12.6 Multiple streams: A brute-force approach is to replicate the initial portions of thepipeline and allow the pipeline to fetch both instructions, making use of twostreams. Prefetch branch target: When a conditional branch is recognized, thetarget of the branch is prefetched, in addition to the instruction following thebranch. This target is then saved until the branch instruction is executed. If thebranch is taken, the target has already been prefetched. Loop buffer: A loop bufferis a small, very-high-speed memory maintained by the instruction fetch stage ofthe pipeline and containing the n most recently fetched instructions, in sequence. Ifa branch is to be taken, the hardware first checks whether the branch target iswithin the buffer. If so, the next instruction is fetched from the buffer. Branchprediction: A prediction is made whether a conditional branch will be taken whenexecuted, and subsequent instructions are fetched accordingly. Delayed branch: Itis possible to improve pipeline performance by automatically rearranginginstructions within a program, so that branch instructions occur later an actuallydesired.
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