LLVM Weekly - #593, May 12th 2025
Welcome to the five hundred and ninety-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 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
Recordings from EuroLLVM 2025 have started to be posted to YouTube.
If you might like to run a workshop the day before the 2025 LLVM Developers' Meeting, now is the time to submit the proposal (deadline June 1st).
My Igalia colleague Mikhail Gadelha has a blog post on work to improve RISC-V LLVM performance as compared to GCC, a project done through RISE and also summarised on their blog. Mikhail’s SpacemiT X60 scheduling model patch was also mentioned on Phoronix.
I talk about tech in general, LLVM Weekly and projects I’ve been involved in
such as RISC-V, LLVM, lowRISC, Raspberry Pi, and work at Igalia on the latest
episode of the TMPDIR podcast hosted by Khem Raj and
Cliff Brake. Not so on-top for LLVM, but if you’re interested in my computer
setup enjoy scrolling through lots of Linux configuration notes you might like
my blog post on the MiniBook X N150 - the netbook isn’t dead
(yet!). I also wrote up
suite-helper, the helper script I split out
to handle my most common tasks when building and diving into llvm-test-suite
configurations - I’d highlight particularly the reduce-ll helper to
llvm-reduce a target assembly snippet for a given .c input. Finally I’m
presenting a talk about improvements to RISC-V vector code generation in LLVM
at the RISC-V
Summit Europe in Paris this week. If you’re here, be sure to say hi!
The next LLVM Bay Area Monthly Meetup will take place on Monday 12th May.
According to the LLVM Calendar in the coming week there will be the following:
- Office hours with the following hosts: Alexey Bader, Alina Sbirlea, Kristof Beyls, Johannes Doerfert, Aaron Ballman.
- Online sync-ups on the following topics: Flang, modules, libc++, LLVM/offload, BOLT, SPIR-V, OpenMP for Flang, memory safety working group.
- For more details see the LLVM calendar, getting involved documentation on online sync ups and office hours.
On the forums
Reid Kleckner found that each class template instantiation in Clang costs about 1KiB of memory.
Utkarsh Saxena and collaborators propose a Polonius-inspired intra-procedural lifetime analysis in Clang intended to detect issues such as use-after-free and use-after-return.
Britton Watson is seeking volunteers for the 2025 LLVM Developers' Meeting Program Committee and for the Student Travel Grant Review Committee.
“wdx727” proposed adding stale profile handling to Propeller, inspired by BOLT.
Alex Zinenko is trying to build a maintainer list for MLIR.
In response to a question, Peter Waller gave guidance on how to use CSPGO.
Ramkumar Ramachandra started an RFC discussion on a new analysis to recognise polynomial hash functions like CRC.
Md Abdullah Shahneous Bari made an MLIR RFC on adding a generic way to imitate/emulate unsupported data types in a target environment.
- VenkataKeerthy started a discussion on upstreaming support for generating IR2Vec embeddings into Machine Learning Guided Optimisation (MLGO) for inlining.
Csanád Hajdú wrote up a summary of current support for execute-only libraries on AArch64, its limitations, and a proposed path forward that adds a new frontend option.
The next MLIR open meeting will be an open design meeting on symbolic expressions and symbolic tensors in MLIR.
LLVM commits
reportFatalInternalError and reportFatalUsageError were introduced and
report_fatal_errorwas deprecated. As discussed at length in a previous RFC,report_fatal_errorgenerates a backtrace and an invitation to submit a bug report unlessGenCrashDiag=falseis passed. You would now usereportFatalInternalErrorfor situations indicating a bug in LLVM (crash dialog generated) andreportFatalUsageErrorfor exiting with an error but no crash dialog. b492ec5, 562a455.An initial scheduler model was added for the SpacemiT-X60 RISC-V CPU. 4eac576.
A new flag was added to disable the SchedModel/Itineraries during scheduling. 00e7a02.
It is now documented that an attempt to evade a non-permanent ban frmo the project will result in being banned permanently. f2f4eac.
The uselist was removed for ConstantData, meaning it is no longer possible to inspect the uses of ConstantData. 9383fb2, 4d60c6d.
Assembly printer passes are now registered in the pass registry meaning you can use
llc -start-before=<target>-asm-printerin tests. 675cb70.As a debug tool, new statistics were added to track the number of instructions that remain in source order after scheduling and the total number of instructions scheduled. A range of other statistics were added too. ddfdecb, cdde6a6.
Initial code generation support was added for the RISC-V Zvqdotq (dot product) extension. 1ac489c.
A new TargetInstrInfo hook was added and used in MachineCopyPropagation to simplify/canonicalise instructions after copy propagation (there’s a pattern where tail duplication followed copy propagation results in operands that are the zero register, which depending on the opcode might mean it can be simplified to a canonical move or load-immediate). 52b345d.
The last mentions of IRC were removed from LLVM’s documentation, as it’s not used by the community any more. 7548cec.
RISC-V SDNodes are now tablegenerated (similar cleanups were made recently to other backends, but I think this is the most in-depth). c60db55.
$HOMEis now passed through to tests run vialit. 635c648.Documentation started to land on MLGO (Machine Learning Guided Optimisation). 77d1db6d.
Clang commits
-Wjump-bypasses-initwas renamed to-Wjump-misses-init. 43c05d9.The core language parts of the C++ trivial relocation proposal were implemented and the previously implemented
__is_trivially_reloctablewas deprecated in favour of__builtin_is_cpp_trivially_relocatable. 300d402, 09c80e2.A
cir-simplifypass was added. 2eb6545.__ptrauthcan now be applied to integer types. 65a6cbd.