Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.arch
Subject: Re: skip instructions
Message-ID: <21271@cbmvax.commodore.com>
Date: 6 May 91 07:22:40 GMT
References: <1182@opus.NMSU.Edu> <3027@spim.mips.COM> <11874@mentor.cc.purdue.edu> <1545@geovision.gvc.com>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 20

In article <1545@geovision.gvc.com> gd@geovision.gvc.com (Gord Deinstadt) writes:
>In a pipelined machine, would it not be more efficient to just deactivate
>a couple of instructions rather than go through the pain of a forward
>branch?  In other words just keep grinding forward, but inhibiting
>execution for a specified number of cycles, rather than trying to
>change course.  There would be no branch delay slot.

	See the Acorn ARM architecture, which I believe has this (encoded
off condition flags - all (or almost all) instructions can be conditionally
executed based on condition codes in order to avoid short forward branches.
(Of course, I may have mis-remembered it, in which case there will be 12 
different rebuttals).

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
Disclaimer: Nothing I say is anything other than my personal opinion.
Thus spake the Master Ninjei: "To program a million-line operating system
is easy, to change a man's temperament is more difficult."
(From "The Zen of Programming")  ;-)