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Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: anton@mips.complang.tuwien.ac.at (Anton Ertl) Newsgroups: comp.arch Subject: Re: Instruction Tracing Date: Sun, 11 Aug 2024 14:44:38 GMT Organization: Institut fuer Computersprachen, Technische Universitaet Wien Lines: 26 Message-ID: <2024Aug11.164438@mips.complang.tuwien.ac.at> References: <v970s3$flpo$1@dont-email.me> <2024Aug10.121802@mips.complang.tuwien.ac.at> <v995pm$1cni$2@gal.iecc.com> Injection-Date: Sun, 11 Aug 2024 16:58:55 +0200 (CEST) Injection-Info: dont-email.me; posting-host="b250ad582970d66a662cc6fd2e2f7eca"; logging-data="2894367"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+1m3JrpHl1j1FK0Zf6NPtJ" Cancel-Lock: sha1:NYRpkFWeUOwdkVQRS0Vi4dEYfEs= X-newsreader: xrn 10.11 Bytes: 2180 John Levine <johnl@taugh.com> writes: >As far as the delayed branches and such, they made sense in the narrow >time window when it was too expensive to put a cache on a workstation >but that time came and went by the time the RT shipped. Delayed branches were put in the first commercial generation of RISCs (except ARM), which all shipped with caches (except ARM). Delayed branches are a natural consequence of the 5-stage (Or, in the 88100 case, four-stage) pipeline. IIRC ARM used a 3-stage implementation for the ARM1/2, which may be a consequence of them rejecting delayed branches; and they did not have caches, so they could not have made use of the higher clock rate that a longer pipeline could have affored. So it seems that the connection between cache and delayed branches, if there is any, is the opposite of what you suggest. Delayed branches provided a speedup on these early 5-stage implementations. They also provided a big headache for more sophisticated implementations, and therefore soon fell out of favour. Power (IIRC) and Alpha don't have delayed branches. - anton -- 'Anyone trying for "industrial quality" ISA should avoid undefined behavior.' Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>