Methods and circuitry for efficient management of local branch history registers

A processor comprising:

• a pipeline comprising a plurality of stages;
• a bit-vector associated with each of in-flight branches associated with the pipeline;
• wherein each bit-vector having a bit corresponding to each local branch history register associated with a respective in-flight branch;
• a recovery counter associated with each local branch history register for tracking a number of bits needing recovery before a local branch history register is valid for participation in branch prediction;
• and
• branch predictor circuitry configured to:
• in response to an update of a local branch history register by a branch, set a bit in a corresponding bit-vector indicative of the update of the local branch history register by the branch,
• upon a flush, identify all local branch history registers requiring recovery by performing a logical OR operation on bit-vectors corresponding to a mis-speculated branch and all younger branches than the mis-speculated branch, and
• discard all bits of all identified local branch history registers requiring recovery and set value of each respective recovery counter of all identified local branch history registers requiring recovery to a maximum value for a recovery counter.

A processor comprising:

• a pipeline comprising a plurality of stages;
• a bit-vector associated with each of in-flight branches associated with the pipeline, wherein each bit-vector having a bit corresponding to each local branch history register associated with a respective in-flight branch;
• a recovery counter associated with each local branch history register for tracking a number of bits needing recovery before a local branch history register is valid for participation in branch prediction;
• and
• branch predictor circuitry configured to:
• in response to an update of a local branch history register by a respective branch:
• (1) set a bit in a corresponding bit-vector indicative of the update of the local branch history register by the respective branch, and (2) set a bit in each of bit-vectors corresponding to all older in-flight branches than the respective branch,
• upon a flush, identify all local branch history registers requiring recovery based on a bit-vector corresponding to a mis-speculated branch, and
• discard all bits of all identified local branch history registers requiring recovery and set value of each respective recovery counter of all identified local branch history registers requiring recovery to a maximum value for a recovery counter.