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

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.

With the release of LLVM 2.7, VMKit has shifted to a great framework for writing virtual machines. VMKit now offers precise and efficient garbage collection with multi-threading support, thanks to the MMTk memory management toolkit, as well as just in time and ahead of time compilation with LLVM. The major changes in VMKit 0.27 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.

DragonEgg: llvm-gcc ported to gcc-4.5

DragonEgg is a port of llvm-gcc to gcc-4.5. Unlike llvm-gcc, which makes many intrusive changes to the underlying gcc-4.2 code, dragonegg in theory does not require any gcc-4.5 modifications whatsoever (currently one small patch is needed). This is thanks to the new gcc plugin architecture, which makes it possible to modify the behaviour of gcc at runtime by loading a plugin, which is nothing more than a dynamic library which conforms to the gcc plugin interface. DragonEgg is a gcc plugin that causes the LLVM optimizers to be run instead of the gcc optimizers, and the LLVM code generators instead of the gcc code generators, just like llvm-gcc. To use it, you add "-fplugin=path/dragonegg.so" to the gcc-4.5 command line, and gcc-4.5 magically becomes llvm-gcc-4.5!

DragonEgg is still a work in progress. Currently C works very well, while C++, Ada and Fortran work fairly well. All other languages either don't work at all, or only work poorly. For the moment only the x86-32 and x86-64 targets are supported, and only on linux.

DragonEgg has not yet been released. Once gcc-4.5 has been released, dragonegg will probably be released as part of the following LLVM release.

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

Unladen Swallow is a branch of Python intended to be fully compatible and significantly faster. It uses LLVM's optimization passes and JIT compiler.

llvm-lua

Need update.

IcedTea Java Virtual Machine Implementation

Need update.

TTA-based Codesign Environment (TCE)

TCE is a toolset for designing application-specific processors (ASP) based on the Transport triggered architecture (TTA). The toolset provides a complete 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.

TCE uses llvm-gcc/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 loads them in to the compiler backend as runtime libraries to avoid per-target recompilation of larger parts of the compiler chain.

SAFECode Compiler

SAFECode is a memory safe C compiler built using LLVM. It takes standard, unannotated C code, analyzes the code to ensure that memory accesses and array indexing operations are safe, and instruments the code with run-time checks when safety cannot be proven statically.

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, along with LowerAllocations pass. 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 / tailcall optimization in CCC mode. New LSR with full strength reduction mode The most awesome sext / zext optimization pass. ? Better code size analysis in loop unswitch, inliner code split out to a new CodeMetrics class for reuse. The ARM backend now has good support for ARMv4 backend (tested on StrongARM hardware), previously only supported ARMv4T and newer. Half-float support in APFloat Indirect branch + address of label (blog post), particularly useful for interpreters. Many changes to the pass ordering for improved optimization effectiveness. Opt now works conservatively if no target data is set (is this fully working?) Target data now has notion of 'native' integer data types which optimizations can use. ARM backend generates instructions in unified assembly syntax. New Analysis/InstructionSimplify.h interface for simplifying instructions that don't exist. Jump threading is now much more aggressive at simplifying correlated conditionals and threading blocks with otherwise complex logic. CondProp pass removed (functionality merged into jump threading). X86 and XCore supports returning arbitrary return values, returning too many values is supported by returning through a hidden pointer. verbose-asm now produces information about spill slots and loop nests Defaults to RTTI off, packagers should build with make REQUIRE_RTTI=1. 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.
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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