LLVM wasm backend progress update

[Alon Zakai]

Hello everyone,

After we stabilized the new build machines we've been asking people to test the new upstream LLVM wasm backend more,

https://v8.dev/blog/emscripten-llvm-wasm

The main bugs are being tracked here:

https://github.com/emscripten-core/emscripten/projects/1

The blockers there should be fixed before we switch emsdk's default from fastcomp to upstream. We've been making good progress, but definitely the increased testing has found issues we were not aware of earlier, in emscripten, LLVM, and wasm-ld.

Please continue to test and file issues, and help with the existing issues is very welcome!

- Alon

[Floh]

Very cool! I have switched the Tiny Emulators page (https://floooh.github.io/tiny8bit/) to upstream-llvm a couple weeks ago,and it worked out of the box. It's not a very complex code base, but it's not completely trivial either, lots of bit-twiddling on 64-bit integers, quite a few EM_JS calls, closure pass, and lots of Dear ImGui C++ code in the debugging UIs.

I'm happy with the performance now too, it's within 10..20% of a native -O3 build on Chrome, size also looks good (it's a tiny bit smaller than before). For some reason fastcomp didn't like this particular type of code (however, it could also be that this is because the WASM implementation in Chrome has improved, I haven't done side-by-side tests in the same Chrome version yet).

Cheers, and keep up the good work :)