LLVM 2.6 Release Notes
- Introduction
- Sub-project Status Update
- External Projects Using LLVM 2.6
- What's New in LLVM 2.6?
- Installation Instructions
- Portability and Supported Platforms
- Known Problems
- Additional Information
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 — 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 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 2.6 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 Clang front-end mailing
list.
In the LLVM 2.6 time-frame, the Clang team has made many improvements:
- Something wonderful!
- AuroraUX / FreeBSD & OpenBSD Toolchain support.
- Many many bugs are fixed and many features have been added.
Previously announced in the 2.4 LLVM release, the Clang project also
includes an early stage static source code analysis tool for automatically finding bugs
in C and Objective-C programs. The tool performs a growing set of checks to find
bugs that occur on a specific path within a program.
In the LLVM 2.6 time-frame there have been many significant improvements to
XYZ.
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 Machines (Microsoft .NET is an
implementation of the CLI) using the Just-In-Time compiler of LLVM.
Following LLVM 2.6, VMKit has its XYZ release that you can find on its
webpage. The release includes
bug fixes, cleanup and new features. The major changes are:
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.
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.
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 bugfixes, and better x86-64 support. This has allowed
some major improvements in LDC, getting us 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.
Rubinius is a new virtual
machine for Ruby. It leverages LLVM to dynamically compile Ruby code down to
machine code using LLVM's JIT.
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 2.6 includes several major new capabilities:
- Something wonderful!
- LLVM 2.6 includes a brand new experimental LLVM bindings to the Ada2005 programming language.
LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
front-ends and driver with the LLVM optimizer and code generator. It currently
includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.
LLVM 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:
In addition to a large array of bug fixes and minor performance tweaks, this
release includes a few major enhancements and additions to the optimizers:
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:
New features of the X86 target include:
New features of the PIC16 target include:
Things not yet supported:
- Floating point.
- Passing/returning aggregate types to and from functions.
- Variable arguments.
- Indirect function calls.
- Interrupts/programs.
- Debug info.
New features of the ARM target include:
- 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. These features are still somewhat experimental
and subject to change. The Neon intrinsics, in particular, may change in future
releases of LLVM.
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.
In addition, many APIs have changed in this release. Some of the major LLVM
API changes are:
- 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 containts embedded null characters.
- If you were using operator plus on the result of getName() and
treating the result as an std::string, you can either
uses 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.
- llvm-dis now fails if output file exists, instead of dumping to stdout.
FIXME: describe any other tool changes due to the raw_fd_ostream change. FIXME:
This is not an API change, maybe there should be a tool changes section?
- temporarely due to Context API change passes should call doInitialization()
method of the pass they inherit from, otherwise Context is NULL.
FIXME: remove this entry when this is no longer needed.
-
LLVM is known to work on the following platforms:
- 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.
- 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/x64 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, and PIC16 backends are experimental.
- The llc "-filetype=asm" (the default) is the only
supported value for this option.
- The X86 backend does not yet support
all inline assembly that uses the X86
floating point stack. It supports the 'f' and 't' constraints, but not
'u'.
- 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.
- The Linux PPC32/ABI support needs testing for the interpreter and static
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.
- The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
support the 64-bit SPARC ABI (-m64).
- The O32 ABI is not fully supported.
- 64-bit MIPS targets are not supported yet.
- On 21164s, some rare FP arithmetic sequences which may trap do not have the
appropriate nops inserted to ensure restartability.
llvm-gcc does not currently support Link-Time
Optimization on most platforms "out-of-the-box". Please inquire on the
LLVMdev mailing list if you are interested.
The only major language feature of GCC not supported by llvm-gcc is
the __builtin_apply family of builtins. However, some extensions
are only supported on some targets. For example, trampolines are only
supported on some targets (these are used when you take the address of a
nested function).
If you run into GCC extensions which are not supported, please let us know.
The C++ front-end is considered to be fully
tested and works for a number of non-trivial programs, including LLVM
itself, Qt, Mozilla, etc.
- Exception handling works well on the X86 and PowerPC targets. Currently
only Linux and Darwin targets are supported (both 32 and 64 bit).
- Fortran support generally works, but there are still several unresolved bugs
in Bugzilla. Please see the tools/gfortran component for details.
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 lli interpreter considers
'main' as generated by the Ada binder to be invalid.
Workaround: hand edit the file to use pointers for argv and
envp rather than integers.
- The -fstack-check option is
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.
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.
LLVM Compiler Infrastructure
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