diff --git a/docs/ReleaseNotes.html b/docs/ReleaseNotes.html index 2f83b9447d1..bc86bd44522 100644 --- a/docs/ReleaseNotes.html +++ b/docs/ReleaseNotes.html @@ -5,11 +5,11 @@ - LLVM 2.8 Release Notes + LLVM 2.9 Release Notes -
LLVM 2.8 Release Notes
+

LLVM 2.9 Release Notes

LLVM Dragon Logo @@ -17,8 +17,8 @@
  1. Introduction
  2. Sub-project Status Update
    3. -
  3. External Projects Using LLVM 2.8
    4. -
  4. What's New in LLVM 2.8?
    5. +
  5. External Projects Using LLVM 2.9
    6. +
  6. What's New in LLVM 2.9?
  7. Installation Instructions
  8. Known Problems
  9. Additional Information
    10. @@ -29,23 +29,23 @@ + --> -
    +

    Introduction -

    +

    This document contains the release notes for the LLVM Compiler -Infrastructure, release 2.8. Here we describe the status of LLVM, including +Infrastructure, release 2.9. Here we describe the status of LLVM, including major improvements from the previous release and significant known problems. All LLVM releases may be downloaded from the LLVM releases web site.

    @@ -62,36 +62,25 @@ current one. To see the release notes for a specific release, please see the releases page.

    - - - - - - - - -
    +

    Sub-project Status Update -

    +

    -The LLVM 2.8 distribution currently consists of code from the core LLVM +The LLVM 2.9 distribution currently consists of code from the core LLVM repository (which roughly includes the LLVM optimizers, code generators and supporting tools), the Clang repository and the llvm-gcc repository. In addition to this code, the LLVM Project includes other sub-projects that are in @@ -102,9 +91,9 @@ development. Here we include updates on these subprojects. -

    +

    Clang: C/C++/Objective-C Frontend Toolkit -

    +
    @@ -115,110 +104,61 @@ 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.

    +(32- and 64-bit), and for darwin/arm targets.

    -

    In the LLVM 2.8 time-frame, the Clang team has made many improvements:

    - -
      -
    • Clang C++ is now feature-complete with respect to the ISO C++ 1998 and 2003 standards.
      • -
    • Added support for Objective-C++.
      • -
    • Clang now uses LLVM-MC to directly generate object code and to parse inline assembly (on Darwin).
      • -
    • Introduced many new warnings, including -Wmissing-field-initializers, -Wshadow, -Wno-protocol, -Wtautological-compare, -Wstrict-selector-match, -Wcast-align, -Wunused improvements, and greatly improved format-string checking.
      • -
    • Introduced the "libclang" library, a C interface to Clang intended to support IDE clients.
      • -
    • Added support for #pragma GCC visibility, #pragma align, and others.
      • -
    • Added support for SSE, AVX, ARM NEON, and AltiVec.
      • -
    • Improved support for many Microsoft extensions.
      • -
    • Implemented support for blocks in C++.
      • -
    • Implemented precompiled headers for C++.
      • -
    • Improved abstract syntax trees to retain more accurate source information.
      • -
    • Added driver support for handling LLVM IR and bitcode files directly.
      • -
    • Major improvements to compiler correctness for exception handling.
      • -
    • Improved generated code quality in some areas: -
        -
      • Good code generation for X86-32 and X86-64 ABI handling.
        • -
      • Improved code generation for bit-fields, although important work remains.
        • -
      -
      • -
    -
    - - -
    -Clang Static Analyzer -
    - -
    - -

    The Clang Static Analyzer - project is an effort to use static source code analysis techniques to - automatically find bugs in C and Objective-C programs (and hopefully C++ in the - future!). The tool is very good at finding bugs that occur on specific - paths through code, such as on error conditions.

    - -

    The LLVM 2.8 release fixes a number of bugs and slightly improves precision - over 2.7, but there are no major new features in the release. +

    In the LLVM 2.9 time-frame, the Clang team has made many improvements in C, +C++ and Objective-C support. C++ support is now generally rock solid, has +been exercised on a broad variety of code, and has several new C++'0x features +implemented (such as rvalue references and variadic templates). LLVM 2.9 has +also brought in a large range of bug fixes and minor features (e.g. __label__ +support), and is much more compatible with the Linux Kernel.

    + +

    If Clang rejects your code but another compiler accepts it, please take a +look at the language +compatibility guide to make sure this is not intentional or a known issue.

    -
    - - -
    -DragonEgg: llvm-gcc ported to gcc-4.5 -
    - -
    -

    -DragonEgg is a port of llvm-gcc to -gcc-4.5. Unlike llvm-gcc, dragonegg in theory does not require any gcc-4.5 -modifications whatsoever (currently one small patch is needed) thanks to the -new gcc plugin architecture. -DragonEgg is a gcc plugin that makes gcc-4.5 use the LLVM optimizers and code -generators instead of gcc's, just like with llvm-gcc. -

    - -

    -DragonEgg is still a work in progress, but it is able to compile a lot of code, -for example all of gcc, LLVM and clang. Currently Ada, C, C++ and Fortran work -well, while all other languages either don't work at all or only work poorly. -For the moment only the x86-32 and x86-64 targets are supported, and only on -linux and darwin (darwin may need additional gcc patches). -

    - -

    -The 2.8 release has the following notable changes:

      -
    • The plugin loads faster due to exporting fewer symbols.
      • -
    • Additional vector operations such as addps256 are now supported.
      • -
    • Ada global variables with no initial value are no longer zero initialized, -resulting in better optimization.
      • -
    • The '-fplugin-arg-dragonegg-enable-gcc-optzns' flag now runs all gcc -optimizers, rather than just a handful.
      • -
    • Fortran programs using common variables now link correctly.
      • -
    • GNU OMP constructs no longer crash the compiler.
      • +
    +
    + + +

    +DragonEgg: GCC front-ends, LLVM back-end +

    + +
    +

    +DragonEgg is a +gcc plugin that replaces GCC's +optimizers and code generators with LLVM's. +Currently it requires a patched version of gcc-4.5. +The plugin can target the x86-32 and x86-64 processor families and has been +used successfully on the Darwin, FreeBSD and Linux platforms. +The Ada, C, C++ and Fortran languages work well. +The plugin is capable of compiling plenty of Obj-C, Obj-C++ and Java but it is +not known whether the compiled code actually works or not! +

    + +

    +The 2.9 release has the following notable changes: +

      +
    • The plugin is much more stable when compiling Fortran.
      • +
    • Inline assembly where an asm output is tied to an input of a different size +is now supported in many more cases.
      • +
    • Basic support for the __float128 type was added. It is now possible to +generate LLVM IR from programs using __float128 but code generation does not +work yet.
      • +
    • Compiling Java programs no longer systematically crashes the plugin.
    -
    -VMKit: JVM/CLI Virtual Machine Implementation -
    - -
    -

    -The VMKit project is an implementation of -a Java Virtual Machine (Java VM or JVM) that uses LLVM for static and -just-in-time compilation. As of LLVM 2.8, VMKit now supports copying garbage -collectors, and can be configured to use MMTk's copy mark-sweep garbage -collector. In LLVM 2.8, the VMKit .NET VM is no longer being maintained. -

    -
    - - -
    +

    compiler-rt: Compiler Runtime Library -

    +

    @@ -231,19 +171,20 @@ 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).

    -

    -All of the code in the compiler-rt project is available under the standard LLVM -License, a "BSD-style" license. New in LLVM 2.8, compiler_rt now supports -soft floating point (for targets that don't have a real floating point unit), -and includes an extensive testsuite for the "blocks" language feature and the -blocks runtime included in compiler_rt.

    +

    In the LLVM 2.9 timeframe, compiler_rt has had several minor changes for + better ARM support, and a fairly major license change. All of the code in the + compiler-rt project is now dual + licensed under MIT and UIUC license, which allows you to use compiler-rt + in applications without the binary copyright reproduction clause. If you + prefer the LLVM/UIUC license, you are free to continue using it under that + license as well.

    -
    +

    LLDB: Low Level Debugger -

    +

    @@ -254,18 +195,18 @@ libraries in the larger LLVM Project, such as the Clang expression parser, the LLVM disassembler and the LLVM JIT.

    -LLDB is in early development and not included as part of the LLVM 2.8 release, -but is mature enough to support basic debugging scenarios on Mac OS X in C, -Objective-C and C++. We'd really like help extending and expanding LLDB to -support new platforms, new languages, new architectures, and new features. -

    +LLDB is has advanced by leaps and bounds in the 2.9 timeframe. It is +dramatically more stable and useful, and includes both a new tutorial and a side-by-side comparison with +GDB.

    -
    +

    libc++: C++ Standard Library -

    +

    @@ -275,19 +216,54 @@ ground up to specifically target the forthcoming C++'0X standard and focus on delivering great performance.

    -As of the LLVM 2.8 release, libc++ is virtually feature complete, but would -benefit from more testing and better integration with Clang++. It is also -looking forward to the C++ committee finalizing the C++'0x standard. +In the LLVM 2.9 timeframe, libc++ has had numerous bugs fixed, and is now being +co-developed with Clang's C++'0x mode.

    + +

    +Like compiler_rt, libc++ is now dual + licensed under the MIT and UIUC license, allowing it to be used more + permissively.

    + +

    +LLBrowse: IR Browser +

    + +
    +

    + + LLBrowse is an interactive viewer for LLVM modules. It can load any LLVM + module and displays its contents as an expandable tree view, facilitating an + easy way to inspect types, functions, global variables, or metadata nodes. It + is fully cross-platform, being based on the popular wxWidgets GUI toolkit. +

    +
    -
    -KLEE: A Symbolic Execution Virtual Machine +

    +VMKit +

    + +
    +

    The VMKit project is an implementation + of a Java Virtual Machine (Java VM or JVM) that uses LLVM for static and + just-in-time compilation. As of LLVM 2.9, VMKit now supports generational + garbage collectors. The garbage collectors are provided by the MMTk framework, + and VMKit can be configured to use one of the numerous implemented collectors + of MMTk. +

    + + + + -
    - External Open Source Projects Using LLVM 2.8 -
    +

    + External Open Source Projects Using LLVM 2.9 +

    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 2.8.

    + projects that have already been updated to work with LLVM 2.9.

    + -
    -TTA-based Codesign Environment (TCE) -
    +

    Crack Programming Language

    -TCE 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 and parallel program binaries. Processor -customization points include the register files, function units, supported -operations, and the interconnection network.

    +Crack 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.

    +
    + + + +

    TTA-based Codesign Environment (TCE)

    + +
    +

    TCE 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 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.

    +
    -

    TCE uses llvm-gcc/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.

    + + +

    PinaVM

    + +
    +

    PinaVM is an open +source, SystemC front-end. Unlike many +other front-ends, PinaVM actually executes the elaboration of the +program analyzed using LLVM's JIT infrastructure. It later enriches the +bitcode with SystemC-specific information.

    -
    -Horizon Bytecode Compiler -
    - +

    Pure

    +
    -

    -Horizon is a bytecode -language and compiler written on top of LLVM, intended for producing -single-address-space managed code operating systems that -run faster than the equivalent multiple-address-space C systems. -More in-depth blurb is available on the wiki.

    - +

    Pure 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 0.47 has been tested and is known to work with LLVM 2.9 + (and continues to work with older LLVM releases >= 2.5).

    -
    -Clam AntiVirus -
    +

    IcedTea Java Virtual Machine Implementation

    -Clam AntiVirus is an open source (GPL) -anti-virus toolkit for UNIX, designed especially for e-mail scanning on mail -gateways. Since version 0.96 it has bytecode -signatures that allow writing detections for complex malware. It -uses LLVM's JIT to speed up the execution of bytecode on -X86, X86-64, PPC32/64, falling back to its own interpreter otherwise. -The git version was updated to work with LLVM 2.8. +IcedTea provides a +harness to build OpenJDK using only free software build tools and to provide +replacements for the not-yet free parts of OpenJDK. One of the extensions that +IcedTea provides is a new JIT compiler named Shark which uses LLVM +to provide native code generation without introducing processor-dependent +code.

    -

    The -ClamAV bytecode compiler uses Clang and LLVM to compile a C-like -language, insert runtime checks, and generate ClamAV bytecode.

    - +

    OpenJDK 7 b112, IcedTea6 1.9 and IcedTea7 1.13 and later have been tested +and are known to work with LLVM 2.9 (and continue to work with older LLVM +releases >= 2.6 as well).

    -
    -Pure -
    - +

    Glasgow Haskell Compiler (GHC)

    +
    -

    -Pure -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. 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 C interface. The interpreter uses -LLVM as a backend to JIT-compile Pure programs to fast native code.

    - -

    Pure versions 0.44 and later have been tested and are known to work with -LLVM 2.8 (and continue to work with older LLVM releases >= 2.5).

    - -
    - - -
    -Glasgow Haskell Compiler (GHC) -
    - -
    -

    -GHC is an open source, -state-of-the-art programming suite for -Haskell, a standard lazy functional programming language. It includes -an optimizing static compiler generating good code for a variety of +

    GHC is an open source, state-of-the-art programming suite for Haskell, +a standard 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.

    In addition to the existing C and native code generators, GHC 7.0 now -supports an LLVM -code generator. GHC supports LLVM 2.7 and later.

    - +supports an LLVM code generator. GHC supports LLVM 2.7 and later.

    -
    -Clay Programming Language -
    - +

    Polly - Polyhedral optimizations for LLVM

    +
    -

    -Clay is a new systems programming -language that is specifically designed for generic programming. It makes -generic programming very concise thanks to whole program type propagation. It -uses LLVM as its backend.

    - +

    Polly is a project that aims to provide advanced memory access optimizations +to better take advantage of SIMD units, cache hierarchies, multiple cores or +even vector accelerators for LLVM. Built around an abstract mathematical +description based on Z-polyhedra, it provides the infrastructure to develop +advanced optimizations in LLVM and to connect complex external optimizers. In +its first year of existence Polly already provides an exact value-based +dependency analysis as well as basic SIMD and OpenMP code generation support. +Furthermore, Polly can use PoCC(Pluto) an advanced optimizer for data-locality +and parallelism.

    -
    -llvm-py Python Bindings for LLVM -
    +

    Rubinius

    -

    -llvm-py has been updated to work -with LLVM 2.8. llvm-py provides Python bindings for LLVM, allowing you to write a -compiler backend or a VM in Python.

    - +

    Rubinius is an environment + for running Ruby code which strives to write as much of the implementation in + Ruby as possible. Combined with a bytecode interpreting VM, it uses LLVM to + optimize and compile ruby code down to machine code. Techniques such as type + feedback, method inlining, and deoptimization are all used to remove dynamism + from ruby execution and increase performance.

    @@ -477,118 +427,14 @@ compiler backend or a VM in Python.

    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 output formats, the -Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7 and -2.8.

    +Faust compiler can now generate LLVM bitcode, and works with LLVM 2.7-2.9.

    - - -
    -Jade Just-in-time Adaptive Decoder Engine -
    - -
    -

    Jade -(Just-in-time Adaptive Decoder Engine) is a generic video decoder engine using -LLVM for just-in-time compilation of video decoder configurations. Those -configurations are designed by MPEG Reconfigurable Video Coding (RVC) committee. -MPEG RVC standard is built on a stream-based dataflow representation of -decoders. It is composed of a standard library of coding tools written in -RVC-CAL language and a dataflow configuration — block diagram — -of a decoder.

    - -

    Jade project is hosted as part of the Open -RVC-CAL Compiler and requires it to translate the RVC-CAL standard library -of video coding tools into an LLVM assembly code.

    - -
    - - -
    -LLVM JIT for Neko VM -
    - -
    -

    Neko LLVM JIT -replaces the standard Neko JIT with an LLVM-based implementation. While not -fully complete, it is already providing a 1.5x speedup on 64-bit systems. -Neko LLVM JIT requires LLVM 2.8 or later.

    - -
    - - -
    -Crack Scripting Language -
    - -
    -

    -Crack 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. Crack 0.2 works with LLVM 2.7, and the forthcoming Crack 0.2.1 release -builds on LLVM 2.8.

    - -
    - - -
    -Dresden TM Compiler (DTMC) -
    - -
    -

    -DTMC provides support for -Transactional Memory, which is an easy-to-use and efficient way to synchronize -accesses to shared memory. Transactions can contain normal C/C++ code (e.g., -__transaction { list.remove(x); x.refCount--; }) and will be executed -virtually atomically and isolated from other transactions.

    - -
    - - -
    -Kai Programming Language -
    - -
    -

    -Kai (Japanese 会 for -meeting/gathering) is an experimental interpreter that provides a highly -extensible runtime environment and explicit control over the compilation -process. Programs are defined using nested symbolic expressions, which are all -parsed into first-class values with minimal intrinsic semantics. Kai can -generate optimised code at run-time (using LLVM) in order to exploit the nature -of the underlying hardware and to integrate with external software libraries. -It is a unique exploration into world of dynamic code compilation, and the -interaction between high level and low level semantics.

    - -
    - - -
    -OSL: Open Shading Language -
    - -
    -

    -OSL is a shading -language designed for use in physically based renderers and in particular -production rendering. By using LLVM instead of the interpreter, it was able to -meet its performance goals (>= C-code) while retaining the benefits of -runtime specialization and a portable high-level language. -

    - -
    - - - + -
    - What's New in LLVM 2.8? -
    +

    + What's New in LLVM 2.9? +

    @@ -601,60 +447,66 @@ in this section.
    -
    +

    Major New Features -

    +
    -

    LLVM 2.8 includes several major new capabilities:

    +

    LLVM 2.9 includes several major new capabilities:

      -
    • As mentioned above, libc++ and LLDB are major new additions to the LLVM collective.
      • -
    • LLVM 2.8 now has pretty decent support for debugging optimized code. You - should be able to reliably get debug info for function arguments, assuming - that the value is actually available where you have stopped.
      • -
    • A new 'llvm-diff' tool is available that does a semantic diff of .ll - files.
      • -
    • The MC subproject has made major progress in this release. - Direct .o file writing support for darwin/x86[-64] is now reliable and - support for other targets and object file formats are in progress.
      • -
    + +
  10. Type Based Alias Analysis (TBAA) is now implemented and turned on by default + in Clang. This allows substantially better load/store optimization in some + cases. TBAA can be disabled by passing -fno-strict-aliasing. +
    11. +
  11. This release has seen a continued focus on quality of debug information. + LLVM now generates much higher fidelity debug information, particularly when + debugging optimized code.
    12. + +
  12. Inline assembly now supports multiple alternative constraints.
    13. + +
  13. A new backend for the NVIDIA PTX virtual ISA (used to target its GPUs) is + under rapid development. It is not generally useful in 2.9, but is making + rapid progress.
    14. + + +
    -
    +

    LLVM IR and Core Improvements -

    +

    LLVM IR has several new features for better support of new targets and that expose new optimization opportunities:

      -
    • The memcpy, memmove, and memset - intrinsics now take address space qualified pointers and a bit to indicate - whether the transfer is "volatile" or not. -
      • -
    • Per-instruction debug info metadata is much faster and uses less memory by - using the new DebugLoc class.
      • -
    • LLVM IR now has a more formalized concept of "trap values", which allow the optimizer - to optimize more aggressively in the presence of undefined behavior, while - still producing predictable results.
      • -
    • LLVM IR now supports two new linkage - types (linker_private_weak and linker_private_weak_def_auto) which map - onto some obscure MachO concepts.
      • +
    • The udiv, ashr, lshr, and shl + instructions now have support exact and nuw/nsw bits to indicate that they + don't overflow or shift out bits. This is useful for optimization of pointer differences and other cases.
      • + +
    • LLVM IR now supports the unnamed_addr + attribute to indicate that constant global variables with identical + initializers can be merged. This fixed an + issue where LLVM would incorrectly merge two globals which were supposed + to have distinct addresses.
      • + +
    • The new hotpatch attribute has been added + to allow runtime patching of functions.
    -
    +

    Optimizer Improvements -

    +
    @@ -662,45 +514,67 @@ expose new optimization opportunities:

    release includes a few major enhancements and additions to the optimizers:

      -
    • As mentioned above, the optimizer now has support for updating debug - information as it goes. A key aspect of this is the new llvm.dbg.value - intrinsic. This intrinsic represents debug info for variables that are - promoted to SSA values (typically by mem2reg or the -scalarrepl passes).
      • +
    • Link Time Optimization (LTO) has been improved to use MC for parsing inline + assembly and now can build large programs like Firefox 4 on both Mac OS X and + Linux.
      • + +
    • The new -loop-idiom pass recognizes memset/memcpy loops (and memset_pattern + on darwin), turning them into library calls, which are typically better + optimized than inline code. If you are building a libc and notice that your + memcpy and memset functions are compiled into infinite recursion, please build + with -ffreestanding or -fno-builtin to disable this pass.
      • + +
    • A new -early-cse pass does a fast pass over functions to fold constants, + simplify expressions, perform simple dead store elimination, and perform + common subexpression elimination. It does a good job at catching some of the + trivial redundancies that exist in unoptimized code, making later passes more + effective.
      • -
    • The JumpThreading pass is now much more aggressive about implied value - relations, allowing it to thread conditions like "a == 4" when a is known to - be 13 in one of the predecessors of a block. It does this in conjunction - with the new LazyValueInfo analysis pass.
      • -
    • The new RegionInfo analysis pass identifies single-entry single-exit regions - in the CFG. You can play with it with the "opt -regions -analyze" or - "opt -view-regions" commands.
      • -
    • The loop optimizer has significantly improved strength reduction and analysis - capabilities. Notably it is able to build on the trap value and signed - integer overflow information to optimize <= and >= loops.
      • -
    • The CallGraphSCCPassManager now has some basic support for iterating within - an SCC when a optimizer devirtualizes a function call. This allows inlining - through indirect call sites that are devirtualized by store-load forwarding - and other optimizations.
      • -
    • The new -loweratomic pass is available - to lower atomic instructions into their non-atomic form. This can be useful - to optimize generic code that expects to run in a single-threaded - environment.
      • +
    • A new -loop-instsimplify pass is used to clean up loop bodies in the loop + optimizer.
      • + +
    • The new TargetLibraryInfo interface allows mid-level optimizations to know + whether the current target's runtime library has certain functions. For + example, the optimizer can now transform integer-only printf calls to call + iprintf, allowing reduced code size for embedded C libraries (e.g. newlib). +
      • + +
    • LLVM has a new RegionPass + infrastructure for region-based optimizations.
      • + +
    • Several optimizer passes have been substantially sped up: + GVN is much faster on functions with deep dominator trees and lots of basic + blocks. The dominator tree and dominance frontier passes are much faster to + compute, and preserved by more passes (so they are computed less often). The + -scalar-repl pass is also much faster and doesn't use DominanceFrontier. +
      • + +
    • The Dead Store Elimination pass is more aggressive optimizing stores of + different types: e.g. a large store following a small one to the same address. + The MemCpyOptimizer pass handles several new forms of memcpy elimination.
      • + +
    • LLVM now optimizes various idioms for overflow detection into check of the + flag register on various CPUs. For example, we now compile: + + 
      +   unsigned long t = a+b;
+   if (t < a) ...
+
      + into: + 
      +   addq %rdi, %rbx
+   jno  LBB0_2
+
      +
      • +
    - -
    -
    +

    MC Level Improvements -

    +

    @@ -709,26 +583,39 @@ 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.

    -

    The MC subproject has made great leaps in LLVM 2.8. For example, support for - directly writing .o files from LLC (and clang) now works reliably for - darwin/x86[-64] (including inline assembly support) and the integrated - assembler is turned on by default in Clang for these targets. This provides - improved compile times among other things.

    -
      -
    • The entire compiler has converted over to using the MCStreamer assembler API - instead of writing out a .s file textually.
      • -
    • The "assembler parser" is far more mature than in 2.7, supporting a full - complement of directives, now supports assembler macros, etc.
      • -
    • The "assembler backend" has been completed, including support for relaxation - relocation processing and all the other things that an assembler does.
      • -
    • The MachO file format support is now fully functional and works.
      • -
    • The MC disassembler now fully supports ARM and Thumb. ARM assembler support - is still in early development though.
      • -
    • The X86 MC assembler now supports the X86 AES and AVX instruction set.
      • -
    • Work on ELF and COFF object files and ARM target support is well underway, - but isn't useful yet in LLVM 2.8. Please contact the llvmdev mailing list - if you're interested in this.
      • +
    • ELF MC support has matured enough for the integrated assembler to be turned + on by default in Clang on X86-32 and X86-64 ELF systems.
      • + +
    • MC supports and CodeGen uses the .file and .loc directives + for producing line number debug info. This produces more compact line + tables and easier to read .s files.
      • + +
    • MC supports the .cfi_* directives for producing DWARF + frame information, but it is still not used by CodeGen by default.
      • + + +
    • The MC assembler now generates much better diagnostics for common errors, + is much faster at matching instructions, is much more bug-compatible with + the GAS assembler, and is now generally useful for a broad range of X86 + assembly.
      • + +
    • We now have some basic internals + documentation for MC.
      • + +
    • .td files can now specify assembler aliases directly with the MnemonicAlias and InstAlias + tblgen classes.
      • + +
    • LLVM now has an experimental format-independent object file manipulation + library (lib/Object). It supports both PE/COFF and ELF. The llvm-nm tool has + been extended to work with native object files, and the new llvm-objdump tool + supports disassembly of object files (but no relocations are displayed yet). +
      • + +
    • Win32 PE-COFF support in the MC assembler has made a lot of progress in the + 2.9 timeframe, but is still not generally useful.
      • +

    For more information, please see the Intro to the LLVM MC Project Blog Post.

    -
    - +
    -
    +

    Target Independent Code Generator Improvements -

    +
    @@ -751,343 +637,187 @@ infrastructure, which allows us to implement more aggressive algorithms and make it run faster:

    -
    +

    X86-32 and X86-64 Target Improvements -

    +

    New features and major changes in the X86 target include:

    -
    +

    ARM Target Improvements -

    +

    New features of the ARM target include:

    +
    + + +

    +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 2.7, this section lists some "gotchas" that you may run into upgrading +on LLVM 2.8, this section lists some "gotchas" that you may run into upgrading from the previous release.

    +
  14. This is the last release to support the llvm-gcc frontend.
    15. - - -

    In addition, many APIs have changed in this release. Some of the major LLVM -API changes are:

    -
    -
    -Development Infrastructure Changes -
    +

    +Internal API Changes +

    -

    This section lists changes to the LLVM development infrastructure. This -mostly impacts users who actively work on LLVM or follow development on -mainline, but may also impact users who leverage the LLVM build infrastructure -or are interested in LLVM qualification.

    +

    In addition, many APIs have changed in this release. Some of the major + LLVM API changes are:

    -
    +

    Known Problems -

    +
    @@ -1100,9 +830,9 @@ there isn't already one.

    -
    +

    Experimental features included with this release -

    +
    @@ -1114,18 +844,19 @@ components, please contact us on the LLVMdev list.

    -
    +

    Known problems with the X86 back-end -

    +
    @@ -1134,21 +865,31 @@ href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVMdev list.

    all inline assembly that uses the X86 floating point stack. It supports the 'f' and 't' constraints, but not 'u'. -
  15. Win64 code generation wasn't widely tested. Everything should work, but we - expect small issues to happen. Also, llvm-gcc cannot build the mingw64 - runtime currently due to lack of support for the 'u' inline assembly - constraint and for X87 floating point inline assembly.
  16. The X86-64 backend does not yet support the LLVM IR instruction va_arg. Currently, front-ends support variadic argument constructs on X86-64 by lowering them manually.
    17. +
  17. Windows x64 (aka Win64) code generator has a few issues. +
      +
    • llvm-gcc cannot build the mingw-w64 runtime currently + due to lack of support for the 'u' inline assembly + constraint and for X87 floating point inline assembly.
      • +
    • On mingw-w64, you will see unresolved symbol __chkstk + due to Bug 8919. + It is fixed in r128206.
      • +
    • Miss-aligned MOVDQA might crash your program. It is due to + Bug 9483, + lack of handling aligned internal globals.
      • +
    +
    18. +
    -
    +

    Known problems with the PowerPC back-end -

    +
    @@ -1160,9 +901,9 @@ compilation, and lacks support for debug information.
    -
    +

    Known problems with the ARM back-end -

    +
    @@ -1177,9 +918,9 @@ results (PR1388).
    -
    +

    Known problems with the SPARC back-end -

    +
    @@ -1191,9 +932,9 @@ results (PR1388).
    -
    +

    Known problems with the MIPS back-end -

    +
    @@ -1204,9 +945,9 @@ results (PR1388).
    -
    +

    Known problems with the Alpha back-end -

    +
    @@ -1219,9 +960,9 @@ appropriate nops inserted to ensure restartability.
    -
    +

    Known problems with the C back-end -

    +
    @@ -1242,12 +983,14 @@ Depending on it for anything serious is not advised.

    -
    +

    Known problems with the llvm-gcc front-end -

    +
    +

    LLVM 2.9 will be the last release of llvm-gcc.

    +

    llvm-gcc is generally very stable for the C family of languages. The only major language feature of GCC not supported by llvm-gcc is the __builtin_apply family of builtins. However, some extensions @@ -1268,9 +1011,9 @@ consider using dragonegg instead.

    -
    +

    Additional Information -

    +