bpred_unit.cc revision 11321
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, 6210785Sgope@wisc.edu params->instShiftAmt), 6310785Sgope@wisc.edu RAS(numThreads), 6410785Sgope@wisc.edu instShiftAmt(params->instShiftAmt) 659480Snilay@cs.wisc.edu{ 6610785Sgope@wisc.edu for (auto& r : RAS) 6710785Sgope@wisc.edu r.init(params->RASSize); 6810785Sgope@wisc.edu} 6910785Sgope@wisc.edu 7010785Sgope@wisc.eduvoid 7110785Sgope@wisc.eduBPredUnit::regStats() 7210785Sgope@wisc.edu{ 7310785Sgope@wisc.edu lookups 7410785Sgope@wisc.edu .name(name() + ".lookups") 7510785Sgope@wisc.edu .desc("Number of BP lookups") 7610785Sgope@wisc.edu ; 7710785Sgope@wisc.edu 7810785Sgope@wisc.edu condPredicted 7910785Sgope@wisc.edu .name(name() + ".condPredicted") 8010785Sgope@wisc.edu .desc("Number of conditional branches predicted") 8110785Sgope@wisc.edu ; 8210785Sgope@wisc.edu 8310785Sgope@wisc.edu condIncorrect 8410785Sgope@wisc.edu .name(name() + ".condIncorrect") 8510785Sgope@wisc.edu .desc("Number of conditional branches incorrect") 8610785Sgope@wisc.edu ; 8710785Sgope@wisc.edu 8810785Sgope@wisc.edu BTBLookups 8910785Sgope@wisc.edu .name(name() + ".BTBLookups") 9010785Sgope@wisc.edu .desc("Number of BTB lookups") 9110785Sgope@wisc.edu ; 9210785Sgope@wisc.edu 9310785Sgope@wisc.edu BTBHits 9410785Sgope@wisc.edu .name(name() + ".BTBHits") 9510785Sgope@wisc.edu .desc("Number of BTB hits") 9610785Sgope@wisc.edu ; 9710785Sgope@wisc.edu 9810785Sgope@wisc.edu BTBCorrect 9910785Sgope@wisc.edu .name(name() + ".BTBCorrect") 10010785Sgope@wisc.edu .desc("Number of correct BTB predictions (this stat may not " 10110785Sgope@wisc.edu "work properly.") 10210785Sgope@wisc.edu ; 10310785Sgope@wisc.edu 10410785Sgope@wisc.edu BTBHitPct 10510785Sgope@wisc.edu .name(name() + ".BTBHitPct") 10610785Sgope@wisc.edu .desc("BTB Hit Percentage") 10710785Sgope@wisc.edu .precision(6); 10810785Sgope@wisc.edu BTBHitPct = (BTBHits / BTBLookups) * 100; 10910785Sgope@wisc.edu 11010785Sgope@wisc.edu usedRAS 11110785Sgope@wisc.edu .name(name() + ".usedRAS") 11210785Sgope@wisc.edu .desc("Number of times the RAS was used to get a target.") 11310785Sgope@wisc.edu ; 11410785Sgope@wisc.edu 11510785Sgope@wisc.edu RASIncorrect 11610785Sgope@wisc.edu .name(name() + ".RASInCorrect") 11710785Sgope@wisc.edu .desc("Number of incorrect RAS predictions.") 11810785Sgope@wisc.edu ; 11910785Sgope@wisc.edu} 12010785Sgope@wisc.edu 12110785Sgope@wisc.eduProbePoints::PMUUPtr 12210785Sgope@wisc.eduBPredUnit::pmuProbePoint(const char *name) 12310785Sgope@wisc.edu{ 12410785Sgope@wisc.edu ProbePoints::PMUUPtr ptr; 12510785Sgope@wisc.edu ptr.reset(new ProbePoints::PMU(getProbeManager(), name)); 12610785Sgope@wisc.edu 12710785Sgope@wisc.edu return ptr; 12810785Sgope@wisc.edu} 12910785Sgope@wisc.edu 13010785Sgope@wisc.eduvoid 13110785Sgope@wisc.eduBPredUnit::regProbePoints() 13210785Sgope@wisc.edu{ 13310785Sgope@wisc.edu ppBranches = pmuProbePoint("Branches"); 13410785Sgope@wisc.edu ppMisses = pmuProbePoint("Misses"); 13510785Sgope@wisc.edu} 13610785Sgope@wisc.edu 13710785Sgope@wisc.eduvoid 13810785Sgope@wisc.eduBPredUnit::drainSanityCheck() const 13910785Sgope@wisc.edu{ 14010785Sgope@wisc.edu // We shouldn't have any outstanding requests when we resume from 14110785Sgope@wisc.edu // a drained system. 14210785Sgope@wisc.edu for (const auto& ph M5_VAR_USED : predHist) 14310785Sgope@wisc.edu assert(ph.empty()); 14410785Sgope@wisc.edu} 14510785Sgope@wisc.edu 14610785Sgope@wisc.edubool 14710785Sgope@wisc.eduBPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum, 14810785Sgope@wisc.edu TheISA::PCState &pc, ThreadID tid) 14910785Sgope@wisc.edu{ 15010785Sgope@wisc.edu // See if branch predictor predicts taken. 15110785Sgope@wisc.edu // If so, get its target addr either from the BTB or the RAS. 15210785Sgope@wisc.edu // Save off record of branch stuff so the RAS can be fixed 15310785Sgope@wisc.edu // up once it's done. 15410785Sgope@wisc.edu 15510785Sgope@wisc.edu bool pred_taken = false; 15610785Sgope@wisc.edu TheISA::PCState target = pc; 15710785Sgope@wisc.edu 15810785Sgope@wisc.edu ++lookups; 15910785Sgope@wisc.edu ppBranches->notify(1); 16010785Sgope@wisc.edu 16110785Sgope@wisc.edu void *bp_history = NULL; 16210785Sgope@wisc.edu 16310785Sgope@wisc.edu if (inst->isUncondCtrl()) { 16410785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Unconditional control.\n", tid); 16510785Sgope@wisc.edu pred_taken = true; 16610785Sgope@wisc.edu // Tell the BP there was an unconditional branch. 16710785Sgope@wisc.edu uncondBranch(pc.instAddr(), bp_history); 1689480Snilay@cs.wisc.edu } else { 16910785Sgope@wisc.edu ++condPredicted; 17010785Sgope@wisc.edu pred_taken = lookup(pc.instAddr(), bp_history); 17110785Sgope@wisc.edu 17210785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i] Branch predictor" 17310785Sgope@wisc.edu " predicted %i for PC %s\n", tid, seqNum, pred_taken, pc); 17410785Sgope@wisc.edu } 17510785Sgope@wisc.edu 17610785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i] Creating prediction history " 17710785Sgope@wisc.edu "for PC %s\n", tid, seqNum, pc); 17810785Sgope@wisc.edu 17910785Sgope@wisc.edu PredictorHistory predict_record(seqNum, pc.instAddr(), 18010785Sgope@wisc.edu pred_taken, bp_history, tid); 18110785Sgope@wisc.edu 18210785Sgope@wisc.edu // Now lookup in the BTB or RAS. 18310785Sgope@wisc.edu if (pred_taken) { 18410785Sgope@wisc.edu if (inst->isReturn()) { 18510785Sgope@wisc.edu ++usedRAS; 18610785Sgope@wisc.edu predict_record.wasReturn = true; 18710785Sgope@wisc.edu // If it's a function return call, then look up the address 18810785Sgope@wisc.edu // in the RAS. 18910785Sgope@wisc.edu TheISA::PCState rasTop = RAS[tid].top(); 19010785Sgope@wisc.edu target = TheISA::buildRetPC(pc, rasTop); 19110785Sgope@wisc.edu 19210785Sgope@wisc.edu // Record the top entry of the RAS, and its index. 19310785Sgope@wisc.edu predict_record.usedRAS = true; 19410785Sgope@wisc.edu predict_record.RASIndex = RAS[tid].topIdx(); 19510785Sgope@wisc.edu predict_record.RASTarget = rasTop; 19610785Sgope@wisc.edu 19710785Sgope@wisc.edu RAS[tid].pop(); 19810785Sgope@wisc.edu 19910785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s is a return, " 20010785Sgope@wisc.edu "RAS predicted target: %s, RAS index: %i.\n", 20110785Sgope@wisc.edu tid, pc, target, predict_record.RASIndex); 20210785Sgope@wisc.edu } else { 20310785Sgope@wisc.edu ++BTBLookups; 20410785Sgope@wisc.edu 20510785Sgope@wisc.edu if (inst->isCall()) { 20610785Sgope@wisc.edu RAS[tid].push(pc); 20710785Sgope@wisc.edu predict_record.pushedRAS = true; 20810785Sgope@wisc.edu 20910785Sgope@wisc.edu // Record that it was a call so that the top RAS entry can 21010785Sgope@wisc.edu // be popped off if the speculation is incorrect. 21110785Sgope@wisc.edu predict_record.wasCall = true; 21210785Sgope@wisc.edu 21310785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s was a " 21410785Sgope@wisc.edu "call, adding %s to the RAS index: %i.\n", 21510785Sgope@wisc.edu tid, pc, pc, RAS[tid].topIdx()); 21610785Sgope@wisc.edu } 21710785Sgope@wisc.edu 21810785Sgope@wisc.edu if (BTB.valid(pc.instAddr(), tid)) { 21910785Sgope@wisc.edu ++BTBHits; 22010785Sgope@wisc.edu 22110785Sgope@wisc.edu // If it's not a return, use the BTB to get the target addr. 22210785Sgope@wisc.edu target = BTB.lookup(pc.instAddr(), tid); 22310785Sgope@wisc.edu 22410785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s predicted" 22510785Sgope@wisc.edu " target is %s.\n", tid, pc, target); 22610785Sgope@wisc.edu 22710785Sgope@wisc.edu } else { 22810785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: BTB doesn't have a " 22910785Sgope@wisc.edu "valid entry.\n",tid); 23010785Sgope@wisc.edu pred_taken = false; 23110785Sgope@wisc.edu // The Direction of the branch predictor is altered because the 23210785Sgope@wisc.edu // BTB did not have an entry 23310785Sgope@wisc.edu // The predictor needs to be updated accordingly 23410785Sgope@wisc.edu if (!inst->isCall() && !inst->isReturn()) { 23510785Sgope@wisc.edu btbUpdate(pc.instAddr(), bp_history); 23610785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]:[sn:%i] btbUpdate" 23710785Sgope@wisc.edu " called for %s\n", tid, seqNum, pc); 23810785Sgope@wisc.edu } else if (inst->isCall() && !inst->isUncondCtrl()) { 23910785Sgope@wisc.edu RAS[tid].pop(); 24010785Sgope@wisc.edu predict_record.pushedRAS = false; 24110785Sgope@wisc.edu } 24210785Sgope@wisc.edu TheISA::advancePC(target, inst); 24310785Sgope@wisc.edu } 24410785Sgope@wisc.edu } 24510785Sgope@wisc.edu } else { 24610785Sgope@wisc.edu if (inst->isReturn()) { 24710785Sgope@wisc.edu predict_record.wasReturn = true; 24810785Sgope@wisc.edu } 24910785Sgope@wisc.edu TheISA::advancePC(target, inst); 25010785Sgope@wisc.edu } 25110785Sgope@wisc.edu 25210785Sgope@wisc.edu pc = target; 25310785Sgope@wisc.edu 25410785Sgope@wisc.edu predHist[tid].push_front(predict_record); 25510785Sgope@wisc.edu 25610785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i]: History entry added." 25710785Sgope@wisc.edu "predHist.size(): %i\n", tid, seqNum, predHist[tid].size()); 25810785Sgope@wisc.edu 25910785Sgope@wisc.edu return pred_taken; 26010785Sgope@wisc.edu} 26110785Sgope@wisc.edu 26210785Sgope@wisc.edubool 26310785Sgope@wisc.eduBPredUnit::predictInOrder(const StaticInstPtr &inst, const InstSeqNum &seqNum, 26410785Sgope@wisc.edu int asid, TheISA::PCState &instPC, 26510785Sgope@wisc.edu TheISA::PCState &predPC, ThreadID tid) 26610785Sgope@wisc.edu{ 26710785Sgope@wisc.edu // See if branch predictor predicts taken. 26810785Sgope@wisc.edu // If so, get its target addr either from the BTB or the RAS. 26910785Sgope@wisc.edu // Save off record of branch stuff so the RAS can be fixed 27010785Sgope@wisc.edu // up once it's done. 27110785Sgope@wisc.edu 27210785Sgope@wisc.edu using TheISA::MachInst; 27310785Sgope@wisc.edu 27410785Sgope@wisc.edu bool pred_taken = false; 27510785Sgope@wisc.edu TheISA::PCState target; 27610785Sgope@wisc.edu 27710785Sgope@wisc.edu ++lookups; 27810785Sgope@wisc.edu ppBranches->notify(1); 27910785Sgope@wisc.edu 28010785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i] [sn:%i] %s ... PC %s doing branch " 28110785Sgope@wisc.edu "prediction\n", tid, seqNum, 28210785Sgope@wisc.edu inst->disassemble(instPC.instAddr()), instPC); 28310785Sgope@wisc.edu 28410785Sgope@wisc.edu void *bp_history = NULL; 28510785Sgope@wisc.edu 28610785Sgope@wisc.edu if (inst->isUncondCtrl()) { 28710785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i] Unconditional control.\n", tid); 28810785Sgope@wisc.edu pred_taken = true; 28910785Sgope@wisc.edu // Tell the BP there was an unconditional branch. 29010785Sgope@wisc.edu uncondBranch(instPC.instAddr(), bp_history); 29110785Sgope@wisc.edu 29210785Sgope@wisc.edu if (inst->isReturn() && RAS[tid].empty()) { 29310785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i] RAS is empty, predicting " 29410785Sgope@wisc.edu "false.\n", tid); 29510785Sgope@wisc.edu pred_taken = false; 29610785Sgope@wisc.edu } 29710785Sgope@wisc.edu } else { 29810785Sgope@wisc.edu ++condPredicted; 29910785Sgope@wisc.edu 30010785Sgope@wisc.edu pred_taken = lookup(predPC.instAddr(), bp_history); 30110785Sgope@wisc.edu } 30210785Sgope@wisc.edu 30310785Sgope@wisc.edu PredictorHistory predict_record(seqNum, predPC.instAddr(), pred_taken, 30410785Sgope@wisc.edu bp_history, tid); 30510785Sgope@wisc.edu 30610785Sgope@wisc.edu // Now lookup in the BTB or RAS. 30710785Sgope@wisc.edu if (pred_taken) { 30810785Sgope@wisc.edu if (inst->isReturn()) { 30910785Sgope@wisc.edu ++usedRAS; 31010785Sgope@wisc.edu 31110785Sgope@wisc.edu // If it's a function return call, then look up the address 31210785Sgope@wisc.edu // in the RAS. 31310785Sgope@wisc.edu TheISA::PCState rasTop = RAS[tid].top(); 31410785Sgope@wisc.edu target = TheISA::buildRetPC(instPC, rasTop); 31510785Sgope@wisc.edu 31610785Sgope@wisc.edu // Record the top entry of the RAS, and its index. 31710785Sgope@wisc.edu predict_record.usedRAS = true; 31810785Sgope@wisc.edu predict_record.RASIndex = RAS[tid].topIdx(); 31910785Sgope@wisc.edu predict_record.RASTarget = rasTop; 32010785Sgope@wisc.edu 32110785Sgope@wisc.edu assert(predict_record.RASIndex < 16); 32210785Sgope@wisc.edu 32310785Sgope@wisc.edu RAS[tid].pop(); 32410785Sgope@wisc.edu 32510785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s is a return, " 32610785Sgope@wisc.edu "RAS predicted target: %s, RAS index: %i.\n", 32710785Sgope@wisc.edu tid, instPC, target, 32810785Sgope@wisc.edu predict_record.RASIndex); 32910785Sgope@wisc.edu } else { 33010785Sgope@wisc.edu ++BTBLookups; 33110785Sgope@wisc.edu 33210785Sgope@wisc.edu if (inst->isCall()) { 33310785Sgope@wisc.edu 33410785Sgope@wisc.edu RAS[tid].push(instPC); 33510785Sgope@wisc.edu predict_record.pushedRAS = true; 33610785Sgope@wisc.edu 33710785Sgope@wisc.edu // Record that it was a call so that the top RAS entry can 33810785Sgope@wisc.edu // be popped off if the speculation is incorrect. 33910785Sgope@wisc.edu predict_record.wasCall = true; 34010785Sgope@wisc.edu 34110785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Instruction %s was a call" 34210785Sgope@wisc.edu ", adding %s to the RAS index: %i.\n", 34310785Sgope@wisc.edu tid, instPC, predPC, 34410785Sgope@wisc.edu RAS[tid].topIdx()); 34510785Sgope@wisc.edu } 34610785Sgope@wisc.edu 34710785Sgope@wisc.edu if (inst->isCall() && 34810785Sgope@wisc.edu inst->isUncondCtrl() && 34910785Sgope@wisc.edu inst->isDirectCtrl()) { 35010785Sgope@wisc.edu target = inst->branchTarget(instPC); 35110785Sgope@wisc.edu } else if (BTB.valid(predPC.instAddr(), asid)) { 35210785Sgope@wisc.edu ++BTBHits; 35310785Sgope@wisc.edu 35410785Sgope@wisc.edu // If it's not a return, use the BTB to get the target addr. 35510785Sgope@wisc.edu target = BTB.lookup(predPC.instAddr(), asid); 35610785Sgope@wisc.edu 35710785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [asid:%i] Instruction %s " 35810785Sgope@wisc.edu "predicted target is %s.\n", 35910785Sgope@wisc.edu tid, asid, instPC, target); 36010785Sgope@wisc.edu } else { 36110785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: BTB doesn't have a " 36210785Sgope@wisc.edu "valid entry, predicting false.\n",tid); 36310785Sgope@wisc.edu pred_taken = false; 36410785Sgope@wisc.edu } 36510785Sgope@wisc.edu } 36610785Sgope@wisc.edu } 36710785Sgope@wisc.edu 36810785Sgope@wisc.edu if (pred_taken) { 36910785Sgope@wisc.edu // Set the PC and the instruction's predicted target. 37010785Sgope@wisc.edu predPC = target; 37110785Sgope@wisc.edu } 37210785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i]: Setting Predicted PC to %s.\n", 37310785Sgope@wisc.edu tid, seqNum, predPC); 37410785Sgope@wisc.edu 37510785Sgope@wisc.edu predHist[tid].push_front(predict_record); 37610785Sgope@wisc.edu 37710785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i] [sn:%i] pushed onto front of predHist " 37810785Sgope@wisc.edu "...predHist.size(): %i\n", 37910785Sgope@wisc.edu tid, seqNum, predHist[tid].size()); 38010785Sgope@wisc.edu 38110785Sgope@wisc.edu return pred_taken; 38210785Sgope@wisc.edu} 38310785Sgope@wisc.edu 38410785Sgope@wisc.eduvoid 38510785Sgope@wisc.eduBPredUnit::update(const InstSeqNum &done_sn, ThreadID tid) 38610785Sgope@wisc.edu{ 38710785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Committing branches until " 38810785Sgope@wisc.edu "[sn:%lli].\n", tid, done_sn); 38910785Sgope@wisc.edu 39010785Sgope@wisc.edu while (!predHist[tid].empty() && 39110785Sgope@wisc.edu predHist[tid].back().seqNum <= done_sn) { 39210785Sgope@wisc.edu // Update the branch predictor with the correct results. 39310785Sgope@wisc.edu if (!predHist[tid].back().wasSquashed) { 39410785Sgope@wisc.edu update(predHist[tid].back().pc, predHist[tid].back().predTaken, 39510785Sgope@wisc.edu predHist[tid].back().bpHistory, false); 39610785Sgope@wisc.edu } else { 39710785Sgope@wisc.edu retireSquashed(predHist[tid].back().bpHistory); 39810785Sgope@wisc.edu } 39910785Sgope@wisc.edu 40010785Sgope@wisc.edu predHist[tid].pop_back(); 4019480Snilay@cs.wisc.edu } 4029480Snilay@cs.wisc.edu} 40310785Sgope@wisc.edu 40410785Sgope@wisc.eduvoid 40510785Sgope@wisc.eduBPredUnit::squash(const InstSeqNum &squashed_sn, ThreadID tid) 40610785Sgope@wisc.edu{ 40710785Sgope@wisc.edu History &pred_hist = predHist[tid]; 40810785Sgope@wisc.edu 40910785Sgope@wisc.edu while (!pred_hist.empty() && 41010785Sgope@wisc.edu pred_hist.front().seqNum > squashed_sn) { 41110785Sgope@wisc.edu if (pred_hist.front().usedRAS) { 41210785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Restoring top of RAS to: %i," 41310785Sgope@wisc.edu " target: %s.\n", tid, 41410785Sgope@wisc.edu pred_hist.front().RASIndex, pred_hist.front().RASTarget); 41510785Sgope@wisc.edu 41610785Sgope@wisc.edu RAS[tid].restore(pred_hist.front().RASIndex, 41710785Sgope@wisc.edu pred_hist.front().RASTarget); 41811321Ssteve.reinhardt@amd.com } else if (pred_hist.front().wasCall && pred_hist.front().pushedRAS) { 41910785Sgope@wisc.edu // Was a call but predicated false. Pop RAS here 42010785Sgope@wisc.edu DPRINTF(Branch, "[tid: %i] Squashing" 42110785Sgope@wisc.edu " Call [sn:%i] PC: %s Popping RAS\n", tid, 42210785Sgope@wisc.edu pred_hist.front().seqNum, pred_hist.front().pc); 42310785Sgope@wisc.edu RAS[tid].pop(); 42410785Sgope@wisc.edu } 42510785Sgope@wisc.edu 42610785Sgope@wisc.edu // This call should delete the bpHistory. 42710785Sgope@wisc.edu squash(pred_hist.front().bpHistory); 42810785Sgope@wisc.edu 42910785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Removing history for [sn:%i] " 43010785Sgope@wisc.edu "PC %s.\n", tid, pred_hist.front().seqNum, 43110785Sgope@wisc.edu pred_hist.front().pc); 43210785Sgope@wisc.edu 43310785Sgope@wisc.edu pred_hist.pop_front(); 43410785Sgope@wisc.edu 43510785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: predHist.size(): %i\n", 43610785Sgope@wisc.edu tid, predHist[tid].size()); 43710785Sgope@wisc.edu } 43810785Sgope@wisc.edu} 43910785Sgope@wisc.edu 44010785Sgope@wisc.eduvoid 44110785Sgope@wisc.eduBPredUnit::squash(const InstSeqNum &squashed_sn, 44210785Sgope@wisc.edu const TheISA::PCState &corrTarget, 44310785Sgope@wisc.edu bool actually_taken, ThreadID tid) 44410785Sgope@wisc.edu{ 44510785Sgope@wisc.edu // Now that we know that a branch was mispredicted, we need to undo 44610785Sgope@wisc.edu // all the branches that have been seen up until this branch and 44710785Sgope@wisc.edu // fix up everything. 44810785Sgope@wisc.edu // NOTE: This should be call conceivably in 2 scenarios: 44910785Sgope@wisc.edu // (1) After an branch is executed, it updates its status in the ROB 45010785Sgope@wisc.edu // The commit stage then checks the ROB update and sends a signal to 45110785Sgope@wisc.edu // the fetch stage to squash history after the mispredict 45210785Sgope@wisc.edu // (2) In the decode stage, you can find out early if a unconditional 45310785Sgope@wisc.edu // PC-relative, branch was predicted incorrectly. If so, a signal 45410785Sgope@wisc.edu // to the fetch stage is sent to squash history after the mispredict 45510785Sgope@wisc.edu 45610785Sgope@wisc.edu History &pred_hist = predHist[tid]; 45710785Sgope@wisc.edu 45810785Sgope@wisc.edu ++condIncorrect; 45910785Sgope@wisc.edu ppMisses->notify(1); 46010785Sgope@wisc.edu 46110785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Squashing from sequence number %i, " 46210785Sgope@wisc.edu "setting target to %s.\n", tid, squashed_sn, corrTarget); 46310785Sgope@wisc.edu 46410785Sgope@wisc.edu // Squash All Branches AFTER this mispredicted branch 46510785Sgope@wisc.edu squash(squashed_sn, tid); 46610785Sgope@wisc.edu 46710785Sgope@wisc.edu // If there's a squash due to a syscall, there may not be an entry 46810785Sgope@wisc.edu // corresponding to the squash. In that case, don't bother trying to 46910785Sgope@wisc.edu // fix up the entry. 47010785Sgope@wisc.edu if (!pred_hist.empty()) { 47110785Sgope@wisc.edu 47210785Sgope@wisc.edu auto hist_it = pred_hist.begin(); 47310785Sgope@wisc.edu //HistoryIt hist_it = find(pred_hist.begin(), pred_hist.end(), 47410785Sgope@wisc.edu // squashed_sn); 47510785Sgope@wisc.edu 47610785Sgope@wisc.edu //assert(hist_it != pred_hist.end()); 47710785Sgope@wisc.edu if (pred_hist.front().seqNum != squashed_sn) { 47810785Sgope@wisc.edu DPRINTF(Branch, "Front sn %i != Squash sn %i\n", 47910785Sgope@wisc.edu pred_hist.front().seqNum, squashed_sn); 48010785Sgope@wisc.edu 48110785Sgope@wisc.edu assert(pred_hist.front().seqNum == squashed_sn); 48210785Sgope@wisc.edu } 48310785Sgope@wisc.edu 48410785Sgope@wisc.edu 48510785Sgope@wisc.edu if ((*hist_it).usedRAS) { 48610785Sgope@wisc.edu ++RASIncorrect; 48710785Sgope@wisc.edu } 48810785Sgope@wisc.edu 48910785Sgope@wisc.edu update((*hist_it).pc, actually_taken, 49010785Sgope@wisc.edu pred_hist.front().bpHistory, true); 49110785Sgope@wisc.edu hist_it->wasSquashed = true; 49210785Sgope@wisc.edu 49310785Sgope@wisc.edu if (actually_taken) { 49410785Sgope@wisc.edu if (hist_it->wasReturn && !hist_it->usedRAS) { 49510785Sgope@wisc.edu DPRINTF(Branch, "[tid: %i] Incorrectly predicted" 49610785Sgope@wisc.edu " return [sn:%i] PC: %s\n", tid, hist_it->seqNum, 49710785Sgope@wisc.edu hist_it->pc); 49810785Sgope@wisc.edu RAS[tid].pop(); 49910785Sgope@wisc.edu hist_it->usedRAS = true; 50010785Sgope@wisc.edu } 50110785Sgope@wisc.edu 50210785Sgope@wisc.edu DPRINTF(Branch,"[tid: %i] BTB Update called for [sn:%i]" 50310785Sgope@wisc.edu " PC: %s\n", tid,hist_it->seqNum, hist_it->pc); 50410785Sgope@wisc.edu 50510785Sgope@wisc.edu BTB.update((*hist_it).pc, corrTarget, tid); 50610785Sgope@wisc.edu 50710785Sgope@wisc.edu } else { 50810785Sgope@wisc.edu //Actually not Taken 50910785Sgope@wisc.edu if (hist_it->usedRAS) { 51010785Sgope@wisc.edu DPRINTF(Branch,"[tid: %i] Incorrectly predicted" 51110785Sgope@wisc.edu " return [sn:%i] PC: %s Restoring RAS\n", tid, 51210785Sgope@wisc.edu hist_it->seqNum, hist_it->pc); 51310785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: Restoring top of RAS" 51410785Sgope@wisc.edu " to: %i, target: %s.\n", tid, 51510785Sgope@wisc.edu hist_it->RASIndex, hist_it->RASTarget); 51610785Sgope@wisc.edu RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget); 51710785Sgope@wisc.edu hist_it->usedRAS = false; 51810785Sgope@wisc.edu } else if (hist_it->wasCall && hist_it->pushedRAS) { 51910785Sgope@wisc.edu //Was a Call but predicated false. Pop RAS here 52010785Sgope@wisc.edu DPRINTF(Branch, "[tid: %i] Incorrectly predicted" 52110785Sgope@wisc.edu " Call [sn:%i] PC: %s Popping RAS\n", tid, 52210785Sgope@wisc.edu hist_it->seqNum, hist_it->pc); 52310785Sgope@wisc.edu RAS[tid].pop(); 52410785Sgope@wisc.edu hist_it->pushedRAS = false; 52510785Sgope@wisc.edu } 52610785Sgope@wisc.edu } 52710785Sgope@wisc.edu } else { 52810785Sgope@wisc.edu DPRINTF(Branch, "[tid:%i]: [sn:%i] pred_hist empty, can't " 52910785Sgope@wisc.edu "update.\n", tid, squashed_sn); 53010785Sgope@wisc.edu } 53110785Sgope@wisc.edu} 53210785Sgope@wisc.edu 53310785Sgope@wisc.eduvoid 53410785Sgope@wisc.eduBPredUnit::dump() 53510785Sgope@wisc.edu{ 53610785Sgope@wisc.edu int i = 0; 53710785Sgope@wisc.edu for (const auto& ph : predHist) { 53810785Sgope@wisc.edu if (!ph.empty()) { 53910785Sgope@wisc.edu auto pred_hist_it = ph.begin(); 54010785Sgope@wisc.edu 54110785Sgope@wisc.edu cprintf("predHist[%i].size(): %i\n", i++, ph.size()); 54210785Sgope@wisc.edu 54310785Sgope@wisc.edu while (pred_hist_it != ph.end()) { 54410785Sgope@wisc.edu cprintf("[sn:%lli], PC:%#x, tid:%i, predTaken:%i, " 54510785Sgope@wisc.edu "bpHistory:%#x\n", 54610785Sgope@wisc.edu pred_hist_it->seqNum, pred_hist_it->pc, 54710785Sgope@wisc.edu pred_hist_it->tid, pred_hist_it->predTaken, 54810785Sgope@wisc.edu pred_hist_it->bpHistory); 54910785Sgope@wisc.edu pred_hist_it++; 55010785Sgope@wisc.edu } 55110785Sgope@wisc.edu 55210785Sgope@wisc.edu cprintf("\n"); 55310785Sgope@wisc.edu } 55410785Sgope@wisc.edu } 55510785Sgope@wisc.edu} 55610785Sgope@wisc.edu 557