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Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]7 <title>LLVM 2.4 Release Notes</title>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]8</head>
9<body>
10
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]11<div class="doc_title">LLVM 2.4 Release Notes</div>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]12
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]13<ol>
14 <li><a href="#intro">Introduction</a></li>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]15 <li><a href="#subproj">Sub-project Status Update</a></li>
16 <li><a href="#whatsnew">What's New in LLVM?</a></li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]17 <li><a href="GettingStarted.html">Installation Instructions</a></li>
18 <li><a href="#portability">Portability and Supported Platforms</a></li>
Dan Gohman0de549c2008-10-14 16:23:02 +0000[diff] [blame]19 <li><a href="#knownproblems">Known Problems</a></li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]20 <li><a href="#additionalinfo">Additional Information</a></li>
21</ol>
22
23<div class="doc_author">
Dan Gohman0de549c2008-10-14 16:23:02 +0000[diff] [blame]24 <p>Written by the <a href="http://llvm.org">LLVM Team</a></p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]25</div>
26
27<!-- *********************************************************************** -->
28<div class="doc_section">
29 <a name="intro">Introduction</a>
30</div>
31<!-- *********************************************************************** -->
32
33<div class="doc_text">
34
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]35<p>This document contains the release notes for the LLVM Compiler
36Infrastructure, release 2.4. Here we describe the status of LLVM, including
37major improvements from the previous release and significant known problems.
38All LLVM releases may be downloaded from the <a
39href="http://llvm.org/releases/">LLVM releases web site</a>.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]40
41<p>For more information about LLVM, including information about the latest
42release, please check out the <a href="http://llvm.org/">main LLVM
43web site</a>. If you have questions or comments, the <a
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]44href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's Mailing
45List</a> is a good place to send them.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]46
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]47<p>Note that if you are reading this file from a Subversion checkout or the
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]48main LLVM web page, this document applies to the <i>next</i> release, not the
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame]49current one. To see the release notes for a specific release, please see the
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]50<a href="http://llvm.org/releases/">releases page</a>.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]51
52</div>
53
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]54<!-- Unfinished features in 2.4:
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]55 Machine LICM
56 Machine Sinking
57 LegalizeDAGTypes
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]58 llc -enable-value-prop, propagation of value info (sign/zero ext info) from
59 one MBB to another
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]60 -->
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]61
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]62 <!-- for announcement email:
63 mention dev mtg
Chris Lattner548493b2008-10-12 22:57:58 +0000[diff] [blame]64 Xcode 3.1 and 3.1.1.
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]65 -->
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]66
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]67<!-- *********************************************************************** -->
68<div class="doc_section">
69 <a name="subproj">Sub-project Status Update</a>
Chris Lattnerf65224f2008-06-08 21:34:41 +0000[diff] [blame]70</div>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]71<!-- *********************************************************************** -->
Chris Lattnerf65224f2008-06-08 21:34:41 +0000[diff] [blame]72
73<div class="doc_text">
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]74<p>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]75The LLVM 2.4 distribution currently consists of code from the core LLVM
Chris Lattnera3c683b2008-10-13 18:11:54 +0000[diff] [blame]76repository (which roughly includes the LLVM optimizers, code generators and
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]77supporting tools) and the llvm-gcc repository. In addition to this code, the
78LLVM Project includes other sub-projects that are in development. The two which
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]79are the most actively developed are the <a href="#clang">Clang Project</a> and
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]80the <a href="#vmkit">VMKit Project</a>.
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]81</p>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]82
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]83</div>
84
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]85
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]86<!--=========================================================================-->
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]87<div class="doc_subsection">
Chris Lattnera3c683b2008-10-13 18:11:54 +0000[diff] [blame]88<a name="clang">Clang: C/C++/Objective-C Frontend Toolkit</a>
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]89</div>
90
91<div class="doc_text">
92
93<p>The <a href="http://clang.llvm.org/">Clang project</a> is an effort to build
94a set of new 'LLVM native' front-end technologies for the LLVM optimizer
95and code generator. Clang is continuing to make major strides forward in all
96areas. Its C and Objective-C parsing support is very solid, and the code
97generation support is far enough along to build many C applications. While not
98yet production quality, it is progressing very nicely. In addition, C++
99front-end work has started to make significant progress.</p>
100
Daniel Dunbarf3e35782008-10-14 23:25:09 +0000[diff] [blame]101Clang, in conjunction with the <tt>ccc</tt> driver, is now usable as a
102replacement for gcc for building some small- to medium-sized C applications.
103Additionally, Clang now has code generation support for Objective-C on Mac OS X
104platform. Major highlights include:
105<ul>
106 <li> Clang/ccc pass almost all of the LLVM test suite on Mac OS X and Linux
107on the 32-bit x86 architecture. This includes significant C
108applications such as <a href="http://www.sqlite.org">sqlite3</a>,
109<a href="http://www.lua.org">lua</a>, and
110<a href="http://www.clamav.net">Clam AntiVirus</a>.
111
112 <li> Clang can build the majority of Objective-C examples shipped with the
113Mac OS X Developer Tools.
114</ul>
115
116Clang code generation still needs considerable testing and development, however.
117Some areas under active development include:
118<ul>
119 <li> Improved support for C and Objective-C features, for example
Gabor Greif8ad68f12008-10-15 10:29:51 +0000[diff] [blame]120 variable-length arrays, va_arg, exception handling (Obj-C), and garbage
Daniel Dunbarf3e35782008-10-14 23:25:09 +0000[diff] [blame]121 collection (Obj-C).
122 <li> ABI compatibility, especially for platforms other than 32-bit x86.
123</ul>
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]124
Chris Lattnera3c683b2008-10-13 18:11:54 +0000[diff] [blame]125</div>
126
127<!--=========================================================================-->
128<div class="doc_subsection">
129<a name="clangsa">Clang Static Analyzer</a>
130</div>
131
132<div class="doc_text">
133
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]134<p>The Clang project also includes an early stage static source code analysis
135tool for <a href="http://clang.llvm.org/StaticAnalysis.html">automatically
136finding bugs</a> in C and Objective-C programs. The tool performs a growing set
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]137of checks to find bugs that occur on a specific path within a program. Examples
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]138of bugs the tool finds include logic errors such as null dereferences,
139violations of various API rules, dead code, and potential memory leaks in
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]140Objective-C programs. Since its inception, public feedback on the tool has been
141extremely positive, and conservative estimates put the number of real bugs it
142has found in industrial-quality software on the order of thousands.</p>
Chris Lattnerc2d84672008-10-14 00:52:49 +0000[diff] [blame]143
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]144<p>The tool also provides a simple web GUI to inspect potential bugs found by
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]145the tool. While still early in development, the GUI illustrates some of the key
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]146features of Clang: accurate source location information, which is used by the
147GUI to highlight specific code expressions that relate to a bug (including those
148that span multiple lines) and built-in knowledge of macros, which is used to
149perform inline expansion of macros within the GUI itself.</p>
150
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]151<p>The set of checks performed by the static analyzer is gradually expanding,
152and
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]153future plans for the tool include full source-level inter-procedural analysis
154and deeper checks such as buffer overrun detection. There are many opportunities
155to extend and enhance the static analyzer, and anyone interested in working on
156this project is encouraged to get involved!</p>
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]157
158</div>
159
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]160<!--=========================================================================-->
161<div class="doc_subsection">
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]162<a name="vmkit">VMKit: JVM/CLI Virtual Machine Implementation</a>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]163</div>
164
165<div class="doc_text">
166<p>
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]167The <a href="http://vmkit.llvm.org/">VMKit project</a> is an implementation of
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]168a JVM and a CLI Virtual Machines (Microsoft .NET is an
169implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
170
Nicolas Geoffray20cfdd42008-10-15 20:25:04 +0000[diff] [blame^]171<p>Following LLVM 2.4, VMKit has its first release 0.24 that you can find on its
172<a href="http://vmkit.llvm.org/releases/">webpage</a>. The release includes
173bug fixes, cleanup and new features. The major changes are:</p>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]174
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]175<ul>
176
Nicolas Geoffray20cfdd42008-10-15 20:25:04 +0000[diff] [blame^]177<li> Support for generics in the .Net virtual machine.
Gabor Greif8ad68f12008-10-15 10:29:51 +0000[diff] [blame]178<li> Initial support for the Mono class libraries.
179<li> Support for MacOSX/x86, following LLVM's support for exceptions in
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]180JIT on MacOSX/x86.
Gabor Greif8ad68f12008-10-15 10:29:51 +0000[diff] [blame]181<li> A new vmkit driver: a program to run java or .net applications. The
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]182driver supports llvm command line arguments including the new "-fast" option.
Gabor Greif8ad68f12008-10-15 10:29:51 +0000[diff] [blame]183<li> A new memory allocation scheme in the JVM that makes unloading a
184class loader very fast.
185<li> VMKit now follows the LLVM Makefile machinery.
Nicolas Geoffray2b139382008-10-14 19:23:04 +0000[diff] [blame]186
187</ul>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]188</div>
189
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]190
191<!-- *********************************************************************** -->
192<div class="doc_section">
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]193 <a name="whatsnew">What's New in LLVM?</a>
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]194</div>
195<!-- *********************************************************************** -->
196
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]197<div class="doc_text">
198
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]199<p>This release includes a huge number of bug fixes, performance tweaks and
200minor improvements. Some of the major improvements and new features are listed
201in this section.
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]202</p>
203</div>
204
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]205<!--=========================================================================-->
Chris Lattnerf65224f2008-06-08 21:34:41 +0000[diff] [blame]206<div class="doc_subsection">
Chris Lattnere0798082008-02-06 18:00:06 +0000[diff] [blame]207<a name="majorfeatures">Major New Features</a>
208</div>
209
210<div class="doc_text">
211
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]212<p>LLVM 2.4 includes several major new capabilities:</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]213
214<ul>
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]215<li><p>The most visible end-user change in LLVM 2.4 is that it includes many
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]216optimizations and changes to make -O0 compile times much faster. You should see
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame]217improvements on the order of 30% (or more) faster than LLVM 2.3. There are many
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]218pieces to this change, described in more detail below. The speedups and new
219components can also be used for JIT compilers that want fast compilation as
220well.</p></li>
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]221
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]222<li><p>The biggest change to the LLVM IR is that Multiple Return Values (which
223were introduced in LLVM 2.3) have been generalized to full support for "First
224Class Aggregate" values in LLVM 2.4. This means that LLVM IR supports using
225structs and arrays as values in a function. This capability is mostly useful
226for front-end authors, who prefer to treat things like complex numbers, simple
227tuples, dope vectors, etc as Value*'s instead of as a tuple of Value*'s or as
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame]228memory values. Bitcode files from LLVM 2.3 will automatically migrate to the
229general representation.</p></li>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]230
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]231<li><p>LLVM 2.4 also includes an initial port for the PIC16 microprocessor. This
Duncan Sandsc16c9242008-10-14 07:06:37 +0000[diff] [blame]232is the LLVM target that only has support for 8 bit registers, and a number of
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]233other crazy constraints. While the port is still in early development stages,
234it shows some interesting things you can do with LLVM.</p></li>
Chris Lattnerba948522008-06-05 06:57:39 +0000[diff] [blame]235
Chris Lattner5ba16862008-02-10 08:18:42 +0000[diff] [blame]236</ul>
237
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]238</div>
239
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]240
241<!--=========================================================================-->
242<div class="doc_subsection">
Chris Lattnerf65224f2008-06-08 21:34:41 +0000[diff] [blame]243<a name="llvm-gcc">llvm-gcc 4.2 Improvements</a>
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]244</div>
245
246<div class="doc_text">
247
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]248<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
249front-ends and driver with the LLVM optimizer and code generator. It currently
250includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]251
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]252<ul>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]253<li>LLVM 2.4 supports the full set of atomic <tt>__sync_*</tt> builtins. LLVM
2542.3 only supported those used by OpenMP, but 2.4 supports them all. While
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]255llvm-gcc supports all of these builtins, note that not all targets do. X86
256support them all in both 32-bit and 64-bit mode and PowerPC supports them all
257except for the 64-bit operations when in 32-bit mode.</li>
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]258
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]259<li>llvm-gcc now supports an <tt>-flimited-precision</tt> option, which tells
260the compiler that it is ok to use low-precision approximations of certain libm
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]261functions (like tan, log, etc). This allows you to get high performance if you
262only need (say) 14-bits of precision.</li>
263
264<li>llvm-gcc now supports a C language extension known as "<a
265href="http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-August/002670.html">Blocks
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame]266</a>". This feature is similar to nested functions and closures, but does not
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]267require stack trampolines (with most ABIs) and supports returning closures
268from functions that define them. Note that actually <em>using</em> Blocks
269requires a small runtime that is not included with llvm-gcc.</li>
270
271<li>llvm-gcc now supports a new <tt>-flto</tt> option. On systems that support
272transparent Link Time Optimization (currently Darwin systems with Xcode 3.1 and
273later) this allows the use of LTO with other optimization levels like -Os.
274Previously, LTO could only be used with -O4, which implied optimizations in
275-O3 that can increase code size.</li>
Gabor Greif0e49cc82008-06-09 06:06:18 +0000[diff] [blame]276</ul>
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]277
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]278</div>
279
280
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]281<!--=========================================================================-->
282<div class="doc_subsection">
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]283<a name="coreimprovements">LLVM Core Improvements</a>
284</div>
285
286<div class="doc_text">
287<p>New features include:
288</p>
289
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]290<ul>
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame]291<li>A major change to the <tt>Use</tt> class landed, which shrank it by 25%. Since
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]292this is a pervasive part of the LLVM, it ended up reducing the memory use of
293LLVM IR in general by 15% for most programs.</li>
294
295<li>Values with no names are now pretty printed by <tt>llvm-dis</tt> more
296nicely. They now print as "<tt>%3 = add i32 %A, 4</tt>" instead of
297"<tt>add i32 %A, 4 ; &lt;i32&gt;:3</tt>", which makes it much easier to read.
298</li>
299
300<li>LLVM 2.4 includes some changes for better vector support. First, the shift
301operations (<tt>shl</tt>, <tt>ashr</tt>, <tt>lshr</tt>) now all support vectors
302and do an element-by-element shift (shifts of the whole vector can be
303accomplished by bitcasting the vector to &lt;1 x i128&gt; for example). Second,
Chris Lattnerc2d84672008-10-14 00:52:49 +0000[diff] [blame]304there is initial support in development for vector comparisons with the
305<a href="LangRef.html#i_fcmp">fcmp</a>/<a href="LangRef.html#i_icmp">icmp</a>
306instructions. These instructions compare two vectors and return a vector of
307i1's for each result. Note that there is very little codegen support available
308for any of these IR features though.</li>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]309
310<li>A new <tt>DebugInfoBuilder</tt> class is available, which makes it much
311easier for front-ends to create debug info descriptors, similar to the way that
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]312<tt>IRBuilder</tt> makes it easier to create LLVM IR.</li>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]313
Dan Gohmand74867f2008-10-14 16:13:59 +0000[diff] [blame]314<li>The <tt>IRBuilder</tt> class is now parameterized by a class responsible
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame]315for constant folding. The default <tt>ConstantFolder</tt> class does target independent
316constant folding. The <tt>NoFolder</tt> class does no constant folding at all, which is
317useful when learning how LLVM works. The <tt>TargetFolder</tt> class folds the most,
Duncan Sandsc16c9242008-10-14 07:06:37 +0000[diff] [blame]318doing target dependent constant folding.</li>
319
320<li>LLVM now supports "function attributes", which allows us to separate return
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]321value attributes from function attributes. LLVM now supports attributes on a
322function itself, a return value, and its parameters. New supported function
323attributes include noinline/alwaysinline and the "opt-size" flag which says the
324function should be optimized for code size.</li>
325
Chris Lattnera5a49382008-10-12 18:30:33 +0000[diff] [blame]326<li>LLVM IR now directly represents "common" linkage, instead of
327 representing it as a form of weak linkage.</li>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]328
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]329</ul>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]330
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]331</div>
332
333<!--=========================================================================-->
334<div class="doc_subsection">
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]335<a name="optimizer">Optimizer Improvements</a>
336</div>
337
338<div class="doc_text">
339
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]340<p>In addition to a huge array of bug fixes and minor performance tweaks, this
341release includes a few major enhancements and additions to the optimizers:</p>
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]342
343<ul>
344
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]345<li>The Global Value Numbering (GVN) pass now does local Partial Redundancy
346Elimination (PRE) to eliminate some partially redundant expressions in cases
347where doing so won't grow code size.</li>
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]348
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]349<li>LLVM 2.4 includes a new loop deletion pass (which removes output-free
350provably-finite loops) and a rewritten Aggressive Dead Code Elimination (ADCE)
351pass that no longer uses control dependence information. These changes speed up
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]352the optimizer and also prevent it from deleting output-free infinite
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]353loops.</li>
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]354
Duncan Sands2aecc3f2008-10-13 18:42:43 +0000[diff] [blame]355<li>The new AddReadAttrs pass works out which functions are read-only or
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]356read-none (these correspond to 'pure' and 'const' in GCC) and marks them
Duncan Sands2aecc3f2008-10-13 18:42:43 +0000[diff] [blame]357with the appropriate attribute.</li>
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]358
359<li>LLVM 2.4 now includes a new SparsePropagation framework, which makes it
360trivial to build lattice-based dataflow solvers that operate over LLVM IR. Using
361this interface means that you just define objects to represent your lattice
362values and the transfer functions that operate on them. It handles the
363mechanics of worklist processing, liveness tracking, handling PHI nodes,
364etc.</li>
365
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]366<li>The Loop Strength Reduction and induction variable optimization passes have
367several improvements to avoid inserting MAX expressions, to optimize simple
368floating point induction variables and to analyze trip counts of more
369loops.</li>
370
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]371<li>Various helper functions (ComputeMaskedBits, ComputeNumSignBits, etc) were
372pulled out of the Instruction Combining pass and put into a new
373<tt>ValueTracking.h</tt> header, where they can be reused by other passes.</li>
374
375<li>The tail duplication pass has been removed from the standard optimizer
376sequence used by llvm-gcc. This pass still exists, but the benefits it once
377provided are now achieved by other passes.</li>
378
Chris Lattner0eef6e42008-06-08 02:45:07 +0000[diff] [blame]379</ul>
380
381</div>
382
383<!--=========================================================================-->
384<div class="doc_subsection">
385<a name="codegen">Code Generator Improvements</a>
386</div>
387
388<div class="doc_text">
389
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]390<p>We have put a significant amount of work into the code generator infrastructure,
Chris Lattner0eef6e42008-06-08 02:45:07 +0000[diff] [blame]391which allows us to implement more aggressive algorithms and make it run
392faster:</p>
393
394<ul>
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]395<li>The target-independent code generator supports (and the X86 backend
396 currently implements) a new interface for "fast" instruction selection. This
397 interface is optimized to produce code as quickly as possible, sacrificing
398 code quality to do it. This is used by default at -O0 or when using
399 "llc -fast" on X86. It is straight-forward to add support for
400 other targets if faster -O0 compilation is desired.</li>
401
402<li>In addition to the new 'fast' instruction selection path, many existing
403 pieces of the code generator have been optimized in significant ways.
404 SelectionDAG's are now pool allocated and use better algorithms in many
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]405 places, the ".s" file printers now use <tt>raw_ostream</tt> to emit text much faster,
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]406 etc. The end result of these improvements is that the compiler also takes
407 substantially less time to generate code that is just as good (and often
408 better) than before.</li>
409
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]410<li>Each target has been split to separate the ".s" file printing logic from the
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]411 rest of the target. This enables JIT compilers that don't link in the
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]412 (somewhat large) code and data tables used for printing a ".s" file.</li>
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]413
414<li>The code generator now includes a "stack slot coloring" pass, which packs
415 together individual spilled values into common stack slots. This reduces
416 the size of stack frames with many spills, which tends to increase L1 cache
417 effectiveness.</li>
418
419<li>Various pieces of the register allocator (e.g. the coalescer and two-address
420 operation elimination pass) now know how to rematerialize trivial operations
421 to avoid copies and include several other optimizations.</li>
422
423<li>The <a href="CodeGenerator.html#selectiondag_process">graphs</a> produced by
424 the <tt>llc -view-*-dags</tt> options are now significantly prettier and
425 easier to read.</li>
426
427<li>LLVM 2.4 includes a new register allocator based on Partitioned Boolean
428 Quadratic Programming (PBQP). This register allocator is still in
429 development, but is very simple and clean.</li>
Chris Lattner0eef6e42008-06-08 02:45:07 +0000[diff] [blame]430
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]431</ul>
432
433</div>
434
435
436<!--=========================================================================-->
437<div class="doc_subsection">
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]438<a name="targetspecific">Target Specific Improvements</a>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]439</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]440
441<div class="doc_text">
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]442<p>New target-specific features include:
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]443</p>
444
445<ul>
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]446<li>Exception handling is supported by default on Linux/x86-64.</li>
Duncan Sandsd8745a92008-10-13 17:32:15 +0000[diff] [blame]447<li>Position Independent Code (PIC) is now supported on Linux/x86-64.</li>
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]448<li>@llvm.frameaddress now supports getting the frame address of stack frames
449 &gt; 0 on x86/x86-64.</li>
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]450<li>MIPS floating point support? [BRUNO]</li>
451<li>The PowerPC backend now supports trampolines.</li>
Chris Lattnere45f18b2008-06-05 08:02:49 +0000[diff] [blame]452</ul>
Chris Lattnere45f18b2008-06-05 08:02:49 +0000[diff] [blame]453
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]454</div>
Chris Lattnere45f18b2008-06-05 08:02:49 +0000[diff] [blame]455
456
457<!--=========================================================================-->
458<div class="doc_subsection">
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]459<a name="otherimprovements">Other Improvements</a>
460</div>
461
462<div class="doc_text">
463<p>New features include:
464</p>
465
466<ul>
Mikhail Glushenkovcc2d3012008-10-13 02:46:01 +0000[diff] [blame]467<li><tt>llvmc2</tt> (the generic compiler driver) gained plugin
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]468 support. It is now easier to experiment with <tt>llvmc2</tt> and
469 build your own tools based on it.</li>
470
471<li>LLVM 2.4 includes a number of new generic algorithms and data structures,
Dan Gohman8d9af692008-10-14 15:14:55 +0000[diff] [blame]472 include a scoped hash table, 'immutable' data structures, a simple
473 free-list manager, and a <tt>raw_ostream</tt> class.
474 The <tt>raw_ostream</tt> class and
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]475 <tt>format</tt> allow for efficient file output, and various pieces of LLVM
476 have switched over to use it. The eventual goal is to eliminate
477 std::ostream in favor of it.</li>
478
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]479</ul>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]480
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]481</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]482
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]483<!--=========================================================================-->
484<div class="doc_subsection">
485<a name="changes">Major Changes and Removed Features</a>
486</div>
487
488<div class="doc_text">
489
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]490<p>If you're already an LLVM user or developer with out-of-tree changes based
491on LLVM 2.3, this section lists some "gotchas" that you may run into upgrading
492from the previous release.</p>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]493
494<ul>
495
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]496<li>The LLVM IR generated by llvm-gcc no longer names all instructions. This
497 makes it run faster, but may be more confusing to some people. If you
498 prefer to have names, the '<tt>opt -instnamer</tt>' pass will add names to
499 all instructions.</li>
500
501<li>The LoadVN and GCSE passes have been removed from the tree. They are
502 obsolete and have been replaced with the GVN and MemoryDependence passes.
503 </li>
504</ul>
505
506
507<p>In addition, many APIs have changed in this release. Some of the major LLVM
508API changes are:</p>
509
510<ul>
511
Devang Patel0e3da1a2008-10-14 20:03:43 +0000[diff] [blame]512<li>Now, function attributes and return value attributes are managed
Gabor Greif45fc8b12008-10-15 10:47:24 +0000[diff] [blame]513separately. Interface exported by <tt>ParameterAttributes.h</tt> header is now
Devang Patel0e3da1a2008-10-14 20:03:43 +0000[diff] [blame]514experted by <tt>Attributes.h</tt> header. The new attributes interface changes are:
515<ul>
516<li><tt>getParamAttrs</tt> method is now replaced by
517<tt>getParamAttributes</tt>, <tt>getRetAttributes</tt> and
518<tt>getFnAttributes</tt> methods.</li>
519<li> Return value attributes are stored at index 0. Function attributes are
520stored at index ~0U. Parameter attributes are stored at index that matches
521parameter number.</li>
522<li> <tt>ParamAttr</tt> namespace is now renamed as <tt>Attribute</tt>.</li>
Gabor Greif8ad68f12008-10-15 10:29:51 +0000[diff] [blame]523<li> The name of the class that manages reference count of opaque
Devang Patel0e3da1a2008-10-14 20:03:43 +0000[diff] [blame]524attributes is changed from <tt>PAListPtr</tt> to <tt>AttrListPtr</tt>.</li>
525<li> <tt>ParamAttrsWithIndex</tt> is now renamed as <tt>AttributeWithIndex</tt>.
526</li>
527</ul>
528</li>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]529
530<li>The <tt>DbgStopPointInst</tt> methods <tt>getDirectory</tt> and
531<tt>getFileName</tt> now return <tt>Value*</tt> instead of strings. These can be
532converted to strings using <tt>llvm::GetConstantStringInfo</tt> defined via
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]533"<tt>llvm/Analysis/ValueTracking.h</tt>".</li>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]534
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]535<li>The APIs to create various instructions have changed from lower case
536 "create" methods to upper case "Create" methods (e.g.
537 <tt>BinaryOperator::create</tt>). LLVM 2.4 includes both cases, but the
538 lower case ones are removed in mainline, please migrate.</li>
539
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]540<li>Various header files like "<tt>llvm/ADT/iterator</tt>" were given a ".h" suffix.
541 Change your code to #include "<tt>llvm/ADT/iterator.h</tt>" instead.</li>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]542
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]543<li>In the code generator, many <tt>MachineOperand</tt> predicates were renamed to be
Chris Lattnerb7b69332008-10-14 06:37:11 +0000[diff] [blame]544 shorter (e.g. <tt>isFrameIndex()</tt> -&gt; <tt>isFI()</tt>),
545 <tt>SDOperand</tt> was renamed to <tt>SDValue</tt> (and the "<tt>Val</tt>"
546 member was changed to be the <tt>getNode()</tt> accessor), and the
547 <tt>MVT::ValueType</tt> enum has been replaced with an "<tt>MVT</tt>"
Dan Gohmanc16fad22008-10-14 17:06:44 +0000[diff] [blame]548 struct. The <tt>getSignExtended</tt> and <tt>getValue</tt> methods in the
549 ConstantSDNode class were renamed to <tt>getSExtValue</tt> and
550 <tt>getZExtValue</tt> respectively, to be more consistent with
551 the <tt>ConstantInt</tt> class.</li>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]552</ul>
553
554</div>
555
556
557
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]558<!-- *********************************************************************** -->
559<div class="doc_section">
560 <a name="portability">Portability and Supported Platforms</a>
561</div>
562<!-- *********************************************************************** -->
563
564<div class="doc_text">
565
566<p>LLVM is known to work on the following platforms:</p>
567
568<ul>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]569<li>Intel and AMD machines (IA32) running Red Hat Linux, Fedora Core and FreeBSD
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]570 (and probably other unix-like systems).</li>
Chris Lattnerbd633de92008-02-06 06:30:34 +0000[diff] [blame]571<li>PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit and
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]572 64-bit modes.</li>
Chris Lattnere0798082008-02-06 18:00:06 +0000[diff] [blame]573<li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]574<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
575 support is available for native builds with Visual C++).</li>
Gabor Greif5e75e652008-06-05 18:39:01 +0000[diff] [blame]576<li>Sun UltraSPARC workstations running Solaris 10.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]577<li>Alpha-based machines running Debian GNU/Linux.</li>
Gabor Greif5e75e652008-06-05 18:39:01 +0000[diff] [blame]578<li>Itanium-based (IA64) machines running Linux and HP-UX.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]579</ul>
580
Chris Lattnerba948522008-06-05 06:57:39 +0000[diff] [blame]581<p>The core LLVM infrastructure uses GNU autoconf to adapt itself
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]582to the machine and operating system on which it is built. However, minor
583porting may be required to get LLVM to work on new platforms. We welcome your
584portability patches and reports of successful builds or error messages.</p>
585
586</div>
587
588<!-- *********************************************************************** -->
589<div class="doc_section">
590 <a name="knownproblems">Known Problems</a>
591</div>
592<!-- *********************************************************************** -->
593
594<div class="doc_text">
595
596<p>This section contains all known problems with the LLVM system, listed by
597component. As new problems are discovered, they will be added to these
598sections. If you run into a problem, please check the <a
599href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
600there isn't already one.</p>
601
602</div>
603
604<!-- ======================================================================= -->
605<div class="doc_subsection">
606 <a name="experimental">Experimental features included with this release</a>
607</div>
608
609<div class="doc_text">
610
611<p>The following components of this LLVM release are either untested, known to
612be broken or unreliable, or are in early development. These components should
613not be relied on, and bugs should not be filed against them, but they may be
614useful to some people. In particular, if you would like to work on one of these
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]615components, please contact us on the <a
616href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]617
618<ul>
Gabor Greifaa53e562008-10-14 11:31:14 +0000[diff] [blame]619<li>The MSIL, IA64, Alpha, SPU, MIPS, and PIC16 backends are experimental.</li>
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]620<li>The llc "<tt>-filetype=asm</tt>" (the default) is the only supported
Chris Lattnerbd633de92008-02-06 06:30:34 +0000[diff] [blame]621 value for this option.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]622</ul>
623
624</div>
625
626<!-- ======================================================================= -->
627<div class="doc_subsection">
628 <a name="x86-be">Known problems with the X86 back-end</a>
629</div>
630
631<div class="doc_text">
632
633<ul>
Anton Korobeynikov77d15e22008-06-08 10:24:13 +0000[diff] [blame]634 <li>The X86 backend does not yet support
635 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
636 floating point stack</a>. It supports the 'f' and 't' constraints, but not
637 'u'.</li>
Chris Lattnerd95b5962008-06-08 21:19:07 +0000[diff] [blame]638 <li>The X86 backend generates inefficient floating point code when configured
639 to generate code for systems that don't have SSE2.</li>
Duncan Sands8b4f3772008-06-08 19:38:43 +0000[diff] [blame]640 <li>Win64 code generation wasn't widely tested. Everything should work, but we
Anton Korobeynikov77d15e22008-06-08 10:24:13 +0000[diff] [blame]641 expect small issues to happen. Also, llvm-gcc cannot build mingw64 runtime
642 currently due
643 to <a href="http://llvm.org/PR2255">several</a>
Chris Lattnerf06141a2008-06-08 23:12:47 +0000[diff] [blame]644 <a href="http://llvm.org/PR2257">bugs</a> due to lack of support for the
645 'u' inline assembly constraint and X87 floating point inline assembly.</li>
Dan Gohman3882ecb2008-06-08 23:05:11 +0000[diff] [blame]646 <li>The X86-64 backend does not yet support the LLVM IR instruction
647 <tt>va_arg</tt>. Currently, the llvm-gcc front-end supports variadic
648 argument constructs on X86-64 by lowering them manually.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]649</ul>
650
651</div>
652
653<!-- ======================================================================= -->
654<div class="doc_subsection">
655 <a name="ppc-be">Known problems with the PowerPC back-end</a>
656</div>
657
658<div class="doc_text">
659
660<ul>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]661<li>The Linux PPC32/ABI support needs testing for the interpreter and static
662compilation, and lacks support for debug information.</li>
663</ul>
664
665</div>
666
667<!-- ======================================================================= -->
668<div class="doc_subsection">
669 <a name="arm-be">Known problems with the ARM back-end</a>
670</div>
671
672<div class="doc_text">
673
674<ul>
675<li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
Duncan Sands1827fa62007-09-26 15:59:54 +0000[diff] [blame]676processors, thumb programs can crash or produce wrong
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]677results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
678<li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
679</li>
Chris Lattnerd95b5962008-06-08 21:19:07 +0000[diff] [blame]680<li>There is a bug in QEMU-ARM (&lt;= 0.9.0) which causes it to incorrectly
681 execute
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]682programs compiled with LLVM. Please use more recent versions of QEMU.</li>
683</ul>
684
685</div>
686
687<!-- ======================================================================= -->
688<div class="doc_subsection">
689 <a name="sparc-be">Known problems with the SPARC back-end</a>
690</div>
691
692<div class="doc_text">
693
694<ul>
695<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
696 support the 64-bit SPARC ABI (-m64).</li>
697</ul>
698
699</div>
700
701<!-- ======================================================================= -->
702<div class="doc_subsection">
703 <a name="alpha-be">Known problems with the Alpha back-end</a>
704</div>
705
706<div class="doc_text">
707
708<ul>
709
710<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
711appropriate nops inserted to ensure restartability.</li>
712
713</ul>
714</div>
715
716<!-- ======================================================================= -->
717<div class="doc_subsection">
718 <a name="ia64-be">Known problems with the IA64 back-end</a>
719</div>
720
721<div class="doc_text">
722
723<ul>
Chris Lattnerf06141a2008-06-08 23:12:47 +0000[diff] [blame]724<li>The Itanium backend is highly experimental, and has a number of known
725 issues. We are looking for a maintainer for the Itanium backend. If you
Gabor Greif45fc8b12008-10-15 10:47:24 +0000[diff] [blame]726 are interested, please contact the LLVMdev mailing list.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]727</ul>
728
729</div>
730
731<!-- ======================================================================= -->
732<div class="doc_subsection">
733 <a name="c-be">Known problems with the C back-end</a>
734</div>
735
736<div class="doc_text">
737
738<ul>
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]739<li><a href="http://llvm.org/PR802">The C backend has only basic support for
740 inline assembly code</a>.</li>
Chris Lattnere0194462007-09-26 06:01:35 +0000[diff] [blame]741<li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
742 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]743 C++ code compiled with llc or native compilers.</li>
Duncan Sandsbd0ad6e2008-02-10 13:40:55 +0000[diff] [blame]744<li>The C backend does not support all exception handling constructs.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]745</ul>
746
747</div>
748
749
750<!-- ======================================================================= -->
751<div class="doc_subsection">
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]752 <a name="c-fe">Known problems with the llvm-gcc C front-end</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]753</div>
754
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]755<div class="doc_text">
756
Chris Lattnere0798082008-02-06 18:00:06 +0000[diff] [blame]757<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
758Optimization</a> on most platforms "out-of-the-box". Please inquire on the
Gabor Greif45fc8b12008-10-15 10:47:24 +0000[diff] [blame]759LLVMdev mailing list if you are interested.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]760
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]761<p>The only major language feature of GCC not supported by llvm-gcc is
762 the <tt>__builtin_apply</tt> family of builtins. However, some extensions
763 are only supported on some targets. For example, trampolines are only
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]764 supported on some targets (these are used when you take the address of a
765 nested function).</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]766
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]767<p>If you run into GCC extensions which are not supported, please let us know.
768</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]769
770</div>
771
772<!-- ======================================================================= -->
773<div class="doc_subsection">
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]774 <a name="c++-fe">Known problems with the llvm-gcc C++ front-end</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]775</div>
776
777<div class="doc_text">
778
779<p>The C++ front-end is considered to be fully
780tested and works for a number of non-trivial programs, including LLVM
781itself, Qt, Mozilla, etc.</p>
782
783<ul>
Anton Korobeynikovd9a17932008-10-11 18:27:16 +0000[diff] [blame]784<li>Exception handling works well on the X86 and PowerPC targets. Currently
785 only linux and darwin targets are supported (both 32 and 64 bit).</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]786</ul>
787
788</div>
789
790
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]791<!-- ======================================================================= -->
792<div class="doc_subsection">
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]793 <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]794</div>
795
796<div class="doc_text">
797The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature
798technology and problems should be expected.
799<ul>
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]800<li>The Ada front-end currently only builds on X86-32. This is mainly due
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]801to lack of trampoline support (pointers to nested functions) on other platforms,
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]802however it <a href="http://llvm.org/PR2006">also fails to build on X86-64</a>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]803which does support trampolines.</li>
804<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
805Workaround: configure with --disable-bootstrap.</li>
Duncan Sands2dbc2e82008-10-13 17:27:23 +0000[diff] [blame]806<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
807and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
808(c380004 also fails with gcc-4.2 mainline).</li>
809<li>Some gcc specific Ada tests continue to crash the compiler.</li>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]810<li>The -E binder option (exception backtraces)
811<a href="http://llvm.org/PR1982">does not work</a> and will result in programs
812crashing if an exception is raised. Workaround: do not use -E.</li>
813<li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
814or finish at a non-byte offset</a> in a record. Workaround: do not pack records
815or use representation clauses that result in a field of a non-discrete type
816starting or finishing in the middle of a byte.</li>
Chris Lattnerd95b5962008-06-08 21:19:07 +0000[diff] [blame]817<li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers
818'main' as generated by the Ada binder to be invalid</a>.
819Workaround: hand edit the file to use pointers for <tt>argv</tt> and
820<tt>envp</tt> rather than integers.</li>
821<li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is
822ignored</a>.</li>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]823</ul>
824</div>
825
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]826<!-- *********************************************************************** -->
827<div class="doc_section">
828 <a name="additionalinfo">Additional Information</a>
829</div>
830<!-- *********************************************************************** -->
831
832<div class="doc_text">
833
834<p>A wide variety of additional information is available on the <a
835href="http://llvm.org">LLVM web page</a>, in particular in the <a
836href="http://llvm.org/docs/">documentation</a> section. The web page also
837contains versions of the API documentation which is up-to-date with the
838Subversion version of the source code.
839You can access versions of these documents specific to this release by going
840into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p>
841
842<p>If you have any questions or comments about LLVM, please feel free to contact
843us via the <a href="http://llvm.org/docs/#maillist"> mailing
844lists</a>.</p>
845
846</div>
847
848<!-- *********************************************************************** -->
849
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