This document contains the release notes for the LLVM compiler
-infrastructure, release 2.0. Here we describe the status of LLVM, including
+infrastructure, release 2.1. 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.
@@ -44,10 +44,9 @@ href="http://mail.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 current one. To see
-the release notes for the current or previous releases, see the releases page.
+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.
@@ -59,415 +58,196 @@ href="http://llvm.org/releases/">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 twelfth public release of the LLVM Compiler Infrastructure.
+It includes many features and refinements from LLVM 2.0.
-
Changes to the LLVM IR itself:
+
LLVM 2.1 brings two new beta C front-ends. First, Duncan, Anton and Devang
+start syncing up llvm-gcc with GCC 4.2, yielding "llvm-gcc 4.2" (creative,
+huh?). llvm-gcc 4.2 has the promise to bring much better FORTRAN and Ada
+support to LLVM as well as features like atomic builtins, OpenMP, and many other
+things. Check it out!
-
-
-- 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.
-
-
-
Major new features:
-
-
-
-- 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.
-
-- A new llvm-upgrade tool
- exists to migrates LLVM 1.9 .ll files to LLVM 2.0 syntax.
-
+
Second, LLVM now includes its own native C and Objective-C front-end (C++ is
+in progress, but is not very far along) code named "clang". This front-end has a number of great
+features, primarily aimed at source-level analysis and speeding up compile-time.
+At this point though, the LLVM Code Generator component is still very early in
+development, so it's mostly useful for people looking to build source-level
+analysis tools or source-to-source translators.
-
New features include:
-
+
+
Some of the most noticable improvements this release have been in the
+optimizer, speeding it up and making it more aggressive
-- 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.
+- Owen DSE and MemDep analysis
+- Owen GVN
+- Owen GVN-PRE, not in llvm-gcc
+- Devang merged ETForest and DomTree into a single easier to use data
+structure.
+- Nick Lewycky improved loop trip count analysis to handle many more common
+cases.
-
+
-
-New features include:
+
New features include:
+- Neil Booth APFloat, foundation for long double support that will be wrapped
+up in 2.2. Dale contributed most of long double support, will be enabled in
+2.2.
-- LLVM now supports software floating point, which allows LLVM to target
- chips that don't have hardware FPUs (e.g. ARM thumb mode).
+- LLVM now provides an LLVMBuilder class which makes it significantly easier
+to create LLVM IR instructions.
-- 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.
-
-- 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.
-
-- LLVM now supports tracking physreg sub-registers and super-registers
- in the code generator, and includes extensive register
- allocator changes to track them.
-
-- There is initial support for virtreg sub-registers
- (PR1350).
-
-
-
-
-Other improvements include:
-
-
-
-
-- 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).
-
-- DWARF debug information generation has been improved. LLVM now passes
- most of the GDB testsuite on MacOS and debug info is more dense.
-
-- 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.
-
-
-
-
In addition, the LLVM target description format has itself been extended in
- several ways:
-
-
-- TargetData now supports 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 now supports describing target calling conventions
- explicitly in .td files, reducing the amount of C++ code that needs
- to be written for a port.
-
-
-
-
-
-
X86-specific Code Generator Enhancements:
-
-
-
-- 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 "mri") which is common in X86 inline asms.
-
-
-
ARM-specific Code Generator Enhancements:
-
-
-- 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), 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.
-
-- Several bugs were fixed for DWARF debug info generation on arm/linux.
-
-
-
-
PowerPC-specific Code Generator Enhancements:
-
-
-- 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.
-
-
-
-
-
-
More specific changes include:
-
-
-- 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.
-
-- LLVM now has significantly fewer static constructors, reducing startup time.
-
-
-- Several classes have been refactored to reduce the amount of code that
- gets linked into apps that use the JIT.
-
-- Construction of intrinsic function declarations has been simplified.
-
-- The gccas/gccld tools have been replaced with small shell scripts.
-
-- Support has been added to llvm-test for running on low-memory
- or slow machines (make SMALL_PROBLEM_SIZE=1).
-
-
-
-
-
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:
-
-
-- 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. Also, the
- Type::isPrimitiveType() method now returns false for integers.
-
-- 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());
-
-
-
-
-- 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.
+
- Reid contributed support for intrinsics that take arbitrary integer typed
+arguments, Dan Gohman and Chandler extended it to support FP and vectors.
-- Module::getNamedFunction() is now called
- Module::getFunction().
-
-- SymbolTable.h has been split into ValueSymbolTable.h and
-TypeSymbolTable.h.
+