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@ -4,11 +4,11 @@
<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>
<title>LLVM 2.2 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.1 Release Notes</div>
<div class="doc_title">LLVM 2.2 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
@ -32,7 +32,7 @@
<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
infrastructure, release 2.2. 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>
@ -58,31 +58,35 @@ current one. To see the release notes for a specific releases, please see the
<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>
<p>This is the thirteenth public release of the LLVM Compiler Infrastructure.
It includes many features and refinements from LLVM 2.1.</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="frontends">New Frontends</a>
<a name="frontends">llvm-gcc 4.0, llvm-gcc 4.2, and clang</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>LLVM 2.2 fully supports both the llvm-gcc 4.0 and llvm-gcc 4.2 front-ends (in
LLVM 2.1, llvm-gcc 4.2 was beta). Since LLVM 2.1, the llvm-gcc 4.2 front-end
has made leaps and bounds and is now at least as good as 4.0 in virtually every
area, and is better in several areas (for example, exception handling
correctness). We strongly recommend that you migrate from llvm-gcc 4.0 to
llvm-gcc 4.2 in this release cycle because <b>LLVM 2.2 is the last release
that will support llvm-gcc 4.0</b>: LLVM 2.3 will only support the llvm-gcc
4.2 front-end.</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>
<p>The <a href="http://clang.llvm.org/">clang project</a> is an effort
to build a set of new front-end technology for the LLVM optimizer and code
generator. Currently, its C and Objective-C support is maturing nicely, and it
has advanced source-to-source analysis and transformation capabilities. If you
are interested in building source-level tools for C and Objective-C (and
eventually C++), you should take a look. However, note that clang is not an
official part of the LLVM 2.2 release. If you are interested in this project,
please see the web site and check it out from SVN head.</p>
</div>
@ -98,24 +102,7 @@ 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>
<li>.</li>
</ul>
@ -133,38 +120,7 @@ optimizer, speeding it up and making it more aggressive. For example:</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 rewrote 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>
<li>.</li>
</ul>
@ -181,19 +137,7 @@ optimizer, speeding it up and making it more aggressive. For example:</p>
</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>
<li>.</li>
</ul>
</div>
@ -209,28 +153,7 @@ optimizer, speeding it up and making it more aggressive. For example:</p>
</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>
<li>.</li>
</ul>
</div>
@ -246,22 +169,7 @@ optimizer, speeding it up and making it more aggressive. For example:</p>
</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>
<li>.</li>
</ul>
</div>
@ -276,13 +184,7 @@ optimizer, speeding it up and making it more aggressive. For example:</p>
</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>
<li>.</li>
</ul>
</div>
@ -300,7 +202,7 @@ optimizer, speeding it up and making it more aggressive. For example:</p>
<ul>
<li>Intel and AMD machines 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 10.2 and above in 32-bit and
<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
@ -350,11 +252,10 @@ components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/l
<ul>
<li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in a
future release.</li>
<li>The MSIL backend is experimental.</li>
<li>The IA64 code generator is experimental.</li>
<li>The Alpha backend is experimental.</li>
<li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
<tt>-filetype</tt> llc option.</li>
<li>The MSIL, IA64, Alpha, and MIPS backends are experimental.</li>
<li>The LLC "<tt>-filetype=asm</tt>" (the default) is the only supported
value for this option.</li>
<li>The llvmc tool is not supported.</li>
</ul>
</div>
@ -384,8 +285,6 @@ components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/l
<div class="doc_text">
<ul>
<li><a href="http://llvm.org/PR642">PowerPC backend does not correctly
implement ordered FP comparisons</a>.</li>
<li>The Linux PPC32/ABI support needs testing for the interpreter and static
compilation, and lacks support for debug information.</li>
</ul>
@ -515,10 +414,6 @@ llvmdev mailing list if you are interested.</p>
<div class="doc_text">
<ul>
<li><p>"long double" is silently transformed by the front-end into "double". There
is no support for floating point data types of any size other than 32 and 64
bits.</p></li>
<li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet.
See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p>
</li>
@ -623,29 +518,7 @@ tested and works for a number of non-trivial programs, including LLVM
itself, Qt, Mozilla, etc.</p>
<ul>
<li>Exception handling only works well on the linux/X86-32 target.
In some cases, illegally throwing an exception does not result
in a call to terminate.</li>
<!-- NO EH Support!
<li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
function and in the <tt>setjmp</tt> receiver function may not be run.
Objects in intervening stack frames will be destroyed, however (which is
better than most compilers).</li>
<li>The LLVM C++ front-end follows the <a
href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
This document, which is not Itanium specific, specifies a standard for name
mangling, class layout, v-table layout, RTTI formats, and other C++
representation issues. Because we use this API, code generated by the LLVM
compilers should be binary compatible with machine code generated by other
Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
<i>However</i>, the exception handling mechanism used by llvm-gcc3 is very
different from the model used in the Itanium ABI, so <b>exceptions will not
interact correctly</b>. </li>
-->
<li>Exception handling only works well on the X86 and PowerPC targets.</li>
</ul>
</div>