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| <title>LLVM 2.2 Release Notes</title> | |
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| <body> | |
| <div class="doc_title">LLVM 2.2 Release Notes</div> | |
| <ol> | |
| <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> | |
| </ol> | |
| <div class="doc_author"> | |
| <p>Written by the <a href="http://llvm.org">LLVM Team</a><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 2.2. Here we describe the status of LLVM, including | |
| major improvements from the previous release and any known problems. All LLVM | |
| releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM | |
| releases web site</a>.</p> | |
| <p>For more information about LLVM, including information about the latest | |
| 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 | |
| list</a> is a good place to send them.</p> | |
| <p>Note that if you are reading this file from a Subversion checkout 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 a specific releases, please see the | |
| <a href="http://llvm.org/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 thirteenth public release of the LLVM Compiler Infrastructure. | |
| It includes many features and refinements from LLVM 2.1.</p> | |
| </div> | |
| <!-- Unfinished features in 2.2: | |
| Index Set Splitting not enabled by default | |
| Machine LICM | |
| Machine Sinking | |
| LegalizeDAGTypes | |
| --> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="deprecation">Deprecated features in LLVM 2.2</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>This is the last LLVM release to support llvm-gcc 4.0, llvm-upgrade, and | |
| llvmc in its current form. llvm-gcc 4.0 has been replaced with llvm-gcc 4.2. | |
| llvm-upgrade is useful for upgrading llvm 1.9 files to llvm 2.x syntax, but you | |
| can always use an old release to do this. llvmc is currently mostly useless in | |
| llvm 2.2, and will be redesigned or removed in llvm 2.3.</p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="frontends">llvm-gcc 4.0, llvm-gcc 4.2, and clang</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>LLVM 2.2 fully supports both the llvm-gcc 4.0 and llvm-gcc 4.2 front-ends (in | |
| LLVM 2.1, llvm-gcc 4.2 was beta). Since LLVM 2.1, the llvm-gcc 4.2 front-end | |
| has made leaps and bounds and is now at least as good as 4.0 in virtually every | |
| area, and is better in several areas (for example, exception handling | |
| correctness, support for Ada and Fortran, better ABI compatibility, etc). We | |
| strongly recommend that you | |
| migrate from llvm-gcc 4.0 to llvm-gcc 4.2 in this release cycle because | |
| <b>LLVM 2.2 is the last release that will support llvm-gcc 4.0</b>: LLVM 2.3 | |
| will only support the llvm-gcc 4.2 front-end.</p> | |
| <p>The <a href="http://clang.llvm.org/">clang project</a> is an effort to build | |
| a set of new 'llvm native' front-end technologies for the LLVM optimizer | |
| and code generator. Currently, its C and Objective-C support is maturing | |
| nicely, and it has advanced source-to-source analysis and transformation | |
| capabilities. If you are interested in building source-level tools for C and | |
| Objective-C (and eventually C++), you should take a look. However, note that | |
| clang is not an official part of the LLVM 2.2 release. If you are interested in | |
| this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="majorfeatures">Major New Features</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>LLVM 2.2 includes several major new capabilities:</p> | |
| <ul> | |
| <li>A research team led by Scott Michel in the Computer Systems Research | |
| Department at The Aerospace Corporation contributed the CellSPU backend, which | |
| generates code for the vector coprocessors on the Sony/Toshiba/IBM Cell BE | |
| processor. llvm-gcc 4.2 supports CellSPU as a 'configure' target and progress | |
| is being made so that libgcc.a compiles cleanly. Notable pieces still in | |
| development include full 64-bit integer and full double precision floating | |
| point support.</li> | |
| <li>Anton and Duncan significantly improved llvm-gcc 4.2 support for the GCC Ada | |
| (GNAT) and Fortran (gfortran) front-ends. These front-ends should still be considered | |
| experimental however: see the <a href="#knownproblems">list of known problems</a>. | |
| The release binaries do not contain either front-end: they need to be built from | |
| source (the Ada front-end only builds on x86-32 linux).</li> | |
| <li>Dale contributed full support for long double on x86/x86-64 (where it is 80 | |
| bits) and on Darwin PPC/PPC64 (where it is 128 bits). In previous LLVM | |
| releases, llvm-gcc silently mapped long double to double.</li> | |
| <li>Gordon Henriksen rewrote most of the <a href="GarbageCollection.html" | |
| >Accurate Garbage Collection</a> code in the code generator, making the | |
| generated code more efficient and adding support for the OCaml garbage collector | |
| metadata format.</li> | |
| <li>Christopher Lamb contributed support for multiple address spaces in LLVM | |
| IR. This is useful for supporting targets that have 'near' vs 'far' pointers, | |
| 'RAM' vs 'ROM' pointers, or that have non-local memory that can be accessed with | |
| special instructions.</li> | |
| <li>LLVM now includes a new set of detailed <a | |
| href="tutorial/index.html">tutorials</a>, which explain how to implement a | |
| language with LLVM and shows how to use several important APIs.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="coreimprovements">LLVM Core Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>New features include: | |
| </p> | |
| <ul> | |
| <li>Gordon contributed support for C and OCaml Bindings for the basic LLVM IR | |
| construction routines as well as several other auxiliary APIs.</li> | |
| <li>Anton added readnone/readonly attributes for modeling function side effects. | |
| Duncan hooked up GCC's pure/const attributes to them and enhanced mod/ref | |
| analysis to use them.</li> | |
| <li>Devang added LLVMFoldingBuilder, a version of LLVMBuilder that implicitly | |
| simplifies the code as it is constructed.</li> | |
| <li>Ted Kremenek added a framework for generic object serialization to bitcode | |
| files. This support is only used by clang right now for ASTs but is extensible | |
| and could be used for serializing arbitrary other data into bitcode files.</li> | |
| <li>Duncan improved TargetData to distinguish between the size/alignment of a | |
| type in a register, in memory according to the platform ABI, and in memory when | |
| we have a choice.</li> | |
| <li>Reid moved parameter attributes off of FunctionType and onto functions | |
| and calls. This makes it much easier to add attributes to a function in a | |
| transformation pass.</li> | |
| <li>Dan Gohman added support for vector sin, cos, and pow intrinsics.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="codegen">Code Generator Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>We put a significant amount of work into the code generator infrastructure, | |
| which allows us to implement more aggressive algorithms and make it run | |
| faster:</p> | |
| <ul> | |
| <li>Owen refactored the existing LLVM dominator and loop information code to | |
| allow it work on the machine code representation. He contributed support for | |
| dominator and loop information on machine code and merged the code for forward | |
| and backward dominator computation.</li> | |
| <li>Dan added support for emitting debug information with .file and .loc | |
| directives on platforms that support it, instead of emitting large tables in the .s | |
| file.</li> | |
| <li>Evan extended the DAG scheduler to model physical register dependencies | |
| explicitly and have the BURR scheduler pick a correct schedule based on the | |
| dependencies. This reduces our use of the 'flag' operand hack.</li> | |
| <li>Evan added initial support for register coalescing of subregister | |
| references.</li> | |
| <li>Rafael Espindola implemented initial support for a new 'byval' attribute, | |
| which allows more efficient by-value argument passing in the LLVM IR. Evan | |
| finished support for it and enabled it in the X86 (32- and 64-bit) and C | |
| backends.</li> | |
| <li>The LLVM TargetInstrInfo class can now answer queries about the mod/ref and | |
| side-effect behavior of MachineInstr's. This information is inferred | |
| automatically by TableGen from .td files for all instructions with | |
| patterns.</li> | |
| <li>Evan implemented simple live interval splitting on basic block boundaries. | |
| This allows the register allocator to be more successful at keeping values in | |
| registers in some parts of a value's live range, even if they need to be spilled | |
| in some other block.</li> | |
| <li>The new MachineRegisterInfo.h class provides support for efficiently | |
| iterating over all defs/uses of a register, and this information is | |
| automatically kept up-to-date. This support is similar to the use_iterator in | |
| the LLVM IR level.</li> | |
| <li>The MachineInstr, MachineOperand and TargetInstrDesc classes are simpler, | |
| more consistent, and better documented.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="optimizer">Optimizer Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>In addition to a huge array of bug fixes and minor performance tweaks, the | |
| LLVM 2.2 optimizers support a few major enhancements:</p> | |
| <ul> | |
| <li>Daniel Berlin and Curtis Dunham rewrote Andersen's alias analysis to be | |
| several orders of magnitude faster, and implemented Offline Variable | |
| Substitution and Lazy Cycle Detection. Note that Andersen's is not enabled in | |
| llvm-gcc by default, but can be accessed through 'opt'.</li> | |
| <li>Dan Gohman contributed several enhancements to Loop Strength Reduction (LSR) | |
| to make it more aggressive with SSE intrinsics and when induction variables are | |
| used by non-memory instructions.</li> | |
| <li>Evan added support for simple exit value substitution to LSR.</li> | |
| <li>Evan enhanced LSR to support induction variable reuse when the induction | |
| variables have different widths.</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="targetspecific">Target Specific Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>New target-specific features include: | |
| </p> | |
| <ul> | |
| <li>Evan contributed support to the X86 backend to model the mod/ref behavior | |
| of the EFLAGS register explicitly in all instructions. This gives more freedom | |
| to the scheduler, and is a more explicit way to model the instructions.</li> | |
| <li>Dale contributed support for exception handling on Darwin/PPC and he and | |
| Anton got x86-64 working.</li> | |
| <li>Evan turned on if-conversion by default for ARM, allowing LLVM to take | |
| advantage of its predication features.</li> | |
| <li>Bruno added PIC support to the MIPS backend, fixed many bugs and improved | |
| support for architecture variants.</li> | |
| <li>Arnold Schwaighofer added initial support for X86 tail calls.</li> | |
| <li>Evan contributed several enhancements to Darwin/x86 debug information.</li> | |
| <li>Duncan added x86-64 support for trampolines (pointers to nested functions).</li> | |
| </ul> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="otherimprovements">Other Improvements</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>New features include: | |
| </p> | |
| <ul> | |
| <li>Gordon expanded and updated the <a href="Passes.html">LLVM Analysis and | |
| Transformation Passes</a> reference to include descriptions for each pass.</li> | |
| <li>We rewrote the lexer and parser used by TableGen to make them simpler | |
| and cleaner. This gives tblgen support for 'caret diagnostics'. The .ll file | |
| lexer was also rewritten to support caret diagnostics but doesn't use this | |
| support yet.</li> | |
| <li>Dale has been grinding through the GCC testsuite, and marked many | |
| LLVM-incompatible tests as not-to-be-run (for example, if they are grepping | |
| through some GCC dump file that LLVM doesn't produce), he also found and fixed | |
| many LLVM bugs exposed by the testsuite.</li> | |
| </ul> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="portability">Portability and Supported Platforms</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>LLVM is known to work on the following platforms:</p> | |
| <ul> | |
| <li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD | |
| (and probably other unix-like systems).</li> | |
| <li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit and | |
| 64-bit modes.</li> | |
| <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</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>Sun UltraSPARC workstations running Solaris 8.</li> | |
| <li>Alpha-based machines running Debian GNU/Linux.</li> | |
| <li>Itanium-based machines running Linux and HP-UX.</li> | |
| </ul> | |
| <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> | |
| <!-- *********************************************************************** --> | |
| <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.org/bugs/">LLVM bug database</a> and submit a bug if | |
| there isn't already one.</p> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="experimental">Experimental features included with this release</a> | |
| </div> | |
| <div class="doc_text"> | |
| <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> | |
| <ul> | |
| <li>The <tt>-cee</tt> pass is known to be buggy and will be removed in | |
| LLVM 2.3.</li> | |
| <li>The MSIL, IA64, Alpha, and MIPS backends are experimental.</li> | |
| <li>The LLC "<tt>-filetype=asm</tt>" (the default) is the only supported | |
| value for this option.</li> | |
| <li>The llvmc tool is not supported.</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 backend does not yet support <a href="http://llvm.org/PR879">inline | |
| assembly that uses the X86 floating point stack</a>.</li> | |
| <li>The X86 backend occasionally has <a href="http://llvm.org/PR1649">alignment | |
| problems</a> on operating systems that don't require 16-byte stack alignment | |
| (including most non-darwin OS's like linux).</li> | |
| <li>The X86 backend generates inefficient floating point code when configured to | |
| generate code for systems that don't have SSE2.</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>The Linux PPC32/ABI support needs testing for the interpreter and static | |
| compilation, and lacks support for debug information.</li> | |
| </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>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 | |
| processors, thumb programs can crash or produce 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>There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly execute | |
| programs compiled with LLVM. Please use more recent versions of QEMU.</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> | |
| <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> | |
| </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><a href="http://llvm.org/PR802">The C backend does not support inline | |
| assembly code</a>.</li> | |
| <li><a href="http://llvm.org/PR1126">The C backend does not support vectors | |
| yet</a>.</li> | |
| <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common | |
| C++ programs</a>, preventing intermixing between C++ compiled by the CBE and | |
| C++ code compiled with LLC or native compilers.</li> | |
| <li>The C backend does not support all exception handling constructs.</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"> | |
| <p>llvm-gcc 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> | |
| </div> | |
| <!-- _______________________________________________________________________ --> | |
| <div class="doc_subsubsection"> | |
| Notes | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet. | |
| See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p> | |
| </li> | |
| <li><p>llvm-gcc <b>partially</b> supports these GCC extensions:</p> | |
| <ol> | |
| <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. | |
| Nested functions are supported, but llvm-gcc does not support | |
| taking the address of a nested function (except on X86 targets) | |
| or non-local gotos.</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>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</tt>, | |
| <tt>const</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>noinline</tt>, | |
| <tt>noreturn</tt>, <tt>nothrow</tt>, <tt>pure</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>malloc</tt>, | |
| <tt>no_instrument_function</tt></li> | |
| </ol> | |
| </li> | |
| <li><p>llvm-gcc supports the vast majority of GCC extensions, including:</p> | |
| <ol> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li> | |
| <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/Other-Builtins.html#Other%20Builtins">Other Builtins</a>: | |
| Other built-in functions.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>: | |
| Specifying attributes of variables.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.</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/Variable-Length.html#Variable%20Length">Variable Length</a>: | |
| Arrays whose length is computed at run time.</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/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 | |
| itself, Qt, Mozilla, etc.</p> | |
| <ul> | |
| <li>Exception handling only works well on the X86 and PowerPC targets. | |
| It works well for x86-64 darwin but not x86-64 linux.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="ada-fe">Known problems with the Ada front-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature | |
| technology and problems should be expected. | |
| <ul> | |
| <li>The Ada front-end currently only builds on x86-32. This is mainly due | |
| to lack of trampoline support (pointers to nested functions) on other platforms, | |
| however it <a href="http://llvm.org/PR2006">also fails to build on x86-64</a> | |
| which does support trampolines.</li> | |
| <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>. | |
| Workaround: configure with --disable-bootstrap.</li> | |
| <li>The c380004 and <a href="http://llvm.org/PR2010">c393010</a> ACATS tests | |
| fail (c380004 also fails with gcc-4.2 mainline).</li> | |
| <li>Many gcc specific Ada tests continue to crash the compiler.</li> | |
| <li>The -E binder option (exception backtraces) | |
| <a href="http://llvm.org/PR1982">does not work</a> and will result in programs | |
| crashing if an exception is raised. Workaround: do not use -E.</li> | |
| <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start | |
| or finish at a non-byte offset</a> in a record. Workaround: do not pack records | |
| or use representation clauses that result in a field of a non-discrete type | |
| starting or finishing in the middle of a byte.</li> | |
| <li>The lli interpreter <a href="http://llvm.org/PR2009">considers 'main' | |
| as generated by the Ada binder to be invalid</a>. | |
| Workaround: hand edit the file to use pointers for argv and envp rather than | |
| integers.</li> | |
| <li>The -fstack-check option <a href="http://llvm.org/PR2008">is ignored</a>.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="fortran-fe">Known problems with the Fortran front-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>The llvm-gcc 4.2 gfortran front-end supports a broad range of Fortran code, but does | |
| <a href="http://llvm.org/PR1971">not support EQUIVALENCE yet</a>.</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 <a | |
| href="http://llvm.org">LLVM web page</a>, in particular in the <a | |
| href="http://llvm.org/docs/">documentation</a> section. The web page also | |
| contains versions of the API documentation which is up-to-date with the | |
| Subversion 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://llvm.org/docs/#maillist"> mailing | |
| lists</a>.</p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
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