Register renaming

• WAR hazards happen when a register is reused
• This could be avoided by the compiler - if instruction set has enough registers
• In a loop, can't avoid reusing registers in successive iterations (except by unrolling)
• Tomasulo's scheme dynamically assigns a tag to each value to be calculated
• You need a distinct tag for each reservation station - so in effect, tags identify additional registers in the machine, invisible to the programmer
• The instruction-level parallelism is not limited by the number of registers available (Tomasulo was working on the IBM 360/91, which had to use an instruction set with just 4 FP registers)