Author: Tom Kerrigan
Date: 11:50:09 02/13/03
Go up one level in this thread
On February 12, 2003 at 20:59:21, Robert Hyatt wrote: >No, but if the compiler does it perfectly, the OOO processor executes everything >_in order_. Which is the point of the idea. OOOE lets the processor overcome >bad instruction scheduling as produced by the compiler. If the compiler gets >it right, OOOE means very little, unless you count X86 with the register issue. This argument isn't going anywhere. We don't have processors where we can turn OOOE on and off (or at least we don't know how) and even if we did and OOOE provided a significant speed increase, you would fall back on your blame-the-compiler position. The UltraSPARC 3 is fast on paper except for its lack of OOOE, and it performs like crap, but I suppose Sun's just been slacking off on their compiler. >>The point of predication is to eliminate dependency on a branch. How can a >>compiler do this? In other words, how can a compiler say "we'll sort out later >>which was crap and which was important" without a branch on a non-predicated >>ISA? >Easy. Do _both_ pathways at the same time, then (say) a cmov (yes, alpha >has 'em as they came up with the idea in the first place) to pick the right >one rather than branching at all... How is cmov not predication? I guess because it's not called "predication." >I wouldn't mind a G4 at all. In fact, I tried to find a good multiple-cpu >PPC machine when I bought my first quad p6/200, but could not find anything >that was much beyond vaporware at the time. The processor looks pretty good >to me however. I suggest you try using one. They're crap. -Tom
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