bpred_unit.cc revision 13831
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, 7313810Spau.cabre@metempsy.com params->numThreads, 7413810Spau.cabre@metempsy.com params->indirectGHRBits), 7510785Sgope@wisc.edu instShiftAmt(params->instShiftAmt) 769480Snilay@cs.wisc.edu{ 7710785Sgope@wisc.edu for (auto& r : RAS) 7810785Sgope@wisc.edu r.init(params->RASSize); 7910785Sgope@wisc.edu} 8010785Sgope@wisc.edu 8110785Sgope@wisc.eduvoid 8210785Sgope@wisc.eduBPredUnit::regStats() 8310785Sgope@wisc.edu{ 8411523Sdavid.guillen@arm.com SimObject::regStats(); 8511523Sdavid.guillen@arm.com 8610785Sgope@wisc.edu lookups 8710785Sgope@wisc.edu .name(name() + ".lookups") 8810785Sgope@wisc.edu .desc("Number of BP lookups") 8910785Sgope@wisc.edu ; 9010785Sgope@wisc.edu 9110785Sgope@wisc.edu condPredicted 9210785Sgope@wisc.edu .name(name() + ".condPredicted") 9310785Sgope@wisc.edu .desc("Number of conditional branches predicted") 9410785Sgope@wisc.edu ; 9510785Sgope@wisc.edu 9610785Sgope@wisc.edu condIncorrect 9710785Sgope@wisc.edu .name(name() + ".condIncorrect") 9810785Sgope@wisc.edu .desc("Number of conditional branches incorrect") 9910785Sgope@wisc.edu ; 10010785Sgope@wisc.edu 10110785Sgope@wisc.edu BTBLookups 10210785Sgope@wisc.edu .name(name() + ".BTBLookups") 10310785Sgope@wisc.edu .desc("Number of BTB lookups") 10410785Sgope@wisc.edu ; 10510785Sgope@wisc.edu 10610785Sgope@wisc.edu BTBHits 10710785Sgope@wisc.edu .name(name() + ".BTBHits") 10810785Sgope@wisc.edu .desc("Number of BTB hits") 10910785Sgope@wisc.edu ; 11010785Sgope@wisc.edu 11110785Sgope@wisc.edu BTBCorrect 11210785Sgope@wisc.edu .name(name() + ".BTBCorrect") 11310785Sgope@wisc.edu .desc("Number of correct BTB predictions (this stat may not " 11410785Sgope@wisc.edu "work properly.") 11510785Sgope@wisc.edu ; 11610785Sgope@wisc.edu 11710785Sgope@wisc.edu BTBHitPct 11810785Sgope@wisc.edu .name(name() + ".BTBHitPct") 11910785Sgope@wisc.edu .desc("BTB Hit Percentage") 12010785Sgope@wisc.edu .precision(6); 12110785Sgope@wisc.edu BTBHitPct = (BTBHits / BTBLookups) * 100; 12210785Sgope@wisc.edu 12310785Sgope@wisc.edu usedRAS 12410785Sgope@wisc.edu .name(name() + ".usedRAS") 12510785Sgope@wisc.edu .desc("Number of times the RAS was used to get a target.") 12610785Sgope@wisc.edu ; 12710785Sgope@wisc.edu 12810785Sgope@wisc.edu RASIncorrect 12910785Sgope@wisc.edu .name(name() + ".RASInCorrect") 13010785Sgope@wisc.edu .desc("Number of incorrect RAS predictions.") 13110785Sgope@wisc.edu ; 13211433Smitch.hayenga@arm.com 13311433Smitch.hayenga@arm.com indirectLookups 13411433Smitch.hayenga@arm.com .name(name() + ".indirectLookups") 13511433Smitch.hayenga@arm.com .desc("Number of indirect predictor lookups.") 13611433Smitch.hayenga@arm.com ; 13711433Smitch.hayenga@arm.com 13811433Smitch.hayenga@arm.com indirectHits 13911433Smitch.hayenga@arm.com .name(name() + ".indirectHits") 14011433Smitch.hayenga@arm.com .desc("Number of indirect target hits.") 14111433Smitch.hayenga@arm.com ; 14211433Smitch.hayenga@arm.com 14311433Smitch.hayenga@arm.com indirectMisses 14411433Smitch.hayenga@arm.com .name(name() + ".indirectMisses") 14511433Smitch.hayenga@arm.com .desc("Number of indirect misses.") 14611433Smitch.hayenga@arm.com ; 14711433Smitch.hayenga@arm.com 14811433Smitch.hayenga@arm.com indirectMispredicted 14911433Smitch.hayenga@arm.com .name(name() + "indirectMispredicted") 15011433Smitch.hayenga@arm.com .desc("Number of mispredicted indirect branches.") 15111433Smitch.hayenga@arm.com ; 15211433Smitch.hayenga@arm.com 15310785Sgope@wisc.edu} 15410785Sgope@wisc.edu 15510785Sgope@wisc.eduProbePoints::PMUUPtr 15610785Sgope@wisc.eduBPredUnit::pmuProbePoint(const char *name) 15710785Sgope@wisc.edu{ 15810785Sgope@wisc.edu ProbePoints::PMUUPtr ptr; 15910785Sgope@wisc.edu ptr.reset(new ProbePoints::PMU(getProbeManager(), name)); 16010785Sgope@wisc.edu 16110785Sgope@wisc.edu return ptr; 16210785Sgope@wisc.edu} 16310785Sgope@wisc.edu 16410785Sgope@wisc.eduvoid 16510785Sgope@wisc.eduBPredUnit::regProbePoints() 16610785Sgope@wisc.edu{ 16710785Sgope@wisc.edu ppBranches = pmuProbePoint("Branches"); 16810785Sgope@wisc.edu ppMisses = pmuProbePoint("Misses"); 16910785Sgope@wisc.edu} 17010785Sgope@wisc.edu 17110785Sgope@wisc.eduvoid 17210785Sgope@wisc.eduBPredUnit::drainSanityCheck() const 17310785Sgope@wisc.edu{ 17410785Sgope@wisc.edu // We shouldn't have any outstanding requests when we resume from 17510785Sgope@wisc.edu // a drained system. 17610785Sgope@wisc.edu for (const auto& ph M5_VAR_USED : predHist) 17710785Sgope@wisc.edu assert(ph.empty()); 17810785Sgope@wisc.edu} 17910785Sgope@wisc.edu 18010785Sgope@wisc.edubool 18110785Sgope@wisc.eduBPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum, 18210785Sgope@wisc.edu TheISA::PCState &pc, ThreadID tid) 18310785Sgope@wisc.edu{ 18410785Sgope@wisc.edu // See if branch predictor predicts taken. 18510785Sgope@wisc.edu // If so, get its target addr either from the BTB or the RAS. 18610785Sgope@wisc.edu // Save off record of branch stuff so the RAS can be fixed 18710785Sgope@wisc.edu // up once it's done. 18810785Sgope@wisc.edu 18910785Sgope@wisc.edu bool pred_taken = false; 19010785Sgope@wisc.edu TheISA::PCState target = pc; 19110785Sgope@wisc.edu 19210785Sgope@wisc.edu ++lookups; 19310785Sgope@wisc.edu ppBranches->notify(1); 19410785Sgope@wisc.edu 19510785Sgope@wisc.edu void *bp_history = NULL; 19613654Sjairo.balart@metempsy.com void *indirect_history = NULL; 19710785Sgope@wisc.edu 19810785Sgope@wisc.edu if (inst->isUncondCtrl()) { 19913831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [sn:%llu] " 20013831SAndrea.Mondelli@ucf.edu "Unconditional control\n", 20113831SAndrea.Mondelli@ucf.edu tid,seqNum); 20210785Sgope@wisc.edu pred_taken = true; 20310785Sgope@wisc.edu // Tell the BP there was an unconditional branch. 20411434Smitch.hayenga@arm.com uncondBranch(tid, pc.instAddr(), bp_history); 2059480Snilay@cs.wisc.edu } else { 20610785Sgope@wisc.edu ++condPredicted; 20711434Smitch.hayenga@arm.com pred_taken = lookup(tid, pc.instAddr(), bp_history); 20810785Sgope@wisc.edu 20913831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [sn:%llu] " 21013831SAndrea.Mondelli@ucf.edu "Branch predictor predicted %i for PC %s\n", 21113831SAndrea.Mondelli@ucf.edu tid, seqNum, pred_taken, pc); 21210785Sgope@wisc.edu } 21310785Sgope@wisc.edu 21413810Spau.cabre@metempsy.com const bool orig_pred_taken = pred_taken; 21513654Sjairo.balart@metempsy.com if (useIndirect) { 21613810Spau.cabre@metempsy.com iPred.genIndirectInfo(tid, indirect_history); 21713654Sjairo.balart@metempsy.com } 21813654Sjairo.balart@metempsy.com 21913831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [sn:%llu] " 22013831SAndrea.Mondelli@ucf.edu "Creating prediction history " 22110785Sgope@wisc.edu "for PC %s\n", tid, seqNum, pc); 22210785Sgope@wisc.edu 22313654Sjairo.balart@metempsy.com PredictorHistory predict_record(seqNum, pc.instAddr(), pred_taken, 22413654Sjairo.balart@metempsy.com bp_history, indirect_history, tid, inst); 22510785Sgope@wisc.edu 22610785Sgope@wisc.edu // Now lookup in the BTB or RAS. 22710785Sgope@wisc.edu if (pred_taken) { 22810785Sgope@wisc.edu if (inst->isReturn()) { 22910785Sgope@wisc.edu ++usedRAS; 23010785Sgope@wisc.edu predict_record.wasReturn = true; 23110785Sgope@wisc.edu // If it's a function return call, then look up the address 23210785Sgope@wisc.edu // in the RAS. 23310785Sgope@wisc.edu TheISA::PCState rasTop = RAS[tid].top(); 23410785Sgope@wisc.edu target = TheISA::buildRetPC(pc, rasTop); 23510785Sgope@wisc.edu 23610785Sgope@wisc.edu // Record the top entry of the RAS, and its index. 23710785Sgope@wisc.edu predict_record.usedRAS = true; 23810785Sgope@wisc.edu predict_record.RASIndex = RAS[tid].topIdx(); 23910785Sgope@wisc.edu predict_record.RASTarget = rasTop; 24010785Sgope@wisc.edu 24110785Sgope@wisc.edu RAS[tid].pop(); 24210785Sgope@wisc.edu 24313831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [sn:%llu] Instruction %s is a return, " 24413831SAndrea.Mondelli@ucf.edu "RAS predicted target: %s, RAS index: %i\n", 24513831SAndrea.Mondelli@ucf.edu tid, seqNum, pc, target, predict_record.RASIndex); 24610785Sgope@wisc.edu } else { 24710785Sgope@wisc.edu ++BTBLookups; 24810785Sgope@wisc.edu 24910785Sgope@wisc.edu if (inst->isCall()) { 25010785Sgope@wisc.edu RAS[tid].push(pc); 25110785Sgope@wisc.edu predict_record.pushedRAS = true; 25210785Sgope@wisc.edu 25310785Sgope@wisc.edu // Record that it was a call so that the top RAS entry can 25410785Sgope@wisc.edu // be popped off if the speculation is incorrect. 25510785Sgope@wisc.edu predict_record.wasCall = true; 25610785Sgope@wisc.edu 25713831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 25813831SAndrea.Mondelli@ucf.edu "[tid:%i] [sn:%llu] Instruction %s was a call, adding " 25913831SAndrea.Mondelli@ucf.edu "%s to the RAS index: %i\n", 26013831SAndrea.Mondelli@ucf.edu tid, seqNum, pc, pc, RAS[tid].topIdx()); 26110785Sgope@wisc.edu } 26210785Sgope@wisc.edu 26311433Smitch.hayenga@arm.com if (inst->isDirectCtrl() || !useIndirect) { 26411433Smitch.hayenga@arm.com // Check BTB on direct branches 26511433Smitch.hayenga@arm.com if (BTB.valid(pc.instAddr(), tid)) { 26611433Smitch.hayenga@arm.com ++BTBHits; 26711433Smitch.hayenga@arm.com // If it's not a return, use the BTB to get target addr. 26811433Smitch.hayenga@arm.com target = BTB.lookup(pc.instAddr(), tid); 26913831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 27013831SAndrea.Mondelli@ucf.edu "[tid:%i] [sn:%llu] Instruction %s predicted " 27113831SAndrea.Mondelli@ucf.edu "target is %s\n", 27213831SAndrea.Mondelli@ucf.edu tid, seqNum, pc, target); 27311433Smitch.hayenga@arm.com } else { 27413831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [sn:%llu] BTB doesn't have a " 27513831SAndrea.Mondelli@ucf.edu "valid entry\n",tid,seqNum); 27611433Smitch.hayenga@arm.com pred_taken = false; 27711433Smitch.hayenga@arm.com // The Direction of the branch predictor is altered 27811433Smitch.hayenga@arm.com // because the BTB did not have an entry 27911433Smitch.hayenga@arm.com // The predictor needs to be updated accordingly 28011433Smitch.hayenga@arm.com if (!inst->isCall() && !inst->isReturn()) { 28111434Smitch.hayenga@arm.com btbUpdate(tid, pc.instAddr(), bp_history); 28213831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 28313831SAndrea.Mondelli@ucf.edu "[tid:%i] [sn:%llu] btbUpdate " 28413831SAndrea.Mondelli@ucf.edu "called for %s\n", 28513831SAndrea.Mondelli@ucf.edu tid, seqNum, pc); 28611433Smitch.hayenga@arm.com } else if (inst->isCall() && !inst->isUncondCtrl()) { 28711433Smitch.hayenga@arm.com RAS[tid].pop(); 28811433Smitch.hayenga@arm.com predict_record.pushedRAS = false; 28911433Smitch.hayenga@arm.com } 29011433Smitch.hayenga@arm.com TheISA::advancePC(target, inst); 29111433Smitch.hayenga@arm.com } 29211429Sandreas.sandberg@arm.com } else { 29311433Smitch.hayenga@arm.com predict_record.wasIndirect = true; 29411433Smitch.hayenga@arm.com ++indirectLookups; 29511433Smitch.hayenga@arm.com //Consult indirect predictor on indirect control 29613654Sjairo.balart@metempsy.com if (iPred.lookup(pc.instAddr(), target, tid)) { 29711433Smitch.hayenga@arm.com // Indirect predictor hit 29811433Smitch.hayenga@arm.com ++indirectHits; 29913831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 30013831SAndrea.Mondelli@ucf.edu "[tid:%i] [sn:%llu] " 30113831SAndrea.Mondelli@ucf.edu "Instruction %s predicted " 30213831SAndrea.Mondelli@ucf.edu "indirect target is %s\n", 30313831SAndrea.Mondelli@ucf.edu tid, seqNum, pc, target); 30411433Smitch.hayenga@arm.com } else { 30511433Smitch.hayenga@arm.com ++indirectMisses; 30611433Smitch.hayenga@arm.com pred_taken = false; 30713831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 30813831SAndrea.Mondelli@ucf.edu "[tid:%i] [sn:%llu] " 30913831SAndrea.Mondelli@ucf.edu "Instruction %s no indirect " 31013831SAndrea.Mondelli@ucf.edu "target\n", 31113831SAndrea.Mondelli@ucf.edu tid, seqNum, pc); 31211433Smitch.hayenga@arm.com if (!inst->isCall() && !inst->isReturn()) { 31311433Smitch.hayenga@arm.com 31411433Smitch.hayenga@arm.com } else if (inst->isCall() && !inst->isUncondCtrl()) { 31511433Smitch.hayenga@arm.com RAS[tid].pop(); 31611433Smitch.hayenga@arm.com predict_record.pushedRAS = false; 31711433Smitch.hayenga@arm.com } 31811433Smitch.hayenga@arm.com TheISA::advancePC(target, inst); 31911426Smitch.hayenga@arm.com } 32011433Smitch.hayenga@arm.com iPred.recordIndirect(pc.instAddr(), target.instAddr(), seqNum, 32111433Smitch.hayenga@arm.com tid); 32210785Sgope@wisc.edu } 32310785Sgope@wisc.edu } 32410785Sgope@wisc.edu } else { 32510785Sgope@wisc.edu if (inst->isReturn()) { 32610785Sgope@wisc.edu predict_record.wasReturn = true; 32710785Sgope@wisc.edu } 32810785Sgope@wisc.edu TheISA::advancePC(target, inst); 32910785Sgope@wisc.edu } 33013626Sjairo.balart@metempsy.com predict_record.target = target.instAddr(); 33110785Sgope@wisc.edu 33210785Sgope@wisc.edu pc = target; 33310785Sgope@wisc.edu 33413810Spau.cabre@metempsy.com if (useIndirect) { 33513810Spau.cabre@metempsy.com // Update the indirect predictor with the direction prediction 33613810Spau.cabre@metempsy.com // Note that this happens after indirect lookup, so it does not use 33713810Spau.cabre@metempsy.com // the new information 33813810Spau.cabre@metempsy.com // Note also that we use orig_pred_taken instead of pred_taken in 33913810Spau.cabre@metempsy.com // as this is the actual outcome of the direction prediction 34013810Spau.cabre@metempsy.com iPred.updateDirectionInfo(tid, orig_pred_taken); 34113810Spau.cabre@metempsy.com } 34213810Spau.cabre@metempsy.com 34310785Sgope@wisc.edu predHist[tid].push_front(predict_record); 34410785Sgope@wisc.edu 34513831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 34613831SAndrea.Mondelli@ucf.edu "[tid:%i] [sn:%llu] History entry added. " 34713831SAndrea.Mondelli@ucf.edu "predHist.size(): %i\n", 34813831SAndrea.Mondelli@ucf.edu tid, seqNum, predHist[tid].size()); 34910785Sgope@wisc.edu 35010785Sgope@wisc.edu return pred_taken; 35110785Sgope@wisc.edu} 35210785Sgope@wisc.edu 35310785Sgope@wisc.eduvoid 35410785Sgope@wisc.eduBPredUnit::update(const InstSeqNum &done_sn, ThreadID tid) 35510785Sgope@wisc.edu{ 35613831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] Committing branches until " 35713831SAndrea.Mondelli@ucf.edu "sn:%llu]\n", tid, done_sn); 35810785Sgope@wisc.edu 35910785Sgope@wisc.edu while (!predHist[tid].empty() && 36010785Sgope@wisc.edu predHist[tid].back().seqNum <= done_sn) { 36110785Sgope@wisc.edu // Update the branch predictor with the correct results. 36211783Sarthur.perais@inria.fr update(tid, predHist[tid].back().pc, 36311783Sarthur.perais@inria.fr predHist[tid].back().predTaken, 36413626Sjairo.balart@metempsy.com predHist[tid].back().bpHistory, false, 36513626Sjairo.balart@metempsy.com predHist[tid].back().inst, 36613626Sjairo.balart@metempsy.com predHist[tid].back().target); 36710785Sgope@wisc.edu 36813810Spau.cabre@metempsy.com if (useIndirect) { 36913810Spau.cabre@metempsy.com iPred.commit(done_sn, tid, predHist[tid].back().indirectHistory); 37013810Spau.cabre@metempsy.com } 37113654Sjairo.balart@metempsy.com 37210785Sgope@wisc.edu predHist[tid].pop_back(); 3739480Snilay@cs.wisc.edu } 3749480Snilay@cs.wisc.edu} 37510785Sgope@wisc.edu 37610785Sgope@wisc.eduvoid 37710785Sgope@wisc.eduBPredUnit::squash(const InstSeqNum &squashed_sn, ThreadID tid) 37810785Sgope@wisc.edu{ 37910785Sgope@wisc.edu History &pred_hist = predHist[tid]; 38010785Sgope@wisc.edu 38113810Spau.cabre@metempsy.com if (useIndirect) { 38213810Spau.cabre@metempsy.com iPred.squash(squashed_sn, tid); 38313810Spau.cabre@metempsy.com } 38413810Spau.cabre@metempsy.com 38510785Sgope@wisc.edu while (!pred_hist.empty() && 38610785Sgope@wisc.edu pred_hist.front().seqNum > squashed_sn) { 38710785Sgope@wisc.edu if (pred_hist.front().usedRAS) { 38813831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [squash sn:%llu]" 38913831SAndrea.Mondelli@ucf.edu " Restoring top of RAS to: %i," 39013831SAndrea.Mondelli@ucf.edu " target: %s\n", tid, squashed_sn, 39110785Sgope@wisc.edu pred_hist.front().RASIndex, pred_hist.front().RASTarget); 39210785Sgope@wisc.edu 39310785Sgope@wisc.edu RAS[tid].restore(pred_hist.front().RASIndex, 39410785Sgope@wisc.edu pred_hist.front().RASTarget); 39511321Ssteve.reinhardt@amd.com } else if (pred_hist.front().wasCall && pred_hist.front().pushedRAS) { 39610785Sgope@wisc.edu // Was a call but predicated false. Pop RAS here 39713831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [squash sn:%llu] Squashing" 39813831SAndrea.Mondelli@ucf.edu " Call [sn:%llu] PC: %s Popping RAS\n", tid, squashed_sn, 39910785Sgope@wisc.edu pred_hist.front().seqNum, pred_hist.front().pc); 40010785Sgope@wisc.edu RAS[tid].pop(); 40110785Sgope@wisc.edu } 40210785Sgope@wisc.edu 40310785Sgope@wisc.edu // This call should delete the bpHistory. 40411434Smitch.hayenga@arm.com squash(tid, pred_hist.front().bpHistory); 40513733Ssrikant.bharadwaj@amd.com if (useIndirect) { 40613810Spau.cabre@metempsy.com iPred.deleteIndirectInfo(tid, pred_hist.front().indirectHistory); 40713733Ssrikant.bharadwaj@amd.com } 40810785Sgope@wisc.edu 40913831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [squash sn:%llu] " 41013831SAndrea.Mondelli@ucf.edu "Removing history for [sn:%llu] " 41113831SAndrea.Mondelli@ucf.edu "PC %#x\n", tid, squashed_sn, pred_hist.front().seqNum, 41210785Sgope@wisc.edu pred_hist.front().pc); 41310785Sgope@wisc.edu 41410785Sgope@wisc.edu pred_hist.pop_front(); 41510785Sgope@wisc.edu 41613831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [squash sn:%llu] predHist.size(): %i\n", 41713831SAndrea.Mondelli@ucf.edu tid, squashed_sn, predHist[tid].size()); 41810785Sgope@wisc.edu } 41910785Sgope@wisc.edu} 42010785Sgope@wisc.edu 42110785Sgope@wisc.eduvoid 42210785Sgope@wisc.eduBPredUnit::squash(const InstSeqNum &squashed_sn, 42310785Sgope@wisc.edu const TheISA::PCState &corrTarget, 42410785Sgope@wisc.edu bool actually_taken, ThreadID tid) 42510785Sgope@wisc.edu{ 42610785Sgope@wisc.edu // Now that we know that a branch was mispredicted, we need to undo 42710785Sgope@wisc.edu // all the branches that have been seen up until this branch and 42810785Sgope@wisc.edu // fix up everything. 42910785Sgope@wisc.edu // NOTE: This should be call conceivably in 2 scenarios: 43010785Sgope@wisc.edu // (1) After an branch is executed, it updates its status in the ROB 43110785Sgope@wisc.edu // The commit stage then checks the ROB update and sends a signal to 43210785Sgope@wisc.edu // the fetch stage to squash history after the mispredict 43310785Sgope@wisc.edu // (2) In the decode stage, you can find out early if a unconditional 43410785Sgope@wisc.edu // PC-relative, branch was predicted incorrectly. If so, a signal 43510785Sgope@wisc.edu // to the fetch stage is sent to squash history after the mispredict 43610785Sgope@wisc.edu 43710785Sgope@wisc.edu History &pred_hist = predHist[tid]; 43810785Sgope@wisc.edu 43910785Sgope@wisc.edu ++condIncorrect; 44010785Sgope@wisc.edu ppMisses->notify(1); 44110785Sgope@wisc.edu 44213831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] Squashing from sequence number %i, " 44313831SAndrea.Mondelli@ucf.edu "setting target to %s\n", tid, squashed_sn, corrTarget); 44410785Sgope@wisc.edu 44510785Sgope@wisc.edu // Squash All Branches AFTER this mispredicted branch 44610785Sgope@wisc.edu squash(squashed_sn, tid); 44710785Sgope@wisc.edu 44810785Sgope@wisc.edu // If there's a squash due to a syscall, there may not be an entry 44910785Sgope@wisc.edu // corresponding to the squash. In that case, don't bother trying to 45010785Sgope@wisc.edu // fix up the entry. 45110785Sgope@wisc.edu if (!pred_hist.empty()) { 45210785Sgope@wisc.edu 45310785Sgope@wisc.edu auto hist_it = pred_hist.begin(); 45410785Sgope@wisc.edu //HistoryIt hist_it = find(pred_hist.begin(), pred_hist.end(), 45510785Sgope@wisc.edu // squashed_sn); 45610785Sgope@wisc.edu 45710785Sgope@wisc.edu //assert(hist_it != pred_hist.end()); 45810785Sgope@wisc.edu if (pred_hist.front().seqNum != squashed_sn) { 45910785Sgope@wisc.edu DPRINTF(Branch, "Front sn %i != Squash sn %i\n", 46010785Sgope@wisc.edu pred_hist.front().seqNum, squashed_sn); 46110785Sgope@wisc.edu 46210785Sgope@wisc.edu assert(pred_hist.front().seqNum == squashed_sn); 46310785Sgope@wisc.edu } 46410785Sgope@wisc.edu 46510785Sgope@wisc.edu 46610785Sgope@wisc.edu if ((*hist_it).usedRAS) { 46710785Sgope@wisc.edu ++RASIncorrect; 46813831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 46913831SAndrea.Mondelli@ucf.edu "[tid:%i] [squash sn:%llu] Incorrect RAS [sn:%llu]\n", 47013831SAndrea.Mondelli@ucf.edu tid, squashed_sn, hist_it->seqNum); 47110785Sgope@wisc.edu } 47210785Sgope@wisc.edu 47311783Sarthur.perais@inria.fr // There are separate functions for in-order and out-of-order 47411783Sarthur.perais@inria.fr // branch prediction, but not for update. Therefore, this 47511783Sarthur.perais@inria.fr // call should take into account that the mispredicted branch may 47611783Sarthur.perais@inria.fr // be on the wrong path (i.e., OoO execution), and that the counter 47711783Sarthur.perais@inria.fr // counter table(s) should not be updated. Thus, this call should 47811783Sarthur.perais@inria.fr // restore the state of the underlying predictor, for instance the 47911783Sarthur.perais@inria.fr // local/global histories. The counter tables will be updated when 48011783Sarthur.perais@inria.fr // the branch actually commits. 48111783Sarthur.perais@inria.fr 48211783Sarthur.perais@inria.fr // Remember the correct direction for the update at commit. 48311783Sarthur.perais@inria.fr pred_hist.front().predTaken = actually_taken; 48413626Sjairo.balart@metempsy.com pred_hist.front().target = corrTarget.instAddr(); 48511783Sarthur.perais@inria.fr 48611434Smitch.hayenga@arm.com update(tid, (*hist_it).pc, actually_taken, 48713626Sjairo.balart@metempsy.com pred_hist.front().bpHistory, true, pred_hist.front().inst, 48813626Sjairo.balart@metempsy.com corrTarget.instAddr()); 48910785Sgope@wisc.edu 49013733Ssrikant.bharadwaj@amd.com if (useIndirect) { 49113733Ssrikant.bharadwaj@amd.com iPred.changeDirectionPrediction(tid, 49213733Ssrikant.bharadwaj@amd.com pred_hist.front().indirectHistory, actually_taken); 49313733Ssrikant.bharadwaj@amd.com } 49413654Sjairo.balart@metempsy.com 49510785Sgope@wisc.edu if (actually_taken) { 49610785Sgope@wisc.edu if (hist_it->wasReturn && !hist_it->usedRAS) { 49713831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [squash sn:%llu] " 49813831SAndrea.Mondelli@ucf.edu "Incorrectly predicted " 49913831SAndrea.Mondelli@ucf.edu "return [sn:%llu] PC: %#x\n", tid, squashed_sn, 50013831SAndrea.Mondelli@ucf.edu hist_it->seqNum, 50113831SAndrea.Mondelli@ucf.edu hist_it->pc); 50210785Sgope@wisc.edu RAS[tid].pop(); 50310785Sgope@wisc.edu hist_it->usedRAS = true; 50410785Sgope@wisc.edu } 50511433Smitch.hayenga@arm.com if (hist_it->wasIndirect) { 50611433Smitch.hayenga@arm.com ++indirectMispredicted; 50713810Spau.cabre@metempsy.com iPred.recordTarget( 50813810Spau.cabre@metempsy.com hist_it->seqNum, pred_hist.front().indirectHistory, 50913810Spau.cabre@metempsy.com corrTarget, tid); 51011433Smitch.hayenga@arm.com } else { 51113831SAndrea.Mondelli@ucf.edu DPRINTF(Branch,"[tid:%i] [squash sn:%llu] " 51213831SAndrea.Mondelli@ucf.edu "BTB Update called for [sn:%llu] " 51313831SAndrea.Mondelli@ucf.edu "PC %#x\n", tid, squashed_sn, 51413831SAndrea.Mondelli@ucf.edu hist_it->seqNum, hist_it->pc); 51510785Sgope@wisc.edu 51611433Smitch.hayenga@arm.com BTB.update((*hist_it).pc, corrTarget, tid); 51711433Smitch.hayenga@arm.com } 51810785Sgope@wisc.edu } else { 51910785Sgope@wisc.edu //Actually not Taken 52010785Sgope@wisc.edu if (hist_it->usedRAS) { 52113831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 52213831SAndrea.Mondelli@ucf.edu "[tid:%i] [squash sn:%llu] Incorrectly predicted " 52313831SAndrea.Mondelli@ucf.edu "return [sn:%llu] PC: %#x Restoring RAS\n", tid, 52413831SAndrea.Mondelli@ucf.edu squashed_sn, 52510785Sgope@wisc.edu hist_it->seqNum, hist_it->pc); 52613831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 52713831SAndrea.Mondelli@ucf.edu "[tid:%i] [squash sn:%llu] Restoring top of RAS " 52813831SAndrea.Mondelli@ucf.edu "to: %i, target: %s\n", tid, squashed_sn, 52910785Sgope@wisc.edu hist_it->RASIndex, hist_it->RASTarget); 53010785Sgope@wisc.edu RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget); 53110785Sgope@wisc.edu hist_it->usedRAS = false; 53210785Sgope@wisc.edu } else if (hist_it->wasCall && hist_it->pushedRAS) { 53310785Sgope@wisc.edu //Was a Call but predicated false. Pop RAS here 53413831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, 53513831SAndrea.Mondelli@ucf.edu "[tid:%i] [squash sn:%llu] " 53613831SAndrea.Mondelli@ucf.edu "Incorrectly predicted " 53713831SAndrea.Mondelli@ucf.edu "Call [sn:%llu] PC: %s Popping RAS\n", 53813831SAndrea.Mondelli@ucf.edu tid, squashed_sn, 53913831SAndrea.Mondelli@ucf.edu hist_it->seqNum, hist_it->pc); 54010785Sgope@wisc.edu RAS[tid].pop(); 54110785Sgope@wisc.edu hist_it->pushedRAS = false; 54210785Sgope@wisc.edu } 54310785Sgope@wisc.edu } 54410785Sgope@wisc.edu } else { 54513831SAndrea.Mondelli@ucf.edu DPRINTF(Branch, "[tid:%i] [sn:%llu] pred_hist empty, can't " 54613831SAndrea.Mondelli@ucf.edu "update\n", tid, squashed_sn); 54710785Sgope@wisc.edu } 54810785Sgope@wisc.edu} 54910785Sgope@wisc.edu 55010785Sgope@wisc.eduvoid 55110785Sgope@wisc.eduBPredUnit::dump() 55210785Sgope@wisc.edu{ 55310785Sgope@wisc.edu int i = 0; 55410785Sgope@wisc.edu for (const auto& ph : predHist) { 55510785Sgope@wisc.edu if (!ph.empty()) { 55610785Sgope@wisc.edu auto pred_hist_it = ph.begin(); 55710785Sgope@wisc.edu 55810785Sgope@wisc.edu cprintf("predHist[%i].size(): %i\n", i++, ph.size()); 55910785Sgope@wisc.edu 56010785Sgope@wisc.edu while (pred_hist_it != ph.end()) { 56113831SAndrea.Mondelli@ucf.edu cprintf("sn:%llu], PC:%#x, tid:%i, predTaken:%i, " 56210785Sgope@wisc.edu "bpHistory:%#x\n", 56310785Sgope@wisc.edu pred_hist_it->seqNum, pred_hist_it->pc, 56410785Sgope@wisc.edu pred_hist_it->tid, pred_hist_it->predTaken, 56510785Sgope@wisc.edu pred_hist_it->bpHistory); 56610785Sgope@wisc.edu pred_hist_it++; 56710785Sgope@wisc.edu } 56810785Sgope@wisc.edu 56910785Sgope@wisc.edu cprintf("\n"); 57010785Sgope@wisc.edu } 57110785Sgope@wisc.edu } 57210785Sgope@wisc.edu} 57310785Sgope@wisc.edu 574