Questions
Multiple fill-in-the-blank
Is there a sequence of branch outcomes that result in never predicting correctly? Type Yes/No [Fill in the blank], If Yes, then type the sequence 1.[Fill in the blank], 2.[Fill in the blank], 3.[Fill in the blank], 4.[Fill in the blank], 5.[Fill in the blank],
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Step-by-Step Analysis
Question restatement and structure:
- The prompt asks: Is there a sequence of branch outcomes that result in never predicting correctly? Type Yes/No [Fill in the blank], and then provide the sequence in five sub-items labeled 1–5 with each entry filled in.
- The given answer array is: ["Yes", "T", "T", "N", "T", "N"]. This implies the intended responses are: First, Yes; then for 1) T, 2) T, 3) N, 4) T, 5) N.
Option 1: Yes
- Why this is considered a valid response here: The provided answer set explicitly declares that a counter-sequence exists in this scenario, indicating that there exists at least one sequence of branch outcomes that leads to never predicting correctly. The reasoning behind this hinges on the behavior of the predictor and the specific rule governing correctness: if the sequence can be chosen to ......Login to view full explanationLog in for full answers
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Similar Questions
Consider the code fragment shown below. We show source code, the actual instructions the compiler generates without using predication, and the instructions generated when using conditional-move predication. Note that lines that begin with "//" are comments. The predicated code is not complete - you need to complete the predicated code by entering register numbers for the last instruction before answering the rest of this question. Suppose that "cond" is true 75% of the time, i.e. out of 1000 times that this code is executes, R1 is zero 250 times and is non-zero 750 times. Recall that "BEQZ" stands for "branch on equal to zero" and that the "N" in MOVN stands for "non-zero". Also suppose that we have a processor with a CPI of exactly 1 when there are no branch mispredictions, and with a branch misprediction penalty of 10 cycles. Complete the following statements (your answers should be numbers):
A processor is executing a long-running program, in which the most frequently executed branch instruction is encountered 8 million times per second. This branch has the following sequence of outcomes (where N stands for not-taken and T stands for taken): N, N, N, T, N, N, N, T, N, N, N, T, etc. In other words, this branch has a repeating pattern where it is not taken three times then taken once. For the first five occurrences of this branch instruction, the following table shows the counter values for the one-bit counter predictor, along with its predictions, and the actual branch outcomes (see above). Note that the counter starts out with an initial value of 1. Fill out the missing entries in the table: Note that the pattern has four branch occurrences while this table has five, i.e. the 5th occurrence of the branch in the table belongs to the second "round" of the pattern. Now suppose that we are measuring the accuracy of this branch during the third second of execution, i.e. after the predictor has already been trained by the first 16 million occurrences of this branch. To simplify things, you should assume that the predictor entries that are used for predicting this branch are only used for this branch, i.e. no other branches are interfering with the prediction, and that the initial values of all bits in the predictor were zeroes - but note that these values have been updated during the first two seconds of execution. Based on this, complete the following statements (your answers should be numbers):
Speedup of perfect predictor is
Speedup of perfect predictor is
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