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<title>LLVM 2.0 Release Notes</title>
<div class="doc_title">LLVM 2.0 Release Notes</div>
<li><a href="#intro">Introduction</a></li>
<li><a href="#whatsnew">What's New?</a></li>
<li><a href="GettingStarted.html">Installation Instructions</a></li>
<li><a href="#portability">Portability and Supported Platforms</a></li>
<li><a href="#knownproblems">Known Problems</a>
<li><a href="#additionalinfo">Additional Information</a></li>
Chris Lattner
committed
<div class="doc_author">
Chris Lattner
committed
<p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
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<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 2.0. Here we describe the status of LLVM, including any
known problems and major improvements from the previous release. All LLVM
releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
releases web site</a>.
<p>For more information about LLVM, including information about the latest
Chris Lattner
committed
release, please check out the <a href="http://llvm.org/">main LLVM
web site</a>. If you have questions or comments, the <a
href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
<p>Note that if you are reading this file from CVS or the main LLVM web page,
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
Chris Lattner
committed
href="http://llvm.org/releases/">releases page</a>.</p>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="whatsnew">What's New?</a>
</div>
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<p>This is the eleventh public release of the LLVM Compiler Infrastructure.
Being the first major release since 1.0, this release is different in several
ways from our previous releases:</p>
<ol>
<li>We took this as an opportunity to
break backwards compatibility with the LLVM 1.x bytecode and .ll file format.
If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we
recommend the use of the stand alone <a href="#llvm-upgrade">llvm-upgrade</a>
tool (which is included with 2.0). We intend to keep compatibility with .ll
and .bc formats within the 2.x release series, like we did within the 1.x
series.</li>
<li>There are several significant change to the LLVM IR and internal APIs, such
as a major overhaul of the type system, the completely new bitcode file
format, etc.</li>
<li>We designed the release around a 6 month release cycle instead of the usual
3-month cycle. This gave us extra time to develop and test some of the
more invasive features in this release.</li>
<li>LLVM 2.0 no longer supports the llvm-gcc3 front-end.</li>
</ol>
<p>Note that while this is a major version bump, this release has been
extensively tested on a wide range of software. It is easy to say that this
is our best release yet, in terms of both features and correctness.</p>
</div>
<!--=========================================================================-->
<a name="newfeatures">New Features in LLVM 2.0</a>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="majorchanges">Major Changes</a></div>
<div class="doc_text">
<p>blah
</p>
<ul>
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<li>llvm-gcc3 is now officially unsupported. Users are required to
upgrade to llvm-gcc4. llvm-gcc4 includes many features over
llvm-gcc3, is faster, and is much easier to build.</li>
<li>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 (<a href="http://llvm.org/PR950">PR950</a>).</li>
<li>Arbitrary bitwidth integers (e.g. i13, i36, i42, etc) are now
supported in the LLVM IR and optimizations. However, neither llvm-gcc nor
the native code generators support non-standard width integers
(<a href="http://llvm.org/PR1043">PR1043</a>).</li>
<li>'type planes' have been removed (<a href="http://llvm.org/PR411">PR411</a>).
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.</li>
<li>Global variables and functions in .ll files are now prefixed with
@ instead of % (<a href="http://llvm.org/PR645">PR645</a>).</li>
<li>The LLVM 1.x "bytecode" format has been replaced with a
completely new binary representation, named 'bitcode'. Because we
plan to maintain binary compatibility between LLVM 2.x ".bc" files,
this is an important change to get right. Bitcode 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.</li>
<li>Support was added for alignment values on load and store
instructions (<a href="http://www.llvm.org/PR400">PR400</a>). This
allows the IR to express loads that are not
sufficiently aligned (e.g. due to pragma packed) or to capture extra
alignment information. </li>
<li>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.</li>
<li>Support has been added for 'protected visibility' in ELF.</li>
<li>Thread Local Storage with the __thread keyword was implemented along
with added codegen support for Linux on X86 and ARM.</li>
<li>ELF symbol aliases supported has been added.</li>
<li>Added support for 'polymorphic intrinsics', allowing things like
llvm.ctpop to work on arbitrary width integers.</li>
</ul>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="llvmgccfeatures">llvm-gcc
Improvements</a></div>
<div class="doc_text">
<p>New features include:
</p>
<ul>
<li>Precompiled Headers (PCH) support has been implemented.</li>
<li>Support for external weak linkage and hidden visibility has been added.</li>
<li>Packed structure types are now supported , which allows LLVM to express
unaligned data more naturally.</li>
<li>Inline assembly support has been improved and many bugs were fixed.
The two large missing features are support for 80-bit floating point stack
registers on X86 (<a href="http://llvm.org/PR879">PR879</a>), and support for inline asm in the C backend (<a href="http://llvm.org/PR802">PR802</a>).</li>
<li>Ada support, such as nested functions, has been improved.</li>
<li>Tracking function parameter/result attributes is now possible.</li>
<li>Its is now easier to configure llvm-gcc for linux.</li>
<li>Many 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, and many other things.</li>
<li>Improved "attribute packed" support in the CFE, and handle many
other obscure struct layout cases correctly.</li>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="optimizer">Optimizer
Improvements</a></div>
<li>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.</li>
<li>The -scalarrepl pass can now promote unions containing FP values into
a register, it can also handle unions of vectors of the same size.</li>
<li>The predicate simplifier pass has been improved, making it able to do
simple value range propagation and eliminate more conditionals.</li>
<li>There is a new new LoopPass class. The passmanager has been
modified to support it, and all existing loop xforms have been
converted to use it. </li>
<li>There is a new loop rotation pass, which converts "for loops" into
"do/while loops", where the condition is at the bottom of the loop.</li>
<li>ModulePasses may now use the result of FunctionPasses.</li>
<li>The [Post]DominatorSet classes have been removed from LLVM and clients switched to use the far-more-efficient ETForest class instead. </li>
<li>The ImmediateDominator class has also been removed, and clients have been switched to use DominatorTree instead.</li>
</div>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="codegen">Code
Generator Enhancements</a></div>
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<li>Support for Zero-cost DWARF exception handling has been added. It is mostly
complete and just in need of continued bug fixes and optimizations at
this point.</li>
<li>Progress has been made on a direct Mach-o .o file writer. Many small
apps work, but it is not quite complete yet.</li>
<li>Support was added for software floating point routines.</li>
<li>DWARF debug information generation has been improved. LLVM now passes
most of the GDB testsuite on MacOS and debug info is more dense.</li>
<li>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.</li>
<li>Heuristics have been added to avoid coalescing vregs with very large live
ranges to physregs.</li>
<li>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.</li>
<li>Significantly improved 'switch' lowering, improving codegen for
sparse switches that have dense subregions, and implemented support
for the shift/and trick.</li>
<li>The code generator now has more accurate and general hooks for
describing addressing modes ("isLegalAddressingMode") to
optimizations like loop strength reduction and code sinking.</li>
<li>The Loop Strength Reduction pass has been improved, and support added
for sinking expressions across blocks to reduce register pressure.</li>
<li>Added support for tracking physreg sub-registers and super-registers
in the code generator, as well as extensive register
allocator changes to track them.</li>
<li>There is initial support for virtreg sub-registers
(<a href="http://llvm.org/PR1350">PR1350</a>).</li>
</ul>
<p>In addition, the LLVM target description format has itself been extended in
several ways:</p>
<ul>
<li>Extended TargetData to support better target parameterization in
the .ll/.bc files, eliminating the 'pointersize/endianness' attributes
in the files (<a href="http://llvm.org/PR761">PR761</a>).</li>
<li>TargetData was generalized for finer grained alignment handling,
handling of vector alignment, and handling of preferred alignment</li>
<li>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.</li>
</ul>
<p>Further, several significant target-specific enhancements are included in
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="specifictargets">Target-Specific
Improvements</a></div>
<div class="doc_text">
<p>X86-Specific Code Generator Enhancements:
<li>The scheduler was improved to better reduce register pressure on
X86 and other targets that are register pressure sensitive</li>
<li>Linux/x86-64 support has been improved.</li>
<li>PIC support for linux/x86 has been added.</li>
<li>Support now exists for the GCC regparm attribute, and code in the X86
backend to respect it.</li>
<li>Various improvements have been made for the X86-64 JIT, allowing it to
generate code in the large code model</li>
<li>LLVM now supports inline asm with multiple constraint letters per operand
(like "ri") which is common in X86 inline asms.</li>
<li>Early support has been added for X86 inline asm in the C backend.</li>
<li>Added support for the X86 MMX instruction set.</li>
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<p>ARM-Specific Code Generator Enhancements:
</p>
<ul>
<li>Several improvements have been made to the ARM backend, including basic
inline asm support, weak linkage support, static ctor/dtor support and
many bug fixes.</li>
<li>There are major enhancements to the ARM backend, including support for ARM
v4-v6, vfp support, soft float, pre/postinc support, load/store multiple
generation, constant pool entry motion (to support large functions),
and enhancements to ARM constant island pass.
</li>
<li>Added support for Thumb code generation (an ARM subtarget).</li>
<li>More aggressive size analysis for ARM inline asm strings was
implemented.</li>
</ul>
</div>
<p>Other Target-Specific Code Generator Enhancements:
</p>
<ul>
<li>The PowerPC 64 JIT now supports addressing code loaded above the 2G
boundary.</li>
<li>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
<li>Many bugs fixed for PowerPC 64.</li>
<li>Support was added for the ARM AAPCS and EABI ABIs and PIC codegen on
arm/linux.</li>
<li>Several bugs in DWARF debug emission on linux and cygwin/mingw were fixed.
Debugging basically works on these targets now.</li>
<li>Support has been added for the X86-64 large code model to the JIT,
which is useful if JIT'd function bodies are more than 2G away from
library functions.</li>
<li>Several bugs were fixed for DWARF debug info generation on arm/linux.</li>
</ul>
<!--_________________________________________________________________________-->
<div class="doc_subsubsection"><a name="other">Other Improvements</a></div>
<p>This release includes many other improvements, including
performance work, specifically designed to tune datastructure
usage. This makes several critical components faster.</p>
<p>More specific changes include:</p>
<li>ConstantBool, ConstantIntegral and ConstantInt classes have been merged
together, we now just have ConstantInt</li>
<li>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.</li>
<li>LLVM now has significantly fewer static constructors, reducing startup time.
</li>
<li>Several classes have been refactored to reduce the amount of code that
gets linked into apps that use the JIT.</li>
<li>Construction of intrinsic function declarations has been simplified.</li>
<li>The llvm-upgrade tool now exists. This migrates LLVM 1.9 .ll files to
LLVM 2.0 syntax.</li>
<li>The gccas/gccld tools have been removed.</li>
<li>Support has been added to llvm-test for running on low-memory
or slow machines (make SMALL_PROBLEM_SIZE=1).</li>
<li>llvm-test is now more portable and should build with MS Visual Studio.</li>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="portability">Portability and Supported Platforms</a>
</div>
<!-- *********************************************************************** -->
<p>LLVM is known to work on the following platforms:</p>
<li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD
(and probably other unix-like systems).</li>
<li>Intel and AMD machines running on Win32 using MinGW libraries (native)</li>
<li>Sun UltraSPARC workstations running Solaris 8.</li>
<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
support is available for native builds with Visual C++).</li>
<li>PowerPC and X86-based Mac OS X systems, running 10.2 and above in 32-bit and
64-bit modes.</li>
<li>Alpha-based machines running Debian GNU/Linux.</li>
<li>Itanium-based machines running Linux and HP-UX.</li>
<p>The core LLVM infrastructure uses
<a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> 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.</p>
<!-- *********************************************************************** -->
<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
Chris Lattner
committed
href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
there isn't already one.</p>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="experimental">Experimental features included with this release</a>
</div>
Misha Brukman
committed
<p>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 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
<li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in in a
future release.</li>
Chris Lattner
committed
<li>The Alpha JIT is experimental.</li>
<li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
<tt>-filetype</tt> llc option.</li>
<!-- ======================================================================= -->
<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 backend does not yet support <a href="http://llvm.org/PR879">inline
assembly that uses the X86 floating point stack</a>.</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="ppc-be">Known problems with the PowerPC back-end</a>
</div>
<div class="doc_text">
<ul>
<li><a href="http://llvm.org/PR642">PowerPC backend does not correctly
implement ordered FP comparisons</a>.</li>
<li>The Linux PPC32/ABI support needs testing for the interpreter and static
compilation, and lacks Dwarf debugging informations.
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="arm-be">Known problems with the ARM back-end</a>
</div>
<div class="doc_text">
<ul>
<li>The Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
processors, any thumb program compiled with LLVM crashes or produces wrong
results. (<a href="http://llvm.org/PR1388">PR1388</a>)</li>
<li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
</li>
<li>QEMU-ARM (<= 0.9.0) wrongly executes programs compiled with LLVM. A non-affected QEMU version must be used or this
<a href="http://cvs.savannah.nongnu.org/viewcvs/qemu/target-arm/translate.c?root=qemu&r1=1.46&r2=1.47&makepatch=1&diff_format=h">
patch</a> must be applied on QEMU.</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 backend only supports the 32-bit SPARC ABI (-m32), it does not
support the 64-bit SPARC ABI (-m64).</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="alpha-be">Known problems with the Alpha back-end</a>
</div>
<div class="doc_text">
<ul>
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<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
appropriate nops inserted to ensure restartability.</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="ia64-be">Known problems with the IA64 back-end</a>
</div>
<div class="doc_text">
<ul>
<li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> 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.)</li>
<li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
ABI compliant layout of v-tables</a>. 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.</li>
<li>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.</li>
<li>Defining vararg functions is not supported (but calling them is ok).</li>
<li>The Itanium backend has bitrotted somewhat.</li>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="c-be">Known problems with the C back-end</a>
</div>
<div class="doc_text">
<ul>
<li><a href="http://llvm.org/PR802">The C backend does not support inline
assembly code</a>.</li>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="c-fe">Known problems with the C front-end</a>
</div>
<!-- _______________________________________________________________________ -->
<p>llvm-gcc4 does not currently support <a href="http://llvm.org/PR869">Link-Time
Optimization</a> on most platforms "out-of-the-box". Please inquire on the
llvmdev mailing list if you are interested.</p>
<p>FIXME: the list of supported stuff below needs to be updated. We do support
tls now, what else??</p>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
Notes
</div>
<div class="doc_text">
<ul>
<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>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/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/Thread_002dLocal.html">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>
<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
<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
<b>Supported:</b> <tt>alias</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
<tt>deprecated</tt>, <tt>fastcall</tt>, <tt>format</tt>,
<tt>format_arg</tt>, <tt>non_null</tt>, <tt>noreturn</tt>, <tt>regparm</tt>
<tt>section</tt>, <tt>stdcall</tt>, <tt>unused</tt>, <tt>used</tt>,
<tt>visibility</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
<b>Ignored:</b> <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> 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>alias</tt>, <tt>cleanup</tt>, <tt>common</tt>,
<tt>nocommon</tt>, <tt>deprecated</tt>, <tt>dllimport</tt>,
<tt>dllexport</tt>, <tt>section</tt>, <tt>transparent_union</tt>,
<tt>unused</tt>, <tt>used</tt>, <tt>weak</tt><br>
<b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
<tt>shared</tt>, <tt>tls_model</tt>,
<tt>vector_size</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>
(currently ignored). We also support builtins for ISO C99 floating
point comparison macros (e.g., <tt>__builtin_islessequal</tt>),
<tt>__builtin_prefetch</tt>, <tt>__builtin_popcount[ll]</tt>,
<tt>__builtin_clz[ll]</tt>, and <tt>__builtin_ctz[ll]</tt>.</li>
<p>The following extensions <b>are</b> known to be supported:</p>
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<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/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-3.4.0/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/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/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/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_002b_002b-Comments.html#C_002b_002b-Comments">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 <ESC>.</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/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/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>The C++ front-end is considered to be fully
tested and works for a number of non-trivial programs, including LLVM
<li>llvm-gcc4 only has partial support for <a href="http://llvm.org/PR870">C++
Exception Handling</a>, and it is not enabled by default.</li>
<!-- NO EH Support!
<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
<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-gcc3 is very
different from the model used in the Itanium ABI, so <b>exceptions will not
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="additionalinfo">Additional Information</a>
</div>
<!-- *********************************************************************** -->
<p>A wide variety of additional information is available on the <a
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href="http://llvm.org">LLVM web page</a>, including <a
href="http://llvm.org/docs/">documentation</a> and <a
href="http://llvm.org/pubs/">publications describing algorithms and
components implemented in LLVM</a>. 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
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us via the <a href="http://llvm.org/docs/#maillist"> mailing
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