Written by the LLVM Team
+ +
This document contains the release notes for the LLVM compiler -infrastructure, release 2.0. Here we describe the status of LLVM, including any -known problems and major improvements from the previous release. All LLVM +infrastructure, release 2.3. Here we describe the status of LLVM, including +major improvements from the previous release and any known problems. All LLVM releases may be downloaded from the LLVM -releases web site. +releases web site.
For more information about LLVM, including information about the latest release, please check out the main LLVM @@ -43,434 +47,496 @@ web site. If you have questions or comments, the LLVM developer's mailing list is a good place to send them.
-Note that if you are reading this file from CVS or the main LLVM web page, -this document applies to the next release, not the current one. To see -the release notes for the current or previous releases, see the releases page.
+Note that if you are reading this file from a Subversion checkout or the +main LLVM web page, this document applies to the next release, not the +current one. To see the release notes for a specific releases, please see the +releases page.
This is the eleventh public release of the LLVM Compiler Infrastructure. -Being the first major release since 1.0, this release is different in several -ways from our previous releases:
- --
-
- We took this as an opportunity to -break backwards compatibility with the LLVM 1.x bytecode and .ll file format. -If you have LLVM 1.9 .ll files that you would like to upgrade to LLVM 2.x, we -recommend the use of the stand alone llvm-upgrade -tool (which is included with 2.0). We intend to keep compatibility with .ll -and .bc formats within the 2.x release series, like we did within the 1.x -series. -
- There are several significant change to the LLVM IR and internal APIs, such - as a major overhaul of the type system, the completely new bitcode file - format, etc (described below). -
- We designed the release around a 6 month release cycle instead of the usual - 3-month cycle. This gave us extra time to develop and test some of the - more invasive features in this release. -
- LLVM 2.0 no longer supports the llvm-gcc3 front-end. Users are required to - upgrade to llvm-gcc4. llvm-gcc4 includes many features over - llvm-gcc3, is faster, and is much easier to - build from source. -
Note that while this is a major version bump, this release has been - extensively tested on a wide range of software. It is easy to say that this - is our best release yet, in terms of both features and correctness. This is - the first LLVM release to correctly compile and optimize major software like - LLVM itself, Mozilla/Seamonkey, Qt 4.3rc1, kOffice, etc out of the box on - linux/x86. -
+This is the fourteenth public release of the LLVM Compiler Infrastructure. +It includes a large number of features and refinements from LLVM 2.2.
Changes to the LLVM IR itself:
+LLVM 2.3 no longer supports llvm-gcc 4.0, it has been replaced with + llvm-gcc 4.2.
--
+
- Integer types are now completely signless. This means that we - have types like i8/i16/i32 instead of ubyte/sbyte/short/ushort/int - etc. LLVM operations that depend on sign have been split up into - separate instructions (PR950). This - eliminates cast instructions that just change the sign of the operands (e.g. - int -> uint), which reduces the size of the IR and makes optimizers - simpler to write. - -
- Integer types with arbitrary bitwidths (e.g. i13, i36, i42, i1057, etc) are - now supported in the LLVM IR and optimizations (PR1043). However, neither llvm-gcc - (PR1284) nor the native code generators - (PR1270) support non-standard width - integers yet. - -
- 'Type planes' have been removed (PR411). - It is no longer possible to have two values with the same name in the - same symbol table. This simplifies LLVM internals, allowing significant - speedups. - -
- Global variables and functions in .ll files are now prefixed with - @ instead of % (PR645). - -
- The LLVM 1.x "bytecode" format has been replaced with a - completely new binary representation, named 'bitcode'. The Bitcode Format brings a - number of advantages to the LLVM over the old bytecode format: it is denser - (files are smaller), more extensible, requires less memory to read, - is easier to keep backwards compatible (so LLVM 2.5 will read 2.0 .bc - files), and has many other nice features. - -
- Load and store instructions now track the alignment of their pointer - (PR400). This allows the IR to - express loads that are not sufficiently aligned (e.g. due to '#pragma - packed') or to capture extra alignment information. -
LLVM 2.3 no longer includes the llvm-upgrade tool. It was useful + for upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a + previous LLVM release to do this. One nice impact of this is that the LLVM + regression test suite no longer depends on llvm-upgrade, which makes it run + faster.
-The llvm2cpp tool has been folded into llc, use + llc -march=cpp instead of llvm2cpp.
-Major new features:
+LLVM API Changes:
-
-
-
- A number of ELF features are now supported by LLVM, including 'visibility', - extern weak linkage, Thread Local Storage (TLS) with the __thread - keyword, and symbol aliases. - Among other things, this means that many of the special options needed to - configure llvm-gcc on linux are no longer needed, and special hacks to build - large C++ libraries like Qt are not needed. - -
- LLVM now has a new MSIL backend. llc -march=msil will now turn LLVM - into MSIL (".net") bytecode. This is still fairly early development - with a number of limitations. +
- Several core LLVM IR classes have migrated to use the + 'FOOCLASS::Create(...)' pattern instead of 'new + FOOCLASS(...)' (e.g. where FOOCLASS=BasicBlock). We hope to + standardize on FOOCLASS::Create for all IR classes in the future, + but not all of them have been moved over yet. +
- LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to + IRBuilder. + +
- MRegisterInfo was renamed to + + TargetRegisterInfo. +
- The MappedFile class is gone, please use + + MemoryBuffer instead. +
- The '-enable-eh' flag to llc has been removed. Now code should + encode whether it is safe to omit unwind information for a function by + tagging the Function object with the 'nounwind' attribute. +
- The ConstantFP::get method that uses APFloat now takes one argument + instead of two. The type argument has been removed, and the type is + now inferred from the size of the given APFloat value.
New features include: +
+The core LLVM 2.3 distribution currently consists of code from the core LLVM +repository (which roughly contains the LLVM optimizer, 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 new vmkit Project +and the Clang Project.
+-
-
- Precompiled Headers (PCH) are now supported. - -
- "#pragma packed" is now supported, as are the various features - described above (visibility, extern weak linkage, __thread, aliases, - etc). - -
- Tracking function parameter/result attributes is now possible. + +
- Many internal enhancements have been added, such as improvements to - NON_LVALUE_EXPR, arrays with non-zero base, structs with variable sized - fields, VIEW_CONVERT_EXPR, CEIL_DIV_EXPR, nested functions, and many other - things. This is primarily to supports non-C GCC front-ends, like Ada. +
- It is simpler to configure llvm-gcc for linux. +
- The pass manager has been entirely - rewritten, making it significantly smaller, simpler, and more extensible. - Support has been added to run FunctionPasses interlaced with - CallGraphSCCPasses, and we now support loop transformations explicitly with - LoopPass. -
- The -scalarrepl pass can now promote unions containing FP values - into a register, it can also handle unions of vectors of the same - size. +
- LLVM 2.0 includes a new loop rotation pass, which converts "for loops" into - "do/while loops", where the condition is at the bottom of the loop. +
- The Loop Strength Reduction pass has been improved, and support added - for sinking expressions across blocks to reduce register pressure. - -
- ModulePasses may now use the result of FunctionPasses. +
- The [Post]DominatorSet classes have been removed from LLVM and clients - switched to use the far-more-efficient ETForest class instead. -
- The ImmediateDominator class has also been removed, and clients have been - switched to use DominatorTree instead. + +
- The predicate simplifier pass has been improved, making it able to do - simple value range propagation and eliminate more conditionals. +
The biggest change in LLVM 2.3 is Multiple Return Value (MRV) support. + MRVs allow LLVM IR to directly represent functions that return multiple + values without having to pass them "by reference" in the LLVM IR. This + allows a front-end to generate more efficient code, as MRVs are generally + returned in registers if a target supports them. See the LLVM IR Reference for more details.
+ +MRVs are fully supported in the LLVM IR, but are not yet fully supported in + on all targets. However, it is generally safe to return up to 2 values from + a function: most targets should be able to handle at least that. MRV + support is a critical requirement for X86-64 ABI support, as X86-64 requires + the ability to return multiple registers from functions, and we use MRVs to + accomplish this in a direct way.
+
+LLVM 2.3 includes a complete reimplementation of the "llvmc" + tool. It is designed to overcome several problems with the original + llvmc and to provide a superset of the features of the + 'gcc' driver.
+ +The main features of llvmc2 are: +
-
+
- Extended handling of command line options and smart rules for + dispatching them to different tools. +
- Flexible (and extensible) rules for defining different tools. +
- The different intermediate steps performed by tools are represented + as edges in the abstract graph. +
- The 'language' for driver behavior definition is tablegen and thus + it's relatively easy to add new features. +
- The definition of driver is transformed into set of C++ classes, thus + no runtime interpretation is needed. +
-- Support was added for software floating point, which allows LLVM to target - chips that don't have hardware FPUs (e.g. ARM thumb mode). +
LLVM 2.3 includes a completely rewritten interface for Link Time Optimization. This interface + is written in C, which allows for easier integration with C code bases, and + incorporates improvements we learned about from the first incarnation of the + interface.
-- A new register scavenger has been implemented, which is useful for - finding free registers after register allocation. This is useful when - rewriting frame references on RISC targets, for example. +
The Kaleidoscope tutorial now + includes a "port" of the tutorial that uses the Ocaml bindings to implement + the Kaleidoscope language.
-- Heuristics have been added to avoid coalescing vregs with very large live - ranges to physregs. This was bad because it effectively pinned the physical - register for the entire lifetime of the virtual register (PR711). +
- Support now exists for very simple (but still very useful) - rematerialization the register allocator, enough to move - instructions like "load immediate" and constant pool loads. +
- Switch statement lowering is significantly better, improving codegen for - sparse switches that have dense subregions, and implemented support - for the shift/and trick. -
- Added support for tracking physreg sub-registers and super-registers - in the code generator, as well as extensive register - allocator changes to track them. + + -
- There is initial support for virtreg sub-registers - (PR1350). +
- llvm-gcc 4.2 includes numerous fixes to better support the Objective-C +front-end. Objective-C now works very well on Mac OS/X. -
- Inline assembly support is much more solid that before. - The two primary features still missing are support for 80-bit floating point - stack registers on X86 (PR879), and - support for inline asm in the C backend (PR802). +
- Fortran EQUIVALENCEs are now supported by the gfortran +front-end. -
- DWARF debug information generation has been improved. LLVM now passes - most of the GDB testsuite on MacOS and debug info is more dense. +
- llvm-gcc 4.2 includes many other fixes which improve conformance with the +relevant parts of the GCC testsuite. -
- Codegen support for Zero-cost DWARF exception handling has been added (PR592). It is mostly - complete and just in need of continued bug fixes and optimizations at - this point. However, support in llvm-g++ is disabled with an - #ifdef for the 2.0 release (PR870). +
- The code generator now has more accurate and general hooks for - describing addressing modes ("isLegalAddressingMode") to - optimizations like loop strength reduction and code sinking. +
- Progress has been made on a direct Mach-o .o file writer. Many small - apps work, but it is still not quite complete. -
+The "vmkit" project is a new addition to the LLVM family. It 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.
+ +The JVM, called JnJVM, executes real-world applications such as Apache +projects (e.g. Felix and Tomcat) and the SpecJVM98 benchmark. It uses the GNU +Classpath project for the base classes. The CLI implementation, called N3, is +its in early stages but can execute simple applications and the "pnetmark" +benchmark. It uses the pnetlib project as its core library.
+ +The 'vmkit' VMs compare in performance with industrial and top open-source +VMs on scientific applications. Besides the JIT, the VMs use many features of +the LLVM framework, including the standard set of optimizations, atomic +operations, custom function provider and memory manager for JITed methods, and +specific virtual machine optimizations. vmkit is not an official part of LLVM +2.3 release. It is publicly available under the LLVM license and can be +downloaded from: +
-svn co http://llvm.org/svn/llvm-project/vmkit/trunk vmkit+
New features include: -
- --
-
The Clang project is an effort to build +a set of new 'LLVM native' front-end technologies for the LLVM optimizer +and code generator. Clang is continuing to make major strides forward in all +areas. Its C and Objective-C parsing support is very solid, and the code +generation support is far enough along to build many C applications. While not +yet production quality, it is progressing very nicely. In addition, C++ +front-end work has started to make significant progress.
-At this point, Clang is most useful if you are interested in source-to-source +transformations (such as refactoring) and other source-level tools for C and +Objective-C. Clang now also includes tools for turning C code into pretty HTML, +and includes a new static +analysis tool in development. This tool focuses on automatically finding +bugs in C and Objective-C code.
-LLVM 2.3 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. +
-New features include: -
+ +LLVM 2.3 includes several major new capabilities:
-
+
LLVM 2.3 fully supports the llvm-gcc 4.2 front-end, and includes support +for the C, C++, Objective-C, Ada, and Fortran front-ends.
-Other improvements include: -
--
+
In addition, the LLVM target description format has itself been extended in - several ways:
- --
-
- Extended TargetData to support better target parameterization in - the .ll/.bc files, eliminating the 'pointersize/endianness' attributes - in the files (PR761). +
- TargetData was generalized for finer grained alignment handling, - handling of vector alignment, and handling of preferred alignment +
- LLVM IR now directly represents "common" linkage, instead of representing it +as a form of weak linkage. -
- LLVM now supports describing target calling conventions - explicitly in .td files, reducing the amount of C++ code that needs - to be written for a port. +
- LLVM IR now has support for atomic operations, and this functionality can be +accessed through the llvm-gcc "__sync_synchronize", +"__sync_val_compare_and_swap", and related builtins. Support for +atomics are available in the Alpha, X86, X86-64, and PowerPC backends. +
- The C and Ocaml bindings have extended to cover pass managers, several +transformation passes, iteration over the LLVM IR, target data, and parameter +attribute lists.
- The MMX instruction set is now supported through intrinsics. -
- The scheduler was improved to better reduce register pressure on - X86 and other targets that are register pressure sensitive. -
- Linux/x86-64 support is much better. -
- PIC support for linux/x86 has been added. -
- The X86 backend now supports the GCC regparm attribute. -
- LLVM now supports inline asm with multiple constraint letters per operand - (like "ri") which is common in X86 inline asms. -
Loop index set splitting on by default. +This transformation hoists conditions from loop bodies and reduces a loop's +iteration space to improve performance. For example,
--
-
- The ARM code generator is now stable and fully supported. +
- There are major new features, including support for ARM - v4-v6 chips, vfp support, soft float point support, pre/postinc support, - load/store multiple generation, constant pool entry motion (to support - large functions), and inline asm support, weak linkage support, static - ctor/dtor support and many bug fixes. -
- Added support for Thumb code generation (llc -march=thumb). +
- The ARM backend now supports the ARM AAPCS/EABI ABI and PIC codegen on - arm/linux. +
+-+for (i = LB; i < UB; ++i) + if (i <= NV) + LOOP_BODY +
+is transformed into:
-++ ++NUB = min(NV+1, UB) +for (i = LB; i < NUB; ++i) + LOOP_BODY +
+
-- Several bugs were fixed for DWARF debug info generation on arm/linux. +
- LLVM now includes a new memcpy optimization pass which removes +dead memcpy calls, unneeded copies of aggregates, and performs +return slot optimization. The LLVM optimizer now notices long sequences of +consecutive stores and merges them into memcpy's where profitable. + +
- Alignment detection for vector memory references and for memcpy and +memset is now more aggressive. + +
- The Aggressive Dead Code Elimination (ADCE) optimization has been rewritten +to make it both faster and safer in the presence of code containing infinite +loops. Some of its prior functionality has been factored out into the loop +deletion pass, which is safe for infinite loops. The new ADCE pass is +no longer based on control dependence, making it run faster. + +
- The 'SimplifyLibCalls' pass, which optimizes calls to libc and libm + functions for C-based languages, has been rewritten to be a FunctionPass + instead a ModulePass. This allows it to be run more often and to be + included at -O1 in llvm-gcc. It was also extended to include more + optimizations and several corner case bugs were fixed. + +
- LLVM now includes a simple 'Jump Threading' pass, which attempts to simplify + conditional branches using information about predecessor blocks, simplifying + the control flow graph. This pass is pretty basic at this point, but + catches some important cases and provides a foundation to build on. + +
- Several corner case bugs which could lead to deleting volatile memory + accesses have been fixed. + +
- Several optimizations have been sped up, leading to faster code generation + with the same code quality. + -
- The PowerPC 64 JIT now supports addressing code loaded above the 2G - boundary. + + -
- Improved support for the Linux/ppc ABI and the linux/ppc JIT is fully - functional now. llvm-gcc and static compilation are not fully supported - yet though. +
- Many PowerPC 64 bug fixes. +
- The code generator now has support for carrying information about memory + references throughout the entire code generation process, via the + + MachineMemOperand class. In the future this will be used to improve + both pre-pass and post-pass scheduling, and to improve compiler-debugging + output. + +
- The target-independent code generator infrastructure now uses LLVM's + APInt + class to handle integer values, which allows it to support integer types + larger than 64 bits (for example i128). Note that support for such types is + also dependent on target-specific support. Use of APInt is also a step + toward support for non-power-of-2 integer sizes. + +
- LLVM 2.3 includes several compile time speedups for code with large basic + blocks, particularly in the instruction selection phase, register + allocation, scheduling, and tail merging/jump threading. +
- LLVM 2.3 includes several improvements which make llc's + --view-sunit-dags visualization of scheduling dependency graphs + easier to understand. + +
- The code generator allows targets to write patterns that generate subreg + references directly in .td files now. + +
- memcpy lowering in the backend is more aggressive, particularly for + memcpy calls introduced by the code generator when handling + pass-by-value structure argument copies. + +
- Inline assembly with multiple register results now returns those results + directly in the appropriate registers, rather than going through memory. + Inline assembly that uses constraints like "ir" with immediates now use the + 'i' form when possible instead of always loading the value in a register. + This saves an instruction and reduces register use. + +
- Added support for PIC/GOT style tail calls on X86/32 and initial + support for tail calls on PowerPC 32 (it may also work on PowerPC 64 but is + not thoroughly tested).
- llvm-gcc's X86-64 ABI conformance is far improved, particularly in the + area of passing and returning structures by value. llvm-gcc compiled code + now interoperates very well on X86-64 systems with other compilers. -
- Support for Win64 was added. This includes code generation itself, JIT + support, and necessary changes to llvm-gcc. -
- LLVM no longer relies on static destructors to shut itself down. Instead, - it lazily initializes itself and shuts down when llvm_shutdown() is - explicitly called. +
- The LLVM X86 backend now supports the support SSE 4.1 instruction set, and + the llvm-gcc 4.2 front-end supports the SSE 4.1 compiler builtins. Various + generic vector operations (insert/extract/shuffle) are much more efficient + when SSE 4.1 is enabled. The JIT automatically takes advantage of these + instructions, but llvm-gcc must be explicitly told to use them, e.g. with + -march=penryn. -
- LLVM now has significantly fewer static constructors, reducing startup time. - +
- The X86 backend now does a number of optimizations that aim to avoid + converting numbers back and forth from SSE registers to the X87 floating + point stack. This is important because most X86 ABIs require return values + to be on the X87 Floating Point stack, but most CPUs prefer computation in + the SSE units. + +
- The X86 backend supports stack realignment, which is particularly useful for + vector code on OS's without 16-byte aligned stacks, such as Linux and + Windows. -
- Several classes have been refactored to reduce the amount of code that - gets linked into apps that use the JIT. +
- The X86 backend now supports the "sseregparm" options in GCC, which allow + functions to be tagged as passing floating point values in SSE + registers. -
- Construction of intrinsic function declarations has been simplified. +
- Trampolines (taking the address of a nested function) now work on + Linux/X86-64. -
- The llvm-upgrade tool now exists. This migrates LLVM 1.9 .ll files to - LLVM 2.0 syntax. +
- __builtin_prefetch is now compiled into the appropriate prefetch + instructions instead of being ignored. -
- The gccas/gccld tools have been removed. +
- 128-bit integers are now supported on X86-64 targets. This can be used + through __attribute__((TImode)) in llvm-gcc. -
- Support has been added to llvm-test for running on low-memory - or slow machines (make SMALL_PROBLEM_SIZE=1). +
- The register allocator can now rematerialize PIC-base computations, which is + an important optimization for register use. -
- llvm-test is now more portable and should build with MS Visual Studio. +
- The "t" and "f" inline assembly constraints for the X87 floating point stack + now work. However, the "u" constraint is still not fully supported.
- Pass registration is slightly different in LLVM 2.0 (you now need an - intptr_t in your constructor), as explained in the Writing an LLVM Pass - document. - -
- ConstantBool, ConstantIntegral and ConstantInt - classes have been merged together, we now just have - ConstantInt. - -
- Type::IntTy, Type::UIntTy, Type::SByteTy, ... are - replaced by Type::Int8Ty, Type::Int16Ty, etc. LLVM types - have always corresponded to fixed size types - (e.g. long was always 64-bits), but the type system no longer includes - information about the sign of the type. - -
- Several classes (CallInst, GetElementPtrInst,
- ConstantArray, etc), that once took std::vector as
- arguments now take ranges instead. For example, you can create a
- GetElementPtrInst with code like:
-
-
- Value *Ops[] = { Op1, Op2, Op3 }; - GEP = new GetElementPtrInst(BasePtr, Ops, 3); -- - This avoids creation of a temporary vector (and a call to malloc/free). If - you have an std::vector, use code like this: -- std::vector<Value*> Ops = ...; - GEP = new GetElementPtrInst(BasePtr, &Ops[0], Ops.size()); -
+ - The LLVM C backend now supports vector code. +
- The Cell SPU backend includes a number of improvements. It generates better + code and its stability/completeness is improving. +
- CastInst is now abstract and its functionality is split into several parts, - one for each of the new cast - instructions. -
- Instruction::getNext()/getPrev() are now private (along with - BasicBlock::getNext, etc), for efficiency reasons (they are now no - longer just simple pointers). Please use BasicBlock::iterator, etc instead. - -
- Module::getNamedFunction() is now called - Module::getFunction(). + + + +
- SymbolTable.h has been split into ValueSymbolTable.h and -TypeSymbolTable.h. +
- LLVM now builds with GCC 4.3. +
- Bugpoint now supports running custom scripts (with the -run-custom + option) to determine how to execute the command and whether it is making + forward process.
- Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD +
- Intel and AMD machines (IA32) running Red Hat Linux, Fedora Core and FreeBSD (and probably other unix-like systems). -
- Intel and AMD machines running on Win32 using MinGW libraries (native) -
- Sun UltraSPARC workstations running Solaris 8. +
- 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++). -
- PowerPC and X86-based Mac OS X systems, running 10.2 and above in 32-bit and - 64-bit modes. +
- Sun UltraSPARC workstations running Solaris 10.
- Alpha-based machines running Debian GNU/Linux. -
- Itanium-based machines running Linux and HP-UX. +
- Itanium-based (IA64) machines running Linux and HP-UX.
- The -cee pass is known to be buggy, and may be removed in in a - future release. -
- C++ EH support -
- The IA64 code generator is experimental. -
- The Alpha JIT is experimental. -
- "-filetype=asm" (the default) is the only supported value for the - -filetype llc option. +
- The MSIL, IA64, Alpha, SPU, and MIPS backends are experimental. +
- The llc "-filetype=asm" (the default) is the only supported + value for this option.
- The X86 backend does not yet support inline - assembly that uses the X86 floating point stack. +
- The X86 backend does not yet support + all inline assembly that uses the X86 + floating point stack. It supports the 'f' and 't' constraints, but not + 'u'. +
- The X86 backend generates inefficient floating point code when configured + to generate code for systems that don't have SSE2. +
- Win64 code generation wasn't widely tested. Everything should work, but we + expect small issues to happen. Also, llvm-gcc cannot build mingw64 runtime + currently due + to several + bugs due to lack of support for the + 'u' inline assembly constraint and X87 floating point inline assembly. +
- The X86-64 backend does not yet support position-independent code (PIC) + generation on Linux targets. +
- The X86-64 backend does not yet support the LLVM IR instruction + va_arg. Currently, the llvm-gcc front-end supports variadic + argument constructs on X86-64 by lowering them manually.
- PowerPC backend does not correctly -implement ordered FP comparisons.
- The Linux PPC32/ABI support needs testing for the interpreter and static -compilation, and lacks Dwarf debugging informations. +compilation, and lacks support for debug information.
New features include: +
--
+
X86-specific Code Generator Enhancements: -
+In addition to a huge array of bug fixes and minor performance tweaks, the +LLVM 2.3 optimizers support a few major enhancements:
-
-
ARM-specific Code Generator Enhancements:
+PowerPC-specific Code Generator Enhancements:
+-
-
We put a significant amount of work into the code generator infrastructure, +which allows us to implement more aggressive algorithms and make it run +faster:
--
+
New target-specific features include: +
-This release includes many other improvements, including -performance work, specifically designed to tune datastructure -usage. This makes several critical components faster.
+-
+
More specific changes include:
+-
-
LLVM 2.0 contains a revamp of the type system and several other significant -internal changes. If you are programming to the C++ API, be aware of the -following major changes:
+New target-specific features include: +
-
-
New features include: +
--
+
LLVM is known to work on the following platforms:
-
-
The core LLVM infrastructure uses -GNU autoconf to adapt itself +
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.
@@ -529,16 +594,13 @@ there isn't already one. be broken or unreliable, or are in early development. These components should not be relied on, and bugs should not be filed against them, but they may be useful to some people. In particular, if you would like to work on one of these -components, please contact us on the LLVMdev list. +components, please contact us on the LLVMdev list.-
-
-
-
-
-
-
-
- The Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 -processors, any thumb program compiled with LLVM crashes or produces wrong -results. (PR1388) +
- Thumb mode works only on ARMv6 or higher processors. On sub-ARMv6 +processors, thumb programs can crash or produce wrong +results (PR1388).
- Compilation for ARM Linux OABI (old ABI) is supported, but not fully tested. -
- QEMU-ARM (<= 0.9.0) wrongly executes programs compiled with LLVM. A non-affected QEMU version must be used or this - -patch must be applied on QEMU. +
- There is a bug in QEMU-ARM (<= 0.9.0) which causes it to incorrectly + execute +programs compiled with LLVM. Please use more recent versions of QEMU.
-
-
-
- C++ programs are likely to fail on IA64, as calls to setjmp are -made where the argument is not 16-byte aligned, as required on IA64. (Strictly -speaking this is not a bug in the IA64 back-end; it will also be encountered -when building C++ programs using the C back-end.) - -
- The C++ front-end does not use IA64 -ABI compliant layout of v-tables. In particular, it just stores function -pointers instead of function descriptors in the vtable. This bug prevents -mixing C++ code compiled with LLVM with C++ objects compiled by other C++ -compilers. - -
- There are a few ABI violations which will lead to problems when mixing LLVM -output with code built with other compilers, particularly for floating-point -programs. - -
- Defining vararg functions is not supported (but calling them is ok). - -
- The Itanium backend has bitrotted somewhat. +
- The Itanium backend is highly experimental, and has a number of known + issues. We are looking for a maintainer for the Itanium backend. If you + are interested, please contact the llvmdev mailing list.
-
-
- The C backend does not support inline - assembly code. +
- The C backend has only basic support for + inline assembly code. +
- The C backend violates the ABI of common + C++ programs, preventing intermixing between C++ compiled by the CBE and + C++ code compiled with llc or native compilers. +
- The C backend does not support all exception handling constructs.
llvm-gcc4 does not currently support Link-Time -Optimization on most platforms "out-of-the-box". Please inquire on the +
llvm-gcc does not currently support Link-Time +Optimization on most platforms "out-of-the-box". Please inquire on the llvmdev mailing list if you are interested.
--
-
-
"long double" is silently transformed by the front-end into "double". There -is no support for floating point data types of any size other than 32 and 64 -bits.
-
-llvm-gcc does not support __builtin_apply yet. - See Constructing Calls: Dispatching a call to another function.
-
-
-llvm-gcc partially supports tthese GCC extensions:
--
-
- Nested Functions: As in Algol and Pascal, lexical scoping of functions.
- Nested functions are supported, but llvm-gcc does not support non-local - gotos or taking the address of a nested function.
-
- - Function Attributes:
-
- Declaring that functions have no side effects or that they can never
- return.
- - Supported: alias, always_inline, cdecl, - constructor, destructor, - deprecated, fastcall, format, - format_arg, non_null, noreturn, regparm - section, stdcall, unused, used, - visibility, warn_unused_result, weak
- - Ignored: noinline, pure, const, nothrow, - malloc, no_instrument_function
-
-
-- Nested Functions: As in Algol and Pascal, lexical scoping of functions.
llvm-gcc supports the vast majority of GCC extensions, including:
- --
-
- Pragmas: Pragmas accepted by GCC. -
- Local Labels: Labels local to a block. -
- Other Builtins: - Other built-in functions. -
- Variable Attributes: - Specifying attributes of variables. -
- Type Attributes: Specifying attributes of types. -
- Thread-Local: Per-thread variables. -
- Variable Length: - Arrays whose length is computed at run time. -
- Labels as Values: Getting pointers to labels and computed gotos. -
- Statement Exprs: Putting statements and declarations inside expressions. -
- Typeof:
typeof: referring to the type of an expression.
- - Lvalues: Using
?:, "," and casts in lvalues.
- - Conditionals: Omitting the middle operand of a
?:expression.
- - Long Long: Double-word integers. -
- Complex: Data types for complex numbers. -
- Hex Floats:Hexadecimal floating-point constants. -
- Zero Length: Zero-length arrays. -
- Empty Structures: Structures with no members. -
- Variadic Macros: Macros with a variable number of arguments. -
- Escaped Newlines: Slightly looser rules for escaped newlines. -
- Extended Asm: Assembler instructions with C expressions as operands. -
- Constraints: Constraints for asm operands. -
- Asm Labels: Specifying the assembler name to use for a C symbol. -
- Explicit Reg Vars: Defining variables residing in specified registers. -
- Vector Extensions: Using vector instructions through built-in functions. -
- Target Builtins: Built-in functions specific to particular targets. -
- Subscripting: Any array can be subscripted, even if not an lvalue. -
- Pointer Arith: Arithmetic on
void-pointers and function pointers.
- - Initializers: Non-constant initializers. -
- Compound Literals: Compound literals give structures, unions, -or arrays as values. -
- Designated Inits: Labeling elements of initializers. -
- Cast to Union: Casting to union type from any member of the union. -
- Case Ranges: `case 1 ... 9' and such. -
- Mixed Declarations: Mixing declarations and code. -
- Function Prototypes: Prototype declarations and old-style definitions. -
- C++ Comments: C++ comments are recognized. -
- Dollar Signs: Dollar sign is allowed in identifiers. -
- Character Escapes:
\estands for the character <ESC>.
- - Alignment: Inquiring about the alignment of a type or variable. -
- Inline: Defining inline functions (as fast as macros). -
- Alternate Keywords:
__const__,__asm__, etc., for header files.
- - Incomplete Enums:
enum foo;, with details to follow.
- - Function Names: Printable strings which are the name of the current function. -
- Return Address: Getting the return or frame address of a function. -
- Unnamed Fields: Unnamed struct/union fields within structs/unions. -
- Attribute Syntax: Formal syntax for attributes. -
+
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).
-If you run into GCC extensions which have not been included in any of these -lists, please let us know (also including whether or not they work).
+If you run into GCC extensions which are not supported, please let us know. +
-
-
- llvm-gcc4 only has partial support for C++ -Exception Handling, and it is not enabled by default. - - +
- Exception handling works well on the X86 and PowerPC targets, including +X86-64 darwin. This works when linking to a libstdc++ compiled by GCC. It is +supported on X86-64 linux, but that is disabled by default in this release.
-
+
- 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. +Workaround: configure with --disable-bootstrap. +
- The c380004 and c393010 ACATS tests +fail (c380004 also fails with gcc-4.2 mainline). When built at -O3, the +cxg2021 ACATS test also fails. +
- Some gcc specific Ada tests continue to crash the compiler. The testsuite +reports most tests as having failed even though they pass. +
- 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. +
A wide variety of additional information is available on the LLVM web page, in particular in the documentation section. The web page also -contains versions of the API documentation which is up-to-date with the CVS -version of the source code. +contains versions of the API documentation which is up-to-date with the +Subversion version of the source code. You can access versions of these documents specific to this release by going into the "llvm/doc/" directory in the LLVM tree.
@@ -853,7 +838,7 @@ lists.
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