1======================
2LLVM 3.3 Release Notes
3======================
4
5.. contents::
6    :local:
7
8.. warning::
9   These are in-progress notes for the upcoming LLVM 3.3 release.  You may
10   prefer the `LLVM 3.2 Release Notes <http://llvm.org/releases/3.2/docs
11   /ReleaseNotes.html>`_.
12
13
14Introduction
15============
16
17This document contains the release notes for the LLVM Compiler Infrastructure,
18release 3.3.  Here we describe the status of LLVM, including major improvements
19from the previous release, improvements in various subprojects of LLVM, and
20some of the current users of the code.  All LLVM releases may be downloaded
21from the `LLVM releases web site <http://llvm.org/releases/>`_.
22
23For more information about LLVM, including information about the latest
24release, please check out the `main LLVM web site <http://llvm.org/>`_.  If you
25have questions or comments, the `LLVM Developer's Mailing List
26<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ is a good place to send
27them.
28
29Note that if you are reading this file from a Subversion checkout or the main
30LLVM web page, this document applies to the *next* release, not the current
31one.  To see the release notes for a specific release, please see the `releases
32page <http://llvm.org/releases/>`_.
33
34Non-comprehensive list of changes in this release
35=================================================
36
37.. NOTE
38   For small 1-3 sentence descriptions, just add an entry at the end of
39   this list. If your description won't fit comfortably in one bullet
40   point (e.g. maybe you would like to give an example of the
41   functionality, or simply have a lot to talk about), see the `NOTE` below
42   for adding a new subsection.
43
44* The CellSPU port has been removed.  It can still be found in older versions.
45
46* The IR-level extended linker APIs (for example, to link bitcode files out of
47  archives) have been removed. Any existing clients of these features should
48  move to using a linker with integrated LTO support.
49
50* LLVM and Clang's documentation has been migrated to the `Sphinx
51  <http://sphinx-doc.org/>`_ documentation generation system which uses
52  easy-to-write reStructuredText. See `llvm/docs/README.txt` for more
53  information.
54
55* TargetTransformInfo (TTI) is a new interface that can be used by IR-level
56  passes to obtain target-specific information, such as the costs of
57  instructions. Only "Lowering" passes such as LSR and the vectorizer are
58  allowed to use the TTI infrastructure.
59
60* We've improved the X86 and ARM cost model.
61
62* The Attributes classes have been completely rewritten and expanded. They now
63  support not only enumerated attributes and alignments, but "string"
64  attributes, which are useful for passing information to code generation. See
65  :doc:`HowToUseAttributes` for more details.
66
67* TableGen's syntax for instruction selection patterns has been simplified.
68  Instead of specifying types indirectly with register classes, you should now
69  specify types directly in the input patterns. See ``SparcInstrInfo.td`` for
70  examples of the new syntax. The old syntax using register classes still
71  works, but it will be removed in a future LLVM release.
72
73* MCJIT now supports exception handling. Support for it in the old jit will be
74  removed in the 3.4 release.
75
76* Command line options can now be grouped into categories which are shown in
77  the output of ``-help``. See :ref:`grouping options into categories`.
78
79* The appearance of command line options in ``-help`` that are inherited by
80  linking with libraries that use the LLVM Command line support library can now
81  be modified at runtime. See :ref:`cl::getRegisteredOptions`.
82
83* ... next change ...
84
85.. NOTE
86   If you would like to document a larger change, then you can add a
87   subsection about it right here. You can copy the following boilerplate
88   and un-indent it (the indentation causes it to be inside this comment).
89
90   Special New Feature
91   -------------------
92
93   Makes programs 10x faster by doing Special New Thing.
94
95AArch64 target
96--------------
97
98We've added support for AArch64, ARM's 64-bit architecture. Development is still
99in fairly early stages, but we expect successful compilation when:
100
101- compiling standard compliant C99 and C++03 with Clang;
102- using Linux as a target platform;
103- where code + static data doesn't exceed 4GB in size (heap allocated data has
104  no limitation).
105
106Some additional functionality is also implemented, notably DWARF debugging,
107GNU-style thread local storage and inline assembly.
108
109Hexagon Target
110--------------
111
112- Removed support for legacy hexagonv2 and hexagonv3 processor
113  architectures which are no longer in use. Currently supported
114  architectures are hexagonv4 and hexagonv5.
115
116Loop Vectorizer
117---------------
118
119We've continued the work on the loop vectorizer. The loop vectorizer now
120has the following features:
121
122- Loops with unknown trip counts.
123- Runtime checks of pointers.
124- Reductions, Inductions.
125- Min/Max reductions of integers.
126- If Conversion.
127- Pointer induction variables.
128- Reverse iterators.
129- Vectorization of mixed types.
130- Vectorization of function calls.
131- Partial unrolling during vectorization.
132
133The loop vectorizer is now enabled by default for -O3.
134
135SLP Vectorizer
136--------------
137
138LLVM now has a new SLP vectorizer. The new SLP vectorizer is not enabled by
139default but can be enabled using the clang flag -fslp-vectorize. The BB-vectorizer
140can also be enabled using the command line flag -fslp-vectorize-aggressive.
141
142R600 Backend
143------------
144
145The R600 backend was added in this release, it supports AMD GPUs
146(HD2XXX - HD7XXX).  This backend is used in AMD's Open Source
147graphics / compute drivers which are developed as part of the `Mesa3D
148<http://www.mesa3d.org>`_ project.
149
150SystemZ/s390x Backend
151---------------------
152
153LLVM and clang now support IBM's z/Architecture.  At present this support
154is restricted to GNU/Linux (GNU triplet s390x-linux-gnu) and requires
155z10 or greater.
156
157
158External Open Source Projects Using LLVM 3.3
159============================================
160
161An exciting aspect of LLVM is that it is used as an enabling technology for
162a lot of other language and tools projects. This section lists some of the
163projects that have already been updated to work with LLVM 3.3.
164
165
166Portable Computing Language (pocl)
167----------------------------------
168
169In addition to producing an easily portable open source OpenCL
170implementation, another major goal of `pocl <http://pocl.sourceforge.net/>`_
171is improving performance portability of OpenCL programs with
172compiler optimizations, reducing the need for target-dependent manual
173optimizations. An important part of pocl is a set of LLVM passes used to
174statically parallelize multiple work-items with the kernel compiler, even in
175the presence of work-group barriers. This enables static parallelization of
176the fine-grained static concurrency in the work groups in multiple ways.
177
178TTA-based Co-design Environment (TCE)
179-------------------------------------
180
181`TCE <http://tce.cs.tut.fi/>`_ is a toolset for designing new
182processors based on the Transport triggered architecture (TTA).
183The toolset provides a complete co-design flow from C/C++
184programs down to synthesizable VHDL/Verilog and parallel program binaries.
185Processor customization points include the register files, function units,
186supported operations, and the interconnection network.
187
188TCE uses Clang and LLVM for C/C++/OpenCL C language support, target independent
189optimizations and also for parts of code generation. It generates new
190LLVM-based code generators "on the fly" for the designed TTA processors and
191loads them in to the compiler backend as runtime libraries to avoid
192per-target recompilation of larger parts of the compiler chain.
193
194
195Additional Information
196======================
197
198A wide variety of additional information is available on the `LLVM web page
199<http://llvm.org/>`_, in particular in the `documentation
200<http://llvm.org/docs/>`_ section.  The web page also contains versions of the
201API documentation which is up-to-date with the Subversion version of the source
202code.  You can access versions of these documents specific to this release by
203going into the ``llvm/docs/`` directory in the LLVM tree.
204
205If you have any questions or comments about LLVM, please feel free to contact
206us via the `mailing lists <http://llvm.org/docs/#maillist>`_.
207
208