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cpu: Added 8KB and 64KB TAGE-SC-L branch predictor

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The original paper of the branch predictor can be found here:
http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf

Change-Id: I684863752407685adaacedebb699205c3559c528
Reviewed-on: https://gem5-review.googlesource.com/c/14855
Reviewed-by: Sudhanshu Jha <sudhanshu.jha@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
This commit is contained in:
Javier Bueno
2019-01-30 01:01:50 +01:00
committed by Pau Cabre
parent 224f2d50a9
commit d39573a9be
18 changed files with 2541 additions and 56 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
src/cpu/pred/loop_predictor.cc
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@@ -36,6 +36,8 @@
#include "cpu/pred/loop_predictor.hh"
#include "base/random.hh"
#include "debug/LTage.hh"
#include "params/LoopPredictor.hh"
LoopPredictor::LoopPredictor(LoopPredictorParams *p)
@@ -166,14 +168,13 @@ LoopPredictor::specLoopUpdate(bool taken, BranchInfo* bi)
}
bool
LoopPredictor::optionalAgeInc(int nrand) const
LoopPredictor::optionalAgeInc() const
{
return false;
}
void
LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred,
int random0, int random1, int random2)
LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred)
{
int idx = finallindex(bi->loopIndex, bi->loopIndexB, bi->loopHit);
if (bi->loopHit >= 0) {
@@ -186,7 +187,8 @@ LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred,
ltable[idx].confidence = 0;
ltable[idx].currentIter = 0;
return;
} else if (bi->loopPred != tage_pred || optionalAgeInc(random0)) {
} else if (bi->loopPred != tage_pred || optionalAgeInc()) {
DPRINTF(LTage, "Loop Prediction success:%lx\n",pc);
unsignedCtrUpdate(ltable[idx].age, true, loopTableAgeBits);
}
}
@@ -206,6 +208,7 @@ LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred,
if (taken != (useDirectionBit ? ltable[idx].dir : true)) {
if (ltable[idx].currentIter == ltable[idx].numIter) {
DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc);
unsignedCtrUpdate(ltable[idx].confidence, true,
loopTableConfidenceBits);
//just do not predict when the loop count is 1 or 2
@@ -217,6 +220,7 @@ LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred,
ltable[idx].confidence = 0;
}
} else {
DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc);
if (ltable[idx].numIter == 0) {
// first complete nest;
ltable[idx].confidence = 0;
@@ -235,13 +239,16 @@ LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred,
}
} else if (useDirectionBit ? (bi->predTaken != taken) : taken) {
if ((random2 & 3) == 0 || !restrictAllocation) {
if ((random_mt.random<int>() & 3) == 0 || !restrictAllocation) {
//try to allocate an entry on taken branch
int nrand = random1;
int nrand = random_mt.random<int>();
for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
int loop_hit = (nrand + i) & ((1 << logLoopTableAssoc) - 1);
idx = finallindex(bi->loopIndex, bi->loopIndexB, loop_hit);
if (ltable[idx].age == 0) {
DPRINTF(LTage,
"Allocating loop pred entry for branch %lx\n",
pc);
ltable[idx].dir = !taken; // ignored if no useDirectionBit
ltable[idx].tag = bi->loopTag;
ltable[idx].numIter = 0;
@@ -318,8 +325,7 @@ LoopPredictor::updateStats(bool taken, BranchInfo* bi)
void
LoopPredictor::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
bool tage_pred, BranchInfo* bi,
unsigned instShiftAmt, int rand0, int rand1,
int rand2)
unsigned instShiftAmt)
{
if (useSpeculation) {
// recalculate loop prediction without speculation
@@ -337,7 +343,7 @@ LoopPredictor::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
}
}
loopUpdate(branch_pc, taken, bi, tage_pred, rand0, rand1, rand2);
loopUpdate(branch_pc, taken, bi, tage_pred);
}
void