Question 1-bit branch predictor Consider the following code Algorithm: // for (x1=3; x1 != 0; x1=x1-1) // x2 = x2 + x3 RISC-V code: 0000 addi x1, x0, 3 // x1 = 3 L: 0004 add x2, x2, x3 // x2 = x2 + x3 0008 subi x1, x1, 1 // x1 = x1 - 1 000C bne x1,0,L // if (x1 != 0) branch to L Complete the following table showing the branch predictor behaviour (ONLY ANSWER ANYTHING DENOTED AS CHOOSE AND CHOOSE ONE OPTION). Note that * indicates an instruction fetch (IF) from a predicted branch. For simplicity, assume that a mis-predicted branch only costs one cycle (the fetch of the instruction following the branch mis-prediction). 1-Bit Branch Predictor Clock Cycle IF Address x1 Branch Predictor Value (start of cycle) Correct Prediction Branch Taken 0 0000 1 0004 3 2 0008 3 000C 2 0 4 000E* 0 no yes 5 0004 1 6 0008 7 000C 1 1 8 0004* CHOOSE: 1 or 0 CHOOSE: yes or no CHOOSE: yes or no 9 0008 10 000C 0 CHOOSE: 1 or 0 11 0004* CHOOSE: 1 or 0 CHOOSE: yes or no CHOOSE: yes or no 12 0010 CHOOSE: 1 or 0

F1XEGJ The Asker · Computer Science

1-bit branch predictor

Consider the following code

Algorithm:

// for (x1=3; x1 != 0; x1=x1-1)
// x2 = x2 + x3

RISC-V code:

0000 addi x1, x0, 3 // x1 = 3
L:
0004 add x2, x2, x3 // x2 = x2 + x3
0008 subi x1, x1, 1 // x1 = x1 - 1
000C bne x1,0,L // if (x1 != 0) branch to L

Complete the following table showing the branch predictor behaviour (ONLY ANSWER ANYTHING DENOTED AS CHOOSE AND CHOOSE ONE OPTION). Note that * indicates an instruction fetch (IF) from a predicted branch. For simplicity, assume that a mis-predicted branch only costs one cycle (the fetch of the instruction following the branch mis-prediction).

1-Bit Branch Predictor
Clock Cycle	IF Address	x1	Branch Predictor Value (start of cycle)	Correct Prediction	Branch Taken
0	0000
1	0004	3
2	0008
3	000C	2	0
4	000E*		0	no	yes
5	0004		1
6	0008
7	000C	1	1
8	0004*		CHOOSE: 1 or 0	CHOOSE: yes or no	CHOOSE: yes or no
9	0008
10	000C	0	CHOOSE: 1 or 0
11	0004*		CHOOSE: 1 or 0	CHOOSE: yes or no	CHOOSE: yes or no
12	0010		CHOOSE: 1 or 0

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Community Answer

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【General guidance】The answer provided below has been developed in a clear step by step manner.Step1/2CyclePCX1X2XBranch PredictionReason10000*300Not takenInitial fetch20004*300Not takenPredict not taken30008*200TakenPredict taken4000C*200Not takenMispredict, correct50004*200TakenMispredict, correct60008*100TakenPredict taken7000C*100Not takenMispredict, correct80004*100TakenMispredict, correct90008*000TakenPredict taken10000C*000Not takenMispredict, correct11done0??N/AEnd of programExplanation:At cycle 1, the initial instruction fetch from address 0x0000 is not a branch instruction, so the branch predictor does not make any prediction.At cycle 2, the add instruction at address 0x0004 is not a branch instruction, so the branch predictor does not make any prediction.ExplanationAt cycle 3, the subi instruction at address 0x0008 is a branch instruction. Since th ... See the full answer