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Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]7 <title>LLVM 2.1 Release Notes</title>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]8</head>
9<body>
10
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]11<div class="doc_title">LLVM 2.1 Release Notes</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]12
13<ol>
14 <li><a href="#intro">Introduction</a></li>
15 <li><a href="#whatsnew">What's New?</a></li>
16 <li><a href="GettingStarted.html">Installation Instructions</a></li>
17 <li><a href="#portability">Portability and Supported Platforms</a></li>
18 <li><a href="#knownproblems">Known Problems</a>
19 <li><a href="#additionalinfo">Additional Information</a></li>
20</ol>
21
22<div class="doc_author">
23 <p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
24</div>
25
26<!-- *********************************************************************** -->
27<div class="doc_section">
28 <a name="intro">Introduction</a>
29</div>
30<!-- *********************************************************************** -->
31
32<div class="doc_text">
33
34<p>This document contains the release notes for the LLVM compiler
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]35infrastructure, release 2.1. Here we describe the status of LLVM, including
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]36major improvements from the previous release and any known problems. All LLVM
37releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
38releases web site</a>.</p>
39
40<p>For more information about LLVM, including information about the latest
41release, please check out the <a href="http://llvm.org/">main LLVM
42web site</a>. If you have questions or comments, the <a
43href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
44list</a> is a good place to send them.</p>
45
46<p>Note that if you are reading this file from a Subversion checkout or the
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]47main LLVM web page, this document applies to the <i>next</i> release, not the
48current one. To see the release notes for a specific releases, please see the
49<a href="http://llvm.org/releases/">releases page</a>.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]50
51</div>
52
53<!-- *********************************************************************** -->
54<div class="doc_section">
55 <a name="whatsnew">What's New?</a>
56</div>
57<!-- *********************************************************************** -->
58
59<div class="doc_text">
60
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]61<p>This is the twelfth public release of the LLVM Compiler Infrastructure.
62It includes many features and refinements from LLVM 2.0.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]63
64</div>
65
66<!--=========================================================================-->
67<div class="doc_subsection">
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]68<a name="frontends">New Frontends</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]69</div>
70
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]71<div class="doc_text">
72
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]73<p>LLVM 2.1 brings two new beta C front-ends. First, Duncan, Anton and Devang
Devang Patel2966bf32007-09-21 18:02:24 +0000[diff] [blame]74has started syncing up llvm-gcc with GCC 4.2, yielding "llvm-gcc 4.2" (creative,
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]75huh?). llvm-gcc 4.2 has the promise to bring much better FORTRAN and Ada
76support to LLVM as well as features like atomic builtins, OpenMP, and many other
77things. Check it out!</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]78
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]79<p>Second, LLVM now includes its own native C and Objective-C front-end (C++ is
80in progress, but is not very far along) code named "<a
81href="http://clang.llvm.org/">clang</a>". This front-end has a number of great
82features, primarily aimed at source-level analysis and speeding up compile-time.
83At this point though, the LLVM Code Generator component is still very early in
84development, so it's mostly useful for people looking to build source-level
85analysis tools or source-to-source translators.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]86
87</div>
88
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]89<!--=========================================================================-->
90<div class="doc_subsection">
91<a name="optimizer">Optimizer Improvements</a>
92</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]93
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]94<div class="doc_text">
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]95
96<p>Some of the most noticable improvements this release have been in the
97optimizer, speeding it up and making it more aggressive</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]98
99<ul>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]100
Owen Anderson5b332932007-09-25 02:10:58 +0000[diff] [blame]101<li>Owen Anderson wrote the new MemoryDependenceAnalysis pass, which provides
102 a lazy, caching layer on top of alias analysis. He then used it to rewrite
103 DeadStoreElimination which resulted in significantly better compile time in
104 common cases, </li>
105<li>Owen implemented the new GVN pass, which is also based on
106 MemoryDependenceAnalysis. This pass replaces GCSE/LoadVN in the standard
107 set of passes, providing more aggressive optimization at a some-what
108 improved compile-time cost.</li>
109<li>Owen implemented GVN-PRE, a partial redundancy elimination algorithm that
110 shares some details with the new GVN pass. It is still in need of compile
111 time tuning, and is not turned on by default.</li>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]112<li>Devang merged ETForest and DomTree into a single easier to use data
113structure.</li>
114<li>Nick Lewycky improved loop trip count analysis to handle many more common
115cases.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]116
117</ul>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]118
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]119</div>
120
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]121<!--=========================================================================-->
122<div class="doc_subsection">
123<a name="codegen">Code Generator Improvements</a>
124</div>
125
126<div class="doc_text">
127
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]128<ul>
129
130<li>Dale finished up the Tail Merging optimization in the code generator,
131enabling it by default. This produces smaller code that is also faster in some
132cases.</li>
133
134<li>Dan Gohman changed the way we represent vectors before legalization,
135significantly simplifying the SelectionDAG representation for these and making
136the code generator faster for vector code.</li>
137
Chris Lattner76dec102007-09-21 17:43:52 +0000[diff] [blame]138<li>Evan remat rewrite (coalesced intervals + folding of remat'd loads) and
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]139live intervals improvements.</li>
140
141<li>Dan Gohman contributed support for better alignment and volatility handling
142in the code generator, and significantly enhanced alignment analysis for SSE
143load/store instructions.</li>
144
145<li>Christopher Lamb virtual register sub-register support, better truncates and
146extends on X86.</li>
147
148<li>Duraid Madina contributed a new "bigblock" register allocator, and Roman
149Levenstein contributed several big improvements. BigBlock is optimized for code
150that uses very large basic blocks. It is slightly slower than the "local"
151allocator, but produces much better code.</li>
152
Chris Lattner76dec102007-09-21 17:43:52 +0000[diff] [blame]153<li>David Greene refactored the register allocator to split coalescing out from
154allocation, making coalescers pluggable.</li>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]155
156</ul>
157
158</div>
159
160
161<!--=========================================================================-->
162<div class="doc_subsection">
163<a name="targetspecific">Target Specific Improvements</a>
164</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]165
166<div class="doc_text">
167<p>New features include:
168</p>
169
170<ul>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]171<li>Bruno Cardoso Lopes contributed initial MIPS support.</li>
172<li>Bill Wendling added SSSE3 support.</li>
173<li>New Target independent if converter, ARM uses it so far</li>
174<li>Nicholas Geoffray contributed improved linux/ppc ABI and JIT support.</li>
175<li>Dale Johannesen rewrote handling of 32-bit float values in the X86 backend
176when using the floating point stack, fixing several nasty bugs.</li>
177<li>Dan contributed rematerialization support for the X86 backend.</li>
178</ul>
179
180</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]181
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]182
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]183<!--=========================================================================-->
184<div class="doc_subsection">
185<a name="llvmgccimprovements">llvm-gcc Improvements</a>
186</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]187
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]188<div class="doc_text">
189<p>New features include:
190</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]191
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]192<ul>
193<li>Duncan and Anton exception handling in llvm-gcc 4.0/4.2</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]194
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]195<li>Devang and Duncan: Bitfields, pragma pack</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]196
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]197<li>Tanya implemented support for __attribute__((noinline)) in llvm-gcc, and
198added support for generic variable annotations which are propagated into the
199LLVM IR, e.g. "<tt>int X __attribute__((annotate("myproperty")));</tt>".</li>
200
201<li>Sheng Zhou and Christopher Lamb implemented alias analysis support for
202'restrict' arguments to functions.</li>
203
204<li>Duncan contributed support for trampolines (pointers to nested functions),
205currently only supported on x86 target.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]206
Devang Patel2966bf32007-09-21 18:02:24 +0000[diff] [blame]207<li> Lauro Ramos Venancio contributed support to encode alignment info in
208load and store instructions.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]209</ul>
210
211</div>
212
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]213
214<!--=========================================================================-->
215<div class="doc_subsection">
216<a name="coreimprovements">LLVM Core Improvements</a>
217</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]218
219<div class="doc_text">
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]220<p>New features include:
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]221</p>
222
223<ul>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]224<li>Neil Booth APFloat, foundation for long double support that will be wrapped
225up in 2.2. Dale contributed most of long double support, will be enabled in
2262.2.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]227
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]228<li>LLVM now provides an LLVMBuilder class which makes it significantly easier
229to create LLVM IR instructions.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]230
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]231<li>Reid contributed support for intrinsics that take arbitrary integer typed
232arguments, Dan Gohman and Chandler extended it to support FP and vectors.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]233</ul>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]234
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]235</div>
236
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]237<!--=========================================================================-->
238<div class="doc_subsection">
239<a name="otherimprovements">Other Improvements</a>
240</div>
241
242<div class="doc_text">
243<p>New features include:
244</p>
245
246<ul>
247<li>BrainF frontend by Sterling Stein.</li>
248
249<li>David Green contributed a new --enable-expensive-checks configure option
250which enables STL checking, and fixed several bugs exposed by it.</li>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]251</ul>
252
253</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]254
255<!-- *********************************************************************** -->
256<div class="doc_section">
257 <a name="portability">Portability and Supported Platforms</a>
258</div>
259<!-- *********************************************************************** -->
260
261<div class="doc_text">
262
263<p>LLVM is known to work on the following platforms:</p>
264
265<ul>
266<li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD
267 (and probably other unix-like systems).</li>
268<li>PowerPC and X86-based Mac OS X systems, running 10.2 and above in 32-bit and
269 64-bit modes.</li>
270<li>Intel and AMD machines running on Win32 using MinGW libraries (native)</li>
271<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
272 support is available for native builds with Visual C++).</li>
273<li>Sun UltraSPARC workstations running Solaris 8.</li>
274<li>Alpha-based machines running Debian GNU/Linux.</li>
275<li>Itanium-based machines running Linux and HP-UX.</li>
276</ul>
277
278<p>The core LLVM infrastructure uses
279<a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
280to the machine and operating system on which it is built. However, minor
281porting may be required to get LLVM to work on new platforms. We welcome your
282portability patches and reports of successful builds or error messages.</p>
283
284</div>
285
286<!-- *********************************************************************** -->
287<div class="doc_section">
288 <a name="knownproblems">Known Problems</a>
289</div>
290<!-- *********************************************************************** -->
291
292<div class="doc_text">
293
294<p>This section contains all known problems with the LLVM system, listed by
295component. As new problems are discovered, they will be added to these
296sections. If you run into a problem, please check the <a
297href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
298there isn't already one.</p>
299
300</div>
301
302<!-- ======================================================================= -->
303<div class="doc_subsection">
304 <a name="experimental">Experimental features included with this release</a>
305</div>
306
307<div class="doc_text">
308
309<p>The following components of this LLVM release are either untested, known to
310be broken or unreliable, or are in early development. These components should
311not be relied on, and bugs should not be filed against them, but they may be
312useful to some people. In particular, if you would like to work on one of these
313components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
314
315<ul>
Bill Wendlingc3aa3502007-09-25 20:45:10 +0000[diff] [blame^]316<li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in a
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]317 future release.</li>
318<li>C++ EH support is disabled for this release.</li>
319<li>The MSIL backend is experimental.</li>
320<li>The IA64 code generator is experimental.</li>
321<li>The Alpha JIT is experimental.</li>
322<li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
323 <tt>-filetype</tt> llc option.</li>
324</ul>
325
326</div>
327
328<!-- ======================================================================= -->
329<div class="doc_subsection">
330 <a name="x86-be">Known problems with the X86 back-end</a>
331</div>
332
333<div class="doc_text">
334
335<ul>
336<li>The X86 backend does not yet support <a href="http://llvm.org/PR879">inline
337 assembly that uses the X86 floating point stack</a>.</li>
338</ul>
339
340</div>
341
342<!-- ======================================================================= -->
343<div class="doc_subsection">
344 <a name="ppc-be">Known problems with the PowerPC back-end</a>
345</div>
346
347<div class="doc_text">
348
349<ul>
350<li><a href="http://llvm.org/PR642">PowerPC backend does not correctly
351implement ordered FP comparisons</a>.</li>
352<li>The Linux PPC32/ABI support needs testing for the interpreter and static
353compilation, and lacks support for debug information.</li>
354</ul>
355
356</div>
357
358<!-- ======================================================================= -->
359<div class="doc_subsection">
360 <a name="arm-be">Known problems with the ARM back-end</a>
361</div>
362
363<div class="doc_text">
364
365<ul>
366<li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
367processors, thumb program can crash or produces wrong
368results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
369<li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
370</li>
371<li>There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly execute
372programs compiled with LLVM. Please use more recent versions of QEMU.</li>
373</ul>
374
375</div>
376
377<!-- ======================================================================= -->
378<div class="doc_subsection">
379 <a name="sparc-be">Known problems with the SPARC back-end</a>
380</div>
381
382<div class="doc_text">
383
384<ul>
385<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
386 support the 64-bit SPARC ABI (-m64).</li>
387</ul>
388
389</div>
390
391<!-- ======================================================================= -->
392<div class="doc_subsection">
393 <a name="alpha-be">Known problems with the Alpha back-end</a>
394</div>
395
396<div class="doc_text">
397
398<ul>
399
400<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
401appropriate nops inserted to ensure restartability.</li>
402
403</ul>
404</div>
405
406<!-- ======================================================================= -->
407<div class="doc_subsection">
408 <a name="ia64-be">Known problems with the IA64 back-end</a>
409</div>
410
411<div class="doc_text">
412
413<ul>
414
415<li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
416made where the argument is not 16-byte aligned, as required on IA64. (Strictly
417speaking this is not a bug in the IA64 back-end; it will also be encountered
418when building C++ programs using the C back-end.)</li>
419
420<li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
421ABI compliant layout of v-tables</a>. In particular, it just stores function
422pointers instead of function descriptors in the vtable. This bug prevents
423mixing C++ code compiled with LLVM with C++ objects compiled by other C++
424compilers.</li>
425
426<li>There are a few ABI violations which will lead to problems when mixing LLVM
427output with code built with other compilers, particularly for floating-point
428programs.</li>
429
430<li>Defining vararg functions is not supported (but calling them is ok).</li>
431
432<li>The Itanium backend has bitrotted somewhat.</li>
433</ul>
434
435</div>
436
437<!-- ======================================================================= -->
438<div class="doc_subsection">
439 <a name="c-be">Known problems with the C back-end</a>
440</div>
441
442<div class="doc_text">
443
444<ul>
445<li><a href="http://llvm.org/PR802">The C backend does not support inline
446 assembly code</a>.</li>
447</ul>
448
449</div>
450
451
452<!-- ======================================================================= -->
453<div class="doc_subsection">
454 <a name="c-fe">Known problems with the C front-end</a>
455</div>
456
457<!-- _______________________________________________________________________ -->
458<div class="doc_subsubsection">Bugs</div>
459
460<div class="doc_text">
461
462<p>llvm-gcc4 does not currently support <a href="http://llvm.org/PR869">Link-Time
463Optimization</a> on most platforms "out-of-the-box". Please inquire on the
464llvmdev mailing list if you are interested.</p>
465
466</div>
467
468<!-- _______________________________________________________________________ -->
469<div class="doc_subsubsection">
470 Notes
471</div>
472
473<div class="doc_text">
474<ul>
475
476<li><p>"long double" is silently transformed by the front-end into "double". There
477is no support for floating point data types of any size other than 32 and 64
478bits.</p></li>
479
480<li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet.
481 See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p>
482</li>
483
484<li><p>llvm-gcc <b>partially</b> supports these GCC extensions:</p>
485 <ol>
486 <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.<br>
487 Nested functions are supported, but llvm-gcc does not support non-local
488 gotos or taking the address of a nested function.</li>
489
490 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
491
492 Declaring that functions have no side effects or that they can never
493 return.<br>
494
495 <b>Supported:</b> <tt>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</tt>,
496 <tt>constructor</tt>, <tt>destructor</tt>,
497 <tt>deprecated</tt>, <tt>fastcall</tt>, <tt>format</tt>,
498 <tt>format_arg</tt>, <tt>non_null</tt>, <tt>noreturn</tt>, <tt>regparm</tt>
499 <tt>section</tt>, <tt>stdcall</tt>, <tt>unused</tt>, <tt>used</tt>,
500 <tt>visibility</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
501
502 <b>Ignored:</b> <tt>noinline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
503 <tt>malloc</tt>, <tt>no_instrument_function</tt></li>
504 </ol>
505</li>
506
507<li><p>llvm-gcc supports the vast majority of GCC extensions, including:</p>
508
509 <ol>
510 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
511 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
512 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
513 Other built-in functions.</li>
514 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
515 Specifying attributes of variables.</li>
516 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.</li>
517 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
518 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
519 Arrays whose length is computed at run time.</li>
520 <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>
521 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
522 <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>
523 <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>
524 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
525 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
526 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
527 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
528 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
529 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
530 <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>
531 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
532 <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>
533 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
534 <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>
535 <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>
536 <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>
537 <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>
538 <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>
539 <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>
540 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
541 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
542or arrays as values.</li>
543 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
544 <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>
545 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
546 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
547 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
548 <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>
549 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
550 <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>
551 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
552 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
553 <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>
554 <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>
555 <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>
556 <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>
557 <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>
558 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
559 </ol></li>
560
561</ul>
562
563<p>If you run into GCC extensions which have not been included in any of these
564lists, please let us know (also including whether or not they work).</p>
565
566</div>
567
568<!-- ======================================================================= -->
569<div class="doc_subsection">
570 <a name="c++-fe">Known problems with the C++ front-end</a>
571</div>
572
573<div class="doc_text">
574
575<p>The C++ front-end is considered to be fully
576tested and works for a number of non-trivial programs, including LLVM
577itself, Qt, Mozilla, etc.</p>
578
579<ul>
580<li>llvm-gcc4 only has partial support for <a href="http://llvm.org/PR870">C++
581Exception Handling</a>, and it is not enabled by default.</li>
582
583<!-- NO EH Support!
584
585<li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
586 performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
587 function and in the <tt>setjmp</tt> receiver function may not be run.
588 Objects in intervening stack frames will be destroyed, however (which is
589 better than most compilers).</li>
590
591<li>The LLVM C++ front-end follows the <a
592 href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
593 This document, which is not Itanium specific, specifies a standard for name
594 mangling, class layout, v-table layout, RTTI formats, and other C++
595 representation issues. Because we use this API, code generated by the LLVM
596 compilers should be binary compatible with machine code generated by other
597 Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
598 <i>However</i>, the exception handling mechanism used by llvm-gcc3 is very
599 different from the model used in the Itanium ABI, so <b>exceptions will not
600 interact correctly</b>. </li>
601-->
602</ul>
603
604</div>
605
606
607
608<!-- *********************************************************************** -->
609<div class="doc_section">
610 <a name="additionalinfo">Additional Information</a>
611</div>
612<!-- *********************************************************************** -->
613
614<div class="doc_text">
615
616<p>A wide variety of additional information is available on the <a
617href="http://llvm.org">LLVM web page</a>, in particular in the <a
618href="http://llvm.org/docs/">documentation</a> section. The web page also
619contains versions of the API documentation which is up-to-date with the
620Subversion version of the source code.
621You can access versions of these documents specific to this release by going
622into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
623
624<p>If you have any questions or comments about LLVM, please feel free to contact
625us via the <a href="http://llvm.org/docs/#maillist"> mailing
626lists</a>.</p>
627
628</div>
629
630<!-- *********************************************************************** -->
631
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