LLVM Weekly - #586, March 24th 2025
Welcome to the five hundred and eighty-sixth 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
Min-Yih Hsu blogged about calculating throughput with LLVM’s scheduling model.
According to the LLVM calendar in the coming week there will be the following:
- Office hours with the following hosts: Kristof Beyls, Amara Emerson, Johannes Doerfert.
- Online sync-ups on the following topics: ClangIR, pointer authentication, OpenMP, Flang, RISC-V backend, LLVM embedded toolchains.
- For more details see the LLVM calendar, getting involved documentation on online sync ups and office hours.
On the forums
Asher Mancinelli started an MLIR RFC discussion on an attribute interface for loop annotation metadata.
The LLVM security response group 2024 transparency report was published.
LLVM 20.1.1 was released.
Maxwell Bland kicked off a discussion about ideas on heap canaries for Linux.
Shilei Tian would like to introduce a sentinel pointer value to DataLayout.
Maksim Levental proposed upstreaming CIRCT’s Verif and SMT dialects.
Nikita Popov suggested that in the future the llvm.experimental prefix shouldn’t be used for intrinsics and they should just be marked as experimental in documentation.
Tom Stellard has created an allow list of third-party GitHub Actions.
Mark de Wever started an RFC thread on breaking
basic_format_string’s ABI for performance improvements.Matthias Springer would like to allow pointers as element type of MLIR’s VectorType.
Asher Mancinelli suggested a volatile representation in Flang.
Andrew Rogers shared a PSA on work to annotate LLVM public interfaces as part of efforts to build LLVM as a DLL on Windows.
LLVM commits
The DAGCombiner learned to avoid store merging across function calls if the spilling is unprofitable. Taken alongside previously committed tweaks to costing, this can make a big difference on some RISC-V inputs, such as a greater than 10% reduction in runtime for 544.nab_r from SPEC on the BananaPi-F3 in the tested configuration. f138e36.
A DXIL instruction legalizer pass was started. a2fbc9a.
update_test_checks learned a new
--filter-out-afteroption which stops the generation of any CHECK lines beyond the line that matches the filter. 194ecef.MC layer (assembler/disassembler) support was added for the RISC-V vendor extensions Xqcibi (branch immediate), Xqcisim (simulation hints), Xqcilb (long branch), and Xqcisync (sync delay) from Qualcomm. 036c6cb, 467e5a1, 0744d49, 3840f78.
LangRef documentation was added for
llvm.readsteadycounter. cc2a86a.Assembler support was added for the RISC-V Zilsd and Zclsd extensions ((compressed) load/store pair instructions). Also experimental assembler support for the Zvqdotq (vector quad widening dot product) extension. 480202f, eb77061.
The 2024 security group transparency report was committed. 9a078a3.
The DirectX root signature binary representation was documented. d0d33d2.
GPU loader utilities were moved from libc to LLVM. bd6df0f.
Support was added for inline SPIR-V types. 864a83d.
LoopIdiomRecognize can now recognise loops implementing strlen/wcslen. ac9049d.
Clang commits
Clang Static Analyzer can now collect statistics per entry point rather than just per translation unit. 57e3641.
Clang adopted support for GCC’s ASM constexpr string extension. 911b200.
ClangIR upstreaming continues to progress, with support added for unary ops, CastOp, scalar conversions, and empty for loops. The cir-translate and cir-lsp-server tools and the cir-canonicalize pass was also upstreamed. 5f86666, 27d8bd3, 1ae307a, 39ce995, f51e5f3.
The cplusplus.PureVirtualCall checker was documented. 9762b8e.
The compilation time overhead of enabling
-Wunsafe-buffer-usagewas reduced by ~88% leaving compile time overhead of ~1.7% on the benchmarked inputs. f5ee105.A bugprone-capturing-this-in-member-variable checker was added. 3b1e18c.