This document contains the release notes for the LLVM Compiler Infrastructure, release 3.8. Here we describe the status of LLVM, including major improvements from the previous release, improvements in various subprojects of LLVM, and some of the current users of the code. All LLVM releases may be downloaded from the 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.
With this release, the minimum Windows version required for running LLVM is Windows 7. Earlier versions, including Windows Vista and XP are no longer supported.
With this release, the autoconf build system is deprecated. It will be removed in the 3.9 release. Please migrate to using CMake. For more information see: Building LLVM with CMake
We have documented our C API stability guarantees for both development and release branches, as well as documented how to extend the C API. Please see the developer documentation for more information.
The C API function LLVMLinkModules is deprecated. It will be removed in the 3.9 release. Please migrate to LLVMLinkModules2. Unlike the old function the new one
- Doesn’t take an unused parameter.
- Destroys the source instead of only damaging it.
- Does not record a message. Use the diagnostic handler instead.
The C API functions LLVMParseBitcode, LLVMParseBitcodeInContext, LLVMGetBitcodeModuleInContext and LLVMGetBitcodeModule have been deprecated. They will be removed in 3.9. Please migrate to the versions with a 2 suffix. Unlike the old ones the new ones do not record a diagnostic message. Use the diagnostic handler instead.
The deprecated C APIs LLVMGetBitcodeModuleProviderInContext and LLVMGetBitcodeModuleProvider have been removed.
The deprecated C APIs LLVMCreateExecutionEngine, LLVMCreateInterpreter, LLVMCreateJITCompiler, LLVMAddModuleProvider and LLVMRemoveModuleProvider have been removed.
With this release, the C API headers have been reorganized to improve build time. Type specific declarations have been moved to Type.h, and error handling routines have been moved to ErrorHandling.h. Both are included in Core.h so nothing should change for projects directly including the headers, but transitive dependencies may be affected.
llvm-ar now supports thin archives.
llvm doesn’t produce .data.rel.ro.local or .data.rel sections anymore.
Aliases to available_externally globals are now rejected by the verifier.
The IR Linker has been split into IRMover that moves bits from one module to another and Linker proper that decides what to link.
Support for dematerializing has been dropped.
RegisterScheduler::setDefault was removed. Targets that used to call into the command line parser to set the DAGScheduler, and that don’t have enough control with setSchedulingPreference, should look into overriding the SubTargetHook “getDAGScheduler()”.
ilist_iterator<T> no longer has implicit conversions to and from T*, since ilist_iterator<T> may be pointing at the sentinel (which is usually not of type T at all). To convert from an iterator I to a pointer, use &*I; to convert from a pointer P to an iterator, use P->getIterator(). Alternatively, explicit conversions via static_cast<T>(U) are still available.
ilist_node<T>::getNextNode() and ilist_node<T>::getPrevNode() now fail at compile time when the node cannot access its parent list. Previously, when the sentinel was was an ilist_half_node<T>, this API could return the sentinel instead of nullptr. Frustrated callers should be updated to use iplist<T>::getNextNode(T*) instead. Alternatively, if the node N is guaranteed not to be the last in the list, it is safe to call &*++N->getIterator() directly.
The Kaleidoscope tutorials have been updated to use the ORC JIT APIs.
ORC now has a basic set of C bindings.
Optional support for linking clang and the LLVM tools with a single libLLVM shared library. To enable this, pass -DLLVM_LINK_LLVM_DYLIB=ON to CMake. See Building LLVM with CMake for more details.
The optimization to move the prologue and epilogue of functions in colder code path (shrink-wrapping) is now enabled by default.
A new target-independent gcc-compatible emulated Thread Local Storage mode is added. When -femultated-tls flag is used, all accesses to TLS variables are converted to calls to __emutls_get_address in the runtime library.
MSVC-compatible exception handling has been completely overhauled. New instructions have been introduced to facilitate this: New exception handling instructions. While we have done our best to test this feature thoroughly, it would not be completely surprising if there were a few lingering issues that early adopters might bump into.
During this release the AArch64 target has:
During this release the ARM target has:
During this release the MIPS target has:
The MIPS target has also fixed various bugs including the following notable fixes:
We have made a large number of improvements to the integrated assembler for MIPS. In this release, the integrated assembler isn’t quite production-ready since there are a few known issues related to bare-metal support, checking immediates on instructions, and the N32/N64 ABI’s. However, the current support should be sufficient for many users of the O32 ABI, particularly those targeting MIPS32 on Linux or bare-metal MIPS32.
If you would like to try the integrated assembler, please use -fintegrated-as.
There are numerous improvements to the PowerPC target in this release:
In addition to general code size and performance improvements, Hexagon target now has basic support for Hexagon V60 architecture and Hexagon Vector Extensions (HVX).
Slightly less than half of the AVR backend has been merged in at this point. It is still missing a number large parts which cause it to be unusable, but is well on the road to being completely merged and workable.
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 3.8.
D is a language with C-like syntax and static typing. It pragmatically combines efficiency, control, and modeling power, with safety and programmer productivity. D supports powerful concepts like Compile-Time Function Execution (CTFE) and Template Meta-Programming, provides an innovative approach to concurrency and offers many classical paradigms.
LDC uses the frontend from the reference compiler combined with LLVM as backend to produce efficient native code. LDC targets x86/x86_64 systems like Linux, OS X and Windows and also PowerPC (32/64 bit) and ARM. Ports to other architectures like AArch64 and MIPS64 are underway.
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 Subversion version of the source code. You can access versions of these documents specific to this release by going into the llvm/docs/ directory in the LLVM tree.
If you have any questions or comments about LLVM, please feel free to contact us via the mailing lists.