LLVM 2.4 Release Notes
  1. Introduction
  2. Sub-project Status Update
  3. What's New in LLVM?
  4. Installation Instructions
  5. Portability and Supported Platforms
  6. Known Problems
  7. Additional Information

Written by the LLVM Team


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 LLVM releases web site.

For more information about LLVM, including information about the latest release, please check out the main LLVM web site. If you have questions or comments, the LLVM Developer's Mailing List is a good place to send them.

Note that if you are reading this file from a Subversion checkout or the main LLVM web page, this document applies to the next release, not the current one. To see the release notes for a specific release, please see the releases page.

Sub-project Status Update

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 Clang Project and the VMKit Project.

Clang: C/C++/Objective-C Frontend Toolkit

The Clang project 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.

Clang, in conjunction with the ccc 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:

Clang code generation still needs considerable testing and development, however. Some areas under active development include:

Clang Static Analyzer

The Clang project also includes an early stage static source code analysis tool for automatically finding bugs 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.

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.

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!

VMKit: JVM/CLI Virtual Machine Implementation

The VMKit project 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.

Following LLVM 2.4, VMKit has its first release 0.24 that you can find on its webpage. The release includes bug fixes, cleanup and new features. The major changes are:

What's New in LLVM?

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.

Major New Features

LLVM 2.4 includes several major new capabilities:

llvm-gcc 4.2 Improvements

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.

LLVM Core Improvements

New features include:

Optimizer Improvements

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:

Code Generator Improvements

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:

Target Specific Improvements

New target-specific features include:

Other Improvements

New features include:

Major Changes and Removed Features

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.

In addition, many APIs have changed in this release. Some of the major LLVM API changes are:

Portability and Supported Platforms

LLVM is known to work on the following platforms:

The core LLVM infrastructure uses GNU autoconf to adapt itself to the machine and operating system on which it is built. However, minor porting may be required to get LLVM to work on new platforms. We welcome your portability patches and reports of successful builds or error messages.

Known Problems

This section contains significant known problems with the LLVM system, listed by component. If you run into a problem, please check the LLVM bug database and submit a bug if there isn't already one.

Experimental features included with this release

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 LLVMdev list.

Known problems with the X86 back-end
Known problems with the PowerPC back-end
Known problems with the ARM back-end
Known problems with the SPARC back-end
Known problems with the MIPS back-end
Known problems with the Alpha back-end
Known problems with the IA64 back-end
Known problems with the C back-end
Known problems with the llvm-gcc C front-end

llvm-gcc does not currently support Link-Time Optimization on most platforms "out-of-the-box". Please inquire on the LLVMdev mailing list if you are interested.

The only major language feature of GCC not supported by llvm-gcc is the __builtin_apply 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).

If you run into GCC extensions which are not supported, please let us know.

Known problems with the llvm-gcc C++ front-end

The C++ front-end is considered to be fully tested and works for a number of non-trivial programs, including LLVM itself, Qt, Mozilla, etc.

Known problems with the llvm-gcc Fortran front-end
Known problems with the llvm-gcc Ada front-end
The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature technology and problems should be expected.
Additional Information

A wide variety of additional information is available on the LLVM web page, in particular in the documentation 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 "llvm/doc/" directory in the LLVM tree.

If you have any questions or comments about LLVM, please feel free to contact us via the mailing lists.

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Last modified: $Date: 2008/11/10 05:54:43 $