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llvm-mirror/docs/ReleaseNotes.html
Jeffrey Yasskin f7833b76ca Make --disable-libffi work on systems with libffi installed. Also 
make no-ffi the default even on systems with libffi.  This fixes
http://llvm.org/PR5018.

llvm-svn: 95712
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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 2.7 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.7 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 2.7</a></li>
<li><a href="#whatsnew">What's New in LLVM 2.7?</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>
<h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.7
release.<br>
You may prefer the
<a href="http://llvm.org/releases/2.6/docs/ReleaseNotes.html">LLVM 2.6
Release Notes</a>.</h1>
<!-- *********************************************************************** -->
<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 2.7. 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>
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include/llvm/Analysis/LiveValues.h => Dan
lib/Transforms/IPO/MergeFunctions.cpp => consider for 2.8.
llvm/Analysis/PointerTracking.h => Edwin wants this, consider for 2.8.
ABCD, SCCVN, GEPSplitterPass
MSIL backend?
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strong phi elim
variable debug info for optimized code
postalloc scheduler: anti dependence breaking, hazard recognizer?
metadata
loop dependence analysis
ELF Writer? How stable?
<li>PostRA scheduler improvements, ARM adoption (David Goodwin).</li>
2.7 supports the GDB 7.0 jit interfaces for debug info.
2.7 eliminates ADT/iterator.h
-->
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Logo web page.
llvm devmtg
compiler_rt
KLEE web page at klee.llvm.org
Many new papers added to /pubs/
Mention gcc plugin.
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<!-- *********************************************************************** -->
<div class="doc_section">
<a name="subproj">Sub-project Status Update</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>
The LLVM 2.7 distribution currently consists of code from the core LLVM
repository (which roughly includes the LLVM optimizers, code generators
and supporting tools), the Clang repository and the llvm-gcc 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>
</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 ...</p>
<p>In the LLVM 2.7 time-frame, the Clang team has made many improvements:</p>
<ul>
<li>...</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, 2.5, and 2.6 LLVM releases, 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 checks to find
bugs that occur on a specific path within a program.</p>
<p>In the LLVM 2.7 time-frame, the analyzer core has ...</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 Machine (Microsoft .NET is an
implementation of the CLI) using LLVM for static and just-in-time
compilation.</p>
<p>
VMKit version ?? builds with LLVM 2.7 and you can find it on its
<a href="http://vmkit.llvm.org/releases/">web page</a>. The release includes
bug fixes, cleanup and new features. The major changes are:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
</div>
<div class="doc_text">
<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>
All of the code in the compiler-rt project is available under the standard LLVM
License, a "BSD-style" license.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="klee">KLEE: Symbolic Execution and Automatic Test Case Generator</a>
</div>
<div class="doc_text">
<p>
The new LLVM <a href="http://klee.llvm.org/">KLEE project</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 algorithms. For more
details, please see the <a
href="http://llvm.org/pubs/2008-12-OSDI-KLEE.html">OSDI 2008 paper</a> about
KLEE.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="dragonegg">DragonEgg: GCC-4.5 as an LLVM frontend</a>
</div>
<div class="doc_text">
<p>
The goal of <a href="http://dragonegg.llvm.org/">DragonEgg</a> is to make
gcc-4.5 act like llvm-gcc without requiring any gcc modifications whatsoever.
<a href="http://dragonegg.llvm.org/">DragonEgg</a> is a shared library (dragonegg.so)
that is loaded by gcc at runtime. It ...
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="mc">llvm-mc: Machine Code Toolkit</a>
</div>
<div class="doc_text">
<p>
The LLVM Machine Code (MC) Toolkit project is ...
</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="externalproj">External Open Source Projects Using LLVM 2.7</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<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 2.7.</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 an environment
for running Ruby code which strives to write as much of the core class
implementation in Ruby as possible. Combined with a bytecode interpreting VM, it
uses LLVM to optimize and compile ruby code down to machine code. Techniques
such as type feedback, method inlining, and uncommon traps are all used to
remove dynamism from ruby execution and increase performance.</p>
<p>Since LLVM 2.5, Rubinius has made several major leaps forward, implementing
a counter based JIT, type feedback and speculative method inlining.
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="macruby">MacRuby</a>
</div>
<div class="doc_text">
<p>
<a href="http://macruby.org">MacRuby</a> is an implementation of Ruby on top of
core Mac OS X technologies, such as the Objective-C common runtime and garbage
collector and the CoreFoundation framework. It is principally developed by
Apple and aims at enabling the creation of full-fledged Mac OS X applications.
</p>
<p>
MacRuby uses LLVM for optimization passes, JIT and AOT compilation of Ruby
expressions. It also uses zero-cost DWARF exceptions to implement Ruby exception
handling.</p>
</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>Pure versions ??? and later have been tested and are known to work with
LLVM 2.7 (and continue to work with older LLVM releases >= 2.3 as well).
</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 bug fixes and better x86-64 support. This has allowed
some major improvements in LDC, getting it 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="UnladenSwallow">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="llvm-lua">llvm-lua</a>
</div>
<div class="doc_text">
<p>
<a href="http://code.google.com/p/llvm-lua/">LLVM-Lua</a> uses LLVM to add JIT
and static compiling support to the Lua VM. Lua bytecode is analyzed to
remove type checks, then LLVM is used to compile the bytecode down to machine
code.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="icedtea">IcedTea Java Virtual Machine Implementation</a>
</div>
<div class="doc_text">
<p>
<a href="http://icedtea.classpath.org/wiki/Main_Page">IcedTea</a> provides a
harness to build OpenJDK using only free software build tools and to provide
replacements for the not-yet free parts of OpenJDK. One of the extensions that
IcedTea provides is a new JIT compiler named <a
href="http://icedtea.classpath.org/wiki/ZeroSharkFaq">Shark</a> which uses LLVM
to provide native code generation without introducing processor-dependent
code.
</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New in LLVM 2.7?</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 2.7 includes several major new capabilities:</p>
<ul>
<li>...</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 for better support of new targets and that
expose new optimization opportunities:</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 large array of minor performance tweaks and bug fixes, this
release includes a few major enhancements and additions to the optimizers:</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="executionengine">Interpreter and JIT Improvements</a>
</div>
<div class="doc_text">
<ul>
<li>The JIT now <a
href="http://llvm.org/viewvc/llvm-project?view=rev&revision=85295">defaults
to compiling eagerly</a> to avoid a race condition in the lazy JIT.
Clients that still want the lazy JIT can switch it on by calling
<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>.</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>...</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>...</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>...</li>
</ul>
<p>Things not yet supported:</p>
<ul>
<li>Variable arguments.</li>
<li>Interrupts/programs.</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>...</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="OtherTarget">Other Target Specific Improvements</a>
</div>
<div class="doc_text">
<p>New features of other targets include:
</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="newapis">New Useful APIs</a>
</div>
<div class="doc_text">
<p>This release includes a number of new APIs that are used internally, which
may also be useful for external clients.
</p>
<ul>
<li>...</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="otherimprovements">Other Improvements and New Features</a>
</div>
<div class="doc_text">
<p>Other miscellaneous 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 2.6, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>
<ul>
<li>The LLVM interpreter now defaults to <em>not</em> using <tt>libffi</tt> even
if you have it installed. This makes it more likely that an LLVM built on one
system will work when copied to a similar system. To use <tt>libffi</tt>,
configure with <tt>--enable-libffi</tt>.
</li>
</ul>
<p>In addition, many APIs have changed in this release. Some of the major LLVM
API changes are:</p>
<ul>
<li><tt>ModuleProvider</tt> has been <a
href="http://llvm.org/viewvc/llvm-project?view=rev&revision=94686">removed</a>
and its methods moved to <tt>Module</tt> and <tt>GlobalValue</tt>.
Most clients can remove uses of <tt>ExistingModuleProvider</tt>,
replace <tt>getBitcodeModuleProvider</tt> with
<tt>getLazyBitcodeModule</tt>, and pass their <tt>Module</tt> to
functions that used to accept <tt>ModuleProvider</tt>. Clients who
wrote their own <tt>ModuleProvider</tt>s will need to derive from
<tt>GVMaterializer</tt> instead and use
<tt>Module::setMaterializer</tt> to attach it to a
<tt>Module</tt>.</li>
<li><tt>GhostLinkage</tt> has given up the ghost.
<tt>GlobalValue</tt>s that have not yet been read from their backing
storage have the same linkage they will have after being read in.
Clients must replace calls to
<tt>GlobalValue::hasNotBeenReadFromBitcode</tt> with
<tt>GlobalValue::isMaterializable</tt>.</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 x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.</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>The llvm-gcc bootstrap will fail with some versions of binutils (e.g. 2.15)
with a message of "<tt><a href="http://llvm.org/PR5004">Error: can not do 8
byte pc-relative relocation</a></tt>" when building C++ code. We intend to
fix this on mainline, but a workaround is to upgrade to binutils 2.17 or
later.</li>
<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="GettingStarted.html#brokengcc">Broken versions of GCC and other tools</a>.
However, A <a href="http://pkg.auroraux.org/GCC">Modern GCC Build</a>
for x86/x86-64 has been made available from the third party AuroraUX Project
that has been meticulously tested for bootstrapping LLVM &amp; 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, PIC16, Blackfin, MSP430 and SystemZ backends are
experimental.</li>
<li>The <tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only
supported value for this option. The ELF writer is experimental.</li>
<li>The implementation of Andersen's Alias Analysis has many known bugs.</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>
</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>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>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 <a href="http://llvm.org/bugs/">Bugzilla</a>. 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 <tt>--disable-bootstrap</tt>.</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 <tt>-E</tt> 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 <tt>-E</tt>.</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_subsection">
<a name="ocaml-bindings">Known problems with the O'Caml bindings</a>
</div>
<div class="doc_text">
<p>The <tt>Llvm.Linkage</tt> module is broken, and has incorrect values. Only
<tt>Llvm.Linkage.External</tt>, <tt>Llvm.Linkage.Available_externally</tt>, and
<tt>Llvm.Linkage.Link_once</tt> will be correct. If you need any of the other linkage
modes, you'll have to write an external C library in order to expose the
functionality. This has been fixed in the trunk.</p>
</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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