Hazards

Goal: schedule execution to prevent hazards from causing stalls. Recall the three kinds of hazard:

• Control (conditional branches)
• Structural (contention for hardware)
• Data
  • RAW (read-after-write)
  • WAW (write-after-write)
  • WAR - new

We will consider two approaches:

• Scoreboarding

  Directly addresses RAW hazards

• Register renaming/Tomasulo

  Overcomes WAW and WAR hazards

Register renaming is the basis for speculative execution, which addresses control hazards.