Apparatus and method for selectively overriding return stack prediction in response to detection of non-standard return sequence

Abstract

A microprocessor for predicting return instruction target addresses is disclosed. A branch target address cache stores a plurality of target address predictions and a corresponding plurality of override indicators for a corresponding plurality of return instructions, and provides a prediction of the target address of the return instruction from the target address predictions and provides a corresponding override indicator from the override indicators. Each has a true value when the return stack has mispredicted the target address of the corresponding return instruction for a most recent execution of the return instruction. A return stack also provides a prediction of the target address of the return instruction. Branch control logic causes the microprocessor to branch to the prediction of the target address provided by the BTAC, and not to the prediction of the target address provided by the return stack, when the override indicator is a true value.