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Commit 35813136 authored by Chandler Carruth's avatar Chandler Carruth
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Fully merge mainline release notes onto the release branch. 

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......@@ -45,7 +45,8 @@ Release Notes</a>.</h1>
<p>This document contains the release notes for the LLVM Compiler
Infrastructure, release 3.0. Here we describe the status of LLVM, including
major improvements from the previous release and significant known problems.
major improvements from the previous release, improvements in various
subprojects of LLVM, and some of the current users of the code.
All LLVM releases may be downloaded from
the <a href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
......@@ -61,16 +62,8 @@ Release Notes</a>.</h1>
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
<!-- Features that need text if they're finished for 3.1:
ARM EHABI
combiner-aa?
strong phi elim
loop dependence analysis
CorrelatedValuePropagation
lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
-->
<!-- *********************************************************************** -->
<h2>
<a name="subproj">Sub-project Status Update</a>
......@@ -81,7 +74,7 @@ Release Notes</a>.</h1>
<p>The LLVM 3.0 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
supporting tools), and the Clang 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>
......@@ -99,37 +92,55 @@ Release Notes</a>.</h1>
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 3.0 time-frame, the Clang team has made many improvements:</p>
(32- and 64-bit), and for Darwin/ARM targets.</p>
<p>In the LLVM 3.0 time-frame, the Clang team has made many improvements:
<ul>
<li>Greatly improved support for building C++ applications, with greater
stability and better diagnostics.</li>
<li><a href="http://clang.llvm.org/cxx_status.html">Improved support</a> for
the <a href="http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=50372">C++
2011</a> standard, including implementations of non-static data member
initializers, alias templates, delegating constructors, the range-based
for loop, and implicitly-generated move constructors and move assignment
2011</a> standard (aka "C++'0x"), including implementations of non-static data member
initializers, alias templates, delegating constructors, range-based
for loops, and implicitly-generated move constructors and move assignment
operators, among others.</li>
<li>Implemented support for some features of the upcoming C1x standard,
including static assertions and generic selections.</li>
<li>Better detection of include and linking paths for system headers and
libraries, especially for Linux distributions.</li>
<li>Implemented support
for <a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">Automatic
Reference Counting</a> for Objective-C.</li>
<li>Several improvements to Objective-C support, including:
<ul>
<li><a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">
Automatic Reference Counting</a> (ARC) and an improved memory model
cleanly separating object and C memory.</li>
<li>A migration tool for moving manual retain/release code to ARC</li>
<li>Better support for data hiding, allowing instance variables to be
declared in implementation contexts or class extensions</li>
<li>Weak linking support for Objective-C classes</li>
<li>Improved static type checking by inferring the return type of methods
such as +alloc and -init.</li>
</ul>
Some new Objective-C features require either the Mac OS X 10.7 / iOS 5
Objective-C runtime, or version 1.6 or later of the GNUstep Objective-C
runtime version.</li>
<li>Implemented a number of optimizations in <tt>libclang</tt>, the Clang C
interface, to improve the performance of code completion and the mapping
from source locations to abstract syntax tree nodes.</li>
</ul>
For more details about the changes to Clang since the 2.9 release, see the
<a href="http://clang.llvm.org/docs/ReleaseNotes.html">Clang release notes</a>
</p>
<p>If Clang rejects your code but another compiler accepts it, please take a
look at the <a href="http://clang.llvm.org/compatibility.html">language
compatibility</a> guide to make sure this is not intentional or a known
......@@ -145,19 +156,31 @@ Release Notes</a>.</h1>
<div>
<p><a href="http://dragonegg.llvm.org/">DragonEgg</a> is a
<a href="http://gcc.gnu.org/wiki/plugins">gcc plugin</a> that replaces GCC's
optimizers and code generators with LLVM's. Currently it requires a patched
version of gcc-4.5. The plugin can target the x86-32 and x86-64 processor
families and has been used successfully on the Darwin, FreeBSD and Linux
platforms. The Ada, C, C++ and Fortran languages work well. The plugin is
capable of compiling plenty of Obj-C, Obj-C++ and Java but it is not known
whether the compiled code actually works or not!</p>
optimizers and code generators with LLVM's. It works with gcc-4.5 or gcc-4.6,
targets the x86-32 and x86-64 processor families, and has been successfully
used on the Darwin, FreeBSD, KFreeBSD, Linux and OpenBSD platforms. It fully
supports Ada, C, C++ and Fortran. It has partial support for Go, Java, Obj-C
and Obj-C++.</p>
<p>The 3.0 release has the following notable changes:</p>
<ul>
<!--
<li></li>
-->
<ul>
<li>GCC version 4.6 is now fully supported.</li>
<li>Patching and building GCC is no longer required: the plugin should work
with your system GCC (version 4.5 or 4.6; on Debian/Ubuntu systems the
gcc-4.5-plugin-dev or gcc-4.6-plugin-dev package is also needed).</li>
<li>The <tt>-fplugin-arg-dragonegg-enable-gcc-optzns</tt> option, which runs
GCC's optimizers as well as LLVM's, now works much better. This is the
option to use if you want ultimate performance! It is still experimental
though: it may cause the plugin to crash. Setting the optimization level
to <tt>-O4</tt> when using this option will optimize even harder, though
this usually doesn't result in any improvement over <tt>-O3<tt>.</li>
<li>The type and constant conversion logic has been almost entirely rewritten,
fixing a multitude of obscure bugs.</li>
</ul>
</div>
......@@ -178,7 +201,9 @@ Release Notes</a>.</h1>
implementations of this and other low-level routines (some are 3x faster than
the equivalent libgcc routines).</p>
<p>In the LLVM 3.0 timeframe,</p>
<p>In the LLVM 3.0 timeframe, the target specific ARM code has converted to
"unified" assembly syntax, and several new functions have been added to the
library.</p>
</div>
......@@ -189,6 +214,11 @@ Release Notes</a>.</h1>
<div>
<p>LLDB is a ground-up implementation of a command line debugger, as well as a
debugger API that can be used from other applications. LLDB makes use of the
Clang parser to provide high-fidelity expression parsing (particularly for
C++) and uses the LLVM JIT for target support.</p>
<p>LLDB has advanced by leaps and bounds in the 3.0 timeframe. It is
dramatically more stable and useful, and includes both a
new <a href="http://lldb.llvm.org/tutorial.html">tutorial</a> and
......@@ -208,6 +238,44 @@ Release Notes</a>.</h1>
licensed</a> under the MIT and UIUC license, allowing it to be used more
permissively.</p>
<p>Libc++ has been ported to FreeBSD and imported into the base system. It is
planned to be the default STL implementation for FreeBSD 10.</p>
</div>
<!--=========================================================================-->
<h3>
<a name="vmkit">VMKit</a>
</h3>
<div>
<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.
<p>In the LLVM 3.0 time-frame, VMKit has had significant improvements on both
runtime and startup performance:</p>
<ul>
<li>Precompilation: by compiling ahead of time a small subset of Java's core
library, the startup performance have been highly optimized to the point that
running a 'Hello World' program takes less than 30 milliseconds.</li>
<li>Customization: by customizing virtual methods for individual classes,
the VM can statically determine the target of a virtual call, and decide to
inline it.</li>
<li>Inlining: the VM does more inlining than it did before, by allowing more
bytecode instructions to be inlined, and thanks to customization. It also
inlines GC barriers, and object allocations.</li>
<li>New exception model: the generated code for a method that does not do
any try/catch is not penalized anymore by the eventuality of calling a
method that throws an exception. Instead, the method that throws the
exception jumps directly to the method that could catch it.</li>
</ul>
</div>
......@@ -227,23 +295,7 @@ Release Notes</a>.</h1>
</div>
<!--=========================================================================-->
<h3>
<a name="vmkit">VMKit</a>
</h3>
<div>
<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. As of LLVM 3.0, VMKit now supports generational
garbage collectors. The garbage collectors are provided by the MMTk
framework, and VMKit can be configured to use one of the numerous implemented
collectors of MMTk.</p>
</div>
<!--=========================================================================-->
<!--
<h3>
......@@ -278,7 +330,7 @@ be used to verify some algorithms.
<!--=========================================================================-->
<h3>AddressSanitizer</h3>
<div>
<p><a href="http://code.google.com/p/address-sanitizer/">AddressSanitizer</a>
......@@ -291,7 +343,7 @@ be used to verify some algorithms.
<!--=========================================================================-->
<h3>ClamAV</h3>
<div>
<p><a href="http://www.clamav.net">Clam AntiVirus</a> is an open source (GPL)
......@@ -300,14 +352,25 @@ be used to verify some algorithms.
<p>Since version 0.96 it
has <a href="http://vrt-sourcefire.blogspot.com/2010/09/introduction-to-clamavs-low-level.html">bytecode
signatures</a> that allow writing detections for complex malware.</p>
<p>It uses LLVM's JIT to speed up the execution of bytecode on X86, X86-64,
signatures</a> that allow writing detections for complex malware.
It uses LLVM's JIT to speed up the execution of bytecode on X86, X86-64,
PPC32/64, falling back to its own interpreter otherwise. The git version was
updated to work with LLVM 3.0.</p>
</div>
<!--=========================================================================-->
<h3>clang_complete for VIM</h3>
<div>
<p><a href="https://github.com/Rip-Rip/clang_complete">clang_complete</a> is a
VIM plugin, that provides accurate C/C++ autocompletion using the clang front
end. The development version of clang complete, can directly use libclang
which can maintain a cache to speed up auto completion.</p>
</div>
<!--=========================================================================-->
<h3>clReflect</h3>
......@@ -328,8 +391,8 @@ be used to verify some algorithms.
<div>
<p><a href="http://cern.ch/cling">Cling</a> is an interactive compiler interface
(aka C++ interpreter). It uses LLVM's JIT and clang; it currently supports
C++ and C. It has a prompt interface, runs source files, calls into shared
(aka C++ interpreter). It supports C++ and C, and uses LLVM's JIT and the
Clang parser. It has a prompt interface, runs source files, calls into shared
libraries, prints the value of expressions, even does runtime lookup of
identifiers (dynamic scopes). And it just behaves like one would expect from
an interpreter.</p>
......@@ -337,21 +400,52 @@ be used to verify some algorithms.
</div>
<!--=========================================================================-->
<!-- FIXME: Comment out
<h3>Crack Programming Language</h3>
<div>
<p>
<a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide the
ease of development of a scripting language with the performance of a compiled
language. The language derives concepts from C++, Java and Python, incorporating
object-oriented programming, operator overloading and strong typing.</p>
<p><a href="http://code.google.com/p/crack-language/">Crack</a> aims to provide
the ease of development of a scripting language with the performance of a
compiled language. The language derives concepts from C++, Java and Python,
incorporating object-oriented programming, operator overloading and strong
typing.</p>
</div>
<!--=========================================================================-->
<h3>Eero</h3>
<div>
<p><a href="http://eerolanguage.org/">Eero</a> is a fully
header-and-binary-compatible dialect of Objective-C 2.0, implemented with a
patched version of the Clang/LLVM compiler. It features a streamlined syntax,
Python-like indentation, and new operators, for improved readability and
reduced code clutter. It also has new features such as limited forms of
operator overloading and namespaces, and strict (type-and-operator-safe)
enumerations. It is inspired by languages such as Smalltalk, Python, and
Ruby.</p>
</div>
<!--=========================================================================-->
<h3>FAUST Real-Time Audio Signal Processing Language</h3>
<div>
<p><a href="http://faust.grame.fr/">FAUST</a> is a compiled language for
real-time audio signal processing. The name FAUST stands for Functional
AUdio STream. Its programming model combines two approaches: functional
programming and block diagram composition. In addition with the C, C++, Java
output formats, the Faust compiler can now generate LLVM bitcode, and works
with LLVM 2.7-3.0.
</p>
</div>
-->
<!--=========================================================================-->
<h3>Glasgow Haskell Compiler (GHC)</h3>
<div>
<p>GHC is an open source, state-of-the-art programming suite for Haskell, a
......@@ -402,6 +496,38 @@ object-oriented programming, operator overloading and strong typing.</p>
</div>
<!--=========================================================================-->
<h3>ispc: The Intel SPMD Program Compiler</h3>
<div>
<p><a href="http://ispc.github.com">ispc</a> is a compiler for "single program,
multiple data" (SPMD) programs. It compiles a C-based SPMD programming
language to run on the SIMD units of CPUs; it often delivers 5-6x speedups on
a single core of a CPU with an 8-wide SIMD unit compared to serial code,
while still providing a clean and easy-to-understand programming model. For
an introduction to the language and its performance,
see <a href="http://ispc.github.com/example.html">the walkthrough</a> of a short
example program. ispc is licensed under the BSD license.</p>
</div>
<!--=========================================================================-->
<h3>The Julia Programming Language</h3>
<div>
<p><a href="http://github.com/JuliaLang/julia">Julia</a> is a high-level,
high-performance dynamic language for technical
computing. It provides a sophisticated compiler, distributed parallel
execution, numerical accuracy, and an extensive mathematical function
library. The compiler uses type inference to generate fast code
without any type declarations, and uses LLVM's optimization passes and
JIT compiler. The language is designed around multiple dispatch,
giving programs a large degree of flexibility. It is ready for use on many
kinds of problems.</p>
</div>
<!--=========================================================================-->
<h3>LanguageKit and Pragmatic Smalltalk</h3>
......@@ -413,7 +539,7 @@ object-oriented programming, operator overloading and strong typing.</p>
its own interpreter. Pragmatic Smalltalk is a dialect of Smalltalk, built on
top of LanguageKit, that interfaces directly with Objective-C, sharing the
same object representation and message sending behaviour. These projects are
developed as part of the &Eacute;toi&eacute; desktop environment.</p>
developed as part of the &Eacute;toil&eacute; desktop environment.</p>
</div>
......@@ -439,8 +565,24 @@ object-oriented programming, operator overloading and strong typing.</p>
binary compatible with Microsoft.NET. Has an optional, dynamically-loaded
LLVM code generation backend in Mini, the JIT compiler.</p>
<p>Note that we use a Git mirror of LLVM with some patches. See:
https://github.com/mono/llvm</p>
<p>Note that we use a Git mirror of LLVM <a
href="https://github.com/mono/llvm">with some patches</a>.</p>
</div>
<!--=========================================================================-->
<h3>Polly</h3>
<div>
<p><a href="http://polly.grosser.es">Polly</a> is an advanced data-locality
optimizer and automatic parallelizer. It uses an advanced, mathematical
model to calculate detailed data dependency information which it uses to
optimize the loop structure of a program. Polly can speed up sequential code
by improving memory locality and consequently the cache use. Furthermore,
Polly is able to expose different kind of parallelism which it exploits by
introducing (basic) OpenMP and SIMD code. A mid-term goal of Polly is to
automatically create optimized GPU code.</p>
</div>
......@@ -459,7 +601,7 @@ object-oriented programming, operator overloading and strong typing.</p>
<!--=========================================================================-->
<h3>Pure</h3>
<div>
<p><a href="http://pure-lang.googlecode.com/">Pure</a> is an
algebraic/functional programming language based on term rewriting. Programs
......@@ -472,7 +614,7 @@ object-oriented programming, operator overloading and strong typing.</p>
languages (including the ability to load LLVM bitcode modules, and inline C,
C++, Fortran and Faust code in Pure programs if the corresponding LLVM-enabled
compilers are installed).</p>
<p>Pure version 0.48 has been tested and is known to work with LLVM 3.0
(and continues to work with older LLVM releases &gt;= 2.5).</p>
......@@ -533,7 +675,7 @@ object-oriented programming, operator overloading and strong typing.</p>
co-design flow from C/C++ programs down to synthesizable VHDL and parallel
program binaries. Processor customization points include the register files,
function units, supported operations, and the interconnection network.</p>
<p>TCE uses Clang and LLVM for C/C++ language support, target independent
optimizations and also for parts of code generation. It generates new
LLVM-based code generators "on the fly" for the designed TTA processors and
......@@ -541,7 +683,7 @@ object-oriented programming, operator overloading and strong typing.</p>
per-target recompilation of larger parts of the compiler chain.</p>
</div>
<!--=========================================================================-->
<h3>Tart Programming Language</h3>
......@@ -577,107 +719,6 @@ object-oriented programming, operator overloading and strong typing.</p>
</div>
<!--=========================================================================-->
<h3>The ZooLib C++ Cross-Platform Application Framework</h3>
<div>
<p><a href="http://www.zoolib.org/">ZooLib</a> is Open Source under the MIT
License. It provides GUI, filesystem access, TCP networking, thread-safe
memory management, threading and locking for Mac OS X, Classic Mac OS,
Microsoft Windows, POSIX operating systems with X11, BeOS, Haiku, Apple's iOS
and Research in Motion's BlackBerry.</p>
<p>My current work is to use CLang's static analyzer to improve ZooLib's code
quality. I also plan to set up LLVM compiles of the demo programs and test
programs using CLang and LLVM on all the platforms that CLang, LLVM and
ZooLib all support.</p>
</div>
<!--=========================================================================-->
<!--
<h3>PinaVM</h3>
<div>
<p><a href="http://gitorious.org/pinavm/pages/Home">PinaVM</a> is an open
source, <a href="http://www.systemc.org/">SystemC</a> front-end. Unlike many
other front-ends, PinaVM actually executes the elaboration of the
program analyzed using LLVM's JIT infrastructure. It later enriches the
bitcode with SystemC-specific information.</p>
</div>
-->
<!--=========================================================================-->
<!--
<h3 id="icedtea">IcedTea Java Virtual Machine Implementation</h3>
<div>
<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>
<p> OpenJDK 7 b112, IcedTea6 1.9 and IcedTea7 1.13 and later have been tested
and are known to work with LLVM 3.0 (and continue to work with older LLVM
releases &gt;= 2.6 as well).</p>
</div>
-->
<!--=========================================================================-->
<!--
<h3>Polly - Polyhedral optimizations for LLVM</h3>
<div>
<p>Polly is a project that aims to provide advanced memory access optimizations
to better take advantage of SIMD units, cache hierarchies, multiple cores or
even vector accelerators for LLVM. Built around an abstract mathematical
description based on Z-polyhedra, it provides the infrastructure to develop
advanced optimizations in LLVM and to connect complex external optimizers. In
its first year of existence Polly already provides an exact value-based
dependency analysis as well as basic SIMD and OpenMP code generation support.
Furthermore, Polly can use PoCC(Pluto) an advanced optimizer for data-locality
and parallelism.</p>
</div>
-->
<!--=========================================================================-->
<!--
<h3>Rubinius</h3>
<div>
<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 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 deoptimization are all used to remove dynamism
from ruby execution and increase performance.</p>
</div>
-->
<!--=========================================================================-->
<!--
<h3>
<a name="FAUST">FAUST Real-Time Audio Signal Processing Language</a>
</h3>
<div>
<p>
<a href="http://faust.grame.fr">FAUST</a> is a compiled language for real-time
audio signal processing. The name FAUST stands for Functional AUdio STream. Its
programming model combines two approaches: functional programming and block
diagram composition. In addition with the C, C++, JAVA output formats, the
Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7-3.0.</p>
</div>
-->
</div>
<!-- *********************************************************************** -->
......@@ -699,18 +740,71 @@ Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7-3.0.</p>
<div>
<p>LLVM 3.0 includes several major new capabilities:</p>
<!-- Features that need text if they're finished for 3.1:
ARM EHABI
combiner-aa?
strong phi elim
loop dependence analysis
CorrelatedValuePropagation
lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.1.
Integrated assembler on by default for arm/thumb?
<ul>
-->
<!--
<li></li>
-->
<!-- Near dead:
Analysis/RegionInfo.h + Dom Frontiers
SparseBitVector: used in LiveVar.
llvm/lib/Archive - replace with lib object?
-->
<p>LLVM 3.0 includes several major changes and big features:</p>
<ul>
<li>llvm-gcc is no longer supported, and not included in the release. We
recommend switching to <a
href="http://clang.llvm.org/">Clang</a> or <a
href="http://dragonegg.llvm.org/">DragonEgg</a>.</li>
<li>The linear scan register allocator has been replaced with a new "greedy"
register allocator, enabling live range splitting and many other
optimizations that lead to better code quality. Please see its <a
href="http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html">blog post</a> or its talk at the <a
href="http://llvm.org/devmtg/2011-11/">Developer Meeting</a>
for more information.</li>
<li>LLVM IR now includes full support for <a href="Atomics.html">atomics
memory operations</a> intended to support the C++'11 and C'1x memory models.
This includes <a href="LangRef.html#memoryops">atomic load and store,
compare and exchange, and read/modify/write instructions</a> as well as a
full set of <a href="LangRef.html#ordering">memory ordering constraints</a>.
Please see the <a href="Atomics.html">Atomics Guide</a> for more
information.
</li>
<li>The LLVM IR exception handling representation has been redesigned and
reimplemented, making it more elegant, fixing a huge number of bugs, and
enabling inlining and other optimizations. Please see its <a href=
"http://blog.llvm.org/2011/11/llvm-30-exception-handling-redesign.html">blog
post</a> and the <a href="ExceptionHandling.html">Exception Handling
documentation</a> for more information.</li>
<li>The LLVM IR Type system has been redesigned and reimplemented, making it
faster and solving some long-standing problems.
Please see its <a
href="http://blog.llvm.org/2011/11/llvm-30-type-system-rewrite.html">blog
post</a> for more information.</li>
<li>The MIPS backend has made major leaps in this release, going from an
experimental target to being virtually production quality and supporting a
wide variety of MIPS subtargets. See the <a href="#MIPS">MIPS section</a>
below for more information.</li>
<li>The optimizer and code generator now supports gprof and gcov-style coverage
and profiling information, and includes a new llvm-cov tool (but also works
with gcov). Clang exposes coverage and profiling through GCC-compatible
command line options.</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="coreimprovements">LLVM IR and Core Improvements</a>
......@@ -721,117 +815,27 @@ Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7-3.0.</p>
<p>LLVM IR has several new features for better support of new targets and that
expose new optimization opportunities:</p>
<p>One of the biggest changes is that 3.0 has a new exception handling
system. The old system used LLVM intrinsics to convey the exception handling
information to the code generator. It worked in most cases, but not
all. Inlining was especially difficult to get right. Also, the intrinsics
could be moved away from the <code>invoke</code> instruction, making it hard
to recover that information.</p>
<p>The new EH system makes exception handling a first-class member of the IR. It
adds two new instructions:</p>
<ul>
<li><a href="LangRef.html#i_landingpad"><code>landingpad</code></a> &mdash;
this instruction defines a landing pad basic block. It contains all of the
information that's needed by the code generator. It's also required to be
the first non-PHI instruction in the landing pad. In addition, a landing
pad may be jumped to only by the unwind edge of an <code>invoke</code>
instruction.</li>
<li><a href="LangRef.html#i_resume"><code>resume</code></a> &mdash; this
instruction causes the current exception to resume traveling up the
stack. It replaces the <code>@llvm.eh.resume</code> intrinsic.</li>
</ul>
<p>Converting from the old EH API to the new EH API is rather simple, because a
lot of complexity has been removed. The two intrinsics,
<code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code> have been
superceded by the <code>landingpad</code> instruction. Instead of generating
a call to <code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code>:
<div class="doc_code">
<pre>
Function *ExcIntr = Intrinsic::getDeclaration(TheModule,
Intrinsic::eh_exception);
Function *SlctrIntr = Intrinsic::getDeclaration(TheModule,
Intrinsic::eh_selector);
// The exception pointer.
Value *ExnPtr = Builder.CreateCall(ExcIntr, "exc_ptr");
std::vector&lt;Value*&gt; Args;
Args.push_back(ExnPtr);
Args.push_back(Builder.CreateBitCast(Personality,
Type::getInt8PtrTy(Context)));
<i>// Add selector clauses to Args.</i>
// The selector call.
Builder.CreateCall(SlctrIntr, Args, "exc_sel");
</pre>
</div>
<p>You should instead generate a <code>landingpad</code> instruction, that
returns an exception object and selector value:</p>
<div class="doc_code">
<pre>
LandingPadInst *LPadInst =
Builder.CreateLandingPad(StructType::get(Int8PtrTy, Int32Ty, NULL),
Personality, 0);
Value *LPadExn = Builder.CreateExtractValue(LPadInst, 0);
Builder.CreateStore(LPadExn, getExceptionSlot());
Value *LPadSel = Builder.CreateExtractValue(LPadInst, 1);
Builder.CreateStore(LPadSel, getEHSelectorSlot());
</pre>
</div>
<p>It's now trivial to add the individual clauses to the <code>landingpad</code>
instruction.</p>
<div class="doc_code">
<pre>
<i><b>// Adding a catch clause</b></i>
Constant *TypeInfo = getTypeInfo();
LPadInst-&gt;addClause(TypeInfo);
<i><b>// Adding a C++ catch-all</b></i>
LPadInst-&gt;addClause(Constant::getNullValue(Builder.getInt8PtrTy()));
<i><b>// Adding a cleanup</b></i>
LPadInst-&gt;setCleanup(true);
<i><b>// Adding a filter clause</b></i>
std::vector&lt;Constant*&gt; TypeInfos;
Constant *TypeInfo = getFilterTypeInfo();
TypeInfos.push_back(Builder.CreateBitCast(TypeInfo, Builder.getInt8PtrTy()));
ArrayType *FilterTy = ArrayType::get(Int8PtrTy, TypeInfos.size());
LPadInst-&gt;addClause(ConstantArray::get(FilterTy, TypeInfos));
</pre>
</div>
<p>Converting from using the <code>@llvm.eh.resume</code> intrinsic to
the <code>resume</code> instruction is trivial. It takes the exception
pointer and exception selector values returned by
the <code>landingpad</code> instruction:</p>
<div class="doc_code">
<pre>
Type *UnwindDataTy = StructType::get(Builder.getInt8PtrTy(),
Builder.getInt32Ty(), NULL);
Value *UnwindData = UndefValue::get(UnwindDataTy);
Value *ExcPtr = Builder.CreateLoad(getExceptionObjSlot());
Value *ExcSel = Builder.CreateLoad(getExceptionSelSlot());
UnwindData = Builder.CreateInsertValue(UnwindData, ExcPtr, 0, "exc_ptr");
UnwindData = Builder.CreateInsertValue(UnwindData, ExcSel, 1, "exc_sel");
Builder.CreateResume(UnwindData);
</pre>
</div>
<ul>
<li><a href="Atomics.html">Atomic memory accesses and memory ordering</a> are
now directly expressible in the IR.</li>
<li>A new <a href="LangRef.html#int_fma">llvm.fma intrinsic</a> directly
represents floating point multiply accumulate operations without an
intermediate rounding stage.</li>
<li>A new llvm.expect intrinsic allows a frontend to express expected control
flow (and the __builtin_expect builtin from GNU C).</li>
<li>The <a href="LangRef.html#int_prefetch">llvm.prefetch intrinsic</a> now
takes a 4th argument that specifies whether the prefetch happens from the
icache or dcache.</li>
<li>The new <a href="LangRef.html#uwtable">uwtable function attribute</a>
allows a frontend to control emission of unwind tables.</li>
<li>The new <a href="LangRef.html#fnattrs">nonlazybind function
attribute</a> allow optimization of Global Offset Table (GOT) accesses.</li>
<li>The new <a href="LangRef.html#returns_twice">returns_twice attribute</a>
allows better modeling of functions like setjmp.</li>
<li>The <a href="LangRef.html#datalayout">target datalayout</a> string can now
encode the natural alignment of the target's stack for better optimization.
</li>
</ul>
</div>
<!--=========================================================================-->
......@@ -841,16 +845,40 @@ Builder.CreateResume(UnwindData);
<div>
<p>In addition to a large array of minor performance tweaks and bug fixes, this
<p>In addition to many minor performance tweaks and bug fixes, this
release includes a few major enhancements and additions to the
optimizers:</p>
<ul>
<!--
<li></li>
-->
</li>
<li>The pass manager now has an extension API that allows front-ends and plugins
to insert their own optimizations in the well-known places in the standard
pass optimization pipeline.</li>
<li>Information about <a href="BranchWeightMetadata.html">branch probability</a>
and basic block frequency is now available within LLVM, based on a
combination of static branch prediction heuristics and
<code>__builtin_expect</code> calls. That information is currently used for
register spill placement and if-conversion, with additional optimizations
planned for future releases. The same framework is intended for eventual
use with profile-guided optimization.</li>
<li>The "-indvars" induction variable simplification pass only modifies
induction variables when profitable. Sign and zero extension
elimination, linear function test replacement, loop unrolling, and
other simplifications that require induction variable analysis have
been generalized so they no longer require loops to be rewritten into
canonical form prior to optimization. This new design
preserves more IR level information, avoids undoing earlier loop
optimizations (particularly hand-optimized loops), and no longer
requires the code generator to reconstruct loops into an optimal form -
an intractable problem.</li>
<li>LLVM now includes a pass to optimize retain/release calls for the
<a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">Automatic
Reference Counting</a> (ARC) Objective-C language feature (in
lib/Transforms/Scalar/ObjCARC.cpp). It is a decent example of implementing
a source-language-specific optimization in LLVM.</li>
</ul>
</div>
......@@ -865,18 +893,37 @@ Builder.CreateResume(UnwindData);
<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>
in. 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>
<ul>
<!--
<li></li>
-->
<li>The MC layer has undergone significant refactoring to eliminate layering
violations that caused it to pull in the LLVM compiler backend code.</li>
<li>The ELF object file writers are much more full featured.</li>
<li>The integrated assembler now supports #line directives.</li>
<li>An early implementation of a JIT built on top of the MC framework (known
as MC-JIT) has been implemented and will eventually replace the old JIT.
It emits object files direct to memory and uses a runtime dynamic linker to
resolve references and drive lazy compilation. The MC-JIT enables much
greater code reuse between the JIT and the static compiler and provides
better integration with the platform ABI as a result.
</li>
<li>The assembly printer now makes uses of assemblers instruction aliases
(InstAliases) to print simplified mneumonics when possible.</li>
<li>TableGen can now autogenerate MC expansion logic for pseudo
instructions that expand to multiple MC instructions (through the
PseudoInstExpansion class).</li>
<li>A new llvm-dwarfdump tool provides a start of a drop-in
replacement for the corresponding tool that use LLVM libraries. As part of
this, LLVM has the beginnings of a dwarf parsing library.</li>
<li>llvm-objdump has more output including, symbol by symbol disassembly,
inline relocations, section headers, symbol tables, and section contents.
Support for archive files has also been added.</li>
<li>llvm-nm has gained support for archives of binary files.</li>
<li>llvm-size has been added. This tool prints out section sizes.</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>
<!--=========================================================================-->
......@@ -891,9 +938,30 @@ Builder.CreateResume(UnwindData);
make it run faster:</p>
<ul>
<!--
<li></li>
-->
<li>LLVM can now produce code that works with libgcc
to <a href="SegmentedStacks.html">dynamically allocate stack
segments</a>, as opposed to allocating a worst-case chunk of
virtual memory for each thread.</li>
<li>LLVM generates substantially better code for indirect gotos due to a new
tail duplication pass, which can be a substantial performance win for
interpreter loops that use them.</li>
<li>Exception handling and debug frame information is now emitted with CFI
directives. This lets the assembler produce more compact info as it knows
the final offsets, yielding <a href="http://blog.mozilla.com/respindola/2011/05/12/cfi-directives/">much smaller executables</a> for some C++ applications.
If the system assembler doesn't support it, MC exands the directives when
the integrated assembler is not used.
</li>
<li>The code generator now supports vector "select" operations on vector
comparisons, turning them into various optimized code sequences (e.g.
using the SSE4/AVX "blend" instructions).</li>
<li>The SSE execution domain fix pass and the ARM NEON move fix pass have been
merged to a target independent execution dependency fix pass. This pass is
used to select alternative equivalent opcodes in a way that minimizes
execution domain crossings. Closely connected instructions are moved to
the same execution domain when possible. Targets can override the
<code>getExecutionDomain</code> and <code>setExecutionDomain</code> hooks
to use the pass.</li>
</ul>
</div>
......@@ -907,13 +975,30 @@ Builder.CreateResume(UnwindData);
<p>New features and major changes in the X86 target include:</p>
<ul>
<li>The CRC32 intrinsics have been renamed. The intrinsics were previously
<code>@llvm.x86.sse42.crc32.[8|16|32]</code>
and <code>@llvm.x86.sse42.crc64.[8|64]</code>. They have been renamed to
<code>@llvm.x86.sse42.crc32.32.[8|16|32]</code> and
<code>@llvm.x86.sse42.crc32.64.[8|64]</code>.</li>
<li>The X86 backend, assembler and disassembler now have full support for AVX 1.
To enable it pass <code>-mavx</code> to the compiler. AVX2 implementation is
underway on mainline.</li>
<li>The integrated assembler and disassembler now support a broad range of new
instructions including Atom, Ivy Bridge, <a
href="http://en.wikipedia.org/wiki/SSE4a">SSE4a/BMI</a> instructions, <a
href="http://en.wikipedia.org/wiki/RdRand">rdrand</a> and many others.</li>
<li>The X86 backend now fully supports the <a href="http://llvm.org/PR879">X87
floating point stack inline assembly constraints</a>.</li>
<li>The integrated assembler now supports the <tt>.code32</tt> and
<tt>.code64</tt> directives to switch between 32-bit and 64-bit
instructions.</li>
<li>The X86 backend now synthesizes horizontal add/sub instructions from generic
vector code when the appropriate instructions are enabled.</li>
<li>The X86-64 backend generates smaller and faster code at -O0 due to
improvements in fast instruction selection.</li>
<li><a href="http://code.google.com/p/nativeclient/">Native Client</a>
subtarget support has been added.</li>
<li>The CRC32 intrinsics have been renamed. The intrinsics were previously
<code>@llvm.x86.sse42.crc32.[8|16|32]</code>
and <code>@llvm.x86.sse42.crc64.[8|64]</code>. They have been renamed to
<code>@llvm.x86.sse42.crc32.32.[8|16|32]</code> and
<code>@llvm.x86.sse42.crc32.64.[8|64]</code>.</li>
</ul>
</div>
......@@ -928,26 +1013,78 @@ Builder.CreateResume(UnwindData);
<p>New features of the ARM target include:</p>
<ul>
<!--
<li></li>
-->
<li>The ARM backend generates much faster code for Cortex-A9 chips.</li>
<li>The ARM backend has improved support for Cortex-M series processors.</li>
<li>The ARM inline assembly constraints have been implemented and are now fully
supported.</li>
<li>NEON code produced by Clang often runs much faster due to improvements in
the Scalar Replacement of Aggregates pass.</li>
<li>The old ARM disassembler is replaced with a new one based on autogenerated
encoding information from ARM .td files.</li>
<li>The integrated assembler has made major leaps forward, but is still beta quality in LLVM 3.0.</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="OtherTS">Other Target Specific Improvements</a>
<a name="MIPS">MIPS Target Improvements</a>
</h3>
<div>
<p>This release has seen major new work on just about every aspect of the MIPS
backend. Some of the major new features include:</p>
<ul>
<li>Most MIPS32r1 and r2 instructions are now supported.</li>
<li>LE/BE MIPS32r1/r2 has been tested extensively.</li>
<li>O32 ABI has been fully tested.</li>
<li>MIPS backend has migrated to using the MC infrastructure for assembly printing. Initial support for direct object code emission has been implemented too.</li>
<li>Delay slot filler has been updated. Now it tries to fill delay slots with useful instructions instead of always filling them with NOPs.</li>
<li>Support for old-style JIT is complete.</li>
<li>Support for old architectures (MIPS1 and MIPS2) has been removed.</li>
<li>Initial support for MIPS64 has been added.</li>
</ul>
</div>
<!--=========================================================================-->
<h3>
<a name="PTX">PTX Target Improvements</a>
</h3>
<p>PPC32/ELF va_arg was implemented.</p>
<p>PPC32 initial support for .o file writing was implemented.</p>
<div>
<p>
The PTX back-end is still experimental, but is fairly usable for compute kernels
in LLVM 3.0. Most scalar arithmetic is implemented, as well as intrinsics to
access the special PTX registers and sync instructions. The major missing
pieces are texture/sampler support and some vector operations.</p>
<p>That said, the backend is already being used for domain-specific languages
and can be used by Clang to
<a href="http://clang.llvm.org/docs/ReleaseNotes.html#opencl">compile OpenCL
C code</a> into PTX.</p>
</div>
<!--=========================================================================-->
<h3>
<a name="OtherTS">Other Target Specific Improvements</a>
</h3>
<div>
<ul>
<!--
<li></li>
-->
<li>Many PowerPC improvements have been implemented for ELF targets, including
support for varargs and initial support for direct .o file emission.</li>
<li>MicroBlaze scheduling itineraries were added that model the
3-stage and the 5-stage pipeline architectures. The 3-stage
pipeline model can be selected with <code>-mcpu=mblaze3</code>
and the 5-stage pipeline model can be selected with
<code>-mcpu=mblaze5</code>.</li>
</ul>
</div>
......@@ -964,19 +1101,31 @@ Builder.CreateResume(UnwindData);
from the previous release.</p>
<ul>
<li>The <code>LLVMC</code> front end code was removed while separating
out language independence.</li>
<li>The <code>LowerSetJmp</code> pass wasn't used effectively by any
target and has been removed.</li>
<li>LLVM 3.0 removes support for reading LLVM 2.8 and earlier files, and LLVM
3.1 will eliminate support for reading LLVM 2.9 files. Going forward, we
aim for all future versions of LLVM to read bitcode files and .ll files
produced by LLVM 3.0.</li>
<li>Tablegen has been split into a library, allowing the clang tblgen pieces
to now live in the clang tree. The llvm version has been renamed to
llvm-tblgen instead of tblgen.</li>
<li>The <code>LLVMC</code> meta compiler driver was removed.</li>
<li>The unused PostOrder Dominator Frontiers and LowerSetJmp passes were removed.</li>
<li>The old <code>TailDup</code> pass was not used in the standard pipeline
and was unable to update ssa form, so it has been removed.
<li>The syntax of volatile loads and stores in IR has been changed to
"<code>load volatile</code>"/"<code>store volatile</code>". The old
syntax ("<code>volatile load</code>"/"<code>volatile store</code>")
is still accepted, but is now considered deprecated.</li>
<li>The old atomic intrinscs (<code>llvm.memory.barrier</code> and
is still accepted, but is now considered deprecated and will be removed in
3.1.</li>
<li>llvm-gcc's frontend tests have been removed from llvm/test/Frontend*, sunk
into the clang and dragonegg testsuites.</li>
<li>The old atomic intrinsics (<code>llvm.memory.barrier</code> and
<code>llvm.atomic.*</code>) are now gone. Please use the new atomic
instructions, described in the <a href="Atomics.html">atomics guide</a>.
<li>LLVM's configure script doesn't depend on llvm-gcc anymore, eliminating a
strange circular dependence between projects.</li>
</ul>
<h4>Windows (32-bit)</h4>
......@@ -1002,10 +1151,15 @@ Builder.CreateResume(UnwindData);
LLVM API changes are:</p>
<ul>
<li>The biggest and most pervasive change is that llvm::Type's are no longer
returned or accepted as 'const' values. Instead, just pass around
non-const Type's.</li>
<li>The biggest and most pervasive change is that the type system has been
rewritten: <code>PATypeHolder</code> and <code>OpaqueType</code> are gone,
and all APIs deal with <code>Type*</code> instead of <code>const
Type*</code>. If you need to create recursive structures, then create a
named structure, and use <code>setBody()</code> when all its elements are
built. Type merging and refining is gone too: named structures are not
merged with other structures, even if their layout is identical. (of
course anonymous structures are still uniqued by layout).</li>
<li><code>PHINode::reserveOperandSpace</code> has been removed. Instead, you
must specify how many operands to reserve space for when you create the
PHINode, by passing an extra argument
......@@ -1079,15 +1233,6 @@ Builder.CreateResume(UnwindData);
use <code>DIBuilder::finalize()</code> at the end of translation unit to
complete debugging information encoding.</li>
<li>The way the type system works has been
rewritten: <code>PATypeHolder</code> and <code>OpaqueType</code> are gone,
and all APIs deal with <code>Type*</code> instead of <code>const
Type*</code>. If you need to create recursive structures, then create a
named structure, and use <code>setBody()</code> when all its elements are
built. Type merging and refining is gone too: named structures are not
merged with other structures, even if their layout is identical. (of
course anonymous structures are still uniqued by layout).</li>
<li>TargetSelect.h moved to Support/ from Target/</li>
<li>UpgradeIntrinsicCall no longer upgrades pre-2.9 intrinsic calls (for
......@@ -1114,223 +1259,180 @@ Builder.CreateResume(UnwindData);
<div>
<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>
<!-- ======================================================================= -->
<h3>
<a name="experimental">Experimental features included with this release</a>
</h3>
<div>
<p>LLVM is generally a production quality compiler, and is used by a broad range
of applications and shipping in many products. That said, not every
subsystem is as mature as the aggregate, particularly the more obscure
targets. 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 or ask on the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev
list</a>.</p>
<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>
<p>Known problem areas include:</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 and ELF X86 systems.</li>
</ul>
</div>
<!-- ======================================================================= -->
<h3>
<a name="x86-be">Known problems with the X86 back-end</a>
</h3>
<div>
<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 X86-64 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>
<li>Windows x64 (aka Win64) code generator has a few issues.
<ul>
<li>llvm-gcc cannot build the mingw-w64 runtime currently due to lack of
support for the 'u' inline assembly constraint and for X87 floating
point inline assembly.</li>
<li>On mingw-w64, you will see unresolved symbol <tt>__chkstk</tt> due
to <a href="http://llvm.org/bugs/show_bug.cgi?id=8919">Bug 8919</a>.
It is fixed
in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">r128206</a>.</li>
<li>Miss-aligned MOVDQA might crash your program. It is due to
<a href="http://llvm.org/bugs/show_bug.cgi?id=9483">Bug 9483</a>, lack
of handling aligned internal globals.</li>
</ul>
<li>The Alpha, Blackfin, CellSPU, MSP430, PTX, SystemZ and
XCore backends are experimental, and the Alpha, Blackfin and SystemZ
targets have already been removed from mainline.</li>
<li>The integrated assembler, disassembler, and JIT is not supported by
several targets. If an integrated assembler is not supported, then a
system assembler is required. For more details, see the <a
href="CodeGenerator.html#targetfeatures">Target Features Matrix</a>.
</li>
<li>The C backend has numerous problems and is not being actively maintained.
Depending on it for anything serious is not advised.</li>
</ul>
</div>
<!-- ======================================================================= -->
<h3>
<a name="ppc-be">Known problems with the PowerPC back-end</a>
</h3>
<div>
<ul>
<li>The PPC32/ELF support lacks PIC support.</li>
</ul>
</div>
<!-- ======================================================================= -->
<h3>
<a name="arm-be">Known problems with the ARM back-end</a>
</h3>
<!-- *********************************************************************** -->
<h2>
<a name="additionalinfo">Additional Information</a>
</h2>
<!-- *********************************************************************** -->
<div>
<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>
<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>
<li>Compilation for ARM Linux OABI (old ABI) is supported but not fully
tested.</li>
</ul>
<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>
<!-- ======================================================================= -->
<h3>
<a name="sparc-be">Known problems with the SPARC back-end</a>
</h3>
<div>
<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>
<!--=========================================================================-->
<!-- ======================================================================= -->
<h3>
<a name="mips-be">Known problems with the MIPS back-end</a>
</h3>
<!-- EH details: to be moved to a blog post:
<div>
<ul>
<li>64-bit MIPS targets are not supported yet.</li>
</ul>
</div>
<!-- ======================================================================= -->
<h3>
<a name="alpha-be">Known problems with the Alpha back-end</a>
</h3>
<p>One of the biggest changes is that 3.0 has a new exception handling
system. The old system used LLVM intrinsics to convey the exception handling
information to the code generator. It worked in most cases, but not
all. Inlining was especially difficult to get right. Also, the intrinsics
could be moved away from the <code>invoke</code> instruction, making it hard
to recover that information.</p>
<div>
<p>The new EH system makes exception handling a first-class member of the IR. It
adds two new instructions:</p>
<ul>
<li>On 21164s, some rare FP arithmetic sequences which may trap do not have
the appropriate nops inserted to ensure restartability.</li>
</ul>
<li><a href="LangRef.html#i_landingpad"><code>landingpad</code></a> &mdash;
this instruction defines a landing pad basic block. It contains all of the
information that's needed by the code generator. It's also required to be
the first non-PHI instruction in the landing pad. In addition, a landing
pad may be jumped to only by the unwind edge of an <code>invoke</code>
instruction.</li>
</div>
<li><a href="LangRef.html#i_resume"><code>resume</code></a> &mdash; this
instruction causes the current exception to resume traveling up the
stack. It replaces the <code>@llvm.eh.resume</code> intrinsic.</li>
</ul>
<!-- ======================================================================= -->
<h3>
<a name="c-be">Known problems with the C back-end</a>
</h3>
<p>Converting from the old EH API to the new EH API is rather simple, because a
lot of complexity has been removed. The two intrinsics,
<code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code> have been
superseded by the <code>landingpad</code> instruction. Instead of generating
a call to <code>@llvm.eh.exception</code> and <code>@llvm.eh.selector</code>:
<div>
<div class="doc_code">
<pre>
Function *ExcIntr = Intrinsic::getDeclaration(TheModule,
Intrinsic::eh_exception);
Function *SlctrIntr = Intrinsic::getDeclaration(TheModule,
Intrinsic::eh_selector);
<p>The C backend has numerous problems and is not being actively maintained.
Depending on it for anything serious is not advised.</p>
// The exception pointer.
Value *ExnPtr = Builder.CreateCall(ExcIntr, "exc_ptr");
<ul>
<li><a href="http://llvm.org/PR802">The C backend has only basic support for
inline assembly code</a>.</li>
std::vector&lt;Value*&gt; Args;
Args.push_back(ExnPtr);
Args.push_back(Builder.CreateBitCast(Personality,
Type::getInt8PtrTy(Context)));
<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>
<i>// Add selector clauses to Args.</i>
<li>The C backend does not support all exception handling constructs.</li>
// The selector call.
Builder.CreateCall(SlctrIntr, Args, "exc_sel");
</pre>
</div>
<li>The C backend does not support arbitrary precision integers.</li>
</ul>
<p>You should instead generate a <code>landingpad</code> instruction, that
returns an exception object and selector value:</p>
</div>
<div class="doc_code">
<pre>
LandingPadInst *LPadInst =
Builder.CreateLandingPad(StructType::get(Int8PtrTy, Int32Ty, NULL),
Personality, 0);
Value *LPadExn = Builder.CreateExtractValue(LPadInst, 0);
Builder.CreateStore(LPadExn, getExceptionSlot());
<!-- ======================================================================= -->
<h3>
<a name="llvm-gcc">Known problems with the llvm-gcc front-end</a>
</h3>
Value *LPadSel = Builder.CreateExtractValue(LPadInst, 1);
Builder.CreateStore(LPadSel, getEHSelectorSlot());
</pre>
</div>
<div>
<p>It's now trivial to add the individual clauses to the <code>landingpad</code>
instruction.</p>
<p><b>LLVM 2.9 was the last release of llvm-gcc.</b></p>
<div class="doc_code">
<pre>
<i><b>// Adding a catch clause</b></i>
Constant *TypeInfo = getTypeInfo();
LPadInst-&gt;addClause(TypeInfo);
<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>
<i><b>// Adding a C++ catch-all</b></i>
LPadInst-&gt;addClause(Constant::getNullValue(Builder.getInt8PtrTy()));
<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>
<i><b>// Adding a cleanup</b></i>
LPadInst-&gt;setCleanup(true);
<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>
<i><b>// Adding a filter clause</b></i>
std::vector&lt;Constant*&gt; TypeInfos;
Constant *TypeInfo = getFilterTypeInfo();
TypeInfos.push_back(Builder.CreateBitCast(TypeInfo, Builder.getInt8PtrTy()));
ArrayType *FilterTy = ArrayType::get(Int8PtrTy, TypeInfos.size());
LPadInst-&gt;addClause(ConstantArray::get(FilterTy, TypeInfos));
</pre>
</div>
<p>Converting from using the <code>@llvm.eh.resume</code> intrinsic to
the <code>resume</code> instruction is trivial. It takes the exception
pointer and exception selector values returned by
the <code>landingpad</code> instruction:</p>
<div class="doc_code">
<pre>
Type *UnwindDataTy = StructType::get(Builder.getInt8PtrTy(),
Builder.getInt32Ty(), NULL);
Value *UnwindData = UndefValue::get(UnwindDataTy);
Value *ExcPtr = Builder.CreateLoad(getExceptionObjSlot());
Value *ExcSel = Builder.CreateLoad(getExceptionSelSlot());
UnwindData = Builder.CreateInsertValue(UnwindData, ExcPtr, 0, "exc_ptr");
UnwindData = Builder.CreateInsertValue(UnwindData, ExcSel, 1, "exc_sel");
Builder.CreateResume(UnwindData);
</pre>
</div>
<!-- *********************************************************************** -->
<h2>
<a name="additionalinfo">Additional Information</a>
</h2>
<!-- *********************************************************************** -->
<div>
<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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