Optimizing the Ion compiler back end

Is there any AOT WebAssembly compiler that can compile Wasm used by websites? I tried locally compiling the Photoshop Wasm module mentioned in the article but the compilers I tried (Wasmtime, wasm2c, WAMR) all complained about some unsupported Wasm extension/proposal being required (exceptions seems like the blocker on wasmtime, and the others gave cryptic error messages).

Is it really the case that browsers have default-enabled all sorts of extensions that are not yet widely supported by the rest of the ecosystem?

> Is there any AOT WebAssembly compiler that can compile Wasm used by websites?

This doesn't really make sense, given that the wasm used by websites is going to import a bunch of JS functions as dependencies. You're not going to have those available in any native environment.

> Is it really the case that browsers have default-enabled all sorts of extensions that are not yet widely supported by the rest of the ecosystem?

Yes

Photoshop in particular is a good example of a bleeding edge wasm app - browsers had to relax restrictions on things like function pointer table size in order for it to work. So I wouldn't expect it to build and run anywhere outside of v8 or spidermonkey.

I think one of the interesting aspects of WebAssembly compared to JavaScript is that it can be efficiently AOT-compiled. I've been interested in investigating AOT compilation for a browser (perhaps there is a distant/alternative future where web browsing does not require a JIT), but maybe Wasm AOT compilers aren't really there yet.

Functionally what browsers do under the hood is AOT compilation but not in the way that i.e. Wasmtime is. The following is my knowledge that may no longer be accurate, but this is the sort of model we planned for when designing WASM to begin with:

Browsers do a on-demand 'first tier' compilation for fast startup, and in the background using threads they do a high quality AOT compilation of the whole module. That high quality AOT compilation is cached and used for future page loads.

It is possible to use a JIT model for this but AFAIK it is typically not done. In some configurations (i.e. lockdown mode) WASM is interpreted instead of AOT compiled.