@HaskRay

Maintainer of LLVM MC, Clang driver, lld/ELF, and libunwind

 California, USA
maskray.me/
Joined November 2012
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In 2020, reviewing lld's --optimize-bb-jumps (reviews.llvm.org/D68065), I asked that the pass run inside finalizeAddressDependentContent "to accommodate thunks and linker script symbol changes." The author replied: "Could we do this in a later patch?" There was no later patch.
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and another lld maintainer independently flagged the misplacement and found my 2020 comment. When I left Google in 2024, --optimize-bb-jumps still had no users. The answer was always "we will use it." Today nothing in llvm-project passes the flag; only three lld tests do.
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Google's requirements have drifted away from the already very broad range that lld, and llvm-project at large, serves. A feature only one company's internal pipeline might need should prove itself there before it lands upstream, where everyone maintains it.
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That placement was a wrong-code bug from day one: the pass shrinks .text after .relr.dyn is computed, so RELR entries point at the wrong words. Since a change this year, .eh_frame_hdr search keys go stale too. An AI-assisted patch surfaced it recently,
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I was junior; he was far more senior. Landing a feature on a promise of future use, and deferring the reviewer's design concern to "a later patch", is not how open source should work.
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maskray.me/blog/who-pays-for… Who pays for Clang Another AI slop post. Commits by employer, What each funder works on, Review, Shared and vendor-specific work

Who pays for Clang

Clang's funders have changed since 2010: Apple and Google, which wrote most of it until the mid-2010s, now write a small share, and GPU and accelerator vendors, Red Hat, and new sponsors of C++...

maskray.me
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I spent many hours driving the agent through Discourse threads, slides, source trees, and LinkedIn profiles to generate this AI slop: maskray.me/blog/clangir-and-… ClangIR and the cost of MLIR

ClangIR and the cost of MLIR

ClangIR (CIR) is an MLIR dialect between the AST and LLVM IR, and in October 2026 the clang area team accepted building it by default. CIR is built on MLIR because each step along the way was locally...

maskray.me
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Comment on "RFC: Enable ClangIR Build By Default-" discourse.llvm.org/t/rfc-ena… Current feeling: it might be a huge opportunity cost

RFC: Enable ClangIR Build By Default-

I worry this would become a large opportunity cost. Several major toolchains are already opting out: Chrome’s toolchain expects to disable CIR downstream (#42), Android plans to configure it off...

discourse.llvm.org
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The new funders build GPU and accelerator compilers, and their other compilers (Flang, Triton, IREE, their own stacks) are built on MLIR. For them, a Clang that emits an MLIR dialect is the point, not an implementation detail.
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For C++ programmers who were Clang's main constituency, CIR has to earn its place by being better at what the AST, the CFG, and classic CodeGen do today: diagnostics, safety analyses, and optimizations that need C++ semantics, without making the compiler slower to build or run
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github.com/MaskRay/ccls/rele… Indexed forwarding functions such as std::make_unique<A>(...) and std::vector<A>::emplace_back(...). Hover on an auto variable in a function template shows the deduced type when the template has exactly one instantiation. Adapt to LLVM 22, 23 and 24.

Release 0.20261004 · MaskRay/ccls

Support the LSP 3.17 type hierarchy: textDocument/prepareTypeHierarchy, typeHierarchy/supertypes and typeHierarchy/subtypes. For a virtual method, supertypes/subtypes are the overridden/overriding ...

github.com
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edgls is a C/C++ language server built on the EDG C/C++ front end. It is a fork of ccls with the clang-based parts replaced: the indexer, diagnostics, compile command handling, code completion, signature help, and formatting. github.com/MaskRay/edgls Verdict: Slower than clang
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Settling an old score: --fortran-common (added in 2020) was removed from lld/ELF in September 2026, removing one blocker of fully parallel input file parsing and symbol resolution.
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Credit where it's due - I'm glad I could connect with the original author six years later. For features added today, I doubt maintainers in one year will be as lucky in finding the original authors.
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I made a typo earlier and wrote 'useful' instead of 'useless' regarding the 'testsuite must pass' requirement. The author agreed without question. Their other replies are almost direct copy pastes.
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Extractive patches from a new contributor to llvm binary tuilities. "But it's Codex output the author doesn't really own, so reviewers end up supplying the understanding." llvm-project really should really adopt a ghostty-style vouch system.
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There is finally a migration path for LLVM's llvm::cl::opt, off dynamic initialization and onto a data-only TableGen representation: one struct per library, constant-initialized, read with a single load. No option spellings change. discourse.llvm.org/t/rfc-dec…

[RFC] Declare library command line options in TableGen, one struct per library

cl::opt globals are how LLVM’s libraries declare their internal developer options (2800+ in 70 components of llvm/lib; 1749 are cl::opt). Each one is a constructor run at startup that registers into...

discourse.llvm.org
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`# RUN: llvm-dwarfdump --debug-names %t.bolt FileCheck --check-prefix=POSTCHECK %s` It passed even if the pipe `|` was missing: llvm::cl:: parsed --check-prefix as grouped -c -h…, hit -h, printed --help, exit 0. FileCheck never ran. No "Unknown command line argument" error.
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An llvm-project contributor whose AI-assisted PRs had all needed heavy pushback just sent a good one: small diff, tests that fail without the fix, no padding. Approved.
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Two things that bug me about Abseil flags: * They call every option a "flag" (I'm used to flags just being boolean options). * Using --noboolflag instead of --no-boolflag
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