Method and apparatus for allocating entries in a branch target buffer

摘要

A method ( 200 ) and apparatus ( 100 ) for allocating entries in a branch target buffer (BTB) ( 144 ) in a pipelined data processing system includes: sequentially fetching instructions; determining that one of the instructions is a branch instruction ( 210, 215, 220 ); decoding the branch instruction to determine a branch target address; determining if the branch target address can be obtained without causing a stall condition in the pipelined data processing system; and selectively allocating an entry of the BTB ( 144 ) based on the determination. In one embodiment, an entry of the BTB ( 144 ) is allocated if the branch instruction is not loaded into a predetermined slot (S 1 ) of a prefetch buffer ( 102 ) and no other stall condition will occur. The method ( 200 ) and apparatus ( 100 ) combine the advantages of using a BTB ( 144 ) and branch lookahead to reduce stall conditions in the data processing system.