It looks like they're just taking the entire eightcc compiler and stuffed into vim buffer memory.
The current code is essentially assembly instructions running as Vim script, this gotta be incredibly slow, probably not much faster than an x86 emulator written in Vim script:
https://raw.githubusercontent.com/rhysd/8cc.vim/master/autol...
- https://github.com/neovim/neovim/issues/170
- https://github.com/neovim/neovim/issues/387
No human hand-authored this giant pile of VimScript: https://raw.githubusercontent.com/rhysd/8cc.vim/master/autol...