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