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======================
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LLVM 3.4 Release Notes
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======================
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.. contents::
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:local:
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Introduction
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============
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This document contains the release notes for the LLVM Compiler Infrastructure,
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release 3.4. Here we describe the status of LLVM, including major improvements
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from the previous release, improvements in various subprojects of LLVM, and
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some of the current users of the code. All LLVM releases may be downloaded
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from the `LLVM releases web site <http://llvm.org/releases/>`_.
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For more information about LLVM, including information about the latest
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release, please check out the `main LLVM web site <http://llvm.org/>`_. If you
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have questions or comments, the `LLVM Developer's Mailing List
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<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ is a good place to send
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them.
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Note that if you are reading this file from a Subversion checkout or the main
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LLVM web page, this document applies to the *next* release, not the current
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one. To see the release notes for a specific release, please see the `releases
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page <http://llvm.org/releases/>`_.
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Non-comprehensive list of changes in this release
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=================================================
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.. NOTE
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For small 1-3 sentence descriptions, just add an entry at the end of
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this list. If your description won't fit comfortably in one bullet
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point (e.g. maybe you would like to give an example of the
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functionality, or simply have a lot to talk about), see the `NOTE` below
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for adding a new subsection.
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* This is expected to be the last release of LLVM which compiles using a C++98
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toolchain. We expect to start using some C++11 features in LLVM and other
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sub-projects starting after this release. That said, we are committed to
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supporting a reasonable set of modern C++ toolchains as the host compiler on
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all of the platforms. This will at least include Visual Studio 2012 on
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Windows, and Clang 3.1 or GCC 4.7.x on Mac and Linux. The final set of
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compilers (and the C++11 features they support) is not set in stone, but we
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wanted users of LLVM to have a heads up that the next release will involve
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a substantial change in the host toolchain requirements.
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* The regression tests now fail if any command in a pipe fails. To disable it in
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a directory, just add ``config.pipefail = False`` to its ``lit.local.cfg``.
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See :doc:`Lit <CommandGuide/lit>` for the details.
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* Support for exception handling has been removed from the old JIT. Use MCJIT
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if you need EH support.
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* The R600 backend is not marked experimental anymore and is built by default.
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* APFloat::isNormal() was renamed to APFloat::isFiniteNonZero() and
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APFloat::isIEEENormal() was renamed to APFloat::isNormal(). This ensures that
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APFloat::isNormal() conforms to IEEE-754R-2008.
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* The library call simplification pass has been removed. Its functionality
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has been integrated into the instruction combiner and function attribute
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marking passes.
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* Support for building using Visual Studio 2008 has been dropped. Use VS 2010
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or later instead. For more information, see the `Getting Started using Visual
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Studio <GettingStartedVS.html>`_ page.
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* The Loop Vectorizer that was previously enabled for -O3 is now enabled for
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-Os and -O2.
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* The new SLP Vectorizer is now enabled by default.
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* llvm-ar now uses the new Object library and produces archives and
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symbol tables in the gnu format.
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* FileCheck now allows specifing -check-prefix multiple times. This
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helps reduce duplicate check lines when using multiple RUN lines.
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* The bitcast instruction no longer allows casting between pointers
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with different address spaces. To achieve this, use the new
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addrspacecast instruction.
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* Different sized pointers for different address spaces should now
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generally work. This is primarily useful for GPU targets.
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* OCaml bindings have been significantly extended to cover almost all of the
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LLVM libraries.
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* ... next change ...
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.. NOTE
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If you would like to document a larger change, then you can add a
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subsection about it right here. You can copy the following boilerplate
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and un-indent it (the indentation causes it to be inside this comment).
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Special New Feature
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-------------------
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Makes programs 10x faster by doing Special New Thing.
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Mips Target
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-----------
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Support for the MIPS SIMD Architecture (MSA) has been added. MSA is supported
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through inline assembly, intrinsics with the prefix '__builtin_msa', and normal
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code generation.
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For more information on MSA (including documentation for the instruction set),
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see the `MIPS SIMD page at Imagination Technologies
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<http://imgtec.com/mips/mips-simd.asp>`_
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External Open Source Projects Using LLVM 3.4
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============================================
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An exciting aspect of LLVM is that it is used as an enabling technology for
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a lot of other language and tools projects. This section lists some of the
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projects that have already been updated to work with LLVM 3.4.
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DXR
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---
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`DXR <https://wiki.mozilla.org/DXR>`_ is Mozilla's code search and navigation
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tool, aimed at making sense of large projects like Firefox. It supports
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full-text and regex searches as well as structural queries like "Find all the
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callers of this function." Behind the scenes, it uses a custom trigram index,
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the re2 library, and structural data collected by a clang compiler plugin.
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LDC - the LLVM-based D compiler
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-------------------------------
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`D <http://dlang.org>`_ is a language with C-like syntax and static typing. It
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pragmatically combines efficiency, control, and modeling power, with safety and
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programmer productivity. D supports powerful concepts like Compile-Time Function
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Execution (CTFE) and Template Meta-Programming, provides an innovative approach
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to concurrency and offers many classical paradigms.
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`LDC <http://wiki.dlang.org/LDC>`_ uses the frontend from the reference compiler
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combined with LLVM as backend to produce efficient native code. LDC targets
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x86/x86_64 systems like Linux, OS X, FreeBSD and Windows and also Linux/PPC64.
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Ports to other architectures like ARM and AArch64 are underway.
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Likely
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------
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`Likely <http://www.liblikely.org/>`_ is an open source domain specific
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language for image recognition. Algorithms are just-in-time compiled using
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LLVM's MCJIT infrastructure to execute on single or multi-threaded CPUs as well
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as OpenCL SPIR or CUDA enabled GPUs. Likely exploits the observation that while
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image processing and statistical learning kernels must be written generically
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to handle any matrix datatype, at runtime they tend to be executed repeatedly
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on the same type.
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Portable Computing Language (pocl)
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----------------------------------
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In addition to producing an easily portable open source OpenCL
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implementation, another major goal of `pocl <http://portablecl.org/>`_
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is improving performance portability of OpenCL programs with
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compiler optimizations, reducing the need for target-dependent manual
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optimizations. An important part of pocl is a set of LLVM passes used to
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statically parallelize multiple work-items with the kernel compiler, even in
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the presence of work-group barriers. This enables static parallelization of
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the fine-grained static concurrency in the work groups in multiple ways.
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Portable Native Client (PNaCl)
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------------------------------
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`Portable Native Client (PNaCl) <http://www.chromium.org/nativeclient/pnacl>`_
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is a Chrome initiative to bring the performance and low-level control of native
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code to modern web browsers, without sacrificing the security benefits and
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portability of web applications. PNaCl works by compiling native C and C++ code
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to an intermediate representation using the LLVM clang compiler. This
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intermediate representation is a subset of LLVM bytecode that is wrapped into a
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portable executable, which can be hosted on a web server like any other website
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asset. When the site is accessed, Chrome fetches and translates the portable
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executable into an architecture-specific machine code optimized directly for
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the underlying device. PNaCl lets developers compile their code once to run on
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any hardware platform and embed their PNaCl application in any website,
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enabling developers to directly leverage the power of the underlying CPU and
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GPU.
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TTA-based Co-design Environment (TCE)
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-------------------------------------
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`TCE <http://tce.cs.tut.fi/>`_ is a toolset for designing new
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exposed datapath processors based on the Transport triggered architecture (TTA).
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The toolset provides a complete co-design flow from C/C++
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programs down to synthesizable VHDL/Verilog and parallel program binaries.
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Processor customization points include the register files, function units,
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supported operations, and the interconnection network.
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TCE uses Clang and LLVM for C/C++/OpenCL C language support, target independent
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optimizations and also for parts of code generation. It generates
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new LLVM-based code generators "on the fly" for the designed processors and
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loads them in to the compiler backend as runtime libraries to avoid
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per-target recompilation of larger parts of the compiler chain.
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WebCL Validator
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---------------
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`WebCL Validator <https://github.com/KhronosGroup/webcl-validator>`_ implements
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validation for WebCL C language which is a subset of OpenCL ES 1.1. Validator
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checks the correctness of WebCL C, and implements memory protection for it as a
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source-2-source transformation. The transformation converts WebCL to memory
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protected OpenCL. The protected OpenCL cannot access any memory ranges which
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were not allocated for it, and its memory is always initialized to prevent
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information leakage from other programs.
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Additional Information
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======================
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A wide variety of additional information is available on the `LLVM web page
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<http://llvm.org/>`_, in particular in the `documentation
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<http://llvm.org/docs/>`_ section. The web page also contains versions of the
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API documentation which is up-to-date with the Subversion version of the source
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code. You can access versions of these documents specific to this release by
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going into the ``llvm/docs/`` directory in the LLVM tree.
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If you have any questions or comments about LLVM, please feel free to contact
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us via the `mailing lists <http://llvm.org/docs/#maillist>`_.
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