In this exercise, we examine how data dependences affect execution

In this exercise, we examine how data dependences affect execution in the basic 5-stage pipeline described in Section 4.5. Problems in this exercise refer to the following sequence of instructions:

or r1,r2,r3 or r2,rl,r4 or r1,r1,r2

Also, assume the following cycle times for each of the options related to forwarding:

Without Forwarding With Full Forwarding With ALU-ALU Forwarding Only 250ps 300ps 290ps

1. Indicate dependences and their type.

2. Assume there is no forwarding in this pipelined processor. Indicate hazards and add nop instructions to eliminate them.

3. Assume there is full forwarding. Indicate hazards and add NOP instructions to eliminate them.

4. What is the total execution time of this instruction sequence without forwarding and with full forwarding? What is the speedup achieved by adding full forwarding to a pipeline that had no forwarding?

5. Add nop instructions to this code to eliminate hazards if there is ALU-ALU forwarding only (no forwarding from the MEM to the EX stage).

6. What is the total execution time of this instruction sequence with only ALU-ALU forwarding? What is the speedup over a no-forwarding pipeline?

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