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O3: Track if the RAS has been pushed or not to pop the RAS if neccessary.

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Add new flag (named pushedRAS) in the PredictorHistory structure.
This flag tracks whether the RAS has been pushed or not during a prediction.
Then, in the squash function it is used to pop the RAS if necessary.
This commit is contained in:
Nathanael Premillieu
2012-06-29 11:18:29 -04:00
parent 71daeb0b2b
commit af2b14a362
2 changed files with 8 additions and 4 deletions
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5
src/cpu/o3/bpred_unit.hh
View File

@@ -207,7 +207,7 @@ class BPredUnit
bool pred_taken, void *bp_history,
ThreadID _tid)
: seqNum(seq_num), pc(instPC), bpHistory(bp_history), RASTarget(0),
RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0),
RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), pushedRAS(0),
wasCall(0), wasReturn(0), validBTB(0)
{}
@@ -242,6 +242,9 @@ class BPredUnit
/** Whether or not the RAS was used. */
bool usedRAS;
/* Wether or not the RAS was pushed */
bool pushedRAS;
/** Whether or not the instruction was a call. */
bool wasCall;

7
src/cpu/o3/bpred_unit_impl.hh
View File

@@ -219,7 +219,7 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
if (inst->isCall()) {
RAS[tid].push(pc);
predict_record.pushedRAS = true;
// Record that it was a call so that the top RAS entry can
// be popped off if the speculation is incorrect.
predict_record.wasCall = true;
@@ -253,6 +253,7 @@ BPredUnit<Impl>::predict(DynInstPtr &inst, TheISA::PCState &pc, ThreadID tid)
tid, inst->seqNum, inst->pcState());
} else if (inst->isCall() && !inst->isUncondCtrl()) {
RAS[tid].pop();
predict_record.pushedRAS = false;
}
TheISA::advancePC(target, inst->staticInst);
}
@@ -308,7 +309,7 @@ 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 && pred_hist.front().validBTB) {
} else if(pred_hist.front().wasCall && pred_hist.front().pushedRAS) {
// Was a call but predicated false. Pop RAS here
DPRINTF(Fetch, "BranchPred: [tid: %i] Squashing"
" Call [sn:%i] PC: %s Popping RAS\n", tid,
@@ -408,7 +409,7 @@ BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn,
hist_it->RASIndex, hist_it->RASTarget);
RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget);
} else if (hist_it->wasCall && hist_it->validBTB) {
} else if (hist_it->wasCall && hist_it->pushedRAS) {
//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,