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Browse Prior Art Database

Adaptive Branch Prediction

IP.com Disclosure Number: IPCOM000105519D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Levitan, DS: AUTHOR [+2]

Abstract

Processor performance can be improved by correctly predicting which Branch instructions result in execution of a new instruction stream and prefetching the new stream. (The new stream may also be executed and results discarded if the Branch is not taken.) Branch prediction can be divided into two broad categories.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Adaptive Branch Prediction

      Processor performance can be improved by correctly predicting
which Branch instructions result in execution of a new instruction
stream and prefetching the new stream.  (The new stream may also be
executed and results discarded if the Branch is not taken.)  Branch
prediction can be divided into two broad categories.

1.  Prediction based on Branch run-time characteristics which is done
    during program execution.
2.  Prediction based on previously gathered statistics and indicated
    by setting a bit in Branch instructions to specify how the Branch
    should be predicted when executed.

         Prediction based on previously gathered statistics is
    reasonable for programs where execution time is very important.
    For some applications, the statistic-based approach will give the
    better performance.  However, the best performance attainable
    should also be achieved for existing programs where the
    statistic-gathering run has not been done.

         This invention combines the two approaches by using the
    run-time rules for Branch prediction until a specific bit in a
    Branch instruction is detected which indicates that the
    statistical-prediction-mode is to be entered.  In this mode, a 1
    in the specific bit of a Branch instruction indicates that the
    Branch should be taken and a 0 indicates the Branch should not be
    taken.  The statistical-...