LLVM 2.7 Release Notes
  1. Introduction
  2. Sub-project Status Update
  3. External Projects Using LLVM 2.7
  4. What's New in LLVM 2.7?
  5. Installation Instructions
  6. Portability and Supported Platforms
  7. Known Problems
  8. Additional Information

Written by the LLVM Team

These are in-progress notes for the upcoming LLVM 2.7 release.
You may prefer the LLVM 2.6 Release Notes.

Introduction

This document contains the release notes for the LLVM Compiler Infrastructure, release 2.7. 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.

FIXME: llvm.org moved to new server, mention new logo, Ted and Doug new code owners.

Sub-project Status Update

The LLVM 2.7 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 addition to this code, the LLVM Project includes other sub-projects that are in development. Here we include updates on these subprojects.

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

The Clang project is ...

In the LLVM 2.7 time-frame, the Clang team has made many improvements:

Clang Static Analyzer

Previously announced in the 2.4, 2.5, and 2.6 LLVM releases, 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 checks to find bugs that occur on a specific path within a program.

In the LLVM 2.7 time-frame, the analyzer core has sprouted legs and...

VMKit: JVM/CLI Virtual Machine Implementation

The VMKit project is an implementation of a JVM and a CLI Virtual Machine (Microsoft .NET is an implementation of the CLI) using LLVM for static and just-in-time compilation.

VMKit version ?? builds with LLVM 2.7 and you can find it on its web page. The release includes bug fixes, cleanup and new features. The major changes are:

compiler-rt: Compiler Runtime Library

The new LLVM compiler-rt project is a simple library that provides an implementation of the low-level target-specific hooks required by code generation and other runtime components. For example, when compiling for a 32-bit target, converting a double to a 64-bit unsigned integer is compiled into a runtime call to the "__fixunsdfdi" function. The compiler-rt library provides highly optimized implementations of this and other low-level routines (some are 3x faster than the equivalent libgcc routines).

All of the code in the compiler-rt project is available under the standard LLVM License, a "BSD-style" license.

KLEE: Symbolic Execution and Automatic Test Case Generator

The new LLVM KLEE project is a symbolic execution framework for programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths through the application and records state transitions that lead to fault states. This allows it to construct testcases that lead to faults and can even be used to verify algorithms. For more details, please see the OSDI 2008 paper about KLEE.

DragonEgg: GCC-4.5 as an LLVM frontend

The goal of DragonEgg is to make gcc-4.5 act like llvm-gcc without requiring any gcc modifications whatsoever. DragonEgg is a shared library (dragonegg.so) that is loaded by gcc at runtime. It ...

llvm-mc: Machine Code Toolkit

The LLVM Machine Code (MC) Toolkit project is ...

External Open Source Projects Using LLVM 2.7

An exciting aspect of LLVM is that it is used as an enabling technology for a lot of other language and tools projects. This section lists some of the projects that have already been updated to work with LLVM 2.7.

Rubinius
Need update.

MacRuby

Need update.

Pure

Pure is an algebraic/functional programming language based on term rewriting. Programs are collections of equations which are used to evaluate expressions in a symbolic fashion. Pure offers dynamic typing, eager and lazy evaluation, lexical closures, a hygienic macro system (also based on term rewriting), built-in list and matrix support (including list and matrix comprehensions) and an easy-to-use C interface. The interpreter uses LLVM as a backend to JIT-compile Pure programs to fast native code.

Pure versions 0.43 and later have been tested and are known to work with LLVM 2.7 (and continue to work with older LLVM releases >= 2.5).

LLVM D Compiler

Need update.

Roadsend PHP

Roadsend PHP (rphp) is an open source implementation of the PHP programming language that uses LLVM for its optimizer, JIT and static compiler. This is a reimplementation of an earlier project that is now based on LLVM.

Unladen Swallow

Need update.

llvm-lua

Need update.

IcedTea Java Virtual Machine Implementation

Need update.

What's New in LLVM 2.7?

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 2.7 includes several major new capabilities:

Extensible metadata solid. Debug info improvements: using metadata instead of llvm.dbg global variables. This brings several enhancements including improved compile times. New instruction selector. GHC Haskell ABI/ calling conv support. Pre-Alpha support for unions in IR. New InlineHint and StackAlignment function attributes Code generator MC'ized except for debug info and EH. New SCEV AA pass: -scev-aa Inliner reuses arrays allocas when inlining multiple callers to reduce stack usage. MC encoding and disassembler apis. Optimal Edge Profiling? Instcombine is now a library, has its own IRBuilder to simplify itself. New llvm/Support/Regex.h API. FileCheck now does regex's Many subtle pointer invalidation bugs in Callgraph have been fixed and it now uses asserting value handles. MC Disassembler (with blog post), MCInstPrinter. Many X86 backend and AsmPrinter simplifications Various tools like llc and opt now read either .ll or .bc files as input. Malloc and free instructions got removed. compiler-rt support for ARM. completely llvm-gcc NEON support. Can transcode from GAS to intel syntax with "llvm-mc foo.s -output-asm-variant=1" JIT debug information with GDB 7.0 New CodeGen Level CSE CMake can now run tests, what other improvements? ARM/Thumb using reg scavenging for stack object address materialization (PEI). New SSAUpdater and MachineSSAUpdater classes for unstructured ssa updating, changed jump threading, GVN, etc to use it which simplified them and speed them up. Combiner-AA improvements, why not on by default? Pre-regalloc tail duplication x86 sibcall optimization New LSR with full strength reduction mode The most awesome sext / zext optimization pass. ? CondProp pass removed (functionality merged into jump threading). AndersAA got removed (from 2.7 or mainline?) PredSimplify, LoopVR, GVNPRE got removed. LLVM command line tools now overwrite their output, before they would only do this with -f. DOUT removed, use DEBUG(errs() instead. Much stuff converted to use raw_ostream instead of std::ostream. TargetAsmInfo renamed to MCAsmInfo llvm/ADT/iterator.h gone.
LLVM IR and Core Improvements

LLVM IR has several new features for better support of new targets and that expose new optimization opportunities:

Optimizer Improvements

In addition to a large array of minor performance tweaks and bug fixes, this release includes a few major enhancements and additions to the optimizers:

Also, -anders-aa was removed

Interpreter and JIT Improvements
Target Independent 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:

X86-32 and X86-64 Target Improvements

New features of the X86 target include:

PIC16 Target Improvements

New features of the PIC16 target include:

Things not yet supported:

ARM Target Improvements

New features of the ARM target include:

Other Target Specific Improvements

New features of other targets include:

New Useful APIs

This release includes a number of new APIs that are used internally, which may also be useful for external clients.

Other Improvements and New Features

Other miscellaneous features include:

Major Changes and Removed Features

If you're already an LLVM user or developer with out-of-tree changes based on LLVM 2.6, 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 C back-end
Known problems with the llvm-gcc C and C++ front-end

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 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.
Known problems with the O'Caml bindings

The Llvm.Linkage module is broken, and has incorrect values. Only Llvm.Linkage.External, Llvm.Linkage.Available_externally, and Llvm.Linkage.Link_once will be correct. If you need any of the other linkage modes, you'll have to write an external C library in order to expose the functionality. This has been fixed in the trunk.

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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