LLVM 1.3 Release Notes
- What's New?
- Installation Instructions
- Portability and Supported Platforms
- Known Problems
- Additional Information
This document contains the release notes for the LLVM compiler
infrastructure, release 1.3. Here we describe the status of LLVM, including any
known problems and bug fixes from the previous release. The most up-to-date
version of this document can be found on the LLVM 1.3 web site. If you are
not reading this on the LLVM web pages, you should probably go there because
this document may be updated after the release.
For more information about LLVM, including information about potentially more
current releases, please check out the main
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, 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.
This is the fourth public release of the LLVM compiler infrastructure. This
release primarily improves the performance of the
code produced by all aspects of the LLVM compiler, adds many new features, fixes a few
bugs, speeds up the compiler, and introduces a new (experimental)
PowerPC code generator.
At this time, LLVM is known to correctly compile and run all C & C++
SPEC CPU95 & 2000 benchmarks, the Olden benchmarks, and the Ptrdist
benchmarks, and many other programs. LLVM now also works
with a broad variety of C++ programs.
- The LLVM select instruction is
now fully implemented and supported by all transformations, native code
generators, and the interpreter.
- Bugpoint can now narrow down code-generation bugs to a loop nest, where
before it could only narrow them down to a function being miscompiled.
- Bugpoint can now debug arbitrary
modes of llc and lli, by passing them command line flags (e.g.
- The Control Flow Graph in the native code generators is no longer
constrained to be the same as the CFG for the LLVM input code.
- The LLVM induction variable analysis routines have been rewritten.
- LLVM now has new loop unrolling and loop unswitching passes.
- The induction variable substitution pass performs linear function test
replacement and exit value replacement optimizations.
- LLVM now has first-class support for Accurate Garbage Collection, enabling the use
of aggressive copying and generational collectors.
- LLVM now includes a simple implementation of Andersen's interprocedural alias
analysis algorithm. NOTE: anders-aa is unfortunately completely broken in LLVM 1.3. See the link
for a trivial patch to fix it.
- Bugpoint can extract individual
basic blocks to track down reduce miscompilation testcases.
- LLVM and the C front-end now work under Win32 using the
Cygwin runtime libraries.
This includes the JIT compiler.
- The LLVM code generator is now being documented.
- LLVM includes a new tool, llvm-bcanalyzer, This tool
can compute various statistics and dump information about LLVM bytecode
- The LLVM bytecode file format is now
- LLVM now provides an llvm.isunordered intrinsic for efficient
implementation of unordered floating point comparisons.
- The llvmgcc front-end now supports the GCC builtins for ISO C99 floating
point comparison macros (e.g., __builtin_islessequal).
- We now generate HTML documentation and man pages
for the tools from a single source (perl-style POD files).
- The LLVM code generator can now dynamically load targets from shared
- LLVM now includes a "skeleton" target, which makes it easier to get
started porting LLVM to new architectures.
- The linear scan register allocator is now enabled by default in the
target-independent code generator.
- LLVM now includes a dead store elimination pass.
- Bugpoint can now debug miscompilations that lead to the program going
into an infinite loop.
- LLVM now provides interfaces to support ML-style pattern matching on the
- LLVM now includes a context-sensitive mod/ref analysis
for global variables, which is now enabled by default in gccld.
- LLVM can now autogenerate assembly printers for code generators from the
tablegen description of the target (before they were hand coded).
- All LLVM tools will now respond to the
--version option which
will tell you the version of LLVM on which the tool is based.
- An experimental PowerPC backend has been added, capable of compiling several
In this release, the following missing features were implemented:
In this release, the following build problems were fixed:
- Fixed: [vmcore] Code quality problem
due to long operand of getelementptr
- The X86 backend now generates substantially better code for 64-bit integer
and floating point operations.
- The -inline pass no longer inlines mutually recursive functions until it
hits the inlining threshold.
- The -inline pass no longer misses obvious inlining opportunities just
because the callee eventually calls into an external function.
- The -simplifycfg pass can now "if convert" simple statements into the
- The -loopsimplify pass can now break natural loops with multiple backedges
into multiple nested loops. This enables a variety of subsequent
- The -adce pass can now eliminate calls to functions that do not not write to
- The link-time optimizer now runs the -prune-eh pass (to remove unused
- The link-time optimizer now runs dead store elimination and uses a simple
interprocedural alias analysis.
- The -simplifycfg pass can now eliminate simple correlated branches (such as
"if (A < B && A < B)", and can turn short-circuiting
operators into the strict versions when useful (such as "if (A < B || A
> C)" into "if (A < B | A > C)"
- LLVM now has infrastructure for (simple and sparse conditional) constant
propagation of function calls. It currently supports a few math library
functions like sqrt/sin/cos/etc.
- The C backend now emits syntactic
loops in the code to help C compilers whose optimizers do not recognize
loops formed from gotos (like GCC).
- The SparcV9 backend no longers spills the null constant to the constant
LLVM is known to work in 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 on Win32 with the Cygwin libraries.
- PowerPC-based Mac OS X boxes, running 10.2 and above. Note that no JIT
support is available yet, and LLC support is beta. The C backend can be used
to produce stable code for this platform.
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.
Note that the LLVM build system does not currently support directories with
spaces on them when running on Win32/cygwin. We strongly recommend running
LLVM and the C frontend out of a top-level directory without spaces (e.g.,
/cygdrive/c/llvm). Also, make sure to install all of the
cygwin packages. By default, many important tools are not installed that
are needed by the LLVM build process or test suite (e.g., /bin/time). Finally,
please make sure that there are no directories with spaces in them in your
PATH environment variable.
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.
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 PowerPC backend is incomplete and is known to miscompile several SPEC
benchmarks. The file llvm/lib/Target/PowerPC/README.txt has
- The following passes are incomplete or buggy: -pgmdep, -memdep,
- The -pre pass is incomplete (there are cases it doesn't handle that
it should) and not thoroughly tested.
- The llvm-ar tool is incomplete and probably buggy.
- The llvm-db tool is in a very early stage of development.
Bugs in 1.3 fixed in 1.4:
Bugs in 1.3 fixed in 1.4:
- Inline assembly is not yet supported.
- "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
- The following Unix system functionality has not been tested and may not
- sigsetjmp, siglongjmp - These are not turned into the
appropriate invoke/unwind instructions. Note that
setjmp and longjmp are compiled correctly.
- 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.
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
- 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:
Declaring that functions have no side effects or that they can never
Supported: format, format_arg, non_null,
constructor, destructor, unused,
deprecated, warn_unused_result, weak
Ignored: noreturn, noinline,
always_inline, pure, const, nothrow,
malloc, no_instrument_function, cdecl
Unsupported: used, section, alias,
visibility, regparm, stdcall,
fastcall, all other target specific attributes
- Variable Attributes:
Specifying attributes of variables.
Supported: cleanup, common, nocommon,
Unsupported: aligned, mode, packed,
section, shared, tls_model,
dllexport, all target specific attributes.
- Type Attributes: Specifying attributes of types.
Supported: transparent_union, unused,
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_constant_p, and __builtin_expect
(currently ignored). We also support builtins for ISO C99 floating
point comparison macros (e.g., __builtin_islessequal).
The following extensions are known to be supported:
- Labels as Values: Getting pointers to labels and computed gotos.
- Statement Exprs: Putting statements and declarations inside expressions.
typeof: referring to the type of an expression.
- Lvalues: Using
," and casts in lvalues.
- Conditionals: Omitting the middle operand of a
- Long Long: Double-word integers.
- Complex: Data types for complex numbers.
- Hex Floats:Hexadecimal floating-point constants.
- Zero Length: Zero-length arrays.
- Empty Structures: Structures with no members.
- Variadic Macros: Macros with a variable number of arguments.
- Escaped Newlines: Slightly looser rules for escaped newlines.
- Subscripting: Any array can be subscripted, even if not an lvalue.
- Pointer Arith: Arithmetic on
void-pointers and function pointers.
- Initializers: Non-constant initializers.
- Compound Literals: Compound literals give structures, unions,
or arrays as values.
- Designated Inits: Labeling elements of initializers.
- Cast to Union: Casting to union type from any member of the union.
- Case Ranges: `case 1 ... 9' and such.
- Mixed Declarations: Mixing declarations and code.
- Function Prototypes: Prototype declarations and old-style definitions.
- C++ Comments: C++ comments are recognized.
- Dollar Signs: Dollar sign is allowed in identifiers.
- Character Escapes:
\e stands for the character <ESC>.
- Alignment: Inquiring about the alignment of a type or variable.
- Inline: Defining inline functions (as fast as macros).
- Alternate Keywords:
__asm__, etc., for header files.
- Incomplete Enums:
enum foo;, with details to follow.
- Function Names: Printable strings which are the name of the current function.
- Return Address: Getting the return or frame address of a function.
- Unnamed Fields: Unnamed struct/union fields within structs/unions.
- 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).
For this release, the C++ front-end is considered to be fully functional but
has not been tested as thoroughly as the C front-end. It has been tested and
works for a number of non-trivial programs, but there may be lurking bugs.
Please report any bugs or problems.
Bugs in 1.3 fixed in 1.4:
- The C++ front-end inherits all problems afflicting the C
- IA-64 specific: 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.
- The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This
parser is significantly more standards compliant (and picky) than prior GCC
versions. For more information, see the C++ section of the GCC 3.4 release notes.
- Destructors for local objects are not always run when a longjmp is
performed. In particular, destructors for objects in the longjmping
function and in the setjmp receiver function may not be run.
Objects in intervening stack frames will be destroyed, however (which is
better than most compilers).
- The LLVM C++ front-end follows the Itanium C++ ABI.
This document, which is not Itanium specific, specifies a standard for name
mangling, class layout, v-table layout, RTTI formats, and other C++
representation issues. Because we use this API, code generated by the LLVM
compilers should be binary compatible with machine code generated by other
Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
However, the exception handling mechanism used by LLVM is very
different from the model used in the Itanium ABI, so exceptions will not
Bugs in 1.3 fixed in 1.4:
- The C back-end produces code that violates the ANSI C Type-Based Alias
Analysis rules. As such, special options may be necessary to compile the code
(for example, GCC requires the -fno-strict-aliasing option). This
problem probably cannot be fixed.
- Initializers for global variables
cannot include special floating point numbers like Not-A-Number or
- Zero arg vararg functions are not
supported. This should not affect LLVM produced by the C or C++
A wide variety of additional information is available on the LLVM web page,
including mailing lists and publications describing algorithms and components
implemented in LLVM. The web page also contains versions of the API
documentation which is up-to-date with the CVS 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
The LLVM Compiler Infrastructure
Last modified: $Date: 2004/12/08 19:14:32 $