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12 <div class="doc_title">LLVM 2.3 Release Notes</div>
15 <li><a href="#intro">Introduction</a></li>
16 <li><a href="#whatsnew">What's New?</a></li>
17 <li><a href="GettingStarted.html">Installation Instructions</a></li>
18 <li><a href="#portability">Portability and Supported Platforms</a></li>
19 <li><a href="#knownproblems">Known Problems</a>
20 <li><a href="#additionalinfo">Additional Information</a></li>
23 <div class="doc_author">
24 <p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
27 <!-- Done through Week-of-Mon-20080324.txt -->
29 <!-- *********************************************************************** -->
30 <div class="doc_section">
31 <a name="intro">Introduction</a>
33 <!-- *********************************************************************** -->
35 <div class="doc_text">
37 <p>This document contains the release notes for the LLVM compiler
38 infrastructure, release 2.3. Here we describe the status of LLVM, including
39 major improvements from the previous release and any known problems. All LLVM
40 releases may be downloaded from the <a href="http://llvm.org/releases/">LLVM
41 releases web site</a>.</p>
43 <p>For more information about LLVM, including information about the latest
44 release, please check out the <a href="http://llvm.org/">main LLVM
45 web site</a>. If you have questions or comments, the <a
46 href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
47 list</a> is a good place to send them.</p>
49 <p>Note that if you are reading this file from a Subversion checkout or the
50 main LLVM web page, this document applies to the <i>next</i> release, not the
51 current one. To see the release notes for a specific releases, please see the
52 <a href="http://llvm.org/releases/">releases page</a>.</p>
56 <!-- *********************************************************************** -->
57 <div class="doc_section">
58 <a name="whatsnew">What's New?</a>
60 <!-- *********************************************************************** -->
62 <div class="doc_text">
64 <p>This is the fourteenth public release of the LLVM Compiler Infrastructure.
65 It includes a large number of features and refinements from LLVM 2.2.</p>
69 <!-- Unfinished features in 2.3:
75 <!--=========================================================================-->
76 <div class="doc_subsection">
77 <a name="changes">Major Changes in LLVM 2.3</a>
80 <div class="doc_text">
82 <p>LLVM 2.2 was the last LLVM release to support llvm-gcc 4.0 and llvm-upgrade.
83 llvm-gcc 4.0 has been replaced with llvm-gcc 4.2. llvm-upgrade was useful for
84 upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a previous
85 LLVM release to do this. One nice impact of this is that the LLVM regression
86 test suite no longer depends on llvm-upgrade, which makes it run faster.</p>
88 <p>LLVM API Changes:</p>
91 <li>Several core LLVM IR classes have migrated to use 'FOOCLASS::Create(...)'
92 instead of 'new FOOCLASS(...)' (e.g. where FOOCLASS=BasicBlock). We hope to
93 standardize on FOOCLASS::Create for all IR classes in the future, but not
94 all of them have been moved over yet.</li>
95 <li>LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to
97 <li>MRegisterInfo was renamed to TargetRegisterInfo.</li>
98 <li>The MappedFile class is gone, please use MemoryBuffer instead.</li>
99 <li>The '-enable-eh' flag to llc has been removed. Now code should encode
100 whether it is safe to not generate unwind information for a function by
101 tagging the Function object with the 'nounwind' attribute.</li>
106 <!--=========================================================================-->
107 <div class="doc_subsection">
108 <a name="majorfeatures">Major New Features</a>
111 <div class="doc_text">
113 <p>LLVM 2.3 includes several major new capabilities:</p>
116 <li>Multiple Return Value Support.</li>
119 <li><p>LLVM 2.3 includes a complete reimplementation of the "llvmc" tool. It is
120 designed to overcome several problems with the original llvmc and to provide a
121 superset of the features of the 'gcc' driver.</p>
123 <p>The main features of llvmc2 is:</p>
126 <li>Extended handling of command line options and smart rules for
127 dispatching them to different tools.</li>
128 <li>Flexible (and extensible) rules for defining different tools.</li>
129 <li>The different intermediate steps performed by tools are represented
130 as edges in the abstract graph.</li>
131 <li>The 'language' for driver behavior definition is tablegen and thus
132 it's relatively easy to add new features.</li>
133 <li>The definition of driver is transformed into set of C++ classes, thus
134 no runtime interpretation is needed.</li>
139 <li>Reimplemented <a href="LinkTimeOptimization.html">LTO interface</a> in
143 <li>Kaleidoscope tutorial in Ocaml.</li>
150 <!--=========================================================================-->
151 <div class="doc_subsection">
152 <a name="frontends">llvm-gcc 4.2 Improvements and Clang</a>
155 <div class="doc_text">
157 <p>LLVM 2.3 fully supports the llvm-gcc 4.2 front-end.</p>
159 <p>llvm-gcc 4.2 includes numerous fixes to better support the Objective-C
160 front-end. Objective-C now works very well on Mac OS/X.</p>
162 <p>llvm-gcc 4.2 includes many other fixes which improve conformance with the
163 relevant parts of the GCC testsuite.</p>
165 <p>The <a href="http://clang.llvm.org/">clang project</a> is an effort to build
166 a set of new 'llvm native' front-end technologies for the LLVM optimizer
167 and code generator. Currently, its C and Objective-C support is maturing
168 nicely, and it has advanced source-to-source analysis and transformation
169 capabilities. If you are interested in building source-level tools for C and
170 Objective-C (and eventually C++), you should take a look. However, note that
171 clang is not an official part of the LLVM 2.3 release. If you are interested in
172 this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
177 <!--=========================================================================-->
178 <div class="doc_subsection">
179 <a name="coreimprovements">LLVM Core Improvements</a>
182 <div class="doc_text">
183 <p>New features include:
189 Atomic operation support, Alpha, X86, X86-64, PowerPC. "__sync_synchronize",
190 "__sync_val_compare_and_swap", etc
193 <li>The C and Ocaml bindings have received additional improvements. The
194 bindings now cover pass managers, several transformation passes, iteration
195 over the LLVM IR, target data, and parameter attribute lists.</li>
200 <!--=========================================================================-->
201 <div class="doc_subsection">
202 <a name="optimizer">Optimizer Improvements</a>
205 <div class="doc_text">
207 <p>In addition to a huge array of bug fixes and minor performance tweaks, the
208 LLVM 2.3 optimizers support a few major enhancements:</p>
212 <li>Loop index set splitting on by default.<p>
213 This transformation hoists conditions from loop bodies and reduces loop's
214 iteration space to improve performance. For example, <p>
216 for (i = LB; i < UB; ++i)
223 for (i = LB; i < NUB; ++i)
228 <li>LLVM includes a new <tt>memcpy</tt> optimization pass removes
229 dead <tt>memcpy</tt> calls, unneeded copies of aggregates, and performs
230 return slot optimization. The LLVM optimizer now notices long sequences of
231 consecutive stores and merges them into <tt>memcpy</tt>'s where profitable.</li>
233 <li>Alignment detection for vector memory references and for <tt>memcpy</tt> and
234 <tt>memset</tt> is now more aggressive.</li>
236 <li>The aggressive dead code elimination (ADCE) optimization has been rewritten
237 to make it both faster and safer in the presence of code containing infinite
238 loops. Some of its prior functionality has been factored out into the loop
239 deletion pass, which <em>is</em> safe for infinite loops.</li>
241 <li>Several optimizations have been sped up, leading to faster code generation
242 with the same code quality.</li>
244 <li>The 'SimplifyLibCalls' pass, which optimizes calls to libc and libm
245 functions for C-based languages, has been rewritten to be a FunctionPass
246 instead a ModulePass. This allows it to be run more often and to be
247 included at -O1 in llvm-gcc. It was also extended to include more
248 optimizations and several corner case bugs were fixed.</li>
250 <li>LLVM now includes a simple 'Jump Threading' pass, which attempts to simplify
251 conditional branches using information about predecessor blocks, simplifying
252 the control flow graph. This pass is pretty basic at this point, but catches
253 some important cases and provides a foundation to build on.</li>
258 <!--=========================================================================-->
259 <div class="doc_subsection">
260 <a name="codegen">Code Generator Improvements</a>
263 <div class="doc_text">
265 <p>We put a significant amount of work into the code generator infrastructure,
266 which allows us to implement more aggressive algorithms and make it run
270 <li>MemOperand in the code generator: describe me!.</li>
272 <li>The target-independent code generator infrastructure now uses LLVM's APInt
273 class to handle integer values, which allows it to support integer types
274 larger than 64 bits. Note that support for such types is also dependent on
275 target-specific support. Use of APInt is also a step toward support for
276 non-power-of-2 integer sizes.</li>
278 <li>Several compile time speedups for code with large basic blocks.</li>
280 <li>Several improvements which make llc's <tt>--view-sunit-dags</tt>
281 visualization of scheduling dependency graphs easier to understand.</li>
283 <li>The code generator allows targets to write patterns that generate subreg
284 references directly in .td files now.</li>
286 <li><tt>memcpy</tt> lowering in the backend is more aggressive, particularly for
287 <tt>memcpy</tt> calls introduced by the code generator when handling
288 pass-by-value structure argument copies.</li>
294 <!--=========================================================================-->
295 <div class="doc_subsection">
296 <a name="x86specific">X86/X86-64 Specific Improvements</a>
299 <div class="doc_text">
300 <p>New target-specific features include:
304 <li>llvm-gcc's X86-64 ABI conformance is far improved, particularly in the
305 area of passing and returning structures by value. llvm-gcc compiled code
306 now interoperates very well on X86-64 systems with other compilers.</li>
308 <li>Support for Win64 was added. This includes code generation itself, JIT
309 support and necessary changes to llvm-gcc.</li>
311 <li>The LLVM X86 backend now supports the support SSE 4.1 instruction set, and
312 the llvm-gcc 4.2 front-end supports the SSE 4.1 compiler builtins. Various
313 generic vector operations (insert/extract/shuffle) are much more efficient
314 when SSE 4.1 is enabled. The JIT automatically takes advantage of these
315 instructions, but llvm-gcc must be explicitly told to use them, e.g. with
316 <tt>-march=penryn</tt>.</li>
318 <li>The X86 backend now does a number of optimizations that aim to avoid
319 converting numbers back and forth from SSE registers to the X87 floating
322 <li>The X86 backend supports stack realignment, which is particularly useful for
323 vector code on OS's without 16-byte aligned stacks.</li>
325 <li>The X86 backend now supports the "sseregparm" options in GCC, which allow
326 functions to be tagged as passing floating point values in SSE
329 <li>Trampolines (taking the address of a nested function) now work on
332 <li><tt>__builtin_prefetch</tt> is now compiled into the appropriate prefetch
333 instructions instead of being ignored.</li>
335 <li>128-bit integers are now supported on X86-64 targets.</li>
337 <li>The register allocator can now rematerialize PIC-base computations.</li>
343 <!--=========================================================================-->
344 <div class="doc_subsection">
345 <a name="targetspecific">Other Target Specific Improvements</a>
348 <div class="doc_text">
349 <p>New target-specific features include:
353 <li>The LLVM C backend now supports vector code.</li>
362 <!--=========================================================================-->
363 <div class="doc_subsection">
364 <a name="otherimprovements">Other Improvements</a>
367 <div class="doc_text">
368 <p>New features include:
372 <li>LLVM now builds with GCC 4.3.</li>
373 <li><tt>llvm2cpp</tt> tool has been folded into llc, use
374 <tt>llc -march=cpp</tt></li>
379 <!-- *********************************************************************** -->
380 <div class="doc_section">
381 <a name="portability">Portability and Supported Platforms</a>
383 <!-- *********************************************************************** -->
385 <div class="doc_text">
387 <p>LLVM is known to work on the following platforms:</p>
390 <li>Intel and AMD machines (IA32) running Red Hat Linux, Fedora Core and FreeBSD
391 (and probably other unix-like systems).</li>
392 <li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit and
394 <li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
395 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
396 support is available for native builds with Visual C++).</li>
397 <li>Sun UltraSPARC workstations running Solaris 10.</li>
398 <li>Alpha-based machines running Debian GNU/Linux.</li>
399 <li>Itanium-based (IA64) machines running Linux and HP-UX.</li>
402 <p>The core LLVM infrastructure uses GNU autoconf to adapt itself
403 to the machine and operating system on which it is built. However, minor
404 porting may be required to get LLVM to work on new platforms. We welcome your
405 portability patches and reports of successful builds or error messages.</p>
409 <!-- *********************************************************************** -->
410 <div class="doc_section">
411 <a name="knownproblems">Known Problems</a>
413 <!-- *********************************************************************** -->
415 <div class="doc_text">
417 <p>This section contains all known problems with the LLVM system, listed by
418 component. As new problems are discovered, they will be added to these
419 sections. If you run into a problem, please check the <a
420 href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
421 there isn't already one.</p>
425 <!-- ======================================================================= -->
426 <div class="doc_subsection">
427 <a name="experimental">Experimental features included with this release</a>
430 <div class="doc_text">
432 <p>The following components of this LLVM release are either untested, known to
433 be broken or unreliable, or are in early development. These components should
434 not be relied on, and bugs should not be filed against them, but they may be
435 useful to some people. In particular, if you would like to work on one of these
436 components, please contact us on the <a
437 href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
440 <li>The MSIL, IA64, Alpha, SPU, and MIPS backends are experimental.</li>
441 <li>The llc "<tt>-filetype=asm</tt>" (the default) is the only supported
442 value for this option.</li>
447 <!-- ======================================================================= -->
448 <div class="doc_subsection">
449 <a name="x86-be">Known problems with the X86 back-end</a>
452 <div class="doc_text">
455 <li>The X86 backend does not yet support
456 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
457 floating point stack</a>. It supports the 'f' and 't' constraints, but not
459 <li>The X86 backend generates inefficient floating point code when configured to
460 generate code for systems that don't have SSE2.</li>
461 <li>Win64 code generation wasn't widely tested. Everything should work, but we
462 expect small issues to happen. Also, llvm-gcc cannot build mingw64 runtime
464 to <a href="http://llvm.org/PR2255">several</a>
465 <a href="http://llvm.org/PR2257">bugs</a> in FP stackifier
470 <!-- ======================================================================= -->
471 <div class="doc_subsection">
472 <a name="ppc-be">Known problems with the PowerPC back-end</a>
475 <div class="doc_text">
478 <li>The Linux PPC32/ABI support needs testing for the interpreter and static
479 compilation, and lacks support for debug information.</li>
484 <!-- ======================================================================= -->
485 <div class="doc_subsection">
486 <a name="arm-be">Known problems with the ARM back-end</a>
489 <div class="doc_text">
492 <li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
493 processors, thumb programs can crash or produce wrong
494 results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
495 <li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
497 <li>There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly execute
498 programs compiled with LLVM. Please use more recent versions of QEMU.</li>
503 <!-- ======================================================================= -->
504 <div class="doc_subsection">
505 <a name="sparc-be">Known problems with the SPARC back-end</a>
508 <div class="doc_text">
511 <li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
512 support the 64-bit SPARC ABI (-m64).</li>
517 <!-- ======================================================================= -->
518 <div class="doc_subsection">
519 <a name="alpha-be">Known problems with the Alpha back-end</a>
522 <div class="doc_text">
526 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
527 appropriate nops inserted to ensure restartability.</li>
532 <!-- ======================================================================= -->
533 <div class="doc_subsection">
534 <a name="ia64-be">Known problems with the IA64 back-end</a>
537 <div class="doc_text">
541 <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
542 made where the argument is not 16-byte aligned, as required on IA64. (Strictly
543 speaking this is not a bug in the IA64 back-end; it will also be encountered
544 when building C++ programs using the C back-end.)</li>
546 <li>The C++ front-end does not use <a href="http://llvm.org/PR406">IA64
547 ABI compliant layout of v-tables</a>. In particular, it just stores function
548 pointers instead of function descriptors in the vtable. This bug prevents
549 mixing C++ code compiled with LLVM with C++ objects compiled by other C++
552 <li>There are a few ABI violations which will lead to problems when mixing LLVM
553 output with code built with other compilers, particularly for floating-point
556 <li>Defining vararg functions is not supported (but calling them is OK).</li>
558 <li>The Itanium backend has bitrotted somewhat.</li>
563 <!-- ======================================================================= -->
564 <div class="doc_subsection">
565 <a name="c-be">Known problems with the C back-end</a>
568 <div class="doc_text">
571 <li><a href="http://llvm.org/PR802">The C backend has only basic support for
572 inline assembly code</a>.</li>
573 <li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
574 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
575 C++ code compiled with llc or native compilers.</li>
576 <li>The C backend does not support all exception handling constructs.</li>
582 <!-- ======================================================================= -->
583 <div class="doc_subsection">
584 <a name="c-fe">Known problems with the llvm-gcc C front-end</a>
587 <!-- _______________________________________________________________________ -->
588 <div class="doc_subsubsection">Bugs</div>
590 <div class="doc_text">
592 <p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
593 Optimization</a> on most platforms "out-of-the-box". Please inquire on the
594 llvmdev mailing list if you are interested.</p>
596 <p>The only major language feature of GCC not supported by llvm-gcc is
597 the <tt>__builtin_apply</tt> family of builtins. However, some extensions
598 are only supported on some targets. For example, trampolines are only
599 supported on some targets (these are used when you take the address of a
600 nested function).</p>
602 <p>If you run into GCC extensions which are not supported, please let us know.
607 <!-- ======================================================================= -->
608 <div class="doc_subsection">
609 <a name="c++-fe">Known problems with the llvm-gcc C++ front-end</a>
612 <div class="doc_text">
614 <p>The C++ front-end is considered to be fully
615 tested and works for a number of non-trivial programs, including LLVM
616 itself, Qt, Mozilla, etc.</p>
619 <li>Exception handling works well on the X86 and PowerPC targets, including
620 X86-64 darwin. This works when linking to a libstdc++ compiled by GCC. It is
621 supported on X86-64 linux, but that is disabled by default in this release.</li>
627 <!-- ======================================================================= -->
628 <div class="doc_subsection">
629 <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>
632 <div class="doc_text">
633 The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature
634 technology and problems should be expected.
636 <li>The Ada front-end currently only builds on X86-32. This is mainly due
637 to lack of trampoline support (pointers to nested functions) on other platforms,
638 however it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
639 which does support trampolines.</li>
640 <li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
641 Workaround: configure with --disable-bootstrap.</li>
642 <li>The c380004 and <a href="http://llvm.org/PR2010">c393010</a> ACATS tests
643 fail (c380004 also fails with gcc-4.2 mainline). When built at -O3, the
644 <a href="http://llvm.org/PR2421">cxg2021</a> ACATS test also fails.</li>
645 <li>Some gcc specific Ada tests continue to crash the compiler. The testsuite
646 reports most tests as having failed even though they pass.</li>
647 <li>The -E binder option (exception backtraces)
648 <a href="http://llvm.org/PR1982">does not work</a> and will result in programs
649 crashing if an exception is raised. Workaround: do not use -E.</li>
650 <li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
651 or finish at a non-byte offset</a> in a record. Workaround: do not pack records
652 or use representation clauses that result in a field of a non-discrete type
653 starting or finishing in the middle of a byte.</li>
654 <li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers 'main'
655 as generated by the Ada binder to be invalid</a>.
656 Workaround: hand edit the file to use pointers for <tt>argv</tt> and <tt>envp</tt> rather than
658 <li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is ignored</a>.</li>
662 <!-- *********************************************************************** -->
663 <div class="doc_section">
664 <a name="additionalinfo">Additional Information</a>
666 <!-- *********************************************************************** -->
668 <div class="doc_text">
670 <p>A wide variety of additional information is available on the <a
671 href="http://llvm.org">LLVM web page</a>, in particular in the <a
672 href="http://llvm.org/docs/">documentation</a> section. The web page also
673 contains versions of the API documentation which is up-to-date with the
674 Subversion version of the source code.
675 You can access versions of these documents specific to this release by going
676 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
678 <p>If you have any questions or comments about LLVM, please feel free to contact
679 us via the <a href="http://llvm.org/docs/#maillist"> mailing
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