As we enter the second half of 2022, we’d like to provide a summary (necessarily highly condensed and selective!) of what we’ve been up to recently, providing some insight into the breadth of technical challenges our team of over 20 compiler engineers has been tackling.
Low-level JS / JSC on 32-bit systems
- A major milestone for this has been the completion of support for WebAssembly in the Low-Level Interpreter (LLInt) for ARMv7. The MIPS support is mostly complete.
- Developed an initial prototype of the concurrency compilation in the DFG tier for 32-bit systems, and the results are promising. The work continues, and we expect to upstream it in 2022H2.
- Code reduction and optimizations: we upstreamed several code reductions and optimizations for 32-bit systems (mainly ARMv7): 25% size reduction in DFGOSRExit blocks, 24% in baseline JIT on JetStream2 and 25% code size reduction from porting EXTRA_CTI_THUNKS.
- Improved our hardware testing infrastructure with more MIPS and faster ARMv7 hardware for the buildbots running in the EWS (Early Warning System), which allows for a smaller response time for regressions.
- Deployed two fuzzing bots that run test JSC 24/7. The bots already found a few issues upstream that we reported to Apple. The bugs that affect 64-bit systems were fixed by the team at Apple, while we are responsible for fixing the ones affecting 32-bit systems. We expect to work on them in 2022H2.
- Added logic to transparently re-run failing JSC tests (on 32-bit platforms) and declare them a pass if they’re simply flaky, as long as the flakiness does not rise above a threshold. This means fewer false alerts for developers submitting patches to the EWS and for the people doing QA work. Naturally, the flakiness information is stored in the WebKit resultsdb and visualized at results.webkit.org.
JS and standards
- Further coverage of the Temporal spec in the Test262 conformance suite, as well as various specification updates. See this blog post for insight into some of the challenges tackled by Temporal.
- Performance improvements for JS class features in V8, such as faster initialisations.
- Work towards supporting snapshots in node.js, including activities such as fixing support for V8 startup snapshots in the presence of class field initializers.
- Collaborating with others on the “types as comments” proposal for JS, successfully reaching stage 1 in the TC39 process.
- Implementing ShadowRealm support in WebKit.
WebAssembly is a low-level compilation target for the web, which we have contributed to in terms of specification proposals, LLVM toolchain modifications, implementation work in the JS engines, and working with customers on use cases both on the server and in web browsers.
Some highlights from the last 6 months include:
- Prototyping Just-In-Time (JIT) compilation within WebAssembly.
- Working to implement support for WebAssembly GC types in Clang and LLVM (with one important use case being efficient and leak-free sharing of object graphs between JS and C++ compiled to Wasm).
- Implementation of support for GC types in WebKit’s implementation of WebAssembly.
We’ve also had opportunities for much-needed face to face time within the team, with many of the compilers team meeting in Brussels in May, and for the company-wide summit held in A Coruña in June. These events provided a great opportunity to discuss current technical challenges, strategy, and ideas for the future, knowledge sharing, and of course socialising.
Our team has grown further this year, being joined by:
- Nicolò Ribaudo – a core maintainer of BabelJS, continuing work on that project after joining Igalia in June as well as contributing to work on JS modules.
- Aditi Singh – previously worked with the team through the Coding Experience program, joining full time in March focusing on the Temporal project.
- Alex Bradbury – a long-time LLVM developer who joined in March and is focusing on WebAssembly and RISC-V work in Clang/LLVM.
We’re keen to continue to grow the team and actively hiring, so if you think you might be interested in working in any of the areas discussed above, please apply here.
More about Igalia
If you’re keen to learn more about how we work at Igalia, a recent article at The New Stack provides a fantastic overview and includes comments from a number of customers who have supported the work described in this post.