This document contains the release notes for the LLVM compiler infrastructure, release 1.4. Here we describe the status of LLVM, including any known problems and improvements from the previous release. The most up-to-date version of this document can be found on the LLVM 1.4 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 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 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 fifth public release of the LLVM compiler infrastructure.

At this time, LLVM is known to correctly compile on a broad range of C and C++ programs, including the SPEC CPU95 & 2000 suite. This release includes several major enhancements to the LLVM system, including a new PowerPC JIT, enhancements to the C/C++ front-end to provide source line number information in LLVM, a new compiler driver, and several other enhancements listed below. It also includes bug fixes for those problems found since the 1.3 release.

Note that this release seperates the LLVM Program Testsuite out of the main LLVM distribution into a seperate CVS repository and tarball. This reduces the size of the main LLVM distribution. Also note that LLVM now builds tools into llvm/Debug/bin by default instead of llvm/tools/Debug.

1. LLVM now includes a Just-In-Time compiler for the PowerPC target.
2. llvmgcc and llvmg++ now emit source line number information when '-g' is passed in, making it possible to map from LLVM code back to source. This information is currently used by llvm-db and can be used with other tools and passes.
3. The test/Programs hierarchy has been moved out of the main LLVM tree into a separate CVS repository and tarball. This shrinks the distribution size of LLVM itself significantly.
4. LLVM now optimizes global variables more aggressively than it did before.
5. LLVM now includes the new 'undef' value and unreachable instruction, which give the optimizer more information about the behavior of the program.
6. Bytecode compression with bzip2 has been implemented. All bytecode files generated by LLVM will now be compressed by default. Compression can be disabled with the -disable-compression option to the tools that can generate bytecode files.
7. A generic compiler driver (llvmc) and an associated generic linker (llvm-ld) have been added. The compiler driver is generic because it can be configured to pre-process, translate, optimize, assemble, and link code from any source language with an LLVM front-end. This makes it easier for compiler writers to hide the multiple steps required to compile a program (compiling, optimizing, linking runtime libraries, etc) in one simple command.
8. The dependent libraries feature has been implemented. This allows front end compilers to indicate in the bytecode which libraries the bytecode needs to be linked with. Both the C/C++ and Stacker front ends support generating the required dependencies. The linker now supports using this information to ensure required libaries are linked into the module. This minimizes the need to use the -l option when using llvmc.
9. The LLVM makefiles have been improved to build LLVM much faster and includes new targets (like dist-check, uninstall). One important user-visible change is that libraries and tools will now be built into $builddir/Debug/{bin,lib} instead of $builddir/tools/Debug and $builddir/lib/Debug (Similarly for Release and Profile builds).
10. The LLVM source code is much more compatible with Microsoft Visual C++, including the JIT and runtime-code generation, though the entire system may not work with it.
11. The JIT-Target interfaces are now much simpler and more powerful.
12. LLVM now provides llvm-ar and llvm-ranlib tools for working with archives of LLVM bytecode files.
13. zlib and libpng are no longer included in the main LLVM tarball.
14. The LLVM code generator now automatically generates assembly code writers from an abstract target descriptions, eliminating the need to write assembly printers manually.
15. LLVM regression and feature tests now use DejaGNU instead of QMTest.

1. JIT interface should support arbitrary calls
2. The llvm-ar tool was previously incomplete and didn't properly support other ar(1) implementations. This has been corrected. llvm-ar now fully supports all archive editing functions, table of contents listing, extraction, and printing. It can also read BSD4.4/MacOSX and SVR4 style archives. See llvm-ar for details.

1. The linker no longer emits many useless warnings when linking C++ programs.
2. The LLVM #include namespace has been made consistent. Files in llvm/include/{Support,Config} are now located in llvm/include/llvm/{Support,Config}.
3. The names of the libraries generated by compiling LLVM source have been changed to ensure they do not conflict with other packages upon installation. Each LLVM library is now prefixed with LLVM and uses mixed clase. For example, the library libasmparser.a in 1.3 has become libLLVMAsmParser.a in release 1.4.
4. The C++ frontend no longer expands and emits all inline functions, even if they are unused. It now properly tracks which functions are needed and only compiles those.
5. Many improvements in the autoconf and makefile systems have been implemented.

1. The optimizer produces more efficient code for std::min/std::max and other similar functions.
2. The X86 backend generates substantially faster code for floating point intensive programs.
3. The PowerPC backend generates more efficient code in many common scenarios.

Bugs fixed in the LLVM Core:

1. [licm] LICM invalidates alias analysis info and uses broken information (optimizer crash)
2. [asmwriter] Asmwriter is really slow for functions with lots of values
3. [anders-aa] Andersen's AA is completely broken in LLVM 1.3
4. [bcwriter] Empty compaction tables defined
5. [X86] llc output for functions w/certain names tickles GNU 'as' bugs
6. [cbackend] Static globals are prototyped as 'extern'

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

1. [llvmg++] not enough templates are instantiated
2. [llvmg++] Extern const globals cannot be marked 'constant' if they have nontrivial ctors or dtors
3. [llvmgcc] Crash compiling unnamed bitfield which does not increase struct size
4. [llvmgcc] llvmgcc emits invalid constant exprs
5. [llvmg++] Crash initializing array with constructors in hard EH situations
6. [llvm-gcc] Inline function redefinitions error due to 'asm' function rename
7. [llvm-gcc] Error when an implicitly external function is re-declared as static
8. [llvmgcc] Structure field with non-constant offset crashes llvmgcc
9. [llvmg++] Crash compiling friend with default argument

Bugs fixed in the Sparc V9 back-end:

1. [sparcv9] regalloc assertion failure with certain indirect calls

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 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.

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.

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 following passes are incomplete or buggy, and may be removed in future releases: -pgmdep, -memdep, -ipmodref, -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.

• 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.

• 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.

• 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 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:
  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. Extended Asm: Assembler instructions with C expressions as operands.
  5. Constraints: Constraints for asm operands.
  6. Asm Labels: Specifying the assembler name to use for a C symbol.
  7. Explicit Reg Vars: Defining variables residing in specified registers.
  8. Vector Extensions: Using vector instructions through built-in functions.
  9. Target Builtins: Built-in functions specific to particular targets.
  10. Thread-Local: Per-thread variables.
  11. 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.

  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. Function Attributes: Declaring that functions have no side effects or that they can never return.
     Supported: format, format_arg, non_null, noreturn, constructor, destructor, unused, deprecated, warn_unused_result, weak
     Ignored: noinline, always_inline, pure, const, nothrow, malloc, no_instrument_function, cdecl
     Unsupported: used, section, alias, visibility, regparm, stdcall, fastcall, all other target specific attributes
  3. Variable Attributes: Specifying attributes of variables.
     Supported: cleanup, common, nocommon, deprecated, transparent_union, unused, weak
     Unsupported: aligned, mode, packed, section, shared, tls_model, vector_size, dllimport, dllexport, all target specific attributes.
  4. Type Attributes: Specifying attributes of types.
     Supported: transparent_union, unused, deprecated, may_alias
     Unsupported: aligned, packed, all target specific attributes.
  5. 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 following extensions are known to be supported:

  1. Labels as Values: Getting pointers to labels and computed gotos.
  2. Statement Exprs: Putting statements and declarations inside expressions.
  3. Typeof: typeof: referring to the type of an expression.
  4. Lvalues: Using ?:, "," and casts in lvalues.
  5. Conditionals: Omitting the middle operand of a ?: expression.
  6. Long Long: Double-word integers.
  7. Complex: Data types for complex numbers.
  8. Hex Floats:Hexadecimal floating-point constants.
  9. Zero Length: Zero-length arrays.
  10. Empty Structures: Structures with no members.
  11. Variadic Macros: Macros with a variable number of arguments.
  12. Escaped Newlines: Slightly looser rules for escaped newlines.
  13. Subscripting: Any array can be subscripted, even if not an lvalue.
  14. Pointer Arith: Arithmetic on void-pointers and function pointers.
  15. Initializers: Non-constant initializers.
  16. Compound Literals: Compound literals give structures, unions, or arrays as values.
  17. Designated Inits: Labeling elements of initializers.
  18. Cast to Union: Casting to union type from any member of the union.
  19. Case Ranges: `case 1 ... 9' and such.
  20. Mixed Declarations: Mixing declarations and code.
  21. Function Prototypes: Prototype declarations and old-style definitions.
  22. C++ Comments: C++ comments are recognized.
  23. Dollar Signs: Dollar sign is allowed in identifiers.
  24. Character Escapes: \e stands for the character <ESC>.
  25. Alignment: Inquiring about the alignment of a type or variable.
  26. Inline: Defining inline functions (as fast as macros).
  27. Alternate Keywords:__const__, __asm__, etc., for header files.
  28. Incomplete Enums: enum foo;, with details to follow.
  29. Function Names: Printable strings which are the name of the current function.
  30. Return Address: Getting the return or frame address of a function.
  31. Unnamed Fields: Unnamed struct/union fields within structs/unions.
  32. 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 tested and works for a number of non-trivial programs, including LLVM itself.

• The C++ front-end inherits all problems afflicting the C front-end.
• 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 interact correctly.

• none yet

• [sparcv9] SparcV9 backend miscompiles several programs in the LLVM test suite

• none yet

• 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.
• Zero arg vararg functions are not supported. This should not affect LLVM produced by the C or C++ frontends.

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 lists.