What commands are run by ALT+F2 and "r"?

Cinnamon, like GNOME from which it was forked, will restart the session when you type 'r' into the Alt-F2 window. Its just telling it to re-execute itself, so it's not invoking a new command, but telling the cinnamon window manager to re-execute.

Since posting this question, and with the help of the discussion following the earlier posted answer, I found the following answer in the Cinnamon source code

https://github.com/linuxmint/cinnamon/blob/master/src/cinnamon-global.c#L1130

/**
 * cinnamon_global_reexec_self:
 * @global: A #CinnamonGlobal
 *
 * Restart the current process.  Only intended for development purposes.
 */
 void cinnamon_global_reexec_self (CinnamonGlobal *global)
 {
     meta_restart ();
 }

I have implemented access to this function as a bash command (restartcinnamon) by adding the following line to my .bashrc file

alias restartcinnamon='dbus-send --type=method_call --print-reply \\
   --dest=org.Cinnamon /org/Cinnamon org.Cinnamon.Eval \\
    string:'\''global.reexec_self()'\'''   \\
    /usr/bin/dbus-send