LLVM Weekly - #391, June 28th 2021

Welcome to the three hundred and ninety-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 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

No particular news to highlight this week.

On the mailing lists

• Leonard Chan started an RFC discussion on building LLVM tools into a single binary (busybox-style), and followed up with a WIP prototype.

• Tom Stellard proposed only changing the libclang.so SONAME when the ABI changes.

• LLVM 12.0.1-rc3 has been tagged.

• Andrew Kaylor started a thread about floating point variance in the test suite, noting that it’s still the case that some tests fail if the floating point calculations don’t exactly match the reference results.

• Nick Desaulniers created an RFC about inlining and mismatched function attributes, noting several cases where inlining can produce unexpected or surprising results.

• Luke Drummond helpfully summarised the various responses on the thread about appropriate use of the ‘NFC’ tag.

• Arthur Eubanks initiated a discussion on ABI attributes on arguments vs parameters.

• Alexander Yermolovich is seeking feedback on refactoring llvm-dwp into a library in order to aid the implementation of BOLT.

• Arthur Eubanks is advertising for help in completing the opaque pointers implementation plan.

• There’s been yet more discussion on moving the LLVM mailing lists to Discourse. Aaron Ballman raised a concern about fracturing the community.

• Anirudh Prasad proposed a new mechanism for tieing a particular inline asm operand to a specific register, that has also been proposed in GCC. Responses so far have been positive.

• David Spickett sent an update on the patches adding AArch64 memory tagging support to LLDB, nothing they are awaiting review.

LLVM commits

• A new flag was added to force all pointers to be opaque pointers, in order to help with testing. 4c8174f.

• The AMDGPU backend gained a new pass to optimise the live ranges of VGPRs. 208332d.

• The IR verifier will now fail on overrunning and invalid indices for the insert/extract vector intrinsics. 3c4dbf6.

• An initial implementation of llvm-sim, an IR similarity visualisation tool, was committed. 9e73f7c.

• New documentation was added on the use of opt and the new pass manager. e15673d.

Clang commits

• clang-format now has basic support for formatting JSON. 8b7881a.

• Install targets were created for scan-build-py. d9cf829.

• clang-format gained a new LambdaBodyIndentation option and an IfMacros option (a list of macros that should be interpreted as conditionals instead of function calls). 64cf5eb, be9a87f.

Other project commits

• A Bazel build configuration was added to the repo, following approval of the proposal to do so. 4aeb2e6.

• LLDB can now use LLVM’s demangling library to demangle symbols using Rust’s v0 scheme. 0a2d4f3.

• The DFSan shadow and origin memory layouts were modified to match MSan. 45f6d55.

• Benchmarks for memcmp and bzero were added to LLVM’s libc. 87065c0.

• Libcxx’s status ranges implementation status page was updated. e7091da.

• MLIR’s async-parallel-for pass was updated to implement recursive async work splitting for scf.parallel operations. 86ad0af.