llvm-mirror/docs/ReleaseNotes.html

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<div class="doc_title">LLVM 2.5 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 2.5</a></li>
  <li><a href="#whatsnew">What's New in LLVM?</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 2.5.  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
  llc -enable-value-prop, 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?

 -->

 <!-- for announcement email:
   -->

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

<div class="doc_text">
<p>
The LLVM 2.5 distribution currently consists of code from the core LLVM
repository (which roughly includes the LLVM optimizers, code generators and
supporting tools) 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 2.5 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 applications for X86-32 and X86-64,
including <a href="http://wiki.freebsd.org/BuildingFreeBSDWithClang">the FreeBSD
kernel</a>.  C++ is also making <a
href="http://clang.llvm.org/cxx_status.html">incredible progress</a>, and work
on templates has recently started.</p>

<p>While Clang is not yet production quality, it is progressing very nicely and
is quite usable for building many C and Objective-C applications.  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 2.5 time-frame, the Clang team has made many improvements:</p>

<ul>
<li>Clang now has a new driver, which is focused on providing a GCC-compatible
    interface.</li>
<li>The X86-64 ABI is now supported.</li>
<li>Precompiled header support is now implemented.</li>
<li>Objective-C support is significantly improved beyond LLVM 2.4, supporting
    many features, such as Objective-C Garbage Collection.</li>
<li>Many many bugs are fixed.</li>
</div>

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

<div class="doc_text">

<p>Previously announced in the last 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 2.5 time-frame there have been many significant improvements to
the analyzer's core path simulation engine and machinery for generating
path-based bug reports to end-users. Particularly noteworthy improvements
include experimental support for full field-sensitivity and reasoning about heap
objects as well as an improved value-constraints subengine that does a much
better job of reasoning about inequality relationships (e.g., <tt>x &gt; 2</tt>)
between variables and constants.

<p>The set of checks performed by the static analyzer continue 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 2.5, VMKit has its first 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>Ahead of Time compiler: compiles .class files to llvm .bc. VMKit uses this
functionality to native compile the standard classes (eg java.lang.String).
Users can compile AOT .class files into dynamic libraries and run them with the
help of VMKit.</li>

<li>New exception model: the dwarf exception model is very slow for
exception-intensive applications, so the JVM has had a new implementation of
exceptions which check at each function call if an exception happened. There is
a low performance penalty on applications without exceptions, but it is a big
gain for exception-intensive applications. For example the jack benchmark in
Spec JVM98 is 6x faster (performance gain of 83%).</li>

<li>New support for OSX/X64, Linux/X64 (with the Boehm GC), Linux/ppc32.</li>

</ul>
</div>

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<div class="doc_section">
  <a name="externalproj">External Projects Using LLVM 2.5</a>
</div>
<!-- *********************************************************************** -->

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

<div class="doc_text">
<p>
http://pure-lang.googlecode.com/
</p>

<p>
Pure 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>
http://www.dsource.org/projects/ldc
</p>

<p>
I'd like to inform that the LDC project (LLVM D
Compiler) is working with release 2.5 of LLVM. In fact we've required
2.5 in our trunk since the release was branched.
The improvements in 2.5 have fixed a lot of problems with LDC, more
specifically the new inline asm constraints, better debug info
support, general bugfixes :) and better x86-64 support have 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>http://code.roadsend.com/rphp</p>

<p>Roadsend PHP is using LLVM for code generation. This is an open source
project.
</p>
</div>


<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="whatsnew">What's New in LLVM?</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 2.5 includes several major new capabilities:</p>

<ul>
<li><p>The code generator now supports arbitrary precision integers.
Types like <tt>i33</tt> have long been valid in the LLVM IR, but previously
could only be used with the interpreter.
Now IR using such types can be compiled to native code on all targets.
All operations are supported if the integer is not bigger than twice the
target machine word size.
Simple operations like loads, stores and shifts by a constant amount are
supported for integers of any size.
</p></li>

<!--
Random stuff:

Pure project: http://code.google.com/p/pure-lang/


xcore backend!
fortran on darwin!

.ll parser rewrite, caret diags, better errors, less fragile (less likely to
   crash on strange things).  No longer depends on flex/bison.
GCC inliner off, llvm handles always-inline.
cmake mature?
x86 backend GS segment -> addr space 256 (r62980)
nocapture
addreadattrs pass renamed to functionattrs; now calculates nocapture
memdep (used by GVN and memcpyopt) is faster / more aggressive.
how to write a backend doc docs/WritingAnLLVMBackend.html
fastisel + exception handling
vector widening <3 x float> -> <4 x float>
arm port improvements? arm jit encoding stuff, constant island support?
JIT TLS support on x86-32 but not x86-64.
mem2reg now faster on code with huge basic blocks
stack protectors/stack canaries, -fstack-protector, controllable on a
  per-function basis with attributes.
shufflevector is generalized to allow different shuffle mask width than its
  input vectors.
loop optimizer improves floating point induction variables
llvm/Analysis/DebugInfo.h classes, llvm-gcc and clang and codegen use them.
    DebugInfoBuilder gone.
asmprinters seperate from targets for jits
PBQP register allocator now supports register coalescing.
JIT supports exceptions on linux/x86-64 and linux/x86-64.
integer overflow intrinsics for [us](add/sub/mul).  Supported on all targets,
  but only generates efficient code on x86.
X86 backend now supports -disable-mmx.
noalias attribute on return value indicates that function returns new memory
  (e.g. malloc).
Jump threading more powerful: it is iterative, handles threading based on values
  with fully redundant and partially redundant loads.
LSR improvements?
ARM debug info support?
unit test framework based on Google Test.

vector shift support + X86 backend.
x86 JIT now detects core i7 and atom, autoconfiguring itself appropriately.
SROA is more aggressive about promoting unions.
non-zero __builtin_return_address values on X86.
x86-64 now uses red zone (unless -mno-red-zone option is specified).
private linkage.

llvm-gcc defaults to -fno-math-errno on all x86 targets.

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

</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>?</li>
</ul>

</div>


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

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

<ul>
<li>?</li>

</ul>

</div>

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

<div class="doc_text">

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

<ul>

<li>?</li>

</ul>

</div>

<!--=========================================================================-->
<div class="doc_subsection">
<a name="codegen">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>The type legalization logic has been completely rewritten, and is now
more powerful (it supports arbitrary precision integer types for example)
and hopefully more correct.
The type legalizer converts operations on types that are not natively
supported by the target machine into equivalent code sequences that only use
natively supported types.
The old type legalizer is still available and will be used if
<tt>-disable-legalize-types</tt> is passed to <tt>llc</tt>.
</li>
<li>?</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>Both direct and indirect load/stores work now.</li>
<li>Logical, bitwise and conditional operations now work for integer data
types.</li>
<li>Function calls involving basic types work now.</li>
<li>Support for integer arrays.</li>
<li>Compiler can now emit libcalls for operations not support by m/c insns.</li>
<li>Support for both data and rom address spaces.</li>
</li>
</ul>

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

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

</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="othertargetspecific">Other Target Specific Improvements</a>
</div>

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

<ul>
<li>?</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>Beginning with LLVM 2.5, <tt>llvmc2</tt> is known as
 just <tt>llvmc</tt>. The old <tt>llvmc</tt> driver was removed.</li>

<li>The Clang plugin was substantially improved and is now enabled
 by default. The command <tt>llvmc --clang</tt> can be now used as a
 synonym to <tt>ccc</tt>.</li>

<li>There is now a <tt>--check-graph</tt> option which is supposed to catch
 common errors like multiple default edges, mismatched output/input language
 names and cycles. In general, these checks can't be done at compile-time
 because of the need to support plugins.</li>

<li>Plugins are now more flexible and can refer to compilation graph nodes and
 options defined in other plugins. To manage dependencies, a priority-sorting
 mechanism was introduced. This change affects the TableGen file syntax; see the
 documentation for details.</li>

<li>Hooks can now be provided with arguments. The syntax is "<tt>$CALL(MyHook,
 'Arg1', 'Arg2', 'Arg #3')</tt>".</li>

<li>A new option type: multi-valued option, for options that take more than one
 argument (for example, "<tt>-foo a b c</tt>").</li>

<li>New option properties: '<tt>one_or_more</tt>', '<tt>zero_or_more</tt>',
'<tt>hidden</tt>' and '<tt>really_hidden</tt>'.</li>

<li>The '<tt>case</tt>' expression gained an '<tt>error</tt>' action and
 an '<tt>empty</tt>' test (equivalent to "<tt>(not (not_empty ...))</tt>").</li>

<li>Documentation now looks more consistent to the rest of the LLVM
 docs. There is also a man page now.</li>

</ul>

</div>


<!--=========================================================================-->
<div class="doc_subsection">
<a name="otherimprovements">Other Improvements</a>
</div>

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

<ul>
<li>?</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 2.4, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>

<ul>

<li>?</li>
</ul>


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

<ul>
<li>?</li>
</ul>

<li>?</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 and FreeBSD (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>
<li>Itanium-based (IA64) machines running Linux and HP-UX.</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>

</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, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li>
<li>The llc "<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 mingw64 runtime
    currently due
    to <a href="http://llvm.org/PR2255">several</a>
    <a href="http://llvm.org/PR2257">bugs</a> due to lack of support for the
    'u' inline assembly constraint and 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 front-end supports 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>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="ia64-be">Known problems with the IA64 back-end</a>
</div>

<div class="doc_text">

<ul>
<li>The Itanium backend is highly experimental, and has a number of known
    issues.  We are looking for a maintainer for the Itanium backend.  If you
    are interested, please contact the LLVMdev mailing list.</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 llc 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>

<li>The Fortran front-end currently does not build on Darwin (without tweaks)
    due to unresolved dependencies on the C front-end.</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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