Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!amdahl!JUTS!rbw00 From: rbw00@ccc.amdahl.com ( 213 Richard Wilmot) Newsgroups: comp.arch Subject: Re: speculative execution Keywords: deferred traps, abomination Message-ID: Date: 15 Oct 90 16:29:03 GMT References: <1990Oct9.212103.363@rice.edu> <12905@encore.Encore.COM> <1990Oct10.164353.21070@rice.edu> <22587@grebyn.com> Reply-To: rbw00@JUTS.ccc.amdahl.com ( 213 Richard Wilmot) Organization: Amdahl Corporation, Sunnyvale CA Lines: 33 In article <22587@grebyn> ckp@grebyn.com says >#pragma MY_TWO_CENTS >Forgive my insolence - I'm not an architecture designer, be gentle >with me, but this just occured to me.. >Why not include condition code bits with each register? Store these when >the register value is stored, when it pops out the end of a pipeline. >Include a flag for NAN (not a new idea, right?), and store this for >things like divide-by-0. Then you can trap when the register is used as >a source operand, and you can code explicit tests (and maybe traps) when >you want to, on operations that could very well be taking place >simultaneously. >-- >First comes the logo: C H E C K P O I N T T E C H N O L O G I E S / / \\ / / >Then, the disclaimer: All expressed opinions are, indeed, opinions. \ / o >Now for the witty part: I'm pink, therefore, I'm spam! \/ Please NO. Save me from deferred traps. The CDC 6600 and some others could produce several FP results that were illegal values FOR ANY OTHER OPERATIONS. So exception traps took place not when/where you produced the result but later when you tried to use it. Then the game was to guess where you produced this value. Well, I finally got used to coding explicit tests (usually not needed) after every potentially violative FP operation (that might produce +- infinity or +- indefinite). This is highly wasteful of code space for something that is most often rare - I can always check in cases where I need to know but please give me the trap when I create the bad result. PRECISELY. -- Dick Wilmot | I declaim that Amdahl might disclaim any of my claims. (408) 746-6108