LLVM 2.1 Release Notes

Introduction @@ -32,7 +35,7 @@

This document contains the release notes for the LLVM compiler -infrastructure, release 2.1. Here we describe the status of LLVM, including +infrastructure, release 2.3. 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.

@@ -58,103 +61,69 @@ current one. To see the release notes for a specific releases, please see the

This is the twelfth public release of the LLVM Compiler Infrastructure. -It includes many features and refinements from LLVM 2.0.

This is the fourteenth public release of the LLVM Compiler Infrastructure. +It includes many features and refinements from LLVM 2.2.

+ +

-New Frontends +Removed features in LLVM 2.3

LLVM 2.1 brings two new beta C front-ends. First, Duncan, Anton and Devang -start syncing up llvm-gcc with GCC 4.2, yielding "llvm-gcc 4.2" (creative, -huh?). llvm-gcc 4.2 has the promise to bring much better FORTRAN and Ada -support to LLVM as well as features like atomic builtins, OpenMP, and many other -things. Check it out!

- -

Second, LLVM now includes its own native C and Objective-C front-end (C++ is -in progress, but is not very far along) code named "clang". This front-end has a number of great -features, primarily aimed at source-level analysis and speeding up compile-time. -At this point though, the LLVM Code Generator component is still very early in -development, so it's mostly useful for people looking to build source-level -analysis tools or source-to-source translators.

LLVM 2.2 was the last LLVM release to support llvm-gcc 4.0 and llvm-upgrade. +llvm-gcc 4.0 has been replaced with llvm-gcc 4.2. llvm-upgrade was useful for +upgrading llvm 1.9 files to llvm 2.x syntax, but you can always use a previous +llvm release to do this.

-Optimizer Improvements +llvm-gcc 4.2 and clang

Some of the most noticable improvements this release have been in the -optimizer, speeding it up and making it more aggressive

- -

Owen DSE and MemDep analysis
Owen GVN
Owen GVN-PRE, not in llvm-gcc
Devang merged ETForest and DomTree into a single easier to use data -structure.
Nick Lewycky improved loop trip count analysis to handle many more common -cases.

LLVM 2.3 fully supports 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 2.3 release. If you are interested in +this project, please see its web site.

-Code Generator Improvements +Major New Features

foo

LLVM 2.3 includes several major new capabilities:

Dale finished up the Tail Merging optimization in the code generator, -enabling it by default. This produces smaller code that is also faster in some -cases.
Dan Gohman changed the way we represent vectors before legalization, -significantly simplifying the SelectionDAG representation for these and making -the code generator faster for vector code.
Evan remat rewrite (coallesced intervals + folding of remat'd loads) and -live intervals improvements.
Dan Gohman contributed support for better alignment and volatility handling -in the code generator, and significantly enhanced alignment analysis for SSE -load/store instructions.
Christopher Lamb virtual register sub-register support, better truncates and -extends on X86.
Duraid Madina contributed a new "bigblock" register allocator, and Roman -Levenstein contributed several big improvements. BigBlock is optimized for code -that uses very large basic blocks. It is slightly slower than the "local" -allocator, but produces much better code.
David Greene refactored the register allocator to split coallescing out from -allocation, making coallescers pluggable.

-Target Specific Improvements +LLVM Core Improvements

@@ -162,68 +131,57 @@ allocation, making coallescers pluggable.

Bruno Cardoso Lopes contributed initial MIPS support.
Bill Wendling added SSSE3 support.
New Target independent if converter, ARM uses it so far
Nicholas Geoffray contributed improved linux/ppc ABI and JIT support.
Dale Johannesen rewrote handling of 32-bit float values in the X86 backend -when using the floating point stack, fixing several nasty bugs.
Dan contributed rematerialization support for the X86 backend.

-llvm-gcc Improvements +Code Generator Improvements

New features include: -

+ +

We put a significant amount of work into the code generator infrastructure, +which allows us to implement more aggressive algorithms and make it run +faster:

Duncan and Anton exception handling in llvm-gcc 4.0/4.2
MemOperand in the code generator.

+ +

Devang and Duncan: Bitfields, pragma pack

+ +

+Optimizer Improvements +

Tanya implemented support for __attribute__((noinline)) in llvm-gcc, and -added support for generic variable annotations which are propagated into the -LLVM IR, e.g. "int X __attribute__((annotate("myproperty")));".

+ +

In addition to a huge array of bug fixes and minor performance tweaks, the +LLVM 2.3 optimizers support a few major enhancements:

Sheng Zhou and Christopher Lamb implemented alias analysis support for -'restrict' arguments to functions.

Duncan contributed support for trampolines (pointers to nested functions), -currently only supported on x86 target.
Index set splitting on by default.

- +

-LLVM Core Improvements +Target Specific Improvements

New features include: +

New target-specific features include:

Neil Booth APFloat, foundation for long double support that will be wrapped -up in 2.2. Dale contributed most of long double support, will be enabled in -2.2.
LLVM now provides an LLVMBuilder class which makes it significantly easier -to create LLVM IR instructions.
Reid contributed support for intrinsics that take arbitrary integer typed -arguments, Dan Gohman and Chandler extended it to support FP and vectors.

@@ -238,13 +196,6 @@ arguments, Dan Gohman and Chandler extended it to support FP and vectors.

BrainF frontend by Sterling Stein.
David Green contributed a new --enable-expensive-checks configure option -which enables STL checking, and fixed several bugs exposed by it.

@@ -262,9 +213,9 @@ which enables STL checking, and fixed several bugs exposed by it.

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 10.2 and above in 32-bit and +
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 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.

LLVMdev list

The -cee pass is known to be buggy, and may be removed in in a - future release.
C++ EH support is disabled for this release.
The MSIL backend is experimental.
The IA64 code generator is experimental.
The Alpha JIT is experimental.
"-filetype=asm" (the default) is the only supported value for the - -filetype llc option.
The MSIL, IA64, Alpha, SPU, 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.

"long double" is silently transformed by the front-end into "double". There -is no support for floating point data types of any size other than 32 and 64 -bits.
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 non-local - gotos or taking the address of a nested function.
2. 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 X86 targets) + or non-local gotos.
3. Function Attributes: Declaring that functions have no side effects or that they can never return.
  - Supported: alias, always_inline, cdecl, - constructor, destructor, + Supported: alias, always_inline, cdecl, + const, constructor, destructor, deprecated, fastcall, format, - format_arg, non_null, noreturn, regparm + format_arg, non_null, noinline, + noreturn, nothrow, pure, regparm section, stdcall, unused, used, visibility, warn_unused_result, weak
  - Ignored: noinline, pure, const, 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 @@ -574,30 +477,57 @@ tested and works for a number of non-trivial programs, including LLVM itself, Qt, Mozilla, etc.

llvm-gcc4 only has partial support for C++ -Exception Handling, and it is not enabled by default.
Exception handling only works well on the X86 and PowerPC targets. +It works well for x86-64 darwin but not x86-64 linux.

+ +

THIS IS A WORK IN PROGRESS FOR LLVM 2.3 (currently in +progress on SVN HEAD)