LLVM Weekly - #344, August 3rd 2020

Welcome to the three hundred and forty-fourth 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 11.0.0-rc1 has been tagged.

The 2020 Linux Plumbers Conference will feature an LLVM microconference.

On the mailing lists

• Andrzej Warzynski shares a new clang tutorial. clang-tutor provides a collection of out-of-tree plugins for Clang with the intent to making it easier for people to get started developing plugins.

• Andrzej Warzynski posted an RFC on refactoring libclangDriver/libclangFrontend to share with Flang.

• Stephen Neuendorffer sent a heads-up that you may need to manually 'unwatch' the llvm/circt repo if you're a member of the LLVM org.

• Johannes Doerfert proposed adding support for heterogeneous LLVM-IR modules.

• Petr Hosek shared challenges he's facing related to the recent change in ld.bfd tombstone behaviour with suggestions for handling changes like this in the future.

• ORC JIT Weekly #18 reports on the addition of the TargetProcessControl API.

• "AE" asked about filesystem support in libcxx on Windows. Stephan T. Lavavej volunteered to contribute Microsoft's implementation to libcxx.

• Zachary Turner enquired about the status of the LLVM re-licensing effort. Hal Finkel reports that it is still in progress and the January 2019 target date will be revised soon.

• Craig Topper raised the issue of SimplifyCFG hoisting fences in if/else branches, and how this may harm attempts to use these fences to mitigate speculative execution vulnerabilities.

• Son Tuan VU kicked off a discussion on maintaining metadata other than debug info through compilation. This triggered thoughts from others, e.g. Lorenzo Casalino.

LLVM commits

• llvm-jitlink gained a new -harness option to enhance testing. 8ce8cee.

• RISC-V Vector MC layer support was updated to bring it in line with the v0.9 draft specification. 47a4a27.

• The XRay infrastructure can now be used for runtime recursion detection. f2ab213.

• llvm-exegesis learned to use LBR for more precise measurements on Skylake and onwards. ee7caa7.

• Support was removed from the PowerPC backend for the IBM BG/Q supercomputer. adffce7.

• The TableGen GlobalISelEmitter now allows output instructions with multiple defs. ee3feef.

• File lock/unlock functions were added to LLVM's support library. 5367369, 032ed39.

• The X86CondBrFolding pass was removed due to correctness issues. e1dd212.

• FileCheck -dump-input was extended with substitutions, and FileCheck will now report captured variables in input dumps and traces. d680711, 9f86b8e.

• The CastContextHint enum was added to getCastInstrCost (e.g. Normal, Masked, GatherScatter, etc). 60280e9.

Clang commits

• Clang's coverage support was fixed to not count lines containing only comments.b46176b.

• Support for the OpenMP 'present' motion modifier was added to Clang. 9f2f3b9.

Other project commits

• The dataflow sanitizer gained an efficient "fast16labels" instrumentation mode, for use when the user needs no more than 16 labels. e2d0b44.

• A WrapperGen tool was added to LLVM's libc implementation, to generate C wrappers for the C++ LLVM libc implementation.s a32af82.

• The LLD ELF linker's CallGraphSort was ported to the COFF linker. 763671f.

• Support for mutable types was added to MLIR. a518299.