On Jan 16, 2012, at 22:30, robin wrote: > From: "Paul Gilmartin" <[email protected]> > Sent: Tuesday, 17 January 2012 7:33 AM > >> CDC 3600/3800 had a "Modify following instruction" instruction > > The S/360 and subsequent machines have one like that also. > In the case of MVC/CLC instructions :- > > stc 1,*+5 > mvc a(0),b > > can be useful. > No, no, no, no, no!:
o RENT!? (How does this affect instruction pipelining?) o The CDC instruction didn't modify the storage; it modified the execution of the instruction after it had been fetched from storage. Even as EX doesn't modify its target instruction in storage. > EX does more than just "insert length" into SS instructions. > The ability to OR in bits from the second byte of the subject instruction > along with the content of the nominated register is probably rarely used > in the case of SS instructions, but can be used to effect with RX > instructions, > where you might want to retain, say, the existing index field in the > subject instruction, yet supply bits for the Register field of the > subject instruction. -- gil
