Branch instruction control apparatus and control method

A branch instruction control apparatus which has a plurality of entries in which data required for the implementation control of the branch instructions and a valid flag for the data are stored in order of decoding of the branch instructions successively from the top entry, wherein

• said apparatus comprises:
• a bubble-up mechanism which, when one or more entries are successively released in order of older decoding from the top entry among the entries whose implementation control for the branch instructions has been completed, moves the contents of the remaining entries in a direction toward the top entry by the number of entries released regardless of a value of the valid flag of the released entries;
• a new-entry data set unit for storing data required for the implementation control of newly decoded branch instructions in one or more empty entries which are near the top entry including the entries which become empty by the movement, in the same cycle as in the movement of the said contents of entries by the bubble-up mechanism;
• an entry data update unit for updating the data required for the implementation control of branch instructions stored in each entry in the same cycle as in the movement of the contents of entries by the bubble-up mechanism;
• and
• an entry release unit for releasing the entries corresponding to new branch instructions in which the order of decoding is newer than the branch instructions when the branch prediction concerning the branch instructions corresponding to the entries in which data required for the implementation control of branch instructions is stored ends in failure and re-instructions are fetched, in the same cycle as in the movement of the contents of entries by the bubble-up mechanism.

A branch instruction control method for controlling branch instructions using a plurality of entries in which data required for the implementation control of branch instructions and a valid flag for the data are stored in order of decoding successively from the top entry, wherein

• when one or more entries are successively released in order of older decoding from the top entry among the entries whose implementation control of the corresponding branch instructions has been completed, the contents of the remaining entries are moved in a direction toward the top entry by the number of entries released by a bubble-up mechanism;
• data required for the implementation control of newly decoded branch instructions is stored in one or more empty entries which are near the top entry including the entries which become empty by the movement, in the same cycle as in the movement of the said contents of entries by the bubble-up mechanism regardless of a value of the valid flag of the released entries;
• the data required for the implementation control of branch instructions stored in each entry is updated in the same cycle as in the movement of the contents of entries by the bubble-up mechanism;
• and
• the entries corresponding to all new branch instructions in which the order of decoding is newer than the branch instructions are released when the branch prediction concerning the branch instructions corresponding to the entries in which data required for the implementation control of the branch instructions is stored ends in failure and re-instructions are fetched, in the same cycle as in the movement of the contents of entries by the bubble-up mechanism.