LLVM Weekly - #343, July 27th 2020

Welcome to the three hundred and forty-third 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

LLVM 10.0.1-final has been tagged.

Hassam Uddin wrote up a quick introduction to register allocation. Note this is a high-level introduction, and isn't tied to any particular compiler framework (sample code is given in OCaml).

On the mailing lists

• Arthur Eubanks started a thread about the new pass manager status, which spawned discussion bout flipping to the new pass manager by default. Sjoerd Meijer shared concerns related to observed code size regressions.

• Varun Gandhi suggested that LLVM should explain the lack of C++ ABI stability in the developer policy, prompting a reasonable amount of discussion about the policy and the possible use of deprecation notices.

• Alexander Richardson posted an RFC on requiring explicit address space arguments for PointerType, motivated by reducing the difficulty of updating out-of-tree targets like CHERI as well as avoiding bugs for in-tree targest like AVR that use non-zero pointer address spaces.

• David Blaikie started a thread to discuss a potential misoptimisation with zero-length functions.

• Tanya Lattner sent a reminder that applications for the LLVM Foundation Board of Directors are due by July 30th.

LLVM commits

• The CMake minimum version has been bumped to 3.13.4. afa1afd.

• Target-specific InstCombine code has now been moved into the targets. 2a6c871.

• An "extract" test utility was added, to support multiple documents / test cases in a single test file. d054c7e.

• update_test_checks and update_cc_test_checks gained a new option to allow function attributes to be checked. 937bad3.

• A new byref argument attribute was introduced. Unlike byval, it doesn't imply that a copy is made anywhere or that the argument is passed on the stack. 5e999cb.

• AMDGPU GlobalISel gained initial support for calls. 61f1f2a.

• A "development-mode InlineAdvisor" was added, supporting loading models with a command-line parameter and collecting training logs. 70f8d0a.

• Loop peeling support was added to the loop fusion pass. 38a8217.

• The abs/umin/umax/smin/smax intrinsics were added. fef0cf0, deb4bb2.

• As part of the work to integrate lowering of GC live operands into the register allocator, GC relocation can now be lowered to virtual registers. 3da1a96.

Clang commits

• A new --ld-path command line flag was added, and should be used in favour of -fuse-ld for specifying the path to the linker. 1bc5c84.

• clang-format gained a new BitFieldColonSpacing option 52ab7aa.

Other project commits

• LLVM's libc gained implementations of strstr, fmin, fminf, fminl, strnlen, fmax, fmaxf, fmaxl and memrchr. d080635, 7ce32f8, f773d37, 4096088, 5a9630b.

• The [[clang::trivial_abi]] annotation has now been added to std::unique_ptr in libcxx, allowing further optimisations. 76887bc.

• MLIR's SPIR-V to LLVM conversion is now documented. b74ab49.

• lld-macho gained partial support for weak definitions. 31d5885.

• LLDB now has support for AArch64 SVE register information and core file register access. 7e017de.