>
+</div>
+<div class="section" id="background">
+<span id="arc-meta-background"></span><h3><a class="toc-backref" href="#id6">Background</a><a class="headerlink" href="#background" title="Permalink to this headline">¶</a></h3>
+<p>This document assumes a basic familiarity with C.</p>
+<p><span class="arc-term">Blocks</span> are a C language extension for creating anonymous functions.
+Users interact with and transfer block objects using <span class="arc-term">block
+pointers</span>, which are represented like a normal pointer. A block may capture
+values from local variables; when this occurs, memory must be dynamically
+allocated. The initial allocation is done on the stack, but the runtime
+provides a <tt class="docutils literal"><span class="pre">Block_copy</span></tt> function which, given a block pointer, either copies
+the underlying block object to the heap, setting its reference count to 1 and
+returning the new block pointer, or (if the block object is already on the
+heap) increases its reference count by 1. The paired function is
+<tt class="docutils literal"><span class="pre">Block_release</span></tt>, which decreases the reference count by 1 and destroys the
+object if the count reaches zero and is on the heap.</p>
+<p>Objective-C is a set of language extensions, significant enough to be
+considered a different language. It is a strict superset of C. The extensions
+can also be imposed on C++, producing a language called Objective-C++. The
+primary feature is a single-inheritance object system; we briefly describe the
+modern dialect.</p>
+<p>Objective-C defines a new type kind, collectively called the <span class="arc-term">object
+pointer types</span>. This kind has two notable builtin members, <tt class="docutils literal"><span class="pre">id</span></tt> and
+<tt class="docutils literal"><span class="pre">Class</span></tt>; <tt class="docutils literal"><span class="pre">id</span></tt> is the final supertype of all object pointers. The validity
+of conversions between object pointer types is not checked at runtime. Users
+may define <span class="arc-term">classes</span>; each class is a type, and the pointer to that
+type is an object pointer type. A class may have a superclass; its pointer
+type is a subtype of its superclass’s pointer type. A class has a set of
+<span class="arc-term">ivars</span>, fields which appear on all instances of that class. For
+every class <em>T</em> there’s an associated metaclass; it has no fields, its
+superclass is the metaclass of <em>T</em>‘s superclass, and its metaclass is a global
+class. Every class has a global object whose class is the class’s metaclass;
+metaclasses have no associated type, so pointers to this object have type
+<tt class="docutils literal"><span class="pre">Class</span></tt>.</p>
+<p>A class declaration (<tt class="docutils literal"><span class="pre">@interface</span></tt>) declares a set of <span class="arc-term">methods</span>. A
+method has a return type, a list of argument types, and a <span class="arc-term">selector</span>:
+a name like <tt class="docutils literal"><span class="pre">foo:bar:baz:</span></tt>, where the number of colons corresponds to the
+number of formal arguments. A method may be an instance method, in which case
+it can be invoked on objects of the class, or a class method, in which case it
+can be invoked on objects of the metaclass. A method may be invoked by
+providing an object (called the <span class="arc-term">receiver</span>) and a list of formal
+arguments interspersed with the selector, like so:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="p">[</span><span class="n">receiver</span> <span class="n">foo</span><span class="o">:</span> <span class="n">fooArg</span> <span class="n">bar</span><span class="o">:</span> <span class="n">barArg</span> <span class="n">baz</span><span class="o">:</span> <span class="n">bazArg</span><span class="p">]</span>
+</pre></div>
+</div>
+<p>This looks in the dynamic class of the receiver for a method with this name,
+then in that class’s superclass, etc., until it finds something it can execute.
+The receiver “expression” may also be the name of a class, in which case the
+actual receiver is the class object for that class, or (within method
+definitions) it may be <tt class="docutils literal"><span class="pre">super</span></tt>, in which case the lookup algorithm starts
+with the static superclass instead of the dynamic class. The actual methods
+dynamically found in a class are not those declared in the <tt class="docutils literal"><span class="pre">@interface</span></tt>, but
+those defined in a separate <tt class="docutils literal"><span class="pre">@implementation</span></tt> declaration; however, when
+compiling a call, typechecking is done based on the methods declared in the
+<tt class="docutils literal"><span class="pre">@interface</span></tt>.</p>
+<p>Method declarations may also be grouped into <span class="arc-term">protocols</span>, which are not
+inherently associated with any class, but which classes may claim to follow.
+Object pointer types may be qualified with additional protocols that the object
+is known to support.</p>
+<p><span class="arc-term">Class extensions</span> are collections of ivars and methods, designed to
+allow a class’s <tt class="docutils literal"><span class="pre">@interface</span></tt> to be split across multiple files; however,
+there is still a primary implementation file which must see the
+<tt class="docutils literal"><span class="pre">@interface</span></tt>s of all class extensions. <span class="arc-term">Categories</span> allow
+methods (but not ivars) to be declared <em>post hoc</em> on an arbitrary class; the
+methods in the category’s <tt class="docutils literal"><span class="pre">@implementation</span></tt> will be dynamically added to that
+class’s method tables which the category is loaded at runtime, replacing those
+methods in case of a collision.</p>
+<p>In the standard environment, objects are allocated on the heap, and their
+lifetime is manually managed using a reference count. This is done using two
+instance methods which all classes are expected to implement: <tt class="docutils literal"><span class="pre">retain</span></tt>
+increases the object’s reference count by 1, whereas <tt class="docutils literal"><span class="pre">release</span></tt> decreases it
+by 1 and calls the instance method <tt class="docutils literal"><span class="pre">dealloc</span></tt> if the count reaches 0. To
+simplify certain operations, there is also an <span class="arc-term">autorelease pool</span>, a
+thread-local list of objects to call <tt class="docutils literal"><span class="pre">release</span></tt> on later; an object can be
+added to this pool by calling <tt class="docutils literal"><span class="pre">autorelease</span></tt> on it.</p>
+<p>Block pointers may be converted to type <tt class="docutils literal"><span class="pre">id</span></tt>; block objects are laid out in a
+way that makes them compatible with Objective-C objects. There is a builtin
+class that all block objects are considered to be objects of; this class
+implements <tt class="docutils literal"><span class="pre">retain</span></tt> by adjusting the reference count, not by calling
+<tt class="docutils literal"><span class="pre">Block_copy</span></tt>.</p>
+</div>
+<div class="section" id="evolution">
+<span id="arc-meta-evolution"></span><h3><a class="toc-backref" href="#id7">Evolution</a><a class="headerlink" href="#evolution" title="Permalink to this headline">¶</a></h3>
+<p>ARC is under continual evolution, and this document must be updated as the
+language progresses.</p>
+<p>If a change increases the expressiveness of the language, for example by
+lifting a restriction or by adding new syntax, the change will be annotated
+with a revision marker, like so:</p>
+<blockquote>
+<div>ARC applies to Objective-C pointer types, block pointer types, and
+<span class="when-revised">[beginning Apple 8.0, LLVM 3.8]</span> <span class="revision">BPTRs declared
+within</span> <tt class="docutils literal"><span class="pre">extern</span> <span class="pre">"BCPL"</span></tt> blocks.</div></blockquote>
+<p>For now, it is sensible to version this document by the releases of its sole
+implementation (and its host project), clang. “LLVM X.Y” refers to an
+open-source release of clang from the LLVM project. “Apple X.Y” refers to an
+Apple-provided release of the Apple LLVM Compiler. Other organizations that
+prepare their own, separately-versioned clang releases and wish to maintain
+similar information in this document should send requests to cfe-dev.</p>
+<p>If a change decreases the expressiveness of the language, for example by
+imposing a new restriction, this should be taken as an oversight in the
+original specification and something to be avoided in all versions. Such
+changes are generally to be avoided.</p>
+</div>
+</div>
+<div class="section" id="general">
+<span id="arc-general"></span><h2><a class="toc-backref" href="#id8">General</a><a class="headerlink" href="#general" title="Permalink to this headline">¶</a></h2>
+<p>Automatic Reference Counting implements automatic memory management for
+Objective-C objects and blocks, freeing the programmer from the need to
+explicitly insert retains and releases. It does not provide a cycle collector;
+users must explicitly manage the lifetime of their objects, breaking cycles
+manually or with weak or unsafe references.</p>
+<p>ARC may be explicitly enabled with the compiler flag <tt class="docutils literal"><span class="pre">-fobjc-arc</span></tt>. It may
+also be explicitly disabled with the compiler flag <tt class="docutils literal"><span class="pre">-fno-objc-arc</span></tt>. The last
+of these two flags appearing on the compile line “wins”.</p>
+<p>If ARC is enabled, <tt class="docutils literal"><span class="pre">__has_feature(objc_arc)</span></tt> will expand to 1 in the
+preprocessor. For more information about <tt class="docutils literal"><span class="pre">__has_feature</span></tt>, see the
+<a class="reference internal" href="LanguageExtensions.html#langext-has-feature-has-extension"><em>language extensions</em></a> document.</p>
+</div>
+<div class="section" id="retainable-object-pointers">
+<span id="arc-objects"></span><h2><a class="toc-backref" href="#id9">Retainable object pointers</a><a class="headerlink" href="#retainable-object-pointers" title="Permalink to this headline">¶</a></h2>
+<p>This section describes retainable object pointers, their basic operations, and
+the restrictions imposed on their use under ARC. Note in particular that it
+covers the rules for pointer <em>values</em> (patterns of bits indicating the location
+of a pointed-to object), not pointer <em>objects</em> (locations in memory which store
+pointer values). The rules for objects are covered in the next section.</p>
+<p>A <span class="arc-term">retainable object pointer</span> (or “retainable pointer”) is a value of
+a <span class="arc-term">retainable object pointer type</span> (“retainable type”). There are
+three kinds of retainable object pointer types:</p>
+<ul class="simple">
+<li>block pointers (formed by applying the caret (<tt class="docutils literal"><span class="pre">^</span></tt>) declarator sigil to a
+function type)</li>
+<li>Objective-C object pointers (<tt class="docutils literal"><span class="pre">id</span></tt>, <tt class="docutils literal"><span class="pre">Class</span></tt>, <tt class="docutils literal"><span class="pre">NSFoo*</span></tt>, etc.)</li>
+<li>typedefs marked with <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt></li>
+</ul>
+<p>Other pointer types, such as <tt class="docutils literal"><span class="pre">int*</span></tt> and <tt class="docutils literal"><span class="pre">CFStringRef</span></tt>, are not subject to
+ARC’s semantics and restrictions.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>We are not at liberty to require all code to be recompiled with ARC;
+therefore, ARC must interoperate with Objective-C code which manages retains
+and releases manually. In general, there are three requirements in order for
+a compiler-supported reference-count system to provide reliable
+interoperation:</p>
+<ul class="last simple">
+<li>The type system must reliably identify which objects are to be managed. An
+<tt class="docutils literal"><span class="pre">int*</span></tt> might be a pointer to a <tt class="docutils literal"><span class="pre">malloc</span></tt>‘ed array, or it might be an
+interior pointer to such an array, or it might point to some field or local
+variable. In contrast, values of the retainable object pointer types are
+never interior.</li>
+<li>The type system must reliably indicate how to manage objects of a type.
+This usually means that the type must imply a procedure for incrementing
+and decrementing retain counts. Supporting single-ownership objects
+requires a lot more explicit mediation in the language.</li>
+<li>There must be reliable conventions for whether and when “ownership” is
+passed between caller and callee, for both arguments and return values.
+Objective-C methods follow such a convention very reliably, at least for
+system libraries on Mac OS X, and functions always pass objects at +0. The
+C-based APIs for Core Foundation objects, on the other hand, have much more
+varied transfer semantics.</li>
+</ul>
+</div>
+<p>The use of <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> typedefs is not recommended. If it’s
+absolutely necessary to use this attribute, be very explicit about using the
+typedef, and do not assume that it will be preserved by language features like
+<tt class="docutils literal"><span class="pre">__typeof</span></tt> and C++ template argument substitution.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Any compiler operation which incidentally strips type “sugar” from a type
+will yield a type without the attribute, which may result in unexpected
+behavior.</p>
+</div>
+<div class="section" id="retain-count-semantics">
+<span id="arc-objects-retains"></span><h3><a class="toc-backref" href="#id10">Retain count semantics</a><a class="headerlink" href="#retain-count-semantics" title="Permalink to this headline">¶</a></h3>
+<p>A retainable object pointer is either a <span class="arc-term">null pointer</span> or a pointer
+to a valid object. Furthermore, if it has block pointer type and is not
+<tt class="docutils literal"><span class="pre">null</span></tt> then it must actually be a pointer to a block object, and if it has
+<tt class="docutils literal"><span class="pre">Class</span></tt> type (possibly protocol-qualified) then it must actually be a pointer
+to a class object. Otherwise ARC does not enforce the Objective-C type system
+as long as the implementing methods follow the signature of the static type.
+It is undefined behavior if ARC is exposed to an invalid pointer.</p>
+<p>For ARC’s purposes, a valid object is one with “well-behaved” retaining
+operations. Specifically, the object must be laid out such that the
+Objective-C message send machinery can successfully send it the following
+messages:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">retain</span></tt>, taking no arguments and returning a pointer to the object.</li>
+<li><tt class="docutils literal"><span class="pre">release</span></tt>, taking no arguments and returning <tt class="docutils literal"><span class="pre">void</span></tt>.</li>
+<li><tt class="docutils literal"><span class="pre">autorelease</span></tt>, taking no arguments and returning a pointer to the object.</li>
+</ul>
+<p>The behavior of these methods is constrained in the following ways. The term
+<span class="arc-term">high-level semantics</span> is an intentionally vague term; the intent is
+that programmers must implement these methods in a way such that the compiler,
+modifying code in ways it deems safe according to these constraints, will not
+violate their requirements. For example, if the user puts logging statements
+in <tt class="docutils literal"><span class="pre">retain</span></tt>, they should not be surprised if those statements are executed
+more or less often depending on optimization settings. These constraints are
+not exhaustive of the optimization opportunities: values held in local
+variables are subject to additional restrictions, described later in this
+document.</p>
+<p>It is undefined behavior if a computation history featuring a send of
+<tt class="docutils literal"><span class="pre">retain</span></tt> followed by a send of <tt class="docutils literal"><span class="pre">release</span></tt> to the same object, with no
+intervening <tt class="docutils literal"><span class="pre">release</span></tt> on that object, is not equivalent under the high-level
+semantics to a computation history in which these sends are removed. Note that
+this implies that these methods may not raise exceptions.</p>
+<p>It is undefined behavior if a computation history features any use whatsoever
+of an object following the completion of a send of <tt class="docutils literal"><span class="pre">release</span></tt> that is not
+preceded by a send of <tt class="docutils literal"><span class="pre">retain</span></tt> to the same object.</p>
+<p>The behavior of <tt class="docutils literal"><span class="pre">autorelease</span></tt> must be equivalent to sending <tt class="docutils literal"><span class="pre">release</span></tt> when
+one of the autorelease pools currently in scope is popped. It may not throw an
+exception.</p>
+<p>When the semantics call for performing one of these operations on a retainable
+object pointer, if that pointer is <tt class="docutils literal"><span class="pre">null</span></tt> then the effect is a no-op.</p>
+<p>All of the semantics described in this document are subject to additional
+<a class="reference internal" href="#arc-optimization"><em>optimization rules</em></a> which permit the removal or
+optimization of operations based on local knowledge of data flow. The
+semantics describe the high-level behaviors that the compiler implements, not
+an exact sequence of operations that a program will be compiled into.</p>
+</div>
+<div class="section" id="retainable-object-pointers-as-operands-and-arguments">
+<span id="arc-objects-operands"></span><h3><a class="toc-backref" href="#id11">Retainable object pointers as operands and arguments</a><a class="headerlink" href="#retainable-object-pointers-as-operands-and-arguments" title="Permalink to this headline">¶</a></h3>
+<p>In general, ARC does not perform retain or release operations when simply using
+a retainable object pointer as an operand within an expression. This includes:</p>
+<ul class="simple">
+<li>loading a retainable pointer from an object with non-weak <a class="reference internal" href="#arc-ownership"><em>ownership</em></a>,</li>
+<li>passing a retainable pointer as an argument to a function or method, and</li>
+<li>receiving a retainable pointer as the result of a function or method call.</li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">While this might seem uncontroversial, it is actually unsafe when multiple
+expressions are evaluated in “parallel”, as with binary operators and calls,
+because (for example) one expression might load from an object while another
+writes to it. However, C and C++ already call this undefined behavior
+because the evaluations are unsequenced, and ARC simply exploits that here to
+avoid needing to retain arguments across a large number of calls.</p>
+</div>
+<p>The remainder of this section describes exceptions to these rules, how those
+exceptions are detected, and what those exceptions imply semantically.</p>
+<div class="section" id="consumed-parameters">
+<span id="arc-objects-operands-consumed"></span><h4><a class="toc-backref" href="#id12">Consumed parameters</a><a class="headerlink" href="#consumed-parameters" title="Permalink to this headline">¶</a></h4>
+<p>A function or method parameter of retainable object pointer type may be marked
+as <span class="arc-term">consumed</span>, signifying that the callee expects to take ownership
+of a +1 retain count. This is done by adding the <tt class="docutils literal"><span class="pre">ns_consumed</span></tt> attribute to
+the parameter declaration, like so:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">foo</span><span class="p">(</span><span class="n">__attribute</span><span class="p">((</span><span class="n">ns_consumed</span><span class="p">))</span> <span class="kt">id</span> <span class="n">x</span><span class="p">);</span>
+<span class="k">-</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="nf">foo:</span> <span class="p">(</span><span class="kt">id</span><span class="p">)</span> <span class="n">__attribute</span><span class="p">((</span><span class="n">ns_consumed</span><span class="p">))</span> <span class="n">x</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>This attribute is part of the type of the function or method, not the type of
+the parameter. It controls only how the argument is passed and received.</p>
+<p>When passing such an argument, ARC retains the argument prior to making the
+call.</p>
+<p>When receiving such an argument, ARC releases the argument at the end of the
+function, subject to the usual optimizations for local values.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">This formalizes direct transfers of ownership from a caller to a callee. The
+most common scenario here is passing the <tt class="docutils literal"><span class="pre">self</span></tt> parameter to <tt class="docutils literal"><span class="pre">init</span></tt>, but
+it is useful to generalize. Typically, local optimization will remove any
+extra retains and releases: on the caller side the retain will be merged with
+a +1 source, and on the callee side the release will be rolled into the
+initialization of the parameter.</p>
+</div>
+<p>The implicit <tt class="docutils literal"><span class="pre">self</span></tt> parameter of a method may be marked as consumed by adding
+<tt class="docutils literal"><span class="pre">__attribute__((ns_consumes_self))</span></tt> to the method declaration. Methods in
+the <tt class="docutils literal"><span class="pre">init</span></tt> <a class="reference internal" href="#arc-method-families"><em>family</em></a> are treated as if they were
+implicitly marked with this attribute.</p>
+<p>It is undefined behavior if an Objective-C message send to a method with
+<tt class="docutils literal"><span class="pre">ns_consumed</span></tt> parameters (other than self) is made with a null receiver. It
+is undefined behavior if the method to which an Objective-C message send
+statically resolves to has a different set of <tt class="docutils literal"><span class="pre">ns_consumed</span></tt> parameters than
+the method it dynamically resolves to. It is undefined behavior if a block or
+function call is made through a static type with a different set of
+<tt class="docutils literal"><span class="pre">ns_consumed</span></tt> parameters than the implementation of the called block or
+function.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Consumed parameters with null receiver are a guaranteed leak. Mismatches
+with consumed parameters will cause over-retains or over-releases, depending
+on the direction. The rule about function calls is really just an
+application of the existing C/C++ rule about calling functions through an
+incompatible function type, but it’s useful to state it explicitly.</p>
+</div>
+</div>
+<div class="section" id="retained-return-values">
+<span id="arc-object-operands-retained-return-values"></span><h4><a class="toc-backref" href="#id13">Retained return values</a><a class="headerlink" href="#retained-return-values" title="Permalink to this headline">¶</a></h4>
+<p>A function or method which returns a retainable object pointer type may be
+marked as returning a retained value, signifying that the caller expects to take
+ownership of a +1 retain count. This is done by adding the
+<tt class="docutils literal"><span class="pre">ns_returns_retained</span></tt> attribute to the function or method declaration, like
+so:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="nf">foo</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">__attribute</span><span class="p">((</span><span class="n">ns_returns_retained</span><span class="p">));</span>
+<span class="k">-</span> <span class="p">(</span><span class="kt">id</span><span class="p">)</span> <span class="nf">foo</span> <span class="n">__attribute</span><span class="p">((</span><span class="n">ns_returns_retained</span><span class="p">));</span>
+</pre></div>
+</div>
+<p>This attribute is part of the type of the function or method.</p>
+<p>When returning from such a function or method, ARC retains the value at the
+point of evaluation of the return statement, before leaving all local scopes.</p>
+<p>When receiving a return result from such a function or method, ARC releases the
+value at the end of the full-expression it is contained within, subject to the
+usual optimizations for local values.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">This formalizes direct transfers of ownership from a callee to a caller. The
+most common scenario this models is the retained return from <tt class="docutils literal"><span class="pre">init</span></tt>,
+<tt class="docutils literal"><span class="pre">alloc</span></tt>, <tt class="docutils literal"><span class="pre">new</span></tt>, and <tt class="docutils literal"><span class="pre">copy</span></tt> methods, but there are other cases in the
+frameworks. After optimization there are typically no extra retains and
+releases required.</p>
+</div>
+<p>Methods in the <tt class="docutils literal"><span class="pre">alloc</span></tt>, <tt class="docutils literal"><span class="pre">copy</span></tt>, <tt class="docutils literal"><span class="pre">init</span></tt>, <tt class="docutils literal"><span class="pre">mutableCopy</span></tt>, and <tt class="docutils literal"><span class="pre">new</span></tt>
+<a class="reference internal" href="#arc-method-families"><em>families</em></a> are implicitly marked
+<tt class="docutils literal"><span class="pre">__attribute__((ns_returns_retained))</span></tt>. This may be suppressed by explicitly
+marking the method <tt class="docutils literal"><span class="pre">__attribute__((ns_returns_not_retained))</span></tt>.</p>
+<p>It is undefined behavior if the method to which an Objective-C message send
+statically resolves has different retain semantics on its result from the
+method it dynamically resolves to. It is undefined behavior if a block or
+function call is made through a static type with different retain semantics on
+its result from the implementation of the called block or function.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Mismatches with returned results will cause over-retains or over-releases,
+depending on the direction. Again, the rule about function calls is really
+just an application of the existing C/C++ rule about calling functions
+through an incompatible function type.</p>
+</div>
+</div>
+<div class="section" id="unretained-return-values">
+<span id="arc-objects-operands-unretained-returns"></span><h4><a class="toc-backref" href="#id14">Unretained return values</a><a class="headerlink" href="#unretained-return-values" title="Permalink to this headline">¶</a></h4>
+<p>A method or function which returns a retainable object type but does not return
+a retained value must ensure that the object is still valid across the return
+boundary.</p>
+<p>When returning from such a function or method, ARC retains the value at the
+point of evaluation of the return statement, then leaves all local scopes, and
+then balances out the retain while ensuring that the value lives across the
+call boundary. In the worst case, this may involve an <tt class="docutils literal"><span class="pre">autorelease</span></tt>, but
+callers must not assume that the value is actually in the autorelease pool.</p>
+<p>ARC performs no extra mandatory work on the caller side, although it may elect
+to do something to shorten the lifetime of the returned value.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">It is common in non-ARC code to not return an autoreleased value; therefore
+the convention does not force either path. It is convenient to not be
+required to do unnecessary retains and autoreleases; this permits
+optimizations such as eliding retain/autoreleases when it can be shown that
+the original pointer will still be valid at the point of return.</p>
+</div>
+<p>A method or function may be marked with
+<tt class="docutils literal"><span class="pre">__attribute__((ns_returns_autoreleased))</span></tt> to indicate that it returns a
+pointer which is guaranteed to be valid at least as long as the innermost
+autorelease pool. There are no additional semantics enforced in the definition
+of such a method; it merely enables optimizations in callers.</p>
+</div>
+<div class="section" id="bridged-casts">
+<span id="arc-objects-operands-casts"></span><h4><a class="toc-backref" href="#id15">Bridged casts</a><a class="headerlink" href="#bridged-casts" title="Permalink to this headline">¶</a></h4>
+<p>A <span class="arc-term">bridged cast</span> is a C-style cast annotated with one of three
+keywords:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">(__bridge</span> <span class="pre">T)</span> <span class="pre">op</span></tt> casts the operand to the destination type <tt class="docutils literal"><span class="pre">T</span></tt>. If
+<tt class="docutils literal"><span class="pre">T</span></tt> is a retainable object pointer type, then <tt class="docutils literal"><span class="pre">op</span></tt> must have a
+non-retainable pointer type. If <tt class="docutils literal"><span class="pre">T</span></tt> is a non-retainable pointer type,
+then <tt class="docutils literal"><span class="pre">op</span></tt> must have a retainable object pointer type. Otherwise the cast
+is ill-formed. There is no transfer of ownership, and ARC inserts no retain
+operations.</li>
+<li><tt class="docutils literal"><span class="pre">(__bridge_retained</span> <span class="pre">T)</span> <span class="pre">op</span></tt> casts the operand, which must have retainable
+object pointer type, to the destination type, which must be a non-retainable
+pointer type. ARC retains the value, subject to the usual optimizations on
+local values, and the recipient is responsible for balancing that +1.</li>
+<li><tt class="docutils literal"><span class="pre">(__bridge_transfer</span> <span class="pre">T)</span> <span class="pre">op</span></tt> casts the operand, which must have
+non-retainable pointer type, to the destination type, which must be a
+retainable object pointer type. ARC will release the value at the end of
+the enclosing full-expression, subject to the usual optimizations on local
+values.</li>
+</ul>
+<p>These casts are required in order to transfer objects in and out of ARC
+control; see the rationale in the section on <a class="reference internal" href="#arc-objects-restrictions-conversion"><em>conversion of retainable
+object pointers</em></a>.</p>
+<p>Using a <tt class="docutils literal"><span class="pre">__bridge_retained</span></tt> or <tt class="docutils literal"><span class="pre">__bridge_transfer</span></tt> cast purely to convince
+ARC to emit an unbalanced retain or release, respectively, is poor form.</p>
+</div>
+</div>
+<div class="section" id="restrictions">
+<span id="arc-objects-restrictions"></span><h3><a class="toc-backref" href="#id16">Restrictions</a><a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="conversion-of-retainable-object-pointers">
+<span id="arc-objects-restrictions-conversion"></span><h4><a class="toc-backref" href="#id17">Conversion of retainable object pointers</a><a class="headerlink" href="#conversion-of-retainable-object-pointers" title="Permalink to this headline">¶</a></h4>
+<p>In general, a program which attempts to implicitly or explicitly convert a
+value of retainable object pointer type to any non-retainable type, or
+vice-versa, is ill-formed. For example, an Objective-C object pointer shall
+not be converted to <tt class="docutils literal"><span class="pre">void*</span></tt>. As an exception, cast to <tt class="docutils literal"><span class="pre">intptr_t</span></tt> is
+allowed because such casts are not transferring ownership. The <a class="reference internal" href="#arc-objects-operands-casts"><em>bridged
+casts</em></a> may be used to perform these conversions
+where necessary.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">We cannot ensure the correct management of the lifetime of objects if they
+may be freely passed around as unmanaged types. The bridged casts are
+provided so that the programmer may explicitly describe whether the cast
+transfers control into or out of ARC.</p>
+</div>
+<p>However, the following exceptions apply.</p>
+</div>
+<div class="section" id="conversion-to-retainable-object-pointer-type-of-expressions-with-known-semantics">
+<span id="arc-objects-restrictions-conversion-with-known-semantics"></span><h4><a class="toc-backref" href="#id18">Conversion to retainable object pointer type of expressions with known semantics</a><a class="headerlink" href="#conversion-to-retainable-object-pointer-type-of-expressions-with-known-semantics" title="Permalink to this headline">¶</a></h4>
+<p><span class="when-revised">[beginning Apple 4.0, LLVM 3.1]</span>
+<span class="revision">These exceptions have been greatly expanded; they previously applied
+only to a much-reduced subset which is difficult to categorize but which
+included null pointers, message sends (under the given rules), and the various
+global constants.</span></p>
+<p>An unbridged conversion to a retainable object pointer type from a type other
+than a retainable object pointer type is ill-formed, as discussed above, unless
+the operand of the cast has a syntactic form which is known retained, known
+unretained, or known retain-agnostic.</p>
+<p>An expression is <span class="arc-term">known retain-agnostic</span> if it is:</p>
+<ul class="simple">
+<li>an Objective-C string literal,</li>
+<li>a load from a <tt class="docutils literal"><span class="pre">const</span></tt> system global variable of <a class="reference internal" href="#arc-misc-c-retainable"><em>C retainable pointer
+type</em></a>, or</li>
+<li>a null pointer constant.</li>
+</ul>
+<p>An expression is <span class="arc-term">known unretained</span> if it is an rvalue of <a class="reference internal" href="#arc-misc-c-retainable"><em>C
+retainable pointer type</em></a> and it is:</p>
+<ul class="simple">
+<li>a direct call to a function, and either that function has the
+<tt class="docutils literal"><span class="pre">cf_returns_not_retained</span></tt> attribute or it is an <a class="reference internal" href="#arc-misc-c-retainable-audit"><em>audited</em></a> function that does not have the
+<tt class="docutils literal"><span class="pre">cf_returns_retained</span></tt> attribute and does not follow the create/copy naming
+convention,</li>
+<li>a message send, and the declared method either has the
+<tt class="docutils literal"><span class="pre">cf_returns_not_retained</span></tt> attribute or it has neither the
+<tt class="docutils literal"><span class="pre">cf_returns_retained</span></tt> attribute nor a <a class="reference internal" href="#arc-method-families"><em>selector family</em></a> that implies a retained result.</li>
+</ul>
+<p>An expression is <span class="arc-term">known retained</span> if it is an rvalue of <a class="reference internal" href="#arc-misc-c-retainable"><em>C
+retainable pointer type</em></a> and it is:</p>
+<ul class="simple">
+<li>a message send, and the declared method either has the
+<tt class="docutils literal"><span class="pre">cf_returns_retained</span></tt> attribute, or it does not have the
+<tt class="docutils literal"><span class="pre">cf_returns_not_retained</span></tt> attribute but it does have a <a class="reference internal" href="#arc-method-families"><em>selector
+family</em></a> that implies a retained result.</li>
+</ul>
+<p>Furthermore:</p>
+<ul class="simple">
+<li>a comma expression is classified according to its right-hand side,</li>
+<li>a statement expression is classified according to its result expression, if
+it has one,</li>
+<li>an lvalue-to-rvalue conversion applied to an Objective-C property lvalue is
+classified according to the underlying message send, and</li>
+<li>a conditional operator is classified according to its second and third
+operands, if they agree in classification, or else the other if one is known
+retain-agnostic.</li>
+</ul>
+<p>If the cast operand is known retained, the conversion is treated as a
+<tt class="docutils literal"><span class="pre">__bridge_transfer</span></tt> cast. If the cast operand is known unretained or known
+retain-agnostic, the conversion is treated as a <tt class="docutils literal"><span class="pre">__bridge</span></tt> cast.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>Bridging casts are annoying. Absent the ability to completely automate the
+management of CF objects, however, we are left with relatively poor attempts
+to reduce the need for a glut of explicit bridges. Hence these rules.</p>
+<p class="last">We’ve so far consciously refrained from implicitly turning retained CF
+results from function calls into <tt class="docutils literal"><span class="pre">__bridge_transfer</span></tt> casts. The worry is
+that some code patterns — for example, creating a CF value, assigning it
+to an ObjC-typed local, and then calling <tt class="docutils literal"><span class="pre">CFRelease</span></tt> when done — are a
+bit too likely to be accidentally accepted, leading to mysterious behavior.</p>
+</div>
+</div>
+<div class="section" id="conversion-from-retainable-object-pointer-type-in-certain-contexts">
+<span id="arc-objects-restrictions-conversion-exception-contextual"></span><h4><a class="toc-backref" href="#id19">Conversion from retainable object pointer type in certain contexts</a><a class="headerlink" href="#conversion-from-retainable-object-pointer-type-in-certain-contexts" title="Permalink to this headline">¶</a></h4>
+<p><span class="when-revised">[beginning Apple 4.0, LLVM 3.1]</span></p>
+<p>If an expression of retainable object pointer type is explicitly cast to a
+<a class="reference internal" href="#arc-misc-c-retainable"><em>C retainable pointer type</em></a>, the program is
+ill-formed as discussed above unless the result is immediately used:</p>
+<ul class="simple">
+<li>to initialize a parameter in an Objective-C message send where the parameter
+is not marked with the <tt class="docutils literal"><span class="pre">cf_consumed</span></tt> attribute, or</li>
+<li>to initialize a parameter in a direct call to an
+<a class="reference internal" href="#arc-misc-c-retainable-audit"><em>audited</em></a> function where the parameter is
+not marked with the <tt class="docutils literal"><span class="pre">cf_consumed</span></tt> attribute.</li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Consumed parameters are left out because ARC would naturally balance them
+with a retain, which was judged too treacherous. This is in part because
+several of the most common consuming functions are in the <tt class="docutils literal"><span class="pre">Release</span></tt> family,
+and it would be quite unfortunate for explicit releases to be silently
+balanced out in this way.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="ownership-qualification">
+<span id="arc-ownership"></span><h2><a class="toc-backref" href="#id20">Ownership qualification</a><a class="headerlink" href="#ownership-qualification" title="Permalink to this headline">¶</a></h2>
+<p>This section describes the behavior of <em>objects</em> of retainable object pointer
+type; that is, locations in memory which store retainable object pointers.</p>
+<p>A type is a <span class="arc-term">retainable object owner type</span> if it is a retainable
+object pointer type or an array type whose element type is a retainable object
+owner type.</p>
+<p>An <span class="arc-term">ownership qualifier</span> is a type qualifier which applies only to
+retainable object owner types. An array type is ownership-qualified according
+to its element type, and adding an ownership qualifier to an array type so
+qualifies its element type.</p>
+<p>A program is ill-formed if it attempts to apply an ownership qualifier to a
+type which is already ownership-qualified, even if it is the same qualifier.
+There is a single exception to this rule: an ownership qualifier may be applied
+to a substituted template type parameter, which overrides the ownership
+qualifier provided by the template argument.</p>
+<p>When forming a function type, the result type is adjusted so that any
+top-level ownership qualifier is deleted.</p>
+<p>Except as described under the <a class="reference internal" href="#arc-ownership-inference"><em>inference rules</em></a>,
+a program is ill-formed if it attempts to form a pointer or reference type to a
+retainable object owner type which lacks an ownership qualifier.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">These rules, together with the inference rules, ensure that all objects and
+lvalues of retainable object pointer type have an ownership qualifier. The
+ability to override an ownership qualifier during template substitution is
+required to counteract the <a class="reference internal" href="#arc-ownership-inference-template-arguments"><em>inference of __strong for template type
+arguments</em></a>. Ownership qualifiers
+on return types are dropped because they serve no purpose there except to
+cause spurious problems with overloading and templates.</p>
+</div>
+<p>There are four ownership qualifiers:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">__autoreleasing</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">__strong</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">__weak</span></tt></li>
+</ul>
+<p>A type is <span class="arc-term">nontrivially ownership-qualified</span> if it is qualified with
+<tt class="docutils literal"><span class="pre">__autoreleasing</span></tt>, <tt class="docutils literal"><span class="pre">__strong</span></tt>, or <tt class="docutils literal"><span class="pre">__weak</span></tt>.</p>
+<div class="section" id="spelling">
+<span id="arc-ownership-spelling"></span><h3><a class="toc-backref" href="#id21">Spelling</a><a class="headerlink" href="#spelling" title="Permalink to this headline">¶</a></h3>
+<p>The names of the ownership qualifiers are reserved for the implementation. A
+program may not assume that they are or are not implemented with macros, or
+what those macros expand to.</p>
+<p>An ownership qualifier may be written anywhere that any other type qualifier
+may be written.</p>
+<p>If an ownership qualifier appears in the <em>declaration-specifiers</em>, the
+following rules apply:</p>
+<ul class="simple">
+<li>if the type specifier is a retainable object owner type, the qualifier
+initially applies to that type;</li>
+<li>otherwise, if the outermost non-array declarator is a pointer
+or block pointer declarator, the qualifier initially applies to
+that type;</li>
+<li>otherwise the program is ill-formed.</li>
+<li>If the qualifier is so applied at a position in the declaration
+where the next-innermost declarator is a function declarator, and
+there is an block declarator within that function declarator, then
+the qualifier applies instead to that block declarator and this rule
+is considered afresh beginning from the new position.</li>
+</ul>
+<p>If an ownership qualifier appears on the declarator name, or on the declared
+object, it is applied to the innermost pointer or block-pointer type.</p>
+<p>If an ownership qualifier appears anywhere else in a declarator, it applies to
+the type there.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Ownership qualifiers are like <tt class="docutils literal"><span class="pre">const</span></tt> and <tt class="docutils literal"><span class="pre">volatile</span></tt> in the sense
+that they may sensibly apply at multiple distinct positions within a
+declarator. However, unlike those qualifiers, there are many
+situations where they are not meaningful, and so we make an effort
+to “move” the qualifier to a place where it will be meaningful. The
+general goal is to allow the programmer to write, say, <tt class="docutils literal"><span class="pre">__strong</span></tt>
+before the entire declaration and have it apply in the leftmost
+sensible place.</p>
+</div>
+<div class="section" id="property-declarations">
+<span id="arc-ownership-spelling-property"></span><h4><a class="toc-backref" href="#id22">Property declarations</a><a class="headerlink" href="#property-declarations" title="Permalink to this headline">¶</a></h4>
+<p>A property of retainable object pointer type may have ownership. If the
+property’s type is ownership-qualified, then the property has that ownership.
+If the property has one of the following modifiers, then the property has the
+corresponding ownership. A property is ill-formed if it has conflicting
+sources of ownership, or if it has redundant ownership modifiers, or if it has
+<tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> ownership.</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">assign</span></tt> implies <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt> ownership.</li>
+<li><tt class="docutils literal"><span class="pre">copy</span></tt> implies <tt class="docutils literal"><span class="pre">__strong</span></tt> ownership, as well as the usual behavior of
+copy semantics on the setter.</li>
+<li><tt class="docutils literal"><span class="pre">retain</span></tt> implies <tt class="docutils literal"><span class="pre">__strong</span></tt> ownership.</li>
+<li><tt class="docutils literal"><span class="pre">strong</span></tt> implies <tt class="docutils literal"><span class="pre">__strong</span></tt> ownership.</li>
+<li><tt class="docutils literal"><span class="pre">unsafe_unretained</span></tt> implies <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt> ownership.</li>
+<li><tt class="docutils literal"><span class="pre">weak</span></tt> implies <tt class="docutils literal"><span class="pre">__weak</span></tt> ownership.</li>
+</ul>
+<p>With the exception of <tt class="docutils literal"><span class="pre">weak</span></tt>, these modifiers are available in non-ARC
+modes.</p>
+<p>A property’s specified ownership is preserved in its metadata, but otherwise
+the meaning is purely conventional unless the property is synthesized. If a
+property is synthesized, then the <span class="arc-term">associated instance variable</span> is
+the instance variable which is named, possibly implicitly, by the
+<tt class="docutils literal"><span class="pre">@synthesize</span></tt> declaration. If the associated instance variable already
+exists, then its ownership qualification must equal the ownership of the
+property; otherwise, the instance variable is created with that ownership
+qualification.</p>
+<p>A property of retainable object pointer type which is synthesized without a
+source of ownership has the ownership of its associated instance variable, if it
+already exists; otherwise, <span class="when-revised">[beginning Apple 3.1, LLVM 3.1]</span>
+<span class="revision">its ownership is implicitly</span> <tt class="docutils literal"><span class="pre">strong</span></tt>. Prior to this revision, it
+was ill-formed to synthesize such a property.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Using <tt class="docutils literal"><span class="pre">strong</span></tt> by default is safe and consistent with the generic ARC rule
+about <a class="reference internal" href="#arc-ownership-inference-variables"><em>inferring ownership</em></a>. It is,
+unfortunately, inconsistent with the non-ARC rule which states that such
+properties are implicitly <tt class="docutils literal"><span class="pre">assign</span></tt>. However, that rule is clearly
+untenable in ARC, since it leads to default-unsafe code. The main merit to
+banning the properties is to avoid confusion with non-ARC practice, which did
+not ultimately strike us as sufficient to justify requiring extra syntax and
+(more importantly) forcing novices to understand ownership rules just to
+declare a property when the default is so reasonable. Changing the rule away
+from non-ARC practice was acceptable because we had conservatively banned the
+synthesis in order to give ourselves exactly this leeway.</p>
+</div>
+<p>Applying <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> to a property not of retainable object
+pointer type has the same behavior it does outside of ARC: it requires the
+property type to be some sort of pointer and permits the use of modifiers other
+than <tt class="docutils literal"><span class="pre">assign</span></tt>. These modifiers only affect the synthesized getter and
+setter; direct accesses to the ivar (even if synthesized) still have primitive
+semantics, and the value in the ivar will not be automatically released during
+deallocation.</p>
+</div>
+</div>
+<div class="section" id="semantics">
+<span id="arc-ownership-semantics"></span><h3><a class="toc-backref" href="#id23">Semantics</a><a class="headerlink" href="#semantics" title="Permalink to this headline">¶</a></h3>
+<p>There are five <span class="arc-term">managed operations</span> which may be performed on an
+object of retainable object pointer type. Each qualifier specifies different
+semantics for each of these operations. It is still undefined behavior to
+access an object outside of its lifetime.</p>
+<p>A load or store with “primitive semantics” has the same semantics as the
+respective operation would have on an <tt class="docutils literal"><span class="pre">void*</span></tt> lvalue with the same alignment
+and non-ownership qualification.</p>
+<p><span class="arc-term">Reading</span> occurs when performing a lvalue-to-rvalue conversion on an
+object lvalue.</p>
+<ul class="simple">
+<li>For <tt class="docutils literal"><span class="pre">__weak</span></tt> objects, the current pointee is retained and then released at
+the end of the current full-expression. This must execute atomically with
+respect to assignments and to the final release of the pointee.</li>
+<li>For all other objects, the lvalue is loaded with primitive semantics.</li>
+</ul>
+<p><span class="arc-term">Assignment</span> occurs when evaluating an assignment operator. The
+semantics vary based on the qualification:</p>
+<ul class="simple">
+<li>For <tt class="docutils literal"><span class="pre">__strong</span></tt> objects, the new pointee is first retained; second, the
+lvalue is loaded with primitive semantics; third, the new pointee is stored
+into the lvalue with primitive semantics; and finally, the old pointee is
+released. This is not performed atomically; external synchronization must be
+used to make this safe in the face of concurrent loads and stores.</li>
+<li>For <tt class="docutils literal"><span class="pre">__weak</span></tt> objects, the lvalue is updated to point to the new pointee,
+unless the new pointee is an object currently undergoing deallocation, in
+which case the lvalue is updated to a null pointer. This must execute
+atomically with respect to other assignments to the object, to reads from the
+object, and to the final release of the new pointee.</li>
+<li>For <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt> objects, the new pointee is stored into the
+lvalue using primitive semantics.</li>
+<li>For <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> objects, the new pointee is retained, autoreleased,
+and stored into the lvalue using primitive semantics.</li>
+</ul>
+<p><span class="arc-term">Initialization</span> occurs when an object’s lifetime begins, which
+depends on its storage duration. Initialization proceeds in two stages:</p>
+<ol class="arabic simple">
+<li>First, a null pointer is stored into the lvalue using primitive semantics.
+This step is skipped if the object is <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt>.</li>
+<li>Second, if the object has an initializer, that expression is evaluated and
+then assigned into the object using the usual assignment semantics.</li>
+</ol>
+<p><span class="arc-term">Destruction</span> occurs when an object’s lifetime ends. In all cases it
+is semantically equivalent to assigning a null pointer to the object, with the
+proviso that of course the object cannot be legally read after the object’s
+lifetime ends.</p>
+<p><span class="arc-term">Moving</span> occurs in specific situations where an lvalue is “moved
+from”, meaning that its current pointee will be used but the object may be left
+in a different (but still valid) state. This arises with <tt class="docutils literal"><span class="pre">__block</span></tt> variables
+and rvalue references in C++. For <tt class="docutils literal"><span class="pre">__strong</span></tt> lvalues, moving is equivalent
+to loading the lvalue with primitive semantics, writing a null pointer to it
+with primitive semantics, and then releasing the result of the load at the end
+of the current full-expression. For all other lvalues, moving is equivalent to
+reading the object.</p>
+</div>
+<div class="section" id="arc-ownership-restrictions">
+<span id="id1"></span><h3><a class="toc-backref" href="#id24">Restrictions</a><a class="headerlink" href="#arc-ownership-restrictions" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="weak-unavailable-types">
+<span id="arc-ownership-restrictions-weak"></span><h4><a class="toc-backref" href="#id25">Weak-unavailable types</a><a class="headerlink" href="#weak-unavailable-types" title="Permalink to this headline">¶</a></h4>
+<p>It is explicitly permitted for Objective-C classes to not support <tt class="docutils literal"><span class="pre">__weak</span></tt>
+references. It is undefined behavior to perform an operation with weak
+assignment semantics with a pointer to an Objective-C object whose class does
+not support <tt class="docutils literal"><span class="pre">__weak</span></tt> references.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Historically, it has been possible for a class to provide its own
+reference-count implementation by overriding <tt class="docutils literal"><span class="pre">retain</span></tt>, <tt class="docutils literal"><span class="pre">release</span></tt>, etc.
+However, weak references to an object require coordination with its class’s
+reference-count implementation because, among other things, weak loads and
+stores must be atomic with respect to the final release. Therefore, existing
+custom reference-count implementations will generally not support weak
+references without additional effort. This is unavoidable without breaking
+binary compatibility.</p>
+</div>
+<p>A class may indicate that it does not support weak references by providing the
+<tt class="docutils literal"><span class="pre">objc_arc_weak_unavailable</span></tt> attribute on the class’s interface declaration. A
+retainable object pointer type is <strong>weak-unavailable</strong> if
+is a pointer to an (optionally protocol-qualified) Objective-C class <tt class="docutils literal"><span class="pre">T</span></tt> where
+<tt class="docutils literal"><span class="pre">T</span></tt> or one of its superclasses has the <tt class="docutils literal"><span class="pre">objc_arc_weak_unavailable</span></tt>
+attribute. A program is ill-formed if it applies the <tt class="docutils literal"><span class="pre">__weak</span></tt> ownership
+qualifier to a weak-unavailable type or if the value operand of a weak
+assignment operation has a weak-unavailable type.</p>
+</div>
+<div class="section" id="storage-duration-of-autoreleasing-objects">
+<span id="arc-ownership-restrictions-autoreleasing"></span><h4><a class="toc-backref" href="#id26">Storage duration of <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> objects</a><a class="headerlink" href="#storage-duration-of-autoreleasing-objects" title="Permalink to this headline">¶</a></h4>
+<p>A program is ill-formed if it declares an <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> object of
+non-automatic storage duration. A program is ill-formed if it captures an
+<tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> object in a block or, unless by reference, in a C++11
+lambda.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Autorelease pools are tied to the current thread and scope by their nature.
+While it is possible to have temporary objects whose instance variables are
+filled with autoreleased objects, there is no way that ARC can provide any
+sort of safety guarantee there.</p>
+</div>
+<p>It is undefined behavior if a non-null pointer is assigned to an
+<tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> object while an autorelease pool is in scope and then that
+object is read after the autorelease pool’s scope is left.</p>
+</div>
+<div class="section" id="conversion-of-pointers-to-ownership-qualified-types">
+<span id="arc-ownership-restrictions-conversion-indirect"></span><h4><a class="toc-backref" href="#id27">Conversion of pointers to ownership-qualified types</a><a class="headerlink" href="#conversion-of-pointers-to-ownership-qualified-types" title="Permalink to this headline">¶</a></h4>
+<p>A program is ill-formed if an expression of type <tt class="docutils literal"><span class="pre">T*</span></tt> is converted,
+explicitly or implicitly, to the type <tt class="docutils literal"><span class="pre">U*</span></tt>, where <tt class="docutils literal"><span class="pre">T</span></tt> and <tt class="docutils literal"><span class="pre">U</span></tt> have
+different ownership qualification, unless:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">T</span></tt> is qualified with <tt class="docutils literal"><span class="pre">__strong</span></tt>, <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt>, or
+<tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt>, and <tt class="docutils literal"><span class="pre">U</span></tt> is qualified with both <tt class="docutils literal"><span class="pre">const</span></tt> and
+<tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt>; or</li>
+<li>either <tt class="docutils literal"><span class="pre">T</span></tt> or <tt class="docutils literal"><span class="pre">U</span></tt> is <tt class="docutils literal"><span class="pre">cv</span> <span class="pre">void</span></tt>, where <tt class="docutils literal"><span class="pre">cv</span></tt> is an optional sequence
+of non-ownership qualifiers; or</li>
+<li>the conversion is requested with a <tt class="docutils literal"><span class="pre">reinterpret_cast</span></tt> in Objective-C++; or</li>
+<li>the conversion is a well-formed <a class="reference internal" href="#arc-ownership-restrictions-pass-by-writeback"><em>pass-by-writeback</em></a>.</li>
+</ul>
+<p>The analogous rule applies to <tt class="docutils literal"><span class="pre">T&</span></tt> and <tt class="docutils literal"><span class="pre">U&</span></tt> in Objective-C++.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">These rules provide a reasonable level of type-safety for indirect pointers,
+as long as the underlying memory is not deallocated. The conversion to
+<tt class="docutils literal"><span class="pre">const</span> <span class="pre">__unsafe_unretained</span></tt> is permitted because the semantics of reads are
+equivalent across all these ownership semantics, and that’s a very useful and
+common pattern. The interconversion with <tt class="docutils literal"><span class="pre">void*</span></tt> is useful for allocating
+memory or otherwise escaping the type system, but use it carefully.
+<tt class="docutils literal"><span class="pre">reinterpret_cast</span></tt> is considered to be an obvious enough sign of taking
+responsibility for any problems.</p>
+</div>
+<p>It is undefined behavior to access an ownership-qualified object through an
+lvalue of a differently-qualified type, except that any non-<tt class="docutils literal"><span class="pre">__weak</span></tt> object
+may be read through an <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt> lvalue.</p>
+<p>It is undefined behavior if a managed operation is performed on a <tt class="docutils literal"><span class="pre">__strong</span></tt>
+or <tt class="docutils literal"><span class="pre">__weak</span></tt> object without a guarantee that it contains a primitive zero
+bit-pattern, or if the storage for such an object is freed or reused without the
+object being first assigned a null pointer.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">ARC cannot differentiate between an assignment operator which is intended to
+“initialize” dynamic memory and one which is intended to potentially replace
+a value. Therefore the object’s pointer must be valid before letting ARC at
+it. Similarly, C and Objective-C do not provide any language hooks for
+destroying objects held in dynamic memory, so it is the programmer’s
+responsibility to avoid leaks (<tt class="docutils literal"><span class="pre">__strong</span></tt> objects) and consistency errors
+(<tt class="docutils literal"><span class="pre">__weak</span></tt> objects).</p>
+</div>
+<p>These requirements are followed automatically in Objective-C++ when creating
+objects of retainable object owner type with <tt class="docutils literal"><span class="pre">new</span></tt> or <tt class="docutils literal"><span class="pre">new[]</span></tt> and destroying
+them with <tt class="docutils literal"><span class="pre">delete</span></tt>, <tt class="docutils literal"><span class="pre">delete[]</span></tt>, or a pseudo-destructor expression. Note
+that arrays of nontrivially-ownership-qualified type are not ABI compatible with
+non-ARC code because the element type is non-POD: such arrays that are
+<tt class="docutils literal"><span class="pre">new[]</span></tt>‘d in ARC translation units cannot be <tt class="docutils literal"><span class="pre">delete[]</span></tt>‘d in non-ARC
+translation units and vice-versa.</p>
+</div>
+<div class="section" id="passing-to-an-out-parameter-by-writeback">
+<span id="arc-ownership-restrictions-pass-by-writeback"></span><h4><a class="toc-backref" href="#id28">Passing to an out parameter by writeback</a><a class="headerlink" href="#passing-to-an-out-parameter-by-writeback" title="Permalink to this headline">¶</a></h4>
+<p>If the argument passed to a parameter of type <tt class="docutils literal"><span class="pre">T</span> <span class="pre">__autoreleasing</span> <span class="pre">*</span></tt> has type
+<tt class="docutils literal"><span class="pre">U</span> <span class="pre">oq</span> <span class="pre">*</span></tt>, where <tt class="docutils literal"><span class="pre">oq</span></tt> is an ownership qualifier, then the argument is a
+candidate for <span class="arc-term">pass-by-writeback`</span> if:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">oq</span></tt> is <tt class="docutils literal"><span class="pre">__strong</span></tt> or <tt class="docutils literal"><span class="pre">__weak</span></tt>, and</li>
+<li>it would be legal to initialize a <tt class="docutils literal"><span class="pre">T</span> <span class="pre">__strong</span> <span class="pre">*</span></tt> with a <tt class="docutils literal"><span class="pre">U</span> <span class="pre">__strong</span> <span class="pre">*</span></tt>.</li>
+</ul>
+<p>For purposes of overload resolution, an implicit conversion sequence requiring
+a pass-by-writeback is always worse than an implicit conversion sequence not
+requiring a pass-by-writeback.</p>
+<p>The pass-by-writeback is ill-formed if the argument expression does not have a
+legal form:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">&var</span></tt>, where <tt class="docutils literal"><span class="pre">var</span></tt> is a scalar variable of automatic storage duration
+with retainable object pointer type</li>
+<li>a conditional expression where the second and third operands are both legal
+forms</li>
+<li>a cast whose operand is a legal form</li>
+<li>a null pointer constant</li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The restriction in the form of the argument serves two purposes. First, it
+makes it impossible to pass the address of an array to the argument, which
+serves to protect against an otherwise serious risk of mis-inferring an
+“array” argument as an out-parameter. Second, it makes it much less likely
+that the user will see confusing aliasing problems due to the implementation,
+below, where their store to the writeback temporary is not immediately seen
+in the original argument variable.</p>
+</div>
+<p>A pass-by-writeback is evaluated as follows:</p>
+<ol class="arabic simple">
+<li>The argument is evaluated to yield a pointer <tt class="docutils literal"><span class="pre">p</span></tt> of type <tt class="docutils literal"><span class="pre">U</span> <span class="pre">oq</span> <span class="pre">*</span></tt>.</li>
+<li>If <tt class="docutils literal"><span class="pre">p</span></tt> is a null pointer, then a null pointer is passed as the argument,
+and no further work is required for the pass-by-writeback.</li>
+<li>Otherwise, a temporary of type <tt class="docutils literal"><span class="pre">T</span> <span class="pre">__autoreleasing</span></tt> is created and
+initialized to a null pointer.</li>
+<li>If the parameter is not an Objective-C method parameter marked <tt class="docutils literal"><span class="pre">out</span></tt>,
+then <tt class="docutils literal"><span class="pre">*p</span></tt> is read, and the result is written into the temporary with
+primitive semantics.</li>
+<li>The address of the temporary is passed as the argument to the actual call.</li>
+<li>After the call completes, the temporary is loaded with primitive
+semantics, and that value is assigned into <tt class="docutils literal"><span class="pre">*p</span></tt>.</li>
+</ol>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">This is all admittedly convoluted. In an ideal world, we would see that a
+local variable is being passed to an out-parameter and retroactively modify
+its type to be <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> rather than <tt class="docutils literal"><span class="pre">__strong</span></tt>. This would be
+remarkably difficult and not always well-founded under the C type system.
+However, it was judged unacceptably invasive to require programmers to write
+<tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> on all the variables they intend to use for
+out-parameters. This was the least bad solution.</p>
+</div>
+</div>
+<div class="section" id="ownership-qualified-fields-of-structs-and-unions">
+<span id="arc-ownership-restrictions-records"></span><h4><a class="toc-backref" href="#id29">Ownership-qualified fields of structs and unions</a><a class="headerlink" href="#ownership-qualified-fields-of-structs-and-unions" title="Permalink to this headline">¶</a></h4>
+<p>A program is ill-formed if it declares a member of a C struct or union to have
+a nontrivially ownership-qualified type.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The resulting type would be non-POD in the C++ sense, but C does not give us
+very good language tools for managing the lifetime of aggregates, so it is
+more convenient to simply forbid them. It is still possible to manage this
+with a <tt class="docutils literal"><span class="pre">void*</span></tt> or an <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt> object.</p>
+</div>
+<p>This restriction does not apply in Objective-C++. However, nontrivally
+ownership-qualified types are considered non-POD: in C++11 terms, they are not
+trivially default constructible, copy constructible, move constructible, copy
+assignable, move assignable, or destructible. It is a violation of C++’s One
+Definition Rule to use a class outside of ARC that, under ARC, would have a
+nontrivially ownership-qualified member.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Unlike in C, we can express all the necessary ARC semantics for
+ownership-qualified subobjects as suboperations of the (default) special
+member functions for the class. These functions then become non-trivial.
+This has the non-obvious result that the class will have a non-trivial copy
+constructor and non-trivial destructor; if this would not normally be true
+outside of ARC, objects of the type will be passed and returned in an
+ABI-incompatible manner.</p>
+</div>
+</div>
+</div>
+<div class="section" id="ownership-inference">
+<span id="arc-ownership-inference"></span><h3><a class="toc-backref" href="#id30">Ownership inference</a><a class="headerlink" href="#ownership-inference" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="objects">
+<span id="arc-ownership-inference-variables"></span><h4><a class="toc-backref" href="#id31">Objects</a><a class="headerlink" href="#objects" title="Permalink to this headline">¶</a></h4>
+<p>If an object is declared with retainable object owner type, but without an
+explicit ownership qualifier, its type is implicitly adjusted to have
+<tt class="docutils literal"><span class="pre">__strong</span></tt> qualification.</p>
+<p>As a special case, if the object’s base type is <tt class="docutils literal"><span class="pre">Class</span></tt> (possibly
+protocol-qualified), the type is adjusted to have <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt>
+qualification instead.</p>
+</div>
+<div class="section" id="indirect-parameters">
+<span id="arc-ownership-inference-indirect-parameters"></span><h4><a class="toc-backref" href="#id32">Indirect parameters</a><a class="headerlink" href="#indirect-parameters" title="Permalink to this headline">¶</a></h4>
+<p>If a function or method parameter has type <tt class="docutils literal"><span class="pre">T*</span></tt>, where <tt class="docutils literal"><span class="pre">T</span></tt> is an
+ownership-unqualified retainable object pointer type, then:</p>
+<ul class="simple">
+<li>if <tt class="docutils literal"><span class="pre">T</span></tt> is <tt class="docutils literal"><span class="pre">const</span></tt>-qualified or <tt class="docutils literal"><span class="pre">Class</span></tt>, then it is implicitly
+qualified with <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt>;</li>
+<li>otherwise, it is implicitly qualified with <tt class="docutils literal"><span class="pre">__autoreleasing</span></tt>.</li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last"><tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> exists mostly for this case, the Cocoa convention for
+out-parameters. Since a pointer to <tt class="docutils literal"><span class="pre">const</span></tt> is obviously not an
+out-parameter, we instead use a type more useful for passing arrays. If the
+user instead intends to pass in a <em>mutable</em> array, inferring
+<tt class="docutils literal"><span class="pre">__autoreleasing</span></tt> is the wrong thing to do; this directs some of the
+caution in the following rules about writeback.</p>
+</div>
+<p>Such a type written anywhere else would be ill-formed by the general rule
+requiring ownership qualifiers.</p>
+<p>This rule does not apply in Objective-C++ if a parameter’s type is dependent in
+a template pattern and is only <em>instantiated</em> to a type which would be a
+pointer to an unqualified retainable object pointer type. Such code is still
+ill-formed.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The convention is very unlikely to be intentional in template code.</p>
+</div>
+</div>
+<div class="section" id="template-arguments">
+<span id="arc-ownership-inference-template-arguments"></span><h4><a class="toc-backref" href="#id33">Template arguments</a><a class="headerlink" href="#template-arguments" title="Permalink to this headline">¶</a></h4>
+<p>If a template argument for a template type parameter is an retainable object
+owner type that does not have an explicit ownership qualifier, it is adjusted
+to have <tt class="docutils literal"><span class="pre">__strong</span></tt> qualification. This adjustment occurs regardless of
+whether the template argument was deduced or explicitly specified.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last"><tt class="docutils literal"><span class="pre">__strong</span></tt> is a useful default for containers (e.g., <tt class="docutils literal"><span class="pre">std::vector<id></span></tt>),
+which would otherwise require explicit qualification. Moreover, unqualified
+retainable object pointer types are unlikely to be useful within templates,
+since they generally need to have a qualifier applied to the before being
+used.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="method-families">
+<span id="arc-method-families"></span><h2><a class="toc-backref" href="#id34">Method families</a><a class="headerlink" href="#method-families" title="Permalink to this headline">¶</a></h2>
+<p>An Objective-C method may fall into a <span class="arc-term">method family</span>, which is a
+conventional set of behaviors ascribed to it by the Cocoa conventions.</p>
+<p>A method is in a certain method family if:</p>
+<ul class="simple">
+<li>it has a <tt class="docutils literal"><span class="pre">objc_method_family</span></tt> attribute placing it in that family; or if
+not that,</li>
+<li>it does not have an <tt class="docutils literal"><span class="pre">objc_method_family</span></tt> attribute placing it in a
+different or no family, and</li>
+<li>its selector falls into the corresponding selector family, and</li>
+<li>its signature obeys the added restrictions of the method family.</li>
+</ul>
+<p>A selector is in a certain selector family if, ignoring any leading
+underscores, the first component of the selector either consists entirely of
+the name of the method family or it begins with that name followed by a
+character other than a lowercase letter. For example, <tt class="docutils literal"><span class="pre">_perform:with:</span></tt> and
+<tt class="docutils literal"><span class="pre">performWith:</span></tt> would fall into the <tt class="docutils literal"><span class="pre">perform</span></tt> family (if we recognized one),
+but <tt class="docutils literal"><span class="pre">performing:with</span></tt> would not.</p>
+<p>The families and their added restrictions are:</p>
+<ul>
+<li><p class="first"><tt class="docutils literal"><span class="pre">alloc</span></tt> methods must return a retainable object pointer type.</p>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">copy</span></tt> methods must return a retainable object pointer type.</p>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">mutableCopy</span></tt> methods must return a retainable object pointer type.</p>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">new</span></tt> methods must return a retainable object pointer type.</p>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">init</span></tt> methods must be instance methods and must return an Objective-C
+pointer type. Additionally, a program is ill-formed if it declares or
+contains a call to an <tt class="docutils literal"><span class="pre">init</span></tt> method whose return type is neither <tt class="docutils literal"><span class="pre">id</span></tt> nor
+a pointer to a super-class or sub-class of the declaring class (if the method
+was declared on a class) or the static receiver type of the call (if it was
+declared on a protocol).</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>There are a fair number of existing methods with <tt class="docutils literal"><span class="pre">init</span></tt>-like selectors
+which nonetheless don’t follow the <tt class="docutils literal"><span class="pre">init</span></tt> conventions. Typically these
+are either accidental naming collisions or helper methods called during
+initialization. Because of the peculiar retain/release behavior of
+<tt class="docutils literal"><span class="pre">init</span></tt> methods, it’s very important not to treat these methods as
+<tt class="docutils literal"><span class="pre">init</span></tt> methods if they aren’t meant to be. It was felt that implicitly
+defining these methods out of the family based on the exact relationship
+between the return type and the declaring class would be much too subtle
+and fragile. Therefore we identify a small number of legitimate-seeming
+return types and call everything else an error. This serves the secondary
+purpose of encouraging programmers not to accidentally give methods names
+in the <tt class="docutils literal"><span class="pre">init</span></tt> family.</p>
+<p class="last">Note that a method with an <tt class="docutils literal"><span class="pre">init</span></tt>-family selector which returns a
+non-Objective-C type (e.g. <tt class="docutils literal"><span class="pre">void</span></tt>) is perfectly well-formed; it simply
+isn’t in the <tt class="docutils literal"><span class="pre">init</span></tt> family.</p>
+</div>
+</li>
+</ul>
+<p>A program is ill-formed if a method’s declarations, implementations, and
+overrides do not all have the same method family.</p>
+<div class="section" id="explicit-method-family-control">
+<span id="arc-family-attribute"></span><h3><a class="toc-backref" href="#id35">Explicit method family control</a><a class="headerlink" href="#explicit-method-family-control" title="Permalink to this headline">¶</a></h3>
+<p>A method may be annotated with the <tt class="docutils literal"><span class="pre">objc_method_family</span></tt> attribute to
+precisely control which method family it belongs to. If a method in an
+<tt class="docutils literal"><span class="pre">@implementation</span></tt> does not have this attribute, but there is a method
+declared in the corresponding <tt class="docutils literal"><span class="pre">@interface</span></tt> that does, then the attribute is
+copied to the declaration in the <tt class="docutils literal"><span class="pre">@implementation</span></tt>. The attribute is
+available outside of ARC, and may be tested for with the preprocessor query
+<tt class="docutils literal"><span class="pre">__has_attribute(objc_method_family)</span></tt>.</p>
+<p>The attribute is spelled
+<tt class="docutils literal"><span class="pre">__attribute__((objc_method_family(</span></tt> <em>family</em> <tt class="docutils literal"><span class="pre">)))</span></tt>. If <em>family</em> is
+<tt class="docutils literal"><span class="pre">none</span></tt>, the method has no family, even if it would otherwise be considered to
+have one based on its selector and type. Otherwise, <em>family</em> must be one of
+<tt class="docutils literal"><span class="pre">alloc</span></tt>, <tt class="docutils literal"><span class="pre">copy</span></tt>, <tt class="docutils literal"><span class="pre">init</span></tt>, <tt class="docutils literal"><span class="pre">mutableCopy</span></tt>, or <tt class="docutils literal"><span class="pre">new</span></tt>, in which case the
+method is considered to belong to the corresponding family regardless of its
+selector. It is an error if a method that is explicitly added to a family in
+this way does not meet the requirements of the family other than the selector
+naming convention.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The rules codified in this document describe the standard conventions of
+Objective-C. However, as these conventions have not heretofore been enforced
+by an unforgiving mechanical system, they are only imperfectly kept,
+especially as they haven’t always even been precisely defined. While it is
+possible to define low-level ownership semantics with attributes like
+<tt class="docutils literal"><span class="pre">ns_returns_retained</span></tt>, this attribute allows the user to communicate
+semantic intent, which is of use both to ARC (which, e.g., treats calls to
+<tt class="docutils literal"><span class="pre">init</span></tt> specially) and the static analyzer.</p>
+</div>
+</div>
+<div class="section" id="semantics-of-method-families">
+<span id="arc-family-semantics"></span><h3><a class="toc-backref" href="#id36">Semantics of method families</a><a class="headerlink" href="#semantics-of-method-families" title="Permalink to this headline">¶</a></h3>
+<p>A method’s membership in a method family may imply non-standard semantics for
+its parameters and return type.</p>
+<p>Methods in the <tt class="docutils literal"><span class="pre">alloc</span></tt>, <tt class="docutils literal"><span class="pre">copy</span></tt>, <tt class="docutils literal"><span class="pre">mutableCopy</span></tt>, and <tt class="docutils literal"><span class="pre">new</span></tt> families —
+that is, methods in all the currently-defined families except <tt class="docutils literal"><span class="pre">init</span></tt> —
+implicitly <a class="reference internal" href="#arc-object-operands-retained-return-values"><em>return a retained object</em></a> as if they were annotated with
+the <tt class="docutils literal"><span class="pre">ns_returns_retained</span></tt> attribute. This can be overridden by annotating
+the method with either of the <tt class="docutils literal"><span class="pre">ns_returns_autoreleased</span></tt> or
+<tt class="docutils literal"><span class="pre">ns_returns_not_retained</span></tt> attributes.</p>
+<p>Properties also follow same naming rules as methods. This means that those in
+the <tt class="docutils literal"><span class="pre">alloc</span></tt>, <tt class="docutils literal"><span class="pre">copy</span></tt>, <tt class="docutils literal"><span class="pre">mutableCopy</span></tt>, and <tt class="docutils literal"><span class="pre">new</span></tt> families provide access
+to <a class="reference internal" href="#arc-object-operands-retained-return-values"><em>retained objects</em></a>. This
+can be overridden by annotating the property with <tt class="docutils literal"><span class="pre">ns_returns_not_retained</span></tt>
+attribute.</p>
+<div class="section" id="semantics-of-init">
+<span id="arc-family-semantics-init"></span><h4><a class="toc-backref" href="#id37">Semantics of <tt class="docutils literal"><span class="pre">init</span></tt></a><a class="headerlink" href="#semantics-of-init" title="Permalink to this headline">¶</a></h4>
+<p>Methods in the <tt class="docutils literal"><span class="pre">init</span></tt> family implicitly <a class="reference internal" href="#arc-objects-operands-consumed"><em>consume</em></a> their <tt class="docutils literal"><span class="pre">self</span></tt> parameter and <a class="reference internal" href="#arc-object-operands-retained-return-values"><em>return a
+retained object</em></a>. Neither of
+these properties can be altered through attributes.</p>
+<p>A call to an <tt class="docutils literal"><span class="pre">init</span></tt> method with a receiver that is either <tt class="docutils literal"><span class="pre">self</span></tt> (possibly
+parenthesized or casted) or <tt class="docutils literal"><span class="pre">super</span></tt> is called a <span class="arc-term">delegate init
+call</span>. It is an error for a delegate init call to be made except from an
+<tt class="docutils literal"><span class="pre">init</span></tt> method, and excluding blocks within such methods.</p>
+<p>As an exception to the <a class="reference internal" href="#arc-misc-self"><em>usual rule</em></a>, the variable <tt class="docutils literal"><span class="pre">self</span></tt>
+is mutable in an <tt class="docutils literal"><span class="pre">init</span></tt> method and has the usual semantics for a <tt class="docutils literal"><span class="pre">__strong</span></tt>
+variable. However, it is undefined behavior and the program is ill-formed, no
+diagnostic required, if an <tt class="docutils literal"><span class="pre">init</span></tt> method attempts to use the previous value
+of <tt class="docutils literal"><span class="pre">self</span></tt> after the completion of a delegate init call. It is conventional,
+but not required, for an <tt class="docutils literal"><span class="pre">init</span></tt> method to return <tt class="docutils literal"><span class="pre">self</span></tt>.</p>
+<p>It is undefined behavior for a program to cause two or more calls to <tt class="docutils literal"><span class="pre">init</span></tt>
+methods on the same object, except that each <tt class="docutils literal"><span class="pre">init</span></tt> method invocation may
+perform at most one delegate init call.</p>
+</div>
+<div class="section" id="related-result-types">
+<span id="arc-family-semantics-result-type"></span><h4><a class="toc-backref" href="#id38">Related result types</a><a class="headerlink" href="#related-result-types" title="Permalink to this headline">¶</a></h4>
+<p>Certain methods are candidates to have <span class="arc-term">related result types</span>:</p>
+<ul class="simple">
+<li>class methods in the <tt class="docutils literal"><span class="pre">alloc</span></tt> and <tt class="docutils literal"><span class="pre">new</span></tt> method families</li>
+<li>instance methods in the <tt class="docutils literal"><span class="pre">init</span></tt> family</li>
+<li>the instance method <tt class="docutils literal"><span class="pre">self</span></tt></li>
+<li>outside of ARC, the instance methods <tt class="docutils literal"><span class="pre">retain</span></tt> and <tt class="docutils literal"><span class="pre">autorelease</span></tt></li>
+</ul>
+<p>If the formal result type of such a method is <tt class="docutils literal"><span class="pre">id</span></tt> or protocol-qualified
+<tt class="docutils literal"><span class="pre">id</span></tt>, or a type equal to the declaring class or a superclass, then it is said
+to have a related result type. In this case, when invoked in an explicit
+message send, it is assumed to return a type related to the type of the
+receiver:</p>
+<ul class="simple">
+<li>if it is a class method, and the receiver is a class name <tt class="docutils literal"><span class="pre">T</span></tt>, the message
+send expression has type <tt class="docutils literal"><span class="pre">T*</span></tt>; otherwise</li>
+<li>if it is an instance method, and the receiver has type <tt class="docutils literal"><span class="pre">T</span></tt>, the message
+send expression has type <tt class="docutils literal"><span class="pre">T</span></tt>; otherwise</li>
+<li>the message send expression has the normal result type of the method.</li>
+</ul>
+<p>This is a new rule of the Objective-C language and applies outside of ARC.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">ARC’s automatic code emission is more prone than most code to signature
+errors, i.e. errors where a call was emitted against one method signature,
+but the implementing method has an incompatible signature. Having more
+precise type information helps drastically lower this risk, as well as
+catching a number of latent bugs.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="optimization">
+<span id="arc-optimization"></span><h2><a class="toc-backref" href="#id39">Optimization</a><a class="headerlink" href="#optimization" title="Permalink to this headline">¶</a></h2>
+<p>Within this section, the word <span class="arc-term">function</span> will be used to
+refer to any structured unit of code, be it a C function, an
+Objective-C method, or a block.</p>
+<p>This specification describes ARC as performing specific <tt class="docutils literal"><span class="pre">retain</span></tt> and
+<tt class="docutils literal"><span class="pre">release</span></tt> operations on retainable object pointers at specific
+points during the execution of a program. These operations make up a
+non-contiguous subsequence of the computation history of the program.
+The portion of this sequence for a particular retainable object
+pointer for which a specific function execution is directly
+responsible is the <span class="arc-term">formal local retain history</span> of the
+object pointer. The corresponding actual sequence executed is the
+<cite>dynamic local retain history</cite>.</p>
+<p>However, under certain circumstances, ARC is permitted to re-order and
+eliminate operations in a manner which may alter the overall
+computation history beyond what is permitted by the general “as if”
+rule of C/C++ and the <a class="reference internal" href="#arc-objects-retains"><em>restrictions</em></a> on
+the implementation of <tt class="docutils literal"><span class="pre">retain</span></tt> and <tt class="docutils literal"><span class="pre">release</span></tt>.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>Specifically, ARC is sometimes permitted to optimize <tt class="docutils literal"><span class="pre">release</span></tt>
+operations in ways which might cause an object to be deallocated
+before it would otherwise be. Without this, it would be almost
+impossible to eliminate any <tt class="docutils literal"><span class="pre">retain</span></tt>/<tt class="docutils literal"><span class="pre">release</span></tt> pairs. For
+example, consider the following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="n">x</span> <span class="o">=</span> <span class="n">_ivar</span><span class="p">;</span>
+<span class="p">[</span><span class="n">x</span> <span class="n">foo</span><span class="p">];</span>
+</pre></div>
+</div>
+<p class="last">If we were not permitted in any event to shorten the lifetime of the
+object in <tt class="docutils literal"><span class="pre">x</span></tt>, then we would not be able to eliminate this retain
+and release unless we could prove that the message send could not
+modify <tt class="docutils literal"><span class="pre">_ivar</span></tt> (or deallocate <tt class="docutils literal"><span class="pre">self</span></tt>). Since message sends are
+opaque to the optimizer, this is not possible, and so ARC’s hands
+would be almost completely tied.</p>
+</div>
+<p>ARC makes no guarantees about the execution of a computation history
+which contains undefined behavior. In particular, ARC makes no
+guarantees in the presence of race conditions.</p>
+<p>ARC may assume that any retainable object pointers it receives or
+generates are instantaneously valid from that point until a point
+which, by the concurrency model of the host language, happens-after
+the generation of the pointer and happens-before a release of that
+object (possibly via an aliasing pointer or indirectly due to
+destruction of a different object).</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">There is very little point in trying to guarantee correctness in the
+presence of race conditions. ARC does not have a stack-scanning
+garbage collector, and guaranteeing the atomicity of every load and
+store operation would be prohibitive and preclude a vast amount of
+optimization.</p>
+</div>
+<p>ARC may assume that non-ARC code engages in sensible balancing
+behavior and does not rely on exact or minimum retain count values
+except as guaranteed by <tt class="docutils literal"><span class="pre">__strong</span></tt> object invariants or +1 transfer
+conventions. For example, if an object is provably double-retained
+and double-released, ARC may eliminate the inner retain and release;
+it does not need to guard against code which performs an unbalanced
+release followed by a “balancing” retain.</p>
+<div class="section" id="object-liveness">
+<span id="arc-optimization-liveness"></span><h3><a class="toc-backref" href="#id40">Object liveness</a><a class="headerlink" href="#object-liveness" title="Permalink to this headline">¶</a></h3>
+<p>ARC may not allow a retainable object <tt class="docutils literal"><span class="pre">X</span></tt> to be deallocated at a
+time <tt class="docutils literal"><span class="pre">T</span></tt> in a computation history if:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">X</span></tt> is the value stored in a <tt class="docutils literal"><span class="pre">__strong</span></tt> object <tt class="docutils literal"><span class="pre">S</span></tt> with
+<a class="reference internal" href="#arc-optimization-precise"><em>precise lifetime semantics</em></a>, or</li>
+<li><tt class="docutils literal"><span class="pre">X</span></tt> is the value stored in a <tt class="docutils literal"><span class="pre">__strong</span></tt> object <tt class="docutils literal"><span class="pre">S</span></tt> with
+imprecise lifetime semantics and, at some point after <tt class="docutils literal"><span class="pre">T</span></tt> but
+before the next store to <tt class="docutils literal"><span class="pre">S</span></tt>, the computation history features a
+load from <tt class="docutils literal"><span class="pre">S</span></tt> and in some way depends on the value loaded, or</li>
+<li><tt class="docutils literal"><span class="pre">X</span></tt> is a value described as being released at the end of the
+current full-expression and, at some point after <tt class="docutils literal"><span class="pre">T</span></tt> but before
+the end of the full-expression, the computation history depends
+on that value.</li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>The intent of the second rule is to say that objects held in normal
+<tt class="docutils literal"><span class="pre">__strong</span></tt> local variables may be released as soon as the value in
+the variable is no longer being used: either the variable stops
+being used completely or a new value is stored in the variable.</p>
+<p class="last">The intent of the third rule is to say that return values may be
+released after they’ve been used.</p>
+</div>
+<p>A computation history depends on a pointer value <tt class="docutils literal"><span class="pre">P</span></tt> if it:</p>
+<ul class="simple">
+<li>performs a pointer comparison with <tt class="docutils literal"><span class="pre">P</span></tt>,</li>
+<li>loads from <tt class="docutils literal"><span class="pre">P</span></tt>,</li>
+<li>stores to <tt class="docutils literal"><span class="pre">P</span></tt>,</li>
+<li>depends on a pointer value <tt class="docutils literal"><span class="pre">Q</span></tt> derived via pointer arithmetic
+from <tt class="docutils literal"><span class="pre">P</span></tt> (including an instance-variable or field access), or</li>
+<li>depends on a pointer value <tt class="docutils literal"><span class="pre">Q</span></tt> loaded from <tt class="docutils literal"><span class="pre">P</span></tt>.</li>
+</ul>
+<p>Dependency applies only to values derived directly or indirectly from
+a particular expression result and does not occur merely because a
+separate pointer value dynamically aliases <tt class="docutils literal"><span class="pre">P</span></tt>. Furthermore, this
+dependency is not carried by values that are stored to objects.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>The restrictions on dependency are intended to make this analysis
+feasible by an optimizer with only incomplete information about a
+program. Essentially, dependence is carried to “obvious” uses of a
+pointer. Merely passing a pointer argument to a function does not
+itself cause dependence, but since generally the optimizer will not
+be able to prove that the function doesn’t depend on that parameter,
+it will be forced to conservatively assume it does.</p>
+<p>Dependency propagates to values loaded from a pointer because those
+values might be invalidated by deallocating the object. For
+example, given the code <tt class="docutils literal"><span class="pre">__strong</span> <span class="pre">id</span> <span class="pre">x</span> <span class="pre">=</span> <span class="pre">p->ivar;</span></tt>, ARC must not
+move the release of <tt class="docutils literal"><span class="pre">p</span></tt> to between the load of <tt class="docutils literal"><span class="pre">p->ivar</span></tt> and the
+retain of that value for storing into <tt class="docutils literal"><span class="pre">x</span></tt>.</p>
+<p>Dependency does not propagate through stores of dependent pointer
+values because doing so would allow dependency to outlive the
+full-expression which produced the original value. For example, the
+address of an instance variable could be written to some global
+location and then freely accessed during the lifetime of the local,
+or a function could return an inner pointer of an object and store
+it to a local. These cases would be potentially impossible to
+reason about and so would basically prevent any optimizations based
+on imprecise lifetime. There are also uncommon enough to make it
+reasonable to require the precise-lifetime annotation if someone
+really wants to rely on them.</p>
+<p class="last">Dependency does propagate through return values of pointer type.
+The compelling source of need for this rule is a property accessor
+which returns an un-autoreleased result; the calling function must
+have the chance to operate on the value, e.g. to retain it, before
+ARC releases the original pointer. Note again, however, that
+dependence does not survive a store, so ARC does not guarantee the
+continued validity of the return value past the end of the
+full-expression.</p>
+</div>
+</div>
+<div class="section" id="no-object-lifetime-extension">
+<span id="arc-optimization-object-lifetime"></span><h3><a class="toc-backref" href="#id41">No object lifetime extension</a><a class="headerlink" href="#no-object-lifetime-extension" title="Permalink to this headline">¶</a></h3>
+<p>If, in the formal computation history of the program, an object <tt class="docutils literal"><span class="pre">X</span></tt>
+has been deallocated by the time of an observable side-effect, then
+ARC must cause <tt class="docutils literal"><span class="pre">X</span></tt> to be deallocated by no later than the occurrence
+of that side-effect, except as influenced by the re-ordering of the
+destruction of objects.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>This rule is intended to prohibit ARC from observably extending the
+lifetime of a retainable object, other than as specified in this
+document. Together with the rule limiting the transformation of
+releases, this rule requires ARC to eliminate retains and release
+only in pairs.</p>
+<p class="last">ARC’s power to reorder the destruction of objects is critical to its
+ability to do any optimization, for essentially the same reason that
+it must retain the power to decrease the lifetime of an object.
+Unfortunately, while it’s generally poor style for the destruction
+of objects to have arbitrary side-effects, it’s certainly possible.
+Hence the caveat.</p>
+</div>
+</div>
+<div class="section" id="precise-lifetime-semantics">
+<span id="arc-optimization-precise"></span><h3><a class="toc-backref" href="#id42">Precise lifetime semantics</a><a class="headerlink" href="#precise-lifetime-semantics" title="Permalink to this headline">¶</a></h3>
+<p>In general, ARC maintains an invariant that a retainable object pointer held in
+a <tt class="docutils literal"><span class="pre">__strong</span></tt> object will be retained for the full formal lifetime of the
+object. Objects subject to this invariant have <span class="arc-term">precise lifetime
+semantics</span>.</p>
+<p>By default, local variables of automatic storage duration do not have precise
+lifetime semantics. Such objects are simply strong references which hold
+values of retainable object pointer type, and these values are still fully
+subject to the optimizations on values under local control.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Applying these precise-lifetime semantics strictly would be prohibitive.
+Many useful optimizations that might theoretically decrease the lifetime of
+an object would be rendered impossible. Essentially, it promises too much.</p>
+</div>
+<p>A local variable of retainable object owner type and automatic storage duration
+may be annotated with the <tt class="docutils literal"><span class="pre">objc_precise_lifetime</span></tt> attribute to indicate that
+it should be considered to be an object with precise lifetime semantics.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Nonetheless, it is sometimes useful to be able to force an object to be
+released at a precise time, even if that object does not appear to be used.
+This is likely to be uncommon enough that the syntactic weight of explicitly
+requesting these semantics will not be burdensome, and may even make the code
+clearer.</p>
+</div>
+</div>
+</div>
+<div class="section" id="miscellaneous">
+<span id="arc-misc"></span><h2><a class="toc-backref" href="#id43">Miscellaneous</a><a class="headerlink" href="#miscellaneous" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="special-methods">
+<span id="arc-misc-special-methods"></span><h3><a class="toc-backref" href="#id44">Special methods</a><a class="headerlink" href="#special-methods" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="memory-management-methods">
+<span id="arc-misc-special-methods-retain"></span><h4><a class="toc-backref" href="#id45">Memory management methods</a><a class="headerlink" href="#memory-management-methods" title="Permalink to this headline">¶</a></h4>
+<p>A program is ill-formed if it contains a method definition, message send, or
+<tt class="docutils literal"><span class="pre">@selector</span></tt> expression for any of the following selectors:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">autorelease</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">release</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">retain</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">retainCount</span></tt></li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p><tt class="docutils literal"><span class="pre">retainCount</span></tt> is banned because ARC robs it of consistent semantics. The
+others were banned after weighing three options for how to deal with message
+sends:</p>
+<p><strong>Honoring</strong> them would work out very poorly if a programmer naively or
+accidentally tried to incorporate code written for manual retain/release code
+into an ARC program. At best, such code would do twice as much work as
+necessary; quite frequently, however, ARC and the explicit code would both
+try to balance the same retain, leading to crashes. The cost is losing the
+ability to perform “unrooted” retains, i.e. retains not logically
+corresponding to a strong reference in the object graph.</p>
+<p><strong>Ignoring</strong> them would badly violate user expectations about their code.
+While it <em>would</em> make it easier to develop code simultaneously for ARC and
+non-ARC, there is very little reason to do so except for certain library
+developers. ARC and non-ARC translation units share an execution model and
+can seamlessly interoperate. Within a translation unit, a developer who
+faithfully maintains their code in non-ARC mode is suffering all the
+restrictions of ARC for zero benefit, while a developer who isn’t testing the
+non-ARC mode is likely to be unpleasantly surprised if they try to go back to
+it.</p>
+<p><strong>Banning</strong> them has the disadvantage of making it very awkward to migrate
+existing code to ARC. The best answer to that, given a number of other
+changes and restrictions in ARC, is to provide a specialized tool to assist
+users in that migration.</p>
+<p class="last">Implementing these methods was banned because they are too integral to the
+semantics of ARC; many tricks which worked tolerably under manual reference
+counting will misbehave if ARC performs an ephemeral extra retain or two. If
+absolutely required, it is still possible to implement them in non-ARC code,
+for example in a category; the implementations must obey the <a class="reference internal" href="#arc-objects-retains"><em>semantics</em></a> laid out elsewhere in this document.</p>
+</div>
+</div>
+<div class="section" id="dealloc">
+<span id="arc-misc-special-methods-dealloc"></span><h4><a class="toc-backref" href="#id46"><tt class="docutils literal"><span class="pre">dealloc</span></tt></a><a class="headerlink" href="#dealloc" title="Permalink to this headline">¶</a></h4>
+<p>A program is ill-formed if it contains a message send or <tt class="docutils literal"><span class="pre">@selector</span></tt>
+expression for the selector <tt class="docutils literal"><span class="pre">dealloc</span></tt>.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">There are no legitimate reasons to call <tt class="docutils literal"><span class="pre">dealloc</span></tt> directly.</p>
+</div>
+<p>A class may provide a method definition for an instance method named
+<tt class="docutils literal"><span class="pre">dealloc</span></tt>. This method will be called after the final <tt class="docutils literal"><span class="pre">release</span></tt> of the
+object but before it is deallocated or any of its instance variables are
+destroyed. The superclass’s implementation of <tt class="docutils literal"><span class="pre">dealloc</span></tt> will be called
+automatically when the method returns.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Even though ARC destroys instance variables automatically, there are still
+legitimate reasons to write a <tt class="docutils literal"><span class="pre">dealloc</span></tt> method, such as freeing
+non-retainable resources. Failing to call <tt class="docutils literal"><span class="pre">[super</span> <span class="pre">dealloc]</span></tt> in such a
+method is nearly always a bug. Sometimes, the object is simply trying to
+prevent itself from being destroyed, but <tt class="docutils literal"><span class="pre">dealloc</span></tt> is really far too late
+for the object to be raising such objections. Somewhat more legitimately, an
+object may have been pool-allocated and should not be deallocated with
+<tt class="docutils literal"><span class="pre">free</span></tt>; for now, this can only be supported with a <tt class="docutils literal"><span class="pre">dealloc</span></tt>
+implementation outside of ARC. Such an implementation must be very careful
+to do all the other work that <tt class="docutils literal"><span class="pre">NSObject</span></tt>‘s <tt class="docutils literal"><span class="pre">dealloc</span></tt> would, which is
+outside the scope of this document to describe.</p>
+</div>
+<p>The instance variables for an ARC-compiled class will be destroyed at some
+point after control enters the <tt class="docutils literal"><span class="pre">dealloc</span></tt> method for the root class of the
+class. The ordering of the destruction of instance variables is unspecified,
+both within a single class and between subclasses and superclasses.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>The traditional, non-ARC pattern for destroying instance variables is to
+destroy them immediately before calling <tt class="docutils literal"><span class="pre">[super</span> <span class="pre">dealloc]</span></tt>. Unfortunately,
+message sends from the superclass are quite capable of reaching methods in
+the subclass, and those methods may well read or write to those instance
+variables. Making such message sends from dealloc is generally discouraged,
+since the subclass may well rely on other invariants that were broken during
+<tt class="docutils literal"><span class="pre">dealloc</span></tt>, but it’s not so inescapably dangerous that we felt comfortable
+calling it undefined behavior. Therefore we chose to delay destroying the
+instance variables to a point at which message sends are clearly disallowed:
+the point at which the root class’s deallocation routines take over.</p>
+<p class="last">In most code, the difference is not observable. It can, however, be observed
+if an instance variable holds a strong reference to an object whose
+deallocation will trigger a side-effect which must be carefully ordered with
+respect to the destruction of the super class. Such code violates the design
+principle that semantically important behavior should be explicit. A simple
+fix is to clear the instance variable manually during <tt class="docutils literal"><span class="pre">dealloc</span></tt>; a more
+holistic solution is to move semantically important side-effects out of
+<tt class="docutils literal"><span class="pre">dealloc</span></tt> and into a separate teardown phase which can rely on working with
+well-formed objects.</p>
+</div>
+</div>
+</div>
+<div class="section" id="autoreleasepool">
+<span id="arc-misc-autoreleasepool"></span><h3><a class="toc-backref" href="#id47"><tt class="docutils literal"><span class="pre">@autoreleasepool</span></tt></a><a class="headerlink" href="#autoreleasepool" title="Permalink to this headline">¶</a></h3>
+<p>To simplify the use of autorelease pools, and to bring them under the control
+of the compiler, a new kind of statement is available in Objective-C. It is
+written <tt class="docutils literal"><span class="pre">@autoreleasepool</span></tt> followed by a <em>compound-statement</em>, i.e. by a new
+scope delimited by curly braces. Upon entry to this block, the current state
+of the autorelease pool is captured. When the block is exited normally,
+whether by fallthrough or directed control flow (such as <tt class="docutils literal"><span class="pre">return</span></tt> or
+<tt class="docutils literal"><span class="pre">break</span></tt>), the autorelease pool is restored to the saved state, releasing all
+the objects in it. When the block is exited with an exception, the pool is not
+drained.</p>
+<p><tt class="docutils literal"><span class="pre">@autoreleasepool</span></tt> may be used in non-ARC translation units, with equivalent
+semantics.</p>
+<p>A program is ill-formed if it refers to the <tt class="docutils literal"><span class="pre">NSAutoreleasePool</span></tt> class.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Autorelease pools are clearly important for the compiler to reason about, but
+it is far too much to expect the compiler to accurately reason about control
+dependencies between two calls. It is also very easy to accidentally forget
+to drain an autorelease pool when using the manual API, and this can
+significantly inflate the process’s high-water-mark. The introduction of a
+new scope is unfortunate but basically required for sane interaction with the
+rest of the language. Not draining the pool during an unwind is apparently
+required by the Objective-C exceptions implementation.</p>
+</div>
+</div>
+<div class="section" id="self">
+<span id="arc-misc-self"></span><h3><a class="toc-backref" href="#id48"><tt class="docutils literal"><span class="pre">self</span></tt></a><a class="headerlink" href="#self" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">self</span></tt> parameter variable of an Objective-C method is never actually
+retained by the implementation. It is undefined behavior, or at least
+dangerous, to cause an object to be deallocated during a message send to that
+object.</p>
+<p>To make this safe, for Objective-C instance methods <tt class="docutils literal"><span class="pre">self</span></tt> is implicitly
+<tt class="docutils literal"><span class="pre">const</span></tt> unless the method is in the <a class="reference internal" href="#arc-family-semantics-init"><em>init family</em></a>. Further, <tt class="docutils literal"><span class="pre">self</span></tt> is <strong>always</strong> implicitly
+<tt class="docutils literal"><span class="pre">const</span></tt> within a class method.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The cost of retaining <tt class="docutils literal"><span class="pre">self</span></tt> in all methods was found to be prohibitive, as
+it tends to be live across calls, preventing the optimizer from proving that
+the retain and release are unnecessary — for good reason, as it’s quite
+possible in theory to cause an object to be deallocated during its execution
+without this retain and release. Since it’s extremely uncommon to actually
+do so, even unintentionally, and since there’s no natural way for the
+programmer to remove this retain/release pair otherwise (as there is for
+other parameters by, say, making the variable <tt class="docutils literal"><span class="pre">__unsafe_unretained</span></tt>), we
+chose to make this optimizing assumption and shift some amount of risk to the
+user.</p>
+</div>
+</div>
+<div class="section" id="fast-enumeration-iteration-variables">
+<span id="arc-misc-enumeration"></span><h3><a class="toc-backref" href="#id49">Fast enumeration iteration variables</a><a class="headerlink" href="#fast-enumeration-iteration-variables" title="Permalink to this headline">¶</a></h3>
+<p>If a variable is declared in the condition of an Objective-C fast enumeration
+loop, and the variable has no explicit ownership qualifier, then it is
+qualified with <tt class="docutils literal"><span class="pre">const</span> <span class="pre">__strong</span></tt> and objects encountered during the
+enumeration are not actually retained.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">This is an optimization made possible because fast enumeration loops promise
+to keep the objects retained during enumeration, and the collection itself
+cannot be synchronously modified. It can be overridden by explicitly
+qualifying the variable with <tt class="docutils literal"><span class="pre">__strong</span></tt>, which will make the variable
+mutable again and cause the loop to retain the objects it encounters.</p>
+</div>
+</div>
+<div class="section" id="blocks">
+<span id="arc-misc-blocks"></span><h3><a class="toc-backref" href="#id50">Blocks</a><a class="headerlink" href="#blocks" title="Permalink to this headline">¶</a></h3>
+<p>The implicit <tt class="docutils literal"><span class="pre">const</span></tt> capture variables created when evaluating a block
+literal expression have the same ownership semantics as the local variables
+they capture. The capture is performed by reading from the captured variable
+and initializing the capture variable with that value; the capture variable is
+destroyed when the block literal is, i.e. at the end of the enclosing scope.</p>
+<p>The <a class="reference internal" href="#arc-ownership-inference"><em>inference</em></a> rules apply equally to
+<tt class="docutils literal"><span class="pre">__block</span></tt> variables, which is a shift in semantics from non-ARC, where
+<tt class="docutils literal"><span class="pre">__block</span></tt> variables did not implicitly retain during capture.</p>
+<p><tt class="docutils literal"><span class="pre">__block</span></tt> variables of retainable object owner type are moved off the stack
+by initializing the heap copy with the result of moving from the stack copy.</p>
+<p>With the exception of retains done as part of initializing a <tt class="docutils literal"><span class="pre">__strong</span></tt>
+parameter variable or reading a <tt class="docutils literal"><span class="pre">__weak</span></tt> variable, whenever these semantics
+call for retaining a value of block-pointer type, it has the effect of a
+<tt class="docutils literal"><span class="pre">Block_copy</span></tt>. The optimizer may remove such copies when it sees that the
+result is used only as an argument to a call.</p>
+</div>
+<div class="section" id="exceptions">
+<span id="arc-misc-exceptions"></span><h3><a class="toc-backref" href="#id51">Exceptions</a><a class="headerlink" href="#exceptions" title="Permalink to this headline">¶</a></h3>
+<p>By default in Objective C, ARC is not exception-safe for normal releases:</p>
+<ul class="simple">
+<li>It does not end the lifetime of <tt class="docutils literal"><span class="pre">__strong</span></tt> variables when their scopes are
+abnormally terminated by an exception.</li>
+<li>It does not perform releases which would occur at the end of a
+full-expression if that full-expression throws an exception.</li>
+</ul>
+<p>A program may be compiled with the option <tt class="docutils literal"><span class="pre">-fobjc-arc-exceptions</span></tt> in order to
+enable these, or with the option <tt class="docutils literal"><span class="pre">-fno-objc-arc-exceptions</span></tt> to explicitly
+disable them, with the last such argument “winning”.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The standard Cocoa convention is that exceptions signal programmer error and
+are not intended to be recovered from. Making code exceptions-safe by
+default would impose severe runtime and code size penalties on code that
+typically does not actually care about exceptions safety. Therefore,
+ARC-generated code leaks by default on exceptions, which is just fine if the
+process is going to be immediately terminated anyway. Programs which do care
+about recovering from exceptions should enable the option.</p>
+</div>
+<p>In Objective-C++, <tt class="docutils literal"><span class="pre">-fobjc-arc-exceptions</span></tt> is enabled by default.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">C++ already introduces pervasive exceptions-cleanup code of the sort that ARC
+introduces. C++ programmers who have not already disabled exceptions are
+much more likely to actual require exception-safety.</p>
+</div>
+<p>ARC does end the lifetimes of <tt class="docutils literal"><span class="pre">__weak</span></tt> objects when an exception terminates
+their scope unless exceptions are disabled in the compiler.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">The consequence of a local <tt class="docutils literal"><span class="pre">__weak</span></tt> object not being destroyed is very
+likely to be corruption of the Objective-C runtime, so we want to be safer
+here. Of course, potentially massive leaks are about as likely to take down
+the process as this corruption is if the program does try to recover from
+exceptions.</p>
+</div>
+</div>
+<div class="section" id="interior-pointers">
+<span id="arc-misc-interior"></span><h3><a class="toc-backref" href="#id52">Interior pointers</a><a class="headerlink" href="#interior-pointers" title="Permalink to this headline">¶</a></h3>
+<p>An Objective-C method returning a non-retainable pointer may be annotated with
+the <tt class="docutils literal"><span class="pre">objc_returns_inner_pointer</span></tt> attribute to indicate that it returns a
+handle to the internal data of an object, and that this reference will be
+invalidated if the object is destroyed. When such a message is sent to an
+object, the object’s lifetime will be extended until at least the earliest of:</p>
+<ul class="simple">
+<li>the last use of the returned pointer, or any pointer derived from it, in the
+calling function or</li>
+<li>the autorelease pool is restored to a previous state.</li>
+</ul>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>Rationale: not all memory and resources are managed with reference counts; it
+is common for objects to manage private resources in their own, private way.
+Typically these resources are completely encapsulated within the object, but
+some classes offer their users direct access for efficiency. If ARC is not
+aware of methods that return such “interior” pointers, its optimizations can
+cause the owning object to be reclaimed too soon. This attribute informs ARC
+that it must tread lightly.</p>
+<p class="last">The extension rules are somewhat intentionally vague. The autorelease pool
+limit is there to permit a simple implementation to simply retain and
+autorelease the receiver. The other limit permits some amount of
+optimization. The phrase “derived from” is intended to encompass the results
+both of pointer transformations, such as casts and arithmetic, and of loading
+from such derived pointers; furthermore, it applies whether or not such
+derivations are applied directly in the calling code or by other utility code
+(for example, the C library routine <tt class="docutils literal"><span class="pre">strchr</span></tt>). However, the implementation
+never need account for uses after a return from the code which calls the
+method returning an interior pointer.</p>
+</div>
+<p>As an exception, no extension is required if the receiver is loaded directly
+from a <tt class="docutils literal"><span class="pre">__strong</span></tt> object with <a class="reference internal" href="#arc-optimization-precise"><em>precise lifetime semantics</em></a>.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Implicit autoreleases carry the risk of significantly inflating memory use,
+so it’s important to provide users a way of avoiding these autoreleases.
+Tying this to precise lifetime semantics is ideal, as for local variables
+this requires a very explicit annotation, which allows ARC to trust the user
+with good cheer.</p>
+</div>
+</div>
+<div class="section" id="c-retainable-pointer-types">
+<span id="arc-misc-c-retainable"></span><h3><a class="toc-backref" href="#id53">C retainable pointer types</a><a class="headerlink" href="#c-retainable-pointer-types" title="Permalink to this headline">¶</a></h3>
+<p>A type is a <span class="arc-term">C retainable pointer type</span> if it is a pointer to
+(possibly qualified) <tt class="docutils literal"><span class="pre">void</span></tt> or a pointer to a (possibly qualifier) <tt class="docutils literal"><span class="pre">struct</span></tt>
+or <tt class="docutils literal"><span class="pre">class</span></tt> type.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">ARC does not manage pointers of CoreFoundation type (or any of the related
+families of retainable C pointers which interoperate with Objective-C for
+retain/release operation). In fact, ARC does not even know how to
+distinguish these types from arbitrary C pointer types. The intent of this
+concept is to filter out some obviously non-object types while leaving a hook
+for later tightening if a means of exhaustively marking CF types is made
+available.</p>
+</div>
+<div class="section" id="auditing-of-c-retainable-pointer-interfaces">
+<span id="arc-misc-c-retainable-audit"></span><h4><a class="toc-backref" href="#id54">Auditing of C retainable pointer interfaces</a><a class="headerlink" href="#auditing-of-c-retainable-pointer-interfaces" title="Permalink to this headline">¶</a></h4>
+<p><span class="when-revised">[beginning Apple 4.0, LLVM 3.1]</span></p>
+<p>A C function may be marked with the <tt class="docutils literal"><span class="pre">cf_audited_transfer</span></tt> attribute to
+express that, except as otherwise marked with attributes, it obeys the
+parameter (consuming vs. non-consuming) and return (retained vs. non-retained)
+conventions for a C function of its name, namely:</p>
+<ul class="simple">
+<li>A parameter of C retainable pointer type is assumed to not be consumed
+unless it is marked with the <tt class="docutils literal"><span class="pre">cf_consumed</span></tt> attribute, and</li>
+<li>A result of C retainable pointer type is assumed to not be returned retained
+unless the function is either marked <tt class="docutils literal"><span class="pre">cf_returns_retained</span></tt> or it follows
+the create/copy naming convention and is not marked
+<tt class="docutils literal"><span class="pre">cf_returns_not_retained</span></tt>.</li>
+</ul>
+<p>A function obeys the <span class="arc-term">create/copy</span> naming convention if its name
+contains as a substring:</p>
+<ul class="simple">
+<li>either “Create” or “Copy” not followed by a lowercase letter, or</li>
+<li>either “create” or “copy” not followed by a lowercase letter and
+not preceded by any letter, whether uppercase or lowercase.</li>
+</ul>
+<p>A second attribute, <tt class="docutils literal"><span class="pre">cf_unknown_transfer</span></tt>, signifies that a function’s
+transfer semantics cannot be accurately captured using any of these
+annotations. A program is ill-formed if it annotates the same function with
+both <tt class="docutils literal"><span class="pre">cf_audited_transfer</span></tt> and <tt class="docutils literal"><span class="pre">cf_unknown_transfer</span></tt>.</p>
+<p>A pragma is provided to facilitate the mass annotation of interfaces:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="cp">#pragma clang arc_cf_code_audited begin</span>
+<span class="p">...</span>
+<span class="cp">#pragma clang arc_cf_code_audited end</span>
+</pre></div>
+</div>
+<p>All C functions declared within the extent of this pragma are treated as if
+annotated with the <tt class="docutils literal"><span class="pre">cf_audited_transfer</span></tt> attribute unless they otherwise have
+the <tt class="docutils literal"><span class="pre">cf_unknown_transfer</span></tt> attribute. The pragma is accepted in all language
+modes. A program is ill-formed if it attempts to change files, whether by
+including a file or ending the current file, within the extent of this pragma.</p>
+<p>It is possible to test for all the features in this section with
+<tt class="docutils literal"><span class="pre">__has_feature(arc_cf_code_audited)</span></tt>.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">A significant inconvenience in ARC programming is the necessity of
+interacting with APIs based around C retainable pointers. These features are
+designed to make it relatively easy for API authors to quickly review and
+annotate their interfaces, in turn improving the fidelity of tools such as
+the static analyzer and ARC. The single-file restriction on the pragma is
+designed to eliminate the risk of accidentally annotating some other header’s
+interfaces.</p>
+</div>
+</div>
+</div>
+</div>
+<div class="section" id="runtime-support">
+<span id="arc-runtime"></span><h2><a class="toc-backref" href="#id55">Runtime support</a><a class="headerlink" href="#runtime-support" title="Permalink to this headline">¶</a></h2>
+<p>This section describes the interaction between the ARC runtime and the code
+generated by the ARC compiler. This is not part of the ARC language
+specification; instead, it is effectively a language-specific ABI supplement,
+akin to the “Itanium” generic ABI for C++.</p>
+<p>Ownership qualification does not alter the storage requirements for objects,
+except that it is undefined behavior if a <tt class="docutils literal"><span class="pre">__weak</span></tt> object is inadequately
+aligned for an object of type <tt class="docutils literal"><span class="pre">id</span></tt>. The other qualifiers may be used on
+explicitly under-aligned memory.</p>
+<p>The runtime tracks <tt class="docutils literal"><span class="pre">__weak</span></tt> objects which holds non-null values. It is
+undefined behavior to direct modify a <tt class="docutils literal"><span class="pre">__weak</span></tt> object which is being tracked
+by the runtime except through an
+<a class="reference internal" href="#arc-runtime-objc-storeweak"><em>objc_storeWeak</em></a>,
+<a class="reference internal" href="#arc-runtime-objc-destroyweak"><em>objc_destroyWeak</em></a>, or
+<a class="reference internal" href="#arc-runtime-objc-moveweak"><em>objc_moveWeak</em></a> call.</p>
+<p>The runtime must provide a number of new entrypoints which the compiler may
+emit, which are described in the remainder of this section.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p>Several of these functions are semantically equivalent to a message send; we
+emit calls to C functions instead because:</p>
+<ul class="simple">
+<li>the machine code to do so is significantly smaller,</li>
+<li>it is much easier to recognize the C functions in the ARC optimizer, and</li>
+<li>a sufficient sophisticated runtime may be able to avoid the message send in
+common cases.</li>
+</ul>
+<p class="last">Several other of these functions are “fused” operations which can be
+described entirely in terms of other operations. We use the fused operations
+primarily as a code-size optimization, although in some cases there is also a
+real potential for avoiding redundant operations in the runtime.</p>
+</div>
+<div class="section" id="arc-runtime-objc-autorelease">
+<span id="id-objc-autorelease-id-value"></span><h3><a class="toc-backref" href="#id56"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_autorelease(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-autorelease" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it adds the object
+to the innermost autorelease pool exactly as if the object had been sent the
+<tt class="docutils literal"><span class="pre">autorelease</span></tt> message.</p>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+</div>
+<div class="section" id="void-objc-autoreleasepoolpop-void-pool">
+<span id="arc-runtime-objc-autoreleasepoolpop"></span><h3><a class="toc-backref" href="#id57"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_autoreleasePoolPop(void</span> <span class="pre">*pool);</span></tt></a><a class="headerlink" href="#void-objc-autoreleasepoolpop-void-pool" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">pool</span></tt> is the result of a previous call to
+<a class="reference internal" href="#arc-runtime-objc-autoreleasepoolpush"><em>objc_autoreleasePoolPush</em></a> on the
+current thread, where neither <tt class="docutils literal"><span class="pre">pool</span></tt> nor any enclosing pool have previously
+been popped.</p>
+<p>Releases all the objects added to the given autorelease pool and any
+autorelease pools it encloses, then sets the current autorelease pool to the
+pool directly enclosing <tt class="docutils literal"><span class="pre">pool</span></tt>.</p>
+</div>
+<div class="section" id="void-objc-autoreleasepoolpush-void">
+<span id="arc-runtime-objc-autoreleasepoolpush"></span><h3><a class="toc-backref" href="#id58"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">*objc_autoreleasePoolPush(void);</span></tt></a><a class="headerlink" href="#void-objc-autoreleasepoolpush-void" title="Permalink to this headline">¶</a></h3>
+<p>Creates a new autorelease pool that is enclosed by the current pool, makes that
+the current pool, and returns an opaque “handle” to it.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">While the interface is described as an explicit hierarchy of pools, the rules
+allow the implementation to just keep a stack of objects, using the stack
+depth as the opaque pool handle.</p>
+</div>
+</div>
+<div class="section" id="arc-runtime-objc-autoreleasereturnvalue">
+<span id="id-objc-autoreleasereturnvalue-id-value"></span><h3><a class="toc-backref" href="#id59"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_autoreleaseReturnValue(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-autoreleasereturnvalue" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it makes a best
+effort to hand off ownership of a retain count on the object to a call to
+<a class="reference internal" href="#arc-runtime-objc-retainautoreleasedreturnvalue"><em>objc_retainAutoreleasedReturnValue</em></a> for the same object in an
+enclosing call frame. If this is not possible, the object is autoreleased as
+above.</p>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+</div>
+<div class="section" id="void-objc-copyweak-id-dest-id-src">
+<span id="arc-runtime-objc-copyweak"></span><h3><a class="toc-backref" href="#id60"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_copyWeak(id</span> <span class="pre">*dest,</span> <span class="pre">id</span> <span class="pre">*src);</span></tt></a><a class="headerlink" href="#void-objc-copyweak-id-dest-id-src" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">src</span></tt> is a valid pointer which either contains a null pointer
+or has been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object. <tt class="docutils literal"><span class="pre">dest</span></tt> is a valid pointer
+which has not been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object.</p>
+<p><tt class="docutils literal"><span class="pre">dest</span></tt> is initialized to be equivalent to <tt class="docutils literal"><span class="pre">src</span></tt>, potentially registering it
+with the runtime. Equivalent to the following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">objc_copyWeak</span><span class="p">(</span><span class="kt">id</span> <span class="o">*</span><span class="n">dest</span><span class="p">,</span> <span class="kt">id</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">objc_release</span><span class="p">(</span><span class="n">objc_initWeak</span><span class="p">(</span><span class="n">dest</span><span class="p">,</span> <span class="n">objc_loadWeakRetained</span><span class="p">(</span><span class="n">src</span><span class="p">)));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Must be atomic with respect to calls to <tt class="docutils literal"><span class="pre">objc_storeWeak</span></tt> on <tt class="docutils literal"><span class="pre">src</span></tt>.</p>
+</div>
+<div class="section" id="void-objc-destroyweak-id-object">
+<span id="arc-runtime-objc-destroyweak"></span><h3><a class="toc-backref" href="#id61"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_destroyWeak(id</span> <span class="pre">*object);</span></tt></a><a class="headerlink" href="#void-objc-destroyweak-id-object" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">object</span></tt> is a valid pointer which either contains a null
+pointer or has been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object.</p>
+<p><tt class="docutils literal"><span class="pre">object</span></tt> is unregistered as a weak object, if it ever was. The current value
+of <tt class="docutils literal"><span class="pre">object</span></tt> is left unspecified; otherwise, equivalent to the following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">objc_destroyWeak</span><span class="p">(</span><span class="kt">id</span> <span class="o">*</span><span class="n">object</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">objc_storeWeak</span><span class="p">(</span><span class="n">object</span><span class="p">,</span> <span class="nb">nil</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Does not need to be atomic with respect to calls to <tt class="docutils literal"><span class="pre">objc_storeWeak</span></tt> on
+<tt class="docutils literal"><span class="pre">object</span></tt>.</p>
+</div>
+<div class="section" id="arc-runtime-objc-initweak">
+<span id="id-objc-initweak-id-object-id-value"></span><h3><a class="toc-backref" href="#id62"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_initWeak(id</span> <span class="pre">*object,</span> <span class="pre">id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-initweak" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">object</span></tt> is a valid pointer which has not been registered as
+a <tt class="docutils literal"><span class="pre">__weak</span></tt> object. <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is a null pointer or the object to which it points has begun
+deallocation, <tt class="docutils literal"><span class="pre">object</span></tt> is zero-initialized. Otherwise, <tt class="docutils literal"><span class="pre">object</span></tt> is
+registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object pointing to <tt class="docutils literal"><span class="pre">value</span></tt>. Equivalent to the
+following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="nf">objc_initWeak</span><span class="p">(</span><span class="kt">id</span> <span class="o">*</span><span class="n">object</span><span class="p">,</span> <span class="kt">id</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
+ <span class="o">*</span><span class="n">object</span> <span class="o">=</span> <span class="nb">nil</span><span class="p">;</span>
+ <span class="k">return</span> <span class="n">objc_storeWeak</span><span class="p">(</span><span class="n">object</span><span class="p">,</span> <span class="n">value</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Returns the value of <tt class="docutils literal"><span class="pre">object</span></tt> after the call.</p>
+<p>Does not need to be atomic with respect to calls to <tt class="docutils literal"><span class="pre">objc_storeWeak</span></tt> on
+<tt class="docutils literal"><span class="pre">object</span></tt>.</p>
+</div>
+<div class="section" id="arc-runtime-objc-loadweak">
+<span id="id-objc-loadweak-id-object"></span><h3><a class="toc-backref" href="#id63"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_loadWeak(id</span> <span class="pre">*object);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-loadweak" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">object</span></tt> is a valid pointer which either contains a null
+pointer or has been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object.</p>
+<p>If <tt class="docutils literal"><span class="pre">object</span></tt> is registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object, and the last value stored
+into <tt class="docutils literal"><span class="pre">object</span></tt> has not yet been deallocated or begun deallocation, retains and
+autoreleases that value and returns it. Otherwise returns null. Equivalent to
+the following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="nf">objc_loadWeak</span><span class="p">(</span><span class="kt">id</span> <span class="o">*</span><span class="n">object</span><span class="p">)</span> <span class="p">{</span>
+ <span class="k">return</span> <span class="n">objc_autorelease</span><span class="p">(</span><span class="n">objc_loadWeakRetained</span><span class="p">(</span><span class="n">object</span><span class="p">));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Must be atomic with respect to calls to <tt class="docutils literal"><span class="pre">objc_storeWeak</span></tt> on <tt class="docutils literal"><span class="pre">object</span></tt>.</p>
+<div class="admonition-rationale admonition">
+<p class="first admonition-title">Rationale</p>
+<p class="last">Loading weak references would be inherently prone to race conditions without
+the retain.</p>
+</div>
+</div>
+<div class="section" id="arc-runtime-objc-loadweakretained">
+<span id="id-objc-loadweakretained-id-object"></span><h3><a class="toc-backref" href="#id64"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_loadWeakRetained(id</span> <span class="pre">*object);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-loadweakretained" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">object</span></tt> is a valid pointer which either contains a null
+pointer or has been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object.</p>
+<p>If <tt class="docutils literal"><span class="pre">object</span></tt> is registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object, and the last value stored
+into <tt class="docutils literal"><span class="pre">object</span></tt> has not yet been deallocated or begun deallocation, retains
+that value and returns it. Otherwise returns null.</p>
+<p>Must be atomic with respect to calls to <tt class="docutils literal"><span class="pre">objc_storeWeak</span></tt> on <tt class="docutils literal"><span class="pre">object</span></tt>.</p>
+</div>
+<div class="section" id="void-objc-moveweak-id-dest-id-src">
+<span id="arc-runtime-objc-moveweak"></span><h3><a class="toc-backref" href="#id65"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_moveWeak(id</span> <span class="pre">*dest,</span> <span class="pre">id</span> <span class="pre">*src);</span></tt></a><a class="headerlink" href="#void-objc-moveweak-id-dest-id-src" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">src</span></tt> is a valid pointer which either contains a null pointer
+or has been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object. <tt class="docutils literal"><span class="pre">dest</span></tt> is a valid pointer
+which has not been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object.</p>
+<p><tt class="docutils literal"><span class="pre">dest</span></tt> is initialized to be equivalent to <tt class="docutils literal"><span class="pre">src</span></tt>, potentially registering it
+with the runtime. <tt class="docutils literal"><span class="pre">src</span></tt> may then be left in its original state, in which
+case this call is equivalent to <a class="reference internal" href="#arc-runtime-objc-copyweak"><em>objc_copyWeak</em></a>, or it may be left as null.</p>
+<p>Must be atomic with respect to calls to <tt class="docutils literal"><span class="pre">objc_storeWeak</span></tt> on <tt class="docutils literal"><span class="pre">src</span></tt>.</p>
+</div>
+<div class="section" id="void-objc-release-id-value">
+<span id="arc-runtime-objc-release"></span><h3><a class="toc-backref" href="#id66"><tt class="docutils literal"><span class="pre">void</span> <span class="pre">objc_release(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#void-objc-release-id-value" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it performs a
+release operation exactly as if the object had been sent the <tt class="docutils literal"><span class="pre">release</span></tt>
+message.</p>
+</div>
+<div class="section" id="arc-runtime-objc-retain">
+<span id="id-objc-retain-id-value"></span><h3><a class="toc-backref" href="#id67"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retain(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-retain" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it performs a retain
+operation exactly as if the object had been sent the <tt class="docutils literal"><span class="pre">retain</span></tt> message.</p>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+</div>
+<div class="section" id="arc-runtime-objc-retainautorelease">
+<span id="id-objc-retainautorelease-id-value"></span><h3><a class="toc-backref" href="#id68"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainAutorelease(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-retainautorelease" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it performs a retain
+operation followed by an autorelease operation. Equivalent to the following
+code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="nf">objc_retainAutorelease</span><span class="p">(</span><span class="kt">id</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
+ <span class="k">return</span> <span class="n">objc_autorelease</span><span class="p">(</span><span class="n">objc_retain</span><span class="p">(</span><span class="n">value</span><span class="p">));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+</div>
+<div class="section" id="arc-runtime-objc-retainautoreleasereturnvalue">
+<span id="id-objc-retainautoreleasereturnvalue-id-value"></span><h3><a class="toc-backref" href="#id69"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainAutoreleaseReturnValue(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-retainautoreleasereturnvalue" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it performs a retain
+operation followed by the operation described in
+<a class="reference internal" href="#arc-runtime-objc-autoreleasereturnvalue"><em>objc_autoreleaseReturnValue</em></a>.
+Equivalent to the following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="nf">objc_retainAutoreleaseReturnValue</span><span class="p">(</span><span class="kt">id</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
+ <span class="k">return</span> <span class="n">objc_autoreleaseReturnValue</span><span class="p">(</span><span class="n">objc_retain</span><span class="p">(</span><span class="n">value</span><span class="p">));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+</div>
+<div class="section" id="arc-runtime-objc-retainautoreleasedreturnvalue">
+<span id="id-objc-retainautoreleasedreturnvalue-id-value"></span><h3><a class="toc-backref" href="#id70"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainAutoreleasedReturnValue(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-retainautoreleasedreturnvalue" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, it attempts to
+accept a hand off of a retain count from a call to
+<a class="reference internal" href="#arc-runtime-objc-autoreleasereturnvalue"><em>objc_autoreleaseReturnValue</em></a> on
+<tt class="docutils literal"><span class="pre">value</span></tt> in a recently-called function or something it calls. If that fails,
+it performs a retain operation exactly like <a class="reference internal" href="#arc-runtime-objc-retain"><em>objc_retain</em></a>.</p>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+</div>
+<div class="section" id="arc-runtime-objc-retainblock">
+<span id="id-objc-retainblock-id-value"></span><h3><a class="toc-backref" href="#id71"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_retainBlock(id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-retainblock" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid block object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is null, this call has no effect. Otherwise, if the block pointed
+to by <tt class="docutils literal"><span class="pre">value</span></tt> is still on the stack, it is copied to the heap and the address
+of the copy is returned. Otherwise a retain operation is performed on the
+block exactly as if it had been sent the <tt class="docutils literal"><span class="pre">retain</span></tt> message.</p>
+</div>
+<div class="section" id="arc-runtime-objc-storestrong">
+<span id="id-objc-storestrong-id-object-id-value"></span><h3><a class="toc-backref" href="#id72"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_storeStrong(id</span> <span class="pre">*object,</span> <span class="pre">id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-storestrong" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">object</span></tt> is a valid pointer to a <tt class="docutils literal"><span class="pre">__strong</span></tt> object which is
+adequately aligned for a pointer. <tt class="docutils literal"><span class="pre">value</span></tt> is null or a pointer to a valid
+object.</p>
+<p>Performs the complete sequence for assigning to a <tt class="docutils literal"><span class="pre">__strong</span></tt> object of
+non-block type <a class="footnote-reference" href="#id3" id="id2">[*]</a>. Equivalent to the following code:</p>
+<div class="highlight-objc"><div class="highlight"><pre><span class="kt">id</span> <span class="nf">objc_storeStrong</span><span class="p">(</span><span class="kt">id</span> <span class="o">*</span><span class="n">object</span><span class="p">,</span> <span class="kt">id</span> <span class="n">value</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">value</span> <span class="o">=</span> <span class="p">[</span><span class="n">value</span> <span class="n">retain</span><span class="p">];</span>
+ <span class="kt">id</span> <span class="n">oldValue</span> <span class="o">=</span> <span class="o">*</span><span class="n">object</span><span class="p">;</span>
+ <span class="o">*</span><span class="n">object</span> <span class="o">=</span> <span class="n">value</span><span class="p">;</span>
+ <span class="p">[</span><span class="n">oldValue</span> <span class="n">release</span><span class="p">];</span>
+ <span class="k">return</span> <span class="n">value</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Always returns <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+<table class="docutils footnote" frame="void" id="id3" rules="none">
+<colgroup><col class="label" /><col /></colgroup>
+<tbody valign="top">
+<tr><td class="label"><a class="fn-backref" href="#id2">[*]</a></td><td>This does not imply that a <tt class="docutils literal"><span class="pre">__strong</span></tt> object of block type is an
+invalid argument to this function. Rather it implies that an <tt class="docutils literal"><span class="pre">objc_retain</span></tt>
+and not an <tt class="docutils literal"><span class="pre">objc_retainBlock</span></tt> operation will be emitted if the argument is
+a block.</td></tr>
+</tbody>
+</table>
+</div>
+<div class="section" id="arc-runtime-objc-storeweak">
+<span id="id-objc-storeweak-id-object-id-value"></span><h3><a class="toc-backref" href="#id73"><tt class="docutils literal"><span class="pre">id</span> <span class="pre">objc_storeWeak(id</span> <span class="pre">*object,</span> <span class="pre">id</span> <span class="pre">value);</span></tt></a><a class="headerlink" href="#arc-runtime-objc-storeweak" title="Permalink to this headline">¶</a></h3>
+<p><em>Precondition:</em> <tt class="docutils literal"><span class="pre">object</span></tt> is a valid pointer which either contains a null
+pointer or has been registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object. <tt class="docutils literal"><span class="pre">value</span></tt> is null or a
+pointer to a valid object.</p>
+<p>If <tt class="docutils literal"><span class="pre">value</span></tt> is a null pointer or the object to which it points has begun
+deallocation, <tt class="docutils literal"><span class="pre">object</span></tt> is assigned null and unregistered as a <tt class="docutils literal"><span class="pre">__weak</span></tt>
+object. Otherwise, <tt class="docutils literal"><span class="pre">object</span></tt> is registered as a <tt class="docutils literal"><span class="pre">__weak</span></tt> object or has its
+registration updated to point to <tt class="docutils literal"><span class="pre">value</span></tt>.</p>
+<p>Returns the value of <tt class="docutils literal"><span class="pre">object</span></tt> after the call.</p>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="Block-ABI-Apple.html">Block Implementation Specification</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="AttributeReference.html">Attributes in Clang</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
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+</html>
\ No newline at end of file
Added: www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.html
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.html?rev=238136&view=auto
==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.html Mon May 25 08:58:01 2015
@@ -0,0 +1,913 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>Block Implementation Specification — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
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+ };
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+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="up" title="Clang Language Extensions" href="LanguageExtensions.html" />
+ <link rel="next" title="Objective-C Automatic Reference Counting (ARC)" href="AutomaticReferenceCounting.html" />
+ <link rel="prev" title="Language Specification for Blocks" href="BlockLanguageSpec.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Block Implementation Specification</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="BlockLanguageSpec.html">Language Specification for Blocks</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="AutomaticReferenceCounting.html">Objective-C Automatic Reference Counting (ARC)</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="block-implementation-specification">
+<h1>Block Implementation Specification<a class="headerlink" href="#block-implementation-specification" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#history" id="id1">History</a></li>
+<li><a class="reference internal" href="#high-level" id="id2">High Level</a></li>
+<li><a class="reference internal" href="#imported-variables" id="id3">Imported Variables</a><ul>
+<li><a class="reference internal" href="#imported-const-copy-variables" id="id4">Imported <tt class="docutils literal"><span class="pre">const</span></tt> copy variables</a></li>
+<li><a class="reference internal" href="#imported-const-copy-of-block-reference" id="id5">Imported <tt class="docutils literal"><span class="pre">const</span></tt> copy of <tt class="docutils literal"><span class="pre">Block</span></tt> reference</a><ul>
+<li><a class="reference internal" href="#importing-attribute-nsobject-variables" id="id6">Importing <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> variables</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#imported-block-marked-variables" id="id7">Imported <tt class="docutils literal"><span class="pre">__block</span></tt> marked variables</a><ul>
+<li><a class="reference internal" href="#layout-of-block-marked-variables" id="id8">Layout of <tt class="docutils literal"><span class="pre">__block</span></tt> marked variables</a></li>
+<li><a class="reference internal" href="#access-to-block-variables-from-within-its-lexical-scope" id="id9">Access to <tt class="docutils literal"><span class="pre">__block</span></tt> variables from within its lexical scope</a></li>
+<li><a class="reference internal" href="#importing-block-variables-into-blocks" id="id10">Importing <tt class="docutils literal"><span class="pre">__block</span></tt> variables into <tt class="docutils literal"><span class="pre">Blocks</span></tt></a></li>
+<li><a class="reference internal" href="#importing-attribute-nsobject-block-variables" id="id11">Importing <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> <tt class="docutils literal"><span class="pre">__block</span></tt> variables</a></li>
+<li><a class="reference internal" href="#block-escapes" id="id12"><tt class="docutils literal"><span class="pre">__block</span></tt> escapes</a></li>
+<li><a class="reference internal" href="#nesting" id="id13">Nesting</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#objective-c-extensions-to-blocks" id="id14">Objective C Extensions to <tt class="docutils literal"><span class="pre">Blocks</span></tt></a><ul>
+<li><a class="reference internal" href="#importing-objects" id="id15">Importing Objects</a></li>
+<li><a class="reference internal" href="#blocks-as-objects" id="id16"><tt class="docutils literal"><span class="pre">Blocks</span></tt> as Objects</a></li>
+<li><a class="reference internal" href="#weak-block-support" id="id17"><tt class="docutils literal"><span class="pre">__weak</span> <span class="pre">__block</span></tt> Support</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#c-support" id="id18">C++ Support</a></li>
+<li><a class="reference internal" href="#runtime-helper-functions" id="id19">Runtime Helper Functions</a></li>
+<li><a class="reference internal" href="#copyright" id="id20">Copyright</a></li>
+</ul>
+</div>
+<div class="section" id="history">
+<h2><a class="toc-backref" href="#id1">History</a><a class="headerlink" href="#history" title="Permalink to this headline">¶</a></h2>
+<ul class="simple">
+<li>2008/7/14 - created.</li>
+<li>2008/8/21 - revised, C++.</li>
+<li>2008/9/24 - add <tt class="docutils literal"><span class="pre">NULL</span></tt> <tt class="docutils literal"><span class="pre">isa</span></tt> field to <tt class="docutils literal"><span class="pre">__block</span></tt> storage.</li>
+<li>2008/10/1 - revise block layout to use a <tt class="docutils literal"><span class="pre">static</span></tt> descriptor structure.</li>
+<li>2008/10/6 - revise block layout to use an unsigned long int flags.</li>
+<li>2008/10/28 - specify use of <tt class="docutils literal"><span class="pre">_Block_object_assign</span></tt> and
+<tt class="docutils literal"><span class="pre">_Block_object_dispose</span></tt> for all “Object” types in helper functions.</li>
+<li>2008/10/30 - revise new layout to have invoke function in same place.</li>
+<li>2008/10/30 - add <tt class="docutils literal"><span class="pre">__weak</span></tt> support.</li>
+<li>2010/3/16 - rev for stret return, signature field.</li>
+<li>2010/4/6 - improved wording.</li>
+<li>2013/1/6 - improved wording and converted to rst.</li>
+</ul>
+<p>This document describes the Apple ABI implementation specification of Blocks.</p>
+<p>The first shipping version of this ABI is found in Mac OS X 10.6, and shall be
+referred to as 10.6.ABI. As of 2010/3/16, the following describes the ABI
+contract with the runtime and the compiler, and, as necessary, will be referred
+to as ABI.2010.3.16.</p>
+<p>Since the Apple ABI references symbols from other elements of the system, any
+attempt to use this ABI on systems prior to SnowLeopard is undefined.</p>
+</div>
+<div class="section" id="high-level">
+<h2><a class="toc-backref" href="#id2">High Level</a><a class="headerlink" href="#high-level" title="Permalink to this headline">¶</a></h2>
+<p>The ABI of <tt class="docutils literal"><span class="pre">Blocks</span></tt> consist of their layout and the runtime functions required
+by the compiler. A <tt class="docutils literal"><span class="pre">Block</span></tt> consists of a structure of the following form:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">Block_literal_1</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span> <span class="c1">// initialized to &_NSConcreteStackBlock or &_NSConcreteGlobalBlock</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="kt">void</span> <span class="o">*</span><span class="p">,</span> <span class="p">...);</span>
+ <span class="k">struct</span> <span class="n">Block_descriptor_1</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span> <span class="c1">// NULL</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">size</span><span class="p">;</span> <span class="c1">// sizeof(struct Block_literal_1)</span>
+ <span class="c1">// optional helper functions</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">copy_helper</span><span class="p">)(</span><span class="kt">void</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span> <span class="c1">// IFF (1<<25)</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">dispose_helper</span><span class="p">)(</span><span class="kt">void</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span> <span class="c1">// IFF (1<<25)</span>
+ <span class="c1">// required ABI.2010.3.16</span>
+ <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">signature</span><span class="p">;</span> <span class="c1">// IFF (1<<30)</span>
+ <span class="p">}</span> <span class="o">*</span><span class="n">descriptor</span><span class="p">;</span>
+ <span class="c1">// imported variables</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>The following flags bits are in use thusly for a possible ABI.2010.3.16:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">enum</span> <span class="p">{</span>
+ <span class="n">BLOCK_HAS_COPY_DISPOSE</span> <span class="o">=</span> <span class="p">(</span><span class="mi">1</span> <span class="o"><<</span> <span class="mi">25</span><span class="p">),</span>
+ <span class="n">BLOCK_HAS_CTOR</span> <span class="o">=</span> <span class="p">(</span><span class="mi">1</span> <span class="o"><<</span> <span class="mi">26</span><span class="p">),</span> <span class="c1">// helpers have C++ code</span>
+ <span class="n">BLOCK_IS_GLOBAL</span> <span class="o">=</span> <span class="p">(</span><span class="mi">1</span> <span class="o"><<</span> <span class="mi">28</span><span class="p">),</span>
+ <span class="n">BLOCK_HAS_STRET</span> <span class="o">=</span> <span class="p">(</span><span class="mi">1</span> <span class="o"><<</span> <span class="mi">29</span><span class="p">),</span> <span class="c1">// IFF BLOCK_HAS_SIGNATURE</span>
+ <span class="n">BLOCK_HAS_SIGNATURE</span> <span class="o">=</span> <span class="p">(</span><span class="mi">1</span> <span class="o"><<</span> <span class="mi">30</span><span class="p">),</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>In 10.6.ABI the (1<<29) was usually set and was always ignored by the runtime -
+it had been a transitional marker that did not get deleted after the
+transition. This bit is now paired with (1<<30), and represented as the pair
+(3<<30), for the following combinations of valid bit settings, and their
+meanings:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">switch</span> <span class="p">(</span><span class="n">flags</span> <span class="o">&</span> <span class="p">(</span><span class="mi">3</span><span class="o"><<</span><span class="mi">29</span><span class="p">))</span> <span class="p">{</span>
+ <span class="k">case</span> <span class="p">(</span><span class="mi">0</span><span class="o"><<</span><span class="mi">29</span><span class="p">)</span>: <span class="mf">10.6</span><span class="p">.</span><span class="n">ABI</span><span class="p">,</span> <span class="n">no</span> <span class="n">signature</span> <span class="n">field</span> <span class="n">available</span>
+ <span class="k">case</span> <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">)</span>: <span class="mf">10.6</span><span class="p">.</span><span class="n">ABI</span><span class="p">,</span> <span class="n">no</span> <span class="n">signature</span> <span class="n">field</span> <span class="n">available</span>
+ <span class="k">case</span> <span class="p">(</span><span class="mi">2</span><span class="o"><<</span><span class="mi">29</span><span class="p">)</span>: <span class="n">ABI</span><span class="mf">.2010.3.16</span><span class="p">,</span> <span class="n">regular</span> <span class="n">calling</span> <span class="n">convention</span><span class="p">,</span> <span class="n">presence</span> <span class="n">of</span> <span class="n">signature</span> <span class="n">field</span>
+ <span class="k">case</span> <span class="p">(</span><span class="mi">3</span><span class="o"><<</span><span class="mi">29</span><span class="p">)</span>: <span class="n">ABI</span><span class="mf">.2010.3.16</span><span class="p">,</span> <span class="n">stret</span> <span class="n">calling</span> <span class="n">convention</span><span class="p">,</span> <span class="n">presence</span> <span class="n">of</span> <span class="n">signature</span> <span class="n">field</span><span class="p">,</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The signature field is not always populated.</p>
+<p>The following discussions are presented as 10.6.ABI otherwise.</p>
+<p><tt class="docutils literal"><span class="pre">Block</span></tt> literals may occur within functions where the structure is created in
+stack local memory. They may also appear as initialization expressions for
+<tt class="docutils literal"><span class="pre">Block</span></tt> variables of global or <tt class="docutils literal"><span class="pre">static</span></tt> local variables.</p>
+<p>When a <tt class="docutils literal"><span class="pre">Block</span></tt> literal expression is evaluated the stack based structure is
+initialized as follows:</p>
+<ol class="arabic simple">
+<li>A <tt class="docutils literal"><span class="pre">static</span></tt> descriptor structure is declared and initialized as follows:</li>
+</ol>
+<blockquote>
+<div><p>a. The <tt class="docutils literal"><span class="pre">invoke</span></tt> function pointer is set to a function that takes the
+<tt class="docutils literal"><span class="pre">Block</span></tt> structure as its first argument and the rest of the arguments (if
+any) to the <tt class="docutils literal"><span class="pre">Block</span></tt> and executes the <tt class="docutils literal"><span class="pre">Block</span></tt> compound statement.</p>
+<p>b. The <tt class="docutils literal"><span class="pre">size</span></tt> field is set to the size of the following <tt class="docutils literal"><span class="pre">Block</span></tt> literal
+structure.</p>
+<p>c. The <tt class="docutils literal"><span class="pre">copy_helper</span></tt> and <tt class="docutils literal"><span class="pre">dispose_helper</span></tt> function pointers are set to
+respective helper functions if they are required by the <tt class="docutils literal"><span class="pre">Block</span></tt> literal.</p>
+</div></blockquote>
+<ol class="arabic" start="2">
+<li><p class="first">A stack (or global) <tt class="docutils literal"><span class="pre">Block</span></tt> literal data structure is created and
+initialized as follows:</p>
+<p>a. The <tt class="docutils literal"><span class="pre">isa</span></tt> field is set to the address of the external
+<tt class="docutils literal"><span class="pre">_NSConcreteStackBlock</span></tt>, which is a block of uninitialized memory supplied
+in <tt class="docutils literal"><span class="pre">libSystem</span></tt>, or <tt class="docutils literal"><span class="pre">_NSConcreteGlobalBlock</span></tt> if this is a static or file
+level <tt class="docutils literal"><span class="pre">Block</span></tt> literal.</p>
+<p>b. The <tt class="docutils literal"><span class="pre">flags</span></tt> field is set to zero unless there are variables imported
+into the <tt class="docutils literal"><span class="pre">Block</span></tt> that need helper functions for program level
+<tt class="docutils literal"><span class="pre">Block_copy()</span></tt> and <tt class="docutils literal"><span class="pre">Block_release()</span></tt> operations, in which case the
+(1<<25) flags bit is set.</p>
+</li>
+</ol>
+<p>As an example, the <tt class="docutils literal"><span class="pre">Block</span></tt> literal expression:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="o">^</span> <span class="p">{</span> <span class="n">printf</span><span class="p">(</span><span class="s">"hello world</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>would cause the following to be created on a 32-bit system:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_1</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_1</span> <span class="o">*</span><span class="p">);</span>
+ <span class="k">struct</span> <span class="n">__block_descriptor_1</span> <span class="o">*</span><span class="n">descriptor</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">__block_invoke_1</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_1</span> <span class="o">*</span><span class="n">_block</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">printf</span><span class="p">(</span><span class="s">"hello world</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="k">struct</span> <span class="n">__block_descriptor_1</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">Block_size</span><span class="p">;</span>
+<span class="p">}</span> <span class="n">__block_descriptor_1</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_1</span><span class="p">),</span> <span class="n">__block_invoke_1</span> <span class="p">};</span>
+</pre></div>
+</div>
+<p>and where the <tt class="docutils literal"><span class="pre">Block</span></tt> literal itself appears:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_1</span> <span class="n">_block_literal</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteStackBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span><span class="p">,</span>
+ <span class="n">__block_invoke_1</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">__block_descriptor_1</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>A <tt class="docutils literal"><span class="pre">Block</span></tt> imports other <tt class="docutils literal"><span class="pre">Block</span></tt> references, <tt class="docutils literal"><span class="pre">const</span></tt> copies of other
+variables, and variables marked <tt class="docutils literal"><span class="pre">__block</span></tt>. In Objective-C, variables may
+additionally be objects.</p>
+<p>When a <tt class="docutils literal"><span class="pre">Block</span></tt> literal expression is used as the initial value of a global
+or <tt class="docutils literal"><span class="pre">static</span></tt> local variable, it is initialized as follows:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_1</span> <span class="n">__block_literal_1</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteGlobalBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">28</span><span class="p">)</span><span class="o">|</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span><span class="p">,</span>
+ <span class="n">__block_invoke_1</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">__block_descriptor_1</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>that is, a different address is provided as the first value and a particular
+(1<<28) bit is set in the <tt class="docutils literal"><span class="pre">flags</span></tt> field, and otherwise it is the same as for
+stack based <tt class="docutils literal"><span class="pre">Block</span></tt> literals. This is an optimization that can be used for
+any <tt class="docutils literal"><span class="pre">Block</span></tt> literal that imports no <tt class="docutils literal"><span class="pre">const</span></tt> or <tt class="docutils literal"><span class="pre">__block</span></tt> storage
+variables.</p>
+</div>
+<div class="section" id="imported-variables">
+<h2><a class="toc-backref" href="#id3">Imported Variables</a><a class="headerlink" href="#imported-variables" title="Permalink to this headline">¶</a></h2>
+<p>Variables of <tt class="docutils literal"><span class="pre">auto</span></tt> storage class are imported as <tt class="docutils literal"><span class="pre">const</span></tt> copies. Variables
+of <tt class="docutils literal"><span class="pre">__block</span></tt> storage class are imported as a pointer to an enclosing data
+structure. Global variables are simply referenced and not considered as
+imported.</p>
+<div class="section" id="imported-const-copy-variables">
+<h3><a class="toc-backref" href="#id4">Imported <tt class="docutils literal"><span class="pre">const</span></tt> copy variables</a><a class="headerlink" href="#imported-const-copy-variables" title="Permalink to this headline">¶</a></h3>
+<p>Automatic storage variables not marked with <tt class="docutils literal"><span class="pre">__block</span></tt> are imported as
+<tt class="docutils literal"><span class="pre">const</span></tt> copies.</p>
+<p>The simplest example is that of importing a variable of type <tt class="docutils literal"><span class="pre">int</span></tt>:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="n">x</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+<span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">vv</span><span class="p">)(</span><span class="kt">void</span><span class="p">)</span> <span class="o">=</span> <span class="o">^</span><span class="p">{</span> <span class="n">printf</span><span class="p">(</span><span class="s">"x is %d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">x</span><span class="p">);</span> <span class="p">}</span>
+<span class="n">x</span> <span class="o">=</span> <span class="mi">11</span><span class="p">;</span>
+<span class="n">vv</span><span class="p">();</span>
+</pre></div>
+</div>
+<p>which would be compiled to:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_2</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_2</span> <span class="o">*</span><span class="p">);</span>
+ <span class="k">struct</span> <span class="n">__block_descriptor_2</span> <span class="o">*</span><span class="n">descriptor</span><span class="p">;</span>
+ <span class="k">const</span> <span class="kt">int</span> <span class="n">x</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">__block_invoke_2</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_2</span> <span class="o">*</span><span class="n">_block</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">printf</span><span class="p">(</span><span class="s">"x is %d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">_block</span><span class="o">-></span><span class="n">x</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="k">struct</span> <span class="n">__block_descriptor_2</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">Block_size</span><span class="p">;</span>
+<span class="p">}</span> <span class="n">__block_descriptor_2</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_2</span><span class="p">)</span> <span class="p">};</span>
+</pre></div>
+</div>
+<p>and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_2</span> <span class="n">__block_literal_2</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteStackBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span><span class="p">,</span>
+ <span class="n">__block_invoke_2</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">__block_descriptor_2</span><span class="p">,</span>
+ <span class="n">x</span>
+ <span class="p">};</span>
+</pre></div>
+</div>
+<p>In summary, scalars, structures, unions, and function pointers are generally
+imported as <tt class="docutils literal"><span class="pre">const</span></tt> copies with no need for helper functions.</p>
+</div>
+<div class="section" id="imported-const-copy-of-block-reference">
+<h3><a class="toc-backref" href="#id5">Imported <tt class="docutils literal"><span class="pre">const</span></tt> copy of <tt class="docutils literal"><span class="pre">Block</span></tt> reference</a><a class="headerlink" href="#imported-const-copy-of-block-reference" title="Permalink to this headline">¶</a></h3>
+<p>The first case where copy and dispose helper functions are required is for the
+case of when a <tt class="docutils literal"><span class="pre">Block</span></tt> itself is imported. In this case both a
+<tt class="docutils literal"><span class="pre">copy_helper</span></tt> function and a <tt class="docutils literal"><span class="pre">dispose_helper</span></tt> function are needed. The
+<tt class="docutils literal"><span class="pre">copy_helper</span></tt> function is passed both the existing stack based pointer and the
+pointer to the new heap version and should call back into the runtime to
+actually do the copy operation on the imported fields within the <tt class="docutils literal"><span class="pre">Block</span></tt>. The
+runtime functions are all described in <a class="reference internal" href="#runtimehelperfunctions"><em>Runtime Helper Functions</em></a>.</p>
+<p>A quick example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">existingBlock</span><span class="p">)(</span><span class="kt">void</span><span class="p">)</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">vv</span><span class="p">)(</span><span class="kt">void</span><span class="p">)</span> <span class="o">=</span> <span class="o">^</span><span class="p">{</span> <span class="n">existingBlock</span><span class="p">();</span> <span class="p">}</span>
+<span class="n">vv</span><span class="p">();</span>
+
+<span class="k">struct</span> <span class="n">__block_literal_3</span> <span class="p">{</span>
+ <span class="p">...;</span> <span class="c1">// existing block</span>
+<span class="p">};</span>
+
+<span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="p">);</span>
+ <span class="k">struct</span> <span class="n">__block_literal_3</span> <span class="o">*</span><span class="k">const</span> <span class="n">existingBlock</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">__block_invoke_4</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_2</span> <span class="o">*</span><span class="n">_block</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">__block</span><span class="o">-></span><span class="n">existingBlock</span><span class="o">-></span><span class="n">invoke</span><span class="p">(</span><span class="n">__block</span><span class="o">-></span><span class="n">existingBlock</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_copy_4</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_copy_assign(&dst->existingBlock, src->existingBlock, 0);</span>
+ <span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">existingBlock</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">existingBlock</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BLOCK</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_dispose_4</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">// was _Block_destroy</span>
+ <span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">src</span><span class="o">-></span><span class="n">existingBlock</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BLOCK</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="k">struct</span> <span class="n">__block_descriptor_4</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">Block_size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">copy_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">dispose_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="o">*</span><span class="p">);</span>
+<span class="p">}</span> <span class="n">__block_descriptor_4</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="mi">0</span><span class="p">,</span>
+ <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_4</span><span class="p">),</span>
+ <span class="n">__block_copy_4</span><span class="p">,</span>
+ <span class="n">__block_dispose_4</span><span class="p">,</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>and where said <tt class="docutils literal"><span class="pre">Block</span></tt> is used:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_4</span> <span class="n">_block_literal</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteStackBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">25</span><span class="p">)</span><span class="o">|</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span>
+ <span class="n">__block_invoke_4</span><span class="p">,</span>
+ <span class="o">&</span> <span class="n">__block_descriptor_4</span>
+ <span class="n">existingBlock</span><span class="p">,</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<div class="section" id="importing-attribute-nsobject-variables">
+<h4><a class="toc-backref" href="#id6">Importing <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> variables</a><a class="headerlink" href="#importing-attribute-nsobject-variables" title="Permalink to this headline">¶</a></h4>
+<p>GCC introduces <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> on structure pointers to mean “this
+is an object”. This is useful because many low level data structures are
+declared as opaque structure pointers, e.g. <tt class="docutils literal"><span class="pre">CFStringRef</span></tt>, <tt class="docutils literal"><span class="pre">CFArrayRef</span></tt>,
+etc. When used from C, however, these are still really objects and are the
+second case where that requires copy and dispose helper functions to be
+generated. The copy helper functions generated by the compiler should use the
+<tt class="docutils literal"><span class="pre">_Block_object_assign</span></tt> runtime helper function and in the dispose helper the
+<tt class="docutils literal"><span class="pre">_Block_object_dispose</span></tt> runtime helper function should be called.</p>
+<p>For example, <tt class="docutils literal"><span class="pre">Block</span></tt> foo in the following:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">Opaque</span> <span class="o">*</span><span class="n">__attribute__</span><span class="p">((</span><span class="n">NSObject</span><span class="p">))</span> <span class="n">objectPointer</span> <span class="o">=</span> <span class="p">...;</span>
+<span class="p">...</span>
+<span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">foo</span><span class="p">)(</span><span class="kt">void</span><span class="p">)</span> <span class="o">=</span> <span class="o">^</span><span class="p">{</span> <span class="n">CFPrint</span><span class="p">(</span><span class="n">objectPointer</span><span class="p">);</span> <span class="p">};</span>
+</pre></div>
+</div>
+<p>would have the following helper functions generated:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">__block_copy_foo</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">objectPointer</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span> <span class="n">objectPointer</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_OBJECT</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_dispose_foo</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">src</span><span class="o">-></span><span class="n">objectPointer</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_OBJECT</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+</div>
+<div class="section" id="imported-block-marked-variables">
+<h3><a class="toc-backref" href="#id7">Imported <tt class="docutils literal"><span class="pre">__block</span></tt> marked variables</a><a class="headerlink" href="#imported-block-marked-variables" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="layout-of-block-marked-variables">
+<h4><a class="toc-backref" href="#id8">Layout of <tt class="docutils literal"><span class="pre">__block</span></tt> marked variables</a><a class="headerlink" href="#layout-of-block-marked-variables" title="Permalink to this headline">¶</a></h4>
+<p>The compiler must embed variables that are marked <tt class="docutils literal"><span class="pre">__block</span></tt> in a specialized
+structure of the form:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_foo</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="k">struct</span> <span class="n">Block_byref</span> <span class="o">*</span><span class="n">forwarding</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span> <span class="c1">//refcount;</span>
+ <span class="kt">int</span> <span class="n">size</span><span class="p">;</span>
+ <span class="n">typeof</span><span class="p">(</span><span class="n">marked_variable</span><span class="p">)</span> <span class="n">marked_variable</span><span class="p">;</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>Variables of certain types require helper functions for when <tt class="docutils literal"><span class="pre">Block_copy()</span></tt>
+and <tt class="docutils literal"><span class="pre">Block_release()</span></tt> are performed upon a referencing <tt class="docutils literal"><span class="pre">Block</span></tt>. At the “C”
+level only variables that are of type <tt class="docutils literal"><span class="pre">Block</span></tt> or ones that have
+<tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> marked require helper functions. In Objective-C
+objects require helper functions and in C++ stack based objects require helper
+functions. Variables that require helper functions use the form:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_foo</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="k">struct</span> <span class="n">_block_byref_foo</span> <span class="o">*</span><span class="n">forwarding</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span> <span class="c1">//refcount;</span>
+ <span class="kt">int</span> <span class="n">size</span><span class="p">;</span>
+ <span class="c1">// helper functions called via Block_copy() and Block_release()</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_keep</span><span class="p">)(</span><span class="kt">void</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_dispose</span><span class="p">)(</span><span class="kt">void</span> <span class="o">*</span><span class="p">);</span>
+ <span class="n">typeof</span><span class="p">(</span><span class="n">marked_variable</span><span class="p">)</span> <span class="n">marked_variable</span><span class="p">;</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>The structure is initialized such that:</p>
+<blockquote>
+<div><p>a. The <tt class="docutils literal"><span class="pre">forwarding</span></tt> pointer is set to the beginning of its enclosing
+structure.</p>
+<p>b. The <tt class="docutils literal"><span class="pre">size</span></tt> field is initialized to the total size of the enclosing
+structure.</p>
+<p>c. The <tt class="docutils literal"><span class="pre">flags</span></tt> field is set to either 0 if no helper functions are needed
+or (1<<25) if they are.</p>
+<ol class="loweralpha simple" start="4">
+<li>The helper functions are initialized (if present).</li>
+<li>The variable itself is set to its initial value.</li>
+<li>The <tt class="docutils literal"><span class="pre">isa</span></tt> field is set to <tt class="docutils literal"><span class="pre">NULL</span></tt>.</li>
+</ol>
+</div></blockquote>
+</div>
+<div class="section" id="access-to-block-variables-from-within-its-lexical-scope">
+<h4><a class="toc-backref" href="#id9">Access to <tt class="docutils literal"><span class="pre">__block</span></tt> variables from within its lexical scope</a><a class="headerlink" href="#access-to-block-variables-from-within-its-lexical-scope" title="Permalink to this headline">¶</a></h4>
+<p>In order to “move” the variable to the heap upon a <tt class="docutils literal"><span class="pre">copy_helper</span></tt> operation the
+compiler must rewrite access to such a variable to be indirect through the
+structures <tt class="docutils literal"><span class="pre">forwarding</span></tt> pointer. For example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="n">__block</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+<span class="n">i</span> <span class="o">=</span> <span class="mi">11</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>would be rewritten to be:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="n">forwarding</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span> <span class="c1">//refcount;</span>
+ <span class="kt">int</span> <span class="n">size</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">captured_i</span><span class="p">;</span>
+<span class="p">}</span> <span class="n">i</span> <span class="o">=</span> <span class="p">{</span> <span class="nb">NULL</span><span class="p">,</span> <span class="o">&</span><span class="n">i</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_i</span><span class="p">),</span> <span class="mi">10</span> <span class="p">};</span>
+
+<span class="n">i</span><span class="p">.</span><span class="n">forwarding</span><span class="o">-></span><span class="n">captured_i</span> <span class="o">=</span> <span class="mi">11</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>In the case of a <tt class="docutils literal"><span class="pre">Block</span></tt> reference variable being marked <tt class="docutils literal"><span class="pre">__block</span></tt> the
+helper code generated must use the <tt class="docutils literal"><span class="pre">_Block_object_assign</span></tt> and
+<tt class="docutils literal"><span class="pre">_Block_object_dispose</span></tt> routines supplied by the runtime to make the
+copies. For example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">__block</span> <span class="kt">void</span> <span class="p">(</span><span class="n">voidBlock</span><span class="p">)(</span><span class="kt">void</span><span class="p">)</span> <span class="o">=</span> <span class="n">blockA</span><span class="p">;</span>
+<span class="n">voidBlock</span> <span class="o">=</span> <span class="n">blockB</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>would translate into:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">forwarding</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span> <span class="c1">//refcount;</span>
+ <span class="kt">int</span> <span class="n">size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_keep</span><span class="p">)(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_dispose</span><span class="p">)(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">captured_voidBlock</span><span class="p">)(</span><span class="kt">void</span><span class="p">);</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">_block_byref_keep_helper</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_copy_assign(&dst->captured_voidBlock, src->captured_voidBlock, 0);</span>
+ <span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">captured_voidBlock</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">captured_voidBlock</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BLOCK</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">_block_byref_dispose_helper</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">param</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_destroy(param->captured_voidBlock, 0);</span>
+ <span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">param</span><span class="o">-></span><span class="n">captured_voidBlock</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BLOCK</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">)}</span>
+</pre></div>
+</div>
+<p>and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="n">voidBlock</span> <span class="o">=</span> <span class="p">{(</span> <span class="p">.</span><span class="n">forwarding</span><span class="o">=&</span><span class="n">voidBlock</span><span class="p">,</span> <span class="p">.</span><span class="n">flags</span><span class="o">=</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">25</span><span class="p">),</span> <span class="p">.</span><span class="n">size</span><span class="o">=</span><span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="p">),</span>
+ <span class="p">.</span><span class="n">byref_keep</span><span class="o">=</span><span class="n">_block_byref_keep_helper</span><span class="p">,</span> <span class="p">.</span><span class="n">byref_dispose</span><span class="o">=</span><span class="n">_block_byref_dispose_helper</span><span class="p">,</span>
+ <span class="p">.</span><span class="n">captured_voidBlock</span><span class="o">=</span><span class="n">blockA</span> <span class="p">)};</span>
+
+<span class="n">voidBlock</span><span class="p">.</span><span class="n">forwarding</span><span class="o">-></span><span class="n">captured_voidBlock</span> <span class="o">=</span> <span class="n">blockB</span><span class="p">;</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="importing-block-variables-into-blocks">
+<h4><a class="toc-backref" href="#id10">Importing <tt class="docutils literal"><span class="pre">__block</span></tt> variables into <tt class="docutils literal"><span class="pre">Blocks</span></tt></a><a class="headerlink" href="#importing-block-variables-into-blocks" title="Permalink to this headline">¶</a></h4>
+<p>A <tt class="docutils literal"><span class="pre">Block</span></tt> that uses a <tt class="docutils literal"><span class="pre">__block</span></tt> variable in its compound statement body must
+import the variable and emit <tt class="docutils literal"><span class="pre">copy_helper</span></tt> and <tt class="docutils literal"><span class="pre">dispose_helper</span></tt> helper
+functions that, in turn, call back into the runtime to actually copy or release
+the <tt class="docutils literal"><span class="pre">byref</span></tt> data block using the functions <tt class="docutils literal"><span class="pre">_Block_object_assign</span></tt> and
+<tt class="docutils literal"><span class="pre">_Block_object_dispose</span></tt>.</p>
+<p>For example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="n">__block</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+<span class="n">functioncall</span><span class="p">(</span><span class="o">^</span><span class="p">{</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span> <span class="p">});</span>
+</pre></div>
+</div>
+<p>would translate to:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span> <span class="c1">// set to NULL</span>
+ <span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">forwarding</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span> <span class="c1">//refcount;</span>
+ <span class="kt">int</span> <span class="n">size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_keep</span><span class="p">)(</span><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_dispose</span><span class="p">)(</span><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="p">);</span>
+ <span class="kt">int</span> <span class="n">captured_i</span><span class="p">;</span>
+<span class="p">};</span>
+
+
+<span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="p">);</span>
+ <span class="k">struct</span> <span class="n">__block_descriptor_5</span> <span class="o">*</span><span class="n">descriptor</span><span class="p">;</span>
+ <span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="n">i_holder</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">__block_invoke_5</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">_block</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">_block</span><span class="o">-></span><span class="n">forwarding</span><span class="o">-></span><span class="n">captured_i</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_copy_5</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_byref_assign_copy(&dst->captured_i, src->captured_i);</span>
+ <span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">captured_i</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">captured_i</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BYREF</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_dispose_5</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_byref_release(src->captured_i);</span>
+ <span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">src</span><span class="o">-></span><span class="n">captured_i</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BYREF</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="k">struct</span> <span class="n">__block_descriptor_5</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">Block_size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">copy_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">dispose_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="p">);</span>
+<span class="p">}</span> <span class="n">__block_descriptor_5</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span><span class="p">)</span> <span class="n">__block_copy_5</span><span class="p">,</span> <span class="n">__block_dispose_5</span> <span class="p">};</span>
+</pre></div>
+</div>
+<p>and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="n">i</span> <span class="o">=</span> <span class="p">{(</span> <span class="p">.</span><span class="n">forwarding</span><span class="o">=&</span><span class="n">i</span><span class="p">,</span> <span class="p">.</span><span class="n">flags</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="p">.</span><span class="n">size</span><span class="o">=</span><span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_i</span><span class="p">)</span> <span class="p">)};</span>
+<span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="n">_block_literal</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteStackBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">25</span><span class="p">)</span><span class="o">|</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span><span class="p">,</span>
+ <span class="n">__block_invoke_5</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">__block_descriptor_5</span><span class="p">,</span>
+ <span class="mi">2</span><span class="p">,</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="importing-attribute-nsobject-block-variables">
+<h4><a class="toc-backref" href="#id11">Importing <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> <tt class="docutils literal"><span class="pre">__block</span></tt> variables</a><a class="headerlink" href="#importing-attribute-nsobject-block-variables" title="Permalink to this headline">¶</a></h4>
+<p>A <tt class="docutils literal"><span class="pre">__block</span></tt> variable that is also marked <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> should
+have <tt class="docutils literal"><span class="pre">byref_keep</span></tt> and <tt class="docutils literal"><span class="pre">byref_dispose</span></tt> helper functions that use
+<tt class="docutils literal"><span class="pre">_Block_object_assign</span></tt> and <tt class="docutils literal"><span class="pre">_Block_object_dispose</span></tt>.</p>
+</div>
+<div class="section" id="block-escapes">
+<h4><a class="toc-backref" href="#id12"><tt class="docutils literal"><span class="pre">__block</span></tt> escapes</a><a class="headerlink" href="#block-escapes" title="Permalink to this headline">¶</a></h4>
+<p>Because <tt class="docutils literal"><span class="pre">Blocks</span></tt> referencing <tt class="docutils literal"><span class="pre">__block</span></tt> variables may have <tt class="docutils literal"><span class="pre">Block_copy()</span></tt>
+performed upon them the underlying storage for the variables may move to the
+heap. In Objective-C Garbage Collection Only compilation environments the heap
+used is the garbage collected one and no further action is required. Otherwise
+the compiler must issue a call to potentially release any heap storage for
+<tt class="docutils literal"><span class="pre">__block</span></tt> variables at all escapes or terminations of their scope. The call
+should be:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_dispose</span><span class="p">(</span><span class="o">&</span><span class="n">_block_byref_foo</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BYREF</span><span class="p">);</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="nesting">
+<h4><a class="toc-backref" href="#id13">Nesting</a><a class="headerlink" href="#nesting" title="Permalink to this headline">¶</a></h4>
+<p><tt class="docutils literal"><span class="pre">Blocks</span></tt> may contain <tt class="docutils literal"><span class="pre">Block</span></tt> literal expressions. Any variables used within
+inner blocks are imported into all enclosing <tt class="docutils literal"><span class="pre">Block</span></tt> scopes even if the
+variables are not used. This includes <tt class="docutils literal"><span class="pre">const</span></tt> imports as well as <tt class="docutils literal"><span class="pre">__block</span></tt>
+variables.</p>
+</div>
+</div>
+</div>
+<div class="section" id="objective-c-extensions-to-blocks">
+<h2><a class="toc-backref" href="#id14">Objective C Extensions to <tt class="docutils literal"><span class="pre">Blocks</span></tt></a><a class="headerlink" href="#objective-c-extensions-to-blocks" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="importing-objects">
+<h3><a class="toc-backref" href="#id15">Importing Objects</a><a class="headerlink" href="#importing-objects" title="Permalink to this headline">¶</a></h3>
+<p>Objects should be treated as <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> variables; all
+<tt class="docutils literal"><span class="pre">copy_helper</span></tt>, <tt class="docutils literal"><span class="pre">dispose_helper</span></tt>, <tt class="docutils literal"><span class="pre">byref_keep</span></tt>, and <tt class="docutils literal"><span class="pre">byref_dispose</span></tt>
+helper functions should use <tt class="docutils literal"><span class="pre">_Block_object_assign</span></tt> and
+<tt class="docutils literal"><span class="pre">_Block_object_dispose</span></tt>. There should be no code generated that uses
+<tt class="docutils literal"><span class="pre">*-retain</span></tt> or <tt class="docutils literal"><span class="pre">*-release</span></tt> methods.</p>
+</div>
+<div class="section" id="blocks-as-objects">
+<h3><a class="toc-backref" href="#id16"><tt class="docutils literal"><span class="pre">Blocks</span></tt> as Objects</a><a class="headerlink" href="#blocks-as-objects" title="Permalink to this headline">¶</a></h3>
+<p>The compiler will treat <tt class="docutils literal"><span class="pre">Blocks</span></tt> as objects when synthesizing property setters
+and getters, will characterize them as objects when generating garbage
+collection strong and weak layout information in the same manner as objects, and
+will issue strong and weak write-barrier assignments in the same manner as
+objects.</p>
+</div>
+<div class="section" id="weak-block-support">
+<h3><a class="toc-backref" href="#id17"><tt class="docutils literal"><span class="pre">__weak</span> <span class="pre">__block</span></tt> Support</a><a class="headerlink" href="#weak-block-support" title="Permalink to this headline">¶</a></h3>
+<p>Objective-C (and Objective-C++) support the <tt class="docutils literal"><span class="pre">__weak</span></tt> attribute on <tt class="docutils literal"><span class="pre">__block</span></tt>
+variables. Under normal circumstances the compiler uses the Objective-C runtime
+helper support functions <tt class="docutils literal"><span class="pre">objc_assign_weak</span></tt> and <tt class="docutils literal"><span class="pre">objc_read_weak</span></tt>. Both
+should continue to be used for all reads and writes of <tt class="docutils literal"><span class="pre">__weak</span> <span class="pre">__block</span></tt>
+variables:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">objc_read_weak</span><span class="p">(</span><span class="o">&</span><span class="n">block</span><span class="o">-></span><span class="n">byref_i</span><span class="o">-></span><span class="n">forwarding</span><span class="o">-></span><span class="n">i</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>The <tt class="docutils literal"><span class="pre">__weak</span></tt> variable is stored in a <tt class="docutils literal"><span class="pre">_block_byref_foo</span></tt> structure and the
+<tt class="docutils literal"><span class="pre">Block</span></tt> has copy and dispose helpers for this structure that call:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dest</span><span class="o">-></span><span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span> <span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_BYREF</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">src</span><span class="o">-></span><span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_BYREF</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>In turn, the <tt class="docutils literal"><span class="pre">block_byref</span></tt> copy support helpers distinguish between whether
+the <tt class="docutils literal"><span class="pre">__block</span></tt> variable is a <tt class="docutils literal"><span class="pre">Block</span></tt> or not and should either call:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dest</span><span class="o">-></span><span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_OBJECT</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>for something declared as an object or:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dest</span><span class="o">-></span><span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">_block_byref_i</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_BLOCK</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>for something declared as a <tt class="docutils literal"><span class="pre">Block</span></tt>.</p>
+<p>A full example follows:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">__block</span> <span class="n">__weak</span> <span class="n">id</span> <span class="n">obj</span> <span class="o">=</span> <span class="o"><</span><span class="n">initialization</span> <span class="n">expression</span><span class="o">></span><span class="p">;</span>
+<span class="n">functioncall</span><span class="p">(</span><span class="o">^</span><span class="p">{</span> <span class="p">[</span><span class="n">obj</span> <span class="n">somemessage</span><span class="p">];</span> <span class="p">});</span>
+</pre></div>
+</div>
+<p>would translate to:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">_block_byref_obj</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span> <span class="c1">// uninitialized</span>
+ <span class="k">struct</span> <span class="n">_block_byref_obj</span> <span class="o">*</span><span class="n">forwarding</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span> <span class="c1">//refcount;</span>
+ <span class="kt">int</span> <span class="n">size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_keep</span><span class="p">)(</span><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">byref_dispose</span><span class="p">)(</span><span class="k">struct</span> <span class="n">_block_byref_i</span> <span class="o">*</span><span class="p">);</span>
+ <span class="n">id</span> <span class="n">captured_obj</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">_block_byref_obj_keep</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_copy_assign(&dst->captured_obj, src->captured_obj, 0);</span>
+ <span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">captured_obj</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">captured_obj</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_OBJECT</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">_block_byref_obj_dispose</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_voidBlock</span> <span class="o">*</span><span class="n">param</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_destroy(param->captured_obj, 0);</span>
+ <span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">param</span><span class="o">-></span><span class="n">captured_obj</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_OBJECT</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">|</span> <span class="n">BLOCK_BYREF_CALLER</span><span class="p">);</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>for the block <tt class="docutils literal"><span class="pre">byref</span></tt> part and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="p">);</span>
+ <span class="k">struct</span> <span class="n">__block_descriptor_5</span> <span class="o">*</span><span class="n">descriptor</span><span class="p">;</span>
+ <span class="k">struct</span> <span class="n">_block_byref_obj</span> <span class="o">*</span><span class="n">byref_obj</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">__block_invoke_5</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">_block</span><span class="p">)</span> <span class="p">{</span>
+ <span class="p">[</span><span class="n">objc_read_weak</span><span class="p">(</span><span class="o">&</span><span class="n">_block</span><span class="o">-></span><span class="n">byref_obj</span><span class="o">-></span><span class="n">forwarding</span><span class="o">-></span><span class="n">captured_obj</span><span class="p">)</span> <span class="n">somemessage</span><span class="p">];</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_copy_5</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_byref_assign_copy(&dst->byref_obj, src->byref_obj);</span>
+ <span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">byref_obj</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">byref_obj</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BYREF</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_WEAK</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_dispose_5</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">//_Block_byref_release(src->byref_obj);</span>
+ <span class="n">_Block_object_dispose</span><span class="p">(</span><span class="n">src</span><span class="o">-></span><span class="n">byref_obj</span><span class="p">,</span> <span class="n">BLOCK_FIELD_IS_BYREF</span> <span class="o">|</span> <span class="n">BLOCK_FIELD_IS_WEAK</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="k">struct</span> <span class="n">__block_descriptor_5</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">Block_size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">copy_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">dispose_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_5</span> <span class="o">*</span><span class="p">);</span>
+<span class="p">}</span> <span class="n">__block_descriptor_5</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_5</span><span class="p">),</span> <span class="n">__block_copy_5</span><span class="p">,</span> <span class="n">__block_dispose_5</span> <span class="p">};</span>
+</pre></div>
+</div>
+<p>and within the compound statement:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">truct</span> <span class="n">_block_byref_obj</span> <span class="n">obj</span> <span class="o">=</span> <span class="p">{(</span> <span class="p">.</span><span class="n">forwarding</span><span class="o">=&</span><span class="n">obj</span><span class="p">,</span> <span class="p">.</span><span class="n">flags</span><span class="o">=</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">25</span><span class="p">),</span> <span class="p">.</span><span class="n">size</span><span class="o">=</span><span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_obj</span><span class="p">),</span>
+ <span class="p">.</span><span class="n">byref_keep</span><span class="o">=</span><span class="n">_block_byref_obj_keep</span><span class="p">,</span> <span class="p">.</span><span class="n">byref_dispose</span><span class="o">=</span><span class="n">_block_byref_obj_dispose</span><span class="p">,</span>
+ <span class="p">.</span><span class="n">captured_obj</span> <span class="o">=</span> <span class="o"><</span><span class="n">initialization</span> <span class="n">expression</span><span class="o">></span> <span class="p">)};</span>
+
+<span class="n">truct</span> <span class="n">__block_literal_5</span> <span class="n">_block_literal</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteStackBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">25</span><span class="p">)</span><span class="o">|</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span><span class="p">,</span>
+ <span class="n">__block_invoke_5</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">__block_descriptor_5</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">obj</span><span class="p">,</span> <span class="c1">// a reference to the on-stack structure containing "captured_obj"</span>
+<span class="p">};</span>
+
+
+<span class="n">functioncall</span><span class="p">(</span><span class="n">_block_literal</span><span class="o">-></span><span class="n">invoke</span><span class="p">(</span><span class="o">&</span><span class="n">_block_literal</span><span class="p">));</span>
+</pre></div>
+</div>
+</div>
+</div>
+<div class="section" id="c-support">
+<h2><a class="toc-backref" href="#id18">C++ Support</a><a class="headerlink" href="#c-support" title="Permalink to this headline">¶</a></h2>
+<p>Within a block stack based C++ objects are copied into <tt class="docutils literal"><span class="pre">const</span></tt> copies using
+the copy constructor. It is an error if a stack based C++ object is used within
+a block if it does not have a copy constructor. In addition both copy and
+destroy helper routines must be synthesized for the block to support the
+<tt class="docutils literal"><span class="pre">Block_copy()</span></tt> operation, and the flags work marked with the (1<<26) bit in
+addition to the (1<<25) bit. The copy helper should call the constructor using
+appropriate offsets of the variable within the supplied stack based block source
+and heap based destination for all <tt class="docutils literal"><span class="pre">const</span></tt> constructed copies, and similarly
+should call the destructor in the destroy routine.</p>
+<p>As an example, suppose a C++ class <tt class="docutils literal"><span class="pre">FOO</span></tt> existed with a copy constructor.
+Within a code block a stack version of a <tt class="docutils literal"><span class="pre">FOO</span></tt> object is declared and used
+within a <tt class="docutils literal"><span class="pre">Block</span></tt> literal expression:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="p">{</span>
+ <span class="n">FOO</span> <span class="n">foo</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">block</span><span class="p">)(</span><span class="kt">void</span><span class="p">)</span> <span class="o">=</span> <span class="o">^</span><span class="p">{</span> <span class="n">printf</span><span class="p">(</span><span class="s">"%d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">foo</span><span class="p">.</span><span class="n">value</span><span class="p">());</span> <span class="p">};</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The compiler would synthesize:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="o">*</span><span class="n">isa</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">flags</span><span class="p">;</span>
+ <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">invoke</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="p">);</span>
+ <span class="k">struct</span> <span class="n">__block_descriptor_10</span> <span class="o">*</span><span class="n">descriptor</span><span class="p">;</span>
+ <span class="k">const</span> <span class="n">FOO</span> <span class="n">foo</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">void</span> <span class="nf">__block_invoke_10</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="n">_block</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">printf</span><span class="p">(</span><span class="s">"%d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">_block</span><span class="o">-></span><span class="n">foo</span><span class="p">.</span><span class="n">value</span><span class="p">());</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_literal_10</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">FOO_ctor</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">foo</span><span class="p">,</span> <span class="o">&</span><span class="n">src</span><span class="o">-></span><span class="n">foo</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">__block_dispose_10</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">FOO_dtor</span><span class="p">(</span><span class="o">&</span><span class="n">src</span><span class="o">-></span><span class="n">foo</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="k">struct</span> <span class="n">__block_descriptor_10</span> <span class="p">{</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">reserved</span><span class="p">;</span>
+ <span class="kt">unsigned</span> <span class="kt">long</span> <span class="kt">int</span> <span class="n">Block_size</span><span class="p">;</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">copy_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="n">src</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">dispose_helper</span><span class="p">)(</span><span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">*</span><span class="p">);</span>
+<span class="p">}</span> <span class="n">__block_descriptor_10</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="k">struct</span> <span class="n">__block_literal_10</span><span class="p">),</span> <span class="n">__block_copy_10</span><span class="p">,</span> <span class="n">__block_dispose_10</span> <span class="p">};</span>
+</pre></div>
+</div>
+<p>and the code would be:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="p">{</span>
+ <span class="n">FOO</span> <span class="n">foo</span><span class="p">;</span>
+ <span class="n">comp_ctor</span><span class="p">(</span><span class="o">&</span><span class="n">foo</span><span class="p">);</span> <span class="c1">// default constructor</span>
+ <span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="n">_block_literal</span> <span class="o">=</span> <span class="p">{</span>
+ <span class="o">&</span><span class="n">_NSConcreteStackBlock</span><span class="p">,</span>
+ <span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">25</span><span class="p">)</span><span class="o">|</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">26</span><span class="p">)</span><span class="o">|</span><span class="p">(</span><span class="mi">1</span><span class="o"><<</span><span class="mi">29</span><span class="p">),</span> <span class="o"><</span><span class="n">uninitialized</span><span class="o">></span><span class="p">,</span>
+ <span class="n">__block_invoke_10</span><span class="p">,</span>
+ <span class="o">&</span><span class="n">__block_descriptor_10</span><span class="p">,</span>
+ <span class="p">};</span>
+ <span class="n">comp_ctor</span><span class="p">(</span><span class="o">&</span><span class="n">_block_literal</span><span class="o">-></span><span class="n">foo</span><span class="p">,</span> <span class="o">&</span><span class="n">foo</span><span class="p">);</span> <span class="c1">// const copy into stack version</span>
+ <span class="k">struct</span> <span class="n">__block_literal_10</span> <span class="o">&</span><span class="n">block</span> <span class="o">=</span> <span class="o">&</span><span class="n">_block_literal</span><span class="p">;</span> <span class="c1">// assign literal to block variable</span>
+ <span class="n">block</span><span class="o">-></span><span class="n">invoke</span><span class="p">(</span><span class="n">block</span><span class="p">);</span> <span class="c1">// invoke block</span>
+ <span class="n">comp_dtor</span><span class="p">(</span><span class="o">&</span><span class="n">_block_literal</span><span class="o">-></span><span class="n">foo</span><span class="p">);</span> <span class="c1">// destroy stack version of const block copy</span>
+ <span class="n">comp_dtor</span><span class="p">(</span><span class="o">&</span><span class="n">foo</span><span class="p">);</span> <span class="c1">// destroy original version</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>C++ objects stored in <tt class="docutils literal"><span class="pre">__block</span></tt> storage start out on the stack in a
+<tt class="docutils literal"><span class="pre">block_byref</span></tt> data structure as do other variables. Such objects (if not
+<tt class="docutils literal"><span class="pre">const</span></tt> objects) must support a regular copy constructor. The <tt class="docutils literal"><span class="pre">block_byref</span></tt>
+data structure will have copy and destroy helper routines synthesized by the
+compiler. The copy helper will have code created to perform the copy
+constructor based on the initial stack <tt class="docutils literal"><span class="pre">block_byref</span></tt> data structure, and will
+also set the (1<<26) bit in addition to the (1<<25) bit. The destroy helper
+will have code to do the destructor on the object stored within the supplied
+<tt class="docutils literal"><span class="pre">block_byref</span></tt> heap data structure. For example,</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">__block</span> <span class="n">FOO</span> <span class="n">blockStorageFoo</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>requires the normal constructor for the embedded <tt class="docutils literal"><span class="pre">blockStorageFoo</span></tt> object:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">FOO_ctor</span><span class="p">(</span><span class="o">&</span> <span class="n">_block_byref_blockStorageFoo</span><span class="o">-></span><span class="n">blockStorageFoo</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>and at scope termination the destructor:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">FOO_dtor</span><span class="p">(</span><span class="o">&</span> <span class="n">_block_byref_blockStorageFoo</span><span class="o">-></span><span class="n">blockStorageFoo</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Note that the forwarding indirection is <em>NOT</em> used.</p>
+<p>The compiler would need to generate (if used from a block literal) the following
+copy/dispose helpers:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">_block_byref_obj_keep</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_blockStorageFoo</span> <span class="o">*</span><span class="n">dst</span><span class="p">,</span> <span class="k">struct</span> <span class="n">_block_byref_blockStorageFoo</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">FOO_ctor</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">blockStorageFoo</span><span class="p">,</span> <span class="o">&</span><span class="n">src</span><span class="o">-></span><span class="n">blockStorageFoo</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="nf">_block_byref_obj_dispose</span><span class="p">(</span><span class="k">struct</span> <span class="n">_block_byref_blockStorageFoo</span> <span class="o">*</span><span class="n">src</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">FOO_dtor</span><span class="p">(</span><span class="o">&</span><span class="n">src</span><span class="o">-></span><span class="n">blockStorageFoo</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>for the appropriately named constructor and destructor for the class/struct
+<tt class="docutils literal"><span class="pre">FOO</span></tt>.</p>
+<p>To support member variable and function access the compiler will synthesize a
+<tt class="docutils literal"><span class="pre">const</span></tt> pointer to a block version of the <tt class="docutils literal"><span class="pre">this</span></tt> pointer.</p>
+</div>
+<div class="section" id="runtime-helper-functions">
+<span id="runtimehelperfunctions"></span><h2><a class="toc-backref" href="#id19">Runtime Helper Functions</a><a class="headerlink" href="#runtime-helper-functions" title="Permalink to this headline">¶</a></h2>
+<p>The runtime helper functions are described in
+<tt class="docutils literal"><span class="pre">/usr/local/include/Block_private.h</span></tt>. To summarize their use, a <tt class="docutils literal"><span class="pre">Block</span></tt>
+requires copy/dispose helpers if it imports any block variables, <tt class="docutils literal"><span class="pre">__block</span></tt>
+storage variables, <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> variables, or C++ <tt class="docutils literal"><span class="pre">const</span></tt>
+copied objects with constructor/destructors. The (1<<26) bit is set and
+functions are generated.</p>
+<p>The block copy helper function should, for each of the variables of the type
+mentioned above, call:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_assign</span><span class="p">(</span><span class="o">&</span><span class="n">dst</span><span class="o">-></span><span class="n">target</span><span class="p">,</span> <span class="n">src</span><span class="o">-></span><span class="n">target</span><span class="p">,</span> <span class="n">BLOCK_FIELD_</span><span class="o"><</span><span class="n">appropo</span><span class="o">></span><span class="p">);</span>
+</pre></div>
+</div>
+<p>in the copy helper and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">_Block_object_dispose</span><span class="p">(</span><span class="o">-></span><span class="n">target</span><span class="p">,</span> <span class="n">BLOCK_FIELD_</span><span class="o"><</span><span class="n">appropo</span><span class="o">></span><span class="p">);</span>
+</pre></div>
+</div>
+<p>in the dispose helper where <tt class="docutils literal"><span class="pre"><appropo></span></tt> is:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">enum</span> <span class="p">{</span>
+ <span class="n">BLOCK_FIELD_IS_OBJECT</span> <span class="o">=</span> <span class="mi">3</span><span class="p">,</span> <span class="c1">// id, NSObject, __attribute__((NSObject)), block, ...</span>
+ <span class="n">BLOCK_FIELD_IS_BLOCK</span> <span class="o">=</span> <span class="mi">7</span><span class="p">,</span> <span class="c1">// a block variable</span>
+ <span class="n">BLOCK_FIELD_IS_BYREF</span> <span class="o">=</span> <span class="mi">8</span><span class="p">,</span> <span class="c1">// the on stack structure holding the __block variable</span>
+
+ <span class="n">BLOCK_FIELD_IS_WEAK</span> <span class="o">=</span> <span class="mi">16</span><span class="p">,</span> <span class="c1">// declared __weak</span>
+
+ <span class="n">BLOCK_BYREF_CALLER</span> <span class="o">=</span> <span class="mi">128</span><span class="p">,</span> <span class="c1">// called from byref copy/dispose helpers</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>and of course the constructors/destructors for <tt class="docutils literal"><span class="pre">const</span></tt> copied C++ objects.</p>
+<p>The <tt class="docutils literal"><span class="pre">block_byref</span></tt> data structure similarly requires copy/dispose helpers for
+block variables, <tt class="docutils literal"><span class="pre">__attribute__((NSObject))</span></tt> variables, or C++ <tt class="docutils literal"><span class="pre">const</span></tt>
+copied objects with constructor/destructors, and again the (1<<26) bit is set
+and functions are generated in the same manner.</p>
+<p>Under ObjC we allow <tt class="docutils literal"><span class="pre">__weak</span></tt> as an attribute on <tt class="docutils literal"><span class="pre">__block</span></tt> variables, and
+this causes the addition of <tt class="docutils literal"><span class="pre">BLOCK_FIELD_IS_WEAK</span></tt> orred onto the
+<tt class="docutils literal"><span class="pre">BLOCK_FIELD_IS_BYREF</span></tt> flag when copying the <tt class="docutils literal"><span class="pre">block_byref</span></tt> structure in the
+<tt class="docutils literal"><span class="pre">Block</span></tt> copy helper, and onto the <tt class="docutils literal"><span class="pre">BLOCK_FIELD_<appropo></span></tt> field within the
+<tt class="docutils literal"><span class="pre">block_byref</span></tt> copy/dispose helper calls.</p>
+<p>The prototypes, and summary, of the helper functions are:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="cm">/* Certain field types require runtime assistance when being copied to the</span>
+<span class="cm"> heap. The following function is used to copy fields of types: blocks,</span>
+<span class="cm"> pointers to byref structures, and objects (including</span>
+<span class="cm"> __attribute__((NSObject)) pointers. BLOCK_FIELD_IS_WEAK is orthogonal to</span>
+<span class="cm"> the other choices which are mutually exclusive. Only in a Block copy</span>
+<span class="cm"> helper will one see BLOCK_FIELD_IS_BYREF.</span>
+<span class="cm">*/</span>
+<span class="kt">void</span> <span class="nf">_Block_object_assign</span><span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="n">destAddr</span><span class="p">,</span> <span class="k">const</span> <span class="kt">void</span> <span class="o">*</span><span class="n">object</span><span class="p">,</span> <span class="k">const</span> <span class="kt">int</span> <span class="n">flags</span><span class="p">);</span>
+
+<span class="cm">/* Similarly a compiler generated dispose helper needs to call back for each</span>
+<span class="cm"> field of the byref data structure. (Currently the implementation only</span>
+<span class="cm"> packs one field into the byref structure but in principle there could be</span>
+<span class="cm"> more). The same flags used in the copy helper should be used for each</span>
+<span class="cm"> call generated to this function:</span>
+<span class="cm">*/</span>
+<span class="kt">void</span> <span class="nf">_Block_object_dispose</span><span class="p">(</span><span class="k">const</span> <span class="kt">void</span> <span class="o">*</span><span class="n">object</span><span class="p">,</span> <span class="k">const</span> <span class="kt">int</span> <span class="n">flags</span><span class="p">);</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="copyright">
+<h2><a class="toc-backref" href="#id20">Copyright</a><a class="headerlink" href="#copyright" title="Permalink to this headline">¶</a></h2>
+<p>Copyright 2008-2010 Apple, Inc.
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the “Software”), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:</p>
+<p>The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.</p>
+<p>THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="BlockLanguageSpec.html">Language Specification for Blocks</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="AutomaticReferenceCounting.html">Objective-C Automatic Reference Counting (ARC)</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
Added: www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.txt
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.txt?rev=238136&view=auto
==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.txt (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/Block-ABI-Apple.txt Mon May 25 08:58:01 2015
@@ -0,0 +1 @@
+*NOTE* This document has moved to http://clang.llvm.org/docs/Block-ABI-Apple.html.
Added: www-releases/trunk/3.6.1/tools/clang/docs/BlockLanguageSpec.html
URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.6.1/tools/clang/docs/BlockLanguageSpec.html?rev=238136&view=auto
==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/BlockLanguageSpec.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/BlockLanguageSpec.html Mon May 25 08:58:01 2015
@@ -0,0 +1,376 @@
+
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+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Language Specification for Blocks</span></h2>
+ </div>
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+
+ <p>
+ « <a href="ObjectiveCLiterals.html">Objective-C Literals</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="Block-ABI-Apple.html">Block Implementation Specification</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="language-specification-for-blocks">
+<h1>Language Specification for Blocks<a class="headerlink" href="#language-specification-for-blocks" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#revisions" id="id1">Revisions</a></li>
+<li><a class="reference internal" href="#overview" id="id2">Overview</a></li>
+<li><a class="reference internal" href="#the-block-type" id="id3">The Block Type</a></li>
+<li><a class="reference internal" href="#block-variable-declarations" id="id4">Block Variable Declarations</a></li>
+<li><a class="reference internal" href="#block-literal-expressions" id="id5">Block Literal Expressions</a></li>
+<li><a class="reference internal" href="#the-invoke-operator" id="id6">The Invoke Operator</a></li>
+<li><a class="reference internal" href="#the-copy-and-release-operations" id="id7">The Copy and Release Operations</a></li>
+<li><a class="reference internal" href="#the-block-storage-qualifier" id="id8">The <tt class="docutils literal"><span class="pre">__block</span></tt> Storage Qualifier</a></li>
+<li><a class="reference internal" href="#control-flow" id="id9">Control Flow</a></li>
+<li><a class="reference internal" href="#objective-c-extensions" id="id10">Objective-C Extensions</a></li>
+<li><a class="reference internal" href="#c-extensions" id="id11">C++ Extensions</a></li>
+</ul>
+</div>
+<div class="section" id="revisions">
+<h2><a class="toc-backref" href="#id1">Revisions</a><a class="headerlink" href="#revisions" title="Permalink to this headline">¶</a></h2>
+<ul class="simple">
+<li>2008/2/25 — created</li>
+<li>2008/7/28 — revised, <tt class="docutils literal"><span class="pre">__block</span></tt> syntax</li>
+<li>2008/8/13 — revised, Block globals</li>
+<li>2008/8/21 — revised, C++ elaboration</li>
+<li>2008/11/1 — revised, <tt class="docutils literal"><span class="pre">__weak</span></tt> support</li>
+<li>2009/1/12 — revised, explicit return types</li>
+<li>2009/2/10 — revised, <tt class="docutils literal"><span class="pre">__block</span></tt> objects need retain</li>
+</ul>
+</div>
+<div class="section" id="overview">
+<h2><a class="toc-backref" href="#id2">Overview</a><a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
+<p>A new derived type is introduced to C and, by extension, Objective-C,
+C++, and Objective-C++</p>
+</div>
+<div class="section" id="the-block-type">
+<h2><a class="toc-backref" href="#id3">The Block Type</a><a class="headerlink" href="#the-block-type" title="Permalink to this headline">¶</a></h2>
+<p>Like function types, the <span class="block-term">Block type</span> is a pair consisting
+of a result value type and a list of parameter types very similar to a
+function type. Blocks are intended to be used much like functions with
+the key distinction being that in addition to executable code they
+also contain various variable bindings to automatic (stack) or managed
+(heap) memory.</p>
+<p>The abstract declarator,</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="p">(</span><span class="o">^</span><span class="p">)(</span><span class="kt">char</span><span class="p">,</span> <span class="kt">float</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>describes a reference to a Block that, when invoked, takes two
+parameters, the first of type char and the second of type float, and
+returns a value of type int. The Block referenced is of opaque data
+that may reside in automatic (stack) memory, global memory, or heap
+memory.</p>
+</div>
+<div class="section" id="block-variable-declarations">
+<h2><a class="toc-backref" href="#id4">Block Variable Declarations</a><a class="headerlink" href="#block-variable-declarations" title="Permalink to this headline">¶</a></h2>
+<p>A <span class="block-term">variable with Block type</span> is declared using function
+pointer style notation substituting <tt class="docutils literal"><span class="pre">^</span></tt> for <tt class="docutils literal"><span class="pre">*</span></tt>. The following are
+valid Block variable declarations:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">blockReturningVoidWithVoidArgument</span><span class="p">)(</span><span class="kt">void</span><span class="p">);</span>
+<span class="kt">int</span> <span class="p">(</span><span class="o">^</span><span class="n">blockReturningIntWithIntAndCharArguments</span><span class="p">)(</span><span class="kt">int</span><span class="p">,</span> <span class="kt">char</span><span class="p">);</span>
+<span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">arrayOfTenBlocksReturningVoidWithIntArgument</span><span class="p">[</span><span class="mi">10</span><span class="p">])(</span><span class="kt">int</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Variadic <tt class="docutils literal"><span class="pre">...</span></tt> arguments are supported. [variadic.c] A Block that
+takes no arguments must specify void in the argument list [voidarg.c].
+An empty parameter list does not represent, as K&R provide, an
+unspecified argument list. Note: both gcc and clang support K&R style
+as a convenience.</p>
+<p>A Block reference may be cast to a pointer of arbitrary type and vice
+versa. [cast.c] A Block reference may not be dereferenced via the
+pointer dereference operator <tt class="docutils literal"><span class="pre">*</span></tt>, and thus a Block’s size may not be
+computed at compile time. [sizeof.c]</p>
+</div>
+<div class="section" id="block-literal-expressions">
+<h2><a class="toc-backref" href="#id5">Block Literal Expressions</a><a class="headerlink" href="#block-literal-expressions" title="Permalink to this headline">¶</a></h2>
+<p>A <span class="block-term">Block literal expression</span> produces a reference to a
+Block. It is introduced by the use of the <tt class="docutils literal"><span class="pre">^</span></tt> token as a unary
+operator.</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">Block_literal_expression</span> <span class="o">::=</span> <span class="o">^</span> <span class="n">block_decl</span> <span class="n">compound_statement_body</span>
+<span class="n">block_decl</span> <span class="o">::=</span>
+<span class="n">block_decl</span> <span class="o">::=</span> <span class="n">parameter_list</span>
+<span class="n">block_decl</span> <span class="o">::=</span> <span class="n">type_expression</span>
+</pre></div>
+</div>
+<p>where type expression is extended to allow <tt class="docutils literal"><span class="pre">^</span></tt> as a Block reference
+(pointer) where <tt class="docutils literal"><span class="pre">*</span></tt> is allowed as a function reference (pointer).</p>
+<p>The following Block literal:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="o">^</span> <span class="kt">void</span> <span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="p">{</span> <span class="n">printf</span><span class="p">(</span><span class="s">"hello world</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>produces a reference to a Block with no arguments with no return value.</p>
+<p>The return type is optional and is inferred from the return
+statements. If the return statements return a value, they all must
+return a value of the same type. If there is no value returned the
+inferred type of the Block is void; otherwise it is the type of the
+return statement value.</p>
+<p>If the return type is omitted and the argument list is <tt class="docutils literal"><span class="pre">(</span> <span class="pre">void</span> <span class="pre">)</span></tt>,
+the <tt class="docutils literal"><span class="pre">(</span> <span class="pre">void</span> <span class="pre">)</span></tt> argument list may also be omitted.</p>
+<p>So:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="o">^</span> <span class="p">(</span> <span class="kt">void</span> <span class="p">)</span> <span class="p">{</span> <span class="n">printf</span><span class="p">(</span><span class="s">"hello world</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="o">^</span> <span class="p">{</span> <span class="n">printf</span><span class="p">(</span><span class="s">"hello world</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>are exactly equivalent constructs for the same expression.</p>
+<p>The type_expression extends C expression parsing to accommodate Block
+reference declarations as it accommodates function pointer
+declarations.</p>
+<p>Given:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">typedef</span> <span class="nf">int</span> <span class="p">(</span><span class="o">*</span><span class="n">pointerToFunctionThatReturnsIntWithCharArg</span><span class="p">)(</span><span class="kt">char</span><span class="p">);</span>
+<span class="n">pointerToFunctionThatReturnsIntWithCharArg</span> <span class="n">functionPointer</span><span class="p">;</span>
+<span class="o">^</span> <span class="n">pointerToFunctionThatReturnsIntWithCharArg</span> <span class="p">(</span><span class="kt">float</span> <span class="n">x</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">functionPointer</span><span class="p">;</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>and:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="o">^</span> <span class="kt">int</span> <span class="p">((</span><span class="o">*</span><span class="p">)(</span><span class="kt">float</span> <span class="n">x</span><span class="p">))(</span><span class="kt">char</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">functionPointer</span><span class="p">;</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>are equivalent expressions, as is:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="o">^</span><span class="p">(</span><span class="kt">float</span> <span class="n">x</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">functionPointer</span><span class="p">;</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>[returnfunctionptr.c]</p>
+<p>The compound statement body establishes a new lexical scope within
+that of its parent. Variables used within the scope of the compound
+statement are bound to the Block in the normal manner with the
+exception of those in automatic (stack) storage. Thus one may access
+functions and global variables as one would expect, as well as static
+local variables. [testme]</p>
+<p>Local automatic (stack) variables referenced within the compound
+statement of a Block are imported and captured by the Block as const
+copies. The capture (binding) is performed at the time of the Block
+literal expression evaluation.</p>
+<p>The compiler is not required to capture a variable if it can prove
+that no references to the variable will actually be evaluated.
+Programmers can force a variable to be captured by referencing it in a
+statement at the beginning of the Block, like so:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="n">foo</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>This matters when capturing the variable has side-effects, as it can
+in Objective-C or C++.</p>
+<p>The lifetime of variables declared in a Block is that of a function;
+each activation frame contains a new copy of variables declared within
+the local scope of the Block. Such variable declarations should be
+allowed anywhere [testme] rather than only when C99 parsing is
+requested, including for statements. [testme]</p>
+<p>Block literal expressions may occur within Block literal expressions
+(nest) and all variables captured by any nested blocks are implicitly
+also captured in the scopes of their enclosing Blocks.</p>
+<p>A Block literal expression may be used as the initialization value for
+Block variables at global or local static scope.</p>
+</div>
+<div class="section" id="the-invoke-operator">
+<h2><a class="toc-backref" href="#id6">The Invoke Operator</a><a class="headerlink" href="#the-invoke-operator" title="Permalink to this headline">¶</a></h2>
+<p>Blocks are <span class="block-term">invoked</span> using function call syntax with a
+list of expression parameters of types corresponding to the
+declaration and returning a result type also according to the
+declaration. Given:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="p">(</span><span class="o">^</span><span class="n">x</span><span class="p">)(</span><span class="kt">char</span><span class="p">);</span>
+<span class="kt">void</span> <span class="p">(</span><span class="o">^</span><span class="n">z</span><span class="p">)(</span><span class="kt">void</span><span class="p">);</span>
+<span class="kt">int</span> <span class="p">(</span><span class="o">^</span><span class="p">(</span><span class="o">*</span><span class="n">y</span><span class="p">))(</span><span class="kt">char</span><span class="p">)</span> <span class="o">=</span> <span class="o">&</span><span class="n">x</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>the following are all legal Block invocations:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">x</span><span class="p">(</span><span class="sc">'a'</span><span class="p">);</span>
+<span class="p">(</span><span class="o">*</span><span class="n">y</span><span class="p">)(</span><span class="sc">'a'</span><span class="p">);</span>
+<span class="p">(</span><span class="nb">true</span> <span class="o">?</span> <span class="n">x</span> <span class="o">:</span> <span class="o">*</span><span class="n">y</span><span class="p">)(</span><span class="sc">'a'</span><span class="p">)</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="the-copy-and-release-operations">
+<h2><a class="toc-backref" href="#id7">The Copy and Release Operations</a><a class="headerlink" href="#the-copy-and-release-operations" title="Permalink to this headline">¶</a></h2>
+<p>The compiler and runtime provide <span class="block-term">copy</span> and
+<span class="block-term">release</span> operations for Block references that create and,
+in matched use, release allocated storage for referenced Blocks.</p>
+<p>The copy operation <tt class="docutils literal"><span class="pre">Block_copy()</span></tt> is styled as a function that takes
+an arbitrary Block reference and returns a Block reference of the same
+type. The release operation, <tt class="docutils literal"><span class="pre">Block_release()</span></tt>, is styled as a
+function that takes an arbitrary Block reference and, if dynamically
+matched to a Block copy operation, allows recovery of the referenced
+allocated memory.</p>
+</div>
+<div class="section" id="the-block-storage-qualifier">
+<h2><a class="toc-backref" href="#id8">The <tt class="docutils literal"><span class="pre">__block</span></tt> Storage Qualifier</a><a class="headerlink" href="#the-block-storage-qualifier" title="Permalink to this headline">¶</a></h2>
+<p>In addition to the new Block type we also introduce a new storage
+qualifier, <span class="block-term">__block</span>, for local variables. [testme: a
+__block declaration within a block literal] The <tt class="docutils literal"><span class="pre">__block</span></tt> storage
+qualifier is mutually exclusive to the existing local storage
+qualifiers auto, register, and static. [testme] Variables qualified by
+<tt class="docutils literal"><span class="pre">__block</span></tt> act as if they were in allocated storage and this storage
+is automatically recovered after last use of said variable. An
+implementation may choose an optimization where the storage is
+initially automatic and only “moved” to allocated (heap) storage upon
+a Block_copy of a referencing Block. Such variables may be mutated as
+normal variables are.</p>
+<p>In the case where a <tt class="docutils literal"><span class="pre">__block</span></tt> variable is a Block one must assume
+that the <tt class="docutils literal"><span class="pre">__block</span></tt> variable resides in allocated storage and as such
+is assumed to reference a Block that is also in allocated storage
+(that it is the result of a <tt class="docutils literal"><span class="pre">Block_copy</span></tt> operation). Despite this
+there is no provision to do a <tt class="docutils literal"><span class="pre">Block_copy</span></tt> or a <tt class="docutils literal"><span class="pre">Block_release</span></tt> if
+an implementation provides initial automatic storage for Blocks. This
+is due to the inherent race condition of potentially several threads
+trying to update the shared variable and the need for synchronization
+around disposing of older values and copying new ones. Such
+synchronization is beyond the scope of this language specification.</p>
+</div>
+<div class="section" id="control-flow">
+<h2><a class="toc-backref" href="#id9">Control Flow</a><a class="headerlink" href="#control-flow" title="Permalink to this headline">¶</a></h2>
+<p>The compound statement of a Block is treated much like a function body
+with respect to control flow in that goto, break, and continue do not
+escape the Block. Exceptions are treated <em>normally</em> in that when
+thrown they pop stack frames until a catch clause is found.</p>
+</div>
+<div class="section" id="objective-c-extensions">
+<h2><a class="toc-backref" href="#id10">Objective-C Extensions</a><a class="headerlink" href="#objective-c-extensions" title="Permalink to this headline">¶</a></h2>
+<p>Objective-C extends the definition of a Block reference type to be
+that also of id. A variable or expression of Block type may be
+messaged or used as a parameter wherever an id may be. The converse is
+also true. Block references may thus appear as properties and are
+subject to the assign, retain, and copy attribute logic that is
+reserved for objects.</p>
+<p>All Blocks are constructed to be Objective-C objects regardless of
+whether the Objective-C runtime is operational in the program or
+not. Blocks using automatic (stack) memory are objects and may be
+messaged, although they may not be assigned into <tt class="docutils literal"><span class="pre">__weak</span></tt> locations
+if garbage collection is enabled.</p>
+<p>Within a Block literal expression within a method definition
+references to instance variables are also imported into the lexical
+scope of the compound statement. These variables are implicitly
+qualified as references from self, and so self is imported as a const
+copy. The net effect is that instance variables can be mutated.</p>
+<p>The <span class="block-term">Block_copy</span> operator retains all objects held in
+variables of automatic storage referenced within the Block expression
+(or form strong references if running under garbage collection).
+Object variables of <tt class="docutils literal"><span class="pre">__block</span></tt> storage type are assumed to hold
+normal pointers with no provision for retain and release messages.</p>
+<p>Foundation defines (and supplies) <tt class="docutils literal"><span class="pre">-copy</span></tt> and <tt class="docutils literal"><span class="pre">-release</span></tt> methods for
+Blocks.</p>
+<p>In the Objective-C and Objective-C++ languages, we allow the
+<tt class="docutils literal"><span class="pre">__weak</span></tt> specifier for <tt class="docutils literal"><span class="pre">__block</span></tt> variables of object type. If
+garbage collection is not enabled, this qualifier causes these
+variables to be kept without retain messages being sent. This
+knowingly leads to dangling pointers if the Block (or a copy) outlives
+the lifetime of this object.</p>
+<p>In garbage collected environments, the <tt class="docutils literal"><span class="pre">__weak</span></tt> variable is set to
+nil when the object it references is collected, as long as the
+<tt class="docutils literal"><span class="pre">__block</span></tt> variable resides in the heap (either by default or via
+<tt class="docutils literal"><span class="pre">Block_copy()</span></tt>). The initial Apple implementation does in fact
+start <tt class="docutils literal"><span class="pre">__block</span></tt> variables on the stack and migrate them to the heap
+only as a result of a <tt class="docutils literal"><span class="pre">Block_copy()</span></tt> operation.</p>
+<p>It is a runtime error to attempt to assign a reference to a
+stack-based Block into any storage marked <tt class="docutils literal"><span class="pre">__weak</span></tt>, including
+<tt class="docutils literal"><span class="pre">__weak</span></tt> <tt class="docutils literal"><span class="pre">__block</span></tt> variables.</p>
+</div>
+<div class="section" id="c-extensions">
+<h2><a class="toc-backref" href="#id11">C++ Extensions</a><a class="headerlink" href="#c-extensions" title="Permalink to this headline">¶</a></h2>
+<p>Block literal expressions within functions are extended to allow const
+use of C++ objects, pointers, or references held in automatic storage.</p>
+<p>As usual, within the block, references to captured variables become
+const-qualified, as if they were references to members of a const
+object. Note that this does not change the type of a variable of
+reference type.</p>
+<p>For example, given a class Foo:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="n">Foo</span> <span class="n">foo</span><span class="p">;</span>
+<span class="n">Foo</span> <span class="o">&</span><span class="n">fooRef</span> <span class="o">=</span> <span class="n">foo</span><span class="p">;</span>
+<span class="n">Foo</span> <span class="o">*</span><span class="n">fooPtr</span> <span class="o">=</span> <span class="o">&</span><span class="n">foo</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>A Block that referenced these variables would import the variables as
+const variations:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">const</span> <span class="n">Foo</span> <span class="n">block_foo</span> <span class="o">=</span> <span class="n">foo</span><span class="p">;</span>
+<span class="n">Foo</span> <span class="o">&</span><span class="n">block_fooRef</span> <span class="o">=</span> <span class="n">fooRef</span><span class="p">;</span>
+<span class="n">Foo</span> <span class="o">*</span><span class="k">const</span> <span class="n">block_fooPtr</span> <span class="o">=</span> <span class="n">fooPtr</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Captured variables are copied into the Block at the instant of
+evaluating the Block literal expression. They are also copied when
+calling <tt class="docutils literal"><span class="pre">Block_copy()</span></tt> on a Block allocated on the stack. In both
+cases, they are copied as if the variable were const-qualified, and
+it’s an error if there’s no such constructor.</p>
+<p>Captured variables in Blocks on the stack are destroyed when control
+leaves the compound statement that contains the Block literal
+expression. Captured variables in Blocks on the heap are destroyed
+when the reference count of the Block drops to zero.</p>
+<p>Variables declared as residing in <tt class="docutils literal"><span class="pre">__block</span></tt> storage may be initially
+allocated in the heap or may first appear on the stack and be copied
+to the heap as a result of a <tt class="docutils literal"><span class="pre">Block_copy()</span></tt> operation. When copied
+from the stack, <tt class="docutils literal"><span class="pre">__block</span></tt> variables are copied using their normal
+qualification (i.e. without adding const). In C++11, <tt class="docutils literal"><span class="pre">__block</span></tt>
+variables are copied as x-values if that is possible, then as l-values
+if not; if both fail, it’s an error. The destructor for any initial
+stack-based version is called at the variable’s normal end of scope.</p>
+<p>References to <tt class="docutils literal"><span class="pre">this</span></tt>, as well as references to non-static members of
+any enclosing class, are evaluated by capturing <tt class="docutils literal"><span class="pre">this</span></tt> just like a
+normal variable of C pointer type.</p>
+<p>Member variables that are Blocks may not be overloaded by the types of
+their arguments.</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ObjectiveCLiterals.html">Objective-C Literals</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="Block-ABI-Apple.html">Block Implementation Specification</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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--- www-releases/trunk/3.6.1/tools/clang/docs/ClangCheck.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/ClangCheck.html Mon May 25 08:58:01 2015
@@ -0,0 +1,107 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>ClangCheck — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
+ <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="ClangFormat" href="ClangFormat.html" />
+ <link rel="prev" title="Overview" href="ClangTools.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>ClangCheck</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="ClangTools.html">Overview</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangFormat.html">ClangFormat</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="clangcheck">
+<h1>ClangCheck<a class="headerlink" href="#clangcheck" title="Permalink to this headline">¶</a></h1>
+<p><cite>ClangCheck</cite> is a small wrapper around <a class="reference internal" href="LibTooling.html"><em>LibTooling</em></a> which can be used to
+do basic error checking and AST dumping.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> cat <span class="s"><<EOF > snippet.cc</span>
+<span class="gp">></span><span class="s"> void f() {</span>
+<span class="gp">></span><span class="s"> int a = 0</span>
+<span class="gp">></span><span class="s"> }</span>
+<span class="gp">></span><span class="s"> EOF</span>
+<span class="gp">$</span> ~/clang/build/bin/clang-check snippet.cc -ast-dump --
+<span class="go">Processing: /Users/danieljasper/clang/llvm/tools/clang/docs/snippet.cc.</span>
+<span class="go">/Users/danieljasper/clang/llvm/tools/clang/docs/snippet.cc:2:12: error: expected ';' at end of</span>
+<span class="go"> declaration</span>
+<span class="go"> int a = 0</span>
+<span class="go"> ^</span>
+<span class="go"> ;</span>
+<span class="go">(TranslationUnitDecl 0x7ff3a3029ed0 <<invalid sloc>></span>
+<span class="go"> (TypedefDecl 0x7ff3a302a410 <<invalid sloc>> __int128_t '__int128')</span>
+<span class="go"> (TypedefDecl 0x7ff3a302a470 <<invalid sloc>> __uint128_t 'unsigned __int128')</span>
+<span class="go"> (TypedefDecl 0x7ff3a302a830 <<invalid sloc>> __builtin_va_list '__va_list_tag [1]')</span>
+<span class="go"> (FunctionDecl 0x7ff3a302a8d0 </Users/danieljasper/clang/llvm/tools/clang/docs/snippet.cc:1:1, line:3:1> f 'void (void)'</span>
+<span class="go"> (CompoundStmt 0x7ff3a302aa10 <line:1:10, line:3:1></span>
+<span class="go"> (DeclStmt 0x7ff3a302a9f8 <line:2:3, line:3:1></span>
+<span class="go"> (VarDecl 0x7ff3a302a980 <line:2:3, col:11> a 'int'</span>
+<span class="go"> (IntegerLiteral 0x7ff3a302a9d8 <col:11> 'int' 0))))))</span>
+<span class="go">1 error generated.</span>
+<span class="go">Error while processing snippet.cc.</span>
+</pre></div>
+</div>
+<p>The ‘–’ at the end is important as it prevents <cite>clang-check</cite> from search for a
+compilation database. For more information on how to setup and use <cite>clang-check</cite>
+in a project, see <a class="reference internal" href="HowToSetupToolingForLLVM.html"><em>How To Setup Clang Tooling For LLVM</em></a>.</p>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ClangTools.html">Overview</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangFormat.html">ClangFormat</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/ClangFormat.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/ClangFormat.html Mon May 25 08:58:01 2015
@@ -0,0 +1,227 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>ClangFormat — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
+ <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="Clang-Format Style Options" href="ClangFormatStyleOptions.html" />
+ <link rel="prev" title="ClangCheck" href="ClangCheck.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>ClangFormat</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="ClangCheck.html">ClangCheck</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangFormatStyleOptions.html">Clang-Format Style Options</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="clangformat">
+<h1>ClangFormat<a class="headerlink" href="#clangformat" title="Permalink to this headline">¶</a></h1>
+<p><cite>ClangFormat</cite> describes a set of tools that are built on top of
+<a class="reference internal" href="LibFormat.html"><em>LibFormat</em></a>. It can support your workflow in a variety of ways including a
+standalone tool and editor integrations.</p>
+<div class="section" id="standalone-tool">
+<h2>Standalone Tool<a class="headerlink" href="#standalone-tool" title="Permalink to this headline">¶</a></h2>
+<p><strong class="program">clang-format</strong> is located in <cite>clang/tools/clang-format</cite> and can be used
+to format C/C++/Obj-C code.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang-format -help
+<span class="go">OVERVIEW: A tool to format C/C++/Obj-C code.</span>
+
+<span class="go">If no arguments are specified, it formats the code from standard input</span>
+<span class="go">and writes the result to the standard output.</span>
+<span class="go">If <file>s are given, it reformats the files. If -i is specified</span>
+<span class="go">together with <file>s, the files are edited in-place. Otherwise, the</span>
+<span class="go">result is written to the standard output.</span>
+
+<span class="go">USAGE: clang-format [options] [<file> ...]</span>
+
+<span class="go">OPTIONS:</span>
+
+<span class="go">Clang-format options:</span>
+
+<span class="go"> -cursor=<uint> - The position of the cursor when invoking</span>
+<span class="go"> clang-format from an editor integration</span>
+<span class="go"> -dump-config - Dump configuration options to stdout and exit.</span>
+<span class="go"> Can be used with -style option.</span>
+<span class="go"> -i - Inplace edit <file>s, if specified.</span>
+<span class="go"> -length=<uint> - Format a range of this length (in bytes).</span>
+<span class="go"> Multiple ranges can be formatted by specifying</span>
+<span class="go"> several -offset and -length pairs.</span>
+<span class="go"> When only a single -offset is specified without</span>
+<span class="go"> -length, clang-format will format up to the end</span>
+<span class="go"> of the file.</span>
+<span class="go"> Can only be used with one input file.</span>
+<span class="go"> -lines=<string> - <start line>:<end line> - format a range of</span>
+<span class="go"> lines (both 1-based).</span>
+<span class="go"> Multiple ranges can be formatted by specifying</span>
+<span class="go"> several -lines arguments.</span>
+<span class="go"> Can't be used with -offset and -length.</span>
+<span class="go"> Can only be used with one input file.</span>
+<span class="go"> -offset=<uint> - Format a range starting at this byte offset.</span>
+<span class="go"> Multiple ranges can be formatted by specifying</span>
+<span class="go"> several -offset and -length pairs.</span>
+<span class="go"> Can only be used with one input file.</span>
+<span class="go"> -output-replacements-xml - Output replacements as XML.</span>
+<span class="go"> -style=<string> - Coding style, currently supports:</span>
+<span class="go"> LLVM, Google, Chromium, Mozilla, WebKit.</span>
+<span class="go"> Use -style=file to load style configuration from</span>
+<span class="go"> .clang-format file located in one of the parent</span>
+<span class="go"> directories of the source file (or current</span>
+<span class="go"> directory for stdin).</span>
+<span class="go"> Use -style="{key: value, ...}" to set specific</span>
+<span class="go"> parameters, e.g.:</span>
+<span class="go"> -style="{BasedOnStyle: llvm, IndentWidth: 8}"</span>
+
+<span class="go">General options:</span>
+
+<span class="go"> -help - Display available options (-help-hidden for more)</span>
+<span class="go"> -help-list - Display list of available options (-help-list-hidden for more)</span>
+<span class="go"> -version - Display the version of this program</span>
+</pre></div>
+</div>
+<p>When the desired code formatting style is different from the available options,
+the style can be customized using the <tt class="docutils literal"><span class="pre">-style="{key:</span> <span class="pre">value,</span> <span class="pre">...}"</span></tt> option or
+by putting your style configuration in the <tt class="docutils literal"><span class="pre">.clang-format</span></tt> or <tt class="docutils literal"><span class="pre">_clang-format</span></tt>
+file in your project’s directory and using <tt class="docutils literal"><span class="pre">clang-format</span> <span class="pre">-style=file</span></tt>.</p>
+<p>An easy way to create the <tt class="docutils literal"><span class="pre">.clang-format</span></tt> file is:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">clang-format -style=llvm -dump-config > .clang-format</span>
+</pre></div>
+</div>
+<p>Available style options are described in <a class="reference internal" href="ClangFormatStyleOptions.html"><em>Clang-Format Style Options</em></a>.</p>
+</div>
+<div class="section" id="vim-integration">
+<h2>Vim Integration<a class="headerlink" href="#vim-integration" title="Permalink to this headline">¶</a></h2>
+<p>There is an integration for <strong class="program">vim</strong> which lets you run the
+<strong class="program">clang-format</strong> standalone tool on your current buffer, optionally
+selecting regions to reformat. The integration has the form of a <cite>python</cite>-file
+which can be found under <cite>clang/tools/clang-format/clang-format.py</cite>.</p>
+<p>This can be integrated by adding the following to your <cite>.vimrc</cite>:</p>
+<div class="highlight-vim"><div class="highlight"><pre>map <span class="p"><</span>C<span class="p">-</span>K<span class="p">></span> :<span class="k">pyf</span> <span class="p"><</span><span class="nb">path</span><span class="p">-</span><span class="k">to</span><span class="p">-</span>this<span class="p">-</span><span class="k">file</span><span class="p">></span>/clang<span class="p">-</span>format.<span class="k">py</span><span class="p"><</span><span class="k">cr</span><span class="p">></span>
+imap <span class="p"><</span>C<span class="p">-</span>K<span class="p">></span> <span class="p"><</span><span class="k">c</span><span class="p">-</span><span class="k">o</span><span class="p">></span>:<span class="k">pyf</span> <span class="p"><</span><span class="nb">path</span><span class="p">-</span><span class="k">to</span><span class="p">-</span>this<span class="p">-</span><span class="k">file</span><span class="p">></span>/clang<span class="p">-</span>format.<span class="k">py</span><span class="p"><</span><span class="k">cr</span><span class="p">></span>
+</pre></div>
+</div>
+<p>The first line enables <strong class="program">clang-format</strong> for NORMAL and VISUAL mode, the
+second line adds support for INSERT mode. Change “C-K” to another binding if
+you need <strong class="program">clang-format</strong> on a different key (C-K stands for Ctrl+k).</p>
+<p>With this integration you can press the bound key and clang-format will
+format the current line in NORMAL and INSERT mode or the selected region in
+VISUAL mode. The line or region is extended to the next bigger syntactic
+entity.</p>
+<p>It operates on the current, potentially unsaved buffer and does not create
+or save any files. To revert a formatting, just undo.</p>
+</div>
+<div class="section" id="emacs-integration">
+<h2>Emacs Integration<a class="headerlink" href="#emacs-integration" title="Permalink to this headline">¶</a></h2>
+<p>Similar to the integration for <strong class="program">vim</strong>, there is an integration for
+<strong class="program">emacs</strong>. It can be found at <cite>clang/tools/clang-format/clang-format.el</cite>
+and used by adding this to your <cite>.emacs</cite>:</p>
+<div class="highlight-common-lisp"><div class="highlight"><pre><span class="p">(</span><span class="nb">load</span> <span class="s">"<path-to-clang>/tools/clang-format/clang-format.el"</span><span class="p">)</span>
+<span class="p">(</span><span class="nv">global-set-key</span> <span class="nv">[C-M-tab]</span> <span class="ss">'clang-format-region</span><span class="p">)</span>
+</pre></div>
+</div>
+<p>This binds the function <cite>clang-format-region</cite> to C-M-tab, which then formats the
+current line or selected region.</p>
+</div>
+<div class="section" id="bbedit-integration">
+<h2>BBEdit Integration<a class="headerlink" href="#bbedit-integration" title="Permalink to this headline">¶</a></h2>
+<p><strong class="program">clang-format</strong> cannot be used as a text filter with BBEdit, but works
+well via a script. The AppleScript to do this integration can be found at
+<cite>clang/tools/clang-format/clang-format-bbedit.applescript</cite>; place a copy in
+<cite>~/Library/Application Support/BBEdit/Scripts</cite>, and edit the path within it to
+point to your local copy of <strong class="program">clang-format</strong>.</p>
+<p>With this integration you can select the script from the Script menu and
+<strong class="program">clang-format</strong> will format the selection. Note that you can rename the
+menu item by renaming the script, and can assign the menu item a keyboard
+shortcut in the BBEdit preferences, under Menus & Shortcuts.</p>
+</div>
+<div class="section" id="visual-studio-integration">
+<h2>Visual Studio Integration<a class="headerlink" href="#visual-studio-integration" title="Permalink to this headline">¶</a></h2>
+<p>Download the latest Visual Studio extension from the <a class="reference external" href="http://llvm.org/builds/">alpha build site</a>. The default key-binding is Ctrl-R,Ctrl-F.</p>
+</div>
+<div class="section" id="script-for-patch-reformatting">
+<h2>Script for patch reformatting<a class="headerlink" href="#script-for-patch-reformatting" title="Permalink to this headline">¶</a></h2>
+<p>The python script <cite>clang/tools/clang-format-diff.py</cite> parses the output of
+a unified diff and reformats all contained lines with <strong class="program">clang-format</strong>.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">usage: clang-format-diff.py [-h] [-i] [-p NUM] [-regex PATTERN] [-style STYLE]</span>
+
+<span class="go">Reformat changed lines in diff. Without -i option just output the diff that</span>
+<span class="go">would be introduced.</span>
+
+<span class="go">optional arguments:</span>
+<span class="go"> -h, --help show this help message and exit</span>
+<span class="go"> -i apply edits to files instead of displaying a diff</span>
+<span class="go"> -p NUM strip the smallest prefix containing P slashes</span>
+<span class="go"> -regex PATTERN custom pattern selecting file paths to reformat</span>
+<span class="go"> -style STYLE formatting style to apply (LLVM, Google, Chromium, Mozilla,</span>
+<span class="go"> WebKit)</span>
+</pre></div>
+</div>
+<p>So to reformat all the lines in the latest <strong class="program">git</strong> commit, just do:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">git diff -U0 HEAD^ | clang-format-diff.py -i -p1</span>
+</pre></div>
+</div>
+<p>In an SVN client, you can do:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">svn diff --diff-cmd=diff -x-U0 | clang-format-diff.py -i</span>
+</pre></div>
+</div>
+<p>The <em class="xref std std-option">-U0</em> will create a diff without context lines (the script would format
+those as well).</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ClangCheck.html">ClangCheck</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangFormatStyleOptions.html">Clang-Format Style Options</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/ClangFormatStyleOptions.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/ClangFormatStyleOptions.html Mon May 25 08:58:01 2015
@@ -0,0 +1,577 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>Clang-Format Style Options — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
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+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Clang-Format Style Options</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="ClangFormat.html">ClangFormat</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="InternalsManual.html">“Clang” CFE Internals Manual</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="clang-format-style-options">
+<h1>Clang-Format Style Options<a class="headerlink" href="#clang-format-style-options" title="Permalink to this headline">¶</a></h1>
+<p><a class="reference internal" href=""><em>Clang-Format Style Options</em></a> describes configurable formatting style options
+supported by <a class="reference internal" href="LibFormat.html"><em>LibFormat</em></a> and <a class="reference internal" href="ClangFormat.html"><em>ClangFormat</em></a>.</p>
+<p>When using <strong class="program">clang-format</strong> command line utility or
+<tt class="docutils literal"><span class="pre">clang::format::reformat(...)</span></tt> functions from code, one can either use one of
+the predefined styles (LLVM, Google, Chromium, Mozilla, WebKit) or create a
+custom style by configuring specific style options.</p>
+<div class="section" id="configuring-style-with-clang-format">
+<h2>Configuring Style with clang-format<a class="headerlink" href="#configuring-style-with-clang-format" title="Permalink to this headline">¶</a></h2>
+<p><strong class="program">clang-format</strong> supports two ways to provide custom style options:
+directly specify style configuration in the <tt class="docutils literal"><span class="pre">-style=</span></tt> command line option or
+use <tt class="docutils literal"><span class="pre">-style=file</span></tt> and put style configuration in the <tt class="docutils literal"><span class="pre">.clang-format</span></tt> or
+<tt class="docutils literal"><span class="pre">_clang-format</span></tt> file in the project directory.</p>
+<p>When using <tt class="docutils literal"><span class="pre">-style=file</span></tt>, <strong class="program">clang-format</strong> for each input file will
+try to find the <tt class="docutils literal"><span class="pre">.clang-format</span></tt> file located in the closest parent directory
+of the input file. When the standard input is used, the search is started from
+the current directory.</p>
+<p>The <tt class="docutils literal"><span class="pre">.clang-format</span></tt> file uses YAML format:</p>
+<div class="highlight-yaml"><div class="highlight"><pre><span class="l-Scalar-Plain">key1</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">value1</span>
+<span class="l-Scalar-Plain">key2</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">value2</span>
+<span class="c1"># A comment.</span>
+<span class="nn">...</span>
+</pre></div>
+</div>
+<p>The configuration file can consist of several sections each having different
+<tt class="docutils literal"><span class="pre">Language:</span></tt> parameter denoting the programming language this section of the
+configuration is targeted at. See the description of the <strong>Language</strong> option
+below for the list of supported languages. The first section may have no
+language set, it will set the default style options for all lanugages.
+Configuration sections for specific language will override options set in the
+default section.</p>
+<p>When <strong class="program">clang-format</strong> formats a file, it auto-detects the language using
+the file name. When formatting standard input or a file that doesn’t have the
+extension corresponding to its language, <tt class="docutils literal"><span class="pre">-assume-filename=</span></tt> option can be
+used to override the file name <strong class="program">clang-format</strong> uses to detect the
+language.</p>
+<p>An example of a configuration file for multiple languages:</p>
+<div class="highlight-yaml"><div class="highlight"><pre><span class="nn">---</span>
+<span class="c1"># We'll use defaults from the LLVM style, but with 4 columns indentation.</span>
+<span class="l-Scalar-Plain">BasedOnStyle</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">LLVM</span>
+<span class="l-Scalar-Plain">IndentWidth</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">4</span>
+<span class="nn">---</span>
+<span class="l-Scalar-Plain">Language</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Cpp</span>
+<span class="c1"># Force pointers to the type for C++.</span>
+<span class="l-Scalar-Plain">DerivePointerAlignment</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">false</span>
+<span class="l-Scalar-Plain">PointerAlignment</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Left</span>
+<span class="nn">---</span>
+<span class="l-Scalar-Plain">Language</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">JavaScript</span>
+<span class="c1"># Use 100 columns for JS.</span>
+<span class="l-Scalar-Plain">ColumnLimit</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">100</span>
+<span class="nn">---</span>
+<span class="l-Scalar-Plain">Language</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Proto</span>
+<span class="c1"># Don't format .proto files.</span>
+<span class="l-Scalar-Plain">DisableFormat</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">true</span>
+<span class="nn">...</span>
+</pre></div>
+</div>
+<p>An easy way to get a valid <tt class="docutils literal"><span class="pre">.clang-format</span></tt> file containing all configuration
+options of a certain predefined style is:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">clang-format -style=llvm -dump-config > .clang-format</span>
+</pre></div>
+</div>
+<p>When specifying configuration in the <tt class="docutils literal"><span class="pre">-style=</span></tt> option, the same configuration
+is applied for all input files. The format of the configuration is:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="go">-style='{key1: value1, key2: value2, ...}'</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="disabling-formatting-on-a-piece-of-code">
+<h2>Disabling Formatting on a Piece of Code<a class="headerlink" href="#disabling-formatting-on-a-piece-of-code" title="Permalink to this headline">¶</a></h2>
+<p>Clang-format understands also special comments that switch formatting in a
+delimited range. The code between a comment <tt class="docutils literal"><span class="pre">//</span> <span class="pre">clang-format</span> <span class="pre">off</span></tt> or
+<tt class="docutils literal"><span class="pre">/*</span> <span class="pre">clang-format</span> <span class="pre">off</span> <span class="pre">*/</span></tt> up to a comment <tt class="docutils literal"><span class="pre">//</span> <span class="pre">clang-format</span> <span class="pre">on</span></tt> or
+<tt class="docutils literal"><span class="pre">/*</span> <span class="pre">clang-format</span> <span class="pre">on</span> <span class="pre">*/</span></tt> will not be formatted. The comments themselves
+will be formatted (aligned) normally.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="n">formatted_code</span><span class="p">;</span>
+<span class="c1">// clang-format off</span>
+ <span class="kt">void</span> <span class="n">unformatted_code</span> <span class="p">;</span>
+<span class="c1">// clang-format on</span>
+<span class="kt">void</span> <span class="n">formatted_code_again</span><span class="p">;</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="configuring-style-in-code">
+<h2>Configuring Style in Code<a class="headerlink" href="#configuring-style-in-code" title="Permalink to this headline">¶</a></h2>
+<p>When using <tt class="docutils literal"><span class="pre">clang::format::reformat(...)</span></tt> functions, the format is specified
+by supplying the <a class="reference external" href="http://clang.llvm.org/doxygen/structclang_1_1format_1_1FormatStyle.html">clang::format::FormatStyle</a>
+structure.</p>
+</div>
+<div class="section" id="configurable-format-style-options">
+<h2>Configurable Format Style Options<a class="headerlink" href="#configurable-format-style-options" title="Permalink to this headline">¶</a></h2>
+<p>This section lists the supported style options. Value type is specified for
+each option. For enumeration types possible values are specified both as a C++
+enumeration member (with a prefix, e.g. <tt class="docutils literal"><span class="pre">LS_Auto</span></tt>), and as a value usable in
+the configuration (without a prefix: <tt class="docutils literal"><span class="pre">Auto</span></tt>).</p>
+<dl class="docutils">
+<dt><strong>BasedOnStyle</strong> (<tt class="docutils literal"><span class="pre">string</span></tt>)</dt>
+<dd><p class="first">The style used for all options not specifically set in the configuration.</p>
+<p>This option is supported only in the <strong class="program">clang-format</strong> configuration
+(both within <tt class="docutils literal"><span class="pre">-style='{...}'</span></tt> and the <tt class="docutils literal"><span class="pre">.clang-format</span></tt> file).</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">LLVM</span></tt>
+A style complying with the <a class="reference external" href="http://llvm.org/docs/CodingStandards.html">LLVM coding standards</a></li>
+<li><tt class="docutils literal"><span class="pre">Google</span></tt>
+A style complying with <a class="reference external" href="http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml">Google’s C++ style guide</a></li>
+<li><tt class="docutils literal"><span class="pre">Chromium</span></tt>
+A style complying with <a class="reference external" href="http://www.chromium.org/developers/coding-style">Chromium’s style guide</a></li>
+<li><tt class="docutils literal"><span class="pre">Mozilla</span></tt>
+A style complying with <a class="reference external" href="https://developer.mozilla.org/en-US/docs/Developer_Guide/Coding_Style">Mozilla’s style guide</a></li>
+<li><tt class="docutils literal"><span class="pre">WebKit</span></tt>
+A style complying with <a class="reference external" href="http://www.webkit.org/coding/coding-style.html">WebKit’s style guide</a></li>
+</ul>
+</dd>
+</dl>
+<dl class="docutils">
+<dt><strong>AccessModifierOffset</strong> (<tt class="docutils literal"><span class="pre">int</span></tt>)</dt>
+<dd>The extra indent or outdent of access modifiers, e.g. <tt class="docutils literal"><span class="pre">public:</span></tt>.</dd>
+<dt><strong>AlignAfterOpenBracket</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd><p class="first">If <tt class="docutils literal"><span class="pre">true</span></tt>, horizontally aligns arguments after an open bracket.</p>
+<p class="last">This applies to round brackets (parentheses), angle brackets and square
+brackets. This will result in formattings like
+code
+someLongFunction(argument1,
+argument2);
+endcode</p>
+</dd>
+<dt><strong>AlignEscapedNewlinesLeft</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, aligns escaped newlines as far left as possible.
+Otherwise puts them into the right-most column.</dd>
+<dt><strong>AlignOperands</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, horizontally align operands of binary and ternary
+expressions.</dd>
+<dt><strong>AlignTrailingComments</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, aligns trailing comments.</dd>
+<dt><strong>AllowAllParametersOfDeclarationOnNextLine</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>Allow putting all parameters of a function declaration onto
+the next line even if <tt class="docutils literal"><span class="pre">BinPackParameters</span></tt> is <tt class="docutils literal"><span class="pre">false</span></tt>.</dd>
+<dt><strong>AllowShortBlocksOnASingleLine</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd><p class="first">Allows contracting simple braced statements to a single line.</p>
+<p class="last">E.g., this allows <tt class="docutils literal"><span class="pre">if</span> <span class="pre">(a)</span> <span class="pre">{</span> <span class="pre">return;</span> <span class="pre">}</span></tt> to be put on a single line.</p>
+</dd>
+<dt><strong>AllowShortCaseLabelsOnASingleLine</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, short case labels will be contracted to a single line.</dd>
+<dt><strong>AllowShortFunctionsOnASingleLine</strong> (<tt class="docutils literal"><span class="pre">ShortFunctionStyle</span></tt>)</dt>
+<dd><p class="first">Dependent on the value, <tt class="docutils literal"><span class="pre">int</span> <span class="pre">f()</span> <span class="pre">{</span> <span class="pre">return</span> <span class="pre">0;</span> <span class="pre">}</span></tt> can be put
+on a single line.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">SFS_None</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">None</span></tt>)
+Never merge functions into a single line.</li>
+<li><tt class="docutils literal"><span class="pre">SFS_Inline</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Inline</span></tt>)
+Only merge functions defined inside a class.</li>
+<li><tt class="docutils literal"><span class="pre">SFS_Empty</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Empty</span></tt>)
+Only merge empty functions.</li>
+<li><tt class="docutils literal"><span class="pre">SFS_All</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">All</span></tt>)
+Merge all functions fitting on a single line.</li>
+</ul>
+</dd>
+<dt><strong>AllowShortIfStatementsOnASingleLine</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, <tt class="docutils literal"><span class="pre">if</span> <span class="pre">(a)</span> <span class="pre">return;</span></tt> can be put on a single
+line.</dd>
+<dt><strong>AllowShortLoopsOnASingleLine</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, <tt class="docutils literal"><span class="pre">while</span> <span class="pre">(true)</span> <span class="pre">continue;</span></tt> can be put on a
+single line.</dd>
+<dt><strong>AlwaysBreakAfterDefinitionReturnType</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd><p class="first">If <tt class="docutils literal"><span class="pre">true</span></tt>, always break after function definition return types.</p>
+<p class="last">More truthfully called ‘break before the identifier following the type
+in a function definition’. PenaltyReturnTypeOnItsOwnLine becomes
+irrelevant.</p>
+</dd>
+<dt><strong>AlwaysBreakBeforeMultilineStrings</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, always break before multiline string literals.</dd>
+<dt><strong>AlwaysBreakTemplateDeclarations</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, always break after the <tt class="docutils literal"><span class="pre">template<...></span></tt> of a
+template declaration.</dd>
+<dt><strong>BinPackArguments</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">false</span></tt>, a function call’s arguments will either be all on the
+same line or will have one line each.</dd>
+<dt><strong>BinPackParameters</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">false</span></tt>, a function declaration’s or function definition’s
+parameters will either all be on the same line or will have one line each.</dd>
+<dt><strong>BreakBeforeBinaryOperators</strong> (<tt class="docutils literal"><span class="pre">BinaryOperatorStyle</span></tt>)</dt>
+<dd><p class="first">The way to wrap binary operators.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">BOS_None</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">None</span></tt>)
+Break after operators.</li>
+<li><tt class="docutils literal"><span class="pre">BOS_NonAssignment</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">NonAssignment</span></tt>)
+Break before operators that aren’t assignments.</li>
+<li><tt class="docutils literal"><span class="pre">BOS_All</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">All</span></tt>)
+Break before operators.</li>
+</ul>
+</dd>
+<dt><strong>BreakBeforeBraces</strong> (<tt class="docutils literal"><span class="pre">BraceBreakingStyle</span></tt>)</dt>
+<dd><p class="first">The brace breaking style to use.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">BS_Attach</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Attach</span></tt>)
+Always attach braces to surrounding context.</li>
+<li><tt class="docutils literal"><span class="pre">BS_Linux</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Linux</span></tt>)
+Like <tt class="docutils literal"><span class="pre">Attach</span></tt>, but break before braces on function, namespace and
+class definitions.</li>
+<li><tt class="docutils literal"><span class="pre">BS_Stroustrup</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Stroustrup</span></tt>)
+Like <tt class="docutils literal"><span class="pre">Attach</span></tt>, but break before function definitions, and ‘else’.</li>
+<li><tt class="docutils literal"><span class="pre">BS_Allman</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Allman</span></tt>)
+Always break before braces.</li>
+<li><tt class="docutils literal"><span class="pre">BS_GNU</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">GNU</span></tt>)
+Always break before braces and add an extra level of indentation to
+braces of control statements, not to those of class, function
+or other definitions.</li>
+</ul>
+</dd>
+<dt><strong>BreakBeforeTernaryOperators</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, ternary operators will be placed after line breaks.</dd>
+<dt><strong>BreakConstructorInitializersBeforeComma</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>Always break constructor initializers before commas and align
+the commas with the colon.</dd>
+<dt><strong>ColumnLimit</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd><p class="first">The column limit.</p>
+<p class="last">A column limit of <tt class="docutils literal"><span class="pre">0</span></tt> means that there is no column limit. In this case,
+clang-format will respect the input’s line breaking decisions within
+statements unless they contradict other rules.</p>
+</dd>
+<dt><strong>CommentPragmas</strong> (<tt class="docutils literal"><span class="pre">std::string</span></tt>)</dt>
+<dd>A regular expression that describes comments with special meaning,
+which should not be split into lines or otherwise changed.</dd>
+<dt><strong>ConstructorInitializerAllOnOneLineOrOnePerLine</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If the constructor initializers don’t fit on a line, put each
+initializer on its own line.</dd>
+<dt><strong>ConstructorInitializerIndentWidth</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The number of characters to use for indentation of constructor
+initializer lists.</dd>
+<dt><strong>ContinuationIndentWidth</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>Indent width for line continuations.</dd>
+<dt><strong>Cpp11BracedListStyle</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd><p class="first">If <tt class="docutils literal"><span class="pre">true</span></tt>, format braced lists as best suited for C++11 braced
+lists.</p>
+<p>Important differences:
+- No spaces inside the braced list.
+- No line break before the closing brace.
+- Indentation with the continuation indent, not with the block indent.</p>
+<p class="last">Fundamentally, C++11 braced lists are formatted exactly like function
+calls would be formatted in their place. If the braced list follows a name
+(e.g. a type or variable name), clang-format formats as if the <tt class="docutils literal"><span class="pre">{}</span></tt> were
+the parentheses of a function call with that name. If there is no name,
+a zero-length name is assumed.</p>
+</dd>
+<dt><strong>DerivePointerAlignment</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, analyze the formatted file for the most common
+alignment of & and *. <tt class="docutils literal"><span class="pre">PointerAlignment</span></tt> is then used only as fallback.</dd>
+<dt><strong>DisableFormat</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>Disables formatting at all.</dd>
+<dt><strong>ExperimentalAutoDetectBinPacking</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd><p class="first">If <tt class="docutils literal"><span class="pre">true</span></tt>, clang-format detects whether function calls and
+definitions are formatted with one parameter per line.</p>
+<p>Each call can be bin-packed, one-per-line or inconclusive. If it is
+inconclusive, e.g. completely on one line, but a decision needs to be
+made, clang-format analyzes whether there are other bin-packed cases in
+the input file and act accordingly.</p>
+<p class="last">NOTE: This is an experimental flag, that might go away or be renamed. Do
+not use this in config files, etc. Use at your own risk.</p>
+</dd>
+<dt><strong>ForEachMacros</strong> (<tt class="docutils literal"><span class="pre">std::vector<std::string></span></tt>)</dt>
+<dd><p class="first">A vector of macros that should be interpreted as foreach loops
+instead of as function calls.</p>
+<p>These are expected to be macros of the form:
+code
+FOREACH(<variable-declaration>, ...)
+<loop-body>
+endcode</p>
+<p class="last">For example: BOOST_FOREACH.</p>
+</dd>
+<dt><strong>IndentCaseLabels</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd><p class="first">Indent case labels one level from the switch statement.</p>
+<p class="last">When <tt class="docutils literal"><span class="pre">false</span></tt>, use the same indentation level as for the switch statement.
+Switch statement body is always indented one level more than case labels.</p>
+</dd>
+<dt><strong>IndentWidth</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The number of columns to use for indentation.</dd>
+<dt><strong>IndentWrappedFunctionNames</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>Indent if a function definition or declaration is wrapped after the
+type.</dd>
+<dt><strong>KeepEmptyLinesAtTheStartOfBlocks</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If true, empty lines at the start of blocks are kept.</dd>
+<dt><strong>Language</strong> (<tt class="docutils literal"><span class="pre">LanguageKind</span></tt>)</dt>
+<dd><p class="first">Language, this format style is targeted at.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">LK_None</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">None</span></tt>)
+Do not use.</li>
+<li><tt class="docutils literal"><span class="pre">LK_Cpp</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Cpp</span></tt>)
+Should be used for C, C++, ObjectiveC, ObjectiveC++.</li>
+<li><tt class="docutils literal"><span class="pre">LK_Java</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Java</span></tt>)
+Should be used for Java.</li>
+<li><tt class="docutils literal"><span class="pre">LK_JavaScript</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">JavaScript</span></tt>)
+Should be used for JavaScript.</li>
+<li><tt class="docutils literal"><span class="pre">LK_Proto</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Proto</span></tt>)
+Should be used for Protocol Buffers
+(<a class="reference external" href="https://developers.google.com/protocol-buffers/">https://developers.google.com/protocol-buffers/</a>).</li>
+</ul>
+</dd>
+<dt><strong>MaxEmptyLinesToKeep</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The maximum number of consecutive empty lines to keep.</dd>
+<dt><strong>NamespaceIndentation</strong> (<tt class="docutils literal"><span class="pre">NamespaceIndentationKind</span></tt>)</dt>
+<dd><p class="first">The indentation used for namespaces.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">NI_None</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">None</span></tt>)
+Don’t indent in namespaces.</li>
+<li><tt class="docutils literal"><span class="pre">NI_Inner</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Inner</span></tt>)
+Indent only in inner namespaces (nested in other namespaces).</li>
+<li><tt class="docutils literal"><span class="pre">NI_All</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">All</span></tt>)
+Indent in all namespaces.</li>
+</ul>
+</dd>
+<dt><strong>ObjCBlockIndentWidth</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The number of characters to use for indentation of ObjC blocks.</dd>
+<dt><strong>ObjCSpaceAfterProperty</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>Add a space after <tt class="docutils literal"><span class="pre">@property</span></tt> in Objective-C, i.e. use
+<tt class="docutils literal"><span class="pre">\@property</span> <span class="pre">(readonly)</span></tt> instead of <tt class="docutils literal"><span class="pre">\@property(readonly)</span></tt>.</dd>
+<dt><strong>ObjCSpaceBeforeProtocolList</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>Add a space in front of an Objective-C protocol list, i.e. use
+<tt class="docutils literal"><span class="pre">Foo</span> <span class="pre"><Protocol></span></tt> instead of <tt class="docutils literal"><span class="pre">Foo<Protocol></span></tt>.</dd>
+<dt><strong>PenaltyBreakBeforeFirstCallParameter</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The penalty for breaking a function call after “call(”.</dd>
+<dt><strong>PenaltyBreakComment</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The penalty for each line break introduced inside a comment.</dd>
+<dt><strong>PenaltyBreakFirstLessLess</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The penalty for breaking before the first <tt class="docutils literal"><span class="pre"><<</span></tt>.</dd>
+<dt><strong>PenaltyBreakString</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The penalty for each line break introduced inside a string literal.</dd>
+<dt><strong>PenaltyExcessCharacter</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The penalty for each character outside of the column limit.</dd>
+<dt><strong>PenaltyReturnTypeOnItsOwnLine</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>Penalty for putting the return type of a function onto its own
+line.</dd>
+<dt><strong>PointerAlignment</strong> (<tt class="docutils literal"><span class="pre">PointerAlignmentStyle</span></tt>)</dt>
+<dd><p class="first">Pointer and reference alignment style.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">PAS_Left</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Left</span></tt>)
+Align pointer to the left.</li>
+<li><tt class="docutils literal"><span class="pre">PAS_Right</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Right</span></tt>)
+Align pointer to the right.</li>
+<li><tt class="docutils literal"><span class="pre">PAS_Middle</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Middle</span></tt>)
+Align pointer in the middle.</li>
+</ul>
+</dd>
+<dt><strong>SpaceAfterCStyleCast</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, a space may be inserted after C style casts.</dd>
+<dt><strong>SpaceBeforeAssignmentOperators</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">false</span></tt>, spaces will be removed before assignment operators.</dd>
+<dt><strong>SpaceBeforeParens</strong> (<tt class="docutils literal"><span class="pre">SpaceBeforeParensOptions</span></tt>)</dt>
+<dd><p class="first">Defines in which cases to put a space before opening parentheses.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">SBPO_Never</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Never</span></tt>)
+Never put a space before opening parentheses.</li>
+<li><tt class="docutils literal"><span class="pre">SBPO_ControlStatements</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">ControlStatements</span></tt>)
+Put a space before opening parentheses only after control statement
+keywords (<tt class="docutils literal"><span class="pre">for/if/while...</span></tt>).</li>
+<li><tt class="docutils literal"><span class="pre">SBPO_Always</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Always</span></tt>)
+Always put a space before opening parentheses, except when it’s
+prohibited by the syntax rules (in function-like macro definitions) or
+when determined by other style rules (after unary operators, opening
+parentheses, etc.)</li>
+</ul>
+</dd>
+<dt><strong>SpaceInEmptyParentheses</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, spaces may be inserted into ‘()’.</dd>
+<dt><strong>SpacesBeforeTrailingComments</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd><p class="first">The number of spaces before trailing line comments
+(<tt class="docutils literal"><span class="pre">//</span></tt> - comments).</p>
+<p class="last">This does not affect trailing block comments (<tt class="docutils literal"><span class="pre">/**/</span></tt> - comments) as those
+commonly have different usage patterns and a number of special cases.</p>
+</dd>
+<dt><strong>SpacesInAngles</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, spaces will be inserted after ‘<’ and before ‘>’ in
+template argument lists</dd>
+<dt><strong>SpacesInCStyleCastParentheses</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, spaces may be inserted into C style casts.</dd>
+<dt><strong>SpacesInContainerLiterals</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, spaces are inserted inside container literals (e.g.
+ObjC and Javascript array and dict literals).</dd>
+<dt><strong>SpacesInParentheses</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, spaces will be inserted after ‘(‘ and before ‘)’.</dd>
+<dt><strong>SpacesInSquareBrackets</strong> (<tt class="docutils literal"><span class="pre">bool</span></tt>)</dt>
+<dd>If <tt class="docutils literal"><span class="pre">true</span></tt>, spaces will be inserted after ‘[‘ and before ‘]’.</dd>
+<dt><strong>Standard</strong> (<tt class="docutils literal"><span class="pre">LanguageStandard</span></tt>)</dt>
+<dd><p class="first">Format compatible with this standard, e.g. use
+<tt class="docutils literal"><span class="pre">A<A<int></span> <span class="pre">></span></tt> instead of <tt class="docutils literal"><span class="pre">A<A<int>></span></tt> for LS_Cpp03.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">LS_Cpp03</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Cpp03</span></tt>)
+Use C++03-compatible syntax.</li>
+<li><tt class="docutils literal"><span class="pre">LS_Cpp11</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Cpp11</span></tt>)
+Use features of C++11 (e.g. <tt class="docutils literal"><span class="pre">A<A<int>></span></tt> instead of
+<tt class="docutils literal"><span class="pre">A<A<int></span> <span class="pre">></span></tt>).</li>
+<li><tt class="docutils literal"><span class="pre">LS_Auto</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Auto</span></tt>)
+Automatic detection based on the input.</li>
+</ul>
+</dd>
+<dt><strong>TabWidth</strong> (<tt class="docutils literal"><span class="pre">unsigned</span></tt>)</dt>
+<dd>The number of columns used for tab stops.</dd>
+<dt><strong>UseTab</strong> (<tt class="docutils literal"><span class="pre">UseTabStyle</span></tt>)</dt>
+<dd><p class="first">The way to use tab characters in the resulting file.</p>
+<p>Possible values:</p>
+<ul class="last simple">
+<li><tt class="docutils literal"><span class="pre">UT_Never</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Never</span></tt>)
+Never use tab.</li>
+<li><tt class="docutils literal"><span class="pre">UT_ForIndentation</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">ForIndentation</span></tt>)
+Use tabs only for indentation.</li>
+<li><tt class="docutils literal"><span class="pre">UT_Always</span></tt> (in configuration: <tt class="docutils literal"><span class="pre">Always</span></tt>)
+Use tabs whenever we need to fill whitespace that spans at least from
+one tab stop to the next one.</li>
+</ul>
+</dd>
+</dl>
+</div>
+<div class="section" id="examples">
+<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
+<p>A style similar to the <a class="reference external" href="https://www.kernel.org/doc/Documentation/CodingStyle">Linux Kernel style</a>:</p>
+<div class="highlight-yaml"><div class="highlight"><pre><span class="l-Scalar-Plain">BasedOnStyle</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">LLVM</span>
+<span class="l-Scalar-Plain">IndentWidth</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">8</span>
+<span class="l-Scalar-Plain">UseTab</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Always</span>
+<span class="l-Scalar-Plain">BreakBeforeBraces</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Linux</span>
+<span class="l-Scalar-Plain">AllowShortIfStatementsOnASingleLine</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">false</span>
+<span class="l-Scalar-Plain">IndentCaseLabels</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">false</span>
+</pre></div>
+</div>
+<p>The result is (imagine that tabs are used for indentation here):</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">test</span><span class="p">()</span>
+<span class="p">{</span>
+ <span class="k">switch</span> <span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="p">{</span>
+ <span class="k">case</span> <span class="mi">0</span>:
+ <span class="k">case</span> <span class="mi">1</span>:
+ <span class="n">do_something</span><span class="p">();</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="k">case</span> <span class="mi">2</span>:
+ <span class="n">do_something_else</span><span class="p">();</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="nl">default:</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="p">}</span>
+ <span class="k">if</span> <span class="p">(</span><span class="n">condition</span><span class="p">)</span>
+ <span class="n">do_something_completely_different</span><span class="p">();</span>
+
+ <span class="k">if</span> <span class="p">(</span><span class="n">x</span> <span class="o">==</span> <span class="n">y</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">q</span><span class="p">();</span>
+ <span class="p">}</span> <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">x</span> <span class="o">></span> <span class="n">y</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">w</span><span class="p">();</span>
+ <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+ <span class="n">r</span><span class="p">();</span>
+ <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>A style similar to the default Visual Studio formatting style:</p>
+<div class="highlight-yaml"><div class="highlight"><pre><span class="l-Scalar-Plain">UseTab</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Never</span>
+<span class="l-Scalar-Plain">IndentWidth</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">4</span>
+<span class="l-Scalar-Plain">BreakBeforeBraces</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">Allman</span>
+<span class="l-Scalar-Plain">AllowShortIfStatementsOnASingleLine</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">false</span>
+<span class="l-Scalar-Plain">IndentCaseLabels</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">false</span>
+<span class="l-Scalar-Plain">ColumnLimit</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">0</span>
+</pre></div>
+</div>
+<p>The result is:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">test</span><span class="p">()</span>
+<span class="p">{</span>
+ <span class="k">switch</span> <span class="p">(</span><span class="n">suffix</span><span class="p">)</span>
+ <span class="p">{</span>
+ <span class="k">case</span> <span class="mi">0</span>:
+ <span class="k">case</span> <span class="mi">1</span>:
+ <span class="n">do_something</span><span class="p">();</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="k">case</span> <span class="mi">2</span>:
+ <span class="n">do_something_else</span><span class="p">();</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="nl">default:</span>
+ <span class="k">break</span><span class="p">;</span>
+ <span class="p">}</span>
+ <span class="k">if</span> <span class="p">(</span><span class="n">condition</span><span class="p">)</span>
+ <span class="n">do_somthing_completely_different</span><span class="p">();</span>
+
+ <span class="k">if</span> <span class="p">(</span><span class="n">x</span> <span class="o">==</span> <span class="n">y</span><span class="p">)</span>
+ <span class="p">{</span>
+ <span class="n">q</span><span class="p">();</span>
+ <span class="p">}</span>
+ <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">x</span> <span class="o">></span> <span class="n">y</span><span class="p">)</span>
+ <span class="p">{</span>
+ <span class="n">w</span><span class="p">();</span>
+ <span class="p">}</span>
+ <span class="k">else</span>
+ <span class="p">{</span>
+ <span class="n">r</span><span class="p">();</span>
+ <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ClangFormat.html">ClangFormat</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="InternalsManual.html">“Clang” CFE Internals Manual</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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==============================================================================
--- www-releases/trunk/3.6.1/tools/clang/docs/ClangPlugins.html (added)
+++ www-releases/trunk/3.6.1/tools/clang/docs/ClangPlugins.html Mon May 25 08:58:01 2015
@@ -0,0 +1,151 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>Clang Plugins — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
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+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="How to write RecursiveASTVisitor based ASTFrontendActions." href="RAVFrontendAction.html" />
+ <link rel="prev" title="LibFormat" href="LibFormat.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Clang Plugins</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="LibFormat.html">LibFormat</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="RAVFrontendAction.html">How to write RecursiveASTVisitor based ASTFrontendActions.</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="clang-plugins">
+<h1>Clang Plugins<a class="headerlink" href="#clang-plugins" title="Permalink to this headline">¶</a></h1>
+<p>Clang Plugins make it possible to run extra user defined actions during a
+compilation. This document will provide a basic walkthrough of how to write and
+run a Clang Plugin.</p>
+<div class="section" id="introduction">
+<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>Clang Plugins run FrontendActions over code. See the <a class="reference internal" href="RAVFrontendAction.html"><em>FrontendAction
+tutorial</em></a> on how to write a <tt class="docutils literal"><span class="pre">FrontendAction</span></tt> using the
+<tt class="docutils literal"><span class="pre">RecursiveASTVisitor</span></tt>. In this tutorial, we’ll demonstrate how to write a
+simple clang plugin.</p>
+</div>
+<div class="section" id="writing-a-pluginastaction">
+<h2>Writing a <tt class="docutils literal"><span class="pre">PluginASTAction</span></tt><a class="headerlink" href="#writing-a-pluginastaction" title="Permalink to this headline">¶</a></h2>
+<p>The main difference from writing normal <tt class="docutils literal"><span class="pre">FrontendActions</span></tt> is that you can
+handle plugin command line options. The <tt class="docutils literal"><span class="pre">PluginASTAction</span></tt> base class declares
+a <tt class="docutils literal"><span class="pre">ParseArgs</span></tt> method which you have to implement in your plugin.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">bool</span> <span class="nf">ParseArgs</span><span class="p">(</span><span class="k">const</span> <span class="n">CompilerInstance</span> <span class="o">&</span><span class="n">CI</span><span class="p">,</span>
+ <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">>&</span> <span class="n">args</span><span class="p">)</span> <span class="p">{</span>
+ <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+ <span class="k">if</span> <span class="p">(</span><span class="n">args</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">==</span> <span class="s">"-some-arg"</span><span class="p">)</span> <span class="p">{</span>
+ <span class="c1">// Handle the command line argument.</span>
+ <span class="p">}</span>
+ <span class="p">}</span>
+ <span class="k">return</span> <span class="nb">true</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="registering-a-plugin">
+<h2>Registering a plugin<a class="headerlink" href="#registering-a-plugin" title="Permalink to this headline">¶</a></h2>
+<p>A plugin is loaded from a dynamic library at runtime by the compiler. To
+register a plugin in a library, use <tt class="docutils literal"><span class="pre">FrontendPluginRegistry::Add<></span></tt>:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">static</span> <span class="n">FrontendPluginRegistry</span><span class="o">::</span><span class="n">Add</span><span class="o"><</span><span class="n">MyPlugin</span><span class="o">></span> <span class="n">X</span><span class="p">(</span><span class="s">"my-plugin-name"</span><span class="p">,</span> <span class="s">"my plugin description"</span><span class="p">);</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="putting-it-all-together">
+<h2>Putting it all together<a class="headerlink" href="#putting-it-all-together" title="Permalink to this headline">¶</a></h2>
+<p>Let’s look at an example plugin that prints top-level function names. This
+example is checked into the clang repository; please take a look at
+the <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/examples/PrintFunctionNames/PrintFunctionNames.cpp?view=markup">latest version of PrintFunctionNames.cpp</a>.</p>
+</div>
+<div class="section" id="running-the-plugin">
+<h2>Running the plugin<a class="headerlink" href="#running-the-plugin" title="Permalink to this headline">¶</a></h2>
+<p>To run a plugin, the dynamic library containing the plugin registry must be
+loaded via the <em class="xref std std-option">-load</em> command line option. This will load all plugins
+that are registered, and you can select the plugins to run by specifying the
+<em class="xref std std-option">-plugin</em> option. Additional parameters for the plugins can be passed with
+<em class="xref std std-option">-plugin-arg-</em>.</p>
+<p>Note that those options must reach clang’s cc1 process. There are two
+ways to do so:</p>
+<ul class="simple">
+<li>Directly call the parsing process by using the <em class="xref std std-option">-cc1</em> option; this
+has the downside of not configuring the default header search paths, so
+you’ll need to specify the full system path configuration on the command
+line.</li>
+<li>Use clang as usual, but prefix all arguments to the cc1 process with
+<em class="xref std std-option">-Xclang</em>.</li>
+</ul>
+<p>For example, to run the <tt class="docutils literal"><span class="pre">print-function-names</span></tt> plugin over a source file in
+clang, first build the plugin, and then call clang with the plugin from the
+source tree:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> <span class="nb">export </span><span class="nv">BD</span><span class="o">=</span>/path/to/build/directory
+<span class="gp">$</span> <span class="o">(</span><span class="nb">cd</span> <span class="nv">$BD</span> <span class="o">&&</span> make PrintFunctionNames <span class="o">)</span>
+<span class="gp">$</span> clang++ -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS <span class="se">\</span>
+<span class="go"> -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -D_GNU_SOURCE \</span>
+<span class="go"> -I$BD/tools/clang/include -Itools/clang/include -I$BD/include -Iinclude \</span>
+<span class="go"> tools/clang/tools/clang-check/ClangCheck.cpp -fsyntax-only \</span>
+<span class="go"> -Xclang -load -Xclang $BD/lib/PrintFunctionNames.so -Xclang \</span>
+<span class="go"> -plugin -Xclang print-fns</span>
+</pre></div>
+</div>
+<p>Also see the print-function-name plugin example’s
+<a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/examples/PrintFunctionNames/README.txt?view=markup">README</a></p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="LibFormat.html">LibFormat</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="RAVFrontendAction.html">How to write RecursiveASTVisitor based ASTFrontendActions.</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>Overview — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
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+ COLLAPSE_INDEX: false,
+ FILE_SUFFIX: '.html',
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+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
+ <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="ClangCheck" href="ClangCheck.html" />
+ <link rel="prev" title="JSON Compilation Database Format Specification" href="JSONCompilationDatabase.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Overview</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="JSONCompilationDatabase.html">JSON Compilation Database Format Specification</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangCheck.html">ClangCheck</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="overview">
+<h1>Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h1>
+<p>Clang Tools are standalone command line (and potentially GUI) tools
+designed for use by C++ developers who are already using and enjoying
+Clang as their compiler. These tools provide developer-oriented
+functionality such as fast syntax checking, automatic formatting,
+refactoring, etc.</p>
+<p>Only a couple of the most basic and fundamental tools are kept in the
+primary Clang Subversion project. The rest of the tools are kept in a
+side-project so that developers who don’t want or need to build them
+don’t. If you want to get access to the extra Clang Tools repository,
+simply check it out into the tools tree of your Clang checkout and
+follow the usual process for building and working with a combined
+LLVM/Clang checkout:</p>
+<ul class="simple">
+<li>With Subversion:<ul>
+<li><tt class="docutils literal"><span class="pre">cd</span> <span class="pre">llvm/tools/clang/tools</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">svn</span> <span class="pre">co</span> <span class="pre">http://llvm.org/svn/llvm-project/clang-tools-extra/trunk</span> <span class="pre">extra</span></tt></li>
+</ul>
+</li>
+<li>Or with Git:<ul>
+<li><tt class="docutils literal"><span class="pre">cd</span> <span class="pre">llvm/tools/clang/tools</span></tt></li>
+<li><tt class="docutils literal"><span class="pre">git</span> <span class="pre">clone</span> <span class="pre">http://llvm.org/git/clang-tools-extra.git</span> <span class="pre">extra</span></tt></li>
+</ul>
+</li>
+</ul>
+<p>This document describes a high-level overview of the organization of
+Clang Tools within the project as well as giving an introduction to some
+of the more important tools. However, it should be noted that this
+document is currently focused on Clang and Clang Tool developers, not on
+end users of these tools.</p>
+<div class="section" id="clang-tools-organization">
+<h2>Clang Tools Organization<a class="headerlink" href="#clang-tools-organization" title="Permalink to this headline">¶</a></h2>
+<p>Clang Tools are CLI or GUI programs that are intended to be directly
+used by C++ developers. That is they are <em>not</em> primarily for use by
+Clang developers, although they are hopefully useful to C++ developers
+who happen to work on Clang, and we try to actively dogfood their
+functionality. They are developed in three components: the underlying
+infrastructure for building a standalone tool based on Clang, core
+shared logic used by many different tools in the form of refactoring and
+rewriting libraries, and the tools themselves.</p>
+<p>The underlying infrastructure for Clang Tools is the
+<a class="reference internal" href="LibTooling.html"><em>LibTooling</em></a> platform. See its documentation for much
+more detailed information about how this infrastructure works. The
+common refactoring and rewriting toolkit-style library is also part of
+LibTooling organizationally.</p>
+<p>A few Clang Tools are developed along side the core Clang libraries as
+examples and test cases of fundamental functionality. However, most of
+the tools are developed in a side repository to provide easy separation
+from the core libraries. We intentionally do not support public
+libraries in the side repository, as we want to carefully review and
+find good APIs for libraries as they are lifted out of a few tools and
+into the core Clang library set.</p>
+<p>Regardless of which repository Clang Tools’ code resides in, the
+development process and practices for all Clang Tools are exactly those
+of Clang itself. They are entirely within the Clang <em>project</em>,
+regardless of the version control scheme.</p>
+</div>
+<div class="section" id="core-clang-tools">
+<h2>Core Clang Tools<a class="headerlink" href="#core-clang-tools" title="Permalink to this headline">¶</a></h2>
+<p>The core set of Clang tools that are within the main repository are
+tools that very specifically complement, and allow use and testing of
+<em>Clang</em> specific functionality.</p>
+<div class="section" id="clang-check">
+<h3><tt class="docutils literal"><span class="pre">clang-check</span></tt><a class="headerlink" href="#clang-check" title="Permalink to this headline">¶</a></h3>
+<p><a class="reference internal" href="ClangCheck.html"><em>ClangCheck</em></a> combines the LibTooling framework for running a
+Clang tool with the basic Clang diagnostics by syntax checking specific files
+in a fast, command line interface. It can also accept flags to re-display the
+diagnostics in different formats with different flags, suitable for use driving
+an IDE or editor. Furthermore, it can be used in fixit-mode to directly apply
+fixit-hints offered by clang. See <a class="reference internal" href="HowToSetupToolingForLLVM.html"><em>How To Setup Clang Tooling For LLVM</em></a> for
+instructions on how to setup and used <cite>clang-check</cite>.</p>
+<div class="section" id="clang-format">
+<h4><tt class="docutils literal"><span class="pre">clang-format</span></tt><a class="headerlink" href="#clang-format" title="Permalink to this headline">¶</a></h4>
+<p>Clang-format is both a <a class="reference internal" href="LibFormat.html"><em>library</em></a> and a <a class="reference internal" href="ClangFormat.html"><em>stand-alone tool</em></a> with the goal of automatically reformatting C++ sources files
+according to configurable style guides. To do so, clang-format uses Clang’s
+<tt class="docutils literal"><span class="pre">Lexer</span></tt> to transform an input file into a token stream and then changes all
+the whitespace around those tokens. The goal is for clang-format to serve both
+as a user tool (ideally with powerful IDE integrations) and as part of other
+refactoring tools, e.g. to do a reformatting of all the lines changed during a
+renaming.</p>
+</div>
+<div class="section" id="clang-modernize">
+<h4><tt class="docutils literal"><span class="pre">clang-modernize</span></tt><a class="headerlink" href="#clang-modernize" title="Permalink to this headline">¶</a></h4>
+<p><tt class="docutils literal"><span class="pre">clang-modernize</span></tt> migrates C++ code to use C++11 features where appropriate.
+Currently it can:</p>
+<ul class="simple">
+<li>convert loops to range-based for loops;</li>
+<li>convert null pointer constants (like <tt class="docutils literal"><span class="pre">NULL</span></tt> or <tt class="docutils literal"><span class="pre">0</span></tt>) to C++11 <tt class="docutils literal"><span class="pre">nullptr</span></tt>;</li>
+<li>replace the type specifier in variable declarations with the <tt class="docutils literal"><span class="pre">auto</span></tt> type specifier;</li>
+<li>add the <tt class="docutils literal"><span class="pre">override</span></tt> specifier to applicable member functions.</li>
+</ul>
+</div>
+</div>
+</div>
+<div class="section" id="extra-clang-tools">
+<h2>Extra Clang Tools<a class="headerlink" href="#extra-clang-tools" title="Permalink to this headline">¶</a></h2>
+<p>As various categories of Clang Tools are added to the extra repository,
+they’ll be tracked here. The focus of this documentation is on the scope
+and features of the tools for other tool developers; each tool should
+provide its own user-focused documentation.</p>
+</div>
+<div class="section" id="ideas-for-new-tools">
+<h2>Ideas for new Tools<a class="headerlink" href="#ideas-for-new-tools" title="Permalink to this headline">¶</a></h2>
+<ul>
+<li><p class="first">C++ cast conversion tool. Will convert C-style casts (<tt class="docutils literal"><span class="pre">(type)</span> <span class="pre">value</span></tt>) to
+appropriate C++ cast (<tt class="docutils literal"><span class="pre">static_cast</span></tt>, <tt class="docutils literal"><span class="pre">const_cast</span></tt> or
+<tt class="docutils literal"><span class="pre">reinterpret_cast</span></tt>).</p>
+</li>
+<li><p class="first">Non-member <tt class="docutils literal"><span class="pre">begin()</span></tt> and <tt class="docutils literal"><span class="pre">end()</span></tt> conversion tool. Will convert
+<tt class="docutils literal"><span class="pre">foo.begin()</span></tt> into <tt class="docutils literal"><span class="pre">begin(foo)</span></tt> and similarly for <tt class="docutils literal"><span class="pre">end()</span></tt>, where
+<tt class="docutils literal"><span class="pre">foo</span></tt> is a standard container. We could also detect similar patterns for
+arrays.</p>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">make_shared</span></tt> / <tt class="docutils literal"><span class="pre">make_unique</span></tt> conversion. Part of this transformation
+can be incorporated into the <tt class="docutils literal"><span class="pre">auto</span></tt> transformation. Will convert</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span> <span class="n">sp</span><span class="p">(</span><span class="k">new</span> <span class="n">Foo</span><span class="p">);</span>
+<span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span> <span class="n">up</span><span class="p">(</span><span class="k">new</span> <span class="n">Foo</span><span class="p">);</span>
+
+<span class="n">func</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span><span class="p">(</span><span class="k">new</span> <span class="n">Foo</span><span class="p">),</span> <span class="n">bar</span><span class="p">());</span>
+</pre></div>
+</div>
+<p>into:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">auto</span> <span class="n">sp</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span><span class="p">();</span>
+<span class="k">auto</span> <span class="n">up</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span><span class="p">();</span> <span class="c1">// In C++14 mode.</span>
+
+<span class="c1">// This also affects correctness. For the cases where bar() throws,</span>
+<span class="c1">// make_shared() is safe and the original code may leak.</span>
+<span class="n">func</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span><span class="p">(),</span> <span class="n">bar</span><span class="p">());</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">tr1</span></tt> removal tool. Will migrate source code from using TR1 library
+features to C++11 library. For example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include <tr1/unordered_map></span>
+<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
+<span class="p">{</span>
+ <span class="n">std</span><span class="o">::</span><span class="n">tr1</span><span class="o">::</span><span class="n">unordered_map</span> <span class="o"><</span><span class="kt">int</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">ma</span><span class="p">;</span>
+ <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o"><<</span> <span class="n">ma</span><span class="p">.</span><span class="n">size</span> <span class="p">()</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
+ <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>should be rewritten to:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include <unordered_map></span>
+<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
+<span class="p">{</span>
+ <span class="n">std</span><span class="o">::</span><span class="n">unordered_map</span> <span class="o"><</span><span class="kt">int</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">ma</span><span class="p">;</span>
+ <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o"><<</span> <span class="n">ma</span><span class="p">.</span><span class="n">size</span> <span class="p">()</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
+ <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first">A tool to remove <tt class="docutils literal"><span class="pre">auto</span></tt>. Will convert <tt class="docutils literal"><span class="pre">auto</span></tt> to an explicit type or add
+comments with deduced types. The motivation is that there are developers
+that don’t want to use <tt class="docutils literal"><span class="pre">auto</span></tt> because they are afraid that they might lose
+control over their code.</p>
+</li>
+<li><p class="first">C++14: less verbose operator function objects (<a class="reference external" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3421.htm">N3421</a>).
+For example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">sort</span><span class="p">(</span><span class="n">v</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span> <span class="n">v</span><span class="p">.</span><span class="n">end</span><span class="p">(),</span> <span class="n">greater</span><span class="o"><</span><span class="n">ValueType</span><span class="o">></span><span class="p">());</span>
+</pre></div>
+</div>
+<p>should be rewritten to:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">sort</span><span class="p">(</span><span class="n">v</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span> <span class="n">v</span><span class="p">.</span><span class="n">end</span><span class="p">(),</span> <span class="n">greater</span><span class="o"><></span><span class="p">());</span>
+</pre></div>
+</div>
+</li>
+</ul>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="JSONCompilationDatabase.html">JSON Compilation Database Format Specification</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangCheck.html">ClangCheck</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
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+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+
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+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>Cross-compilation using Clang — Clang 3.6 documentation</title>
+
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+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
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+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
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+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
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+ <link rel="prev" title="Attributes in Clang" href="AttributeReference.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Cross-compilation using Clang</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="AttributeReference.html">Attributes in Clang</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ThreadSafetyAnalysis.html">Thread Safety Analysis</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="cross-compilation-using-clang">
+<h1>Cross-compilation using Clang<a class="headerlink" href="#cross-compilation-using-clang" title="Permalink to this headline">¶</a></h1>
+<div class="section" id="introduction">
+<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>This document will guide you in choosing the right Clang options
+for cross-compiling your code to a different architecture. It assumes you
+already know how to compile the code in question for the host architecture,
+and that you know how to choose additional include and library paths.</p>
+<p>However, this document is <em>not</em> a “how to” and won’t help you setting your
+build system or Makefiles, nor choosing the right CMake options, etc.
+Also, it does not cover all the possible options, nor does it contain
+specific examples for specific architectures. For a concrete example, the
+<a class="reference external" href="http://llvm.org/docs/HowToCrossCompileLLVM.html">instructions for cross-compiling LLVM itself</a> may be of interest.</p>
+<p>After reading this document, you should be familiar with the main issues
+related to cross-compilation, and what main compiler options Clang provides
+for performing cross-compilation.</p>
+</div>
+<div class="section" id="cross-compilation-issues">
+<h2>Cross compilation issues<a class="headerlink" href="#cross-compilation-issues" title="Permalink to this headline">¶</a></h2>
+<p>In GCC world, every host/target combination has its own set of binaries,
+headers, libraries, etc. So, it’s usually simple to download a package
+with all files in, unzip to a directory and point the build system to
+that compiler, that will know about its location and find all it needs to
+when compiling your code.</p>
+<p>On the other hand, Clang/LLVM is natively a cross-compiler, meaning that
+one set of programs can compile to all targets by setting the <tt class="docutils literal"><span class="pre">-target</span></tt>
+option. That makes it a lot easier for programers wishing to compile to
+different platforms and architectures, and for compiler developers that
+only have to maintain one build system, and for OS distributions, that
+need only one set of main packages.</p>
+<p>But, as is true to any cross-compiler, and given the complexity of
+different architectures, OS’s and options, it’s not always easy finding
+the headers, libraries or binutils to generate target specific code.
+So you’ll need special options to help Clang understand what target
+you’re compiling to, where your tools are, etc.</p>
+<p>Another problem is that compilers come with standard libraries only (like
+<tt class="docutils literal"><span class="pre">compiler-rt</span></tt>, <tt class="docutils literal"><span class="pre">libcxx</span></tt>, <tt class="docutils literal"><span class="pre">libgcc</span></tt>, <tt class="docutils literal"><span class="pre">libm</span></tt>, etc), so you’ll have to
+find and make available to the build system, every other library required
+to build your software, that is specific to your target. It’s not enough to
+have your host’s libraries installed.</p>
+<p>Finally, not all toolchains are the same, and consequently, not every Clang
+option will work magically. Some options, like <tt class="docutils literal"><span class="pre">--sysroot</span></tt> (which
+effectively changes the logical root for headers and libraries), assume
+all your binaries and libraries are in the same directory, which may not
+true when your cross-compiler was installed by the distribution’s package
+management. So, for each specific case, you may use more than one
+option, and in most cases, you’ll end up setting include paths (<tt class="docutils literal"><span class="pre">-I</span></tt>) and
+library paths (<tt class="docutils literal"><span class="pre">-L</span></tt>) manually.</p>
+<dl class="docutils">
+<dt>To sum up, different toolchains can:</dt>
+<dd><ul class="first last simple">
+<li>be host/target specific or more flexible</li>
+<li>be in a single directory, or spread out across your system</li>
+<li>have different sets of libraries and headers by default</li>
+<li>need special options, which your build system won’t be able to figure
+out by itself</li>
+</ul>
+</dd>
+</dl>
+</div>
+<div class="section" id="general-cross-compilation-options-in-clang">
+<h2>General Cross-Compilation Options in Clang<a class="headerlink" href="#general-cross-compilation-options-in-clang" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="target-triple">
+<h3>Target Triple<a class="headerlink" href="#target-triple" title="Permalink to this headline">¶</a></h3>
+<p>The basic option is to define the target architecture. For that, use
+<tt class="docutils literal"><span class="pre">-target</span> <span class="pre"><triple></span></tt>. If you don’t specify the target, CPU names won’t
+match (since Clang assumes the host triple), and the compilation will
+go ahead, creating code for the host platform, which will break later
+on when assembling or linking.</p>
+<dl class="docutils">
+<dt>The triple has the general format <tt class="docutils literal"><span class="pre"><arch><sub>-<vendor>-<sys>-<abi></span></tt>, where:</dt>
+<dd><ul class="first last simple">
+<li><tt class="docutils literal"><span class="pre">arch</span></tt> = <tt class="docutils literal"><span class="pre">x86</span></tt>, <tt class="docutils literal"><span class="pre">arm</span></tt>, <tt class="docutils literal"><span class="pre">thumb</span></tt>, <tt class="docutils literal"><span class="pre">mips</span></tt>, etc.</li>
+<li><tt class="docutils literal"><span class="pre">sub</span></tt> = for ex. on ARM: <tt class="docutils literal"><span class="pre">v5</span></tt>, <tt class="docutils literal"><span class="pre">v6m</span></tt>, <tt class="docutils literal"><span class="pre">v7a</span></tt>, <tt class="docutils literal"><span class="pre">v7m</span></tt>, etc.</li>
+<li><tt class="docutils literal"><span class="pre">vendor</span></tt> = <tt class="docutils literal"><span class="pre">pc</span></tt>, <tt class="docutils literal"><span class="pre">apple</span></tt>, <tt class="docutils literal"><span class="pre">nvidia</span></tt>, <tt class="docutils literal"><span class="pre">ibm</span></tt>, etc.</li>
+<li><tt class="docutils literal"><span class="pre">sys</span></tt> = <tt class="docutils literal"><span class="pre">none</span></tt>, <tt class="docutils literal"><span class="pre">linux</span></tt>, <tt class="docutils literal"><span class="pre">win32</span></tt>, <tt class="docutils literal"><span class="pre">darwin</span></tt>, <tt class="docutils literal"><span class="pre">cuda</span></tt>, etc.</li>
+<li><tt class="docutils literal"><span class="pre">abi</span></tt> = <tt class="docutils literal"><span class="pre">eabi</span></tt>, <tt class="docutils literal"><span class="pre">gnu</span></tt>, <tt class="docutils literal"><span class="pre">android</span></tt>, <tt class="docutils literal"><span class="pre">macho</span></tt>, <tt class="docutils literal"><span class="pre">elf</span></tt>, etc.</li>
+</ul>
+</dd>
+</dl>
+<p>The sub-architecture options are available for their own architectures,
+of course, so “x86v7a” doesn’t make sense. The vendor needs to be
+specified only if there’s a relevant change, for instance between PC
+and Apple. Most of the time it can be omitted (and Unknown)
+will be assumed, which sets the defaults for the specified architecture.
+The system name is generally the OS (linux, darwin), but could be special
+like the bare-metal “none”.</p>
+<p>When a parameter is not important, they can be omitted, or you can
+choose <tt class="docutils literal"><span class="pre">unknown</span></tt> and the defaults will be used. If you choose a parameter
+that Clang doesn’t know, like <tt class="docutils literal"><span class="pre">blerg</span></tt>, it’ll ignore and assume
+<tt class="docutils literal"><span class="pre">unknown</span></tt>, which is not always desired, so be careful.</p>
+<p>Finally, the ABI option is something that will pick default CPU/FPU,
+define the specific behaviour of your code (PCS, extensions),
+and also choose the correct library calls, etc.</p>
+</div>
+<div class="section" id="cpu-fpu-abi">
+<h3>CPU, FPU, ABI<a class="headerlink" href="#cpu-fpu-abi" title="Permalink to this headline">¶</a></h3>
+<p>Once your target is specified, it’s time to pick the hardware you’ll
+be compiling to. For every architecture, a default set of CPU/FPU/ABI
+will be chosen, so you’ll almost always have to change it via flags.</p>
+<dl class="docutils">
+<dt>Typical flags include:</dt>
+<dd><ul class="first last simple">
+<li><tt class="docutils literal"><span class="pre">-mcpu=<cpu-name></span></tt>, like x86-64, swift, cortex-a15</li>
+<li><tt class="docutils literal"><span class="pre">-fpu=<fpu-name></span></tt>, like SSE3, NEON, controlling the FP unit available</li>
+<li><tt class="docutils literal"><span class="pre">-mfloat-abi=<fabi></span></tt>, like soft, hard, controlling which registers
+to use for floating-point</li>
+</ul>
+</dd>
+</dl>
+<p>The default is normally the common denominator, so that Clang doesn’t
+generate code that breaks. But that also means you won’t get the best
+code for your specific hardware, which may mean orders of magnitude
+slower than you expect.</p>
+<p>For example, if your target is <tt class="docutils literal"><span class="pre">arm-none-eabi</span></tt>, the default CPU will
+be <tt class="docutils literal"><span class="pre">arm7tdmi</span></tt> using soft float, which is extremely slow on modern cores,
+whereas if your triple is <tt class="docutils literal"><span class="pre">armv7a-none-eabi</span></tt>, it’ll be Cortex-A8 with
+NEON, but still using soft-float, which is much better, but still not
+great.</p>
+</div>
+<div class="section" id="toolchain-options">
+<h3>Toolchain Options<a class="headerlink" href="#toolchain-options" title="Permalink to this headline">¶</a></h3>
+<p>There are three main options to control access to your cross-compiler:
+<tt class="docutils literal"><span class="pre">--sysroot</span></tt>, <tt class="docutils literal"><span class="pre">-I</span></tt>, and <tt class="docutils literal"><span class="pre">-L</span></tt>. The two last ones are well known,
+but they’re particularly important for additional libraries
+and headers that are specific to your target.</p>
+<p>There are two main ways to have a cross-compiler:</p>
+<ol class="arabic">
+<li><p class="first">When you have extracted your cross-compiler from a zip file into
+a directory, you have to use <tt class="docutils literal"><span class="pre">--sysroot=<path></span></tt>. The path is the
+root directory where you have unpacked your file, and Clang will
+look for the directories <tt class="docutils literal"><span class="pre">bin</span></tt>, <tt class="docutils literal"><span class="pre">lib</span></tt>, <tt class="docutils literal"><span class="pre">include</span></tt> in there.</p>
+<p>In this case, your setup should be pretty much done (if no
+additional headers or libraries are needed), as Clang will find
+all binaries it needs (assembler, linker, etc) in there.</p>
+</li>
+<li><p class="first">When you have installed via a package manager (modern Linux
+distributions have cross-compiler packages available), make
+sure the target triple you set is <em>also</em> the prefix of your
+cross-compiler toolchain.</p>
+<p>In this case, Clang will find the other binaries (assembler,
+linker), but not always where the target headers and libraries
+are. People add system-specific clues to Clang often, but as
+things change, it’s more likely that it won’t find than the
+other way around.</p>
+<p>So, here, you’ll be a lot safer if you specify the include/library
+directories manually (via <tt class="docutils literal"><span class="pre">-I</span></tt> and <tt class="docutils literal"><span class="pre">-L</span></tt>).</p>
+</li>
+</ol>
+</div>
+</div>
+<div class="section" id="target-specific-libraries">
+<h2>Target-Specific Libraries<a class="headerlink" href="#target-specific-libraries" title="Permalink to this headline">¶</a></h2>
+<p>All libraries that you compile as part of your build will be
+cross-compiled to your target, and your build system will probably
+find them in the right place. But all dependencies that are
+normally checked against (like <tt class="docutils literal"><span class="pre">libxml</span></tt> or <tt class="docutils literal"><span class="pre">libz</span></tt> etc) will match
+against the host platform, not the target.</p>
+<p>So, if the build system is not aware that you want to cross-compile
+your code, it will get every dependency wrong, and your compilation
+will fail during build time, not configure time.</p>
+<p>Also, finding the libraries for your target are not as easy
+as for your host machine. There aren’t many cross-libraries available
+as packages to most OS’s, so you’ll have to either cross-compile them
+from source, or download the package for your target platform,
+extract the libraries and headers, put them in specific directories
+and add <tt class="docutils literal"><span class="pre">-I</span></tt> and <tt class="docutils literal"><span class="pre">-L</span></tt> pointing to them.</p>
+<p>Also, some libraries have different dependencies on different targets,
+so configuration tools to find dependencies in the host can get the
+list wrong for the target platform. This means that the configuration
+of your build can get things wrong when setting their own library
+paths, and you’ll have to augment it via additional flags (configure,
+Make, CMake, etc).</p>
+<div class="section" id="multilibs">
+<h3>Multilibs<a class="headerlink" href="#multilibs" title="Permalink to this headline">¶</a></h3>
+<p>When you want to cross-compile to more than one configuration, for
+example hard-float-ARM and soft-float-ARM, you’ll have to have multiple
+copies of your libraries and (possibly) headers.</p>
+<p>Some Linux distributions have support for Multilib, which handle that
+for you in an easier way, but if you’re not careful and, for instance,
+forget to specify <tt class="docutils literal"><span class="pre">-ccc-gcc-name</span> <span class="pre">armv7l-linux-gnueabihf-gcc</span></tt> (which
+uses hard-float), Clang will pick the <tt class="docutils literal"><span class="pre">armv7l-linux-gnueabi-ld</span></tt>
+(which uses soft-float) and linker errors will happen.</p>
+<p>The same is true if you’re compiling for different ABIs, like <tt class="docutils literal"><span class="pre">gnueabi</span></tt>
+and <tt class="docutils literal"><span class="pre">androideabi</span></tt>, and might even link and run, but produce run-time
+errors, which are much harder to track down and fix.</p>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="AttributeReference.html">Attributes in Clang</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ThreadSafetyAnalysis.html">Thread Safety Analysis</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
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+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>DataFlowSanitizer</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="MemorySanitizer.html">MemorySanitizer</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="DataFlowSanitizerDesign.html">DataFlowSanitizer Design Document</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="dataflowsanitizer">
+<h1>DataFlowSanitizer<a class="headerlink" href="#dataflowsanitizer" title="Permalink to this headline">¶</a></h1>
+<div class="toctree-wrapper compound">
+</div>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
+<li><a class="reference internal" href="#usage" id="id2">Usage</a><ul>
+<li><a class="reference internal" href="#abi-list" id="id3">ABI List</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#example" id="id4">Example</a></li>
+<li><a class="reference internal" href="#current-status" id="id5">Current status</a></li>
+<li><a class="reference internal" href="#design" id="id6">Design</a></li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id1">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>DataFlowSanitizer is a generalised dynamic data flow analysis.</p>
+<p>Unlike other Sanitizer tools, this tool is not designed to detect a
+specific class of bugs on its own. Instead, it provides a generic
+dynamic data flow analysis framework to be used by clients to help
+detect application-specific issues within their own code.</p>
+</div>
+<div class="section" id="usage">
+<h2><a class="toc-backref" href="#id2">Usage</a><a class="headerlink" href="#usage" title="Permalink to this headline">¶</a></h2>
+<p>With no program changes, applying DataFlowSanitizer to a program
+will not alter its behavior. To use DataFlowSanitizer, the program
+uses API functions to apply tags to data to cause it to be tracked, and to
+check the tag of a specific data item. DataFlowSanitizer manages
+the propagation of tags through the program according to its data flow.</p>
+<p>The APIs are defined in the header file <tt class="docutils literal"><span class="pre">sanitizer/dfsan_interface.h</span></tt>.
+For further information about each function, please refer to the header
+file.</p>
+<div class="section" id="abi-list">
+<h3><a class="toc-backref" href="#id3">ABI List</a><a class="headerlink" href="#abi-list" title="Permalink to this headline">¶</a></h3>
+<p>DataFlowSanitizer uses a list of functions known as an ABI list to decide
+whether a call to a specific function should use the operating system’s native
+ABI or whether it should use a variant of this ABI that also propagates labels
+through function parameters and return values. The ABI list file also controls
+how labels are propagated in the former case. DataFlowSanitizer comes with a
+default ABI list which is intended to eventually cover the glibc library on
+Linux but it may become necessary for users to extend the ABI list in cases
+where a particular library or function cannot be instrumented (e.g. because
+it is implemented in assembly or another language which DataFlowSanitizer does
+not support) or a function is called from a library or function which cannot
+be instrumented.</p>
+<p>DataFlowSanitizer’s ABI list file is a <a class="reference internal" href="SanitizerSpecialCaseList.html"><em>Sanitizer special case list</em></a>.
+The pass treats every function in the <tt class="docutils literal"><span class="pre">uninstrumented</span></tt> category in the
+ABI list file as conforming to the native ABI. Unless the ABI list contains
+additional categories for those functions, a call to one of those functions
+will produce a warning message, as the labelling behavior of the function
+is unknown. The other supported categories are <tt class="docutils literal"><span class="pre">discard</span></tt>, <tt class="docutils literal"><span class="pre">functional</span></tt>
+and <tt class="docutils literal"><span class="pre">custom</span></tt>.</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">discard</span></tt> – To the extent that this function writes to (user-accessible)
+memory, it also updates labels in shadow memory (this condition is trivially
+satisfied for functions which do not write to user-accessible memory). Its
+return value is unlabelled.</li>
+<li><tt class="docutils literal"><span class="pre">functional</span></tt> – Like <tt class="docutils literal"><span class="pre">discard</span></tt>, except that the label of its return value
+is the union of the label of its arguments.</li>
+<li><tt class="docutils literal"><span class="pre">custom</span></tt> – Instead of calling the function, a custom wrapper <tt class="docutils literal"><span class="pre">__dfsw_F</span></tt>
+is called, where <tt class="docutils literal"><span class="pre">F</span></tt> is the name of the function. This function may wrap
+the original function or provide its own implementation. This category is
+generally used for uninstrumentable functions which write to user-accessible
+memory or which have more complex label propagation behavior. The signature
+of <tt class="docutils literal"><span class="pre">__dfsw_F</span></tt> is based on that of <tt class="docutils literal"><span class="pre">F</span></tt> with each argument having a
+label of type <tt class="docutils literal"><span class="pre">dfsan_label</span></tt> appended to the argument list. If <tt class="docutils literal"><span class="pre">F</span></tt>
+is of non-void return type a final argument of type <tt class="docutils literal"><span class="pre">dfsan_label</span> <span class="pre">*</span></tt>
+is appended to which the custom function can store the label for the
+return value. For example:</li>
+</ul>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">f</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span><span class="p">);</span>
+<span class="kt">void</span> <span class="nf">__dfsw_f</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span><span class="p">,</span> <span class="n">dfsan_label</span> <span class="n">x_label</span><span class="p">);</span>
+
+<span class="kt">void</span> <span class="o">*</span><span class="nf">memcpy</span><span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="n">dest</span><span class="p">,</span> <span class="k">const</span> <span class="kt">void</span> <span class="o">*</span><span class="n">src</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">n</span><span class="p">);</span>
+<span class="kt">void</span> <span class="o">*</span><span class="nf">__dfsw_memcpy</span><span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="n">dest</span><span class="p">,</span> <span class="k">const</span> <span class="kt">void</span> <span class="o">*</span><span class="n">src</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">n</span><span class="p">,</span>
+ <span class="n">dfsan_label</span> <span class="n">dest_label</span><span class="p">,</span> <span class="n">dfsan_label</span> <span class="n">src_label</span><span class="p">,</span>
+ <span class="n">dfsan_label</span> <span class="n">n_label</span><span class="p">,</span> <span class="n">dfsan_label</span> <span class="o">*</span><span class="n">ret_label</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>If a function defined in the translation unit being compiled belongs to the
+<tt class="docutils literal"><span class="pre">uninstrumented</span></tt> category, it will be compiled so as to conform to the
+native ABI. Its arguments will be assumed to be unlabelled, but it will
+propagate labels in shadow memory.</p>
+<p>For example:</p>
+<div class="highlight-none"><div class="highlight"><pre># main is called by the C runtime using the native ABI.
+fun:main=uninstrumented
+fun:main=discard
+
+# malloc only writes to its internal data structures, not user-accessible memory.
+fun:malloc=uninstrumented
+fun:malloc=discard
+
+# tolower is a pure function.
+fun:tolower=uninstrumented
+fun:tolower=functional
+
+# memcpy needs to copy the shadow from the source to the destination region.
+# This is done in a custom function.
+fun:memcpy=uninstrumented
+fun:memcpy=custom
+</pre></div>
+</div>
+</div>
+</div>
+<div class="section" id="example">
+<h2><a class="toc-backref" href="#id4">Example</a><a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2>
+<p>The following program demonstrates label propagation by checking that
+the correct labels are propagated.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include <sanitizer/dfsan_interface.h></span>
+<span class="cp">#include <assert.h></span>
+
+<span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> <span class="p">{</span>
+ <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
+ <span class="n">dfsan_label</span> <span class="n">i_label</span> <span class="o">=</span> <span class="n">dfsan_create_label</span><span class="p">(</span><span class="s">"i"</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>
+ <span class="n">dfsan_set_label</span><span class="p">(</span><span class="n">i_label</span><span class="p">,</span> <span class="o">&</span><span class="n">i</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="n">i</span><span class="p">));</span>
+
+ <span class="kt">int</span> <span class="n">j</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+ <span class="n">dfsan_label</span> <span class="n">j_label</span> <span class="o">=</span> <span class="n">dfsan_create_label</span><span class="p">(</span><span class="s">"j"</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>
+ <span class="n">dfsan_set_label</span><span class="p">(</span><span class="n">j_label</span><span class="p">,</span> <span class="o">&</span><span class="n">j</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="n">j</span><span class="p">));</span>
+
+ <span class="kt">int</span> <span class="n">k</span> <span class="o">=</span> <span class="mi">3</span><span class="p">;</span>
+ <span class="n">dfsan_label</span> <span class="n">k_label</span> <span class="o">=</span> <span class="n">dfsan_create_label</span><span class="p">(</span><span class="s">"k"</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>
+ <span class="n">dfsan_set_label</span><span class="p">(</span><span class="n">k_label</span><span class="p">,</span> <span class="o">&</span><span class="n">k</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="n">k</span><span class="p">));</span>
+
+ <span class="n">dfsan_label</span> <span class="n">ij_label</span> <span class="o">=</span> <span class="n">dfsan_get_label</span><span class="p">(</span><span class="n">i</span> <span class="o">+</span> <span class="n">j</span><span class="p">);</span>
+ <span class="n">assert</span><span class="p">(</span><span class="n">dfsan_has_label</span><span class="p">(</span><span class="n">ij_label</span><span class="p">,</span> <span class="n">i_label</span><span class="p">));</span>
+ <span class="n">assert</span><span class="p">(</span><span class="n">dfsan_has_label</span><span class="p">(</span><span class="n">ij_label</span><span class="p">,</span> <span class="n">j_label</span><span class="p">));</span>
+ <span class="n">assert</span><span class="p">(</span><span class="o">!</span><span class="n">dfsan_has_label</span><span class="p">(</span><span class="n">ij_label</span><span class="p">,</span> <span class="n">k_label</span><span class="p">));</span>
+
+ <span class="n">dfsan_label</span> <span class="n">ijk_label</span> <span class="o">=</span> <span class="n">dfsan_get_label</span><span class="p">(</span><span class="n">i</span> <span class="o">+</span> <span class="n">j</span> <span class="o">+</span> <span class="n">k</span><span class="p">);</span>
+ <span class="n">assert</span><span class="p">(</span><span class="n">dfsan_has_label</span><span class="p">(</span><span class="n">ijk_label</span><span class="p">,</span> <span class="n">i_label</span><span class="p">));</span>
+ <span class="n">assert</span><span class="p">(</span><span class="n">dfsan_has_label</span><span class="p">(</span><span class="n">ijk_label</span><span class="p">,</span> <span class="n">j_label</span><span class="p">));</span>
+ <span class="n">assert</span><span class="p">(</span><span class="n">dfsan_has_label</span><span class="p">(</span><span class="n">ijk_label</span><span class="p">,</span> <span class="n">k_label</span><span class="p">));</span>
+
+ <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="current-status">
+<h2><a class="toc-backref" href="#id5">Current status</a><a class="headerlink" href="#current-status" title="Permalink to this headline">¶</a></h2>
+<p>DataFlowSanitizer is a work in progress, currently under development for
+x86_64 Linux.</p>
+</div>
+<div class="section" id="design">
+<h2><a class="toc-backref" href="#id6">Design</a><a class="headerlink" href="#design" title="Permalink to this headline">¶</a></h2>
+<p>Please refer to the <a class="reference internal" href="DataFlowSanitizerDesign.html"><em>design document</em></a>.</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="MemorySanitizer.html">MemorySanitizer</a>
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+ ::
+ <a href="DataFlowSanitizerDesign.html">DataFlowSanitizer Design Document</a> »
+ </p>
+
+ </div>
+
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+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>DataFlowSanitizer Design Document</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="DataFlowSanitizer.html">DataFlowSanitizer</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="LeakSanitizer.html">LeakSanitizer</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="dataflowsanitizer-design-document">
+<h1>DataFlowSanitizer Design Document<a class="headerlink" href="#dataflowsanitizer-design-document" title="Permalink to this headline">¶</a></h1>
+<p>This document sets out the design for DataFlowSanitizer, a general
+dynamic data flow analysis. Unlike other Sanitizer tools, this tool is
+not designed to detect a specific class of bugs on its own. Instead,
+it provides a generic dynamic data flow analysis framework to be used
+by clients to help detect application-specific issues within their
+own code.</p>
+<p>DataFlowSanitizer is a program instrumentation which can associate
+a number of taint labels with any data stored in any memory region
+accessible by the program. The analysis is dynamic, which means that
+it operates on a running program, and tracks how the labels propagate
+through that program. The tool shall support a large (>100) number
+of labels, such that programs which operate on large numbers of data
+items may be analysed with each data item being tracked separately.</p>
+<div class="section" id="use-cases">
+<h2>Use Cases<a class="headerlink" href="#use-cases" title="Permalink to this headline">¶</a></h2>
+<p>This instrumentation can be used as a tool to help monitor how data
+flows from a program’s inputs (sources) to its outputs (sinks).
+This has applications from a privacy/security perspective in that
+one can audit how a sensitive data item is used within a program and
+ensure it isn’t exiting the program anywhere it shouldn’t be.</p>
+</div>
+<div class="section" id="interface">
+<h2>Interface<a class="headerlink" href="#interface" title="Permalink to this headline">¶</a></h2>
+<p>A number of functions are provided which will create taint labels,
+attach labels to memory regions and extract the set of labels
+associated with a specific memory region. These functions are declared
+in the header file <tt class="docutils literal"><span class="pre">sanitizer/dfsan_interface.h</span></tt>.</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="c1">/// Creates and returns a base label with the given description and user data.</span>
+<span class="n">dfsan_label</span> <span class="nf">dfsan_create_label</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">desc</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="n">userdata</span><span class="p">);</span>
+
+<span class="c1">/// Sets the label for each address in [addr,addr+size) to \c label.</span>
+<span class="kt">void</span> <span class="nf">dfsan_set_label</span><span class="p">(</span><span class="n">dfsan_label</span> <span class="n">label</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="n">addr</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">size</span><span class="p">);</span>
+
+<span class="c1">/// Sets the label for each address in [addr,addr+size) to the union of the</span>
+<span class="c1">/// current label for that address and \c label.</span>
+<span class="kt">void</span> <span class="nf">dfsan_add_label</span><span class="p">(</span><span class="n">dfsan_label</span> <span class="n">label</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="n">addr</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">size</span><span class="p">);</span>
+
+<span class="c1">/// Retrieves the label associated with the given data.</span>
+<span class="c1">///</span>
+<span class="c1">/// The type of 'data' is arbitrary. The function accepts a value of any type,</span>
+<span class="c1">/// which can be truncated or extended (implicitly or explicitly) as necessary.</span>
+<span class="c1">/// The truncation/extension operations will preserve the label of the original</span>
+<span class="c1">/// value.</span>
+<span class="n">dfsan_label</span> <span class="nf">dfsan_get_label</span><span class="p">(</span><span class="kt">long</span> <span class="n">data</span><span class="p">);</span>
+
+<span class="c1">/// Retrieves a pointer to the dfsan_label_info struct for the given label.</span>
+<span class="k">const</span> <span class="k">struct</span> <span class="n">dfsan_label_info</span> <span class="o">*</span><span class="nf">dfsan_get_label_info</span><span class="p">(</span><span class="n">dfsan_label</span> <span class="n">label</span><span class="p">);</span>
+
+<span class="c1">/// Returns whether the given label label contains the label elem.</span>
+<span class="kt">int</span> <span class="nf">dfsan_has_label</span><span class="p">(</span><span class="n">dfsan_label</span> <span class="n">label</span><span class="p">,</span> <span class="n">dfsan_label</span> <span class="n">elem</span><span class="p">);</span>
+
+<span class="c1">/// If the given label label contains a label with the description desc, returns</span>
+<span class="c1">/// that label, else returns 0.</span>
+<span class="n">dfsan_label</span> <span class="nf">dfsan_has_label_with_desc</span><span class="p">(</span><span class="n">dfsan_label</span> <span class="n">label</span><span class="p">,</span> <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">desc</span><span class="p">);</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="taint-label-representation">
+<h2>Taint label representation<a class="headerlink" href="#taint-label-representation" title="Permalink to this headline">¶</a></h2>
+<p>As stated above, the tool must track a large number of taint
+labels. This poses an implementation challenge, as most multiple-label
+tainting systems assign one label per bit to shadow storage, and
+union taint labels using a bitwise or operation. This will not scale
+to clients which use hundreds or thousands of taint labels, as the
+label union operation becomes O(n) in the number of supported labels,
+and data associated with it will quickly dominate the live variable
+set, causing register spills and hampering performance.</p>
+<p>Instead, a low overhead approach is proposed which is best-case O(log<sub>2</sub> n) during execution. The underlying assumption is that
+the required space of label unions is sparse, which is a reasonable
+assumption to make given that we are optimizing for the case where
+applications mostly copy data from one place to another, without often
+invoking the need for an actual union operation. The representation
+of a taint label is a 16-bit integer, and new labels are allocated
+sequentially from a pool. The label identifier 0 is special, and means
+that the data item is unlabelled.</p>
+<p>When a label union operation is requested at a join point (any
+arithmetic or logical operation with two or more operands, such as
+addition), the code checks whether a union is required, whether the
+same union has been requested before, and whether one union label
+subsumes the other. If so, it returns the previously allocated union
+label. If not, it allocates a new union label from the same pool used
+for new labels.</p>
+<p>Specifically, the instrumentation pass will insert code like this
+to decide the union label <tt class="docutils literal"><span class="pre">lu</span></tt> for a pair of labels <tt class="docutils literal"><span class="pre">l1</span></tt>
+and <tt class="docutils literal"><span class="pre">l2</span></tt>:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="n">l1</span> <span class="o">==</span> <span class="n">l2</span><span class="p">)</span>
+ <span class="n">lu</span> <span class="o">=</span> <span class="n">l1</span><span class="p">;</span>
+<span class="k">else</span>
+ <span class="n">lu</span> <span class="o">=</span> <span class="n">__dfsan_union</span><span class="p">(</span><span class="n">l1</span><span class="p">,</span> <span class="n">l2</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>The equality comparison is outlined, to provide an early exit in
+the common cases where the program is processing unlabelled data, or
+where the two data items have the same label. <tt class="docutils literal"><span class="pre">__dfsan_union</span></tt> is
+a runtime library function which performs all other union computation.</p>
+<p>Further optimizations are possible, for example if <tt class="docutils literal"><span class="pre">l1</span></tt> is known
+at compile time to be zero (e.g. it is derived from a constant),
+<tt class="docutils literal"><span class="pre">l2</span></tt> can be used for <tt class="docutils literal"><span class="pre">lu</span></tt>, and vice versa.</p>
+</div>
+<div class="section" id="memory-layout-and-label-management">
+<h2>Memory layout and label management<a class="headerlink" href="#memory-layout-and-label-management" title="Permalink to this headline">¶</a></h2>
+<p>The following is the current memory layout for Linux/x86_64:</p>
+<table border="1" class="docutils">
+<colgroup>
+<col width="30%" />
+<col width="30%" />
+<col width="40%" />
+</colgroup>
+<thead valign="bottom">
+<tr class="row-odd"><th class="head">Start</th>
+<th class="head">End</th>
+<th class="head">Use</th>
+</tr>
+</thead>
+<tbody valign="top">
+<tr class="row-even"><td>0x700000008000</td>
+<td>0x800000000000</td>
+<td>application memory</td>
+</tr>
+<tr class="row-odd"><td>0x200200000000</td>
+<td>0x700000008000</td>
+<td>unused</td>
+</tr>
+<tr class="row-even"><td>0x200000000000</td>
+<td>0x200200000000</td>
+<td>union table</td>
+</tr>
+<tr class="row-odd"><td>0x000000010000</td>
+<td>0x200000000000</td>
+<td>shadow memory</td>
+</tr>
+<tr class="row-even"><td>0x000000000000</td>
+<td>0x000000010000</td>
+<td>reserved by kernel</td>
+</tr>
+</tbody>
+</table>
+<p>Each byte of application memory corresponds to two bytes of shadow
+memory, which are used to store its taint label. As for LLVM SSA
+registers, we have not found it necessary to associate a label with
+each byte or bit of data, as some other tools do. Instead, labels are
+associated directly with registers. Loads will result in a union of
+all shadow labels corresponding to bytes loaded (which most of the
+time will be short circuited by the initial comparison) and stores will
+result in a copy of the label to the shadow of all bytes stored to.</p>
+</div>
+<div class="section" id="propagating-labels-through-arguments">
+<h2>Propagating labels through arguments<a class="headerlink" href="#propagating-labels-through-arguments" title="Permalink to this headline">¶</a></h2>
+<p>In order to propagate labels through function arguments and return values,
+DataFlowSanitizer changes the ABI of each function in the translation unit.
+There are currently two supported ABIs:</p>
+<ul class="simple">
+<li>Args – Argument and return value labels are passed through additional
+arguments and by modifying the return type.</li>
+<li>TLS – Argument and return value labels are passed through TLS variables
+<tt class="docutils literal"><span class="pre">__dfsan_arg_tls</span></tt> and <tt class="docutils literal"><span class="pre">__dfsan_retval_tls</span></tt>.</li>
+</ul>
+<p>The main advantage of the TLS ABI is that it is more tolerant of ABI mismatches
+(TLS storage is not shared with any other form of storage, whereas extra
+arguments may be stored in registers which under the native ABI are not used
+for parameter passing and thus could contain arbitrary values). On the other
+hand the args ABI is more efficient and allows ABI mismatches to be more easily
+identified by checking for nonzero labels in nominally unlabelled programs.</p>
+</div>
+<div class="section" id="implementing-the-abi-list">
+<h2>Implementing the ABI list<a class="headerlink" href="#implementing-the-abi-list" title="Permalink to this headline">¶</a></h2>
+<p>The <a class="reference external" href="DataFlowSanitizer.html#abi-list">ABI list</a> provides a list of functions
+which conform to the native ABI, each of which is callable from an instrumented
+program. This is implemented by replacing each reference to a native ABI
+function with a reference to a function which uses the instrumented ABI.
+Such functions are automatically-generated wrappers for the native functions.
+For example, given the ABI list example provided in the user manual, the
+following wrappers will be generated under the args ABI:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">define</span> <span class="k">linkonce_odr</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="vg">@"dfsw$malloc"</span><span class="p">(</span><span class="k">i64</span> <span class="nv-Anonymous">%0</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%1</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+ <span class="nv-Anonymous">%2</span> <span class="p">=</span> <span class="k">call</span> <span class="k">i8</span><span class="p">*</span> <span class="vg">@malloc</span><span class="p">(</span><span class="k">i64</span> <span class="nv-Anonymous">%0</span><span class="p">)</span>
+ <span class="nv-Anonymous">%3</span> <span class="p">=</span> <span class="k">insertvalue</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="k">undef</span><span class="p">,</span> <span class="k">i8</span><span class="p">*</span> <span class="nv-Anonymous">%2</span><span class="p">,</span> <span class="m">0</span>
+ <span class="nv-Anonymous">%4</span> <span class="p">=</span> <span class="k">insertvalue</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="nv-Anonymous">%3</span><span class="p">,</span> <span class="k">i16</span> <span class="m">0</span><span class="p">,</span> <span class="m">1</span>
+ <span class="k">ret</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="nv-Anonymous">%4</span>
+<span class="p">}</span>
+
+<span class="k">define</span> <span class="k">linkonce_odr</span> <span class="p">{</span> <span class="k">i32</span><span class="p">,</span> <span class="k">i16</span> <span class="p">}</span> <span class="vg">@"dfsw$tolower"</span><span class="p">(</span><span class="k">i32</span> <span class="nv-Anonymous">%0</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%1</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+ <span class="nv-Anonymous">%2</span> <span class="p">=</span> <span class="k">call</span> <span class="k">i32</span> <span class="vg">@tolower</span><span class="p">(</span><span class="k">i32</span> <span class="nv-Anonymous">%0</span><span class="p">)</span>
+ <span class="nv-Anonymous">%3</span> <span class="p">=</span> <span class="k">insertvalue</span> <span class="p">{</span> <span class="k">i32</span><span class="p">,</span> <span class="k">i16</span> <span class="p">}</span> <span class="k">undef</span><span class="p">,</span> <span class="k">i32</span> <span class="nv-Anonymous">%2</span><span class="p">,</span> <span class="m">0</span>
+ <span class="nv-Anonymous">%4</span> <span class="p">=</span> <span class="k">insertvalue</span> <span class="p">{</span> <span class="k">i32</span><span class="p">,</span> <span class="k">i16</span> <span class="p">}</span> <span class="nv-Anonymous">%3</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%1</span><span class="p">,</span> <span class="m">1</span>
+ <span class="k">ret</span> <span class="p">{</span> <span class="k">i32</span><span class="p">,</span> <span class="k">i16</span> <span class="p">}</span> <span class="nv-Anonymous">%4</span>
+<span class="p">}</span>
+
+<span class="k">define</span> <span class="k">linkonce_odr</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="vg">@"dfsw$memcpy"</span><span class="p">(</span><span class="k">i8</span><span class="p">*</span> <span class="nv-Anonymous">%0</span><span class="p">,</span> <span class="k">i8</span><span class="p">*</span> <span class="nv-Anonymous">%1</span><span class="p">,</span> <span class="k">i64</span> <span class="nv-Anonymous">%2</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%3</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%4</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%5</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+ <span class="nv">%labelreturn</span> <span class="p">=</span> <span class="k">alloca</span> <span class="k">i16</span>
+ <span class="nv-Anonymous">%6</span> <span class="p">=</span> <span class="k">call</span> <span class="k">i8</span><span class="p">*</span> <span class="vg">@__dfsw_memcpy</span><span class="p">(</span><span class="k">i8</span><span class="p">*</span> <span class="nv-Anonymous">%0</span><span class="p">,</span> <span class="k">i8</span><span class="p">*</span> <span class="nv-Anonymous">%1</span><span class="p">,</span> <span class="k">i64</span> <span class="nv-Anonymous">%2</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%3</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%4</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%5</span><span class="p">,</span> <span class="k">i16</span><span class="p">*</span> <span class="nv">%labelreturn</span><span class="p">)</span>
+ <span class="nv-Anonymous">%7</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i16</span><span class="p">*</span> <span class="nv">%labelreturn</span>
+ <span class="nv-Anonymous">%8</span> <span class="p">=</span> <span class="k">insertvalue</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="k">undef</span><span class="p">,</span> <span class="k">i8</span><span class="p">*</span> <span class="nv-Anonymous">%6</span><span class="p">,</span> <span class="m">0</span>
+ <span class="nv-Anonymous">%9</span> <span class="p">=</span> <span class="k">insertvalue</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="nv-Anonymous">%8</span><span class="p">,</span> <span class="k">i16</span> <span class="nv-Anonymous">%7</span><span class="p">,</span> <span class="m">1</span>
+ <span class="k">ret</span> <span class="p">{</span> <span class="k">i8</span><span class="p">*,</span> <span class="k">i16</span> <span class="p">}</span> <span class="nv-Anonymous">%9</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>As an optimization, direct calls to native ABI functions will call the
+native ABI function directly and the pass will compute the appropriate label
+internally. This has the advantage of reducing the number of union operations
+required when the return value label is known to be zero (i.e. <tt class="docutils literal"><span class="pre">discard</span></tt>
+functions, or <tt class="docutils literal"><span class="pre">functional</span></tt> functions with known unlabelled arguments).</p>
+</div>
+<div class="section" id="checking-abi-consistency">
+<h2>Checking ABI Consistency<a class="headerlink" href="#checking-abi-consistency" title="Permalink to this headline">¶</a></h2>
+<p>DFSan changes the ABI of each function in the module. This makes it possible
+for a function with the native ABI to be called with the instrumented ABI,
+or vice versa, thus possibly invoking undefined behavior. A simple way
+of statically detecting instances of this problem is to prepend the prefix
+“dfs$” to the name of each instrumented-ABI function.</p>
+<p>This will not catch every such problem; in particular function pointers passed
+across the instrumented-native barrier cannot be used on the other side.
+These problems could potentially be caught dynamically.</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="DataFlowSanitizer.html">DataFlowSanitizer</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="LeakSanitizer.html">LeakSanitizer</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
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@@ -0,0 +1,456 @@
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+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Driver Design & Internals</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="InternalsManual.html">“Clang” CFE Internals Manual</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="PTHInternals.html">Pretokenized Headers (PTH)</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="driver-design-internals">
+<h1>Driver Design & Internals<a class="headerlink" href="#driver-design-internals" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
+<li><a class="reference internal" href="#features-and-goals" id="id3">Features and Goals</a><ul>
+<li><a class="reference internal" href="#gcc-compatibility" id="id4">GCC Compatibility</a></li>
+<li><a class="reference internal" href="#flexible" id="id5">Flexible</a></li>
+<li><a class="reference internal" href="#low-overhead" id="id6">Low Overhead</a></li>
+<li><a class="reference internal" href="#simple" id="id7">Simple</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#internal-design-and-implementation" id="id8">Internal Design and Implementation</a><ul>
+<li><a class="reference internal" href="#internals-introduction" id="id9">Internals Introduction</a></li>
+<li><a class="reference internal" href="#design-overview" id="id10">Design Overview</a></li>
+<li><a class="reference internal" href="#driver-stages" id="id11">Driver Stages</a></li>
+<li><a class="reference internal" href="#additional-notes" id="id12">Additional Notes</a><ul>
+<li><a class="reference internal" href="#the-compilation-object" id="id13">The Compilation Object</a></li>
+<li><a class="reference internal" href="#unified-parsing-pipelining" id="id14">Unified Parsing & Pipelining</a></li>
+<li><a class="reference internal" href="#toolchain-argument-translation" id="id15">ToolChain Argument Translation</a></li>
+<li><a class="reference internal" href="#unused-argument-warnings" id="id16">Unused Argument Warnings</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#relation-to-gcc-driver-concepts" id="id17">Relation to GCC Driver Concepts</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id2">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>This document describes the Clang driver. The purpose of this document
+is to describe both the motivation and design goals for the driver, as
+well as details of the internal implementation.</p>
+</div>
+<div class="section" id="features-and-goals">
+<h2><a class="toc-backref" href="#id3">Features and Goals</a><a class="headerlink" href="#features-and-goals" title="Permalink to this headline">¶</a></h2>
+<p>The Clang driver is intended to be a production quality compiler driver
+providing access to the Clang compiler and tools, with a command line
+interface which is compatible with the gcc driver.</p>
+<p>Although the driver is part of and driven by the Clang project, it is
+logically a separate tool which shares many of the same goals as Clang:</p>
+<div class="contents local topic" id="features">
+<p class="topic-title first">Features</p>
+<ul class="simple">
+<li><a class="reference internal" href="#gcc-compatibility" id="id18">GCC Compatibility</a></li>
+<li><a class="reference internal" href="#flexible" id="id19">Flexible</a></li>
+<li><a class="reference internal" href="#low-overhead" id="id20">Low Overhead</a></li>
+<li><a class="reference internal" href="#simple" id="id21">Simple</a></li>
+</ul>
+</div>
+<div class="section" id="gcc-compatibility">
+<h3><a class="toc-backref" href="#id18">GCC Compatibility</a><a class="headerlink" href="#gcc-compatibility" title="Permalink to this headline">¶</a></h3>
+<p>The number one goal of the driver is to ease the adoption of Clang by
+allowing users to drop Clang into a build system which was designed to
+call GCC. Although this makes the driver much more complicated than
+might otherwise be necessary, we decided that being very compatible with
+the gcc command line interface was worth it in order to allow users to
+quickly test clang on their projects.</p>
+</div>
+<div class="section" id="flexible">
+<h3><a class="toc-backref" href="#id19">Flexible</a><a class="headerlink" href="#flexible" title="Permalink to this headline">¶</a></h3>
+<p>The driver was designed to be flexible and easily accommodate new uses
+as we grow the clang and LLVM infrastructure. As one example, the driver
+can easily support the introduction of tools which have an integrated
+assembler; something we hope to add to LLVM in the future.</p>
+<p>Similarly, most of the driver functionality is kept in a library which
+can be used to build other tools which want to implement or accept a gcc
+like interface.</p>
+</div>
+<div class="section" id="low-overhead">
+<h3><a class="toc-backref" href="#id20">Low Overhead</a><a class="headerlink" href="#low-overhead" title="Permalink to this headline">¶</a></h3>
+<p>The driver should have as little overhead as possible. In practice, we
+found that the gcc driver by itself incurred a small but meaningful
+overhead when compiling many small files. The driver doesn’t do much
+work compared to a compilation, but we have tried to keep it as
+efficient as possible by following a few simple principles:</p>
+<ul class="simple">
+<li>Avoid memory allocation and string copying when possible.</li>
+<li>Don’t parse arguments more than once.</li>
+<li>Provide a few simple interfaces for efficiently searching arguments.</li>
+</ul>
+</div>
+<div class="section" id="simple">
+<h3><a class="toc-backref" href="#id21">Simple</a><a class="headerlink" href="#simple" title="Permalink to this headline">¶</a></h3>
+<p>Finally, the driver was designed to be “as simple as possible”, given
+the other goals. Notably, trying to be completely compatible with the
+gcc driver adds a significant amount of complexity. However, the design
+of the driver attempts to mitigate this complexity by dividing the
+process into a number of independent stages instead of a single
+monolithic task.</p>
+</div>
+</div>
+<div class="section" id="internal-design-and-implementation">
+<h2><a class="toc-backref" href="#id8">Internal Design and Implementation</a><a class="headerlink" href="#internal-design-and-implementation" title="Permalink to this headline">¶</a></h2>
+<div class="contents local topic" id="id1">
+<ul class="simple">
+<li><a class="reference internal" href="#internals-introduction" id="id22">Internals Introduction</a></li>
+<li><a class="reference internal" href="#design-overview" id="id23">Design Overview</a></li>
+<li><a class="reference internal" href="#driver-stages" id="id24">Driver Stages</a></li>
+<li><a class="reference internal" href="#additional-notes" id="id25">Additional Notes</a></li>
+<li><a class="reference internal" href="#relation-to-gcc-driver-concepts" id="id26">Relation to GCC Driver Concepts</a></li>
+</ul>
+</div>
+<div class="section" id="internals-introduction">
+<h3><a class="toc-backref" href="#id22">Internals Introduction</a><a class="headerlink" href="#internals-introduction" title="Permalink to this headline">¶</a></h3>
+<p>In order to satisfy the stated goals, the driver was designed to
+completely subsume the functionality of the gcc executable; that is, the
+driver should not need to delegate to gcc to perform subtasks. On
+Darwin, this implies that the Clang driver also subsumes the gcc
+driver-driver, which is used to implement support for building universal
+images (binaries and object files). This also implies that the driver
+should be able to call the language specific compilers (e.g. cc1)
+directly, which means that it must have enough information to forward
+command line arguments to child processes correctly.</p>
+</div>
+<div class="section" id="design-overview">
+<h3><a class="toc-backref" href="#id23">Design Overview</a><a class="headerlink" href="#design-overview" title="Permalink to this headline">¶</a></h3>
+<p>The diagram below shows the significant components of the driver
+architecture and how they relate to one another. The orange components
+represent concrete data structures built by the driver, the green
+components indicate conceptually distinct stages which manipulate these
+data structures, and the blue components are important helper classes.</p>
+<img alt="Driver Architecture Diagram" class="align-center" src="_images/DriverArchitecture.png" />
+</div>
+<div class="section" id="driver-stages">
+<h3><a class="toc-backref" href="#id24">Driver Stages</a><a class="headerlink" href="#driver-stages" title="Permalink to this headline">¶</a></h3>
+<p>The driver functionality is conceptually divided into five stages:</p>
+<ol class="arabic">
+<li><p class="first"><strong>Parse: Option Parsing</strong></p>
+<p>The command line argument strings are decomposed into arguments
+(<tt class="docutils literal"><span class="pre">Arg</span></tt> instances). The driver expects to understand all available
+options, although there is some facility for just passing certain
+classes of options through (like <tt class="docutils literal"><span class="pre">-Wl,</span></tt>).</p>
+<p>Each argument corresponds to exactly one abstract <tt class="docutils literal"><span class="pre">Option</span></tt>
+definition, which describes how the option is parsed along with some
+additional metadata. The Arg instances themselves are lightweight and
+merely contain enough information for clients to determine which
+option they correspond to and their values (if they have additional
+parameters).</p>
+<p>For example, a command line like “-Ifoo -I foo” would parse to two
+Arg instances (a JoinedArg and a SeparateArg instance), but each
+would refer to the same Option.</p>
+<p>Options are lazily created in order to avoid populating all Option
+classes when the driver is loaded. Most of the driver code only needs
+to deal with options by their unique ID (e.g., <tt class="docutils literal"><span class="pre">options::OPT_I</span></tt>),</p>
+<p>Arg instances themselves do not generally store the values of
+parameters. In many cases, this would simply result in creating
+unnecessary string copies. Instead, Arg instances are always embedded
+inside an ArgList structure, which contains the original vector of
+argument strings. Each Arg itself only needs to contain an index into
+this vector instead of storing its values directly.</p>
+<p>The clang driver can dump the results of this stage using the
+<tt class="docutils literal"><span class="pre">-ccc-print-options</span></tt> flag (which must precede any actual command
+line arguments). For example:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -ccc-print-options -Xarch_i386 -fomit-frame-pointer -Wa,-fast -Ifoo -I foo t.c
+<span class="go">Option 0 - Name: "-Xarch_", Values: {"i386", "-fomit-frame-pointer"}</span>
+<span class="go">Option 1 - Name: "-Wa,", Values: {"-fast"}</span>
+<span class="go">Option 2 - Name: "-I", Values: {"foo"}</span>
+<span class="go">Option 3 - Name: "-I", Values: {"foo"}</span>
+<span class="go">Option 4 - Name: "<input>", Values: {"t.c"}</span>
+</pre></div>
+</div>
+<p>After this stage is complete the command line should be broken down
+into well defined option objects with their appropriate parameters.
+Subsequent stages should rarely, if ever, need to do any string
+processing.</p>
+</li>
+<li><p class="first"><strong>Pipeline: Compilation Job Construction</strong></p>
+<p>Once the arguments are parsed, the tree of subprocess jobs needed for
+the desired compilation sequence are constructed. This involves
+determining the input files and their types, what work is to be done
+on them (preprocess, compile, assemble, link, etc.), and constructing
+a list of Action instances for each task. The result is a list of one
+or more top-level actions, each of which generally corresponds to a
+single output (for example, an object or linked executable).</p>
+<p>The majority of Actions correspond to actual tasks, however there are
+two special Actions. The first is InputAction, which simply serves to
+adapt an input argument for use as an input to other Actions. The
+second is BindArchAction, which conceptually alters the architecture
+to be used for all of its input Actions.</p>
+<p>The clang driver can dump the results of this stage using the
+<tt class="docutils literal"><span class="pre">-ccc-print-phases</span></tt> flag. For example:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -ccc-print-phases -x c t.c -x assembler t.s
+<span class="go">0: input, "t.c", c</span>
+<span class="go">1: preprocessor, {0}, cpp-output</span>
+<span class="go">2: compiler, {1}, assembler</span>
+<span class="go">3: assembler, {2}, object</span>
+<span class="go">4: input, "t.s", assembler</span>
+<span class="go">5: assembler, {4}, object</span>
+<span class="go">6: linker, {3, 5}, image</span>
+</pre></div>
+</div>
+<p>Here the driver is constructing seven distinct actions, four to
+compile the “t.c” input into an object file, two to assemble the
+“t.s” input, and one to link them together.</p>
+<p>A rather different compilation pipeline is shown here; in this
+example there are two top level actions to compile the input files
+into two separate object files, where each object file is built using
+<tt class="docutils literal"><span class="pre">lipo</span></tt> to merge results built for two separate architectures.</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -ccc-print-phases -c -arch i386 -arch x86_64 t0.c t1.c
+<span class="go">0: input, "t0.c", c</span>
+<span class="go">1: preprocessor, {0}, cpp-output</span>
+<span class="go">2: compiler, {1}, assembler</span>
+<span class="go">3: assembler, {2}, object</span>
+<span class="go">4: bind-arch, "i386", {3}, object</span>
+<span class="go">5: bind-arch, "x86_64", {3}, object</span>
+<span class="go">6: lipo, {4, 5}, object</span>
+<span class="go">7: input, "t1.c", c</span>
+<span class="go">8: preprocessor, {7}, cpp-output</span>
+<span class="go">9: compiler, {8}, assembler</span>
+<span class="go">10: assembler, {9}, object</span>
+<span class="go">11: bind-arch, "i386", {10}, object</span>
+<span class="go">12: bind-arch, "x86_64", {10}, object</span>
+<span class="go">13: lipo, {11, 12}, object</span>
+</pre></div>
+</div>
+<p>After this stage is complete the compilation process is divided into
+a simple set of actions which need to be performed to produce
+intermediate or final outputs (in some cases, like <tt class="docutils literal"><span class="pre">-fsyntax-only</span></tt>,
+there is no “real” final output). Phases are well known compilation
+steps, such as “preprocess”, “compile”, “assemble”, “link”, etc.</p>
+</li>
+<li><p class="first"><strong>Bind: Tool & Filename Selection</strong></p>
+<p>This stage (in conjunction with the Translate stage) turns the tree
+of Actions into a list of actual subprocess to run. Conceptually, the
+driver performs a top down matching to assign Action(s) to Tools. The
+ToolChain is responsible for selecting the tool to perform a
+particular action; once selected the driver interacts with the tool
+to see if it can match additional actions (for example, by having an
+integrated preprocessor).</p>
+<p>Once Tools have been selected for all actions, the driver determines
+how the tools should be connected (for example, using an inprocess
+module, pipes, temporary files, or user provided filenames). If an
+output file is required, the driver also computes the appropriate
+file name (the suffix and file location depend on the input types and
+options such as <tt class="docutils literal"><span class="pre">-save-temps</span></tt>).</p>
+<p>The driver interacts with a ToolChain to perform the Tool bindings.
+Each ToolChain contains information about all the tools needed for
+compilation for a particular architecture, platform, and operating
+system. A single driver invocation may query multiple ToolChains
+during one compilation in order to interact with tools for separate
+architectures.</p>
+<p>The results of this stage are not computed directly, but the driver
+can print the results via the <tt class="docutils literal"><span class="pre">-ccc-print-bindings</span></tt> option. For
+example:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -ccc-print-bindings -arch i386 -arch ppc t0.c
+<span class="gp">#</span> <span class="s2">"i386-apple-darwin9"</span> - <span class="s2">"clang"</span>, inputs: <span class="o">[</span><span class="s2">"t0.c"</span><span class="o">]</span>, output: <span class="s2">"/tmp/cc-Sn4RKF.s"</span>
+<span class="gp">#</span> <span class="s2">"i386-apple-darwin9"</span> - <span class="s2">"darwin::Assemble"</span>, inputs: <span class="o">[</span><span class="s2">"/tmp/cc-Sn4RKF.s"</span><span class="o">]</span>, output: <span class="s2">"/tmp/cc-gvSnbS.o"</span>
+<span class="gp">#</span> <span class="s2">"i386-apple-darwin9"</span> - <span class="s2">"darwin::Link"</span>, inputs: <span class="o">[</span><span class="s2">"/tmp/cc-gvSnbS.o"</span><span class="o">]</span>, output: <span class="s2">"/tmp/cc-jgHQxi.out"</span>
+<span class="gp">#</span> <span class="s2">"ppc-apple-darwin9"</span> - <span class="s2">"gcc::Compile"</span>, inputs: <span class="o">[</span><span class="s2">"t0.c"</span><span class="o">]</span>, output: <span class="s2">"/tmp/cc-Q0bTox.s"</span>
+<span class="gp">#</span> <span class="s2">"ppc-apple-darwin9"</span> - <span class="s2">"gcc::Assemble"</span>, inputs: <span class="o">[</span><span class="s2">"/tmp/cc-Q0bTox.s"</span><span class="o">]</span>, output: <span class="s2">"/tmp/cc-WCdicw.o"</span>
+<span class="gp">#</span> <span class="s2">"ppc-apple-darwin9"</span> - <span class="s2">"gcc::Link"</span>, inputs: <span class="o">[</span><span class="s2">"/tmp/cc-WCdicw.o"</span><span class="o">]</span>, output: <span class="s2">"/tmp/cc-HHBEBh.out"</span>
+<span class="gp">#</span> <span class="s2">"i386-apple-darwin9"</span> - <span class="s2">"darwin::Lipo"</span>, inputs: <span class="o">[</span><span class="s2">"/tmp/cc-jgHQxi.out"</span>, <span class="s2">"/tmp/cc-HHBEBh.out"</span><span class="o">]</span>, output: <span class="s2">"a.out"</span>
+</pre></div>
+</div>
+<p>This shows the tool chain, tool, inputs and outputs which have been
+bound for this compilation sequence. Here clang is being used to
+compile t0.c on the i386 architecture and darwin specific versions of
+the tools are being used to assemble and link the result, but generic
+gcc versions of the tools are being used on PowerPC.</p>
+</li>
+<li><p class="first"><strong>Translate: Tool Specific Argument Translation</strong></p>
+<p>Once a Tool has been selected to perform a particular Action, the
+Tool must construct concrete Jobs which will be executed during
+compilation. The main work is in translating from the gcc style
+command line options to whatever options the subprocess expects.</p>
+<p>Some tools, such as the assembler, only interact with a handful of
+arguments and just determine the path of the executable to call and
+pass on their input and output arguments. Others, like the compiler
+or the linker, may translate a large number of arguments in addition.</p>
+<p>The ArgList class provides a number of simple helper methods to
+assist with translating arguments; for example, to pass on only the
+last of arguments corresponding to some option, or all arguments for
+an option.</p>
+<p>The result of this stage is a list of Jobs (executable paths and
+argument strings) to execute.</p>
+</li>
+<li><p class="first"><strong>Execute</strong></p>
+<p>Finally, the compilation pipeline is executed. This is mostly
+straightforward, although there is some interaction with options like
+<tt class="docutils literal"><span class="pre">-pipe</span></tt>, <tt class="docutils literal"><span class="pre">-pass-exit-codes</span></tt> and <tt class="docutils literal"><span class="pre">-time</span></tt>.</p>
+</li>
+</ol>
+</div>
+<div class="section" id="additional-notes">
+<h3><a class="toc-backref" href="#id25">Additional Notes</a><a class="headerlink" href="#additional-notes" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="the-compilation-object">
+<h4><a class="toc-backref" href="#id13">The Compilation Object</a><a class="headerlink" href="#the-compilation-object" title="Permalink to this headline">¶</a></h4>
+<p>The driver constructs a Compilation object for each set of command line
+arguments. The Driver itself is intended to be invariant during
+construction of a Compilation; an IDE should be able to construct a
+single long lived driver instance to use for an entire build, for
+example.</p>
+<p>The Compilation object holds information that is particular to each
+compilation sequence. For example, the list of used temporary files
+(which must be removed once compilation is finished) and result files
+(which should be removed if compilation fails).</p>
+</div>
+<div class="section" id="unified-parsing-pipelining">
+<h4><a class="toc-backref" href="#id14">Unified Parsing & Pipelining</a><a class="headerlink" href="#unified-parsing-pipelining" title="Permalink to this headline">¶</a></h4>
+<p>Parsing and pipelining both occur without reference to a Compilation
+instance. This is by design; the driver expects that both of these
+phases are platform neutral, with a few very well defined exceptions
+such as whether the platform uses a driver driver.</p>
+</div>
+<div class="section" id="toolchain-argument-translation">
+<h4><a class="toc-backref" href="#id15">ToolChain Argument Translation</a><a class="headerlink" href="#toolchain-argument-translation" title="Permalink to this headline">¶</a></h4>
+<p>In order to match gcc very closely, the clang driver currently allows
+tool chains to perform their own translation of the argument list (into
+a new ArgList data structure). Although this allows the clang driver to
+match gcc easily, it also makes the driver operation much harder to
+understand (since the Tools stop seeing some arguments the user
+provided, and see new ones instead).</p>
+<p>For example, on Darwin <tt class="docutils literal"><span class="pre">-gfull</span></tt> gets translated into two separate
+arguments, <tt class="docutils literal"><span class="pre">-g</span></tt> and <tt class="docutils literal"><span class="pre">-fno-eliminate-unused-debug-symbols</span></tt>. Trying to
+write Tool logic to do something with <tt class="docutils literal"><span class="pre">-gfull</span></tt> will not work, because
+Tool argument translation is done after the arguments have been
+translated.</p>
+<p>A long term goal is to remove this tool chain specific translation, and
+instead force each tool to change its own logic to do the right thing on
+the untranslated original arguments.</p>
+</div>
+<div class="section" id="unused-argument-warnings">
+<h4><a class="toc-backref" href="#id16">Unused Argument Warnings</a><a class="headerlink" href="#unused-argument-warnings" title="Permalink to this headline">¶</a></h4>
+<p>The driver operates by parsing all arguments but giving Tools the
+opportunity to choose which arguments to pass on. One downside of this
+infrastructure is that if the user misspells some option, or is confused
+about which options to use, some command line arguments the user really
+cared about may go unused. This problem is particularly important when
+using clang as a compiler, since the clang compiler does not support
+anywhere near all the options that gcc does, and we want to make sure
+users know which ones are being used.</p>
+<p>To support this, the driver maintains a bit associated with each
+argument of whether it has been used (at all) during the compilation.
+This bit usually doesn’t need to be set by hand, as the key ArgList
+accessors will set it automatically.</p>
+<p>When a compilation is successful (there are no errors), the driver
+checks the bit and emits an “unused argument” warning for any arguments
+which were never accessed. This is conservative (the argument may not
+have been used to do what the user wanted) but still catches the most
+obvious cases.</p>
+</div>
+</div>
+<div class="section" id="relation-to-gcc-driver-concepts">
+<h3><a class="toc-backref" href="#id26">Relation to GCC Driver Concepts</a><a class="headerlink" href="#relation-to-gcc-driver-concepts" title="Permalink to this headline">¶</a></h3>
+<p>For those familiar with the gcc driver, this section provides a brief
+overview of how things from the gcc driver map to the clang driver.</p>
+<ul>
+<li><p class="first"><strong>Driver Driver</strong></p>
+<p>The driver driver is fully integrated into the clang driver. The
+driver simply constructs additional Actions to bind the architecture
+during the <em>Pipeline</em> phase. The tool chain specific argument
+translation is responsible for handling <tt class="docutils literal"><span class="pre">-Xarch_</span></tt>.</p>
+<p>The one caveat is that this approach requires <tt class="docutils literal"><span class="pre">-Xarch_</span></tt> not be used
+to alter the compilation itself (for example, one cannot provide
+<tt class="docutils literal"><span class="pre">-S</span></tt> as an <tt class="docutils literal"><span class="pre">-Xarch_</span></tt> argument). The driver attempts to reject
+such invocations, and overall there isn’t a good reason to abuse
+<tt class="docutils literal"><span class="pre">-Xarch_</span></tt> to that end in practice.</p>
+<p>The upside is that the clang driver is more efficient and does little
+extra work to support universal builds. It also provides better error
+reporting and UI consistency.</p>
+</li>
+<li><p class="first"><strong>Specs</strong></p>
+<p>The clang driver has no direct correspondent for “specs”. The
+majority of the functionality that is embedded in specs is in the
+Tool specific argument translation routines. The parts of specs which
+control the compilation pipeline are generally part of the <em>Pipeline</em>
+stage.</p>
+</li>
+<li><p class="first"><strong>Toolchains</strong></p>
+<p>The gcc driver has no direct understanding of tool chains. Each gcc
+binary roughly corresponds to the information which is embedded
+inside a single ToolChain.</p>
+<p>The clang driver is intended to be portable and support complex
+compilation environments. All platform and tool chain specific code
+should be protected behind either abstract or well defined interfaces
+(such as whether the platform supports use as a driver driver).</p>
+</li>
+</ul>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="InternalsManual.html">“Clang” CFE Internals Manual</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="PTHInternals.html">Pretokenized Headers (PTH)</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
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+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
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+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>External Clang Examples — Clang 3.6 documentation</title>
+
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+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
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+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
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+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="Introduction to the Clang AST" href="IntroductionToTheClangAST.html" />
+ <link rel="prev" title="Choosing the Right Interface for Your Application" href="Tooling.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>External Clang Examples</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="Tooling.html">Choosing the Right Interface for Your Application</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="IntroductionToTheClangAST.html">Introduction to the Clang AST</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="external-clang-examples">
+<h1>External Clang Examples<a class="headerlink" href="#external-clang-examples" title="Permalink to this headline">¶</a></h1>
+<div class="section" id="introduction">
+<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>This page provides some examples of the kinds of things that people have
+done with Clang that might serve as useful guides (or starting points) from
+which to develop your own tools. They may be helpful even for something as
+banal (but necessary) as how to set up your build to integrate Clang.</p>
+<p>Clang’s library-based design is deliberately aimed at facilitating use by
+external projects, and we are always interested in improving Clang to
+better serve our external users. Some typical categories of applications
+where Clang is used are:</p>
+<ul class="simple">
+<li>Static analysis.</li>
+<li>Documentation/cross-reference generation.</li>
+</ul>
+<p>If you know of (or wrote!) a tool or project using Clang, please send an
+email to Clang’s <a class="reference external" href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">development discussion mailing list</a> to have it added.
+(or if you are already a Clang contributor, feel free to directly commit
+additions). Since the primary purpose of this page is to provide examples
+that can help developers, generally they must have code available.</p>
+</div>
+<div class="section" id="list-of-projects-and-tools">
+<h2>List of projects and tools<a class="headerlink" href="#list-of-projects-and-tools" title="Permalink to this headline">¶</a></h2>
+<dl class="docutils">
+<dt><a class="reference external" href="https://github.com/Andersbakken/rtags/">https://github.com/Andersbakken/rtags/</a></dt>
+<dd>“RTags is a client/server application that indexes c/c++ code and keeps
+a persistent in-memory database of references, symbolnames, completions
+etc.”</dd>
+<dt><a class="reference external" href="http://rprichard.github.com/sourceweb/">http://rprichard.github.com/sourceweb/</a></dt>
+<dd>“A C/C++ source code indexer and navigator”</dd>
+<dt><a class="reference external" href="https://github.com/etaoins/qconnectlint">https://github.com/etaoins/qconnectlint</a></dt>
+<dd>“qconnectlint is a Clang tool for statically verifying the consistency
+of signal and slot connections made with Qt’s <tt class="docutils literal"><span class="pre">QObject::connect</span></tt>.”</dd>
+<dt><a class="reference external" href="https://github.com/woboq/woboq_codebrowser">https://github.com/woboq/woboq_codebrowser</a></dt>
+<dd>“The Woboq Code Browser is a web-based code browser for C/C++ projects.
+Check out <a class="reference external" href="http://code.woboq.org/">http://code.woboq.org/</a> for an example!”</dd>
+<dt><a class="reference external" href="https://github.com/mozilla/dxr">https://github.com/mozilla/dxr</a></dt>
+<dd>“DXR is a source code cross-reference tool that uses static analysis
+data collected by instrumented compilers.”</dd>
+<dt><a class="reference external" href="https://github.com/eschulte/clang-mutate">https://github.com/eschulte/clang-mutate</a></dt>
+<dd>“This tool performs a number of operations on C-language source files.”</dd>
+<dt><a class="reference external" href="https://github.com/gmarpons/Crisp">https://github.com/gmarpons/Crisp</a></dt>
+<dd>“A coding rule validation add-on for LLVM/clang. Crisp rules are written
+in Prolog. A high-level declarative DSL to easily write new rules is under
+development. It will be called CRISP, an acronym for <em>Coding Rules in
+Sugared Prolog</em>.”</dd>
+<dt><a class="reference external" href="https://github.com/drothlis/clang-ctags">https://github.com/drothlis/clang-ctags</a></dt>
+<dd>“Generate tag file for C++ source code.”</dd>
+<dt><a class="reference external" href="https://github.com/exclipy/clang_indexer">https://github.com/exclipy/clang_indexer</a></dt>
+<dd>“This is an indexer for C and C++ based on the libclang library.”</dd>
+<dt><a class="reference external" href="https://github.com/holtgrewe/linty">https://github.com/holtgrewe/linty</a></dt>
+<dd>“Linty - C/C++ Style Checking with Python & libclang.”</dd>
+<dt><a class="reference external" href="https://github.com/axw/cmonster">https://github.com/axw/cmonster</a></dt>
+<dd>“cmonster is a Python wrapper for the Clang C++ parser.”</dd>
+<dt><a class="reference external" href="https://github.com/rizsotto/Constantine">https://github.com/rizsotto/Constantine</a></dt>
+<dd>“Constantine is a toy project to learn how to write clang plugin.
+Implements pseudo const analysis. Generates warnings about variables,
+which were declared without const qualifier.”</dd>
+<dt><a class="reference external" href="https://github.com/jessevdk/cldoc">https://github.com/jessevdk/cldoc</a></dt>
+<dd>“cldoc is a Clang based documentation generator for C and C++.
+cldoc tries to solve the issue of writing C/C++ software documentation
+with a modern, non-intrusive and robust approach.”</dd>
+<dt><a class="reference external" href="https://github.com/AlexDenisov/ToyClangPlugin">https://github.com/AlexDenisov/ToyClangPlugin</a></dt>
+<dd>“The simplest Clang plugin implementing a semantic check for Objective-C.
+This example shows how to use the <tt class="docutils literal"><span class="pre">DiagnosticsEngine</span></tt> (emit warnings,
+errors, fixit hints). See also <a class="reference external" href="http://l.rw.rw/clang_plugin">http://l.rw.rw/clang_plugin</a> for
+step-by-step instructions.”</dd>
+</dl>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="Tooling.html">Choosing the Right Interface for Your Application</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="IntroductionToTheClangAST.html">Introduction to the Clang AST</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
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+
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+ };
+ </script>
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+ <link rel="next" title="Choosing the Right Interface for Your Application" href="Tooling.html" />
+ <link rel="prev" title="MSVC compatibility" href="MSVCCompatibility.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Frequently Asked Questions (FAQ)</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="MSVCCompatibility.html">MSVC compatibility</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="Tooling.html">Choosing the Right Interface for Your Application</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="frequently-asked-questions-faq">
+<h1>Frequently Asked Questions (FAQ)<a class="headerlink" href="#frequently-asked-questions-faq" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#driver" id="id1">Driver</a><ul>
+<li><a class="reference internal" href="#i-run-clang-cc1-and-get-weird-errors-about-missing-headers" id="id2">I run <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span> <span class="pre">...</span></tt> and get weird errors about missing headers</a></li>
+<li><a class="reference internal" href="#i-get-errors-about-some-headers-being-missing-stddef-h-stdarg-h" id="id3">I get errors about some headers being missing (<tt class="docutils literal"><span class="pre">stddef.h</span></tt>, <tt class="docutils literal"><span class="pre">stdarg.h</span></tt>)</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="driver">
+<h2><a class="toc-backref" href="#id1">Driver</a><a class="headerlink" href="#driver" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="i-run-clang-cc1-and-get-weird-errors-about-missing-headers">
+<h3><a class="toc-backref" href="#id2">I run <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span> <span class="pre">...</span></tt> and get weird errors about missing headers</a><a class="headerlink" href="#i-run-clang-cc1-and-get-weird-errors-about-missing-headers" title="Permalink to this headline">¶</a></h3>
+<p>Given this source file:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="cp">#include <stdio.h></span>
+
+<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
+ <span class="n">printf</span><span class="p">(</span><span class="s">"Hello world</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>If you run:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -cc1 hello.c
+<span class="go">hello.c:1:10: fatal error: 'stdio.h' file not found</span>
+<span class="gp">#</span>include <stdio.h>
+<span class="go"> ^</span>
+<span class="go">1 error generated.</span>
+</pre></div>
+</div>
+<p><tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt> is the frontend, <tt class="docutils literal"><span class="pre">clang</span></tt> is the <a class="reference internal" href="DriverInternals.html"><em>driver</em></a>. The driver invokes the frontend with options appropriate
+for your system. To see these options, run:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang -### -c hello.c
+</pre></div>
+</div>
+<p>Some clang command line options are driver-only options, some are frontend-only
+options. Frontend-only options are intended to be used only by clang developers.
+Users should not run <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt> directly, because <tt class="docutils literal"><span class="pre">-cc1</span></tt> options are not
+guaranteed to be stable.</p>
+<p>If you want to use a frontend-only option (“a <tt class="docutils literal"><span class="pre">-cc1</span></tt> option”), for example
+<tt class="docutils literal"><span class="pre">-ast-dump</span></tt>, then you need to take the <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt> line generated by the
+driver and add the option you need. Alternatively, you can run
+<tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-Xclang</span> <span class="pre"><option></span> <span class="pre">...</span></tt> to force the driver pass <tt class="docutils literal"><span class="pre"><option></span></tt> to
+<tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span></tt>.</p>
+</div>
+<div class="section" id="i-get-errors-about-some-headers-being-missing-stddef-h-stdarg-h">
+<h3><a class="toc-backref" href="#id3">I get errors about some headers being missing (<tt class="docutils literal"><span class="pre">stddef.h</span></tt>, <tt class="docutils literal"><span class="pre">stdarg.h</span></tt>)</a><a class="headerlink" href="#i-get-errors-about-some-headers-being-missing-stddef-h-stdarg-h" title="Permalink to this headline">¶</a></h3>
+<p>Some header files (<tt class="docutils literal"><span class="pre">stddef.h</span></tt>, <tt class="docutils literal"><span class="pre">stdarg.h</span></tt>, and others) are shipped with
+Clang — these are called builtin includes. Clang searches for them in a
+directory relative to the location of the <tt class="docutils literal"><span class="pre">clang</span></tt> binary. If you moved the
+<tt class="docutils literal"><span class="pre">clang</span></tt> binary, you need to move the builtin headers, too.</p>
+<p>More information can be found in the <a class="reference internal" href="LibTooling.html#libtooling-builtin-includes"><em>Builtin includes</em></a>
+section.</p>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="MSVCCompatibility.html">MSVC compatibility</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="Tooling.html">Choosing the Right Interface for Your Application</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
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@@ -0,0 +1,240 @@
+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>How To Setup Clang Tooling For LLVM — Clang 3.6 documentation</title>
+
+ <link rel="stylesheet" href="_static/haiku.css" type="text/css" />
+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
+ <link rel="stylesheet" href="_static/print.css" type="text/css" />
+
+ <script type="text/javascript">
+ var DOCUMENTATION_OPTIONS = {
+ URL_ROOT: '',
+ VERSION: '3.6',
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+ FILE_SUFFIX: '.html',
+ HAS_SOURCE: true
+ };
+ </script>
+ <script type="text/javascript" src="_static/jquery.js"></script>
+ <script type="text/javascript" src="_static/underscore.js"></script>
+ <script type="text/javascript" src="_static/doctools.js"></script>
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+ <script type="text/javascript" src="_static/theme_extras.js"></script>
+ <link rel="top" title="Clang 3.6 documentation" href="index.html" />
+ <link rel="next" title="JSON Compilation Database Format Specification" href="JSONCompilationDatabase.html" />
+ <link rel="prev" title="Matching the Clang AST" href="LibASTMatchers.html" />
+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>How To Setup Clang Tooling For LLVM</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="LibASTMatchers.html">Matching the Clang AST</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="JSONCompilationDatabase.html">JSON Compilation Database Format Specification</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="how-to-setup-clang-tooling-for-llvm">
+<h1>How To Setup Clang Tooling For LLVM<a class="headerlink" href="#how-to-setup-clang-tooling-for-llvm" title="Permalink to this headline">¶</a></h1>
+<p>Clang Tooling provides infrastructure to write tools that need syntactic
+and semantic information about a program. This term also relates to a set
+of specific tools using this infrastructure (e.g. <tt class="docutils literal"><span class="pre">clang-check</span></tt>). This
+document provides information on how to set up and use Clang Tooling for
+the LLVM source code.</p>
+<div class="section" id="introduction">
+<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>Clang Tooling needs a compilation database to figure out specific build
+options for each file. Currently it can create a compilation database
+from the <tt class="docutils literal"><span class="pre">compilation_commands.json</span></tt> file, generated by CMake. When
+invoking clang tools, you can either specify a path to a build directory
+using a command line parameter <tt class="docutils literal"><span class="pre">-p</span></tt> or let Clang Tooling find this
+file in your source tree. In either case you need to configure your
+build using CMake to use clang tools.</p>
+</div>
+<div class="section" id="setup-clang-tooling-using-cmake-and-make">
+<h2>Setup Clang Tooling Using CMake and Make<a class="headerlink" href="#setup-clang-tooling-using-cmake-and-make" title="Permalink to this headline">¶</a></h2>
+<p>If you intend to use make to build LLVM, you should have CMake 2.8.6 or
+later installed (can be found <a class="reference external" href="http://cmake.org">here</a>).</p>
+<p>First, you need to generate Makefiles for LLVM with CMake. You need to
+make a build directory and run CMake from it:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> mkdir your/build/directory
+<span class="gp">$</span> <span class="nb">cd </span>your/build/directory
+<span class="gp">$</span> cmake -DCMAKE_EXPORT_COMPILE_COMMANDS<span class="o">=</span>ON path/to/llvm/sources
+</pre></div>
+</div>
+<p>If you want to use clang instead of GCC, you can add
+<tt class="docutils literal"><span class="pre">-DCMAKE_C_COMPILER=/path/to/clang</span> <span class="pre">-DCMAKE_CXX_COMPILER=/path/to/clang++</span></tt>.
+You can also use <tt class="docutils literal"><span class="pre">ccmake</span></tt>, which provides a curses interface to configure
+CMake variables for lazy people.</p>
+<p>As a result, the new <tt class="docutils literal"><span class="pre">compile_commands.json</span></tt> file should appear in the
+current directory. You should link it to the LLVM source tree so that
+Clang Tooling is able to use it:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> ln -s <span class="nv">$PWD</span>/compile_commands.json path/to/llvm/source/
+</pre></div>
+</div>
+<p>Now you are ready to build and test LLVM using make:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> make check-all
+</pre></div>
+</div>
+</div>
+<div class="section" id="using-clang-tools">
+<h2>Using Clang Tools<a class="headerlink" href="#using-clang-tools" title="Permalink to this headline">¶</a></h2>
+<p>After you completed the previous steps, you are ready to run clang tools. If
+you have a recent clang installed, you should have <tt class="docutils literal"><span class="pre">clang-check</span></tt> in
+<tt class="docutils literal"><span class="pre">$PATH</span></tt>. Try to run it on any <tt class="docutils literal"><span class="pre">.cpp</span></tt> file inside the LLVM source tree:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang-check tools/clang/lib/Tooling/CompilationDatabase.cpp
+</pre></div>
+</div>
+<p>If you’re using vim, it’s convenient to have clang-check integrated. Put
+this into your <tt class="docutils literal"><span class="pre">.vimrc</span></tt>:</p>
+<div class="highlight-python"><pre>function! ClangCheckImpl(cmd)
+ if &autowrite | wall | endif
+ echo "Running " . a:cmd . " ..."
+ let l:output = system(a:cmd)
+ cexpr l:output
+ cwindow
+ let w:quickfix_title = a:cmd
+ if v:shell_error != 0
+ cc
+ endif
+ let g:clang_check_last_cmd = a:cmd
+endfunction
+
+function! ClangCheck()
+ let l:filename = expand('%')
+ if l:filename =~ '\.\(cpp\|cxx\|cc\|c\)$'
+ call ClangCheckImpl("clang-check " . l:filename)
+ elseif exists("g:clang_check_last_cmd")
+ call ClangCheckImpl(g:clang_check_last_cmd)
+ else
+ echo "Can't detect file's compilation arguments and no previous clang-check invocation!"
+ endif
+endfunction
+
+nmap <silent> <F5> :call ClangCheck()<CR><CR></pre>
+</div>
+<p>When editing a .cpp/.cxx/.cc/.c file, hit F5 to reparse the file. In
+case the current file has a different extension (for example, .h), F5
+will re-run the last clang-check invocation made from this vim instance
+(if any). The output will go into the error window, which is opened
+automatically when clang-check finds errors, and can be re-opened with
+<tt class="docutils literal"><span class="pre">:cope</span></tt>.</p>
+<p>Other <tt class="docutils literal"><span class="pre">clang-check</span></tt> options that can be useful when working with clang
+AST:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">-ast-print</span></tt> — Build ASTs and then pretty-print them.</li>
+<li><tt class="docutils literal"><span class="pre">-ast-dump</span></tt> — Build ASTs and then debug dump them.</li>
+<li><tt class="docutils literal"><span class="pre">-ast-dump-filter=<string></span></tt> — Use with <tt class="docutils literal"><span class="pre">-ast-dump</span></tt> or <tt class="docutils literal"><span class="pre">-ast-print</span></tt> to
+dump/print only AST declaration nodes having a certain substring in a
+qualified name. Use <tt class="docutils literal"><span class="pre">-ast-list</span></tt> to list all filterable declaration node
+names.</li>
+<li><tt class="docutils literal"><span class="pre">-ast-list</span></tt> — Build ASTs and print the list of declaration node qualified
+names.</li>
+</ul>
+<p>Examples:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> clang-check tools/clang/tools/clang-check/ClangCheck.cpp -ast-dump -ast-dump-filter ActionFactory::newASTConsumer
+<span class="go">Processing: tools/clang/tools/clang-check/ClangCheck.cpp.</span>
+<span class="go">Dumping ::ActionFactory::newASTConsumer:</span>
+<span class="go">clang::ASTConsumer *newASTConsumer() (CompoundStmt 0x44da290 </home/alexfh/local/llvm/tools/clang/tools/clang-check/ClangCheck.cpp:64:40, line:72:3></span>
+<span class="go"> (IfStmt 0x44d97c8 <line:65:5, line:66:45></span>
+<span class="go"> <<<NULL>>></span>
+<span class="go"> (ImplicitCastExpr 0x44d96d0 <line:65:9> '_Bool':'_Bool' <UserDefinedConversion></span>
+<span class="go">...</span>
+<span class="gp">$</span> clang-check tools/clang/tools/clang-check/ClangCheck.cpp -ast-print -ast-dump-filter ActionFactory::newASTConsumer
+<span class="go">Processing: tools/clang/tools/clang-check/ClangCheck.cpp.</span>
+<span class="go">Printing <anonymous namespace>::ActionFactory::newASTConsumer:</span>
+<span class="go">clang::ASTConsumer *newASTConsumer() {</span>
+<span class="go"> if (this->ASTList.operator _Bool())</span>
+<span class="go"> return clang::CreateASTDeclNodeLister();</span>
+<span class="go"> if (this->ASTDump.operator _Bool())</span>
+<span class="go"> return clang::CreateASTDumper(this->ASTDumpFilter);</span>
+<span class="go"> if (this->ASTPrint.operator _Bool())</span>
+<span class="go"> return clang::CreateASTPrinter(&llvm::outs(), this->ASTDumpFilter);</span>
+<span class="go"> return new clang::ASTConsumer();</span>
+<span class="go">}</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="experimental-using-ninja-build-system">
+<h2>(Experimental) Using Ninja Build System<a class="headerlink" href="#experimental-using-ninja-build-system" title="Permalink to this headline">¶</a></h2>
+<p>Optionally you can use the <a class="reference external" href="https://github.com/martine/ninja">Ninja</a>
+build system instead of make. It is aimed at making your builds faster.
+Currently this step will require building Ninja from sources.</p>
+<p>To take advantage of using Clang Tools along with Ninja build you need
+at least CMake 2.8.9.</p>
+<p>Clone the Ninja git repository and build Ninja from sources:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> git clone git://github.com/martine/ninja.git
+<span class="gp">$</span> <span class="nb">cd </span>ninja/
+<span class="gp">$</span> ./bootstrap.py
+</pre></div>
+</div>
+<p>This will result in a single binary <tt class="docutils literal"><span class="pre">ninja</span></tt> in the current directory.
+It doesn’t require installation and can just be copied to any location
+inside <tt class="docutils literal"><span class="pre">$PATH</span></tt>, say <tt class="docutils literal"><span class="pre">/usr/local/bin/</span></tt>:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> sudo cp ninja /usr/local/bin/
+<span class="gp">$</span> sudo chmod a+rx /usr/local/bin/ninja
+</pre></div>
+</div>
+<p>After doing all of this, you’ll need to generate Ninja build files for
+LLVM with CMake. You need to make a build directory and run CMake from
+it:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> mkdir your/build/directory
+<span class="gp">$</span> <span class="nb">cd </span>your/build/directory
+<span class="gp">$</span> cmake -G Ninja -DCMAKE_EXPORT_COMPILE_COMMANDS<span class="o">=</span>ON path/to/llvm/sources
+</pre></div>
+</div>
+<p>If you want to use clang instead of GCC, you can add
+<tt class="docutils literal"><span class="pre">-DCMAKE_C_COMPILER=/path/to/clang</span> <span class="pre">-DCMAKE_CXX_COMPILER=/path/to/clang++</span></tt>.
+You can also use <tt class="docutils literal"><span class="pre">ccmake</span></tt>, which provides a curses interface to configure
+CMake variables in an interactive manner.</p>
+<p>As a result, the new <tt class="docutils literal"><span class="pre">compile_commands.json</span></tt> file should appear in the
+current directory. You should link it to the LLVM source tree so that
+Clang Tooling is able to use it:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> ln -s <span class="nv">$PWD</span>/compile_commands.json path/to/llvm/source/
+</pre></div>
+</div>
+<p>Now you are ready to build and test LLVM using Ninja:</p>
+<div class="highlight-console"><div class="highlight"><pre><span class="gp">$</span> ninja check-all
+</pre></div>
+</div>
+<p>Other target names can be used in the same way as with make.</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="LibASTMatchers.html">Matching the Clang AST</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="JSONCompilationDatabase.html">JSON Compilation Database Format Specification</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
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@@ -0,0 +1,1880 @@
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+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+ <head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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+ <title>âClangâ CFE Internals Manual — Clang 3.6 documentation</title>
+
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+ <link rel="stylesheet" href="_static/pygments.css" type="text/css" />
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+
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+ };
+ </script>
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+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>âClangâ CFE Internals Manual</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="ClangFormatStyleOptions.html">Clang-Format Style Options</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="DriverInternals.html">Driver Design & Internals</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="clang-cfe-internals-manual">
+<h1>“Clang” CFE Internals Manual<a class="headerlink" href="#clang-cfe-internals-manual" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
+<li><a class="reference internal" href="#llvm-support-library" id="id3">LLVM Support Library</a></li>
+<li><a class="reference internal" href="#the-clang-basic-library" id="id4">The Clang “Basic” Library</a><ul>
+<li><a class="reference internal" href="#the-diagnostics-subsystem" id="id5">The Diagnostics Subsystem</a><ul>
+<li><a class="reference internal" href="#the-diagnostic-kinds-td-files" id="id6">The <tt class="docutils literal"><span class="pre">Diagnostic*Kinds.td</span></tt> files</a></li>
+<li><a class="reference internal" href="#the-format-string" id="id7">The Format String</a></li>
+<li><a class="reference internal" href="#formatting-a-diagnostic-argument" id="id8">Formatting a Diagnostic Argument</a></li>
+<li><a class="reference internal" href="#producing-the-diagnostic" id="id9">Producing the Diagnostic</a></li>
+<li><a class="reference internal" href="#fix-it-hints" id="id10">Fix-It Hints</a></li>
+<li><a class="reference internal" href="#the-diagnosticclient-interface" id="id11">The <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt> Interface</a></li>
+<li><a class="reference internal" href="#adding-translations-to-clang" id="id12">Adding Translations to Clang</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#the-sourcelocation-and-sourcemanager-classes" id="id13">The <tt class="docutils literal"><span class="pre">SourceLocation</span></tt> and <tt class="docutils literal"><span class="pre">SourceManager</span></tt> classes</a></li>
+<li><a class="reference internal" href="#sourcerange-and-charsourcerange" id="id14"><tt class="docutils literal"><span class="pre">SourceRange</span></tt> and <tt class="docutils literal"><span class="pre">CharSourceRange</span></tt></a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#the-driver-library" id="id15">The Driver Library</a></li>
+<li><a class="reference internal" href="#precompiled-headers" id="id16">Precompiled Headers</a></li>
+<li><a class="reference internal" href="#the-frontend-library" id="id17">The Frontend Library</a></li>
+<li><a class="reference internal" href="#the-lexer-and-preprocessor-library" id="id18">The Lexer and Preprocessor Library</a><ul>
+<li><a class="reference internal" href="#the-token-class" id="id19">The Token class</a></li>
+<li><a class="reference internal" href="#annotation-tokens" id="id20">Annotation Tokens</a></li>
+<li><a class="reference internal" href="#the-lexer-class" id="id21">The <tt class="docutils literal"><span class="pre">Lexer</span></tt> class</a></li>
+<li><a class="reference internal" href="#the-tokenlexer-class" id="id22">The <tt class="docutils literal"><span class="pre">TokenLexer</span></tt> class</a></li>
+<li><a class="reference internal" href="#the-multipleincludeopt-class" id="id23">The <tt class="docutils literal"><span class="pre">MultipleIncludeOpt</span></tt> class</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#the-parser-library" id="id24">The Parser Library</a></li>
+<li><a class="reference internal" href="#the-ast-library" id="id25">The AST Library</a><ul>
+<li><a class="reference internal" href="#the-type-class-and-its-subclasses" id="id26">The <tt class="docutils literal"><span class="pre">Type</span></tt> class and its subclasses</a><ul>
+<li><a class="reference internal" href="#canonical-types" id="id27">Canonical Types</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#the-qualtype-class" id="id28">The <tt class="docutils literal"><span class="pre">QualType</span></tt> class</a></li>
+<li><a class="reference internal" href="#declaration-names" id="id29">Declaration names</a></li>
+<li><a class="reference internal" href="#declaration-contexts" id="id30">Declaration contexts</a><ul>
+<li><a class="reference internal" href="#redeclarations-and-overloads" id="id31">Redeclarations and Overloads</a></li>
+<li><a class="reference internal" href="#lexical-and-semantic-contexts" id="id32">Lexical and Semantic Contexts</a></li>
+<li><a class="reference internal" href="#transparent-declaration-contexts" id="id33">Transparent Declaration Contexts</a></li>
+<li><a class="reference internal" href="#multiply-defined-declaration-contexts" id="id34">Multiply-Defined Declaration Contexts</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#the-cfg-class" id="id35">The <tt class="docutils literal"><span class="pre">CFG</span></tt> class</a><ul>
+<li><a class="reference internal" href="#basic-blocks" id="id36">Basic Blocks</a></li>
+<li><a class="reference internal" href="#entry-and-exit-blocks" id="id37">Entry and Exit Blocks</a></li>
+<li><a class="reference internal" href="#conditional-control-flow" id="id38">Conditional Control-Flow</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#constant-folding-in-the-clang-ast" id="id39">Constant Folding in the Clang AST</a><ul>
+<li><a class="reference internal" href="#implementation-approach" id="id40">Implementation Approach</a></li>
+<li><a class="reference internal" href="#extensions" id="id41">Extensions</a></li>
+</ul>
+</li>
+</ul>
+</li>
+<li><a class="reference internal" href="#the-sema-library" id="id42">The Sema Library</a></li>
+<li><a class="reference internal" href="#the-codegen-library" id="id43">The CodeGen Library</a></li>
+<li><a class="reference internal" href="#how-to-change-clang" id="id44">How to change Clang</a><ul>
+<li><a class="reference internal" href="#how-to-add-an-attribute" id="id45">How to add an attribute</a><ul>
+<li><a class="reference internal" href="#attribute-basics" id="id46">Attribute Basics</a></li>
+<li><a class="reference internal" href="#include-clang-basic-attr-td" id="id47"><tt class="docutils literal"><span class="pre">include/clang/Basic/Attr.td</span></tt></a></li>
+<li><a class="reference internal" href="#boilerplate" id="id48">Boilerplate</a></li>
+<li><a class="reference internal" href="#the-meat-of-your-attribute" id="id49">The meat of your attribute</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#how-to-add-an-expression-or-statement" id="id50">How to add an expression or statement</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="introduction">
+<h2><a class="toc-backref" href="#id2">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>This document describes some of the more important APIs and internal design
+decisions made in the Clang C front-end. The purpose of this document is to
+both capture some of this high level information and also describe some of the
+design decisions behind it. This is meant for people interested in hacking on
+Clang, not for end-users. The description below is categorized by libraries,
+and does not describe any of the clients of the libraries.</p>
+</div>
+<div class="section" id="llvm-support-library">
+<h2><a class="toc-backref" href="#id3">LLVM Support Library</a><a class="headerlink" href="#llvm-support-library" title="Permalink to this headline">¶</a></h2>
+<p>The LLVM <tt class="docutils literal"><span class="pre">libSupport</span></tt> library provides many underlying libraries and
+<a class="reference external" href="http://llvm.org/docs/ProgrammersManual.html">data-structures</a>, including
+command line option processing, various containers and a system abstraction
+layer, which is used for file system access.</p>
+</div>
+<div class="section" id="the-clang-basic-library">
+<h2><a class="toc-backref" href="#id4">The Clang “Basic” Library</a><a class="headerlink" href="#the-clang-basic-library" title="Permalink to this headline">¶</a></h2>
+<p>This library certainly needs a better name. The “basic” library contains a
+number of low-level utilities for tracking and manipulating source buffers,
+locations within the source buffers, diagnostics, tokens, target abstraction,
+and information about the subset of the language being compiled for.</p>
+<p>Part of this infrastructure is specific to C (such as the <tt class="docutils literal"><span class="pre">TargetInfo</span></tt>
+class), other parts could be reused for other non-C-based languages
+(<tt class="docutils literal"><span class="pre">SourceLocation</span></tt>, <tt class="docutils literal"><span class="pre">SourceManager</span></tt>, <tt class="docutils literal"><span class="pre">Diagnostics</span></tt>, <tt class="docutils literal"><span class="pre">FileManager</span></tt>).
+When and if there is future demand we can figure out if it makes sense to
+introduce a new library, move the general classes somewhere else, or introduce
+some other solution.</p>
+<p>We describe the roles of these classes in order of their dependencies.</p>
+<div class="section" id="the-diagnostics-subsystem">
+<h3><a class="toc-backref" href="#id5">The Diagnostics Subsystem</a><a class="headerlink" href="#the-diagnostics-subsystem" title="Permalink to this headline">¶</a></h3>
+<p>The Clang Diagnostics subsystem is an important part of how the compiler
+communicates with the human. Diagnostics are the warnings and errors produced
+when the code is incorrect or dubious. In Clang, each diagnostic produced has
+(at the minimum) a unique ID, an English translation associated with it, a
+<a class="reference internal" href="#sourcelocation"><em>SourceLocation</em></a> to “put the caret”, and a severity
+(e.g., <tt class="docutils literal"><span class="pre">WARNING</span></tt> or <tt class="docutils literal"><span class="pre">ERROR</span></tt>). They can also optionally include a number of
+arguments to the dianostic (which fill in “%0“‘s in the string) as well as a
+number of source ranges that related to the diagnostic.</p>
+<p>In this section, we’ll be giving examples produced by the Clang command line
+driver, but diagnostics can be <a class="reference internal" href="#diagnosticclient"><em>rendered in many different ways</em></a> depending on how the <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt> interface is
+implemented. A representative example of a diagnostic is:</p>
+<div class="highlight-c++"><pre>t.c:38:15: error: invalid operands to binary expression ('int *' and '_Complex float')
+P = (P-42) + Gamma*4;
+ ~~~~~~ ^ ~~~~~~~</pre>
+</div>
+<p>In this example, you can see the English translation, the severity (error), you
+can see the source location (the caret (“<tt class="docutils literal"><span class="pre">^</span></tt>”) and file/line/column info),
+the source ranges “<tt class="docutils literal"><span class="pre">~~~~</span></tt>”, arguments to the diagnostic (“<tt class="docutils literal"><span class="pre">int*</span></tt>” and
+“<tt class="docutils literal"><span class="pre">_Complex</span> <span class="pre">float</span></tt>”). You’ll have to believe me that there is a unique ID
+backing the diagnostic :).</p>
+<p>Getting all of this to happen has several steps and involves many moving
+pieces, this section describes them and talks about best practices when adding
+a new diagnostic.</p>
+<div class="section" id="the-diagnostic-kinds-td-files">
+<h4><a class="toc-backref" href="#id6">The <tt class="docutils literal"><span class="pre">Diagnostic*Kinds.td</span></tt> files</a><a class="headerlink" href="#the-diagnostic-kinds-td-files" title="Permalink to this headline">¶</a></h4>
+<p>Diagnostics are created by adding an entry to one of the
+<tt class="docutils literal"><span class="pre">clang/Basic/Diagnostic*Kinds.td</span></tt> files, depending on what library will be
+using it. From this file, <strong class="program">tblgen</strong> generates the unique ID of the
+diagnostic, the severity of the diagnostic and the English translation + format
+string.</p>
+<p>There is little sanity with the naming of the unique ID’s right now. Some
+start with <tt class="docutils literal"><span class="pre">err_</span></tt>, <tt class="docutils literal"><span class="pre">warn_</span></tt>, <tt class="docutils literal"><span class="pre">ext_</span></tt> to encode the severity into the name.
+Since the enum is referenced in the C++ code that produces the diagnostic, it
+is somewhat useful for it to be reasonably short.</p>
+<p>The severity of the diagnostic comes from the set {<tt class="docutils literal"><span class="pre">NOTE</span></tt>, <tt class="docutils literal"><span class="pre">REMARK</span></tt>,
+<tt class="docutils literal"><span class="pre">WARNING</span></tt>,
+<tt class="docutils literal"><span class="pre">EXTENSION</span></tt>, <tt class="docutils literal"><span class="pre">EXTWARN</span></tt>, <tt class="docutils literal"><span class="pre">ERROR</span></tt>}. The <tt class="docutils literal"><span class="pre">ERROR</span></tt> severity is used for
+diagnostics indicating the program is never acceptable under any circumstances.
+When an error is emitted, the AST for the input code may not be fully built.
+The <tt class="docutils literal"><span class="pre">EXTENSION</span></tt> and <tt class="docutils literal"><span class="pre">EXTWARN</span></tt> severities are used for extensions to the
+language that Clang accepts. This means that Clang fully understands and can
+represent them in the AST, but we produce diagnostics to tell the user their
+code is non-portable. The difference is that the former are ignored by
+default, and the later warn by default. The <tt class="docutils literal"><span class="pre">WARNING</span></tt> severity is used for
+constructs that are valid in the currently selected source language but that
+are dubious in some way. The <tt class="docutils literal"><span class="pre">REMARK</span></tt> severity provides generic information
+about the compilation that is not necessarily related to any dubious code. The
+<tt class="docutils literal"><span class="pre">NOTE</span></tt> level is used to staple more information onto previous diagnostics.</p>
+<p>These <em>severities</em> are mapped into a smaller set (the <tt class="docutils literal"><span class="pre">Diagnostic::Level</span></tt>
+enum, {<tt class="docutils literal"><span class="pre">Ignored</span></tt>, <tt class="docutils literal"><span class="pre">Note</span></tt>, <tt class="docutils literal"><span class="pre">Remark</span></tt>, <tt class="docutils literal"><span class="pre">Warning</span></tt>, <tt class="docutils literal"><span class="pre">Error</span></tt>, <tt class="docutils literal"><span class="pre">Fatal</span></tt>}) of
+output
+<em>levels</em> by the diagnostics subsystem based on various configuration options.
+Clang internally supports a fully fine grained mapping mechanism that allows
+you to map almost any diagnostic to the output level that you want. The only
+diagnostics that cannot be mapped are <tt class="docutils literal"><span class="pre">NOTE</span></tt>s, which always follow the
+severity of the previously emitted diagnostic and <tt class="docutils literal"><span class="pre">ERROR</span></tt>s, which can only
+be mapped to <tt class="docutils literal"><span class="pre">Fatal</span></tt> (it is not possible to turn an error into a warning, for
+example).</p>
+<p>Diagnostic mappings are used in many ways. For example, if the user specifies
+<tt class="docutils literal"><span class="pre">-pedantic</span></tt>, <tt class="docutils literal"><span class="pre">EXTENSION</span></tt> maps to <tt class="docutils literal"><span class="pre">Warning</span></tt>, if they specify
+<tt class="docutils literal"><span class="pre">-pedantic-errors</span></tt>, it turns into <tt class="docutils literal"><span class="pre">Error</span></tt>. This is used to implement
+options like <tt class="docutils literal"><span class="pre">-Wunused_macros</span></tt>, <tt class="docutils literal"><span class="pre">-Wundef</span></tt> etc.</p>
+<p>Mapping to <tt class="docutils literal"><span class="pre">Fatal</span></tt> should only be used for diagnostics that are considered so
+severe that error recovery won’t be able to recover sensibly from them (thus
+spewing a ton of bogus errors). One example of this class of error are failure
+to <tt class="docutils literal"><span class="pre">#include</span></tt> a file.</p>
+</div>
+<div class="section" id="the-format-string">
+<h4><a class="toc-backref" href="#id7">The Format String</a><a class="headerlink" href="#the-format-string" title="Permalink to this headline">¶</a></h4>
+<p>The format string for the diagnostic is very simple, but it has some power. It
+takes the form of a string in English with markers that indicate where and how
+arguments to the diagnostic are inserted and formatted. For example, here are
+some simple format strings:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="s">"binary integer literals are an extension"</span>
+<span class="s">"format string contains '</span><span class="se">\\</span><span class="s">0' within the string body"</span>
+<span class="s">"more '%%' conversions than data arguments"</span>
+<span class="s">"invalid operands to binary expression (%0 and %1)"</span>
+<span class="s">"overloaded '%0' must be a %select{unary|binary|unary or binary}2 operator"</span>
+ <span class="s">" (has %1 parameter%s1)"</span>
+</pre></div>
+</div>
+<p>These examples show some important points of format strings. You can use any
+plain ASCII character in the diagnostic string except “<tt class="docutils literal"><span class="pre">%</span></tt>” without a
+problem, but these are C strings, so you have to use and be aware of all the C
+escape sequences (as in the second example). If you want to produce a “<tt class="docutils literal"><span class="pre">%</span></tt>”
+in the output, use the “<tt class="docutils literal"><span class="pre">%%</span></tt>” escape sequence, like the third diagnostic.
+Finally, Clang uses the “<tt class="docutils literal"><span class="pre">%...[digit]</span></tt>” sequences to specify where and how
+arguments to the diagnostic are formatted.</p>
+<p>Arguments to the diagnostic are numbered according to how they are specified by
+the C++ code that <a class="reference internal" href="#internals-producing-diag"><em>produces them</em></a>, and are
+referenced by <tt class="docutils literal"><span class="pre">%0</span></tt> .. <tt class="docutils literal"><span class="pre">%9</span></tt>. If you have more than 10 arguments to your
+diagnostic, you are doing something wrong :). Unlike <tt class="docutils literal"><span class="pre">printf</span></tt>, there is no
+requirement that arguments to the diagnostic end up in the output in the same
+order as they are specified, you could have a format string with “<tt class="docutils literal"><span class="pre">%1</span> <span class="pre">%0</span></tt>”
+that swaps them, for example. The text in between the percent and digit are
+formatting instructions. If there are no instructions, the argument is just
+turned into a string and substituted in.</p>
+<p>Here are some “best practices” for writing the English format string:</p>
+<ul class="simple">
+<li>Keep the string short. It should ideally fit in the 80 column limit of the
+<tt class="docutils literal"><span class="pre">DiagnosticKinds.td</span></tt> file. This avoids the diagnostic wrapping when
+printed, and forces you to think about the important point you are conveying
+with the diagnostic.</li>
+<li>Take advantage of location information. The user will be able to see the
+line and location of the caret, so you don’t need to tell them that the
+problem is with the 4th argument to the function: just point to it.</li>
+<li>Do not capitalize the diagnostic string, and do not end it with a period.</li>
+<li>If you need to quote something in the diagnostic string, use single quotes.</li>
+</ul>
+<p>Diagnostics should never take random English strings as arguments: you
+shouldn’t use “<tt class="docutils literal"><span class="pre">you</span> <span class="pre">have</span> <span class="pre">a</span> <span class="pre">problem</span> <span class="pre">with</span> <span class="pre">%0</span></tt>” and pass in things like “<tt class="docutils literal"><span class="pre">your</span>
+<span class="pre">argument</span></tt>” or “<tt class="docutils literal"><span class="pre">your</span> <span class="pre">return</span> <span class="pre">value</span></tt>” as arguments. Doing this prevents
+<a class="reference internal" href="#internals-diag-translation"><em>translating</em></a> the Clang diagnostics to other
+languages (because they’ll get random English words in their otherwise
+localized diagnostic). The exceptions to this are C/C++ language keywords
+(e.g., <tt class="docutils literal"><span class="pre">auto</span></tt>, <tt class="docutils literal"><span class="pre">const</span></tt>, <tt class="docutils literal"><span class="pre">mutable</span></tt>, etc) and C/C++ operators (<tt class="docutils literal"><span class="pre">/=</span></tt>).
+Note that things like “pointer” and “reference” are not keywords. On the other
+hand, you <em>can</em> include anything that comes from the user’s source code,
+including variable names, types, labels, etc. The “<tt class="docutils literal"><span class="pre">select</span></tt>” format can be
+used to achieve this sort of thing in a localizable way, see below.</p>
+</div>
+<div class="section" id="formatting-a-diagnostic-argument">
+<h4><a class="toc-backref" href="#id8">Formatting a Diagnostic Argument</a><a class="headerlink" href="#formatting-a-diagnostic-argument" title="Permalink to this headline">¶</a></h4>
+<p>Arguments to diagnostics are fully typed internally, and come from a couple
+different classes: integers, types, names, and random strings. Depending on
+the class of the argument, it can be optionally formatted in different ways.
+This gives the <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt> information about what the argument means
+without requiring it to use a specific presentation (consider this MVC for
+Clang :).</p>
+<p>Here are the different diagnostic argument formats currently supported by
+Clang:</p>
+<p><strong>“s” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"requires</span> <span class="pre">%1</span> <span class="pre">parameter%s1"</span></tt></dd>
+<dt>Class:</dt>
+<dd>Integers</dd>
+<dt>Description:</dt>
+<dd>This is a simple formatter for integers that is useful when producing English
+diagnostics. When the integer is 1, it prints as nothing. When the integer
+is not 1, it prints as “<tt class="docutils literal"><span class="pre">s</span></tt>”. This allows some simple grammatical forms to
+be to be handled correctly, and eliminates the need to use gross things like
+<tt class="docutils literal"><span class="pre">"requires</span> <span class="pre">%1</span> <span class="pre">parameter(s)"</span></tt>.</dd>
+</dl>
+<p><strong>“select” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"must</span> <span class="pre">be</span> <span class="pre">a</span> <span class="pre">%select{unary|binary|unary</span> <span class="pre">or</span> <span class="pre">binary}2</span> <span class="pre">operator"</span></tt></dd>
+<dt>Class:</dt>
+<dd>Integers</dd>
+<dt>Description:</dt>
+<dd>This format specifier is used to merge multiple related diagnostics together
+into one common one, without requiring the difference to be specified as an
+English string argument. Instead of specifying the string, the diagnostic
+gets an integer argument and the format string selects the numbered option.
+In this case, the “<tt class="docutils literal"><span class="pre">%2</span></tt>” value must be an integer in the range [0..2]. If
+it is 0, it prints “unary”, if it is 1 it prints “binary” if it is 2, it
+prints “unary or binary”. This allows other language translations to
+substitute reasonable words (or entire phrases) based on the semantics of the
+diagnostic instead of having to do things textually. The selected string
+does undergo formatting.</dd>
+</dl>
+<p><strong>“plural” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"you</span> <span class="pre">have</span> <span class="pre">%1</span> <span class="pre">%plural{1:mouse|:mice}1</span> <span class="pre">connected</span> <span class="pre">to</span> <span class="pre">your</span> <span class="pre">computer"</span></tt></dd>
+<dt>Class:</dt>
+<dd>Integers</dd>
+<dt>Description:</dt>
+<dd><p class="first">This is a formatter for complex plural forms. It is designed to handle even
+the requirements of languages with very complex plural forms, as many Baltic
+languages have. The argument consists of a series of expression/form pairs,
+separated by ”:”, where the first form whose expression evaluates to true is
+the result of the modifier.</p>
+<p>An expression can be empty, in which case it is always true. See the example
+at the top. Otherwise, it is a series of one or more numeric conditions,
+separated by ”,”. If any condition matches, the expression matches. Each
+numeric condition can take one of three forms.</p>
+<ul class="simple">
+<li>number: A simple decimal number matches if the argument is the same as the
+number. Example: <tt class="docutils literal"><span class="pre">"%plural{1:mouse|:mice}4"</span></tt></li>
+<li>range: A range in square brackets matches if the argument is within the
+range. Then range is inclusive on both ends. Example:
+<tt class="docutils literal"><span class="pre">"%plural{0:none|1:one|[2,5]:some|:many}2"</span></tt></li>
+<li>modulo: A modulo operator is followed by a number, and equals sign and
+either a number or a range. The tests are the same as for plain numbers
+and ranges, but the argument is taken modulo the number first. Example:
+<tt class="docutils literal"><span class="pre">"%plural{%100=0:even</span> <span class="pre">hundred|%100=[1,50]:lower</span> <span class="pre">half|:everything</span> <span class="pre">else}1"</span></tt></li>
+</ul>
+<p class="last">The parser is very unforgiving. A syntax error, even whitespace, will abort,
+as will a failure to match the argument against any expression.</p>
+</dd>
+</dl>
+<p><strong>“ordinal” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"ambiguity</span> <span class="pre">in</span> <span class="pre">%ordinal0</span> <span class="pre">argument"</span></tt></dd>
+<dt>Class:</dt>
+<dd>Integers</dd>
+<dt>Description:</dt>
+<dd>This is a formatter which represents the argument number as an ordinal: the
+value <tt class="docutils literal"><span class="pre">1</span></tt> becomes <tt class="docutils literal"><span class="pre">1st</span></tt>, <tt class="docutils literal"><span class="pre">3</span></tt> becomes <tt class="docutils literal"><span class="pre">3rd</span></tt>, and so on. Values less
+than <tt class="docutils literal"><span class="pre">1</span></tt> are not supported. This formatter is currently hard-coded to use
+English ordinals.</dd>
+</dl>
+<p><strong>“objcclass” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"method</span> <span class="pre">%objcclass0</span> <span class="pre">not</span> <span class="pre">found"</span></tt></dd>
+<dt>Class:</dt>
+<dd><tt class="docutils literal"><span class="pre">DeclarationName</span></tt></dd>
+<dt>Description:</dt>
+<dd>This is a simple formatter that indicates the <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> corresponds
+to an Objective-C class method selector. As such, it prints the selector
+with a leading “<tt class="docutils literal"><span class="pre">+</span></tt>”.</dd>
+</dl>
+<p><strong>“objcinstance” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"method</span> <span class="pre">%objcinstance0</span> <span class="pre">not</span> <span class="pre">found"</span></tt></dd>
+<dt>Class:</dt>
+<dd><tt class="docutils literal"><span class="pre">DeclarationName</span></tt></dd>
+<dt>Description:</dt>
+<dd>This is a simple formatter that indicates the <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> corresponds
+to an Objective-C instance method selector. As such, it prints the selector
+with a leading “<tt class="docutils literal"><span class="pre">-</span></tt>”.</dd>
+</dl>
+<p><strong>“q” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"candidate</span> <span class="pre">found</span> <span class="pre">by</span> <span class="pre">name</span> <span class="pre">lookup</span> <span class="pre">is</span> <span class="pre">%q0"</span></tt></dd>
+<dt>Class:</dt>
+<dd><tt class="docutils literal"><span class="pre">NamedDecl</span> <span class="pre">*</span></tt></dd>
+<dt>Description:</dt>
+<dd>This formatter indicates that the fully-qualified name of the declaration
+should be printed, e.g., “<tt class="docutils literal"><span class="pre">std::vector</span></tt>” rather than “<tt class="docutils literal"><span class="pre">vector</span></tt>”.</dd>
+</dl>
+<p><strong>“diff” format</strong></p>
+<dl class="docutils">
+<dt>Example:</dt>
+<dd><tt class="docutils literal"><span class="pre">"no</span> <span class="pre">known</span> <span class="pre">conversion</span> <span class="pre">%diff{from</span> <span class="pre">$</span> <span class="pre">to</span> <span class="pre">$|from</span> <span class="pre">argument</span> <span class="pre">type</span> <span class="pre">to</span> <span class="pre">parameter</span> <span class="pre">type}1,2"</span></tt></dd>
+<dt>Class:</dt>
+<dd><tt class="docutils literal"><span class="pre">QualType</span></tt></dd>
+<dt>Description:</dt>
+<dd>This formatter takes two <tt class="docutils literal"><span class="pre">QualType</span></tt>s and attempts to print a template
+difference between the two. If tree printing is off, the text inside the
+braces before the pipe is printed, with the formatted text replacing the $.
+If tree printing is on, the text after the pipe is printed and a type tree is
+printed after the diagnostic message.</dd>
+</dl>
+<p>It is really easy to add format specifiers to the Clang diagnostics system, but
+they should be discussed before they are added. If you are creating a lot of
+repetitive diagnostics and/or have an idea for a useful formatter, please bring
+it up on the cfe-dev mailing list.</p>
+</div>
+<div class="section" id="producing-the-diagnostic">
+<span id="internals-producing-diag"></span><h4><a class="toc-backref" href="#id9">Producing the Diagnostic</a><a class="headerlink" href="#producing-the-diagnostic" title="Permalink to this headline">¶</a></h4>
+<p>Now that you’ve created the diagnostic in the <tt class="docutils literal"><span class="pre">Diagnostic*Kinds.td</span></tt> file, you
+need to write the code that detects the condition in question and emits the new
+diagnostic. Various components of Clang (e.g., the preprocessor, <tt class="docutils literal"><span class="pre">Sema</span></tt>,
+etc.) provide a helper function named “<tt class="docutils literal"><span class="pre">Diag</span></tt>”. It creates a diagnostic and
+accepts the arguments, ranges, and other information that goes along with it.</p>
+<p>For example, the binary expression error comes from code like this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="n">various</span> <span class="n">things</span> <span class="n">that</span> <span class="n">are</span> <span class="n">bad</span><span class="p">)</span>
+ <span class="n">Diag</span><span class="p">(</span><span class="n">Loc</span><span class="p">,</span> <span class="n">diag</span><span class="o">::</span><span class="n">err_typecheck_invalid_operands</span><span class="p">)</span>
+ <span class="o"><<</span> <span class="n">lex</span><span class="o">-></span><span class="n">getType</span><span class="p">()</span> <span class="o"><<</span> <span class="n">rex</span><span class="o">-></span><span class="n">getType</span><span class="p">()</span>
+ <span class="o"><<</span> <span class="n">lex</span><span class="o">-></span><span class="n">getSourceRange</span><span class="p">()</span> <span class="o"><<</span> <span class="n">rex</span><span class="o">-></span><span class="n">getSourceRange</span><span class="p">();</span>
+</pre></div>
+</div>
+<p>This shows that use of the <tt class="docutils literal"><span class="pre">Diag</span></tt> method: it takes a location (a
+<a class="reference internal" href="#sourcelocation"><em>SourceLocation</em></a> object) and a diagnostic enum value
+(which matches the name from <tt class="docutils literal"><span class="pre">Diagnostic*Kinds.td</span></tt>). If the diagnostic takes
+arguments, they are specified with the <tt class="docutils literal"><span class="pre"><<</span></tt> operator: the first argument
+becomes <tt class="docutils literal"><span class="pre">%0</span></tt>, the second becomes <tt class="docutils literal"><span class="pre">%1</span></tt>, etc. The diagnostic interface
+allows you to specify arguments of many different types, including <tt class="docutils literal"><span class="pre">int</span></tt> and
+<tt class="docutils literal"><span class="pre">unsigned</span></tt> for integer arguments, <tt class="docutils literal"><span class="pre">const</span> <span class="pre">char*</span></tt> and <tt class="docutils literal"><span class="pre">std::string</span></tt> for
+string arguments, <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> and <tt class="docutils literal"><span class="pre">const</span> <span class="pre">IdentifierInfo</span> <span class="pre">*</span></tt> for names,
+<tt class="docutils literal"><span class="pre">QualType</span></tt> for types, etc. <tt class="docutils literal"><span class="pre">SourceRange</span></tt>s are also specified with the
+<tt class="docutils literal"><span class="pre"><<</span></tt> operator, but do not have a specific ordering requirement.</p>
+<p>As you can see, adding and producing a diagnostic is pretty straightforward.
+The hard part is deciding exactly what you need to say to help the user,
+picking a suitable wording, and providing the information needed to format it
+correctly. The good news is that the call site that issues a diagnostic should
+be completely independent of how the diagnostic is formatted and in what
+language it is rendered.</p>
+</div>
+<div class="section" id="fix-it-hints">
+<h4><a class="toc-backref" href="#id10">Fix-It Hints</a><a class="headerlink" href="#fix-it-hints" title="Permalink to this headline">¶</a></h4>
+<p>In some cases, the front end emits diagnostics when it is clear that some small
+change to the source code would fix the problem. For example, a missing
+semicolon at the end of a statement or a use of deprecated syntax that is
+easily rewritten into a more modern form. Clang tries very hard to emit the
+diagnostic and recover gracefully in these and other cases.</p>
+<p>However, for these cases where the fix is obvious, the diagnostic can be
+annotated with a hint (referred to as a “fix-it hint”) that describes how to
+change the code referenced by the diagnostic to fix the problem. For example,
+it might add the missing semicolon at the end of the statement or rewrite the
+use of a deprecated construct into something more palatable. Here is one such
+example from the C++ front end, where we warn about the right-shift operator
+changing meaning from C++98 to C++11:</p>
+<div class="highlight-c++"><pre>test.cpp:3:7: warning: use of right-shift operator ('>>') in template argument
+ will require parentheses in C++11
+A<100 >> 2> *a;
+ ^
+ ( )</pre>
+</div>
+<p>Here, the fix-it hint is suggesting that parentheses be added, and showing
+exactly where those parentheses would be inserted into the source code. The
+fix-it hints themselves describe what changes to make to the source code in an
+abstract manner, which the text diagnostic printer renders as a line of
+“insertions” below the caret line. <a class="reference internal" href="#diagnosticclient"><em>Other diagnostic clients</em></a> might choose to render the code differently (e.g., as
+markup inline) or even give the user the ability to automatically fix the
+problem.</p>
+<p>Fix-it hints on errors and warnings need to obey these rules:</p>
+<ul class="simple">
+<li>Since they are automatically applied if <tt class="docutils literal"><span class="pre">-Xclang</span> <span class="pre">-fixit</span></tt> is passed to the
+driver, they should only be used when it’s very likely they match the user’s
+intent.</li>
+<li>Clang must recover from errors as if the fix-it had been applied.</li>
+</ul>
+<p>If a fix-it can’t obey these rules, put the fix-it on a note. Fix-its on notes
+are not applied automatically.</p>
+<p>All fix-it hints are described by the <tt class="docutils literal"><span class="pre">FixItHint</span></tt> class, instances of which
+should be attached to the diagnostic using the <tt class="docutils literal"><span class="pre"><<</span></tt> operator in the same way
+that highlighted source ranges and arguments are passed to the diagnostic.
+Fix-it hints can be created with one of three constructors:</p>
+<ul>
+<li><p class="first"><tt class="docutils literal"><span class="pre">FixItHint::CreateInsertion(Loc,</span> <span class="pre">Code)</span></tt></p>
+<blockquote>
+<div><p>Specifies that the given <tt class="docutils literal"><span class="pre">Code</span></tt> (a string) should be inserted before the
+source location <tt class="docutils literal"><span class="pre">Loc</span></tt>.</p>
+</div></blockquote>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">FixItHint::CreateRemoval(Range)</span></tt></p>
+<blockquote>
+<div><p>Specifies that the code in the given source <tt class="docutils literal"><span class="pre">Range</span></tt> should be removed.</p>
+</div></blockquote>
+</li>
+<li><p class="first"><tt class="docutils literal"><span class="pre">FixItHint::CreateReplacement(Range,</span> <span class="pre">Code)</span></tt></p>
+<blockquote>
+<div><p>Specifies that the code in the given source <tt class="docutils literal"><span class="pre">Range</span></tt> should be removed,
+and replaced with the given <tt class="docutils literal"><span class="pre">Code</span></tt> string.</p>
+</div></blockquote>
+</li>
+</ul>
+</div>
+<div class="section" id="the-diagnosticclient-interface">
+<span id="diagnosticclient"></span><h4><a class="toc-backref" href="#id11">The <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt> Interface</a><a class="headerlink" href="#the-diagnosticclient-interface" title="Permalink to this headline">¶</a></h4>
+<p>Once code generates a diagnostic with all of the arguments and the rest of the
+relevant information, Clang needs to know what to do with it. As previously
+mentioned, the diagnostic machinery goes through some filtering to map a
+severity onto a diagnostic level, then (assuming the diagnostic is not mapped
+to “<tt class="docutils literal"><span class="pre">Ignore</span></tt>”) it invokes an object that implements the <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt>
+interface with the information.</p>
+<p>It is possible to implement this interface in many different ways. For
+example, the normal Clang <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt> (named
+<tt class="docutils literal"><span class="pre">TextDiagnosticPrinter</span></tt>) turns the arguments into strings (according to the
+various formatting rules), prints out the file/line/column information and the
+string, then prints out the line of code, the source ranges, and the caret.
+However, this behavior isn’t required.</p>
+<p>Another implementation of the <tt class="docutils literal"><span class="pre">DiagnosticClient</span></tt> interface is the
+<tt class="docutils literal"><span class="pre">TextDiagnosticBuffer</span></tt> class, which is used when Clang is in <tt class="docutils literal"><span class="pre">-verify</span></tt>
+mode. Instead of formatting and printing out the diagnostics, this
+implementation just captures and remembers the diagnostics as they fly by.
+Then <tt class="docutils literal"><span class="pre">-verify</span></tt> compares the list of produced diagnostics to the list of
+expected ones. If they disagree, it prints out its own output. Full
+documentation for the <tt class="docutils literal"><span class="pre">-verify</span></tt> mode can be found in the Clang API
+documentation for <a class="reference external" href="/doxygen/classclang_1_1VerifyDiagnosticConsumer.html#details">VerifyDiagnosticConsumer</a>.</p>
+<p>There are many other possible implementations of this interface, and this is
+why we prefer diagnostics to pass down rich structured information in
+arguments. For example, an HTML output might want declaration names be
+linkified to where they come from in the source. Another example is that a GUI
+might let you click on typedefs to expand them. This application would want to
+pass significantly more information about types through to the GUI than a
+simple flat string. The interface allows this to happen.</p>
+</div>
+<div class="section" id="adding-translations-to-clang">
+<span id="internals-diag-translation"></span><h4><a class="toc-backref" href="#id12">Adding Translations to Clang</a><a class="headerlink" href="#adding-translations-to-clang" title="Permalink to this headline">¶</a></h4>
+<p>Not possible yet! Diagnostic strings should be written in UTF-8, the client can
+translate to the relevant code page if needed. Each translation completely
+replaces the format string for the diagnostic.</p>
+</div>
+</div>
+<div class="section" id="the-sourcelocation-and-sourcemanager-classes">
+<span id="sourcemanager"></span><span id="sourcelocation"></span><h3><a class="toc-backref" href="#id13">The <tt class="docutils literal"><span class="pre">SourceLocation</span></tt> and <tt class="docutils literal"><span class="pre">SourceManager</span></tt> classes</a><a class="headerlink" href="#the-sourcelocation-and-sourcemanager-classes" title="Permalink to this headline">¶</a></h3>
+<p>Strangely enough, the <tt class="docutils literal"><span class="pre">SourceLocation</span></tt> class represents a location within the
+source code of the program. Important design points include:</p>
+<ol class="arabic simple">
+<li><tt class="docutils literal"><span class="pre">sizeof(SourceLocation)</span></tt> must be extremely small, as these are embedded
+into many AST nodes and are passed around often. Currently it is 32 bits.</li>
+<li><tt class="docutils literal"><span class="pre">SourceLocation</span></tt> must be a simple value object that can be efficiently
+copied.</li>
+<li>We should be able to represent a source location for any byte of any input
+file. This includes in the middle of tokens, in whitespace, in trigraphs,
+etc.</li>
+<li>A <tt class="docutils literal"><span class="pre">SourceLocation</span></tt> must encode the current <tt class="docutils literal"><span class="pre">#include</span></tt> stack that was
+active when the location was processed. For example, if the location
+corresponds to a token, it should contain the set of <tt class="docutils literal"><span class="pre">#include</span></tt>s active
+when the token was lexed. This allows us to print the <tt class="docutils literal"><span class="pre">#include</span></tt> stack
+for a diagnostic.</li>
+<li><tt class="docutils literal"><span class="pre">SourceLocation</span></tt> must be able to describe macro expansions, capturing both
+the ultimate instantiation point and the source of the original character
+data.</li>
+</ol>
+<p>In practice, the <tt class="docutils literal"><span class="pre">SourceLocation</span></tt> works together with the <tt class="docutils literal"><span class="pre">SourceManager</span></tt>
+class to encode two pieces of information about a location: its spelling
+location and its instantiation location. For most tokens, these will be the
+same. However, for a macro expansion (or tokens that came from a <tt class="docutils literal"><span class="pre">_Pragma</span></tt>
+directive) these will describe the location of the characters corresponding to
+the token and the location where the token was used (i.e., the macro
+instantiation point or the location of the <tt class="docutils literal"><span class="pre">_Pragma</span></tt> itself).</p>
+<p>The Clang front-end inherently depends on the location of a token being tracked
+correctly. If it is ever incorrect, the front-end may get confused and die.
+The reason for this is that the notion of the “spelling” of a <tt class="docutils literal"><span class="pre">Token</span></tt> in
+Clang depends on being able to find the original input characters for the
+token. This concept maps directly to the “spelling location” for the token.</p>
+</div>
+<div class="section" id="sourcerange-and-charsourcerange">
+<h3><a class="toc-backref" href="#id14"><tt class="docutils literal"><span class="pre">SourceRange</span></tt> and <tt class="docutils literal"><span class="pre">CharSourceRange</span></tt></a><a class="headerlink" href="#sourcerange-and-charsourcerange" title="Permalink to this headline">¶</a></h3>
+<p>Clang represents most source ranges by [first, last], where “first” and “last”
+each point to the beginning of their respective tokens. For example consider
+the <tt class="docutils literal"><span class="pre">SourceRange</span></tt> of the following statement:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">x</span> <span class="o">=</span> <span class="n">foo</span> <span class="o">+</span> <span class="n">bar</span><span class="p">;</span>
+<span class="o">^</span><span class="n">first</span> <span class="o">^</span><span class="n">last</span>
+</pre></div>
+</div>
+<p>To map from this representation to a character-based representation, the “last”
+location needs to be adjusted to point to (or past) the end of that token with
+either <tt class="docutils literal"><span class="pre">Lexer::MeasureTokenLength()</span></tt> or <tt class="docutils literal"><span class="pre">Lexer::getLocForEndOfToken()</span></tt>. For
+the rare cases where character-level source ranges information is needed we use
+the <tt class="docutils literal"><span class="pre">CharSourceRange</span></tt> class.</p>
+</div>
+</div>
+<div class="section" id="the-driver-library">
+<h2><a class="toc-backref" href="#id15">The Driver Library</a><a class="headerlink" href="#the-driver-library" title="Permalink to this headline">¶</a></h2>
+<p>The clang Driver and library are documented <a class="reference internal" href="DriverInternals.html"><em>here</em></a>.</p>
+</div>
+<div class="section" id="precompiled-headers">
+<h2><a class="toc-backref" href="#id16">Precompiled Headers</a><a class="headerlink" href="#precompiled-headers" title="Permalink to this headline">¶</a></h2>
+<p>Clang supports two implementations of precompiled headers. The default
+implementation, precompiled headers (<a class="reference internal" href="PCHInternals.html"><em>PCH</em></a>) uses a
+serialized representation of Clang’s internal data structures, encoded with the
+<a class="reference external" href="http://llvm.org/docs/BitCodeFormat.html">LLVM bitstream format</a>.
+Pretokenized headers (<a class="reference internal" href="PTHInternals.html"><em>PTH</em></a>), on the other hand, contain a
+serialized representation of the tokens encountered when preprocessing a header
+(and anything that header includes).</p>
+</div>
+<div class="section" id="the-frontend-library">
+<h2><a class="toc-backref" href="#id17">The Frontend Library</a><a class="headerlink" href="#the-frontend-library" title="Permalink to this headline">¶</a></h2>
+<p>The Frontend library contains functionality useful for building tools on top of
+the Clang libraries, for example several methods for outputting diagnostics.</p>
+</div>
+<div class="section" id="the-lexer-and-preprocessor-library">
+<h2><a class="toc-backref" href="#id18">The Lexer and Preprocessor Library</a><a class="headerlink" href="#the-lexer-and-preprocessor-library" title="Permalink to this headline">¶</a></h2>
+<p>The Lexer library contains several tightly-connected classes that are involved
+with the nasty process of lexing and preprocessing C source code. The main
+interface to this library for outside clients is the large <tt class="docutils literal"><span class="pre">Preprocessor</span></tt>
+class. It contains the various pieces of state that are required to coherently
+read tokens out of a translation unit.</p>
+<p>The core interface to the <tt class="docutils literal"><span class="pre">Preprocessor</span></tt> object (once it is set up) is the
+<tt class="docutils literal"><span class="pre">Preprocessor::Lex</span></tt> method, which returns the next <a class="reference internal" href="#token"><em>Token</em></a> from
+the preprocessor stream. There are two types of token providers that the
+preprocessor is capable of reading from: a buffer lexer (provided by the
+<a class="reference internal" href="#lexer"><em>Lexer</em></a> class) and a buffered token stream (provided by the
+<a class="reference internal" href="#tokenlexer"><em>TokenLexer</em></a> class).</p>
+<div class="section" id="the-token-class">
+<span id="token"></span><h3><a class="toc-backref" href="#id19">The Token class</a><a class="headerlink" href="#the-token-class" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">Token</span></tt> class is used to represent a single lexed token. Tokens are
+intended to be used by the lexer/preprocess and parser libraries, but are not
+intended to live beyond them (for example, they should not live in the ASTs).</p>
+<p>Tokens most often live on the stack (or some other location that is efficient
+to access) as the parser is running, but occasionally do get buffered up. For
+example, macro definitions are stored as a series of tokens, and the C++
+front-end periodically needs to buffer tokens up for tentative parsing and
+various pieces of look-ahead. As such, the size of a <tt class="docutils literal"><span class="pre">Token</span></tt> matters. On a
+32-bit system, <tt class="docutils literal"><span class="pre">sizeof(Token)</span></tt> is currently 16 bytes.</p>
+<p>Tokens occur in two forms: <a class="reference internal" href="#annotationtoken"><em>annotation tokens</em></a> and
+normal tokens. Normal tokens are those returned by the lexer, annotation
+tokens represent semantic information and are produced by the parser, replacing
+normal tokens in the token stream. Normal tokens contain the following
+information:</p>
+<ul class="simple">
+<li><strong>A SourceLocation</strong> — This indicates the location of the start of the
+token.</li>
+<li><strong>A length</strong> — This stores the length of the token as stored in the
+<tt class="docutils literal"><span class="pre">SourceBuffer</span></tt>. For tokens that include them, this length includes
+trigraphs and escaped newlines which are ignored by later phases of the
+compiler. By pointing into the original source buffer, it is always possible
+to get the original spelling of a token completely accurately.</li>
+<li><strong>IdentifierInfo</strong> — If a token takes the form of an identifier, and if
+identifier lookup was enabled when the token was lexed (e.g., the lexer was
+not reading in “raw” mode) this contains a pointer to the unique hash value
+for the identifier. Because the lookup happens before keyword
+identification, this field is set even for language keywords like “<tt class="docutils literal"><span class="pre">for</span></tt>”.</li>
+<li><strong>TokenKind</strong> — This indicates the kind of token as classified by the
+lexer. This includes things like <tt class="docutils literal"><span class="pre">tok::starequal</span></tt> (for the “<tt class="docutils literal"><span class="pre">*=</span></tt>”
+operator), <tt class="docutils literal"><span class="pre">tok::ampamp</span></tt> for the “<tt class="docutils literal"><span class="pre">&&</span></tt>” token, and keyword values (e.g.,
+<tt class="docutils literal"><span class="pre">tok::kw_for</span></tt>) for identifiers that correspond to keywords. Note that
+some tokens can be spelled multiple ways. For example, C++ supports
+“operator keywords”, where things like “<tt class="docutils literal"><span class="pre">and</span></tt>” are treated exactly like the
+“<tt class="docutils literal"><span class="pre">&&</span></tt>” operator. In these cases, the kind value is set to <tt class="docutils literal"><span class="pre">tok::ampamp</span></tt>,
+which is good for the parser, which doesn’t have to consider both forms. For
+something that cares about which form is used (e.g., the preprocessor
+“stringize” operator) the spelling indicates the original form.</li>
+<li><strong>Flags</strong> — There are currently four flags tracked by the
+lexer/preprocessor system on a per-token basis:<ol class="arabic">
+<li><strong>StartOfLine</strong> — This was the first token that occurred on its input
+source line.</li>
+<li><strong>LeadingSpace</strong> — There was a space character either immediately before
+the token or transitively before the token as it was expanded through a
+macro. The definition of this flag is very closely defined by the
+stringizing requirements of the preprocessor.</li>
+<li><strong>DisableExpand</strong> — This flag is used internally to the preprocessor to
+represent identifier tokens which have macro expansion disabled. This
+prevents them from being considered as candidates for macro expansion ever
+in the future.</li>
+<li><strong>NeedsCleaning</strong> — This flag is set if the original spelling for the
+token includes a trigraph or escaped newline. Since this is uncommon,
+many pieces of code can fast-path on tokens that did not need cleaning.</li>
+</ol>
+</li>
+</ul>
+<p>One interesting (and somewhat unusual) aspect of normal tokens is that they
+don’t contain any semantic information about the lexed value. For example, if
+the token was a pp-number token, we do not represent the value of the number
+that was lexed (this is left for later pieces of code to decide).
+Additionally, the lexer library has no notion of typedef names vs variable
+names: both are returned as identifiers, and the parser is left to decide
+whether a specific identifier is a typedef or a variable (tracking this
+requires scope information among other things). The parser can do this
+translation by replacing tokens returned by the preprocessor with “Annotation
+Tokens”.</p>
+</div>
+<div class="section" id="annotation-tokens">
+<span id="annotationtoken"></span><h3><a class="toc-backref" href="#id20">Annotation Tokens</a><a class="headerlink" href="#annotation-tokens" title="Permalink to this headline">¶</a></h3>
+<p>Annotation tokens are tokens that are synthesized by the parser and injected
+into the preprocessor’s token stream (replacing existing tokens) to record
+semantic information found by the parser. For example, if “<tt class="docutils literal"><span class="pre">foo</span></tt>” is found
+to be a typedef, the “<tt class="docutils literal"><span class="pre">foo</span></tt>” <tt class="docutils literal"><span class="pre">tok::identifier</span></tt> token is replaced with an
+<tt class="docutils literal"><span class="pre">tok::annot_typename</span></tt>. This is useful for a couple of reasons: 1) this makes
+it easy to handle qualified type names (e.g., “<tt class="docutils literal"><span class="pre">foo::bar::baz<42>::t</span></tt>”) in
+C++ as a single “token” in the parser. 2) if the parser backtracks, the
+reparse does not need to redo semantic analysis to determine whether a token
+sequence is a variable, type, template, etc.</p>
+<p>Annotation tokens are created by the parser and reinjected into the parser’s
+token stream (when backtracking is enabled). Because they can only exist in
+tokens that the preprocessor-proper is done with, it doesn’t need to keep
+around flags like “start of line” that the preprocessor uses to do its job.
+Additionally, an annotation token may “cover” a sequence of preprocessor tokens
+(e.g., “<tt class="docutils literal"><span class="pre">a::b::c</span></tt>” is five preprocessor tokens). As such, the valid fields
+of an annotation token are different than the fields for a normal token (but
+they are multiplexed into the normal <tt class="docutils literal"><span class="pre">Token</span></tt> fields):</p>
+<ul class="simple">
+<li><strong>SourceLocation “Location”</strong> — The <tt class="docutils literal"><span class="pre">SourceLocation</span></tt> for the annotation
+token indicates the first token replaced by the annotation token. In the
+example above, it would be the location of the “<tt class="docutils literal"><span class="pre">a</span></tt>” identifier.</li>
+<li><strong>SourceLocation “AnnotationEndLoc”</strong> — This holds the location of the last
+token replaced with the annotation token. In the example above, it would be
+the location of the “<tt class="docutils literal"><span class="pre">c</span></tt>” identifier.</li>
+<li><strong>void* “AnnotationValue”</strong> — This contains an opaque object that the
+parser gets from <tt class="docutils literal"><span class="pre">Sema</span></tt>. The parser merely preserves the information for
+<tt class="docutils literal"><span class="pre">Sema</span></tt> to later interpret based on the annotation token kind.</li>
+<li><strong>TokenKind “Kind”</strong> — This indicates the kind of Annotation token this is.
+See below for the different valid kinds.</li>
+</ul>
+<p>Annotation tokens currently come in three kinds:</p>
+<ol class="arabic simple">
+<li><strong>tok::annot_typename</strong>: This annotation token represents a resolved
+typename token that is potentially qualified. The <tt class="docutils literal"><span class="pre">AnnotationValue</span></tt> field
+contains the <tt class="docutils literal"><span class="pre">QualType</span></tt> returned by <tt class="docutils literal"><span class="pre">Sema::getTypeName()</span></tt>, possibly with
+source location information attached.</li>
+<li><strong>tok::annot_cxxscope</strong>: This annotation token represents a C++ scope
+specifier, such as “<tt class="docutils literal"><span class="pre">A::B::</span></tt>”. This corresponds to the grammar
+productions “<em>::</em>” and “<em>:: [opt] nested-name-specifier</em>”. The
+<tt class="docutils literal"><span class="pre">AnnotationValue</span></tt> pointer is a <tt class="docutils literal"><span class="pre">NestedNameSpecifier</span> <span class="pre">*</span></tt> returned by the
+<tt class="docutils literal"><span class="pre">Sema::ActOnCXXGlobalScopeSpecifier</span></tt> and
+<tt class="docutils literal"><span class="pre">Sema::ActOnCXXNestedNameSpecifier</span></tt> callbacks.</li>
+<li><strong>tok::annot_template_id</strong>: This annotation token represents a C++
+template-id such as “<tt class="docutils literal"><span class="pre">foo<int,</span> <span class="pre">4></span></tt>”, where “<tt class="docutils literal"><span class="pre">foo</span></tt>” is the name of a
+template. The <tt class="docutils literal"><span class="pre">AnnotationValue</span></tt> pointer is a pointer to a <tt class="docutils literal"><span class="pre">malloc</span></tt>‘d
+<tt class="docutils literal"><span class="pre">TemplateIdAnnotation</span></tt> object. Depending on the context, a parsed
+template-id that names a type might become a typename annotation token (if
+all we care about is the named type, e.g., because it occurs in a type
+specifier) or might remain a template-id token (if we want to retain more
+source location information or produce a new type, e.g., in a declaration of
+a class template specialization). template-id annotation tokens that refer
+to a type can be “upgraded” to typename annotation tokens by the parser.</li>
+</ol>
+<p>As mentioned above, annotation tokens are not returned by the preprocessor,
+they are formed on demand by the parser. This means that the parser has to be
+aware of cases where an annotation could occur and form it where appropriate.
+This is somewhat similar to how the parser handles Translation Phase 6 of C99:
+String Concatenation (see C99 5.1.1.2). In the case of string concatenation,
+the preprocessor just returns distinct <tt class="docutils literal"><span class="pre">tok::string_literal</span></tt> and
+<tt class="docutils literal"><span class="pre">tok::wide_string_literal</span></tt> tokens and the parser eats a sequence of them
+wherever the grammar indicates that a string literal can occur.</p>
+<p>In order to do this, whenever the parser expects a <tt class="docutils literal"><span class="pre">tok::identifier</span></tt> or
+<tt class="docutils literal"><span class="pre">tok::coloncolon</span></tt>, it should call the <tt class="docutils literal"><span class="pre">TryAnnotateTypeOrScopeToken</span></tt> or
+<tt class="docutils literal"><span class="pre">TryAnnotateCXXScopeToken</span></tt> methods to form the annotation token. These
+methods will maximally form the specified annotation tokens and replace the
+current token with them, if applicable. If the current tokens is not valid for
+an annotation token, it will remain an identifier or “<tt class="docutils literal"><span class="pre">::</span></tt>” token.</p>
+</div>
+<div class="section" id="the-lexer-class">
+<span id="lexer"></span><h3><a class="toc-backref" href="#id21">The <tt class="docutils literal"><span class="pre">Lexer</span></tt> class</a><a class="headerlink" href="#the-lexer-class" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">Lexer</span></tt> class provides the mechanics of lexing tokens out of a source
+buffer and deciding what they mean. The <tt class="docutils literal"><span class="pre">Lexer</span></tt> is complicated by the fact
+that it operates on raw buffers that have not had spelling eliminated (this is
+a necessity to get decent performance), but this is countered with careful
+coding as well as standard performance techniques (for example, the comment
+handling code is vectorized on X86 and PowerPC hosts).</p>
+<p>The lexer has a couple of interesting modal features:</p>
+<ul class="simple">
+<li>The lexer can operate in “raw” mode. This mode has several features that
+make it possible to quickly lex the file (e.g., it stops identifier lookup,
+doesn’t specially handle preprocessor tokens, handles EOF differently, etc).
+This mode is used for lexing within an “<tt class="docutils literal"><span class="pre">#if</span> <span class="pre">0</span></tt>” block, for example.</li>
+<li>The lexer can capture and return comments as tokens. This is required to
+support the <tt class="docutils literal"><span class="pre">-C</span></tt> preprocessor mode, which passes comments through, and is
+used by the diagnostic checker to identifier expect-error annotations.</li>
+<li>The lexer can be in <tt class="docutils literal"><span class="pre">ParsingFilename</span></tt> mode, which happens when
+preprocessing after reading a <tt class="docutils literal"><span class="pre">#include</span></tt> directive. This mode changes the
+parsing of “<tt class="docutils literal"><span class="pre"><</span></tt>” to return an “angled string” instead of a bunch of tokens
+for each thing within the filename.</li>
+<li>When parsing a preprocessor directive (after “<tt class="docutils literal"><span class="pre">#</span></tt>”) the
+<tt class="docutils literal"><span class="pre">ParsingPreprocessorDirective</span></tt> mode is entered. This changes the parser to
+return EOD at a newline.</li>
+<li>The <tt class="docutils literal"><span class="pre">Lexer</span></tt> uses a <tt class="docutils literal"><span class="pre">LangOptions</span></tt> object to know whether trigraphs are
+enabled, whether C++ or ObjC keywords are recognized, etc.</li>
+</ul>
+<p>In addition to these modes, the lexer keeps track of a couple of other features
+that are local to a lexed buffer, which change as the buffer is lexed:</p>
+<ul class="simple">
+<li>The <tt class="docutils literal"><span class="pre">Lexer</span></tt> uses <tt class="docutils literal"><span class="pre">BufferPtr</span></tt> to keep track of the current character being
+lexed.</li>
+<li>The <tt class="docutils literal"><span class="pre">Lexer</span></tt> uses <tt class="docutils literal"><span class="pre">IsAtStartOfLine</span></tt> to keep track of whether the next
+lexed token will start with its “start of line” bit set.</li>
+<li>The <tt class="docutils literal"><span class="pre">Lexer</span></tt> keeps track of the current “<tt class="docutils literal"><span class="pre">#if</span></tt>” directives that are active
+(which can be nested).</li>
+<li>The <tt class="docutils literal"><span class="pre">Lexer</span></tt> keeps track of an <a class="reference internal" href="#multipleincludeopt"><em>MultipleIncludeOpt</em></a> object, which is used to detect whether the buffer uses
+the standard “<tt class="docutils literal"><span class="pre">#ifndef</span> <span class="pre">XX</span></tt> / <tt class="docutils literal"><span class="pre">#define</span> <span class="pre">XX</span></tt>” idiom to prevent multiple
+inclusion. If a buffer does, subsequent includes can be ignored if the
+“<tt class="docutils literal"><span class="pre">XX</span></tt>” macro is defined.</li>
+</ul>
+</div>
+<div class="section" id="the-tokenlexer-class">
+<span id="tokenlexer"></span><h3><a class="toc-backref" href="#id22">The <tt class="docutils literal"><span class="pre">TokenLexer</span></tt> class</a><a class="headerlink" href="#the-tokenlexer-class" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">TokenLexer</span></tt> class is a token provider that returns tokens from a list of
+tokens that came from somewhere else. It typically used for two things: 1)
+returning tokens from a macro definition as it is being expanded 2) returning
+tokens from an arbitrary buffer of tokens. The later use is used by
+<tt class="docutils literal"><span class="pre">_Pragma</span></tt> and will most likely be used to handle unbounded look-ahead for the
+C++ parser.</p>
+</div>
+<div class="section" id="the-multipleincludeopt-class">
+<span id="multipleincludeopt"></span><h3><a class="toc-backref" href="#id23">The <tt class="docutils literal"><span class="pre">MultipleIncludeOpt</span></tt> class</a><a class="headerlink" href="#the-multipleincludeopt-class" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">MultipleIncludeOpt</span></tt> class implements a really simple little state
+machine that is used to detect the standard “<tt class="docutils literal"><span class="pre">#ifndef</span> <span class="pre">XX</span></tt> / <tt class="docutils literal"><span class="pre">#define</span> <span class="pre">XX</span></tt>”
+idiom that people typically use to prevent multiple inclusion of headers. If a
+buffer uses this idiom and is subsequently <tt class="docutils literal"><span class="pre">#include</span></tt>‘d, the preprocessor can
+simply check to see whether the guarding condition is defined or not. If so,
+the preprocessor can completely ignore the include of the header.</p>
+</div>
+</div>
+<div class="section" id="the-parser-library">
+<span id="parser"></span><h2><a class="toc-backref" href="#id24">The Parser Library</a><a class="headerlink" href="#the-parser-library" title="Permalink to this headline">¶</a></h2>
+<p>This library contains a recursive-descent parser that polls tokens from the
+preprocessor and notifies a client of the parsing progress.</p>
+<p>Historically, the parser used to talk to an abstract <tt class="docutils literal"><span class="pre">Action</span></tt> interface that
+had virtual methods for parse events, for example <tt class="docutils literal"><span class="pre">ActOnBinOp()</span></tt>. When Clang
+grew C++ support, the parser stopped supporting general <tt class="docutils literal"><span class="pre">Action</span></tt> clients –
+it now always talks to the <a class="reference internal" href="#sema"><em>Sema libray</em></a>. However, the Parser
+still accesses AST objects only through opaque types like <tt class="docutils literal"><span class="pre">ExprResult</span></tt> and
+<tt class="docutils literal"><span class="pre">StmtResult</span></tt>. Only <a class="reference internal" href="#sema"><em>Sema</em></a> looks at the AST node contents of these
+wrappers.</p>
+</div>
+<div class="section" id="the-ast-library">
+<span id="ast"></span><h2><a class="toc-backref" href="#id25">The AST Library</a><a class="headerlink" href="#the-ast-library" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="the-type-class-and-its-subclasses">
+<span id="type"></span><h3><a class="toc-backref" href="#id26">The <tt class="docutils literal"><span class="pre">Type</span></tt> class and its subclasses</a><a class="headerlink" href="#the-type-class-and-its-subclasses" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">Type</span></tt> class (and its subclasses) are an important part of the AST.
+Types are accessed through the <tt class="docutils literal"><span class="pre">ASTContext</span></tt> class, which implicitly creates
+and uniques them as they are needed. Types have a couple of non-obvious
+features: 1) they do not capture type qualifiers like <tt class="docutils literal"><span class="pre">const</span></tt> or <tt class="docutils literal"><span class="pre">volatile</span></tt>
+(see <a class="reference internal" href="#qualtype"><em>QualType</em></a>), and 2) they implicitly capture typedef
+information. Once created, types are immutable (unlike decls).</p>
+<p>Typedefs in C make semantic analysis a bit more complex than it would be without
+them. The issue is that we want to capture typedef information and represent it
+in the AST perfectly, but the semantics of operations need to “see through”
+typedefs. For example, consider this code:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">func</span><span class="p">()</span> <span class="p">{</span>
+ <span class="k">typedef</span> <span class="kt">int</span> <span class="n">foo</span><span class="p">;</span>
+ <span class="n">foo</span> <span class="n">X</span><span class="p">,</span> <span class="o">*</span><span class="n">Y</span><span class="p">;</span>
+ <span class="k">typedef</span> <span class="n">foo</span> <span class="o">*</span><span class="n">bar</span><span class="p">;</span>
+ <span class="n">bar</span> <span class="n">Z</span><span class="p">;</span>
+ <span class="o">*</span><span class="n">X</span><span class="p">;</span> <span class="c1">// error</span>
+ <span class="o">**</span><span class="n">Y</span><span class="p">;</span> <span class="c1">// error</span>
+ <span class="o">**</span><span class="n">Z</span><span class="p">;</span> <span class="c1">// error</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The code above is illegal, and thus we expect there to be diagnostics emitted
+on the annotated lines. In this example, we expect to get:</p>
+<div class="highlight-c++"><pre>test.c:6:1: error: indirection requires pointer operand ('foo' invalid)
+ *X; // error
+ ^~
+test.c:7:1: error: indirection requires pointer operand ('foo' invalid)
+ **Y; // error
+ ^~~
+test.c:8:1: error: indirection requires pointer operand ('foo' invalid)
+ **Z; // error
+ ^~~</pre>
+</div>
+<p>While this example is somewhat silly, it illustrates the point: we want to
+retain typedef information where possible, so that we can emit errors about
+“<tt class="docutils literal"><span class="pre">std::string</span></tt>” instead of “<tt class="docutils literal"><span class="pre">std::basic_string<char,</span> <span class="pre">std:...</span></tt>”. Doing this
+requires properly keeping typedef information (for example, the type of <tt class="docutils literal"><span class="pre">X</span></tt>
+is “<tt class="docutils literal"><span class="pre">foo</span></tt>”, not “<tt class="docutils literal"><span class="pre">int</span></tt>”), and requires properly propagating it through the
+various operators (for example, the type of <tt class="docutils literal"><span class="pre">*Y</span></tt> is “<tt class="docutils literal"><span class="pre">foo</span></tt>”, not
+“<tt class="docutils literal"><span class="pre">int</span></tt>”). In order to retain this information, the type of these expressions
+is an instance of the <tt class="docutils literal"><span class="pre">TypedefType</span></tt> class, which indicates that the type of
+these expressions is a typedef for “<tt class="docutils literal"><span class="pre">foo</span></tt>”.</p>
+<p>Representing types like this is great for diagnostics, because the
+user-specified type is always immediately available. There are two problems
+with this: first, various semantic checks need to make judgements about the
+<em>actual structure</em> of a type, ignoring typedefs. Second, we need an efficient
+way to query whether two types are structurally identical to each other,
+ignoring typedefs. The solution to both of these problems is the idea of
+canonical types.</p>
+<div class="section" id="canonical-types">
+<h4><a class="toc-backref" href="#id27">Canonical Types</a><a class="headerlink" href="#canonical-types" title="Permalink to this headline">¶</a></h4>
+<p>Every instance of the <tt class="docutils literal"><span class="pre">Type</span></tt> class contains a canonical type pointer. For
+simple types with no typedefs involved (e.g., “<tt class="docutils literal"><span class="pre">int</span></tt>”, “<tt class="docutils literal"><span class="pre">int*</span></tt>”,
+“<tt class="docutils literal"><span class="pre">int**</span></tt>”), the type just points to itself. For types that have a typedef
+somewhere in their structure (e.g., “<tt class="docutils literal"><span class="pre">foo</span></tt>”, “<tt class="docutils literal"><span class="pre">foo*</span></tt>”, “<tt class="docutils literal"><span class="pre">foo**</span></tt>”,
+“<tt class="docutils literal"><span class="pre">bar</span></tt>”), the canonical type pointer points to their structurally equivalent
+type without any typedefs (e.g., “<tt class="docutils literal"><span class="pre">int</span></tt>”, “<tt class="docutils literal"><span class="pre">int*</span></tt>”, “<tt class="docutils literal"><span class="pre">int**</span></tt>”, and
+“<tt class="docutils literal"><span class="pre">int*</span></tt>” respectively).</p>
+<p>This design provides a constant time operation (dereferencing the canonical type
+pointer) that gives us access to the structure of types. For example, we can
+trivially tell that “<tt class="docutils literal"><span class="pre">bar</span></tt>” and “<tt class="docutils literal"><span class="pre">foo*</span></tt>” are the same type by dereferencing
+their canonical type pointers and doing a pointer comparison (they both point
+to the single “<tt class="docutils literal"><span class="pre">int*</span></tt>” type).</p>
+<p>Canonical types and typedef types bring up some complexities that must be
+carefully managed. Specifically, the <tt class="docutils literal"><span class="pre">isa</span></tt>/<tt class="docutils literal"><span class="pre">cast</span></tt>/<tt class="docutils literal"><span class="pre">dyn_cast</span></tt> operators
+generally shouldn’t be used in code that is inspecting the AST. For example,
+when type checking the indirection operator (unary “<tt class="docutils literal"><span class="pre">*</span></tt>” on a pointer), the
+type checker must verify that the operand has a pointer type. It would not be
+correct to check that with “<tt class="docutils literal"><span class="pre">isa<PointerType>(SubExpr->getType())</span></tt>”, because
+this predicate would fail if the subexpression had a typedef type.</p>
+<p>The solution to this problem are a set of helper methods on <tt class="docutils literal"><span class="pre">Type</span></tt>, used to
+check their properties. In this case, it would be correct to use
+“<tt class="docutils literal"><span class="pre">SubExpr->getType()->isPointerType()</span></tt>” to do the check. This predicate will
+return true if the <em>canonical type is a pointer</em>, which is true any time the
+type is structurally a pointer type. The only hard part here is remembering
+not to use the <tt class="docutils literal"><span class="pre">isa</span></tt>/<tt class="docutils literal"><span class="pre">cast</span></tt>/<tt class="docutils literal"><span class="pre">dyn_cast</span></tt> operations.</p>
+<p>The second problem we face is how to get access to the pointer type once we
+know it exists. To continue the example, the result type of the indirection
+operator is the pointee type of the subexpression. In order to determine the
+type, we need to get the instance of <tt class="docutils literal"><span class="pre">PointerType</span></tt> that best captures the
+typedef information in the program. If the type of the expression is literally
+a <tt class="docutils literal"><span class="pre">PointerType</span></tt>, we can return that, otherwise we have to dig through the
+typedefs to find the pointer type. For example, if the subexpression had type
+“<tt class="docutils literal"><span class="pre">foo*</span></tt>”, we could return that type as the result. If the subexpression had
+type “<tt class="docutils literal"><span class="pre">bar</span></tt>”, we want to return “<tt class="docutils literal"><span class="pre">foo*</span></tt>” (note that we do <em>not</em> want
+“<tt class="docutils literal"><span class="pre">int*</span></tt>”). In order to provide all of this, <tt class="docutils literal"><span class="pre">Type</span></tt> has a
+<tt class="docutils literal"><span class="pre">getAsPointerType()</span></tt> method that checks whether the type is structurally a
+<tt class="docutils literal"><span class="pre">PointerType</span></tt> and, if so, returns the best one. If not, it returns a null
+pointer.</p>
+<p>This structure is somewhat mystical, but after meditating on it, it will make
+sense to you :).</p>
+</div>
+</div>
+<div class="section" id="the-qualtype-class">
+<span id="qualtype"></span><h3><a class="toc-backref" href="#id28">The <tt class="docutils literal"><span class="pre">QualType</span></tt> class</a><a class="headerlink" href="#the-qualtype-class" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">QualType</span></tt> class is designed as a trivial value class that is small,
+passed by-value and is efficient to query. The idea of <tt class="docutils literal"><span class="pre">QualType</span></tt> is that it
+stores the type qualifiers (<tt class="docutils literal"><span class="pre">const</span></tt>, <tt class="docutils literal"><span class="pre">volatile</span></tt>, <tt class="docutils literal"><span class="pre">restrict</span></tt>, plus some
+extended qualifiers required by language extensions) separately from the types
+themselves. <tt class="docutils literal"><span class="pre">QualType</span></tt> is conceptually a pair of “<tt class="docutils literal"><span class="pre">Type*</span></tt>” and the bits
+for these type qualifiers.</p>
+<p>By storing the type qualifiers as bits in the conceptual pair, it is extremely
+efficient to get the set of qualifiers on a <tt class="docutils literal"><span class="pre">QualType</span></tt> (just return the field
+of the pair), add a type qualifier (which is a trivial constant-time operation
+that sets a bit), and remove one or more type qualifiers (just return a
+<tt class="docutils literal"><span class="pre">QualType</span></tt> with the bitfield set to empty).</p>
+<p>Further, because the bits are stored outside of the type itself, we do not need
+to create duplicates of types with different sets of qualifiers (i.e. there is
+only a single heap allocated “<tt class="docutils literal"><span class="pre">int</span></tt>” type: “<tt class="docutils literal"><span class="pre">const</span> <span class="pre">int</span></tt>” and “<tt class="docutils literal"><span class="pre">volatile</span>
+<span class="pre">const</span> <span class="pre">int</span></tt>” both point to the same heap allocated “<tt class="docutils literal"><span class="pre">int</span></tt>” type). This
+reduces the heap size used to represent bits and also means we do not have to
+consider qualifiers when uniquing types (<a class="reference internal" href="#type"><em>Type</em></a> does not even
+contain qualifiers).</p>
+<p>In practice, the two most common type qualifiers (<tt class="docutils literal"><span class="pre">const</span></tt> and <tt class="docutils literal"><span class="pre">restrict</span></tt>)
+are stored in the low bits of the pointer to the <tt class="docutils literal"><span class="pre">Type</span></tt> object, together with
+a flag indicating whether extended qualifiers are present (which must be
+heap-allocated). This means that <tt class="docutils literal"><span class="pre">QualType</span></tt> is exactly the same size as a
+pointer.</p>
+</div>
+<div class="section" id="declaration-names">
+<span id="declarationname"></span><h3><a class="toc-backref" href="#id29">Declaration names</a><a class="headerlink" href="#declaration-names" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> class represents the name of a declaration in Clang.
+Declarations in the C family of languages can take several different forms.
+Most declarations are named by simple identifiers, e.g., “<tt class="docutils literal"><span class="pre">f</span></tt>” and “<tt class="docutils literal"><span class="pre">x</span></tt>” in
+the function declaration <tt class="docutils literal"><span class="pre">f(int</span> <span class="pre">x)</span></tt>. In C++, declaration names can also name
+class constructors (“<tt class="docutils literal"><span class="pre">Class</span></tt>” in <tt class="docutils literal"><span class="pre">struct</span> <span class="pre">Class</span> <span class="pre">{</span> <span class="pre">Class();</span> <span class="pre">}</span></tt>), class
+destructors (“<tt class="docutils literal"><span class="pre">~Class</span></tt>”), overloaded operator names (“<tt class="docutils literal"><span class="pre">operator+</span></tt>”), and
+conversion functions (“<tt class="docutils literal"><span class="pre">operator</span> <span class="pre">void</span> <span class="pre">const</span> <span class="pre">*</span></tt>”). In Objective-C,
+declaration names can refer to the names of Objective-C methods, which involve
+the method name and the parameters, collectively called a <em>selector</em>, e.g.,
+“<tt class="docutils literal"><span class="pre">setWidth:height:</span></tt>”. Since all of these kinds of entities — variables,
+functions, Objective-C methods, C++ constructors, destructors, and operators
+— are represented as subclasses of Clang’s common <tt class="docutils literal"><span class="pre">NamedDecl</span></tt> class,
+<tt class="docutils literal"><span class="pre">DeclarationName</span></tt> is designed to efficiently represent any kind of name.</p>
+<p>Given a <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> <tt class="docutils literal"><span class="pre">N</span></tt>, <tt class="docutils literal"><span class="pre">N.getNameKind()</span></tt> will produce a value
+that describes what kind of name <tt class="docutils literal"><span class="pre">N</span></tt> stores. There are 10 options (all of
+the names are inside the <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> class).</p>
+<p><tt class="docutils literal"><span class="pre">Identifier</span></tt></p>
+<blockquote>
+<div>The name is a simple identifier. Use <tt class="docutils literal"><span class="pre">N.getAsIdentifierInfo()</span></tt> to retrieve
+the corresponding <tt class="docutils literal"><span class="pre">IdentifierInfo*</span></tt> pointing to the actual identifier.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">ObjCZeroArgSelector</span></tt>, <tt class="docutils literal"><span class="pre">ObjCOneArgSelector</span></tt>, <tt class="docutils literal"><span class="pre">ObjCMultiArgSelector</span></tt></p>
+<blockquote>
+<div>The name is an Objective-C selector, which can be retrieved as a <tt class="docutils literal"><span class="pre">Selector</span></tt>
+instance via <tt class="docutils literal"><span class="pre">N.getObjCSelector()</span></tt>. The three possible name kinds for
+Objective-C reflect an optimization within the <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> class:
+both zero- and one-argument selectors are stored as a masked
+<tt class="docutils literal"><span class="pre">IdentifierInfo</span></tt> pointer, and therefore require very little space, since
+zero- and one-argument selectors are far more common than multi-argument
+selectors (which use a different structure).</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">CXXConstructorName</span></tt></p>
+<blockquote>
+<div>The name is a C++ constructor name. Use <tt class="docutils literal"><span class="pre">N.getCXXNameType()</span></tt> to retrieve
+the <a class="reference internal" href="#qualtype"><em>type</em></a> that this constructor is meant to construct. The
+type is always the canonical type, since all constructors for a given type
+have the same name.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">CXXDestructorName</span></tt></p>
+<blockquote>
+<div>The name is a C++ destructor name. Use <tt class="docutils literal"><span class="pre">N.getCXXNameType()</span></tt> to retrieve
+the <a class="reference internal" href="#qualtype"><em>type</em></a> whose destructor is being named. This type is
+always a canonical type.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">CXXConversionFunctionName</span></tt></p>
+<blockquote>
+<div>The name is a C++ conversion function. Conversion functions are named
+according to the type they convert to, e.g., “<tt class="docutils literal"><span class="pre">operator</span> <span class="pre">void</span> <span class="pre">const</span> <span class="pre">*</span></tt>”.
+Use <tt class="docutils literal"><span class="pre">N.getCXXNameType()</span></tt> to retrieve the type that this conversion function
+converts to. This type is always a canonical type.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">CXXOperatorName</span></tt></p>
+<blockquote>
+<div>The name is a C++ overloaded operator name. Overloaded operators are named
+according to their spelling, e.g., “<tt class="docutils literal"><span class="pre">operator+</span></tt>” or “<tt class="docutils literal"><span class="pre">operator</span> <span class="pre">new</span> <span class="pre">[]</span></tt>”.
+Use <tt class="docutils literal"><span class="pre">N.getCXXOverloadedOperator()</span></tt> to retrieve the overloaded operator (a
+value of type <tt class="docutils literal"><span class="pre">OverloadedOperatorKind</span></tt>).</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">CXXLiteralOperatorName</span></tt></p>
+<blockquote>
+<div>The name is a C++11 user defined literal operator. User defined
+Literal operators are named according to the suffix they define,
+e.g., “<tt class="docutils literal"><span class="pre">_foo</span></tt>” for “<tt class="docutils literal"><span class="pre">operator</span> <span class="pre">""</span> <span class="pre">_foo</span></tt>”. Use
+<tt class="docutils literal"><span class="pre">N.getCXXLiteralIdentifier()</span></tt> to retrieve the corresponding
+<tt class="docutils literal"><span class="pre">IdentifierInfo*</span></tt> pointing to the identifier.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">CXXUsingDirective</span></tt></p>
+<blockquote>
+<div>The name is a C++ using directive. Using directives are not really
+NamedDecls, in that they all have the same name, but they are
+implemented as such in order to store them in DeclContext
+effectively.</div></blockquote>
+<p><tt class="docutils literal"><span class="pre">DeclarationName</span></tt>s are cheap to create, copy, and compare. They require
+only a single pointer’s worth of storage in the common cases (identifiers,
+zero- and one-argument Objective-C selectors) and use dense, uniqued storage
+for the other kinds of names. Two <tt class="docutils literal"><span class="pre">DeclarationName</span></tt>s can be compared for
+equality (<tt class="docutils literal"><span class="pre">==</span></tt>, <tt class="docutils literal"><span class="pre">!=</span></tt>) using a simple bitwise comparison, can be ordered
+with <tt class="docutils literal"><span class="pre"><</span></tt>, <tt class="docutils literal"><span class="pre">></span></tt>, <tt class="docutils literal"><span class="pre"><=</span></tt>, and <tt class="docutils literal"><span class="pre">>=</span></tt> (which provide a lexicographical ordering
+for normal identifiers but an unspecified ordering for other kinds of names),
+and can be placed into LLVM <tt class="docutils literal"><span class="pre">DenseMap</span></tt>s and <tt class="docutils literal"><span class="pre">DenseSet</span></tt>s.</p>
+<p><tt class="docutils literal"><span class="pre">DeclarationName</span></tt> instances can be created in different ways depending on
+what kind of name the instance will store. Normal identifiers
+(<tt class="docutils literal"><span class="pre">IdentifierInfo</span></tt> pointers) and Objective-C selectors (<tt class="docutils literal"><span class="pre">Selector</span></tt>) can be
+implicitly converted to <tt class="docutils literal"><span class="pre">DeclarationNames</span></tt>. Names for C++ constructors,
+destructors, conversion functions, and overloaded operators can be retrieved
+from the <tt class="docutils literal"><span class="pre">DeclarationNameTable</span></tt>, an instance of which is available as
+<tt class="docutils literal"><span class="pre">ASTContext::DeclarationNames</span></tt>. The member functions
+<tt class="docutils literal"><span class="pre">getCXXConstructorName</span></tt>, <tt class="docutils literal"><span class="pre">getCXXDestructorName</span></tt>,
+<tt class="docutils literal"><span class="pre">getCXXConversionFunctionName</span></tt>, and <tt class="docutils literal"><span class="pre">getCXXOperatorName</span></tt>, respectively,
+return <tt class="docutils literal"><span class="pre">DeclarationName</span></tt> instances for the four kinds of C++ special function
+names.</p>
+</div>
+<div class="section" id="declaration-contexts">
+<span id="declcontext"></span><h3><a class="toc-backref" href="#id30">Declaration contexts</a><a class="headerlink" href="#declaration-contexts" title="Permalink to this headline">¶</a></h3>
+<p>Every declaration in a program exists within some <em>declaration context</em>, such
+as a translation unit, namespace, class, or function. Declaration contexts in
+Clang are represented by the <tt class="docutils literal"><span class="pre">DeclContext</span></tt> class, from which the various
+declaration-context AST nodes (<tt class="docutils literal"><span class="pre">TranslationUnitDecl</span></tt>, <tt class="docutils literal"><span class="pre">NamespaceDecl</span></tt>,
+<tt class="docutils literal"><span class="pre">RecordDecl</span></tt>, <tt class="docutils literal"><span class="pre">FunctionDecl</span></tt>, etc.) will derive. The <tt class="docutils literal"><span class="pre">DeclContext</span></tt> class
+provides several facilities common to each declaration context:</p>
+<p>Source-centric vs. Semantics-centric View of Declarations</p>
+<blockquote>
+<div><tt class="docutils literal"><span class="pre">DeclContext</span></tt> provides two views of the declarations stored within a
+declaration context. The source-centric view accurately represents the
+program source code as written, including multiple declarations of entities
+where present (see the section <a class="reference internal" href="#redeclarations"><em>Redeclarations and Overloads</em></a>), while the semantics-centric view represents the program
+semantics. The two views are kept synchronized by semantic analysis while
+the ASTs are being constructed.</div></blockquote>
+<p>Storage of declarations within that context</p>
+<blockquote>
+<div>Every declaration context can contain some number of declarations. For
+example, a C++ class (represented by <tt class="docutils literal"><span class="pre">RecordDecl</span></tt>) contains various member
+functions, fields, nested types, and so on. All of these declarations will
+be stored within the <tt class="docutils literal"><span class="pre">DeclContext</span></tt>, and one can iterate over the
+declarations via [<tt class="docutils literal"><span class="pre">DeclContext::decls_begin()</span></tt>,
+<tt class="docutils literal"><span class="pre">DeclContext::decls_end()</span></tt>). This mechanism provides the source-centric
+view of declarations in the context.</div></blockquote>
+<p>Lookup of declarations within that context</p>
+<blockquote>
+<div>The <tt class="docutils literal"><span class="pre">DeclContext</span></tt> structure provides efficient name lookup for names within
+that declaration context. For example, if <tt class="docutils literal"><span class="pre">N</span></tt> is a namespace we can look
+for the name <tt class="docutils literal"><span class="pre">N::f</span></tt> using <tt class="docutils literal"><span class="pre">DeclContext::lookup</span></tt>. The lookup itself is
+based on a lazily-constructed array (for declaration contexts with a small
+number of declarations) or hash table (for declaration contexts with more
+declarations). The lookup operation provides the semantics-centric view of
+the declarations in the context.</div></blockquote>
+<p>Ownership of declarations</p>
+<blockquote>
+<div>The <tt class="docutils literal"><span class="pre">DeclContext</span></tt> owns all of the declarations that were declared within
+its declaration context, and is responsible for the management of their
+memory as well as their (de-)serialization.</div></blockquote>
+<p>All declarations are stored within a declaration context, and one can query
+information about the context in which each declaration lives. One can
+retrieve the <tt class="docutils literal"><span class="pre">DeclContext</span></tt> that contains a particular <tt class="docutils literal"><span class="pre">Decl</span></tt> using
+<tt class="docutils literal"><span class="pre">Decl::getDeclContext</span></tt>. However, see the section
+<a class="reference internal" href="#lexicalandsemanticcontexts"><em>Lexical and Semantic Contexts</em></a> for more information about how to interpret
+this context information.</p>
+<div class="section" id="redeclarations-and-overloads">
+<span id="redeclarations"></span><h4><a class="toc-backref" href="#id31">Redeclarations and Overloads</a><a class="headerlink" href="#redeclarations-and-overloads" title="Permalink to this headline">¶</a></h4>
+<p>Within a translation unit, it is common for an entity to be declared several
+times. For example, we might declare a function “<tt class="docutils literal"><span class="pre">f</span></tt>” and then later
+re-declare it as part of an inlined definition:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">f</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span><span class="p">,</span> <span class="kt">int</span> <span class="n">y</span><span class="p">,</span> <span class="kt">int</span> <span class="n">z</span> <span class="o">=</span> <span class="mi">1</span><span class="p">);</span>
+
+<span class="kr">inline</span> <span class="kt">void</span> <span class="nf">f</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span><span class="p">,</span> <span class="kt">int</span> <span class="n">y</span><span class="p">,</span> <span class="kt">int</span> <span class="n">z</span><span class="p">)</span> <span class="p">{</span> <span class="cm">/* ... */</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>The representation of “<tt class="docutils literal"><span class="pre">f</span></tt>” differs in the source-centric and
+semantics-centric views of a declaration context. In the source-centric view,
+all redeclarations will be present, in the order they occurred in the source
+code, making this view suitable for clients that wish to see the structure of
+the source code. In the semantics-centric view, only the most recent “<tt class="docutils literal"><span class="pre">f</span></tt>”
+will be found by the lookup, since it effectively replaces the first
+declaration of “<tt class="docutils literal"><span class="pre">f</span></tt>”.</p>
+<p>In the semantics-centric view, overloading of functions is represented
+explicitly. For example, given two declarations of a function “<tt class="docutils literal"><span class="pre">g</span></tt>” that are
+overloaded, e.g.,</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="nf">g</span><span class="p">();</span>
+<span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>the <tt class="docutils literal"><span class="pre">DeclContext::lookup</span></tt> operation will return a
+<tt class="docutils literal"><span class="pre">DeclContext::lookup_result</span></tt> that contains a range of iterators over
+declarations of “<tt class="docutils literal"><span class="pre">g</span></tt>”. Clients that perform semantic analysis on a program
+that is not concerned with the actual source code will primarily use this
+semantics-centric view.</p>
+</div>
+<div class="section" id="lexical-and-semantic-contexts">
+<span id="lexicalandsemanticcontexts"></span><h4><a class="toc-backref" href="#id32">Lexical and Semantic Contexts</a><a class="headerlink" href="#lexical-and-semantic-contexts" title="Permalink to this headline">¶</a></h4>
+<p>Each declaration has two potentially different declaration contexts: a
+<em>lexical</em> context, which corresponds to the source-centric view of the
+declaration context, and a <em>semantic</em> context, which corresponds to the
+semantics-centric view. The lexical context is accessible via
+<tt class="docutils literal"><span class="pre">Decl::getLexicalDeclContext</span></tt> while the semantic context is accessible via
+<tt class="docutils literal"><span class="pre">Decl::getDeclContext</span></tt>, both of which return <tt class="docutils literal"><span class="pre">DeclContext</span></tt> pointers. For
+most declarations, the two contexts are identical. For example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">X</span> <span class="p">{</span>
+<span class="nl">public:</span>
+ <span class="kt">void</span> <span class="n">f</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span><span class="p">);</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>Here, the semantic and lexical contexts of <tt class="docutils literal"><span class="pre">X::f</span></tt> are the <tt class="docutils literal"><span class="pre">DeclContext</span></tt>
+associated with the class <tt class="docutils literal"><span class="pre">X</span></tt> (itself stored as a <tt class="docutils literal"><span class="pre">RecordDecl</span></tt> AST node).
+However, we can now define <tt class="docutils literal"><span class="pre">X::f</span></tt> out-of-line:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="n">X</span><span class="o">::</span><span class="n">f</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span> <span class="o">=</span> <span class="mi">17</span><span class="p">)</span> <span class="p">{</span> <span class="cm">/* ... */</span> <span class="p">}</span>
+</pre></div>
+</div>
+<p>This definition of “<tt class="docutils literal"><span class="pre">f</span></tt>” has different lexical and semantic contexts. The
+lexical context corresponds to the declaration context in which the actual
+declaration occurred in the source code, e.g., the translation unit containing
+<tt class="docutils literal"><span class="pre">X</span></tt>. Thus, this declaration of <tt class="docutils literal"><span class="pre">X::f</span></tt> can be found by traversing the
+declarations provided by [<tt class="docutils literal"><span class="pre">decls_begin()</span></tt>, <tt class="docutils literal"><span class="pre">decls_end()</span></tt>) in the
+translation unit.</p>
+<p>The semantic context of <tt class="docutils literal"><span class="pre">X::f</span></tt> corresponds to the class <tt class="docutils literal"><span class="pre">X</span></tt>, since this
+member function is (semantically) a member of <tt class="docutils literal"><span class="pre">X</span></tt>. Lookup of the name <tt class="docutils literal"><span class="pre">f</span></tt>
+into the <tt class="docutils literal"><span class="pre">DeclContext</span></tt> associated with <tt class="docutils literal"><span class="pre">X</span></tt> will then return the definition
+of <tt class="docutils literal"><span class="pre">X::f</span></tt> (including information about the default argument).</p>
+</div>
+<div class="section" id="transparent-declaration-contexts">
+<h4><a class="toc-backref" href="#id33">Transparent Declaration Contexts</a><a class="headerlink" href="#transparent-declaration-contexts" title="Permalink to this headline">¶</a></h4>
+<p>In C and C++, there are several contexts in which names that are logically
+declared inside another declaration will actually “leak” out into the enclosing
+scope from the perspective of name lookup. The most obvious instance of this
+behavior is in enumeration types, e.g.,</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">enum</span> <span class="n">Color</span> <span class="p">{</span>
+ <span class="n">Red</span><span class="p">,</span>
+ <span class="n">Green</span><span class="p">,</span>
+ <span class="n">Blue</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>Here, <tt class="docutils literal"><span class="pre">Color</span></tt> is an enumeration, which is a declaration context that contains
+the enumerators <tt class="docutils literal"><span class="pre">Red</span></tt>, <tt class="docutils literal"><span class="pre">Green</span></tt>, and <tt class="docutils literal"><span class="pre">Blue</span></tt>. Thus, traversing the list of
+declarations contained in the enumeration <tt class="docutils literal"><span class="pre">Color</span></tt> will yield <tt class="docutils literal"><span class="pre">Red</span></tt>,
+<tt class="docutils literal"><span class="pre">Green</span></tt>, and <tt class="docutils literal"><span class="pre">Blue</span></tt>. However, outside of the scope of <tt class="docutils literal"><span class="pre">Color</span></tt> one can
+name the enumerator <tt class="docutils literal"><span class="pre">Red</span></tt> without qualifying the name, e.g.,</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Color</span> <span class="n">c</span> <span class="o">=</span> <span class="n">Red</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>There are other entities in C++ that provide similar behavior. For example,
+linkage specifications that use curly braces:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">extern</span> <span class="s">"C"</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="n">f</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+<span class="p">}</span>
+<span class="c1">// f and g are visible here</span>
+</pre></div>
+</div>
+<p>For source-level accuracy, we treat the linkage specification and enumeration
+type as a declaration context in which its enclosed declarations (“<tt class="docutils literal"><span class="pre">Red</span></tt>”,
+“<tt class="docutils literal"><span class="pre">Green</span></tt>”, and “<tt class="docutils literal"><span class="pre">Blue</span></tt>”; “<tt class="docutils literal"><span class="pre">f</span></tt>” and “<tt class="docutils literal"><span class="pre">g</span></tt>”) are declared. However, these
+declarations are visible outside of the scope of the declaration context.</p>
+<p>These language features (and several others, described below) have roughly the
+same set of requirements: declarations are declared within a particular lexical
+context, but the declarations are also found via name lookup in scopes
+enclosing the declaration itself. This feature is implemented via
+<em>transparent</em> declaration contexts (see
+<tt class="docutils literal"><span class="pre">DeclContext::isTransparentContext()</span></tt>), whose declarations are visible in the
+nearest enclosing non-transparent declaration context. This means that the
+lexical context of the declaration (e.g., an enumerator) will be the
+transparent <tt class="docutils literal"><span class="pre">DeclContext</span></tt> itself, as will the semantic context, but the
+declaration will be visible in every outer context up to and including the
+first non-transparent declaration context (since transparent declaration
+contexts can be nested).</p>
+<p>The transparent <tt class="docutils literal"><span class="pre">DeclContext</span></tt>s are:</p>
+<ul>
+<li><p class="first">Enumerations (but not C++11 “scoped enumerations”):</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">enum</span> <span class="n">Color</span> <span class="p">{</span>
+ <span class="n">Red</span><span class="p">,</span>
+ <span class="n">Green</span><span class="p">,</span>
+ <span class="n">Blue</span>
+<span class="p">};</span>
+<span class="c1">// Red, Green, and Blue are in scope</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first">C++ linkage specifications:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">extern</span> <span class="s">"C"</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="n">f</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+ <span class="kt">void</span> <span class="nf">g</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+<span class="p">}</span>
+<span class="c1">// f and g are in scope</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first">Anonymous unions and structs:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">struct</span> <span class="n">LookupTable</span> <span class="p">{</span>
+ <span class="kt">bool</span> <span class="n">IsVector</span><span class="p">;</span>
+ <span class="k">union</span> <span class="p">{</span>
+ <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Item</span><span class="o">></span> <span class="o">*</span><span class="n">Vector</span><span class="p">;</span>
+ <span class="n">std</span><span class="o">::</span><span class="n">set</span><span class="o"><</span><span class="n">Item</span><span class="o">></span> <span class="o">*</span><span class="n">Set</span><span class="p">;</span>
+ <span class="p">};</span>
+<span class="p">};</span>
+
+<span class="n">LookupTable</span> <span class="n">LT</span><span class="p">;</span>
+<span class="n">LT</span><span class="p">.</span><span class="n">Vector</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="c1">// Okay: finds Vector inside the unnamed union</span>
+</pre></div>
+</div>
+</li>
+<li><p class="first">C++11 inline namespaces:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">namespace</span> <span class="n">mylib</span> <span class="p">{</span>
+ <span class="kr">inline</span> <span class="k">namespace</span> <span class="n">debug</span> <span class="p">{</span>
+ <span class="k">class</span> <span class="nc">X</span><span class="p">;</span>
+ <span class="p">}</span>
+<span class="p">}</span>
+<span class="n">mylib</span><span class="o">::</span><span class="n">X</span> <span class="o">*</span><span class="n">xp</span><span class="p">;</span> <span class="c1">// okay: mylib::X refers to mylib::debug::X</span>
+</pre></div>
+</div>
+</li>
+</ul>
+</div>
+<div class="section" id="multiply-defined-declaration-contexts">
+<span id="multideclcontext"></span><h4><a class="toc-backref" href="#id34">Multiply-Defined Declaration Contexts</a><a class="headerlink" href="#multiply-defined-declaration-contexts" title="Permalink to this headline">¶</a></h4>
+<p>C++ namespaces have the interesting — and, so far, unique — property that
+the namespace can be defined multiple times, and the declarations provided by
+each namespace definition are effectively merged (from the semantic point of
+view). For example, the following two code snippets are semantically
+indistinguishable:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Snippet #1:</span>
+<span class="k">namespace</span> <span class="n">N</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="n">f</span><span class="p">();</span>
+<span class="p">}</span>
+<span class="k">namespace</span> <span class="n">N</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="n">f</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">// Snippet #2:</span>
+<span class="k">namespace</span> <span class="n">N</span> <span class="p">{</span>
+ <span class="kt">void</span> <span class="n">f</span><span class="p">();</span>
+ <span class="kt">void</span> <span class="nf">f</span><span class="p">(</span><span class="kt">int</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>In Clang’s representation, the source-centric view of declaration contexts will
+actually have two separate <tt class="docutils literal"><span class="pre">NamespaceDecl</span></tt> nodes in Snippet #1, each of which
+is a declaration context that contains a single declaration of “<tt class="docutils literal"><span class="pre">f</span></tt>”.
+However, the semantics-centric view provided by name lookup into the namespace
+<tt class="docutils literal"><span class="pre">N</span></tt> for “<tt class="docutils literal"><span class="pre">f</span></tt>” will return a <tt class="docutils literal"><span class="pre">DeclContext::lookup_result</span></tt> that contains a
+range of iterators over declarations of “<tt class="docutils literal"><span class="pre">f</span></tt>”.</p>
+<p><tt class="docutils literal"><span class="pre">DeclContext</span></tt> manages multiply-defined declaration contexts internally. The
+function <tt class="docutils literal"><span class="pre">DeclContext::getPrimaryContext</span></tt> retrieves the “primary” context for
+a given <tt class="docutils literal"><span class="pre">DeclContext</span></tt> instance, which is the <tt class="docutils literal"><span class="pre">DeclContext</span></tt> responsible for
+maintaining the lookup table used for the semantics-centric view. Given the
+primary context, one can follow the chain of <tt class="docutils literal"><span class="pre">DeclContext</span></tt> nodes that define
+additional declarations via <tt class="docutils literal"><span class="pre">DeclContext::getNextContext</span></tt>. Note that these
+functions are used internally within the lookup and insertion methods of the
+<tt class="docutils literal"><span class="pre">DeclContext</span></tt>, so the vast majority of clients can ignore them.</p>
+</div>
+</div>
+<div class="section" id="the-cfg-class">
+<span id="cfg"></span><h3><a class="toc-backref" href="#id35">The <tt class="docutils literal"><span class="pre">CFG</span></tt> class</a><a class="headerlink" href="#the-cfg-class" title="Permalink to this headline">¶</a></h3>
+<p>The <tt class="docutils literal"><span class="pre">CFG</span></tt> class is designed to represent a source-level control-flow graph
+for a single statement (<tt class="docutils literal"><span class="pre">Stmt*</span></tt>). Typically instances of <tt class="docutils literal"><span class="pre">CFG</span></tt> are
+constructed for function bodies (usually an instance of <tt class="docutils literal"><span class="pre">CompoundStmt</span></tt>), but
+can also be instantiated to represent the control-flow of any class that
+subclasses <tt class="docutils literal"><span class="pre">Stmt</span></tt>, which includes simple expressions. Control-flow graphs
+are especially useful for performing <a class="reference external" href="http://en.wikipedia.org/wiki/Data_flow_analysis#Sensitivities">flow- or path-sensitive</a> program
+analyses on a given function.</p>
+<div class="section" id="basic-blocks">
+<h4><a class="toc-backref" href="#id36">Basic Blocks</a><a class="headerlink" href="#basic-blocks" title="Permalink to this headline">¶</a></h4>
+<p>Concretely, an instance of <tt class="docutils literal"><span class="pre">CFG</span></tt> is a collection of basic blocks. Each basic
+block is an instance of <tt class="docutils literal"><span class="pre">CFGBlock</span></tt>, which simply contains an ordered sequence
+of <tt class="docutils literal"><span class="pre">Stmt*</span></tt> (each referring to statements in the AST). The ordering of
+statements within a block indicates unconditional flow of control from one
+statement to the next. <a class="reference internal" href="#conditionalcontrolflow"><em>Conditional control-flow</em></a> is represented using edges between basic blocks. The
+statements within a given <tt class="docutils literal"><span class="pre">CFGBlock</span></tt> can be traversed using the
+<tt class="docutils literal"><span class="pre">CFGBlock::*iterator</span></tt> interface.</p>
+<p>A <tt class="docutils literal"><span class="pre">CFG</span></tt> object owns the instances of <tt class="docutils literal"><span class="pre">CFGBlock</span></tt> within the control-flow
+graph it represents. Each <tt class="docutils literal"><span class="pre">CFGBlock</span></tt> within a CFG is also uniquely numbered
+(accessible via <tt class="docutils literal"><span class="pre">CFGBlock::getBlockID()</span></tt>). Currently the number is based on
+the ordering the blocks were created, but no assumptions should be made on how
+<tt class="docutils literal"><span class="pre">CFGBlocks</span></tt> are numbered other than their numbers are unique and that they
+are numbered from 0..N-1 (where N is the number of basic blocks in the CFG).</p>
+</div>
+<div class="section" id="entry-and-exit-blocks">
+<h4><a class="toc-backref" href="#id37">Entry and Exit Blocks</a><a class="headerlink" href="#entry-and-exit-blocks" title="Permalink to this headline">¶</a></h4>
+<p>Each instance of <tt class="docutils literal"><span class="pre">CFG</span></tt> contains two special blocks: an <em>entry</em> block
+(accessible via <tt class="docutils literal"><span class="pre">CFG::getEntry()</span></tt>), which has no incoming edges, and an
+<em>exit</em> block (accessible via <tt class="docutils literal"><span class="pre">CFG::getExit()</span></tt>), which has no outgoing edges.
+Neither block contains any statements, and they serve the role of providing a
+clear entrance and exit for a body of code such as a function body. The
+presence of these empty blocks greatly simplifies the implementation of many
+analyses built on top of CFGs.</p>
+</div>
+<div class="section" id="conditional-control-flow">
+<span id="conditionalcontrolflow"></span><h4><a class="toc-backref" href="#id38">Conditional Control-Flow</a><a class="headerlink" href="#conditional-control-flow" title="Permalink to this headline">¶</a></h4>
+<p>Conditional control-flow (such as those induced by if-statements and loops) is
+represented as edges between <tt class="docutils literal"><span class="pre">CFGBlocks</span></tt>. Because different C language
+constructs can induce control-flow, each <tt class="docutils literal"><span class="pre">CFGBlock</span></tt> also records an extra
+<tt class="docutils literal"><span class="pre">Stmt*</span></tt> that represents the <em>terminator</em> of the block. A terminator is
+simply the statement that caused the control-flow, and is used to identify the
+nature of the conditional control-flow between blocks. For example, in the
+case of an if-statement, the terminator refers to the <tt class="docutils literal"><span class="pre">IfStmt</span></tt> object in the
+AST that represented the given branch.</p>
+<p>To illustrate, consider the following code example:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">foo</span><span class="p">(</span><span class="kt">int</span> <span class="n">x</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">x</span> <span class="o">=</span> <span class="n">x</span> <span class="o">+</span> <span class="mi">1</span><span class="p">;</span>
+ <span class="k">if</span> <span class="p">(</span><span class="n">x</span> <span class="o">></span> <span class="mi">2</span><span class="p">)</span>
+ <span class="n">x</span><span class="o">++</span><span class="p">;</span>
+ <span class="k">else</span> <span class="p">{</span>
+ <span class="n">x</span> <span class="o">+=</span> <span class="mi">2</span><span class="p">;</span>
+ <span class="n">x</span> <span class="o">*=</span> <span class="mi">2</span><span class="p">;</span>
+ <span class="p">}</span>
+
+ <span class="k">return</span> <span class="n">x</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>After invoking the parser+semantic analyzer on this code fragment, the AST of
+the body of <tt class="docutils literal"><span class="pre">foo</span></tt> is referenced by a single <tt class="docutils literal"><span class="pre">Stmt*</span></tt>. We can then construct
+an instance of <tt class="docutils literal"><span class="pre">CFG</span></tt> representing the control-flow graph of this function
+body by single call to a static class method:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Stmt</span> <span class="o">*</span><span class="n">FooBody</span> <span class="o">=</span> <span class="p">...</span>
+<span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">CFG</span><span class="o">></span> <span class="n">FooCFG</span> <span class="o">=</span> <span class="n">CFG</span><span class="o">::</span><span class="n">buildCFG</span><span class="p">(</span><span class="n">FooBody</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Along with providing an interface to iterate over its <tt class="docutils literal"><span class="pre">CFGBlocks</span></tt>, the
+<tt class="docutils literal"><span class="pre">CFG</span></tt> class also provides methods that are useful for debugging and
+visualizing CFGs. For example, the method <tt class="docutils literal"><span class="pre">CFG::dump()</span></tt> dumps a
+pretty-printed version of the CFG to standard error. This is especially useful
+when one is using a debugger such as gdb. For example, here is the output of
+<tt class="docutils literal"><span class="pre">FooCFG->dump()</span></tt>:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="p">[</span> <span class="n">B5</span> <span class="p">(</span><span class="n">ENTRY</span><span class="p">)</span> <span class="p">]</span>
+ <span class="n">Predecessors</span> <span class="p">(</span><span class="mi">0</span><span class="p">)</span><span class="o">:</span>
+ <span class="n">Successors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B4</span>
+
+<span class="p">[</span> <span class="n">B4</span> <span class="p">]</span>
+ <span class="mi">1</span><span class="o">:</span> <span class="n">x</span> <span class="o">=</span> <span class="n">x</span> <span class="o">+</span> <span class="mi">1</span>
+ <span class="mi">2</span><span class="o">:</span> <span class="p">(</span><span class="n">x</span> <span class="o">></span> <span class="mi">2</span><span class="p">)</span>
+ <span class="nl">T:</span> <span class="k">if</span> <span class="p">[</span><span class="n">B4</span><span class="mf">.2</span><span class="p">]</span>
+ <span class="n">Predecessors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B5</span>
+ <span class="n">Successors</span> <span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="o">:</span> <span class="n">B3</span> <span class="n">B2</span>
+
+<span class="p">[</span> <span class="n">B3</span> <span class="p">]</span>
+ <span class="mi">1</span><span class="o">:</span> <span class="n">x</span><span class="o">++</span>
+ <span class="n">Predecessors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B4</span>
+ <span class="n">Successors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B1</span>
+
+<span class="p">[</span> <span class="n">B2</span> <span class="p">]</span>
+ <span class="mi">1</span><span class="o">:</span> <span class="n">x</span> <span class="o">+=</span> <span class="mi">2</span>
+ <span class="mi">2</span><span class="o">:</span> <span class="n">x</span> <span class="o">*=</span> <span class="mi">2</span>
+ <span class="n">Predecessors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B4</span>
+ <span class="n">Successors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B1</span>
+
+<span class="p">[</span> <span class="n">B1</span> <span class="p">]</span>
+ <span class="mi">1</span><span class="o">:</span> <span class="k">return</span> <span class="n">x</span><span class="p">;</span>
+ <span class="n">Predecessors</span> <span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="o">:</span> <span class="n">B2</span> <span class="n">B3</span>
+ <span class="n">Successors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B0</span>
+
+<span class="p">[</span> <span class="n">B0</span> <span class="p">(</span><span class="n">EXIT</span><span class="p">)</span> <span class="p">]</span>
+ <span class="n">Predecessors</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">:</span> <span class="n">B1</span>
+ <span class="n">Successors</span> <span class="p">(</span><span class="mi">0</span><span class="p">)</span><span class="o">:</span>
+</pre></div>
+</div>
+<p>For each block, the pretty-printed output displays for each block the number of
+<em>predecessor</em> blocks (blocks that have outgoing control-flow to the given
+block) and <em>successor</em> blocks (blocks that have control-flow that have incoming
+control-flow from the given block). We can also clearly see the special entry
+and exit blocks at the beginning and end of the pretty-printed output. For the
+entry block (block B5), the number of predecessor blocks is 0, while for the
+exit block (block B0) the number of successor blocks is 0.</p>
+<p>The most interesting block here is B4, whose outgoing control-flow represents
+the branching caused by the sole if-statement in <tt class="docutils literal"><span class="pre">foo</span></tt>. Of particular
+interest is the second statement in the block, <tt class="docutils literal"><span class="pre">(x</span> <span class="pre">></span> <span class="pre">2)</span></tt>, and the terminator,
+printed as <tt class="docutils literal"><span class="pre">if</span> <span class="pre">[B4.2]</span></tt>. The second statement represents the evaluation of
+the condition of the if-statement, which occurs before the actual branching of
+control-flow. Within the <tt class="docutils literal"><span class="pre">CFGBlock</span></tt> for B4, the <tt class="docutils literal"><span class="pre">Stmt*</span></tt> for the second
+statement refers to the actual expression in the AST for <tt class="docutils literal"><span class="pre">(x</span> <span class="pre">></span> <span class="pre">2)</span></tt>. Thus
+pointers to subclasses of <tt class="docutils literal"><span class="pre">Expr</span></tt> can appear in the list of statements in a
+block, and not just subclasses of <tt class="docutils literal"><span class="pre">Stmt</span></tt> that refer to proper C statements.</p>
+<p>The terminator of block B4 is a pointer to the <tt class="docutils literal"><span class="pre">IfStmt</span></tt> object in the AST.
+The pretty-printer outputs <tt class="docutils literal"><span class="pre">if</span> <span class="pre">[B4.2]</span></tt> because the condition expression of
+the if-statement has an actual place in the basic block, and thus the
+terminator is essentially <em>referring</em> to the expression that is the second
+statement of block B4 (i.e., B4.2). In this manner, conditions for
+control-flow (which also includes conditions for loops and switch statements)
+are hoisted into the actual basic block.</p>
+</div>
+</div>
+<div class="section" id="constant-folding-in-the-clang-ast">
+<h3><a class="toc-backref" href="#id39">Constant Folding in the Clang AST</a><a class="headerlink" href="#constant-folding-in-the-clang-ast" title="Permalink to this headline">¶</a></h3>
+<p>There are several places where constants and constant folding matter a lot to
+the Clang front-end. First, in general, we prefer the AST to retain the source
+code as close to how the user wrote it as possible. This means that if they
+wrote “<tt class="docutils literal"><span class="pre">5+4</span></tt>”, we want to keep the addition and two constants in the AST, we
+don’t want to fold to “<tt class="docutils literal"><span class="pre">9</span></tt>”. This means that constant folding in various
+ways turns into a tree walk that needs to handle the various cases.</p>
+<p>However, there are places in both C and C++ that require constants to be
+folded. For example, the C standard defines what an “integer constant
+expression” (i-c-e) is with very precise and specific requirements. The
+language then requires i-c-e’s in a lot of places (for example, the size of a
+bitfield, the value for a case statement, etc). For these, we have to be able
+to constant fold the constants, to do semantic checks (e.g., verify bitfield
+size is non-negative and that case statements aren’t duplicated). We aim for
+Clang to be very pedantic about this, diagnosing cases when the code does not
+use an i-c-e where one is required, but accepting the code unless running with
+<tt class="docutils literal"><span class="pre">-pedantic-errors</span></tt>.</p>
+<p>Things get a little bit more tricky when it comes to compatibility with
+real-world source code. Specifically, GCC has historically accepted a huge
+superset of expressions as i-c-e’s, and a lot of real world code depends on
+this unfortuate accident of history (including, e.g., the glibc system
+headers). GCC accepts anything its “fold” optimizer is capable of reducing to
+an integer constant, which means that the definition of what it accepts changes
+as its optimizer does. One example is that GCC accepts things like “<tt class="docutils literal"><span class="pre">case</span>
+<span class="pre">X-X:</span></tt>” even when <tt class="docutils literal"><span class="pre">X</span></tt> is a variable, because it can fold this to 0.</p>
+<p>Another issue are how constants interact with the extensions we support, such
+as <tt class="docutils literal"><span class="pre">__builtin_constant_p</span></tt>, <tt class="docutils literal"><span class="pre">__builtin_inf</span></tt>, <tt class="docutils literal"><span class="pre">__extension__</span></tt> and many
+others. C99 obviously does not specify the semantics of any of these
+extensions, and the definition of i-c-e does not include them. However, these
+extensions are often used in real code, and we have to have a way to reason
+about them.</p>
+<p>Finally, this is not just a problem for semantic analysis. The code generator
+and other clients have to be able to fold constants (e.g., to initialize global
+variables) and has to handle a superset of what C99 allows. Further, these
+clients can benefit from extended information. For example, we know that
+“<tt class="docutils literal"><span class="pre">foo()</span> <span class="pre">||</span> <span class="pre">1</span></tt>” always evaluates to <tt class="docutils literal"><span class="pre">true</span></tt>, but we can’t replace the
+expression with <tt class="docutils literal"><span class="pre">true</span></tt> because it has side effects.</p>
+<div class="section" id="implementation-approach">
+<h4><a class="toc-backref" href="#id40">Implementation Approach</a><a class="headerlink" href="#implementation-approach" title="Permalink to this headline">¶</a></h4>
+<p>After trying several different approaches, we’ve finally converged on a design
+(Note, at the time of this writing, not all of this has been implemented,
+consider this a design goal!). Our basic approach is to define a single
+recursive method evaluation method (<tt class="docutils literal"><span class="pre">Expr::Evaluate</span></tt>), which is implemented
+in <tt class="docutils literal"><span class="pre">AST/ExprConstant.cpp</span></tt>. Given an expression with “scalar” type (integer,
+fp, complex, or pointer) this method returns the following information:</p>
+<ul class="simple">
+<li>Whether the expression is an integer constant expression, a general constant
+that was folded but has no side effects, a general constant that was folded
+but that does have side effects, or an uncomputable/unfoldable value.</li>
+<li>If the expression was computable in any way, this method returns the
+<tt class="docutils literal"><span class="pre">APValue</span></tt> for the result of the expression.</li>
+<li>If the expression is not evaluatable at all, this method returns information
+on one of the problems with the expression. This includes a
+<tt class="docutils literal"><span class="pre">SourceLocation</span></tt> for where the problem is, and a diagnostic ID that explains
+the problem. The diagnostic should have <tt class="docutils literal"><span class="pre">ERROR</span></tt> type.</li>
+<li>If the expression is not an integer constant expression, this method returns
+information on one of the problems with the expression. This includes a
+<tt class="docutils literal"><span class="pre">SourceLocation</span></tt> for where the problem is, and a diagnostic ID that
+explains the problem. The diagnostic should have <tt class="docutils literal"><span class="pre">EXTENSION</span></tt> type.</li>
+</ul>
+<p>This information gives various clients the flexibility that they want, and we
+will eventually have some helper methods for various extensions. For example,
+<tt class="docutils literal"><span class="pre">Sema</span></tt> should have a <tt class="docutils literal"><span class="pre">Sema::VerifyIntegerConstantExpression</span></tt> method, which
+calls <tt class="docutils literal"><span class="pre">Evaluate</span></tt> on the expression. If the expression is not foldable, the
+error is emitted, and it would return <tt class="docutils literal"><span class="pre">true</span></tt>. If the expression is not an
+i-c-e, the <tt class="docutils literal"><span class="pre">EXTENSION</span></tt> diagnostic is emitted. Finally it would return
+<tt class="docutils literal"><span class="pre">false</span></tt> to indicate that the AST is OK.</p>
+<p>Other clients can use the information in other ways, for example, codegen can
+just use expressions that are foldable in any way.</p>
+</div>
+<div class="section" id="extensions">
+<h4><a class="toc-backref" href="#id41">Extensions</a><a class="headerlink" href="#extensions" title="Permalink to this headline">¶</a></h4>
+<p>This section describes how some of the various extensions Clang supports
+interacts with constant evaluation:</p>
+<ul class="simple">
+<li><tt class="docutils literal"><span class="pre">__extension__</span></tt>: The expression form of this extension causes any
+evaluatable subexpression to be accepted as an integer constant expression.</li>
+<li><tt class="docutils literal"><span class="pre">__builtin_constant_p</span></tt>: This returns true (as an integer constant
+expression) if the operand evaluates to either a numeric value (that is, not
+a pointer cast to integral type) of integral, enumeration, floating or
+complex type, or if it evaluates to the address of the first character of a
+string literal (possibly cast to some other type). As a special case, if
+<tt class="docutils literal"><span class="pre">__builtin_constant_p</span></tt> is the (potentially parenthesized) condition of a
+conditional operator expression (“<tt class="docutils literal"><span class="pre">?:</span></tt>”), only the true side of the
+conditional operator is considered, and it is evaluated with full constant
+folding.</li>
+<li><tt class="docutils literal"><span class="pre">__builtin_choose_expr</span></tt>: The condition is required to be an integer
+constant expression, but we accept any constant as an “extension of an
+extension”. This only evaluates one operand depending on which way the
+condition evaluates.</li>
+<li><tt class="docutils literal"><span class="pre">__builtin_classify_type</span></tt>: This always returns an integer constant
+expression.</li>
+<li><tt class="docutils literal"><span class="pre">__builtin_inf,</span> <span class="pre">nan,</span> <span class="pre">...</span></tt>: These are treated just like a floating-point
+literal.</li>
+<li><tt class="docutils literal"><span class="pre">__builtin_abs,</span> <span class="pre">copysign,</span> <span class="pre">...</span></tt>: These are constant folded as general
+constant expressions.</li>
+<li><tt class="docutils literal"><span class="pre">__builtin_strlen</span></tt> and <tt class="docutils literal"><span class="pre">strlen</span></tt>: These are constant folded as integer
+constant expressions if the argument is a string literal.</li>
+</ul>
+</div>
+</div>
+</div>
+<div class="section" id="the-sema-library">
+<span id="sema"></span><h2><a class="toc-backref" href="#id42">The Sema Library</a><a class="headerlink" href="#the-sema-library" title="Permalink to this headline">¶</a></h2>
+<p>This library is called by the <a class="reference internal" href="#parser"><em>Parser library</em></a> during parsing to
+do semantic analysis of the input. For valid programs, Sema builds an AST for
+parsed constructs.</p>
+</div>
+<div class="section" id="the-codegen-library">
+<span id="codegen"></span><h2><a class="toc-backref" href="#id43">The CodeGen Library</a><a class="headerlink" href="#the-codegen-library" title="Permalink to this headline">¶</a></h2>
+<p>CodeGen takes an <a class="reference internal" href="#ast"><em>AST</em></a> as input and produces <a class="reference external" href="//llvm.org/docs/LangRef.html">LLVM IR code</a> from it.</p>
+</div>
+<div class="section" id="how-to-change-clang">
+<h2><a class="toc-backref" href="#id44">How to change Clang</a><a class="headerlink" href="#how-to-change-clang" title="Permalink to this headline">¶</a></h2>
+<div class="section" id="how-to-add-an-attribute">
+<h3><a class="toc-backref" href="#id45">How to add an attribute</a><a class="headerlink" href="#how-to-add-an-attribute" title="Permalink to this headline">¶</a></h3>
+<div class="section" id="attribute-basics">
+<h4><a class="toc-backref" href="#id46">Attribute Basics</a><a class="headerlink" href="#attribute-basics" title="Permalink to this headline">¶</a></h4>
+<p>Attributes in clang come in two forms: parsed form, and semantic form. Both
+forms are represented via a tablegen definition of the attribute, specified in
+Attr.td.</p>
+</div>
+<div class="section" id="include-clang-basic-attr-td">
+<h4><a class="toc-backref" href="#id47"><tt class="docutils literal"><span class="pre">include/clang/Basic/Attr.td</span></tt></a><a class="headerlink" href="#include-clang-basic-attr-td" title="Permalink to this headline">¶</a></h4>
+<p>First, add your attribute to the <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?view=markup">include/clang/Basic/Attr.td</a>
+file.</p>
+<p>Each attribute gets a <tt class="docutils literal"><span class="pre">def</span></tt> inheriting from <tt class="docutils literal"><span class="pre">Attr</span></tt> or one of its
+subclasses. <tt class="docutils literal"><span class="pre">InheritableAttr</span></tt> means that the attribute also applies to
+subsequent declarations of the same name. <tt class="docutils literal"><span class="pre">InheritableParamAttr</span></tt> is similar
+to <tt class="docutils literal"><span class="pre">InheritableAttr</span></tt>, except that the attribute is written on a parameter
+instead of a declaration, type or statement. Attributes inheriting from
+<tt class="docutils literal"><span class="pre">TypeAttr</span></tt> are pure type attributes which generally are not given a
+representation in the AST. Attributes inheriting from <tt class="docutils literal"><span class="pre">TargetSpecificAttr</span></tt>
+are attributes specific to one or more target architectures. An attribute that
+inherits from <tt class="docutils literal"><span class="pre">IgnoredAttr</span></tt> is parsed, but will generate an ignored attribute
+diagnostic when used. The attribute type may be useful when an attribute is
+supported by another vendor, but not supported by clang.</p>
+<p><tt class="docutils literal"><span class="pre">Spellings</span></tt> lists the strings that can appear in <tt class="docutils literal"><span class="pre">__attribute__((here))</span></tt> or
+<tt class="docutils literal"><span class="pre">[[here]]</span></tt>. All such strings will be synonymous. Possible <tt class="docutils literal"><span class="pre">Spellings</span></tt>
+are: <tt class="docutils literal"><span class="pre">GNU</span></tt> (for use with GNU-style __attribute__ spellings), <tt class="docutils literal"><span class="pre">Declspec</span></tt>
+(for use with Microsoft Visual Studio-style __declspec spellings), <tt class="docutils literal"><span class="pre">CXX11`</span>
+<span class="pre">(for</span> <span class="pre">use</span> <span class="pre">with</span> <span class="pre">C++11-style</span> <span class="pre">[[foo]]</span> <span class="pre">and</span> <span class="pre">[[foo::bar]]</span> <span class="pre">spellings),</span> <span class="pre">and</span> <span class="pre">``Keyword</span></tt>
+(for use with attributes that are implemented as keywords, like C++11’s
+<tt class="docutils literal"><span class="pre">override</span></tt> or <tt class="docutils literal"><span class="pre">final</span></tt>). If you want to allow the <tt class="docutils literal"><span class="pre">[[]]</span></tt> C++11 syntax, you
+have to define a list of <tt class="docutils literal"><span class="pre">Namespaces</span></tt>, which will let users write
+<tt class="docutils literal"><span class="pre">[[namespace::spelling]]</span></tt>. Using the empty string for a namespace will allow
+users to write just the spelling with no “<tt class="docutils literal"><span class="pre">::</span></tt>”. Attributes which g++-4.8
+or later accepts should also have a <tt class="docutils literal"><span class="pre">CXX11<"gnu",</span> <span class="pre">"spelling"></span></tt> spelling.</p>
+<p><tt class="docutils literal"><span class="pre">Subjects</span></tt> restricts what kinds of AST node to which this attribute can
+appertain (roughly, attach). The subjects are specified via a <tt class="docutils literal"><span class="pre">SubjectList</span></tt>,
+which specify the list of subjects. Additionally, subject-related diagnostics
+can be specified to be warnings or errors, with the default being a warning.
+The diagnostics displayed to the user are automatically determined based on
+the subjects in the list, but a custom diagnostic parameter can also be
+specified in the <tt class="docutils literal"><span class="pre">SubjectList</span></tt>. The diagnostics generated for subject list
+violations are either <tt class="docutils literal"><span class="pre">diag::warn_attribute_wrong_decl_type</span></tt> or
+<tt class="docutils literal"><span class="pre">diag::err_attribute_wrong_decl_type</span></tt>, and the parameter enumeration is
+found in <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/AttributeList.h?view=markup">include/clang/Sema/AttributeList.h</a>
+If you add new Decl nodes to the <tt class="docutils literal"><span class="pre">SubjectList</span></tt>, you may need to update the
+logic used to automatically determine the diagnostic parameter in <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/utils/TableGen/ClangAttrEmitter.cpp?view=markup">utils/TableGen/ClangAttrEmitter.cpp</a>.</p>
+<p>Diagnostic checking for attribute subject lists is automated except when
+<tt class="docutils literal"><span class="pre">HasCustomParsing</span></tt> is set to <tt class="docutils literal"><span class="pre">1</span></tt>.</p>
+<p>By default, all subjects in the SubjectList must either be a Decl node defined
+in <tt class="docutils literal"><span class="pre">DeclNodes.td</span></tt>, or a statement node defined in <tt class="docutils literal"><span class="pre">StmtNodes.td</span></tt>. However,
+more complex subjects can be created by creating a <tt class="docutils literal"><span class="pre">SubsetSubject</span></tt> object.
+Each such object has a base subject which it appertains to (which must be a
+Decl or Stmt node, and not a SubsetSubject node), and some custom code which is
+called when determining whether an attribute appertains to the subject. For
+instance, a <tt class="docutils literal"><span class="pre">NonBitField</span></tt> SubsetSubject appertains to a <tt class="docutils literal"><span class="pre">FieldDecl</span></tt>, and
+tests whether the given FieldDecl is a bit field. When a SubsetSubject is
+specified in a SubjectList, a custom diagnostic parameter must also be provided.</p>
+<p><tt class="docutils literal"><span class="pre">Args</span></tt> names the arguments the attribute takes, in order. If <tt class="docutils literal"><span class="pre">Args</span></tt> is
+<tt class="docutils literal"><span class="pre">[StringArgument<"Arg1">,</span> <span class="pre">IntArgument<"Arg2">]</span></tt> then
+<tt class="docutils literal"><span class="pre">__attribute__((myattribute("Hello",</span> <span class="pre">3)))</span></tt> will be a valid use. Attribute
+arguments specify both the parsed form and the semantic form of the attribute.
+The previous example shows an attribute which requires two attributes while
+parsing, and the Attr subclass’ constructor for the attribute will require a
+string and integer argument.</p>
+<p>Diagnostic checking for argument counts is automated except when
+<tt class="docutils literal"><span class="pre">HasCustomParsing</span></tt> is set to <tt class="docutils literal"><span class="pre">1</span></tt>, or when the attribute uses an optional or
+variadic argument. Diagnostic checking for argument semantics is not automated.</p>
+<p>If the parsed form of the attribute is more complex, or differs from the
+semantic form, the <tt class="docutils literal"><span class="pre">HasCustomParsing</span></tt> bit can be set to <tt class="docutils literal"><span class="pre">1</span></tt> for the class,
+and the parsing code in <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParseDecl.cpp?view=markup">Parser::ParseGNUAttributeArgs</a>
+can be updated for the special case. Note that this only applies to arguments
+with a GNU spelling – attributes with a __declspec spelling currently ignore
+this flag and are handled by <tt class="docutils literal"><span class="pre">Parser::ParseMicrosoftDeclSpec</span></tt>.</p>
+<p>Custom accessors can be generated for an attribute based on the spelling list
+for that attribute. For instance, if an attribute has two different spellings:
+‘Foo’ and ‘Bar’, accessors can be created:
+<tt class="docutils literal"><span class="pre">[Accessor<"isFoo",</span> <span class="pre">[GNU<"Foo">]>,</span> <span class="pre">Accessor<"isBar",</span> <span class="pre">[GNU<"Bar">]>]</span></tt>
+These accessors will be generated on the semantic form of the attribute,
+accepting no arguments and returning a Boolean.</p>
+<p>Attributes which do not require an AST node should set the <tt class="docutils literal"><span class="pre">ASTNode</span></tt> field to
+<tt class="docutils literal"><span class="pre">0</span></tt> to avoid polluting the AST. Note that anything inheriting from
+<tt class="docutils literal"><span class="pre">TypeAttr</span></tt> or <tt class="docutils literal"><span class="pre">IgnoredAttr</span></tt> automatically do not generate an AST node. All
+other attributes generate an AST node by default. The AST node is the semantic
+representation of the attribute.</p>
+<p>Attributes which do not require custom semantic handling should set the
+<tt class="docutils literal"><span class="pre">SemaHandler</span></tt> field to <tt class="docutils literal"><span class="pre">0</span></tt>. Note that anything inheriting from
+<tt class="docutils literal"><span class="pre">IgnoredAttr</span></tt> automatically do not get a semantic handler. All other
+attributes are assumed to use a semantic handler by default. Attributes
+without a semantic handler are not given a parsed attribute Kind enumeration.</p>
+<p>The <tt class="docutils literal"><span class="pre">LangOpts</span></tt> field can be used to specify a list of language options
+required by the attribute. For instance, all of the CUDA-specific attributes
+specify <tt class="docutils literal"><span class="pre">[CUDA]</span></tt> for the <tt class="docutils literal"><span class="pre">LangOpts</span></tt> field, and when the CUDA language
+option is not enabled, an “attribute ignored” warning diagnostic is emitted.
+Since language options are not table generated nodes, new language options must
+be created manually and should specify the spelling used by <tt class="docutils literal"><span class="pre">LangOptions</span></tt> class.</p>
+<p>Target-specific attribute sometimes share a spelling with other attributes in
+different targets. For instance, the ARM and MSP430 targets both have an
+attribute spelled <tt class="docutils literal"><span class="pre">GNU<"interrupt"></span></tt>, but with different parsing and semantic
+requirements. To support this feature, an attribute inheriting from
+<tt class="docutils literal"><span class="pre">TargetSpecificAttribute</span></tt> make specify a <tt class="docutils literal"><span class="pre">ParseKind</span></tt> field. This field
+should be the same value between all arguments sharing a spelling, and
+corresponds to the parsed attribute’s Kind enumeration. This allows attributes
+to share a parsed attribute kind, but have distinct semantic attribute classes.
+For instance, <tt class="docutils literal"><span class="pre">AttributeList::AT_Interrupt</span></tt> is the shared parsed attribute
+kind, but ARMInterruptAttr and MSP430InterruptAttr are the semantic attributes
+generated.</p>
+<p>By default, when declarations are merging attributes, an attribute will not be
+duplicated. However, if an attribute can be duplicated during this merging
+stage, set <tt class="docutils literal"><span class="pre">DuplicatesAllowedWhileMerging</span></tt> to <tt class="docutils literal"><span class="pre">1</span></tt>, and the attribute will
+be merged.</p>
+<p>By default, attribute arguments are parsed in an evaluated context. If the
+arguments for an attribute should be parsed in an unevaluated context (akin to
+the way the argument to a <tt class="docutils literal"><span class="pre">sizeof</span></tt> expression is parsed), you can set
+<tt class="docutils literal"><span class="pre">ParseArgumentsAsUnevaluated</span></tt> to <tt class="docutils literal"><span class="pre">1</span></tt>.</p>
+<p>If additional functionality is desired for the semantic form of the attribute,
+the <tt class="docutils literal"><span class="pre">AdditionalMembers</span></tt> field specifies code to be copied verbatim into the
+semantic attribute class object.</p>
+<p>All attributes must have one or more form of documentation, which is provided
+in the <tt class="docutils literal"><span class="pre">Documentation</span></tt> list. Generally, the documentation for an attribute
+is a stand-alone definition in <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/AttdDocs.td?view=markup">include/clang/Basic/AttrDocs.td</a>
+that is named after the attribute being documented. Each documentation element
+is given a <tt class="docutils literal"><span class="pre">Category</span></tt> (variable, function, or type) and <tt class="docutils literal"><span class="pre">Content</span></tt>. A single
+attribute may contain multiple documentation elements for distinct categories.
+For instance, an attribute which can appertain to both function and types (such
+as a calling convention attribute), should contain two documentation elements.
+The <tt class="docutils literal"><span class="pre">Content</span></tt> for an attribute uses reStructuredText (RST) syntax.</p>
+<p>If an attribute is used internally by the compiler, but is not written by users
+(such as attributes with an empty spelling list), it can use the
+<tt class="docutils literal"><span class="pre">Undocumented</span></tt> documentation element.</p>
+</div>
+<div class="section" id="boilerplate">
+<h4><a class="toc-backref" href="#id48">Boilerplate</a><a class="headerlink" href="#boilerplate" title="Permalink to this headline">¶</a></h4>
+<p>All semantic processing of declaration attributes happens in <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?view=markup">lib/Sema/SemaDeclAttr.cpp</a>,
+and generally starts in the <tt class="docutils literal"><span class="pre">ProcessDeclAttribute</span></tt> function. If your
+attribute is a “simple” attribute – meaning that it requires no custom
+semantic processing aside from what is automatically provided for you, you can
+add a call to <tt class="docutils literal"><span class="pre">handleSimpleAttribute<YourAttr>(S,</span> <span class="pre">D,</span> <span class="pre">Attr);</span></tt> to the switch
+statement. Otherwise, write a new <tt class="docutils literal"><span class="pre">handleYourAttr()</span></tt> function, and add that
+to the switch statement.</p>
+<p>If your attribute causes extra warnings to fire, define a <tt class="docutils literal"><span class="pre">DiagGroup</span></tt> in
+<a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?view=markup">include/clang/Basic/DiagnosticGroups.td</a>
+named after the attribute’s <tt class="docutils literal"><span class="pre">Spelling</span></tt> with “_”s replaced by “-“s. If you’re
+only defining one diagnostic, you can skip <tt class="docutils literal"><span class="pre">DiagnosticGroups.td</span></tt> and use
+<tt class="docutils literal"><span class="pre">InGroup<DiagGroup<"your-attribute">></span></tt> directly in <a class="reference external" href="http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?view=markup">DiagnosticSemaKinds.td</a></p>
+<p>All semantic diagnostics generated for your attribute, including automatically-
+generated ones (such as subjects and argument counts), should have a
+corresponding test case.</p>
+</div>
+<div class="section" id="the-meat-of-your-attribute">
+<h4><a class="toc-backref" href="#id49">The meat of your attribute</a><a class="headerlink" href="#the-meat-of-your-attribute" title="Permalink to this headline">¶</a></h4>
+<p>Find an appropriate place in Clang to do whatever your attribute needs to do.
+Check for the attribute’s presence using <tt class="docutils literal"><span class="pre">Decl::getAttr<YourAttr>()</span></tt>.</p>
+<p>Update the <a class="reference internal" href="LanguageExtensions.html"><em>Clang Language Extensions</em></a> document to describe your new attribute.</p>
+</div>
+</div>
+<div class="section" id="how-to-add-an-expression-or-statement">
+<h3><a class="toc-backref" href="#id50">How to add an expression or statement</a><a class="headerlink" href="#how-to-add-an-expression-or-statement" title="Permalink to this headline">¶</a></h3>
+<p>Expressions and statements are one of the most fundamental constructs within a
+compiler, because they interact with many different parts of the AST, semantic
+analysis, and IR generation. Therefore, adding a new expression or statement
+kind into Clang requires some care. The following list details the various
+places in Clang where an expression or statement needs to be introduced, along
+with patterns to follow to ensure that the new expression or statement works
+well across all of the C languages. We focus on expressions, but statements
+are similar.</p>
+<ol class="arabic simple">
+<li>Introduce parsing actions into the parser. Recursive-descent parsing is
+mostly self-explanatory, but there are a few things that are worth keeping
+in mind:<ul>
+<li>Keep as much source location information as possible! You’ll want it later
+to produce great diagnostics and support Clang’s various features that map
+between source code and the AST.</li>
+<li>Write tests for all of the “bad” parsing cases, to make sure your recovery
+is good. If you have matched delimiters (e.g., parentheses, square
+brackets, etc.), use <tt class="docutils literal"><span class="pre">Parser::BalancedDelimiterTracker</span></tt> to give nice
+diagnostics when things go wrong.</li>
+</ul>
+</li>
+<li>Introduce semantic analysis actions into <tt class="docutils literal"><span class="pre">Sema</span></tt>. Semantic analysis should
+always involve two functions: an <tt class="docutils literal"><span class="pre">ActOnXXX</span></tt> function that will be called
+directly from the parser, and a <tt class="docutils literal"><span class="pre">BuildXXX</span></tt> function that performs the
+actual semantic analysis and will (eventually!) build the AST node. It’s
+fairly common for the <tt class="docutils literal"><span class="pre">ActOnCXX</span></tt> function to do very little (often just
+some minor translation from the parser’s representation to <tt class="docutils literal"><span class="pre">Sema</span></tt>‘s
+representation of the same thing), but the separation is still important:
+C++ template instantiation, for example, should always call the <tt class="docutils literal"><span class="pre">BuildXXX</span></tt>
+variant. Several notes on semantic analysis before we get into construction
+of the AST:<ul>
+<li>Your expression probably involves some types and some subexpressions.
+Make sure to fully check that those types, and the types of those
+subexpressions, meet your expectations. Add implicit conversions where
+necessary to make sure that all of the types line up exactly the way you
+want them. Write extensive tests to check that you’re getting good
+diagnostics for mistakes and that you can use various forms of
+subexpressions with your expression.</li>
+<li>When type-checking a type or subexpression, make sure to first check
+whether the type is “dependent” (<tt class="docutils literal"><span class="pre">Type::isDependentType()</span></tt>) or whether a
+subexpression is type-dependent (<tt class="docutils literal"><span class="pre">Expr::isTypeDependent()</span></tt>). If any of
+these return <tt class="docutils literal"><span class="pre">true</span></tt>, then you’re inside a template and you can’t do much
+type-checking now. That’s normal, and your AST node (when you get there)
+will have to deal with this case. At this point, you can write tests that
+use your expression within templates, but don’t try to instantiate the
+templates.</li>
+<li>For each subexpression, be sure to call <tt class="docutils literal"><span class="pre">Sema::CheckPlaceholderExpr()</span></tt>
+to deal with “weird” expressions that don’t behave well as subexpressions.
+Then, determine whether you need to perform lvalue-to-rvalue conversions
+(<tt class="docutils literal"><span class="pre">Sema::DefaultLvalueConversions</span></tt>) or the usual unary conversions
+(<tt class="docutils literal"><span class="pre">Sema::UsualUnaryConversions</span></tt>), for places where the subexpression is
+producing a value you intend to use.</li>
+<li>Your <tt class="docutils literal"><span class="pre">BuildXXX</span></tt> function will probably just return <tt class="docutils literal"><span class="pre">ExprError()</span></tt> at
+this point, since you don’t have an AST. That’s perfectly fine, and
+shouldn’t impact your testing.</li>
+</ul>
+</li>
+<li>Introduce an AST node for your new expression. This starts with declaring
+the node in <tt class="docutils literal"><span class="pre">include/Basic/StmtNodes.td</span></tt> and creating a new class for your
+expression in the appropriate <tt class="docutils literal"><span class="pre">include/AST/Expr*.h</span></tt> header. It’s best to
+look at the class for a similar expression to get ideas, and there are some
+specific things to watch for:<ul>
+<li>If you need to allocate memory, use the <tt class="docutils literal"><span class="pre">ASTContext</span></tt> allocator to
+allocate memory. Never use raw <tt class="docutils literal"><span class="pre">malloc</span></tt> or <tt class="docutils literal"><span class="pre">new</span></tt>, and never hold any
+resources in an AST node, because the destructor of an AST node is never
+called.</li>
+<li>Make sure that <tt class="docutils literal"><span class="pre">getSourceRange()</span></tt> covers the exact source range of your
+expression. This is needed for diagnostics and for IDE support.</li>
+<li>Make sure that <tt class="docutils literal"><span class="pre">children()</span></tt> visits all of the subexpressions. This is
+important for a number of features (e.g., IDE support, C++ variadic
+templates). If you have sub-types, you’ll also need to visit those
+sub-types in <tt class="docutils literal"><span class="pre">RecursiveASTVisitor</span></tt> and <tt class="docutils literal"><span class="pre">DataRecursiveASTVisitor</span></tt>.</li>
+<li>Add printing support (<tt class="docutils literal"><span class="pre">StmtPrinter.cpp</span></tt>) for your expression.</li>
+<li>Add profiling support (<tt class="docutils literal"><span class="pre">StmtProfile.cpp</span></tt>) for your AST node, noting the
+distinguishing (non-source location) characteristics of an instance of
+your expression. Omitting this step will lead to hard-to-diagnose
+failures regarding matching of template declarations.</li>
+<li>Add serialization support (<tt class="docutils literal"><span class="pre">ASTReaderStmt.cpp</span></tt>, <tt class="docutils literal"><span class="pre">ASTWriterStmt.cpp</span></tt>)
+for your AST node.</li>
+</ul>
+</li>
+<li>Teach semantic analysis to build your AST node. At this point, you can wire
+up your <tt class="docutils literal"><span class="pre">Sema::BuildXXX</span></tt> function to actually create your AST. A few
+things to check at this point:<ul>
+<li>If your expression can construct a new C++ class or return a new
+Objective-C object, be sure to update and then call
+<tt class="docutils literal"><span class="pre">Sema::MaybeBindToTemporary</span></tt> for your just-created AST node to be sure
+that the object gets properly destructed. An easy way to test this is to
+return a C++ class with a private destructor: semantic analysis should
+flag an error here with the attempt to call the destructor.</li>
+<li>Inspect the generated AST by printing it using <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span> <span class="pre">-ast-print</span></tt>,
+to make sure you’re capturing all of the important information about how
+the AST was written.</li>
+<li>Inspect the generated AST under <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span> <span class="pre">-ast-dump</span></tt> to verify that
+all of the types in the generated AST line up the way you want them.
+Remember that clients of the AST should never have to “think” to
+understand what’s going on. For example, all implicit conversions should
+show up explicitly in the AST.</li>
+<li>Write tests that use your expression as a subexpression of other,
+well-known expressions. Can you call a function using your expression as
+an argument? Can you use the ternary operator?</li>
+</ul>
+</li>
+<li>Teach code generation to create IR to your AST node. This step is the first
+(and only) that requires knowledge of LLVM IR. There are several things to
+keep in mind:<ul>
+<li>Code generation is separated into scalar/aggregate/complex and
+lvalue/rvalue paths, depending on what kind of result your expression
+produces. On occasion, this requires some careful factoring of code to
+avoid duplication.</li>
+<li><tt class="docutils literal"><span class="pre">CodeGenFunction</span></tt> contains functions <tt class="docutils literal"><span class="pre">ConvertType</span></tt> and
+<tt class="docutils literal"><span class="pre">ConvertTypeForMem</span></tt> that convert Clang’s types (<tt class="docutils literal"><span class="pre">clang::Type*</span></tt> or
+<tt class="docutils literal"><span class="pre">clang::QualType</span></tt>) to LLVM types. Use the former for values, and the
+later for memory locations: test with the C++ “<tt class="docutils literal"><span class="pre">bool</span></tt>” type to check
+this. If you find that you are having to use LLVM bitcasts to make the
+subexpressions of your expression have the type that your expression
+expects, STOP! Go fix semantic analysis and the AST so that you don’t
+need these bitcasts.</li>
+<li>The <tt class="docutils literal"><span class="pre">CodeGenFunction</span></tt> class has a number of helper functions to make
+certain operations easy, such as generating code to produce an lvalue or
+an rvalue, or to initialize a memory location with a given value. Prefer
+to use these functions rather than directly writing loads and stores,
+because these functions take care of some of the tricky details for you
+(e.g., for exceptions).</li>
+<li>If your expression requires some special behavior in the event of an
+exception, look at the <tt class="docutils literal"><span class="pre">push*Cleanup</span></tt> functions in <tt class="docutils literal"><span class="pre">CodeGenFunction</span></tt>
+to introduce a cleanup. You shouldn’t have to deal with
+exception-handling directly.</li>
+<li>Testing is extremely important in IR generation. Use <tt class="docutils literal"><span class="pre">clang</span> <span class="pre">-cc1</span>
+<span class="pre">-emit-llvm</span></tt> and <a class="reference external" href="http://llvm.org/docs/CommandGuide/FileCheck.html">FileCheck</a> to verify that you’re
+generating the right IR.</li>
+</ul>
+</li>
+<li>Teach template instantiation how to cope with your AST node, which requires
+some fairly simple code:<ul>
+<li>Make sure that your expression’s constructor properly computes the flags
+for type dependence (i.e., the type your expression produces can change
+from one instantiation to the next), value dependence (i.e., the constant
+value your expression produces can change from one instantiation to the
+next), instantiation dependence (i.e., a template parameter occurs
+anywhere in your expression), and whether your expression contains a
+parameter pack (for variadic templates). Often, computing these flags
+just means combining the results from the various types and
+subexpressions.</li>
+<li>Add <tt class="docutils literal"><span class="pre">TransformXXX</span></tt> and <tt class="docutils literal"><span class="pre">RebuildXXX</span></tt> functions to the <tt class="docutils literal"><span class="pre">TreeTransform</span></tt>
+class template in <tt class="docutils literal"><span class="pre">Sema</span></tt>. <tt class="docutils literal"><span class="pre">TransformXXX</span></tt> should (recursively)
+transform all of the subexpressions and types within your expression,
+using <tt class="docutils literal"><span class="pre">getDerived().TransformYYY</span></tt>. If all of the subexpressions and
+types transform without error, it will then call the <tt class="docutils literal"><span class="pre">RebuildXXX</span></tt>
+function, which will in turn call <tt class="docutils literal"><span class="pre">getSema().BuildXXX</span></tt> to perform
+semantic analysis and build your expression.</li>
+<li>To test template instantiation, take those tests you wrote to make sure
+that you were type checking with type-dependent expressions and dependent
+types (from step #2) and instantiate those templates with various types,
+some of which type-check and some that don’t, and test the error messages
+in each case.</li>
+</ul>
+</li>
+<li>There are some “extras” that make other features work better. It’s worth
+handling these extras to give your expression complete integration into
+Clang:<ul>
+<li>Add code completion support for your expression in
+<tt class="docutils literal"><span class="pre">SemaCodeComplete.cpp</span></tt>.</li>
+<li>If your expression has types in it, or has any “interesting” features
+other than subexpressions, extend libclang’s <tt class="docutils literal"><span class="pre">CursorVisitor</span></tt> to provide
+proper visitation for your expression, enabling various IDE features such
+as syntax highlighting, cross-referencing, and so on. The
+<tt class="docutils literal"><span class="pre">c-index-test</span></tt> helper program can be used to test these features.</li>
+</ul>
+</li>
+</ol>
+</div>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ClangFormatStyleOptions.html">Clang-Format Style Options</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="DriverInternals.html">Driver Design & Internals</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
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+</html>
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+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>Introduction to the Clang AST</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="ExternalClangExamples.html">External Clang Examples</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="LibTooling.html">LibTooling</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="introduction-to-the-clang-ast">
+<h1>Introduction to the Clang AST<a class="headerlink" href="#introduction-to-the-clang-ast" title="Permalink to this headline">¶</a></h1>
+<p>This document gives a gentle introduction to the mysteries of the Clang
+AST. It is targeted at developers who either want to contribute to
+Clang, or use tools that work based on Clang’s AST, like the AST
+matchers.</p>
+<center><iframe width="560" height="315" src="http://www.youtube.com/embed/VqCkCDFLSsc?vq=hd720" frameborder="0" allowfullscreen></iframe></center><p><a class="reference external" href="http://llvm.org/devmtg/2013-04/klimek-slides.pdf">Slides</a></p>
+<div class="section" id="introduction">
+<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
+<p>Clang’s AST is different from ASTs produced by some other compilers in
+that it closely resembles both the written C++ code and the C++
+standard. For example, parenthesis expressions and compile time
+constants are available in an unreduced form in the AST. This makes
+Clang’s AST a good fit for refactoring tools.</p>
+<p>Documentation for all Clang AST nodes is available via the generated
+<a class="reference external" href="http://clang.llvm.org/doxygen">Doxygen</a>. The doxygen online
+documentation is also indexed by your favorite search engine, which will
+make a search for clang and the AST node’s class name usually turn up
+the doxygen of the class you’re looking for (for example, search for:
+clang ParenExpr).</p>
+</div>
+<div class="section" id="examining-the-ast">
+<h2>Examining the AST<a class="headerlink" href="#examining-the-ast" title="Permalink to this headline">¶</a></h2>
+<p>A good way to familarize yourself with the Clang AST is to actually look
+at it on some simple example code. Clang has a builtin AST-dump mode,
+which can be enabled with the flag <tt class="docutils literal"><span class="pre">-ast-dump</span></tt>.</p>
+<p>Let’s look at a simple example AST:</p>
+<div class="highlight-python"><pre>$ cat test.cc
+int f(int x) {
+ int result = (x / 42);
+ return result;
+}
+
+# Clang by default is a frontend for many tools; -Xclang is used to pass
+# options directly to the C++ frontend.
+$ clang -Xclang -ast-dump -fsyntax-only test.cc
+TranslationUnitDecl 0x5aea0d0 <<invalid sloc>>
+... cutting out internal declarations of clang ...
+`-FunctionDecl 0x5aeab50 <test.cc:1:1, line:4:1> f 'int (int)'
+ |-ParmVarDecl 0x5aeaa90 <line:1:7, col:11> x 'int'
+ `-CompoundStmt 0x5aead88 <col:14, line:4:1>
+ |-DeclStmt 0x5aead10 <line:2:3, col:24>
+ | `-VarDecl 0x5aeac10 <col:3, col:23> result 'int'
+ | `-ParenExpr 0x5aeacf0 <col:16, col:23> 'int'
+ | `-BinaryOperator 0x5aeacc8 <col:17, col:21> 'int' '/'
+ | |-ImplicitCastExpr 0x5aeacb0 <col:17> 'int' <LValueToRValue>
+ | | `-DeclRefExpr 0x5aeac68 <col:17> 'int' lvalue ParmVar 0x5aeaa90 'x' 'int'
+ | `-IntegerLiteral 0x5aeac90 <col:21> 'int' 42
+ `-ReturnStmt 0x5aead68 <line:3:3, col:10>
+ `-ImplicitCastExpr 0x5aead50 <col:10> 'int' <LValueToRValue>
+ `-DeclRefExpr 0x5aead28 <col:10> 'int' lvalue Var 0x5aeac10 'result' 'int'</pre>
+</div>
+<p>The toplevel declaration in
+a translation unit is always the <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1TranslationUnitDecl.html">translation unit
+declaration</a>.
+In this example, our first user written declaration is the <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1FunctionDecl.html">function
+declaration</a>
+of “<tt class="docutils literal"><span class="pre">f</span></tt>”. The body of “<tt class="docutils literal"><span class="pre">f</span></tt>” is a <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1CompoundStmt.html">compound
+statement</a>,
+whose child nodes are a <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1DeclStmt.html">declaration
+statement</a>
+that declares our result variable, and the <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1ReturnStmt.html">return
+statement</a>.</p>
+</div>
+<div class="section" id="ast-context">
+<h2>AST Context<a class="headerlink" href="#ast-context" title="Permalink to this headline">¶</a></h2>
+<p>All information about the AST for a translation unit is bundled up in
+the class
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1ASTContext.html">ASTContext</a>.
+It allows traversal of the whole translation unit starting from
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1ASTContext.html#abd909fb01ef10cfd0244832a67b1dd64">getTranslationUnitDecl</a>,
+or to access Clang’s <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1ASTContext.html#a4f95adb9958e22fbe55212ae6482feb4">table of
+identifiers</a>
+for the parsed translation unit.</p>
+</div>
+<div class="section" id="ast-nodes">
+<h2>AST Nodes<a class="headerlink" href="#ast-nodes" title="Permalink to this headline">¶</a></h2>
+<p>Clang’s AST nodes are modeled on a class hierarchy that does not have a
+common ancestor. Instead, there are multiple larger hierarchies for
+basic node types like
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Decl.html">Decl</a> and
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Stmt.html">Stmt</a>. Many
+important AST nodes derive from
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Type.html">Type</a>,
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Decl.html">Decl</a>,
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1DeclContext.html">DeclContext</a>
+or <a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Stmt.html">Stmt</a>, with
+some classes deriving from both Decl and DeclContext.</p>
+<p>There are also a multitude of nodes in the AST that are not part of a
+larger hierarchy, and are only reachable from specific other nodes, like
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1CXXBaseSpecifier.html">CXXBaseSpecifier</a>.</p>
+<p>Thus, to traverse the full AST, one starts from the
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1TranslationUnitDecl.html">TranslationUnitDecl</a>
+and then recursively traverses everything that can be reached from that
+node - this information has to be encoded for each specific node type.
+This algorithm is encoded in the
+<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1RecursiveASTVisitor.html">RecursiveASTVisitor</a>.
+See the <a class="reference external" href="http://clang.llvm.org/docs/RAVFrontendAction.html">RecursiveASTVisitor
+tutorial</a>.</p>
+<p>The two most basic nodes in the Clang AST are statements
+(<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Stmt.html">Stmt</a>) and
+declarations
+(<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Decl.html">Decl</a>). Note
+that expressions
+(<a class="reference external" href="http://clang.llvm.org/doxygen/classclang_1_1Expr.html">Expr</a>) are
+also statements in Clang’s AST.</p>
+</div>
+</div>
+
+
+ </div>
+ <div class="bottomnav">
+
+ <p>
+ « <a href="ExternalClangExamples.html">External Clang Examples</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="LibTooling.html">LibTooling</a> »
+ </p>
+
+ </div>
+
+ <div class="footer">
+ © Copyright 2007-2014, The Clang Team.
+ Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.
+ </div>
+ </body>
+</html>
\ No newline at end of file
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+
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+
+ <title>JSON Compilation Database Format Specification — Clang 3.6 documentation</title>
+
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+ };
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+ <link rel="next" title="Overview" href="ClangTools.html" />
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+ </head>
+ <body>
+ <div class="header"><h1 class="heading"><a href="index.html">
+ <span>Clang 3.6 documentation</span></a></h1>
+ <h2 class="heading"><span>JSON Compilation Database Format Specification</span></h2>
+ </div>
+ <div class="topnav">
+
+ <p>
+ « <a href="HowToSetupToolingForLLVM.html">How To Setup Clang Tooling For LLVM</a>
+ ::
+ <a class="uplink" href="index.html">Contents</a>
+ ::
+ <a href="ClangTools.html">Overview</a> »
+ </p>
+
+ </div>
+ <div class="content">
+
+
+ <div class="section" id="json-compilation-database-format-specification">
+<h1>JSON Compilation Database Format Specification<a class="headerlink" href="#json-compilation-database-format-specification" title="Permalink to this headline">¶</a></h1>
+<p>This document describes a format for specifying how to replay single
+compilations independently of the build system.</p>
+<div class="section" id="background">
+<h2>Background<a class="headerlink" href="#background" title="Permalink to this headline">¶</a></h2>
+<p>Tools based on the C++ Abstract Syntax Tree need full information how to
+parse a translation unit. Usually this information is implicitly
+available in the build system, but running tools as part of the build
+system is not necessarily the best solution:</p>
+<ul class="simple">
+<li>Build systems are inherently change driven, so running multiple tools
+over the same code base without changing the code does not fit into
+the architecture of many build systems.</li>
+<li>Figuring out whether things have changed is often an IO bound
+process; this makes it hard to build low latency end user tools based
+on the build system.</li>
+<li>Build systems are inherently sequential in the build graph, for
+example due to generated source code. While tools that run
+independently of the build still need the generated source code to
+exist, running tools multiple times over unchanging source does not
+require serialization of the runs according to the build dependency
+graph.</li>
+</ul>
+</div>
+<div class="section" id="supported-systems">
+<h2>Supported Systems<a class="headerlink" href="#supported-systems" title="Permalink to this headline">¶</a></h2>
+<p>Currently <a class="reference external" href="http://cmake.org">CMake</a> (since 2.8.5) supports generation
+of compilation databases for Unix Makefile builds (Ninja builds in the
+works) with the option <tt class="docutils literal"><span class="pre">CMAKE_EXPORT_COMPILE_COMMANDS</span></tt>.</p>
+<p>For projects on Linux, there is an alternative to intercept compiler
+calls with a tool called <a class="reference external" href="https://github.com/rizsotto/Bear">Bear</a>.</p>
+<p>Clang’s tooling interface supports reading compilation databases; see
+the <a class="reference internal" href="LibTooling.html"><em>LibTooling documentation</em></a>. libclang and its
+python bindings also support this (since clang 3.2); see
+<a class="reference external" href="/doxygen/group__COMPILATIONDB.html">CXCompilationDatabase.h</a>.</p>
+</div>
+<div class="section" id="format">
+<h2>Format<a class="headerlink" href="#format" title="Permalink to this headline">¶</a></h2>
+<p>A compilation database is a JSON file, which consist of an array of
+“command objects”, where each command object specifies one way a
+translation unit is compiled in the project.</p>
+<p>Each command object contains the translation unit’s main file, the
+working directory of the compile run and the actual compile command.</p>
+<p>Example:</p>
+<div class="highlight-python"><div class="highlight"><pre><span class="p">[</span>
+ <span class="p">{</span> <span class="s">"directory"</span><span class="p">:</span> <span class="s">"/home/user/llvm/build"</span><span class="p">,</span>
+ <span class="s">"command"</span><span class="p">:</span> <span class="s">"/usr/bin/clang++ -Irelative -DSOMEDEF=</span><span class="se">\"</span><span class="s">With spaces, quotes and </span><span class="se">\\</span><span class="s">-es.</span><span class="se">\"</span><span class="s"> -c -o file.o file.cc"</span><span class="p">,</span>
+ <span class="s">"file"</span><span class="p">:</span> <span class="s">"file.cc"</span> <span class="p">},</span>
+ <span class="o">...</span>
+<span class="p">]</span>
+</pre></div>
+</div>
+<p>The contracts for each field in the command object are:</p>
+<ul class="simple">
+<li><strong>directory:</strong> The working directory of the compilation. All paths
+specified in the <strong>command</strong> or <strong>file</strong> fields must be either
+absolute or relative to this directory.</li>
+<li><strong>file:</strong> The main translation unit source processed by this
+compilation step. This is used by tools as the key into the
+compilation database. There can be multiple command objects for the
+same file, for example if the same source file is compiled with
+different configurations.</li>
+<li><strong>command:</strong> The compile command executed. After JSON unescaping,
+this must be a valid command to rerun the exact compilation step for
+the translation unit in the environment the build system uses.
+Parameters use shell quoting and shell escaping of quotes, with ‘<tt class="docutils literal"><span class="pre">"</span></tt>‘
+and ‘<tt class="docutils literal"><span class="pre">\</span></tt>‘ being the only special characters. Shell expansion is not
+supported.</li>
+</ul>
+</div>
+<div class="section" id="build-system-integration">
+<h2>Build System Integration<a class="headerlink" href="#build-system-integration" title="Permalink to this headline">¶</a></h2>
+<p>The convention is to name the file compile_commands.json and put it at
+the top of the build directory. Clang tools are pointed to the top of
+the build directory to detect the file and use the compilation database
+to parse C++ code in the source tree.</p>
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