How to make Firefox builds 17% faster
This deep dive explains how a clever application of buildcache's Lua plugin system can significantly accelerate Firefox's build process. By targeting the WebIDL C++ binding code generation step, which was previously uncached by traditional compilers, the author achieved a 17% reduction in warm build times. This article resonates on HN for showcasing practical build system optimization techniques applicable to large, complex software projects.
The Lowdown
Andreas Farre details a specific optimization implemented to make Firefox builds faster, focusing on the often-overlooked WebIDL binding code generation step. This technical deep dive showcases the power and flexibility of buildcache's Lua plugin system to cache non-compiler-related build processes.<ul><li>The WebIDL step generates C++ binding code from .webidl files and runs on every clobber build, making it a prime candidate for caching due to its deterministic nature.</li><li>Traditional compiler caches like ccache and sccache couldn't cache this Python-based code generation process.</li><li>buildcache's unique Lua plugin system allows custom wrappers to define inputs and outputs for arbitrary command caching.</li><li>A small change in dom/bindings/Makefile.in now conditionally passes $(CCACHE) to the py_action call, enabling buildcache to intercept the WebIDL step.</li><li>The webidl.lua wrapper tells buildcache how to handle the command, identifying .webidl source files and Python scripts as inputs, and generated C++ files as outputs.</li><li>Benchmarks show that enabling this webidl.lua plugin reduces warm Firefox build times by 15 seconds, bringing the total from 1m27s down to 1m12s, which is roughly a 17% speedup.</li><li>This serves as a proof-of-concept, suggesting that other deterministic code generation steps within Firefox's build process could benefit from similar buildcache Lua wrappers.</li></ul>Farre concludes that while this specific optimization is a modest improvement on its own, it powerfully demonstrates the general utility of buildcache's flexible plugin architecture for tackling complex build performance challenges beyond traditional compilation.