Improve performance by compiling to webassembly about sucrase HOT 6 OPEN

After working through more details to get the Sucrase parser working in full, I tried this again on a more realistic dataset and the results seem more promising now! It's a TypeScript/JSX codebase that's about 4000 files and about 550,000 lines, and the task was to run the Sucrase parser to count the total number of tokens in all files. I confirmed that the number of tokens was the same for js and wasm, so hopefully this means that both are indeed doing a full correct parse.

Here are the numbers:

Dataset                JS time   wasm time
First 100 files        195ms     29ms
First 1000 files       906ms     302ms
All files              1805ms    860ms
All files, 10 times    8620ms    8345ms
All files, 100 times   77250ms   81142ms

As expected, V8 runs JS better on larger datasets since it has more time to identify hot code paths and compile them with good optimizations. It looks like JS still does slightly better at the largest scale, around 50 million lines of code, but even then the difference is small. In my own use cases, the typical scale is 1000-4000 files, so at least here, I'd expect a 2-3x speedup. It's unclear if the improvements are due to the more realistic dataset or improvements in AssemblyScript, but it looks like AssemblyScript will improve perf, especially on smaller datasets.

So this seems like a good enough justification to get the code fully working in AssemblyScript, including using i32 types instead of number and things like that. I'm still hoping to get the code into a state where the same codebase can run both, especially because debugging JS seems much nicer than debugging wasm.

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FWIW, we have successfully used sucrase with nodegun to get rid of the node start time and the JIT warmup time.

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Wow, that's awesome, I hadn't seen nodegun! I'll have to try it out when I get a chance.

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@alangpierce I think wasm should be faster than js for large dataset with latest AssemblyScript as well. Also if you change --optimize to -O3 here you could get much better performance

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Is there any link to a working prototype for using Sucrase via WASM? I'd really appreciate it.

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Your parser performance is astonishing, it would be super cool to use your parser in webpack to decrease build time

This way you would also get native typescript support 😛

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