Usefulness indication for indirect branch prediction training

A method, comprising:

• storing, in a first memory, a first plurality of entries, wherein each entry of the first plurality of entries includes a tag value, a target value, and prediction accuracy value;
• storing, in a second memory, a second plurality of entries, wherein each entry of the second plurality of entries includes a tag value, a target value, a prediction accuracy value, and a hysteresis value that includes information indicative of a number of mispredictions of corresponding entry of the second plurality of entries;
• receiving an index value and a tag value corresponding to an indirect branch;
• comparing, dependent upon the received index value, tag values in each or the first and second plurality of entries to the received tag value corresponding to the indirect branch;
• selecting, in response to determining that the received tag value does not match the tag value of compared entries, an entry of the first plurality of entries dependent upon the prediction accuracy values of the plurality of entries;
• allocating the selected entry to the indirect branch;
• and
• setting the prediction accuracy value of the allocated entry to indicate an accurate prediction.

A system, comprising:

• a processor;
• and
• one or more memories;
• wherein the processor includes a first branch target buffer, a second branch target buffer, and a control module coupled to the first and second branch target buffers, and configured to receive an indirect branch;
• wherein the first branch target buffer is configured to store a first plurality of entries, wherein each entry includes a tag value, a target value, and a prediction accuracy value;
• wherein the second branch target buffer is configured to store a second plurality of entries, wherein each entry of the second plurality of entries includes a tag value, a target value, a prediction accuracy value, and a hysteresis value that includes information indicative of a number of mispredictions of corresponding entry of the second plurality of entries;
• wherein the control module is further configured to, in response to a determination that the received indirect branch does not match an entry in either of the first or second branch target buffers, select a least frequently used entry in the first branch target buffer, and allocate the received indirect branch to the least frequently used entry dependent upon the prediction accuracy value of the least frequently used entry.

A branch predictor, comprising:

• a first branch target buffer configured to store a first plurality of entries, wherein each entry of the first plurality of entries includes a tag value, a target value, and a prediction accuracy value;
• a second branch target buffer configured to store a second plurality of entries, where in each entry of the second plurality of entries includes a tag value, a target value, a prediction accuracy value, and a hysteresis value that includes information indicative of a number of mispredictions of corresponding entry of the second plurality of entries;
• and
• a control module coupled to the first branch target buffer and the second branch target buffer, and configured to receive an indirect branch;
• wherein the control module is configured to, in response to a determination that the received indirect branch does not match an entry in either the first plurality of entries and the second plurality of entries, select a least frequently used entry in the first branch target buffer, and allocate the indirect branch to the selected least frequently used entry dependent upon the accuracy of the selected least frequently used entry.

A method, comprising:

• storing, in a first table, a first plurality of entries, wherein each entry of the first plurality of entries includes a tag value, a target value, and a prediction accuracy value;
• storing, in a second table, a second plurality of entries, wherein each entry of the second plurality of entries includes a tag value, a target value, and a hysteresis value that includes information indicative of a number of mispredictions of corresponding entry of the second plurality of entries;
• receiving an index value and a tag value, wherein the index value and the tag value correspond to an indirect instruction branch;
• comparing, dependent upon the received index value, the received tag value corresponding to the indirect instruction branch to tag values of first plurality of entries and the second plurality of entries;
• selecting, in response to determining that the received tag value does not match the tag value of each compared entry in the first plurality of entries and the second plurality of entries, an entry in the first plurality of entries dependent upon the prediction accuracy values of the first plurality of entries;
• allocating the selected entry to the indirect instruction branch;
• and
• setting the prediction accuracy of the allocated selected entry in the first plurality to indicate an accurate prediction.