Problem B . A loop and an if-statement are written in Assembly code as below. Lo
ID: 3713800 • Letter: P
Question
Problem B. A loop and an if-statement are written in Assembly code as below.
Loop: IF-Statement:
…. …
DO SUB R6, R6, #4 TST R1, #0x80000000
ADD R3, R3, #1 BEQ STORE
CMP R6, R5 MVN R1, R1
BGE DO ADD R1, R1, #1
LDR R2, [R6] STORE STR R1, [R4]
… …
The recent history of “BGE DO” in the Loop is “not-taken” and the recent history of “BEQ STORE” in the IF-statement is “taken”. Assuming that [R6] = 0x00008080 and [R5] = 0x00008070 when “BGE DO” is fetched in the Loop and [R1] = 0x12345678 when “BEQ STORE” is fetched in the IF-statement.
(Hint: in each question, the 1st blank needs to be filled with the instruction fetched after the branch instruction; and the 2nd blank needs to be filled with “proceeds with full speed” or “stalls”.
The pipeline with static or dynamic branch prediction is assumed to use the example approach given in the PPT slides.) (a) A MIPS pipeline fetches _______________________ after “BGE DO” and ____________________.
A MIPS pipeline fetches _______________________ after “BEQ STORE” and ____________________.
A pipeline with static branch prediction fetches _______________________ after “BGE DO” and ____________________.
A pipeline with static branch prediction fetches _______________________ after “BEQ STORE” and ____________________.
A pipeline with dynamic branch prediction fetches _______________________ after “BGE DO” and ____________________.
A pipeline with dynamic branch prediction fetches _______________________ after “BEQ STORE” and ___________________.
Explanation / Answer
Answer is as follows :
For the given scnario the fill ups are as follows :
a) MIPS pipeline fetches SUB R6, R6, #4 after “BGE DO” and Stalls.
b) A MIPS pipeline fetches MVN R1, R1 after “BEQ STORE” and Full Forwarding.
c) A pipeline with static branch prediction fetches SUB R6, R6, #4 after “BGE DO” and Full Forwarding.
d) A pipeline with dynamic branch prediction fetches LDR R2, [R6] after “BGE DO” and Full Forwading.
e) A pipeline with dynamic branch prediction fetches STR R1, [R4] after “BEQ STORE” and Stalls.
Bold letters are required answers.
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