LLVM Weekly - #561, September 30th 2024

Welcome to the five hundred and sixty-first 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, @llvmweekly or @asbradbury on Twitter, or @llvmweekly@fosstodon.org or @asb@fosstodon.org.

News and articles from around the web and events

Joseph Huber has a rather neat port of Doom that runs on AMDGPU with ROCm and LLVM’s libc.

James Hamilton provided a high level introduction to LLVM.

According to the LLVM calendar in the coming week there will be the following:

• Office hours with the following hosts: Renato Golin, Anastasia Stulova, Quentin Colombet, Johannes Doerfert.
• Online sync-ups on the following topics: Flang, libc++, LLVM/Offload, Clang C/C++ language working group, OpenMP for Flang, MLIR, HLSL, MLGO.
• For more details see the LLVM calendar, getting involved documentation on online sync ups and office hours.

On the forums

• Chris Bieneman provided an update on efforts to establish a new LLVM project governance model, noting the hope to conduct the first elections in January 2025 if the proposal is adopted.

• Erich Keane posted an RFC on updating the supported host compiler versions for LLVM 20. A large chunk of the ensuing discussion was about the expectations for whether builds should be -Werror-clean on all supported toolchains or not (they’re not today), though it was agreed this discussion belongs in a separate RFC.

• Nikita Popov suggested improvements to capture tracking in LLVM.

• Anton Korobeynikov provided a detailed update on pointer authentication support as of the LLVM 19 release as well as listing work that is still in progress.

• David Blaikie proposed a tweak to LLVM’s header including policy. Some respondents were keen to ensure the policy isn’t interpreted in a way that suggests running include-what-you-use is required.

• Rahul Joshi proposed support for auto in TableGen and also shared recent improvements to formatting/printing helpers in LLVM.

• Kadir Çetinkaya provided a revised RFC proposal for adding support for controlling Clang diagnostic severities at the file level.

• Nikita Popov started an RFC thread on introducing a samesign flag for icmp for use in cases where the two compared values are known to have the same sign and so ult will have the same result as slt.

• Andrew Savonichev shared a draft implementation plan for a DWARF reduction tool.

• Donald Chen shared a PSA about the semantics of program points in MLIR dataflow analysis changing.

• Neil Henning kicked off a discussion around adding the ability to make asserts runtime togglable.

LLVM commits

• LLVM’s release notes are now in Markdown rather than RST. b9f09a4.

• WebAssembly’s AsmTypeCheck can now detect multiple errors in a single function. b62075e.

• A new update_mc_test_checks.py utility was added, to update test files using llvm-mc. 2b892b0.

• The computed properties IsSSA, NoPHIs, and NoVRegs can now be overridden in MIR input. 8ba334b.

• An llvm.atan2.* intrinsic was added. 26029d7.

• The Zacas RISC-V extension is no longer marked as experimental. 614aeda.

• ConstantFPRange was added in order to in the future enable range-based optimisations for floating point values. fa824dc.

• The SLP vectorizer learned to do “clustered” vectorization for instructions other than loads. 3469db8.

• The DirectX target gained a pass to scalarize vectors in global scope into arrays. 324bdd6.

Clang commits

• clang-tidy’s documentation gained a section to list examples of external projects using the tool. ce9a2c6.

• The static analyzer taint propagation checker is no longer marked as alpha. f82fb06.

• SPIRV memory scopes support was reworked and expanded. 3cfd0c0.

• The -basic-block-sections=labels option was deprecated. 7b7747d.

• Command-line options were introduced for RISC-V CFI. 9f33eb8.

• TestLanguage.def can now be used to specify all tested language versions. 7dfdca1.

Other project commits

• An ABI option was added to libcxx to harden operator[] for unique_ptr<T[]> when the size of the allocation is known. 45a09d1.

• MLIR gained support for LLVM operand bundles. fde3c16.

• Documentation on adding support for a new language was added back to LLDB. a3cf01d.

• Errors from LLDB’s inline expression evaluator are now much prettier. d33fa70.