unsigned
MachineOutliner::findCandidates(SuffixTree &ST, const TargetInstrInfo &TII,
InstructionMapper &Mapper,
std::vector<Candidate> &CandidateList,
std::vector<OutlinedFunction> &FunctionList) {
CandidateList.clear();
FunctionList.clear();
unsigned MaxLen = 0;
// FIXME: Visit internal nodes instead of leaves.
for (SuffixTreeNode *Leaf : ST.LeafVector) {
assert(Leaf && "Leaves in LeafVector cannot be null!");
if (!Leaf->IsInTree)
continue;
assert(Leaf->Parent && "All leaves must have parents!");
SuffixTreeNode &Parent = *(Leaf->Parent);
// If it doesn't appear enough, or we already outlined from it, skip it.
if (Parent.OccurrenceCount < 2 || Parent.isRoot() || !Parent.IsInTree)
continue;
// Figure out if this candidate is beneficial.
unsigned StringLen = Leaf->ConcatLen - (unsigned)Leaf->size();
// Too short to be beneficial; skip it.
// FIXME: This isn't necessarily true for, say, X86. If we factor in
// instruction lengths we need more information than this.
if (StringLen < 2)
continue;
// If this is a beneficial class of candidate, then every one is stored in
// this vector.
std::vector<Candidate> CandidatesForRepeatedSeq;
// Describes the start and end point of each candidate. This allows the
// target to infer some information about each occurrence of each repeated
// sequence.
// FIXME: CandidatesForRepeatedSeq and this should be combined.
std::vector<
std::pair<MachineBasicBlock::iterator, MachineBasicBlock::iterator>>
RepeatedSequenceLocs;
// Figure out the call overhead for each instance of the sequence.
for (auto &ChildPair : Parent.Children) {
SuffixTreeNode *M = ChildPair.second;
if (M && M->IsInTree && M->isLeaf()) {
// Each sequence is over [StartIt, EndIt].
MachineBasicBlock::iterator StartIt = Mapper.InstrList[M->SuffixIdx];
MachineBasicBlock::iterator EndIt =
Mapper.InstrList[M->SuffixIdx + StringLen - 1];
CandidatesForRepeatedSeq.emplace_back(M->SuffixIdx, StringLen,
FunctionList.size());
RepeatedSequenceLocs.emplace_back(std::make_pair(StartIt, EndIt));
// Never visit this leaf again.
M->IsInTree = false;
}
}
// We've found something we might want to outline.
// Create an OutlinedFunction to store it and check if it'd be beneficial
// to outline.
TargetInstrInfo::MachineOutlinerInfo MInfo =
TII.getOutlininingCandidateInfo(RepeatedSequenceLocs);
std::vector<unsigned> Seq;
for (unsigned i = Leaf->SuffixIdx; i < Leaf->SuffixIdx + StringLen; i++)
Seq.push_back(ST.Str[i]);
OutlinedFunction OF(FunctionList.size(), Parent.OccurrenceCount, Seq,
MInfo);
unsigned Benefit = OF.getBenefit();
// Is it better to outline this candidate than not?
if (Benefit < 1) {
// Outlining this candidate would take more instructions than not
// outlining.
// Emit a remark explaining why we didn't outline this candidate.
std::pair<MachineBasicBlock::iterator, MachineBasicBlock::iterator> C =
RepeatedSequenceLocs[0];
MachineOptimizationRemarkEmitter MORE(
*(C.first->getParent()->getParent()), nullptr);
MachineOptimizationRemarkMissed R(DEBUG_TYPE, "NotOutliningCheaper",
C.first->getDebugLoc(),
C.first->getParent());
R << "Did not outline " << NV("Length", StringLen) << " instructions"
<< " from " << NV("NumOccurrences", RepeatedSequenceLocs.size())
<< " locations."
<< " Instructions from outlining all occurrences ("
<< NV("OutliningCost", OF.getOutliningCost()) << ")"
<< " >= Unoutlined instruction count ("
<< NV("NotOutliningCost", StringLen * OF.OccurrenceCount) << ")"
<< " (Also found at: ";
// Tell the user the other places the candidate was found.
for (unsigned i = 1, e = RepeatedSequenceLocs.size(); i < e; i++) {
R << NV((Twine("OtherStartLoc") + Twine(i)).str(),
RepeatedSequenceLocs[i].first->getDebugLoc());
if (i != e - 1)
R << ", ";
}
R << ")";
MORE.emit(R);
// Move to the next candidate.
continue;
}
if (StringLen > MaxLen)
MaxLen = StringLen;
// At this point, the candidate class is seen as beneficial. Set their
// benefit values and save them in the candidate list.
for (Candidate &C : CandidatesForRepeatedSeq) {
C.Benefit = Benefit;
C.MInfo = MInfo;
CandidateList.push_back(C);
}
FunctionList.push_back(OF);
// Move to the next function.
Parent.IsInTree = false;
}
return MaxLen;
}
