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<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="llvm.css" type="text/css">
<title>LLVM 2.0 Release Notes</title>
<title>LLVM 2.1 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.0 Release Notes</div>
<div class="doc_title">LLVM 2.1 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 2.0. Here we describe the status of LLVM, including
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>
@ -44,10 +44,9 @@ 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 the current or previous releases, see the <a
href="http://llvm.org/releases/">releases page</a>.</p>
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>
@ -59,415 +58,196 @@ href="http://llvm.org/releases/">releases page</a>.</p>
<div class="doc_text">
<p>This is the eleventh public release of the LLVM Compiler Infrastructure.
Being the first major release since 1.0, this release is different in several
ways from our previous releases:</p>
<ol>
<li>We took this as an opportunity to
break backwards compatibility with the LLVM 1.x bytecode and .ll file format.
If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we
recommend the use of the stand alone <a href="#llvm-upgrade">llvm-upgrade</a>
tool (which is included with 2.0). We intend to keep compatibility with .ll
and .bc formats within the 2.x release series, like we did within the 1.x
series.</li>
<li>There are several significant change to the LLVM IR and internal APIs, such
as a major overhaul of the type system, the completely new bitcode file
format, etc (described below).</li>
<li>We designed the release around a 6 month release cycle instead of the usual
3-month cycle. This gave us extra time to develop and test some of the
more invasive features in this release.</li>
<li>LLVM 2.0 no longer supports the llvm-gcc3 front-end. Users are required to
upgrade to llvm-gcc4. llvm-gcc4 includes many features over
llvm-gcc3, is faster, and is <a href="CFEBuildInstrs.html">much easier to
build from source</a>.</li>
</ol>
<p>Note that while this is a major version bump, this release has been
extensively tested on a wide range of software. It is easy to say that this
is our best release yet, in terms of both features and correctness. This is
the first LLVM release to correctly compile and optimize major software like
LLVM itself, Mozilla/Seamonkey, Qt 4.3rc1, kOffice, etc out of the box on
linux/x86.
</p>
<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="newfeatures">New Features in LLVM 2.0</a>
<a name="frontends">New Frontends</a>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="majorchanges">Major Changes</a></div>
<div class="doc_text">
<p>Changes to the LLVM IR itself:</p>
<p>LLVM 2.1 brings two new beta C front-ends. First, Duncan, Anton and Devang
start syncing up llvm-gcc with GCC 4.2, yielding "llvm-gcc 4.2" (creative,
huh?). llvm-gcc 4.2 has the promise to bring much better FORTRAN and Ada
support to LLVM as well as features like atomic builtins, OpenMP, and many other
things. Check it out!</p>
<ul>
<li>Integer types are now completely signless. This means that we
have types like i8/i16/i32 instead of ubyte/sbyte/short/ushort/int
etc. LLVM operations that depend on sign have been split up into
separate instructions (<a href="http://llvm.org/PR950">PR950</a>). This
eliminates cast instructions that just change the sign of the operands (e.g.
int -> uint), which reduces the size of the IR and makes optimizers
simpler to write.</li>
<li>Integer types with arbitrary bitwidths (e.g. i13, i36, i42, i1057, etc) are
now supported in the LLVM IR and optimizations (<a
href="http://llvm.org/PR1043">PR1043</a>). However, neither llvm-gcc
(<a href="http://llvm.org/PR1284">PR1284</a>) nor the native code generators
(<a href="http://llvm.org/PR1270">PR1270</a>) support non-standard width
integers yet.</li>
<li>'Type planes' have been removed (<a href="http://llvm.org/PR411">PR411</a>).
It is no longer possible to have two values with the same name in the
same symbol table. This simplifies LLVM internals, allowing significant
speedups.</li>
<li>Global variables and functions in .ll files are now prefixed with
@ instead of % (<a href="http://llvm.org/PR645">PR645</a>).</li>
<li>The LLVM 1.x "bytecode" format has been replaced with a
completely new binary representation, named 'bitcode'. The <a
href="BitCodeFormat.html">Bitcode Format</a> brings a
number of advantages to the LLVM over the old bytecode format: it is denser
(files are smaller), more extensible, requires less memory to read,
is easier to keep backwards compatible (so LLVM 2.5 will read 2.0 .bc
files), and has many other nice features.</li>
<li>Load and store instructions now track the alignment of their pointer
(<a href="http://www.llvm.org/PR400">PR400</a>). This allows the IR to
express loads that are not sufficiently aligned (e.g. due to '<tt>#pragma
packed</tt>') or to capture extra alignment information.</li>
</ul>
<p>Major new features:</p>
<ul>
<li>A number of ELF features are now supported by LLVM, including 'visibility',
extern weak linkage, Thread Local Storage (TLS) with the <tt>__thread</tt>
keyword, and symbol aliases.
Among other things, this means that many of the special options needed to
configure llvm-gcc on linux are no longer needed, and special hacks to build
large C++ libraries like Qt are not needed.</li>
<li>LLVM now has a new MSIL backend. <tt>llc -march=msil</tt> will now turn LLVM
into MSIL (".net") bytecode. This is still fairly early development
with a number of limitations.</li>
<li>A new <a href="CommandGuide/html/llvm-upgrade.html">llvm-upgrade</a> tool
exists to migrates LLVM 1.9 .ll files to LLVM 2.0 syntax.</li>
</ul>
<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_subsubsection"><a name="llvmgccfeatures">llvm-gcc
Improvements</a></div>
<div class="doc_text">
<p>New features include:
</p>
<p>Some of the most noticable improvements this release have been in the
optimizer, speeding it up and making it more aggressive</p>
<ul>
<li>Precompiled Headers (PCH) are now supported.</li>
<li>"<tt>#pragma packed</tt>" is now supported, as are the various features
described above (visibility, extern weak linkage, __thread, aliases,
etc).</li>
<li>Tracking function parameter/result attributes is now possible.</li>
<li>Many internal enhancements have been added, such as improvements to
NON_LVALUE_EXPR, arrays with non-zero base, structs with variable sized
fields, VIEW_CONVERT_EXPR, CEIL_DIV_EXPR, nested functions, and many other
things. This is primarily to supports non-C GCC front-ends, like Ada.</li>
<li>It is simpler to configure llvm-gcc for linux.</li>
<li>Owen DSE and MemDep analysis</li>
<li>Owen GVN</li>
<li>Owen GVN-PRE, not in llvm-gcc</li>
<li>Devang merged ETForest and DomTree into a single easier to use data
structure.</li>
<li>Nick Lewycky improved loop trip count analysis to handle many more common
cases.</li>
</ul>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="optimizer">Optimizer
Improvements</a></div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="codegen">Code Generator Improvements</a>
</div>
<div class="doc_text">
<p>foo</p>
<ul>
<li>Dale finished up the Tail Merging optimization in the code generator,
enabling it by default. This produces smaller code that is also faster in some
cases.</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 remat rewrite (coallesced intervals + folding of remat'd loads) and
live intervals improvements.</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.</li>
<li>Christopher Lamb virtual register sub-register support, better truncates and
extends on X86.</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 coallescing out from
allocation, making coallescers 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>The <a href="WritingAnLLVMPass.html">pass manager</a> has been entirely
rewritten, making it significantly smaller, simpler, and more extensible.
Support has been added to run <tt>FunctionPass</tt>es interlaced with
<tt>CallGraphSCCPass</tt>es, we now support loop transformations
explicitly with <tt>LoopPass</tt>, and <tt>ModulePass</tt>es may now use the
result of <tt>FunctionPass</tt>es.</li>
<li>Bruno Cardoso Lopes contributed initial MIPS support.</li>
<li>Bill Wendling added SSSE3 support.</li>
<li>New Target independent if converter, ARM uses it so far</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.</li>
</ul>
</div>
<li>LLVM 2.0 includes a new loop rotation pass, which converts "for loops" into
"do/while loops", where the condition is at the bottom of the loop.</li>
<li>The Loop Strength Reduction pass has been improved, and we now support
sinking expressions across blocks to reduce register pressure.</li>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="llvmgccimprovements">llvm-gcc Improvements</a>
</div>
<li>The <tt>-scalarrepl</tt> pass can now promote unions containing FP values
into a register, it can also handle unions of vectors of the same
size.</li>
<div class="doc_text">
<p>New features include:
</p>
<li>The [Post]DominatorSet classes have been removed from LLVM and clients
switched to use the more-efficient ETForest class instead.</li>
<ul>
<li>Duncan and Anton exception handling in llvm-gcc 4.0/4.2</li>
<li>The ImmediateDominator class has also been removed, and clients have been
switched to use DominatorTree instead.</li>
<li>Devang and Duncan: Bitfields, pragma pack</li>
<li>The predicate simplifier pass has been improved, making it able to do
simple value range propagation and eliminate more conditionals. However,
note that predsimplify is not enabled by default in llvm-gcc.</li>
<li>Tanya implemented support for __attribute__((noinline)) 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' arguments to functions.</li>
<li>Duncan contributed support for trampolines (pointers to nested functions),
currently only supported on x86 target.</li>
</ul>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="codegen">Code
Generator Enhancements</a></div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="coreimprovements">LLVM Core Improvements</a>
</div>
<div class="doc_text">
<p>
New features include:
<p>New features include:
</p>
<ul>
<li>Neil Booth APFloat, foundation for long double support that will be wrapped
up in 2.2. Dale contributed most of long double support, will be enabled in
2.2.</li>
<li>LLVM now supports software floating point, which allows LLVM to target
chips that don't have hardware FPUs (e.g. ARM thumb mode).</li>
<li>LLVM now provides an LLVMBuilder class which makes it significantly easier
to create LLVM IR instructions.</li>
<li>A new register scavenger has been implemented, which is useful for
finding free registers after register allocation. This is useful when
rewriting frame references on RISC targets, for example.</li>
<li>Heuristics have been added to avoid coalescing vregs with very large live
ranges to physregs. This was bad because it effectively pinned the physical
register for the entire lifetime of the virtual register (<a
href="http://llvm.org/PR711">PR711</a>).</li>
<li>Support now exists for very simple (but still very useful)
rematerialization the register allocator, enough to move
instructions like "load immediate" and constant pool loads.</li>
<li>Switch statement lowering is significantly better, improving codegen for
sparse switches that have dense subregions, and implemented support
for the shift/and trick.</li>
<li>LLVM now supports tracking physreg sub-registers and super-registers
in the code generator, and includes extensive register
allocator changes to track them.</li>
<li>There is initial support for virtreg sub-registers
(<a href="http://llvm.org/PR1350">PR1350</a>).</li>
</ul>
<p>
Other improvements include:
</p>
<ul>
<li>Inline assembly support is much more solid that before.
The two primary features still missing are support for 80-bit floating point
stack registers on X86 (<a href="http://llvm.org/PR879">PR879</a>), and
support for inline asm in the C backend (<a
href="http://llvm.org/PR802">PR802</a>).</li>
<li>DWARF debug information generation has been improved. LLVM now passes
most of the GDB testsuite on MacOS and debug info is more dense.</li>
<li>Codegen support for Zero-cost DWARF exception handling has been added (<a
href="http://llvm.org/PR592">PR592</a>). It is mostly
complete and just in need of continued bug fixes and optimizations at
this point. However, support in llvm-g++ is disabled with an
#ifdef for the 2.0 release (<a
href="http://llvm.org/PR870">PR870</a>).</li>
<li>The code generator now has more accurate and general hooks for
describing addressing modes ("isLegalAddressingMode") to
optimizations like loop strength reduction and code sinking.</li>
<li>Progress has been made on a direct Mach-o .o file writer. Many small
apps work, but it is still not quite complete.</li>
</ul>
<p>In addition, the LLVM target description format has itself been extended in
several ways:</p>
<ul>
<li>TargetData now supports better target parameterization in
the .ll/.bc files, eliminating the 'pointersize/endianness' attributes
in the files (<a href="http://llvm.org/PR761">PR761</a>).</li>
<li>TargetData was generalized for finer grained alignment handling,
handling of vector alignment, and handling of preferred alignment</li>
<li>LLVM now supports describing target calling conventions
explicitly in .td files, reducing the amount of C++ code that needs
to be written for a port.</li>
</ul>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="specifictargets">Target-Specific
Improvements</a></div>
<div class="doc_text">
<p>X86-specific Code Generator Enhancements:
</p>
<ul>
<li>The MMX instruction set is now supported through intrinsics.</li>
<li>The scheduler was improved to better reduce register pressure on
X86 and other targets that are register pressure sensitive.</li>
<li>Linux/x86-64 support is much better.</li>
<li>PIC support for linux/x86 has been added.</li>
<li>The X86 backend now supports the GCC regparm attribute.</li>
<li>LLVM now supports inline asm with multiple constraint letters per operand
(like "mri") which is common in X86 inline asms.</li>
</ul>
<p>ARM-specific Code Generator Enhancements:</p>
<ul>
<li>The ARM code generator is now stable and fully supported.</li>
<li>There are major new features, including support for ARM
v4-v6 chips, vfp support, soft float point support, pre/postinc support,
load/store multiple generation, constant pool entry motion (to support
large functions), inline asm support, weak linkage support, static
ctor/dtor support and many bug fixes.</li>
<li>Added support for Thumb code generation (<tt>llc -march=thumb</tt>).</li>
<li>The ARM backend now supports the ARM AAPCS/EABI ABI and PIC codegen on
arm/linux.</li>
<li>Several bugs were fixed for DWARF debug info generation on arm/linux.</li>
</ul>
<p>PowerPC-specific Code Generator Enhancements:</p>
<ul>
<li>The PowerPC 64 JIT now supports addressing code loaded above the 2G
boundary.</li>
<li>Improved support for the Linux/ppc ABI and the linux/ppc JIT is fully
functional now. llvm-gcc and static compilation are not fully supported
yet though.</li>
<li>Many PowerPC 64 bug fixes.</li>
</ul>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="other">Other Improvements</a></div>
<div class="doc_text">
<p>More specific changes include:</p>
<ul>
<li>LLVM no longer relies on static destructors to shut itself down. Instead,
it lazily initializes itself and shuts down when <tt>llvm_shutdown()</tt> is
explicitly called.</li>
<li>LLVM now has significantly fewer static constructors, reducing startup time.
</li>
<li>Several classes have been refactored to reduce the amount of code that
gets linked into apps that use the JIT.</li>
<li>Construction of intrinsic function declarations has been simplified.</li>
<li>The gccas/gccld tools have been replaced with small shell scripts.</li>
<li>Support has been added to llvm-test for running on low-memory
or slow machines (make SMALL_PROBLEM_SIZE=1).</li>
</ul>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="apichanges">API Changes</a></div>
<div class="doc_text">
<p>LLVM 2.0 contains a revamp of the type system and several other significant
internal changes. If you are programming to the C++ API, be aware of the
following major changes:</p>
<ul>
<li>Pass registration is slightly different in LLVM 2.0 (you now need an
<tt>intptr_t</tt> in your constructor), as explained in the <a
href="WritingAnLLVMPass.html#basiccode">Writing an LLVM Pass</a>
document.</li>
<li><tt>ConstantBool</tt>, <tt>ConstantIntegral</tt> and <tt>ConstantInt</tt>
classes have been merged together, we now just have
<tt>ConstantInt</tt>.</li>
<li><tt>Type::IntTy</tt>, <tt>Type::UIntTy</tt>, <tt>Type::SByteTy</tt>, ... are
replaced by <tt>Type::Int8Ty</tt>, <tt>Type::Int16Ty</tt>, etc. LLVM types
have always corresponded to fixed size types
(e.g. long was always 64-bits), but the type system no longer includes
information about the sign of the type. Also, the
<tt>Type::isPrimitiveType()</tt> method now returns false for integers.</li>
<li>Several classes (<tt>CallInst</tt>, <tt>GetElementPtrInst</tt>,
<tt>ConstantArray</tt>, etc), that once took <tt>std::vector</tt> as
arguments now take ranges instead. For example, you can create a
<tt>GetElementPtrInst</tt> with code like:
<pre>
Value *Ops[] = { Op1, Op2, Op3 };
GEP = new GetElementPtrInst(BasePtr, Ops, 3);
</pre>
This avoids creation of a temporary vector (and a call to malloc/free). If
you have an <tt>std::vector</tt>, use code like this:
<pre>
std::vector&lt;Value*&gt; Ops = ...;
GEP = new GetElementPtrInst(BasePtr, &amp;Ops[0], Ops.size());
</pre>
</li>
<li><tt>CastInst</tt> is now abstract and its functionality is split into
several parts, one for each of the <a href="LangRef.html#convertops">new
cast instructions</a>.</li>
<li><tt>Instruction::getNext()/getPrev()</tt> are now private (along with
<tt>BasicBlock::getNext</tt>, etc), for efficiency reasons (they are now no
longer just simple pointers). Please use <tt>BasicBlock::iterator</tt>, etc
instead.
<li>Reid contributed support for intrinsics that take arbitrary integer typed
arguments, Dan Gohman and Chandler extended it to support FP and vectors.</li>
</li>
<li><tt>Module::getNamedFunction()</tt> is now called
<tt>Module::getFunction()</tt>.</li>
<li><tt>SymbolTable.h</tt> has been split into <tt>ValueSymbolTable.h</tt> and
<tt>TypeSymbolTable.h</tt>.</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>BrainF frontend by Sterling Stein.</li>
<li>David Green contributed a new --enable-expensive-checks configure option
which enables STL checking, and fixed several bugs exposed by it.</li>
</li>
</ul>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">