This document contains the release notes for the LLVM compiler -infrastructure, release 2.0. Here we describe the status of LLVM, including any -known problems and major improvements from the previous release. All LLVM +infrastructure, release 2.0. 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. +releases web site.

For more information about LLVM, including information about the latest release, please check out the main LLVM @@ -43,7 +43,8 @@ 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 CVS or the main LLVM web page, +

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 the current or previous releases, see the releases page.

@@ -67,20 +68,28 @@ ways from our previous releases:

break backwards compatibility with the LLVM 1.x bytecode and .ll file format. If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we recommend the use of the stand alone llvm-upgrade -tool. We intend to keep compatibility with .ll and .bc formats within the 2.x -release series, like we did within the 1.x series. +tool (which is included with 2.0). We intend to keep compatibility with .ll +and .bc formats within the 2.x release series, like we did within the 1.x +series.

There are several significant change to the LLVM IR and internal APIs, such as a major overhaul of the type system, the completely new bitcode file - format, etc.

+ format, etc (described below).

We designed the release around a 6 month release cycle instead of the usual 3-month cycle. This gave us extra time to develop and test some of the more invasive features in this release.

LLVM 2.0 no longer supports the llvm-gcc3 front-end.

LLVM 2.0 no longer supports the llvm-gcc3 front-end. Users are required to + upgrade to llvm-gcc4. llvm-gcc4 includes many features over + llvm-gcc3, is faster, and is much easier to + build from source.

Note that while this is a major version bump, this release has been extensively tested on a wide range of software. It is easy to say that this - is our best release yet, in terms of both features and correctness.

+ is our best release yet, in terms of both features and correctness. This is + the first LLVM release to correctly compile and optimize major software like + LLVM itself, Mozilla/Seamonkey, Qt 4.3rc1, kOffice, etc out of the box on + linux/x86. +

blah -

+ +

Changes to the LLVM IR itself:

ding dong llvm-gcc3 is dead
bytecode -> bitcode
Integer types are now completely signless. This means that we + have types like i8/i16/i32 instead of ubyte/sbyte/short/ushort/int + etc. LLVM operations that depend on sign have been split up into + separate instructions (PR950). This + eliminates cast instructions that just change the sign of the operands (e.g. + int -> uint), which reduces the size of the IR and makes optimizers + simpler to write.
Integer types with arbitrary bitwidths (e.g. i13, i36, i42, i1057, etc) are + now supported in the LLVM IR and optimizations (PR1043). However, neither llvm-gcc + (PR1284) nor the native code generators + (PR1270) support non-standard width + integers yet.
'Type planes' have been removed (PR411). + It is no longer possible to have two values with the same name in the + same symbol table. This simplifies LLVM internals, allowing significant + speedups.
Global variables and functions in .ll files are now prefixed with + @ instead of % (PR645).
The LLVM 1.x "bytecode" format has been replaced with a + completely new binary representation, named 'bitcode'. The Bitcode Format brings a + number of advantages to the LLVM over the old bytecode format: it is denser + (files are smaller), more extensible, requires less memory to read, + is easier to keep backwards compatible (so LLVM 2.5 will read 2.0 .bc + files), and has many other nice features.
Load and store instructions now track the alignment of their pointer + (PR400). This allows the IR to + express loads that are not sufficiently aligned (e.g. due to '#pragma + packed') or to capture extra alignment information.

- + +

Major new features:

+ +

A number of ELF features are now supported by LLVM, including 'visibility', + extern weak linkage, Thread Local Storage (TLS) with the __thread + keyword, and symbol aliases. + Among other things, this means that many of the special options needed to + configure llvm-gcc on linux are no longer needed, and special hacks to build + large C++ libraries like Qt are not needed.
LLVM now has a new MSIL backend. llc -march=msil will now turn LLVM + into MSIL (".net") bytecode. This is still fairly early development + with a number of limitations.
A new llvm-upgrade tool + exists to migrates LLVM 1.9 .ll files to LLVM 2.0 syntax.

New features include:

The pass manager has been entirely + rewritten, making it significantly smaller, simpler, and more extensible. + Support has been added to run FunctionPasses interlaced with + CallGraphSCCPasses, we now support loop transformations + explicitly with LoopPass, and ModulePasses may now use the + result of FunctionPasses.
LLVM 2.0 includes a new loop rotation pass, which converts "for loops" into + "do/while loops", where the condition is at the bottom of the loop.
The Loop Strength Reduction pass has been improved, and we now support + sinking expressions across blocks to reduce register pressure.
The -scalarrepl pass can now promote unions containing FP values + into a register, it can also handle unions of vectors of the same + size.
The [Post]DominatorSet classes have been removed from LLVM and clients + switched to use the more-efficient ETForest class instead.
The ImmediateDominator class has also been removed, and clients have been + switched to use DominatorTree instead.
The predicate simplifier pass has been improved, making it able to do + simple value range propagation and eliminate more conditionals. However, + note that predsimplify is not enabled by default in llvm-gcc.

In addition, the LLVM target description format has itself been extended in several ways:

Further, several significant target-specific enhancements are included in -LLVM 2.0:

New features include: +

X86-specific Code Generator Enhancements:

The MMX instruction set is now supported through intrinsics.
The scheduler was improved to better reduce register pressure on + X86 and other targets that are register pressure sensitive.
Linux/x86-64 support is much better.
PIC support for linux/x86 has been added.
The X86 backend now supports the GCC regparm attribute.
LLVM now supports inline asm with multiple constraint letters per operand + (like "mri") which is common in X86 inline asms.

- + +

ARM-specific Code Generator Enhancements:

+ +

The ARM code generator is now stable and fully supported.
There are major new features, including support for ARM + v4-v6 chips, vfp support, soft float point support, pre/postinc support, + load/store multiple generation, constant pool entry motion (to support + large functions), inline asm support, weak linkage support, static + ctor/dtor support and many bug fixes.
Added support for Thumb code generation (llc -march=thumb).
The ARM backend now supports the ARM AAPCS/EABI ABI and PIC codegen on + arm/linux.
Several bugs were fixed for DWARF debug info generation on arm/linux.

+ +

PowerPC-specific Code Generator Enhancements:

+ +

The PowerPC 64 JIT now supports addressing code loaded above the 2G + boundary.
Improved support for the Linux/ppc ABI and the linux/ppc JIT is fully + functional now. llvm-gcc and static compilation are not fully supported + yet though.
Many PowerPC 64 bug fixes.

More specific changes include:

LLVM no longer relies on static destructors to shut itself down. Instead, + it lazily initializes itself and shuts down when llvm_shutdown() is + explicitly called.
LLVM now has significantly fewer static constructors, reducing startup time. +
Several classes have been refactored to reduce the amount of code that + gets linked into apps that use the JIT.
Construction of intrinsic function declarations has been simplified.
The gccas/gccld tools have been replaced with small shell scripts.
Support has been added to llvm-test for running on low-memory + or slow machines (make SMALL_PROBLEM_SIZE=1).

+ +

LLVM 2.0 contains a revamp of the type system and several other significant +internal changes. If you are programming to the C++ API, be aware of the +following major changes:

+ +

Pass registration is slightly different in LLVM 2.0 (you now need an + intptr_t in your constructor), as explained in the Writing an LLVM Pass + document.
ConstantBool, ConstantIntegral and ConstantInt + classes have been merged together, we now just have + ConstantInt.
Type::IntTy, Type::UIntTy, Type::SByteTy, ... are + replaced by Type::Int8Ty, Type::Int16Ty, etc. LLVM types + have always corresponded to fixed size types + (e.g. long was always 64-bits), but the type system no longer includes + information about the sign of the type. Also, the + Type::isPrimitiveType() method now returns false for integers.
Several classes (CallInst, GetElementPtrInst, + ConstantArray, etc), that once took std::vector as + arguments now take ranges instead. For example, you can create a + GetElementPtrInst with code like: + +
```
+      Value *Ops[] = { Op1, Op2, Op3 };
+      GEP = new GetElementPtrInst(BasePtr, Ops, 3);
+    
```
+ + This avoids creation of a temporary vector (and a call to malloc/free). If + you have an std::vector, use code like this: +
```
+      std::vector<Value*> Ops = ...;
+      GEP = new GetElementPtrInst(BasePtr, &Ops[0], Ops.size());
+    
```
+ +
CastInst is now abstract and its functionality is split into + several parts, one for each of the new + cast instructions.
Instruction::getNext()/getPrev() are now private (along with + BasicBlock::getNext, etc), for efficiency reasons (they are now no + longer just simple pointers). Please use BasicBlock::iterator, etc + instead. +
Module::getNamedFunction() is now called + Module::getFunction().
SymbolTable.h has been split into ValueSymbolTable.h and +TypeSymbolTable.h.

The Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 -processors, any thumb program compiled with LLVM crashes or produces wrong -results. (PR1388)
Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 +processors, thumb program can crash or produces wrong +results (PR1388).
Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
QEMU-ARM (<= 0.9.0) wrongly executes programs compiled with LLVM. A non-affected QEMU version must be used or this - -patch must be applied on QEMU.
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.

FIXME: the list of supported stuff below needs to be updated. We do support -tls now, what else??

"long double" is 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.
"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.
Although many GCC extensions are supported, some are not. In particular, - the following extensions are known to not be supported: -
1. Local Labels: Labels local to a block.
2. Nested Functions: As in Algol and Pascal, lexical scoping of functions.
3. Constructing Calls: Dispatching a call to another function.
4. Thread-Local: Per-thread variables.
5. Pragmas: Pragmas accepted by GCC.
- -
The following GCC extensions are partially supported. An ignored - attribute means that the LLVM compiler ignores the presence of the attribute, - but the code should still work. An unsupported attribute is one which is - ignored by the LLVM compiler and will cause a different interpretation of - the program.
+
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. Variable Length: - Arrays whose length is computed at run time.
  - Supported, but allocated stack space is not freed until the function returns (noted above).
2. 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.
3. Function Attributes: Declaring that functions have no side effects or that they can never return.
  - Supported: alias, constructor, destructor, + Supported: alias, always_inline, cdecl, + constructor, destructor, deprecated, fastcall, format, format_arg, non_null, noreturn, regparm section, stdcall, unused, used, visibility, warn_unused_result, weak
  - Ignored: noinline, - always_inline, pure, const, nothrow, - malloc, no_instrument_function, cdecl
  - - Unsupported: All other target specific attributes
4. Variable Attributes: - Specifying attributes of variables.
  - Supported: alias, cleanup, common, - nocommon, deprecated, dllimport, - dllexport, section, transparent_union, - unused, used, weak
  - - Unsupported: aligned, mode, packed, - shared, tls_model, - vector_size, all target specific attributes. -
5. Type Attributes: Specifying attributes of types.
  - Supported: transparent_union, unused, - deprecated, may_alias
  - - Unsupported: aligned, packed, - all target specific attributes.
6. Other Builtins: - Other built-in functions.
  - We support all builtins which have a C language equivalent (e.g., - __builtin_cos), __builtin_alloca, - __builtin_types_compatible_p, __builtin_choose_expr, - __builtin_constant_p, and __builtin_expect - (currently ignored). We also support builtins for ISO C99 floating - point comparison macros (e.g., __builtin_islessequal), - __builtin_prefetch, __builtin_popcount[ll], - __builtin_clz[ll], and __builtin_ctz[ll].
+

The following extensions are known to be supported:

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.