docs/ReleaseNotes.html

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  10
  11 <div class="doc_title">LLVM 2.8 Release Notes</div>
  12
  13 <img align=right src="http://llvm.org/img/DragonSmall.png"
  14     width="136" height="136" alt="LLVM Dragon Logo">
  15
  16 <ol>
  17   <li><a href="#intro">Introduction</a></li>
  18   <li><a href="#subproj">Sub-project Status Update</a></li>
  19   <li><a href="#externalproj">External Projects Using LLVM 2.8</a></li>
  20   <li><a href="#whatsnew">What's New in LLVM 2.8?</a></li>
  21   <li><a href="GettingStarted.html">Installation Instructions</a></li>
  22   <li><a href="#portability">Portability and Supported Platforms</a></li>
  23   <li><a href="#knownproblems">Known Problems</a></li>
  24   <li><a href="#additionalinfo">Additional Information</a></li>
  25 </ol>
  26
  27 <div class="doc_author">
  28   <p>Written by the <a href="http://llvm.org">LLVM Team</a></p>
  29 </div>
  30
  31 <h1 style="color:red">These are in-progress notes for the upcoming LLVM 2.8
  32 release.<br>
  33 You may prefer the
  34 <a href="http://llvm.org/releases/2.7/docs/ReleaseNotes.html">LLVM 2.7
  35 Release Notes</a>.</h1>
  36
  37 <!-- *********************************************************************** -->
  38 <div class="doc_section">
  39   <a name="intro">Introduction</a>
  40 </div>
  41 <!-- *********************************************************************** -->
  42
  43 <div class="doc_text">
  44
  45 <p>This document contains the release notes for the LLVM Compiler
  46 Infrastructure, release 2.8.  Here we describe the status of LLVM, including
  47 major improvements from the previous release and significant known problems.
  48 All LLVM releases may be downloaded from the <a
  49 href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
  50
  51 <p>For more information about LLVM, including information about the latest
  52 release, please check out the <a href="http://llvm.org/">main LLVM
  53 web site</a>.  If you have questions or comments, the <a
  54 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's
  55 Mailing List</a> is a good place to send them.</p>
  56
  57 <p>Note that if you are reading this file from a Subversion checkout or the
  58 main LLVM web page, this document applies to the <i>next</i> release, not the
  59 current one.  To see the release notes for a specific release, please see the
  60 <a href="http://llvm.org/releases/">releases page</a>.</p>
  61
  62 </div>
  63
  64
  65 <!--
  66 Almost dead code.
  67   include/llvm/Analysis/LiveValues.h => Dan
  68   lib/Transforms/IPO/MergeFunctions.cpp => consider for 2.8.
  69   llvm/Analysis/PointerTracking.h => Edwin wants this, consider for 2.8.
  70   ABCD, GEPSplitterPass
  71   MSIL backend?
  72   lib/Transforms/Utils/SSI.cpp  -> ABCD depends on it.
  73 -->
  74
  75
  76 <!-- Features that need text if they're finished for 2.8:
  77   combiner-aa?
  78   strong phi elim
  79   llvm.dbg.value: variable debug info for optimized code
  80   loop dependence analysis
  81  -->
  82
  83  <!-- for announcement email:
  84  Logo web page.
  85  Many new papers added to /pubs/
  86    -->
  87
  88 <!-- *********************************************************************** -->
  89 <div class="doc_section">
  90   <a name="subproj">Sub-project Status Update</a>
  91 </div>
  92 <!-- *********************************************************************** -->
  93
  94 <div class="doc_text">
  95 <p>
  96 The LLVM 2.8 distribution currently consists of code from the core LLVM
  97 repository (which roughly includes the LLVM optimizers, code generators
  98 and supporting tools), the Clang repository and the llvm-gcc repository.  In
  99 addition to this code, the LLVM Project includes other sub-projects that are in
 100 development.  Here we include updates on these subprojects.
 101 </p>
 102
 103 </div>
 104
 105
 106 <!--=========================================================================-->
 107 <div class="doc_subsection">
 108 <a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
 109 </div>
 110
 111 <div class="doc_text">
 112
 113 <p><a href="http://clang.llvm.org/">Clang</a> is an LLVM front end for the C,
 114 C++, and Objective-C languages. Clang aims to provide a better user experience
 115 through expressive diagnostics, a high level of conformance to language
 116 standards, fast compilation, and low memory use. Like LLVM, Clang provides a
 117 modular, library-based architecture that makes it suitable for creating or
 118 integrating with other development tools. Clang is considered a
 119 production-quality compiler for C and Objective-C on x86 (32- and 64-bit).</p>
 120
 121 <p>In the LLVM 2.8 time-frame, the Clang team has made many improvements:</p>
 122
 123 <ul>
 124
 125 </ul>
 126 </div>
 127
 128 <!--=========================================================================-->
 129 <div class="doc_subsection">
 130 <a name="clangsa">Clang Static Analyzer</a>
 131 </div>
 132
 133 <div class="doc_text">
 134
 135 <p>The <a href="http://clang-analyzer.llvm.org/">Clang Static Analyzer</a>
 136    project is an effort to use static source code analysis techniques to
 137    automatically find bugs in C and Objective-C programs (and hopefully <a
 138    href="http://clang-analyzer.llvm.org/dev_cxx.html">C++ in the
 139    future</a>!).  The tool is very good at finding bugs that occur on specific
 140    paths through code, such as on error conditions.</p>
 141
 142 <p>In the LLVM 2.8 time-frame,
 143 </p>
 144
 145 </div>
 146
 147 <!--=========================================================================-->
 148 <div class="doc_subsection">
 149 <a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
 150 </div>
 151
 152 <div class="doc_text">
 153 <p>
 154 The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
 155 a JVM and a CLI Virtual Machine (Microsoft .NET is an
 156 implementation of the CLI) using LLVM for static and just-in-time
 157 compilation.</p>
 158
 159 <p>With the release of LLVM 2.8, ...</p>
 160
 161 </div>
 162
 163
 164 <!--=========================================================================-->
 165 <div class="doc_subsection">
 166 <a name="compiler-rt">compiler-rt: Compiler Runtime Library</a>
 167 </div>
 168
 169 <div class="doc_text">
 170 <p>
 171 The new LLVM <a href="http://compiler-rt.llvm.org/">compiler-rt project</a>
 172 is a simple library that provides an implementation of the low-level
 173 target-specific hooks required by code generation and other runtime components.
 174 For example, when compiling for a 32-bit target, converting a double to a 64-bit
 175 unsigned integer is compiled into a runtime call to the "__fixunsdfdi"
 176 function. The compiler-rt library provides highly optimized implementations of
 177 this and other low-level routines (some are 3x faster than the equivalent
 178 libgcc routines).</p>
 179
 180 <p>
 181 All of the code in the compiler-rt project is available under the standard LLVM
 182 License, a "BSD-style" license.  New in LLVM 2.8:
 183
 184 Soft float support
 185 </p>
 186
 187 </div>
 188
 189 <!--=========================================================================-->
 190 <div class="doc_subsection">
 191 <a name="dragonegg">DragonEgg: llvm-gcc ported to gcc-4.5</a>
 192 </div>
 193
 194 <div class="doc_text">
 195 <p>
 196 <a href="http://dragonegg.llvm.org/">DragonEgg</a> is a port of llvm-gcc to
 197 gcc-4.5.  Unlike llvm-gcc, which makes many intrusive changes to the underlying
 198 gcc-4.2 code, dragonegg in theory does not require any gcc-4.5 modifications
 199 whatsoever (currently one small patch is needed).  This is thanks to the new
 200 <a href="http://gcc.gnu.org/wiki/plugins">gcc plugin architecture</a>, which
 201 makes it possible to modify the behaviour of gcc at runtime by loading a plugin,
 202 which is nothing more than a dynamic library which conforms to the gcc plugin
 203 interface.  DragonEgg is a gcc plugin that causes the LLVM optimizers to be run
 204 instead of the gcc optimizers, and the LLVM code generators instead of the gcc
 205 code generators, just like llvm-gcc.  To use it, you add
 206 "-fplugin=path/dragonegg.so" to the gcc-4.5 command line, and gcc-4.5 magically
 207 becomes llvm-gcc-4.5!
 208 </p>
 209
 210 <p>
 211 DragonEgg is still a work in progress.  Currently C works very well, while C++,
 212 Ada and Fortran work fairly well.  All other languages either don't work at all,
 213 or only work poorly.  For the moment only the x86-32 and x86-64 targets are
 214 supported, and only on linux and darwin (darwin needs an additional gcc patch).
 215 </p>
 216
 217 <p>
 218 2.8 status here.
 219 </p>
 220
 221 </div>
 222
 223
 224 <!--=========================================================================-->
 225 <div class="doc_subsection">
 226 <a name="mc">llvm-mc: Machine Code Toolkit</a>
 227 </div>
 228
 229 <div class="doc_text">
 230 <p>
 231 The LLVM Machine Code (aka MC) sub-project of LLVM was created to solve a number
 232 of problems in the realm of assembly, disassembly, object file format handling,
 233 and a number of other related areas that CPU instruction-set level tools work
 234 in. It is a sub-project of LLVM which provides it with a number of advantages
 235 over other compilers that do not have tightly integrated assembly-level tools.
 236 For a gentle introduction, please see the <a
 237 href="http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html">Intro to the
 238 LLVM MC Project Blog Post</a>.
 239 </p>
 240
 241 <p>2.8 status here</p>
 242 </div>
 243
 244
 245 <!-- *********************************************************************** -->
 246 <div class="doc_section">
 247   <a name="externalproj">External Open Source Projects Using LLVM 2.8</a>
 248 </div>
 249 <!-- *********************************************************************** -->
 250
 251 <div class="doc_text">
 252
 253 <p>An exciting aspect of LLVM is that it is used as an enabling technology for
 254    a lot of other language and tools projects.  This section lists some of the
 255    projects that have already been updated to work with LLVM 2.8.</p>
 256 </div>
 257
 258
 259 <!-- *********************************************************************** -->
 260 <div class="doc_section">
 261   <a name="whatsnew">What's New in LLVM 2.8?</a>
 262 </div>
 263 <!-- *********************************************************************** -->
 264
 265 <div class="doc_text">
 266
 267 <p>This release includes a huge number of bug fixes, performance tweaks and
 268 minor improvements.  Some of the major improvements and new features are listed
 269 in this section.
 270 </p>
 271
 272 </div>
 273
 274 <!--=========================================================================-->
 275 <div class="doc_subsection">
 276 <a name="orgchanges">LLVM Community Changes</a>
 277 </div>
 278
 279 <div class="doc_text">
 280
 281 <p>In addition to changes to the code, between LLVM 2.7 and 2.8, a number of
 282 organization changes have happened:
 283 </p>
 284
 285 <ul>
 286 </ul>
 287 </div>
 288
 289 <!--=========================================================================-->
 290 <div class="doc_subsection">
 291 <a name="majorfeatures">Major New Features</a>
 292 </div>
 293
 294 <div class="doc_text">
 295
 296 <p>LLVM 2.8 includes several major new capabilities:</p>
 297
 298 <ul>
 299 <li>.</li>
 300 </ul>
 301
 302 </div>
 303
 304 <!--=========================================================================-->
 305 <div class="doc_subsection">
 306 <a name="coreimprovements">LLVM IR and Core Improvements</a>
 307 </div>
 308
 309 <div class="doc_text">
 310 <p>LLVM IR has several new features for better support of new targets and that
 311 expose new optimization opportunities:</p>
 312
 313 <ul>
 314
 315 <li>LLVM 2.8 changes the internal order of operands in <a
 316   href="http://llvm.org/doxygen/classllvm_1_1InvokeInst.html"><tt>InvokeInst</tt></a>
 317   and <a href="http://llvm.org/doxygen/classllvm_1_1CallInst.html"><tt>CallInst</tt></a>.
 318   To be portable across releases, resort to <tt>CallSite</tt> and the
 319   high-level accessors, such as <tt>getCalledValue</tt> and <tt>setUnwindDest</tt>.
 320 </li>
 321 <li>
 322   You can no longer pass use_iterators directly to cast<> (and similar), because
 323   these routines tend to perform costly dereference operations more than once. You
 324   have to dereference the iterators yourself and pass them in.
 325 </li>
 326 <li>
 327   llvm.memcpy.*, llvm.memset.*, llvm.memmove.* (and possibly other?) intrinsics
 328   take an extra parameter now (i1 isVolatile), totaling 5 parameters.
 329   If you were creating these intrinsic calls and prototypes yourself (as opposed
 330   to using Intrinsic::getDeclaration), you can use UpgradeIntrinsicFunction/UpgradeIntrinsicCall
 331   to be portable accross releases.
 332   Note that you cannot use Intrinsic::getDeclaration() in a backwards compatible
 333   way (needs 2/3 types now, in 2.7 it needed just 1).
 334 </li>
 335 <li>
 336   SetCurrentDebugLocation takes a DebugLoc now instead of a MDNode.
 337   Change your code to use
 338   SetCurrentDebugLocation(DebugLoc::getFromDILocation(...)).
 339 </li>
 340 <li>
 341   VISIBILITY_HIDDEN is gone.
 342 </li>
 343 <li>
 344   The <tt>RegisterPass</tt> and <tt>RegisterAnalysisGroup</tt> templates are
 345   considered deprecated, but continue to function in LLVM 2.8.  Clients are
 346   strongly advised to use the upcoming <tt>INITIALIZE_PASS()</tt> and
 347   <tt>INITIALIZE_AG_PASS()</tt> macros instead.
 348 <li>
 349   SMDiagnostic takes different parameters now. //FIXME: how to upgrade?
 350 </li>
 351 <li>
 352   Some APIs got renamed:
 353   <ul>
 354       <li>llvm_report_error -&gt; report_fatal_error</li>
 355       <li>llvm_install_error_handler -&gt; install_fatal_error_handler</li>
 356       <li>llvm::DwarfExceptionHandling -&gt; llvm::JITExceptionHandling</li>
 357   </ul>
 358 </li>
 359 </ul>
 360
 361 </div>
 362
 363 <!--=========================================================================-->
 364 <div class="doc_subsection">
 365 <a name="optimizer">Optimizer Improvements</a>
 366 </div>
 367
 368 <div class="doc_text">
 369
 370 <p>In addition to a large array of minor performance tweaks and bug fixes, this
 371 release includes a few major enhancements and additions to the optimizers:</p>
 372
 373 <ul>
 374
 375 <li></li>
 376
 377 </ul>
 378
 379 </div>
 380
 381
 382 <!--=========================================================================-->
 383 <div class="doc_subsection">
 384 <a name="executionengine">Interpreter and JIT Improvements</a>
 385 </div>
 386
 387 <div class="doc_text">
 388
 389 <ul>
 390 <li></li>
 391
 392 </ul>
 393
 394 </div>
 395
 396 <!--=========================================================================-->
 397 <div class="doc_subsection">
 398 <a name="codegen">Target Independent Code Generator Improvements</a>
 399 </div>
 400
 401 <div class="doc_text">
 402
 403 <p>We have put a significant amount of work into the code generator
 404 infrastructure, which allows us to implement more aggressive algorithms and make
 405 it run faster:</p>
 406
 407 <ul>
 408 <li>MachO writer works.</li>
 409 </ul>
 410 </div>
 411
 412 <!--=========================================================================-->
 413 <div class="doc_subsection">
 414 <a name="x86">X86-32 and X86-64 Target Improvements</a>
 415 </div>
 416
 417 <div class="doc_text">
 418 <p>New features of the X86 target include:
 419 </p>
 420
 421 <ul>
 422 <li>The X86 backend now supports holding X87 floating point stack values
 423     in registers across basic blocks, dramatically improving performance of code
 424     that uses long double, and when targetting CPUs that don't support SSE.</li>
 425
 426 </ul>
 427
 428 </div>
 429
 430 <!--=========================================================================-->
 431 <div class="doc_subsection">
 432 <a name="ARM">ARM Target Improvements</a>
 433 </div>
 434
 435 <div class="doc_text">
 436 <p>New features of the ARM target include:
 437 </p>
 438
 439 <ul>
 440
 441 <li></li>
 442
 443 </ul>
 444
 445
 446 </div>
 447
 448 <!--=========================================================================-->
 449 <div class="doc_subsection">
 450 <a name="newapis">New Useful APIs</a>
 451 </div>
 452
 453 <div class="doc_text">
 454
 455 <p>This release includes a number of new APIs that are used internally, which
 456    may also be useful for external clients.
 457 </p>
 458
 459 <ul>
 460 <li></li>
 461 </ul>
 462
 463
 464 </div>
 465
 466 <!--=========================================================================-->
 467 <div class="doc_subsection">
 468 <a name="otherimprovements">Other Improvements and New Features</a>
 469 </div>
 470
 471 <div class="doc_text">
 472 <p>Other miscellaneous features include:</p>
 473
 474 <ul>
 475 <li></li>
 476 </ul>
 477
 478 </div>
 479
 480
 481 <!--=========================================================================-->
 482 <div class="doc_subsection">
 483 <a name="changes">Major Changes and Removed Features</a>
 484 </div>
 485
 486 <div class="doc_text">
 487
 488 <p>If you're already an LLVM user or developer with out-of-tree changes based
 489 on LLVM 2.7, this section lists some "gotchas" that you may run into upgrading
 490 from the previous release.</p>
 491
 492 <ul>
 493
 494 <li>.</li>
 495 </ul>
 496
 497 <p>In addition, many APIs have changed in this release.  Some of the major LLVM
 498 API changes are:</p>
 499
 500 <ul>
 501 </ul>
 502
 503 </div>
 504
 505
 506
 507 <!-- *********************************************************************** -->
 508 <div class="doc_section">
 509   <a name="portability">Portability and Supported Platforms</a>
 510 </div>
 511 <!-- *********************************************************************** -->
 512
 513 <div class="doc_text">
 514
 515 <p>LLVM is known to work on the following platforms:</p>
 516
 517 <ul>
 518 <li>Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat
 519     Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like
 520     systems).</li>
 521 <li>PowerPC and X86-based Mac OS X systems, running 10.4 and above in 32-bit
 522     and 64-bit modes.</li>
 523 <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
 524 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
 525     support is available for native builds with Visual C++).</li>
 526 <li>Sun x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.</li>
 527 <li>Alpha-based machines running Debian GNU/Linux.</li>
 528 </ul>
 529
 530 <p>The core LLVM infrastructure uses GNU autoconf to adapt itself
 531 to the machine and operating system on which it is built.  However, minor
 532 porting may be required to get LLVM to work on new platforms.  We welcome your
 533 portability patches and reports of successful builds or error messages.</p>
 534
 535 </div>
 536
 537 <!-- *********************************************************************** -->
 538 <div class="doc_section">
 539   <a name="knownproblems">Known Problems</a>
 540 </div>
 541 <!-- *********************************************************************** -->
 542
 543 <div class="doc_text">
 544
 545 <p>This section contains significant known problems with the LLVM system,
 546 listed by component.  If you run into a problem, please check the <a
 547 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
 548 there isn't already one.</p>
 549
 550 <ul>
 551 <li>LLVM will not correctly compile on Solaris and/or OpenSolaris
 552 using the stock GCC 3.x.x series 'out the box',
 553 See: <a href="GettingStarted.html#brokengcc">Broken versions of GCC and other tools</a>.
 554 However, A <a href="http://pkg.auroraux.org/GCC">Modern GCC Build</a>
 555 for x86/x86-64 has been made available from the third party AuroraUX Project
 556 that has been meticulously tested for bootstrapping LLVM &amp; Clang.</li>
 557 <li>There have been reports of Solaris and/or OpenSolaris build failures due
 558 to an incompatibility in the nm program as well. The nm from binutils does seem
 559 to work.</li>
 560 </ul>
 561
 562 </div>
 563
 564 <!-- ======================================================================= -->
 565 <div class="doc_subsection">
 566   <a name="experimental">Experimental features included with this release</a>
 567 </div>
 568
 569 <div class="doc_text">
 570
 571 <p>The following components of this LLVM release are either untested, known to
 572 be broken or unreliable, or are in early development.  These components should
 573 not be relied on, and bugs should not be filed against them, but they may be
 574 useful to some people.  In particular, if you would like to work on one of these
 575 components, please contact us on the <a
 576 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
 577
 578 <ul>
 579 <li>The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430, SystemZ and MicroBlaze
 580     backends are experimental.</li>
 581 <li><tt>llc</tt> "<tt>-filetype=asm</tt>" (the default) is the only
 582     supported value for this option.  XXX Update me</li>
 583 </ul>
 584
 585 </div>
 586
 587 <!-- ======================================================================= -->
 588 <div class="doc_subsection">
 589   <a name="x86-be">Known problems with the X86 back-end</a>
 590 </div>
 591
 592 <div class="doc_text">
 593
 594 <ul>
 595   <li>The X86 backend does not yet support
 596     all <a href="http://llvm.org/PR879">inline assembly that uses the X86
 597     floating point stack</a>.  It supports the 'f' and 't' constraints, but not
 598     'u'.</li>
 599   <li>Win64 code generation wasn't widely tested. Everything should work, but we
 600     expect small issues to happen. Also, llvm-gcc cannot build the mingw64
 601     runtime currently due to lack of support for the 'u' inline assembly
 602     constraint and for X87 floating point inline assembly.</li>
 603   <li>The X86-64 backend does not yet support the LLVM IR instruction
 604       <tt>va_arg</tt>. Currently, front-ends support variadic
 605       argument constructs on X86-64 by lowering them manually.</li>
 606 </ul>
 607
 608 </div>
 609
 610 <!-- ======================================================================= -->
 611 <div class="doc_subsection">
 612   <a name="ppc-be">Known problems with the PowerPC back-end</a>
 613 </div>
 614
 615 <div class="doc_text">
 616
 617 <ul>
 618 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
 619 compilation, and lacks support for debug information.</li>
 620 </ul>
 621
 622 </div>
 623
 624 <!-- ======================================================================= -->
 625 <div class="doc_subsection">
 626   <a name="arm-be">Known problems with the ARM back-end</a>
 627 </div>
 628
 629 <div class="doc_text">
 630
 631 <ul>
 632 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
 633 processors, thumb programs can crash or produce wrong
 634 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
 635 <li>Compilation for ARM Linux OABI (old ABI) is supported but not fully tested.
 636 </li>
 637 </ul>
 638
 639 </div>
 640
 641 <!-- ======================================================================= -->
 642 <div class="doc_subsection">
 643   <a name="sparc-be">Known problems with the SPARC back-end</a>
 644 </div>
 645
 646 <div class="doc_text">
 647
 648 <ul>
 649 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32); it does not
 650     support the 64-bit SPARC ABI (-m64).</li>
 651 </ul>
 652
 653 </div>
 654
 655 <!-- ======================================================================= -->
 656 <div class="doc_subsection">
 657   <a name="mips-be">Known problems with the MIPS back-end</a>
 658 </div>
 659
 660 <div class="doc_text">
 661
 662 <ul>
 663 <li>64-bit MIPS targets are not supported yet.</li>
 664 </ul>
 665
 666 </div>
 667
 668 <!-- ======================================================================= -->
 669 <div class="doc_subsection">
 670   <a name="alpha-be">Known problems with the Alpha back-end</a>
 671 </div>
 672
 673 <div class="doc_text">
 674
 675 <ul>
 676
 677 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
 678 appropriate nops inserted to ensure restartability.</li>
 679
 680 </ul>
 681 </div>
 682
 683 <!-- ======================================================================= -->
 684 <div class="doc_subsection">
 685   <a name="c-be">Known problems with the C back-end</a>
 686 </div>
 687
 688 <div class="doc_text">
 689
 690 <ul>
 691 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
 692     inline assembly code</a>.</li>
 693 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
 694     C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
 695     C++ code compiled with <tt>llc</tt> or native compilers.</li>
 696 <li>The C backend does not support all exception handling constructs.</li>
 697 <li>The C backend does not support arbitrary precision integers.</li>
 698 </ul>
 699
 700 </div>
 701
 702
 703 <!-- ======================================================================= -->
 704 <div class="doc_subsection">
 705   <a name="c-fe">Known problems with the llvm-gcc C and C++ front-end</a>
 706 </div>
 707
 708 <div class="doc_text">
 709
 710 <p>The only major language feature of GCC not supported by llvm-gcc is
 711     the <tt>__builtin_apply</tt> family of builtins.   However, some extensions
 712     are only supported on some targets.  For example, trampolines are only
 713     supported on some targets (these are used when you take the address of a
 714     nested function).</p>
 715
 716 </div>
 717
 718 <!-- ======================================================================= -->
 719 <div class="doc_subsection">
 720   <a name="fortran-fe">Known problems with the llvm-gcc Fortran front-end</a>
 721 </div>
 722
 723 <div class="doc_text">
 724 <ul>
 725 <li>Fortran support generally works, but there are still several unresolved bugs
 726     in <a href="http://llvm.org/bugs/">Bugzilla</a>.  Please see the
 727     tools/gfortran component for details.</li>
 728 </ul>
 729 </div>
 730
 731 <!-- ======================================================================= -->
 732 <div class="doc_subsection">
 733   <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>
 734 </div>
 735
 736 <div class="doc_text">
 737 The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature
 738 technology, and problems should be expected.
 739 <ul>
 740 <li>The Ada front-end currently only builds on X86-32.  This is mainly due
 741 to lack of trampoline support (pointers to nested functions) on other platforms.
 742 However, it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
 743 which does support trampolines.</li>
 744 <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
 745 This is due to lack of LLVM support for <tt>setjmp</tt>/<tt>longjmp</tt> style
 746 exception handling, which is used internally by the compiler.
 747 Workaround: configure with <tt>--disable-bootstrap</tt>.</li>
 748 <li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
 749 and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
 750 (c380004 also fails with gcc-4.2 mainline).
 751 If the compiler is built with checks disabled then <a href="http://llvm.org/PR2010">c393010</a>
 752 causes the compiler to go into an infinite loop, using up all system memory.</li>
 753 <li>Some GCC specific Ada tests continue to crash the compiler.</li>
 754 <li>The <tt>-E</tt> binder option (exception backtraces)
 755 <a href="http://llvm.org/PR1982">does not work</a> and will result in programs
 756 crashing if an exception is raised.  Workaround: do not use <tt>-E</tt>.</li>
 757 <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
 758 or finish at a non-byte offset</a> in a record.  Workaround: do not pack records
 759 or use representation clauses that result in a field of a non-discrete type
 760 starting or finishing in the middle of a byte.</li>
 761 <li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers
 762 'main' as generated by the Ada binder to be invalid</a>.
 763 Workaround: hand edit the file to use pointers for <tt>argv</tt> and
 764 <tt>envp</tt> rather than integers.</li>
 765 <li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is
 766 ignored</a>.</li>
 767 </ul>
 768 </div>
 769
 770 <!-- *********************************************************************** -->
 771 <div class="doc_section">
 772   <a name="additionalinfo">Additional Information</a>
 773 </div>
 774 <!-- *********************************************************************** -->
 775
 776 <div class="doc_text">
 777
 778 <p>A wide variety of additional information is available on the <a
 779 href="http://llvm.org">LLVM web page</a>, in particular in the <a
 780 href="http://llvm.org/docs/">documentation</a> section.  The web page also
 781 contains versions of the API documentation which is up-to-date with the
 782 Subversion version of the source code.
 783 You can access versions of these documents specific to this release by going
 784 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
 785
 786 <p>If you have any questions or comments about LLVM, please feel free to contact
 787 us via the <a href="http://llvm.org/docs/#maillist"> mailing
 788 lists</a>.</p>
 789
 790 </div>
 791
 792 <!-- *********************************************************************** -->
 793
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