xref: /gem5/src/cpu/pred/BranchPredictor.py

# Copyright (c) 2012 Mark D. Hill and David A. Wood
# Copyright (c) 2015 The University of Wisconsin
# All rights reserved.
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# modification, are permitted provided that the following conditions are
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# notice, this list of conditions and the following disclaimer;
# redistributions in binary form must reproduce the above copyright
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# documentation and/or other materials provided with the distribution;
# neither the name of the copyright holders nor the names of its
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# this software without specific prior written permission.
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# Authors: Nilay Vaish and Dibakar Gope

from m5.SimObject import SimObject
from m5.params import *

class BranchPredictor(SimObject):
    type = 'BranchPredictor'
    cxx_class = 'BPredUnit'
    cxx_header = "cpu/pred/bpred_unit.hh"
    abstract = True

    numThreads = Param.Unsigned(1, "Number of threads")
    BTBEntries = Param.Unsigned(4096, "Number of BTB entries")
    BTBTagSize = Param.Unsigned(16, "Size of the BTB tags, in bits")
    RASSize = Param.Unsigned(16, "RAS size")
    instShiftAmt = Param.Unsigned(2, "Number of bits to shift instructions by")

    useIndirect = Param.Bool(True, "Use indirect branch predictor")
    indirectHashGHR = Param.Bool(True, "Hash branch predictor GHR")
    indirectHashTargets = Param.Bool(True, "Hash path history targets")
    indirectSets = Param.Unsigned(256, "Cache sets for indirect predictor")
    indirectWays = Param.Unsigned(2, "Ways for indirect predictor")
    indirectTagSize = Param.Unsigned(16, "Indirect target cache tag bits")
    indirectPathLength = Param.Unsigned(3,
        "Previous indirect targets to use for path history")



class LocalBP(BranchPredictor):
    type = 'LocalBP'
    cxx_class = 'LocalBP'
    cxx_header = "cpu/pred/2bit_local.hh"

    localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
    localCtrBits = Param.Unsigned(2, "Bits per counter")


class TournamentBP(BranchPredictor):
    type = 'TournamentBP'
    cxx_class = 'TournamentBP'
    cxx_header = "cpu/pred/tournament.hh"

    localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
    localCtrBits = Param.Unsigned(2, "Bits per counter")
    localHistoryTableSize = Param.Unsigned(2048, "size of local history table")
    globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
    globalCtrBits = Param.Unsigned(2, "Bits per counter")
    choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
    choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")


class BiModeBP(BranchPredictor):
    type = 'BiModeBP'
    cxx_class = 'BiModeBP'
    cxx_header = "cpu/pred/bi_mode.hh"

    globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
    globalCtrBits = Param.Unsigned(2, "Bits per counter")
    choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
    choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")

class LTAGE(BranchPredictor):
    type = 'LTAGE'
    cxx_class = 'LTAGE'
    cxx_header = "cpu/pred/ltage.hh"

    logSizeBiMP = Param.Unsigned(14, "Log size of Bimodal predictor in bits")
    logSizeTagTables = Param.Unsigned(11, "Log size of tag table in LTAGE")
    logSizeLoopPred = Param.Unsigned(8, "Log size of the loop predictor")
    nHistoryTables = Param.Unsigned(12, "Number of history tables")
    tagTableCounterBits = Param.Unsigned(3, "Number of tag table counter bits")
    histBufferSize = Param.Unsigned(2097152,
            "A large number to track all branch histories(2MEntries default)")
    minHist = Param.Unsigned(4, "Minimum history size of LTAGE")
    maxHist = Param.Unsigned(640, "Maximum history size of LTAGE")
    minTagWidth = Param.Unsigned(7, "Minimum tag size in tag tables")