LLVM Weekly - #607, August 18th 2025

Welcome to the six hundred and seventh 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 via email: asb@asbradbury.org, or Mastodon: @llvmweekly@fosstodon.org / @asb@fosstodon.org, or Bluesky: @llvmweekly.org / @asbradbury.org.

News and articles from around the web and events

The 2025-08 WG21 C++ mailing has been posted.

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

• Office hours with the following hosts: Phoebe Wang, Johannes Doerfert.
• Online sync-ups on the following topics: Flang, vectorizer improvements, modules, lifetime safety breaktout group, LLVM/Offload, Clang C/C++ language working group, SPIR-V, OpenMP for Flang, HLSL.
• For more details see the LLVM calendar, getting involved documentation on online sync ups and office hours.

On the forums

• Renato Golin noted that the draft document on LLVM maintainer policy has been updated after feedback.

• Tobias Hieta asked for and received on advice for reducing executable size of a heavily optimised program.

• Kshitij Jain is surveying people on their opinions on how TableGen could be better utilised in MLIR.

• Slides and a recording from the MLIR open meeting on properties design are now available.

• Owen Anderson posted an RFC on adding a riscv32 subarchitecture for CHERIoT. Discussion is currently focused on whether adding a subarchitecture is necessary/best vs e.g. relying on selection via -march flags and/or the target OS in the triple.

• Trevor Gross is seeking feedback on the idea of adding matrix-style preprocessing to lit to reuse tests across backends.

• LLVM 21.1.0-rc3 was released. This is intended to be the last release candidate in the 21.x series.

• There are quite a few meetings / special interest groups within LLVM now, some of them taking notes or minutes and posting them to Discourse. I don’t tend to collect these right now in LLVM Weekly, but made a post to suggest such posts be given a meeting-minutes tag so they can be easily found. Respondents so far seem to be supportive.

• Sergey Shcherbinin started an RFC thread on extending the ExtBinary sample profile format with TypifiedProfileSection to support attahcing multiple typed profile payloads to each functions.

• David Spickett kicked off a discussion about removing the PDB plugin from LLDB build using Microsoft’s DIA SDK.

• Alex Bradbury wrote a quick note sharing some numbers on the impact on dynamic instruction count of SPEC 2017 benchmarks on RISC-V for -ffp-contract=fast (matching GCC) vs LLVM’s default.

LLVM commits

• An initial Content Addressable Storage (CAS) library was added to LLVM. dda996b.

• Backend calling convention lowering implementations can now access the original IR type. e92b7e9, 498ef36.

• Multiple save/restore points can now be represented in MachineIR. bbde6be.

• The documentation on cross-compiling builtins for Arm was further updated. dc41571.

• Codegen for most significant bit extraction was improved for RISC-V. 18782db.

• MC level support was added for more instructions from the proposed RISC-V P (packed SIMD) extension. e2eaea4.

• The output of the debugify coverage tracking was slimmed down by adding a mechanism to handle cases where single errors end up being reported many times after being propagated to other instructions in later passes. bc216b0.

Clang commits

• By default, clang-tidy no longer attempts to analyse code form system headers. This improves performance significantly. bd77e9a.

• __builtin_elementwise_{fshl,fshr} was added. c3bf73b.

• ClangIR gained initial support for atomic types. 331a5db.

• The newly introduced cfi_salt attribute can be used to specify a ‘salt’ for control-flow integrity (CFI) checks to distinguish between functions with the same type signature. aa4805a.

• The list documenting the C features backported to previous C standards was made more accurate. ed6d505.

Other project commits

• A skeleton of an importer for Wasm binaries was started in MLIR. 6bb8f6f.

• The Dexter debug experience tester now has Debug Adapter Protocol (DAP) compatibility. d934554.

• f[no]-open-simd was added to Flang to enable OpenMP support only for SIMD onstructs. d3d96e2.

• LLVM libc’s GPU benchmarking infrastructure was improved. 08ff017, cf5f311.

• LLDB learned to parse the Wasm symbol table. 5be2063.

• A new MLIR pass was added for vector to AMX conversion. 7d1b9ca.

• The XeVM target and XeVM dialect integration tests were added to MLIR. baae949.