Representing loop branches in a branch history register with multiple bits

摘要

In response to a property of a conditional branch instruction associated with a loop, such as a property indicating that the branch is a loop-ending branch, a count of the number of iterations of the loop is maintained, and a multi-bit value indicative of the loop iteration count is stored in a Branch History Register (BHR). In one embodiment, the multi-bit value may comprise the actual loop count, in which case the number of bits is variable. In another embodiment, the number of bits is fixed (e.g., two) and loop iteration counts are mapped to one of a fixed number of multi-bit values (e.g., four) by comparison to thresholds. Separate iteration counts may be maintained for nested loops, and a multi-bit value stored in the BHR may indicate a loop iteration count of only an inner loop, only the outer loop, or both.