LLVM 1.5 Release Notes

-This release implements the following new features: +

+New Features in LLVM 2.0

+ +

Major Changes

LLVM now includes an - Interprocedural Sparse Conditional Constant Propagation pass, named - -ipsccp, which is run by default at link-time.
LLVM 1.5 is now about 15% faster than LLVM 1.4 and its core data structures - use about 30% less memory.
LLVM includes new experimental native code generators for SparcV8 and - Alpha.
Support for Microsoft Visual Studio is improved, and now documented.

Changes to the LLVM IR itself:

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.

- -

-In this release, the following missing features were implemented:

+ + +

llvm-gcc +Improvements

New features include: +

Precompiled Headers (PCH) are now supported.

"#pragma packed" is now supported, as are the various features + described above (visibility, extern weak linkage, __thread, aliases, + etc).

- -

-In this release, the following Quality of Implementation -issues were fixed: +

Tracking function parameter/result attributes is now possible.

+ +

Many internal enhancements have been added, such as improvements to + NON_LVALUE_EXPR, arrays with non-zero base, structs with variable sized + fields, VIEW_CONVERT_EXPR, CEIL_DIV_EXPR, nested functions, and many other + things. This is primarily to supports non-C GCC front-ends, like Ada.

+ +

It is simpler to configure llvm-gcc for linux.

+ + +

+ +

Optimizer +Improvements

New features include: +

Building LLVM in optimized mode - should no longer cause GCC to hit swap in the PowerPC backend.

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.

- -

-This release includes the following Code Quality -improvements: + +

Code +Generator Enhancements

+ +

+New features include: +

+ +

LLVM now supports software floating point, which allows LLVM to target + chips that don't have hardware FPUs (e.g. ARM thumb mode).
A new register scavenger has been implemented, which is useful for + finding free registers after register allocation. This is useful when + rewriting frame references on RISC targets, for example.
Heuristics have been added to avoid coalescing vregs with very large live + ranges to physregs. This was bad because it effectively pinned the physical + register for the entire lifetime of the virtual register (PR711).
Support now exists for very simple (but still very useful) + rematerialization the register allocator, enough to move + instructions like "load immediate" and constant pool loads.
Switch statement lowering is significantly better, improving codegen for + sparse switches that have dense subregions, and implemented support + for the shift/and trick.
LLVM now supports tracking physreg sub-registers and super-registers + in the code generator, and includes extensive register + allocator changes to track them.
There is initial support for virtreg sub-registers + (PR1350).

+ +

+Other improvements include: +

+ +

Inline assembly support is much more solid that before. + The two primary features still missing are support for 80-bit floating point + stack registers on X86 (PR879), and + support for inline asm in the C backend (PR802).
DWARF debug information generation has been improved. LLVM now passes + most of the GDB testsuite on MacOS and debug info is more dense.
Codegen support for Zero-cost DWARF exception handling has been added (PR592). It is mostly + complete and just in need of continued bug fixes and optimizations at + this point. However, support in llvm-g++ is disabled with an + #ifdef for the 2.0 release (PR870).
The code generator now has more accurate and general hooks for + describing addressing modes ("isLegalAddressingMode") to + optimizations like loop strength reduction and code sinking.
Progress has been made on a direct Mach-o .o file writer. Many small + apps work, but it is still not quite complete.

+ +

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

+ +

TargetData now supports better target parameterization in + the .ll/.bc files, eliminating the 'pointersize/endianness' attributes + in the files (PR761).
TargetData was generalized for finer grained alignment handling, + handling of vector alignment, and handling of preferred alignment
LLVM now supports describing target calling conventions + explicitly in .td files, reducing the amount of C++ code that needs + to be written for a port.

+ +

Target-Specific +Improvements

+ +

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.

- -

-In this release, the following bugs in the previous release -were fixed: + + +

Other Improvements

+ +

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).

+ +

API Changes

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:

Bugs fixed in the LLVM Core:

[dse] DSE deletes stores that - are partially overwritten by smaller stores

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.

Code Generator Bugs:

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. +

Bugs in the C/C++ front-end:

Module::getNamedFunction() is now called + Module::getFunction().
SymbolTable.h has been split into ValueSymbolTable.h and +TypeSymbolTable.h.

Portability and Supported Platforms @@ -177,12 +480,16 @@ were fixed:

LLVM is known to work on the following platforms:

Intel and AMD machines running Red Hat Linux and FreeBSD (and probably - other unix-like systems).
Sun UltraSPARC workstations running Solaris 8.
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 + 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++).
PowerPC-based Mac OS X systems, running 10.2 and above.
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 @@ -204,7 +511,7 @@ portability patches and reports of successful builds or error messages.

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 +href="http://llvm.org/bugs/">LLVM bug database and submit a bug if there isn't already one.

@@ -220,167 +527,213 @@ there isn't already one.

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.

+components, please contact us on the LLVMdev list.

The following passes are incomplete or buggy, and may be removed in future - releases: -cee, -branch-combine, -instloops, -paths, -pre
The llvm-db tool is in a very early stage of development, but can - be used to step through programs and inspect the stack.
The "iterative scan" register allocator (enabled with -regalloc=iterativescan) - is not stable.
The SparcV8 and Alpha ports are experimental.
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.

- Known problems with the LLVM Core + Known problems with the X86 back-end

In the JIT, dlsym on a symbol compiled by the JIT will not work. -
The JIT does not use mutexes to protect its internal data structures. As - such, execution of a threaded program could cause these data structures to be - corrupted. -
The lower-invoke pass does not - mark values live across a setjmp as volatile. This missing feature - only affects targets whose setjmp/longjmp libraries do not save and restore - the entire register file.
The X86 backend does not yet support inline + assembly that uses the X86 floating point stack.

- Known problems with the C front-end + Known problems with the PowerPC back-end

- -

Bugs

+ +

PowerPC backend does not correctly +implement ordered FP comparisons.
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 +

C99 Variable sized arrays do not release stack memory when they go out of - scope. Thus, the following program may run out of stack space: -
```
-    for (i = 0; i != 1000000; ++i) {
-      int X[n];
-      foo(X);
-    }
-
```
Initialization of global union variables can only be done with the largest union member.
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. +
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).

- -

- Notes + +

+ Known problems with the Alpha back-end

Inline assembly is not yet supported.
On 21164s, some rare FP arithmetic sequences which may trap do not have the +appropriate nops inserted to ensure restartability.
"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.
The following Unix system functionality has not been tested and may not -work: -
1. sigsetjmp, siglongjmp - These are not turned into the - appropriate invoke/unwind instructions. Note that - setjmp and longjmp are compiled correctly. -
2. getcontext, setcontext, makecontext - - These functions have not been tested. -

Although many GCC extensions are supported, some are not. In particular, - the following extensions are known to not be supported: -

Local Labels: Labels local to a block.
Nested Functions: As in Algol and Pascal, lexical scoping of functions.
Constructing Calls: Dispatching a call to another function.
Extended Asm: Assembler instructions with C expressions as operands.
Constraints: Constraints for asm operands.
Asm Labels: Specifying the assembler name to use for a C symbol.
Explicit Reg Vars: Defining variables residing in specified registers.
Vector Extensions: Using vector instructions through built-in functions.
Target Builtins: Built-in functions specific to particular targets.
Thread-Local: Per-thread variables.
Pragmas: Pragmas accepted by GCC.

+ +

+ Known problems with the IA64 back-end +

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.

Variable Length: - Arrays whose length is computed at run time.
- Supported, but allocated stack space is not freed until the function returns (noted above).

Function Attributes: +
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.

Supported:

format

format_arg

non_null

noreturn

constructor

destructor

unused

deprecated

warn_unused_result

weak

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.

Ignored:

noinline

always_inline

pure

const

nothrow

malloc

no_instrument_function

cdecl

Defining vararg functions is not supported (but calling them is ok).

Unsupported:

used

section

alias

visibility

regparm

stdcall

fastcall

Variable Attributes: - Specifying attributes of variables.
- Supported: cleanup, common, nocommon, - deprecated, transparent_union, - unused, weak
+
The Itanium backend has bitrotted somewhat.

Unsupported:

aligned

mode

packed

section

shared

tls_model

vector_size

dllimport

dllexport

Type Attributes: Specifying attributes of types.
- Supported: transparent_union, unused, - deprecated, may_alias
+ +

+ Known problems with the C back-end +

- Unsupported: aligned, packed, - all target specific attributes.

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).

The C backend does not support inline + assembly code.

+ +

+ + + +

+ Known problems with the C front-end +

+ + +

Bugs

+ +

llvm-gcc4 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 +

+ +

"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. Function Attributes: + + Declaring that functions have no side effects or that they can never + return.
  + + 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, pure, const, nothrow, + malloc, no_instrument_function
+

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.
11. Empty Structures: Structures with no members.
12. Variadic Macros: Macros with a variable number of arguments.
13. Escaped Newlines: Slightly looser rules for escaped newlines.
14. Extended Asm: Assembler instructions with C expressions as operands.
15. Constraints: Constraints for asm operands.
16. Asm Labels: Specifying the assembler name to use for a C symbol.
17. Explicit Reg Vars: Defining variables residing in specified registers.
18. Vector Extensions: Using vector instructions through built-in functions.
19. Target Builtins: Built-in functions specific to particular targets.
20. Subscripting: Any array can be subscripted, even if not an lvalue.
21. Pointer Arith: Arithmetic on void-pointers and function pointers.
22. Initializers: Non-constant initializers.