LLVM 2.2 Release Notes

1. Introduction
2. What's New?
3. Installation Instructions
4. Portability and Supported Platforms
5. Known Problems
6. Additional Information

Written by the LLVM Team

# THIS IS A WORK IN PROGRESS FOR THE LLVM 2.2 RELEASE
Introduction

This document contains the release notes for the LLVM compiler infrastructure, release 2.2. Here we describe the status of LLVM, including major improvements from the previous release and any 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 releases, please see the releases page.

What's New?

This is the thirteenth public release of the LLVM Compiler Infrastructure. It includes many features and refinements from LLVM 2.1.

llvm-gcc 4.0, llvm-gcc 4.2, and clang

LLVM 2.2 fully supports both the llvm-gcc 4.0 and llvm-gcc 4.2 front-ends (in LLVM 2.1, llvm-gcc 4.2 was beta). Since LLVM 2.1, the llvm-gcc 4.2 front-end has made leaps and bounds and is now at least as good as 4.0 in virtually every area, and is better in several areas (for example, exception handling correctness). We strongly recommend that you migrate from llvm-gcc 4.0 to llvm-gcc 4.2 in this release cycle because LLVM 2.2 is the last release that will support llvm-gcc 4.0: LLVM 2.3 will only support the llvm-gcc 4.2 front-end.

The clang project is an effort to build a set of new 'llvm native' front-end technologies for the LLVM optimizer and code generator. Currently, its C and Objective-C support is maturing nicely, and it has advanced source-to-source analysis and transformation capabilities. If you are interested in building source-level tools for C and Objective-C (and eventually C++), you should take a look. However, note that clang is not an official part of the LLVM 2.2 release. If you are interested in this project, please see the web site.

Major New Features

Dale contributed full support for long double on x86/x86-64 (where it is 80 bits) and on Darwin PPC/PPC64 (where it is 128 bits).

Ada, gfortran

debug improvements -O0 EH. Gordon: GC Revamp. docs/GarbageCollection.html Kaleidescope: docs/tutorial Gordon: C and Ocaml Bindings

Optimizer Improvements

Some of the most noticable feature improvements this release have been in the optimizer, speeding it up and making it more aggressive. For example:

- Daniel Berlin and (Curtis?) rewrote Andersen's alias analysis (which is not enabled by default) to be several orders of magnitude faster, implmented Offline Variable Substitution.
Devang: LoopIndexSplit is enabled by default.

Code Generator Improvements

foci of this release was performance tuning and bug fixing. In addition to these, several new major changes occurred:

- Owen contributed Machine Loop info, domintors, etc. Merged dom and postdom.
- Dan added support for emitting debug information with .file and .loc on targets that support it
- Evan physical register dependencies in the BURR scheduler
- Evan EXTRACT_SUBREG coalescing support

Target Specific Improvements

New features include:

- Evan X86 now models EFLAGS in instructions.
- Evan: If conversion on by default for ARM.
- Bruno: MIPS PIC support.
- Arnold Schwaighofer: X86 tail call support.

llvm-gcc Improvements

New features include:

- .

LLVM Core Improvements

New features include:

- Devang added LLVMFoldingBuilder.
- Dan added support for vector sin, cos, and pow intrinsics.

Other Improvements

New features include:

- .

Portability and Supported Platforms

LLVM is known to work on the following platforms:

- Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD (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 8.
- Alpha-based machines running Debian GNU/Linux.
- Itanium-based machines running Linux and HP-UX.

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

Known Problems

This section contains all known problems with the LLVM system, listed by component. As new problems are discovered, they will be added to these sections. If you run into a problem, please check the LLVM bug database and submit a bug if there isn't already one.

Experimental features included with this release

The following components of this LLVM release are either untested, known to be broken or unreliable, or are in early development. These components should not be relied on, and bugs should not be filed against them, but they may be useful to some people. In particular, if you would like to work on one of these components, please contact us on the LLVMdev list.

- The `-cee` pass is known to be buggy and will be removed in LLVM 2.3.
- The MSIL, IA64, Alpha, and MIPS backends are experimental.
- The LLC "`-filetype=asm`" (the default) is the only supported value for this option.
- The llvmc tool is not supported.

Known problems with the X86 back-end

- The X86 backend does not yet support inline assembly that uses the X86 floating point stack.
- The X86 backend occasionally has alignment problems on operating systems that don't require 16-byte stack alignment (including most non-darwin OS's like linux).

Known problems with the PowerPC back-end

- The Linux PPC32/ABI support needs testing for the interpreter and static compilation, and lacks support for debug information.

Known problems with the ARM back-end

- 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.

Known problems with the SPARC back-end

- The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not support the 64-bit SPARC ABI (-m64).

Known problems with the Alpha back-end

- On 21164s, some rare FP arithmetic sequences which may trap do not have the appropriate nops inserted to ensure restartability.

Known problems with the IA64 back-end

- C++ programs are likely to fail on IA64, as calls to `setjmp` are made where the argument is not 16-byte aligned, as required on IA64. (Strictly speaking this is not a bug in the IA64 back-end; it will also be encountered when building C++ programs using the C back-end.)
- The C++ front-end does not use IA64 ABI compliant layout of v-tables. In particular, it just stores function pointers instead of function descriptors in the vtable. This bug prevents mixing C++ code compiled with LLVM with C++ objects compiled by other C++ compilers.
- There are a few ABI violations which will lead to problems when mixing LLVM output with code built with other compilers, particularly for floating-point programs.
- Defining vararg functions is not supported (but calling them is ok).
- The Itanium backend has bitrotted somewhat.

Known problems with the C back-end

- The C backend does not support inline assembly code.
- The C backend does not support vectors yet.
- The C backend violates the ABI of common C++ programs, preventing intermixing between C++ compiled by the CBE and C++ code compiled with LLC or native compilers.

Known problems with the C front-end
Bugs

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.

Notes

- llvm-gcc does not support `__builtin_apply` yet. See Constructing Calls: Dispatching a call to another function.

- llvm-gcc partially supports these GCC extensions:

  1. Nested Functions: As in Algol and Pascal, lexical scoping of functions. Nested functions are supported, but llvm-gcc does not support taking the address of a nested function (except on the X86-32 target) or non-local gotos.
  2. Function Attributes: Declaring that functions have no side effects or that they can never return.
     Supported: `alias`, `always_inline`, `cdecl`, `const`, `constructor`, `destructor`, `deprecated`, `fastcall`, `format`, `format_arg`, `non_null`, `noinline`, `noreturn`, `pure`, `regparm` `section`, `stdcall`, `unused`, `used`, `visibility`, `warn_unused_result`, `weak`
     Ignored: `nothrow`, `malloc`, `no_instrument_function`

- llvm-gcc supports the vast majority of GCC extensions, including:

  1. Pragmas: Pragmas accepted by GCC.
  2. Local Labels: Labels local to a block.
  3. Other Builtins: Other built-in functions.
  4. Variable Attributes: Specifying attributes of variables.
  5. Type Attributes: Specifying attributes of types.
  6. Thread-Local: Per-thread variables.
  7. Variable Length: Arrays whose length is computed at run time.
  8. Labels as Values: Getting pointers to labels and computed gotos.
  9. Statement Exprs: Putting statements and declarations inside expressions.
  10. Typeof: `typeof`: referring to the type of an expression.
  11. Lvalues: Using `?:`, "`,`" and casts in lvalues.
  12. Conditionals: Omitting the middle operand of a `?:` expression.
  13. Long Long: Double-word integers.
  14. Complex: Data types for complex numbers.
  15. Hex Floats:Hexadecimal floating-point constants.
  16. Zero Length: Zero-length arrays.
  17. Empty Structures: Structures with no members.
  18. Variadic Macros: Macros with a variable number of arguments.
  19. Escaped Newlines: Slightly looser rules for escaped newlines.
  20. Extended Asm: Assembler instructions with C expressions as operands.
  21. Constraints: Constraints for asm operands.
  22. Asm Labels: Specifying the assembler name to use for a C symbol.
  23. Explicit Reg Vars: Defining variables residing in specified registers.
  24. Vector Extensions: Using vector instructions through built-in functions.
  25. Target Builtins: Built-in functions specific to particular targets.
  26. Subscripting: Any array can be subscripted, even if not an lvalue.
  27. Pointer Arith: Arithmetic on `void`-pointers and function pointers.
  28. Initializers: Non-constant initializers.
  29. Compound Literals: Compound literals give structures, unions, or arrays as values.
  30. Designated Inits: Labeling elements of initializers.
  31. Cast to Union: Casting to union type from any member of the union.
  32. Case Ranges: `case 1 ... 9' and such.
  33. Mixed Declarations: Mixing declarations and code.
  34. Function Prototypes: Prototype declarations and old-style definitions.
  35. C++ Comments: C++ comments are recognized.
  36. Dollar Signs: Dollar sign is allowed in identifiers.
  37. Character Escapes: `\e` stands for the character <ESC>.
  38. Alignment: Inquiring about the alignment of a type or variable.
  39. Inline: Defining inline functions (as fast as macros).
  40. Alternate Keywords:`__const__`, `__asm__`, etc., for header files.
  41. Incomplete Enums: `enum foo;`, with details to follow.
  42. Function Names: Printable strings which are the name of the current function.
  43. Return Address: Getting the return or frame address of a function.
  44. Unnamed Fields: Unnamed struct/union fields within structs/unions.
  45. Attribute Syntax: Formal syntax for attributes.

If you run into GCC extensions which have not been included in any of these lists, please let us know (also including whether or not they work).

Known problems with the C++ front-end

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

- Exception handling only works well on the X86 and PowerPC targets.

Additional Information

A wide variety of additional information is available on the LLVM web page, in particular in the documentation section. The web page also contains versions of the API documentation which is up-to-date with the Subversion version of the source code. You can access versions of these documents specific to this release by going into the "`llvm/doc/`" directory in the LLVM tree.

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