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11 <div class="doc_title">LLVM 1.5 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.cs.uiuc.edu">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 1.5. Here we describe the status of LLVM, including any
36 known problems and major improvements from the previous release. The most
37 up-to-date version of this document can be found on the <a
38 href="http://llvm.cs.uiuc.edu/releases/1.5/">LLVM 1.5 web site</a>. If you are
39 not reading this on the LLVM web pages, you should probably go there because
40 this document may be updated after the release.</p>
42 <p>For more information about LLVM, including information about the latest
43 release, please check out the <a href="http://llvm.cs.uiuc.edu">main LLVM
44 web site</a>. If you have questions or comments, the <a
45 href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing
46 list</a> is a good place to send them.</p>
48 <p>Note that if you are reading this file from CVS or the main LLVM web page,
49 this document applies to the <i>next</i> release, not the current one. To see
50 the release notes for the current or previous releases, see the <a
51 href="http://llvm.cs.uiuc.edu/releases/">releases page</a>.</p>
55 <!-- *********************************************************************** -->
56 <div class="doc_section">
57 <a name="whatsnew">What's New?</a>
59 <!-- *********************************************************************** -->
61 <div class="doc_text">
63 <p>This is the sixth public release of the LLVM Compiler Infrastructure.</p>
65 <p>LLVM 1.5 is known to correctly compile a wide range of C and C++ programs,
66 includes bug fixes for those problems found since the 1.4 release, and includes
67 a large number of new features and enhancements, described below.</p>
71 <!--=========================================================================-->
72 <div class="doc_subsection">
73 <a name="newfeatures">New Features in LLVM 1.5</a>
76 <!--_________________________________________________________________________-->
77 <div class="doc_subsubsection"><a name="newcg">New Native Code
80 <div class="doc_text">
82 This release includes new native code generators for <a
83 href="#alpha-be">Alpha</a>, <a href="#ia64-be">IA-64</a>, and <a
84 href="#sparcv8">SPARC-V8</a> (32-bit SPARC). These code generators are still
85 beta quality, but are progressing rapidly. The Alpha backend is implemented
86 with an eye towards being compatible with the widely used SimpleScalar
91 <!--_________________________________________________________________________-->
92 <div class="doc_subsubsection"><a name="selectiondag">New Instruction
93 Selector Framework</a></div>
95 <div class="doc_text">
96 <p>This release includes a <a href="CodeGenerator.html#instselect">new framework
97 for building instruction selectors</a>, which has long been the hardest part of
98 building a new LLVM target. This framework handles a lot of the mundane (but
99 easy to get wrong) details of writing the instruction selector, such as
100 generating efficient code for <a
101 href="LangRef.html#i_getelementptr">getelementptr</a> instructions, promoting
102 small integer types to larger types (e.g. for RISC targets with one size of
103 integer registers), expanding 64-bit integer operations for 32-bit targets, etc.
104 Currently, the X86, PowerPC, Alpha, and IA-64 backends use this framework. The
105 SPARC backends will be migrated when time permits.
109 <!--_________________________________________________________________________-->
110 <div class="doc_subsubsection"><a name="customccs">New Support for Per-Function
111 Calling Conventions</a></div>
113 <div class="doc_text">
114 <p>LLVM 1.5 adds supports for <a href="LangRef.html#callingconv">per-function
115 calling conventions</a>. Traditionally, the LLVM code generators match the
116 native C calling conventions for a target. This is important for compatibility,
117 but is not very flexible. This release allows custom calling conventions to be
118 established for functions, and defines three target-independent conventions (<a
119 href="LangRef.html#callingconv">C call, fast call, and cold call</a>) which may
120 be supported by code generators. When possible, the LLVM optimizer promotes C
121 functions to use the "fastcc" convention, allowing the use of more efficient
122 calling sequences (e.g., parameters are passed in registers in the X86 target).
125 <p>Targets may now also define target-specific calling conventions, allowing
126 LLVM to fully support calling convention altering options (e.g. GCC's
127 <tt>-mregparm</tt> flag) and well-defined target conventions (e.g. stdcall and
128 fastcall on X86).</p>
131 <!--_________________________________________________________________________-->
132 <div class="doc_subsubsection"><a name="tailcalls">New Support for
133 Proper Tail Calls</a></div>
135 <div class="doc_text">
136 <p>The release now includes support for <a
137 href="http://doi.acm.org/10.1145/277650.277719">proper tail calls</a>, as
138 required to implement languages like Scheme. Tail calls make use of two
139 features: custom calling conventions (described above), which allow the code
140 generator to use a convention where the caller deallocates its stack before it
141 returns. The second feature is a flag on the <a href="LangRef.html#i_call">call
142 instruction</a>, which indicates that the callee does not access the caller's
143 stack frame (indicating that it is acceptable to deallocate the caller stack
144 before invoking the callee). LLVM proper tail calls run on the system stack (as
145 do normal calls), supports indirect tail calls, tail calls with arbitrary
146 numbers of arguments, tail calls where the callee requires more argument space
147 than the caller, etc. The only case not supported are varargs calls, but that
148 could be added if desired.
151 <p>In order for a front-end to get a guaranteed tail call, it must mark
152 functions as "fastcc", mark calls with the 'tail' marker, and follow the call
153 with a return of the called value (or void). The optimizer and code generator
154 attempt to handle more general cases, but the simple case will always work if
155 the code generator supports tail calls. Here is an example:</p>
158 fastcc int %bar(int %X, int(double, int)* %FP) { ;<i> fastcc</i>
159 %Y = tail call fastcc int %FP(double 0.0, int %X) ;<i> tail, fastcc</i>
164 <p>In LLVM 1.5, the X86 code generator is the only target that has been enhanced
165 to support proper tail calls (other targets will be enhanced in future).
166 Further, because this support was added very close to the release, it is
167 disabled by default. Pass <tt>-enable-x86-fastcc</tt> to llc to enable it (this
168 will be enabled by default in the next release). The example above compiles to:
173 sub ESP, 8 # Callee uses more space than the caller
174 mov ECX, DWORD PTR [ESP + 8] # Get the old return address
175 mov DWORD PTR [ESP + 4], 0 # First half of 0.0
176 mov DWORD PTR [ESP + 8], 0 # Second half of 0.0
177 mov DWORD PTR [ESP], ECX # Put the return address where it belongs
178 jmp EDX # Tail call "FP"
182 With fastcc on X86, the first two integer arguments are passed in EAX/EDX, the
183 callee pops its arguments off the stack, and the argument area is always a
184 multiple of 8 bytes in size.
189 <!--_________________________________________________________________________-->
190 <div class="doc_subsubsection">Other New Features</div>
192 <div class="doc_text">
194 <li>LLVM now includes an <a href="http://llvm.cs.uiuc.edu/PR415">
195 Interprocedural Sparse Conditional Constant Propagation</a> pass, named
196 -ipsccp, which is run by default at link-time.</li>
197 <li>LLVM 1.5 is now about 15% faster than LLVM 1.4 and its core data
198 structures use about 30% less memory.</li>
199 <li>Support for Microsoft Visual Studio is improved, and <a
200 href="GettingStartedVS.html">now documented</a>. Most LLVM tools build
201 natively with Visual C++ now.</li>
202 <li><a href="GettingStarted.html#config">Configuring LLVM to build a subset
203 of the available targets</a> is now implemented, via the
204 <tt>--enable-targets=</tt> option.</li>
205 <li>LLVM can now create native shared libraries with '<tt>llvm-gcc ...
206 -shared -Wl,-native</tt>' (or with <tt>-Wl,-native-cbe</tt>).</li>
207 <li>LLVM now supports a new "<a href="LangRef.html#i_prefetch">llvm.prefetch
208 </a>" intrinsic, and llvm-gcc now supports __builtin_prefetch.
209 <li>LLVM now supports intrinsics for <a href="LangRef.html#int_count">bit
210 counting</a> and llvm-gcc now implements the GCC
211 <tt>__builtin_popcount</tt>, <tt>__builtin_ctz</tt>, and
212 <tt>__builtin_clz</tt> builtins.</li>
213 <li>LLVM now mostly builds on HP-UX with the HP aCC Compiler.</li>
214 <li>The LLVM X86 backend can now emit Cygwin-compatible .s files.</li>
215 <li>LLVM now includes workarounds in the code generator generator which
216 reduces the likelyhood of <a href="http://llvm.cs.uiuc.edu/PR448">GCC
217 hitting swap during optimized builds</a>.</li>
218 <li>The <a href="http://llvm.cs.uiuc.edu/ProjectsWithLLVM/#llvmtv">LLVM
219 Transformation Visualizer</a> (llvm-tv) project has been updated to
220 work with LLVM CVS.</li>
221 <li>Nightly tester output is now archived on the <a
222 href="http://mail.cs.uiuc.edu/pipermail/llvm-testresults/">
223 llvm-testresults</a> mailing list.</li>
228 <!--=========================================================================-->
229 <div class="doc_subsection">
230 <a name="codequality">Code Quality Improvements in LLVM 1.5</a>
233 <div class="doc_text">
235 <li>The new -simplify-libcalls pass improves code generated for well-known
236 library calls. The pass optimizes calls to many of the string, memory, and
237 standard I/O functions (e.g. replace the calls with simpler/faster calls) when
238 possible, given information known statically about the arguments to the call.
241 <li>The -globalopt pass now promotes non-address-taken static globals that are
242 only accessed in main to SSA registers.</li>
244 <li>Loops with trip counts based on array pointer comparisons (e.g. "<tt>for (i
245 = 0; &A[i] != &A[n]; ++i) ...</tt>") are optimized better than before,
246 which primarily helps iterator-intensive C++ codes.</li>
248 <li>The optimizer now eliminates simple cases where redundant conditions exist
249 between neighboring blocks.</li>
251 <li>The reassociation pass (which turns (1+X+3) into (X+1+3) among other
252 things), is more aggressive and intelligent.</li>
254 <li>The -prune-eh pass now detects no-return functions in addition to the
255 no-unwind functions it did before.</li>
257 <li>The -globalsmodref alias analysis generates more precise results in some
263 <!--=========================================================================-->
264 <div class="doc_subsection">
265 <a name="codequality">Code Generator Improvements in LLVM 1.5</a>
268 <div class="doc_text">
270 <li>The code generator now can provide and use information about commutative
271 two-address instructions when performing register allocation.</li>
273 <li>The code generator now tracks function live-in registers explicitly,
274 instead of requiring the target to generate 'implicit defs' at the
275 entry to a function.</li>
277 <li>The code generator can lower integer division by a constant to
278 multiplication by a magic constant and multiplication by a constant into
279 shift/add sequences.</li>
281 <li>The code generator compiles fabs/fneg/sin/cos/sqrt to assembly instructions
284 <li>The PowerPC backend generates better code in many cases, making use of
285 FMA instructions and the recording ("dot") forms of various PowerPC
291 <!--=========================================================================-->
292 <div class="doc_subsection">
293 <a name="bugfix">Significant Bugs Fixed in LLVM 1.5</a>
296 <div class="doc_text">
299 <p>Bugs fixed in the LLVM Core:</p>
301 <li><a href="http://llvm.cs.uiuc.edu/PR491">[dse] DSE deletes stores that
302 are partially overwritten by smaller stores</a></li>
303 <li><a href="http://llvm.cs.uiuc.edu/PR548">[instcombine] miscompilation of
304 setcc or setcc in one case</a></li>
305 <li>Transition code for LLVM 1.0 style varargs was removed from the .ll file
306 parser. LLVM 1.0 bytecode files are still supported. </li>
309 <p>Code Generator Bugs:</p>
311 <li><a href="http://llvm.cs.uiuc.edu/PR490">[cbackend] Logical constant
312 expressions (and/or/xor) not implemented</a>.</li>
313 <li><a href="http://llvm.cs.uiuc.edu/PR511">[cbackend] C backend does not
314 respect 'volatile'</a>.</li>
315 <li>The JIT sometimes miscompiled globals and constant pool entries for
316 64-bit integer constants on 32-bit hosts.</li>
317 <li>The C backend should no longer produce code that crashes ICC 8.1.</li>
320 <p>Bugs in the C/C++ front-end:</p>
322 <li><a href="http://llvm.cs.uiuc.edu/PR487">[llvmgcc] llvm-gcc incorrectly
323 rejects some constant initializers involving the addresses of array
325 <li><a href="http://llvm.cs.uiuc.edu/PR501">[llvm-g++] Crash compiling
326 anonymous union</a></li>
327 <li><a href="http://llvm.cs.uiuc.edu/PR509">[llvm-g++] Do not use dynamic
328 initialization where static init will do</a></li>
329 <li><a href="http://llvm.cs.uiuc.edu/PR510">[llvmgcc] Field offset
330 miscalculated for some structure fields following bit fields</a></li>
331 <li><a href="http://llvm.cs.uiuc.edu/PR513">[llvm-g++] Temporary lifetimes
332 incorrect for short circuit logical operations</a></li>
333 <li><a href="http://llvm.cs.uiuc.edu/PR517">[llvm-gcc] Crash compiling
334 bitfield <-> aggregate assignment</a></li>
335 <li><a href="http://llvm.cs.uiuc.edu/PR520">[llvm-g++] Error compiling
336 virtual function thunk with an unnamed argument</a></li>
337 <li><a href="http://llvm.cs.uiuc.edu/PR522">[llvm-gcc] Crash on certain
338 C99 complex number routines</a></li>
339 <li><a href="http://llvm.cs.uiuc.edu/PR529">[llvm-g++] Crash using placement
340 new on an array type</a></li>
345 <!-- *********************************************************************** -->
346 <div class="doc_section">
347 <a name="portability">Portability and Supported Platforms</a>
349 <!-- *********************************************************************** -->
351 <div class="doc_text">
353 <p>LLVM is known to work on the following platforms:</p>
356 <li>Intel and AMD machines running Red Hat Linux and FreeBSD (and probably
357 other unix-like systems).</li>
358 <li>Sun UltraSPARC workstations running Solaris 8.</li>
359 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
360 support is available for native builds with Visual C++).</li>
361 <li>PowerPC-based Mac OS X systems, running 10.2 and above.</li>
362 <li>Alpha-based machines running Debian GNU/Linux.</li>
363 <li>Itanium-based machines running Linux and HP-UX.</li>
366 <p>The core LLVM infrastructure uses
367 <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
368 to the machine and operating system on which it is built. However, minor
369 porting may be required to get LLVM to work on new platforms. We welcome your
370 portability patches and reports of successful builds or error messages.</p>
374 <!-- *********************************************************************** -->
375 <div class="doc_section">
376 <a name="knownproblems">Known Problems</a>
378 <!-- *********************************************************************** -->
380 <div class="doc_text">
382 <p>This section contains all known problems with the LLVM system, listed by
383 component. As new problems are discovered, they will be added to these
384 sections. If you run into a problem, please check the <a
385 href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
386 there isn't already one.</p>
390 <!-- ======================================================================= -->
391 <div class="doc_subsection">
392 <a name="experimental">Experimental features included with this release</a>
395 <div class="doc_text">
397 <p>The following components of this LLVM release are either untested, known to
398 be broken or unreliable, or are in early development. These components should
399 not be relied on, and bugs should not be filed against them, but they may be
400 useful to some people. In particular, if you would like to work on one of these
401 components, please contact us on the llvmdev list.</p>
404 <li>The following passes are incomplete or buggy, and may be removed in future
405 releases: <tt>-cee, -branch-combine, -instloops, -paths, -pre</tt></li>
406 <li>The <tt>llvm-db</tt> tool is in a very early stage of development, but can
407 be used to step through programs and inspect the stack.</li>
408 <li>The "iterative scan" register allocator (enabled with
409 <tt>-regalloc=iterativescan</tt>) is not stable.</li>
410 <li>The SparcV8, Alpha, and IA64 code generators are experimental.</li>
415 <!-- ======================================================================= -->
416 <div class="doc_subsection">
417 <a name="core">Known problems with the LLVM Core</a>
420 <div class="doc_text">
423 <li>In the JIT, <tt>dlsym()</tt> on a symbol compiled by the JIT will not
425 <li>The JIT does not use mutexes to protect its internal data structures. As
426 such, execution of a threaded program could cause these data structures to be
429 <li><a href="http://llvm.cs.uiuc.edu/PR240">The lower-invoke pass does not
430 mark values live across a setjmp as volatile</a>. This missing feature
431 only affects targets whose setjmp/longjmp libraries do not save and restore
432 the entire register file.</li>
436 <!-- ======================================================================= -->
437 <div class="doc_subsection">
438 <a name="c-fe">Known problems with the C front-end</a>
441 <!-- _______________________________________________________________________ -->
442 <div class="doc_subsubsection">Bugs</div>
444 <div class="doc_text">
446 <li>C99 Variable sized arrays do not release stack memory when they go out of
447 scope. Thus, the following program may run out of stack space:
449 for (i = 0; i != 1000000; ++i) {
455 <li>Initialization of global union variables can only be done <a
456 href="http://llvm.cs.uiuc.edu/PR162">with the largest union member</a>.</li>
461 <!-- _______________________________________________________________________ -->
462 <div class="doc_subsubsection">
466 <div class="doc_text">
470 <li>Inline assembly is not yet supported.</li>
472 <li>"long double" is transformed by the front-end into "double". There is no
473 support for floating point data types of any size other than 32 and 64
476 <li>The following Unix system functionality has not been tested and may not
479 <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
480 appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions. Note that
481 <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
482 <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
483 - These functions have not been tested.
486 <li>Although many GCC extensions are supported, some are not. In particular,
487 the following extensions are known to <b>not be</b> supported:
489 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
490 <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.</li>
491 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
492 <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>
493 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
494 <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>
495 <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>
496 <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>
497 <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>
498 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
499 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
502 <p>The following GCC extensions are <b>partially</b> supported. An ignored
503 attribute means that the LLVM compiler ignores the presence of the attribute,
504 but the code should still work. An unsupported attribute is one which is
505 ignored by the LLVM compiler and will cause a different interpretation of
509 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
510 Arrays whose length is computed at run time.<br>
511 Supported, but allocated stack space is not freed until the function returns (noted above).</li>
513 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
515 Declaring that functions have no side effects or that they can never
518 <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
519 <tt>noreturn</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
521 <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
523 <b>Ignored:</b> <tt>noinline</tt>,
524 <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
525 <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>
527 <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
528 <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
529 <tt>fastcall</tt>, all other target specific attributes</li>
531 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
532 Specifying attributes of variables.<br>
533 <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
534 <tt>deprecated</tt>, <tt>transparent_union</tt>,
535 <tt>unused</tt>, <tt>weak</tt><br>
537 <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
538 <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
539 <tt>vector_size</tt>, <tt>dllimport</tt>,
540 <tt>dllexport</tt>, all target specific attributes.</li>
542 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.<br>
543 <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
544 <tt>deprecated</tt>, <tt>may_alias</tt><br>
546 <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>,
547 all target specific attributes.</li>
549 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
550 Other built-in functions.<br>
551 We support all builtins which have a C language equivalent (e.g.,
552 <tt>__builtin_cos</tt>), <tt>__builtin_alloca</tt>,
553 <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
554 <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt>
555 (currently ignored). We also support builtins for ISO C99 floating
556 point comparison macros (e.g., <tt>__builtin_islessequal</tt>),
557 <tt>__builtin_prefetch</tt>, <tt>__builtin_popcount[ll]</tt>,
558 <tt>__builtin_clz[ll]</tt>, and <tt>__builtin_ctz[ll]</tt>.</li>
561 <p>The following extensions <b>are</b> known to be supported:</p>
564 <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>
565 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
566 <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>
567 <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>
568 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
569 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
570 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
571 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
572 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
573 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
574 <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>
575 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
576 <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>
577 <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>
578 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
579 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
580 or arrays as values.</li>
581 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
582 <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>
583 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
584 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
585 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
586 <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>
587 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
588 <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>
589 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
590 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
591 <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>
592 <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>
593 <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>
594 <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>
595 <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>
596 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
601 <p>If you run into GCC extensions which have not been included in any of these
602 lists, please let us know (also including whether or not they work).</p>
606 <!-- ======================================================================= -->
607 <div class="doc_subsection">
608 <a name="c++-fe">Known problems with the C++ front-end</a>
611 <div class="doc_text">
613 <p>For this release, the C++ front-end is considered to be fully
614 tested and works for a number of non-trivial programs, including LLVM
619 <!-- _______________________________________________________________________ -->
620 <div class="doc_subsubsection">Bugs</div>
622 <div class="doc_text">
625 <li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
632 <!-- _______________________________________________________________________ -->
633 <div class="doc_subsubsection">
637 <div class="doc_text">
641 <li>The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This
642 parser is significantly more standards compliant (and picky) than prior GCC
643 versions. For more information, see the C++ section of the <a
644 href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>
646 <li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
647 performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
648 function and in the <tt>setjmp</tt> receiver function may not be run.
649 Objects in intervening stack frames will be destroyed, however (which is
650 better than most compilers).</li>
652 <li>The LLVM C++ front-end follows the <a
653 href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
654 This document, which is not Itanium specific, specifies a standard for name
655 mangling, class layout, v-table layout, RTTI formats, and other C++
656 representation issues. Because we use this API, code generated by the LLVM
657 compilers should be binary compatible with machine code generated by other
658 Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
659 <i>However</i>, the exception handling mechanism used by LLVM is very
660 different from the model used in the Itanium ABI, so <b>exceptions will not
661 interact correctly</b>. </li>
667 <!-- ======================================================================= -->
668 <div class="doc_subsection">
669 <a name="c-be">Known problems with the C back-end</a>
672 <div class="doc_text">
676 <li>The C back-end produces code that violates the ANSI C Type-Based Alias
677 Analysis rules. As such, special options may be necessary to compile the code
678 (for example, GCC requires the <tt>-fno-strict-aliasing</tt> option). This
679 problem probably cannot be fixed.</li>
681 <li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not
682 supported</a>. This should not affect LLVM produced by the C or C++
689 <!-- ======================================================================= -->
690 <div class="doc_subsection">
691 <a name="x86-be">Known problems with the X86 back-end</a>
694 <div class="doc_text">
702 <!-- ======================================================================= -->
703 <div class="doc_subsection">
704 <a name="ppc-be">Known problems with the PowerPC back-end</a>
707 <div class="doc_text">
715 <!-- ======================================================================= -->
716 <div class="doc_subsection">
717 <a name="sparcv9-be">Known problems with the SparcV9 back-end</a>
720 <div class="doc_text">
723 <li><a href="http://llvm.cs.uiuc.edu/PR60">[sparcv9] SparcV9 backend miscompiles
724 several programs in the LLVM test suite</a></li>
729 <!-- ======================================================================= -->
730 <div class="doc_subsection">
731 <a name="alpha-be">Known problems with the Alpha back-end</a>
734 <div class="doc_text">
738 <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
739 appropriate nops inserted to ensure restartability.</li>
741 <li>Defining vararg functions is not supported (but calling them is ok).</li>
743 <li>Due to the vararg problems, C++ exceptions do not work. Small changes are required to the CFE (which break correctness in the exception handler) to compile the exception handling library (and thus the C++ standard library).</li>
749 <!-- ======================================================================= -->
750 <div class="doc_subsection">
751 <a name="ia64-be">Known problems with the IA64 back-end</a>
754 <div class="doc_text">
758 <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
759 made where the argument is not 16-byte aligned, as required on IA64. (Strictly
760 speaking this is not a bug in the IA64 back-end; it will also be encountered
761 when building C++ programs using the C back-end.)</li>
763 <li>The C++ front-end does not use <a href="http://llvm.cs.uiuc.edu/PR406">IA64
764 ABI compliant layout of v-tables</a>. In particular, it just stores function
765 pointers instead of function descriptors in the vtable. This bug prevents
766 mixing C++ code compiled with LLVM with C++ objects compiled by other C++
769 <li>There are a few ABI violations which will lead to problems when mixing LLVM
770 output with code built with other compilers, particularly for floating-point
773 <li>Defining vararg functions is not supported (but calling them is ok).</li>
779 <!-- ======================================================================= -->
780 <div class="doc_subsection">
781 <a name="sparcv8">Known problems with the SPARC-V8 back-end</a>
784 <div class="doc_text">
787 <li>Many features are still missing (e.g. support for 64-bit integer
790 <li>This backend needs to be updated to use the SelectionDAG instruction
791 selection framework.</li>
796 <!-- *********************************************************************** -->
797 <div class="doc_section">
798 <a name="additionalinfo">Additional Information</a>
800 <!-- *********************************************************************** -->
802 <div class="doc_text">
804 <p>A wide variety of additional information is available on the <a
805 href="http://llvm.cs.uiuc.edu">LLVM web page</a>, including <a
806 href="http://llvm.cs.uiuc.edu/docs/">documentation</a> and <a
807 href="http://llvm.cs.uiuc.edu/pubs/">publications describing algorithms and
808 components implemented in LLVM</a>. The web page also contains versions of the
809 API documentation which is up-to-date with the CVS version of the source code.
810 You can access versions of these documents specific to this release by going
811 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
813 <p>If you have any questions or comments about LLVM, please feel free to contact
814 us via the <a href="http://llvm.cs.uiuc.edu/docs/#maillist"> mailing
819 <!-- *********************************************************************** -->
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