LLVM Weekly - #329, Apr 20th 2020

Welcome to the three hundred and twenty-ninth 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

The 2020 US LLVM Developers' Meeting has been announced for September 28-29 in San Jose. "Given the current situation regarding COVID-19, we feel it is best to be totally transparent with our planning process. We are closely monitoring the news regarding restrictions on travel and large gatherings and also following the World Health Organization's advice. It takes about 9-12 months of planning for our developers’ meetings and given we do not know the situation in September, we are moving forward with the hope that it will be safe to host our event."

Nick Desaulniers has written up "Off by Two", a programming 'war story' about investigating a bug when building the Linux kernel with Clang.

Emmanuel Roche has written up a four-part blog series on building a JIT C++ compiler with LLVM on Windows 10: part 1, part 2, part 3, part 4.

Version 3.0.0 of Microsoft's implementation of the C++ Core Guidelines Support Library (GSL) has been released.

On the mailing lists

• Simon Moll provided a status update on LLVM-VP, the effort to bring vector predication to LLVM.

• ORC JIT Weekly #11 just missed last week's issue, catch up, on its coverage of C API improvements. ORC JIT Weekly #12 is out and includes a sketch of a planned API for removable code in OrcV2.

• The fifth MLIR (bi)weekly newsletter is out.

• Fangrui Song asks if support for the 'NaCl' OS target can be removed from LLVM. If you're using this support, do speak up.

• Scott Linder shared a a proposal for backwards compatible extensions to DWARF for heterogeneous debugging.

• Kelvin Li started a thread to discuss how to express Fortran alias information in LLVM IR.

• Neil Henning reports that LLVM 10 is around 7-8% slower than LLVM 9 for the same inputs.

LLVM commits

• Waymarking is no longer used to find the User from a Use instance. This slightly improves compile time performance for a small cost in peak memory use. ff9379f.

• A lost debug locations verifier was added for GlobalISel. d9085f6.

• All additional STLExtras helpers from MLIR have now been moved into LLVM. 8cbe371, 204c3b55, 2f21a57.

• When passing --show-suites to lit it will now print availability substitutions as well as available features. dd3feec.

• An llvm::is_sorted wrapper was introduced. 1647ff6.

• A new fix-irreducible pass was introduced, which will convert an irreducible strongly connected component to a natural loop. 8c11bc0.

Clang commits

• Arbitrary (non-power-of-two) width integers are now supported with the _ExtInt(N) language extension. 61ba148.

• Builtins were added for contiguous loads/stores with SVE. 17a68c6.

• Clang now supports AST files larger than 512M. a7afb21.

Other project commits

• LLVM's libc gained fwrite and write implementations. 99aea57, 5793c84.

• MSan was enabled for SystemZ. 921009e.

• The scudo secure memory allocator gained support for diagnosing memory errors when memory tagging is enabled. 21d5001.

• LLDB's active and passive reproducer replay and test suite structure was documented. c5a3991, 3a6b60f.