Glossary

A.13 Logical and Physical Registers

Logical register numbers are dynamically mapped onto physical register numbers. This mapping uses mapping tables which are updated after each instruction is decoded; each new result is written into a new physical register. This value is temporary and the previous contents of each logical register can be restored if its instruction must be aborted following an exception or a mispredicted branch.

Register renaming simplifies dependency checks. Logical register numbers can be ambiguous when instructions are executed out of order, since a succession of different values may be assigned to the same register. But physical register numbers uniquely identify each result, making dependency checking unambiguous.

The queues and execution units use physical register numbers. Integer and floating-point registers are implemented with separate renaming hardware and multi-port register files.