LLVM 3.9 Release Notes


These are in-progress notes for the upcoming LLVM 3.9 release. You may prefer the LLVM 3.8 Release Notes.


This document contains the release notes for the LLVM Compiler Infrastructure, release 3.9. 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.

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 release, please see the releases page.

Non-comprehensive list of changes in this release

  • The LLVMContext gains a new runtime check (see LLVMContext::discardValueNames()) that can be set to discard Value names (other than GlobalValue). This is intended to be used in release builds by clients that are interested in saving CPU/memory as much as possible.
  • There is no longer a “global context” available in LLVM, except for the C API.
  • The C API function LLVMLinkModules has been removed.
  • The C API function LLVMAddTargetData has been removed.
  • The C API function LLVMGetDataLayout is deprecated in favor of LLVMGetDataLayoutStr.
  • The C API enum LLVMAttribute and associated API is deprecated in favor of the new LLVMAttributeRef API. The deprecated functions are LLVMAddFunctionAttr, LLVMAddTargetDependentFunctionAttr, LLVMRemoveFunctionAttr, LLVMGetFunctionAttr, LLVMAddAttribute, LLVMRemoveAttribute, LLVMGetAttribute, LLVMAddInstrAttribute, LLVMRemoveInstrAttribute and LLVMSetInstrParamAlignment.
  • TargetFrameLowering::eliminateCallFramePseudoInstr now returns an iterator to the next instruction instead of void. Targets that previously did MBB.erase(I); return; now probably want return MBB.erase(I);.
  • SelectionDAGISel::Select now returns void. Out of tree targets will need to be updated to replace the argument node and remove any dead nodes in cases where they currently return an SDNode * from this interface.
  • Introduction of ThinLTO: [FIXME: needs to be documented more extensively in /docs/ ; ping Mehdi/Teresa before the release if not done]
  • Raised the minimum required CMake version to 3.4.3.
  • ... next change ...

Changes to the LLVM IR

  • New intrinsics llvm.masked.load, llvm.masked.store, llvm.masked.gather and llvm.masked.scatter were introduced to the LLVM IR to allow selective memory access for vector data types.

Changes to LLVM’s IPO model

LLVM no longer does inter-procedural analysis and optimization (except inlining) on functions with comdat linkage. Doing IPO over such functions is unsound because the implementation the linker chooses at link-time may be differently optimized than the one what was visible during optimization, and may have arbitrarily different observable behavior. See PR26774 for more details.

Changes to the ARM Backend

During this release ...

Changes to the MIPS Target

During this release ...

Changes to the PowerPC Target

Moved some optimizations from O3 to O2 (D18562)
  • Enable sibling call optimization on ppc64 ELFv1/ELFv2 abi

Changes to the X86 Target

  • LLVM now supports the Intel CPU codenamed Skylake Server with AVX-512 extensions using -march=skylake-avx512. The switch enables the ISA extensions AVX-512{F, CD, VL, BW, DQ}.
  • LLVM now supports the Intel CPU codenamed Knights Landing with AVX-512 extensions using -march=knl. The switch enables the ISA extensions AVX-512{F, CD, ER, PF}.

Changes to the AMDGPU Target

  • Mesa 11.0.x is no longer supported

Changes to the OCaml bindings

During this release ...

Support for attribute ‘notail’ has been added

This marker prevents optimization passes from adding ‘tail’ or ‘musttail’ markers to a call. It is used to prevent tail call optimization from being performed on the call.

External Open Source Projects Using LLVM 3.9

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 3.9.

  • A project

Additional Information

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.