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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
                      "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <link rel="stylesheet" href="llvm.css" type="text/css">
  <title>LLVM 2.6 Release Notes</title>
</head>
<body>

<div class="doc_title">LLVM 2.6 Release Notes</div>

<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 2.6</a></li>
  <li><a href="#whatsnew">What's New in LLVM 2.6?</a></li>
  <li><a href="GettingStarted.html">Installation Instructions</a></li>
  <li><a href="#portability">Portability and Supported Platforms</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>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="intro">Introduction</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This document contains the release notes for the LLVM Compiler
Infrastructure, release 2.6.  Here we describe the status of LLVM, including
major improvements from the previous release and significant known problems.
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://mail.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>

<!-- Unfinished features in 2.5:
  Machine LICM
  Machine Sinking
  target-specific intrinsics
  gold lto plugin
  pre-alloc splitter, strong phi elim
  <tt>llc -enable-value-prop</tt>, propagation of value info
       (sign/zero ext info) from one MBB to another
  debug info for optimized code
  interpreter + libffi
  postalloc scheduler: anti dependence breaking, hazard recognizer?

initial support for debug line numbers when optimization enabled, not useful in
  2.5 but will be for 2.6.

 -->

 <!-- for announcement email:
   -->

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

<div class="doc_text">
<p>
The LLVM 2.6 distribution currently consists of code from the core LLVM
repository &mdash;which roughly includes the LLVM optimizers, code generators
and supporting tools &mdash; and the llvm-gcc repository.  In addition to this
code, the LLVM Project includes other sub-projects that are in development.  The
two which are the most actively developed are the <a href="#clang">Clang
Project</a> and the <a href="#vmkit">VMKit Project</a>.
</p>

</div>


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

<div class="doc_text">

<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
a set of new 'LLVM native' front-end technologies for the LLVM optimizer and
code generator.  While Clang is not included in the LLVM 2.6 release, it is
continuing to make major strides forward in all areas.  Its C and Objective-C
parsing and code generation support is now very solid.  For example, it is
capable of successfully building many real-world applications for X86-32
and X86-64,
including the <a href="http://wiki.freebsd.org/BuildingFreeBSDWithClang">FreeBSD
kernel</a> and <a href="http://gcc.gnu.org/gcc-4.2/">gcc 4.2</a>.  C++ is also
making <a href="http://clang.llvm.org/cxx_status.html">incredible progress</a>,
and work on templates has recently started.  If you are
interested in fast compiles and good diagnostics, we encourage you to try it out
by <a href="http://clang.llvm.org/get_started.html">building from mainline</a>
and reporting any issues you hit to the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">Clang front-end mailing
list</a>.</p>

<p>In the LLVM 2.6 time-frame, the Clang team has made many improvements:</p>

<ul>
<li>Something wonderful!</li>
<li>AuroraUX / FreeBSD & OpenBSD Toolchain support.</li>
<li>Many many bugs are fixed and many features have been added.</li>
</ul>
</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="clangsa">Clang Static Analyzer</a>
</div>

<div class="doc_text">

<p>Previously announced in the 2.4 LLVM release, the Clang project also
includes an early stage static source code analysis tool for <a
href="http://clang.llvm.org/StaticAnalysis.html">automatically finding bugs</a>
in C and Objective-C programs. The tool performs a growing set of checks to find
bugs that occur on a specific path within a program.</p>

<p>In the LLVM 2.6 time-frame there have been many significant improvements to
XYZ.</p>

<p>The set of checks performed by the static analyzer continues to expand, and
future plans for the tool include full source-level inter-procedural analysis
and deeper checks such as buffer overrun detection. There are many opportunities
to extend and enhance the static analyzer, and anyone interested in working on
this project is encouraged to get involved!</p>

</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
</div>

<div class="doc_text">
<p>
The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
a JVM and a CLI Virtual Machines (Microsoft .NET is an
implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>

<p>Following LLVM 2.6, VMKit has its XYZ release that you can find on its
<a href="http://vmkit.llvm.org/releases/">webpage</a>. The release includes
bug fixes, cleanup and new features. The major changes are:</p>

<ul>

<li>Something wonderful!</li>

</ul>
</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="externalproj">External Projects Using LLVM 2.6</a>
</div>
<!-- *********************************************************************** -->

<!--=========================================================================-->
<div class="doc_subsection">
<a name="pure">Pure</a>
</div>

<div class="doc_text">
<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. 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 C interface. The interpreter uses LLVM as a backend to
 JIT-compile Pure programs to fast native code.</p>

<p>In addition to the usual algebraic data structures, Pure also has
MATLAB-style matrices in order to support numeric computations and signal
processing in an efficient way. Pure is mainly aimed at mathematical
applications right now, but it has been designed as a general purpose language.
The dynamic interpreter environment and the C interface make it possible to use
it as a kind of functional scripting language for many application areas.
</p>
</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="ldc">LLVM D Compiler</a>
</div>

<div class="doc_text">
<p>
<a href="http://www.dsource.org/projects/ldc">LDC</a> is an implementation of
the D Programming Language using the LLVM optimizer and code generator.
The LDC project works great with the LLVM 2.6 release.  General improvements in
this
cycle have included new inline asm constraint handling, better debug info
support, general bugfixes, and better x86-64 support.  This has allowed
some major improvements in LDC, getting us much closer to being as
fully featured as the original DMD compiler from DigitalMars.
</p>
</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="RoadsendPHP">Roadsend PHP</a>
</div>

<div class="doc_text">
<p><a href="http://code.roadsend.com/rphp">Roadsend PHP</a> (rphp) is an open
source implementation of the PHP programming 
language that uses LLVM for its optimizer, JIT, and static compiler. This is a 
reimplementation of an earlier project that is now based on LLVM.</p>
</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="Unladen Swallow">Unladen Swallow</a>
</div>

<div class="doc_text">
<p><a href="http://code.google.com/p/unladen-swallow/">Unladen Swallow</a> is a
branch of <a href="http://python.org/">Python</a> intended to be fully
compatible and significantly faster.  It uses LLVM's optimization passes and JIT
compiler.</p>
</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="Rubinius">Rubinius</a>
</div>

<div class="doc_text">
<p><a href="http://github.com/evanphx/rubinius">Rubinius</a> is a new virtual
machine for Ruby. It leverages LLVM to dynamically compile Ruby code down to
machine code using LLVM's JIT.</p>
</div>


<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="whatsnew">What's New in LLVM 2.6?</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<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>
</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="majorfeatures">Major New Features</a>
</div>

<div class="doc_text">

<p>LLVM 2.6 includes several major new capabilities:</p>

<ul>
<li>Something wonderful!</li>
<li>LLVM 2.6 includes a brand new experimental LLVM bindings to the Ada2005 programming language.</li>
</ul>

</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="llvm-gcc">llvm-gcc 4.2 Improvements</a>
</div>

<div class="doc_text">

<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
front-ends and driver with the LLVM optimizer and code generator.  It currently
includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>

<ul>
<li>Something wonderful!</li>
</ul>

</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="coreimprovements">LLVM IR and Core Improvements</a>
</div>

<div class="doc_text">
<p>LLVM IR has several new features that are used by our existing front-ends and
can be useful if you are writing a front-end for LLVM:</p>

<ul>
<li>Something wonderful!</li>
</ul>

</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="optimizer">Optimizer Improvements</a>
</div>

<div class="doc_text">

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

<ul>

<li>Something wonderful!</li>

</ul>

</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="codegen">Target Independent Code Generator Improvements</a>
</div>

<div class="doc_text">

<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>Something wonderful!</li>
</ul>
</div>

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

<div class="doc_text">
<p>New features of the X86 target include:
</p>

<ul>

<li>Something wonderful!</li>
</ul>

</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="pic16">PIC16 Target Improvements</a>
</div>

<div class="doc_text">
<p>New features of the PIC16 target include:
</p>

<ul>
<li>Something wonderful!</li>
</ul>

<p>Things not yet supported:</p>

<ul>
<li>Floating point.</li>
<li>Passing/returning aggregate types to and from functions.</li>
<li>Variable arguments.</li>
<li>Indirect function calls.</li>
<li>Interrupts/programs.</li>
<li>Debug info.</li>
</ul>

</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="ARM">ARM Target Improvements</a>
</div>

<div class="doc_text">
<p>New features of the ARM target include:
</p>

<ul>

<li>Preliminary support for processors, such as the Cortex-A8 and Cortex-A9,
that implement version v7-A of the ARM architecture.  The ARM backend now
supports both the Thumb2 and Advanced SIMD (Neon) instruction sets. The
AAPCS-VFP "hard float" calling conventions are also supported with the
<tt>-float-abi=hard</tt> flag. These features are still somewhat experimental
and subject to change. The Neon intrinsics, in particular, may change in future
releases of LLVM.
</li>
</ul>

</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="llvmc">Improvements in LLVMC</a>
</div>

<div class="doc_text">
<p>New features include:</p>

<ul>
<li>Something wonderful!</li>
</ul>

</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="changes">Major Changes and Removed Features</a>
</div>

<div class="doc_text">

<p>If you're already an LLVM user or developer with out-of-tree changes based
on LLVM 2.5, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>

<ul>

<li>Something horrible!</li>

</ul>


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

<ul>
<li>LLVM's global uniquing tables for <tt>Type</tt>s and <tt>Constant</tt>s have
    been privatized into members of an <tt>LLVMContext</tt>.  A number of APIs
    now take an <tt>LLVMContext</tt> as a parameter.  To smooth the transition
    for clients that will only ever use a single context, the new 
    <tt>getGlobalContext()</tt> API can be used to access a default global 
    context which can be passed in any and all cases where a context is 
    required.
<li>The <tt>getABITypeSize</tt> methods are now called <tt>getAllocSize</tt>.</li>
<li>The <tt>Add</tt>, <tt>Sub</tt>, and <tt>Mul</tt> operators are no longer
    overloaded for floating-point types. Floating-point addition, subtraction,
    and multiplication are now represented with new operators <tt>FAdd</tt>,
    <tt>FSub</tt>, and <tt>FMul</tt>. In the <tt>IRBuilder</tt> API,
    <tt>CreateAdd</tt>, <tt>CreateSub</tt>, <tt>CreateMul</tt>, and
    <tt>CreateNeg</tt> should only be used for integer arithmetic now;
    <tt>CreateFAdd</tt>, <tt>CreateFSub</tt>, <tt>CreateFMul</tt>, and
    <tt>CreateFNeg</tt> should now be used for floating-point arithmetic.</li>
<li>The DynamicLibrary class can no longer be constructed, its functionality has
    moved to static member functions.</li>
<li><tt>raw_fd_ostream</tt>'s constructor for opening a given filename now
    takes an extra <tt>Force</tt> argument. If <tt>Force</tt> is set to
    <tt>false</tt>, an error will be reported if a file with the given name
    already exists. If <tt>Force</tt> is set to <tt>true</tt>, the file will
    be silently truncated (which is the behavior before this flag was
    added).</li>
<li><tt>SCEVHandle</tt> no longer exists, because reference counting is no
longer done for <tt>SCEV*</tt> objects, instead <tt>const SCEV*</tt> should be
used.</li>

<li>Many APIs, notably <tt>llvm::Value</tt>, now use the <tt>StringRef</tt>
and <tt>Twine</tt> classes instead of passing <tt>const char*</tt>
or <tt>std::string</tt>, as described in
the <a href="ProgrammersManual.html#string_apis">Programmer's Manual</a>. Most
clients should be unaffected by this transition, unless they are used to <tt>Value::getName()</tt> returning a string. Here are some tips on updating to 2.6:
  <ul>
    <li><tt>getNameStr()</tt> is still available, and matches the old
      behavior. Replacing <tt>getName()</tt> calls with this is an safe option,
      although more efficient alternatives are now possible.</li>

    <li>If you were just relying on <tt>getName()</tt> being able to be sent to
      a <tt>std::ostream</tt>, consider migrating
      to <tt>llvm::raw_ostream</tt>.</li>
      
    <li>If you were using <tt>getName().c_str()</tt> to get a <tt>const
        char*</tt> pointer to the name, you can use <tt>getName().data()</tt>.
        Note that this string (as before), may not be the entire name if the
        name containts embedded null characters.</li>

    <li>If you were using operator plus on the result of <tt>getName()</tt> and
      treating the result as an <tt>std::string</tt>, you can either
      uses <tt>Twine::str</tt> to get the result as an <tt>std::string</tt>, or
      could move to a <tt>Twine</tt> based design.</li>

    <li><tt>isName()</tt> should be replaced with comparison
      against <tt>getName()</tt> (this is now efficient).
  </ul>
</li>

<li>The registration interfaces for backend Targets has changed (what was
previously TargetMachineRegistry). For backend authors, see the <a href="WritingAnLLVMBackend.html#TargetRegistration">Writing An LLVM Backend</a> guide. For clients, the notable API changes are:
  <ul>
    <li><tt>TargetMachineRegistry</tt> has been renamed
      to <tt>TargetRegistry</tt>.</li>

    <li>Clients should move to using the <tt>TargetRegistry::lookupTarget()</tt>
      function to find targets.</li>
  </ul>
</li>

<li>llvm-dis now fails if output file exists, instead of dumping to stdout.
FIXME: describe any other tool changes due to the raw_fd_ostream change.  FIXME:
This is not an API change, maybe there should be a tool changes section?</li>
<li>temporarely due to Context API change passes should call doInitialization()
method of the pass they inherit from, otherwise Context is NULL.
FIXME: remove this entry when this is no longer needed.<li>
</ul>

</div>



<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="portability">Portability and Supported Platforms</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>LLVM is known to work on the following platforms:</p>

<ul>
<li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat
Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like systems).</li>
<li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit
and 64-bit modes.</li>
<li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
    support is available for native builds with Visual C++).</li>
<li>Sun UltraSPARC workstations running Solaris 10.</li>
<li>Alpha-based machines running Debian GNU/Linux.</li>
</ul>

<p>The core LLVM infrastructure uses GNU autoconf to adapt itself
to the machine and operating system on which it is built.  However, minor
porting may be required to get LLVM to work on new platforms.  We welcome your
portability patches and reports of successful builds or error messages.</p>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="knownproblems">Known Problems</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This section contains significant known problems with the LLVM system,
listed by component.  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.</p>

<ul>
<li>LLVM will not correctly compile on Solaris and/or OpenSolaris
using the stock GCC 3.x.x series 'out the box',
See: <a href="#brokengcc">Broken versions of GCC and other tools</a>.
However, A <a href="http://pkg.auroraux.org/GCC">Modern GCC Build</a>
for x86/x64 has been made available from the third party AuroraUX Project
that has been meticulously tested for bootstrapping LLVM & Clang.</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="experimental">Experimental features included with this release</a>
</div>

<div class="doc_text">

<p>The following components of this LLVM release are either untested, known to
be broken or unreliable, or are in early development.  These components should
not be relied on, and bugs should not be filed against them, but they may be
useful to some people.  In particular, if you would like to work on one of these
components, please contact us on the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>

<ul>
<li>The MSIL, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li>
<li>The <tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only
    supported value for this option.</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="x86-be">Known problems with the X86 back-end</a>
</div>

<div class="doc_text">

<ul>
  <li>The X86 backend does not yet support
    all <a href="http://llvm.org/PR879">inline assembly that uses the X86
    floating point stack</a>.  It supports the 'f' and 't' constraints, but not
    'u'.</li>
  <li>The X86 backend generates inefficient floating point code when configured
    to generate code for systems that don't have SSE2.</li>
  <li>Win64 code generation wasn't widely tested. Everything should work, but we
    expect small issues to happen. Also, llvm-gcc cannot build the mingw64
    runtime currently due
    to <a href="http://llvm.org/PR2255">several</a>
    <a href="http://llvm.org/PR2257">bugs</a> and due to lack of support for
    the
    'u' inline assembly constraint and for X87 floating point inline assembly.</li>
  <li>The X86-64 backend does not yet support the LLVM IR instruction
      <tt>va_arg</tt>. Currently, the llvm-gcc and front-ends support variadic
      argument constructs on X86-64 by lowering them manually.</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="ppc-be">Known problems with the PowerPC back-end</a>
</div>

<div class="doc_text">

<ul>
<li>The Linux PPC32/ABI support needs testing for the interpreter and static
compilation, and lacks support for debug information.</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="arm-be">Known problems with the ARM back-end</a>
</div>

<div class="doc_text">

<ul>
<li>Support for the Advanced SIMD (Neon) instruction set is still incomplete
and not well tested.  Some features may not work at all, and the code quality
may be poor in some cases.</li>
<li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
processors, thumb programs can crash or produce wrong
results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
<li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
</li>
<li>There is a bug in QEMU-ARM (&lt;= 0.9.0) which causes it to incorrectly
 execute
programs compiled with LLVM.  Please use more recent versions of QEMU.</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="sparc-be">Known problems with the SPARC back-end</a>
</div>

<div class="doc_text">

<ul>
<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
    support the 64-bit SPARC ABI (-m64).</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="mips-be">Known problems with the MIPS back-end</a>
</div>

<div class="doc_text">

<ul>
<li>The O32 ABI is not fully supported.</li>
<li>64-bit MIPS targets are not supported yet.</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="alpha-be">Known problems with the Alpha back-end</a>
</div>

<div class="doc_text">

<ul>

<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
appropriate nops inserted to ensure restartability.</li>

</ul>
</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c-be">Known problems with the C back-end</a>
</div>

<div class="doc_text">

<ul>
<li><a href="http://llvm.org/PR802">The C backend has only basic support for
    inline assembly code</a>.</li>
<li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
    C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
    C++ code compiled with <tt>llc</tt> or native compilers.</li>
<li>The C backend does not support all exception handling constructs.</li>
<li>The C backend does not support arbitrary precision integers.</li>
</ul>

</div>


<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c-fe">Known problems with the llvm-gcc C front-end</a>
</div>

<div class="doc_text">

<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
Optimization</a> on most platforms "out-of-the-box".  Please inquire on the
LLVMdev mailing list if you are interested.</p>

<p>The only major language feature of GCC not supported by llvm-gcc is
    the <tt>__builtin_apply</tt> family of builtins.   However, some extensions
    are only supported on some targets.  For example, trampolines are only
    supported on some targets (these are used when you take the address of a
    nested function).</p>

<p>If you run into GCC extensions which are not supported, please let us know.
</p>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c++-fe">Known problems with the llvm-gcc C++ front-end</a>
</div>

<div class="doc_text">

<p>The C++ front-end is considered to be fully
tested and works for a number of non-trivial programs, including LLVM
itself, Qt, Mozilla, etc.</p>

<ul>
<li>Exception handling works well on the X86 and PowerPC targets. Currently
  only Linux and Darwin targets are supported (both 32 and 64 bit).</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>
</div>

<div class="doc_text">
<ul>
<li>Fortran support generally works, but there are still several unresolved bugs
    in Bugzilla.  Please see the tools/gfortran component for details.</li>
</ul>
</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>
</div>

<div class="doc_text">
The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature
technology, and problems should be expected.
<ul>
<li>The Ada front-end currently only builds on X86-32.  This is mainly due
to lack of trampoline support (pointers to nested functions) on other platforms.
However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
which does support trampolines.</li>
<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style
exception handling, which is used internally by the compiler.
Workaround: configure with --disable-bootstrap.</li>
<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
(c380004 also fails with gcc-4.2 mainline).
If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a>
causes the compiler to go into an infinite loop, using up all system memory.</li>
<li>Some GCC specific Ada tests continue to crash the compiler.</li>
<li>The -E binder option (exception backtraces)
<a href="http://llvm.org/PR1982">does not work</a> and will result in programs
crashing if an exception is raised.  Workaround: do not use -E.</li>
<li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
or finish at a non-byte offset</a> in a record.  Workaround: do not pack records
or use representation clauses that result in a field of a non-discrete type
starting or finishing in the middle of a byte.</li>
<li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers
'main' as generated by the Ada binder to be invalid</a>.
Workaround: hand edit the file to use pointers for <tt>argv</tt> and
<tt>envp</tt> rather than integers.</li>
<li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is
ignored</a>.</li>
</ul>
</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="additionalinfo">Additional Information</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<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>

<!-- *********************************************************************** -->

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