Register Renaming

Done in the Extended Instruction Pipeline . Mapping of physical registers to logical registers. This is done to prevent Anti dependencies (read …write) or Output dependencies (write … write) .

Two methods:

• Register Renaming via Merged Register File
• Register Renaming via Reorder Buffer

Comparison #

1. Allocatoin / release

   • Merged register file
     • allocation based on free list
     • hard to decide if register is no longer needed
   • ROB
     • no free list
     • release requires id of physical register
     • instructions in issue queue need to be updated

2. Transfer of data

   • Merged register file
     • Requre more read ports
     • Less data transfers
   • ROB
     • Data fist stored in ROB and then transferred to register file then copied to the issue queue entry and then to then functional unit -> Many data transfers (cost energy)