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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 2.1 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.1 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#whatsnew">What's New?</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><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 2.1. Here we describe the status of LLVM, including
major improvements from the previous release and any 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 releases, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New?</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This is the twelfth public release of the LLVM Compiler Infrastructure.
It includes many features and refinements from LLVM 2.0.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="frontends">New Frontends</a>
</div>
<div class="doc_text">
<p>LLVM 2.1 brings two new beta C front-ends. First, a new version of llvm-gcc
based on GCC 4.2, innovatively called "llvm-gcc-4.2". This promises to bring
FORTRAN and Ada support to LLVM as well as features like atomic builtins and
OpenMP. None of these actually work yet, but don't let that stop you checking
it out!</p>
<p>Second, LLVM now includes its own native C and Objective-C front-end (C++ is
in progress, but is not very far along) code named "<a
href="http://clang.llvm.org/">clang</a>". This front-end has a number of great
features, primarily aimed at source-level analysis and speeding up compile-time.
At this point though, the LLVM Code Generator component is still very early in
development, so it's mostly useful for people looking to build source-level
analysis tools or source-to-source translators.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="optimizer">Optimizer Improvements</a>
</div>
<div class="doc_text">
<p>Some of the most noticable feature improvements this release have been in the
optimizer, speeding it up and making it more aggressive. For example:</p>
<ul>
<li>Owen Anderson wrote the new MemoryDependenceAnalysis pass, which provides
a lazy, caching layer on top of <a
href="AliasAnalysis.html">AliasAnalysis</a>. He then used it to rewrite
DeadStoreElimination which resulted in significantly better compile time in
common cases, </li>
<li>Owen implemented the new GVN pass, which is also based on
MemoryDependenceAnalysis. This pass replaces GCSE/LoadVN in the standard
set of passes, providing more aggressive optimization at a some-what
improved compile-time cost.</li>
<li>Owen implemented GVN-PRE, a partial redundancy elimination algorithm that
shares some details with the new GVN pass. It is still in need of compile
time tuning, and is not turned on by default.</li>
<li>Devang merged ETForest and DomTree into a single easier to use data
structure. This makes it more obvious which datastructure to choose
(because there is only one) and makes the compiler more memory and time
efficient (less stuff to keep up-to-date).</li>
<li>Nick Lewycky improved loop trip count analysis to handle many more common
cases.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="codegen">Code Generator Improvements</a>
</div>
<div class="doc_text">
<p>One of the main focuses of this release was performance tuning and bug
fixing. In addition to these, several new major changes occurred:</p>
<ul>
<li>Dale finished up the Tail Merging optimization in the code generator, and
enabled it by default. This produces smaller code that is also faster in
some cases.</li>
<li>Christopher Lamb implemented support for virtual register sub-registers,
which can be used to better model many forms of subregisters. As an example
use, he modified the X86 backend to use this to model truncates and
extends more accurately (leading to better code).</li>
<li>Dan Gohman changed the way we represent vectors before legalization,
significantly simplifying the SelectionDAG representation for these and
making the code generator faster for vector code.</li>
<li>Evan contributed a new target independent if-converter. While it is
target independent, so far only the ARM backend uses it.</li>
<li>Evan rewrite the way the register allocator handles rematerialization,
allowing it to be much more effective on two-address targets like X86,
and taught it to fold loads away when possible (also a big win on X86).</li>
<li>Dan Gohman contributed support for better alignment and volatility handling
in the code generator, and significantly enhanced alignment analysis for SSE
load/store instructions. With his changes, an insufficiently-aligned SSE
load instruction turns into <tt>movups</tt>, for example.</li>
<li>Duraid Madina contributed a new "bigblock" register allocator, and Roman
Levenstein contributed several big improvements. BigBlock is optimized for
code that uses very large basic blocks. It is slightly slower than the
"local" allocator, but produces much better code.</li>
<li>David Greene refactored the register allocator to split coalescing out from
allocation, making coalescers pluggable.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="targetspecific">Target Specific Improvements</a>
</div>
<div class="doc_text">
<p>New features include:
</p>
<ul>
<li>Bruno Cardoso Lopes contributed initial MIPS support. It is sufficient to
run many small programs, but is still incomplete and is not yet
fully performant.</li>
<li>Bill Wendling added SSSE3 support to the X86 backend.</li>
<li>Nicholas Geoffray contributed improved linux/ppc ABI and JIT support.</li>
<li>Dale Johannesen rewrote handling of 32-bit float values in the X86 backend
when using the floating point stack, fixing several nasty bugs.</li>
<li>Dan contributed rematerialization support for the X86 backend, in addition
to several X86-specific micro optimizations.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="llvmgccimprovements">llvm-gcc Improvements</a>
</div>
<div class="doc_text">
<p>New features include:
</p>
<ul>
<li>Duncan and Anton made significant progress chasing down a number of problems
with C++ Zero-Cost exception handling in llvm-gcc 4.0 and 4.2. It is now at
the point where it "just works" on linux/X86-32 and has partial support on
other targets.</li>
<li>Devang and Duncan fixed a huge number of bugs relating to bitfields, pragma
pack, and variable sized fields in structures.</li>
<li>Tanya implemented support for <tt>__attribute__((noinline))</tt> in
llvm-gcc, and added support for generic variable annotations which are
propagated into the LLVM IR, e.g.
"<tt>int X __attribute__((annotate("myproperty")));</tt>".</li>
<li>Sheng Zhou and Christopher Lamb implemented alias analysis support for
"restrict" pointer arguments to functions.</li>
<li>Duncan contributed support for trampolines (taking the address of a nested
function). Currently this is only supported on the X86-32 target.</li>
<li>Lauro Ramos Venancio contributed support to encode alignment info in
load and store instructions, the foundation for other alignment-related
work.</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>Neil Booth contributed a new "APFloat" class, which ensures that floating
point representation and constant folding is not dependent on the host
architecture that builds the application. This support is the foundation
for "long double" support that will be wrapped up in LLVM 2.2.</li>
<li>Based on the APFloat class, Dale redesigned the internals of the ConstantFP
class and has been working on extending the core and optimizer components to
support various target-specific 'long double's. We expect this work to be
completed in LLVM 2.2.</li>
<li>LLVM now provides an LLVMBuilder class, which makes it significantly easier
to create LLVM IR instructions.</li>
<li>Reid contributed support for intrinsics that take arbitrary integer typed
arguments. Dan Gohman and Chandler extended it to support arbitrary
floating point arguments and vectors.</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>Sterling Stein contributed a new BrainF frontend, located in llvm/examples.
This shows a some of the more modern APIs for building a front-end, and
demonstrates JIT compiler support.</li>
<li>David Green contributed a new <tt>--enable-expensive-checks</tt> configure
option which enables STL checking, and fixed several bugs exposed by
it.</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 running Red Hat Linux, Fedora Core and FreeBSD
(and probably other unix-like systems).</li>
<
|
