LLVM Weekly - #130, Jun 27th 2016

Welcome to the one hundred and thirtieth issue of LLVM Weekly, a weekly newsletter (published every Monday) covering developments in LLVM, Clang, and related projects. LLVM Weekly is brought to you by Alex Bradbury. Subscribe to future issues at https://llvmweekly.org and pass it on to anyone else you think may be interested. Please send any tips or feedback to asb@asbradbury.org, or @llvmweekly or @asbradbury on Twitter.

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News and articles from around the web

After recently being taken down due to excessive resource usage, the LLVM apt repositories are now back.

A detailed introduction to ThinLTO has been published on the LLVM blog. This covers the background, design, current status, and usage information for ThinLTO.

A post on Reddit gives a summary of notable language features voted into the C++17 working draft at the Oulu meeting.

On the mailing lists

• Sanjoy Das has written an RFC on strong GC references in LLVM. The motivating case for this proposal is supporting a precise, relocating garbage collector.

• LLVM version 3.8.1-final has been tagged.

• The Google Summer of Code mid-terms have snuck up on us already. The participating students have posted to the mailing lists with a summary of their work so far:

  • Finding and reporting bugs caused by copy and paste
  • Enabling LLVM's self-hosted modules builds using libstdc++
  • Capture tracking improvements
  • Improvement of vectorization process in Polly
  • Better alias analysis by default
  • Interprocedural register allocation
  • Polly as an analysis pass
  • Enabling polyhedral optimisations in Julia

• Vivek Pandya wrote the mailing list seeking advice on adding a new calling convention for interprocedural register allocation. Matthias Braun summarised some follow-up discussion.

LLVM commits

• The new representation for control-flow integrity and virtual call metadata has landed. The commit message further details the problems this change addresses. r273729.

• The llvm.type.checked.load intrinsic was added. It loads a function pointer from a virtual table pointer using type metadata. r273576.

• As part of the work on CFL-AA, interprocedural function summaries were added. These avoid recomputation for many properties of a function. r273219, r273596.

• MemorySSA gained new APIs for PHI creation and MemoryAccess creation. r273295.

• Metadata attachments are now allowed for declarations. r273336.

• A new runtimes directory was added to the LLVM tree. r273620.

• LLVM's dynamic loader gained basic support for COFF ARM. r273682.

Clang commits

• constexpr if support has been added to Clang. r273602.

• clang-tidy has a new modernize-use-emplace check that will replace calls of push_back to emplace_back. r273275.

• The CMake build system for Clang gained a ENABLE_X86_RELAX_RELOCATIONS option. r273224.

Other project commits

• Basic support for versioned symbols was added to LLD. r273143.

• LLD now handles both single and double dashes for all options. r273256.