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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>
19 <li><a href="#knownproblems">Known Problems</a>
20 <li><a href="#additionalinfo">Additional Information</a></li>
21</ol>
22
23<div class="doc_author">
24 <p>Written by the <a href="http://llvm.org">LLVM Team</a><p>
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
Duncan Sands275d1e02008-10-13 18:33:28 +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
Chris Lattnerc2d84672008-10-14 00:52:49 +0000[diff] [blame]101<p>Codegen progress/state [DANIEL]</p>
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]102
Chris Lattnera3c683b2008-10-13 18:11:54 +0000[diff] [blame]103</div>
104
105<!--=========================================================================-->
106<div class="doc_subsection">
107<a name="clangsa">Clang Static Analyzer</a>
108</div>
109
110<div class="doc_text">
111
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]112<p>The Clang project also includes an early stage static source code analysis
113tool for <a href="http://clang.llvm.org/StaticAnalysis.html">automatically
114finding bugs</a> in C and Objective-C programs. The tool performs a growing set
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]115of checks to find bugs that occur on a specific path within a program. Examples
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]116of bugs the tool finds include logic errors such as null dereferences,
117violations of various API rules, dead code, and potential memory leaks in
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]118Objective-C programs. Since its inception, public feedback on the tool has been
119extremely positive, and conservative estimates put the number of real bugs it
120has found in industrial-quality software on the order of thousands.</p>
Chris Lattnerc2d84672008-10-14 00:52:49 +0000[diff] [blame]121
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]122<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]123the tool. While still early in development, the GUI illustrates some of the key
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]124features of Clang: accurate source location information, which is used by the
125GUI to highlight specific code expressions that relate to a bug (including those
126that span multiple lines) and built-in knowledge of macros, which is used to
127perform inline expansion of macros within the GUI itself.</p>
128
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]129<p>The set of checks performed by the static analyzer is gradually expanding,
130and
Ted Kremenek0437b2c2008-10-14 05:14:21 +0000[diff] [blame]131future plans for the tool include full source-level inter-procedural analysis
132and deeper checks such as buffer overrun detection. There are many opportunities
133to extend and enhance the static analyzer, and anyone interested in working on
134this project is encouraged to get involved!</p>
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]135
136</div>
137
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]138<!--=========================================================================-->
139<div class="doc_subsection">
Chris Lattnera3c683b2008-10-13 18:11:54 +0000[diff] [blame]140<a name="vmkit">vmkit: JVM/CLI Virtual Machine Implementation</a>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]141</div>
142
143<div class="doc_text">
144<p>
Chris Lattnera3c683b2008-10-13 18:11:54 +0000[diff] [blame]145The <a href="http://vmkit.llvm.org/">vmkit project</a> is an implementation of
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]146a JVM and a CLI Virtual Machines (Microsoft .NET is an
147implementation of the CLI) using the Just-In-Time compiler of LLVM.</p>
148
Chris Lattnerc2d84672008-10-14 00:52:49 +0000[diff] [blame]149<p>[NICOLAS]</p>
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]150
151</div>
152
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]153
154<!-- *********************************************************************** -->
155<div class="doc_section">
Chris Lattner78a130b2008-10-13 18:01:01 +0000[diff] [blame]156 <a name="whatsnew">What's New in LLVM?</a>
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]157</div>
158<!-- *********************************************************************** -->
159
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]160<div class="doc_text">
161
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]162<p>This release includes a huge number of bug fixes, performance tweaks and
163minor improvements. Some of the major improvements and new features are listed
164in this section.
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]165</p>
166</div>
167
Chris Lattnerf6a0d382008-06-08 21:58:17 +0000[diff] [blame]168<!--=========================================================================-->
Chris Lattnerf65224f2008-06-08 21:34:41 +0000[diff] [blame]169<div class="doc_subsection">
Chris Lattnere0798082008-02-06 18:00:06 +0000[diff] [blame]170<a name="majorfeatures">Major New Features</a>
171</div>
172
173<div class="doc_text">
174
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]175<p>LLVM 2.4 includes several major new capabilities:</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]176
177<ul>
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]178<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]179optimizations and changes to make -O0 compile times much faster. You should see
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame^]180improvements 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]181pieces to this change, described in more detail below. The speedups and new
182components can also be used for JIT compilers that want fast compilation as
183well.</p></li>
Chris Lattner2c3ef982008-10-11 18:18:28 +0000[diff] [blame]184
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]185<li><p>The biggest change to the LLVM IR is that Multiple Return Values (which
186were introduced in LLVM 2.3) have been generalized to full support for "First
187Class Aggregate" values in LLVM 2.4. This means that LLVM IR supports using
188structs and arrays as values in a function. This capability is mostly useful
189for front-end authors, who prefer to treat things like complex numbers, simple
190tuples, 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^]191memory values. Bitcode files from LLVM 2.3 will automatically migrate to the
192general representation.</p></li>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]193
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]194<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]195is 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]196other crazy constraints. While the port is still in early development stages,
197it shows some interesting things you can do with LLVM.</p></li>
Chris Lattnerba948522008-06-05 06:57:39 +0000[diff] [blame]198
Chris Lattner5ba16862008-02-10 08:18:42 +0000[diff] [blame]199</ul>
200
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]201</div>
202
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]203
204<!--=========================================================================-->
205<div class="doc_subsection">
Chris Lattnerf65224f2008-06-08 21:34:41 +0000[diff] [blame]206<a name="llvm-gcc">llvm-gcc 4.2 Improvements</a>
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]207</div>
208
209<div class="doc_text">
210
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]211<p>LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC
212front-ends and driver with the LLVM optimizer and code generator. It currently
213includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]214
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]215<ul>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]216<li>LLVM 2.4 supports the full set of atomic <tt>__sync_*</tt> builtins. LLVM
2172.3 only supported those used by OpenMP, but 2.4 supports them all. While
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]218llvm-gcc supports all of these builtins, note that not all targets do. X86
219support them all in both 32-bit and 64-bit mode and PowerPC supports them all
220except for the 64-bit operations when in 32-bit mode.</li>
Chris Lattner5cce7a52008-06-08 22:59:35 +0000[diff] [blame]221
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]222<li>llvm-gcc now supports an <tt>-flimited-precision</tt> option, which tells
223the compiler that it is ok to use low-precision approximations of certain libm
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]224functions (like tan, log, etc). This allows you to get high performance if you
225only need (say) 14-bits of precision.</li>
226
227<li>llvm-gcc now supports a C language extension known as "<a
228href="http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-August/002670.html">Blocks
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame^]229</a>". This feature is similar to nested functions and closures, but does not
Chris Lattner4352cc82008-10-13 20:47:20 +0000[diff] [blame]230require stack trampolines (with most ABIs) and supports returning closures
231from functions that define them. Note that actually <em>using</em> Blocks
232requires a small runtime that is not included with llvm-gcc.</li>
233
234<li>llvm-gcc now supports a new <tt>-flto</tt> option. On systems that support
235transparent Link Time Optimization (currently Darwin systems with Xcode 3.1 and
236later) this allows the use of LTO with other optimization levels like -Os.
237Previously, LTO could only be used with -O4, which implied optimizations in
238-O3 that can increase code size.</li>
Gabor Greif0e49cc82008-06-09 06:06:18 +0000[diff] [blame]239</ul>
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]240
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]241</div>
242
243
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]244<!--=========================================================================-->
245<div class="doc_subsection">
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]246<a name="coreimprovements">LLVM Core Improvements</a>
247</div>
248
249<div class="doc_text">
250<p>New features include:
251</p>
252
Chris Lattnerc5a4e312008-06-05 06:25:56 +0000[diff] [blame]253<ul>
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame^]254<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]255this is a pervasive part of the LLVM, it ended up reducing the memory use of
256LLVM IR in general by 15% for most programs.</li>
257
258<li>Values with no names are now pretty printed by <tt>llvm-dis</tt> more
259nicely. They now print as "<tt>%3 = add i32 %A, 4</tt>" instead of
260"<tt>add i32 %A, 4 ; &lt;i32&gt;:3</tt>", which makes it much easier to read.
261</li>
262
263<li>LLVM 2.4 includes some changes for better vector support. First, the shift
264operations (<tt>shl</tt>, <tt>ashr</tt>, <tt>lshr</tt>) now all support vectors
265and do an element-by-element shift (shifts of the whole vector can be
266accomplished by bitcasting the vector to &lt;1 x i128&gt; for example). Second,
Chris Lattnerc2d84672008-10-14 00:52:49 +0000[diff] [blame]267there is initial support in development for vector comparisons with the
268<a href="LangRef.html#i_fcmp">fcmp</a>/<a href="LangRef.html#i_icmp">icmp</a>
269instructions. These instructions compare two vectors and return a vector of
270i1's for each result. Note that there is very little codegen support available
271for any of these IR features though.</li>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]272
273<li>A new <tt>DebugInfoBuilder</tt> class is available, which makes it much
274easier for front-ends to create debug info descriptors, similar to the way that
275IRBuilder makes it easier to create LLVM IR.</li>
276
Duncan Sandsc16c9242008-10-14 07:06:37 +0000[diff] [blame]277<li>The <tt>IRBuilder</tt> class is now parametrized by a class responsible
Gabor Greif7c65c4f2008-10-14 11:00:32 +0000[diff] [blame^]278for constant folding. The default <tt>ConstantFolder</tt> class does target independent
279constant folding. The <tt>NoFolder</tt> class does no constant folding at all, which is
280useful when learning how LLVM works. The <tt>TargetFolder</tt> class folds the most,
Duncan Sandsc16c9242008-10-14 07:06:37 +0000[diff] [blame]281doing target dependent constant folding.</li>
282
283<li>LLVM now supports "function attributes", which allows us to separate return
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]284value attributes from function attributes. LLVM now supports attributes on a
285function itself, a return value, and its parameters. New supported function
286attributes include noinline/alwaysinline and the "opt-size" flag which says the
287function should be optimized for code size.</li>
288
Chris Lattnera5a49382008-10-12 18:30:33 +0000[diff] [blame]289<li>LLVM IR now directly represents "common" linkage, instead of
290 representing it as a form of weak linkage.</li>
Chris Lattnerf7bae6d2008-10-13 20:59:32 +0000[diff] [blame]291
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]292</ul>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]293
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]294</div>
295
296<!--=========================================================================-->
297<div class="doc_subsection">
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]298<a name="optimizer">Optimizer Improvements</a>
299</div>
300
301<div class="doc_text">
302
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]303<p>In addition to a huge array of bug fixes and minor performance tweaks, this
304release includes a few major enhancements and additions to the optimizers:</p>
Chris Lattner8fda4952008-02-10 07:46:44 +0000[diff] [blame]305
306<ul>
307
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]308<li>The Global Value Numbering (GVN) pass now does local Partial Redundancy
309Elimination (PRE) to eliminate some partially redundant expressions in cases
310where doing so won't grow code size.</li>
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]311
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]312<li>LLVM 2.4 includes a new loop deletion pass (which removes output-free
313provably-finite loops) and a rewritten Aggressive Dead Code Elimination (ADCE)
314pass that no longer uses control dependence information. These changes speed up
315the optimizer and also prevents it from deleting output-free infinite
316loops.</li>
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]317
Duncan Sands2aecc3f2008-10-13 18:42:43 +0000[diff] [blame]318<li>The new AddReadAttrs pass works out which functions are read-only or
319read-none (these correspond to 'pure' and 'const' in C) and marks them
320with the appropriate attribute.</li>
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]321
322<li>LLVM 2.4 now includes a new SparsePropagation framework, which makes it
323trivial to build lattice-based dataflow solvers that operate over LLVM IR. Using
324this interface means that you just define objects to represent your lattice
325values and the transfer functions that operate on them. It handles the
326mechanics of worklist processing, liveness tracking, handling PHI nodes,
327etc.</li>
328
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]329<li>The Loop Strength Reduction and induction variable optimization passes have
330several improvements to avoid inserting MAX expressions, to optimize simple
331floating point induction variables and to analyze trip counts of more
332loops.</li>
333
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]334<li>Various helper functions (ComputeMaskedBits, ComputeNumSignBits, etc) were
335pulled out of the Instruction Combining pass and put into a new
336<tt>ValueTracking.h</tt> header, where they can be reused by other passes.</li>
337
338<li>The tail duplication pass has been removed from the standard optimizer
339sequence used by llvm-gcc. This pass still exists, but the benefits it once
340provided are now achieved by other passes.</li>
341
Chris Lattner0eef6e42008-06-08 02:45:07 +0000[diff] [blame]342</ul>
343
344</div>
345
346<!--=========================================================================-->
347<div class="doc_subsection">
348<a name="codegen">Code Generator Improvements</a>
349</div>
350
351<div class="doc_text">
352
353<p>We put a significant amount of work into the code generator infrastructure,
354which allows us to implement more aggressive algorithms and make it run
355faster:</p>
356
357<ul>
Chris Lattnerea9c2242008-10-13 21:50:36 +0000[diff] [blame]358<li>The target-independent code generator supports (and the X86 backend
359 currently implements) a new interface for "fast" instruction selection. This
360 interface is optimized to produce code as quickly as possible, sacrificing
361 code quality to do it. This is used by default at -O0 or when using
362 "llc -fast" on X86. It is straight-forward to add support for
363 other targets if faster -O0 compilation is desired.</li>
364
365<li>In addition to the new 'fast' instruction selection path, many existing
366 pieces of the code generator have been optimized in significant ways.
367 SelectionDAG's are now pool allocated and use better algorithms in many
368 places, the ".s" file printers now use raw_ostream to emit text much faster,
369 etc. The end result of these improvements is that the compiler also takes
370 substantially less time to generate code that is just as good (and often
371 better) than before.</li>
372
373<li>Each target has been split to separate the .s file printing logic from the
374 rest of the target. This enables JIT compilers that don't link in the
375 (somewhat large) code and data tables used for printing a .s file.</li>
376
377<li>The code generator now includes a "stack slot coloring" pass, which packs
378 together individual spilled values into common stack slots. This reduces
379 the size of stack frames with many spills, which tends to increase L1 cache
380 effectiveness.</li>
381
382<li>Various pieces of the register allocator (e.g. the coalescer and two-address
383 operation elimination pass) now know how to rematerialize trivial operations
384 to avoid copies and include several other optimizations.</li>
385
386<li>The <a href="CodeGenerator.html#selectiondag_process">graphs</a> produced by
387 the <tt>llc -view-*-dags</tt> options are now significantly prettier and
388 easier to read.</li>
389
390<li>LLVM 2.4 includes a new register allocator based on Partitioned Boolean
391 Quadratic Programming (PBQP). This register allocator is still in
392 development, but is very simple and clean.</li>
Chris Lattner0eef6e42008-06-08 02:45:07 +0000[diff] [blame]393
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]394</ul>
395
396</div>
397
398
399<!--=========================================================================-->
400<div class="doc_subsection">
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]401<a name="targetspecific">Target Specific Improvements</a>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]402</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]403
404<div class="doc_text">
Chris Lattnerc3649452008-02-10 08:17:19 +0000[diff] [blame]405<p>New target-specific features include:
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]406</p>
407
408<ul>
Chris Lattner4f076402008-10-12 19:47:48 +0000[diff] [blame]409<li>Exception handling is supported by default on Linux/x86-64.</li>
Duncan Sandsd8745a92008-10-13 17:32:15 +0000[diff] [blame]410<li>Position Independent Code (PIC) is now supported on Linux/x86-64.</li>
Chris Lattnerff170152008-10-14 06:02:29 +0000[diff] [blame]411<li>@llvm.frameaddress now supports getting the frame address of stack frames
412 &gt; 0 on x86/x86-64.</li>
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]413<li>MIPS floating point support? [BRUNO]</li>
414<li>The PowerPC backend now supports trampolines.</li>
Chris Lattnere45f18b2008-06-05 08:02:49 +0000[diff] [blame]415</ul>
Chris Lattnere45f18b2008-06-05 08:02:49 +0000[diff] [blame]416
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]417</div>
Chris Lattnere45f18b2008-06-05 08:02:49 +0000[diff] [blame]418
419
420<!--=========================================================================-->
421<div class="doc_subsection">
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]422<a name="otherimprovements">Other Improvements</a>
423</div>
424
425<div class="doc_text">
426<p>New features include:
427</p>
428
429<ul>
Mikhail Glushenkovcc2d3012008-10-13 02:46:01 +0000[diff] [blame]430<li><tt>llvmc2</tt> (the generic compiler driver) gained plugin
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]431 support. It is now easier to experiment with <tt>llvmc2</tt> and
432 build your own tools based on it.</li>
433
434<li>LLVM 2.4 includes a number of new generic algorithms and data structures,
435 include a scoped hash table, 'immutable' data structures, and a
436 <tt>raw_ostream</tt> class. The <tt>raw_ostream</tt> class and
437 <tt>format</tt> allow for efficient file output, and various pieces of LLVM
438 have switched over to use it. The eventual goal is to eliminate
439 std::ostream in favor of it.</li>
440
441<li>Recycler + pool allocation stuff? [DAN]</li>
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]442</ul>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]443
Chris Lattnerb0d6c502007-09-21 03:54:09 +0000[diff] [blame]444</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]445
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]446<!--=========================================================================-->
447<div class="doc_subsection">
448<a name="changes">Major Changes and Removed Features</a>
449</div>
450
451<div class="doc_text">
452
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]453<p>If you're already an LLVM user or developer with out-of-tree changes based
454on LLVM 2.3, this section lists some "gotchas" that you may run into upgrading
455from the previous release.</p>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]456
457<ul>
458
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]459<li>The LLVM IR generated by llvm-gcc no longer names all instructions. This
460 makes it run faster, but may be more confusing to some people. If you
461 prefer to have names, the '<tt>opt -instnamer</tt>' pass will add names to
462 all instructions.</li>
463
464<li>The LoadVN and GCSE passes have been removed from the tree. They are
465 obsolete and have been replaced with the GVN and MemoryDependence passes.
466 </li>
467</ul>
468
469
470<p>In addition, many APIs have changed in this release. Some of the major LLVM
471API changes are:</p>
472
473<ul>
474
475<li>Attributes changes [DEVANG] </li>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]476
477<li>The <tt>DbgStopPointInst</tt> methods <tt>getDirectory</tt> and
478<tt>getFileName</tt> now return <tt>Value*</tt> instead of strings. These can be
479converted to strings using <tt>llvm::GetConstantStringInfo</tt> defined via
480"llvm/Analysis/ValueTracking.h".</li>
481
Chris Lattnercc64a322008-10-13 22:06:31 +0000[diff] [blame]482<li>The APIs to create various instructions have changed from lower case
483 "create" methods to upper case "Create" methods (e.g.
484 <tt>BinaryOperator::create</tt>). LLVM 2.4 includes both cases, but the
485 lower case ones are removed in mainline, please migrate.</li>
486
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]487<li>Various header files like "llvm/ADT/iterator" were given a .h suffix.
488 Change your code to #include "llvm/ADT/iterator.h" instead.</li>
489
Chris Lattnerb7b69332008-10-14 06:37:11 +0000[diff] [blame]490<li>In the code generator, many MachineOperand predicates were renamed to be
491 shorter (e.g. <tt>isFrameIndex()</tt> -&gt; <tt>isFI()</tt>),
492 <tt>SDOperand</tt> was renamed to <tt>SDValue</tt> (and the "<tt>Val</tt>"
493 member was changed to be the <tt>getNode()</tt> accessor), and the
494 <tt>MVT::ValueType</tt> enum has been replaced with an "<tt>MVT</tt>"
495 struct.</li>
Chris Lattner92eacf82008-10-13 17:57:36 +0000[diff] [blame]496</ul>
497
498</div>
499
500
501
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]502<!-- *********************************************************************** -->
503<div class="doc_section">
504 <a name="portability">Portability and Supported Platforms</a>
505</div>
506<!-- *********************************************************************** -->
507
508<div class="doc_text">
509
510<p>LLVM is known to work on the following platforms:</p>
511
512<ul>
Mikhail Glushenkov808cd3e2008-10-13 02:08:34 +0000[diff] [blame]513<li>Intel and AMD machines (IA32) running Red Hat Linux, Fedora Core and FreeBSD
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]514 (and probably other unix-like systems).</li>
Chris Lattnerbd633de92008-02-06 06:30:34 +0000[diff] [blame]515<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]516 64-bit modes.</li>
Chris Lattnere0798082008-02-06 18:00:06 +0000[diff] [blame]517<li>Intel and AMD machines running on Win32 using MinGW libraries (native).</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]518<li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited
519 support is available for native builds with Visual C++).</li>
Gabor Greif5e75e652008-06-05 18:39:01 +0000[diff] [blame]520<li>Sun UltraSPARC workstations running Solaris 10.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]521<li>Alpha-based machines running Debian GNU/Linux.</li>
Gabor Greif5e75e652008-06-05 18:39:01 +0000[diff] [blame]522<li>Itanium-based (IA64) machines running Linux and HP-UX.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]523</ul>
524
Chris Lattnerba948522008-06-05 06:57:39 +0000[diff] [blame]525<p>The core LLVM infrastructure uses GNU autoconf to adapt itself
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]526to the machine and operating system on which it is built. However, minor
527porting may be required to get LLVM to work on new platforms. We welcome your
528portability patches and reports of successful builds or error messages.</p>
529
530</div>
531
532<!-- *********************************************************************** -->
533<div class="doc_section">
534 <a name="knownproblems">Known Problems</a>
535</div>
536<!-- *********************************************************************** -->
537
538<div class="doc_text">
539
540<p>This section contains all known problems with the LLVM system, listed by
541component. As new problems are discovered, they will be added to these
542sections. If you run into a problem, please check the <a
543href="http://llvm.org/bugs/">LLVM bug database</a> and submit a bug if
544there isn't already one.</p>
545
546</div>
547
548<!-- ======================================================================= -->
549<div class="doc_subsection">
550 <a name="experimental">Experimental features included with this release</a>
551</div>
552
553<div class="doc_text">
554
555<p>The following components of this LLVM release are either untested, known to
556be broken or unreliable, or are in early development. These components should
557not be relied on, and bugs should not be filed against them, but they may be
558useful 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]559components, please contact us on the <a
560href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list</a>.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]561
562<ul>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]563<li>The MSIL, IA64, Alpha, SPU, and MIPS backends are experimental.</li>
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]564<li>The llc "<tt>-filetype=asm</tt>" (the default) is the only supported
Chris Lattnerbd633de92008-02-06 06:30:34 +0000[diff] [blame]565 value for this option.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]566</ul>
567
568</div>
569
570<!-- ======================================================================= -->
571<div class="doc_subsection">
572 <a name="x86-be">Known problems with the X86 back-end</a>
573</div>
574
575<div class="doc_text">
576
577<ul>
Anton Korobeynikov77d15e22008-06-08 10:24:13 +0000[diff] [blame]578 <li>The X86 backend does not yet support
579 all <a href="http://llvm.org/PR879">inline assembly that uses the X86
580 floating point stack</a>. It supports the 'f' and 't' constraints, but not
581 'u'.</li>
Chris Lattnerd95b5962008-06-08 21:19:07 +0000[diff] [blame]582 <li>The X86 backend generates inefficient floating point code when configured
583 to generate code for systems that don't have SSE2.</li>
Duncan Sands8b4f3772008-06-08 19:38:43 +0000[diff] [blame]584 <li>Win64 code generation wasn't widely tested. Everything should work, but we
Anton Korobeynikov77d15e22008-06-08 10:24:13 +0000[diff] [blame]585 expect small issues to happen. Also, llvm-gcc cannot build mingw64 runtime
586 currently due
587 to <a href="http://llvm.org/PR2255">several</a>
Chris Lattnerf06141a2008-06-08 23:12:47 +0000[diff] [blame]588 <a href="http://llvm.org/PR2257">bugs</a> due to lack of support for the
589 'u' inline assembly constraint and X87 floating point inline assembly.</li>
Dan Gohman3882ecb2008-06-08 23:05:11 +0000[diff] [blame]590 <li>The X86-64 backend does not yet support the LLVM IR instruction
591 <tt>va_arg</tt>. Currently, the llvm-gcc front-end supports variadic
592 argument constructs on X86-64 by lowering them manually.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]593</ul>
594
595</div>
596
597<!-- ======================================================================= -->
598<div class="doc_subsection">
599 <a name="ppc-be">Known problems with the PowerPC back-end</a>
600</div>
601
602<div class="doc_text">
603
604<ul>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]605<li>The Linux PPC32/ABI support needs testing for the interpreter and static
606compilation, and lacks support for debug information.</li>
607</ul>
608
609</div>
610
611<!-- ======================================================================= -->
612<div class="doc_subsection">
613 <a name="arm-be">Known problems with the ARM back-end</a>
614</div>
615
616<div class="doc_text">
617
618<ul>
619<li>Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6
Duncan Sands1827fa62007-09-26 15:59:54 +0000[diff] [blame]620processors, thumb programs can crash or produce wrong
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]621results (<a href="http://llvm.org/PR1388">PR1388</a>).</li>
622<li>Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested.
623</li>
Chris Lattnerd95b5962008-06-08 21:19:07 +0000[diff] [blame]624<li>There is a bug in QEMU-ARM (&lt;= 0.9.0) which causes it to incorrectly
625 execute
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]626programs compiled with LLVM. Please use more recent versions of QEMU.</li>
627</ul>
628
629</div>
630
631<!-- ======================================================================= -->
632<div class="doc_subsection">
633 <a name="sparc-be">Known problems with the SPARC back-end</a>
634</div>
635
636<div class="doc_text">
637
638<ul>
639<li>The SPARC backend only supports the 32-bit SPARC ABI (-m32), it does not
640 support the 64-bit SPARC ABI (-m64).</li>
641</ul>
642
643</div>
644
645<!-- ======================================================================= -->
646<div class="doc_subsection">
647 <a name="alpha-be">Known problems with the Alpha back-end</a>
648</div>
649
650<div class="doc_text">
651
652<ul>
653
654<li>On 21164s, some rare FP arithmetic sequences which may trap do not have the
655appropriate nops inserted to ensure restartability.</li>
656
657</ul>
658</div>
659
660<!-- ======================================================================= -->
661<div class="doc_subsection">
662 <a name="ia64-be">Known problems with the IA64 back-end</a>
663</div>
664
665<div class="doc_text">
666
667<ul>
Chris Lattnerf06141a2008-06-08 23:12:47 +0000[diff] [blame]668<li>The Itanium backend is highly experimental, and has a number of known
669 issues. We are looking for a maintainer for the Itanium backend. If you
670 are interested, please contact the llvmdev mailing list.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]671</ul>
672
673</div>
674
675<!-- ======================================================================= -->
676<div class="doc_subsection">
677 <a name="c-be">Known problems with the C back-end</a>
678</div>
679
680<div class="doc_text">
681
682<ul>
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]683<li><a href="http://llvm.org/PR802">The C backend has only basic support for
684 inline assembly code</a>.</li>
Chris Lattnere0194462007-09-26 06:01:35 +0000[diff] [blame]685<li><a href="http://llvm.org/PR1658">The C backend violates the ABI of common
686 C++ programs</a>, preventing intermixing between C++ compiled by the CBE and
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]687 C++ code compiled with llc or native compilers.</li>
Duncan Sandsbd0ad6e2008-02-10 13:40:55 +0000[diff] [blame]688<li>The C backend does not support all exception handling constructs.</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]689</ul>
690
691</div>
692
693
694<!-- ======================================================================= -->
695<div class="doc_subsection">
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]696 <a name="c-fe">Known problems with the llvm-gcc C front-end</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]697</div>
698
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]699<div class="doc_text">
700
Chris Lattnere0798082008-02-06 18:00:06 +0000[diff] [blame]701<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
702Optimization</a> on most platforms "out-of-the-box". Please inquire on the
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]703llvmdev mailing list if you are interested.</p>
704
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]705<p>The only major language feature of GCC not supported by llvm-gcc is
706 the <tt>__builtin_apply</tt> family of builtins. However, some extensions
707 are only supported on some targets. For example, trampolines are only
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]708 supported on some targets (these are used when you take the address of a
709 nested function).</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]710
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]711<p>If you run into GCC extensions which are not supported, please let us know.
712</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]713
714</div>
715
716<!-- ======================================================================= -->
717<div class="doc_subsection">
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]718 <a name="c++-fe">Known problems with the llvm-gcc C++ front-end</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]719</div>
720
721<div class="doc_text">
722
723<p>The C++ front-end is considered to be fully
724tested and works for a number of non-trivial programs, including LLVM
725itself, Qt, Mozilla, etc.</p>
726
727<ul>
Anton Korobeynikovd9a17932008-10-11 18:27:16 +0000[diff] [blame]728<li>Exception handling works well on the X86 and PowerPC targets. Currently
729 only linux and darwin targets are supported (both 32 and 64 bit).</li>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]730</ul>
731
732</div>
733
734
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]735<!-- ======================================================================= -->
736<div class="doc_subsection">
Chris Lattner499c07c2008-06-05 06:35:40 +0000[diff] [blame]737 <a name="ada-fe">Known problems with the llvm-gcc Ada front-end</a>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]738</div>
739
740<div class="doc_text">
741The llvm-gcc 4.2 Ada compiler works fairly well, however this is not a mature
742technology and problems should be expected.
743<ul>
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]744<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]745to lack of trampoline support (pointers to nested functions) on other platforms,
Duncan Sandsa73561c2008-06-08 20:18:35 +0000[diff] [blame]746however 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]747which does support trampolines.</li>
748<li>The Ada front-end <a href="http://llvm.org/PR2007">fails to bootstrap</a>.
749Workaround: configure with --disable-bootstrap.</li>
Duncan Sands2dbc2e82008-10-13 17:27:23 +0000[diff] [blame]750<li>The c380004, <a href="http://llvm.org/PR2010">c393010</a>
751and <a href="http://llvm.org/PR2421">cxg2021</a> ACATS tests fail
752(c380004 also fails with gcc-4.2 mainline).</li>
753<li>Some gcc specific Ada tests continue to crash the compiler.</li>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]754<li>The -E binder option (exception backtraces)
755<a href="http://llvm.org/PR1982">does not work</a> and will result in programs
756crashing if an exception is raised. Workaround: do not use -E.</li>
757<li>Only discrete types <a href="http://llvm.org/PR1981">are allowed to start
758or finish at a non-byte offset</a> in a record. Workaround: do not pack records
759or use representation clauses that result in a field of a non-discrete type
760starting or finishing in the middle of a byte.</li>
Chris Lattnerd95b5962008-06-08 21:19:07 +0000[diff] [blame]761<li>The <tt>lli</tt> interpreter <a href="http://llvm.org/PR2009">considers
762'main' as generated by the Ada binder to be invalid</a>.
763Workaround: hand edit the file to use pointers for <tt>argv</tt> and
764<tt>envp</tt> rather than integers.</li>
765<li>The <tt>-fstack-check</tt> option <a href="http://llvm.org/PR2008">is
766ignored</a>.</li>
Chris Lattnerdaeb3232008-02-12 06:29:45 +0000[diff] [blame]767</ul>
768</div>
769
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