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11 <div class="doc_title">LLVM 2.0 Release Notes</div>
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>
22 <div class="doc_author">
23 <p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
26 <!-- *********************************************************************** -->
27 <div class="doc_section">
28 <a name="intro">Introduction</a>
30 <!-- *********************************************************************** -->
32 <div class="doc_text">
34 <p>This document contains the release notes for the LLVM compiler
35 infrastructure, release 2.0. Here we describe the status of LLVM, including any
36 known problems and major improvements from the previous release. All LLVM
37 releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
38 releases web site</a>.
40 <p>For more information about LLVM, including information about the latest
41 release, please check out the <a href="http://llvm.org/">main LLVM
42 web site</a>. If you have questions or comments, the <a
43 href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
44 list</a> is a good place to send them.</p>
46 <p>Note that if you are reading this file from CVS or the main LLVM web page,
47 this document applies to the <i>next</i> release, not the current one. To see
48 the release notes for the current or previous releases, see the <a
49 href="http://llvm.org/releases/">releases page</a>.</p>
53 <!-- *********************************************************************** -->
54 <div class="doc_section">
55 <a name="whatsnew">What's New?</a>
57 <!-- *********************************************************************** -->
59 <div class="doc_text">
61 <p>This is the eleventh public release of the LLVM Compiler Infrastructure.
62 Being the first major release since 1.0, this release is different in several
63 ways from our previous releases:</p>
66 <li>We took this as an opportunity to
67 break backwards compatibility with the LLVM 1.x bytecode and .ll file format.
68 If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we
69 recommend the use of the stand alone <a href="#llvm-upgrade">llvm-upgrade</a>
70 tool (which is included with 2.0). We intend to keep compatibility with .ll
71 and .bc formats within the 2.x release series, like we did within the 1.x
73 <li>There are several significant change to the LLVM IR and internal APIs, such
74 as a major overhaul of the type system, the completely new bitcode file
76 <li>We designed the release around a 6 month release cycle instead of the usual
77 3-month cycle. This gave us extra time to develop and test some of the
78 more invasive features in this release.</li>
79 <li>LLVM 2.0 no longer supports the llvm-gcc3 front-end.</li>
82 <p>Note that while this is a major version bump, this release has been
83 extensively tested on a wide range of software. It is easy to say that this
84 is our best release yet, in terms of both features and correctness.</p>
88 <!--=========================================================================-->
89 <div class="doc_subsection">
90 <a name="newfeatures">New Features in LLVM 2.0</a>
93 <!--_________________________________________________________________________-->
94 <div class="doc_subsubsection"><a name="majorchanges">Major Changes</a></div>
95 <div class="doc_text">
101 <li>llvm-gcc3 is now officially unsupported. Users are required to
102 upgrade to llvm-gcc4. llvm-gcc4 includes many features over
103 llvm-gcc3, is faster, and is much easier to build.</li>
105 <li>Integer types are now completely signless. This means that we
106 have types like i8/i16/i32 instead of ubyte/sbyte/short/ushort/int
107 etc. LLVM operations that depend on sign have been split up into
108 separate instructions (<a href="http://llvm.org/PR950">PR950</a>).</li>
110 <li>Arbitrary bitwidth integers (e.g. i13, i36, i42, etc) are now
111 supported in the LLVM IR and optimizations. However, neither llvm-gcc nor
112 the native code generators support non-standard width integers
113 (<a href="http://llvm.org/PR1043">PR1043</a>).</li>
115 <li>'type planes' have been removed (<a href="http://llvm.org/PR411">PR411</a>).
116 It is no longer possible to have two values with the same name in the
117 same symbol table. This simplifies LLVM internals, allowing significant
120 <li>Global variables and functions in .ll files are now prefixed with
121 @ instead of % (<a href="http://llvm.org/PR645">PR645</a>).</li>
123 <li>The LLVM 1.x "bytecode" format has been replaced with a
124 completely new binary representation, named 'bitcode'. Because we
125 plan to maintain binary compatibility between LLVM 2.x ".bc" files,
126 this is an important change to get right. Bitcode brings a number of
127 advantages to the LLVM over the old bytecode format. It is denser
128 (files are smaller), more extensible, requires less memory to read,
129 is easier to keep backwards compatible (so LLVM 2.5 will read 2.0 .bc
130 files), and has many other nice features.</li>
132 <li>Support was added for alignment values on load and store
133 instructions (<a href="http://www.llvm.org/PR400">PR400</a>). This
134 allows the IR to express loads that are not
135 sufficiently aligned (e.g. due to pragma packed) or to capture extra
136 alignment information. </li>
138 <li>LLVM now has a new MSIL backend. llc - march=msil will now turn LLVM
139 into MSIL (".net") bytecode. This is still fairly early development
140 with a number of limitations.</li>
142 <li>Support has been added for 'protected visibility' in ELF.</li>
144 <li>Thread Local Storage with the __thread keyword was implemented along
145 with added codegen support for Linux on X86 and ARM.</li>
147 <li>ELF symbol aliases supported has been added.</li>
149 <li>Added support for 'polymorphic intrinsics', allowing things like
150 llvm.ctpop to work on arbitrary width integers.</li>
157 <!--_________________________________________________________________________-->
158 <div class="doc_subsubsection"><a name="llvmgccfeatures">llvm-gcc
159 Improvements</a></div>
160 <div class="doc_text">
161 <p>New features include:
165 <li>Precompiled Headers (PCH) support has been implemented.</li>
167 <li>Support for external weak linkage and hidden visibility has been added.</li>
169 <li>Packed structure types are now supported , which allows LLVM to express
170 unaligned data more naturally.</li>
172 <li>Inline assembly support has been improved and many bugs were fixed.
173 The two large missing features are support for 80-bit floating point stack
174 registers on X86 (<a href="http://llvm.org/PR879">PR879</a>), and support for inline asm in the C backend (<a href="http://llvm.org/PR802">PR802</a>).</li>
176 <li>Ada support, such as nested functions, has been improved.</li>
178 <li>Tracking function parameter/result attributes is now possible.</li>
180 <li>Its is now easier to configure llvm-gcc for linux.</li>
182 <li>Many enhancements have been added, such as improvements to NON_LVALUE_EXPR,
183 arrays with non-zero base, structs with variable sized fields,
184 VIEW_CONVERT_EXPR, CEIL_DIV_EXPR, and many other things.</li>
186 <li>Improved "attribute packed" support in the CFE, and handle many
187 other obscure struct layout cases correctly.</li>
193 <!--_________________________________________________________________________-->
194 <div class="doc_subsubsection"><a name="optimizer">Optimizer
195 Improvements</a></div>
196 <div class="doc_text">
197 <p>New features include:
201 <li>The pass manager has been entirely rewritten, making it significantly
202 smaller, simpler, and more extensible. Support has been added to run
203 FunctionPasses interlaced with CallGraphSCCPasses.</li>
205 <li>The -scalarrepl pass can now promote unions containing FP values into
206 a register, it can also handle unions of vectors of the same size.</li>
208 <li>The predicate simplifier pass has been improved, making it able to do
209 simple value range propagation and eliminate more conditionals.</li>
211 <li>There is a new new LoopPass class. The passmanager has been
212 modified to support it, and all existing loop xforms have been
213 converted to use it. </li>
215 <li>There is a new loop rotation pass, which converts "for loops" into
216 "do/while loops", where the condition is at the bottom of the loop.</li>
218 <li>ModulePasses may now use the result of FunctionPasses.</li>
220 <li>The [Post]DominatorSet classes have been removed from LLVM and clients switched to use the far-more-efficient ETForest class instead. </li>
222 <li>The ImmediateDominator class has also been removed, and clients have been switched to use DominatorTree instead.</li>
228 <!--_________________________________________________________________________-->
229 <div class="doc_subsubsection"><a name="codegen">Code
230 Generator Enhancements</a></div>
232 <div class="doc_text">
234 New features include:
238 <li>Support for Zero-cost DWARF exception handling has been added. It is mostly
239 complete and just in need of continued bug fixes and optimizations at
242 <li>Progress has been made on a direct Mach-o .o file writer. Many small
243 apps work, but it is not quite complete yet.</li>
245 <li>Support was added for software floating point routines.</li>
247 <li>DWARF debug information generation has been improved. LLVM now passes
248 most of the GDB testsuite on MacOS and debug info is more dense.</li>
250 <li>A new register scavenger has been implemented, which is useful for
251 finding free registers after register allocation. This is useful when
252 rewriting frame references on RISC targets, for example.</li>
254 <li>Heuristics have been added to avoid coalescing vregs with very large live
255 ranges to physregs.</li>
257 <li>Support now exists for very simple (but still very useful)
258 rematerialization the register allocator, enough to move
259 instructions like "load immediate" and constant pool loads.</li>
261 <li>Significantly improved 'switch' lowering, improving codegen for
262 sparse switches that have dense subregions, and implemented support
263 for the shift/and trick.</li>
265 <li>The code generator now has more accurate and general hooks for
266 describing addressing modes ("isLegalAddressingMode") to
267 optimizations like loop strength reduction and code sinking.</li>
269 <li>The Loop Strength Reduction pass has been improved, and support added
270 for sinking expressions across blocks to reduce register pressure.</li>
272 <li>Added support for tracking physreg sub-registers and super-registers
273 in the code generator, as well as extensive register
274 allocator changes to track them.</li>
276 <li>There is initial support for virtreg sub-registers
277 (<a href="http://llvm.org/PR1350">PR1350</a>).</li>
281 <p>In addition, the LLVM target description format has itself been extended in
285 <li>Extended TargetData to support better target parameterization in
286 the .ll/.bc files, eliminating the 'pointersize/endianness' attributes
287 in the files (<a href="http://llvm.org/PR761">PR761</a>).</li>
289 <li>TargetData was generalized for finer grained alignment handling,
290 handling of vector alignment, and handling of preferred alignment</li>
292 <li>LLVM now supports describing target calling conventions
293 explicitly in .td files, reducing the amount of C++ code that needs
294 to be written for a port.</li>
300 <!--_________________________________________________________________________-->
301 <div class="doc_subsubsection"><a name="specifictargets">Target-Specific
302 Improvements</a></div>
304 <div class="doc_text">
306 <p>X86-Specific Code Generator Enhancements:
310 <li>The scheduler was improved to better reduce register pressure on
311 X86 and other targets that are register pressure sensitive</li>
312 <li>Linux/x86-64 support has been improved.</li>
313 <li>PIC support for linux/x86 has been added.</li>
314 <li>Support now exists for the GCC regparm attribute, and code in the X86
315 backend to respect it.</li>
316 <li>Various improvements have been made for the X86-64 JIT, allowing it to
317 generate code in the large code model</li>
318 <li>LLVM now supports inline asm with multiple constraint letters per operand
319 (like "ri") which is common in X86 inline asms.</li>
320 <li>Early support has been added for X86 inline asm in the C backend.</li>
321 <li>Added support for the X86 MMX instruction set.</li>
325 <p>ARM-Specific Code Generator Enhancements:
329 <li>Several improvements have been made to the ARM backend, including basic
330 inline asm support, weak linkage support, static ctor/dtor support and
332 <li>There are major enhancements to the ARM backend, including support for ARM
333 v4-v6, vfp support, soft float, pre/postinc support, load/store multiple
334 generation, constant pool entry motion (to support large functions),
335 and enhancements to ARM constant island pass.
337 <li>Added support for Thumb code generation (an ARM subtarget).</li>
338 <li>More aggressive size analysis for ARM inline asm strings was
342 <p>Other Target-Specific Code Generator Enhancements:
346 <li>The PowerPC 64 JIT now supports addressing code loaded above the 2G
349 <li>Improved support for the Linux/ppc ABI and the linux/ppc JIT is fully
350 functional now. llvm-gcc and static compilation are not fully supported
353 <li>Many bugs fixed for PowerPC 64.</li>
355 <li>Support was added for the ARM AAPCS and EABI ABIs and PIC codegen on
358 <li>Several bugs in DWARF debug emission on linux and cygwin/mingw were fixed.
359 Debugging basically works on these targets now.</li>
361 <li>Support has been added for the X86-64 large code model to the JIT,
362 which is useful if JIT'd function bodies are more than 2G away from
363 library functions.</li>
365 <li>Several bugs were fixed for DWARF debug info generation on arm/linux.</li>
372 <!--_________________________________________________________________________-->
373 <div class="doc_subsubsection"><a name="other">Other Improvements</a></div>
374 <div class="doc_text">
376 <p>This release includes many other improvements, including
377 performance work, specifically designed to tune datastructure
378 usage. This makes several critical components faster.</p>
380 <p>More specific changes include:</p>
383 <li>LLVM no longer relies on static destructors to shut itself down. Instead,
384 it lazily initializes itself and shuts down when llvm_shutdown() is
385 explicitly called.</li>
387 <li>LLVM now has significantly fewer static constructors, reducing startup time.
390 <li>Several classes have been refactored to reduce the amount of code that
391 gets linked into apps that use the JIT.</li>
393 <li>Construction of intrinsic function declarations has been simplified.</li>
395 <li>The llvm-upgrade tool now exists. This migrates LLVM 1.9 .ll files to
396 LLVM 2.0 syntax.</li>
398 <li>The gccas/gccld tools have been removed.</li>
400 <li>Support has been added to llvm-test for running on low-memory
401 or slow machines (make SMALL_PROBLEM_SIZE=1).</li>
403 <li>llvm-test is now more portable and should build with MS Visual Studio.</li>
408 <!--_________________________________________________________________________-->
409 <div class="doc_subsubsection"><a name="apichanges">API Changes</a></div>
410 <div class="doc_text">
412 <p>LLVM 2.0 contains a revamp of the type system and several other significant
413 internal changes. If you are programming to the C++ API, be aware of the
414 following major changes:</p>
417 <li>Pass registration is slightly different in LLVM 2.0 (you now needs an
418 intptr_t in your constructor), as explained in the <a
419 href="WritingAnLLVMPass.html#basiccode">Writing an LLVM Pass</a>
422 <li><tt>ConstantBool</tt>, <tt>ConstantIntegral</tt> and <tt>ConstantInt</tt>
423 classes have been merged together, we now just have
424 <tt>ConstantInt</tt>.</li>
426 <li><tt>Type::IntTy</tt>, <tt>Type::UIntTy</tt>, <tt>Type::SByteTy</tt>, ... are
427 replaced by <tt>Type::Int8Ty</tt>, <tt>Type::Int16Ty</tt>, etc. LLVM types
428 have always corresponded to fixed size types
429 (e.g. long was always 64-bits), but the type system no longer includes
430 information about the sign of the type.</li>
432 <li>Several classes (<tt>CallInst</tt>, <tt>GetElementPtrInst</tt>,
433 <tt>ConstantArray</tt>, etc), that once took <tt>std::vector</tt> as
434 arguments now take ranges instead. For example, you can create a
435 <tt>GetElementPtrInst</tt> with code like:
438 Value *Ops[] = { Op1, Op2, Op3 };
439 GEP = new GetElementPtrInst(BasePtr, Ops, 3);
442 This avoids creation of a temporary vector (and a call to malloc/free). If
443 you have an std::vector, use code like this:
445 std::vector<Value*> Ops = ...;
446 GEP = new GetElementPtrInst(BasePtr, &Ops[0], Ops.size());
451 <li>CastInst is now abstract and its functionality is split into several parts,
452 one for each of the <a href="LangRef.html#convertops">new cast
453 instructions</a>.</li>
455 <li><tt>Instruction::getNext()/getPrev()</tt> are now private (along with
456 <tt>BasicBlock::getNext</tt>, etc), for efficiency reasons (they are now no
457 longer just simple pointers). Please use BasicBlock::iterator, etc instead.
460 <li><tt>Module::getNamedFunction()</tt> is now called
461 <tt>Module::getFunction()</tt>.</li>
463 <li><tt>SymbolTable.h</tt> has been split into <tt>ValueSymbolTable.h</tt> and
464 <tt>TypeSymbolTable.h</tt>.</li>
469 <!-- *********************************************************************** -->
470 <div class="doc_section">
471 <a name="portability">Portability and Supported Platforms</a>
473 <!-- *********************************************************************** -->
475 <div class="doc_text">
477 <p>LLVM is known to work on the following platforms:</p>
480 <li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD
481 (and probably other unix-like systems).</li>
482 <li>Intel and AMD machines running on Win32 using MinGW libraries (native)</li>
483 <li>Sun UltraSPARC workstations running Solaris 8.</li>
484 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
485 support is available for native builds with Visual C++).</li>
486 <li>PowerPC and X86-based Mac OS X systems, running 10.2 and above in 32-bit and
488 <li>Alpha-based machines running Debian GNU/Linux.</li>
489 <li>Itanium-based machines running Linux and HP-UX.</li>
492 <p>The core LLVM infrastructure uses
493 <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
494 to the machine and operating system on which it is built. However, minor
495 porting may be required to get LLVM to work on new platforms. We welcome your
496 portability patches and reports of successful builds or error messages.</p>
500 <!-- *********************************************************************** -->
501 <div class="doc_section">
502 <a name="knownproblems">Known Problems</a>
504 <!-- *********************************************************************** -->
506 <div class="doc_text">
508 <p>This section contains all known problems with the LLVM system, listed by
509 component. As new problems are discovered, they will be added to these
510 sections. If you run into a problem, please check the <a
511 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
512 there isn't already one.</p>
516 <!-- ======================================================================= -->
517 <div class="doc_subsection">
518 <a name="experimental">Experimental features included with this release</a>
521 <div class="doc_text">
523 <p>The following components of this LLVM release are either untested, known to
524 be broken or unreliable, or are in early development. These components should
525 not be relied on, and bugs should not be filed against them, but they may be
526 useful to some people. In particular, if you would like to work on one of these
527 components, please contact us on the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
530 <li>The <tt>-cee</tt> pass is known to be buggy, and may be removed in in a
532 <li>C++ EH support</li>
533 <li>The IA64 code generator is experimental.</li>
534 <li>The Alpha JIT is experimental.</li>
535 <li>"<tt>-filetype=asm</tt>" (the default) is the only supported value for the
536 <tt>-filetype</tt> llc option.</li>
541 <!-- ======================================================================= -->
542 <div class="doc_subsection">
543 <a name="x86-be">Known problems with the X86 back-end</a>
546 <div class="doc_text">
549 <li>The X86 backend does not yet support <a href="http://llvm.org/PR879">inline
550 assembly that uses the X86 floating point stack</a>.</li>
555 <!-- ======================================================================= -->
556 <div class="doc_subsection">
557 <a name="ppc-be">Known problems with the PowerPC back-end</a>
560 <div class="doc_text">
563 <li><a href="http://llvm.org/PR642">PowerPC backend does not correctly
564 implement ordered FP comparisons</a>.</li>
565 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
566 compilation, and lacks Dwarf debugging informations.
571 <!-- ======================================================================= -->
572 <div class="doc_subsection">
573 <a name="arm-be">Known problems with the ARM back-end</a>
576 <div class="doc_text">
579 <li>The Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
580 processors, any thumb program compiled with LLVM crashes or produces wrong
581 results. (<a href="http://llvm.org/PR1388">PR1388</a>)</li>
582 <li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
584 <li>QEMU-ARM (<= 0.9.0) wrongly executes programs compiled with LLVM. A non-affected QEMU version must be used or this
585 <a href="http://cvs.savannah.nongnu.org/viewcvs/qemu/target-arm/translate.c?root=qemu&r1=1.46&r2=1.47&makepatch=1&diff_format=h">
586 patch</a> must be applied on QEMU.</li>
591 <!-- ======================================================================= -->
592 <div class="doc_subsection">
593 <a name="sparc-be">Known problems with the SPARC back-end</a>
596 <div class="doc_text">
599 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
600 support the 64-bit SPARC ABI (-m64).</li>
605 <!-- ======================================================================= -->
606 <div class="doc_subsection">
607 <a name="alpha-be">Known problems with the Alpha back-end</a>
610 <div class="doc_text">
614 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
615 appropriate nops inserted to ensure restartability.</li>
620 <!-- ======================================================================= -->
621 <div class="doc_subsection">
622 <a name="ia64-be">Known problems with the IA64 back-end</a>
625 <div class="doc_text">
629 <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
630 made where the argument is not 16-byte aligned, as required on IA64. (Strictly
631 speaking this is not a bug in the IA64 back-end; it will also be encountered
632 when building C++ programs using the C back-end.)</li>
634 <li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
635 ABI compliant layout of v-tables</a>. In particular, it just stores function
636 pointers instead of function descriptors in the vtable. This bug prevents
637 mixing C++ code compiled with LLVM with C++ objects compiled by other C++
640 <li>There are a few ABI violations which will lead to problems when mixing LLVM
641 output with code built with other compilers, particularly for floating-point
644 <li>Defining vararg functions is not supported (but calling them is ok).</li>
646 <li>The Itanium backend has bitrotted somewhat.</li>
651 <!-- ======================================================================= -->
652 <div class="doc_subsection">
653 <a name="c-be">Known problems with the C back-end</a>
656 <div class="doc_text">
659 <li><a href="http://llvm.org/PR802">The C backend does not support inline
660 assembly code</a>.</li>
666 <!-- ======================================================================= -->
667 <div class="doc_subsection">
668 <a name="c-fe">Known problems with the C front-end</a>
671 <!-- _______________________________________________________________________ -->
672 <div class="doc_subsubsection">Bugs</div>
674 <div class="doc_text">
676 <p>llvm-gcc4 does not currently support <a href="http://llvm.org/PR869">Link-Time
677 Optimization</a> on most platforms "out-of-the-box". Please inquire on the
678 llvmdev mailing list if you are interested.</p>
682 <!-- _______________________________________________________________________ -->
683 <div class="doc_subsubsection">
687 <div class="doc_text">
690 <li><p>"long double" is silently transformed by the front-end into "double". There
691 is no support for floating point data types of any size other than 32 and 64
694 <li><p>llvm-gcc does <b>not</b> support <tt>__builtin_apply</tt> yet.
695 See <a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</p>
698 <li><p>llvm-gcc <b>partially</b> supports tthese GCC extensions:</p>
700 <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>
701 Nested functions are supported, but llvm-gcc does not support non-local
702 gotos or taking the address of a nested function.</li>
704 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
706 Declaring that functions have no side effects or that they can never
709 <b>Supported:</b> <tt>alias</tt>, <tt>always_inline</tt>, <tt>cdecl</tt>,
710 <tt>constructor</tt>, <tt>destructor</tt>,
711 <tt>deprecated</tt>, <tt>fastcall</tt>, <tt>format</tt>,
712 <tt>format_arg</tt>, <tt>non_null</tt>, <tt>noreturn</tt>, <tt>regparm</tt>
713 <tt>section</tt>, <tt>stdcall</tt>, <tt>unused</tt>, <tt>used</tt>,
714 <tt>visibility</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
716 <b>Ignored:</b> <tt>noinline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
717 <tt>malloc</tt>, <tt>no_instrument_function</tt></li>
721 <li><p>llvm-gcc supports the vast majority of GCC extensions, including:</p>
724 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
725 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
726 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
727 Other built-in functions.</li>
728 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
729 Specifying attributes of variables.</li>
730 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.</li>
731 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
732 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
733 Arrays whose length is computed at run time.</li>
734 <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>
735 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
736 <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>
737 <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>
738 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
739 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
740 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
741 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
742 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
743 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
744 <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>
745 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
746 <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>
747 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
748 <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>
749 <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>
750 <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>
751 <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>
752 <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>
753 <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>
754 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
755 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
756 or arrays as values.</li>
757 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
758 <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>
759 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
760 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
761 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
762 <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>
763 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
764 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character <ESC>.</li>
765 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
766 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
767 <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>
768 <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>
769 <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>
770 <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>
771 <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>
772 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
777 <p>If you run into GCC extensions which have not been included in any of these
778 lists, please let us know (also including whether or not they work).</p>
782 <!-- ======================================================================= -->
783 <div class="doc_subsection">
784 <a name="c++-fe">Known problems with the C++ front-end</a>
787 <div class="doc_text">
789 <p>The C++ front-end is considered to be fully
790 tested and works for a number of non-trivial programs, including LLVM
791 itself, Qt, Mozilla, etc.</p>
794 <li>llvm-gcc4 only has partial support for <a href="http://llvm.org/PR870">C++
795 Exception Handling</a>, and it is not enabled by default.</li>
799 <li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
800 performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
801 function and in the <tt>setjmp</tt> receiver function may not be run.
802 Objects in intervening stack frames will be destroyed, however (which is
803 better than most compilers).</li>
805 <li>The LLVM C++ front-end follows the <a
806 href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
807 This document, which is not Itanium specific, specifies a standard for name
808 mangling, class layout, v-table layout, RTTI formats, and other C++
809 representation issues. Because we use this API, code generated by the LLVM
810 compilers should be binary compatible with machine code generated by other
811 Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
812 <i>However</i>, the exception handling mechanism used by llvm-gcc3 is very
813 different from the model used in the Itanium ABI, so <b>exceptions will not
814 interact correctly</b>. </li>
822 <!-- *********************************************************************** -->
823 <div class="doc_section">
824 <a name="additionalinfo">Additional Information</a>
826 <!-- *********************************************************************** -->
828 <div class="doc_text">
830 <p>A wide variety of additional information is available on the <a
831 href="http://llvm.org">LLVM web page</a>, in particular in the <a
832 href="http://llvm.org/docs/">documentation</a> section. The web page also
833 contains versions of the API documentation which is up-to-date with the CVS
834 version of the source code.
835 You can access versions of these documents specific to this release by going
836 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
838 <p>If you have any questions or comments about LLVM, please feel free to contact
839 us via the <a href="http://llvm.org/docs/#maillist"> mailing
844 <!-- *********************************************************************** -->
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