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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="llvm.css" type="text/css">
<title>LLVM 2.3 Release Notes</title>
<title>LLVM 2.4 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.3 Release Notes</div>
<div class="doc_title">LLVM 2.4 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#changes">Major Changes and Sub-project Status</a></li>
<li><a href="#whatsnew">What's New?</a></li>
<li><a href="#subproj">Sub-project Status Update</a></li>
<li><a href="#whatsnew">What's New in LLVM?</a></li>
<li><a href="GettingStarted.html">Installation Instructions</a></li>
<li><a href="#portability">Portability and Supported Platforms</a></li>
<li><a href="#knownproblems">Known Problems</a>
<li><a href="#knownproblems">Known Problems</a></li>
<li><a href="#additionalinfo">Additional Information</a></li>
</ol>
<div class="doc_author">
<p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
<p>Written by the <a href="http://llvm.org">LLVM Team</a></p>
</div>
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<!-- *********************************************************************** -->
<div class="doc_section">
<a name="intro">Introduction</a>
......@@ -35,174 +32,175 @@
<div class="doc_text">
<p>This document contains the release notes for the LLVM compiler
infrastructure, release 2.3. Here we describe the status of LLVM, including
major improvements from the previous release and any known problems. All LLVM
releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
releases web site</a>.</p>
<p>This document contains the release notes for the LLVM Compiler
Infrastructure, release 2.4. Here we describe the status of LLVM, including
major improvements from the previous release and significant known problems.
All LLVM releases may be downloaded from the <a
href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
<p>For more information about LLVM, including information about the latest
release, please check out the <a href="http://llvm.org/">main LLVM
web site</a>. If you have questions or comments, the <a
href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
list</a> is a good place to send them.</p>
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
<p>Note that if you are reading this file from a Subversion checkout or the
main LLVM web page, this document applies to the <i>next</i> release, not the
current one. To see the release notes for a specific releases, please see the
current one. To see the release notes for a specific release, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
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Machine LICM
Machine Sinking
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llc -enable-value-prop, propagation of value info (sign/zero ext info) from
one MBB to another
-->
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mention dev mtg
Xcode 3.1 and 3.1.1.
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<!-- *********************************************************************** -->
<div class="doc_section">
<a name="changes">Major Changes and Sub-project Status</a>
<a name="subproj">Sub-project Status Update</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This is the fourteenth public release of the LLVM Compiler Infrastructure.
It includes a large number of features and refinements from LLVM 2.2.</p>
<p>
The LLVM 2.4 distribution currently consists of code from the core LLVM
repository (which roughly includes the LLVM optimizers, code generators and
supporting tools) and the llvm-gcc repository. In addition to this code, the
LLVM Project includes other sub-projects that are in development. The two which
are the most actively developed are the <a href="#clang">Clang Project</a> and
the <a href="#vmkit">VMKit Project</a>.
</p>
</div>
<!-- Unfinished features in 2.3:
Machine LICM
Machine Sinking
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-->
<!--=========================================================================-->
<div class="doc_subsection">
<a name="changes">Major Changes in LLVM 2.3</a>
<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
</div>
<div class="doc_text">
<p>LLVM 2.3 no longer supports llvm-gcc 4.0, it has been replaced with
llvm-gcc 4.2.</p>
<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
a set of new 'LLVM native' front-end technologies for the LLVM optimizer
and code generator. Clang is continuing to make major strides forward in all
areas. Its C and Objective-C parsing support is very solid, and the code
generation support is far enough along to build many C applications. While not
yet production quality, it is progressing very nicely. In addition, C++
front-end work has started to make significant progress.</p>
<p>LLVM 2.3 no longer includes the <tt>llvm-upgrade</tt> tool. It was useful
for upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a
previous LLVM release to do this. One nice impact of this is that the LLVM
regression test suite no longer depends on llvm-upgrade, which makes it run
faster.</p>
<p>Clang, in conjunction with the <tt>ccc</tt> driver, is now usable as a
replacement for gcc for building some small- to medium-sized C applications.
Additionally, Clang now has code generation support for Objective-C on Mac OS X
platform. Major highlights include:</p>
<p>The <tt>llvm2cpp</tt> tool has been folded into llc, use
<tt>llc -march=cpp</tt> instead of <tt>llvm2cpp</tt>.</p>
<ul>
<li> Clang/ccc pass almost all of the LLVM test suite on Mac OS X and Linux
on the 32-bit x86 architecture. This includes significant C
applications such as <a href="http://www.sqlite.org">sqlite3</a>,
<a href="http://www.lua.org">lua</a>, and
<a href="http://www.clamav.net">Clam AntiVirus</a>. </li>
<li> Clang can build the majority of Objective-C examples shipped with the
Mac OS X Developer Tools. </li>
</ul>
<p>LLVM API Changes:</p>
<p>Clang code generation still needs considerable testing and development,
however. Some areas under active development include:</p>
<ul>
<li>Several core LLVM IR classes have migrated to use the
'<tt>FOOCLASS::Create(...)</tt>' pattern instead of '<tt>new
FOOCLASS(...)</tt>' (e.g. where FOOCLASS=<tt>BasicBlock</tt>). We hope to
standardize on <tt>FOOCLASS::Create</tt> for all IR classes in the future,
but not all of them have been moved over yet.</li>
<li>LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to
<a href="http://llvm.org/doxygen/classllvm_1_1IRBuilder.html">IRBuilder</a>.
</li>
<li>MRegisterInfo was renamed to
<a href="http://llvm.org/doxygen/classllvm_1_1TargetRegisterInfo.html">
TargetRegisterInfo</a>.</li>
<li>The MappedFile class is gone, please use
<a href="http://llvm.org/doxygen/classllvm_1_1MemoryBuffer.html">
MemoryBuffer</a> instead.</li>
<li>The '<tt>-enable-eh</tt>' flag to llc has been removed. Now code should
encode whether it is safe to omit unwind information for a function by
tagging the Function object with the '<tt>nounwind</tt>' attribute.</li>
<li>The ConstantFP::get method that uses APFloat now takes one argument
instead of two. The type argument has been removed, and the type is
now inferred from the size of the given APFloat value.</li>
<li> Improved support for C and Objective-C features, for example
variable-length arrays, va_arg, exception handling (Obj-C), and garbage
collection (Obj-C). </li>
<li> ABI compatibility, especially for platforms other than 32-bit
x86. </li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="otherprojects">Other LLVM Sub-Projects</a>
<a name="clangsa">Clang Static Analyzer</a>
</div>
<div class="doc_text">
<p>
The core LLVM 2.3 distribution currently consists of code from the core LLVM
repository (which roughly contains the LLVM optimizer, code generators and
supporting tools) and the llvm-gcc repository. In addition to this code, the
LLVM Project includes other sub-projects that are in development. The two which
are the most actively developed are the new <a href="#vmkit">vmkit Project</a>
and the <a href="#clang">Clang Project</a>.
</p>
</div>
<!--=========================================================================-->
<div class="doc_subsubsection">
<a name="vmkit">vmkit</a>
</div>
<p>The Clang project also includes an early stage static source code analysis
tool for <a href="http://clang.llvm.org/StaticAnalysis.html">automatically
finding bugs</a> in C and Objective-C programs. The tool performs a growing set
of checks to find bugs that occur on a specific path within a program. Examples
of bugs the tool finds include logic errors such as null dereferences,
violations of various API rules, dead code, and potential memory leaks in
Objective-C programs. Since its inception, public feedback on the tool has been
extremely positive, and conservative estimates put the number of real bugs it
has found in industrial-quality software on the order of thousands.</p>
<div class="doc_text">
<p>
The "vmkit" project is a new addition to the LLVM family. It is an
implementation of a JVM and a CLI Virtual Machines (Microsoft .NET is an
implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
<p>The tool also provides a simple web GUI to inspect potential bugs found by
the tool. While still early in development, the GUI illustrates some of the key
features of Clang: accurate source location information, which is used by the
GUI to highlight specific code expressions that relate to a bug (including those
that span multiple lines); and built-in knowledge of macros, which is used to
perform inline expansion of macros within the GUI itself.</p>
<p>The JVM, called JnJVM, executes real-world applications such as Apache
projects (e.g. Felix and Tomcat) and the SpecJVM98 benchmark. It uses the GNU
Classpath project for the base classes. The CLI implementation, called N3, is
its in early stages but can execute simple applications and the "pnetmark"
benchmark. It uses the pnetlib project as its core library.</p>
<p>The 'vmkit' VMs compare in performance with industrial and top open-source
VMs on scientific applications. Besides the JIT, the VMs use many features of
the LLVM framework, including the standard set of optimizations, atomic
operations, custom function provider and memory manager for JITed methods, and
specific virtual machine optimizations. vmkit is not an official part of LLVM
2.3 release. It is publicly available under the LLVM license and can be
downloaded from:
</p>
<div class="doc_code">
<pre>svn co http://llvm.org/svn/llvm-project/vmkit/trunk vmkit</pre>
</div>
<p>The set of checks performed by the static analyzer is gradually expanding,
and future plans for the tool include full source-level inter-procedural
analysis and deeper checks such as buffer overrun detection. There are many
opportunities to extend and enhance the static analyzer, and anyone interested
in working on this project is encouraged to get involved!</p>
</div>
<!--=========================================================================-->
<div class="doc_subsubsection">
<a name="clang">Clang</a>
<div class="doc_subsection">
<a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
</div>
<div class="doc_text">
<p>
The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
a JVM and a CLI Virtual Machines (Microsoft .NET is an
implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
a set of new 'LLVM native' front-end technologies for the LLVM optimizer
and code generator. Clang is continuing to make major strides forward in all
areas. Its C and Objective-C parsing support is very solid, and the code
generation support is far enough along to build many C applications. While not
yet production quality, it is progressing very nicely. In addition, C++
front-end work has started to make significant progress.</p>
<p>Following LLVM 2.4, VMKit has its first release 0.24 that you can find on its
<a href="http://vmkit.llvm.org/releases/">webpage</a>. The release includes
bug fixes, cleanup and new features. The major changes are:</p>
<p>At this point, Clang is most useful if you are interested in source-to-source
transformations (such as refactoring) and other source-level tools for C and
Objective-C. Clang now also includes tools for turning C code into pretty HTML,
and includes a new <a href="http://clang.llvm.org/StaticAnalysis.html">static
analysis tool</a> in development. This tool focuses on automatically finding
bugs in C and Objective-C code.</p>
<ul>
<li> Support for generics in the .Net virtual machine.</li>
<li> Initial support for the Mono class libraries. </li>
<li> Support for MacOSX/x86, following LLVM's support for exceptions in
JIT on MacOSX/x86. </li>
<li> A new vmkit driver: a program to run java or .net applications. The driver
supports llvm command line arguments including the new "-fast" option. </li>
<li> A new memory allocation scheme in the JVM that makes unloading a
class loader very fast. </li>
<li> VMKit now follows the LLVM Makefile machinery. </li>
</ul>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New?</a>
<a name="whatsnew">What's New in LLVM?</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM 2.3 includes a huge number of bug fixes, performance tweaks and minor
improvements. Some of the major improvements and new features are listed in
this section.
<p>This release includes a huge number of bug fixes, performance tweaks, and
minor improvements. Some of the major improvements and new features are listed
in this section.
</p>
</div>
......@@ -213,52 +211,29 @@ this section.
<div class="doc_text">
<p>LLVM 2.3 includes several major new capabilities:</p>
<p>LLVM 2.4 includes several major new capabilities:</p>
<ul>
<li><p>The biggest change in LLVM 2.3 is Multiple Return Value (MRV) support.
MRVs allow LLVM IR to directly represent functions that return multiple
values without having to pass them "by reference" in the LLVM IR. This
allows a front-end to generate more efficient code, as MRVs are generally
returned in registers if a target supports them. See the <a
href="LangRef.html#i_getresult">LLVM IR Reference</a> for more details.</p>
<p>MRVs are fully supported in the LLVM IR, but are not yet fully supported in
on all targets. However, it is generally safe to return up to 2 values from
a function: most targets should be able to handle at least that. MRV
support is a critical requirement for X86-64 ABI support, as X86-64 requires
the ability to return multiple registers from functions, and we use MRVs to
accomplish this in a direct way.</p></li>
<li><p>LLVM 2.3 includes a complete reimplementation of the "<tt>llvmc</tt>"
tool. It is designed to overcome several problems with the original
<tt>llvmc</tt> and to provide a superset of the features of the
'<tt>gcc</tt>' driver.</p>
<p>The main features of <tt>llvmc2</tt> are:
<ul>
<li>Extended handling of command line options and smart rules for
dispatching them to different tools.</li>
<li>Flexible (and extensible) rules for defining different tools.</li>
<li>The different intermediate steps performed by tools are represented
as edges in the abstract graph.</li>
<li>The 'language' for driver behavior definition is tablegen and thus
it's relatively easy to add new features.</li>
<li>The definition of driver is transformed into set of C++ classes, thus
no runtime interpretation is needed.</li>
</ul>
</li>
<li><p>LLVM 2.3 includes a completely rewritten interface for <a
href="LinkTimeOptimization.html">Link Time Optimization</a>. This interface
is written in C, which allows for easier integration with C code bases, and
incorporates improvements we learned about from the first incarnation of the
interface.</p></li>
<li><p>The <a href="tutorial/LangImpl1.html">Kaleidoscope tutorial</a> now
includes a "port" of the tutorial that <a
href="tutorial/OCamlLangImpl1.html">uses the Ocaml bindings</a> to implement
the Kaleidoscope language.</p></li>
<li><p>The most visible end-user change in LLVM 2.4 is that it includes many
optimizations and changes to make -O0 compile times much faster. You should see
improvements in speed on the order of 30% (or more) than in LLVM 2.3. There are
many pieces to this change described in more detail below. The speedups and new
components can also be used for JIT compilers that want fast
compilation.</p></li>
<li><p>The biggest change to the LLVM IR is that Multiple Return Values (which
were introduced in LLVM 2.3) have been generalized to full support for "First
Class Aggregate" values in LLVM 2.4. This means that LLVM IR supports using
structs and arrays as values in a function. This capability is mostly useful
for front-end authors, who prefer to treat things like complex numbers, simple
tuples, dope vectors, etc., as Value*'s instead of as a tuple of Value*'s or as
memory values. Bitcode files from LLVM 2.3 will automatically migrate to the
general representation.</p></li>
<li><p>LLVM 2.4 also includes an initial port for the PIC16 microprocessor. This
target only has support for 8 bit registers, and a number of other crazy
constraints. While the port is still in early development stages, it shows some
interesting things you can do with LLVM.</p></li>
</ul>
......@@ -272,20 +247,34 @@ this section.
<div class="doc_text">
<p>LLVM 2.3 fully supports the llvm-gcc 4.2 front-end, and includes support
for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
front-ends and driver with the LLVM optimizer and code generator. It currently
includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
<p>
<ul>
<li>llvm-gcc 4.2 includes numerous fixes to better support the Objective-C
front-end. Objective-C now works very well on Mac OS/X.</li>
<li>Fortran <tt>EQUIVALENCE</tt>s are now supported by the gfortran
front-end.</li>
<li>llvm-gcc 4.2 includes many other fixes which improve conformance with the
relevant parts of the GCC testsuite.</li>
<li>LLVM 2.4 supports the full set of atomic <tt>__sync_*</tt> builtins. LLVM
2.3 only supported those used by OpenMP, but 2.4 supports them all. Note that
while llvm-gcc supports all of these builtins, not all targets do. X86 support
them all in both 32-bit and 64-bit mode and PowerPC supports them all except for
the 64-bit operations when in 32-bit mode.</li>
<li>llvm-gcc now supports an <tt>-flimited-precision</tt> option, which tells
the compiler that it is okay to use low-precision approximations of certain libm
functions (like <tt>exp</tt>, <tt>log</tt>, etc). This allows you to get high
performance if you only need (say) 12-bits of precision.</li>
<li>llvm-gcc now supports a C language extension known as "<a
href="http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-August/002670.html">Blocks</a>".
This feature is similar to nested functions and closures, but does not
require stack trampolines (with most ABIs), and supports returning closures
from functions that define them. Note that actually <em>using</em> Blocks
requires a small runtime that is not included with llvm-gcc.</li>
<li>llvm-gcc now supports a new <tt>-flto</tt> option. On systems that support
transparent Link Time Optimization (currently Darwin systems with Xcode 3.1 and
later) this allows the use of LTO with other optimization levels like -Os.
Previously, LTO could only be used with -O4, which implied optimizations in
-O3 that can increase code size.</li>
</ul>
</div>
......@@ -297,23 +286,49 @@ relevant parts of the GCC testsuite.</li>
</div>
<div class="doc_text">
<p>New features include:
</p>
<p>New features include:</p>
<ul>
<li>LLVM IR now directly represents "common" linkage, instead of representing it
as a form of weak linkage.</li>
<li>A major change to the <tt>Use</tt> class landed, which shrank it by 25%. Since
this is a pervasive part of the LLVM, it ended up reducing the memory use of
LLVM IR in general by 15% for most programs.</li>
<li>LLVM IR now has support for atomic operations, and this functionality can be
accessed through the llvm-gcc "<tt>__sync_synchronize</tt>",
"<tt>__sync_val_compare_and_swap</tt>", and related builtins. Support for
atomics are available in the Alpha, X86, X86-64, and PowerPC backends.</li>
<li>Values with no names are now pretty printed by <tt>llvm-dis</tt> more
nicely. They now print as "<tt>%3 = add i32 %A, 4</tt>" instead of
"<tt>add i32 %A, 4 ; &lt;i32&gt;:3</tt>", which makes it much easier to read.
</li>
<li>The C and Ocaml bindings have extended to cover pass managers, several
transformation passes, iteration over the LLVM IR, target data, and parameter
attribute lists.</li>
<li>LLVM 2.4 includes some changes for better vector support. First, the shift
operations (<tt>shl</tt>, <tt>ashr</tt>, and <tt>lshr</tt>) now all support
vectors and do an element-by-element shift (shifts of the whole vector can be
accomplished by bitcasting the vector to <tt>&lt;1 x i128&gt;</tt>, for example). Second,
there is initial support in development for vector comparisons with the
<tt><a href="LangRef.html#i_fcmp">fcmp</a>/<a href="LangRef.html#i_icmp">icmp</a></tt>
instructions. These instructions compare two vectors and return a vector of
<tt>i1</tt>'s for each result. Note that there is very little codegen support
available for any of these IR features though.</li>
<li>A new <tt>DebugInfoBuilder</tt> class is available, which makes it much
easier for front-ends to create debug info descriptors, similar to the way that
<tt>IRBuilder</tt> makes it easier to create LLVM IR.</li>
<li>The <tt>IRBuilder</tt> class is now parameterized by a class responsible
for constant folding. The default <tt>ConstantFolder</tt> class does target independent
constant folding. The <tt>NoFolder</tt> class does no constant folding at all, which is
useful when learning how LLVM works. The <tt>TargetFolder</tt> class folds the most,
doing target dependent constant folding.</li>
<li>LLVM now supports "function attributes", which allow us to separate return
value attributes from function attributes. LLVM now supports attributes on a
function itself, a return value, and its parameters. New supported function
attributes include <tt>noinline/alwaysinline</tt> and the <tt>opt-size</tt> flag,
which says the function should be optimized for code size.</li>
<li>LLVM IR now directly represents "common" linkage, instead of
representing it as a form of weak linkage.</li>
</ul>
</div>
<!--=========================================================================-->
......@@ -323,66 +338,45 @@ attribute lists.</li>
<div class="doc_text">
<p>In addition to a huge array of bug fixes and minor performance tweaks, the
LLVM 2.3 optimizers support a few major enhancements:</p>
<p>In addition to a huge array of bug fixes and minor performance tweaks, this
release includes a few major enhancements and additions to the optimizers:</p>
<ul>
<li><p>Loop index set splitting on by default.
This transformation hoists conditions from loop bodies and reduces a loop's
iteration space to improve performance. For example,</p>
<li>The Global Value Numbering (GVN) pass now does local Partial Redundancy
Elimination (PRE) to eliminate some partially redundant expressions in cases
where doing so won't grow code size.</li>
<div class="doc_code">
<pre>
for (i = LB; i &lt; UB; ++i)
if (i &lt;= NV)
LOOP_BODY
</pre>
</div>
<li>LLVM 2.4 includes a new loop deletion pass (which removes output-free
provably-finite loops) and a rewritten Aggressive Dead Code Elimination (ADCE)
pass that no longer uses control dependence information. These changes speed up
the optimizer and also prevent it from deleting output-free infinite
loops.</li>
<p>is transformed into:</p>
<li>The new AddReadAttrs pass works out which functions are read-only or
read-none (these correspond to 'pure' and 'const' in GCC) and marks them
with the appropriate attribute.</li>
<p><div class="doc_code">
<pre>
NUB = min(NV+1, UB)
for (i = LB; i &lt; NUB; ++i)
LOOP_BODY
</pre>
</div>
</p>
</li>
<li>LLVM 2.4 now includes a new SparsePropagation framework, which makes it
trivial to build lattice-based dataflow solvers that operate over LLVM IR. Using
this interface means that you just define objects to represent your lattice
values and the transfer functions that operate on them. It handles the
mechanics of worklist processing, liveness tracking, handling PHI nodes,
etc.</li>
<li>LLVM now includes a new <tt>memcpy</tt> optimization pass which removes
dead <tt>memcpy</tt> calls, unneeded copies of aggregates, and performs
return slot optimization. The LLVM optimizer now notices long sequences of
consecutive stores and merges them into <tt>memcpy</tt>'s where profitable.</li>
<li>Alignment detection for vector memory references and for <tt>memcpy</tt> and
<tt>memset</tt> is now more aggressive.</li>
<li>The Aggressive Dead Code Elimination (ADCE) optimization has been rewritten
to make it both faster and safer in the presence of code containing infinite
loops. Some of its prior functionality has been factored out into the loop
deletion pass, which <em>is</em> safe for infinite loops. The new ADCE pass is
no longer based on control dependence, making it run faster.</li>
<li>The 'SimplifyLibCalls' pass, which optimizes calls to libc and libm
functions for C-based languages, has been rewritten to be a FunctionPass
instead a ModulePass. This allows it to be run more often and to be
included at -O1 in llvm-gcc. It was also extended to include more
optimizations and several corner case bugs were fixed.</li>
<li>LLVM now includes a simple 'Jump Threading' pass, which attempts to simplify
conditional branches using information about predecessor blocks, simplifying
the control flow graph. This pass is pretty basic at this point, but
catches some important cases and provides a foundation to build on.</li>
<li>Several corner case bugs which could lead to deleting volatile memory
accesses have been fixed.</li>
<li>The Loop Strength Reduction and induction variable optimization passes have
several improvements to avoid inserting MAX expressions, to optimize simple
floating point induction variables and to analyze trip counts of more
loops.</li>
<li>Various helper functions (ComputeMaskedBits, ComputeNumSignBits, etc) were
pulled out of the Instruction Combining pass and put into a new
<tt>ValueTracking.h</tt> header, where they can be reused by other passes.</li>
<li>The tail duplication pass has been removed from the standard optimizer
sequence used by llvm-gcc. This pass still exists, but the benefits it once
provided are now achieved by other passes.</li>
<li>Several optimizations have been sped up, leading to faster code generation
with the same code quality.</li>
</ul>
</div>
......@@ -394,50 +388,47 @@ no longer based on control dependence, making it run faster.</li>
<div class="doc_text">
<p>We put a significant amount of work into the code generator infrastructure,
<p>We have put a significant amount of work into the code generator infrastructure,
which allows us to implement more aggressive algorithms and make it run
faster:</p>
<ul>
<li>The code generator now has support for carrying information about memory
references throughout the entire code generation process, via the
<a href="http://llvm.org/doxygen/classllvm_1_1MachineMemOperand.html">
MachineMemOperand</a> class. In the future this will be used to improve
both pre-pass and post-pass scheduling, and to improve compiler-debugging
output.</li>
<li>The target-independent code generator infrastructure now uses LLVM's
<a href="http://llvm.org/doxygen/classllvm_1_1APInt.html">APInt</a>
class to handle integer values, which allows it to support integer types
larger than 64 bits (for example i128). Note that support for such types is
also dependent on target-specific support. Use of APInt is also a step
toward support for non-power-of-2 integer sizes.</li>
<li>LLVM 2.3 includes several compile time speedups for code with large basic
blocks, particularly in the instruction selection phase, register
allocation, scheduling, and tail merging/jump threading.</li>
<li>The target-independent code generator supports (and the X86 backend
currently implements) a new interface for "fast" instruction selection. This
interface is optimized to produce code as quickly as possible, sacrificing
code quality to do it. This is used by default at -O0 or when using
"llc -fast" on X86. It is straight-forward to add support for
other targets if faster -O0 compilation is desired.</li>
<li>In addition to the new 'fast' instruction selection path, many existing
pieces of the code generator have been optimized in significant ways.
SelectionDAG's are now pool allocated and use better algorithms in many
places, the ".s" file printers now use <tt>raw_ostream</tt> to emit text much faster,
etc. The end result of these improvements is that the compiler also takes
substantially less time to generate code that is just as good (and often
better) than before.</li>
<li>Each target has been split to separate the ".s" file printing logic from the
rest of the target. This enables JIT compilers that don't link in the
(somewhat large) code and data tables used for printing a ".s" file.</li>
<li>The code generator now includes a "stack slot coloring" pass, which packs
together individual spilled values into common stack slots. This reduces
the size of stack frames with many spills, which tends to increase L1 cache
effectiveness.</li>
<li>Various pieces of the register allocator (e.g. the coalescer and two-address
operation elimination pass) now know how to rematerialize trivial operations
to avoid copies and include several other optimizations.</li>
<li>The <a href="CodeGenerator.html#selectiondag_process">graphs</a> produced by
the <tt>llc -view-*-dags</tt> options are now significantly prettier and
easier to read.</li>
<li>LLVM 2.4 includes a new register allocator based on Partitioned Boolean
Quadratic Programming (PBQP). This register allocator is still in
development, but is very simple and clean.</li>
<li>LLVM 2.3 includes several improvements which make llc's
<tt>--view-sunit-dags</tt> visualization of scheduling dependency graphs
easier to understand.</li>
<li>The code generator allows targets to write patterns that generate subreg
references directly in .td files now.</li>
<li><tt>memcpy</tt> lowering in the backend is more aggressive, particularly for
<tt>memcpy</tt> calls introduced by the code generator when handling
pass-by-value structure argument copies.</li>
<li>Inline assembly with multiple register results now returns those results
directly in the appropriate registers, rather than going through memory.
Inline assembly that uses constraints like "ir" with immediates now use the
'i' form when possible instead of always loading the value in a register.
This saves an instruction and reduces register use.</li>
<li>Added support for PIC/GOT style <a
href="CodeGenerator.html#tailcallopt">tail calls</a> on X86/32 and initial
support for tail calls on PowerPC 32 (it may also work on PowerPC 64 but is
not thoroughly tested).</li>
</ul>
</div>
......@@ -445,7 +436,7 @@ faster:</p>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="x86specific">X86/X86-64 Specific Improvements</a>
<a name="targetspecific">Target Specific Improvements</a>
</div>
<div class="doc_text">
......@@ -453,90 +444,131 @@ faster:</p>
</p>
<ul>
<li>llvm-gcc's X86-64 ABI conformance is far improved, particularly in the
area of passing and returning structures by value. llvm-gcc compiled code
now interoperates very well on X86-64 systems with other compilers.</li>
<li>Support for Win64 was added. This includes code generation itself, JIT
support, and necessary changes to llvm-gcc.</li>
<li>The LLVM X86 backend now supports the support SSE 4.1 instruction set, and
the llvm-gcc 4.2 front-end supports the SSE 4.1 compiler builtins. Various
generic vector operations (insert/extract/shuffle) are much more efficient
when SSE 4.1 is enabled. The JIT automatically takes advantage of these
instructions, but llvm-gcc must be explicitly told to use them, e.g. with
<tt>-march=penryn</tt>.</li>
<li>The X86 backend now does a number of optimizations that aim to avoid
converting numbers back and forth from SSE registers to the X87 floating
point stack. This is important because most X86 ABIs require return values
to be on the X87 Floating Point stack, but most CPUs prefer computation in
the SSE units.</li>
<li>The X86 backend supports stack realignment, which is particularly useful for
vector code on OS's without 16-byte aligned stacks, such as Linux and
Windows.</li>
<li>The X86 backend now supports the "sseregparm" options in GCC, which allow
functions to be tagged as passing floating point values in SSE
registers.</li>
<li>Exception handling is supported by default on Linux/x86-64.</li>
<li>Position Independent Code (PIC) is now supported on Linux/x86-64.</li>
<li><tt>@llvm.frameaddress</tt> now supports getting the frame address of stack frames
&gt; 0 on x86/x86-64.</li>
<li>MIPS has improved a lot since last release, the most important changes
are: Little endian support, floating point support, allegrex core and
intrinsics support. O32 ABI is improved but isn't complete. The EABI
was implemented and is fully supported. We also have support for small
sections and gp_rel relocation for its access, a threshold in bytes can be
specified through command line.</li>
<li>The PowerPC backend now supports trampolines.</li>
</ul>
<li>Trampolines (taking the address of a nested function) now work on
Linux/X86-64.</li>
</div>
<li><tt>__builtin_prefetch</tt> is now compiled into the appropriate prefetch
instructions instead of being ignored.</li>
<li>128-bit integers are now supported on X86-64 targets. This can be used
through <tt>__attribute__((TImode))</tt> in llvm-gcc.</li>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="otherimprovements">Other Improvements</a>
</div>
<li>The register allocator can now rematerialize PIC-base computations, which is
an important optimization for register use.</li>
<div class="doc_text">
<p>New features include:
</p>
<li>The "t" and "f" inline assembly constraints for the X87 floating point stack
now work. However, the "u" constraint is still not fully supported.</li>
<ul>
<li><tt>llvmc2</tt> (the generic compiler driver) gained plugin
support. It is now easier to experiment with <tt>llvmc2</tt> and
build your own tools based on it.</li>
<li>LLVM 2.4 includes a number of new generic algorithms and data structures,
including a scoped hash table, 'immutable' data structures, a simple
free-list manager, and a <tt>raw_ostream</tt> class.
The <tt>raw_ostream</tt> class and
<tt>format</tt> allow for efficient file output, and various pieces of LLVM
have switched over to use it. The eventual goal is to eliminate
use of <tt>std::ostream</tt> in favor of it.</li>
<li>LLVM 2.4 includes an optional build system based on CMake. It
still is in its early stages but can be useful for Visual C++
users who can not use the Visual Studio IDE.</li>
</ul>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="targetspecific">Other Target Specific Improvements</a>
<a name="changes">Major Changes and Removed Features</a>
</div>
<div class="doc_text">
<p>New target-specific features include:
</p>
<p>If you're already an LLVM user or developer with out-of-tree changes based
on LLVM 2.3, this section lists some "gotchas" that you may run into upgrading
from the previous release.</p>
<ul>
<li>The LLVM C backend now supports vector code.</li>
<li>The Cell SPU backend includes a number of improvements. It generates better
code and its stability/completeness is improving.</li>
</ul>
</div>
<li>The LLVM IR generated by llvm-gcc no longer names all instructions. This
makes it run faster, but may be more confusing to some people. If you
prefer to have names, the '<tt>opt -instnamer</tt>' pass will add names to
all instructions.</li>
<li>The LoadVN and GCSE passes have been removed from the tree. They are
obsolete and have been replaced with the GVN and MemoryDependence passes.
</li>
</ul>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="otherimprovements">Other Improvements</a>
</div>
<div class="doc_text">
<p>New features include:
</p>
<p>In addition, many APIs have changed in this release. Some of the major LLVM
API changes are:</p>
<ul>
<li>LLVM now builds with GCC 4.3.</li>
<li>Bugpoint now supports running custom scripts (with the <tt>-run-custom</tt>
option) to determine how to execute the command and whether it is making
forward process.</li>
<li>Now, function attributes and return value attributes are managed
separately. Interface exported by <tt>ParameterAttributes.h</tt> header is now
exported by <tt>Attributes.h</tt> header. The new attributes interface changes are:
<ul>
<li><tt>getParamAttrs</tt> method is now replaced by
<tt>getParamAttributes</tt>, <tt>getRetAttributes</tt> and
<tt>getFnAttributes</tt> methods.</li>
<li> Return value attributes are stored at index 0. Function attributes are
stored at index ~0U. Parameter attributes are stored at index that matches
parameter number.</li>
<li> <tt>ParamAttr</tt> namespace is now renamed as <tt>Attribute</tt>.</li>
<li> The name of the class that manages reference count of opaque
attributes is changed from <tt>PAListPtr</tt> to <tt>AttrListPtr</tt>.</li>
<li> <tt>ParamAttrsWithIndex</tt> is now renamed as <tt>AttributeWithIndex</tt>.
</li>
</ul>
</li>
<li>The <tt>DbgStopPointInst</tt> methods <tt>getDirectory</tt> and
<tt>getFileName</tt> now return <tt>Value*</tt> instead of strings. These can be
converted to strings using <tt>llvm::GetConstantStringInfo</tt> defined via
"<tt>llvm/Analysis/ValueTracking.h</tt>".</li>
<li>The APIs to create various instructions have changed from lower case
"create" methods to upper case "Create" methods (e.g.
<tt>BinaryOperator::create</tt>). LLVM 2.4 includes both cases, but the
lower case ones are removed in mainline (2.5 and later), please migrate.</li>
<li>Various header files like "<tt>llvm/ADT/iterator</tt>" were given a ".h" suffix.
Change your code to #include "<tt>llvm/ADT/iterator.h</tt>" instead.</li>
<li>The <tt>getresult</tt> instruction has been removed and replaced with the
<tt>extractvalue</tt> instruction. This is part of support for first class
aggregates.</li>
<li>In the code generator, many <tt>MachineOperand</tt> predicates were renamed to be
shorter (e.g. <tt>isFrameIndex()</tt> -&gt; <tt>isFI()</tt>),
<tt>SDOperand</tt> was renamed to <tt>SDValue</tt> (and the "<tt>Val</tt>"
member was changed to be the <tt>getNode()</tt> accessor), and the
<tt>MVT::ValueType</tt> enum has been replaced with an "<tt>MVT</tt>"
struct. The <tt>getSignExtended</tt> and <tt>getValue</tt> methods in the
ConstantSDNode class were renamed to <tt>getSExtValue</tt> and
<tt>getZExtValue</tt> respectively, to be more consistent with
the <tt>ConstantInt</tt> class.</li>
</ul>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="portability">Portability and Supported Platforms</a>
......@@ -548,10 +580,10 @@ faster:</p>
<p>LLVM is known to work on the following platforms:</p>
<ul>
<li>Intel and AMD machines (IA32) 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 10.3 and above in 32-bit and
64-bit modes.</li>
<li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) 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 10.3 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
support is available for native builds with Visual C++).</li>
......@@ -575,9 +607,8 @@ portability patches and reports of successful builds or error messages.</p>
<div class="doc_text">
<p>This section contains all known problems with the LLVM system, listed by
component. As new problems are discovered, they will be added to these
sections. If you run into a problem, please check the <a
<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>
......@@ -598,7 +629,7 @@ components, please contact us on the <a
href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
<ul>
<li>The MSIL, IA64, Alpha, SPU, and MIPS backends are experimental.</li>
<li>The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li>
<li>The llc "<tt>-filetype=asm</tt>" (the default) is the only supported
value for this option.</li>
</ul>
......@@ -625,8 +656,6 @@ href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
to <a href="http://llvm.org/PR2255">several</a>
<a href="http://llvm.org/PR2257">bugs</a> due to lack of support for the
'u' inline assembly constraint and X87 floating point inline assembly.</li>
<li>The X86-64 backend does not yet support position-independent code (PIC)
generation on Linux targets.</li>
<li>The X86-64 backend does not yet support the LLVM IR instruction
<tt>va_arg</tt>. Currently, the llvm-gcc front-end supports variadic
argument constructs on X86-64 by lowering them manually.</li>
......@@ -682,6 +711,20 @@ programs compiled with LLVM. Please use more recent versions of QEMU.</li>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="mips-be">Known problems with the MIPS back-end</a>
</div>
<div class="doc_text">
<ul>
<li>The O32 ABI is not fully supported.</li>
<li>64-bit MIPS targets are not supported yet.</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="alpha-be">Known problems with the Alpha back-end</a>
......@@ -707,7 +750,7 @@ appropriate nops inserted to ensure restartability.</li>
<ul>
<li>The Itanium backend is highly experimental, and has a number of known
issues. We are looking for a maintainer for the Itanium backend. If you
are interested, please contact the llvmdev mailing list.</li>
are interested, please contact the LLVMdev mailing list.</li>
</ul>
</div>
......@@ -740,7 +783,7 @@ appropriate nops inserted to ensure restartability.</li>
<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
Optimization</a> on most platforms "out-of-the-box". Please inquire on the
llvmdev mailing list if you are interested.</p>
LLVMdev mailing list if you are interested.</p>
<p>The only major language feature of GCC not supported by llvm-gcc is
the <tt>__builtin_apply</tt> family of builtins. However, some extensions
......@@ -765,13 +808,26 @@ tested and works for a number of non-trivial programs, including LLVM
itself, Qt, Mozilla, etc.</p>
<ul>
<li>Exception handling works well on the X86 and PowerPC targets, including
X86-64 darwin. This works when linking to a libstdc++ compiled by GCC. It is
supported on X86-64 linux, but that is disabled by default in this release.</li>
<li>Exception handling works well on the X86 and PowerPC targets. Currently
only Linux and Darwin targets are supported (both 32 and 64 bit).</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>
</div>
<div class="doc_text">
<ul>
<li>Fortran support generally works, but there are still several unresolved bugs
in Bugzilla. Please see the tools/gfortran component for details.</li>
<li>The Fortran front-end currently does not build on Darwin (without tweaks)
due to unresolved dependencies on the C front-end.</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
......@@ -788,11 +844,10 @@ however it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
which does support trampolines.</li>
<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
Workaround: configure with --disable-bootstrap.</li>
<li>The c380004 and <a href="http://llvm.org/PR2010">c393010</a> ACATS tests
fail (c380004 also fails with gcc-4.2 mainline). When built at -O3, the
<a href="http://llvm.org/PR2421">cxg2021</a> ACATS test also fails.</li>
<li>Some gcc specific Ada tests continue to crash the compiler. The testsuite
reports most tests as having failed even though they pass.</li>
<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
(c380004 also fails with gcc-4.2 mainline).</li>
<li>Some gcc specific Ada tests continue to crash the compiler.</li>
<li>The -E binder option (exception backtraces)
<a href="http://llvm.org/PR1982">does not work</a> and will result in programs
crashing if an exception is raised. Workaround: do not use -E.</li>
......
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