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Rafael Espindola 77b5251619 Some release notes. 
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2011-03-18 04:07:44 +00:00

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<title>LLVM 2.9 Release Notes</title>
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<body>
<div class="doc_title">LLVM 2.9 Release Notes</div>
<img align=right src="http://llvm.org/img/DragonSmall.png"
width="136" height="136" alt="LLVM Dragon Logo">
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#subproj">Sub-project Status Update</a></li>
<li><a href="#externalproj">External Projects Using LLVM 2.9</a></li>
<li><a href="#whatsnew">What's New in LLVM 2.9?</a></li>
<li><a href="GettingStarted.html">Installation Instructions</a></li>
<li><a href="#knownproblems">Known Problems</a></li>
<li><a href="#additionalinfo">Additional Information</a></li>
</ol>
<div class="doc_author">
<p>Written by the <a href="http://llvm.org">LLVM Team</a></p>
</div>
<h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.9
release.<br>
You may prefer the
<a href="http://llvm.org/releases/2.8/docs/ReleaseNotes.html">LLVM 2.8
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 2.9. 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://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's
Mailing List</a> is a good place to send them.</p>
<p>Note that if you are reading this file from a Subversion checkout or the
main LLVM web page, this document applies to the <i>next</i> release, not the
current one. To see the release notes for a specific release, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
<!-- NOTE: last release for llvm-gcc -->
<!--
Almost dead code.
lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.0.
-->
<!-- Features that need text if they're finished for 3.0:
combiner-aa?
strong phi elim
loop dependence analysis
TBAA
CorrelatedValuePropagation
-->
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="subproj">Sub-project Status Update</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>
The LLVM 2.9 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><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
C++, and Objective-C languages. Clang aims to provide a better user experience
through expressive diagnostics, a high level of conformance to language
standards, fast compilation, and low memory use. Like LLVM, Clang provides a
modular, library-based architecture that makes it suitable for creating or
integrating with other development tools. Clang is considered a
production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
(32- and 64-bit), and for darwin-arm targets.</p>
<p>In the LLVM 2.9 time-frame, the Clang team has made many improvements:</p>
<ul>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="clangsa">Clang Static Analyzer</a>
</div>
<div class="doc_text">
<p>The <a href="http://clang-analyzer.llvm.org/">Clang Static Analyzer</a>
project is an effort to use static source code analysis techniques to
automatically find bugs in C and Objective-C programs (and hopefully <a
href="http://clang-analyzer.llvm.org/dev_cxx.html">C++ in the
future</a>!). The tool is very good at finding bugs that occur on specific
paths through code, such as on error conditions.</p>
<p>The LLVM 2.9 release...
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="dragonegg">DragonEgg: llvm-gcc ported to gcc-4.5</a>
</div>
<div class="doc_text">
NOTE: This should be written to be self-contained without referencing llvm-gcc.
<p>
<a href="http://dragonegg.llvm.org/">DragonEgg</a> is a port of llvm-gcc to
gcc-4.5. Unlike llvm-gcc, dragonegg in theory does not require any gcc-4.5
modifications whatsoever (currently one small patch is needed) thanks to the
new <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin architecture</a>.
DragonEgg is a gcc plugin that makes gcc-4.5 use the LLVM optimizers and code
generators instead of gcc's, just like with llvm-gcc.
</p>
<p>
DragonEgg is still a work in progress, but it is able to compile a lot of code,
for example all of gcc, LLVM and clang. Currently Ada, C, C++ and Fortran work
well, while all other languages either don't work at all or only work poorly.
For the moment only the x86-32 and x86-64 targets are supported, and only on
linux and darwin (darwin may need additional gcc patches).
</p>
<p>
The 2.9 release has the following notable changes:
<ul>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="vmkit">VMKit: JVM 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 Java Virtual Machine (Java VM or JVM) that uses LLVM for static and
just-in-time compilation.
UPDATE.
</p>
</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.
NEW: MIT License as well.
New in LLVM 2.9, UPDATE</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="lldb">LLDB: Low Level Debugger</a>
</div>
<div class="doc_text">
<p>
<a href="http://lldb.llvm.org/">LLDB</a> is a brand new member of the LLVM
umbrella of projects. LLDB is a next generation, high-performance debugger. It
is built as a set of reusable components which highly leverage existing
libraries in the larger LLVM Project, such as the Clang expression parser, the
LLVM disassembler and the LLVM JIT.</p>
<p>
LLDB is in early development and not included as part of the LLVM 2.9 release,
UPDATE!
<!--
but is mature enough to support basic debugging scenarios on Mac OS X in C,
Objective-C and C++. We'd really like help extending and expanding LLDB to
support new platforms, new languages, new architectures, and new features.-->
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="libc++">libc++: C++ Standard Library</a>
</div>
<div class="doc_text">
<p>
<a href="http://libcxx.llvm.org/">libc++</a> is another new member of the LLVM
family. It is an implementation of the C++ standard library, written from the
ground up to specifically target the forthcoming C++'0X standard and focus on
delivering great performance.</p>
<p>
As of the LLVM 2.9 release, UPDATE!
<!--libc++ is virtually feature complete, but would
benefit from more testing and better integration with Clang++. It is also
looking forward to the C++ committee finalizing the C++'0x standard.-->
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="klee">KLEE: A Symbolic Execution Virtual Machine</a>
</div>
<div class="doc_text">
<p>
<a href="http://klee.llvm.org/">KLEE</a> is a symbolic execution framework for
programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths
through the application and records state transitions that lead to fault
states. This allows it to construct testcases that lead to faults and can even
be used to verify some algorithms.
</p>
<p>UPDATE!</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="externalproj">External Open Source Projects Using LLVM 2.9</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 2.9.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New in LLVM 2.9?</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 2.9 includes several major new capabilities:</p>
<ul>
</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>
</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>TBAA.</li>
<li>LTO has been improved to use MC for parsing inline asm and now
can build large programs like Firefox 4 on both OS X and Linux.</li>
</ul>
<!--
<p>In addition to these features that are done in 2.8, there is preliminary
support in the release for Type Based Alias Analysis
Preliminary work on TBAA but not usable in 2.8.
New CorrelatedValuePropagation pass, not on by default in 2.8 yet.
-->
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="mc">MC Level Improvements</a>
</div>
<div class="doc_text">
<p>
The LLVM Machine Code (aka MC) subsystem was created to solve a number
of problems in the realm of assembly, disassembly, object file format handling,
and a number of other related areas that CPU instruction-set level tools work
in.</p>
<ul>
<li>MC is now used by default for ELF systems on x86 and
x86-64.</li>
<li>MC supports and CodeGen uses the <tt>.loc</tt> directives for
producing line number debug info. This produces more compact line
tables.</li>
<li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
frame information, but it is still not used by CodeGen by default.</li>
<li>COFF support?</li>
</ul>
<p>For more information, please see the <a
href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the
LLVM MC Project Blog Post</a>.
</p>
</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>
<!-- SplitKit -->
FastISel for ARM.
</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 and major changes in the X86 target include:
</p>
<ul>
</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>
</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 2.8, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>
<ul>
</ul>
<p>In addition, many APIs have changed in this release. Some of the major LLVM
API changes are:</p>
<ul>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="devtree_changes">Development Infrastructure Changes</a>
</div>
<div class="doc_text">
<p>This section lists changes to the LLVM development infrastructure. This
mostly impacts users who actively work on LLVM or follow development on
mainline, but may also impact users who leverage the LLVM build infrastructure
or are interested in LLVM qualification.</p>
<ul>
</ul>
</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 Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, PTX, SystemZ
and XCore backends are experimental.</li>
<li><tt>llc</tt> "<tt>-filetype=obj</tt>" is experimental on all targets
other than darwin-i386 and darwin-x86_64. FIXME: Not true on ELF anymore?</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>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 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, 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>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">
<p>The C backend has numerous problems and is not being actively maintained.
Depending on it for anything serious is not advised.</p>
<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="llvm-gcc">Known problems with the llvm-gcc front-end</a>
</div>
<div class="doc_text">
<p>llvm-gcc is generally very stable for the C family of languages. 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>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. Note that llvm-gcc is missing major
Fortran performance work in the frontend and library that went into GCC after
4.2. If you are interested in Fortran, we recommend that you consider using
<a href="#dragonegg">dragonegg</a> instead.</p>
<p>The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being
actively maintained. If you are interested in Ada, we recommend that you
consider using <a href="#dragonegg">dragonegg</a> instead.</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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