Reducing branch prediction interference of opposite well behaved branches sharing history entry by static prediction correctness based updating

摘要

Interference in a branch history table of a microprocessor is reduced by methods and apparatus which predict the outcome of branch instructions (taken or not taken) through a combination of static and dynamic prediction techniques. Static prediction information (e.g., a compiler hint) may be stored in instruction memory, and dynamic prediction information is stored in a branch history table. A branch prediction results from an exclusive OR of static and dynamic prediction information. After execution of a branch instruction, an indication as to whether a branch was taken or not taken is exclusively ORed with the static prediction information for the branch instruction, and the result of this exclusive OR is used to update an appropriate entry in the branch history table. Using the methods and apparatus disclosed herein, two well-behaved branches may share an entry in a branch history table, yet not interfere with one another (even when the two well-behaved branches include one which is mostly taken, and one which is mostly not taken).