A follow-up question I'd like to ask to the author: if I understand correctly, one of the ideas is that you can write "high-level", almost platform-independent translations like:

    regs.eax = 3;
    regs.eax = add(regs.eax, 4);
    windows_api();  // some native implementation of the API that was called

It depends on what results you’re expecting! Relative to an interpreter, even the simplest unoptimized translation of that code is already significantly more efficient code at runtime.

In the post there is a godbolt link showing a compiler inlining a simple add, but a real implementation of x86 add would be much more complex.

I have read other projects where the authors put some effort into getting exactly the machine code they wanted out. For example, maybe you want the virtual regs.eax to actually exist in a machine register, and one way you might be able to convince a compiler to do that is by passing it around as a function parameter everywhere instead as a struct element. I have not investigated this myself.