LLVM Weekly - #461, October 31st 2022

Welcome to the four 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, or @llvmweekly or @asbradbury on Twitter.

News and articles from around the web

Tanya Lattner is seeking moderators for the LLVM Dev Meeting. Volunteer and get a free t-shirt!

Jakub Beránek blogged about speeding up rustc, primarily through improvements to how it’s compiled (including LTO, PGO, and application of BOLT).

On the forums

• Patrick Walton initiated a discussion on marking SSA values as pointing to immutable memory, with the intention of better optimising Rust generated IR.

• Jakub Kuderski and collaborators made a proposal on poison semantics for MLIR.

• Tom Stellard is seeking input on desired GitHub pull request features, and is intending to submit a list to GitHub on Wed 2nd November.

• David Blaikie shared news of an ABI break in Clang 16 due to fixes for the GCC Itanium ABI.

• Lang Hames provided an update on ORC JIT.

• “tmatheson” raised concerns about the expansion of volatile/const atomics to LLSC/cmpxchg loops.

LLVM commits

• The “Writing an LLVM backend” document was updated to used named operand matching. 5713c29.

• Patches implementing the llvm-debuginfo-analyzer continue to land, with an ELF reader now committed. 4f06d46.

• Support was added for the new X86 CMPCCXADD, AVX-VNNI-INT8, and other instruction. fdac4c4, 23f0269.

• Vectorisation of epilogue loops was disabled for RISC-V. 269bc68.

• Function specialisation based on literals was fixed. 38f44cc.

• !logtwo was added to TableGen. 64d5aed.

• Scalar FP ceil/floor/trunc/rint/round/roundeven are now inlined rather than relying on a libcall. e94dc58.

Clang commits

• -Wcast-function-type-strict was added to provide warnings for function type casts with mismatched types (which may lead to runtime CFI failures). 1aad641.

• P2513, the “char8_t Compatibility and Portability Fix” was implemented. This allows initialising an array of unsigned char or char from u8 string literals in C++. d0d2772.

• -fstrict-flex-array=3 is now supported. 7f93ae8.

Other project commits

• LLVM’s libc gained implementations of difftime, clock, time, and fgets functions. The initial scanf parser was also added. 1220442, 22ea0e5, 2d52283, 7a129f0.

• Documentation was written on side effects and speculation in MLIR. 49e2d36.

• Minimal LoongArch support was added to LLDB. a3be778.

• Debug info started to be added to the MLIR LLVM dialect. 3bef1e0.

• Fastmath flag attribute support was added to the MLIR arithmetic dialect. b56e65d.

• A new plugin infrastructure was implemented for libomptarget alongside a new CUDA plugin. 8469041.