From: anton@mips.complang.tuwien.ac.at   
      
   John Levine  writes:   
   [indirect branches through auto-increment locations]   
   >I suppose you could use them for threaded code, but I didn't run into   
   >any PDP-8 progams that used that.   
      
   You can use them for (direct) threaded code if the indirect branch is   
   not to the auto-incremented address, but if there is one additional   
   indirection involved.  E.g, on RISC-V this is a direct-threaded code   
   dispatch:   
      
   addi    s5,s5,8   
   ld      a5,0(s5)   
   jr      a5   
      
   If the use of the auto-increment location would be equivalent to   
      
   addi    s5,s5,8   
   jr      s5   
      
   it would not be useful for direct-threaded code.   
      
   The paper on (direct) threaded code was only published in 1973, so   
   that technique may not have been widely known at the time when much of   
   the PDP-8 software was developed.   
      
   - anton   
   --   
   'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'   
     Mitch Alsup,    
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)