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  <title>LLVM 1.2 Release Notes</title>
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<div class="doc_title">
  LLVM 1.2 Release Notes
</div>
 
<ol>
  <li><a href="#intro">Introduction</a></li>
  <li><a href="#whatsnew">What's New?</a></li>
  <li><a href="#portability">Portability and Supported Platforms</a></li>
  <li><a href="#install-instructions">Installation Instructions</a></li>
  <li><a href="#knownproblems">Known Problems</a>
  <ul>
    <li><a href="#core">Known problems with the LLVM Core</a>
    <li><a href="#c-fe">Known problems with the C Front-end</a>
    <li><a href="#c++-fe">Known problems with the C++ Front-end</a>
    <li><a href="#x86-be">Known problems with the X86 Back-end</a>
    <li><a href="#sparc-be">Known problems with the Sparc Back-end</a>
    <li><a href="#c-be">Known problems with the C back-end</a>
  </ul></li>
  <li><a href="#additionalinfo">Additional Information</a></li>
</ol>

<div class="doc_text">
  <p><b>Written by the <a href="http://llvm.cs.uiuc.edu">LLVM team</a></b><p>
</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="intro">Introduction</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This document contains the release notes for the LLVM compiler
infrastructure, release 1.2.  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 <a
href="http://llvm.cs.uiuc.edu/releases/1.2/">LLVM 1.2 web site</a>.  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.</p>

<p>For more information about LLVM, including information about potentially more
current releases, please check out the <a href="http://llvm.cs.uiuc.edu">main
web site</a>.  If you have questions or comments, the <a
href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
list</a> is a good place to send them.</p>

<p>Note that if you are reading this file from CVS, this document applies
to the <i>next</i> release, not the current one.  To see the release notes for
the current or previous releases, see the <a
href="http://llvm.cs.uiuc.edu/releases/">releases page</a>.</p>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="whatsnew">What's New?</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This is the third public release of the LLVM compiler infrastructure.
</p>

<p>At this time, LLVM is known to correctly compile and run all non-unwinding C
&amp; C++ SPEC CPU2000 benchmarks, the Olden benchmarks, and the Ptrdist
benchmarks.  It has also been used to compile <b>many</b> other programs.  LLVM
now also works with a broad variety of C++ programs, though it has still
received much less testing than the C front-end.
</p>

<p>
The LLVM native code generators are very stable but do not currently support
unwinding (exception throwing or <tt>longjmp</tt>ing), which prevent them from
working with programs like the <tt>253.perlbmk</tt> in SPEC CPU2000.  The C
backend and the rest of LLVM supports these programs, so you can
still use LLVM with them.  Support for unwinding will be added in a future
release.
</p>


<!--=========================================================================-->
<div class="doc_subsubsection">
This release implements the following new features:
</div>

<ol>
<li></li>
<li></li>
</ol>


<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following missing features were implemented:
</div>

<ol>
<li></li>
<li></li>
</ol>


<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following Quality of Implementation issues were fixed:
</div>

<ol>

<li><a href="http://llvm.cs.uiuc.edu/PR135">JIT should lazily initialize global variables</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR192">[X86] X86 Backend never releases memory for machine code structures</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR196">[vmcore] OpaqueType objects memory leak</a></li>
</ol>

<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following Code Quality issues were fixed:
</div>

<ol>

<li><a href="http://llvm.cs.uiuc.edu/PR187">[loopsimplify] Many pointless phi nodes are created</a></li>

<li></li>
</ol>


<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following bugs in the previous release were fixed:
</div>

<p>Bugs in the LLVM Core:</p>

<ol>
<li><a href="http://llvm.cs.uiuc.edu/PR179">[licm] LICM promotes volatile memory
locations to registers</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR191">[licm] Memory read after free causes 
infrequent crash</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR194">[indvars] Induction variable 
canonicalization always makes 32-bit indvars</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR193">[constantmerge] Merging globals can
cause use of invalid pointers!</a></li>

</ol>


<p>Bugs in the C/C++ front-end:</p>

<ol>
<li><a href="http://llvm.cs.uiuc.edu/PR186">Need weak linkage on memory
management functions in libc runtime to allow them to be overriden</a></li>
<li></li>
</ol>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="portability">Portability and Supported Platforms</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>LLVM has been extensively tested on Intel and AMD machines running Red
Hat Linux and FreeBSD.  It has also been tested on Sun UltraSPARC workstations running Solaris 8.
Additionally, 
LLVM works on Mac OS X 10.3 and above, but only with the C backend or 
interpreter (no native backend for the PowerPC is available yet).
The core LLVM infrastructure uses "autoconf" for portability, so hopefully we
work on more platforms than that.  However, it is likely that we
missed something and that minor porting is required to get LLVM to work on 
new platforms.  We welcome portability patches and error messages.</p>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="knownproblems">Known Problems</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>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 <a
href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one.</p>

</div>

<!-- _______________________________________________________________________ -->
<!--
</ul><h4><a name="portability"><hr size=0>Portability Problems</h4><ul>
-->


<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="core">Known problems with the LLVM Core</a>
</div>

<div class="doc_text">

<ul>

<li>In the JIT, <tt>dlsym</tt> on a symbol compiled by the JIT will not
work.</li>

<li>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.</li>

<li>It is not possible to <tt>dlopen</tt> an LLVM bytecode file in the JIT.</li>

<li>Linking in static archive files (.a files) is very slow (there is no symbol
table in the archive).</li>

<li><a href="http://llvm.cs.uiuc.edu/PR82">LLVM cannot handle structures with
more than 256 elements</a>.</li>

<li>
The gccld program 
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=139">
does not link objects/archives in the order specified on the command line.
</a>
</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=174">
Tail duplication does not update SSA form correctly.
</a>
</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c-fe">Known problems with the C front-end</a>
</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">Bugs</div>

<div class="doc_text">
<ul>
<li>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:
<pre>
    for (i = 0; i != 1000000; ++i) {
      int X[n];
      foo(X);
    }
</pre></li>

<li>
Initialization of global union variables can only be done
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=162">with the largest
union member</a>.
</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=182">
Functions marked "extern inline" are not compiled into LLVM with linkonce
linkage.
</a>
</li>


<li>
The memory management functions in the libc runtime
<a href="http://llvm.cs.uiuc.edu/PR186">need weak linkage so that they can be
overridden.
</a>
</li>
</ul>
</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  Notes
</div>

<div class="doc_text">

<ul>

<li>Inline assembly is not yet supported.</li>

<li>"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.</li>
    
<li>The following Unix system functionality has not been tested and may not
work:
  <ol>
  <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
      appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions.  Note that
      <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
  <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
      - These functions have not been tested.
  </ol></li>

<li>Although many GCC extensions are supported, some are not.  In particular,
    the following extensions are known to <b>not be</b> supported:
  <ol>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html#Return%20Address">Return Address</a>: Getting the return or frame address of a function.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>:   Built-in functions specific to particular targets.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html#Thread-Local">Thread-Local</a>: Per-thread variables.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
  </ol>

  <p>The following GCC extensions are <b>partially</b> 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.</p>

  <ol>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
      Arrays whose length is computed at run time.<br>
      Supported, but allocated stack space is not freed until the function returns (noted above).</li>

  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:

      Declaring that functions have no side effects or that they can never
      return.<br>

      <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
      <tt>constructor</tt>, <tt>destructor</tt>, <tt>unused</tt>,
      <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>

      <b>Ignored:</b> <tt>noreturn</tt>, <tt>noinline</tt>,
      <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
      <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>

      <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
      <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
      <tt>fastcall</tt>, all other target specific attributes</li>
   
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
      Specifying attributes of variables.<br>
      <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
                        <tt>deprecated</tt>, <tt>transparent_union</tt>,
                        <tt>unused</tt>, <tt>weak</tt><br>

      <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
                        <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
                        <tt>vector_size</tt>, <tt>dllimport</tt>, 
                        <tt>dllexport</tt>, all target specific attributes.</li>

  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>:	Specifying attributes of types.<br>
      <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
                        <tt>deprecated</tt>, <tt>may_alias</tt><br>

      <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>, 
                        all target specific attributes.</li>

  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
      Other built-in functions.<br>
      We support all builtins which have a C language equivalent (e.g., 
         <tt>__builtin_cos</tt>),  <tt>__builtin_alloca</tt>, 
         <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
         <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt> (ignored).</li>

  </ol>

  <p>The following extensions <b>are</b> known to be supported:</p>

  <ol>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>:   Putting statements and declarations inside expressions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Lvalues.html#Lvalues">Lvalues</a>: Using <code>?:</code>, "<code>,</code>" and casts in lvalues.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>:   Data types for complex numbers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>:  Slightly looser rules for escaped newlines.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
or arrays as values.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast%20to%20Union">Cast to Union</a>: Casting to union type from any member of the union.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/C---Comments.html#C++%20Comments">C++ Comments</a>: C++ comments are recognized.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character &lt;ESC&gt;.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html#Alternate%20Keywords">Alternate Keywords</a>:<code>__const__</code>, <code>__asm__</code>, etc., for header files.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete%20Enums">Incomplete Enums</a>:  <code>enum foo;</code>, with details to follow.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function%20Names">Function Names</a>: Printable strings which are the name of the current function.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed%20Fields">Unnamed Fields</a>: Unnamed struct/union fields within structs/unions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
  </ol></li>

</ul>

<p>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).</p>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c++-fe">Known problems with the C++ front-end</a>
</div>

<div class="doc_text">

<p>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.</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  Bugs
</div>

<div class="doc_text">

<ul>
<li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
    front-end</a>.</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=137">
Code is generated for empty classes.
</a>
</li>
</ul>
</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  Notes
</div>

<div class="doc_text">

<ul>

<li>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 <a
href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>

<li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
    performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
    function and in the <tt>setjmp</tt> receiver function may not be run.
    Objects in intervening stack frames will be destroyed, however (which is
    better than most compilers).</li>

<li>The LLVM C++ front-end follows the <a
    href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
    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).
    <i>However</i>, the exception handling mechanism used by LLVM is very
    different from the model used in the Itanium ABI, so <b>exceptions will not
    interact correctly</b>. </li>

</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="x86-be">Known problems with the X86 back-end</a>
</div>

<div class="doc_text">

<ul>

<li>The X86 code generator <a
href="http://llvm.cs.uiuc.edu/PR16">does not currently
support the <tt>unwind</tt> instruction</a>, so code that throws a C++ exception
or calls the C <tt>longjmp</tt> function will abort.</li>

</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="sparc-be">Known problems with the Sparc back-end</a>
</div>

<div class="doc_text">

<ul>

<li>The Sparc code generator <a
href="http://llvm.cs.uiuc.edu/PR15">does not currently
support the <tt>unwind</tt> instruction</a>, so code that throws a C++ exception
or calls the C <tt>longjmp</tt> function will abort.</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=167">
The llc program can crash on legal code.
</a>
</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c-be">Known problems with the C back-end</a>
</div>

<div class="doc_text">

<ul>

<li>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 <tt>-fno-strict-aliasing</tt> option).  This
problem probably cannot be fixed.</li>

<li><a href="http://llvm.cs.uiuc.edu/PR33">Initializers for global variables</a>
cannot include special floating point numbers like Not-A-Number or
Infinity.</li>

<li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not 
supported</a>.  This should not affect LLVM produced by the C or C++ 
frontends.</li>

</ul>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="additionalinfo">Additional Information</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>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 "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>

<p>If you have any questions or comments about LLVM, please feel free to contact
us via the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">mailing
lists</a>.</p>

</div>

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<head>
  <link rel="stylesheet" href="llvm.css" type="text/css">
  <title>LLVM 1.2 Release Notes</title>
</head>
<body>

<div class="doc_title">
  LLVM 1.2 Release Notes
</div>
 
<ol>
  <li><a href="#intro">Introduction</a></li>
  <li><a href="#whatsnew">What's New?</a></li>
  <li><a href="#portability">Portability and Supported Platforms</a></li>
  <li><a href="#install-instructions">Installation Instructions</a></li>
  <li><a href="#knownproblems">Known Problems</a>
  <ul>
    <li><a href="#core">Known problems with the LLVM Core</a>
    <li><a href="#c-fe">Known problems with the C Front-end</a>
    <li><a href="#c++-fe">Known problems with the C++ Front-end</a>
    <li><a href="#x86-be">Known problems with the X86 Back-end</a>
    <li><a href="#sparc-be">Known problems with the Sparc Back-end</a>
    <li><a href="#c-be">Known problems with the C back-end</a>
  </ul></li>
  <li><a href="#additionalinfo">Additional Information</a></li>
</ol>

<div class="doc_text">
  <p><b>Written by the <a href="http://llvm.cs.uiuc.edu">LLVM team</a></b><p>
</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="intro">Introduction</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This document contains the release notes for the LLVM compiler
infrastructure, release 1.2.  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 <a
href="http://llvm.cs.uiuc.edu/releases/1.2/">LLVM 1.2 web site</a>.  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.</p>

<p>For more information about LLVM, including information about potentially more
current releases, please check out the <a href="http://llvm.cs.uiuc.edu">main
web site</a>.  If you have questions or comments, the <a
href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
list</a> is a good place to send them.</p>

<p>Note that if you are reading this file from CVS, this document applies
to the <i>next</i> release, not the current one.  To see the release notes for
the current or previous releases, see the <a
href="http://llvm.cs.uiuc.edu/releases/">releases page</a>.</p>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="whatsnew">What's New?</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>This is the third public release of the LLVM compiler infrastructure.
</p>

<p>At this time, LLVM is known to correctly compile and run all non-unwinding C
&amp; C++ SPEC CPU2000 benchmarks, the Olden benchmarks, and the Ptrdist
benchmarks.  It has also been used to compile <b>many</b> other programs.  LLVM
now also works with a broad variety of C++ programs, though it has still
received much less testing than the C front-end.
</p>

<p>
The LLVM native code generators are very stable but do not currently support
unwinding (exception throwing or <tt>longjmp</tt>ing), which prevent them from
working with programs like the <tt>253.perlbmk</tt> in SPEC CPU2000.  The C
backend and the rest of LLVM supports these programs, so you can
still use LLVM with them.  Support for unwinding will be added in a future
release.
</p>


<!--=========================================================================-->
<div class="doc_subsubsection">
This release implements the following new features:
</div>

<ol>
<li></li>
<li></li>
</ol>


<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following missing features were implemented:
</div>

<ol>
<li></li>
<li></li>
</ol>


<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following Quality of Implementation issues were fixed:
</div>

<ol>

<li><a href="http://llvm.cs.uiuc.edu/PR135">JIT should lazily initialize global variables</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR192">[X86] X86 Backend never releases memory for machine code structures</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR196">[vmcore] OpaqueType objects memory leak</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR182">[llvmgcc] C front-end does not compile "extern inline" into linkonce</a></li>
</ol>

<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following Code Quality issues were fixed:
</div>

<ol>

<li><a href="http://llvm.cs.uiuc.edu/PR187">[loopsimplify] Many pointless phi nodes are created</a></li>

<li></li>
</ol>


<!--=========================================================================-->
<div class="doc_subsubsection">
In this release, the following bugs in the previous release were fixed:
</div>

<p>Bugs in the LLVM Core:</p>

<ol>
<li><a href="http://llvm.cs.uiuc.edu/PR179">[licm] LICM promotes volatile memory
locations to registers</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR191">[licm] Memory read after free causes 
infrequent crash</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR194">[indvars] Induction variable 
canonicalization always makes 32-bit indvars</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR193">[constantmerge] Merging globals can
cause use of invalid pointers!</a></li>

</ol>


<p>Bugs in the C/C++ front-end:</p>

<ol>
<li><a href="http://llvm.cs.uiuc.edu/PR186">Need weak linkage on memory
management functions in libc runtime to allow them to be overriden</a></li>
<li><a href="http://llvm.cs.uiuc.edu/PR202">[llvm-gcc] asserts when an extern inline function is redefined</a></li>
</ol>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="portability">Portability and Supported Platforms</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>LLVM has been extensively tested on Intel and AMD machines running Red
Hat Linux and FreeBSD.  It has also been tested on Sun UltraSPARC workstations running Solaris 8.
Additionally, 
LLVM works on Mac OS X 10.3 and above, but only with the C backend or 
interpreter (no native backend for the PowerPC is available yet).
The core LLVM infrastructure uses "autoconf" for portability, so hopefully we
work on more platforms than that.  However, it is likely that we
missed something and that minor porting is required to get LLVM to work on 
new platforms.  We welcome portability patches and error messages.</p>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="knownproblems">Known Problems</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>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 <a
href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one.</p>

</div>

<!-- _______________________________________________________________________ -->
<!--
</ul><h4><a name="portability"><hr size=0>Portability Problems</h4><ul>
-->


<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="core">Known problems with the LLVM Core</a>
</div>

<div class="doc_text">

<ul>

<li>In the JIT, <tt>dlsym</tt> on a symbol compiled by the JIT will not
work.</li>

<li>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.</li>

<li>It is not possible to <tt>dlopen</tt> an LLVM bytecode file in the JIT.</li>

<li>Linking in static archive files (.a files) is very slow (there is no symbol
table in the archive).</li>

<li><a href="http://llvm.cs.uiuc.edu/PR82">LLVM cannot handle structures with
more than 256 elements</a>.</li>

<li>
The gccld program 
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=139">
does not link objects/archives in the order specified on the command line.
</a>
</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=174">
Tail duplication does not update SSA form correctly.
</a>
</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c-fe">Known problems with the C front-end</a>
</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">Bugs</div>

<div class="doc_text">
<ul>
<li>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:
<pre>
    for (i = 0; i != 1000000; ++i) {
      int X[n];
      foo(X);
    }
</pre></li>

<li>
Initialization of global union variables can only be done
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=162">with the largest
union member</a>.
</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=182">
Functions marked "extern inline" are not compiled into LLVM with linkonce
linkage.
</a>
</li>


<li>
The memory management functions in the libc runtime
<a href="http://llvm.cs.uiuc.edu/PR186">need weak linkage so that they can be
overridden.
</a>
</li>
</ul>
</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  Notes
</div>

<div class="doc_text">

<ul>

<li>Inline assembly is not yet supported.</li>

<li>"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.</li>
    
<li>The following Unix system functionality has not been tested and may not
work:
  <ol>
  <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
      appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions.  Note that
      <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
  <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
      - These functions have not been tested.
  </ol></li>

<li>Although many GCC extensions are supported, some are not.  In particular,
    the following extensions are known to <b>not be</b> supported:
  <ol>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html#Return%20Address">Return Address</a>: Getting the return or frame address of a function.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>:   Built-in functions specific to particular targets.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html#Thread-Local">Thread-Local</a>: Per-thread variables.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
  </ol>

  <p>The following GCC extensions are <b>partially</b> 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.</p>

  <ol>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
      Arrays whose length is computed at run time.<br>
      Supported, but allocated stack space is not freed until the function returns (noted above).</li>

  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:

      Declaring that functions have no side effects or that they can never
      return.<br>

      <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
      <tt>constructor</tt>, <tt>destructor</tt>, <tt>unused</tt>,
      <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>

      <b>Ignored:</b> <tt>noreturn</tt>, <tt>noinline</tt>,
      <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
      <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>

      <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
      <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
      <tt>fastcall</tt>, all other target specific attributes</li>
   
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
      Specifying attributes of variables.<br>
      <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
                        <tt>deprecated</tt>, <tt>transparent_union</tt>,
                        <tt>unused</tt>, <tt>weak</tt><br>

      <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
                        <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
                        <tt>vector_size</tt>, <tt>dllimport</tt>, 
                        <tt>dllexport</tt>, all target specific attributes.</li>

  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>:	Specifying attributes of types.<br>
      <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
                        <tt>deprecated</tt>, <tt>may_alias</tt><br>

      <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>, 
                        all target specific attributes.</li>

  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
      Other built-in functions.<br>
      We support all builtins which have a C language equivalent (e.g., 
         <tt>__builtin_cos</tt>),  <tt>__builtin_alloca</tt>, 
         <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
         <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt> (ignored).</li>

  </ol>

  <p>The following extensions <b>are</b> known to be supported:</p>

  <ol>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>:   Putting statements and declarations inside expressions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Lvalues.html#Lvalues">Lvalues</a>: Using <code>?:</code>, "<code>,</code>" and casts in lvalues.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>:   Data types for complex numbers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>:  Slightly looser rules for escaped newlines.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
or arrays as values.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast%20to%20Union">Cast to Union</a>: Casting to union type from any member of the union.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/C---Comments.html#C++%20Comments">C++ Comments</a>: C++ comments are recognized.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character &lt;ESC&gt;.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html#Alternate%20Keywords">Alternate Keywords</a>:<code>__const__</code>, <code>__asm__</code>, etc., for header files.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete%20Enums">Incomplete Enums</a>:  <code>enum foo;</code>, with details to follow.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function%20Names">Function Names</a>: Printable strings which are the name of the current function.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed%20Fields">Unnamed Fields</a>: Unnamed struct/union fields within structs/unions.</li>
  <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
  </ol></li>

</ul>

<p>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).</p>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c++-fe">Known problems with the C++ front-end</a>
</div>

<div class="doc_text">

<p>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.</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  Bugs
</div>

<div class="doc_text">

<ul>
<li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
    front-end</a>.</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=137">
Code is generated for empty classes.
</a>
</li>
</ul>
</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  Notes
</div>

<div class="doc_text">

<ul>

<li>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 <a
href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>

<li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
    performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
    function and in the <tt>setjmp</tt> receiver function may not be run.
    Objects in intervening stack frames will be destroyed, however (which is
    better than most compilers).</li>

<li>The LLVM C++ front-end follows the <a
    href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
    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).
    <i>However</i>, the exception handling mechanism used by LLVM is very
    different from the model used in the Itanium ABI, so <b>exceptions will not
    interact correctly</b>. </li>

</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="x86-be">Known problems with the X86 back-end</a>
</div>

<div class="doc_text">

<ul>

<li>The X86 code generator <a
href="http://llvm.cs.uiuc.edu/PR16">does not currently
support the <tt>unwind</tt> instruction</a>, so code that throws a C++ exception
or calls the C <tt>longjmp</tt> function will abort.</li>

</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="sparc-be">Known problems with the Sparc back-end</a>
</div>

<div class="doc_text">

<ul>

<li>The Sparc code generator <a
href="http://llvm.cs.uiuc.edu/PR15">does not currently
support the <tt>unwind</tt> instruction</a>, so code that throws a C++ exception
or calls the C <tt>longjmp</tt> function will abort.</li>

<li>
<a href="http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=167">
The llc program can crash on legal code.
</a>
</li>
</ul>

</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="c-be">Known problems with the C back-end</a>
</div>

<div class="doc_text">

<ul>

<li>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 <tt>-fno-strict-aliasing</tt> option).  This
problem probably cannot be fixed.</li>

<li><a href="http://llvm.cs.uiuc.edu/PR33">Initializers for global variables</a>
cannot include special floating point numbers like Not-A-Number or
Infinity.</li>

<li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not 
supported</a>.  This should not affect LLVM produced by the C or C++ 
frontends.</li>

</ul>

</div>

<!-- *********************************************************************** -->
<div class="doc_section">
  <a name="additionalinfo">Additional Information</a>
</div>
<!-- *********************************************************************** -->

<div class="doc_text">

<p>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 "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>

<p>If you have any questions or comments about LLVM, please feel free to contact
us via the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">mailing
lists</a>.</p>

</div>

<!-- *********************************************************************** -->

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