LLVM Weekly - #113, Feb 29th 2016

Welcome to the one hundred and thirteenth 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.

News and articles from around the web

LLVM and Clang 3.8RC3 has been tagged.

EuroLLVM 2016 is less than a month away. If you want to attend, be sure to register.

The Red Hat blog has a summary of new features in the upcoming GCC 6 release.

The Meeting C++ blog has a helpful summary of a subset of the proposals for the next C++ committee meeting.

On the mailing lists

• Chandler Carruth has suggested moving the LLVM test-suite repository to Github. In response to some concerns, Chris Lattner points out that using GitHub in this case doesn't mean abandoning the current development workflow, it just means it can be augmented with GitHub-style pull requests for those who prefer it. Chandler summarised the thread and provided a list of next steps.

• Sanjoy Das pointed out a potential soundness issue with the available_externally linkage type. This triggered a very long discussion. James Knight pointed out the same issue could happen with normal functions in a shared library. There was some back and forth between Hal Finkel and Chandler Carruth on the best approach to addressing this problem.

• Philip Reames asks whether a PHI depending on another PHI in the same basic block is valid. It's currently accepted by the verifier but arguably shouldn't be. So far, nobody has argued that it should be valid.

• Matthias Braun kicked off a discussion on better defining the semantics of reserved and unallocatable registers. After more discussion, he followed up with a revised definition.

• David Li has posted a proposal for supporting in-process merging of profile data.

LLVM commits

• The Sparc backend now contains definitions for all registers and instructions defined in the Sparc v8 manual. r262133.

• LLVM gained a basic LoopPassManager, though it currently only contains dummy passes. r261831.

• A number of TargetInstrInfo predicates now take a reference to a MachineInstr rather than a pointer. r261605.

• The WebAssembly backend gained redzone support for the userspace stack. r261662.

Clang commits

• Whole-program vtable optimisation is now available in Clang using the -fwhole-program-vtables flag. r261767.

• Clang gained __builtin_canonicalize which returns the platform-specific canonical encoding of a floating point number. r262122.

• A hasAnyName matcher was added. r261574.

• The pointer arithmetic checker has been improved to report fewer false positives. r261632.

Other project commits

• The new ELF linker gained support for identical code folding (ICF). This reduces the size of an LLD binary by 3.6% and of a Clang binary by 2.7%. As described in the commit message, this is not a "safe" version of ICF as implemented in GNU gold, so will cause issues if the input relies on two distinct functions always having distinct addresses. r261912.

• Polly's tree now contains an update_check.py script that may be useful to other LLVM devs. It updates a FileCheck-based lit test by updating the CHECK: lines with the actual output of the RUN: command. r261899.

• LLDB gained a new set of plugins to help debug Java programs, specifically Java code JIT-ed by the Android runtime. r262015.

• The new OpenMP 4.5 affinity API is now supported in LLVM's openmp implementation. r261915.

• The new ELF linker gained support for the -r command-line option, which produces relocatable output (partial linking). r261838.

• The CMake/lit runner for SPEC in the LLVM test-suite can now run the C CPU2006 floating point benchmarks (but not the Fortran ones). r261816.

• The old ELF linker has been deleted from LLD. r262158.