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would have an even larger loss. To ameliorate the loss, some machines implement branch target prediction: given the address of a branch, they predict the target of that branch. A refinement of the idea predicts the start of a sequential run of instructions given the address of the start of the previous sequential run of instructions.
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In machines where this recurrence takes two cycles, the machine loses one full cycle of fetch after every predicted taken branch. As predicted branches happen every 10 instructions or so, this can force a substantial drop in fetch bandwidth. Some machines with longer instruction cache latencies
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As the predictor RAM can be 5–10% of the size of the instruction cache, the fetch happens much faster than the instruction cache fetch, and so this recurrence is much faster. If it were not fast enough, it could be parallelized, by predicting target addresses of target branches.
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is the part of a processor that predicts the target, i.e. the address of the instruction that is executed next, of a taken
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latency grows longer and the fetch width grows wider, branch target extraction becomes a bottleneck. The recurrence is:
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which attempts to guess whether a conditional branch will be taken or not-taken (i.e., binary).
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Fetch the prediction for the addresses of the targets of branches in that run of instructions
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Please help update this article to reflect recent events or newly available information.
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The
Behavior of Efficient Virtual Machine Interpreters on Modern Architectures
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Select the address corresponding to the branch predicted taken
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Instructions in block are scanned to identify branches
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is computed by the execution unit of the processor.
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373:"The microarchitecture of Intel, AMD and VIA CPUs"
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323:Single thread indirect branch predictor
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338:Accurate Indirect Branch Prediction
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