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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 2.4 Release Notes</title>
</head>
<body>
<div class="doc_title">LLVM 2.4 Release Notes</div>
<ol>
<li><a href="#intro">Introduction</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="#additionalinfo">Additional Information</a></li>
</ol>
<div class="doc_author">
<p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="intro">Introduction</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>This document contains the release notes for the LLVM Compiler
Infrastructure, release 2.4. 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>
<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 release, please see the
<a href="http://llvm.org/releases/">releases page</a>.</p>
</div>
<!-- Unfinished features in 2.4:
Machine LICM
Machine Sinking
LegalizeDAGTypes
llc -enable-value-prop, propagation of value info (sign/zero ext info) from
one MBB to another
-->
<!-- for announcement email:
mention dev mtg
Xcode 3.1 and 3.1.1.
-->
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="subproj">Sub-project Status Update</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<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>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
</div>
<div class="doc_text">
<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>Codegen progress/state [DANIEL]</p>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="clangsa">Clang Static Analyzer</a>
</div>
<div class="doc_text">
<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>
<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 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_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>[NICOLAS]</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New in LLVM?</a>
</div>
<!-- *********************************************************************** -->
<div class="doc_text">
<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>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="majorfeatures">Major New Features</a>
</div>
<div class="doc_text">
<p>LLVM 2.4 includes several major new capabilities:</p>
<ul>
<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 on the order of 30% (or more) faster than 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 as
well.</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
is the LLVM target that 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>
</div>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="llvm-gcc">llvm-gcc 4.2 Improvements</a>
</div>
<div class="doc_text">
<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>
<ul>
<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. While
llvm-gcc supports all of these builtins, note that 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 ok to use low-precision approximations of certain libm
functions (like tan, log, etc). This allows you to get high performance if you
only need (say) 14-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>
<!--=========================================================================-->
<div class="doc_subsection">
<a name="coreimprovements">LLVM Core Improvements</a>
</div>
<div class="doc_text">
<p>New features include:
</p>
<ul>
<
|
