I think a large part of that might be the language they choose. Every C++ code example in the paper feels extremely verbose to me, and I wonder to which degree that is inherently required for encoding language semantics, and to which degree it's C++ syntax being noisy.
This is not a critique of the authors, btw. Considering the breadth and depthtof various types of domain-specific knowledge that have to be "synthesized" on a project like this, developing a mastery of C++ is almost a given. So implementing things in C++ was likely the most natural approach for them. It technically also might be the most portable choice, since anyone who has LLVM installed will also have a C++ compiler.
I do wonder what it would be like if this were built upon a language with more appropriate "ergonomics" though. Maybe they can invent and implement DSL for Deegen in Deegen, haha.
Well... if you look at an opcode example, eg [1], it's actually almost entirely ordinary C++ which would only look slightly different if this were a non-JIT-compiling interpreter without Deegen. I say that being moderately familiar with the PUC Lua, LuaJIT, Squirrel and other VM codebases. If this is enough to produce a good JIT, that's incredible. It's quite verbose C++ but that's code style, not due to Deegen. The Deegen bit is a few lines at the bottom, which is DSL-like. I think C++ is a good choice, because it's a good choice for writing a VM.
[1] https://github.com/luajit-remake/luajit-remake/blob/master/a...