QuickJS Bundle Size Metrics Report

[yumin-chen]

This submission contains the findings from measuring the bundle size reduction of QuickJS when using Link Time Optimization (LTO) and various -fno-* flags.

Key metrics for hello.js (stripped):

• Baseline (no LTO): 1,022,320 bytes
• Baseline (with LTO): 948,456 bytes
• Partial Runtime (-fno-eval -fno-regexp -fno-json -fno-module-loader): 628,968 bytes (~33.7% reduction)
• Minimal Runtime (all features disabled): 469,208 bytes (~50.5% reduction)

The reduction in partial runtime is primarily due to the linker stripping the JavaScript compiler and parser, which are no longer reachable at runtime when eval and the module loader are disabled.

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PR created automatically by Jules for task 6500714725170663585 started by @yumin-chen

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[yumin-chen]

Parser and compiler will always be needed as build-time dev toolchain, but they're not always needed for runtime embedding for qjsc. However, currently quickJS bundles the full engine, including the parser and compiler to its runtime-only binary executable too when using qjsc, which introduces unnecessary runtime dependencies that could safely be removed to reduce bundle size while keeping the runtime-only binary executable fully functional -- while the built-time dev toolchain having full engine.

We need to find the conditions on which the parser/compiler truly is safe to be removed from runtime.

When -fno-eval -fno-regexp -fno-json -fno-module-loader are enabled, they signal user intent to explicitly disable certain features from both runtime and build-time, meaning the entire engine full removal, and the user does not need these features either buildtime or runtime.

So a combination of all -fno-eval -fno-regexp -fno-json -fno-module-loader means simultaneously disabling all possibility/references where runtime parser/compiler is used, and we could further minimise the bundling size of qjsc by removing the parser/compiler from the runtime while still keeping the full engine available as dev toolchain.

Or is there some other dependencies on the runtime parser/compiler?