bpred_unit.cc revision 13654
11689SN/A/* 210785Sgope@wisc.edu * Copyright (c) 2011-2012, 2014 ARM Limited 39480Snilay@cs.wisc.edu * Copyright (c) 2010 The University of Edinburgh 49480Snilay@cs.wisc.edu * Copyright (c) 2012 Mark D. Hill and David A. Wood 510785Sgope@wisc.edu * All rights reserved 610785Sgope@wisc.edu * 710785Sgope@wisc.edu * The license below extends only to copyright in the software and shall 810785Sgope@wisc.edu * not be construed as granting a license to any other intellectual 910785Sgope@wisc.edu * property including but not limited to intellectual property relating 1010785Sgope@wisc.edu * to a hardware implementation of the functionality of the software 1110785Sgope@wisc.edu * licensed hereunder. You may use the software subject to the license 1210785Sgope@wisc.edu * terms below provided that you ensure that this notice is replicated 1310785Sgope@wisc.edu * unmodified and in its entirety in all distributions of the software, 1410785Sgope@wisc.edu * modified or unmodified, in source code or in binary form. 1510785Sgope@wisc.edu * 1610785Sgope@wisc.edu * Copyright (c) 2004-2005 The Regents of The University of Michigan 171689SN/A * All rights reserved. 181689SN/A * 191689SN/A * Redistribution and use in source and binary forms, with or without 201689SN/A * modification, are permitted provided that the following conditions are 211689SN/A * met: redistributions of source code must retain the above copyright 221689SN/A * notice, this list of conditions and the following disclaimer; 231689SN/A * redistributions in binary form must reproduce the above copyright 241689SN/A * notice, this list of conditions and the following disclaimer in the 251689SN/A * documentation and/or other materials provided with the distribution; 261689SN/A * neither the name of the copyright holders nor the names of its 271689SN/A * contributors may be used to endorse or promote products derived from 281689SN/A * this software without specific prior written permission. 291689SN/A * 301689SN/A * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 311689SN/A * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 321689SN/A * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 331689SN/A * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 341689SN/A * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 351689SN/A * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 361689SN/A * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 371689SN/A * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 381689SN/A * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 391689SN/A * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 401689SN/A * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 412665SN/A * 422665SN/A * Authors: Kevin Lim 431689SN/A */ 441061SN/A 4510785Sgope@wisc.edu#include "cpu/pred/bpred_unit.hh" 461061SN/A 4710785Sgope@wisc.edu#include <algorithm> 4810785Sgope@wisc.edu 4910785Sgope@wisc.edu#include "arch/isa_traits.hh" 5010785Sgope@wisc.edu#include "arch/types.hh" 5110785Sgope@wisc.edu#include "arch/utility.hh" 5210785Sgope@wisc.edu#include "base/trace.hh" 5310785Sgope@wisc.edu#include "config/the_isa.hh" 5410785Sgope@wisc.edu#include "debug/Branch.hh" 5510785Sgope@wisc.edu 5610785Sgope@wisc.eduBPredUnit::BPredUnit(const Params *params) 5710785Sgope@wisc.edu : SimObject(params), 5810785Sgope@wisc.edu numThreads(params->numThreads), 5910785Sgope@wisc.edu predHist(numThreads), 6010785Sgope@wisc.edu BTB(params->BTBEntries, 6110785Sgope@wisc.edu params->BTBTagSize, 6211432Smitch.hayenga@arm.com params->instShiftAmt, 6311432Smitch.hayenga@arm.com params->numThreads), 6410785Sgope@wisc.edu RAS(numThreads), 6511433Smitch.hayenga@arm.com useIndirect(params->useIndirect), 6611433Smitch.hayenga@arm.com iPred(params->indirectHashGHR, 6711433Smitch.hayenga@arm.com params->indirectHashTargets, 6811433Smitch.hayenga@arm.com params->indirectSets, 6911433Smitch.hayenga@arm.com params->indirectWays, 7011433Smitch.hayenga@arm.com params->indirectTagSize, 7111433Smitch.hayenga@arm.com params->indirectPathLength, 7211433Smitch.hayenga@arm.com params->instShiftAmt, 7311433Smitch.hayenga@arm.com params->numThreads), 7410785Sgope@wisc.edu instShiftAmt(params->instShiftAmt) 759480Snilay@cs.wisc.edu{ 7610785Sgope@wisc.edu for (auto& r : RAS) 7710785Sgope@wisc.edu r.init(params->RASSize); 7810785Sgope@wisc.edu} 7910785Sgope@wisc.edu 8010785Sgope@wisc.eduvoid 8110785Sgope@wisc.eduBPredUnit::regStats() 8210785Sgope@wisc.edu{ 8311523Sdavid.guillen@arm.com SimObject::regStats(); 8411523Sdavid.guillen@arm.com 8510785Sgope@wisc.edu lookups 8610785Sgope@wisc.edu .name(name() + ".lookups") 8710785Sgope@wisc.edu .desc("Number of BP lookups") 8810785Sgope@wisc.edu ; 8910785Sgope@wisc.edu 9010785Sgope@wisc.edu condPredicted 9110785Sgope@wisc.edu .name(name() + ".condPredicted") 9210785Sgope@wisc.edu .desc("Number of conditional branches predicted") 9310785Sgope@wisc.edu ; 9410785Sgope@wisc.edu 9510785Sgope@wisc.edu condIncorrect 9610785Sgope@wisc.edu .name(name() + ".condIncorrect") 9710785Sgope@wisc.edu .desc("Number of conditional branches incorrect") 9810785Sgope@wisc.edu ; 9910785Sgope@wisc.edu 10010785Sgope@wisc.edu BTBLookups 10110785Sgope@wisc.edu .name(name() + ".BTBLookups") 10210785Sgope@wisc.edu .desc("Number of BTB lookups") 10310785Sgope@wisc.edu ; 10410785Sgope@wisc.edu 10510785Sgope@wisc.edu BTBHits 10610785Sgope@wisc.edu .name(name() + ".BTBHits") 10710785Sgope@wisc.edu .desc("Number of BTB hits") 10810785Sgope@wisc.edu ; 10910785Sgope@wisc.edu 11010785Sgope@wisc.edu BTBCorrect 11110785Sgope@wisc.edu .name(name() + ".BTBCorrect") 11210785Sgope@wisc.edu .desc("Number of correct BTB predictions (this stat may not " 11310785Sgope@wisc.edu "work properly.") 11410785Sgope@wisc.edu ; 11510785Sgope@wisc.edu 11610785Sgope@wisc.edu BTBHitPct 11710785Sgope@wisc.edu .name(name() + ".BTBHitPct") 11810785Sgope@wisc.edu .desc("BTB Hit Percentage") 11910785Sgope@wisc.edu .precision(6); 12010785Sgope@wisc.edu BTBHitPct = (BTBHits / BTBLookups) * 100; 12110785Sgope@wisc.edu 12210785Sgope@wisc.edu usedRAS 12310785Sgope@wisc.edu .name(name() + ".usedRAS") 12410785Sgope@wisc.edu .desc("Number of times the RAS was used to get a target.") 12510785Sgope@wisc.edu ; 12610785Sgope@wisc.edu 12710785Sgope@wisc.edu RASIncorrect 12810785Sgope@wisc.edu .name(name() + ".RASInCorrect") 12910785Sgope@wisc.edu .desc("Number of incorrect RAS predictions.") 13010785Sgope@wisc.edu ; 13111433Smitch.hayenga@arm.com 13211433Smitch.hayenga@arm.com indirectLookups 13311433Smitch.hayenga@arm.com .name(name() + ".indirectLookups") 13411433Smitch.hayenga@arm.com .desc("Number of indirect predictor lookups.") 13511433Smitch.hayenga@arm.com ; 13611433Smitch.hayenga@arm.com 13711433Smitch.hayenga@arm.com indirectHits 13811433Smitch.hayenga@arm.com .name(name() + ".indirectHits") 13911433Smitch.hayenga@arm.com .desc("Number of indirect target hits.") 14011433Smitch.hayenga@arm.com ; 14111433Smitch.hayenga@arm.com 14211433Smitch.hayenga@arm.com indirectMisses 14311433Smitch.hayenga@arm.com .name(name() + ".indirectMisses") 14411433Smitch.hayenga@arm.com .desc("Number of indirect misses.") 14511433Smitch.hayenga@arm.com ; 14611433Smitch.hayenga@arm.com 14711433Smitch.hayenga@arm.com indirectMispredicted 14811433Smitch.hayenga@arm.com .name(name() + "indirectMispredicted") 14911433Smitch.hayenga@arm.com .desc("Number of mispredicted indirect branches.") 15011433Smitch.hayenga@arm.com ; 15111433Smitch.hayenga@arm.com 15210785Sgope@wisc.edu} 15310785Sgope@wisc.edu 15410785Sgope@wisc.eduProbePoints::PMUUPtr 15510785Sgope@wisc.eduBPredUnit::pmuProbePoint(const char *name) 15610785Sgope@wisc.edu{ 15710785Sgope@wisc.edu ProbePoints::PMUUPtr ptr; 15810785Sgope@wisc.edu ptr.reset(new ProbePoints::PMU(getProbeManager(), name)); 15910785Sgope@wisc.edu 16010785Sgope@wisc.edu return ptr; 16110785Sgope@wisc.edu} 16210785Sgope@wisc.edu 16310785Sgope@wisc.eduvoid 16410785Sgope@wisc.eduBPredUnit::regProbePoints() 16510785Sgope@wisc.edu{ 16610785Sgope@wisc.edu ppBranches = pmuProbePoint("Branches"); 16710785Sgope@wisc.edu ppMisses = pmuProbePoint("Misses"); 16810785Sgope@wisc.edu} 16910785Sgope@wisc.edu 17010785Sgope@wisc.eduvoid 17110785Sgope@wisc.eduBPredUnit::drainSanityCheck() const 17210785Sgope@wisc.edu{ 17310785Sgope@wisc.edu // We shouldn't have any outstanding requests when we resume from 17410785Sgope@wisc.edu // a drained system. 17510785Sgope@wisc.edu for (const auto& ph M5_VAR_USED : predHist) 17610785Sgope@wisc.edu assert(ph.empty()); 17710785Sgope@wisc.edu} 17810785Sgope@wisc.edu 17910785Sgope@wisc.edubool 18010785Sgope@wisc.eduBPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum, 18110785Sgope@wisc.edu TheISA::PCState &pc, ThreadID tid) 18210785Sgope@wisc.edu{ 18310785Sgope@wisc.edu // See if branch predictor predicts taken. 18410785Sgope@wisc.edu // If so, get its target addr either from the BTB or the RAS. 18510785Sgope@wisc.edu // Save off record of branch stuff so the RAS can be fixed 18610785Sgope@wisc.edu // up once it's done. 18710785Sgope@wisc.edu 18810785Sgope@wisc.edu bool pred_taken = false; 18910785Sgope@wisc.edu TheISA::PCState target = pc; 19010785Sgope@wisc.edu 19110785Sgope@wisc.edu ++lookups; 19210785Sgope@wisc.edu ppBranches->notify(1); 19310785Sgope@wisc.edu 19410785Sgope@wisc.edu void *bp_history = NULL; 19513654Sjairo.balart@metempsy.com void *indirect_history = NULL; 19610785Sgope@wisc.edu 19710785Sgope@wisc.edu if (inst->isUncondCtrl()) { 19810785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Unconditional control.\n", tid); 19910785Sgope@wisc.edu pred_taken = true; 20010785Sgope@wisc.edu // Tell the BP there was an unconditional branch. 20111434Smitch.hayenga@arm.com uncondBranch(tid, pc.instAddr(), bp_history); 2029480Snilay@cs.wisc.edu } else { 20310785Sgope@wisc.edu ++condPredicted; 20411434Smitch.hayenga@arm.com pred_taken = lookup(tid, pc.instAddr(), bp_history); 20510785Sgope@wisc.edu 20610785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i] Branch predictor" 20710785Sgope@wisc.edu " predicted %i for PC %s\n", tid, seqNum, pred_taken, pc); 20810785Sgope@wisc.edu } 20910785Sgope@wisc.edu 21013654Sjairo.balart@metempsy.com if (useIndirect) { 21113654Sjairo.balart@metempsy.com iPred.updateDirectionInfo(tid, pred_taken, indirect_history); 21213654Sjairo.balart@metempsy.com } 21313654Sjairo.balart@metempsy.com 21410785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i] Creating prediction history " 21510785Sgope@wisc.edu "for PC %s\n", tid, seqNum, pc); 21610785Sgope@wisc.edu 21713654Sjairo.balart@metempsy.com PredictorHistory predict_record(seqNum, pc.instAddr(), pred_taken, 21813654Sjairo.balart@metempsy.com bp_history, indirect_history, tid, inst); 21910785Sgope@wisc.edu 22010785Sgope@wisc.edu // Now lookup in the BTB or RAS. 22110785Sgope@wisc.edu if (pred_taken) { 22210785Sgope@wisc.edu if (inst->isReturn()) { 22310785Sgope@wisc.edu ++usedRAS; 22410785Sgope@wisc.edu predict_record.wasReturn = true; 22510785Sgope@wisc.edu // If it's a function return call, then look up the address 22610785Sgope@wisc.edu // in the RAS. 22710785Sgope@wisc.edu TheISA::PCState rasTop = RAS[tid].top(); 22810785Sgope@wisc.edu target = TheISA::buildRetPC(pc, rasTop); 22910785Sgope@wisc.edu 23010785Sgope@wisc.edu // Record the top entry of the RAS, and its index. 23110785Sgope@wisc.edu predict_record.usedRAS = true; 23210785Sgope@wisc.edu predict_record.RASIndex = RAS[tid].topIdx(); 23310785Sgope@wisc.edu predict_record.RASTarget = rasTop; 23410785Sgope@wisc.edu 23510785Sgope@wisc.edu RAS[tid].pop(); 23610785Sgope@wisc.edu 23710785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s is a return, " 23810785Sgope@wisc.edu "RAS predicted target: %s, RAS index: %i.\n", 23910785Sgope@wisc.edu tid, pc, target, predict_record.RASIndex); 24010785Sgope@wisc.edu } else { 24110785Sgope@wisc.edu ++BTBLookups; 24210785Sgope@wisc.edu 24310785Sgope@wisc.edu if (inst->isCall()) { 24410785Sgope@wisc.edu RAS[tid].push(pc); 24510785Sgope@wisc.edu predict_record.pushedRAS = true; 24610785Sgope@wisc.edu 24710785Sgope@wisc.edu // Record that it was a call so that the top RAS entry can 24810785Sgope@wisc.edu // be popped off if the speculation is incorrect. 24910785Sgope@wisc.edu predict_record.wasCall = true; 25010785Sgope@wisc.edu 25110785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s was a " 25210785Sgope@wisc.edu "call, adding %s to the RAS index: %i.\n", 25310785Sgope@wisc.edu tid, pc, pc, RAS[tid].topIdx()); 25410785Sgope@wisc.edu } 25510785Sgope@wisc.edu 25611433Smitch.hayenga@arm.com if (inst->isDirectCtrl() || !useIndirect) { 25711433Smitch.hayenga@arm.com // Check BTB on direct branches 25811433Smitch.hayenga@arm.com if (BTB.valid(pc.instAddr(), tid)) { 25911433Smitch.hayenga@arm.com ++BTBHits; 26010785Sgope@wisc.edu 26111433Smitch.hayenga@arm.com // If it's not a return, use the BTB to get target addr. 26211433Smitch.hayenga@arm.com target = BTB.lookup(pc.instAddr(), tid); 26310785Sgope@wisc.edu 26411433Smitch.hayenga@arm.com DPRINTF(Branch, "[tid:%i]: Instruction %s predicted" 26511433Smitch.hayenga@arm.com " target is %s.\n", tid, pc, target); 26610785Sgope@wisc.edu 26711433Smitch.hayenga@arm.com } else { 26811433Smitch.hayenga@arm.com DPRINTF(Branch, "[tid:%i]: BTB doesn't have a " 26911433Smitch.hayenga@arm.com "valid entry.\n",tid); 27011433Smitch.hayenga@arm.com pred_taken = false; 27111433Smitch.hayenga@arm.com // The Direction of the branch predictor is altered 27211433Smitch.hayenga@arm.com // because the BTB did not have an entry 27311433Smitch.hayenga@arm.com // The predictor needs to be updated accordingly 27411433Smitch.hayenga@arm.com if (!inst->isCall() && !inst->isReturn()) { 27511434Smitch.hayenga@arm.com btbUpdate(tid, pc.instAddr(), bp_history); 27611433Smitch.hayenga@arm.com DPRINTF(Branch, "[tid:%i]:[sn:%i] btbUpdate" 27711433Smitch.hayenga@arm.com " called for %s\n", tid, seqNum, pc); 27811433Smitch.hayenga@arm.com } else if (inst->isCall() && !inst->isUncondCtrl()) { 27911433Smitch.hayenga@arm.com RAS[tid].pop(); 28011433Smitch.hayenga@arm.com predict_record.pushedRAS = false; 28111433Smitch.hayenga@arm.com } 28211433Smitch.hayenga@arm.com TheISA::advancePC(target, inst); 28311433Smitch.hayenga@arm.com } 28411429Sandreas.sandberg@arm.com } else { 28511433Smitch.hayenga@arm.com predict_record.wasIndirect = true; 28611433Smitch.hayenga@arm.com ++indirectLookups; 28711433Smitch.hayenga@arm.com //Consult indirect predictor on indirect control 28813654Sjairo.balart@metempsy.com if (iPred.lookup(pc.instAddr(), target, tid)) { 28911433Smitch.hayenga@arm.com // Indirect predictor hit 29011433Smitch.hayenga@arm.com ++indirectHits; 29111433Smitch.hayenga@arm.com DPRINTF(Branch, "[tid:%i]: Instruction %s predicted " 29211433Smitch.hayenga@arm.com "indirect target is %s.\n", tid, pc, target); 29311433Smitch.hayenga@arm.com } else { 29411433Smitch.hayenga@arm.com ++indirectMisses; 29511433Smitch.hayenga@arm.com pred_taken = false; 29611433Smitch.hayenga@arm.com DPRINTF(Branch, "[tid:%i]: Instruction %s no indirect " 29711433Smitch.hayenga@arm.com "target.\n", tid, pc); 29811433Smitch.hayenga@arm.com if (!inst->isCall() && !inst->isReturn()) { 29911433Smitch.hayenga@arm.com 30011433Smitch.hayenga@arm.com } else if (inst->isCall() && !inst->isUncondCtrl()) { 30111433Smitch.hayenga@arm.com RAS[tid].pop(); 30211433Smitch.hayenga@arm.com predict_record.pushedRAS = false; 30311433Smitch.hayenga@arm.com } 30411433Smitch.hayenga@arm.com TheISA::advancePC(target, inst); 30511426Smitch.hayenga@arm.com } 30611433Smitch.hayenga@arm.com iPred.recordIndirect(pc.instAddr(), target.instAddr(), seqNum, 30711433Smitch.hayenga@arm.com tid); 30810785Sgope@wisc.edu } 30910785Sgope@wisc.edu } 31010785Sgope@wisc.edu } else { 31110785Sgope@wisc.edu if (inst->isReturn()) { 31210785Sgope@wisc.edu predict_record.wasReturn = true; 31310785Sgope@wisc.edu } 31410785Sgope@wisc.edu TheISA::advancePC(target, inst); 31510785Sgope@wisc.edu } 31613626Sjairo.balart@metempsy.com predict_record.target = target.instAddr(); 31710785Sgope@wisc.edu 31810785Sgope@wisc.edu pc = target; 31910785Sgope@wisc.edu 32010785Sgope@wisc.edu predHist[tid].push_front(predict_record); 32110785Sgope@wisc.edu 32210785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i]: History entry added." 32310785Sgope@wisc.edu "predHist.size(): %i\n", tid, seqNum, predHist[tid].size()); 32410785Sgope@wisc.edu 32510785Sgope@wisc.edu return pred_taken; 32610785Sgope@wisc.edu} 32710785Sgope@wisc.edu 32810785Sgope@wisc.eduvoid 32910785Sgope@wisc.eduBPredUnit::update(const InstSeqNum &done_sn, ThreadID tid) 33010785Sgope@wisc.edu{ 33110785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Committing branches until " 33210785Sgope@wisc.edu "[sn:%lli].\n", tid, done_sn); 33310785Sgope@wisc.edu 33410785Sgope@wisc.edu while (!predHist[tid].empty() && 33510785Sgope@wisc.edu predHist[tid].back().seqNum <= done_sn) { 33610785Sgope@wisc.edu // Update the branch predictor with the correct results. 33711783Sarthur.perais@inria.fr update(tid, predHist[tid].back().pc, 33811783Sarthur.perais@inria.fr predHist[tid].back().predTaken, 33913626Sjairo.balart@metempsy.com predHist[tid].back().bpHistory, false, 34013626Sjairo.balart@metempsy.com predHist[tid].back().inst, 34113626Sjairo.balart@metempsy.com predHist[tid].back().target); 34210785Sgope@wisc.edu 34313654Sjairo.balart@metempsy.com iPred.commit(done_sn, tid, predHist[tid].back().indirectHistory); 34413654Sjairo.balart@metempsy.com 34510785Sgope@wisc.edu predHist[tid].pop_back(); 3469480Snilay@cs.wisc.edu } 3479480Snilay@cs.wisc.edu} 34810785Sgope@wisc.edu 34910785Sgope@wisc.eduvoid 35010785Sgope@wisc.eduBPredUnit::squash(const InstSeqNum &squashed_sn, ThreadID tid) 35110785Sgope@wisc.edu{ 35210785Sgope@wisc.edu History &pred_hist = predHist[tid]; 35310785Sgope@wisc.edu 35411433Smitch.hayenga@arm.com iPred.squash(squashed_sn, tid); 35510785Sgope@wisc.edu while (!pred_hist.empty() && 35610785Sgope@wisc.edu pred_hist.front().seqNum > squashed_sn) { 35710785Sgope@wisc.edu if (pred_hist.front().usedRAS) { 35810785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Restoring top of RAS to: %i," 35910785Sgope@wisc.edu " target: %s.\n", tid, 36010785Sgope@wisc.edu pred_hist.front().RASIndex, pred_hist.front().RASTarget); 36110785Sgope@wisc.edu 36210785Sgope@wisc.edu RAS[tid].restore(pred_hist.front().RASIndex, 36310785Sgope@wisc.edu pred_hist.front().RASTarget); 36411321Ssteve.reinhardt@amd.com } else if (pred_hist.front().wasCall && pred_hist.front().pushedRAS) { 36510785Sgope@wisc.edu // Was a call but predicated false. Pop RAS here 36610785Sgope@wisc.edu DPRINTF(Branch, "[tid: %i] Squashing" 36710785Sgope@wisc.edu " Call [sn:%i] PC: %s Popping RAS\n", tid, 36810785Sgope@wisc.edu pred_hist.front().seqNum, pred_hist.front().pc); 36910785Sgope@wisc.edu RAS[tid].pop(); 37010785Sgope@wisc.edu } 37110785Sgope@wisc.edu 37210785Sgope@wisc.edu // This call should delete the bpHistory. 37311434Smitch.hayenga@arm.com squash(tid, pred_hist.front().bpHistory); 37413654Sjairo.balart@metempsy.com iPred.deleteDirectionInfo(tid, pred_hist.front().indirectHistory); 37510785Sgope@wisc.edu 37610785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Removing history for [sn:%i] " 37710785Sgope@wisc.edu "PC %s.\n", tid, pred_hist.front().seqNum, 37810785Sgope@wisc.edu pred_hist.front().pc); 37910785Sgope@wisc.edu 38010785Sgope@wisc.edu pred_hist.pop_front(); 38110785Sgope@wisc.edu 38210785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: predHist.size(): %i\n", 38310785Sgope@wisc.edu tid, predHist[tid].size()); 38410785Sgope@wisc.edu } 38510785Sgope@wisc.edu} 38610785Sgope@wisc.edu 38710785Sgope@wisc.eduvoid 38810785Sgope@wisc.eduBPredUnit::squash(const InstSeqNum &squashed_sn, 38910785Sgope@wisc.edu const TheISA::PCState &corrTarget, 39010785Sgope@wisc.edu bool actually_taken, ThreadID tid) 39110785Sgope@wisc.edu{ 39210785Sgope@wisc.edu // Now that we know that a branch was mispredicted, we need to undo 39310785Sgope@wisc.edu // all the branches that have been seen up until this branch and 39410785Sgope@wisc.edu // fix up everything. 39510785Sgope@wisc.edu // NOTE: This should be call conceivably in 2 scenarios: 39610785Sgope@wisc.edu // (1) After an branch is executed, it updates its status in the ROB 39710785Sgope@wisc.edu // The commit stage then checks the ROB update and sends a signal to 39810785Sgope@wisc.edu // the fetch stage to squash history after the mispredict 39910785Sgope@wisc.edu // (2) In the decode stage, you can find out early if a unconditional 40010785Sgope@wisc.edu // PC-relative, branch was predicted incorrectly. If so, a signal 40110785Sgope@wisc.edu // to the fetch stage is sent to squash history after the mispredict 40210785Sgope@wisc.edu 40310785Sgope@wisc.edu History &pred_hist = predHist[tid]; 40410785Sgope@wisc.edu 40510785Sgope@wisc.edu ++condIncorrect; 40610785Sgope@wisc.edu ppMisses->notify(1); 40710785Sgope@wisc.edu 40810785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Squashing from sequence number %i, " 40910785Sgope@wisc.edu "setting target to %s.\n", tid, squashed_sn, corrTarget); 41010785Sgope@wisc.edu 41110785Sgope@wisc.edu // Squash All Branches AFTER this mispredicted branch 41210785Sgope@wisc.edu squash(squashed_sn, tid); 41310785Sgope@wisc.edu 41410785Sgope@wisc.edu // If there's a squash due to a syscall, there may not be an entry 41510785Sgope@wisc.edu // corresponding to the squash. In that case, don't bother trying to 41610785Sgope@wisc.edu // fix up the entry. 41710785Sgope@wisc.edu if (!pred_hist.empty()) { 41810785Sgope@wisc.edu 41910785Sgope@wisc.edu auto hist_it = pred_hist.begin(); 42010785Sgope@wisc.edu //HistoryIt hist_it = find(pred_hist.begin(), pred_hist.end(), 42110785Sgope@wisc.edu // squashed_sn); 42210785Sgope@wisc.edu 42310785Sgope@wisc.edu //assert(hist_it != pred_hist.end()); 42410785Sgope@wisc.edu if (pred_hist.front().seqNum != squashed_sn) { 42510785Sgope@wisc.edu DPRINTF(Branch, "Front sn %i != Squash sn %i\n", 42610785Sgope@wisc.edu pred_hist.front().seqNum, squashed_sn); 42710785Sgope@wisc.edu 42810785Sgope@wisc.edu assert(pred_hist.front().seqNum == squashed_sn); 42910785Sgope@wisc.edu } 43010785Sgope@wisc.edu 43110785Sgope@wisc.edu 43210785Sgope@wisc.edu if ((*hist_it).usedRAS) { 43310785Sgope@wisc.edu ++RASIncorrect; 43411433Smitch.hayenga@arm.com DPRINTF(Branch, "[tid:%i]: Incorrect RAS [sn:%i]\n", 43511433Smitch.hayenga@arm.com tid, hist_it->seqNum); 43610785Sgope@wisc.edu } 43710785Sgope@wisc.edu 43811783Sarthur.perais@inria.fr // There are separate functions for in-order and out-of-order 43911783Sarthur.perais@inria.fr // branch prediction, but not for update. Therefore, this 44011783Sarthur.perais@inria.fr // call should take into account that the mispredicted branch may 44111783Sarthur.perais@inria.fr // be on the wrong path (i.e., OoO execution), and that the counter 44211783Sarthur.perais@inria.fr // counter table(s) should not be updated. Thus, this call should 44311783Sarthur.perais@inria.fr // restore the state of the underlying predictor, for instance the 44411783Sarthur.perais@inria.fr // local/global histories. The counter tables will be updated when 44511783Sarthur.perais@inria.fr // the branch actually commits. 44611783Sarthur.perais@inria.fr 44711783Sarthur.perais@inria.fr // Remember the correct direction for the update at commit. 44811783Sarthur.perais@inria.fr pred_hist.front().predTaken = actually_taken; 44913626Sjairo.balart@metempsy.com pred_hist.front().target = corrTarget.instAddr(); 45011783Sarthur.perais@inria.fr 45111434Smitch.hayenga@arm.com update(tid, (*hist_it).pc, actually_taken, 45213626Sjairo.balart@metempsy.com pred_hist.front().bpHistory, true, pred_hist.front().inst, 45313626Sjairo.balart@metempsy.com corrTarget.instAddr()); 45410785Sgope@wisc.edu 45513654Sjairo.balart@metempsy.com iPred.changeDirectionPrediction(tid, pred_hist.front().indirectHistory, 45613654Sjairo.balart@metempsy.com actually_taken); 45713654Sjairo.balart@metempsy.com 45810785Sgope@wisc.edu if (actually_taken) { 45910785Sgope@wisc.edu if (hist_it->wasReturn && !hist_it->usedRAS) { 46010785Sgope@wisc.edu DPRINTF(Branch, "[tid: %i] Incorrectly predicted" 46110785Sgope@wisc.edu " return [sn:%i] PC: %s\n", tid, hist_it->seqNum, 46210785Sgope@wisc.edu hist_it->pc); 46310785Sgope@wisc.edu RAS[tid].pop(); 46410785Sgope@wisc.edu hist_it->usedRAS = true; 46510785Sgope@wisc.edu } 46611433Smitch.hayenga@arm.com if (hist_it->wasIndirect) { 46711433Smitch.hayenga@arm.com ++indirectMispredicted; 46813654Sjairo.balart@metempsy.com iPred.recordTarget(hist_it->seqNum, corrTarget, tid); 46911433Smitch.hayenga@arm.com } else { 47011433Smitch.hayenga@arm.com DPRINTF(Branch,"[tid: %i] BTB Update called for [sn:%i]" 47111433Smitch.hayenga@arm.com " PC: %s\n", tid,hist_it->seqNum, hist_it->pc); 47210785Sgope@wisc.edu 47311433Smitch.hayenga@arm.com BTB.update((*hist_it).pc, corrTarget, tid); 47411433Smitch.hayenga@arm.com } 47510785Sgope@wisc.edu } else { 47610785Sgope@wisc.edu //Actually not Taken 47710785Sgope@wisc.edu if (hist_it->usedRAS) { 47810785Sgope@wisc.edu DPRINTF(Branch,"[tid: %i] Incorrectly predicted" 47910785Sgope@wisc.edu " return [sn:%i] PC: %s Restoring RAS\n", tid, 48010785Sgope@wisc.edu hist_it->seqNum, hist_it->pc); 48110785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Restoring top of RAS" 48210785Sgope@wisc.edu " to: %i, target: %s.\n", tid, 48310785Sgope@wisc.edu hist_it->RASIndex, hist_it->RASTarget); 48410785Sgope@wisc.edu RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget); 48510785Sgope@wisc.edu hist_it->usedRAS = false; 48610785Sgope@wisc.edu } else if (hist_it->wasCall && hist_it->pushedRAS) { 48710785Sgope@wisc.edu //Was a Call but predicated false. Pop RAS here 48810785Sgope@wisc.edu DPRINTF(Branch, "[tid: %i] Incorrectly predicted" 48910785Sgope@wisc.edu " Call [sn:%i] PC: %s Popping RAS\n", tid, 49010785Sgope@wisc.edu hist_it->seqNum, hist_it->pc); 49110785Sgope@wisc.edu RAS[tid].pop(); 49210785Sgope@wisc.edu hist_it->pushedRAS = false; 49310785Sgope@wisc.edu } 49410785Sgope@wisc.edu } 49510785Sgope@wisc.edu } else { 49610785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i] pred_hist empty, can't " 49710785Sgope@wisc.edu "update.\n", tid, squashed_sn); 49810785Sgope@wisc.edu } 49910785Sgope@wisc.edu} 50010785Sgope@wisc.edu 50110785Sgope@wisc.eduvoid 50210785Sgope@wisc.eduBPredUnit::dump() 50310785Sgope@wisc.edu{ 50410785Sgope@wisc.edu int i = 0; 50510785Sgope@wisc.edu for (const auto& ph : predHist) { 50610785Sgope@wisc.edu if (!ph.empty()) { 50710785Sgope@wisc.edu auto pred_hist_it = ph.begin(); 50810785Sgope@wisc.edu 50910785Sgope@wisc.edu cprintf("predHist[%i].size(): %i\n", i++, ph.size()); 51010785Sgope@wisc.edu 51110785Sgope@wisc.edu while (pred_hist_it != ph.end()) { 51210785Sgope@wisc.edu cprintf("[sn:%lli], PC:%#x, tid:%i, predTaken:%i, " 51310785Sgope@wisc.edu "bpHistory:%#x\n", 51410785Sgope@wisc.edu pred_hist_it->seqNum, pred_hist_it->pc, 51510785Sgope@wisc.edu pred_hist_it->tid, pred_hist_it->predTaken, 51610785Sgope@wisc.edu pred_hist_it->bpHistory); 51710785Sgope@wisc.edu pred_hist_it++; 51810785Sgope@wisc.edu } 51910785Sgope@wisc.edu 52010785Sgope@wisc.edu cprintf("\n"); 52110785Sgope@wisc.edu } 52210785Sgope@wisc.edu } 52310785Sgope@wisc.edu} 52410785Sgope@wisc.edu 525