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diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst new file mode 100644 index 0000000000..a5922ad983 --- /dev/null +++ b/docs/ReleaseNotes.rst @@ -0,0 +1,564 @@ +.. raw:: html + + <style> .red {color:red} </style> + +.. role:: red + +====================== +LLVM 3.2 Release Notes +====================== + +.. contents:: + :local: + +Written by the `LLVM Team <http://llvm.org/>`_ + +:red:`These are in-progress notes for the upcoming LLVM 3.2 release. You may +prefer the` `LLVM 3.1 Release Notes <http://llvm.org/releases/3.1/docs +/ReleaseNotes.html>`_. + +Introduction +============ + +This document contains the release notes for the LLVM Compiler Infrastructure, +release 3.2. Here we describe the status of LLVM, including major improvements +from the previous release, improvements in various subprojects of LLVM, and +some of the current users of the code. All LLVM releases may be downloaded +from the `LLVM releases web site <http://llvm.org/releases/>`_. + +For more information about LLVM, including information about the latest +release, please check out the `main LLVM web site <http://llvm.org/>`_. If you +have questions or comments, the `LLVM Developer's Mailing List +<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ is a good place to send +them. + +Note that if you are reading this file from a Subversion checkout or the main +LLVM web page, this document applies to the *next* release, not the current +one. To see the release notes for a specific release, please see the `releases +page <http://llvm.org/releases/>`_. + +Sub-project Status Update +========================= + +The LLVM 3.2 distribution currently consists of code from the core LLVM +repository, which roughly includes the LLVM optimizers, code generators and +supporting tools, and the Clang repository. In addition to this code, the LLVM +Project includes other sub-projects that are in development. Here we include +updates on these subprojects. + +Clang: C/C++/Objective-C Frontend Toolkit +----------------------------------------- + +`Clang <http://clang.llvm.org/>`_ is an LLVM front end for the C, C++, and +Objective-C languages. Clang aims to provide a better user experience through +expressive diagnostics, a high level of conformance to language standards, fast +compilation, and low memory use. Like LLVM, Clang provides a modular, +library-based architecture that makes it suitable for creating or integrating +with other development tools. Clang is considered a production-quality +compiler for C, Objective-C, C++ and Objective-C++ on x86 (32- and 64-bit), and +for Darwin/ARM targets. + +In the LLVM 3.2 time-frame, the Clang team has made many improvements. +Highlights include: + +#. ... + +For more details about the changes to Clang since the 3.1 release, see the +`Clang release notes. <http://clang.llvm.org/docs/ReleaseNotes.html>`_ + +If Clang rejects your code but another compiler accepts it, please take a look +at the `language compatibility <http://clang.llvm.org/compatibility.html>`_ +guide to make sure this is not intentional or a known issue. + +DragonEgg: GCC front-ends, LLVM back-end +---------------------------------------- + +`DragonEgg <http://dragonegg.llvm.org/>`_ is a `gcc plugin +<http://gcc.gnu.org/wiki/plugins>`_ that replaces GCC's optimizers and code +generators with LLVM's. It works with gcc-4.5 and gcc-4.6 (and partially with +gcc-4.7), can target the x86-32/x86-64 and ARM processor families, and has been +successfully used on the Darwin, FreeBSD, KFreeBSD, Linux and OpenBSD +platforms. It fully supports Ada, C, C++ and Fortran. It has partial support +for Go, Java, Obj-C and Obj-C++. + +The 3.2 release has the following notable changes: + +#. ... + +compiler-rt: Compiler Runtime Library +------------------------------------- + +The new LLVM `compiler-rt project <http://compiler-rt.llvm.org/>`_ is a simple +library that provides an implementation of the low-level target-specific hooks +required by code generation and other runtime components. For example, when +compiling for a 32-bit target, converting a double to a 64-bit unsigned integer +is compiled into a runtime call to the ``__fixunsdfdi`` function. The +``compiler-rt`` library provides highly optimized implementations of this and +other low-level routines (some are 3x faster than the equivalent libgcc +routines). + +The 3.2 release has the following notable changes: + +#. ... + +LLDB: Low Level Debugger +------------------------ + +`LLDB <http://lldb.llvm.org>`_ is a ground-up implementation of a command line +debugger, as well as a debugger API that can be used from other applications. +LLDB makes use of the Clang parser to provide high-fidelity expression parsing +(particularly for C++) and uses the LLVM JIT for target support. + +The 3.2 release has the following notable changes: + +#. ... + +libc++: C++ Standard Library +---------------------------- + +Like compiler_rt, libc++ is now :ref:`dual licensed +<copyright-license-patents>` under the MIT and UIUC license, allowing it to be +used more permissively. + +Within the LLVM 3.2 time-frame there were the following highlights: + +#. ... + +VMKit +----- + +The `VMKit project <http://vmkit.llvm.org/>`_ is an implementation of a Java +Virtual Machine (Java VM or JVM) that uses LLVM for static and just-in-time +compilation. + +The 3.2 release has the following notable changes: + +#. ... + +Polly: Polyhedral Optimizer +--------------------------- + +`Polly <http://polly.llvm.org/>`_ is an *experimental* optimizer for data +locality and parallelism. It provides high-level loop optimizations and +automatic parallelisation. + +Within the LLVM 3.2 time-frame there were the following highlights: + +#. isl, the integer set library used by Polly, was relicensed to the MIT license +#. isl based code generation +#. MIT licensed replacement for CLooG (LGPLv2) +#. Fine grained option handling (separation of core and border computations, + control overhead vs. code size) +#. Support for FORTRAN and dragonegg +#. OpenMP code generation fixes + +External Open Source Projects Using LLVM 3.2 +============================================ + +An exciting aspect of LLVM is that it is used as an enabling technology for a +lot of other language and tools projects. This section lists some of the +projects that have already been updated to work with LLVM 3.2. + +Crack +----- + +`Crack <http://code.google.com/p/crack-language/>`_ aims to provide the ease of +development of a scripting language with the performance of a compiled +language. The language derives concepts from C++, Java and Python, +incorporating object-oriented programming, operator overloading and strong +typing. + +FAUST +----- + +`FAUST <http://faust.grame.fr/>`_ is a compiled language for real-time audio +signal processing. The name FAUST stands for Functional AUdio STream. Its +programming model combines two approaches: functional programming and block +diagram composition. In addition with the C, C++, Java, JavaScript output +formats, the Faust compiler can generate LLVM bitcode, and works with LLVM +2.7-3.1. + +Glasgow Haskell Compiler (GHC) +------------------------------ + +`GHC <http://www.haskell.org/ghc/>`_ is an open source compiler and programming +suite for Haskell, a lazy functional programming language. It includes an +optimizing static compiler generating good code for a variety of platforms, +together with an interactive system for convenient, quick development. + +GHC 7.0 and onwards include an LLVM code generator, supporting LLVM 2.8 and +later. + +Julia +----- + +`Julia <https://github.com/JuliaLang/julia>`_ is a high-level, high-performance +dynamic language for technical computing. It provides a sophisticated +compiler, distributed parallel execution, numerical accuracy, and an extensive +mathematical function library. The compiler uses type inference to generate +fast code without any type declarations, and uses LLVM's optimization passes +and JIT compiler. The `Julia Language <http://julialang.org/>`_ is designed +around multiple dispatch, giving programs a large degree of flexibility. It is +ready for use on many kinds of problems. + +LLVM D Compiler +--------------- + +`LLVM D Compiler <https://github.com/ldc-developers/ldc>`_ (LDC) is a compiler +for the D programming Language. It is based on the DMD frontend and uses LLVM +as backend. + +Open Shading Language +--------------------- + +`Open Shading Language (OSL) +<https://github.com/imageworks/OpenShadingLanguage/>`_ is a small but rich +language for programmable shading in advanced global illumination renderers and +other applications, ideal for describing materials, lights, displacement, and +pattern generation. It uses LLVM to JIT complex shader networks to x86 code at +runtime. + +OSL was developed by Sony Pictures Imageworks for use in its in-house renderer +used for feature film animation and visual effects, and is distributed as open +source software with the "New BSD" license. + +Portable OpenCL (pocl) +---------------------- + +In addition to producing an easily portable open source OpenCL implementation, +another major goal of `pocl <http://pocl.sourceforge.net/>`_ is improving +performance portability of OpenCL programs with compiler optimizations, +reducing the need for target-dependent manual optimizations. An important part +of pocl is a set of LLVM passes used to statically parallelize multiple +work-items with the kernel compiler, even in the presence of work-group +barriers. This enables static parallelization of the fine-grained static +concurrency in the work groups in multiple ways (SIMD, VLIW, superscalar, ...). + +Pure +---- + +`Pure <http://pure-lang.googlecode.com/>`_ is an algebraic/functional +programming language based on term rewriting. Programs are collections of +equations which are used to evaluate expressions in a symbolic fashion. The +interpreter uses LLVM as a backend to JIT-compile Pure programs to fast native +code. Pure offers dynamic typing, eager and lazy evaluation, lexical closures, +a hygienic macro system (also based on term rewriting), built-in list and +matrix support (including list and matrix comprehensions) and an easy-to-use +interface to C and other programming languages (including the ability to load +LLVM bitcode modules, and inline C, C++, Fortran and Faust code in Pure +programs if the corresponding LLVM-enabled compilers are installed). + +Pure version 0.54 has been tested and is known to work with LLVM 3.1 (and +continues to work with older LLVM releases >= 2.5). + +TTA-based Co-design Environment (TCE) +------------------------------------- + +`TCE <http://tce.cs.tut.fi/>`_ is a toolset for designing application-specific +processors (ASP) based on the Transport triggered architecture (TTA). The +toolset provides a complete co-design flow from C/C++ programs down to +synthesizable VHDL/Verilog and parallel program binaries. Processor +customization points include the register files, function units, supported +operations, and the interconnection network. + +TCE uses Clang and LLVM for C/C++ language support, target independent +optimizations and also for parts of code generation. It generates new +LLVM-based code generators "on the fly" for the designed TTA processors and +loads them in to the compiler backend as runtime libraries to avoid per-target +recompilation of larger parts of the compiler chain. + +Installation Instructions +========================= + +See :doc:`GettingStarted`. + +What's New in LLVM 3.2? +======================= + +This release includes a huge number of bug fixes, performance tweaks and minor +improvements. Some of the major improvements and new features are listed in +this section. + +Major New Features +------------------ + +.. + + Features that need text if they're finished for 3.2: + ARM EHABI + combiner-aa? + strong phi elim + loop dependence analysis + CorrelatedValuePropagation + lib/Transforms/IPO/MergeFunctions.cpp => consider for 3.2. + Integrated assembler on by default for arm/thumb? + + Near dead: + Analysis/RegionInfo.h + Dom Frontiers + SparseBitVector: used in LiveVar. + llvm/lib/Archive - replace with lib object? + + +LLVM 3.2 includes several major changes and big features: + +#. New NVPTX back-end (replacing existing PTX back-end) based on NVIDIA sources +#. ... + +LLVM IR and Core Improvements +----------------------------- + +LLVM IR has several new features for better support of new targets and that +expose new optimization opportunities: + +#. Thread local variables may have a specified TLS model. See the :ref:`Language + Reference Manual <globalvars>`. +#. ... + +Optimizer Improvements +---------------------- + +In addition to many minor performance tweaks and bug fixes, this release +includes a few major enhancements and additions to the optimizers: + +Loop Vectorizer - We've added a loop vectorizer and we are now able to +vectorize small loops. The loop vectorizer is disabled by default and can be +enabled using the ``-mllvm -vectorize-loops`` flag. The SIMD vector width can +be specified using the flag ``-mllvm -force-vector-width=4``. The default +value is ``0`` which means auto-select. + +We can now vectorize this function: + +.. code-block:: c++ + + unsigned sum_arrays(int *A, int *B, int start, int end) { + unsigned sum = 0; + for (int i = start; i < end; ++i) + sum += A[i] + B[i] + i; + return sum; + } + +We vectorize under the following loops: + +#. The inner most loops must have a single basic block. +#. The number of iterations are known before the loop starts to execute. +#. The loop counter needs to be incremented by one. +#. The loop trip count **can** be a variable. +#. Loops do **not** need to start at zero. +#. The induction variable can be used inside the loop. +#. Loop reductions are supported. +#. Arrays with affine access pattern do **not** need to be marked as + '``noalias``' and are checked at runtime. +#. ... + +SROA - We've re-written SROA to be significantly more powerful. + +#. Branch weight metadata is preseved through more of the optimizer. +#. ... + +MC Level Improvements +--------------------- + +The LLVM Machine Code (aka MC) subsystem was created to solve a number of +problems in the realm of assembly, disassembly, object file format handling, +and a number of other related areas that CPU instruction-set level tools work +in. For more information, please see the `Intro to the LLVM MC Project Blog +Post <http://blog.llvm.org/2010/04/intro-to-llvm-mc-project.html>`_. + +#. ... + +.. _codegen: + +Target Independent Code Generator Improvements +---------------------------------------------- + +Stack Coloring - We have implemented a new optimization pass to merge stack +objects which are used in disjoin areas of the code. This optimization reduces +the required stack space significantly, in cases where it is clear to the +optimizer that the stack slot is not shared. We use the lifetime markers to +tell the codegen that a certain alloca is used within a region. + +We now merge consecutive loads and stores. + +We have put a significant amount of work into the code generator +infrastructure, which allows us to implement more aggressive algorithms and +make it run faster: + +#. ... + +We added new TableGen infrastructure to support bundling for Very Long +Instruction Word (VLIW) architectures. TableGen can now automatically generate +a deterministic finite automaton from a VLIW target's schedule description +which can be queried to determine legal groupings of instructions in a bundle. + +We have added a new target independent VLIW packetizer based on the DFA +infrastructure to group machine instructions into bundles. + +Basic Block Placement +^^^^^^^^^^^^^^^^^^^^^ + +A probability based block placement and code layout algorithm was added to +LLVM's code generator. This layout pass supports probabilities derived from +static heuristics as well as source code annotations such as +``__builtin_expect``. + +X86-32 and X86-64 Target Improvements +------------------------------------- + +New features and major changes in the X86 target include: + +#. ... + +.. _ARM: + +ARM Target Improvements +----------------------- + +New features of the ARM target include: + +#. ... + +.. _armintegratedassembler: + +ARM Integrated Assembler +^^^^^^^^^^^^^^^^^^^^^^^^ + +The ARM target now includes a full featured macro assembler, including +direct-to-object module support for clang. The assembler is currently enabled +by default for Darwin only pending testing and any additional necessary +platform specific support for Linux. + +Full support is included for Thumb1, Thumb2 and ARM modes, along with subtarget +and CPU specific extensions for VFP2, VFP3 and NEON. + +The assembler is Unified Syntax only (see ARM Architecural Reference Manual for +details). While there is some, and growing, support for pre-unfied (divided) +syntax, there are still significant gaps in that support. + +MIPS Target Improvements +------------------------ + +New features and major changes in the MIPS target include: + +#. ... + +PowerPC Target Improvements +--------------------------- + +Many fixes and changes across LLVM (and Clang) for better compliance with the +64-bit PowerPC ELF Application Binary Interface, interoperability with GCC, and +overall 64-bit PowerPC support. Some highlights include: + +#. MCJIT support added. +#. PPC64 relocation support and (small code model) TOC handling added. +#. Parameter passing and return value fixes (alignment issues, padding, varargs + support, proper register usage, odd-sized structure support, float support, + extension of return values for i32 return values). +#. Fixes in spill and reload code for vector registers. +#. C++ exception handling enabled. +#. Changes to remediate double-rounding compatibility issues with respect to + GCC behavior. +#. Refactoring to disentangle ``ppc64-elf-linux`` ABI from Darwin ppc64 ABI + support. +#. Assorted new test cases and test case fixes (endian and word size issues). +#. Fixes for big-endian codegen bugs, instruction encodings, and instruction + constraints. +#. Implemented ``-integrated-as`` support. +#. Additional support for Altivec compare operations. +#. IBM long double support. + +There have also been code generation improvements for both 32- and 64-bit code. +Instruction scheduling support for the Freescale e500mc and e5500 cores has +been added. + +PTX/NVPTX Target Improvements +----------------------------- + +The PTX back-end has been replaced by the NVPTX back-end, which is based on the +LLVM back-end used by NVIDIA in their CUDA (nvcc) and OpenCL compiler. Some +highlights include: + +#. Compatibility with PTX 3.1 and SM 3.5. +#. Support for NVVM intrinsics as defined in the NVIDIA Compiler SDK. +#. Full compatibility with old PTX back-end, with much greater coverage of LLVM + SIR. + +Please submit any back-end bugs to the LLVM Bugzilla site. + +Other Target Specific Improvements +---------------------------------- + +#. ... + +Major Changes and Removed Features +---------------------------------- + +If you're already an LLVM user or developer with out-of-tree changes based on +LLVM 3.2, this section lists some "gotchas" that you may run into upgrading +from the previous release. + +#. The CellSPU port has been removed. It can still be found in older versions. +#. ... + +Internal API Changes +-------------------- + +In addition, many APIs have changed in this release. Some of the major LLVM +API changes are: + +We've added a new interface for allowing IR-level passes to access +target-specific information. A new IR-level pass, called +``TargetTransformInfo`` provides a number of low-level interfaces. LSR and +LowerInvoke already use the new interface. + +The ``TargetData`` structure has been renamed to ``DataLayout`` and moved to +``VMCore`` to remove a dependency on ``Target``. + +#. ... + +Tools Changes +------------- + +In addition, some tools have changed in this release. Some of the changes are: + +#. ... + +Python Bindings +--------------- + +Officially supported Python bindings have been added! Feature support is far +from complete. The current bindings support interfaces to: + +#. ... + +Known Problems +============== + +LLVM is generally a production quality compiler, and is used by a broad range +of applications and shipping in many products. That said, not every subsystem +is as mature as the aggregate, particularly the more obscure1 targets. If you +run into a problem, please check the `LLVM bug database +<http://llvm.org/bugs/>`_ and submit a bug if there isn't already one or ask on +the `LLVMdev list <http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_. + +Known problem areas include: + +#. The CellSPU, MSP430, and XCore backends are experimental. + +#. The integrated assembler, disassembler, and JIT is not supported by several + targets. If an integrated assembler is not supported, then a system + assembler is required. For more details, see the + :ref:`target-feature-matrix`. + +Additional Information +====================== + +A wide variety of additional information is available on the `LLVM web page +<http://llvm.org/>`_, in particular in the `documentation +<http://llvm.org/docs/>`_ section. The web page also contains versions of the +API documentation which is up-to-date with the Subversion version of the source +code. You can access versions of these documents specific to this release by +going into the ``llvm/docs/`` directory in the LLVM tree. + +If you have any questions or comments about LLVM, please feel free to contact +us via the `mailing lists <http://llvm.org/docs/#maillist>`_. + |