This is not a good thing though, meaning the language and abstractions are not expressive and not reusable enough. Self-hosting compilers, like the author's, feel wrong to me because of that, meta DSLs for compilers should serve as much better abstractions and save a lot of work.
Except that your meta DSL probably isn't able to solve the problem that this compiler is solving, which is putting an entire compiler natively onto the GPU in a way that the code is actually maintainable in a "native GPU" version, rather than requiring translation from some other state.
This compiler has gone through many core paradigm shifts in an attempt to find an appropriate way to express a solution to the problems that it encountered. Each iteration revealed some new insight into how to solve the problem, but inevitably lead to a need to rethink the system.
Now, the system is so expressive and capable that reusability isn't even an issue. At this point reusability is about as useful in the compiler as having a new word to represent the word "the". Why? Why not just write the? Anything else you could write is likely to create confounding layers of indirection and distance between definition and use in the code that will actually obscure clarity.
Instead, I take the intentional approach to make the code as "disposable" as possible. Why change a compiler pass that is two lines long when you can just rewrite it from scratch in less time? By leveraging a different aesthetic, architecture, and language, I'm able to have more expressivity by removing unnecessary abstraction and making it as easy as possible to re-engineer the whole thing at the drop of a hat. This means that I never have to "live with" code bloat or some design decision that's annoying me. The cost to re-engineer is so low that I have almost no technical debt. If an architecture fails to scale, replace it and move on, without any loss of productivity, and a net gain since the code gets easier and easier to work with on each iteration.
