LLVM 2.8 Release Notes

@@ -66,24 +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 --> - - - + + +

@@ -116,44 +114,32 @@ 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 and Objective-C on x86 (32- and 64-bit).

- -

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

- -

C++ Support: Clang is now capable of self-hosting! While still -alpha-quality, Clang's C++ support has matured enough to build LLVM and Clang, -and C++ is now enabled by default. See the Clang C++ compatibility -page for common C++ migration issues.
Objective-C: Clang now includes experimental support for an updated -Objective-C ABI on non-Darwin platforms. This includes support for non-fragile -instance variables and accelerated proxies, as well as greater potential for -future optimisations. The new ABI is used when compiling with the --fobjc-nonfragile-abi and -fgnu-runtime options. Code compiled with these -options may be mixed with code compiled with GCC or clang using the old GNU ABI, -but requires the libobjc2 runtime from the GNUstep project.
New warnings: Clang contains a number of new warnings, including -control-flow warnings (unreachable code, missing return statements in a -non-void function, etc.), sign-comparison warnings, and improved -format-string warnings.
CIndex API and Python bindings: Clang now includes a C API as part of the -CIndex library. Although we may 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 includes a 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 beta quality ARM compiler.

+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.
+

@@ -170,48 +156,64 @@ suitable for use as a beta quality ARM compiler. 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 made several major and - minor improvements, including better support for tracking the fields of - structures, initial support (not enabled by default yet) for doing - interprocedural (cross-function) analysis, and new checks have been added. +

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.

-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. -

+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. +

-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.

-DragonEgg is a new project which is seeing its first release with llvm-2.7. +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.

+ +

+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.

-The LLVM Machine Code (aka MC) sub-project of LLVM 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. It is a sub-project of LLVM which provides it with a number of advantages -over other compilers that do not have tightly integrated assembly-level tools. -For a gentle introduction, please see the Intro to the -LLVM MC Project Blog Post. +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.

2.7 includes major parts of the work required by the new MC Project. A few - targets have been refactored to support it, and work is underway to support a - native assembler in LLVM. This work is not complete in LLVM 2.7, but it has - made substantially more progress on LLVM mainline.

- -

One minor example of what MC can do is to transcode an AT&T syntax - X86 .s file into intel syntax. You can do this with something like:

-  llvm-mc foo.s -output-asm-variant=1 -o foo-intel.s
-

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.

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.

-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 (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 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.

-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 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.

-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. -

Icedtea6 1.8 and later have been tested and are known to work with -LLVM 2.7 (and continue to work with older LLVM releases >= 2.6 as well). -

+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.

-LLVM-Lua uses LLVM - to add JIT and static compiling support to the Lua VM. Lua -bytecode is analyzed to remove type checks, then LLVM is used to compile the -bytecode down to machine code. -

LLVM-Lua 1.2.0 have been tested and is known to work with LLVM 2.7. -

+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.

-MacRuby is an implementation of Ruby based on -core Mac OS technologies, sponsored by Apple Inc. It uses LLVM at runtime for -optimization passes, JIT compilation and exception handling. It also allows -static (ahead-of-time) compilation of Ruby code straight to machine code. -

The upcoming MacRuby 0.6 release works with LLVM 2.7. -

+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.

-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.

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.

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

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.

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.

- -

- What's New in LLVM 2.7?

- + + +

+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.

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. -

+ + +

+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.

-LLVM Community Changes +Kai Programming Language

+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.

+ +

+ + +

+OSL: Open Shading Language +

In addition to changes to the code, between LLVM 2.6 and 2.7, a number of -organization changes have happened: +

+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.

LLVM has a new official logo!

Ted Kremenek and Doug Gregor have stepped forward as Code Owners of the - Clang static analyzer and the Clang frontend, respectively.

LLVM now has an official Blog at - http://blog.llvm.org. This is a great way - to learn about new LLVM-related features as they are implemented. Several - features in this release are already explained on the blog.

The LLVM web pages are now checked into the SVN server, in the "www", - "www-pubs" and "www-releases" SVN modules. Previously they were hidden in a - largely inaccessible old CVS server.

+ +

+ 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. +

llvm.org is now hosted on a new (and much - faster) server. It is still graciously hosted at the University of Illinois - of Urbana Champaign.

@@ -529,43 +607,19 @@ organization changes have happened:

LLVM 2.7 includes several major new capabilities:

LLVM 2.8 includes several major new capabilities:

2.7 includes initial support for the MicroBlaze target. - MicroBlaze is a soft processor core designed for Xilinx FPGAs.
2.7 includes a new LLVM IR "extensible metadata" feature. This feature - supports many different use cases, including allowing front-end authors to - encode source level information into LLVM IR, which is consumed by later - language-specific passes. This is a great way to do high-level optimizations - like devirtualization, type-based alias analysis, etc. See the - Extensible Metadata Blog Post for more information.
2.7 encodes debug information -in a completely new way, built on extensible metadata. The new implementation -is much more memory efficient and paves the way for improvements to optimized -code debugging experience.
2.7 now directly supports taking the address of a label and doing an - indirect branch through a pointer. This is particularly useful for - interpreter loops, and is used to implement the GCC "address of label" - extension. For more information, see the -Address of Label and Indirect Branches in LLVM IR Blog Post. - -
2.7 is the first release to start supporting APIs for assembling and - disassembling target machine code. These APIs are useful for a variety of - low level clients, and are surfaced in the new "enhanced disassembly" API. - For more information see the The X86 - Disassembler Blog Post for more information.
2.7 includes major parts of the work required by the new MC Project, - see the MC update above for more information.
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.

@@ -580,39 +634,19 @@ Address of Label and Indirect Branches in LLVM IR Blog Post. expose new optimization opportunities:

LLVM IR now supports a 16-bit "half float" data type through two new intrinsics and APFloat support.
LLVM IR supports two new function - attributes: inlinehint and alignstack(n). The former is a hint to the - optimizer that a function was declared 'inline' and thus the inliner should - weight it higher when considering inlining it. The later - indicates to the code generator that the function diverges from the platform - ABI on stack alignment.
The new llvm.objectsize intrinsic - allows the optimizer to infer the sizes of memory objects in some cases. - This intrinsic is used to implement the GCC __builtin_object_size - extension.
LLVM IR now supports marking load and store instructions with "non-temporal" hints (building on the new - metadata feature). This hint encourages the code - generator to generate non-temporal accesses when possible, which are useful - for code that is carefully managing cache behavior. Currently, only the - X86 backend provides target support for this feature.
LLVM 2.7 has pre-alpha support for unions in LLVM IR. - Unfortunately, this support is not really usable in 2.7, so if you're - interested in pushing it forward, please help contribute to LLVM mainline.
LLVM 2.8 changes the internal order of operands in InvokeInst - and CallInst. - To be portable across releases, resort to CallSite and the - high-level accessors, such as getCalledValue and setUnwindDest. +
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 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 JIT now supports generating debug information and is compatible with -the new GDB 7.0 (and later) interfaces for registering dynamically generated -debug info.

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 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).

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.

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.

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

@@ -715,49 +751,58 @@ infrastructure, which allows us to implement more aggressive algorithms and make it run faster:

The 'llc -asm-verbose' option (which is now the default) has been enhanced - to emit many useful comments to .s files indicating information about spill - slots and loop nest structure. This should make it much easier to read and - understand assembly files. This is wired up in llvm-gcc and clang to - the -fverbose-asm option.
New LSR with "full strength reduction" mode, which can reduce address - register pressure in loops where address generation is important.
A new codegen level Common Subexpression Elimination pass (MachineCSE) - is available and enabled by default. It catches redundancies exposed by - lowering.
A new pre-register-allocation tail duplication pass is available and enabled - by default, it can substantially improve branch prediction quality in some - cases.
A new sign and zero extension optimization pass (OptimizeExtsPass) - is available and enabled by default. This pass can takes advantage - architecture features like x86-64 implicit zero extension behavior and - sub-registers.
The code generator now supports a mode where it attempts to preserve the - order of instructions in the input code. This is important for source that - is hand scheduled and extremely sensitive to scheduling. It is compatible - with the GCC -fno-schedule-insns option.
The target-independent code generator now supports generating code with - arbitrary numbers of result values. Returning more values than was - previously supported is handled by returning through a hidden pointer. In - 2.7, only the X86 and XCore targets have adopted support for this - though.
The code generator now supports generating code that follows the - Glasgow Haskell Compiler Calling - Convention and ABI.
The "DAG instruction - selection" phase of the code generator has been largely rewritten for - 2.7. Previously, tblgen spit out tons of C++ code which was compiled and - linked into the target to do the pattern matching, now it emits a much - smaller table which is read by the target-independent code. The primary - advantages of this approach is that the size and compile time of various - targets is much improved. The X86 code generator shrunk by 1.5MB of code, - for example.
Almost the entire code generator has switched to emitting code through the - MC interfaces instead of printing textually to the .s file. This led to a - number of cleanups and speedups. In 2.7, debug an exception handling - information does not go through MC yet.
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: +
1. The hybrid scheduler schedules aggressively to minimize schedule length when registers are available and avoid overscheduling in high pressure situations.
2. 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 features of the X86 target include: +

New features and major changes in the X86 target include:

The X86 backend now optimizes tails calls much more aggressively for - functions that use the standard C calling convention.
The X86 backend now models scalar SSE registers as subregs of the SSE vector - registers, making the code generator more aggressive in cases where scalars - and vector types are mixed.
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]
+
```
+

- -

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

- -

The optimizer uses the new CodeMetrics class to measure the size of code. - Various passes (like the inliner, loop unswitcher, etc) all use this to make - more accurate estimates of the code size impact of various - optimizations.
A new - llvm/Analysis/InstructionSimplify.h interface is available for doing - symbolic simplification of instructions (e.g. a+0 -> a) - without requiring the instruction to exist. This centralizes a lot of - ad-hoc symbolic manipulation code scattered in various passes.
The optimizer now uses a new SSAUpdater - class which efficiently supports - doing unstructured SSA update operations. This centralized a bunch of code - scattered throughout various passes (e.g. jump threading, lcssa, - loop rotate, etc) for doing this sort of thing. The code generator has a - similar - MachineSSAUpdater class.
The - llvm/Support/Regex.h header exposes a platform independent regular - expression API. Building on this, the FileCheck utility now supports - regular exressions.
raw_ostream now supports a circular "debug stream" accessed with "dbgs()". - By default, this stream works the same way as "errs()", but if you pass - -debug-buffer-size=1000 to opt, the debug stream is capped to a - fixed sized circular buffer and the output is printed at the end of the - program's execution. This is helpful if you have a long lived compiler - process and you're interested in seeing snapshots in time.

- - -

Other miscellaneous features include:

- -

You can now build LLVM as a big dynamic library (e.g. "libllvm2.7.so"). To - get this, configure LLVM with the --enable-shared option.
LLVM command line tools now overwrite their output by default. Previously, - they would only do this with -f. This makes them more convenient to use, and - behave more like standard unix tools.
The ARM NEON intrinsics have been substantially reworked to reduce + redundancy and improve code generation. Some of the major changes are: +
1. + 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. +
2. + 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. +
3. + 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. +
4. + The llvm.arm.neon.vmovn intrinsic has been removed. Calls of this intrinsic + are now replaced by vector truncate operations. +
5. + 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. +
6. + 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. +
7. + 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. +
+
The opt and llc tools now autodetect whether their input is a .ll or .bc - file, and automatically do the right thing. This means you don't need to - explicitly use the llvm-as tool for most things.

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 Andersen's alias analysis ("anders-aa") pass, the Predicate Simplifier -("predsimplify") pass, the LoopVR pass, the GVNPRE pass, and the random sampling -profiling ("rsprofiling") passes have all been removed. They were not being -actively maintained and had substantial problems. If you are interested in -these components, you are welcome to ressurect them from SVN, fix the -correctness problems, and resubmit them to mainline.
LLVM now defaults to building most libraries with RTTI turned off, providing -a code size reduction. Packagers who are interested in building LLVM to support -plugins that require RTTI information should build with "make REQUIRE_RTTI=1" -and should read the new Advice on Packaging LLVM -document.
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.
Debug information uses a completely different representation, an LLVM 2.6 -.bc file should work with LLVM 2.7, but debug info won't come forward.
The LLVM 2.6 (and earlier) "malloc" and "free" instructions got removed, - along with LowerAllocations pass. Now you should just use a call to the - malloc and free functions in libc. These calls are optimized as well as - the old instructions were.
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:

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
+
The add, sub, and mul instructions no longer -support floating-point operands. The fadd, fsub, and -fmul instructions should be used for this purpose instead.
+ 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 10.4 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.

@@ -987,15 +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.

The C backend has numerous problems and is not being actively maintained. +Depending on it for anything serious is not advised.

The C backend has only basic support for inline assembly code.

- Known problems with the llvm-gcc C and C++ front-end + Known problems with the llvm-gcc front-end

The only major language feature of GCC not supported by llvm-gcc is - the __builtin_apply family of builtins. However, some extensions - are only supported on some targets. For example, trampolines are only - supported on some targets (these are used when you take the address of a - nested function).

- -

- Known problems with the llvm-gcc Fortran front-end -

Fortran support generally works, but there are still several unresolved bugs - in Bugzilla. Please see the - tools/gfortran component for details.

- Known problems with the llvm-gcc Ada front-end -

-The llvm-gcc 4.2 Ada compiler works fairly well; however, this is not a mature -technology, and problems should be expected. -

The Ada front-end currently only builds on X86-32. This is mainly due -to lack of trampoline support (pointers to nested functions) on other platforms. -However, it also fails to build on X86-64 -which does support trampolines.
The Ada front-end fails to bootstrap. -This is due to lack of LLVM support for setjmp/longjmp style -exception handling, which is used internally by the compiler. -Workaround: configure with --disable-bootstrap.
The c380004, c393010 -and cxg2021 ACATS tests fail -(c380004 also fails with gcc-4.2 mainline). -If the compiler is built with checks disabled then c393010 -causes the compiler to go into an infinite loop, using up all system memory.
Some GCC specific Ada tests continue to crash the compiler.
The -E binder option (exception backtraces) -does not work and will result in programs -crashing if an exception is raised. Workaround: do not use -E.
Only discrete types are allowed to start -or finish at a non-byte offset in a record. Workaround: do not pack records -or use representation clauses that result in a field of a non-discrete type -starting or finishing in the middle of a byte.
The lli interpreter considers -'main' as generated by the Ada binder to be invalid. -Workaround: hand edit the file to use pointers for argv and -envp rather than integers.
The -fstack-check option is -ignored.

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 + are only supported on some targets. For example, trampolines are only + supported on some targets (these are used when you take the address of a + nested function).

+ +

Fortran support generally works, but there are still several unresolved bugs + in Bugzilla. Please see the + tools/gfortran component for details. Note that llvm-gcc is missing major + Fortran performance work in the frontend and library that went into GCC after + 4.2. If you are interested in Fortran, we recommend that you consider using + dragonegg instead.

+ +

The llvm-gcc 4.2 Ada compiler has basic functionality, but is no longer being +actively maintained. If you are interested in Ada, we recommend that you +consider using dragonegg instead.