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<h1>LLVM 3.0 Release Notes</h1>

<img align=right src="http://llvm.org/img/DragonSmall.png"
    width="136" height="136" alt="LLVM Dragon Logo">

<ol>
  <li><a href="#intro">Introduction</a></li>
  <li><a href="#subproj">Sub-project Status Update</a></li>
  <li><a href="#externalproj">External Projects Using LLVM 3.0</a></li>
  <li><a href="#whatsnew">What's New in LLVM 3.0?</a></li>
  <li><a href="GettingStarted.html">Installation Instructions</a></li>
  <li><a href="#knownproblems">Known Problems</a></li>
  <li><a href="#additionalinfo">Additional Information</a></li>
</ol>

<div class="doc_author">
  <p>Written by the <a href="http://llvm.org/">LLVM Team</a></p>
</div>

<!--
<h1 style="color:red">These are in-progress notes for the upcoming LLVM 3.0
release.<br>
You may prefer the
<a href="http://llvm.org/releases/2.9/docs/ReleaseNotes.html">LLVM 2.9
Release Notes</a>.</h1>
 -->

<!-- *********************************************************************** -->
<h2>
  <a name="intro">Introduction</a>
</h2>
<!-- *********************************************************************** -->

<div>

<p>This document contains the release notes for the LLVM Compiler
   Infrastructure, release 3.0.  Here we describe the status of LLVM, including
   major improvements from the previous release, improvements in various
   subprojects of LLVM, and some of the current users of the code.
   All LLVM releases may be downloaded from
   the <a href="http://llvm.org/releases/">LLVM releases web site</a>.</p>

<p>For more information about LLVM, including information about the latest
   release, please check out the <a href="http://llvm.org/">main LLVM web
   site</a>.  If you have questions or comments,
   the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
   Developer's Mailing List</a> is a good place to send them.</p>

<p>Note that if you are reading this file from a Subversion checkout or the main
   LLVM web page, this document applies to the <i>next</i> release, not the
   current one.  To see the release notes for a specific release, please see the
   <a href="http://llvm.org/releases/">releases page</a>.</p>

</div>
   
 
<!-- *********************************************************************** -->
<h2>
  <a name="subproj">Sub-project Status Update</a>
</h2>
<!-- *********************************************************************** -->

<div>

<p>The LLVM 3.0 distribution currently consists of code from the core LLVM
   repository (which roughly includes the LLVM optimizers, code generators and
   supporting tools), and the Clang repository.  In
   addition to this code, the LLVM Project includes other sub-projects that are
   in development.  Here we include updates on these subprojects.</p>

<!--=========================================================================-->
<h3>
<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
</h3>

<div>

<p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
   C++, and Objective-C languages. Clang aims to provide a better user
   experience through expressive diagnostics, a high level of conformance to
   language standards, fast compilation, and low memory use. Like LLVM, Clang
   provides a modular, library-based architecture that makes it suitable for
   creating or integrating with other development tools. Clang is considered a
   production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
   (32- and 64-bit), and for Darwin/ARM targets.</p>

<p>In the LLVM 3.0 time-frame, the Clang team has made many improvements:</p>

<ul>
  <li>Greatly improved support for building C++ applications, with greater
      stability and better diagnostics.</li>
  
  <li><a href="http://clang.llvm.org/cxx_status.html">Improved support</a> for
      the <a href="http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=50372">C++
      2011</a> standard (aka "C++'0x"), including implementations of non-static data member
      initializers, alias templates, delegating constructors, range-based
      for loops, and implicitly-generated move constructors and move assignment
      operators, among others.</li>

  <li>Implemented support for some features of the upcoming C1x standard,
      including static assertions and generic selections.</li>
  
  <li>Better detection of include and linking paths for system headers and
      libraries, especially for Linux distributions.</li>

  <li>Several improvements to Objective-C support, including:

    <ul>
      <li><a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">
          Automatic Reference Counting</a> (ARC) and an improved memory model
          cleanly separating object and C memory.</li>

      <li>A migration tool for moving manual retain/release code to ARC</li>

      <li>Better support for data hiding, allowing instance variables to be
          declared in implementation contexts or class extensions</li>
      <li>Weak linking support for Objective-C classes</li>
      <li>Improved static type checking by inferring the return type of methods
      such as +alloc and -init.</li>
    </ul>

    Some new Objective-C features require either the Mac OS X 10.7 / iOS 5
    Objective-C runtime, or version 1.6 or later of the GNUstep Objective-C
    runtime version.</li>

  <li>Implemented a number of optimizations in <tt>libclang</tt>, the Clang C
      interface, to improve the performance of code completion and the mapping
      from source locations to abstract syntax tree nodes.</li>
</ul>

  
<p>If Clang rejects your code but another compiler accepts it, please take a
   look at the <a href="http://clang.llvm.org/compatibility.html">language
   compatibility</a> guide to make sure this is not intentional or a known
   issue.</p>

</div>

<!--=========================================================================-->
<h3>
<a name="dragonegg">DragonEgg: GCC front-ends, LLVM back-end</a>
</h3>

<div>
<p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
   <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
   optimizers and code generators with LLVM's. It works with gcc-4.5 or gcc-4.6,
   targets the x86-32 and x86-64 processor families, and has been successfully
   used on the Darwin, FreeBSD, KFreeBSD, Linux and OpenBSD platforms.  It fully
   supports Ada, C, C++ and Fortran.  It has partial support for Go, Java, Obj-C
   and Obj-C++.</p>

<p>The 3.0 release has the following notable changes:</p>

  <ul>
  <li>GCC version 4.6 is now fully supported.</li>

  <li>Patching and building GCC is no longer required: the plugin should work
      with your system GCC (version 4.5 or 4.6; on Debian/Ubuntu systems the
      gcc-4.5-plugin-dev or gcc-4.6-plugin-dev package is also needed).</li>

  <li>The <tt>-fplugin-arg-dragonegg-enable-gcc-optzns</tt> option, which runs
      GCC's optimizers as well as LLVM's, now works much better.  This is the
      option to use if you want ultimate performance! It is still experimental
      though: it may cause the plugin to crash.</li>

  <li>The type and constant conversion logic has been almost entirely rewritten,
      fixing a multitude of obscure bugs.</li>

</ul>

</div>

<!--=========================================================================-->
<h3>
<a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
</h3>

<div>

<p>The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
   is a simple library that provides an implementation of the low-level
   target-specific hooks required by code generation and other runtime
   components.  For example, when compiling for a 32-bit target, converting a
   double to a 64-bit unsigned integer is compiled into a runtime call to the
   "__fixunsdfdi" function. The compiler-rt library provides highly optimized
   implementations of this and other low-level routines (some are 3x faster than
   the equivalent libgcc routines).</p>

<p>In the LLVM 3.0 timeframe, the target specific ARM code has converted to
   "unified" assembly syntax, and several new functions have been added to the
   library.</p>

</div>

<!--=========================================================================-->
<h3>
<a name="lldb">LLDB: Low Level Debugger</a>
</h3>

<div>
  
<p>LLDB is a ground-up implementation of a command line debugger, as well as a
   debugger API that can be used from other applications.  LLDB makes use of the
   Clang parser to provide high-fidelity expression parsing (particularly for
   C++) and uses the LLVM JIT for target support.</p>

<p>LLDB has advanced by leaps and bounds in the 3.0 timeframe.  It is
   dramatically more stable and useful, and includes both a
   new <a href="http://lldb.llvm.org/tutorial.html">tutorial</a> and
   a <a href="http://lldb.llvm.org/lldb-gdb.html">side-by-side comparison with
   GDB</a>.</p>

</div>

<!--=========================================================================-->
<h3>
<a name="libc++">libc++: C++ Standard Library</a>
</h3>

<div>

<p>Like compiler_rt, libc++ is now <a href="DeveloperPolicy.html#license">dual
   licensed</a> under the MIT and UIUC license, allowing it to be used more
   permissively.</p>

<p>Libc++ has been ported to FreeBSD and imported into the base system.  It is
   planned to be the default STL implementation for FreeBSD 10.</p>

</div>

<!--=========================================================================-->
<h3>
<a name="vmkit">VMKit</a>
</h3>

<div>

  <p>The <a href="http://vmkit.llvm.org/">VMKit project</a> is an
  implementation of a Java Virtual Machine (Java VM or JVM) that uses LLVM for
  static and just-in-time compilation.

  <p>In the LLVM 3.0 time-frame, VMKit has had significant improvements on both
  runtime and startup performance:</p>

  <ul>
  <li>Precompilation: by compiling ahead of time a small subset of Java's core
  library, the startup performance have been highly optimized to the point that
  running a 'Hello World' program takes less than 30 milliseconds.</li>

  <li>Customization: by customizing virtual methods for individual classes,
  the VM can statically determine the target of a virtual call, and decide to
  inline it.</li>

  <li>Inlining: the VM does more inlining than it did before, by allowing more
  bytecode instructions to be inlined, and thanks to customization. It also
  inlines GC barriers, and object allocations.</li>

  <li>New exception model: the generated code for a method that does not do
  any try/catch is not penalized anymore by the eventuality of calling a
  method that throws an exception. Instead, the method that throws the
  exception jumps directly to the method that could catch it.</li>
  </ul>

</div>
  

<!--=========================================================================-->
<h3>
<a name="LLBrowse">LLBrowse: IR Browser</a>
</h3>

<div>

<p><a href="http://llvm.org/svn/llvm-project/llbrowse/trunk/doc/LLBrowse.html">
   LLBrowse</a> is an interactive viewer for LLVM modules. It can load any LLVM
   module and displays its contents as an expandable tree view, facilitating an
   easy way to inspect types, functions, global variables, or metadata nodes. It
   is fully cross-platform, being based on the popular wxWidgets GUI
   toolkit.</p>

</div>


<!--=========================================================================-->
<!--
<h3>
<a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
</h3>

<div>
<p>
<a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
through the application and records state transitions that lead to fault
states. This allows it to construct testcases that lead to faults and can even
be used to verify some algorithms.
</p>

<p>UPDATE!</p>
</div>-->

</div>

<!-- *********************************************************************** -->
<h2>
  <a name="externalproj">External Open Source Projects Using LLVM 3.0</a>
</h2>
<!-- *********************************************************************** -->

<div>

<p>An exciting aspect of LLVM is that it is used as an enabling technology for
   a lot of other language and tools projects.  This section lists some of the
   projects that have already been updated to work with LLVM 3.0.</p>

<!--=========================================================================-->
<h3>AddressSanitizer</h3>
  
<div>

<p><a href="http://code.google.com/p/address-sanitizer/">AddressSanitizer</a>
   uses compiler instrumentation and a specialized malloc library to find C/C++
   bugs such as use-after-free and out-of-bound accesses to heap, stack, and
   globals. The key feature of the tool is speed: the average slowdown
   introduced by AddressSanitizer is less than 2x.</p>

</div>

<!--=========================================================================-->
<h3>ClamAV</h3>
  
<div>

<p><a href="http://www.clamav.net">Clam AntiVirus</a> is an open source (GPL)
   anti-virus toolkit for UNIX, designed especially for e-mail scanning on mail
   gateways.</p>

<p>Since version 0.96 it
   has <a href="http://vrt-sourcefire.blogspot.com/2010/09/introduction-to-clamavs-low-level.html">bytecode
   signatures</a> that allow writing detections for complex malware.
   It uses LLVM's JIT to speed up the execution of bytecode on X86, X86-64,
   PPC32/64, falling back to its own interpreter otherwise.  The git version was
   updated to work with LLVM 3.0.</p>

</div>

<!--=========================================================================-->
<h3>clang_complete for VIM</h3>

<div>

<p><a href="https://github.com/Rip-Rip/clang_complete">clang_complete</a> is a
   VIM plugin, that provides accurate C/C++ autocompletion using the clang front
   end. The development version of clang complete, can directly use libclang
   which can maintain a cache to speed up auto completion.</p>

</div>

<!--=========================================================================-->
<h3>clReflect</h3>

<div>

<p><a href="https://bitbucket.org/dwilliamson/clreflect">clReflect</a> is a C++
   parser that uses clang/LLVM to derive a light-weight reflection database
   suitable for use in game development. It comes with a very simple runtime
   library for loading and querying the database, requiring no external
   dependencies (including CRT), and an additional utility library for object
   management and serialisation.</p>

</div>

<!--=========================================================================-->
<h3>Cling C++ Interpreter</h3>

<div>

<p><a href="http://cern.ch/cling">Cling</a> is an interactive compiler interface
  (aka C++ interpreter). It supports C++ and C, and uses LLVM's JIT and the
  Clang parser. It has a prompt interface, runs source files, calls into shared
   libraries, prints the value of expressions, even does runtime lookup of
   identifiers (dynamic scopes). And it just behaves like one would expect from
   an interpreter.</p>

</div>

<!--=========================================================================-->
<h3>Crack Programming Language</h3>

<div>

<p><a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide
   the ease of development of a scripting language with the performance of a
   compiled language. The language derives concepts from C++, Java and Python,
   incorporating object-oriented programming, operator overloading and strong
   typing.</p>

</div>
  
<!--=========================================================================-->
<h3>Eero</h3>
  
<div>

<p><a href="http://eerolanguage.org/">Eero</a> is a fully
   header-and-binary-compatible dialect of Objective-C 2.0, implemented with a
   patched version of the Clang/LLVM compiler. It features a streamlined syntax,
   Python-like indentation, and new operators, for improved readability and
   reduced code clutter. It also has new features such as limited forms of
   operator overloading and namespaces, and strict (type-and-operator-safe)
   enumerations. It is inspired by languages such as Smalltalk, Python, and
   Ruby.</p>

</div>

<!--=========================================================================-->
<h3>FAUST Real-Time Audio Signal Processing Language</h3>
  
<div>

<p><a href="http://faust.grame.fr/">FAUST</a> is a compiled language for
  real-time audio signal processing. The name FAUST stands for Functional
  AUdio STream. Its programming model combines two approaches: functional
  programming and block diagram composition. In addition with the C, C++, Java
  output formats, the Faust compiler can now generate LLVM bitcode, and works
  with LLVM 2.7-3.0.
  </p>

</div>

<!--=========================================================================-->
<h3>Glasgow Haskell Compiler (GHC)</h3>
  
<div>

<p>GHC is an open source, state-of-the-art programming suite for Haskell, a
   standard lazy functional programming language. It includes an optimizing
   static compiler generating good code for a variety of platforms, together
   with an interactive system for convenient, quick development.</p>

<p>GHC 7.0 and onwards include an LLVM code generator, supporting LLVM 2.8 and
   later. Since LLVM 2.9, GHC now includes experimental support for the ARM
   platform with LLVM 3.0.</p>

</div>

<!--=========================================================================-->
<h3>gwXscript</h3>

<div>

<p><a href="http://botwars.tk/gwscript/">gwXscript</a> is an object oriented,
   aspect oriented programming language which can create both executables (ELF,
   EXE) and shared libraries (DLL, SO, DYNLIB). The compiler is implemented in
   its own language and translates scripts into LLVM-IR which can be optimized
   and translated into native code by the LLVM framework. Source code in
   gwScript contains definitions that expand the namespaces. So you can build
   your project and simply 'plug out' features by removing a file. The remaining
   project does not leave scars since you directly separate concerns by the
   'template' feature of gwX. It is also possible to add new features to a
   project by just adding files and without editing the original project. This
   language is used for example to create games or content management systems
   that should be extendable.</p>

<p>gwXscript is strongly typed and offers comfort with its native types string,
   hash and array. You can easily write new libraries in gwXscript or native
   code. gwXscript is type safe and users should not be able to crash your
   program or execute malicious code except code that is eating CPU time.</p>

</div>

<!--=========================================================================-->
<h3>include-what-you-use</h3>

<div>

<p><a href="http://code.google.com/p/include-what-you-use">include-what-you-use</a>
   is a tool to ensure that a file directly <code>#include</code>s
   all <code>.h</code> files that provide a symbol that the file uses. It also
   removes superfluous <code>#include</code>s from source files.</p>

</div>

<!--=========================================================================-->
<h3>ispc: The Intel SPMD Program Compiler</h3>

<div>

<p><a href="http://ispc.github.com">ispc</a> is a compiler for "single program,
   multiple data" (SPMD) programs. It compiles a C-based SPMD programming
   language to run on the SIMD units of CPUs; it often delivers 5-6x speedups on
   a single core of a CPU with an 8-wide SIMD unit compared to serial code,
   while still providing a clean and easy-to-understand programming model.  For
   an introduction to the language and its performance,
   see <a href="http://ispc.github.com/example.html">the walkthrough</a> of a short
   example program.  ispc is licensed under the BSD license.</p>

</div>
  
<!--=========================================================================-->
<h3>The Julia Programming Language</h3>

<div>

<p><a href="http://github.com/JuliaLang/julia">Julia</a> is a high-level,
  high-performance dynamic language for technical
  computing. It provides a sophisticated compiler, distributed parallel
  execution, numerical accuracy, and an extensive mathematical function
  library. The compiler uses type inference to generate fast code
  without any type declarations, and uses LLVM's optimization passes and
  JIT compiler. The language is designed around multiple dispatch,
  giving programs a large degree of flexibility. It is ready for use on many
  kinds of problems.</p>
</div>

<!--=========================================================================-->
<h3>LanguageKit and Pragmatic Smalltalk</h3>

<div>

<p><a href="http://etoileos.com/etoile/features/languagekit/">LanguageKit</a> is
   a framework for implementing dynamic languages sharing an object model with
   Objective-C. It provides static and JIT compilation using LLVM along with
   its own interpreter. Pragmatic Smalltalk is a dialect of Smalltalk, built on
   top of LanguageKit, that interfaces directly with Objective-C, sharing the
   same object representation and message sending behaviour. These projects are
   developed as part of the &Eacute;toil&eacute; desktop environment.</p>

</div>

<!--=========================================================================-->
<h3>LuaAV</h3>

<div>

<p><a href="http://lua-av.mat.ucsb.edu/blog/">LuaAV</a> is a real-time
   audiovisual scripting environment based around the Lua language and a
   collection of libraries for sound, graphics, and other media protocols. LuaAV
   uses LLVM and Clang to JIT compile efficient user-defined audio synthesis
   routines specified in a declarative syntax.</p>

</div>

<!--=========================================================================-->
<h3>Mono</h3>

<div>

<p>An open source, cross-platform implementation of C# and the CLR that is
   binary compatible with Microsoft.NET. Has an optional, dynamically-loaded
   LLVM code generation backend in Mini, the JIT compiler.</p>

<p>Note that we use a Git mirror of LLVM <a
    href="https://github.com/mono/llvm">with some patches</a>.</p>

</div>

<!--=========================================================================-->
<h3>Polly</h3>

<div>

<p><a href="http://polly.grosser.es">Polly</a> is an advanced data-locality
   optimizer and automatic parallelizer. It uses an advanced, mathematical
   model to calculate detailed data dependency information which it uses to
   optimize the loop structure of a program. Polly can speed up sequential code
   by improving memory locality and consequently the cache use. Furthermore,
   Polly is able to expose different kind of parallelism which it exploits by
   introducing (basic) OpenMP and SIMD code. A mid-term goal of Polly is to
   automatically create optimized GPU code.</p>

</div>

<!--=========================================================================-->
<h3>Portable OpenCL (pocl)</h3>

<div>

<p>Portable OpenCL is an open source implementation of the OpenCL standard which
   can be easily adapted for new targets. One of the goals of the project is
   improving performance portability of OpenCL programs, avoiding the need for
   target-dependent manual optimizations. A "native" target is included, which
   allows running OpenCL kernels on the host (CPU).</p>

</div>

<!--=========================================================================-->
<h3>Pure</h3>
  
<div>
<p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
  algebraic/functional programming language based on term rewriting. Programs
  are collections of equations which are used to evaluate expressions in a
  symbolic fashion. The interpreter uses LLVM as a backend to JIT-compile Pure
  programs to fast native code. Pure offers dynamic typing, eager and lazy
  evaluation, lexical closures, a hygienic macro system (also based on term
  rewriting), built-in list and matrix support (including list and matrix
  comprehensions) and an easy-to-use interface to C and other programming
  languages (including the ability to load LLVM bitcode modules, and inline C,
  C++, Fortran and Faust code in Pure programs if the corresponding LLVM-enabled
  compilers are installed).</p>
  
<p>Pure version 0.48 has been tested and is known to work with LLVM 3.0
  (and continues to work with older LLVM releases &gt;= 2.5).</p>

</div>

<!--=========================================================================-->
<h3>Renderscript</h3>

<div>

<p><a href="http://developer.android.com/guide/topics/renderscript/index.html">Renderscript</a>
   is Android's advanced 3D graphics rendering and compute API. It provides a
   portable C99-based language with extensions to facilitate common use cases
   for enhancing graphics and thread level parallelism. The Renderscript
   compiler frontend is based on Clang/LLVM. It emits a portable bitcode format
   for the actual compiled script code, as well as reflects a Java interface for
   developers to control the execution of the compiled bitcode. Executable
   machine code is then generated from this bitcode by an LLVM backend on the
   device. Renderscript is thus able to provide a mechanism by which Android
   developers can improve performance of their applications while retaining
   portability.</p>

</div>

<!--=========================================================================-->
<h3>SAFECode</h3>

<div>

<p><a href="http://safecode.cs.illinois.edu">SAFECode</a> is a memory safe C/C++
   compiler built using LLVM.  It takes standard, unannotated C/C++ code,
   analyzes the code to ensure that memory accesses and array indexing
   operations are safe, and instruments the code with run-time checks when
   safety cannot be proven statically.  SAFECode can be used as a debugging aid
   (like Valgrind) to find and repair memory safety bugs.  It can also be used
   to protect code from security attacks at run-time.</p>

</div>

<!--=========================================================================-->
<h3>The Stupid D Compiler (SDC)</h3>

<div>

<p><a href="https://github.com/bhelyer/SDC">The Stupid D Compiler</a> is a
   project seeking to write a self-hosting compiler for the D programming
   language without using the frontend of the reference compiler (DMD).</p>

</div>

<!--=========================================================================-->
<h3>TTA-based Co-design Environment (TCE)</h3>

<div>

<p>TCE is a toolset for designing application-specific processors (ASP) based on
   the Transport triggered architecture (TTA). The toolset provides a complete
   co-design flow from C/C++ programs down to synthesizable VHDL and parallel
   program binaries. Processor customization points include the register files,
   function units, supported operations, and the interconnection network.</p>
  
<p>TCE uses Clang and LLVM for C/C++ language support, target independent
   optimizations and also for parts of code generation. It generates new
   LLVM-based code generators "on the fly" for the designed TTA processors and
   loads them in to the compiler backend as runtime libraries to avoid
   per-target recompilation of larger parts of the compiler chain.</p>

</div>
  
<!--=========================================================================-->
<h3>Tart Programming Language</h3>

<div>

<p><a href="http://code.google.com/p/tart/">Tart</a> is a general-purpose,
   strongly typed programming language designed for application
   developers. Strongly inspired by Python and C#, Tart focuses on practical
   solutions for the professional software developer, while avoiding the clutter
   and boilerplate of legacy languages like Java and C++. Although Tart is still
   in development, the current implementation supports many features expected of
   a modern programming language, such as garbage collection, powerful
   bidirectional type inference, a greatly simplified syntax for template
   metaprogramming, closures and function literals, reflection, operator
   overloading, explicit mutability and immutability, and much more. Tart is
   flexible enough to accommodate a broad range of programming styles and
   philosophies, while maintaining a strong commitment to simplicity, minimalism
   and elegance in design.</p>

</div>

<!--=========================================================================-->
<h3>ThreadSanitizer</h3>

<div>

<p><a href="http://code.google.com/p/data-race-test/">ThreadSanitizer</a> is a
   data race detector for (mostly) C and C++ code, available for Linux, Mac OS
   and Windows. On different systems, we use binary instrumentation frameworks
   (Valgrind and Pin) as frontends that generate the program events for the race
   detection algorithm. On Linux, there's an option of using LLVM-based
   compile-time instrumentation.</p>

</div>

</div>

<!-- *********************************************************************** -->
<h2>
  <a name="whatsnew">What's New in LLVM 3.0?</a>
</h2>
<!-- *********************************************************************** -->

<div>

<p>This release includes a huge number of bug fixes, performance tweaks and
   minor improvements.  Some of the major improvements and new features are
   listed in this section.</p>

<!--=========================================================================-->
<h3>
<a name="majorfeatures">Major New Features</a>
</h3>

<div>

  <!-- Features that need text if they're finished for 3.1:
   ARM EHABI
   combiner-aa?
   strong phi elim
   loop dependence analysis
   CorrelatedValuePropagation
   lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
   Integrated assembler on by default for arm/thumb?

   -->

  <!-- Near dead:
   Analysis/RegionInfo.h + Dom Frontiers
   SparseBitVector: used in LiveVar.
   llvm/lib/Archive - replace with lib object?
   -->

<p>LLVM 3.0 includes several major changes and big features:</p>

<ul>
<li>llvm-gcc is no longer supported, and not included in the release.  We 
    recommend switching to <a
       href="http://clang.llvm.org/">Clang</a> or <a 
       href="http://dragonegg.llvm.org/">DragonEgg</a>.</li>

<li>The linear scan register allocator has been replaced with a new "greedy"
    register allocator, enabling live range splitting and many other
    optimizations that lead to better code quality.  Please see its <a
    href="http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html">blog post</a> or its talk at the <a 
      href="http://llvm.org/devmtg/2011-11/">Developer Meeting</a>
    for more information.</li>
<li>LLVM IR now includes full support for <a href="Atomics.html">atomics
    memory operations</a> intended to support the C++'11 and C'1x memory models.
    This includes <a href="LangRef.html#memoryops">atomic load and store,
    compare and exchange, and read/modify/write instructions</a> as well as a
    full set of <a href="LangRef.html#ordering">memory ordering constraints</a>.
    Please see the <a href="Atomics.html">Atomics Guide</a> for more
    information.
</li>
<li>The LLVM IR exception handling representation has been redesigned and
    reimplemented, making it more elegant, fixing a huge number of bugs, and
    enabling inlining and other optimizations.  Please see its blog post (XXX
    not yet) and the <a href="ExceptionHandling.html">Exception Handling
    documentation</a> for more information.</li>
<li>The LLVM IR Type system has been redesigned and reimplemented, making it
    faster and solving some long-standing problems.
    Please see its <a 
    href="http://blog.llvm.org/2011/11/llvm-30-type-system-rewrite.html">blog
    post</a> for more information.</li>
  
<li>The MIPS backend has made major leaps in this release, going from an
    experimental target to being virtually production quality and supporting a
    wide variety of MIPS subtargets.  See the <a href="#MIPS">MIPS section</a>
    below for more information.</li>
  
<li>The optimizer and code generator now supports gprof and gcov-style coverage
    and profiling information, and includes a new llvm-cov tool (but also works
    with gcov).  Clang exposes coverage and profiling through GCC-compatible
    command line options.</li>
</ul>

</div>

  
<!--=========================================================================-->
<h3>
<a name="coreimprovements">LLVM IR and Core Improvements</a>
</h3>

<div>

<p>LLVM IR has several new features for better support of new targets and that
   expose new optimization opportunities:</p>

  <ul>
  <li><a href="Atomics.html">Atomic memory accesses and memory ordering</a> are
      now directly expressible in the IR.</li>
  <li>A new <a href="LangRef.html#int_fma">llvm.fma intrinsic</a> directly
    represents floating point multiply accumulate operations without an
    intermediate rounding stage.</li>
  <li>A new llvm.expect intrinsic (XXX not documented in langref) allows a
     frontend to express expected control flow (and the __builtin_expect builtin
    from GNU C).</li>
  <li>The <a href="LangRef.html#int_prefetch">llvm.prefetch intrinsic</a> now
    takes a 4th argument that specifies whether the prefetch happens from the
    icache or dcache.</li>
  <li>The new <a href="LangRef.html#uwtable">uwtable function attribute</a>
    allows a frontend to control emission of unwind tables.</li>
  <li>The new <a href="LangRef.html#fnattrs">nonlazybind function
    attribute</a> allow optimization of Global Offset Table (GOT) accesses.</li>
  <li>The new <a href="LangRef.html#returns_twice">returns_twice attribute</a>
    allows better modeling of functions like setjmp.</li>
  <li>The <a href="LangRef.html#datalayout">target datalayout</a> string can now
    encode the natural alignment of the target's stack for better optimization.
    </li>
  </ul>
</div>

<!--=========================================================================-->
<h3>
<a name="optimizer">Optimizer Improvements</a>
</h3>

<div>

<p>In addition to many minor performance tweaks and bug fixes, this
   release includes a few major enhancements and additions to the
   optimizers:</p>

<ul>
<li>The pass manager now has an extension API that allows front-ends and plugins
    to insert their own optimizations in the well-known places in the standard
    pass optimization pipeline.</li>

<li>Information about <a href="BranchWeightMetadata.html">branch probability</a>
    and basic block frequency is now available within LLVM, based on a
    combination of static branch prediction heuristics and
    <code>__builtin_expect</code> calls.  That information is currently used for
    register spill placement and if-conversion, with additional optimizations
    planned for future releases.  The same framework is intended for eventual
    use with profile-guided optimization.</li>
  
<li>The "-indvars" induction variable simplification pass only modifies
    induction variables when profitable. Sign and zero extension
    elimination, linear function test replacement, loop unrolling, and
    other simplifications that require induction variable analysis have
    been generalized so they no longer require loops to be rewritten into 
    canonical form prior to optimization. This new design
    preserves more IR level information, avoids undoing earlier loop
    optimizations (particularly hand-optimized loops), and no longer
    requires the code generator to reconstruct loops into an optimal form -
    an intractable problem.</li>

<li>LLVM now includes a pass to optimize retain/release calls for the
  <a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">Automatic
    Reference Counting</a> (ARC) Objective-C language feature (in
    lib/Transforms/Scalar/ObjCARC.cpp).  It is a decent example of implementing
    a source-language-specific optimization in LLVM.</li>

</ul>

</div>

<!--=========================================================================-->
<h3>
<a name="mc">MC Level Improvements</a>
</h3>

<div>

<p>The LLVM Machine Code (aka MC) subsystem was created to solve a number of
   problems in the realm of assembly, disassembly, object file format handling,
   and a number of other related areas that CPU instruction-set level tools work
   in. For more information, please see
  the <a href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro
    to the LLVM MC Project Blog Post</a>.</p>

<ul>
  <li>The MC layer has undergone significant refactoring to eliminate layering
    violations that caused it to pull in the LLVM compiler backend code.</li>
  <li>The ELF object file writers are much more full featured.</li>
  <li>The integrated assembler now supports #line directives.</li>
  <li>An early implementation of a JIT built on top of the MC framework (known
      as MC-JIT) has been implemented and will eventually replace the old JIT.
    It emits object files direct to memory and uses a runtime dynamic linker to
    resolve references and drive lazy compilation.  The MC-JIT enables much
    greater code reuse between the JIT and the static compiler and provides
    better integration with the platform ABI as a result.
  </li>
  <li>The assembly printer now makes uses of assemblers instruction aliases
    (InstAliases) to print simplified mneumonics when possible.</li>
  <li>TableGen can now autogenerate MC expansion logic for pseudo
    instructions that expand to multiple MC instructions (through the
    PseudoInstExpansion class).</li>
  <li>A new llvm-objdump and llvm-dwarfdump tools provide a start of a drop-in 
    replacement for the corresponding tools that use LLVM libraries.  As part of
    this, LLVM has the beginnings of a dwarf parsing library.</li>
  <li>XXX: object file parsing stuff and llvm-size (mspencer).  Status?</li>
</ul>

</div>

<!--=========================================================================-->
<h3>
<a name="codegen">Target Independent Code Generator Improvements</a>
</h3>

<div>

<p>We have put a significant amount of work into the code generator
   infrastructure, which allows us to implement more aggressive algorithms and
   make it run faster:</p>

<ul>
<li>XXX: Segmented stacks.</li>
<li>LLVM generates substantially better code for indirect gotos due to a new
    tail duplication pass, which can be a substantial performance win for
    interpreter loops that use them.</li>
<li>Exception handling and debug information is now emitted with CFI directives,
    yielding <a href="http://blog.mozilla.com/respindola/2011/05/12/cfi-directives/">much smaller executables</a> for some C++ applications.
</li>

<li>The code generator now supports vector "select" operations on vector
    comparisons, turning them into various optimized code sequences (e.g.
    using the SSE4/AVX "blend" instructions).</li>
<li>The SSE execution domain fix pass and the ARM NEON move fix pass have been
    merged to a target independent execution dependency fix pass. This pass is
    used to select alternative equivalent opcodes in a way that minimizes
    execution domain crossings. Closely connected instructions are moved to
    the same execution domain when possible. Targets can override the
    <code>getExecutionDomain</code> and <code>setExecutionDomain</code> hooks
    to use the pass.</li>
</ul>
</div>

<!--=========================================================================-->
<h3>
<a name="x86">X86-32 and X86-64 Target Improvements</a>
</h3>

<div>

<p>New features and major changes in the X86 target include:</p>

<ul>
<li>The X86 backend, assembler and disassembler now have full support for AVX 1.
    To enable it pass <code>-mavx</code> to the compiler. AVX2 implementation is
    underway on mainline.</li>
<li>The integrated assembler and disassembler now support a broad range of new
    instructions including Atom, Ivy Bridge, <a
    href="http://en.wikipedia.org/wiki/SSE4a">SSE4a/BMI</a> instructions, <a
   href="http://en.wikipedia.org/wiki/RdRand">rdrand</a> and many others.</li>
<li>The X86 backend now fully supports the <a href="http://llvm.org/PR879">X87
  floating point stack inline assembly constraints</a>.</li>
<li>The integrated assembler now supports the <tt>.code32</tt> and
    <tt>.code64</tt> directives to switch between 32-bit and 64-bit
    instructions.</li>
<li>The X86 backend now synthesizes horizontal add/sub instructions from generic
    vector code when the appropriate instructions are enabled.</li>
<li>The X86-64 backend generates smaller and faster code at -O0 due to
    improvements in fast instruction selection.</li>
<li><a href="http://code.google.com/p/nativeclient/">Native Client</a>
    subtarget support has been added.</li>

<li>The CRC32 intrinsics have been renamed.  The intrinsics were previously
    <code>@llvm.x86.sse42.crc32.[8|16|32]</code>
    and <code>@llvm.x86.sse42.crc64.[8|64]</code>. They have been renamed to
    <code>@llvm.x86.sse42.crc32.32.[8|16|32]</code> and
    <code>@llvm.x86.sse42.crc32.64.[8|64]</code>.</li>
</ul>

</div>

<!--=========================================================================-->
<h3>
<a name="ARM">ARM Target Improvements</a>
</h3>

<div>

<p>New features of the ARM target include:</p>

<ul>
<li>The ARM backend generates much faster code for Cortex-A9 chips.</li>
<li>The ARM backend has improved support for Cortex-M series processors.</li>
<li>The ARM inline assembly constraints have been implemented and are now fully
    supported.</li>
<li>NEON code produced by Clang often runs much faster due to improvements in
    the Scalar Replacement of Aggregates pass.</li>
<li>The old ARM disassembler is replaced with a new one based on autogenerated
    encoding information from ARM .td files.</li>
<li>The integrated assembler has made major leaps forward, but is still beta quality in LLVM 3.0.</li>
</ul>
</div>

  
<!--=========================================================================-->
<h3>
<a name="MIPS">MIPS Target Improvements</a>
</h3>

<div>

<p>This release has seen major new work on just about every aspect of the MIPS
  backend.  Some of the major new features include:</p>

<ul>
  <li>Most MIPS32r1 and r2 instructions are now supported.</li>
  <li>LE/BE MIPS32r1/r2 has been tested extensively.</li>
  <li>O32 ABI has been fully tested.</li>
  <li>MIPS backend has migrated to using the MC infrastructure for assembly printing. Initial support for direct object code emission has been implemented too.</li>
  <li>Delay slot filler has been updated. Now it tries to fill delay slots with useful instructions instead of always filling them with NOPs.</li> 
  <li>Support for old-style JIT is complete.</li>
  <li>Support for old architectures (MIPS1 and MIPS2) has been removed.</li>
  <li>Initial support for MIPS64 has been added.</li>
</ul>
</div>

<!--=========================================================================-->
<h3>
  <a name="PTX">PTX Target Improvements</a>
</h3>

<div>
  
  <p>
  The PTX back-end is still experimental, but is fairly usable for compute kernels
  in LLVM 3.0.  Most scalar arithmetic is implemented, as well as intrinsics to
  access the special PTX registers and sync instructions.  The major missing
  pieces are texture/sampler support and some vector operations.</p>
  
  <p>That said, the backend is already being used for domain-specific languages
  and works well with the <a href="http://www.pcc.me.uk/~peter/libclc/">libclc
    library</a> to supply OpenCL built-ins.  With it, you can use Clang to compile
  OpenCL code into PTX and execute it by loading the resulting PTX as a binary
  blob using the nVidia OpenCL library.  It has been tested with several OpenCL
  programs, including some from the nVidia GPU Computing SDK, and the performance
  is on par with the nVidia compiler.</p>
  
</div>

<!--=========================================================================-->
<h3>
<a name="OtherTS">Other Target Specific Improvements</a>
</h3>

<div>

<ul>
<li>Many PowerPC improvements have been implemented for ELF targets, including
   support for varargs and initial support for direct .o file emission.</li>
  
<li>MicroBlaze scheduling itineraries were added that model the
   3-stage and the 5-stage pipeline architectures. The 3-stage
   pipeline model can be selected with <code>-mcpu=mblaze3</code> 
   and the 5-stage pipeline model can be selected with 
   <code>-mcpu=mblaze5</code>.</li>

</ul>

</div>

<!--=========================================================================-->
<h3>
<a name="changes">Major Changes and Removed Features</a>
</h3>

<div>

<p>If you're already an LLVM user or developer with out-of-tree changes based on
   LLVM 2.9, this section lists some "gotchas" that you may run into upgrading
   from the previous release.</p>

<ul>
<li>LLVM 3.0 removes support for reading LLVM 2.8 and earlier files, and LLVM
    3.1 will eliminate support for reading LLVM 2.9 files.  Going forward, we
    aim for all future versions of LLVM to read bitcode files and .ll files 
    produced by LLVM 3.0.</li>
<li>Tablegen has been split into a library, allowing the clang tblgen pieces
    now live in the clang tree.  The llvm version has been renamed to
    llvm-tblgen instead of tblgen.</li>
  <li>The <code>LLVMC</code> meta compiler driver was removed.</li>
  <li>The unused PostOrder Dominator Frontiers and LowerSetJmp passes were removed.</li>


  <li>The old <code>TailDup</code> pass was not used in the standard pipeline
      and was unable to update ssa form, so it has been removed.
  <li>The syntax of volatile loads and stores in IR has been changed to
      "<code>load volatile</code>"/"<code>store volatile</code>".  The old
      syntax ("<code>volatile load</code>"/"<code>volatile store</code>")
      is still accepted, but is now considered deprecated and will be removed in
      3.1.</li>
  <li>llvm-gcc's frontend tests have been removed from llvm/test/Frontend*, sunk
    into the clang and dragonegg testsuites.</li>
  <li>The old atomic intrinsics (<code>llvm.memory.barrier</code> and
      <code>llvm.atomic.*</code>) are now gone.  Please use the new atomic
      instructions, described in the <a href="Atomics.html">atomics guide</a>.
  <li>LLVM's configure script doesn't depend on llvm-gcc anymore, eliminating a
      strange circular dependence between projects.</li>
</ul>

<h4>Windows (32-bit)</h4>
<div>

<ul>
  <li>On Win32(MinGW32 and MSVC), Windows 2000 will not be supported.
      Windows XP or higher is required.</li>
</ul>

</div>

</div>

<!--=========================================================================-->
<h3>
<a name="api_changes">Internal API Changes</a>
</h3>

<div>

<p>In addition, many APIs have changed in this release.  Some of the major
   LLVM API changes are:</p>

<ul>
  <li>The biggest and most pervasive change is that llvm::Types are no longer
      returned or accepted as 'const' values.  Instead, just pass around
      non-const Types.</li>
  
  <li><code>PHINode::reserveOperandSpace</code> has been removed. Instead, you
      must specify how many operands to reserve space for when you create the
      PHINode, by passing an extra argument
      into <code>PHINode::Create</code>.</li>

  <li>PHINodes no longer store their incoming BasicBlocks as operands. Instead,
      the list of incoming BasicBlocks is stored separately, and can be accessed
      with new functions <code>PHINode::block_begin</code>
      and <code>PHINode::block_end</code>.</li>

  <li>Various functions now take an <code>ArrayRef</code> instead of either a
      pair of pointers (or iterators) to the beginning and end of a range, or a
      pointer and a length. Others now return an <code>ArrayRef</code> instead
      of a reference to a <code>SmallVector</code>
      or <code>std::vector</code>. These include:
<ul>
<!-- Please keep this list sorted. -->
<li><code>CallInst::Create</code></li>
<li><code>ComputeLinearIndex</code> (in <code>llvm/CodeGen/Analysis.h</code>)</li>
<li><code>ConstantArray::get</code></li>
<li><code>ConstantExpr::getExtractElement</code></li>
<li><code>ConstantExpr::getGetElementPtr</code></li>
<li><code>ConstantExpr::getInBoundsGetElementPtr</code></li>
<li><code>ConstantExpr::getIndices</code></li>
<li><code>ConstantExpr::getInsertElement</code></li>
<li><code>ConstantExpr::getWithOperands</code></li>
<li><code>ConstantFoldCall</code> (in <code>llvm/Analysis/ConstantFolding.h</code>)</li>
<li><code>ConstantFoldInstOperands</code> (in <code>llvm/Analysis/ConstantFolding.h</code>)</li>
<li><code>ConstantVector::get</code></li>
<li><code>DIBuilder::createComplexVariable</code></li>
<li><code>DIBuilder::getOrCreateArray</code></li>
<li><code>ExtractValueInst::Create</code></li>
<li><code>ExtractValueInst::getIndexedType</code></li>
<li><code>ExtractValueInst::getIndices</code></li>
<li><code>FindInsertedValue</code> (in <code>llvm/Analysis/ValueTracking.h</code>)</li>
<li><code>gep_type_begin</code> (in <code>llvm/Support/GetElementPtrTypeIterator.h</code>)</li>
<li><code>gep_type_end</code> (in <code>llvm/Support/GetElementPtrTypeIterator.h</code>)</li>
<li><code>GetElementPtrInst::Create</code></li>
<li><code>GetElementPtrInst::CreateInBounds</code></li>
<li><code>GetElementPtrInst::getIndexedType</code></li>
<li><code>InsertValueInst::Create</code></li>
<li><code>InsertValueInst::getIndices</code></li>
<li><code>InvokeInst::Create</code></li>
<li><code>IRBuilder::CreateCall</code></li>
<li><code>IRBuilder::CreateExtractValue</code></li>
<li><code>IRBuilder::CreateGEP</code></li>
<li><code>IRBuilder::CreateInBoundsGEP</code></li>
<li><code>IRBuilder::CreateInsertValue</code></li>
<li><code>IRBuilder::CreateInvoke</code></li>
<li><code>MDNode::get</code></li>
<li><code>MDNode::getIfExists</code></li>
<li><code>MDNode::getTemporary</code></li>
<li><code>MDNode::getWhenValsUnresolved</code></li>
<li><code>SimplifyGEPInst</code> (in <code>llvm/Analysis/InstructionSimplify.h</code>)</li>
<li><code>TargetData::getIndexedOffset</code></li>
</ul></li>

  <li>All forms of <code>StringMap::getOrCreateValue</code> have been remove
      except for the one which takes a <code>StringRef</code>.</li>

  <li>The <code>LLVMBuildUnwind</code> function from the C API was removed. The
      LLVM <code>unwind</code> instruction has been deprecated for a long time
      and isn't used by the current front-ends. So this was removed during the
      exception handling rewrite.</li>

  <li>The <code>LLVMAddLowerSetJmpPass</code> function from the C API was
      removed because the <code>LowerSetJmp</code> pass was removed.</li>

  <li>The <code>DIBuilder</code> interface used by front ends to encode
      debugging information in the LLVM IR now expects clients to
      use <code>DIBuilder::finalize()</code> at the end of translation unit to
      complete debugging information encoding.</li>

  <li>The way the type system works has been
      rewritten: <code>PATypeHolder</code> and <code>OpaqueType</code> are gone,
      and all APIs deal with <code>Type*</code> instead of <code>const
      Type*</code>.  If you need to create recursive structures, then create a
      named structure, and use <code>setBody()</code> when all its elements are
      built.  Type merging and refining is gone too: named structures are not
      merged with other structures, even if their layout is identical.  (of
      course anonymous structures are still uniqued by layout).</li>

  <li>TargetSelect.h moved to Support/ from Target/</li>

  <li>UpgradeIntrinsicCall no longer upgrades pre-2.9 intrinsic calls (for
      example <code>llvm.memset.i32</code>).</li>

  <li>It is mandatory to initialize all out-of-tree passes too and their dependencies now with
      <code>INITIALIZE_PASS{BEGIN,END,}</code>
      and <code>INITIALIZE_{PASS,AG}_DEPENDENCY</code>.</li>

  <li>The interface for MemDepResult in MemoryDependenceAnalysis has been
      enhanced with new return types Unknown and NonFuncLocal, in addition to
      the existing types Clobber, Def, and NonLocal.</li>
</ul>

</div>

</div>

<!-- *********************************************************************** -->
<h2>
  <a name="knownproblems">Known Problems</a>
</h2>
<!-- *********************************************************************** -->

<div>

<p>LLVM is generally a production quality compiler, and is used by a broad range
   of applications and shipping in many products.  That said, not every
   subsystem is as mature as the aggregate, particularly the more obscure
   targets.  If you run into a problem, please check the <a
   href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
   there isn't already one or ask on the <a
    href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
    list</a>.</p>
  
  <p>Known problem areas include:</p>
  
<ul>
  <li>The Alpha, Blackfin, CellSPU, MSP430, PTX, SystemZ and
      XCore backends are experimental, and the Alpha, Blackfin and SystemZ
      targets have already been removed from mainline.</li>

  <li>The integrated assembler, disassembler, and JIT is not supported by
      several targets.  If an integrated assembler is not supported, then a
      system assembler is required.  For more details, see the <a
      href="CodeGenerator.html#targetfeatures">Target Features Matrix</a>.
  </li>
  
  <li>The C backend has numerous problems and is not being actively maintained.
    Depending on it for anything serious is not advised.</li>
</ul>

</div>

</div>

<!-- *********************************************************************** -->
<h2>
  <a name="additionalinfo">Additional Information</a>
</h2>
<!-- *********************************************************************** -->

<div>

<p>A wide variety of additional information is available on
   the <a href="http://llvm.org/">LLVM web page</a>, in particular in
   the <a href="http://llvm.org/docs/">documentation</a> section.  The web page
   also contains versions of the API documentation which is up-to-date with the
   Subversion version of the source code.  You can access versions of these
   documents specific to this release by going into the "<tt>llvm/doc/</tt>"
   directory in the LLVM tree.</p>

<p>If you have any questions or comments about LLVM, please feel free to contact
   us via the <a href="http://llvm.org/docs/#maillist"> mailing lists</a>.</p>

</div>

<!--=========================================================================-->

<!-- EH details: to be moved to a blog post:
 

<p>One of the biggest changes is that 3.0 has a new exception handling
   system. The old system used LLVM intrinsics to convey the exception handling
   information to the code generator. It worked in most cases, but not
   all. Inlining was especially difficult to get right. Also, the intrinsics
   could be moved away from the <code>invoke</code> instruction, making it hard
   to recover that information.</p>

<p>The new EH system makes exception handling a first-class member of the IR. It
   adds two new instructions:</p>

<ul>
  <li><a href="LangRef.html#i_landingpad"><code>landingpad</code></a> &mdash;
      this instruction defines a landing pad basic block. It contains all of the
      information that's needed by the code generator. It's also required to be
      the first non-PHI instruction in the landing pad. In addition, a landing
      pad may be jumped to only by the unwind edge of an <code>invoke</code>
      instruction.</li>

  <li><a href="LangRef.html#i_resume"><code>resume</code></a> &mdash; this
      instruction causes the current exception to resume traveling up the
      stack. It replaces the <code>@llvm.eh.resume</code> intrinsic.</li>
</ul>

<p>Converting from the old EH API to the new EH API is rather simple, because a
   lot of complexity has been removed. The two intrinsics,
   <code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code> have been
   superseded by the <code>landingpad</code> instruction. Instead of generating
   a call to <code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code>:

<div class="doc_code">
<pre>
Function *ExcIntr = Intrinsic::getDeclaration(TheModule,
                                              Intrinsic::eh_exception);
Function *SlctrIntr = Intrinsic::getDeclaration(TheModule,
                                                Intrinsic::eh_selector);

// The exception pointer.
Value *ExnPtr = Builder.CreateCall(ExcIntr, "exc_ptr");

std::vector&lt;Value*&gt; Args;
Args.push_back(ExnPtr);
Args.push_back(Builder.CreateBitCast(Personality,
                                     Type::getInt8PtrTy(Context)));

<i>// Add selector clauses to Args.</i>

// The selector call.
Builder.CreateCall(SlctrIntr, Args, "exc_sel");
</pre>
</div>

<p>You should instead generate a <code>landingpad</code> instruction, that
   returns an exception object and selector value:</p>

<div class="doc_code">
<pre>
LandingPadInst *LPadInst =
  Builder.CreateLandingPad(StructType::get(Int8PtrTy, Int32Ty, NULL),
                           Personality, 0);

Value *LPadExn = Builder.CreateExtractValue(LPadInst, 0);
Builder.CreateStore(LPadExn, getExceptionSlot());

Value *LPadSel = Builder.CreateExtractValue(LPadInst, 1);
Builder.CreateStore(LPadSel, getEHSelectorSlot());
</pre>
</div>

<p>It's now trivial to add the individual clauses to the <code>landingpad</code>
   instruction.</p>

<div class="doc_code">
<pre>
<i><b>// Adding a catch clause</b></i>
Constant *TypeInfo = getTypeInfo();
LPadInst-&gt;addClause(TypeInfo);

<i><b>// Adding a C++ catch-all</b></i>
LPadInst-&gt;addClause(Constant::getNullValue(Builder.getInt8PtrTy()));

<i><b>// Adding a cleanup</b></i>
LPadInst-&gt;setCleanup(true);

<i><b>// Adding a filter clause</b></i>
std::vector&lt;Constant*&gt; TypeInfos;
Constant *TypeInfo = getFilterTypeInfo();
TypeInfos.push_back(Builder.CreateBitCast(TypeInfo, Builder.getInt8PtrTy()));

ArrayType *FilterTy = ArrayType::get(Int8PtrTy, TypeInfos.size());
LPadInst-&gt;addClause(ConstantArray::get(FilterTy, TypeInfos));
</pre>
</div>

<p>Converting from using the <code>@llvm.eh.resume</code> intrinsic to
   the <code>resume</code> instruction is trivial. It takes the exception
   pointer and exception selector values returned by
   the <code>landingpad</code> instruction:</p>

<div class="doc_code">
<pre>
Type *UnwindDataTy = StructType::get(Builder.getInt8PtrTy(),
                                     Builder.getInt32Ty(), NULL);
Value *UnwindData = UndefValue::get(UnwindDataTy);
Value *ExcPtr = Builder.CreateLoad(getExceptionObjSlot());
Value *ExcSel = Builder.CreateLoad(getExceptionSelSlot());
UnwindData = Builder.CreateInsertValue(UnwindData, ExcPtr, 0, "exc_ptr");
UnwindData = Builder.CreateInsertValue(UnwindData, ExcSel, 1, "exc_sel");
Builder.CreateResume(UnwindData);
</pre>
</div>


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