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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> At this time, LLVM is known to correctly compile a wide range of C and C++
66 programs, including the SPEC CPU95 & 2000 suite. It includes bug fixes for
67 those problems found since the 1.4 release and a large number of new features
68 and enhancements, described below.</p>
72 <!--=========================================================================-->
73 <div class="doc_subsection">
74 <a name="newfeatures">New Features in LLVM 1.5</a>
77 <!--_________________________________________________________________________-->
78 <div class="doc_subsubsection"><a href="newcg">New Native Code
81 <div class="doc_text">
83 This release includes new native code generators for <a
84 href="#alpha-be">Alpha</a>, <a href="#ia64-be">IA-64</a>, and SPARC-V8 (32-bit
85 SPARC). These code generators are still beta quality, but are progressing
90 <!--_________________________________________________________________________-->
91 <div class="doc_subsubsection"><a name="selectiondag">New Instruction
92 Selector Framework</a></div>
94 <div class="doc_text">
95 <p>This release includes a <a href="CodeGenerator.html#instselect">new framework
96 for building instruction selectors</a>, which has long been the hardest part of
97 building a new LLVM target. This framework handles a lot of the mundane (but
98 easy to get wrong) details of writing the instruction selector, such as
99 generating efficient code for <a
100 href="LangRef.html#i_getelementptr">getelementptr</a> instructions, promoting
101 small integer types to larger types (e.g. for RISC targets with one size of
102 integer registers), expanding 64-bit integer operations for 32-bit hosts, etc.
103 Currently, the X86, PowerPC, Alpha, and IA-64 backends use this framework. The
104 SPARC backends will be migrated when time permits.
108 <!--_________________________________________________________________________-->
109 <div class="doc_subsubsection"><a name="customccs">New Support For Custom
110 Calling Conventions</a></div>
112 <div class="doc_text">
113 <p>LLVM 1.5 adds supports for <a href="LangRef.html#callingconv">custom and
114 target-specific calling conventions</a>. Traditionally, the LLVM code
115 generators match the native C calling conventions for a target. This is
116 important for compatibility, but is not very flexible. This release allows
117 custom calling conventions to be established for functions, and defines three
118 target-independent conventions (C call, fast call, and cold call) which may be
119 supported by code generators. When possible, the LLVM optimizer promotes C
120 functions to use the "fastcc" convention, allowing the use of more efficient
121 calling sequences (e.g., parameters are passed in registers in the X86 target).
124 <p>Targets may now also define target-specific calling conventions, allowing
125 LLVM to fully support calling convention altering options (e.g. GCC's
126 <tt>-mregparm</tt> flag) and well-defined target conventions (e.g. stdcall and
127 fastcall on X86).</p>
130 <!--_________________________________________________________________________-->
131 <div class="doc_subsubsection"><a name="tailcalls">New Support for
132 "Proper Tail Calls"</a></div>
134 <div class="doc_text">
135 <p>The release now includes support for <a
136 href="http://doi.acm.org/10.1145/277650.277719">proper tail calls</a>, as
137 required to implement languages like Scheme. Tail calls make use of two
138 features: custom calling conventions (described above), which allow the code
139 generator to emit code for the caller to deallocate its own stack when it
140 returns. The second feature is a flag on the <a href="LangRef.html#i_call">call
141 instruction</a>, which indicates that the callee does not access the callers
142 stack frame (indicating that it is acceptable to deallocate the caller stack
143 before invoking the callee). LLVM proper tail calls run on the system stack (as
144 do normal calls), supports indirect tail calls, tail calls with arbitrary
145 numbers of arguments, tail calls where the callee requires more argument space
146 than the caller, etc. The only case not supported are varargs calls, but that
147 could be added if desired.
150 <p>In order for a front-end to get guaranteed tail call, it must mark functions
151 as "fastcc", mark calls with the 'tail' marker, and follow the call with a
152 return of the called value (or void). The optimizer and code generator attempt
153 to handle more general cases, but the simple case will always work if the code
154 generator supports tail calls. Here is a simple example:</p>
157 fastcc int %bar(int %X, int(double, int)* %FP) { ;<i> fastcc</i>
158 %Y = tail call fastcc int %FP(double 0.0, int %X) ;<i> tail, fastcc</i>
163 <p>In LLVM 1.5, the X86 code generator is the only target that has been enhanced
164 to support proper tail calls (other targets will be enhanced in future).
165 Further, because this support was added very close to the release, it is
166 disabled by default. Pass <tt>-enable-x86-fastcc</tt> to llc to enable it (this
167 will be enabled by default in the next release). The example above compiles to:
172 sub ESP, 8 # Callee uses more space than the caller
173 mov ECX, DWORD PTR [ESP + 8] # Get the old return address
174 mov DWORD PTR [ESP + 4], 0 # First half of 0.0
175 mov DWORD PTR [ESP + 8], 0 # Second half of 0.0
176 mov DWORD PTR [ESP], ECX # Put the return address where it belongs
177 jmp EDX # Tail call "FP"
181 With fastcc on X86, the first two integer arguments are passed in EAX/EDX, the
182 callee pops its arguments off the stack, and the argument area is always a
183 multiple of 8 bytes in size.
188 <!--_________________________________________________________________________-->
189 <div class="doc_subsubsection">Other New Features</div>
191 <div class="doc_text">
193 <li>LLVM now includes an <a href="http://llvm.cs.uiuc.edu/PR415">
194 Interprocedural Sparse Conditional Constant Propagation</a> pass, named
195 -ipsccp, which is run by default at link-time.</li>
196 <li>LLVM 1.5 is now about 15% faster than LLVM 1.4 and its core data
197 structures use about 30% less memory.</li>
198 <li>Support for Microsoft Visual Studio is improved, and <a
199 href="GettingStartedVS.html">now documented</a>.</li>
200 <li><a href="GettingStarted.html#config">Configuring LLVM to build a subset
201 of the available targets</a> is now implemented, via the
202 <tt>--enable-targets=</tt> option.</li>
203 <li>LLVM can now create native shared libraries with '<tt>llvm-gcc ...
204 -shared -Wl,-native</tt>' (or with <tt>-Wl,-native-cbe</tt>).</li>
205 <li>LLVM now supports a new "<a href="LangRef.html#i_prefetch">llvm.prefetch
206 </a>" intrinsic, and llvm-gcc now supports __builtin_prefetch.
207 <li>LLVM now supports intrinsics for <a href="LangRef.html#int_count">bit
208 counting</a> and llvm-gcc now implements the GCC
209 <tt>__builtin_popcount</tt>, <tt>__builtin_ctz</tt>, and
210 <tt>__builtin_clz</tt> builtins.</li>
211 <li>LLVM now builds on HP-UX with the HP aCC Compiler.</li>
212 <li>The LLVM X86 backend can now emit Cygwin-compatible .s files.</li>
213 <li>LLVM now includes workarounds in the code generator generator which
214 reduces the likelyhood of <a href="http://llvm.cs.uiuc.edu/PR448">GCC
215 hitting swap during optimized builds</a>.</li>
216 <li>The PowerPC backend generates far better code than in LLVM 1.4.</li>
220 <!--=========================================================================-->
221 <div class="doc_subsection">
222 <a name="codequality">Code Quality Improvements in LLVM 1.5</a>
225 <div class="doc_text">
227 <li>The -globalopt pass now promotes non-address-taken static globals that are
228 only accessed in main to SSA registers.</li>
230 <li>The new -simplify-libcalls pass improves code generated for well-known
231 library calls. The pass optimizes calls to many of the string, memory, and
232 standard I/O functions (e.g. replace the calls with simpler/faster calls) when
233 possible, given information known statically about the arguments to the call.
236 <li>Loops with trip counts based on array pointer comparisons (e.g. "<tt>for (i
237 = 0; &A[i] != &A[100]; ++i) ...</tt>") are optimized better than before,
238 which primarily helps iterator-intensive C++ codes.</li>
240 <li>The code generator now uses information about takes advantage of commutative
241 two-address instructions when performing register allocation.</li>
247 <!--=========================================================================-->
248 <div class="doc_subsection">
249 <a name="bugfix">Significant Bugs Fixed in LLVM 1.5</a>
252 <div class="doc_text">
255 <p>Bugs fixed in the LLVM Core:</p>
257 <li><a href="http://llvm.cs.uiuc.edu/PR491">[dse] DSE deletes stores that
258 are partially overwritten by smaller stores</a></li>
259 <li><a href="http://llvm.cs.uiuc.edu/PR548">[instcombine] miscompilation of
260 setcc or setcc in one case</a></li>
261 <li>Transition code for LLVM 1.0 style varargs was removed from the .ll file
262 parser. LLVM 1.0 bytecode files are still supported. </li>
265 <p>Code Generator Bugs:</p>
267 <li><a href="http://llvm.cs.uiuc.edu/PR490">[cbackend] Logical constant
268 expressions (and/or/xor) not implemented</a></li>
269 <li><a href="http://llvm.cs.uiuc.edu/PR511">[cbackend] C backend does not
270 respect 'volatile'</a></li>
273 <p>Bugs in the C/C++ front-end:</p>
275 <li><a href="http://llvm.cs.uiuc.edu/PR487">[llvmgcc] llvm-gcc incorrectly
276 rejects some constant initializers involving the addresses of array
278 <li><a href="http://llvm.cs.uiuc.edu/PR501">[llvm-g++] Crash compiling
279 anonymous union</a></li>
280 <li><a href="http://llvm.cs.uiuc.edu/PR509">[llvm-g++] Do not use dynamic
281 initialization where static init will do</a></li>
282 <li><a href="http://llvm.cs.uiuc.edu/PR510">[llvmgcc] Field offset
283 miscalculated for some structure fields following bit fields</a></li>
284 <li><a href="http://llvm.cs.uiuc.edu/PR513">[llvm-g++] Temporary lifetimes
285 incorrect for short circuit logical operations</a></li>
286 <li><a href="http://llvm.cs.uiuc.edu/PR517">[llvm-gcc] Crash compiling
287 bitfield <-> aggregate assignment</a></li>
288 <li><a href="http://llvm.cs.uiuc.edu/PR520">[llvm-g++] Error compiling
289 virtual function thunk with an unnamed argument</a></li>
290 <li><a href="http://llvm.cs.uiuc.edu/PR522">[llvm-gcc] Crash on certain
291 C99 complex number routines</a></li>
292 <li><a href="http://llvm.cs.uiuc.edu/PR529">[llvm-g++] Crash using placement
293 new on an array type</a></li>
298 <!-- *********************************************************************** -->
299 <div class="doc_section">
300 <a name="portability">Portability and Supported Platforms</a>
302 <!-- *********************************************************************** -->
304 <div class="doc_text">
306 <p>LLVM is known to work on the following platforms:</p>
309 <li>Intel and AMD machines running Red Hat Linux and FreeBSD (and probably
310 other unix-like systems).</li>
311 <li>Sun UltraSPARC workstations running Solaris 8.</li>
312 <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
313 support is available for native builds with Visual C++).</li>
314 <li>PowerPC-based Mac OS X systems, running 10.2 and above.</li>
315 <li>Alpha-based machines running Debian GNU/Linux.</li>
316 <li>Itanium-based machines running Linux and HP-UX.</li>
319 <p>The core LLVM infrastructure uses
320 <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself
321 to the machine and operating system on which it is built. However, minor
322 porting may be required to get LLVM to work on new platforms. We welcome your
323 portability patches and reports of successful builds or error messages.</p>
327 <!-- *********************************************************************** -->
328 <div class="doc_section">
329 <a name="knownproblems">Known Problems</a>
331 <!-- *********************************************************************** -->
333 <div class="doc_text">
335 <p>This section contains all known problems with the LLVM system, listed by
336 component. As new problems are discovered, they will be added to these
337 sections. If you run into a problem, please check the <a
338 href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if
339 there isn't already one.</p>
343 <!-- ======================================================================= -->
344 <div class="doc_subsection">
345 <a name="experimental">Experimental features included with this release</a>
348 <div class="doc_text">
350 <p>The following components of this LLVM release are either untested, known to
351 be broken or unreliable, or are in early development. These components should
352 not be relied on, and bugs should not be filed against them, but they may be
353 useful to some people. In particular, if you would like to work on one of these
354 components, please contact us on the llvmdev list.</p>
357 <li>The following passes are incomplete or buggy, and may be removed in future
358 releases: <tt>-cee, -branch-combine, -instloops, -paths, -pre</tt></li>
359 <li>The <tt>llvm-db</tt> tool is in a very early stage of development, but can
360 be used to step through programs and inspect the stack.</li>
361 <li>The "iterative scan" register allocator (enabled with
362 <tt>-regalloc=iterativescan</tt>) is not stable.</li>
363 <li>The SparcV8, Alpha, and IA64 code generators are experimental.</li>
368 <!-- ======================================================================= -->
369 <div class="doc_subsection">
370 <a name="core">Known problems with the LLVM Core</a>
373 <div class="doc_text">
376 <li>In the JIT, <tt>dlsym()</tt> on a symbol compiled by the JIT will not
378 <li>The JIT does not use mutexes to protect its internal data structures. As
379 such, execution of a threaded program could cause these data structures to be
382 <li><a href="http://llvm.cs.uiuc.edu/PR240">The lower-invoke pass does not
383 mark values live across a setjmp as volatile</a>. This missing feature
384 only affects targets whose setjmp/longjmp libraries do not save and restore
385 the entire register file.</li>
389 <!-- ======================================================================= -->
390 <div class="doc_subsection">
391 <a name="c-fe">Known problems with the C front-end</a>
394 <!-- _______________________________________________________________________ -->
395 <div class="doc_subsubsection">Bugs</div>
397 <div class="doc_text">
399 <li>C99 Variable sized arrays do not release stack memory when they go out of
400 scope. Thus, the following program may run out of stack space:
402 for (i = 0; i != 1000000; ++i) {
408 <li>Initialization of global union variables can only be done <a
409 href="http://llvm.cs.uiuc.edu/PR162">with the largest union member</a>.</li>
414 <!-- _______________________________________________________________________ -->
415 <div class="doc_subsubsection">
419 <div class="doc_text">
423 <li>Inline assembly is not yet supported.</li>
425 <li>"long double" is transformed by the front-end into "double". There is no
426 support for floating point data types of any size other than 32 and 64
429 <li>The following Unix system functionality has not been tested and may not
432 <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the
433 appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions. Note that
434 <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly.
435 <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt>
436 - These functions have not been tested.
439 <li>Although many GCC extensions are supported, some are not. In particular,
440 the following extensions are known to <b>not be</b> supported:
442 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li>
443 <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>
444 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li>
445 <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>
446 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li>
447 <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>
448 <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>
449 <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>
450 <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>
451 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li>
452 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li>
455 <p>The following GCC extensions are <b>partially</b> supported. An ignored
456 attribute means that the LLVM compiler ignores the presence of the attribute,
457 but the code should still work. An unsupported attribute is one which is
458 ignored by the LLVM compiler and will cause a different interpretation of
462 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>:
463 Arrays whose length is computed at run time.<br>
464 Supported, but allocated stack space is not freed until the function returns (noted above).</li>
466 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>:
468 Declaring that functions have no side effects or that they can never
471 <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>,
472 <tt>noreturn</tt>, <tt>constructor</tt>, <tt>destructor</tt>,
474 <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br>
476 <b>Ignored:</b> <tt>noinline</tt>,
477 <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>,
478 <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br>
480 <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>,
481 <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>,
482 <tt>fastcall</tt>, all other target specific attributes</li>
484 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>:
485 Specifying attributes of variables.<br>
486 <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>,
487 <tt>deprecated</tt>, <tt>transparent_union</tt>,
488 <tt>unused</tt>, <tt>weak</tt><br>
490 <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>,
491 <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>,
492 <tt>vector_size</tt>, <tt>dllimport</tt>,
493 <tt>dllexport</tt>, all target specific attributes.</li>
495 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.<br>
496 <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>,
497 <tt>deprecated</tt>, <tt>may_alias</tt><br>
499 <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>,
500 all target specific attributes.</li>
502 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>:
503 Other built-in functions.<br>
504 We support all builtins which have a C language equivalent (e.g.,
505 <tt>__builtin_cos</tt>), <tt>__builtin_alloca</tt>,
506 <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>,
507 <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt>
508 (currently ignored). We also support builtins for ISO C99 floating
509 point comparison macros (e.g., <tt>__builtin_islessequal</tt>),
510 <tt>__builtin_prefetch</tt>, <tt>__builtin_popcount[ll]</tt>,
511 <tt>__builtin_clz[ll]</tt>, and <tt>__builtin_ctz[ll]</tt>.</li>
514 <p>The following extensions <b>are</b> known to be supported:</p>
517 <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>
518 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li>
519 <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>
520 <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>
521 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li>
522 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li>
523 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li>
524 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li>
525 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li>
526 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li>
527 <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>
528 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li>
529 <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>
530 <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>
531 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li>
532 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions,
533 or arrays as values.</li>
534 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li>
535 <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>
536 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li>
537 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li>
538 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li>
539 <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>
540 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li>
541 <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>
542 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li>
543 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li>
544 <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>
545 <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>
546 <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>
547 <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>
548 <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>
549 <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li>
554 <p>If you run into GCC extensions which have not been included in any of these
555 lists, please let us know (also including whether or not they work).</p>
559 <!-- ======================================================================= -->
560 <div class="doc_subsection">
561 <a name="c++-fe">Known problems with the C++ front-end</a>
564 <div class="doc_text">
566 <p>For this release, the C++ front-end is considered to be fully
567 tested and works for a number of non-trivial programs, including LLVM
572 <!-- _______________________________________________________________________ -->
573 <div class="doc_subsubsection">Bugs</div>
575 <div class="doc_text">
578 <li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C
581 <li><b>IA-64 specific</b>: The C++ front-end does not use <a
582 href="http://llvm.cs.uiuc.edu/PR406">IA64 ABI compliant layout of v-tables</a>.
583 In particular, it just stores function pointers instead of function
584 descriptors in the vtable. This bug prevents mixing C++ code compiled with
585 LLVM with C++ objects compiled by other C++ compilers.</li>
591 <!-- _______________________________________________________________________ -->
592 <div class="doc_subsubsection">
596 <div class="doc_text">
600 <li>The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This
601 parser is significantly more standards compliant (and picky) than prior GCC
602 versions. For more information, see the C++ section of the <a
603 href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li>
605 <li>Destructors for local objects are not always run when a <tt>longjmp</tt> is
606 performed. In particular, destructors for objects in the <tt>longjmp</tt>ing
607 function and in the <tt>setjmp</tt> receiver function may not be run.
608 Objects in intervening stack frames will be destroyed, however (which is
609 better than most compilers).</li>
611 <li>The LLVM C++ front-end follows the <a
612 href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>.
613 This document, which is not Itanium specific, specifies a standard for name
614 mangling, class layout, v-table layout, RTTI formats, and other C++
615 representation issues. Because we use this API, code generated by the LLVM
616 compilers should be binary compatible with machine code generated by other
617 Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc).
618 <i>However</i>, the exception handling mechanism used by LLVM is very
619 different from the model used in the Itanium ABI, so <b>exceptions will not
620 interact correctly</b>. </li>
626 <!-- ======================================================================= -->
627 <div class="doc_subsection">
628 <a name="x86-be">Known problems with the X86 back-end</a>
631 <div class="doc_text">
639 <!-- ======================================================================= -->
640 <div class="doc_subsection">
641 <a name="sparcv9-be">Known problems with the SparcV9 back-end</a>
644 <div class="doc_text">
647 <li><a href="http://llvm.cs.uiuc.edu/PR60">[sparcv9] SparcV9 backend miscompiles
648 several programs in the LLVM test suite</a></li>
653 <!-- ======================================================================= -->
654 <div class="doc_subsection">
655 <a name="ppc-be">Known problems with the PowerPC back-end</a>
658 <div class="doc_text">
666 <!-- ======================================================================= -->
667 <div class="doc_subsection">
668 <a name="c-be">Known problems with the C back-end</a>
671 <div class="doc_text">
675 <li>The C back-end produces code that violates the ANSI C Type-Based Alias
676 Analysis rules. As such, special options may be necessary to compile the code
677 (for example, GCC requires the <tt>-fno-strict-aliasing</tt> option). This
678 problem probably cannot be fixed.</li>
680 <li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not
681 supported</a>. This should not affect LLVM produced by the C or C++
688 <!-- ======================================================================= -->
689 <div class="doc_subsection">
690 <a name="alpha-be">Known problems with the Alpha back-end</a>
693 <div class="doc_text">
697 <li>On 21164s, some rare FP arithmatic sequences which may trap do not have the appropriate nops inserted to ensure restartability.</li>
699 <li>Vararg functions are not supported.</li>
701 <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>
707 <!-- ======================================================================= -->
708 <div class="doc_subsection">
709 <a name="ia64-be">Known problems with the IA64 back-end</a>
712 <div class="doc_text">
716 <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are
717 made where the argument is not 16-byte aligned, as required on IA64. (Strictly
718 speaking this is not a bug in the IA64 back-end; it will also be encountered
719 when building C++ programs using the C back-end.)</li>
721 <li>There are a few ABI violations which will lead to problems
722 when mixing LLVM output with code built with other compilers,
723 particularly for C++ and floating-point programs.</li>
725 <li>Vararg functions are not supported.</li>
731 <!-- *********************************************************************** -->
732 <div class="doc_section">
733 <a name="additionalinfo">Additional Information</a>
735 <!-- *********************************************************************** -->
737 <div class="doc_text">
739 <p>A wide variety of additional information is available on the LLVM web page,
740 including <a href="http://llvm.cs.uiuc.edu/docs/#maillist">mailing lists</a> and
741 <a href="http://llvm.cs.uiuc.edu/pubs/">publications describing algorithms and
742 components implemented in LLVM</a>. The web page also contains versions of the
743 API documentation which is up-to-date with the CVS version of the source code.
744 You can access versions of these documents specific to this release by going
745 into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
747 <p>If you have any questions or comments about LLVM, please feel free to contact
748 us via the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">mailing
753 <!-- *********************************************************************** -->
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