binaryen VS asyncify

The Binaryen wasm optimizer (mentioned in the article) is always open for contributions,

https://github.com/WebAssembly/binaryen

The end of the related work section cites both wasm-smith and the Binaryen fuzzer (https://github.com/WebAssembly/binaryen/wiki/Fuzzing) and says, "They both provide a fuzzer that turns a stream of bytes into a WebAssembly module in order to test implementations. Their fuzzers always generate semantically valid test cases, but lack the targeting and tuning that Xsmith provides."

I look forward to reading more about how they do the targeting and tuning.

Binaryen or the LLVM of wasm: https://github.com/WebAssembly/binaryen

Download Binaryen

Probably https://github.com/WebAssembly/binaryen/, there were various rust bindings to it.

The final phase of our compiler is code generation. This phase takes the AST and converts it to a set of executable instructions. In our case, WebAssembly. To accomplish this, we are going to use a popular WebAssembly compiler toolchain called binaryen.

In this guide, we will be using TypeScript and NodeJS. The concepts are highly portable, so feel free to use the environment you're most comfortable with. Our only major dependency, binaryen, has a simple C API. You are welcome to skip ahead to the next section if you're using a different language.

What are the size and performance benefits of processing the Wasm payload with wasm-opt?

I would recommend looking into binaryen as it has it's own IR and can perform optimizations over it. It's also simpler than LLVM and has the option to produce binaries with debug names.

You can also use binaryen to optimize your wasm output

The asyncification is achieved by unwinding and rewinding the local stack. With wasm-opt, this is done on a WASM level as post-build transformation. This makes it a language-agnostic approach. Once a WASM module is asyncified it needs to be used through the JavaScript wrapper Asyncify. A good introduction to asyncify can be found here: Using asynchronous web APIs from WebAssembly.