LLVM is bounded by what its IR can express, and what it can express is constrained by what is portable and what it can prove. There is a reason `ffmpeg`, OpenSSL, OpenBLAS, glibc's string routines, LuaJIT's interpreter, etc. all still leverage hand-written assembly.
As for the editor, even if it isn't necessarily optimal assembly (I have no clue), a reduced feature set and relying on OS APIs instead of frameworks will still probably result in something which feels faster than Electron programs like VSCode.
As for the editor, even if it isn't necessarily optimal assembly (I have no clue), a reduced feature set and relying on OS APIs instead of frameworks will still probably result in something which feels faster than Electron programs like VSCode.