Depends on the company in my experience. I've seen some suppliers that basically just wire up the diagram in Matlab/simulink and hit Autocode. No humans actually touch the C that comes out.
Honestly I think that's probably the correct way to write high reliability code.
You’re joking right? That autogenerated code is generally garbage and spaghetti code. It was probably the reason for Toyotas unintended acceleration glitch.