Author: Gian-Carlo Pascutto
Date: 11:47:04 06/05/01
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On June 05, 2001 at 14:17:03, Robert Hyatt wrote: >Part of that looks wrong. The usual idea has always been "If a branch target >has not been seen previously (which means no prediction entry is avaliable) then >look at the _direction_ of the jump. If it is backward, assume it will be >taken (a safe assumption since a backward branch is likely a loop) while if it >is forward, assume it is not taken. > >I had seen someone from Intel claim this is what they do, although I am not >certain. That is easier to do in the hardware than to assume that if it is >taken, move it to ST and go from there... A simple explanation would be that your method is used when no or insufficient prediction information for that branch is available. Actually, I'm pretty sure that's how it works. With 20 instruction deep pipelines you need something more clever than a static criterion. -- GCP
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