summaryrefslogtreecommitdiff
path: root/src/cpu
diff options
context:
space:
mode:
Diffstat (limited to 'src/cpu')
-rw-r--r--src/cpu/o3/bpred_unit.hh18
-rw-r--r--src/cpu/o3/bpred_unit_impl.hh61
-rw-r--r--src/cpu/o3/commit_impl.hh4
-rw-r--r--src/cpu/pred/tournament.cc97
4 files changed, 123 insertions, 57 deletions
diff --git a/src/cpu/o3/bpred_unit.hh b/src/cpu/o3/bpred_unit.hh
index d3ae93b38..673472b69 100644
--- a/src/cpu/o3/bpred_unit.hh
+++ b/src/cpu/o3/bpred_unit.hh
@@ -1,4 +1,16 @@
/*
+ * Copyright (c) 2011 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder. You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
* Copyright (c) 2004-2005 The Regents of The University of Michigan
* All rights reserved.
*
@@ -196,7 +208,7 @@ class BPredUnit
ThreadID _tid)
: seqNum(seq_num), pc(instPC), RASTarget(0), RASIndex(0),
tid(_tid), predTaken(pred_taken), usedRAS(0),
- wasCall(0), bpHistory(bp_history)
+ wasCall(0), wasReturn(0), validBTB(0), bpHistory(bp_history)
{}
bool operator==(const PredictorHistory &entry) const {
@@ -227,6 +239,10 @@ class BPredUnit
/** Whether or not the instruction was a call. */
bool wasCall;
+ /** Whether or not the instruction was a return. */
+ bool wasReturn;
+ /** Whether or not the instruction had a valid BTB entry. */
+ bool validBTB;
/** Pointer to the history object passed back from the branch
* predictor. It is used to update or restore state of the
* branch predictor.
diff --git a/src/cpu/o3/bpred_unit_impl.hh b/src/cpu/o3/bpred_unit_impl.hh
index 8502f342c..1e75de90c 100644
--- a/src/cpu/o3/bpred_unit_impl.hh
+++ b/src/cpu/o3/bpred_unit_impl.hh
@@ -196,7 +196,7 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
if (pred_taken) {
if (inst->isReturn()) {
++usedRAS;
-
+ predict_record.wasReturn = true;
// If it's a function return call, then look up the address
// in the RAS.
TheISA::PCState rasTop = RAS[tid].top();
@@ -231,6 +231,7 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
if (BTB.valid(pc.instAddr(), tid)) {
++BTBHits;
+ predict_record.validBTB = true;
// If it's not a return, use the BTB to get the target addr.
target = BTB.lookup(pc.instAddr(), tid);
@@ -250,12 +251,17 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
DPRINTF(Fetch, "BranchPred: [tid:%i]:[sn:%i] BPBTBUpdate"
" called for %s\n",
tid, inst->seqNum, inst->pcState());
+ } else if (inst->isCall() && !inst->isUncondCtrl()) {
+ RAS[tid].pop();
}
TheISA::advancePC(target, inst->staticInst);
}
}
} else {
+ if (inst->isReturn()) {
+ predict_record.wasReturn = true;
+ }
TheISA::advancePC(target, inst->staticInst);
}
@@ -302,12 +308,13 @@ BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn, ThreadID tid)
RAS[tid].restore(pred_hist.front().RASIndex,
pred_hist.front().RASTarget);
- } else if (pred_hist.front().wasCall) {
- DPRINTF(Fetch, "BranchPred: [tid:%i]: Removing speculative entry "
- "added to the RAS.\n",tid);
-
- RAS[tid].pop();
- }
+ } else if(pred_hist.front().wasCall && pred_hist.front().validBTB) {
+ // Was a call but predicated false. Pop RAS here
+ DPRINTF(Fetch, "BranchPred: [tid: %i] Squashing"
+ " Call [sn:%i] PC: %s Popping RAS\n", tid,
+ pred_hist.front().seqNum, pred_hist.front().pc);
+ RAS[tid].pop();
+ }
// This call should delete the bpHistory.
BPSquash(pred_hist.front().bpHistory);
@@ -377,18 +384,46 @@ BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn,
BPUpdate((*hist_it).pc, actually_taken,
pred_hist.front().bpHistory, true);
- if (actually_taken){
- DPRINTF(Fetch,"BranchPred: [tid: %i] BTB Update called for [sn:%i]"
- " PC: %s\n", tid,(*hist_it).seqNum, (*hist_it).pc);
+ if (actually_taken) {
+ if (hist_it->wasReturn && !hist_it->usedRAS) {
+ DPRINTF(Fetch, "BranchPred: [tid: %i] Incorrectly predicted"
+ " return [sn:%i] PC: %s\n", tid, hist_it->seqNum,
+ hist_it->pc);
+ RAS[tid].pop();
+ }
+ DPRINTF(Fetch,"BranchPred: [tid: %i] BTB Update called for [sn:%i]"
+ " PC: %s\n", tid,hist_it->seqNum, hist_it->pc);
+
+
BTB.update((*hist_it).pc, corrTarget, tid);
+
+ } else {
+ //Actually not Taken
+ if (hist_it->usedRAS) {
+ DPRINTF(Fetch,"BranchPred: [tid: %i] Incorrectly predicted"
+ " return [sn:%i] PC: %s Restoring RAS\n", tid,
+ hist_it->seqNum, hist_it->pc);
+ DPRINTF(Fetch, "BranchPred: [tid:%i]: Restoring top of RAS"
+ " to: %i, target: %s.\n", tid,
+ hist_it->RASIndex, hist_it->RASTarget);
+ RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget);
+
+ } else if (hist_it->wasCall && hist_it->validBTB) {
+ //Was a Call but predicated false. Pop RAS here
+ DPRINTF(Fetch, "BranchPred: [tid: %i] Incorrectly predicted"
+ " Call [sn:%i] PC: %s Popping RAS\n", tid,
+ hist_it->seqNum, hist_it->pc);
+ RAS[tid].pop();
+ }
}
DPRINTF(Fetch, "BranchPred: [tid:%i]: Removing history for [sn:%i]"
- " PC %s Actually Taken: %i\n", tid, (*hist_it).seqNum,
- (*hist_it).pc, actually_taken);
+ " PC %s Actually Taken: %i\n", tid, hist_it->seqNum,
+ hist_it->pc, actually_taken);
pred_hist.erase(hist_it);
- DPRINTF(Fetch, "[tid:%i]: predHist.size(): %i\n", tid, predHist[tid].size());
+ DPRINTF(Fetch, "[tid:%i]: predHist.size(): %i\n", tid,
+ predHist[tid].size());
}
}
diff --git a/src/cpu/o3/commit_impl.hh b/src/cpu/o3/commit_impl.hh
index b4cc4b017..bb82c37a8 100644
--- a/src/cpu/o3/commit_impl.hh
+++ b/src/cpu/o3/commit_impl.hh
@@ -1232,6 +1232,10 @@ DefaultCommit<Impl>::commitHead(DynInstPtr &head_inst, unsigned inst_num)
delete head_inst->traceData;
head_inst->traceData = NULL;
}
+ if (head_inst->isReturn()) {
+ DPRINTF(Commit,"Return Instruction Committed [sn:%lli] PC %s \n",
+ head_inst->seqNum, head_inst->pcState());
+ }
// Update the commit rename map
for (int i = 0; i < head_inst->numDestRegs(); i++) {
diff --git a/src/cpu/pred/tournament.cc b/src/cpu/pred/tournament.cc
index 3adafb608..b6320ca8a 100644
--- a/src/cpu/pred/tournament.cc
+++ b/src/cpu/pred/tournament.cc
@@ -258,59 +258,70 @@ TournamentBP::update(Addr &branch_addr, bool taken, void *bp_history,
local_predictor_hist = localHistoryTable[local_history_idx];
local_predictor_idx = local_predictor_hist & localPredictorMask;
- // Update the choice predictor to tell it which one was correct if
- // there was a prediction.
if (bp_history) {
BPHistory *history = static_cast<BPHistory *>(bp_history);
- if (history->localPredTaken != history->globalPredTaken) {
- // If the local prediction matches the actual outcome,
- // decerement the counter. Otherwise increment the
- // counter.
- if (history->localPredTaken == taken) {
- choiceCtrs[history->globalHistory].decrement();
- } else if (history->globalPredTaken == taken){
- choiceCtrs[history->globalHistory].increment();
- }
-
- }
-
- // Update the counters and local history with the proper
- // resolution of the branch. Global history is updated
- // speculatively and restored upon squash() calls, so it does not
- // need to be updated.
+ // Update may also be called if the Branch target is incorrect even if
+ // the prediction is correct. In that case do not update the counters.
+ bool historyPred = false;
unsigned old_local_pred_index = history->localHistory
- & localPredictorMask;
- if (taken) {
- globalCtrs[history->globalHistory].increment();
- if (old_local_pred_index != invalidPredictorIndex) {
- localCtrs[old_local_pred_index].increment();
- }
+ & localPredictorMask;
+ if (history->globalUsed) {
+ historyPred = history->globalPredTaken;
} else {
- globalCtrs[history->globalHistory].decrement();
- if (old_local_pred_index != invalidPredictorIndex) {
- localCtrs[old_local_pred_index].decrement();
- }
- }
-
- if (squashed) {
- if (taken) {
- globalHistory = (history->globalHistory << 1) | 1;
- globalHistory = globalHistory & globalHistoryMask;
- if (history->localHistory != invalidPredictorIndex)
- localHistoryTable[local_history_idx] =
+ historyPred = history->localPredTaken;
+ }
+ if (historyPred != taken || !squashed) {
+ // Update the choice predictor to tell it which one was correct if
+ // there was a prediction.
+ if (history->localPredTaken != history->globalPredTaken) {
+ // If the local prediction matches the actual outcome,
+ // decerement the counter. Otherwise increment the
+ // counter.
+ if (history->localPredTaken == taken) {
+ choiceCtrs[history->globalHistory].decrement();
+ } else if (history->globalPredTaken == taken) {
+ choiceCtrs[history->globalHistory].increment();
+ }
+
+ }
+
+ // Update the counters and local history with the proper
+ // resolution of the branch. Global history is updated
+ // speculatively and restored upon squash() calls, so it does not
+ // need to be updated.
+ if (taken) {
+ globalCtrs[history->globalHistory].increment();
+ if (old_local_pred_index != invalidPredictorIndex) {
+ localCtrs[old_local_pred_index].increment();
+ }
+ } else {
+ globalCtrs[history->globalHistory].decrement();
+ if (old_local_pred_index != invalidPredictorIndex) {
+ localCtrs[old_local_pred_index].decrement();
+ }
+ }
+ }
+ if (squashed) {
+ if (taken) {
+ globalHistory = (history->globalHistory << 1) | 1;
+ globalHistory = globalHistory & globalHistoryMask;
+ if (old_local_pred_index != invalidPredictorIndex) {
+ localHistoryTable[old_local_pred_index] =
(history->localHistory << 1) | 1;
- } else {
- globalHistory = (history->globalHistory << 1);
- globalHistory = globalHistory & globalHistoryMask;
- if (history->localHistory != invalidPredictorIndex) {
- localHistoryTable[local_history_idx] =
+ }
+ } else {
+ globalHistory = (history->globalHistory << 1);
+ globalHistory = globalHistory & globalHistoryMask;
+ if (old_local_pred_index != invalidPredictorIndex) {
+ localHistoryTable[old_local_pred_index] =
history->localHistory << 1;
- }
- }
+ }
+ }
}
// We're done with this history, now delete it.
delete history;
+
}
assert(globalHistory < globalPredictorSize &&
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-05 01:08:28 +0000