Question

The elimination stage of WAR and WAW hazards is often called:

• A. Anti-dependence
• B. Dispatch
• C. Data hazards
• D. Execution

Hint:

- WAR (Write After Read) and WAW (Write After Write) hazards are resolved using register renaming. - These hazards are called anti-dependence and output dependence, respectively.

Answer 1

The Correct Option is A

Step 1: Understanding Hazards in Instruction Execution
- Hazards occur in pipelined execution due to dependencies between instructions.
- The three major types of hazards are:
1. RAW (Read After Write) – True dependency.
2. WAR (Write After Read) – Anti-dependency.
3. WAW (Write After Write) – Output dependency

Step 2: Elimination of WAR and WAW Hazards
- WAR (Write After Read) Hazard: Occurs when an instruction writes to a register before a previous instruction reads it.
- WAW (Write After Write) Hazard: Occurs when two instructions try to write to the same register in a different order than intended.
- These hazards are resolved using register renaming, which eliminates anti-dependencies.
Step 3: Evaluating the Options
- (A) Correct: Anti-dependence refers to WAR hazards, and register renaming eliminates both WAR and WAW hazards.
- (B) Incorrect: Dispatch is a stage in instruction scheduling, not related to hazard elimination.
- (C) Incorrect: Data hazards include RAW, but WAR and WAW are control hazards.
- (D) Incorrect: Execution stage does not handle WAR and WAW hazards directly.