This document contains the release notes for the LLVM Compiler
-Infrastructure, release 2.6. 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.
-The LLVM 2.6 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.
-
The Clang project is an effort to build
-a set of new 'LLVM native' front-end technologies for the C family of languages.
-LLVM 2.6 is the first release to officially include Clang, and it provides a
-production quality C and Objective-C compiler. If you are interested in fast compiles and
-good diagnostics, we
-encourage you to try it out. Clang currently compiles typical Objective-C code
-3x faster than GCC and compiles C code about 30% faster than GCC at -O0 -g
-(which is when the most pressure is on the frontend).
-
-
In addition to supporting these languages, C++ support is also well under way, and mainline
-Clang is able to parse the libstdc++ 4.2 headers and even codegen simple apps.
-If you are interested in Clang C++ support or any other Clang feature, we
-strongly encourage you to get involved on the Clang front-end mailing
-list.
-
-
In the LLVM 2.6 time-frame, the Clang team has made many improvements:
-
-
-
C and Objective-C support are now considered production quality.
-
AuroraUX, FreeBSD and OpenBSD are now supported.
-
Most of Objective-C 2.0 is now supported with the GNU runtime.
-
Many many bugs are fixed and lots of features have been added.
Previously announced in the 2.4 and 2.5 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 2.6 time-frame, the analyzer core has undergone several important
-improvements and cleanups and now includes a new Checker interface that
-is intended to eventually serve as a basis for domain-specific checks. Further,
-in addition to generating HTML files for reporting analysis results, the
-analyzer can now also emit bug reports in a structured XML format that is
-intended to be easily readable by other programs.
-
-
The set of checks performed by the static analyzer continues to expand, 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!
-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 0.26 builds with LLVM 2.6 and you can find it on its
-web page. The release includes
-bug fixes, cleanup and new features. The major changes are:
-
-
-
-
A new llcj tool to generate shared libraries or executables of Java
- files.
-
Cooperative garbage collection.
-
Fast subtype checking (paper from Click et al [JGI'02]).
-
Implementation of a two-word header for Java objects instead of the original
- three-word header.
-
Better Java specification-compliance: division by zero checks, stack
- overflow checks, finalization and references support.
-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.
-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.
-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 (llvm.so)
-that is loaded by gcc at runtime. It uses the new gcc plugin architecture to
-disable the GCC optimizers and code generators, and schedule the LLVM optimizers
-and code generators (or direct output of LLVM IR) instead. Currently only Linux
-and Darwin are supported, and only on x86-32 and x86-64. It should be easy to
-add additional unix-like architectures and other processor families. In theory
-it should be possible to use DragonEgg
-with any language supported by gcc, however only C and Fortran work well for the
-moment. Ada and C++ work to some extent, while Java, Obj-C and Obj-C++ are so
-far entirely untested. Since gcc-4.5 has not yet been released, neither has
-DragonEgg. To build
-DragonEgg you will need to check out the
-development versions of gcc,
-llvm and
-DragonEgg from their respective
-subversion repositories, and follow the instructions in the
-DragonEgg README.
-
-The LLVM Machine Code (MC) Toolkit project is a (very early) effort to build
-better tools for dealing with machine code, object file formats, etc. The idea
-is to be able to generate most of the target specific details of assemblers and
-disassemblers from existing LLVM target .td files (with suitable enhancements),
-and to build infrastructure for reading and writing common object file formats.
-One of the first deliverables is to build a full assembler and integrate it into
-the compiler, which is predicted to substantially reduce compile time in some
-scenarios.
-
-
-
In the LLVM 2.6 timeframe, the MC framework has grown to the point where it
-can reliably parse and pretty print (with some encoding information) a
-darwin/x86 .s file successfully, and has the very early phases of a Mach-O
-assembler in progress. Beyond the MC framework itself, major refactoring of the
-LLVM code generator has started. The idea is to make the code generator reason
-about the code it is producing in a much more semantic way, rather than a
-textual way. For example, the code generator now uses MCSection objects to
-represent section assignments, instead of text strings that print to .section
-directives.
-
-
MC is an early and ongoing project that will hopefully continue to lead to
-many improvements in the code generator and build infrastructure useful for many
-other situations.
-
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 2.6.
Rubinius is an environment
-for running Ruby code which strives to write as much of the core class
-implementation in Ruby as possible. Combined with a bytecode interpreting VM, it
-uses LLVM to optimize and compile ruby code down to machine code. Techniques
-such as type feedback, method inlining, and uncommon traps are all used to
-remove dynamism from ruby execution and increase performance.
-
-
Since LLVM 2.5, Rubinius has made several major leaps forward, implementing
-a counter based JIT, type feedback and speculative method inlining.
-
-MacRuby is an implementation of Ruby on top of
-core Mac OS X technologies, such as the Objective-C common runtime and garbage
-collector and the CoreFoundation framework. It is principally developed by
-Apple and aims at enabling the creation of full-fledged Mac OS X applications.
-
-
-
-MacRuby uses LLVM for optimization passes, JIT and AOT compilation of Ruby
-expressions. It also uses zero-cost DWARF exceptions to implement Ruby exception
-handling.
-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 0.31 and later have been tested and are known to work with
-LLVM 2.6 (and continue to work with older LLVM releases >= 2.3 as well).
-
-LDC is an implementation of
-the D Programming Language using the LLVM optimizer and code generator.
-The LDC project works great with the LLVM 2.6 release. General improvements in
-this
-cycle have included new inline asm constraint handling, better debug info
-support, general bug fixes and better x86-64 support. This has allowed
-some major improvements in LDC, getting it much closer to being as
-fully featured as the original DMD compiler from DigitalMars.
-
-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 is a
-branch of Python intended to be fully
-compatible and significantly faster. It uses LLVM's optimization passes and JIT
-compiler.
-LLVM-Lua uses LLVM to add JIT
-and static compiling support to the Lua VM. Lua bytecode is analyzed to
-remove type checks, then LLVM is used to compile the bytecode down to machine
-code.
-IcedTea provides a
-harness to build OpenJDK using only free software build tools and to provide
-replacements for the not-yet free parts of OpenJDK. One of the extensions that
-IcedTea provides is a new JIT compiler named Shark which uses LLVM
-to provide native code generation without introducing processor-dependent
-code.
-
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.
-
Debug information now includes line numbers when optimizations are enabled.
- This allows statistical sampling tools like OProfile and Shark to map
- samples back to source lines.
-
LLVM now includes new experimental backends to support the MSP430, SystemZ
- and BlackFin architectures.
LLVM now supports doing optimization and code generation on multiple
- threads. Please see the LLVM
- Programmer's Manual for more information.
-
LLVM now has experimental support for embedded
- metadata in LLVM IR, though the implementation is not guaranteed to be
- final and the .bc file format may change in future releases. Debug info
- does not yet use this format in LLVM 2.6.
LLVM IR has several new features for better support of new targets and that
-expose new optimization opportunities:
-
-
-
The add, sub and mul
- instructions have been split into integer and floating point versions (like
- divide and remainder), introducing new fadd, fsub,
- and fmul instructions.
-
The add, sub and mul
- instructions now support optional "nsw" and "nuw" bits which indicate that
- the operation is guaranteed to not overflow (in the signed or
- unsigned case, respectively). This gives the optimizer more information and
- can be used for things like C signed integer values, which are undefined on
- overflow.
-
The sdiv instruction now supports an
- optional "exact" flag which indicates that the result of the division is
- guaranteed to have a remainder of zero. This is useful for optimizing pointer
- subtraction in C.
-
The getelementptr instruction now
- supports arbitrary integer index values for array/pointer indices. This
- allows for better code generation on 16-bit pointer targets like PIC16.
-
The getelementptr instruction now
- supports an "inbounds" optimization hint that tells the optimizer that the
- pointer is guaranteed to be within its allocated object.
-
LLVM now support a series of new linkage types for global values which allow
- for better optimization and new capabilities:
-
-
linkonce_odr and
- weak_odr have the same linkage
- semantics as the non-"odr" linkage types. The difference is that these
- linkage types indicate that all definitions of the specified function
- are guaranteed to have the same semantics. This allows inlining
- templates functions in C++ but not inlining weak functions in C,
- which previously both got the same linkage type.
-
available_externally
- is a new linkage type that gives the optimizer visibility into the
- definition of a function (allowing inlining and side effect analysis)
- but that does not cause code to be generated. This allows better
- optimization of "GNU inline" functions, extern templates, etc.
-
linker_private is a
- new linkage type (which is only useful on Mac OS X) that is used for
- some metadata generation and other obscure things.
-
-
Finally, target-specific intrinsics can now return multiple values, which
- is useful for modeling target operations with multiple results.
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:
-
-
-
-
The Scalar Replacement of Aggregates
- pass has many improvements that allow it to better promote vector unions,
- variables which are memset, and much more strange code that can happen to
- do bitfield accesses to register operations. An interesting change is that
- it now produces "unusual" integer sizes (like i1704) in some cases and lets
- other optimizers clean things up.
-
The Loop Strength Reduction pass now
- promotes small integer induction variables to 64-bit on 64-bit targets,
- which provides a major performance boost for much numerical code. It also
- promotes shorts to int on 32-bit hosts, etc. LSR now also analyzes pointer
- expressions (e.g. getelementptrs), as well as integers.
-
The GVN pass now eliminates partial
- redundancies of loads in simple cases.
-
The Inliner now reuses stack space when
- inlining similar arrays from multiple callees into one caller.
-
LLVM includes a new experimental Static Single Information (SSI)
- construction pass.
LLVM has a new "EngineBuilder" class which makes it more obvious how to
- set up and configure an ExecutionEngine (a JIT or interpreter).
-
The JIT now supports generating more than 16M of code.
-
When configured with --with-oprofile, the JIT can now inform
- OProfile about JIT'd code, allowing OProfile to get line number and function
- name information for JIT'd functions.
-
When "libffi" is available, the LLVM interpreter now uses it, which supports
- calling almost arbitrary external (natively compiled) functions.
-
Clients of the JIT can now register a 'JITEventListener' object to receive
- callbacks when the JIT emits or frees machine code. The OProfile support
- uses this mechanism.
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:
-
-
-
-
The llc -asm-verbose option (exposed from llvm-gcc as -dA
- and clang as -fverbose-asm or -dA) now adds a lot of
- useful information in comments to
- the generated .s file. This information includes location information (if
- built with -g) and loop nest information.
-
The code generator now supports a new MachineVerifier pass which is useful
- for finding bugs in targets and codegen passes.
-
The Machine LICM is now enabled by default. It hoists instructions out of
- loops (such as constant pool loads, loads from read-only stubs, vector
- constant synthesization code, etc.) and is currently configured to only do
- so when the hoisted operation can be rematerialized.
-
The Machine Sinking pass is now enabled by default. This pass moves
- side-effect free operations down the CFG so that they are executed on fewer
- paths through a function.
-
The code generator now performs "stack slot coloring" of register spills,
- which allows spill slots to be reused. This leads to smaller stack frames
- in cases where there are lots of register spills.
-
The register allocator has many improvements to take better advantage of
- commutable operations, various spiller peephole optimizations, and can now
- coalesce cross-register-class copies.
-
Tblgen now supports multiclass inheritance and a number of new string and
- list operations like !(subst), !(foreach), !car,
- !cdr, !null, !if, !cast.
- These make the .td files more expressive and allow more aggressive factoring
- of duplication across instruction patterns.
-
Target-specific intrinsics can now be added without having to hack VMCore to
- add them. This makes it easier to maintain out-of-tree targets.
-
The instruction selector is better at propagating information about values
- (such as whether they are sign/zero extended etc.) across basic block
- boundaries.
-
The SelectionDAG datastructure has new nodes for representing buildvector
- and vector shuffle operations. This
- makes operations and pattern matching more efficient and easier to get
- right.
-
The Prolog/Epilog Insertion Pass now has experimental support for performing
- the "shrink wrapping" optimization, which moves spills and reloads around in
- the CFG to avoid doing saves on paths that don't need them.
-
LLVM includes new experimental support for writing ELF .o files directly
- from the compiler. It works well for many simple C testcases, but doesn't
- support exception handling, debug info, inline assembly, etc.
-
Targets can now specify register allocation hints through
- MachineRegisterInfo::setRegAllocationHint. A regalloc hint consists
- of hint type and physical register number. A hint type of zero specifies a
- register allocation preference. Other hint type values are target specific
- which are resolved by TargetRegisterInfo::ResolveRegAllocHint. An
- example is the ARM target which uses register hints to request that the
- register allocator provide an even / odd register pair to two virtual
- registers.
GCC-compatible soft float modes are now supported, which are typically used
- by OS kernels.
-
X86-64 now models implicit zero extensions better, which allows the code
- generator to remove a lot of redundant zexts. It also models the 8-bit "H"
- registers as subregs, which allows them to be used in some tricky
- situations.
-
X86-64 now supports the "local exec" and "initial exec" thread local storage
- model.
-
The vector forms of the icmp and fcmp instructions now select to efficient
- SSE operations.
-
Support for the win64 calling conventions have improved. The primary
- missing feature is support for varargs function definitions. It seems to
- work well for many win64 JIT purposes.
-
The X86 backend has preliminary support for mapping address spaces to segment
- register references. This allows you to write GS or FS relative memory
- accesses directly in LLVM IR for cases where you know exactly what you're
- doing (such as in an OS kernel). There are some known problems with this
- support, but it works in simple cases.
-
The X86 code generator has been refactored to move all global variable
- reference logic to one place
- (X86Subtarget::ClassifyGlobalReference) which
- makes it easier to reason about.
Preliminary support for processors, such as the Cortex-A8 and Cortex-A9,
-that implement version v7-A of the ARM architecture. The ARM backend now
-supports both the Thumb2 and Advanced SIMD (Neon) instruction sets.
-
-
The AAPCS-VFP "hard float" calling conventions are also supported with the
--float-abi=hard flag.
-
-
The ARM calling convention code is now tblgen generated instead of resorting
- to C++ code.
-
-
-
These features are still somewhat experimental
-and subject to change. The Neon intrinsics, in particular, may change in future
-releases of LLVM. ARMv7 support has progressed a lot on top of tree since 2.6
-branched.
This release includes a number of new APIs that are used internally, which
- may also be useful for external clients.
-
-
-
-
New
- PrettyStackTrace class allows crashes of llvm tools (and applications
- that integrate them) to provide more detailed indication of what the
- compiler was doing at the time of the crash (e.g. running a pass).
- At the top level for each LLVM tool, it includes the command line arguments.
-
-
New StringRef
- and Twine classes
- make operations on character ranges and
- string concatenation to be more efficient. StringRef is just a const
- char* with a length, Twine is a light-weight rope.
-
LLVM has new WeakVH, AssertingVH and CallbackVH
- classes, which make it easier to write LLVM IR transformations. WeakVH
- is automatically drops to null when the referenced Value is deleted,
- and is updated across a replaceAllUsesWith operation.
- AssertingVH aborts the program if the
- referenced value is destroyed while it is being referenced. CallbackVH
- is a customizable class for handling value references. See ValueHandle.h
- for more information.
-
The new 'Triple
- ' class centralizes a lot of logic that reasons about target
- triples.
-
The new '
- llvm_report_error()' set of APIs allows tools to embed the LLVM
- optimizer and backend and recover from previously unrecoverable errors.
LLVM has new
- SourceMgr and SMLoc classes which implement caret
- diagnostics and basic include stack processing for simple parsers. It is
- used by tablegen, llvm-mc, the .ll parser and FileCheck.
LLVM now includes a new internal 'FileCheck' tool which allows
- writing much more accurate regression tests that run faster. Please see the
- FileCheck section of the Testing
- Guide for more information.
-
LLVM profile information support has been significantly improved to produce
-correct use counts, and has support for edge profiling with reduced runtime
-overhead. Combined, the generated profile information is both more correct and
-imposes about half as much overhead (2.6. from 12% to 6% overhead on SPEC
-CPU2000).
-
The C bindings (in the llvm/include/llvm-c directory) include many newly
- supported APIs.
-
LLVM 2.6 includes a brand new experimental LLVM bindings to the Ada2005
- programming language.
-
-
The LLVMC driver has several new features:
-
-
Dynamic plugins now work on Windows.
-
New option property: init. Makes possible to provide default values for
- options defined in plugins (interface to cl::init).
-
New example: Skeleton, shows how to create a standalone LLVMC-based
- driver.
-
New example: mcc16, a driver for the PIC16 toolchain.
If you're already an LLVM user or developer with out-of-tree changes based
-on LLVM 2.5, this section lists some "gotchas" that you may run into upgrading
-from the previous release.
-
-
-
The Itanium (IA64) backend has been removed. It was not actively supported
- and had bitrotted.
-
The BigBlock register allocator has been removed, it had also bitrotted.
-
The C Backend (-march=c) is no longer considered part of the LLVM release
-criteria. We still want it to work, but no one is maintaining it and it lacks
-support for arbitrary precision integers and other important IR features.
-
-
All LLVM tools now default to overwriting their output file, behaving more
- like standard unix tools. Previously, this only happened with the '-f'
- option.
-
LLVM build now builds all libraries as .a files instead of some
- libraries as relinked .o files. This requires some APIs like
- InitializeAllTargets.h.
-
-
-
-
-
In addition, many APIs have changed in this release. Some of the major LLVM
-API changes are:
-
-
-
All uses of hash_set and hash_map have been removed from
- the LLVM tree and the wrapper headers have been removed.
-
The llvm/Streams.h and DOUT member of Debug.h have been removed. The
- llvm::Ostream class has been completely removed and replaced with
- uses of raw_ostream.
-
LLVM's global uniquing tables for Types and Constants have
- been privatized into members of an LLVMContext. A number of APIs
- now take an LLVMContext as a parameter. To smooth the transition
- for clients that will only ever use a single context, the new
- getGlobalContext() API can be used to access a default global
- context which can be passed in any and all cases where a context is
- required.
-
The getABITypeSize methods are now called getAllocSize.
-
The Add, Sub and Mul operators are no longer
- overloaded for floating-point types. Floating-point addition, subtraction
- and multiplication are now represented with new operators FAdd,
- FSub and FMul. In the IRBuilder API,
- CreateAdd, CreateSub, CreateMul and
- CreateNeg should only be used for integer arithmetic now;
- CreateFAdd, CreateFSub, CreateFMul and
- CreateFNeg should now be used for floating-point arithmetic.
-
The DynamicLibrary class can no longer be constructed, its functionality has
- moved to static member functions.
-
raw_fd_ostream's constructor for opening a given filename now
- takes an extra Force argument. If Force is set to
- false, an error will be reported if a file with the given name
- already exists. If Force is set to true, the file will
- be silently truncated (which is the behavior before this flag was
- added).
-
SCEVHandle no longer exists, because reference counting is no
- longer done for SCEV* objects, instead const SCEV*
- should be used.
-
-
Many APIs, notably llvm::Value, now use the StringRef
-and Twine classes instead of passing const char*
-or std::string, as described in
-the Programmer's Manual. Most
-clients should be unaffected by this transition, unless they are used to
-Value::getName() returning a string. Here are some tips on updating to
-2.6:
-
-
getNameStr() is still available, and matches the old
- behavior. Replacing getName() calls with this is an safe option,
- although more efficient alternatives are now possible.
-
-
If you were just relying on getName() being able to be sent to
- a std::ostream, consider migrating
- to llvm::raw_ostream.
-
-
If you were using getName().c_str() to get a const
- char* pointer to the name, you can use getName().data().
- Note that this string (as before), may not be the entire name if the
- name contains embedded null characters.
-
-
If you were using operator + on the result of getName() and
- treating the result as an std::string, you can either
- use Twine::str to get the result as an std::string, or
- could move to a Twine based design.
-
-
isName() should be replaced with comparison
- against getName() (this is now efficient).
-
-
-
-
The registration interfaces for backend Targets has changed (what was
-previously TargetMachineRegistry). For backend authors, see the Writing An LLVM Backend
-guide. For clients, the notable API changes are:
-
-
TargetMachineRegistry has been renamed
- to TargetRegistry.
-
-
Clients should move to using the TargetRegistry::lookupTarget()
- function to find targets.
Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat
- Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like
- systems).
-
PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit
- and 64-bit modes.
-
Intel and AMD machines running on Win32 using MinGW libraries (native).
-
Intel and AMD machines running on Win32 with the Cygwin libraries (limited
- support is available for native builds with Visual C++).
-
Sun UltraSPARC workstations running Solaris 10.
-
Alpha-based machines running Debian GNU/Linux.
-
-
-
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.
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.
-
-
-
The llvm-gcc bootstrap will fail with some versions of binutils (e.g. 2.15)
- with a message of "Error: can not do 8
- byte pc-relative relocation" when building C++ code. We intend to
- fix this on mainline, but a workaround for 2.6 is to upgrade to binutils
- 2.17 or later.
-
-
LLVM will not correctly compile on Solaris and/or OpenSolaris
-using the stock GCC 3.x.x series 'out the box',
-See: Broken versions of GCC and other tools.
-However, A Modern GCC Build
-for x86/x86-64 has been made available from the third party AuroraUX Project
-that has been meticulously tested for bootstrapping LLVM & Clang.
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.
-
-
-
The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430 and SystemZ backends are
- experimental.
-
The llc "-filetype=asm" (the default) is the only
- supported value for this option. The ELF writer is experimental.
-
The implementation of Andersen's Alias Analysis has many known bugs.
The X86 backend generates inefficient floating point code when configured
- to generate code for systems that don't have SSE2.
-
Win64 code generation wasn't widely tested. Everything should work, but we
- expect small issues to happen. Also, llvm-gcc cannot build the mingw64
- runtime currently due
- to several
- bugs and due to lack of support for
- the
- 'u' inline assembly constraint and for X87 floating point inline assembly.
-
The X86-64 backend does not yet support the LLVM IR instruction
- va_arg. Currently, the llvm-gcc and front-ends support variadic
- argument constructs on X86-64 by lowering them manually.
Support for the Advanced SIMD (Neon) instruction set is still incomplete
-and not well tested. Some features may not work at all, and the code quality
-may be poor in some cases.
-
Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
-processors, thumb programs can crash or produce wrong
-results (PR1388).
-
Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
-
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.
-
-The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature
-technology, and problems should be expected.
-
-
The Ada front-end currently only builds on X86-32. This is mainly due
-to lack of trampoline support (pointers to nested functions) on other platforms.
-However, it also fails to build on X86-64
-which does support trampolines.
-
The Ada front-end fails to bootstrap.
-This is due to lack of LLVM support for setjmp/longjmp style
-exception handling, which is used internally by the compiler.
-Workaround: configure with --disable-bootstrap.
-
The c380004, c393010
-and cxg2021 ACATS tests fail
-(c380004 also fails with gcc-4.2 mainline).
-If the compiler is built with checks disabled then c393010
-causes the compiler to go into an infinite loop, using up all system memory.
-
Some GCC specific Ada tests continue to crash the compiler.
-
The -E binder option (exception backtraces)
-does not work and will result in programs
-crashing if an exception is raised. Workaround: do not use -E.
-
Only discrete types are allowed to start
-or finish at a non-byte offset in a record. Workaround: do not pack records
-or use representation clauses that result in a field of a non-discrete type
-starting or finishing in the middle of a byte.
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.
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.
This document contains the release notes for the LLVM Compiler
-Infrastructure, release 2.5. Here we describe the status of LLVM, including
+Infrastructure, release 2.6. 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.
@@ -51,25 +51,37 @@ current one. To see the release notes for a specific release, please see the
releases page.
+
-
+
+
+
@@ -80,12 +92,11 @@ initial support for debug line numbers when optimization enabled, not useful in
-The LLVM 2.5 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.
+The LLVM 2.6 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.
The Clang project is an effort to build
-a set of new 'LLVM native' front-end technologies for the LLVM optimizer and
-code generator. While Clang is not included in the LLVM 2.5 release, it is
-continuing to make major strides forward in all areas. Its C and Objective-C
-parsing and code generation support is now very solid. For example, it is
-capable of successfully building many real-world applications for X86-32
-and X86-64,
-including the FreeBSD
-kernel and gcc 4.2. C++ is also
-making incredible progress,
-and work on templates has recently started. If you are
-interested in fast compiles and good diagnostics, we encourage you to try it out
-by building from mainline
-and reporting any issues you hit to the fast compiles and
+good diagnostics, we
+encourage you to try it out. Clang currently compiles typical Objective-C code
+3x faster than GCC and compiles C code about 30% faster than GCC at -O0 -g
+(which is when the most pressure is on the frontend).
+
+
In addition to supporting these languages, C++ support is also well under way, and mainline
+Clang is able to parse the libstdc++ 4.2 headers and even codegen simple apps.
+If you are interested in Clang C++ support or any other Clang feature, we
+strongly encourage you to get involved on the Clang front-end mailing
list.
-
In the LLVM 2.5 time-frame, the Clang team has made many improvements:
+
In the LLVM 2.6 time-frame, the Clang team has made many improvements:
-
Clang now has a new driver, which is focused on providing a GCC-compatible
- interface.
-
The X86-64 ABI is now supported, including support for the Apple
- 64-bit Objective-C runtime and zero cost exception handling.
-
Precompiled header support is now implemented.
-
Objective-C support is significantly improved beyond LLVM 2.4, supporting
- many features, such as Objective-C Garbage Collection.
-
Variable length arrays are now fully supported.
-
C99 designated initializers are now fully supported.
-
Clang now includes all major compiler headers, including a
- redesigned tgmath.h and several more intrinsic headers.
-
Many many bugs are fixed and many features have been added.
+
C and Objective-C support are now considered production quality.
+
AuroraUX, FreeBSD and OpenBSD are now supported.
+
Most of Objective-C 2.0 is now supported with the GNU runtime.
+
Many many bugs are fixed and lots of features have been added.
@@ -140,19 +144,18 @@ list.
-
Previously announced in the last LLVM release, the Clang project also
+
Previously announced in the 2.4 and 2.5 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 a growing set of checks to find
+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 2.5 time-frame there have been many significant improvements to
-the analyzer's core path simulation engine and machinery for generating
-path-based bug reports to end-users. Particularly noteworthy improvements
-include experimental support for full field-sensitivity and reasoning about heap
-objects as well as an improved value-constraints subengine that does a much
-better job of reasoning about inequality relationships (e.g., x > 2)
-between variables and constants.
+
In the LLVM 2.6 time-frame, the analyzer core has undergone several important
+improvements and cleanups and now includes a new Checker interface that
+is intended to eventually serve as a basis for domain-specific checks. Further,
+in addition to generating HTML files for reporting analysis results, the
+analyzer can now also emit bug reports in a structured XML format that is
+intended to be easily readable by other programs.
The set of checks performed by the static analyzer continues to expand, and
future plans for the tool include full source-level inter-procedural analysis
@@ -170,44 +173,191 @@ this project is encouraged to get involved!
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.
+a JVM and a CLI Virtual Machine (Microsoft .NET is an
+implementation of the CLI) using LLVM for static and just-in-time
+compilation.
-
Following LLVM 2.5, VMKit has its second release that you can find on its
-webpage. The release includes
+
+VMKit version 0.26 builds with LLVM 2.6 and you can find it on its
+web page. The release includes
bug fixes, cleanup and new features. The major changes are:
-
Ahead of Time compiler: compiles .class files to llvm .bc. VMKit uses this
-functionality to native compile the standard classes (e.g. java.lang.String).
-Users can compile AoT .class files into dynamic libraries and run them with the
-help of VMKit.
-
-
New exception model: the dwarf exception model is very slow for
-exception-intensive applications, so the JVM has had a new implementation of
-exceptions which check at each function call if an exception happened. There is
-a low performance penalty on applications without exceptions, but it is a big
-gain for exception-intensive applications. For example the jack benchmark in
-Spec JVM98 is 6x faster (performance gain of 83%).
-
-
User-level management of thread stacks, so that thread local data access
-at runtime is fast and portable.
-
-
Implementation of biased locking for faster object synchronizations at
-runtime.
-
-
New support for OSX/X64, Linux/X64 (with the Boehm GC) and Linux/ppc32.
+
A new llcj tool to generate shared libraries or executables of Java
+ files.
+
Cooperative garbage collection.
+
Fast subtype checking (paper from Click et al [JGI'02]).
+
Implementation of a two-word header for Java objects instead of the original
+ three-word header.
+
Better Java specification-compliance: division by zero checks, stack
+ overflow checks, finalization and references support.
+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.
+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.
+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 (llvm.so)
+that is loaded by gcc at runtime. It uses the new gcc plugin architecture to
+disable the GCC optimizers and code generators, and schedule the LLVM optimizers
+and code generators (or direct output of LLVM IR) instead. Currently only Linux
+and Darwin are supported, and only on x86-32 and x86-64. It should be easy to
+add additional unix-like architectures and other processor families. In theory
+it should be possible to use DragonEgg
+with any language supported by gcc, however only C and Fortran work well for the
+moment. Ada and C++ work to some extent, while Java, Obj-C and Obj-C++ are so
+far entirely untested. Since gcc-4.5 has not yet been released, neither has
+DragonEgg. To build
+DragonEgg you will need to check out the
+development versions of gcc,
+llvm and
+DragonEgg from their respective
+subversion repositories, and follow the instructions in the
+DragonEgg README.
+
+The LLVM Machine Code (MC) Toolkit project is a (very early) effort to build
+better tools for dealing with machine code, object file formats, etc. The idea
+is to be able to generate most of the target specific details of assemblers and
+disassemblers from existing LLVM target .td files (with suitable enhancements),
+and to build infrastructure for reading and writing common object file formats.
+One of the first deliverables is to build a full assembler and integrate it into
+the compiler, which is predicted to substantially reduce compile time in some
+scenarios.
+
+
+
In the LLVM 2.6 timeframe, the MC framework has grown to the point where it
+can reliably parse and pretty print (with some encoding information) a
+darwin/x86 .s file successfully, and has the very early phases of a Mach-O
+assembler in progress. Beyond the MC framework itself, major refactoring of the
+LLVM code generator has started. The idea is to make the code generator reason
+about the code it is producing in a much more semantic way, rather than a
+textual way. For example, the code generator now uses MCSection objects to
+represent section assignments, instead of text strings that print to .section
+directives.
+
+
MC is an early and ongoing project that will hopefully continue to lead to
+many improvements in the code generator and build infrastructure useful for many
+other situations.
+
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 2.6.
Rubinius is an environment
+for running Ruby code which strives to write as much of the core class
+implementation in Ruby as possible. Combined with a bytecode interpreting VM, it
+uses LLVM to optimize and compile ruby code down to machine code. Techniques
+such as type feedback, method inlining, and uncommon traps are all used to
+remove dynamism from ruby execution and increase performance.
+
+
Since LLVM 2.5, Rubinius has made several major leaps forward, implementing
+a counter based JIT, type feedback and speculative method inlining.
+
+MacRuby is an implementation of Ruby on top of
+core Mac OS X technologies, such as the Objective-C common runtime and garbage
+collector and the CoreFoundation framework. It is principally developed by
+Apple and aims at enabling the creation of full-fledged Mac OS X applications.
+
+
+
+MacRuby uses LLVM for optimization passes, JIT and AOT compilation of Ruby
+expressions. It also uses zero-cost DWARF exceptions to implement Ruby exception
+handling.
+
+
+
+
Pure
@@ -224,12 +374,8 @@ 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.
-
In addition to the usual algebraic data structures, Pure also has
-MATLAB-style matrices in order to support numeric computations and signal
-processing in an efficient way. Pure is mainly aimed at mathematical
-applications right now, but it has been designed as a general purpose language.
-The dynamic interpreter environment and the C interface make it possible to use
-it as a kind of functional scripting language for many application areas.
+
Pure versions 0.31 and later have been tested and are known to work with
+LLVM 2.6 (and continue to work with older LLVM releases >= 2.3 as well).
@@ -243,11 +389,11 @@ it as a kind of functional scripting language for many application areas.
LDC is an implementation of
the D Programming Language using the LLVM optimizer and code generator.
-The LDC project works great with the LLVM 2.5 release. General improvements in
+The LDC project works great with the LLVM 2.6 release. General improvements in
this
cycle have included new inline asm constraint handling, better debug info
-support, general bugfixes, and better x86-64 support. This has allowed
-some major improvements in LDC, getting us much closer to being as
+support, general bug fixes and better x86-64 support. This has allowed
+some major improvements in LDC, getting it much closer to being as
fully featured as the original DMD compiler from DigitalMars.
@@ -258,25 +404,71 @@ fully featured as the original DMD compiler from DigitalMars.
+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
+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 is a
+branch of Python intended to be fully
+compatible and significantly faster. It uses LLVM's optimization passes and JIT
+compiler.
+LLVM-Lua uses LLVM to add JIT
+and static compiling support to the Lua VM. Lua bytecode is analyzed to
+remove type checks, then LLVM is used to compile the bytecode down to machine
+code.
+IcedTea provides a
+harness to build OpenJDK using only free software build tools and to provide
+replacements for the not-yet free parts of OpenJDK. One of the extensions that
+IcedTea provides is a new JIT compiler named Shark which uses LLVM
+to provide native code generation without introducing processor-dependent
+code.
+
This release includes a huge number of bug fixes, performance tweaks, and
+
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.
llvm-gcc now generally supports the GFortran front-end, and the precompiled
-release binaries now support Fortran, even on Mac OS/X.
-
-
CMake is now used by the LLVM build process
-on Windows. It automatically generates Visual Studio project files (and
-more) from a set of simple text files. This makes it much easier to
-maintain. In time, we'd like to standardize on CMake for everything.
-
-
LLVM 2.5 now uses (and includes) Google Test for unit testing.
-
-
The LLVM native code generator now supports arbitrary precision integers.
-Types like i33 have long been valid in the LLVM IR, but were previously
-only supported by the interpreter. Note that the C backend still does not
-support these.
-
-
LLVM 2.5 no longer uses 'bison,' so it is easier to build on Windows.
Debug information now includes line numbers when optimizations are enabled.
+ This allows statistical sampling tools like OProfile and Shark to map
+ samples back to source lines.
+
LLVM now includes new experimental backends to support the MSP430, SystemZ
+ and BlackFin architectures.
LLVM now supports doing optimization and code generation on multiple
+ threads. Please see the LLVM
+ Programmer's Manual for more information.
+
LLVM now has experimental support for embedded
+ metadata in LLVM IR, though the implementation is not guaranteed to be
+ final and the .bc file format may change in future releases. Debug info
+ does not yet use this format in LLVM 2.6.
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.
-
-
-
In this release, the GCC inliner is completely disabled. Previously the GCC
-inliner was used to handle always-inline functions and other cases. This caused
-problems with code size growth, and it is completely disabled in this
-release.
-
-
llvm-gcc (and LLVM in general) now support code generation for stack
-canaries, which is an effective form of buffer overflow
-protection. llvm-gcc supports this with the -fstack-protector
-command line option (just like GCC). In LLVM IR, you can request code
-generation for stack canaries with function attributes.
-
LLVM IR has several new features that are used by our existing front-ends and
-can be useful if you are writing a front-end for LLVM:
+
LLVM IR has several new features for better support of new targets and that
+expose new optimization opportunities:
-
The shufflevector instruction
-has been generalized to allow different shuffle mask width than its input
-vectors. This allows you to use shufflevector to combine two
-"<4 x float>" vectors into a "<8 x float>" for example.
-
-
LLVM IR now supports new intrinsics for computing and acting on overflow of integer operations. This allows
-efficient code generation for languages that must trap or throw an exception on
-overflow. While these intrinsics work on all targets, they only generate
-efficient code on X86 so far.
-
-
LLVM IR now supports a new private
-linkage type to produce labels that are stripped by the assembler before it
-produces a .o file (thus they are invisible to the linker).
-
-
LLVM IR supports two new attributes for better alias analysis. The noalias attribute can now be used on the
-return value of a function to indicate that it returns new memory (e.g.
-'malloc', 'calloc', etc).
-The new nocapture attribute can be used
-on pointer arguments to indicate that the function does not return the pointer,
-store it in an object that outlives the call, or let the value of the pointer
-escape from the function in any other way.
-Note that it is the pointer itself that must not escape, not the value it
-points to: loading a value out of the pointer is perfectly fine.
-Many standard library functions (e.g. 'strlen', 'memcpy') have this property.
-
-
-
-
The parser for ".ll" files in lib/AsmParser is now completely rewritten as a
-recursive descent parser. This parser produces better error messages (including
-caret diagnostics), is less fragile (less likely to crash on strange things),
-does not leak memory, is more efficient, and eliminates LLVM's last use of the
-'bison' tool.
-
-
Debug information representation and manipulation internals have been
- consolidated to use a new set of classes in
- llvm/Analysis/DebugInfo.h. These routines are more
- efficient, robust, and extensible and replace the older mechanisms.
- llvm-gcc, clang, and the code generator now use them to create and process
- debug information.
-
+
The add, sub and mul
+ instructions have been split into integer and floating point versions (like
+ divide and remainder), introducing new fadd, fsub,
+ and fmul instructions.
+
The add, sub and mul
+ instructions now support optional "nsw" and "nuw" bits which indicate that
+ the operation is guaranteed to not overflow (in the signed or
+ unsigned case, respectively). This gives the optimizer more information and
+ can be used for things like C signed integer values, which are undefined on
+ overflow.
+
The sdiv instruction now supports an
+ optional "exact" flag which indicates that the result of the division is
+ guaranteed to have a remainder of zero. This is useful for optimizing pointer
+ subtraction in C.
+
The getelementptr instruction now
+ supports arbitrary integer index values for array/pointer indices. This
+ allows for better code generation on 16-bit pointer targets like PIC16.
+
The getelementptr instruction now
+ supports an "inbounds" optimization hint that tells the optimizer that the
+ pointer is guaranteed to be within its allocated object.
+
LLVM now support a series of new linkage types for global values which allow
+ for better optimization and new capabilities:
+
+
linkonce_odr and
+ weak_odr have the same linkage
+ semantics as the non-"odr" linkage types. The difference is that these
+ linkage types indicate that all definitions of the specified function
+ are guaranteed to have the same semantics. This allows inlining
+ templates functions in C++ but not inlining weak functions in C,
+ which previously both got the same linkage type.
+
available_externally
+ is a new linkage type that gives the optimizer visibility into the
+ definition of a function (allowing inlining and side effect analysis)
+ but that does not cause code to be generated. This allows better
+ optimization of "GNU inline" functions, extern templates, etc.
+
linker_private is a
+ new linkage type (which is only useful on Mac OS X) that is used for
+ some metadata generation and other obscure things.
+
+
Finally, target-specific intrinsics can now return multiple values, which
+ is useful for modeling target operations with multiple results.
@@ -405,27 +569,53 @@ does not leak memory, is more efficient, and eliminates LLVM's last use of the
-
In addition to a large array of bug fixes and minor performance tweaks, this
+
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:
-
The loop optimizer now improves floating point induction variables in
-several ways, including adding shadow induction variables to avoid
-"integer <-> floating point" conversions in loops when safe.
+
The Scalar Replacement of Aggregates
+ pass has many improvements that allow it to better promote vector unions,
+ variables which are memset, and much more strange code that can happen to
+ do bitfield accesses to register operations. An interesting change is that
+ it now produces "unusual" integer sizes (like i1704) in some cases and lets
+ other optimizers clean things up.
+
The Loop Strength Reduction pass now
+ promotes small integer induction variables to 64-bit on 64-bit targets,
+ which provides a major performance boost for much numerical code. It also
+ promotes shorts to int on 32-bit hosts, etc. LSR now also analyzes pointer
+ expressions (e.g. getelementptrs), as well as integers.
+
The GVN pass now eliminates partial
+ redundancies of loads in simple cases.
+
The Inliner now reuses stack space when
+ inlining similar arrays from multiple callees into one caller.
+
LLVM includes a new experimental Static Single Information (SSI)
+ construction pass.
-
The "-mem2reg" pass is now much faster on code with large basic blocks.
+
-
The "-jump-threading" pass is more powerful: it is iterative
- and handles threading based on values with fully and partially redundant
- loads.
+
-
The "-memdep" memory dependence analysis pass (used by GVN and memcpyopt) is
- both faster and more aggressive.
-
The "-scalarrepl" scalar replacement of aggregates pass is more aggressive
- about promoting unions to registers.
LLVM has a new "EngineBuilder" class which makes it more obvious how to
+ set up and configure an ExecutionEngine (a JIT or interpreter).
+
The JIT now supports generating more than 16M of code.
+
When configured with --with-oprofile, the JIT can now inform
+ OProfile about JIT'd code, allowing OProfile to get line number and function
+ name information for JIT'd functions.
+
When "libffi" is available, the LLVM interpreter now uses it, which supports
+ calling almost arbitrary external (natively compiled) functions.
+
Clients of the JIT can now register a 'JITEventListener' object to receive
+ callbacks when the JIT emits or frees machine code. The OProfile support
+ uses this mechanism.
@@ -442,33 +632,55 @@ infrastructure, which allows us to implement more aggressive algorithms and make
it run faster:
The SelectionDAG type legalization logic has been completely rewritten, is
-now more powerful (it supports arbitrary precision integer types for example),
-and is more correct in several corner cases. The type legalizer converts
-operations on types that are not natively supported by the target machine into
-equivalent code sequences that only use natively supported types. The old type
-legalizer is still available (for now) and will be used if
--disable-legalize-types is passed to the code generator.
-
-
-
The code generator now supports widening illegal vectors to larger legal
-ones (for example, converting operations on <3 x float> to work on
-<4 x float>) which is very important for common graphics
-applications.
-
-
The assembly printers for each target are now split out into their own
-libraries that are separate from the main code generation logic. This reduces
-the code size of JIT compilers by not requiring them to be linked in.
-
-
The 'fast' instruction selection path (used at -O0 and for fast JIT
- compilers) now supports accelerating codegen for code that uses exception
- handling constructs.
-
-
The optional PBQP register allocator now supports register coalescing.
+
The llc -asm-verbose option (exposed from llvm-gcc as -dA
+ and clang as -fverbose-asm or -dA) now adds a lot of
+ useful information in comments to
+ the generated .s file. This information includes location information (if
+ built with -g) and loop nest information.
+
The code generator now supports a new MachineVerifier pass which is useful
+ for finding bugs in targets and codegen passes.
+
The Machine LICM is now enabled by default. It hoists instructions out of
+ loops (such as constant pool loads, loads from read-only stubs, vector
+ constant synthesization code, etc.) and is currently configured to only do
+ so when the hoisted operation can be rematerialized.
+
The Machine Sinking pass is now enabled by default. This pass moves
+ side-effect free operations down the CFG so that they are executed on fewer
+ paths through a function.
+
The code generator now performs "stack slot coloring" of register spills,
+ which allows spill slots to be reused. This leads to smaller stack frames
+ in cases where there are lots of register spills.
+
The register allocator has many improvements to take better advantage of
+ commutable operations, various spiller peephole optimizations, and can now
+ coalesce cross-register-class copies.
+
Tblgen now supports multiclass inheritance and a number of new string and
+ list operations like !(subst), !(foreach), !car,
+ !cdr, !null, !if, !cast.
+ These make the .td files more expressive and allow more aggressive factoring
+ of duplication across instruction patterns.
+
Target-specific intrinsics can now be added without having to hack VMCore to
+ add them. This makes it easier to maintain out-of-tree targets.
+
The instruction selector is better at propagating information about values
+ (such as whether they are sign/zero extended etc.) across basic block
+ boundaries.
+
The SelectionDAG datastructure has new nodes for representing buildvector
+ and vector shuffle operations. This
+ makes operations and pattern matching more efficient and easier to get
+ right.
+
The Prolog/Epilog Insertion Pass now has experimental support for performing
+ the "shrink wrapping" optimization, which moves spills and reloads around in
+ the CFG to avoid doing saves on paths that don't need them.
+
LLVM includes new experimental support for writing ELF .o files directly
+ from the compiler. It works well for many simple C testcases, but doesn't
+ support exception handling, debug info, inline assembly, etc.
+
Targets can now specify register allocation hints through
+ MachineRegisterInfo::setRegAllocationHint. A regalloc hint consists
+ of hint type and physical register number. A hint type of zero specifies a
+ register allocation preference. Other hint type values are target specific
+ which are resolved by TargetRegisterInfo::ResolveRegAllocHint. An
+ example is the ARM target which uses register hints to request that the
+ register allocator provide an even / odd register pair to two virtual
+ registers.
@@ -482,37 +694,33 @@ the code size of JIT compilers by not requiring them to be linked in.
-
The llvm.returnaddress
-intrinsic (which is used to implement __builtin_return_address) now
-supports non-zero stack depths on X86.
-
The X86 backend now supports code generation of vector shift operations
-using SSE instructions.
+
SSE 4.2 builtins are now supported.
+
GCC-compatible soft float modes are now supported, which are typically used
+ by OS kernels.
+
X86-64 now models implicit zero extensions better, which allows the code
+ generator to remove a lot of redundant zexts. It also models the 8-bit "H"
+ registers as subregs, which allows them to be used in some tricky
+ situations.
+
X86-64 now supports the "local exec" and "initial exec" thread local storage
+ model.
+
The vector forms of the icmp and fcmp instructions now select to efficient
+ SSE operations.
+
Support for the win64 calling conventions have improved. The primary
+ missing feature is support for varargs function definitions. It seems to
+ work well for many win64 JIT purposes.
+
The X86 backend has preliminary support for mapping address spaces to segment
+ register references. This allows you to write GS or FS relative memory
+ accesses directly in LLVM IR for cases where you know exactly what you're
+ doing (such as in an OS kernel). There are some known problems with this
+ support, but it works in simple cases.
+
The X86 code generator has been refactored to move all global variable
+ reference logic to one place
+ (X86Subtarget::ClassifyGlobalReference) which
+ makes it easier to reason about.
-
X86-64 code generation now takes advantage of red zone, unless the
--mno-red-zone option is specified.
-
-
The X86 backend now supports using address space #256 in LLVM IR as a way of
-performing memory references off the GS segment register. This allows a
-front-end to take advantage of very low-level programming techniques when
-targeting X86 CPUs. See test/CodeGen/X86/movgs.ll for a simple
-example.
-
-
The X86 backend now supports a -disable-mmx command line option to
- prevent use of MMX even on chips that support it. This is important for cases
- where code does not contain the proper llvm.x86.mmx.emms
- intrinsics.
-
-
The X86 JIT now detects the new Intel Core i7 and Atom chips and
- auto-configures itself appropriately for the features of these chips.
-
-
The JIT now supports exception handling constructs on Linux/X86-64 and
- Darwin/x86-64.
-
-
The JIT supports Thread Local Storage (TLS) on Linux/X86-32 but not yet on
- X86-64.
@@ -527,70 +735,156 @@ example.
-
Both direct and indirect load/stores work now.
-
Logical, bitwise and conditional operations now work for integer data
-types.
-
Function calls involving basic types work now.
-
Support for integer arrays.
-
The compiler can now emit libcalls for operations not supported by m/c
-instructions.
-
Support for both data and ROM address spaces.
+
Support for floating-point, indirect function calls, and
+ passing/returning aggregate types to functions.
+
The code generator is able to generate debug info into output COFF files.
+
Support for placing an object into a specific section or at a specific
+ address in memory.
Things not yet supported:
-
Floating point.
-
Passing/returning aggregate types to and from functions.
Beginning with LLVM 2.5, llvmc2 is known as
- just llvmc. The old llvmc driver was removed.
-
The Clang plugin was substantially improved and is now enabled
- by default. The command llvmc --clang can be now used as a
- synonym to ccc.
+
Preliminary support for processors, such as the Cortex-A8 and Cortex-A9,
+that implement version v7-A of the ARM architecture. The ARM backend now
+supports both the Thumb2 and Advanced SIMD (Neon) instruction sets.
-
There is now a --check-graph option, which is supposed to catch
- common errors like multiple default edges, mismatched output/input language
- names and cycles. In general, these checks can't be done at compile-time
- because of the need to support plugins.
+
The AAPCS-VFP "hard float" calling conventions are also supported with the
+-float-abi=hard flag.
-
Plugins are now more flexible and can refer to compilation graph nodes and
- options defined in other plugins. To manage dependencies, a priority-sorting
- mechanism was introduced. This change affects the TableGen file syntax. See the
- documentation for details.
+
The ARM calling convention code is now tblgen generated instead of resorting
+ to C++ code.
+
-
Hooks can now be provided with arguments. The syntax is "$CALL(MyHook,
- 'Arg1', 'Arg2', 'Arg3')".
+
These features are still somewhat experimental
+and subject to change. The Neon intrinsics, in particular, may change in future
+releases of LLVM. ARMv7 support has progressed a lot on top of tree since 2.6
+branched.
-
A new option type: multi-valued option, for options that take more than one
- argument (for example, "-foo a b c").
-
New option properties: 'one_or_more', 'zero_or_more',
-'hidden' and 'really_hidden'.
+
-
The 'case' expression gained an 'error' action and
- an 'empty' test (equivalent to "(not (not_empty ...))").
This release includes a number of new APIs that are used internally, which
+ may also be useful for external clients.
+
+
+
+
New
+ PrettyStackTrace class allows crashes of llvm tools (and applications
+ that integrate them) to provide more detailed indication of what the
+ compiler was doing at the time of the crash (e.g. running a pass).
+ At the top level for each LLVM tool, it includes the command line arguments.
+
+
New StringRef
+ and Twine classes
+ make operations on character ranges and
+ string concatenation to be more efficient. StringRef is just a const
+ char* with a length, Twine is a light-weight rope.
+
LLVM has new WeakVH, AssertingVH and CallbackVH
+ classes, which make it easier to write LLVM IR transformations. WeakVH
+ is automatically drops to null when the referenced Value is deleted,
+ and is updated across a replaceAllUsesWith operation.
+ AssertingVH aborts the program if the
+ referenced value is destroyed while it is being referenced. CallbackVH
+ is a customizable class for handling value references. See ValueHandle.h
+ for more information.
+
The new 'Triple
+ ' class centralizes a lot of logic that reasons about target
+ triples.
+
The new '
+ llvm_report_error()' set of APIs allows tools to embed the LLVM
+ optimizer and backend and recover from previously unrecoverable errors.
LLVM has new
+ SourceMgr and SMLoc classes which implement caret
+ diagnostics and basic include stack processing for simple parsers. It is
+ used by tablegen, llvm-mc, the .ll parser and FileCheck.
LLVM now includes a new internal 'FileCheck' tool which allows
+ writing much more accurate regression tests that run faster. Please see the
+ FileCheck section of the Testing
+ Guide for more information.
+
LLVM profile information support has been significantly improved to produce
+correct use counts, and has support for edge profiling with reduced runtime
+overhead. Combined, the generated profile information is both more correct and
+imposes about half as much overhead (2.6. from 12% to 6% overhead on SPEC
+CPU2000).
+
The C bindings (in the llvm/include/llvm-c directory) include many newly
+ supported APIs.
+
LLVM 2.6 includes a brand new experimental LLVM bindings to the Ada2005
+ programming language.
+
+
The LLVMC driver has several new features:
+
+
Dynamic plugins now work on Windows.
+
New option property: init. Makes possible to provide default values for
+ options defined in plugins (interface to cl::init).
+
New example: Skeleton, shows how to create a standalone LLVMC-based
+ driver.
+
New example: mcc16, a driver for the PIC16 toolchain.
+
+
@@ -605,13 +899,24 @@ instructions.
If you're already an LLVM user or developer with out-of-tree changes based
-on LLVM 2.4, this section lists some "gotchas" that you may run into upgrading
+on LLVM 2.5, this section lists some "gotchas" that you may run into upgrading
from the previous release.
+
The Itanium (IA64) backend has been removed. It was not actively supported
+ and had bitrotted.
+
The BigBlock register allocator has been removed, it had also bitrotted.
+
The C Backend (-march=c) is no longer considered part of the LLVM release
+criteria. We still want it to work, but no one is maintaining it and it lacks
+support for arbitrary precision integers and other important IR features.
-
llvm-gcc defaults to -fno-math-errno on all X86 targets.
-
+
All LLVM tools now default to overwriting their output file, behaving more
+ like standard unix tools. Previously, this only happened with the '-f'
+ option.
+
LLVM build now builds all libraries as .a files instead of some
+ libraries as relinked .o files. This requires some APIs like
+ InitializeAllTargets.h.
+
@@ -619,8 +924,82 @@ from the previous release.
API changes are:
-
Some deprecated interfaces to create Instruction subclasses, that
- were spelled with lower case "create," have been removed.
+
All uses of hash_set and hash_map have been removed from
+ the LLVM tree and the wrapper headers have been removed.
+
The llvm/Streams.h and DOUT member of Debug.h have been removed. The
+ llvm::Ostream class has been completely removed and replaced with
+ uses of raw_ostream.
+
LLVM's global uniquing tables for Types and Constants have
+ been privatized into members of an LLVMContext. A number of APIs
+ now take an LLVMContext as a parameter. To smooth the transition
+ for clients that will only ever use a single context, the new
+ getGlobalContext() API can be used to access a default global
+ context which can be passed in any and all cases where a context is
+ required.
+
The getABITypeSize methods are now called getAllocSize.
+
The Add, Sub and Mul operators are no longer
+ overloaded for floating-point types. Floating-point addition, subtraction
+ and multiplication are now represented with new operators FAdd,
+ FSub and FMul. In the IRBuilder API,
+ CreateAdd, CreateSub, CreateMul and
+ CreateNeg should only be used for integer arithmetic now;
+ CreateFAdd, CreateFSub, CreateFMul and
+ CreateFNeg should now be used for floating-point arithmetic.
+
The DynamicLibrary class can no longer be constructed, its functionality has
+ moved to static member functions.
+
raw_fd_ostream's constructor for opening a given filename now
+ takes an extra Force argument. If Force is set to
+ false, an error will be reported if a file with the given name
+ already exists. If Force is set to true, the file will
+ be silently truncated (which is the behavior before this flag was
+ added).
+
SCEVHandle no longer exists, because reference counting is no
+ longer done for SCEV* objects, instead const SCEV*
+ should be used.
+
+
Many APIs, notably llvm::Value, now use the StringRef
+and Twine classes instead of passing const char*
+or std::string, as described in
+the Programmer's Manual. Most
+clients should be unaffected by this transition, unless they are used to
+Value::getName() returning a string. Here are some tips on updating to
+2.6:
+
+
getNameStr() is still available, and matches the old
+ behavior. Replacing getName() calls with this is an safe option,
+ although more efficient alternatives are now possible.
+
+
If you were just relying on getName() being able to be sent to
+ a std::ostream, consider migrating
+ to llvm::raw_ostream.
+
+
If you were using getName().c_str() to get a const
+ char* pointer to the name, you can use getName().data().
+ Note that this string (as before), may not be the entire name if the
+ name contains embedded null characters.
+
+
If you were using operator + on the result of getName() and
+ treating the result as an std::string, you can either
+ use Twine::str to get the result as an std::string, or
+ could move to a Twine based design.
+
+
isName() should be replaced with comparison
+ against getName() (this is now efficient).
+
+
+
+
The registration interfaces for backend Targets has changed (what was
+previously TargetMachineRegistry). For backend authors, see the Writing An LLVM Backend
+guide. For clients, the notable API changes are:
+
+
TargetMachineRegistry has been renamed
+ to TargetRegistry.
+
+
Clients should move to using the TargetRegistry::lookupTarget()
+ function to find targets.
+
+
@@ -639,15 +1018,15 @@ API changes are:
Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat
-Linux, Fedora Core and FreeBSD (and probably other unix-like systems).
+ Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like
+ systems).
PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit
-and 64-bit modes.
+ and 64-bit modes.
Intel and AMD machines running on Win32 using MinGW libraries (native).
Intel and AMD machines running on Win32 with the Cygwin libraries (limited
support is available for native builds with Visual C++).
Sun UltraSPARC workstations running Solaris 10.
Alpha-based machines running Debian GNU/Linux.
-
Itanium-based (IA64) machines running Linux and HP-UX.
The core LLVM infrastructure uses GNU autoconf to adapt itself
@@ -670,6 +1049,21 @@ 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.
+
+
The llvm-gcc bootstrap will fail with some versions of binutils (e.g. 2.15)
+ with a message of "Error: can not do 8
+ byte pc-relative relocation" when building C++ code. We intend to
+ fix this on mainline, but a workaround for 2.6 is to upgrade to binutils
+ 2.17 or later.
+
+
LLVM will not correctly compile on Solaris and/or OpenSolaris
+using the stock GCC 3.x.x series 'out the box',
+See: Broken versions of GCC and other tools.
+However, A Modern GCC Build
+for x86/x86-64 has been made available from the third party AuroraUX Project
+that has been meticulously tested for bootstrapping LLVM & Clang.
+
+
@@ -687,9 +1081,11 @@ components, please contact us on the LLVMdev list.
-
The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.
+
The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430 and SystemZ backends are
+ experimental.
The llc "-filetype=asm" (the default) is the only
- supported value for this option.
+ supported value for this option. The ELF writer is experimental.
+
The implementation of Andersen's Alias Analysis has many known bugs.
@@ -744,14 +1140,14 @@ compilation, and lacks support for debug information.
+
Support for the Advanced SIMD (Neon) instruction set is still incomplete
+and not well tested. Some features may not work at all, and the code quality
+may be poor in some cases.
Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
processors, thumb programs can crash or produce wrong
results (PR1388).
Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
-
There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly
- execute
-programs compiled with LLVM. Please use more recent versions of QEMU.
@@ -778,7 +1174,6 @@ programs compiled with LLVM. Please use more recent versions of QEMU.
-
The O32 ABI is not fully supported.
64-bit MIPS targets are not supported yet.
@@ -799,21 +1194,6 @@ appropriate nops inserted to ensure restartability.
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.
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
@@ -882,7 +1258,8 @@ itself, Qt, Mozilla, etc.
Fortran support generally works, but there are still several unresolved bugs
- in Bugzilla. Please see the tools/gfortran component for details.
+ in Bugzilla. Please see the
+ tools/gfortran component for details.
@@ -902,16 +1279,16 @@ which does support trampolines.
The Ada front-end fails to bootstrap.
This is due to lack of LLVM support for setjmp/longjmp style
exception handling, which is used internally by the compiler.
-Workaround: configure with --disable-bootstrap.
+Workaround: configure with --disable-bootstrap.
The c380004, c393010
and cxg2021 ACATS tests fail
(c380004 also fails with gcc-4.2 mainline).
If the compiler is built with checks disabled then c393010
causes the compiler to go into an infinite loop, using up all system memory.
Some GCC specific Ada tests continue to crash the compiler.
-
The -E binder option (exception backtraces)
+
The -E binder option (exception backtraces)
does not work and will result in programs
-crashing if an exception is raised. Workaround: do not use -E.
+crashing if an exception is raised. Workaround: do not use -E.
Only discrete types are allowed to start
or finish at a non-byte offset in a record. Workaround: do not pack records
or use representation clauses that result in a field of a non-discrete type
@@ -925,6 +1302,20 @@ ignored.
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.
