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  10
  11 <div class="doc_title">LLVM 2.2 Release Notes</div>
  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 <!-- *********************************************************************** -->
  28 <div class="doc_section">
  29   <a name="intro">Introduction</a>
  30 </div>
  31 <!-- *********************************************************************** -->
  32
  33 <div class="doc_text">
  34
  35 <p>This document contains the release notes for the LLVM compiler
  36 infrastructure, release 2.2.  Here we describe the status of LLVM, including
  37 major improvements from the previous release and any known problems.  All LLVM
  38 releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
  39 releases web site</a>.</p>
  40
  41 <p>For more information about LLVM, including information about the latest
  42 release, please check out the <a href="http://llvm.org/">main LLVM
  43 web site</a>.  If you have questions or comments, the <a
  44 href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
  45 list</a> is a good place to send them.</p>
  46
  47 <p>Note that if you are reading this file from a Subversion checkout or the
  48 main LLVM web page, this document applies to the <i>next</i> release, not the
  49 current one.  To see the release notes for a specific releases, please see the
  50 <a href="http://llvm.org/releases/">releases page</a>.</p>
  51
  52 </div>
  53
  54 <!-- *********************************************************************** -->
  55 <div class="doc_section">
  56   <a name="whatsnew">What's New?</a>
  57 </div>
  58 <!-- *********************************************************************** -->
  59
  60 <div class="doc_text">
  61
  62 <p>This is the thirteenth public release of the LLVM Compiler Infrastructure.
  63 It includes many features and refinements from LLVM 2.1.</p>
  64
  65 </div>
  66
  67 <!-- Unfinished features in 2.2:
  68   Index Set Splitting not enabled by default
  69   Machine LICM
  70   Machine Sinking
  71   LegalizeDAGTypes
  72  -->
  73
  74 <!--=========================================================================-->
  75 <div class="doc_subsection">
  76 <a name="deprecation">Deprecated features in LLVM 2.2</a>
  77 </div>
  78
  79 <div class="doc_text">
  80
  81 <p>This is the last LLVM release to support llvm-gcc 4.0, llvm-upgrade, and
  82 llvmc in its current form.  llvm-gcc 4.0 has been replaced with llvm-gcc 4.2.
  83 llvm-upgrade is useful for upgrading llvm 1.9 files to llvm 2.x syntax, but you
  84 can always use an old release to do this.  llvmc is currently mostly useless in
  85 llvm 2.2, and will be redesigned or removed in llvm 2.3.</p>
  86
  87 </div>
  88
  89 <!--=========================================================================-->
  90 <div class="doc_subsection">
  91 <a name="frontends">llvm-gcc 4.0, llvm-gcc 4.2, and clang</a>
  92 </div>
  93
  94 <div class="doc_text">
  95
  96 <p>LLVM 2.2 fully supports both the llvm-gcc 4.0 and llvm-gcc 4.2 front-ends (in
  97 LLVM 2.1, llvm-gcc 4.2 was beta).  Since LLVM 2.1, the llvm-gcc 4.2 front-end
  98 has made leaps and bounds and is now at least as good as 4.0 in virtually every
  99 area, and is better in several areas (for example, exception handling
 100 correctness, support for Ada and Fortran, better ABI compatibility, etc).  We
 101 strongly recommend that you
 102 migrate from llvm-gcc 4.0 to llvm-gcc 4.2 in this release cycle because
 103 <b>LLVM 2.2 is the last release that will support llvm-gcc 4.0</b>:  LLVM 2.3
 104 will only support the llvm-gcc 4.2 front-end.</p>
 105
 106 <p>The <a href="http://clang.llvm.org/">clang project</a> is an effort to build
 107 a set of new 'llvm native' front-end technologies for the LLVM optimizer
 108 and code generator.  Currently, its C and Objective-C support is maturing
 109 nicely, and it has advanced source-to-source analysis and transformation
 110 capabilities.  If you are interested in building source-level tools for C and
 111 Objective-C (and eventually C++), you should take a look.  However, note that
 112 clang is not an official part of the LLVM 2.2 release.  If you are interested in
 113 this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
 114
 115 </div>
 116
 117 <!--=========================================================================-->
 118 <div class="doc_subsection">
 119 <a name="majorfeatures">Major New Features</a>
 120 </div>
 121
 122 <div class="doc_text">
 123
 124 <p>LLVM 2.2 includes several major new capabilities:</p>
 125
 126 <ul>
 127 <li>A research team led by Scott Michel in the Computer Systems Research
 128 Department at The Aerospace Corporation contributed the CellSPU backend, which
 129 generates code for the vector coprocessors on the Sony/Toshiba/IBM Cell BE
 130 processor. llvm-gcc 4.2 supports CellSPU as a 'configure' target and progress
 131 is being made so that libgcc.a compiles cleanly. Notable pieces still in
 132 development include full 64-bit integer and full double precision floating
 133 point support.</li>
 134
 135 <li>Anton and Duncan significantly improved llvm-gcc 4.2 support for the GCC Ada
 136 (GNAT) and Fortran (gfortran) front-ends.  These front-ends should still be considered
 137 experimental however: see the <a href="#knownproblems">list of known problems</a>.
 138 The release binaries do not contain either front-end: they need to be built from
 139 source (the Ada front-end only builds on x86-32 linux).</li>
 140
 141 <li>Dale contributed full support for long double on x86/x86-64 (where it is 80
 142 bits) and on Darwin PPC/PPC64 (where it is 128 bits).  In previous LLVM
 143 releases, llvm-gcc silently mapped long double to double.</li>
 144
 145 <li>Gordon Henriksen rewrote most of the <a href="GarbageCollection.html"
 146 >Accurate Garbage Collection</a> code in the code generator, making the
 147 generated code more efficient and adding support for the OCaml garbage collector
 148 metadata format.</li>
 149
 150 <li>Christopher Lamb contributed support for multiple address spaces in LLVM
 151 IR.  This is useful for supporting targets that have 'near' vs 'far' pointers,
 152 'RAM' vs 'ROM' pointers, or that have non-local memory that can be accessed with
 153 special instructions.</li>
 154
 155 <li>LLVM now includes a new set of detailed <a
 156 href="tutorial/index.html">tutorials</a>, which explain how to implement a
 157 language with LLVM and shows how to use several important APIs.</li>
 158
 159 </ul>
 160
 161 </div>
 162
 163 <!--=========================================================================-->
 164 <div class="doc_subsection">
 165 <a name="coreimprovements">LLVM Core Improvements</a>
 166 </div>
 167
 168 <div class="doc_text">
 169 <p>New features include:
 170 </p>
 171
 172 <ul>
 173 <li>Gordon contributed support for C and OCaml Bindings for the basic LLVM IR
 174 construction routines as well as several other auxiliary APIs.</li>
 175
 176 <li>Anton added readnone/readonly attributes for modeling function side effects.
 177 Duncan hooked up GCC's pure/const attributes to them and enhanced mod/ref
 178 analysis to use them.</li>
 179
 180 <li>Devang added LLVMFoldingBuilder, a version of LLVMBuilder that implicitly
 181 simplifies the code as it is constructed.</li>
 182
 183 <li>Ted Kremenek added a framework for generic object serialization to bitcode
 184 files. This support is only used by clang right now for ASTs but is extensible
 185 and could be used for serializing arbitrary other data into bitcode files.</li>
 186
 187 <li>Duncan improved TargetData to distinguish between the size/alignment of a
 188 type in a register, in memory according to the platform ABI, and in memory when
 189 we have a choice.</li>
 190
 191 <li>Reid moved parameter attributes off of FunctionType and onto functions
 192 and calls.  This makes it much easier to add attributes to a function in a
 193 transformation pass.</li>
 194
 195 <li>Dan Gohman added support for vector sin, cos, and pow intrinsics.</li>
 196
 197 </ul>
 198
 199 </div>
 200
 201 <!--=========================================================================-->
 202 <div class="doc_subsection">
 203 <a name="codegen">Code Generator Improvements</a>
 204 </div>
 205
 206 <div class="doc_text">
 207
 208 <p>We put a significant amount of work into the code generator infrastructure,
 209 which allows us to implement more aggressive algorithms and make it run
 210 faster:</p>
 211
 212 <ul>
 213
 214 <li>Owen refactored the existing LLVM dominator and loop information code to
 215 allow it work on the machine code representation.  He contributed support for
 216 dominator and loop information on machine code and merged the code for forward
 217 and backward dominator computation.</li>
 218
 219 <li>Dan added support for emitting debug information with .file and .loc
 220 directives on platforms that support it, instead of emitting large tables in the .s
 221 file.</li>
 222
 223 <li>Evan extended the DAG scheduler to model physical register dependencies
 224 explicitly and have the BURR scheduler pick a correct schedule based on the
 225 dependencies.  This reduces our use of the 'flag' operand hack.</li>
 226
 227 <li>Evan added initial support for register coalescing of subregister
 228 references.</li>
 229
 230 <li>Rafael Espindola implemented initial support for a new 'byval' attribute,
 231 which allows more efficient by-value argument passing in the LLVM IR.  Evan
 232 finished support for it and enabled it in the X86 (32- and 64-bit) and C
 233 backends.</li>
 234
 235 <li>The LLVM TargetInstrInfo class can now answer queries about the mod/ref and
 236 side-effect behavior of MachineInstr's.  This information is inferred
 237 automatically by TableGen from .td files for all instructions with
 238 patterns.</li>
 239
 240 <li>Evan implemented simple live interval splitting on basic block boundaries.
 241 This allows the register allocator to be more successful at keeping values in
 242 registers in some parts of a value's live range, even if they need to be spilled
 243 in some other block.</li>
 244
 245 <li>The new MachineRegisterInfo.h class provides support for efficiently
 246 iterating over all defs/uses of a register, and this information is
 247 automatically kept up-to-date.  This support is similar to the  use_iterator in
 248 the LLVM IR level.</li>
 249
 250 <li>The MachineInstr, MachineOperand and TargetInstrDesc classes are simpler,
 251 more consistent, and better documented.</li>
 252 </ul>
 253
 254 </div>
 255
 256 <!--=========================================================================-->
 257 <div class="doc_subsection">
 258 <a name="optimizer">Optimizer Improvements</a>
 259 </div>
 260
 261 <div class="doc_text">
 262
 263 <p>In addition to a huge array of bug fixes and minor performance tweaks, the
 264 LLVM 2.2 optimizers support a few major enhancements:</p>
 265
 266 <ul>
 267
 268 <li>Daniel Berlin and Curtis Dunham rewrote Andersen's alias analysis to be
 269 several orders of magnitude faster, and implemented Offline Variable
 270 Substitution and Lazy Cycle Detection.  Note that Andersen's is not enabled in
 271 llvm-gcc by default, but can be accessed through 'opt'.</li>
 272
 273 <li>Dan Gohman contributed several enhancements to Loop Strength Reduction (LSR)
 274 to make it more aggressive with SSE intrinsics and when induction variables are
 275 used by non-memory instructions.</li>
 276
 277 <li>Evan added support for simple exit value substitution to LSR.</li>
 278
 279 <li>Evan enhanced LSR to support induction variable reuse when the induction
 280 variables have different widths.</li>
 281
 282 </ul>
 283
 284 </div>
 285
 286
 287 <!--=========================================================================-->
 288 <div class="doc_subsection">
 289 <a name="targetspecific">Target Specific Improvements</a>
 290 </div>
 291
 292 <div class="doc_text">
 293 <p>New target-specific features include:
 294 </p>
 295
 296 <ul>
 297 <li>Evan contributed support to the X86 backend to model the mod/ref behavior
 298 of the EFLAGS register explicitly in all instructions.  This gives more freedom
 299 to the scheduler, and is a more explicit way to model the instructions.</li>
 300 <li>Dale contributed support for exception handling on Darwin/PPC and he and
 301 Anton got x86-64 working.</li>
 302 <li>Evan turned on if-conversion by default for ARM, allowing LLVM to take
 303 advantage of its predication features.</li>
 304 <li>Bruno added PIC support to the MIPS backend, fixed many bugs and improved
 305 support for architecture variants.</li>
 306 <li>Arnold Schwaighofer added initial support for X86 tail calls.</li>
 307 <li>Evan contributed several enhancements to Darwin/x86 debug information.</li>
 308 <li>Duncan added x86-64 support for trampolines (pointers to nested functions).</li>
 309 </ul>
 310
 311 </div>
 312
 313 <!--=========================================================================-->
 314 <div class="doc_subsection">
 315 <a name="otherimprovements">Other Improvements</a>
 316 </div>
 317
 318 <div class="doc_text">
 319 <p>New features include:
 320 </p>
 321
 322 <ul>
 323 <li>Gordon expanded and updated the <a href="Passes.html">LLVM Analysis and
 324 Transformation Passes</a> reference to include descriptions for each pass.</li>
 325
 326 <li>We rewrote the lexer and parser used by TableGen to make them simpler
 327 and cleaner.  This gives tblgen support for 'caret diagnostics'.  The .ll file
 328 lexer was also rewritten to support caret diagnostics but doesn't use this
 329 support yet.</li>
 330
 331 <li>Dale has been grinding through the GCC testsuite, and marked many
 332 LLVM-incompatible tests as not-to-be-run (for example, if they are grepping
 333 through some GCC dump file that LLVM doesn't produce), he also found and fixed
 334 many LLVM bugs exposed by the testsuite.</li>
 335 </ul>
 336
 337 </div>
 338
 339 <!-- *********************************************************************** -->
 340 <div class="doc_section">
 341   <a name="portability">Portability and Supported Platforms</a>
 342 </div>
 343 <!-- *********************************************************************** -->
 344
 345 <div class="doc_text">
 346
 347 <p>LLVM is known to work on the following platforms:</p>
 348
 349 <ul>
 350 <li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD
 351       (and probably other unix-like systems).</li>
 352 <li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit and
 353     64-bit modes.</li>
 354 <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
 355 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
 356     support is available for native builds with Visual C++).</li>
 357 <li>Sun UltraSPARC workstations running Solaris 8.</li>
 358 <li>Alpha-based machines running Debian GNU/Linux.</li>
 359 <li>Itanium-based machines running Linux and HP-UX.</li>
 360 </ul>
 361
 362 <p>The core LLVM infrastructure uses
 363 <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
 364 to the machine and operating system on which it is built.  However, minor
 365 porting may be required to get LLVM to work on new platforms.  We welcome your
 366 portability patches and reports of successful builds or error messages.</p>
 367
 368 </div>
 369
 370 <!-- *********************************************************************** -->
 371 <div class="doc_section">
 372   <a name="knownproblems">Known Problems</a>
 373 </div>
 374 <!-- *********************************************************************** -->
 375
 376 <div class="doc_text">
 377
 378 <p>This section contains all known problems with the LLVM system, listed by
 379 component.  As new problems are discovered, they will be added to these
 380 sections.  If you run into a problem, please check the <a
 381 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
 382 there isn't already one.</p>
 383
 384 </div>
 385
 386 <!-- ======================================================================= -->
 387 <div class="doc_subsection">
 388   <a name="experimental">Experimental features included with this release</a>
 389 </div>
 390
 391 <div class="doc_text">
 392
 393 <p>The following components of this LLVM release are either untested, known to
 394 be broken or unreliable, or are in early development.  These components should
 395 not be relied on, and bugs should not be filed against them, but they may be
 396 useful to some people.  In particular, if you would like to work on one of these
 397 components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
 398
 399 <ul>
 400 <li>The <tt>-cee</tt> pass is known to be buggy and will be removed in
 401     LLVM 2.3.</li>
 402 <li>The MSIL, IA64, Alpha, and MIPS backends are experimental.</li>
 403 <li>The LLC "<tt>-filetype=asm</tt>" (the default) is the only supported
 404     value for this option.</li>
 405 <li>The llvmc tool is not supported.</li>
 406 </ul>
 407
 408 </div>
 409
 410 <!-- ======================================================================= -->
 411 <div class="doc_subsection">
 412   <a name="x86-be">Known problems with the X86 back-end</a>
 413 </div>
 414
 415 <div class="doc_text">
 416
 417 <ul>
 418 <li>The X86 backend does not yet support <a href="http://llvm.org/PR879">inline
 419     assembly that uses the X86 floating point stack</a>.</li>
 420 <li>The X86 backend occasionally has <a href="http://llvm.org/PR1649">alignment
 421     problems</a> on operating systems that don't require 16-byte stack alignment
 422     (including most non-darwin OS's like linux).</li>
 423 <li>The X86 backend generates inefficient floating point code when configured to
 424     generate code for systems that don't have SSE2.</li>
 425 </ul>
 426
 427 </div>
 428
 429 <!-- ======================================================================= -->
 430 <div class="doc_subsection">
 431   <a name="ppc-be">Known problems with the PowerPC back-end</a>
 432 </div>
 433
 434 <div class="doc_text">
 435
 436 <ul>
 437 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
 438 compilation, and lacks support for debug information.</li>
 439 </ul>
 440
 441 </div>
 442
 443 <!-- ======================================================================= -->
 444 <div class="doc_subsection">
 445   <a name="arm-be">Known problems with the ARM back-end</a>
 446 </div>
 447
 448 <div class="doc_text">
 449
 450 <ul>
 451 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
 452 processors, thumb programs can crash or produce wrong
 453 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
 454 <li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
 455 </li>
 456 <li>There is a bug in QEMU-ARM (&lt;= 0.9.0) which causes it to incorrectly execute
 457 programs compiled with LLVM.  Please use more recent versions of QEMU.</li>
 458 </ul>
 459
 460 </div>
 461
 462 <!-- ======================================================================= -->
 463 <div class="doc_subsection">
 464   <a name="sparc-be">Known problems with the SPARC back-end</a>
 465 </div>
 466
 467 <div class="doc_text">
 468
 469 <ul>
 470 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
 471     support the 64-bit SPARC ABI (-m64).</li>
 472 </ul>
 473
 474 </div>
 475
 476 <!-- ======================================================================= -->
 477 <div class="doc_subsection">
 478   <a name="alpha-be">Known problems with the Alpha back-end</a>
 479 </div>
 480
 481 <div class="doc_text">
 482
 483 <ul>
 484
 485 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
 486 appropriate nops inserted to ensure restartability.</li>
 487
 488 </ul>
 489 </div>
 490
 491 <!-- ======================================================================= -->
 492 <div class="doc_subsection">
 493   <a name="ia64-be">Known problems with the IA64 back-end</a>
 494 </div>
 495
 496 <div class="doc_text">
 497
 498 <ul>
 499
 500 <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
 501 made where the argument is not 16-byte aligned, as required on IA64. (Strictly
 502 speaking this is not a bug in the IA64 back-end; it will also be encountered
 503 when building C++ programs using the C back-end.)</li>
 504
 505 <li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
 506 ABI compliant layout of v-tables</a>.  In particular, it just stores function
 507 pointers instead of function descriptors in the vtable.  This bug prevents
 508 mixing C++ code compiled with LLVM with C++ objects compiled by other C++
 509 compilers.</li>
 510
 511 <li>There are a few ABI violations which will lead to problems when mixing LLVM
 512 output with code built with other compilers, particularly for floating-point
 513 programs.</li>
 514
 515 <li>Defining vararg functions is not supported (but calling them is ok).</li>
 516
 517 <li>The Itanium backend has bitrotted somewhat.</li>
 518 </ul>
 519
 520 </div>
 521
 522 <!-- ======================================================================= -->
 523 <div class="doc_subsection">
 524   <a name="c-be">Known problems with the C back-end</a>
 525 </div>
 526
 527 <div class="doc_text">
 528
 529 <ul>
 530 <li><a href="http://llvm.org/PR802">The C backend does not support inline
 531     assembly code</a>.</li>
 532 <li><a href="http://llvm.org/PR1126">The C backend does not support vectors
 533     yet</a>.</li>
 534 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
 535     C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
 536     C++ code compiled with LLC or native compilers.</li>
 537 <li>The C backend does not support all exception handling constructs.</li>
 538 </ul>
 539
 540 </div>
 541
 542
 543 <!-- ======================================================================= -->
 544 <div class="doc_subsection">
 545   <a name="c-fe">Known problems with the C front-end</a>
 546 </div>
 547
 548 <!-- _______________________________________________________________________ -->
 549 <div class="doc_subsubsection">Bugs</div>
 550
 551 <div class="doc_text">
 552
 553 <p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
 554 Optimization</a> on most platforms "out-of-the-box".  Please inquire on the
 555 llvmdev mailing list if you are interested.</p>
 556
 557 </div>
 558
 559 <!-- _______________________________________________________________________ -->
 560 <div class="doc_subsubsection">
 561   Notes
 562 </div>
 563
 564 <div class="doc_text">
 565 <ul>
 566
 567 <li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet.
 568   See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p>
 569 </li>
 570
 571 <li><p>llvm-gcc <b>partially</b> supports these GCC extensions:</p>
 572   <ol>
 573   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>:
 574
 575       As in Algol and Pascal, lexical scoping of functions.
 576       Nested functions are supported, but llvm-gcc does not support
 577       taking the address of a nested function (except on X86 targets)
 578       or non-local gotos.</li>
 579
 580   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
 581
 582       Declaring that functions have no side effects or that they can never
 583       return.<br>
 584
 585       <b>Supported:</b> <tt>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</tt>,
 586       <tt>const</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
 587       <tt>deprecated</tt>, <tt>fastcall</tt>, <tt>format</tt>,
 588       <tt>format_arg</tt>, <tt>non_null</tt>, <tt>noinline</tt>,
 589       <tt>noreturn</tt>, <tt>nothrow</tt>, <tt>pure</tt>, <tt>regparm</tt>
 590       <tt>section</tt>, <tt>stdcall</tt>, <tt>unused</tt>, <tt>used</tt>,
 591       <tt>visibility</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
 592
 593       <b>Ignored:</b> <tt>malloc</tt>,
 594       <tt>no_instrument_function</tt></li>
 595   </ol>
 596 </li>
 597
 598 <li><p>llvm-gcc supports the vast majority of GCC extensions, including:</p>
 599
 600   <ol>
 601   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
 602   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
 603   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
 604       Other built-in functions.</li>
 605   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
 606       Specifying attributes of variables.</li>
 607   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>:   Specifying attributes of types.</li>
 608   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
 609   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
 610       Arrays whose length is computed at run time.</li>
 611   <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>
 612   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>:   Putting statements and declarations inside expressions.</li>
 613   <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>
 614   <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>
 615   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
 616   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
 617   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>:   Data types for complex numbers.</li>
 618   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
 619   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
 620   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
 621   <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>
 622   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>:  Slightly looser rules for escaped newlines.</li>
 623   <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>
 624   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
 625   <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>
 626   <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>
 627   <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>
 628   <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>
 629   <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>
 630   <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>
 631   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
 632   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
 633 or arrays as values.</li>
 634   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
 635   <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>
 636   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
 637   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
 638   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
 639   <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>
 640   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
 641   <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>
 642   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
 643   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
 644   <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>
 645   <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>
 646   <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>
 647   <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>
 648   <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>
 649   <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
 650   </ol></li>
 651
 652 </ul>
 653
 654 <p>If you run into GCC extensions which have not been included in any of these
 655 lists, please let us know (also including whether or not they work).</p>
 656
 657 </div>
 658
 659 <!-- ======================================================================= -->
 660 <div class="doc_subsection">
 661   <a name="c++-fe">Known problems with the C++ front-end</a>
 662 </div>
 663
 664 <div class="doc_text">
 665
 666 <p>The C++ front-end is considered to be fully
 667 tested and works for a number of non-trivial programs, including LLVM
 668 itself, Qt, Mozilla, etc.</p>
 669
 670 <ul>
 671 <li>Exception handling only works well on the X86 and PowerPC targets.
 672 It works well for x86-64 darwin but not x86-64 linux.</li>
 673 </ul>
 674
 675 </div>
 676
 677
 678
 679 <!-- ======================================================================= -->
 680 <div class="doc_subsection">
 681   <a name="ada-fe">Known problems with the Ada front-end</a>
 682 </div>
 683
 684 <div class="doc_text">
 685 The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature
 686 technology and problems should be expected.
 687 <ul>
 688 <li>The Ada front-end currently only builds on x86-32.  This is mainly due
 689 to lack of trampoline support (pointers to nested functions) on other platforms,
 690 however it <a href="http://llvm.org/PR2006">also fails to build on x86-64</a>
 691 which does support trampolines.</li>
 692 <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
 693 Workaround: configure with --disable-bootstrap.</li>
 694 <li>The c380004 and <a href="http://llvm.org/PR2010">c393010</a> ACATS tests
 695 fail (c380004 also fails with gcc-4.2 mainline).</li>
 696 <li>Many gcc specific Ada tests continue to crash the compiler.</li>
 697 <li>The -E binder option (exception backtraces)
 698 <a href="http://llvm.org/PR1982">does not work</a> and will result in programs
 699 crashing if an exception is raised.  Workaround: do not use -E.</li>
 700 <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
 701 or finish at a non-byte offset</a> in a record.  Workaround: do not pack records
 702 or use representation clauses that result in a field of a non-discrete type
 703 starting or finishing in the middle of a byte.</li>
 704 <li>The lli interpreter <a href="http://llvm.org/PR2009">considers 'main'
 705 as generated by the Ada binder to be invalid</a>.
 706 Workaround: hand edit the file to use pointers for argv and envp rather than
 707 integers.</li>
 708 <li>The -fstack-check option <a href="http://llvm.org/PR2008">is ignored</a>.</li>
 709 </ul>
 710 </div>
 711
 712 <!-- ======================================================================= -->
 713 <div class="doc_subsection">
 714   <a name="fortran-fe">Known problems with the Fortran front-end</a>
 715 </div>
 716
 717 <div class="doc_text">
 718
 719 <ul>
 720 <li>The llvm-gcc 4.2 gfortran front-end supports a broad range of Fortran code, but does
 721 <a href="http://llvm.org/PR1971">not support EQUIVALENCE yet</a>.</li>
 722 </ul>
 723 </div>
 724
 725
 726 <!-- *********************************************************************** -->
 727 <div class="doc_section">
 728   <a name="additionalinfo">Additional Information</a>
 729 </div>
 730 <!-- *********************************************************************** -->
 731
 732 <div class="doc_text">
 733
 734 <p>A wide variety of additional information is available on the <a
 735 href="http://llvm.org">LLVM web page</a>, in particular in the <a
 736 href="http://llvm.org/docs/">documentation</a> section.  The web page also
 737 contains versions of the API documentation which is up-to-date with the
 738 Subversion version of the source code.
 739 You can access versions of these documents specific to this release by going
 740 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
 741
 742 <p>If you have any questions or comments about LLVM, please feel free to contact
 743 us via the <a href="http://llvm.org/docs/#maillist"> mailing
 744 lists</a>.</p>
 745
 746 </div>
 747
 748 <!-- *********************************************************************** -->
 749
 750 <hr>
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