Method and apparatus for restoring register renaming mapping

Abstract

A technique for restoring a register renaming map is described. In one example, a restore table with multiple storage locations holds a copy of the register renaming map whenever a flow risk instruction is passed to the reorder buffer. When all storage locations are full, further instructions are still passed to the reorder buffer, but no copy of the mapping is kept. A storage location then becomes available when the process risk instruction associated with that storage location is executed. A state of a register rename map for unrecorded flow-risk instructions passed to the reorder buffer when the plurality of memory locations are full is generated and stored in the available locations. The state of the register renaming map is generated using a restore table entry for a previous flow-risk instruction and a reorder buffer value for an intermediate instruction between the previous flow-risk instruction and the Between the above undocumented process risk instructions. The restore table can be used to restore the mapping if an unexpected change occurs in the instruction flow.

Description

Background technique [0001] Out-of-order microprocessors can provide improved computing performance by executing instructions in a sequence different from the order in the program, such that instructions are executed when their input data is available, rather than waiting for execution of previous instructions in the program. To allow instructions to run out of order on a microprocessor, it is useful to be able to rename registers used by instructions. This enables the removal of "write-after-read" (WAR) dependencies from directives, since these dependencies are not real dependencies. By using register renaming and removing these dependencies, more instructions can be executed out of program sequence and performance is further improved. Register renaming is performed by maintaining a map in which registers named in instructions (called architectural registers) are mapped onto physical registers of the microprocessor. [0002] But the flow of instructions in a program sometim...

AI Technical Summary

Problems solved by technology

However, this requires providing a large amount of storage in which to hold all the snapshots, because if all the snapshot storage is used, the instruction flow must be stalled until the snapshot can be saved again, sacrificing performance

Images