> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:[EMAIL PROTECTED] On Behalf Of Art Celestini > Sent: Friday, December 14, 2007 8:49 AM > To: [email protected] > Subject: Re: Mainframe Assembler Coding Contest > > > Much of what I was talking about is described here: > > http://www.research.ibm.com/journal/rd/446/webb.html > > although even this paper is somewhat "dated" by now. My > understanding is that the z9 > class microprocessors have a much deeper (longer) pipeline, > and the logic that looks at > instructions very "early" doesn't distinguish "BCTR Rx,0" as > a special case, only that > BCTR, in general, is not in an instruction "class" that can > potentially be executed > immediately (out of order), at least not in the very early > pipeline stages. An "AHI > Rx,-1" on the other hand, is more readily identified as a > good candidate, and thus > stands a better chance of being executed for "free" > (simultaneously with one or more > other instructions).
But just to put in a single warning on this. The BCTR instruction does not affect the condition code. The AHI instruction does. In 99.9+% (guess) of the times, this is not important. -- John McKown Senior Systems Programmer HealthMarkets Keeping the Promise of Affordable Coverage Administrative Services Group Information Technology The information contained in this e-mail message may be privileged and/or confidential. It is for intended addressee(s) only. If you are not the intended recipient, you are hereby notified that any disclosure, reproduction, distribution or other use of this communication is strictly prohibited and could, in certain circumstances, be a criminal offense. If you have received this e-mail in error, please notify the sender by reply and delete this message without copying or disclosing it. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
