Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Why is SPARC so slow?
Message-ID: <1987Dec17.010321.2977@utzoo.uucp>
Keywords: RISC, R2000, SPARC
Organization: U of Toronto Zoology
References: <1078@quacky.UUCP> <8809@sgi.SGI.COM> <1941@ncr-sd.SanDiego.NCR.COM>, <1115@winchester.UUCP>
Date: Thu, 17-Dec-87 01:03:17 EST

> ALso, in looking at SPARC assembly code, one notes that cmp's are usually
> moved away from the conditional branches, so that perhaps these CPUs,
> or later ones, will take advantage of cases where the condition code setting
> is early enough to avoid the extra I-fetch.

AT&T's CRISP machine in fact takes this to its logical (?) extreme:  it
basically has one condition-code bit, and if you can manage to set that
slightly ahead of time, then the execution time for an in-cache branch
is *zero*.  (The actual story is a bit more complicated, but that's the
general idea, as I recall it from the paper in Sigarch 14.)
-- 
Those who do not understand Unix are |  Henry Spencer @ U of Toronto Zoology
condemned to reinvent it, poorly.    | {allegra,ihnp4,decvax,utai}!utzoo!henry