Add a rollup plugin for tree shaking Emscripten output. #23964
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Rollup has built in tree shaking which can inform the plugin which exports are no longer used. If those exports correspond to wasm exports they can potentially be removed from wasm file too. Overview: While the modules are parsed, we collect info about the exports before any tree shaking occurs to build a map from ESM export name to Wasm export name and info about the local function name within the JS e.g. _foo. During bundle generation rollup provides a list of exports that are removed. We then try to match the removed exports to Wasm exports. However, they all cannot simply be removed though since they may be used internally in the file still. A new list of the used wasm exports is generated and passed to wasm-metadce to remove any unused exports. Note: there are a lot more things we could do there, but this seemed like a good stopping point. It also shows that even for specific output, tree shaking is hard to do soundly for dynamically loaded wasm.
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Rollup has built in tree shaking which can inform the plugin which exports are no longer used. If those exports correspond to wasm exports they can potentially be removed from wasm file too.
Overview:
While the modules are parsed, we collect info about the exports before any tree shaking occurs to build a map from ESM export name to Wasm export name and info about the local function name within the JS e.g. _foo.
During bundle generation rollup provides a list of exports that are removed. We then try to match the removed exports to Wasm exports. However, they all cannot simply be removed though since they may be used internally in the file still. A new list of the used wasm exports is generated and passed to wasm-metadce to remove any unused exports.
Note: there are a lot more things we could do there, but this seemed like a good stopping point. It also shows that even for specific output, tree shaking is hard to do soundly for dynamically loaded wasm.