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<title>Clang 3.2 Release Notes</title>
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<link type="text/css" rel="stylesheet" href="../content.css">
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<!--#include virtual="../menu.html.incl"-->
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<div id="content">
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<h1>Clang 3.2 Release Notes</h1>
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<img style="float:right" src="http://llvm.org/img/DragonSmall.png"
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width="136" height="136" alt="LLVM Dragon Logo">
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<ul>
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<li><a href="#intro">Introduction</a></li>
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<li><a href="#whatsnew">What's New in Clang 3.2?</a>
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<ul>
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<li><a href="#majorfeatures">Major New Features</a></li>
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<li><a href="#newflags">New Compiler Flags</a></li>
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<li><a href="#cchanges">C Language Changes</a></li>
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<li><a href="#cxxchanges">C++ Language Changes</a></li>
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<li><a href="#objcchanges">Objective-C Language Changes</a></li>
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<li><a href="#apichanges">Internal API Changes</a></li>
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<li><a href="#pythonchanges">Python Binding Changes</a></li>
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</ul>
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</li>
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<li><a href="#knownproblems">Known Problems</a></li>
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<li><a href="#additionalinfo">Additional Information</a></li>
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</ul>
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<div class="doc_author">
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<p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
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</div>
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<h1 style="color:red">These are in-progress notes for the upcoming Clang 3.2
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release.<br>
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You may prefer the
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<a href="http://llvm.org/releases/3.1/docs/ClangReleaseNotes.html">Clang 3.1
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Release Notes</a>.</h1>
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<!-- ======================================================================= -->
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<h2 id="intro">Introduction</h2>
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<!-- ======================================================================= -->
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<p>This document contains the release notes for the Clang C/C++/Objective-C
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frontend, part of the LLVM Compiler Infrastructure, release 3.2. Here we
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describe the status of Clang in some detail, including major improvements
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from the previous release and new feature work. For the general LLVM release
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notes, see <a href="http://llvm.org/docs/ReleaseNotes.html">the LLVM
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documentation</a>. All LLVM releases may be downloaded from the
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<a href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
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<p>For more information about Clang or LLVM, including information about the
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latest release, please check out the main please see the
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<a href="http://clang.llvm.org">Clang Web Site</a> or the
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<a href="http://llvm.org">LLVM Web Site</a>.
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<p>Note that if you are reading this file from a Subversion checkout or the main
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Clang web page, this document applies to the <i>next</i> release, not the
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current one. To see the release notes for a specific release, please see the
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<a href="http://llvm.org/releases/">releases page</a>.</p>
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<!-- ======================================================================= -->
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<h2 id="whatsnew">What's New in Clang 3.2?</h2>
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<!-- ======================================================================= -->
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<p>Some of the major new features and improvements to Clang are listed here.
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Generic improvements to Clang as a whole or to its underlying infrastructure
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are described first, followed by language-specific sections with improvements
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to Clang's support for those languages.</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="majorfeatures">Major New Features</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h4 id="diagnostics">Improvements to Clang's diagnostics</h4>
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<p>Clang's diagnostics are constantly being improved to catch more issues,
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explain them more clearly, and provide more accurate source information about
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them. The improvements since the 3.1 release include:</p>
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<ul>
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<li><tt>-Wuninitialized</tt> has been taught to recognise uninitialized uses
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which always occur when an explicitly-written non-constant condition is either
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<tt>true</tt> or <tt>false</tt>. For example:
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<pre>
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int f(bool b) {
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int n;
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if (b)
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n = 1;
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return n;
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}
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<b>sometimes-uninit.cpp:3:7: <span class="warning">warning:</span> variable 'n' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]</b>
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if (b)
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<span class="caret">^</span>
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<b>sometimes-uninit.cpp:5:10: <span class="note">note:</span></b> uninitialized use occurs here
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return n;
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<span class="caret">^</span>
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<b>sometimes-uninit.cpp:3:3: <span class="note">note:</span></b> remove the 'if' if its condition is always true
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if (b)
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<span class="caret">^~~~~~</span>
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<b>sometimes-uninit.cpp:2:8: <span class="note">note:</span></b> initialize the variable 'n' to silence this warning
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int n;
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<span class="caret">^</span>
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<span class="caret"> = 0</span>
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</pre>
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This functionality can be enabled or disabled separately from
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<tt>-Wuninitialized</tt> with the <tt>-Wsometimes-uninitialized</tt> warning
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flag.</li>
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<li>Template type diffing improves the display of diagnostics with templated
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types in them.
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<pre>
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int f(vector<map<int, double>>);
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int x = f(vector<map<int, float>>());
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</pre>
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The error message is the same, but the note is different based on the options selected.
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<pre>
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<b>template-diff.cpp:5:9: <span class="error">error:</span> no matching function for call to 'f'</b>
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int x = f(vector<map<int, float>>());
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<span class="caret">^</span>
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</pre>
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Templated type diffing with type elision (default):
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<pre>
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<b>template-diff.cpp:4:5: <span class="note">note:</span></b> candidate function not viable: no known conversion from 'vector<map<[...], <span class="template-highlight">float</span>>>' to 'vector<map<[...], <span class="template-highlight">double</span>>>' for 1st argument;
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int f(vector<map<int, double>>);
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<span class="caret">^</span>
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</pre>
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Templated type diffing without type elision (-fno-elide-type):
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<pre>
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<b>template-diff.cpp:4:5: <span class="note">note:</span></b> candidate function not viable: no known conversion from 'vector<map<int, <span class="template-highlight">float</span>>>' to 'vector<map<int, <span class="template-highlight">double</span>>>' for 1st argument;
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int f(vector<map<int, double>>);
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<span class="caret">^</span>
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</pre>
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Templated tree printing with type elision (-fdiagnostics-show-template-tree):
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<pre>
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<b>template-diff.cpp:4:5: <span class="note">note:</span></b> candidate function not viable: no known conversion for 1st argument;
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vector<
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map<
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[...],
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[<span class="template-highlight">float</span> != <span class="template-highlight">double</span>]>>
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int f(vector<map<int, double>>);
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<span class="caret">^</span>
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</pre>
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Templated tree printing without type elision (-fdiagnostics-show-template-tree -fno-elide-type):
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<pre>
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<b>template-diff.cpp:4:5: <span class="note">note:</span></b> candidate function not viable: no known conversion for 1st argument;
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vector<
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map<
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int,
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[<span class="template-highlight">float</span> != <span class="template-highlight">double</span>]>>
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int f(vector<map<int, double>>);
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<span class="caret">^</span>
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</pre>
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</li>
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<li>Clang's <tt>-fcatch-undefined-behavior</tt> option has been renamed to
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<tt>-fsanitize=undefined</tt> and has grown the ability to check for several
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new types of undefined behavior. See the Users Manual for more information.
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<!-- Flesh this out prior to release. -->
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<!-- Document renaming of -faddress-sanitizer and -fthread-sanitizer. -->
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</li>
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</ul>
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<h4 id="tlsmodel">Support for <code>tls_model</code> attribute</h4>
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<p>Clang now supports the <code>tls_model</code> attribute, allowing code that
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uses thread-local storage to explicitly select which model to use. The available
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models are <code>"global-dynamic"</code>, <code>"local-dynamic"</code>,
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<code>"initial-exec"</code> and <code>"local-exec"</code>. See
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<a href="http://www.akkadia.org/drepper/tls.pdf">ELF Handling For Thread-Local
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Storage</a> for more information.</p>
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<p>The compiler is free to choose a different model if the specified model is not
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supported by the target, or if the compiler determines that a more specific
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model can be used.
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</p>
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<h4>Type safety attributes</h4>
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<p>Clang now supports type safety attributes that allow checking during compile
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time that 'void *' function arguments and arguments for variadic functions are
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of a particular type which is determined by some other argument to the same
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function call.</p>
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<p>Usecases include:</p>
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<ul>
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<li>MPI library implementations, where these attributes enable checking that
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buffer type matches the passed <code>MPI_Datatype</code>;</li>
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<li> HDF5 library -- similar usecase as for MPI;</li>
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<li> checking types of variadic functions' arguments for functions like
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<code>fcntl()</code> and <code>ioctl()</code>.</li>
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</ul>
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<p>See entries for <code>argument_with_type_tag</code>,
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<code>pointer_with_type_tag</code> and <code>type_tag_for_datatype</code>
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attributes in Clang language extensions documentation.</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="newflags">New Compiler Flags</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<ul>
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<li><tt>-gline-tables-only</tt> controls the
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<a href="http://clang.llvm.org/docs/UsersManual.html#debuginfosize">size of debug information</a>.
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This flag tells Clang to emit debug info which is just enough to obtain stack traces with
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function names, file names and line numbers (by such tools as gdb or addr2line).
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Debug info for variables or function parameters is not produced, which reduces
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the size of the resulting binary.
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<li><tt>-ftls-model</tt> controls which TLS model to use for thread-local
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variables. This can be overridden per variable using the
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<a href="#tlsmodel"><tt>tls_model</tt> attribute</a> mentioned above.
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For more details, see the <a href="UsersManual.html#opt_ftls-model">User's
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Manual</a>.</li>
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</ul>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="cchanges">C Language Changes in Clang</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h4 id="c11changes">C11 Feature Support</h4>
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<p>...</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="cxxchanges">C++ Language Changes in Clang</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h4 id="cxx11changes">C++11 Feature Support</h4>
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<p>...</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="objcchanges">Objective-C Language Changes in Clang</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<p>...</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="apichanges">Internal API Changes</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<p>These are major API changes that have happened since the 3.1 release of
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Clang. If upgrading an external codebase that uses Clang as a library, this
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section should help get you past the largest hurdles of upgrading.</p>
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<h4 id="api1">API change 1</h4>
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<p>...</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="pythonchanges">Python Binding Changes</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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The following methods have been added:
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<ul>
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<li>...</li>
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</ul>
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<!-- ======================================================================= -->
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<h2 id="knownproblems">Significant Known Problems</h2>
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<!-- ======================================================================= -->
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<!-- ======================================================================= -->
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<h2 id="additionalinfo">Additional Information</h2>
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<!-- ======================================================================= -->
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<p>A wide variety of additional information is available on the
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<a href="http://clang.llvm.org/">Clang web page</a>. The web page contains
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versions of the API documentation which are up-to-date with the Subversion
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version of the source code. You can access versions of these documents
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specific to this release by going into the "<tt>clang/doc/</tt>" directory in
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the Clang tree.</p>
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<p>If you have any questions or comments about Clang, please feel free to
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contact us via
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the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev"> mailing
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list</a>.</p>
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<!-- ======================================================================= -->
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<!-- Likely 3.1 release notes -->
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<!-- ======================================================================= -->
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<!--
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This is just a section to hold things that have already gotten started and
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should likely pick up proper release notes in 3.1.
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- C1X and C++11 atomics infrastructure and support
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- CUDA support?
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-->
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</div>
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</body>
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</html>
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