thanks for the reply @tlively !
Do you think it's reasonable for someone unfamiliar to the binaryen codebase to dive in and implement it in some weeks?

It's hard to say. If you start with a good understanding of how the code needs to be transformed, then figuring out how to do that transformation in a Binaryen pass probably wouldn't be so bad. But if you're hoping to figure out the correct transformation as you go, then I would expect it to be extremely difficult.

I believe this might be doable in some weeks. Each invoke call could be replaced with a try-catch around a normal call. There would just be a single tag type, which contains a single integer (the thrown pointer). The only other thing you'd need to change is the actual throwing (to create a tag and throw it), which calls out to JS to throw - but that would require a hack of some kind (finding the right import in a minified build is not trivial, as the imports aren't marked).

Thanks for the replies people!
I'll explore the other options further (using a different emscripten/llvm version in unity and passing -fwasm-exceptions in the correct places of the unity build system) and if they fail come back to this if necessary.

Also so far I cannot prove that we'd get lots of perf improvements with wasm exceptions but estimate the upper bound to be around 2% or so

thanks again and thanks for your work on binaryen!