Method and apparatus for state recovery following branch mispred

Details Method and apparatus for state recovery following branch mispred Method and apparatus for state recovery following branch mispred

1996-04-22

1996-12-17

Harrell, Robert B.

395586, 395393, G06F 938

Patent

active

055862780

ABSTRACT:
A method of state recovery following a branch misprediction or an undetected branch instruction. If, during execution of a branch instruction in an out-of-order unit, it is determined that the branch has been mispredicted, or if a taken branch has not been detected, then a JEClear signal is asserted to flush the instruction fetch unit and decoder section, and to change the instruction pointer to the actual target address. Within the out-of-order section, the instructions preceding the branch instruction are allowed to continue execution and proceed to in-order retirement. Simultaneously, instructions fetched at the actual target address are decoded, but not allowed to issue therefrom until the branch instruction has been retired from the out-of-order section, after which all instructions within the out-of-order section are flushed, and then decoded instructions are allowed to issue from the decoder. The state recovery method advantageously provides efficient utilization of processor time.

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Johnson, Mike, "Superscalar Microprocessor Design", Prentice Hall, Inc., 1991, pp. 1-287.

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