Author: Tom Kerrigan
Date: 14:41:55 07/22/03
Go up one level in this thread
On July 22, 2003 at 15:27:10, Robert Hyatt wrote: >On July 22, 2003 at 15:02:46, Tom Kerrigan wrote: > >>On July 22, 2003 at 14:18:23, Robert Hyatt wrote: >> >>>>Of course, this is contrary to the point of a conditional move instruction. My >>>>only comment to that is that Intel must have decided to add the conditional move >>>>after they were done designing the relevant parts of the core. The decision to >>>>add the instruction makes sense for forward-compatibility, i.e., "use this >>>>instruction and you will see a performance improvement with it on later >>>>processors." >>> >>>That could be. However, the idea was not new. The alpha did this 10+ years >>>ago. So the advantage to a real CMOV implementation should be real. >> >>Did I ever say it was new? > >I'll play the game. > >Did I _say_ you said it was new?? No, but that's what I read into the "However" part of "However, the idea was not new." What in the world were you Howevering if you didn't think I thought it was new? (And BTW, it was new, for the x86.) >> Did I say that Intel's implementation is ideal? > >Did I say you said it was ideal? Similar argument. Another "however." >If Intel implemented it poorly, when it had been implemented _correctly_ 12 >years previously, then I hardly think "I am being an ass for criticizing them >for doing it _badly_." > >Had they left it out, I _would_ have had complaints, because the alpha has >an instruction that directly addresses a common operation in C, the conditional >assignment operator. > >So I feel perfectly sane in complaining if they omit something that has been >around long enough for them to include it, or if they include something but >implement it poorly so that it doesn't do what the "concept" suggests it >does, namely eliminate branch mis-predictions by eliminating branches. It's >not hard to do this in hardware. It's been done more than once already. Oh, come now. You can't seriously mean this. I'll do you one better--ARM had a fully predicated ISA in '83, so Intel is a bunch of idiots for not adding full predication to the 386. (Well, DEC too, for that matter, because they only have cmove.) -Tom
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.