LLVM 2.5 Release Notes

Introduction @@ -34,7 +43,7 @@

This document contains the release notes for the LLVM Compiler -Infrastructure, release 2.5. 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.

@@ -42,8 +51,8 @@ href="http://llvm.org/releases/">LLVM releases web site.

For more information about LLVM, including information about the latest release, please check out the main LLVM web site. If you have questions or comments, the LLVM Developer's Mailing -List is a good place to send them.

+href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM Developer's +Mailing List is a good place to send them.

Note that if you are reading this file from a Subversion checkout or the main LLVM web page, this document applies to the next release, not the @@ -51,25 +60,29 @@ current one. To see the release notes for a specific release, please see the releases page.

- - + + + @@ -80,12 +93,11 @@ initial support for debug line numbers when optimization enabled, not useful in

-The LLVM 2.5 distribution currently consists of code from the core LLVM -repository —which roughly includes the LLVM optimizers, code generators -and supporting tools — and the llvm-gcc repository. In addition to this -code, the LLVM Project includes other sub-projects that are in development. The -two which are the most actively developed are the Clang -Project and the VMKit Project. +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 +development. Here we include updates on these subprojects.

@@ -98,36 +110,49 @@ Project and the VMKit Project.

The Clang project is an effort to build -a set of new 'LLVM native' front-end technologies for the LLVM optimizer and -code generator. While Clang is not included in the LLVM 2.5 release, it is -continuing to make major strides forward in all areas. Its C and Objective-C -parsing and code generation support is now very solid. For example, it is -capable of successfully building many real-world applications for X86-32 -andX86-64, -including the FreeBSD -kernel. C++ is also -making incredible progress, -and work on templates has recently started.

- -

While Clang is not yet production quality, it is progressing very nicely and -is quite usable for building many C and Objective-C applications. If you are -interested in fast compiles and good diagnostics, we encourage you to try it out -by building from mainline -and reporting any issues you hit to the Clang front-end mailing -list.

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 and Objective-C on x86 (32- and 64-bit).

In the LLVM 2.5 time-frame, the Clang team has made many improvements:

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

Clang now has a new driver, which is focused on providing a GCC-compatible - interface.
The X86-64 ABI is now supported.
Precompiled header support is now implemented.
Objective-C support is significantly improved beyond LLVM 2.4, supporting - many features, such as Objective-C Garbage Collection.
Many many bugs are fixed and many features have been added.
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.

@@ -138,25 +163,18 @@ list.

Previously announced in the last LLVM release, 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 a growing set of checks to find -bugs that occur on a specific path within a program.

- -

In the LLVM 2.5 time-frame there have been many significant improvements to -the analyzer's core path simulation engine and machinery for generating -path-based bug reports to end-users. Particularly noteworthy improvements -include experimental support for full field-sensitivity and reasoning about heap -objects as well as an improved value-constraints subengine that does a much -better job of reasoning about inequality relationships (e.g., x > 2) -between variables and constants. - -

The set of checks performed by the static analyzer continue to expand, and -future plans for the tool include full source-level inter-procedural analysis -and deeper checks such as buffer overrun detection. There are many opportunities -to extend and enhance the static analyzer, and anyone interested in working on -this project is encouraged to get involved!

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 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. +

@@ -168,44 +186,135 @@ this project is encouraged to get involved!

The VMKit project is an implementation of -a JVM and a CLI Virtual Machines (Microsoft .NET is an -implementation of the CLI) using the Just-In-Time compiler of LLVM.

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

Following LLVM 2.5, VMKit has its second release that you can find on its -webpage. The release includes -bug fixes, cleanup and new features. The major changes are:

+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:

Ahead of Time compiler: compiles .class files to llvm .bc. VMKit uses this -functionality to native compile the standard classes (eg java.lang.String). -Users can compile AOT .class files into dynamic libraries and run them with the -help of VMKit.
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. +

New exception model: the dwarf exception model is very slow for -exception-intensive applications, so the JVM has had a new implementation of -exceptions which check at each function call if an exception happened. There is -a low performance penalty on applications without exceptions, but it is a big -gain for exception-intensive applications. For example the jack benchmark in -Spec JVM98 is 6x faster (performance gain of 83%).

User-level management of thread stacks, so that thread local data access -at runtime is fast and portable.

+ +

+compiler-rt: Compiler Runtime Library +

Implementation of biased locking for faster object synchronizations at -runtime.

+The new LLVM compiler-rt project +is a simple library that provides an implementation of the low-level +target-specific hooks required by code generation and other runtime components. +For example, when compiling for a 32-bit target, converting a double to a 64-bit +unsigned integer is compiled into a runtime call to the "__fixunsdfdi" +function. The compiler-rt library provides highly optimized implementations of +this and other low-level routines (some are 3x faster than the equivalent +libgcc routines).

New support for OSX/X64, Linux/X64 (with the Boehm GC) and Linux/ppc32.

+All of the code in the compiler-rt project is available under the standard LLVM +License, a "BSD-style" license. New in LLVM 2.7: compiler_rt now +supports ARM targets.

+ +

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

+ +

+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! +

+ +

+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). +

+ +

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

+ +

+ + + +

+llvm-mc: Machine Code Toolkit +

+ +

+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. +

+ +

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
+

+ +

- External Projects Using LLVM 2.5 + External Open Source Projects Using LLVM 2.7

+ +

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 @@ -222,171 +331,278 @@ 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.

In addition to the usual algebraic data structures, Pure also has -MATLAB-style matrices in order to support numeric computations and signal -processing in an efficient way. Pure is mainly aimed at mathematical -applications right now, but it has been designed as a general purpose language. -The dynamic interpreter environment and the C interface make it possible to use -it as a kind of functional scripting language for many application areas. +

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).

+ +

+ + +

+Roadsend PHP +

+ +

+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. +

+ + +

+Unladen Swallow +

+ +

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

+ +

+TTA-based Codesign Environment (TCE) +

+ +

+TCE is a toolset for designing +application-specific processors (ASP) based on the Transport triggered +architecture (TTA). The toolset provides a complete co-design flow from C/C++ +programs down to synthesizable VHDL and parallel program binaries. Processor +customization points include the register files, function units, supported +operations, and the interconnection network.

+ +

TCE uses 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.

+ +

-LLVM D Compiler +SAFECode Compiler

-LDC is an implementation of -the D Programming Language using the LLVM optimizer and code generator. -LDC project works great with the LLVM 2.5 release. General improvements in this -cycle have included new inline asm constraint handling, better debug info -support, general bugfixes, and better x86-64 support. This has allowed -some major improvements in LDC, getting us much closer to being as -fully featured as the original DMD compiler from DigitalMars. +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.

-Roadsend PHP +IcedTea Java Virtual Machine Implementation +

+ +

+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). +

+ + +

+LLVM-Lua +

+ +

+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. +

+ + +

+MacRuby

Roadsend PHP (rphp) is an open -source compiler for 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 the LLVM.

+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. +

+ + +

+Glasgow Haskell Compiler (GHC) +

+ +

+GHC is an open source, +state-of-the-art programming suite for Haskell, a standard lazy +functional programming language. It includes an optimizing static +compiler generating good code for a variety of platforms, together +with an interactive system for convenient, quick development.

+ +

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

- What's New in LLVM 2.5? + What's New in LLVM 2.7?

This release includes a huge number of bug fixes, performance tweaks, and +

This release includes a huge number of bug fixes, performance tweaks and minor improvements. Some of the major improvements and new features are listed in this section.

-Major New Features +LLVM Community Changes

LLVM 2.5 includes several major new capabilities:

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

LLVM 2.5 includes a brand new XCore backend.
llvm-gcc now generally supports the GFortran front-end, and the precompiled -release binaries now support Fortran, even on Mac OS/X.
LLVM has a new official logo!
CMake is now used by the LLVM build process -on Windows. It automatically generates Visual Studio project files (and -more) from a set of simple text files. This makes it much easier to -maintain. In time, we'd like to standardize on CMake for everything.
Ted Kremenek and Doug Gregor have stepped forward as Code Owners of the + Clang static analyzer and the Clang frontend, respectively.
LLVM 2.5 now uses (and includes) Google Test for unit testing.
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 native code generator now supports arbitrary precision integers. -Types like i33 have long been valid in the LLVM IR, but were previously -only supported by the interpreter. Note that the C backend still does not -support these.
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.
LLVM 2.5 no longer uses 'bison', so it is easier to build on Windows.
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.

-llvm-gcc 4.2 Improvements +Major New Features

LLVM fully supports the llvm-gcc 4.2 front-end, which marries the GCC -front-ends and driver with the LLVM optimizer and code generator. It currently -includes support for the C, C++, Objective-C, Ada, and Fortran front-ends.

LLVM 2.7 includes several major new capabilities:

In this release, the GCC inliner is completely disabled. Previously the GCC -inliner was used to handle always-inline functions and other cases. This caused -problems with code size growth, and it is completely disabled in this -release.
llvm-gcc (and LLVM in general) now support code generation for stack -canaries, which is an effective form of buffer overflow -protection. llvm-gcc supports this with the -fstack-protector -command line option (just like GCC). In LLVM IR, you can request code -generation for stack canaries with function attributes. -
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.

LLVM IR and Core Improvements

LLVM IR has several new features that are used by our existing front-ends and -can be useful if you are writing a front-end for LLVM:

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

The shufflevector instruction -has been generalized to allow different shuffle mask width than its input -vectors. This allows you to use shufflevector to combine two -"<4 x float>" vectors into a "<8 x float>" for example.
LLVM IR now supports new intrinsics for computing and acting on overflow of integer operations. This allows -efficient code generation for languages that must trap or throw an exception on -overflow. While these intrinsics work on all targets, they only generate -efficient code on X86 so far.
LLVM IR now supports a new private -linkage type to produce labels that are stripped by the assembler before it -produces a .o file (thus they are invisible to the linker).
LLVM IR supports two new attributes for better alias analysis. The noalias attribute can now be used on the -return value of a function to indicate that it returns new memory (e.g. -'malloc', 'calloc', etc).
The new nocapture attribute can be -used on pointer arguments to functions that access through but do not return the -pointer in a data structure that out lives the call (e.g. 'strlen', 'memcpy', -and many others). The simplifylibcalls pass applies these attributes to -standard libc functions.
The parser for ".ll" files in lib/AsmParser is now completely rewritten as a -recursive descent parser. This parser produces better error messages (including -caret diagnostics) is less fragile (less likely to crash on strange things) does -not leak memory, is more efficient, and eliminates LLVM's last use of the -'bison' tool.
Debug information representation and manipulation internals have been - consolidated to use a new set of classes in - llvm/Analysis/DebugInfo.h classes. These routines are more - efficient, robust, and extensible and replace the older mechanisms. - llvm-gcc, clang, and the code generator now use them to create and process - debug information.
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.

@@ -399,26 +615,80 @@ not leak memory, is more efficient, and eliminates LLVM's last use of the

In addition to a huge array of bug fixes and minor performance tweaks, this +

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:

The loop optimizer now improves floating point induction variables in -several ways, including adding shadow induction variables to avoid -"integer <-> floating point" conversions in loops when safe.
The inliner now merges arrays stack objects in different callees when + inlining multiple call sites into one function. This reduces the stack size + of the resultant function.
The -basicaa alias analysis pass (which is the default) has been improved to + be less dependent on "type safe" pointers. It can now look through bitcasts + and other constructs more aggressively, allowing better load/store + optimization.
The load elimination optimization in the GVN Pass [intro + blog post] has been substantially improved to be more aggressive about + partial redundancy elimination and do more aggressive phi translation. Please + see the + Advanced Topics in Redundant Load Elimination with a Focus on PHI Translation + Blog Post for more details.
The module target data string now + includes a notion of 'native' integer data types for the target. This + helps mid-level optimizations avoid promoting complex sequences of + operations to data types that are not natively supported (e.g. converting + i32 operations to i64 on 32-bit chips).
The mid-level optimizer is now conservative when operating on a module with + no target data. Previously, it would default to SparcV9 settings, which is + not what most people expected.
Jump threading is now much more aggressive at simplifying correlated + conditionals and threading blocks with otherwise complex logic. It has + subsumed the old "Conditional Propagation" pass, and -condprop has been + removed from LLVM 2.7.
The -instcombine pass has been refactored from being one huge file to being + a library of its own. Internally, it uses a customized IRBuilder to clean + it up and simplify it.
The optimal edge profiling pass is reliable and much more complete than in + 2.6. It can be used with the llvm-prof tool but isn't wired up to the + llvm-gcc and clang command line options yet.
A new experimental alias analysis implementation, -scev-aa, has been added. + It uses LLVM's Scalar Evolution implementation to do symbolic analysis of + pointer offset expressions to disambiguate pointers. It can catch a few + cases that basicaa cannot, particularly in complex loop nests.
The default pass ordering has been tweaked for improved optimization + effectiveness.

+ +

+ + + +

+Interpreter and JIT Improvements +

The "-mem2reg" pass is now much faster on code with huge basic blocks.

The "-jump-threading" pass is more powerful: it is iterative - and handles threading based on values with fully and partially redundant - loads.

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 "-memdep" memory dependence analysis pass (used by GVN and memcpyopt) is - both faster and more aggressive.
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 "-scalarrepl" scalar replacement of aggregates pass is more aggressive - about promoting unions to registers.
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.

@@ -436,33 +706,49 @@ infrastructure, which allows us to implement more aggressive algorithms and make it run faster:

The Writing an LLVM Compiler -Backend document has been greatly expanded and is substantially more -complete.
The SelectionDAG type legalization logic has been completely rewritten, is -now more powerful (it supports arbitrary precision integer types for example), -and more correct in several corner cases. The type legalizer converts -operations on types that are not natively supported by the target machine into -equivalent code sequences that only use natively supported types. The old type -legalizer is still available (for now) and will be used if --disable-legalize-types is passed to the code generator. -
The code generator now supports widening illegal vectors to larger legal -ones (for example, converting operations on <3 x float> to work on -<4 x float>) which is very important for common graphics -applications.
The assembly printers for each target are now split out into their own -libraries that are separate from the main code generation logic. This reduces -code size of JIT compilers by not requiring them to be linked in.
The 'fast' instruction selection path (used at -O0 and for fast JIT - compilers) now supports accelerating codegen for code that uses exception - handling constructs.
The optional PBQP register allocator now supports register coalescing.
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.

@@ -476,116 +762,118 @@ code size of JIT compilers by not requiring them to be linked in.

The llvm.returnaddress -intrinsic (which is used to implement __builtin_return_address) now -supports non-zero stack depths on X86.
The X86 backend now supports code generation of vector shift operations -using SSE instructions.
X86-64 code generation now takes advantage of red zone, unless the --mno-red-zone option is specified.
The X86 backend now supports using address space #256 in LLVM IR as a way of -performing memory references off the GS segment register. This allows a -front-end to take advantage of very low-level programming techniques when -targetting X86 CPUs. See test/CodeGen/X86/movgs.ll for a simple -example.
The X86 backend now supports a -disable-mmx command line option to - prevent use of MMX even on chips that support it. This is important for cases - where code does not contain the proper llvm.x86.mmx.emms - intrinsics.
The X86 JIT now detects the new Intel Core i7 and Atom chips; - auto-configuring itself appropriately for the features of these chips.
The JIT now supports exception handling constructs on Linux/X86-64 and - Darwin/x86-64.
The JIT supports Thread Local Storage (TLS) on Linux/X86-32 but not yet on - X86-64.
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.

-PIC16 Target Improvements +ARM Target Improvements

New features of the PIC16 target include: +

New features of the ARM target include:

Both direct and indirect load/stores work now.
Logical, bitwise and conditional operations now work for integer data -types.
Function calls involving basic types work now.
Support for integer arrays.
Compiler can now emit libcalls for operations not support by m/c -instructions.
Support for both data and ROM address spaces.

Things not yet supported:

The ARM backend now generates instructions in unified assembly syntax.

+ +

llvm-gcc now has complete support for the ARM v7 NEON instruction set. This + support differs slightly from the GCC implementation. Please see the + + ARM Advanced SIMD (NEON) Intrinsics and Types in LLVM Blog Post for + helpful information if migrating code from GCC to LLVM-GCC.

+ +

The ARM and Thumb code generators now use register scavenging for stack + object address materialization. This allows the use of R3 as a general + purpose register in Thumb1 code, as it was previous reserved for use in + stack address materialization. Secondly, sequential uses of the same + value will now re-use the materialized constant.

+ +

The ARM backend now has good support for ARMv4 targets and has been tested + on StrongARM hardware. Previously, LLVM only supported ARMv4T and + newer chips.

+ +

Atomic builtins are now supported for ARMv6 and ARMv7 (__sync_synchronize, + __sync_fetch_and_add, etc.).

Floating point.
Passing/returning aggregate types to and from functions.
Variable arguments.
Indirect function calls.
Interrupts/programs.
Debug info.

The core LLVM infrastructure uses GNU autoconf to adapt itself @@ -663,6 +978,15 @@ 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.

These are in-progress notes for the upcoming LLVM 2.8 +release. +You may prefer the +LLVM 2.7 +Release Notes.

These are in-progress notes for the upcoming LLVM 2.8 +release.
+You may prefer the +LLVM 2.7 +Release Notes.