LLVM Weekly - #50, Dec 15th 2014

Welcome to the fiftieth 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 http://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.

I'll be at MICRO-47 this week. If you're there do say hi, especially if you want to chat about LLVM or lowRISC/RISC-V.

The canonical home for this issue can be found here at llvmweekly.org.

News and articles from around the web

The videos and slides from the 2014 LLVM dev meeting went online last week. I already linked to them then, but there's enough interesting stuff there I think I can justify linking again.

LLVM/Clang 3.5.1-rc1 has been tagged. Volunteer testers are very welcome.

Clang UPC 3.4.1 has been released. This is a Unified Parallel C compiler that can target SMP systems or Portals4.

On the mailing lists

Discussion has continued on future plans for GC in LLVM with input from Russel Hadley at Microsoft and Ben Karel, who seems to be the most extensive user of the existing GC infrastructure with his Foster language.
Chris Bieneman started a discussion about supporting stripping out unused instrinsics with the aim of reducing the size of libLLVM. The proposed patches reduce binary size by ~500k, which he later points out is more significant in the context of their already size-reduced build.
Marshall Clow has shared a proposal on how to manage ABI changes in libc++. The proposal involves introducing macros to enable ABI-breaking changes.

LLVM commits

The LLVM Kaleidoscope tutorial has been extended with an 8th chapter, describing how to add debug information using DWARF And DIBuilder. r223671. A rendered version can be found here.
Extensive documentation has been added for the MergeFunctions pass. r223931.
A monster commit to split Metadata from the Value class hierarchy has landed. r223802.
InstrProf has been born. This involves the llvm.instrprof_increment instrinsic and the -instrprof pass. This moves logic from Clang's CodeGenPGO into LLVM. r223672.
With the addition of support for SELECT nodes, the MIPS backend now supports codegen of MIPS-II targets on the LLVM test-suite. Code generation has also been enabled for MIPS-III. r224124, r224128.
Work has started on an LLVM-based dsymutil tool, with the aim to replace Darwin's dsymutil (a DWARF linker). r223793.
LiveInterval has gained support to track the liveness of subregisters. r223877.
Work has started on converting moves to pushes on X86 when appropriate. r223757.
Print and verify passes are now added after each MachineFunctionPass by default, rather than on some arbitrarily chosen subset. r224042.
LLVM now requires Python 2.7. Previously 2.5 was required. r224129.

Clang commits

The __builtin_call_with_static_chain GNU extension has been implemented. r224167.
Clang's CodeGenPGO has moved to using the new LLVM -instrprof pass. r223683.
Clang now accepts Intel microarchitecture names as the -march argument. r223776.

Other project commits

libcxx gained relational operators in std::experimental::optional. r223775.
libcxx can now be built as a 32-bit library. r224096.
The lldb unwinder has learned to use unwind information from the compact-unwind section for x86-64 and i386 on Darwin. r223625.