RAW dependencies

Question

ADD R₁ , R₂, R_2; 

ADD R₃, R₂, R₁;

SUB R₄, R₁ , R₅;

ADD R₃, R₃, R₄;

FIND THE NUMBER OF READ AFTER WRITE(RAW) DEPENDENCIES IN THE ABOVE CODE.

Comments

Will I be able to understand in this very birth, WHY RAW is checked in adjacent only.

SOMEBODY please clarify this.

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:D

If you've finally understood please let me know. I am struggling with the same question.

Answer 1

RAW dependency are those in which one instruction tries to read before its write operation and also they are occured only in adjacent instruction:

1.

ADD R1 , R2, R2; 

ADD R3, R2, R1;

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2.

SUB R4, R1 , R5;

ADD R3, R3, R4;

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total there are 2 (RAW) dpendecy..

Comments

No, this is not the right answer.

See this link

https://gateoverflow.in/29896/number-of-war-dependencies

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completely wrong

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someone should mark this answer as incorrect

Answer 2

4 RAW Dependencies.............

and they need not to be adjacent (its Made easy students myth)

Comments

I have also faced huge confusion due to this myth

Answer 3

There are total 4 RAW dependencies … you have to add non adjacent cases also.