LLVM 2.7 Release Notes

@@ -44,7 +45,7 @@ Release Notes.-->

This document contains the release notes for the LLVM Compiler -Infrastructure, release 2.7. Here we describe the status of LLVM, including +Infrastructure, release 2.8. 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.

@@ -60,10 +61,6 @@ 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.

- -

FIXME: llvm.org moved to new server, mention new logo, Ted and Doug new code - owners, web page in llvm-www repos.

@@ -71,32 +68,20 @@ current one. To see the release notes for a specific release, please see the Almost dead code. include/llvm/Analysis/LiveValues.h => Dan lib/Transforms/IPO/MergeFunctions.cpp => consider for 2.8. - llvm/Analysis/PointerTracking.h => Edwin wants this, consider for 2.8. - ABCD, GEPSplitterPass - MSIL backend? - lib/Transforms/Utils/SSI.cpp -> ABCD depends on it. + GEPSplitterPass --> - - - + + +

@@ -106,7 +91,7 @@ Almost dead code.

-The LLVM 2.7 distribution currently consists of code from the core LLVM +The LLVM 2.8 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 @@ -123,27 +108,38 @@ development. Here we include updates on these subprojects.

The Clang project is ...

- -

In the LLVM 2.7 time-frame, the Clang team has made many improvements:

- -

FIXME: C++! Include a link to cxx_compatibility.html
FIXME: Static Analyzer improvements?
CIndex API and Python bindings: Clang now includes a C API as part of the -CIndex library. Although we make make some changes to the API in the future, it -is intended to be stable and has been designed for use by external projects. See -the Clang -doxygen CIndex -documentation for more details. The CIndex API also includings an preliminary -set of Python bindings.
ARM Support: Clang now has ABI support for both the Darwin and Linux ARM -ABIs. Coupled with many improvements to the LLVM ARM backend, Clang is now -suitable for use as a a beta quality ARM compiler.

Clang 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 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.
+

@@ -153,50 +149,71 @@ suitable for use as a a beta quality ARM compiler.

Previously announced in the 2.4, 2.5, and 2.6 LLVM releases, the Clang project also -includes an early stage static source code analysis tool for automatically finding bugs -in C and Objective-C programs. The tool performs checks to find -bugs that occur on a specific path within a program.

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.

In the LLVM 2.7 time-frame, the analyzer core has sprouted legs and...

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. +

-VMKit: JVM/CLI Virtual Machine Implementation +DragonEgg: llvm-gcc ported to gcc-4.5

-The VMKit project is an implementation of -a JVM and a CLI Virtual Machine (Microsoft .NET is an -implementation of the CLI) using LLVM for static and just-in-time -compilation.

+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. +

-With the release of LLVM 2.7, VMKit has shifted to a great framework for writing -virtual machines. VMKit now offers precise and efficient garbage collection with -multi-threading support, thanks to the MMTk memory management toolkit, as well -as just in time and ahead of time compilation with LLVM. The major changes in -VMKit 0.27 are:

+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.

Garbage collection: VMKit now uses the MMTk toolkit for garbage collectors. - The first collector to be ported is the MarkSweep collector, which is precise, - and drastically improves the performance of VMKit.

Line number information in the JVM: by using the debug metadata of LLVM, the - JVM now supports precise line number information, useful when printing a stack - trace.

Interface calls in the JVM: we implemented a variant of the Interface Method - Table technique for interface calls in the JVM. -

- + +

+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. +

@@ -216,61 +233,96 @@ libgcc routines).

All of the code in the compiler-rt project is available under the standard LLVM -License, a "BSD-style" license.

+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.

-DragonEgg: llvm-gcc ported to gcc-4.5 +LLDB: Low Level Debugger

-DragonEgg is a port of llvm-gcc to -gcc-4.5. Unlike llvm-gcc, which makes many intrusive changes to the underlying -gcc-4.2 code, dragonegg in theory does not require any gcc-4.5 modifications -whatsoever (currently one small patch is needed). This is thanks to the new -gcc plugin architecture, which -makes it possible to modify the behaviour of gcc at runtime by loading a plugin, -which is nothing more than a dynamic library which conforms to the gcc plugin -interface. DragonEgg is a gcc plugin that causes the LLVM optimizers to be run -instead of the gcc optimizers, and the LLVM code generators instead of the gcc -code generators, just like llvm-gcc. To use it, you add -"-fplugin=path/dragonegg.so" to the gcc-4.5 command line, and gcc-4.5 magically -becomes llvm-gcc-4.5! -

+LLDB is a brand new member of the LLVM +umbrella of projects. LLDB is a next generation, high-performance debugger. It +is built as a set of reusable components which highly leverage existing +libraries in the larger LLVM Project, such as the Clang expression parser, the +LLVM disassembler and the LLVM JIT.

-DragonEgg is still a work in progress. Currently C works very well, while C++, -Ada and Fortran work fairly well. 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 needs an additional gcc patch). +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.

+ + +

+libc++: C++ Standard Library +

+ +

+libc++ is another new member of the LLVM +family. It is an implementation of the C++ standard library, written from the +ground up to specifically target the forthcoming C++'0X standard and focus on +delivering great performance.

-The first dragonegg release will occur shortly after llvm-2.7 is released. +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.

-llvm-mc: Machine Code Toolkit +KLEE: A Symbolic Execution Virtual Machine

-The LLVM Machine Code (MC) Toolkit project is ... +KLEE is a symbolic execution framework for +programs in LLVM bitcode form. KLEE tries to symbolically evaluate "all" paths +through the application and records state transitions that lead to fault +states. This allows it to construct testcases that lead to faults and can even +be used to verify some algorithms.

Although KLEE does not have any major new features as of 2.8, we have made +various minor improvements, particular to ease development:

Added support for LLVM 2.8. KLEE currently maintains compatibility with + LLVM 2.6, 2.7, and 2.8.
Added a buildbot for 2.6, 2.7, and trunk. A 2.8 buildbot will be coming + soon following release.
Fixed many C++ code issues to allow building with Clang++. Mostly + complete, except for the version of MiniSAT which is inside the KLEE STP + version.
Improved support for building with separate source and build + directories.
Added support for "long double" on x86.
Initial work on KLEE support for using 'lit' test runner instead of + DejaGNU.
Added configure support for using an external version of + STP.

+ +

- External Open Source Projects Using LLVM 2.7 + External Open Source Projects Using LLVM 2.8

@@ -278,380 +330,609 @@ The LLVM Machine Code (MC) Toolkit project is ...

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 2.7.

+ projects that have already been updated to work with LLVM 2.8.

-Pure +TTA-based Codesign Environment (TCE)

-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.

+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.

Pure versions 0.43 and later have been tested and are known to work with -LLVM 2.7 (and continue to work with older LLVM releases >= 2.5).

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.

-Roadsend PHP +Horizon Bytecode Compiler

-Roadsend PHP (rphp) is an open -source implementation of the PHP programming -language that uses LLVM for its optimizer, JIT and static compiler. This is a -reimplementation of an earlier project that is now based on LLVM. -

+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.

-Unladen Swallow +Clam AntiVirus

-Unladen Swallow is a -branch of Python intended to be fully -compatible and significantly faster. It uses LLVM's optimization passes and JIT -compiler. +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.

+ +

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

-TTA-based Codesign Environment (TCE) +Pure

-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.

+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.

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.

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).

-SAFECode Compiler +Glasgow Haskell Compiler (GHC)

-SAFECode is a memory safe C -compiler built using LLVM. It takes standard, unannotated C code, analyzes the -code to ensure that memory accesses and array indexing operations are safe, and -instruments the code with run-time checks when safety cannot be proven -statically. -

+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.

- -

- What's New in LLVM 2.7?

- -

+ +

+Clay Programming Language +

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. -

+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.

-Major New Features +llvm-py Python Bindings for LLVM

+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.

LLVM 2.7 includes several major new capabilities:

-Extensible metadata solid. - -Debug info improvements: using metadata instead of llvm.dbg global variables. -This brings several enhancements including improved compile times. - -New instruction selector. -GHC Haskell ABI/ calling conv support. -Pre-Alpha support for unions in IR. -New InlineHint and StackAlignment function attributes -Code generator MC'ized except for debug info and EH. -New SCEV AA pass: -scev-aa -Inliner reuses arrays allocas when inlining multiple callers to reduce stack usage. -MC encoding and disassembler apis. -Optimal Edge Profiling? -Instcombine is now a library, has its own IRBuilder to simplify itself. -New llvm/Support/Regex.h API. FileCheck now does regex's -Many subtle pointer invalidation bugs in Callgraph have been fixed and it now uses asserting value handles. -MC Disassembler (with blog post), MCInstPrinter. Many X86 backend and AsmPrinter simplifications -Various tools like llc and opt now read either .ll or .bc files as input. -Malloc and free instructions got removed, along with LowerAllocations pass. -compiler-rt support for ARM. -completely llvm-gcc NEON support. -Can transcode from GAS to intel syntax with "llvm-mc foo.s -output-asm-variant=1" -JIT debug information with GDB 7.0 -New CodeGen Level CSE -CMake can now run tests, what other improvements? -ARM/Thumb using reg scavenging for stack object address materialization (PEI). -New SSAUpdater and MachineSSAUpdater classes for unstructured ssa updating, - changed jump threading, GVN, etc to use it which simplified them and speed - them up. -Combiner-AA improvements, why not on by default? -Pre-regalloc tail duplication -x86 sibcall / tailcall optimization in CCC mode. -New LSR with "full strength reduction" mode. Description? -Codegen level OptimizeExtsPass pass, takes advantage of x86 subregs. -Better code size analysis in loop unswitch, inliner code split out to a new - CodeMetrics class for reuse. -The ARM backend now has good support for ARMv4 backend (tested on StrongARM - hardware), previously only supported ARMv4T and newer. -Half-float support in APFloat -Indirect branch + address of label (blog post), particularly useful for interpreters. -Many changes to the pass ordering for improved optimization effectiveness. -BasicAA improved to be less dependent on "type safe" pointers, it can now look - through bitcasts more aggressively. -GVN PHI Translation improvements. blog post: http://blog.llvm.org/2009/12/advanced-topics-in-redundant-load.html -llvm.objectsize. -MachineSSAUpdater.h -PostRA scheduler for X86? -llvm.dbg.value, not being used by default though, more in 2.8. Many improvements to debug info -Support for the GCC option -fno-schedule-insns -non-temporal load/store -libllvm2.7.so?? configure with --enable-shared -dbgs() and -debug-buffer-size=N -New MicroBlaze backend. http://en.wikipedia.org/wiki/MicroBlaze -XMM subreg modeling for extraction of the low element. - - -Opt now works conservatively if no target data is set (is this fully working?) -Target data now has notion of 'native' integer data types which optimizations can use. -ARM backend generates instructions in unified assembly syntax. -New Analysis/InstructionSimplify.h interface for simplifying instructions that don't exist. -Jump threading is now much more aggressive at simplifying correlated - conditionals and threading blocks with otherwise complex logic. CondProp pass - removed (functionality merged into jump threading). -X86 and XCore supports returning arbitrary return values, returning too many values is - supported by returning through a hidden pointer. -verbose-asm now produces information about spill slots and loop nests - - -Defaults to RTTI off (smaller code size!), packagers should build with make REQUIRE_RTTI=1. -AndersAA got removed -PredSimplify, LoopVR, GVNPRE, RSProfiling (random sampling profiling) got removed. -LLVM command line tools now overwrite their output, before they would only do this with -f. -DOUT removed, use DEBUG(errs() instead. -Much stuff converted to use raw_ostream instead of std::ostream. -TargetAsmInfo renamed to MCAsmInfo -llvm/ADT/iterator.h gone. + +

+FAUST Real-Time Audio Signal Processing Language +

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

-LLVM IR and Core Improvements +Jade Just-in-time Adaptive Decoder Engine

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

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.

-Optimizer Improvements +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.

In addition to a large array of minor performance tweaks and bug fixes, this -release includes a few major enhancements and additions to the optimizers:

- -

...

+ +

+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.

Also, -anders-aa was removed

+ +

+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.

+ +

-Interpreter and JIT Improvements +Kai Programming Language

- -

The JIT now defaults -to compiling eagerly to avoid a race condition in the lazy JIT. -Clients that still want the lazy JIT can switch it on by calling -ExecutionEngine::DisableLazyCompilation(false).
It is now possible to create more than one JIT instance in the same process. -These JITs can generate machine code in parallel, -although you -still have to obey the other threading restrictions.

+Kai (Japanese ä¼ 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.

-Target Independent Code Generator Improvements +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. +

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:

+ + +

+ What's New in LLVM 2.8? +

+ + +

+ +

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. +

-X86-32 and X86-64 Target Improvements +Major New Features

New features of the X86 target include: -

- -

LLVM 2.8 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.

-PIC16 Target Improvements +LLVM IR and Core Improvements

New features of the PIC16 target include: -

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.

Things not yet supported:

+ + +

+Optimizer Improvements +

+ +

In addition to a large array of minor performance tweaks and bug fixes, this +release includes a few major enhancements and additions to the optimizers:

Variable arguments.
Interrupts/programs.
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).
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.

+ +

-ARM Target Improvements +MC Level Improvements

New features of the ARM target include: -

+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.

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.

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

-Other Target Specific Improvements +Target Independent Code Generator Improvements

New features of other targets include: -

+ +

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:

The clang/gcc -momit-leaf-frame-pointer argument is now supported.

The clang/gcc -ffunction-sections and -fdata-sections arguments are now + supported on ELF targets (like GCC).

The MachineCSE pass is now tuned and on by default. It eliminates common + subexpressions that are exposed when lowering to machine instructions.

The "local" register allocator was replaced by a new "fast" register + allocator. This new allocator (which is often used at -O0) is substantially + faster and produces better code than the old local register allocator.

A new LLC "-regalloc=default" option is available, which automatically + chooses a register allocator based on the -O optimization level.

The common code generator code was modified to promote illegal argument and + return value vectors to wider ones when possible instead of scalarizing + them. For example, <3 x float> will now pass in one SSE register + instead of 3 on X86. This generates substantially better code since the + rest of the code generator was already expecting this.

The code generator uses a new "COPY" machine instruction. This speeds up + the code generator and eliminates the need for targets to implement the + isMoveInstr hook. Also, the copyRegToReg hook was renamed to copyPhysReg + and simplified.

The code generator now has a "LocalStackSlotPass", which optimizes stack + slot access for targets (like ARM) that have limited stack displacement + addressing.

A new "PeepholeOptimizer" is available, which eliminates sign and zero + extends, and optimizes away compare instructions when the condition result + is available from a previous instruction.

Atomic operations now get legalized into simpler atomic operations if not + natively supported, easing the implementation burden on targets.

We have added two new bottom-up pre-allocation register pressure aware schedulers: +

The hybrid scheduler schedules aggressively to minimize schedule length when registers are available and avoid overscheduling in high pressure situations.
The instruction-level-parallelism scheduler schedules for maximum ILP when registers are available and avoid overscheduling in high pressure situations.

The tblgen type inference algorithm was rewritten to be more consistent and + diagnose more target bugs. If you have an out-of-tree backend, you may + find that it finds bugs in your target description. This support also + allows limited support for writing patterns for instructions that return + multiple results (e.g. a virtual register and a flag result). The + 'parallel' modifier in tblgen was removed, you should use the new support + for multiple results instead.

A new (experimental) "-rendermf" pass is available which renders a + MachineFunction into HTML, showing live ranges and other useful + details.

The new SubRegIndex tablegen class allows subregisters to be indexed + symbolically instead of numerically. If your target uses subregisters you + will need to adapt to use SubRegIndex when you upgrade to 2.8.

+ + +

The -fast-isel instruction selection path (used at -O0 on X86) was rewritten + to work bottom-up on basic blocks instead of top down. This makes it + slightly faster (because the MachineDCE pass is not needed any longer) and + allows it to generate better code in some cases.

-New Useful APIs +X86-32 and X86-64 Target Improvements

- -

This release includes a number of new APIs that are used internally, which - may also be useful for external clients. +

New features and major changes in the X86 target include:

...
The X86 backend now supports holding X87 floating point stack values + in registers across basic blocks, dramatically improving performance of code + that uses long double, and when targeting CPUs that don't support SSE.
The X86 backend now uses a SSEDomainFix pass to optimize SSE operations. On + Nehalem ("Core i7") and newer CPUs there is a 2 cycle latency penalty on + using a register in a different domain than where it was defined. This pass + optimizes away these stalls.
The X86 backend now promotes 16-bit integer operations to 32-bits when + possible. This avoids 0x66 prefixes, which are slow on some + microarchitectures and bloat the code on all of them.
The X86 backend now supports the Microsoft "thiscall" calling convention, + and a calling convention to support + ghc.
The X86 backend supports a new "llvm.x86.int" intrinsic, which maps onto + the X86 "int $42" and "int3" instructions.
At the IR level, the <2 x float> datatype is now promoted and passed + around as a <4 x float> instead of being passed and returned as an MMX + vector. If you have a frontend that uses this, please pass and return a + <2 x i32> instead (using bitcasts).
When printing .s files in verbose assembly mode (the default for clang -S), + the X86 backend now decodes X86 shuffle instructions and prints human + readable comments after the most inscrutable of them, e.g.: + +
```
+  insertps $113, %xmm3, %xmm0 # xmm0 = zero,xmm0[1,2],xmm3[1]
+  unpcklps %xmm1, %xmm0       # xmm0 = xmm0[0],xmm1[0],xmm0[1],xmm1[1]
+  pshufd   $1, %xmm1, %xmm1   # xmm1 = xmm1[1,0,0,0]
+
```
+

-Other Improvements and New Features +ARM Target Improvements

Other miscellaneous features include:

New features of the ARM target include: +

The ARM backend now optimizes tail calls into jumps.

Scheduling is improved through the new list-hybrid scheduler as well + as through better modeling of structural hazards.

Half float instructions are now + supported.

NEON support has been improved to model instructions which operate onto + multiple consecutive registers more aggressively. This avoids lots of + extraneous register copies.

The ARM backend now uses a new "ARMGlobalMerge" pass, which merges several + global variables into one, saving extra address computation (all the global + variables can be accessed via same base address) and potentially reducing + register pressure.

+ +

The ARM backend has received many minor improvements and tweaks which lead + to substantially better performance in a wide range of different scenarios. +

The ARM NEON intrinsics have been substantially reworked to reduce + redundancy and improve code generation. Some of the major changes are: +

+ All of the NEON load and store intrinsics (llvm.arm.neon.vld* and + llvm.arm.neon.vst*) take an extra parameter to specify the alignment in bytes + of the memory being accessed. +
+ The llvm.arm.neon.vaba intrinsic (vector absolute difference and + accumulate) has been removed. This operation is now represented using + the llvm.arm.neon.vabd intrinsic (vector absolute difference) followed by a + vector add. +
+ The llvm.arm.neon.vabdl and llvm.arm.neon.vabal intrinsics (lengthening + vector absolute difference with and without accumulation) have been removed. + They are represented using the llvm.arm.neon.vabd intrinsic (vector absolute + difference) followed by a vector zero-extend operation, and for vabal, + a vector add. +
+ The llvm.arm.neon.vmovn intrinsic has been removed. Calls of this intrinsic + are now replaced by vector truncate operations. +
+ The llvm.arm.neon.vmovls and llvm.arm.neon.vmovlu intrinsics have been + removed. They are now represented as vector sign-extend (vmovls) and + zero-extend (vmovlu) operations. +
+ The llvm.arm.neon.vaddl*, llvm.arm.neon.vaddw*, llvm.arm.neon.vsubl*, and + llvm.arm.neon.vsubw* intrinsics (lengthening vector add and subtract) have + been removed. They are replaced by vector add and vector subtract operations + where one (vaddw, vsubw) or both (vaddl, vsubl) of the operands are either + sign-extended or zero-extended. +
+ The llvm.arm.neon.vmulls, llvm.arm.neon.vmullu, llvm.arm.neon.vmlal*, and + llvm.arm.neon.vmlsl* intrinsics (lengthening vector multiply with and without + accumulation and subtraction) have been removed. These operations are now + represented as vector multiplications where the operands are either + sign-extended or zero-extended, followed by a vector add for vmlal or a + vector subtract for vmlsl. Note that the polynomial vector multiply + intrinsic, llvm.arm.neon.vmullp, remains unchanged. +

+ +

@@ -663,84 +944,144 @@ it run faster:

If you're already an LLVM user or developer with out-of-tree changes based -on LLVM 2.6, this section lists some "gotchas" that you may run into upgrading +on LLVM 2.7, this section lists some "gotchas" that you may run into upgrading from the previous release.

The LLVM interpreter now defaults to not using libffi even -if you have it installed. This makes it more likely that an LLVM built on one -system will work when copied to a similar system. To use libffi, -configure with --enable-libffi. -
The build configuration machinery changed the output directory names. It + wasn't clear to many people that a "Release-Asserts" build was a release build + without asserts. To make this more clear, "Release" does not include + assertions and "Release+Asserts" does (likewise, "Debug" and + "Debug+Asserts").
The MSIL Backend was removed, it was unsupported and broken.
The ABCD, SSI, and SCCVN passes were removed. These were not fully + functional and their behavior has been or will be subsumed by the + LazyValueInfo pass.
The LLVM IR 'Union' feature was removed. While this is a desirable feature + for LLVM IR to support, the existing implementation was half baked and + barely useful. We'd really like anyone interested to resurrect the work and + finish it for a future release.
If you're used to reading .ll files, you'll probably notice that .ll file + dumps don't produce #uses comments anymore. To get them, run a .bc file + through "llvm-dis --show-annotations".
Target triples are now stored in a normalized form, and all inputs from + humans are expected to be normalized by Triple::normalize before being + stored in a module triple or passed to another library.

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

ModuleProvider has been removed -and its methods moved to Module and GlobalValue. -Most clients can remove uses of ExistingModuleProvider, -replace getBitcodeModuleProvider with -getLazyBitcodeModule, and pass their Module to -functions that used to accept ModuleProvider. Clients who -wrote their own ModuleProviders will need to derive from -GVMaterializer instead and use -Module::setMaterializer to attach it to a -Module.
GhostLinkage has given up the ghost. -GlobalValues that have not yet been read from their backing -storage have the same linkage they will have after being read in. -Clients must replace calls to -GlobalValue::hasNotBeenReadFromBitcode with -GlobalValue::isMaterializable.
FIXME: Debug info has been totally redone. Add pointers to new APIs. Substantial caveats about compatibility of .ll and .bc files.
The llvm/Support/DataTypes.h header has moved -to llvm/System/DataTypes.h.
The isInteger, isIntOrIntVector, isFloatingPoint, -isFPOrFPVector and isFPOrFPVector methods have been renamed -isIntegerTy, isIntOrIntVectorTy, isFloatingPointTy, -isFPOrFPVectorTy and isFPOrFPVectorTy respectively.
LLVM 2.8 changes the internal order of operands in InvokeInst + and CallInst. + To be portable across releases, please use the CallSite class and the + high-level accessors, such as getCalledValue and + setUnwindDest. +
+ You can no longer pass use_iterators directly to cast<> (and similar), + because these routines tend to perform costly dereference operations more + than once. You have to dereference the iterators yourself and pass them in. +
+ llvm.memcpy.*, llvm.memset.*, llvm.memmove.* intrinsics take an extra + parameter now ("i1 isVolatile"), totaling 5 parameters, and the pointer + operands are now address-space qualified. + If you were creating these intrinsic calls and prototypes yourself (as opposed + to using Intrinsic::getDeclaration), you can use + UpgradeIntrinsicFunction/UpgradeIntrinsicCall to be portable across releases. +
+ SetCurrentDebugLocation takes a DebugLoc now instead of a MDNode. + Change your code to use + SetCurrentDebugLocation(DebugLoc::getFromDILocation(...)). +
+ The RegisterPass and RegisterAnalysisGroup templates are + considered deprecated, but continue to function in LLVM 2.8. Clients are + strongly advised to use the upcoming INITIALIZE_PASS() and + INITIALIZE_AG_PASS() macros instead. +
+ The constructor for the Triple class no longer tries to understand odd triple + specifications. Frontends should ensure that they only pass valid triples to + LLVM. The Triple::normalize utility method has been added to help front-ends + deal with funky triples. +
+ The signature of the GCMetadataPrinter::finishAssembly virtual + function changed: the raw_ostream and MCAsmInfo arguments + were dropped. GC plugins which compute stack maps must be updated to avoid + having the old definition overload the new signature. +
+ The signature of MemoryBuffer::getMemBuffer changed. Unfortunately + calls intended for the old version still compile, but will not work correctly, + leading to a confusing error about an invalid header in the bitcode. +
+ Some APIs were renamed: +
- llvm_report_error -> report_fatal_error
- llvm_install_error_handler -> install_fatal_error_handler
- llvm::DwarfExceptionHandling -> llvm::JITExceptionHandling
- VISIBILITY_HIDDEN -> LLVM_LIBRARY_VISIBILITY
+
+ Some public headers were renamed: +
- llvm/Assembly/AsmAnnotationWriter.h was renamed + to llvm/Assembly/AssemblyAnnotationWriter.h +

- - - -

- Portability and Supported Platforms + +

+Development Infrastructure Changes

LLVM is known to work on the following platforms:

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.

Intel and AMD machines (IA32, X86-64, AMD64, EMT-64) running Red Hat - Linux, Fedora Core, FreeBSD and AuroraUX (and probably other unix-like - systems).
PowerPC and X86-based Mac OS X systems, running 10.3 and above in 32-bit - and 64-bit modes.
Intel and AMD machines running on Win32 using MinGW libraries (native).
Intel and AMD machines running on Win32 with the Cygwin libraries (limited - support is available for native builds with Visual C++).
Sun x86 and AMD64 machines running Solaris 10, OpenSolaris 0906.
Alpha-based machines running Debian GNU/Linux.
The default for make check is now to use + the lit testing tool, which is + part of LLVM itself. You can use lit directly as well, or use + the llvm-lit tool which is created as part of a Makefile or CMake + build (and knows how to find the appropriate tools). See the lit + documentation and the blog + post, and PR5217 + for more information.
The LLVM test-suite infrastructure has a new "simple" test format + (make TEST=simple). The new format is intended to require only a + compiler and not a full set of LLVM tools. This makes it useful for testing + released compilers, for running the test suite with other compilers (for + performance comparisons), and makes sure that we are testing the compiler as + users would see it. The new format is also designed to work using reference + outputs instead of comparison to a baseline compiler, which makes it run much + faster and makes it less system dependent.
Significant progress has been made on a new interface to running the + LLVM test-suite (aka the LLVM "nightly tests") using + the LNT infrastructure. The LNT + interface to the test-suite brings significantly improved reporting + capabilities for monitoring the correctness and generated code quality + produced by LLVM over time.

- -

The core LLVM infrastructure uses GNU autoconf to adapt itself -to the machine and operating system on which it is built. However, minor -porting may be required to get LLVM to work on new platforms. We welcome your -portability patches and reports of successful builds or error messages.

@@ -756,15 +1097,6 @@ listed by component. If you run into a problem, please check the LLVM bug database and submit a bug if there isn't already one.

LLVM will not correctly compile on Solaris and/or OpenSolaris -using the stock GCC 3.x.x series 'out the box', -See: Broken versions of GCC and other tools. -However, A Modern GCC Build -for x86/x86-64 has been made available from the third party AuroraUX Project -that has been meticulously tested for bootstrapping LLVM & Clang.

@@ -782,11 +1114,10 @@ components, please contact us on the LLVMdev list.

The MSIL, Alpha, SPU, MIPS, PIC16, Blackfin, MSP430, SystemZ and MicroBlaze - backends are experimental.
The llc "-filetype=asm" (the default) is the only - supported value for this option. The MachO writer is experimental, and - works much better in mainline SVN.
The Alpha, Blackfin, CellSPU, MicroBlaze, MSP430, MIPS, SystemZ + and XCore backends are experimental.
llc "-filetype=obj" is experimental on all targets + other than darwin-i386 and darwin-x86_64.